Physics Colloquium, "Building Complexity 1-2-3" by Dr. Jennifer Ross, Department of Physics, UMASS Amherst Monday, 11/16/2009, 4:00 PM-5:00 PM
Kinesin and cytoplasmic dynein are microtubule-based motor proteins that actively transport material throughout the cell. This transport is vital to effectively moving cargo around the cell. This is especially important in the very long axons that connect the spine to the extremities. Impediments of cargo transport down the axons leads to neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), also known as Lou Gehrigs disease, which is the disease affecting physicist Stephen Hawking. To understand the physical properties of these motors, we investigate the innate transport abilities of these motor proteins in vitro. We find that dynein has a greater ability to stay bound in the presence of obstacles on the microtubule track. Kinesin, on the other hand, can move robustly, but dissociates when confronted by a blocked path. Dynein's ability to hang on is likely due to its inherent flexibility and ability to move in reverse. These in vitro capabilities have implications for the cellular roles of these motors.
Refreshments will be served in Olin Hall 223 at 3:40 P.M.
Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "Lipid Membrane-Assisted 2D Assembly of Bionanoparticles at Liquid Interfaces" by Masafumi Fukuto, Brookhaven National Lab Monday, 11/9/2009, 4:00 PM-5:00 AM
Lipid monolayers at planar aqueous solution-vapor and solution-substrate interfaces provide an ideal platform for facilitating two-dimensional(2D) assembly of biomolecular nanoparticles like proteins and virus particles. In order to illustrate the utility and versatility of this approach to promoting the ordered assembly of nanoscale objects, we will describe the results of two of our recent studies: (i) the effects of surface biotin density on the 2D crystallization of the soluble protein streptavidin, and (ii) the electrostatic 2D assembly of virus particles, with emphasis on cowpea mosaic virus (CPMV). The structures of these systems have been probed by synchrotron x-ray scattering (GISAXS & XR), AFM, and optical microscopy measurements. We will also illustrate the capability of these techniques for in-situ characterization of structures at liquid interfaces.
Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "EXX Phenomena in Macroscopic, Microscopic and Nanoscopic Structures," by Dr. S. A. Solin, Washington University, St. Louis, Department of Physics and Center for Materials Innovation Monday, 11/2/2009, 4:00 PM-5:00 PM
The new "EXX" phenomena in macroscopic, microscopic and nanoscopic metal-semiconductor hybrid structures will be described. Here E = extraordinary and XX = magnetoresistance (EMR), piezoconductance (EPC), optoconductance (EOC), and electroconductance (EEC). This new class of phenomena is based on the control and dominance of the geometric contributions, e.g. sample shape, lead placement, the presence of inhomogenieties, etc., to the transport properties of a physical system in contrast to traditional transport phenomena which are dominated by the intrinsic properties, e.g. mobility, carrier density, band structure, etc. The underlying phyiscs of EXX phenomena will be elucidated with particular emphasis on the use of analytic and finite element analysis methods to quantitatively account for the observed EXX signal enhancement. Surprising new aspects of the mesoscopic physics of the nano-hybrid structures will be addressed. A recently discovered inverse EOC (I-EOC) effect in which, nanoscopic devices (dimensions < 500 nm) show a decrease in conductivity with increased illumination intensity with an I-EOC ~ 1000% and a specific detectivity as high as D* = 3.2_1011 cmHz/W in a 250 nm device will be reported. It will be shown that I-EOC can be attributed to optical switching induced by the transition from ballistic to diffusive transport. The use of individual EXX sensors and EXX nano arrays to study, with ultrahigh spatial and temporal resolution, biologically relevant properties of cells such as surface charge density measured with a fluid-gated EEC device will be described.
Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "The cytoskeletal machinery is essential for polarized expansion of plant cells" by Dr. Luis Vidali, Assistant Professor, Department of Biology and Biotechnology, WPI Monday, 10/5/2009, 4:00 PM-5:00 PM
Photosynthetic organisms are the primary transducers of solar energy into bioenergy. Hence, understanding the basic molecular and cellular mechanisms underlying their growth is essential to harvest their potential for biofuels and other forms of clean and renewable energy. Plant growth and development are the result of cell growth and cell division. These two basic processes are modified and coordinated in different plants to create an immense diversity of shapes and structures. Plant cells expand by balancing their internal turgor pressure with changes in the extensible properties of their cell walls . This is accomplished by the regulated deposition of cell wall material. Once the cell reaches a certain size, or during specific developmental processes, the cell will enter mitosis and divide. Plant division is completed when a new cell wall is built to separate the two new cells.
Polarized cell expansion or "tip growth" has been extensively studied as a paradigm to understand cell expansion. Pollen tubes, root hairs, and the protonemata of ferns and mosses, grow exclusively by this type of expansion, which is achieved by focusing all the growth resources to one end of the cell. It is well established that the actin cytoskeleton plays an essential role in polarized expansion, most likely by polarizing the vesicle transport machinery via the actin-based motor myosin XI. Nevertheless, because of the large number of myosin XI genes in vascular plants, it has been difficult to determine their precise role in cell expansion. In contrast, in the moss Physcomitrella patens, there are only two myosin XI genes, which encode proteins that are 94% identical. To determine the role of myosin XI in polarized expansion, we simultaneously silenced the expression of both myosin XIs by RNA interference (RNAi). Loss of myosin XI function results in a dramatic loss of polarized expansion; plants are stunted and composed of small rounded cells. We also show that a green fluorescent protein fusion of myosin XI localizes to the site of expansion a the tip of the growing cell. Together these results indicate that myosin XI is responsible for the transport of components important for polarized expansion.
Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "Block Copolymer Droplets, Thin Films and Wrinkles," by Dr. Andrew B. Croll, University of Massachusetts, Amherst, Department of Polymer Science and Engineering Monday, 9/28/2009, 4:00 PM-5:00 PM
Block Copolymers are long chain molecules made of segments of more than one polymer variety covalently joined together. This molecular architecture leads to many technologically important phenomena which are useful in applications that range from the semiconductor to the commodity polymer industries. Many of the most important properties of these systems result from the nanoscopic structures that form due to the chemical incompatibility of the blocks. In this talk I will present our progress towards a more detailed understanding of the physics of these systems. I will focus on the simplest system, that of symmetric diblock copolymers (where the chain consists of two distinct blocks of equal size) in a variety of different experimental confining geometries. I will show how the micro-phase separated structures lead to conically shaped fluid droplets, how the thin film geometry can be adapted into a very simple measurement of the Flory-Huggins interaction parameter and how the structured surface of a thin film can be used to drive a simple wrinkled geometry into a state of stress localization.
Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "Studying Heterogeneity in Bacterial Lipopolysaccharides with Atomic Force Microscopy " by Dr. Terri Camesano, WPI Chemical Engineering Department Monday, 9/21/2009, 4:00 PM-12:50 PM
Gram-negative bacteria have a layer of lipopolysaccharides (LPS) on the outer portion of their membrane. These LPS molecules are very important in controlling virulence and bacterial adhesion to host tissue or biomaterials. Heterogeneity in the properties of bacterial LPS can affect how they interact with, and ultimately attach to, various surfaces. We are working with two model microorganisms, which exhibit different kinds of heterogeneity. For example, Escherichia coli (E. coli) express LPS which vary from strain to strain, but are chemically the same within a single subspecies. However, physical heterogeneities (such as length of the polymer molecules) can vary as a function of growth conditions, even on a single strain of bacteria. Pseudomonas aeruginosa represents a different scenario, in which the same bacterium can express chemically and physically distinct saccharide units on a single LPS molecule. Using atomic force microscopy, we are exploring how this heterogeneity, especially in the physical properties of LPS, controls the attachment and adhesion of Gram-negative bacteria to numerous surfaces.
Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
WPI Physics Department 2nd Annual Robert Goddard Rocket Competition Saturday, 6/13/2009, 10:00 AM-1:00 PM
This years Robert Goddard Competition will be a water rocket competition for all schools in the Worcester Area. It is geared at having an adult member along with a group of students work together to find the best way to launch a water rocket into a designated area. A website is available and will be updated periodically.
Sponsored by: WPI Physics Department
Physics Department M.S. Thesis Defense, "Temperature Dependence of the Contact Angle of Water on Graphite, Silicon and Gold," by Kenneth Osborne, Physics Department Graduate Student Friday, 4/24/2009, 4:00 PM-5:00 AM
The temperature dependence of the contact angle of water on graphite, silicon and gold was investigated under various conditions to test the Sharp-Kink Approximation. Despite correctly predicting the contact angle at room temperature, the ideal Sharp-Kink Approximation was not found to accurately describe the contact angle's temperature dependence. The discrepancies from the predicted contact angle were characterized in terms of a correction H(T) to the liquid-solid surface tension. H(T) was found to be linear in temperature and decreasing, and is consistent with electrostatic charge effects.
Sponsored by: Dr. Rafael Garcia
Special Topic, "A Personal View of Rural Development in Vietnam and Cambodia" by Dr. Nancy Burnham and Mr. Frederick Hutson, WPI Physics Department Wednesday, 4/22/2009, 4:00 PM-5:00 PM
For two weeks over winter break, we traveled around Vietnam and Cambodia on a study tour organized by Heifer International, a rural development charity that we have been supporting for some years. In this talk, we will, a) explain Heifer's history and current activities, b) describe where we went and what we did, and c) tell you our personal experiences of and thoughts on rural development. We plan to speak and show slides for approximately thirty minutes, after which we hope for an interesting discussion.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department Ph.D. Defense, "Electromagnetic Nucleus - Nucleus Cross Sections using Energy Dependent Branching Ratios," Anne Marie Adamczyk, WPI Physic Graduate Student Monday, 4/20/2009, 10:00 AM-2:00 PM
It is important that accurate estimates of crew exposure to radiation are obtained for future long - term space missions. To predict the radiation environment, a few space radiation transport codes exist, all of which use basic nuclear cross section information for transport of radiation through materials.
Little theoretical and experimental work has been conducted on reactions induced by the electromagnetic (EM) force, especially with regard to differential cross sections. Therefore, radiation transport codes have typically neglected to incorporate EM nuclear collision cross sections. EM cross sections for single nucleon removal have been included in some radiation codes, but better values can be obtained by using an energy dependent branching ratio. Most previous theoretical and experimental work has been devoted to total cross sections. Therefore, the energy dependent branching ratios presented can be extensively compared to past theory and experiment. Such comparisons indicate that using energy dependent branching ratios yield better estimates of total cross sections.
Differential cross sections for electromagnetic dissociation in nuclear collisions are calculated for the first time. In order to be useful for three - dimensional transport codes, these cross sections have been calculated in both the projectile and lab frames. The formulas for these cross sections are such that they can be immediately used in space radiation transport codes. Only a limited amount of data exists, but the comparison between theory and experiment is good.
Sponsored by: WPI Physics Department, Dr. P.K. Aravind
Physics Colloquium, "Mid-Infrared Semiconductor Laser Development at MIT/Lincoln Laboratory" By Dr. George W. Turner, Lincoln Laboratory Monday, 4/13/2009, 4:00 PM-5:00 PM
MIT / Lincoln Laboratory has been continuously involved in the development of semiconductor laser sources since the very initial demonstrations of the diode laser in 1962. In this lecture, a historical overview of the various semiconductor laser efforts at MIT / Lincoln Laboratory will be presented, with an emphasis on the evolution of mid-infrared (2-5 µm) semiconductor laser technology. Results from both electrically-pumped and optically-pumped semiconductor laser structures will be reviewed. Recent results and new research directions in mid-infrared, high-power quantum cascade lasers, operating near room temperature, will also be discussed.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium,"Manganese Cell Labeling and Tissue Delivery UsingManganesse (III)- Transferrin, by Dr. Christopher Sotak, WPI Biomedical Engineering Monday, 4/6/2009, 4:00 PM-5:00 PM
Although most manganese-enhanced MRI (MEMRI) methods employ Mn2+ as a Ca2+ analogue, other mechanisms for delivering manganese into cells and tissue are also possible. For example, transferrins (Tf) a major class of plasma iron-binding proteins can accommodate a variety of other metal ions (including manganese) in the two available iron-binding domains of the Tf molecule. In particular, Tf has been shown to be one of the major manganese plasma-transport proteins for both rodents and humans in the form of Mn(III)-Tf.
Metal-Tf transport is initiated when the metalloprotein binds to transferrin receptor 1 (TfR1) at the cell surface. The metal-Tf/TfR1 complex is then transported into the cell via TfR1-mediated endocytosis. The acidic pH (~5.5) that develops within the resulting endosomal compartment releases the metal from the internalized protein complex. The free manganese is then reduced and transported across the endosomal membrane into the cytosol; where it can function as an effective MRI contrast agent. The metal-free apo-Tf/TfR1 complex is recycled back to the cell surface, where both proteins are reused in another cycle of cellular metal-ion uptake. The cyclical nature of this process can potentially label cells with relatively high concentrations of manganese.
TfR1-mediated endocytosis has been investigated as a novel approach for manganese cell labeling and tissue delivery using Mn(III)-Tf. The degree of manganese cell labeling following incubation of murine hepatocytes for 2-7 h in 31.5 M Mn(III)-Tf was comparable to that of hepatocytes incubated in 500 M Mn2+ for 1 h. Manganese delivery and transport has also been investigated in vivo following direct intracerebral injection of Mn(III)-Tf into the rat brain. Intracerebral infusions of from 5-20 L of ~1 mM Mn(III)-Tf resulted in significant T1-relaxation-time enhancement; comparable to that observed following direct injection of Mn2+ alone at the same concentration. Furthermore, the subsequent transport of manganese along neuronal tracts originating from the injection site provides further evidence for the in vivo cellular delivery of Mn2+ via TfR1-mediated endocytosis. This approach represents a novel way to use a biological pathway for targeting and to release an MRI contrast agent into cells.
Physics Colloquium, "Fingerprints of Prefibrilar Amyloid Oligomers in the Magnetic Resonance of Water" by Dr. Florin Despa, Department of Pharmacology, University of California, Davis Wednesday, 3/25/2009, 4:00 PM-5:00 PM
Hydration shells of normal proteins display both structured and bulk-like
waters. Isomers with considerable bulk-like hydration tend to aggregate.
Our data show that different morphological states of aggregated isomers
differ by hydration distribution profiles and water magnetic resonance
(MR) signals. The results help explain the MR contrast patterns of the
amyloids, a subject of long controversy, and suggest a new approach for
identifying unusual protein aggregation related to disease. As an example,
I will present water proton MR spectroscopic data, thioflavin T
fluorescence, gel electrophoresis and cell toxicity measurements revealing
the relationship between amyloid conformation and amyloid-induced cellular
dysfunction. Developing strategies to detect the amyloids at an early
stage of development and to assess the induced cellular damage are crucial
for diagnosis and treatment of protein conformational diseases, such as
Alzheimers disease, type 2 diabetes mellitus and diabetic cardiomyopathy.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium,"High magnetic field studies of the field induced ordering and of the itinerant electron metamagnetism in heavy fermion compounds URu2-xRexSi2 and URu1.92Rh0.08Si2,by Dr. Sonia Francoual, Monday, 3/23/2009, 4:00 PM-5:00 PM
URu2Si2 is a heavy-fermion compound the low temperatures and high magnetic fields phase diagram of which is characterized by the presence of a Hidden-Order phase below 17 K up to 36 T, multiple ordered phases below 7 K between 36 and 42 T and itinerant electron metamagnetism (IEMM):
(1)* Rhenium doping of URu2Si2 yields unusual magnetic and electronic behaviors at low temperatures with a smearing of the Hidden-Order at x ~ 0.10, Non Fermi Liquid behavior from x ~ 0.15 and weak ferromagnetism from x ~ 0.30. In order to address the effects of Re doping on the multiple field-induced ordering and on the IEMM, we measured the magnetization and magnetoresistance properties of URu2-xRexSi2 single-crystals in pulsed magnetic fields up to 65 T allowing it to determine a comprehensive (T, B, x) phase diagram. The field-induced ordering is suppressed at x = 0.05, the Heavy-Fermion (HF) state and the IEMM at x = 0.35. The suppression of the HF state is found to condition the suppression of the IEMM and the emergence of the ferromagnetism.
(2)** Rhodium doping yields the growing of a single ordered phase, so called phase II, below 10 K at fields above 27 T and complete suppression of the Hidden order phase. In order to get some clues about the nature of the order parameter in phase II, we measured magnetostriction and thermal expansion on a URu1.92Rh0.04Si2 single-crystal using a capacitive dilatometer. Important dilation effects are evidenced in the underlying Fermi liquid outside phase II as observed previously in the 4f analog compound CeRu2Si2 as well as anisotropic and significant length changes in phase II.
Physics Faculty Candidate, "Conformational Sculpting of DNA: Nanofluidics for Single Molecule DNA Analysis and Manipulation," by Dr. Walter Reisner, Brown University Monday, 3/2/2009, 4:00 PM-5:00 PM
My work uses sub micron nanofabrication tools like electron beam lithography to
explore the fundamental physics of polymers in confinement and to develop
nanotechnology approaches to key problems in biology. When a polymer is confined in a
structure with dimension below the polymers free solution gyration radius the confining
geometry will alter the polymer equilibrium conformation. This fundamental result of
statistical physics has a key technological implication: polymer conformation can be
manipulated and controlled onchip by design of the nanofludic confining geometry. This
talk will consider two implications of this notion of conformational sculpting for the
field of single molecule DNA analysis. In a nanochannel, self-exclusion interactions
within the polymer will create a linear unscrolling of the genome along the channel for
analysis. Nanochannel based DNA stretching can serve as a platform for a new optical
mapping technique based on measuring the pattern of partial melting along the extended
molecules. We believe this melting mapping technology is the first optically based single
molecule technique sensitive to genome wide sequence variation that does not require an
additional enzymatic labeling or restriction scheme. In addition, by embedding sub
micron nanotopographies in a slit-like nanochannel, we can create spatial variation in
confinement across the slit. The confinement variation in turns varies a molecules
configurational freedom, or entropy. Consequently, by controlling device geometry, we
can create a user-defined free energy landscape that allows us to sculpt the equilibrium
configuration of a molecule. Individual square depressions, or nanopits, can be used to
trap DNA at specific points in the slit. Arrays of nanopits will lead to complex
digitized conformations with a single molecule linking a number of pits.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Emerging Fields of Nematic Liquid Crystals: Transformative Biaxial Nematic & Unconventional Bio-Detection Technology," by Dr. Bharat R. Archarya, Kent University Monday, 2/23/2009, 4:00 PM-5:00 AM
Nematic liquid crystals (NLCs), the electrically responsive fluid behind most of the flat panel displays, consist of anisotropic molecules that possess long range orientational correlation but lack positional order. In recent years, there have been significant advances leading to discovery of a much sought-after biaxial nematic LC and in unconventional applications of the classical (uniaxial) nematic in photonics, sensors, and diagnostics. Two such advances will be discussed, one of enormous basic scientific interest with potential to give rise to a transformative technology and the second to enable hitherto unexplored technological applications of the well known NLCs.
The use of x-ray diffraction technique to probe structural features of the nematic phase of bent-core molecules will be discussed. Experimental results, combined with the ab-initio calculations of the molecular form factor and structure factor have led to the discovery of the biaxial nematic phase in thermotropic mesogens. The biaxial nematic holds the potential of leading to new generation display technology that will be 100 times faster than current HDTVs. Application of NLCs in rapid viral detection will be discussed in the second half of the presentation. Surfaces decorated with enveloped viruses promote vertical (homeotropic) alignment of NLCs. Unique nature of the interaction between the enveloped viruses and NLCs has been exploited to detect, amplify, and confirm the presence of viruses. Electrokinetic effects associated with a non-uniform AC field have been employed to accelerate the transport of viruses to the surface. The combination of these two approaches has been used to enable rapid (~10 min) detection of viruses, much faster than the incubation time at clinically relevant concentrations.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Coarse-grained modeling of complex fluids and bio-polymers," by Dr. Erkan Tuzel, University of Minnesota Wednesday, 2/11/2009, 4:00 PM-5:00 AM
The dynamic behavior of complex liquids and soft materials is of great importance in a wide
range of disciplines. Computational studies of these phenomena are particularly demanding because
of the presence of disparate length and energy scales, the complicated coupling between the embedded
objects, and the hydrodynamic
ow eld and thermal
uctuations. In the rst part of this presen-
tation, I will introduce one such recently introduced particle-based mesoscale algorithm|stochastic
rotation dynamics|which solves the hydrodynamic equations by following the discrete time dynamics
of particles with continuous coordinates and velocities, using ecient multi-particle collisions. It will
be shown how the algorithm can be generalized to model dense
uids, immiscible binary and am-
phiphilic mixtures. The phase diagram of the entropically driven de-mixing transition and a detailed
analysis of the capillary wave spectrum for binary droplets will be presented. The second part of
my talk will focus on mesoscale modeling microtubule-motor interactions in gliding assays and living
cells. In living cells microtubules are often viewed as mechanically rigid compressive struts that help
maintain cell shape and aid in the transport of cellular cargo by serving as tracks for the molecular
motors. However, recent experiments on LLC-PK1 epithelial cells strongly suggest that microtubules
are often dynamic and deforming continuously and dominantly being transported anterogradely by
molecular motors. Surprisingly, quantitative analysis of these deformations exhibit striking similari-
ties to in vitro gliding assays. Motivated by these experiments, we have modeled microtubule-motor
interactions using coarse-grained simulations. Simulation results support our experimental ndings
and further elucidate on the interplay between molecular motors and passive cross-linkers. Our results
suggest that molecular motors are not necessarily just cargo carriers, but can play a dynamic role in
the deformation and positioning the microtubule array.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Sensing and Adaptation in Directed Cell Migration," by Dr. Yevgeniy Kalinin, School of Chemical and Biomolecular Engineering, Cornell University Monday, 2/2/2009, 4:00 PM-5:00 AM
Microfluidic technology has presented us with the opportunities to precisely control the cellular microenvironments (both chemical and mechanical) and, in combination with live cell imaging, to reveal the cellular responses at the single cell levels. In this talk I will present applications of microfluidics to the studies of receptor-mediated cell responses using bacterial chemotaxis as a model system. Using a comprehensive set of linear chemical gradients we verify unambiguously that E.
coli sense chemical concentration on the logarithmic scale (this is similar to sensory systems of higher organisms where the logarithm of the signal strength simply compacts a wide range of signal into a manageable one). This result, when combined with a theoretical model of bacterial chemotactic behavior, makes it possible to understand macroscopic cellular behavior by modeling the underlying microscopic pathway kinetics. In the case of multiple chemical gradients I will show that E. coli make their decisions on which chemical they should pursue first depending upon the receptor number ratio. More interestingly we find that in natural environments E. coli are able to modify their chemical tastes by changing the number of receptors of a given kind. While this behavior is undoubtedly related to E. colis survival strategy the exact reasons for it and its mechanisms remain to be discovered.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Swimming in Viscoelastic Fluids and Gels," by Dr. Henry Fu, Brown University Friday, 1/30/2009, 4:00 PM-5:00 AM
The swimming of microorganisms in Newtonian fluids has been, and still remains, an active area of research. However, in many cases the natural environments which microorganisms navigate are non- Newtonian fluids or even gels. For example, mammalian sperm swim through mucus in the female reproductive tract. In this talk I focus on swimming through polymeric viscoelastic fluids and gels. First, the forces exerted by a viscoelastic medium are different from those exerted by a Newtonian fluid. I address how this affects swimming shapes and speeds of flexible swimmers such as sperm. Second, the kinematic reversibility of the zero-Reynolds-number Stokes flow constrains what types of swimming motions are effective in Newtonian fluids (Purcell's "Scallop theorem"). I discuss how this is altered in nonlinearly viscoelastic fluids, and whether any new swimming strategies become available to swimmers in viscoelastic media. Finally, I describe issues that arise for swimmers moving through viscoelastic gels, which are solids rather than fluids.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department Wonderful Speaker, "USE IT, LOSE IT, OR SAVE IT-The Science of Renewable Energy Storage" by Dr. Albert Migliori, National High Magnetic Field Laboratory of the Los Alamos National Laboratory Friday, 1/23/2009, 4:00 PM-5:00 PM
Today, we can usefully consume all of the little solar, wind, and other renewable energy we produce. But for total energy production to shift significantly toward inherently unpredictable renewables, energy must be stored when available and recovered when needed else precious renewable energy sources will stand idle. This lecture will present an overview of the science of energy storage and new nanotechnology approaches to it. The science will take time to mature, but with legislative and economic shelters to nurture it, effective distributed electrical energy storage solutions can be found before the need is urgent
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "The Physics of Swimming Microorganisms" by Dr. Thomas Powers, Brown University Wednesday, 12/10/2008, 4:00 PM-5:00 PM
I will discuss model problems inspired by the mechanics of swimming microorganisms. First we study the swimming velocity of a swimmer with prescribed stroke in a complex fluid. Then, inspired by the coordination of beating cilia, we present an experimental model for hydrodynamic synchronization.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department Wonders Speaker, "Phonons Under Spatial Confinement," by Professor Janice Musfeldt, University of Tennessee, Department of Chemistry Wednesday, 12/3/2008, 4:00 PM-5:00 PM
Understanding the consequences of nanoscale confinement on materials functionality is one of the ``grand challenges" in the physical sciences. In this talk, I will focus on the issue of phonon confinement, discussing our recent measurements of both optical and acoustic phonons in model materials. Specific systems of interest include transition metal dichalcogenides (such as 2H- and IF-WS2) and complex oxides such as the spinels. In each case, we work with both traditional bulk analogs + chemically identical but morphologically different nanoscale materials, allowing us to quantify changes in bonding, phonon density of states, strain-induced changes in local structure, and engineering properties that derive from finite length scale effects.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Engineering Vascular Tissue from Cells and Cell-Derived Extracellular Matrix," by Dr. Marsha Rolle, WPI Biomedical Engineering Monday, 12/1/2008, 4:00 PM-5:00 PM
Tissue engineering has shown promise toward creating blood vessel substitutes for cardiovascular surgery. Recent clinical studies suggest that tissue engineered vascular grafts fabricated entirely from cultured cell sheets and cell-derived extracellular matrix (ECM) may be used as autologous arteriovenous fistulas in dialysis patients. However, the lengthy process required for their fabrication (~28 weeks), may limit their use. The focus of our research is to develop systems to more rapidly generate cell-based tissue constructs for systematic evaluation of the effects of soluble and genetic factors on tissue structure, ECM synthesis, and mechanical function. The seminar will focus on our recent work involving generation of cell-derived tissue rings by seeding smooth muscle cells (SMC) into custom, non-adhesive, circular wells. After only 8 days in culture, the resulting tissue rings were subjected to mechanical testing, and exhibited properties approaching those of native tissues. If successful, this system may allow rapid fabrication of vascular tissue constructs to facilitate the discovery of factors that control ECM synthesis and organization as a means of engineering tissue mechanical properties.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "The Physics of Line-tying in Magnetohydrodynamics" by Dr. Gian Luca Delzanno, Los Alamos National Laboratory Monday, 11/24/2008, 4:00 PM-5:00 PM
The study of Magnetohydrodynamic (MHD) linear stability with line-tying
has been the subject of intense research in the solar physics community
for several decades, in an attempt to understand the dynamics of solar
flares and the related mechanisms of energy release (see the review paper
[1]). Moreover, recent experiments on two cylindrical devices [2-3] have
brought even further interest on this subject. It is important to notice,
however, that applications to solar physics or to laboratory experiments
span a wide range of values of the Lundquist number S (proportional to the
inverse of plasma resistivity), S>10^10 in the solar corona while S~50 for
the experiments. In this presentation, I will therefore analyze the effect of plasma resistivity on line-tied modes in cylindrical geometry and discuss the
existence of tearing modes in line-tied plasmas [4]. Tearing modes occur in a plasma due to plasma resistivity. They are commonly associated to boundary layers and have growth rates proportional to a fractional power of plasma resistivity. Whether they can exist in a line-tied plasma has been matter of debate for a long time. I will show that the physics of line-tying prevents the existence of tearing modes and the only resistive unstable modes left in the plasma have a (much smaller) growth rate proportional to plasma resistivity.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Protein Dynamics" by Dr. Hans Frauenfelder, Senior Fellow at Los alamos National Laboratory Wednesday, 11/19/2008, 4:00 PM-5:00 PM
Proteins are complex systems that connect biology, biophysics, biochemistry, chemistry, physics,
and even mathematics. Proteins share similarities with supercooled liquids and glasses, such
frustration, the existence of an energy landscape, and alpha and beta fluctuations. Protein are,
however, far more complex than glasses and they can be modified and studied in much more detail.
Protein research therefore has not only impact in the life sciences, but also in other fields.
The beautiful pictures of protein structures that appear in many publications often create the
impression that proteins are rigid and function independently of their environment. Proteins are,
however, surrounded by hydration water and they are embedded in a bulk solvent. The motions in the
hydration shell and the bulk solvent actually control the internal protein motions. Experiments
with myoglobin that separately monitor the external and internal fluctuations show that the alpha
fluctuations of the bulk solvent drive the large-scale protein motions and that the beta
fluctuations of the hydration water drive the internal protein motions. These results hint that
the protein surface is functionally as important as the interior. The data also prove that there
is no dynamic transition or "fragile-to-strong transition" near 200 K in proteins.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department, Wonderful Speaker, "Wolfgang Pauli Stories - Personal Recollections" by Dr. Hans Frauenfelder, Senior Fellow at Los Alamos National Laboratory Monday, 11/17/2008, 4:00 PM-5:00 PM
Wolfgang Pauli was one of the most influential and remarkable physicists
involved in the revolution in physics that took place after about 1900. I was fortunate to be at
the Physics Institute of the ETH in Zurich from 1941 to 1952. The Institute was one of the few in
Europe that was not impacted severely by the war and so it became an unofficial European center. It was an exciting time for a graduate student. The scientific atmosphere became even more remarkable when Pauli returned from Princeton after the war. Bohr, Heisenberg, Kramers, Stern, Weisskopf, Wentzel,and, Zwicky could be encountered and there were many young brilliant theoreticians, for instance Glauber, Dyson, and Kallen who enjoyed stays in Zurich. Robert Schafroth, who later produced a theory similar to BCS, was my best friend. We sat every day in my little lab for a few hours, drank coffee, and discussed physics. Schafroth was Pauli's student and later his assistant. Thus Pauli came every day at about 3 PM to have coffee with us.
This gave me a chance to get to know Pauli well, learn about the many
Pauli stories, and observe his sharp wit in action. Read: Gino Segre, Faust in Copenhagen. Viking 2007.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Effects of Frustration and Disorder in Condensed Matter" by Dr. Frederick W. Fabris, Los Alamos National Laboratory Monday, 11/10/2008, 4:00 PM-5:00 PM
In this presentation I will discuss the frustration effects in some disordered systems. In the first part of this talk I will present the main types of magnets and how is possible to achieve high magnetic fields which have been used for the study of different physical properties of the materials. There are many kinds of compounds and systems who presents frustration and disorder. Frustrated systems have been studied for more than 50 years in materials ranging from spin glasses to quantum magnets. Frustration is a state of matter in which competing interactions cannot be satisfied simultaneously and consequently the ground state is degenerate. The effects of frustration can be identified in many experimental techniques. I will show how these effects are affecting phase transitions in high-temperature superconductors by measuring magnetotransport and DC magnetization. In some magnetic compounds (spin glasses and reentrant compounds) we can observe frustration effects in the Anomalous Hall Effect. Finally, in our current project, it has been proposed theoretically that a natural mineral named Azurite could be considered as a frustrated quantum magnet. We have performed dilatometry technique in order to investigate the magnetic phase diagram of this system.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Cationic Polymers and Naturally Occurring Vaults as Vectors for Delivery of Therapeutic Molecules" by Dr. Muri Han, David Geffen School of Medicine, University of California, Los Angeles Wednesday, 11/5/2008, 4:00 PM-5:00 PM
A carrier molecule, vector, facilitates the delivery of therapeutic drugs, proteins, and/or nucleic acids into the target sites in effective and safe ways. The vector should be easy to be modified in order to improve the stability, and to facilitate the transportation of therapeutic materials. A variety of non-viral vectors have received much attention in the past decade ; 1) Polyplexes are formed by the electrostatic interaction between plasmid DNA and polycations. They have been designed to condense pDNA and to facilitate
their cellular uptake in order to achieve effective gene delivery based on their versatility and ease of modification. Among such modifications, PEGylation of therapeutic particles is widely used to mask particles from the phagocytic system. PEG-block-polycation copolymers having the N-(2-aminoethyl)-2-aminoethyl group in the side chain (PEG-b-P[Asp(DET)]) were developed, which show high transfection efficiencies and low cytotoxicity. 2) Vaults are naturally occurring 13-MDa ribonucleoprotein particles with a highly conserved structure composed of three different proteins: major vault protein (MVP), vault poly (ADP-ribose) polymerase
(VPARP) and telomerase-associated protein 1 (TEP1). Recombinant vaults can be engineered by expressing MVP using the baculovirus system. Vaults have several advantages as a delivery system including low immunogenicity and structural stability. The hollow vault particle is able to encapsulate sequestered materials within the central cavity using a targeting peptide derived from the VPARP protein. The vault shell is a dynamic structure which can disassemble into halves in response to low pH. Considering the low pH of the endosome compartment, dissociation of vaults may allow
the intracellular release of molecules.
Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "A Comparative Study of General Finite Element Techniques in Atomistic-to-Continuum Coupling" by Dr. Peter W. Chung, U.S. Army Research Laboratory Monday, 9/15/2008, 4:00 AM-5:00 AM
It is well known that continuum based techniques such as Lagrangian or Eulerian numerical methods, which use constitutive relations that do not account for the atomistic structure, are invalid beyond the scope of their calibration. In regions containing dislocations, mobile defects, or nonlinear material, these numerical methods have to be modified to capture important phenomena. Yet they remain useful for dealing with field variations that occur slowly relative to atomic spacings. Molecular dynamics (MD), on the other hand, is an excellent means for modeling interactions on an atomic scale as well as predicting the response when sub-micron scale phenomena occur. However, MD can be computationally expensive beyond relatively small sample sizes. Therefore, to alleviate these problems multiscale methods have been developed in recent years to couple the continuum and atomistic scales together.
After a brief introduction of motivational problems currently being considered at the
U. S. Army Research Laboratory, we show a comparative study of the quality of interpolation that best suits continuum methods in regions at and near the interface with a molecular dynamics region. We specifically examine interpolation functions prominent in general finite element methods and meshless methods - Bubnov-Galerkin, partition of unity, and moving least squares - and assess their ability to capture a travelling wave through a discrete/continuum interface and a graded finite element mesh (increasing element size away from the MD region). Within the interface region, where the continuum and atomistic scales overlap, the displacements on the continuum are dictated by the atomistic results generated from MD.
The results of our study show that using simple changes to the interpolation quality of fields in the continuum, namely using partition of unity interpolation functions, produces accurate results compared to finite elements and moving least squares interpolation functions. For example, we demonstrate the effectiveness of partition of unity shape functions by simulating a Gaussian wave propagating throughout a 1D domain with a harmonic potential between neighbouring atoms. As the wave moves through the atomistic-continuum interface and through the graded mesh, the effectiveness of the partition of unity shape functions are clearly seen. In spite of the higher computational costs, the improvement in accuracy appears beneficial in practice. The presentation will conclude with a discussion of open issues related to the problem from the point of view of phonon transport and the on-going development of numerical methods that can adequately represent the physics through modeling methods representing multiple scales.
Sponsored by: WPI Physics Department, Izabela Stroe
Physics Colloquium, "Microflyidic Devices for Single Cells," by Dr. Amy Rowat, Harvard University Monday, 4/28/2008, 4:00 PM-5:00 PM
We have developed microfluidic tools for studying populations of single
cells. We encapsulate individual cells using polydimethylsiloxane
(PDMS) devices. Cells are trapped either in chambers as wide as a
single cell and long enough to contain many generations of cells, or in
15 micron droplets of a water-in-oil emulsion generated in PDMS
microfluidic devices. In the chambers, cells are maintained under
constant flow conditions, and divide for many generations. All progeny
deriving from the single cell are contained in the chamber, facilitating
studies of gene expression, stress response, and DNA repair as a
function of cell genealogy and replicative age. Drops of a water-in-oil
emulsion also function to isolate single cells over the experimental
timecourse. We have developed a device to immobilize drops, allowing us
to track single cell growth, and to quantify levels of secreted enzymes
that rapidly attain high concentrations due to the small drop volume.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Department Ph.D Defense, "Resonance Production and Nuclear Fragmentation for Space Radiation," by Ryan B. Norman, WPI Physics Department Graduate Student Thursday, 4/17/2008, 10:00 AM-11:00 AM
Space radiation and its effects on human life and sensitive equipment are of concern to a safe exploration of space. Radiation fields are modified in quality and quantity by intervening shielding materials. The modification of space radiation by shielding materials is modeled by deterministic transport codes using the Boltzmann transport equation.
Databases of cross sections for particle production are needed as input for transport codes. A simple model of nucleon-nucleon interactions is developed and used to derive differential and total cross sections. The validity of the model is verified for proton-proton elastic scattering and applied to Δ-resonance production. Additionally, a comprehensive validation program of the nucleus-nucleus fragmentation cross section models NUCFRG2 and QMSFRG is performed. A database of over 300 experiments was assembled and used to compare to model fragmentation cross sections.
Sponsored by: WPI Physics Department
Physics Faculty Search Candidate, "Precision Condensed Matter Measurements Applied to Biology" by Dr. Izabela Stroe, National High Magnetic Field Laboratory-Los Alamos National Laboratory Thursday, 4/10/2008, 4:00 PM-5:00 PM
I describe three experimental techniques, resonant ultrasound spectroscopy (RUS), relaxation calorimetry (RC), and dielectric relaxation spectroscopy (DRS). All are used extensively in condensed matter physics, and also are successfully applied to biological systems, proteins and DNA. These techniques have a common theme-they all probe normal modes of vibration. RUS probes mechanical oscillator strength (phonons), DRS probes the low-frequency sum of all the infrared-active oscillator strengths, and RHC probes entropy from all types of vibrational modes.
RUS measures the mechanical resonances of a material to determine all elastic constants at once. Its accuracy and high sensitivity can be useful in investigating the hydration and dehydration of protein crystals. The RC that we developed at LANL improves accuracy and reduces noise by eliminating digitization artifacts present in all commercial calorimeters. Originally developed for high temperature superconductors, we describe here its application to DNA melting. DRS, another popular condensed matter technique, measures the dielectric response of a system and is sensitive to the dynamics and hydration properties of proteins. We recently studied protein-solvent interactions of horse myoglobin (Mb) in glycerol/H2O mixtures with DRS from 40Hz-110MHz and showed that the Myoglobin (Mb)-related process is associated with the conformational uctuations of the whole Mb protein.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Nanomagnets: Long-Range Order, Wide-Range Applications" by Dr. Mark Tuominen, NSF Center for Hierarchical Manufacturing, UMASS Amherst Monday, 4/7/2008, 4:00 PM-5:00 PM
From data storage to generators to sensors, ferromagnetic materials
play a vital role in modern technology one that is continuously
evolving. Recent techniques for producing nanoscale ferromagnets are
changing the way magnetic materials and components are designed and
leading to new functional paradigms: rings, clusters, spin-polarized
current devices, nanostructured composites and more. This
presentation will discuss some of key experimental approaches in the
development to advance nanomagnetic technologies and the underlying
Physics behind these applications.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Snakes on a Plane" by Dr. David Hu, Courant Institute of Mathematical Sciences, New York University Monday, 3/31/2008, 4:00 PM-5:00 PM
Snakes propel themselves over land using a variety of techniques, including sidewinding, lateral sinuous slithering and a unidirectional accordion-like mode. We explore these friction-based propulsion mechanisms through a combined experimental and theoretical investigation. Particular attention is given to classifying the gaits of snakes according to Froude number and the relative magnitudes of the frictional forces in the tangential and normal directions. In a simple kinematic model, we prescribe the waveform of the snake and calculate its motion as required by the torque and force balances on its body. A key feature of our model is that it allows us to rationalize the snake's gait on the basis of speed and mechanical efficiency. We also provide a historical survey of our previous work on the propulsion of water-walking insects.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Case-Control Study of Lung-Cancer Risk from Residential Radon Exposure in Worcester County, MA," by Dr. Donald Nelson, Professor Emeritus of Physics at WPI Monday, 2/25/2008, 4:00 PM-5:00 PM
The risk of lung cancer from exposure to residential radon and its radioactive progeny has been thought to follow the Linear-No-Threshold hypothesis, that is, any amount is bad for a person and twice the amount is twice as bad. This has been difficult to establish because the risk at typical residential exposures is small and because of confounding factors, such as smoking. Individual North American case/control studies have been unable to establish the LNT relationship with the requisite statistical certainty, and a recently published pooling of those studies has also been unable to do so. During 199097 WPI in cooperation with the Fallon Health Maintenance Organization (lead researchers: Joel H. Popkin and Zenaida Popkin) undertook a case/control study of this risk. Our results have been analyzed by a Johns Hopkins University biostatistician, Richard E. Thompson. Forty-three IQP students were involved in the study over the seven years of data taking. The study enrolled 200 lung cancer cases and 397 controls matched in age and sex, all from the Fallon clientele. Each was administered a questionnaire concerning smoking habits, use of the house, job exposures to known or suspected carcinogens, etc. Multiple, year-long measurements of radon concentrations were made in each house. The risk was analyzed by conditional logistic regression by both stratifying the data with respect to radon concentration and by a natural cubic spline fitting technique, each of which let the data determine its own functional form. Smoking, years of residency, education, income, and exposure to known or suspected carcinogens were controlled for. Contrary to the LNT hypothesis, we found that small concentrations of radon typical of most houses (but not large concentrations) are actually protective with respect to lung cancer. Furthermore, over a portion of the exposure range the results are statistically significant, an unusual result for a study of this size.. Opposition to our non-LNT results not our methodology has delayed publication to the present time.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Faculty Search Candidate, "Bright Shining Nanosensor Platforms," by Dr. Jeffery Anker, Northwestern University Friday, 2/22/2008, 4:00 PM-5:00 PM
Fluorescent and plasmonic nanoparticles are increasingly used in cellular imaging applications because they fluorescence and scatter light so brightly that single nanoparticles can be observed over extended periods without bleaching. In addition, nanoparticles can act as a platform onto which many components can be loaded. By loading new components onto nanoparticle platforms, new properties are created with diverse applications. For example, using vapor deposition to coat a fluorescent nanosphere with a hemispherical half-shell of opaque metal breaks the nanosphere's optical symmetry so that it reflects and fluoresces light in an orientation-dependent manner. If the nanoparticle is magnetic, it aligns with an external magnetic and rotates to follow a rotating magnetic field.
The particle blinks as it rotates through bright and dark orientations. The blinking signal from these magnetically modulated optical nanoprobes
(MagMOONs) can be separated from unmodulated autofluorescence backgrounds.
The blinking frequency provides a measure of the local viscosity, while the fluorescence spectrum provides a measure of the concentration of chemicals that interact with the fluorophores in the nanosensors.
Plasmonic chemical nanosensors are another example of multifunctional nanoplatforms. In addition to serving as brightly scattering spatial labels, silver nanoprisms exhibit exquisite sensitivity to changes in local refractive index. When molecules adsorb to the nanoparticle surface, the resulting increase in local refractive index causes the nanoparticle extinction and scattering spectrum to redshift. Tracking this redshift in real-time facilitates the study of molecular binding kinetics and interactions. Overall, combinations of top-down and bottom-up nanofabrication processes provide control over nanoparticle optical, magnetic, and chemical properties allowing integration of features for a wide range of biomedical applications.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Phyisics Department Faculty Search Candidate, "Single Molecule Biophysics in Femtoliter Containers," by Dr. Lori S. Goldner, NIST Monday, 2/18/2008, 4:00 PM-5:00 PM
Biomolecular function can now be studied with unprecedented detail by optically observing the motion and conformational changes of single molecules. Typically, biomolecules or long-lived molecular complexes are tethered to a surface and studied on an individual basis utilizing the optical properties of attached dyes or nanoparticles. In contrast, more commonly-occurring short-lived complexes are not easily studied on an individual basis because each of the molecular components must be localized and yet permitted to interact in the observation region. I will demonstrate a new technique that uses aqueous nanodroplets as femtoliter "test tubes" to confine, study, and mix individual molecules. The nanodroplets can be manipulated, mixed and held immobile using optical tweezers. Confined molecules are studied by optical techniques that are sensitive to the fluorescence from a single dye molecule. I will discuss how single molecular-pair fluorescence resonance energy transfer can be used to study RNA antisense interactions or RNA/protein interactions, and how polarization anisotropy lifetime can be used to investigate the rotational dynamics of confined biomolecules.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Department Faculty Search Candidate, "Perturbed Dynamics of Soft Materials," by Dr. Chanjoong Kim, Harvard University Wednesday, 2/13/2008, 4:00 PM-5:00 PM
Soft matter is neither simple liquid nor crystalline solid, but in an in-between state, including bio materials, lipid membranes, liquid crystals, and colloidal suspensions. We are in fact familiar with soft matter from every-day life - paints, cheese, foams, or liquid crystal display - and are also made of soft matter. In contrast to hard condensed matter, soft matter is easily perturbed by a small stress, which also affects its dynamics and mechanical properties. I will discuss our recent findings on the perturbed dynamics of two soft materials; a colloidal glass and a gel. We find that diffusive behavior of colloidal particles is recovered by application of perturbation to a glassy system. These model systems may provide a valuable insight to the biological systems.
Physics Faculty Search Candidate, "Dynamics of Intramolecular Contact Formation in Islet Amyloid Polypeptied (IAPP)", by Dr. Sara Vaiana, NIH Wednesday, 2/6/2008, 4:00 PM-5:00 PM
Measuring the dynamical properties of unfolded chains in solution, and in particular of amyloid forming peptides, is of key importance to understand the first elementary steps in folding, misfolding and aggregation. Protein misfolding and aggregation is at the basis of a vast class of diseases (including Alzheimer's and type II Diabetes) called amyloid diseases, where aggregates of specific structure, called amyloid fibrils, are formed. In type II Diabetes a peptide called human islet amyloid polypeptide (hIAPP) forms amyloid fibrils inside the b-cells of the pancreas (where insulin is produced) contributing to b-cell death and consequent impairment of insulin production.
In order to understand aggregation it is critical to know what the constituents are. As an example I will present a study of IAPP, where we have directly compared an aggregating variant (hIAPP) to a non-aggregating variant (rIAPP), in their monomeric states. Before aggregating into highly ordered amyloid fibrils the hIAPP monomer is known to be unstructured. This poses the fundamental question of how to parameterize an unstructured chain. We do this by measuring the rates of intra-molecular end-to-end contact formation using tryptophan triplet quenching by cystine. We find a significant chain collapse in aqueous solvent for both peptides, and the appearance of kinetic traps that slow down chain dynamics. Interestingly rIAPP shows an increased chain stiffness with respect to hIAPP.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Department Faculty Search Candidate, "Flagella and Swimming Bacteria", by Dr. Nicholas Darnton, Amherst College Wednesday, 1/30/2008, 4:00 PM-5:00 PM
Many bacteria swim by rotating flagella. The swimming cell is an ideal candidate for a physicist's approximation: it is very nearly a prolate spheroid (the cell body) pushed by a simple helical propeller (the flagellum). Moreover, since the motion occurs at low Reynolds number it can be solved analytically. Unfortunately, most bacteria, including common pathogens such as Escherichia coli and Salmonella, have several flagella that operate simultaneously. This slightly more complicated problem - propulsion by several interacting flagella - has not been solved satisfactorily, either analytically or numerically.
I will summarize the simple physics of swimming cells and of the flagellar rotary motor, and point out as-yet-unresolved issues involving interacting flagella, such as the unknown mechanism that causes flagella to bundle. From high-speed video of fluorescently labeled bacteria, we have attempted a complete force-balance accounting of swimming cells. We find that, contrary to physical intuition, adding flagella does not allow a cell to swim faster. In light of this conclusion, I will offer some ideas as to the purpose of having multiple flagella.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "The Domino Effect and the Flagellar Motor" by Dr. Greg Huber, UCONN Monday, 1/28/2008, 4:00 PM-5:00 PM
The flagellar motor of bacteria is a nearly-stoichiometric rotary molecular machine, perhaps the most elaborate engineered by evolution. It harnesses the chemical energy associated with a proton gradient for its rotation (typically hundreds of Hz), while, at longer time scales, stochastically switching between clockwise (CW) and counterclockwise (CCW) rotations. And while the switching of the rotational direction of the flagellar motor plays a crucial role in bacterial chemotaxis, its mechanism remains poorly understood. Here, I'll present recent work on the switch statistics of the flagellar motor of Caulobacter crescentus. I'll show how the interval distribution of the CW and CCW rotation provides insight into the switching, and describe a model that combines first-passage-time theory and dynamic binding to explain the switching mechanism. The model accounts for the motor's dependence on CheYp concentration, and predicts that dynamic binding of CheYp to the switch-complex proteins is the key to the signal amplification of the motor.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Surface Fluctuations on Polymer Films" by Dr. Ophelia K.C. Tsui, Boston University Monday, 1/21/2008, 4:00 PM-5:00 PM
Classical phase transition theory predicts that a homogeneous system is unstable against spontaneous phase-separation into an inhomogeneous structure if the second derivative of its free energy, G, as a function of the order parameter, h0, is negative. However, this prediction a result of the mean-field formalism is expected to fail if the fluctuations in the system order parameter due to thermal fluctuations are larger than the average order parameter, which occurs either when |h0 hsp|/hsp 0 (where hsp is the order parameter such that G(hsp) = 0) or when the dimension of the system is less than six. This prediction is well attested in three-dimensional (3D) systems, where the effects of fluctuations are usually found to be important only when h0 is within a few % from hsp. No experimental study has been performed on 2D systems, where the effects of fluctuations is stronger. Here, we use polystyrene films deposited on oxide coated silicon as a model 2D system to study the effect of fluctuations on the stability of a system for which the order parameter, h0, is the film thickness. We examine the temporal growth of surface capillary waves on this system of films with different h0. For the most unstable film (where h0 is within 98.8% from hsp), the data fits well to the mean-field theory. But as h0 is increased slightly such that h0 is within 97.7% from hsp, the mean-field theory demonstrates marked disagreement with experiment. We verify that the deviations are caused by large-amplitude fluctuations on the film surface due to stochastic thermal noises. Our results thus show that the stability of a low dimensional system can be easily compromised by spontaneous fluctuations, and cannot be predicted at all by the mean-field theory. We thank the support of NSF through project no. DMR 0706096.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Wonderful Speaker Series, "Small-Particles-Big Qulestions" by Dr. Ulrich Heintz, Boston University Monday, 12/3/2007, 4:00 PM-5:00 PM
Dr. Heintz will present recent findings from the accelerator at Fermilab and tell us about the smallest particles: the W Boson, the Top Quark as well as the Technicolor/Z'Search.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Fundamental Physics Through Astrophysics", Dr. Christopher Stubbs, Harvard University Monday, 11/12/2007, 4:00 PM-5:00 PM
We now have persuasive evidence for physics beyond the standard model,
from astrophysical observations. The motion of luminous stars and gas
in galaxies and galaxy clusters imply the existence of dark matter, which
is probably made of something other than protons, neutrons, and electrons.
More recently the convergence of multiple lines of evidence that indicate
an accelerating expansion of the Universe points to new physics ("Dark Energy")
at the troublesome interface between gravity and quantum mechanics.
I will describe projects our group has undertaken to address the Dark Energy problem,
including bouncing laser pulses off the moon and looking for exploding stars
halfway across the Universe.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Photonic Crystal Defect Mode Analysis" by John Albrecht, Air Force Research Laboratory, Wright-Patterson Air Force Base-Ohio Monday, 11/5/2007, 4:00 PM-5:00 PM
Photonic crystals, in this case periodic structures of dielectrics, can be used to control light propagation through geometric features and dielectric contrast. An especially attractive application for photonic crystals is to construct localized electromagnetic modes by introducing defects in the periodic structure. These confined modes could be used as optical resonators, laser cavities being the most obvious application. In this seminar, I will discuss a theoretical approach for calculating the photonic structure of defects in 2D photonic crystals. The central feature of this approach is the construction of a basis set of local vector Wannier functions from the perfect crystal eigenstates. It has been proposed[1] that this basis be used to expand photonic crystal defect states analogous to the famous expansion in linear combinations of atomic orbitals of the electronic structure of the ideal silicon vacancy[2]. These approaches rely on a small number of basis states local to the defect region. Here, we replace the Fourier expansion of the perfect crystal by a real-space description in vector finite-elements. This method allows the computation of the Wannier basis on the same grid used to compute the perfect structure and results in a straightforward defect eigenvalue problem. I will present results [3] that verify the eigenmodes of the crystal and examine the physics of selected defect modes.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Comet Acoustic Surface Sounding Experiment Within the European ROSETTA Mission" by W. Arnold, Fraunhofer-Institute for Nondestructive Testing (IZFP), Saarbrucken, Germany Friday, 11/2/2007, 3:00 PM-4:00 PM
Comets are thought to contain pristine material from the time of the formation of the planets.
The Comet Acoustic Surface Sounding Experiment
(CASSE) is an instrument of the Surface Electric Sounding and Acoustic Monitoring Experiment
(SESAME) within the Rosetta mission built in international European co-operation. The Rosetta mission spacecraft was launched in April 2004.
The spacecraft itself carries a number of experiments and also a lander called Philae which will land on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of SESAME are to measure mechanical and electrical properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface. Most of the sensors are mounted within the six soles of the landing gear feet, in order to provide good contact with or proximity to the cometary surface.
CASSE is designed to obtain data on the elastic properties of the comet surface by measuring the time-of-flight of surface P- and S-wave signals around 1 kHz. The sounding experiments to be performed are also used to obtain information on the structure of the comet material by means of backscattering. The sounding signals are generated by piezo-composites mounted in the lander-soles. The piezo-composites were built by the IZFP.
This contribution discusses the concept and the scientific and engineering aspects of the CASSE experiment. In particular the construction of the transducers and the expected scenario of wave propagation on a comet surface will be discussed, as well as the inversion of the data in order to obtain the wanted quantities, in particular elasticity and porosity. Some of the concepts for the inversion of the data are lent from NDE of porous materials. In highly attenuating fine-grained sand the obtainable signal-to-noise ratio of piezo-composites of the CASSE instrument was evaluated. Data which were used in the design of CASSE were also obtained by measurement of sound attenuation and sound velocity in comet-analog material which is a watery suspension of minerals, mostly olivine injected via spray guns into a dewar vessel, filled with liquid nitrogen (LN2) and producing a fluffy ice/mineral mixture.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Menagerie of Viruses: Diverse Chemical Sequences or Simple Electrostatics?", by Professor M. Muthukumar, UMASS Amherst Monday, 10/29/2007, 4:00 PM-5:00 PM
The genome packing in hundreds of viruses is investigated by analyzing the
chemical sequences of the genomes and the corresponding capsid proteins, in
combination with experimental facts on the structures of the packaged genomes. A
universal model, based simply on non-specific electrostatic interactions, is able to predict
the essential aspects of genome packing in diversely different viruses, such as the genome
size and its density distribution. Our result is in contrast to the long-held view that
specific interactions between the sequenced amino acid residues and the nucleotides of
the genome control the genome packing. Implications of this finding in the evolution and
biotechnology will be discussed.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Swarming bacteria: a self-propelled 2D gas", by Professor Nicholas Darton, Amherst College Monday, 10/8/2007, 4:00 PM-5:00 PM
Under appropriate conditions of wetness and temperature, many commonly studied bacteria form a thin, highly dynamic layer that quickly grows to cover an agar plate. This phenomenon, known as swarming, enables rapid colonization of a rich medium. Swarmer cells are phenotypically distinct from vegetative cells they are longer, more highly flagellated, and more motile and some of the genes that govern swarm differentiation have been identified.
The edge of a swarm colony is an extensive monolayer of billions of constantly moving cells. Formally, this should be described by the two-dimensional statistical mechanics of a self-propelled gas, sometimes known as 'boid' theory. Versions of this theory predict phase transitions and the emergence of long-range symmetry-breaking order. We are currently measuring the statistical properties of cell motion in Escherichia coli swarm monolayers, and comparing them to the better-known statistics of cell swimming in bulk (3D) fluid. To date, we have high-magnification data covering the motion of individual cells, but we have seen coherent motions over length scales of more than two orders of magnitude limited only by our ability to make large, homogeneous swarms. I will discuss our observed short-range anisotropic velocity correlation function as a combination of nematic liquid crystal order and self-propulsion.
Physics Colloquium, "Approaching and Leaving Metastability" by Professor Harvey Gould, Physics Department, Clark University Monday, 10/1/2007, 4:00 PM-5:00 PM
I will discuss the approach to metastable equilibrium in the Ising model using a cluster representation and find that the system is still changing at the microscopic level even after the mean values of various global quantities have ceased to change. I then will discuss the nature of nucleation in both Ising models and supercooled Lennard-Jones liquids.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Ordering and Flocking in a Collection of Fluidised Rods" by Professor Narayanan Menon, Physics Department, UMASS, Amherst Monday, 9/24/2007, 4:00 PM-5:00 PM
I will discuss experiments that study the ordering of fluidised rod-like grains into orientationally ordered states and compare these to the phases of equilibrium liquid crystalline systems. The most dramatic phenomena in the system, however, are associated with the motions of the rods rather than their order. These nonequilibrium effects include persistent vortices and large-scale swirling. Most importantly, the population of rods shows giant, persistent density fluctuations, which I will discuss in the context of recent ideas of the flocking and
swarming of active, or self-propelled, particles.
Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Atomic Scale Friction and Microscale Machines: These Squeaky Wheels will get no Grease" by Professor Jacqueline Krim, North Carolina State University, Physics Department Monday, 4/30/2007, 4:00 PM-5:00 PM
There is widespread belief that the future is likely to be dominated by MEMS (Micro-Electro-Mechanical Systems) and/or NEMS (Nano-Electro-Mechanical Systems) devices, which will be used in such diverse applications as gas and pressure sensors, accelerometers, chemical analytic ``microlaboratories'', and airborne ``nanosatellites''. Because MEMS devices must react to mechanical signals, many employ construction topologies that require physical motion and the concomitant lubrication which prevents heating/melting and wear of the device. It is well established however that the macroscopic laws governing friction and wear are inapplicable at the molecular scale. The need to carry out new and fundamental research relevant to the development of optimal, or even operational submicron-scale mechanical systems is therefore increasingly important.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloqium, M.S thesis presentation, "Mori Projected Dynamics On a Quantum System", by Rachel Nasto, WPI Physics Department Graduate Student Thursday, 4/26/2007, 4:00 PM-5:00 PM
In this thesis we discuss Mori Projected Time Dynamics in a quantum mechanical system. As a
precursor to calculating the time derivative of a mixed state of the system we examine the derivation
of the Mori-Zwanzig formalism. We consider the exact calculation of the time derivative of a mixed
state. We then calculate the same time evolution using Mori Theory and compare the two results.
From the general calculation of the Mori Equation we were able to perform a series of simple tests
to compare Mori Theory to the known result. We discovered that in each of the four simple cases
the Mori Equation and the direct calculation of the time evolution give the same result, but in the
more complicated situations the two calculations differed. This result leads us to believe that the
Mori Equation is an accurate way of calculating the derivative of a mechanical variable in a quantum
system.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department, Ph.D. Dissertation, "Summing the Infinite Ladder", by Frank Dick, WPI Physics Department Graduate Student Monday, 4/23/2007, 4:00 PM-5:00 PM
In quantum field theory, the Dyson scattering matrix is a perturbation expansion in the interaction Hamiltonian that generates an infinite series of Feynman diagrams. A holy grail of QFT is to sum the series. The Bethe-Salpeter equation (BSE) sums all diagrams in what is known as the ladder approximation, but is restricted to elastic scattering processes. As part of my research, I developed a generalized Bethe-Salpeter equation (GBSE) to handle inelastic processes in the ladder approximation. The GBSE, formulated using quantized scalar field theory introduces a systematic method for analyzing families of coupled reactions. A formalism is developed centered around the amplitude matrix M' defined for a given Lagrangian. M' gives the amplitudes of a family of reactions that arise from the Lagrangian. The formalism demonstrates how these amplitudes, to 2nd order, segregate into independent groups of coupled BSEs. A proof is given of the equivalence of the series of ladder diagrams generated by M' and the S-matrix. The GBSE formalism is applied to the coupled BSE (CBSE) of Faassen and Tjon, showing that the CBSE is missing a coupling channel, and in the expansion, under counts ladder diagrams.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Atomoptics and Atomtronics", by James Stickney, WPI Physics Department - Graduate Student Monday, 4/16/2007, 4:00 PM-5:00 PM
The invention of the laser in the early 1960s caused a revolution in modern optics. Lasers found applications in medicine, telecommunications, information storage, and, perhaps most importantly, precision measurements. The state of matter known as Bose-Einstein condensate (BEC) is the matter-wave equivalent of laser light. Because they are much more sensitive, it is believed that BEC-based "atomoptical" devices will eventually replace many current laser-based devices used in precision measurements. BEC based devices that are analogous to electronic devices may also be possible. In an "atomtronic" device, the atoms in the BEC play the role of the electrons in an electronic circuit. In this presentation, the current state of BEC-based devices will be discussed, with particular emphasis how atom-atom interactions affect their operation.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Optical Cooling in High Power Solid State Lasers", by Dr. Richard S. Quimby, Physics Deparartment, WPI Monday, 4/2/2007, 4:00 PM-5:00 PM
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "Colloidal Interactions and Controlled Self-Assembly in Ordered Soft and Biomolecular Materials," by Dr. Ivan Smalyukh, University of Illinois, Urbana Monday, 3/5/2007, 4:00 PM-5:00 PM
Self-assembly of colloidal particles and molecules into ordered structures is a fascinating phenomenon of both fundamental and applied interest. This lecture will demonstrate that the self-assembly phenomena in elastic liquid crystal (LC) media are particularly rich and can be controlled. In LCs the embedded spherical particles can cause elastic distortions of either dipolar or quadrupolar symmetry because of the anisotropic molecular interactions at the colloid-LC interfaces. I will show that the surface treatment of the colloidal particles and the LC confinement determine the nature of inter-particle interactions as well as the formation of colloidal structures. For example, the particles with the dipolar elastic distortions interact similar to the electrostatic dipoles and form chains along the far-field LC director. The particles with tangential surface anchoring and quadrupolar elastic distortions aggregate into chains directed at about 30 degrees to the average orientation of the LC molecules far from the spheres. When the elasticity-mediated colloidal interactions between particles take place at the surfaces of anisotropic fluids, the particle arrangements strongly depend on the boundary conditions at the confining surfaces and can vary from linear chains to hexagonal colloidal structures. Moreover, both in the LC bulk and at the surfaces, the inter-particle interactions and the structures are strongly altered by adding tiny amounts of chiral additives, resulting in twisted colloidal chains and spirals. I will show that even live biological cells (such as Pseudomonas aeruginosa) can be orientationally ordered when placed into the elastic liquid-crystalline matrices of DNA biopolymers. The particle motions are monitored using video-rate optical imaging and the interactions are explored using laser tweezers. The inter-particle colloidal forces exhibit rich angular and distance dependencies, consistent with the symmetry of the elastic distortions around the particles. The experimental observations are modeled considering the LC elastic properties and correctly reproduce the experimentally measured parameters. These findings impinge broadly on understanding of phenomena as diverse as colloidal interactions in anisotropic media and biofilm formation in the presence of extracellular biopolymers, as well as demonstrate the possibility of controlled colloidal self-assembly into tunable photonic crystal structures.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "Particulate Flows" by Dr. Stephan Koehler, Emory University Monday, 2/26/2007, 4:00 PM-5:00 PM
Foams and granular materials are two fundamental model systems of complex fluids studied by soft condensed matter physicists. A common feature is their cellular structure, which consists of bubbles and grains respectively. Their particle sizes exceed microns, and therefore at rest these materials are jammed, athermal systems. The packing and shearing of these cellular elements and their micro-scale interactions lead to fascinating macroscopic continuum-type behaviors. Familiar examples include foam drainage of freshly-poured beer and the sudden onset of granular flow causing landslides. The mechanical properties of these complex fluids span a large dynamical range of continuum behavior and include elasticity, viscosity and plasticity.
I will compare and contrast behaviors of foams and granular materials based upon various experiments performed in my lab. I will discuss the similarity between Darcy flow through soils and foam drainage in the limit of large surface viscosity. Moreover, foams and granular particles have similar rheological behaviors, which depend on pressure between particles, shearing rates and shearing displacements. For example, both systems are prone to shear band formation, and have a finite yield stress. I will conclude with recent experimental results for self-propulsion that were inspired by sand-swimming animals such as desert vipers and lizards.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "From Imaging to Therapy: The Physics of Gas Bubbles for Medical Applications of Ultrasound," by Dr. Elisabetta Sassaroli, Dept. of Radiology, Brigham & Women's Hospital and Harvard Medical School Wednesday, 2/21/2007, 4:00 PM-5:00 PM
Gas bubbles powerfully influence the acoustics in tissues and liquids. This presentation gives an introduction to the physics of gas bubbles, focusing primarily on biomedical applications. In a sound field of sufficient amplitude, bubbles oscillate nonlinearly and emit harmonic and subharmonic components of the driving frequency. In practice, microscopic bubbles are injected into the blood stream to increase the echo from blood, in particular at the level of the microcirculation. As the pressure is further increased, bubbles may undergo inertial cavitation. Inertial cavitation is characterized by the sudden expansion and then rapid collapse of the bubble. Bubble collapse can generate shock waves and shear, which can produce erosion and bioeffects. There is clear evidence that the permeability of the cell membrane to large molecules is increased when suspensions of cells are exposed to ultrasound in the presence of microbubbles.
The understanding of bubble acoustical behavior in a confined geometry is essential for their control and exploitation when injected into the blood stream. Experimental and numerical modeling of microbubble behavior in micron-sized tubes and tunnels embedded in gel will be presented
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "Colloids in action: Microscopic insights into clogging and jamming", by Dr. Daniel Blair, Harvard University Monday, 2/12/2007, 4:00 PM-5:00 PM
Suspensions of colloidal particles are astounding model systems used
to study a variety of fundamentally important problems in soft matter
physics. The versatility of colloids is due in large part to the
increasing sophistication of their synthesis, and the relative
simplicity of their interactions. This talk will discuss recent
experimental results on two soft-matter topics that utilize colloidal
particles; clogging during flow and jamming in glasses.
I will first present results from microfluidic studies of clogging in
model porous media. By using simple imaging techniques, and a minimal
geometric model, I will describe the physical origins of clogging in
microfluidic devices. These results demonstrate that the aggregation
of micron sized particles, in a low Reynolds number flow, is dominated
by single particle interactions. In the second half of the talk, I
will discuss the microscopic response of colloidal glasses to a
macroscopically applied compressive stress. Using time resolved laser
scanning confocal microscopy, I identify and track the motion of
thousands of colloidal particles in real space over very long times.
With this technique, and ideas garnered from metallic glasses, the
complete local strain tensor for each particle is determined. I will
demonstrate that highly localized, correlated shear and compression
transformations are necessary for colloidal glasses to approach a
maximally jammed state.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Faculty Candidate Colloquium,"Fingers and Holes in Shear Thickening Fluids" by Dr. Robert Deegan, Bristol,UK Monday, 2/5/2007, 4:00 PM-5:00 PM
The simplest models of matter posit a linear relationship between the stress
and deformation, as for example in Hooke's law. However, many useful and
important fluids (such as, shampoos, industrial slurries, geophysical fluids, polymeric melts) exhibit a nonlinear response to stress. I will discuss the behaviour of shear thickening fluids subjected to vertical vibrations in the context of pattern forming systems. I will show that a mixture of cornflour/water or glass beads/water vibrated above a critical acceleration (approximately 10 g) is unstable to perturbations. At low accelerations a small indentation of the fluid surface will grow until it reaches the bottom of the container, forming a circular hole. At higher accelerations the rim of the hole becomes unstable and develops an upward
growing tongue. At even higher accelerations, the entire layer writhes in
a disordered manner. The mechanism for these instabilities is unknown. I will present experimental correlations between these instabilities and the fluid's rheological proprieties.
Wonderful Speaker Series, "Dripping, Jetting, Drops and Wetting: the Magic of Microfluides" by Dr. David Weitz, Department of Physics, Harvard University Monday, 1/15/2007, 4:00 PM-5:00 PM
This talk will discuss some of the new opportunities that arise by precisely controlling fluid flow and mixing using microfluidic devices. I describe studies to elucidate mechanisms of drop formation and use these to create new fluid structures that are difficult to achieve with any other method. I also show how the exquisite control afforded by the microfluidic devices provides the enabling technology to use droplets as nanoreactors to qualitatively increase the rate of combinatorial screening of chemical reactions.
Physics Colloquium, "Casimir Forces and New Principles for Understanding the Wetting of Liquids" by Dr. Rafael Garcia, Physics Department, WPI Monday, 12/11/2006, 4:00 PM-5:00 PM
Despite the fact that during the last century there has been a lot of research into wetting and the properties of liquids, many things are not known and discoveries, potentially of great importance to science, technology and society, continue to be made about how, why and when liquids wet solid surfaces. During the last 20 years, we have seen the discovery of thermodynamic Casimir effects, triple point wetting, prewetting and critical wetting, to name a few. The wetting of a liquid droplet on a solid surface is universally characterized by its contact angle, the angle between the liquid surface and the solid surface. For a liquid which completely wets a surface (contact angle of zero), the wetting is characterized by the thickness of the adsorbed film. New experimental research at WPI is focused on discovering the principles necessary for predicting how the wetting of polar liquids and liquid crystals changes as we vary the temperature. Being investigated are water, nitrous oxide and the cigar-shaped n-alkylcyanobisphenyl liquid crystals. Despite the ordinary nature of these materials, preliminary data demonstrate a variety of extraordinary behaviors not anticipated by theory. Our goal is to try to confirm and understand these phenomena within the framework of Cheng-Cole-Saam-Treiner approximation for the difference between the liquid-solid and gas-solid surface tensions.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "High-power, Low-noise 1.5-m Slab-coupled Optical Waveguide Amplifiers (SCOWAs) and their Applications", by Dr. Paul W. Juodawlkis, MIT Monday, 12/4/2006
The slab-coupled optical waveguide amplifier (SCOWA) is a new class of semiconductor optical gain medium that was invented at MIT Lincoln Laboratory. The SCOWA architecture enables devices having Watt-level optical output power, low internal loss (~ 0.5 cm-1), and large (> 5 x 5 m) symmetric fundamental-mode operation. In this talk, we will review the SCOWA operating principles and describe applications of the SCOWA technology ranging from high-power semiconductor optical amplifiers (SOAs), to monolithic and ring-cavity mode-locked lasers, to single-frequency external cavity lasers. The talk will also begin with a brief overview of MIT Lincoln Laboratory.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Why Do Silos Fail and Hourglasses Tick?" by, Dr. Bulbul Chakraborty, Brandeis University Monday, 10/30/2006, 4:00 PM-5:00 PM
Materials as diverse as molecular liquids, foams and granular matter experience a transition from a fluid-like state to a solid-like state characterized only by a sudden arrest of their dynamics. These sudden arrests are difficult to predict and lead to catastrophic events such as the buckling of grain silos. Numerous experiments and simulations indicate the appearance of large-scale dynamical heterogeneities and an associated growing dynamical length scale. In colloids near the glass transition, for example, fast-moving particles were observed to be spatially correlated with a characteristic cluster size that increased as the glass transition was approached. In granular materials, spatial structures have been directly observed in experiments on flowing systems. Several questions naturally arise: (1) Are dynamical heterogeneities a necessary precursor to dynamical arrest of the jamming kind? (2) Do these heterogeneities and their mesoscopic scale lead to any kind of universal dynamical behavior irrespective of significant differences in microscopic dynamics? (3) Do static structures such as force chains observed in jammed granular packings emerge out of dynamical heterogeneities? In this talk I will address these questions through the analysis of a simple model that focuses on the essential effects of driving and dissipation in a flowing granular system.
Sponsored by: physics Dept., Dr. Stephen Jasperson
Physics Colloquium, "New Materials for Sprintronic Applications" by Dr. Don Heiman, Northeastern University Monday, 10/9/2006, 4:00 PM-5:00 PM
Devices for spin-electronic applications are expected to benefit from new materials and unique device structures. With that goal in mind, my research group is currently focusing on two main areas: making new semiconductors which are ferromagnetic; and fabricating novel ferromagnetic metals which are compatible with semiconductors. I will briefly review spintronic mechanisms and devices, followed by discussion of our current work on the MBE fabrication of GaAs-based ferromagnetic materials.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Special Physics Colloquium, "Medical Physics as a Career" by Dr. Alex Cardenas, Department of Radiation Oncology, Lehigh Valley Hospital, Allentown, PA Friday, 10/6/2006, 4:00 PM-5:00 PM
This talk will give an overview of careers in medical physics based on the speakers own experience. He graduated with a B.S. in Physics from WPI in 1996, then received a Ph.D. in nuclear physics from Purdue University, following which he entered the field of medical physics. The talk will be informal, with plenty of opportunities for questions from the audience. All are invited.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Colloquium, "Photoluminescence Competitiveness in GaAs/AlGaAs Single Heterojuction", by Dr. Abdellah Dakhama, Physics Department, WPI Monday, 9/25/2006, 4:00 PM-5:00 PM
Near-field photoluminescence using a near-field scanning optical microscope (NSOM) has been a valuable tool in studying excitons in GaAs-based quantum wells. The resolution that is beyond the diffraction limit revealed striking, new results that cannot be captured by far-field photoluminescence.
We report low temperature near-field photoluminescence imaging of the electron density in a modulation doped GaAs/AlGaAs single heterojunction with a spatial resolution of 100 nm. We discovered an unusual competitiveness in the photoluminescence between the first electron subband to first heavy-hole subband transition and the second electron subband to first heavy-hole subband transition. We attribute this competitiveness to the fluctuations in the electron density which results from fluctuations in the donor (Si) density.
NSOM is itself a technique that is still under research and development. Our goal is not limited to just imaging the surface topography but extends to imaging physical properties of buried quantum structures. In the first part of the talk we will discuss the experimental setup used for near-field scanning photoluminescence experiments. In the second part we will present our results for a two-dimensional electron gas. Finally, preliminary results from near-field scanning fluorescence will be briefly discussed.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Colloquium, "Structure and Dynamics of Nano-colloidal Silica Gel Dispersion", By Dr. Germano Iannacchione, Physics Department, WPI Monday, 9/18/2006, 4:00 PM-5:00 PM
This talk presents a study on the structure and the dynamics of a nano-colloidal silica gel dispersed in an organic solvent (octylcyanobiphenyl, 8CB) as a function of silica density by x-ray intensity fluctuation spectroscopy (XIFS). The silica density of the dispersed aerosil gel samples ranged from 0.03 to 0.20 g cm-3 and the autocorrelation of the silica scattering were probed over the q range from 0.03 to 0.15 nm-1 (corresponding to length scales from 42 to 209 nm) at a constant room temperature at which 8CB is in the smectic-A phase. The gel structure has a fractal dimension in this density range of df ~ 2.15. The time autocorrelation functions of the gels show clear density-dependent and complex dynamics. The gel relaxation times are very long and become bimodal with nonergodic character for densities from 0.10 to 0.16 g cm-3. In this same density range, the fluctuation contrast (strength) is a minimum while the relaxation time becomes independent of wavevector. Together, these results indicate that there is a narrow silica density range for these gels in which the dynamics changes dramatically. This suggests a complex phase diagram for the dynamics of aerosil gels as a function of densification.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Baked Alaska: Inhomogeneous Phases of Bosons Trapped in an Optical Lattice," by Dr. Courtney Lannert, Wellesley University Monday, 5/1/2006, 4:00 PM-5:00 PM
Abstract: Recent work with bosonic atoms at ultra-low temperatures in an optical lattice has opened new avenues for exploring the superfluid and Mott-insulating phases of bosons. The presence of the (usually harmonic) confining trap in the experimental set-up is likely to cause complications that are either a nuisance or a boon, depending on one's perspective.
Adopting the latter state of mind, we can see how, when properly designed, these experiments might create novel spatially-inhomogeneous phases. I will describe some recent work on the Mott-insulating and superfluid regions present in these systems. The stability of the Mott phases is an important consideration. I will describe a proposed experiment for spatially resolving the spatial structure of the system and some unique physics associated with the superfluid regions.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "Atomic Scale Friction and Microscale Machines: These Squeaky Wheels Will Get No Grease", by Prof. Jacqueline Krim, N. Carolina University Physics Department Sunday, 4/30/2006, 4:00 PM-5:00 PM
There is widespread belief that the future is likely to be dominated by MEMS (Micro-Electro-Mechanical Systems) and/or NEMS (Nano-Electro-Mechanical Systems) devices, which will be used in such diverse applications as gas and pressure sensors, accelerometers, chemical analytic ``microlaboratories'', and airborne ``nanosatellites''. Because MEMS devices must react to mechanical signals, many employ construction topologies that require physical motion and the concomitant lubrication which prevents heating/melting and wear of the device. It is well established however that the macroscopic laws governing friction and wear are inapplicable at the molecular scale. The need to carry out new and fundamental research relevant to the development of optimal, or even operational submicron-scale mechanical systems is therefore increasingly important.
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium and Ph.D. Defense, "Reciprocity Between Emission and Absorption for Rare Earth Ions in Glass", by Rodica Martin, WPI Physics Graduate Student Tuesday, 4/25/2006, 9:00 AM-10:00 AM
The McCumber theory allows optical emission cross section spectra to be determined from measured absorption spectra, and vice versa. The present work is a detailed study of the range of validity of the McCumber theory, focusing particularly on those aspects that most critically affect its applicability to transitions of rare earth ions in glasses. When the various possible sources of systematic error are properly accounted for, we find in all cases an excellent agreement between the calculated and the measured cross section spectra. This suggests that at room temperature, the McCumber theory is not limited to crystalline hosts, as has been asserted in the literature, but describes quite well the reciprocity between emission and absorption for the broader transitions of rare earths in glassy hosts. At lower temperatures, however, discrepancies are observed, and our results suggest that the McCumber theory must be used with caution for temperatures below 200 K.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "A New Approach to Diffusion Analysis for Multicomponent Systems", by Dr. L. R. Ram-Mohan, WPI Physics Department Monday, 4/24/2006, 4:00 PM-5:00 PM
--Local Averages of Diffusion Coefficients and the Transfer Matrix Method--
The diffusion of matter from one region into another is a universal phenomenon occurring in gases, liquids and solids. In metallic alloys, we can study diffusion by putting two alloys together and allowing the components of one alloy to diffuse into the other alloy at high temperature, and then quenching the system to freeze the diffusion. We can then experimentally determine the concentration profiles. Such diffusion under controlled conditions gives us information about the diffusion process and the stability of the interface. This has wide applications in the welding of metals and similar industrial processes.
Until recently, the diffusion coefficients could not be determined in a reliable manner in multicomponent diffusion, such as ternary or quaternary diffusion. They are functions of composition, making diffusion an intrinsically nonlinear process. I will present a new method of determining the diffusion coefficients developed recently, and show how the concentration profiles can be reconstructed, given the diffusion coefficients, using a transfer-matrix method (TMM). The TMM developed by me is applicable to any number of diffusion components.
I will also mention the directions in research we are pursuing. We are close to being able to predict the diffusion path in a diffusion couple given the end compositions. Diffusion in three- and four-component systems already displays a rich variety of complex phenomena. I will illustrate these with examples. We are starting on an investigation of grain boundary diffusion and triple junction diffusion in macroscopic and nanoscopic systems.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium, "Fascination of Diamonds," by Dr. A. K. Ramdas, Purdue University, Department of Physics Monday, 4/17/2006, 4:00 PM-5:00 PM
Laymen and Scientists alike have had a longstanding fascination for diamond, thanks to its hypnotizing appeal as a gemstone and its unique physical properties. Its incomparable hardness makes it the best abrasive; it exceeds the thermal conductivity of even copper at room temperature; it is a perfect electrical insulator, unless it is boron doped when its resistivity is reduced by orders of magnitude. Even superconductivity has been reported very recently in such specimens. It is a material with the largest atomic density. These and many other striking properties have commanded the attention of scientists like Newton, Lavoisier, Humphrey Davy, Einstein, Lawrence and William Bragg. A short account of the extraordinary aspects of the genesis and, in modern times, the laboratory synthesis of diamond will be followed by illustrative examples from the Brillioun, Raman, and Infrared researches of my collaborators and me.
Addressing Grand Energy Challenges through Advanced Materials, by Mildred Dresselhaus, MIT Dept. of Physics Monday, 4/10/2006, 4:00 PM-5:00 PM
Advanced materials, utilizing nanostructures to provide new materials properties and opportunities for the independent control of materials structures and properties, offer new promise for addressing some of the grand energy challenges facing our future. This talk will review opportunities opened up at the nanoscale, with materials of reduced dimensionality and enhanced surface-to-volume ratio. Some examples of research accomplishments and opportunities at the nanoscale will be described, with special attention given to the potential of advanced materials and nanoscience to have an impact on addressing grand challenges related to a sustainable energy supply for the 21st century and beyond.
Sponsored by: Rafael Garcia
The End of the Solar System by Prof. John Belcher, Massachusetts Institute of Technology, Astrophysics Division Wednesday, 4/5/2006, 5:00 PM-6:00 PM
The Voyager spacecraft, after a 30 year journey, are finally at the boundaries of the solar system and approaching entry into the local interstellar medium. We will review some of the outstanding science accomplishments of this mission to the outer planets, and what is to come as they explore regions beyond the influence of the sun.
Sponsored by: Rafael Garcia
Physics Colloquium, "Ballistic Electro Photonics," by Dr. V. Narayanamurti, Harvard University Monday, 4/3/2006, 4:00 PM-5:00 PM
The ballistic transport of hot electrons in semiconductors has long been a subject of interest. Over the last decade enormous progress has been made in the study of such transport using tunneling-based hot electron (or hole) injectors. In this talk, I will present several exciting new results which have broad implications for the study of new semiconductor nanostructures that feature the transport of spin. These are: (1) the development of Ballistic Electron Emission Luminescence (BEEL), a technique which allows the simultaneous monitoring of electron transport and luminescence for quantum dot structures placed below the surface; (2) the demonstration of several new types of hot electron based devices, such as spin valve photodiodes and avalanche spin valve transistors; and
(3) exciting new studies of transport and luminescence in semiconductor nanowires such as ZnON and GaN.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "Some Secrets in the Life of Escherichia Coli," by Dr. Howard Berg, Harvard University Wednesday, 3/22/2006, 5:00 PM-6:00 PM
Flagellated bacteria swim by rotating long, thin, helical filaments that arise at different points on the cell surface. Each filament is driven at its base by a rotary motor only 45 nm in diameter made from about 20 different kinds of parts. Control of the direction of rotation of such motors is the basis for the chemotactic response, i.e., for the ability of cells to swim up spatial gradients of chemical attractants. I will review the history of this subject, tell you about some of the physics that E. coli knows, and outline the signal transduction pathway that links chemoreceptors to flagella. I will describe some of the methods (fluorescence, FRET, BRET) that we have used to probe this remarkable molecular system.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "Atomic Force of Biological Structures", by Dr. Bryan D. Huey, UCONN, Institute of Materials Science Monday, 2/27/2006, 4:00 PM-5:00 PM
Atomic Force Microscopy provides an opportunity to map topography as well as local properties at the nanoscale. During this presentation, careful experiments of local mechanical properties will be described for two distinct systems: ceramic ferroelectric thin films, and living hamster cells. In each case, assessing the mechanical response as a function of position reveals important details about spatial variations of the sample properties. With respect to PZT ferroelectric thin films, the piezoelectric hysteresis has been found to vary in the vicinity of grain boundaries, due to built in strain resulting from the local microstructure of this anisotropic material as supported by complimentary electron beam diffraction and 2-d finite element modeling. For biological structures, the mechanics of individual cells are shown to vary depending on their health as well as exposure to quantum dots. By recording the vibration spectrum of cell membranes, sounds emanating from a cell can also be heard and will be played during the seminar.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "A New Approach to Diffusion Analysis for Multicomponent Systems", by Dr. L. Ramdas Ram-Mohan, WPI Physics Department Monday, 2/20/2006, 4:00 PM-5:00 PM
The diffusion of matter from one region into another is a universal phenomenon occurring in gases, liquids and solids. In metallic alloys, we can study diffusion by putting two alloys together and allowing the components of one alloy to diffuse into the other alloy at high temperature, and then quenching the system to freeze the diffusion. We can then experimentally determine the concentration profiles. Such diffusion under controlled conditions gives us information about the diffusion process and the stability of the interface. This has wide applications in the welding of metals and similar industrial processes.
Until recently, the diffusion coefficients could not be determined in a reliable manner in multicomponent diffusion, such as ternary or quaternary diffusion. They are functions of composition, making diffusion an intrinsically nonlinear process. I will present a new method of determining the diffusion coefficients developed recently, and show how the concentration profiles can be reconstructed, given the diffusion coefficients, using a transfer-matrix method (TMM). The TMM developed by me is applicable to any number of diffusion components.
I will also mention the directions in research we are pursuing. We are close to being able to predict the diffusion path in a diffusion couple given the end compositions. Diffusion in three- and four-component systems already displays a rich variety of complex phenomena. I will illustrate these with examples. We are starting on an investigation of grain boundary diffusion and triple junction diffusion in macroscopic and nanoscopic systems.
Undergraduate and graduate students are encouraged to attend.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "The History of the Universe in One Hour', by Dr. Max Tegmark, MIT Physics Department Wednesday, 2/15/2006, 5:00 PM-6:00 PM
With a cosmic flight simulator, we'll take a scenic journey through space and time. After exploring our local Galactic neighborhood, we'll travel back 13.7 billion years back to explore the Big Bang itself and how state-of-the-art measurements are transforming our understanding of our cosmic origin and ultimate fate. If you have questions about dark matter, dark energy, black holes, parallel universes or other things cosmological, this will be a great opportunity to ask them!
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "Acoustic Amplification from Coherent Quantum Condensation in Superfluid He-4", by Dr. Fred Ellis, Weslyan University, Department of Physics Monday, 2/13/2006, 4:00 PM-5:00 PM
The atoms of superfluid helium are in a macroscopic state of coherent quantum de Broglie waves. Vapor atoms evaporating from, or condensing into, the superfluid do so while preserving the macroscopic phase structure of the coherent quantum waves. This remarkable process in superfluids is the matter equivalent of the laser.. The physics of this process and progress on an experiment to demonstrate this equivalence by the stimulated amplification of acoustic waves in superfluid films will be described.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "New Forms of Quantum Matter Near Absolute Zero Temperature", by Dr. Wolfgang Ketterle, Physics Department, MIT Monday, 2/6/2006, 4:00 PM-5:00 PM
Why do physicists freeze matter to extremely low temperatures? Why is it worthwhile to cool to temperatures which are more than a million times lower than that of interstellar space? This lecture will discuss new forms of matter, which only exist at extremely low temperatures. Low temperatures open a new door to the quantum world where particles behave as waves and march in lockstep. In 1925, Einstein predicted such a new form of matter, the Bose-Einstein condensate, but it was realized only in 1995 in laboratories at Boulder and at MIT. More recently, Bose-Einstein condensates of molecules and fermion pairs have been created and may show behavior similar to electrons in superconducting materials. A new form of high-temperature superfluidity has been discovered. In the future, we hope to use ultracold gases to create designer matter, i.e. to realize new forms of matter in the laboratory which have been discussed as model systems for many-body phenomena, but have not been observed in nature.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "How to Find Splice Junctions in mRNA", by Dr. Daniel Aalberts, Williams College Monday, 1/30/2006, 4:00 PM-5:00 PM
Before being translated into proteins, messenger RNA is processed in the nucleus. The spliceosome directs precursor mRNA to remove intervening sequences (introns), and to splice the remaining expressed sequences (exons) back together to form mature mRNA. The alternation of coding and noncoding regions makes eukaryotic genes difficult to predict from primary sequence alone, so the ability to correctly identify the intron-exon boundaries is also crucial to gene finding efforts. Splicing is done with great specificity, even though the apparent splicing signals are rather weak. Methods from statistics have proven most effective to identify the splice sites, but we know that cells don't perform Hidden Markov calculations. Cells use thermodynamics. I will present results of our thermodynamic model of splice site recognition. I will then discuss how statistical-mechanical scaling ideas led us to improve upon statistics methods.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "A Known Unknown: Directly Detecting the Missing Mass of the Universe",Dr. Richard Gaitskell, Brown University Physics Department Wednesday, 11/30/2005, 5:00 PM-6:00 PM
The majority of the mass of the Universe is still unidentified. Many different astrophysics and cosmological measurements support the hypothesis that Cold Dark Matter dominates the gravitational behavior of galaxies and galactic clusters. I will discuss the interpretation of existing data, and focus on a number of experiments that are being conducted deep underground to directly detect a new type of dark matter particle: one which arises naturally from the extension of existing particle physics theories.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
"Extrasolar Planets in Binary Star Systems", By Dr. Matthew Muterspaugh, MIT Center for Research Monday, 11/28/2005, 4:00 PM-5:00 PM
Ten years ago, there was a revolution in astronomy as planets orbiting sunlike stars were first discovered in large numbers. Their properties have introduced many changes to the way in which we understand planet formation and evolution, and provide context for our own solar system.
Many of the systems now known occur in environments once thought to be incompatible with planet formation. Several planets have now been discovered orbiting stars that have additional distant stellar companions.
I will present recent results from planet searches targeting systems are known to contain stellar companions in much closer orbits, in which the second star may have significant gravitational effects on the planet system during formation. These searches probe the extent to which these interactions enhance or prohibit planet formation, and provide constraints on the timescales on which planet formation can happen. I will conclude by discussing similar results from the study of systems with three or more stars.
Sponsored by: WPI Physics Department
Colloquium, "Rapid Movements in the Plant Kingdom: Nature's Weapons of Mass Reproduction", by Dr. Dwight Whitaker, Williams College Monday, 11/21/2005, 4:00 PM-5:00 PM
While most people might think that rapid movements in biological systems are limited to the muscle driven motion of animals, this is not the case. A number of plant species have developed mechanisms to quickly transfer stored elastic energy into kinetic energy. The most famous of these cases is the closing of the Venus flytrap, which happens in a timescale of less that 0.1 s. However there are a number of other plants, which have devised methods for moving even faster. We have used a high-speed video camera to capture the sub-millisecond actions of the bunchberry flower, Sphagnum moss, and a several other local plant species. Through video analysis and measurements of elastic properties we have been able to model these explosive movements whose quickness matches or exceeds any recorded motion in the animal kingdom.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: "Playing with Virtual Photons: Measurement and Design of Long-Range QED Forces and Torques and Their Application in Nanomechanics", by Dr. Federico Capasso, Harvard University Monday, 10/31/2005, 4:00 PM-5:00 PM
High precision measurements of the Casimir force between metallic surfaces using Micro/Nanomechanical Systems (MEMS/NEMS), along with attempts to tune them using hydrogen switchable mirrors, have clearly demonstrated the skin-depth effect on these forces as well as have elucidated a counterintuitive aspect of the underlying Lifshitz- Dzyaloshinskii-Pitaevski theory. Nonlinear Casimir oscillators have been implemented which could find use as nanometric position sensors.
Calculations of the expected mechanical torque between birefringent plates induced by quantum fluctuations will be discussed along with a proposed experiment to observe it. The scheme utilizes repulsive QED forces between plates separated by a liquid of suitable dielectric constant, which creates a virtually frictionless bearing.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium" DNA in a tight squeeze: The physics of viral infection and gene regulation", by Dr. Jane' Kondev, Physics Department, Brandeis University Wednesday, 10/26/2005, 5:00 PM-6:00 PM
DNA in cells and viruses finds itself packed into a tight space, occupying a volume much smaller that the volume it adopts free in solution. This state of confinement places important constraints on a variety of biological processes, such as viral infection, gene expression, and DNA recombination. Quantitative experimental techniques such as laser tweezers, cryo-electron microscopy and fluorescence microscopy have recently begun to probe the confined state of DNA, both in live cells and in the test tube. In this talk I will describe this emerging experimental landscape and outline the theoretical challenges it poses. The particular examples I will focus on will be provided by DNA packing in viruses and gene regulation in bacteria where physics models can be used to propose a new generation of quantitative biology experiments.
Sponsored by: WPI Physics Dept., Dr. Rafael Garcia
Wonderful Speaker Series, " How Einstein Rocked the World of Physics in 1905: A 100 Year Celebration", by Dr. Phil Deutchman, Emeritus Professor, University of Idaho Wednesday, 10/5/2005, 4:00 PM-5:00 PM
The presentation, aimed at the undergraduate and general audiences, will be a discussion (mathematics kept to a minimum) of Einsteins five papers that rocked the world of physics. There will be a gentle introduction, with visual examples, to the basic ideas contained in each paper and the emphasis will be on the impact each paper had on the field of physics. Phils hope is to convey the pleasure and excitement of these ideas to the audience and to marvel at how Albert Einstein could have produced work of such profusion, profundity and prescience in such a short period of time.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "Analogies, Categories, Language and Physics", by Dr. Leslie Atkins, Dartmouth College Wednesday, 9/28/2005, 4:00 PM-5:00 PM
In the field of education, lines between disciplines are getting blurry. In order to understand how one learns physics, many researchers are not only drawing on the traditional fields related to education (such as cognitive science and psychology), but also fields ranging from linguistics to animal behavior to art history. My research (which, broadly, is interested in discourse in science) focuses on how students and scientists use analogy and categorization in physics, and this work has been informed by many of those disciplines. In this talk, I will outline some of the ways in which we understand mind and language and how these are brought to bear on how we understand science and learning.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium, "Building a Better Snail: Lubrication and Adhesive Locomotion", by Dr. Annette Peko Hosoi, MIT Monday, 9/19/2005, 4:00 PM-5:00 PM
Many gastropods, such as slugs and snails, crawl via an unusual mechanism known as adhesive locomotion. We investigate this method of propulsion using two mathematicalmodels, one for direct waves and one for retrograde waves. We then test the effectiveness of both proposed mechanisms by constructing two mechanical crawlers. Each crawler uses a different mechanical strategy to move on a thin layer of viscous fluid. The first uses a flexible flapping sheet to generate lubrication pressures in a Newtonian fluid which in turn propel the mechanical snail. The second generates a wave of compression on a layer of Laponite, a non-Newtonian, finite- yield stress fluid with characteristics similar to those of snail mucus. This second design can climb smooth vertical walls and perform an inverted traverse.
Sponsored by: free
Wonderful Speaker Series, "From Rocks to Brains- Using Physics and Nuclear Magnetic Resonance to Characterize Structure", by Dr. Karl Helmer, WPI Biomedical Engineering Wednesday, 9/7/2005, 4:00 PM-5:00 PM
Nuclear Magnetic Resonance imaging has become a standard tool in medicine because it provides a non-invasive window into the body. It can provide contrast between normal and pathological tissue and measure changes in physiological parameters such as blood flow. In some cases, the onset of pathology results in a change in tissue structure. I use the diffusion of water in tissue to probe changes in tissue structure that are the results of diseases such as stroke and cancer. This work grew out of my experience in characterizing the pore structure of rocks using similar methods. In this talk, I will give some background on these types of problems (inverse problems), show what kind of information can be measured, discuss the complexities of building physically-relevant models, and show results from both rocks and biological tissue that will convince you that the two are not so far apart.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: "Using the Atomic Force Microscope to Quantify Adhesion of a Few Asperity Contacts" by Graduate Student, Erik Thoreson Monday, 8/29/2005, 4:00 PM-5:00 PM
Nanoscale and macroscale adhesion data have given seemingly inconsistent results. Despite the importance of bridging the gap between the two regimes, little experimental work has been done, presumably due to the difficulty of the experiment needed to determine how small amounts of surface roughness might influence adhesion data lying in between the two scales. We observed that the pull-off (adhesion) force was independent of the radius of the AFM (Atomic Force Microscope) tip, which was contrary to all continuum-mechanics model predictions. In this talk, I will derive how the cantilever and tip parameters contribute to the measured pull-off force, show that applying a simple correction to the experimental data results in agreement with continuum mechanics, and demonstrate how the AFM probes were calibrated. Although much work is still needed, the work presented here should progress the understanding of adhesion data lying between the nanoscale and macroscale.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Special Speaker, "Radiation Protection for Space Missions" by Dr. Ram Tripathi, NASA Langley Research Center Tuesday, 8/23/2005, 4:00 PM-5:00 PM
Protecting astronauts and electronics from the harmful effects of space radiation is becoming critically important for long duration missions such as space stations and Lunar and Martion missions. This talk will discuss the latest developments in this field and will also focus on the relavant nuclear physics issues that remain unresolved.
Sponsored by: WPI Physics Department, Dr. John Norbury
Wonderful Speaker Series; The Physics of Brass Musical Instruments, or, what do horn players do with their right hands, anyway? by, Prof. Brian Holmes, San Jose State University Wednesday, 4/13/2005, 3:00 PM-4:00 PM
A brass instrument such as a trumpet consists of a cup-shaped mouthpiece, a conical lead pipe, a cylindrical section (including valves) and a flared bell.
By building a trumpet, I will demonstrate the acoustical significance of these parts. In the days before valves, horn players learned to augment their supply of notes by moving their right hands in the bell. Even though this technique is obsolete, the hand is acoustically necessary in the modern horn. I will explain the underlying physics. I conclude with a performance of Beethoven's horn sonata, played on a valveless horn.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: Research Opportunities in the Physics Department, Presented by the Physics Faculty Monday, 4/11/2005, 4:00 PM-5:00 PM
WPI Physics Faculty Research Interests Monday, 4/11/2005, 4:00 PM-5:00 PM
Principally for the benefit of physics undergraduates, but also for members of other departments, the faculty of the Physics Department will provide short descriptions of their research, IQP, and MQP interests. The tentative order of the presentations, each less than five minutes including questions, is: Drs.,Aravind, Burnham, Garcia, Iannacchione, Norbury, Phillies, Quimby, Zozuyla.
Sponsored by: WPI Physics Department
Colloquium: World Year of Physics 2005 Lecture: "Einstein's Boxes", by Dr. Travis Norsen, Marlboro College Monday, 4/4/2005, 4:00 PM-5:00 PM
Everyone knows that Albert Einstein was uncomfortable with the "orthodox" interpretation of quantum theory, and was never willing to accept its allegedly radical implications. Most physicists dismiss Einstein's obstinateness, attributing it to his being past his scientific prime by the time quantum theory came around, and to his simply being unable to fully comprehend and assess the new ideas. But this turns out to be a complete myth. More careful historical analysis shows that the dismissal of Einstein's ideas is largely based on a failure to understand what Einstein's objections actually were. In this talk I will attempt to clarify those objections, by focusing on a little-known thought experiment -- "Einstein's Boxes" -- which permits a streamlined version of the more widely-known EPR argument for the incompleteness of quantum mechanics, due to Einstein, Podolsky and Rosen. We will also connect up Einstein's objections to orthodox quantum theory with more recent work in the foundations of physics such as Bell's Theorem and its empirical tests. It will be argued that, although Einstein's specific vision of an alternative to QM isn't viable, his criticism of the orthodox interpretation nevertheless plays a major role in determining what sorts of views are viable.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
SPS Seminar, "Calculating the Ising Density of States", by Professor Louis Colonna-Romano Wednesday, 3/23/2005, 3:30 PM-4:30 PM
In statistical mechanics, much of our knowledge comes from the study of model systems. One of the most important models is the Ising model because it is relative simple and it has a phase transition. In this model, spins must be in one of two allowed states (up or down), are fixed on a lattice and interact only with their nearest neighbors. Even in this simple model, little can be solved exactly and approximate methods must be used. As an example, we calculate the density of states using the recently-developed Wang-Landau algorithm and consider the efficiency of this approach for Ising models of different dimensions. The density of states, the number of configurations that have a particular energy, can be used to calculate most thermodynamic quantities.
Sponsored by: WPI Physics Department
Graduate Seminar: "Fermi's Virtual Photons" by Frank Dick, WPI Graduate Student Wednesday, 3/9/2005, 3:30 PM-4:30 PM
In 1924, at the age of 23, Enrico Fermi published a method to simplify the analysis of relativistic heavy ion collisions. The electromagnetic field surrounding a relativistic ion looks to a nearby "observer ion" very much like a passing pulse of EM radiation, brief but intense. According to Fermi "this time-dependent electromagnetic field can be replaced by the field of radiation with a corresponding frequency distribution". He called this "aquivalente strahlung", equivalent radiation. The spectrum of these photons can be calculated from the kinematics of the collision process, and the subsequent dynamics of the observer ion can be effectively treated as the interaction of the ion with the EM pulse. The method was extended 10 years later by C. Weizsacker and E. Williams, and is now called the Weizsacker-Williams Method (WWM) or Equivalent Photon Approximation (EPA). WWM continues to be extended, and finds widespread use in high energy physics. Prof. Norbury has applied the method to analyze the effects of the heavy ion component of space radiation, the production of pions in proton-proton collisions, and in investigations of new phenomena, such as the production of Higgs bosons by photon-photon interactions.
Sponsored by: WPI Physics Department
SPS Seminar; "The World Year of Physics 2005: Einstein and Brownian Motion", by Dr. Germano Iannacchione, WPI Wednesday, 3/2/2005, 3:30 PM-4:30 PM
The year 2005 celebrates the centennial of the miraculous year 1905 in which Albert Einstein published five papers that changed the world.
While we may be familiar with the ideas of relativity and the quantum nature of light that were introduced, this talk will focus on the work explaining Brownian Motion. Einstein's theoretical treatment of Brownian Motion via the molecular-kinetic view of heat marks a milestone in the development of statistical mechanics. This talk presents the historical perspective of this phenomena, Einstein's approach, and the ramification to modern physics.
Sponsored by: WPI Physics Department, Dr. Iannacchione
Colloquium: Particle-Based Computational Techniques for Modeling Charge Transport in Nanoscale Devices and Biological Channels, by Dr. Shela Aboud, WPI Monday, 2/28/2005, 4:00 PM-5:00 PM
Particle-based methods have long demonstrated success in simulating the electrical properties of semiconductor devices. These approaches are based on a semi-classical description of the charge transport through the use of an ensemble of "computational" particles. The time and/or space averages of the quantities carried by these particles then yield the macroscopic properties of the system. Particle-based approaches provide an excellent probe to analyze the microscopic behavior of complex systems, such as electron devices, and are important in the development of the next generations of nanoelectronic devices.
In this talk, a fast and efficient particle-based simulation approach is presented, which represents the state-of-the-art in semi-classical semiconductor modeling capabilities. The simulation tool is then used to model and characterize several high performance field-effect transistors.
This simulation tool has also been extended to model ionic charge transport through complex protein structures in biological systems. The focus of this work is to model the flux of ions through ion channels, which are a class of proteins responsible for controlling the flow of ions into and out of biological cells. Ion channels are also interesting for their possible application in hybrid bioelectronic sensors ntegrated with existing semiconductor technologies.
Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Graduate Seminar: "The Art of the Hubble" by Anne Adamczyk, WPI Physics Graduate Student Wednesday, 2/23/2005, 3:30 PM-4:00 PM
Hubble Space Telescope, the first space based optical telescope, is noted for providing beautiful and often bizarre color images of the galaxies,planets, and nebula. Take a peak behind the scenes to discover how Hubble actually makes images. Hubble has changed the way the public sees astronomy. The pictures truly are art.
The five science instruments its cameras, spectrographs, and fine guidance sensors, work together or individually to capture light from the cosmos, convert it into digital data and transmit it back to Earth. These instruments bring stunning images from the farthest reaches of space. Find out about the inner workings of this telescope.
The periodic maintenance and upgrading of Hubble has clearly been the key to its success as one of the premier scientific facilities in human history. The contributions Hubble has made and still can make to science and public understanding of the heavens is worth the cost of a fourth servicing mission.
Sponsored by: WPI Physics Department
Colloquium: "Controversial Precision-Final Results from the Muon g-2 Experiment at BNL" by Dr. Robert Carey, BU Monday, 2/14/2005, 4:00 PM-5:00 PM
The muon g-2 experiment at Brookhaven National Laboratory is a 0.55 parts per million measurement of the muon's anomalous magnetic moment. Our final result represents a 13-fold improvement over those made at CERN in the late 60s and 70s, provides a stringent test of the Standard Model and serves as a probe of physics at the TeV scale. In the talk, I will explain how, with the help of a few fundamental insights, a value of the anomaly can be extracted from the detection of decay-electrons in our muon storage ring. I will explain our schemes for minimizing statistical and systematic errors, present our recently published number from the 2001 run, and shed light on the controversy surrounding its interpretation.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: "Prospects for Hard X-ray Astronomy" by Dr. Tomohiko Narita, College of the Holy Cross Monday, 2/7/2005, 4:00 PM-5:00 PM
The hard X-ray band, from 10-600 keV, is a relatively unexplored part of the spectrum for the study of astrophysical processes. Black holes and the Gamma-ray bursts that are believed to accompany their birth emit most of their power in the hard X-ray band. This band is also key for study of the obscured universe, particularly the obscured massive black holes in the centers of galaxies, which are invisible in the soft X-ray and optical wavebands. We are currently fabricating a prototype hard X-ray telescope using an array of Cadmium-Zinc-Telluride detectors. We report on our progress and also illustrate the concept for a future space mission.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
SPS Event: "Looking at Blue Lights from Red Stars and What Happens When Good Optics Go Bad", by Carol Carveth, WPI Physics Student Wednesday, 2/2/2005, 3:30 PM-4:00 PM
In the early days of Astronomy the idea was to study the way stars look. The development of spectroscopy has started to drive out the study of the appearance of stars as "serious" science, but since spectra seem to vary widely between stars, reasons behind certain spectroscopic features are still unknown. A study of the Ca II K absorption line in Red Giant stars was started this past spring at McDonald Observatory.
In 1997 the Hobby Eberly Telescope was opened for the first time atop Mount Folkes in Fort Davis, TX. Since then the reflectivity of the silvered mirrors has dropped significantly. Three years ago mirror coating samples were placed in different spots around McDonald Observatory, and identical samples were kept in a desicator. Total Reflectivities and Scattering values were compared for each mirror using a Cary 100 Spectrophotometer which the Observatory obtained for the purpose.
Sponsored by: Society of Physics Students
Colloquium: An Optical Vortex Coronagraph by Dr. David Palacios Monday, 1/31/2005, 4:00 PM-5:00 PM
A coronagraph is a device used to block light from a star so nearby objects may be seen. Bernard Lyot first used such a device in 1939 to block the intense glare of the sun so that the solar corona could be imaged. Similarly, an optical vortex coronagraph opens a dark window in the glare of a distant star so nearby terrestrial sized planets and exo-zodiacal dust may be detected. An optical vortex may be characterized as a dark core of destructive interference in a beam of spatially coherent light. This dark core may be used as a filter to attenuate a coherent beam of light so an incoherent background signal may be detected. Applications of such a filter include: eye and sensor protection, forward-scattered light measurement, and the detection of extra-solar planets. An optical vortex coronagraph may hold several advantages over other techniques presently being developed at JPL for the Terrestrial Planet Finder Mission. These advantages include: broadband nulling, nearly on-axis planet detection, and low aberration sensitivity. During this talk I will discuss the nulling properties of an optical vortex coronagraph. I will also provide both experimental and numerical results demonstrating the versatility of an optical vortex coronagraph.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Graduate Seminar, "Reciprocity Between Absorption and Emission", by Rodica Martin, WPI Physics Graduate Student Wednesday, 1/26/2005, 3:30 PM-4:00 PM
When designing optical amplifiers, accurate knowledge of the emission cross-section is required. Unfortunately, emission spectra are not always easy and straightforward to obtain. McCumber theory is a generalization of Einstein A and B coefficients for broadband transitions used to predict emission cross-sections from measured absorption spectra. Although widely used, the theory is still controversial when applied to broad transitions of the rare earths. Experimental studies have been performed to investigate the accuracy of the method for a number of rare earth doped samples.
Sponsored by: WPI Physics Graduate Students
Colloquium: Atom Optics in the Presence of Gravity by Dr. Timothy Roach, College of the Holy Cross Monday, 1/24/2005, 4:00 PM-5:00 PM
Slow, laser-cooled atoms are the basis for many experiments on matter wave optics because of their relatively large deBroglie wavelength. The earth's gravity presents challenges to experimental design, however. For example, during the transfer of low momentum atoms from a source (e.g., MOT or BEC) to an optical element, the momentum increase due to gravity is orders of magnitude larger than the thermal momentum. As a complement to our ongoing experiments with magnetic diffraction gratings, we have analyzed how gravity influences the results of various experimental diffraction geometries. We will present a model of how gravity affects the fringe resolvability and compare this to experimental results of several research groups. We will also report on progress on our current round of diffraction experiments with laser-cooled rubidium atoms.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "Protection of Astronauts from Cosmic Radiation", by Dr. John Norbury, Physics Department Head, WPI Wednesday, 1/19/2005, 11:00 AM-12:00 PM
The two most important medical problems that astronauts face on long duration space missions are the effects of microgravity and radiation due to cosmic rays.
The radiation comes from three separate sources, namely geomagnetically trapped particles, energetic solar particles and Galactic cosmic rays. The talk will review these radiations and discuss research relevant to the general space radiation problem.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: An Optical Vortex Coherence Filter, by Dr. David Palacios Monday, 1/17/2005, 4:00 PM-5:00 PM
Sponsored by: WPI Physics Dept., Dr. Garcia
SPS event: High-Resolution AC-Calorimetry by RF-Field Heating for Complex Fluids by Saimir Barjami Wednesday, 12/15/2004, 3:30 PM-4:30 PM
A new, high-resolution, modulation calorimetric technique using Radio Frequency or Dielectric heating of the sample, has been developed for the study of complex fluids. This powerful method is sensitive to both the heat capacity and permittivity of organic liquids. The employment of this calorimeter on dispersions of aerosils in the liquid crystal octylcyanobiphenyl (8CB) is described. There is no enhancement of the dielectric permittivity through SmA to N transition in the disordered liquid crystal at the studied density consistent with recent NMR work, suggesting decoupling of the nematic and smectic order parameters.
Sponsored by: WPI Physics Department, Dr. Germano Iannacchione
SPS speaker, Summer Job Opportunities in Physics, by Deanna Wolfson Wednesday, 12/8/2004, 3:30 PM-4:30 PM
The presentation will be an overview of summer job opportunities in physics. The talk will focus on NSF-funded Research Experience for Undergrads. It will include the opportunities and benefits of REUs, as well as the process for applying for one. Non-REU job opportunities will also be discussed.
Colloquium, Non-Lithographic fabrication of superlattices for nanometric electro-magnetic-optic applications, by Dr. Jianyu Liang Monday, 12/6/2004, 4:00 PM-5:00 PM
Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Lateral Superlattices for Nanometric Electro-Magnetic-Optic Applications by Dr. Jianya Liang Monday, 12/6/2004, 4:00 PM-5:00 PM
Exploiting materials of dimension less than 100 nm for potential applications has been proved a fascinating enterprise. However, efforts so far have concentrated on individual nanostructures. The collective behaviors of nanostructures in a large ensemble remain largely unexplored.
As the first step into the nano realm, investigation of isolated nanostructures and characterization of individual nanodevices are of great importance and naturally of strong appeal to researchers. Yet more challenging and probably of greater impact is the assembly and manipulation of multiple nanostructures into integrable functional units. It is both desirable and timely to seek for ways to advance both the fabrication capabilities and the science explorations beyond the realm of individual nanostructures.
In this talk, a non-lithographic technique that utilizes highly ordered anodized aluminum oxide (AAO) porous membrane as a template will be introduced as a general fabrication means for the formation of an array of vastly different 2-dimensional lateral superlattices. The fact that material systems as different as metals, semiconductors, and carbon nanotubes can be treated with the same ease attest to the generality of this nano-fabrication approach. The original AAO membranes determine the uniformity, packing density, and size of the nanostructures. The flexibility of using a variety of materials, the accurate control over fabrication process, and the command over AAO template attributes give us the freedom of engineering various physical properties determined by the shape, size, composition, and doping of the nanostructures.
A fundamentally new nanoheteroepitaxial growth method based on the as fabricated semiconductor nanostructures will also be presented. Employing this approach, high quality semiconductor thin films and quantum dots have been successfully grown by molecular beam epitaxy on nanopatterned semiconductor substrates.
Optical and structural characterizations have shown that the novel nanomaterial platform realized by this unique non-lithographic technique is powerfully enabling a broad range of applications.
Sponsored by: WPI Physics Department, Dr. N. A. Burnham
Colloquium: Physics of Red Blood Cell Shapes by Dr. Ranjan Mukhopadhyay, Clark University Monday, 11/29/2004, 4:00 PM-5:00 PM
A mature human red blood cell normally assumes the shape of a flattened biconcave disc. However, under a variety of chemical or physical treatments, the cell undergoes a quasi-universal sequence of reversible shape transformations. Since a red blood cell has no internal structure, its shape is encoded in the mechanical properties of its membrane. Using a simple physical model we show how the full sequence of shapes can be driven by variation in a single control parameter. Our predicted shapes are in surprisingly detailed agreement with observations. Our results make it possible to use shape transformations as a quantitative tool to probe the physics and biochemistry of cell membranes.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: Data and Modeling of Dendrites Subject to a Step Change in Pressure, by Dr. Matthew B. Koss , College of the Holy Cross Monday, 11/22/2004, 4:00 PM-5:00 PM
Current theories and models of dendritic growth generally couple diffusion effects in the melt with the physics of the interface. Data and subsequent analysis of the tip growth speed and radii of thermal succinonitrile dendrites in the near-convection free, on-orbit, free-fall environment demonstrate that these theories yield predictions that are reasonably in agreement with the results of experiment. However, data and analysis for assessing the interfacial physics component of theory are not sufficiently detailed or definitive. To study fundamental aspects of dendritic interface stability we subject thermal dendrites, growing under steady-state conditions, to a rapid change in pressure. This leads to a rapid change in thermal driving force from the corresponding change in both the equilibrium melting temperature due to the Clapeyron effect, and a change in the far-field temperature due to adiabatic temperature changes in the bulk liquid and solid.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "The Accelerating Universe", by Dr. Robert Kirshner, Harvard University Wednesday, 11/17/2004, 3:30 AM-4:30 AM
Observations of exploding stars halfway across the observable universe show that cosmic expansion is not slowing down, as expected due to gravity. It is speeding up. We attribute this to the effect of "Dark Energy." Quantitative estimates of the expected vacuum energy for gravitation miss the observed amount by 10^120! This points to a deep theoretical problem right at the heart of physics. At present, the only evidence for the dark energy is from astronomical observations.
This talk will describe Dark Energy as an idea, show the astronomical evidence from supernovae, and describe future work to learn more about this strange new component that makes up 2/3 of the mass-energy of the Universe.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: Nanomechanics: Quantum and Other Aspects by Dr. Raj Mohanty, Boston University Monday, 11/15/2004, 4:00 PM-5:00 PM
Engineered nanomechanical systems offer exiciting prospects for studying a variety of phenomena of fundamental and technical interests. Recent technological advances have made it possible to create mechanical structures that can move over a billion times in a second. If cooled to sub-kelvin temperatures, such nanomechanical oscillators enter the quantum regime of mechanical motion, becoming text-book quantum "mechanical" oscillators. Experimental realization of motion in the quantum regime will prospect the ground for a new direction for studies of quantum measurement and quantum computation. I will describe the recent experiments in our group, which demonstrate the first observation of mechanical motion in the quantum regime with the fastest-moving manmade structures.
In addition, I will discuss the prospect of classical nanomechanical computation with memory elements created by nanomechanical silicon beams, reminiscent of Babbage's original idea of analytical computing. This technology has the potential to supercede the current memory technologies in both speed and density.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
COLLOQUIUM: From Atoms to Quantum Computers: The Classical and Quantum Faces of Matter, by Dr. Antonio Castro Neto, Boston University Monday, 11/8/2004, 4:00 PM-5:00 PM
In this seminar I am going to discuss the problem of the transition from a quantum to a classical description of the world. I will argue that this transition can be better studied and understood in condensed matter systems where many particles interact with each other and the environment that surround them. I will show that the understanding of the classical/quantum duality has direct consequences in basic science as well as emerging technologies.
Sponsored by: WPI Physics Department, Dr. Garcia
Wonderful Speaker:"Physics and the Boundary of a Boundary" by Professor Khin Maung Maung, Hampton University Wednesday, 11/3/2004, 3:30 PM-4:30 PM
There is one geometrical principle behind Maxwell's Equations of Electromagnetism, Yang-Mill's Equations of Quantum Chromodynamics and Einstein's Equations of General Relativity. The geometrical theme behind all this is that boundary of a boundary is zero.
These ideas will be presented in an elementary manner and anyone with a little knowledge of calculus and matrices will be able to follow.
Sponsored by: WPI Physics Department, Dr. John Norbury
Colloquium: "Investigating structural properties of carbon nanotubes using inelastic light scattering" by Dr. Wolfgang Bacsa, Solid State Physics Laboratory, University of Toulouse, France Monday, 11/1/2004, 4:00 PM-5:00 PM
Carbon nanotubes have properties characteristic of molecules and yet they are macroscopic in their length. For single shell carbon nanotubes all atoms are located at the surface. The combination of these and other unique characteristics makes nanotubes an extraordinary material.
Structural properties of carbon nanotubes such as helicity and response to external pressure can be explored using inelastic light scattering.
Recent results will be summarized after giving an introduction on nanotubes and inelastic light scattering.
GPSO Event: Dielectric Spectroscopy of Liquid Crystals by Florentin Cruceanu Wednesday, 10/27/2004, 3:30 PM-4:30 PM
I will review the progress to date in constructing a high-resolution, narrow-band, dielectric spectrometer suitable for phase transition studies of fluids and solids. Background on the theory of the technique and experimental details will be given. Initial studies on the phase behavior of the liquid crystal octylcyanobiphenyl (8CB) will be presented as well as some preliminary results on a nano-colloidal dispersion of an aerosil gel in 8CB. Future directions will also be discussed.
Sponsored by: WPI Physics Department
Colloquium:Quantum Entaglement and its Ramifications by Dr. A.K. Rajagopal Monday, 10/11/2004, 4:00 PM-5:00 PM
Walter Arnold.Naval Research Labs, Washington, D.C.
QUANTUM ENTANGLEMENT AND ITS RAMIFICATIONS.
After a quick review of ideas of classical bits (cbit) leading to modern conveniences such as telephone, TV, Computer technology etc, a discussion of quantum bits (qubits) is given. This discussion includes a review of quantum mechanics superposition principle and uncertainty relations whose implications for qubits are explored. Consideration of two qubits in detail will be shown to lead to new features, most importantly, entanglement. Several applications of this (encryption, no copying, teleportation, computing) are briefly discussed. Considerations of continuous variables where light sources play the role of qubits will be touched upon.
Sponsored by: Dr. L. R. Ram-Mohan, WPI Physics Department
GPSO Event: Ellipsometric measurements of packaged samples to detect changes to die surfaces through packaging and correlation with MEMS performance, by Erika Shutte Wednesday, 10/6/2004, 3:00 PM-3:30 PM
Reliability and performance of low-g accelerometers are closely linked to sensor surface characteristics. Surface film changes after packaging of only a few angstroms have altered performance and wear life in inertial MEMS, but standard characterization techniques cannot measure nanometer films on packaged die. To meet the need for sensor surface characterization of packaged devices, we installed micro-spot optics on a manual ellipsometer and developed a sample preparation and test protocol to measure die surface films after packaging. Experiments were conducted to characterize the effects of outgassing from die attach materials, the influence of a diphenyl siloxane coating, and the packaging process. This presentation will outline the equipment, calibration, and measurement protocol developed to ensure reliable thickness data in the 10A range, then results from our studies of packaging variants will be discussed.
Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Calibrated AFM measurements to detect changes in die surfaces after packaging, by Erik Thoreson Wednesday, 10/6/2004, 3:30 PM-4:00 PM
If moving micro- or nanostructures touch, recovery requires that restoring forces overcome the surface adhesive forces. To study restoring forces, we have calibrated cantilever probes for an Autoprobe M5 AFM (Atomic-Force Microscope) from Veeco, so that the work of adhesion can be determined to an accuracy of about 13% 1,2 . This presentation will provide an overview of the AFM, describe how to calibrate the AFM, and show our results for the calibrated works of adhesion between AFM tips (less than 1 m radius tip, 2 m, 12 m, and 120 m) and unpatterned silicon die that were solder-sealed in 5 mm x 5 mm LCC (Leadless Ceramic Chip Carrier) packages. Two sample variables were examined; four die attach conditions (no attachment, silicone, polyimide silicone, and silver glass) and two surface conditions (with and without a few angstroms of vapor-deposited diphenylsiloxane). All measurements were made at a relative humidity of 24.5 1.5 % and a temperature of 22.5 1.9 C.
Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Colloquium: Wetting Transitions of Liquids on Solid Surfaces by Milton W. Cole Monday, 10/4/2004, 4:00 PM-5:00 PM
Milton W. Cole, Penn State University, Physics Department.
Water beads up to form little droplets on a teflon frying plan. In contrast, water films spread uniformly across other surfaces. What determines this differing behavior? The answer to this question can be understood in simple physical terms, as described in this talk. Also discussed is a remarkable wetting phase transition that has been in seen for various liquid films and surfaces. At low temperature, these liquids bead up while at high temperature they spread. This transition is observed in both equilibrium studies and flow measurements. Although thie transition is predicted to occur for water, such a transition has never been studied in the laboratory. The talk will feature a movie demonstrating the behavior.
Sponsored by: Dr. Rafael Garcia, WPI Physics Dept.
Wonderful Speaker,"Physics of the Piano", by Dr. Nick Giordano, Purdue University Wednesday, 9/29/2004, 3:30 PM-4:30 PM
While a piano is a complicated mechanical device, it can presumably be described by physics at the level of freshman mechanics (i.e., field theory should not be required).
In spite of this apparent simplicity, it is very difficult to use Newton's laws to calculate the sound produced by a piano. In this talk I will give a brief introduction to the physics of the piano, and describe a few of the interesting problems involved in constructing such a physical model of the instrument. I will then describe our attempts to calculate the sound produced by a piano from first principles; i.e., using F=ma.
Sponsored by: WPI Physics Department, Dr. Rafael Garcia
GSPO, Overview of research Wednesday, 9/22/2004, 3:30 PM-4:30 PM
Sponsored by: Graduate Physics Student Organization
SPS Event, Vortex Cannon Wednesday, 9/15/2004, 3:30 PM-4:40 PM
Sponsored by: Society of Physics Students
Colloquium: Ongoing and Future Research and Teaching Collaborations Between WPI and MIT Lincoln Laboratory, by Dr. Bob O'Donnell Thursday, 9/2/2004, 4:00 PM-5:00 PM
Dr. Bob ODonnell.
MIT
Lincoln Laboratory.
Beginning in 2002, WPI and MIT Lincoln Laboratory have developed an extensive collaborative effort. This talk will begin with a brief overview in MIT Lincoln Laboratory its mission an the nature of the research performed there. The WPI - MIT LL collabortive effforts (MQP, sponsored research, summer internships) will be described and it is hoped that this information will spark discussions, both at and after the meeting, that will lead to further joint efforts of this nature.
Sponsored by: WPI Physics Department, Dr. John Norbury
Colloquium:Quantitative Contact Spectroscopy by Atomic-Force Acoustic Microscopy, by Dr. Walter Arnold Monday, 8/30/2004, 4:00 PM-5:00 PM
Walter Arnold, Fraunhofer-Institute for Nondestructive Testing, Bldg. 37, University
D-66123 Saarbrücken, Germany.Quantitative Contact Spectroscoy by Atomic-Force Acoustic Microscopy.
In Atomic Force Microscopy deflection of a micro-fabricated elastic beam with a sensor tip is used to generate high-resolution images of surfaces.
Dynamic modes, where the cantilever is vibrated while the sample surface is scanned, are quite common allowing to obtain images whose contrast depend for example on the elasticity of the sample surface. However, quantitative determination of Young's modulus is still a challenge especially when stiff materials are encountered. Here, the evaluation of the cantilever vibration spectra at ultrasonic frequencies is discussed in order to discern local elastic indentation modulus quantitatively.
Nano-crystalline magnetic and piezoelectric materials, nano-crystalline nickel, multi-domain piezoelectric ceramics, diamond-like carbon layers, polymeric materials, clay in rocks, crystalline silicon and other materials have been examined. Both the measurement procedures as well as the material physics underlying the data are discussed. The spatial resolution obtained is 10 nm and less.
In the piezo-mode a sinusoidal voltage is applied between the sensor tip in contact with a piezoelectric sample. The ac-field at the tip generates a local vibration by the inverse piezoelectric effect. Selecting a frequency close to a resonance leads to an enhanced vibration of the cantilever and allows one to image the ferroelectric domain structure and to obtain information on the local piezoelectric constant. This technique has been applied to a large variety of thin films produced by combinational chemistry and to thin films forming a Schottky barrier on Si.
Shear stiffness and friction phenomena can be investigated by evaluating the torsional or lateral resonances of AFM cantilevers. Both types of resonances are excited by a piezoelectric transducer placed below the sample which generates in-plane sample surface vibrations while the sensor tip is in contact with the sample. At low lateral surface vibration amplitudes the sensor tip remains in elastic contact with the sample surface, and the cantilever behaves like a linear oscillator with viscous damping and a certain set of resonances frequencies. If the surface vibration is increased above a critical amplitude, typically 0.2 nm for torsional resonances, the maximum of the resonance curves does not increase any more and the curves develop a plateau at their highest amplitude. Numerical simulations of a corresponding nonlinear oscillator driven by a dry friction element produced curve shapes as in the experiment. This led us to the conclusion that the plateaus in the resonance curves indicate the onset of stick-slip in the relative tip-sample oscillation. This is confirmed by the fact that the critical surface amplitude increases with increasing static cantilever load.
Furthermore, for dry samples this amplitude is higher than for lubricated surfaces.
Sponsored by: Dr. Nancy Burnham, WPI Physics Dept.
Progress towards SI traceable small force metrology, by Dr. Jon R. Pratt Monday, 4/26/2004, 4:00 PM-5:00 PM
Dr. Jon R. Pratt.NIST.Gaithersburg, Maryland.
With all this scientific and technical activity focused on measuring seemingly imperceptible levels of force, it seems prudent to consider just how accurately such forces can be measured in terms of standard units. After all, within the International System of Units (SI) force is derived from the Kilogram, so that in order to derive an SI nanonewton we are presumably faced with the daunting task of subdividing the weight of a single Kilogram by ten orders of magnitude. Or are we? Recent experiments with the NIST Electrostatic Force Balance (EFB) have achieved agreement between an SI electrostatic force and an SI gravitational force of 10-5 N to within a few hundred pN/mN. This result suggests that a force derived from SI measurements of length, capacitance, and voltage provides a viable small force standard, circumventing the need to directly subdivide from the Kilogram. In this talk, we'll examine just what I mean by an SI traceable electricalforce, consider how one constructs an Electrostatic Force Balance as a practical realization of a nanonewton, and learn how such a balance has been used to calibrate the most sensitive of force measuring equipment, an AFM
Sponsored by: Dr. Nancy Burnham
From Cathode to Counting House, a quick, dirty, and detailed expose of a Precision Nuclear Physics Experiment through the eyes on one harried PhD student, by Dr. Eric Clinton Monday, 4/19/2004, 4:00 PM-5:00 PM
Eric Clinton.
Thomas Jefferson National Laboratory.
The business of the Thomas Jefferson National Acclerator Facility is to
make high energy electron and photon beams. These beams are used to make detailed measurements of nuclear and particles reactions that lead to a deeper understanding of the Standard Model of Physics. But what really goes on in this governement installation? How does a 6 GeV electron beam get acceration from .511 MeV to almost 2000 times its rest mass? How does this electron beam make a secondary beam of bremmstrahlung photons, and how in the name of Feynnman does a lowly, underpaid, overworked, misunderstood, alumnus of WPI plan to use that photon beam to make a Precision Measurement of the Neutral Pion Life- time Via the Primakoff Effect? Come find out April 19 when Eric Clinton, class of 1999, gives a whirlwind tour of Accelerator Physics and his PhD prospectus.
Sponsored by: Dr. Germano Iannacchione
Discovery of Supersolidity in Helium, by Dr. Moses H. W. Chan Tuesday, 4/13/2004, 4:00 PM-5:00 PM
Moses Chan.
Penn State Dept. of Physics.
When liquid 4He is cooled below 2.176 K, it undergoes a phase
transition-Bose-Einstein condensation-and becomes a superfluid with zero
viscosity. Once in such a state, it can flow without dissipation even
through pores of atomic dimensions. Although it is intuitive to
associate superflow only with the liquid phase, it has been proposed
theoretically that superflow can also occur in the solid phase of 4He.
Owing to quantum mechanical fluctuations, delocalized vacancies and
defects are expected to be present in crystalline solid 4He, even in the
limit of zero temperature. These zero-point vacancies can in principle
allow the appearance of superfluidity in the solid. However, in spite of
many attempts, such a 'supersolid' phase has yet to be observed in bulk
solid 4He. Here we report torsional oscillator measurements on solid
helium confined in a porous medium, a configuration that is likely to be
more heavily populated with vacancies than bulk helium. We find an
abrupt drop in the rotational inertia of the confined solid below a
certain critical temperature. The most likely interpretation of the
inertia drop is entry into the supersolid phase. If confirmed, our
results show that all three states of matter-gas, liquid and solid-can
undergo Bose-Einstein condensation.
Sponsored by: Dr. Rafael Garcia
High temperature superconductivity and strong correlation phyiscs, by Dr. Patrick Lee Monday, 4/5/2004, 4:00 PM-5:00 PM
Dr. Patrick Lee. MIT Physics Department. After 17 years of intense studies, a great deal is known about the high Tc superconductors. There is broad agreement that it should be understood in the context of strong correlation. By strong correlation we mean the repulsion between electrons is playing a crucial role and superconductivity arises as a result of adding carriers to what is called a Mott insulator. I shall explain some of the key concepts and review some experiments.
Sponsored by: Dr. Rafael Garcia
Contradictions with Local Realism from Rotational Properties of Entangled States, by Dr. Walter E. Lawrence Monday, 3/29/2004, 2:00 PM-3:00 PM
Dr. Walter E. Lawrence
Dartmouth College
Department of Physics and Astronomy.
A measurement on one member of an entangled pair of particles determines the state of the other. It is natural to ask whether rotation of one changes the state of the other. The answer to this question provides a new perspective on the nature of quantum entanglement and the nonlocality that comes with it. It also provides a way of predicting large numbers of measurements that produce absolute contradictions with local realism-measurements whose outcomes are certain (for which the system must be prepared in an eigenstate of the measurement operator), which nevertheless contradict the predictions of any local hidden
Sponsored by: Dr. P.K. Aravind
The Electronic Kilogram, by David B. Newell Monday, 3/22/2004, 4:00 PM-5:00 PM
David B. Newell.
National Institute of Standards and Technology.
In the International System of Units (SI), the kilogram is the last base unit to be defined in terms of an artifact, a century-old platinum-iridium alloy cylinder. This talk will describe one effort towards a new
definition of the kilogram in terms of invariant quantities, the NIST (National Institute of Standards and Technology) Electronic Kilogram project. The project uses a watt balance which measures the ratio of mechanical to electrical work, linking the meter, the artifact kilogram, and the second to the practical realizations of the ohm and the volt derived from the quantum Hall and the Josephson effects. In 1998, the NIST watt balance set an upper limit on the drift rate of the artifact kilogram
of 2 x 108/yr (PRL Sept. 21, '98). By using the theoretical values for the Josephson and von Klitzing constants, the same results yield an SI determination of Planck's constant with a combined relative uncertainty of 8.7 x 10-8, the most accurate determination to date.
Sponsored by: Dr. Nancy Burnham
Spin Fluctuations and High Temperature Superconductivity, by Robert Birgeneau Monday, 3/8/2004, 4:00 PM-5:00 PM
Dr. Robert Birgeneau
University of Toronto
Department of Physics.
The most striking feature of high temperature superconductors is that they are created by doping planar antiferromagnetic copper oxide ceramics. It turns out that the magnetic behavior and the interplay between magnetism and superconductivity are remarkably rich and subtle. In this talk we will discuss recent experiments probing the static and dynamic spin fluctuations in various high-Tc materials. These experiments reveal new, interesting quantum many body behavior but the problem of the mechanism of high-Tc superconductivity remains open.
Sponsored by: Dr. Rafael Garcia
Long-lived states of positronium in crossed electric and magnetic fields, by Janine Shertzer Monday, 3/1/2004, 4:00 PM-5:00 PM
Dr. Janine Shertzer
College of the Holy Cross
Department of Physics.
Long-lived states of positronium in crossed electric and magnetic fields.
Abstract
Crossed electric and magnetic fields provide a unique way for stabilizing simple matter-antimatter systems. Theoretical calculations on positronium in crossed fields predict the existence of long-lived states in which the average positron-electron separation is several thousand Angstroms. These states are due to formation of a second attractive well in the potential for certain values of pseudomomentum and field strength. The near zero probability for positron-electron overlap suppresses direct annihilation processes resulting in excessively long lifetimes.
Sponsored by: WPI Department of Physics
Nanomechanical Investigations Using Scanning Force Microscopy, by Dr. Udo D. Schwarz Monday, 2/23/2004, 4:00 PM-5:00 PM
Dr. Udo D. Schwarz
Yale University
Department of Mechanical Engineering.
Nanomechanical Investigations Using Scanning Force Microscopy.
Abstract
The ability of the scanning force microscope to study the nanomechanics of materials down to the atomic scale is illustrated with two different examples. First, I will show how data acquired during the sliding of nanometer-sized tip-sample contacts provide new insight into the atomic origins of friction, which lead to a deeper understanding of Amontons and Coulombs phenomenological laws of friction. Interestingly, friction is on the nanometer scale proportional to the contact area, in opposition to the corresponding macroscopic law, whereas the macroscopically observed independence of friction from the sliding velocity remains approximately valid.
In the second part of the talk, I will present an experimental set-up optimized for the operation in the so-called dynamic mode of scanning force microscopy at low temperatures and in ultrahigh vacuum. The instrument achieves a resolution comparable to the one of low-temperature scanning tunneling microscopes, but yields complementary information. Moreover, it provides atomic resolution even on insulating materials, which can otherwise not be investigated. In particular, I will introduce a method that allows the continuous measurement of the tip-sample interaction potential. Comparison of such data with model potentials gives access to a profound analysis of the interactions at and between surfaces, including nano-elastic and nano-contact mechanical effects.
Protection of Astronauts from Cosmic Radiation, by John Norbury Thursday, 2/19/2004, 11:00 AM-12:00 PM
Dr. John Norbury
University of Wisconsin-Milwaukee
Department of Physics.
Protection of Astronauts from Space Radiation
The two most important medical problems that astronauts face on long duration space missions are the effects of microgravity and radiation due to cosmic rays. The radiation comes from three separate sources, namely geomagnetically trapped particles, energetic solar particles and Galactic cosmic rays. The talk will review these radiations and discuss research relevant to the general space radiation problem.
Sponsored by: WPI Department of Physics
Solid State Semiconductor Quantum Computing, by Vladimir Privman Monday, 2/16/2004, 11:00 AM-12:00 PM
Dr. Vladimir Privman
NSF Center for Quantum Device Technology
Clarkson University, Physics Department.
Solid State Semiconductor Quantum Computing.
An overview is presented of the ideas of quantum information and computing, with emphasis on their impact on recent solid-state research. The introduction is followed by survey of our groups work on evaluation of decoherence and relaxation in systems which are candidate for quantum computing implementations. Our results include investigations of interactions and decoherence in semiconductor heterostructures, with initial applications for quantum dots and for nuclear and donor-electron spins.
Sponsored by: WPI Department of Physics
Freshman Physics, Ideas and Innovation, by Bill Goodhue Thursday, 2/12/2004, 11:00 AM-12:00 PM
Bill Goodhue, UMASS Lowell.
As an experimentalist, the books most worn out on my bookshelf are those
dealing with freshman physics. The material in those books has been a
guiding force in my research; giving me many ideas, which I have
developed, or help develop into practical semiconductor and optical
devices. In this talk I'll show by example some of these devices and
discuss my philosophy on research and teaching.
Sponsored by: WPI Department of Physics
The Optical Amplifier Revolution, by John Zyskind Monday, 2/2/2004, 11:00 AM-12:00 PM
Sponsored by: WPI Department of Physics
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Physics Colloquium, "Building Complexity 1-2-3" by Dr. Jennifer Ross, Department of Physics, UMASS Amherst Monday, 11/16/2009, 4:00 PM-5:00 PM
Kinesin and cytoplasmic dynein are microtubule-based motor proteins that actively transport material throughout the cell. This transport is vital to effectively moving cargo around the cell. This is especially important in the very long axons that connect the spine to the extremities. Impediments of cargo transport down the axons leads to neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), also known as Lou Gehrigs disease, which is the disease affecting physicist Stephen Hawking. To understand the physical properties of these motors, we investigate the innate transport abilities of these motor proteins in vitro. We find that dynein has a greater ability to stay bound in the presence of obstacles on the microtubule track. Kinesin, on the other hand, can move robustly, but dissociates when confronted by a blocked path. Dynein's ability to hang on is likely due to its inherent flexibility and ability to move in reverse. These in vitro capabilities have implications for the cellular roles of these motors. Refreshments will be served in Olin Hall 223 at 3:40 P.M. Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "Lipid Membrane-Assisted 2D Assembly of Bionanoparticles at Liquid Interfaces" by Masafumi Fukuto, Brookhaven National Lab Monday, 11/9/2009, 4:00 PM-5:00 AM
Lipid monolayers at planar aqueous solution-vapor and solution-substrate interfaces provide an ideal platform for facilitating two-dimensional(2D) assembly of biomolecular nanoparticles like proteins and virus particles. In order to illustrate the utility and versatility of this approach to promoting the ordered assembly of nanoscale objects, we will describe the results of two of our recent studies: (i) the effects of surface biotin density on the 2D crystallization of the soluble protein streptavidin, and (ii) the electrostatic 2D assembly of virus particles, with emphasis on cowpea mosaic virus (CPMV). The structures of these systems have been probed by synchrotron x-ray scattering (GISAXS & XR), AFM, and optical microscopy measurements. We will also illustrate the capability of these techniques for in-situ characterization of structures at liquid interfaces. Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "EXX Phenomena in Macroscopic, Microscopic and Nanoscopic Structures," by Dr. S. A. Solin, Washington University, St. Louis, Department of Physics and Center for Materials Innovation Monday, 11/2/2009, 4:00 PM-5:00 PM
The new "EXX" phenomena in macroscopic, microscopic and nanoscopic metal-semiconductor hybrid structures will be described. Here E = extraordinary and XX = magnetoresistance (EMR), piezoconductance (EPC), optoconductance (EOC), and electroconductance (EEC). This new class of phenomena is based on the control and dominance of the geometric contributions, e.g. sample shape, lead placement, the presence of inhomogenieties, etc., to the transport properties of a physical system in contrast to traditional transport phenomena which are dominated by the intrinsic properties, e.g. mobility, carrier density, band structure, etc. The underlying phyiscs of EXX phenomena will be elucidated with particular emphasis on the use of analytic and finite element analysis methods to quantitatively account for the observed EXX signal enhancement. Surprising new aspects of the mesoscopic physics of the nano-hybrid structures will be addressed. A recently discovered inverse EOC (I-EOC) effect in which, nanoscopic devices (dimensions < 500 nm) show a decrease in conductivity with increased illumination intensity with an I-EOC ~ 1000% and a specific detectivity as high as D* = 3.2_1011 cmHz/W in a 250 nm device will be reported. It will be shown that I-EOC can be attributed to optical switching induced by the transition from ballistic to diffusive transport. The use of individual EXX sensors and EXX nano arrays to study, with ultrahigh spatial and temporal resolution, biologically relevant properties of cells such as surface charge density measured with a fluid-gated EEC device will be described. Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "The cytoskeletal machinery is essential for polarized expansion of plant cells" by Dr. Luis Vidali, Assistant Professor, Department of Biology and Biotechnology, WPI Monday, 10/5/2009, 4:00 PM-5:00 PM
Photosynthetic organisms are the primary transducers of solar energy into bioenergy. Hence, understanding the basic molecular and cellular mechanisms underlying their growth is essential to harvest their potential for biofuels and other forms of clean and renewable energy. Plant growth and development are the result of cell growth and cell division. These two basic processes are modified and coordinated in different plants to create an immense diversity of shapes and structures. Plant cells expand by balancing their internal turgor pressure with changes in the extensible properties of their cell walls . This is accomplished by the regulated deposition of cell wall material. Once the cell reaches a certain size, or during specific developmental processes, the cell will enter mitosis and divide. Plant division is completed when a new cell wall is built to separate the two new cells. Polarized cell expansion or "tip growth" has been extensively studied as a paradigm to understand cell expansion. Pollen tubes, root hairs, and the protonemata of ferns and mosses, grow exclusively by this type of expansion, which is achieved by focusing all the growth resources to one end of the cell. It is well established that the actin cytoskeleton plays an essential role in polarized expansion, most likely by polarizing the vesicle transport machinery via the actin-based motor myosin XI. Nevertheless, because of the large number of myosin XI genes in vascular plants, it has been difficult to determine their precise role in cell expansion. In contrast, in the moss Physcomitrella patens, there are only two myosin XI genes, which encode proteins that are 94% identical. To determine the role of myosin XI in polarized expansion, we simultaneously silenced the expression of both myosin XIs by RNA interference (RNAi). Loss of myosin XI function results in a dramatic loss of polarized expansion; plants are stunted and composed of small rounded cells. We also show that a green fluorescent protein fusion of myosin XI localizes to the site of expansion a the tip of the growing cell. Together these results indicate that myosin XI is responsible for the transport of components important for polarized expansion. Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "Block Copolymer Droplets, Thin Films and Wrinkles," by Dr. Andrew B. Croll, University of Massachusetts, Amherst, Department of Polymer Science and Engineering Monday, 9/28/2009, 4:00 PM-5:00 PM
Block Copolymers are long chain molecules made of segments of more than one polymer variety covalently joined together. This molecular architecture leads to many technologically important phenomena which are useful in applications that range from the semiconductor to the commodity polymer industries. Many of the most important properties of these systems result from the nanoscopic structures that form due to the chemical incompatibility of the blocks. In this talk I will present our progress towards a more detailed understanding of the physics of these systems. I will focus on the simplest system, that of symmetric diblock copolymers (where the chain consists of two distinct blocks of equal size) in a variety of different experimental confining geometries. I will show how the micro-phase separated structures lead to conically shaped fluid droplets, how the thin film geometry can be adapted into a very simple measurement of the Flory-Huggins interaction parameter and how the structured surface of a thin film can be used to drive a simple wrinkled geometry into a state of stress localization. Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
Physics Colloquium, "Studying Heterogeneity in Bacterial Lipopolysaccharides with Atomic Force Microscopy " by Dr. Terri Camesano, WPI Chemical Engineering Department Monday, 9/21/2009, 4:00 PM-12:50 PM
Gram-negative bacteria have a layer of lipopolysaccharides (LPS) on the outer portion of their membrane. These LPS molecules are very important in controlling virulence and bacterial adhesion to host tissue or biomaterials. Heterogeneity in the properties of bacterial LPS can affect how they interact with, and ultimately attach to, various surfaces. We are working with two model microorganisms, which exhibit different kinds of heterogeneity. For example, Escherichia coli (E. coli) express LPS which vary from strain to strain, but are chemically the same within a single subspecies. However, physical heterogeneities (such as length of the polymer molecules) can vary as a function of growth conditions, even on a single strain of bacteria. Pseudomonas aeruginosa represents a different scenario, in which the same bacterium can express chemically and physically distinct saccharide units on a single LPS molecule. Using atomic force microscopy, we are exploring how this heterogeneity, especially in the physical properties of LPS, controls the attachment and adhesion of Gram-negative bacteria to numerous surfaces. Sponsored by: WPI Physics Department, Dr. Erkan Tuzel
WPI Physics Department 2nd Annual Robert Goddard Rocket Competition Saturday, 6/13/2009, 10:00 AM-1:00 PM
This years Robert Goddard Competition will be a water rocket competition for all schools in the Worcester Area. It is geared at having an adult member along with a group of students work together to find the best way to launch a water rocket into a designated area. A website is available and will be updated periodically. Sponsored by: WPI Physics Department
Physics Department M.S. Thesis Defense, "Temperature Dependence of the Contact Angle of Water on Graphite, Silicon and Gold," by Kenneth Osborne, Physics Department Graduate Student Friday, 4/24/2009, 4:00 PM-5:00 AM
The temperature dependence of the contact angle of water on graphite, silicon and gold was investigated under various conditions to test the Sharp-Kink Approximation. Despite correctly predicting the contact angle at room temperature, the ideal Sharp-Kink Approximation was not found to accurately describe the contact angle's temperature dependence. The discrepancies from the predicted contact angle were characterized in terms of a correction H(T) to the liquid-solid surface tension. H(T) was found to be linear in temperature and decreasing, and is consistent with electrostatic charge effects. Sponsored by: Dr. Rafael Garcia
Special Topic, "A Personal View of Rural Development in Vietnam and Cambodia" by Dr. Nancy Burnham and Mr. Frederick Hutson, WPI Physics Department Wednesday, 4/22/2009, 4:00 PM-5:00 PM
For two weeks over winter break, we traveled around Vietnam and Cambodia on a study tour organized by Heifer International, a rural development charity that we have been supporting for some years. In this talk, we will, a) explain Heifer's history and current activities, b) describe where we went and what we did, and c) tell you our personal experiences of and thoughts on rural development. We plan to speak and show slides for approximately thirty minutes, after which we hope for an interesting discussion. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department Ph.D. Defense, "Electromagnetic Nucleus - Nucleus Cross Sections using Energy Dependent Branching Ratios," Anne Marie Adamczyk, WPI Physic Graduate Student Monday, 4/20/2009, 10:00 AM-2:00 PM
It is important that accurate estimates of crew exposure to radiation are obtained for future long - term space missions. To predict the radiation environment, a few space radiation transport codes exist, all of which use basic nuclear cross section information for transport of radiation through materials. Little theoretical and experimental work has been conducted on reactions induced by the electromagnetic (EM) force, especially with regard to differential cross sections. Therefore, radiation transport codes have typically neglected to incorporate EM nuclear collision cross sections. EM cross sections for single nucleon removal have been included in some radiation codes, but better values can be obtained by using an energy dependent branching ratio. Most previous theoretical and experimental work has been devoted to total cross sections. Therefore, the energy dependent branching ratios presented can be extensively compared to past theory and experiment. Such comparisons indicate that using energy dependent branching ratios yield better estimates of total cross sections. Differential cross sections for electromagnetic dissociation in nuclear collisions are calculated for the first time. In order to be useful for three - dimensional transport codes, these cross sections have been calculated in both the projectile and lab frames. The formulas for these cross sections are such that they can be immediately used in space radiation transport codes. Only a limited amount of data exists, but the comparison between theory and experiment is good. Sponsored by: WPI Physics Department, Dr. P.K. Aravind
Physics Colloquium, "Mid-Infrared Semiconductor Laser Development at MIT/Lincoln Laboratory" By Dr. George W. Turner, Lincoln Laboratory Monday, 4/13/2009, 4:00 PM-5:00 PM
MIT / Lincoln Laboratory has been continuously involved in the development of semiconductor laser sources since the very initial demonstrations of the diode laser in 1962. In this lecture, a historical overview of the various semiconductor laser efforts at MIT / Lincoln Laboratory will be presented, with an emphasis on the evolution of mid-infrared (2-5 µm) semiconductor laser technology. Results from both electrically-pumped and optically-pumped semiconductor laser structures will be reviewed. Recent results and new research directions in mid-infrared, high-power quantum cascade lasers, operating near room temperature, will also be discussed. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium,"Manganese Cell Labeling and Tissue Delivery UsingManganesse (III)- Transferrin, by Dr. Christopher Sotak, WPI Biomedical Engineering Monday, 4/6/2009, 4:00 PM-5:00 PM
Although most manganese-enhanced MRI (MEMRI) methods employ Mn2+ as a Ca2+ analogue, other mechanisms for delivering manganese into cells and tissue are also possible. For example, transferrins (Tf) a major class of plasma iron-binding proteins can accommodate a variety of other metal ions (including manganese) in the two available iron-binding domains of the Tf molecule. In particular, Tf has been shown to be one of the major manganese plasma-transport proteins for both rodents and humans in the form of Mn(III)-Tf. Metal-Tf transport is initiated when the metalloprotein binds to transferrin receptor 1 (TfR1) at the cell surface. The metal-Tf/TfR1 complex is then transported into the cell via TfR1-mediated endocytosis. The acidic pH (~5.5) that develops within the resulting endosomal compartment releases the metal from the internalized protein complex. The free manganese is then reduced and transported across the endosomal membrane into the cytosol; where it can function as an effective MRI contrast agent. The metal-free apo-Tf/TfR1 complex is recycled back to the cell surface, where both proteins are reused in another cycle of cellular metal-ion uptake. The cyclical nature of this process can potentially label cells with relatively high concentrations of manganese. TfR1-mediated endocytosis has been investigated as a novel approach for manganese cell labeling and tissue delivery using Mn(III)-Tf. The degree of manganese cell labeling following incubation of murine hepatocytes for 2-7 h in 31.5 M Mn(III)-Tf was comparable to that of hepatocytes incubated in 500 M Mn2+ for 1 h. Manganese delivery and transport has also been investigated in vivo following direct intracerebral injection of Mn(III)-Tf into the rat brain. Intracerebral infusions of from 5-20 L of ~1 mM Mn(III)-Tf resulted in significant T1-relaxation-time enhancement; comparable to that observed following direct injection of Mn2+ alone at the same concentration. Furthermore, the subsequent transport of manganese along neuronal tracts originating from the injection site provides further evidence for the in vivo cellular delivery of Mn2+ via TfR1-mediated endocytosis. This approach represents a novel way to use a biological pathway for targeting and to release an MRI contrast agent into cells.
Physics Colloquium, "Fingerprints of Prefibrilar Amyloid Oligomers in the Magnetic Resonance of Water" by Dr. Florin Despa, Department of Pharmacology, University of California, Davis Wednesday, 3/25/2009, 4:00 PM-5:00 PM
Hydration shells of normal proteins display both structured and bulk-like waters. Isomers with considerable bulk-like hydration tend to aggregate. Our data show that different morphological states of aggregated isomers differ by hydration distribution profiles and water magnetic resonance (MR) signals. The results help explain the MR contrast patterns of the amyloids, a subject of long controversy, and suggest a new approach for identifying unusual protein aggregation related to disease. As an example, I will present water proton MR spectroscopic data, thioflavin T fluorescence, gel electrophoresis and cell toxicity measurements revealing the relationship between amyloid conformation and amyloid-induced cellular dysfunction. Developing strategies to detect the amyloids at an early stage of development and to assess the induced cellular damage are crucial for diagnosis and treatment of protein conformational diseases, such as Alzheimers disease, type 2 diabetes mellitus and diabetic cardiomyopathy. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium,"High magnetic field studies of the field induced ordering and of the itinerant electron metamagnetism in heavy fermion compounds URu2-xRexSi2 and URu1.92Rh0.08Si2,by Dr. Sonia Francoual, Monday, 3/23/2009, 4:00 PM-5:00 PM
URu2Si2 is a heavy-fermion compound the low temperatures and high magnetic fields phase diagram of which is characterized by the presence of a Hidden-Order phase below 17 K up to 36 T, multiple ordered phases below 7 K between 36 and 42 T and itinerant electron metamagnetism (IEMM): (1)* Rhenium doping of URu2Si2 yields unusual magnetic and electronic behaviors at low temperatures with a smearing of the Hidden-Order at x ~ 0.10, Non Fermi Liquid behavior from x ~ 0.15 and weak ferromagnetism from x ~ 0.30. In order to address the effects of Re doping on the multiple field-induced ordering and on the IEMM, we measured the magnetization and magnetoresistance properties of URu2-xRexSi2 single-crystals in pulsed magnetic fields up to 65 T allowing it to determine a comprehensive (T, B, x) phase diagram. The field-induced ordering is suppressed at x = 0.05, the Heavy-Fermion (HF) state and the IEMM at x = 0.35. The suppression of the HF state is found to condition the suppression of the IEMM and the emergence of the ferromagnetism. (2)** Rhodium doping yields the growing of a single ordered phase, so called phase II, below 10 K at fields above 27 T and complete suppression of the Hidden order phase. In order to get some clues about the nature of the order parameter in phase II, we measured magnetostriction and thermal expansion on a URu1.92Rh0.04Si2 single-crystal using a capacitive dilatometer. Important dilation effects are evidenced in the underlying Fermi liquid outside phase II as observed previously in the 4f analog compound CeRu2Si2 as well as anisotropic and significant length changes in phase II.
Physics Faculty Candidate, "Conformational Sculpting of DNA: Nanofluidics for Single Molecule DNA Analysis and Manipulation," by Dr. Walter Reisner, Brown University Monday, 3/2/2009, 4:00 PM-5:00 PM
My work uses sub micron nanofabrication tools like electron beam lithography to explore the fundamental physics of polymers in confinement and to develop nanotechnology approaches to key problems in biology. When a polymer is confined in a structure with dimension below the polymers free solution gyration radius the confining geometry will alter the polymer equilibrium conformation. This fundamental result of statistical physics has a key technological implication: polymer conformation can be manipulated and controlled onchip by design of the nanofludic confining geometry. This talk will consider two implications of this notion of conformational sculpting for the field of single molecule DNA analysis. In a nanochannel, self-exclusion interactions within the polymer will create a linear unscrolling of the genome along the channel for analysis. Nanochannel based DNA stretching can serve as a platform for a new optical mapping technique based on measuring the pattern of partial melting along the extended molecules. We believe this melting mapping technology is the first optically based single molecule technique sensitive to genome wide sequence variation that does not require an additional enzymatic labeling or restriction scheme. In addition, by embedding sub micron nanotopographies in a slit-like nanochannel, we can create spatial variation in confinement across the slit. The confinement variation in turns varies a molecules configurational freedom, or entropy. Consequently, by controlling device geometry, we can create a user-defined free energy landscape that allows us to sculpt the equilibrium configuration of a molecule. Individual square depressions, or nanopits, can be used to trap DNA at specific points in the slit. Arrays of nanopits will lead to complex digitized conformations with a single molecule linking a number of pits. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Emerging Fields of Nematic Liquid Crystals: Transformative Biaxial Nematic & Unconventional Bio-Detection Technology," by Dr. Bharat R. Archarya, Kent University Monday, 2/23/2009, 4:00 PM-5:00 AM
Nematic liquid crystals (NLCs), the electrically responsive fluid behind most of the flat panel displays, consist of anisotropic molecules that possess long range orientational correlation but lack positional order. In recent years, there have been significant advances leading to discovery of a much sought-after biaxial nematic LC and in unconventional applications of the classical (uniaxial) nematic in photonics, sensors, and diagnostics. Two such advances will be discussed, one of enormous basic scientific interest with potential to give rise to a transformative technology and the second to enable hitherto unexplored technological applications of the well known NLCs. The use of x-ray diffraction technique to probe structural features of the nematic phase of bent-core molecules will be discussed. Experimental results, combined with the ab-initio calculations of the molecular form factor and structure factor have led to the discovery of the biaxial nematic phase in thermotropic mesogens. The biaxial nematic holds the potential of leading to new generation display technology that will be 100 times faster than current HDTVs. Application of NLCs in rapid viral detection will be discussed in the second half of the presentation. Surfaces decorated with enveloped viruses promote vertical (homeotropic) alignment of NLCs. Unique nature of the interaction between the enveloped viruses and NLCs has been exploited to detect, amplify, and confirm the presence of viruses. Electrokinetic effects associated with a non-uniform AC field have been employed to accelerate the transport of viruses to the surface. The combination of these two approaches has been used to enable rapid (~10 min) detection of viruses, much faster than the incubation time at clinically relevant concentrations. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Coarse-grained modeling of complex fluids and bio-polymers," by Dr. Erkan Tuzel, University of Minnesota Wednesday, 2/11/2009, 4:00 PM-5:00 AM
The dynamic behavior of complex liquids and soft materials is of great importance in a wide range of disciplines. Computational studies of these phenomena are particularly demanding because of the presence of disparate length and energy scales, the complicated coupling between the embedded objects, and the hydrodynamic ow eld and thermal uctuations. In the rst part of this presen- tation, I will introduce one such recently introduced particle-based mesoscale algorithm|stochastic rotation dynamics|which solves the hydrodynamic equations by following the discrete time dynamics of particles with continuous coordinates and velocities, using ecient multi-particle collisions. It will be shown how the algorithm can be generalized to model dense uids, immiscible binary and am- phiphilic mixtures. The phase diagram of the entropically driven de-mixing transition and a detailed analysis of the capillary wave spectrum for binary droplets will be presented. The second part of my talk will focus on mesoscale modeling microtubule-motor interactions in gliding assays and living cells. In living cells microtubules are often viewed as mechanically rigid compressive struts that help maintain cell shape and aid in the transport of cellular cargo by serving as tracks for the molecular motors. However, recent experiments on LLC-PK1 epithelial cells strongly suggest that microtubules are often dynamic and deforming continuously and dominantly being transported anterogradely by molecular motors. Surprisingly, quantitative analysis of these deformations exhibit striking similari- ties to in vitro gliding assays. Motivated by these experiments, we have modeled microtubule-motor interactions using coarse-grained simulations. Simulation results support our experimental ndings and further elucidate on the interplay between molecular motors and passive cross-linkers. Our results suggest that molecular motors are not necessarily just cargo carriers, but can play a dynamic role in the deformation and positioning the microtubule array. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Sensing and Adaptation in Directed Cell Migration," by Dr. Yevgeniy Kalinin, School of Chemical and Biomolecular Engineering, Cornell University Monday, 2/2/2009, 4:00 PM-5:00 AM
Microfluidic technology has presented us with the opportunities to precisely control the cellular microenvironments (both chemical and mechanical) and, in combination with live cell imaging, to reveal the cellular responses at the single cell levels. In this talk I will present applications of microfluidics to the studies of receptor-mediated cell responses using bacterial chemotaxis as a model system. Using a comprehensive set of linear chemical gradients we verify unambiguously that E. coli sense chemical concentration on the logarithmic scale (this is similar to sensory systems of higher organisms where the logarithm of the signal strength simply compacts a wide range of signal into a manageable one). This result, when combined with a theoretical model of bacterial chemotactic behavior, makes it possible to understand macroscopic cellular behavior by modeling the underlying microscopic pathway kinetics. In the case of multiple chemical gradients I will show that E. coli make their decisions on which chemical they should pursue first depending upon the receptor number ratio. More interestingly we find that in natural environments E. coli are able to modify their chemical tastes by changing the number of receptors of a given kind. While this behavior is undoubtedly related to E. colis survival strategy the exact reasons for it and its mechanisms remain to be discovered. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Faculty Candidate, "Swimming in Viscoelastic Fluids and Gels," by Dr. Henry Fu, Brown University Friday, 1/30/2009, 4:00 PM-5:00 AM
The swimming of microorganisms in Newtonian fluids has been, and still remains, an active area of research. However, in many cases the natural environments which microorganisms navigate are non- Newtonian fluids or even gels. For example, mammalian sperm swim through mucus in the female reproductive tract. In this talk I focus on swimming through polymeric viscoelastic fluids and gels. First, the forces exerted by a viscoelastic medium are different from those exerted by a Newtonian fluid. I address how this affects swimming shapes and speeds of flexible swimmers such as sperm. Second, the kinematic reversibility of the zero-Reynolds-number Stokes flow constrains what types of swimming motions are effective in Newtonian fluids (Purcell's "Scallop theorem"). I discuss how this is altered in nonlinearly viscoelastic fluids, and whether any new swimming strategies become available to swimmers in viscoelastic media. Finally, I describe issues that arise for swimmers moving through viscoelastic gels, which are solids rather than fluids. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department Wonderful Speaker, "USE IT, LOSE IT, OR SAVE IT-The Science of Renewable Energy Storage" by Dr. Albert Migliori, National High Magnetic Field Laboratory of the Los Alamos National Laboratory Friday, 1/23/2009, 4:00 PM-5:00 PM
Today, we can usefully consume all of the little solar, wind, and other renewable energy we produce. But for total energy production to shift significantly toward inherently unpredictable renewables, energy must be stored when available and recovered when needed else precious renewable energy sources will stand idle. This lecture will present an overview of the science of energy storage and new nanotechnology approaches to it. The science will take time to mature, but with legislative and economic shelters to nurture it, effective distributed electrical energy storage solutions can be found before the need is urgent Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "The Physics of Swimming Microorganisms" by Dr. Thomas Powers, Brown University Wednesday, 12/10/2008, 4:00 PM-5:00 PM
I will discuss model problems inspired by the mechanics of swimming microorganisms. First we study the swimming velocity of a swimmer with prescribed stroke in a complex fluid. Then, inspired by the coordination of beating cilia, we present an experimental model for hydrodynamic synchronization. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department Wonders Speaker, "Phonons Under Spatial Confinement," by Professor Janice Musfeldt, University of Tennessee, Department of Chemistry Wednesday, 12/3/2008, 4:00 PM-5:00 PM
Understanding the consequences of nanoscale confinement on materials functionality is one of the ``grand challenges" in the physical sciences. In this talk, I will focus on the issue of phonon confinement, discussing our recent measurements of both optical and acoustic phonons in model materials. Specific systems of interest include transition metal dichalcogenides (such as 2H- and IF-WS2) and complex oxides such as the spinels. In each case, we work with both traditional bulk analogs + chemically identical but morphologically different nanoscale materials, allowing us to quantify changes in bonding, phonon density of states, strain-induced changes in local structure, and engineering properties that derive from finite length scale effects. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Engineering Vascular Tissue from Cells and Cell-Derived Extracellular Matrix," by Dr. Marsha Rolle, WPI Biomedical Engineering Monday, 12/1/2008, 4:00 PM-5:00 PM
Tissue engineering has shown promise toward creating blood vessel substitutes for cardiovascular surgery. Recent clinical studies suggest that tissue engineered vascular grafts fabricated entirely from cultured cell sheets and cell-derived extracellular matrix (ECM) may be used as autologous arteriovenous fistulas in dialysis patients. However, the lengthy process required for their fabrication (~28 weeks), may limit their use. The focus of our research is to develop systems to more rapidly generate cell-based tissue constructs for systematic evaluation of the effects of soluble and genetic factors on tissue structure, ECM synthesis, and mechanical function. The seminar will focus on our recent work involving generation of cell-derived tissue rings by seeding smooth muscle cells (SMC) into custom, non-adhesive, circular wells. After only 8 days in culture, the resulting tissue rings were subjected to mechanical testing, and exhibited properties approaching those of native tissues. If successful, this system may allow rapid fabrication of vascular tissue constructs to facilitate the discovery of factors that control ECM synthesis and organization as a means of engineering tissue mechanical properties. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "The Physics of Line-tying in Magnetohydrodynamics" by Dr. Gian Luca Delzanno, Los Alamos National Laboratory Monday, 11/24/2008, 4:00 PM-5:00 PM
The study of Magnetohydrodynamic (MHD) linear stability with line-tying has been the subject of intense research in the solar physics community for several decades, in an attempt to understand the dynamics of solar flares and the related mechanisms of energy release (see the review paper [1]). Moreover, recent experiments on two cylindrical devices [2-3] have brought even further interest on this subject. It is important to notice, however, that applications to solar physics or to laboratory experiments span a wide range of values of the Lundquist number S (proportional to the inverse of plasma resistivity), S>10^10 in the solar corona while S~50 for the experiments. In this presentation, I will therefore analyze the effect of plasma resistivity on line-tied modes in cylindrical geometry and discuss the existence of tearing modes in line-tied plasmas [4]. Tearing modes occur in a plasma due to plasma resistivity. They are commonly associated to boundary layers and have growth rates proportional to a fractional power of plasma resistivity. Whether they can exist in a line-tied plasma has been matter of debate for a long time. I will show that the physics of line-tying prevents the existence of tearing modes and the only resistive unstable modes left in the plasma have a (much smaller) growth rate proportional to plasma resistivity. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Protein Dynamics" by Dr. Hans Frauenfelder, Senior Fellow at Los alamos National Laboratory Wednesday, 11/19/2008, 4:00 PM-5:00 PM
Proteins are complex systems that connect biology, biophysics, biochemistry, chemistry, physics, and even mathematics. Proteins share similarities with supercooled liquids and glasses, such frustration, the existence of an energy landscape, and alpha and beta fluctuations. Protein are, however, far more complex than glasses and they can be modified and studied in much more detail. Protein research therefore has not only impact in the life sciences, but also in other fields. The beautiful pictures of protein structures that appear in many publications often create the impression that proteins are rigid and function independently of their environment. Proteins are, however, surrounded by hydration water and they are embedded in a bulk solvent. The motions in the hydration shell and the bulk solvent actually control the internal protein motions. Experiments with myoglobin that separately monitor the external and internal fluctuations show that the alpha fluctuations of the bulk solvent drive the large-scale protein motions and that the beta fluctuations of the hydration water drive the internal protein motions. These results hint that the protein surface is functionally as important as the interior. The data also prove that there is no dynamic transition or "fragile-to-strong transition" near 200 K in proteins. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Department, Wonderful Speaker, "Wolfgang Pauli Stories - Personal Recollections" by Dr. Hans Frauenfelder, Senior Fellow at Los Alamos National Laboratory Monday, 11/17/2008, 4:00 PM-5:00 PM
Wolfgang Pauli was one of the most influential and remarkable physicists involved in the revolution in physics that took place after about 1900. I was fortunate to be at the Physics Institute of the ETH in Zurich from 1941 to 1952. The Institute was one of the few in Europe that was not impacted severely by the war and so it became an unofficial European center. It was an exciting time for a graduate student. The scientific atmosphere became even more remarkable when Pauli returned from Princeton after the war. Bohr, Heisenberg, Kramers, Stern, Weisskopf, Wentzel,and, Zwicky could be encountered and there were many young brilliant theoreticians, for instance Glauber, Dyson, and Kallen who enjoyed stays in Zurich. Robert Schafroth, who later produced a theory similar to BCS, was my best friend. We sat every day in my little lab for a few hours, drank coffee, and discussed physics. Schafroth was Pauli's student and later his assistant. Thus Pauli came every day at about 3 PM to have coffee with us. This gave me a chance to get to know Pauli well, learn about the many Pauli stories, and observe his sharp wit in action. Read: Gino Segre, Faust in Copenhagen. Viking 2007. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Effects of Frustration and Disorder in Condensed Matter" by Dr. Frederick W. Fabris, Los Alamos National Laboratory Monday, 11/10/2008, 4:00 PM-5:00 PM
In this presentation I will discuss the frustration effects in some disordered systems. In the first part of this talk I will present the main types of magnets and how is possible to achieve high magnetic fields which have been used for the study of different physical properties of the materials. There are many kinds of compounds and systems who presents frustration and disorder. Frustrated systems have been studied for more than 50 years in materials ranging from spin glasses to quantum magnets. Frustration is a state of matter in which competing interactions cannot be satisfied simultaneously and consequently the ground state is degenerate. The effects of frustration can be identified in many experimental techniques. I will show how these effects are affecting phase transitions in high-temperature superconductors by measuring magnetotransport and DC magnetization. In some magnetic compounds (spin glasses and reentrant compounds) we can observe frustration effects in the Anomalous Hall Effect. Finally, in our current project, it has been proposed theoretically that a natural mineral named Azurite could be considered as a frustrated quantum magnet. We have performed dilatometry technique in order to investigate the magnetic phase diagram of this system. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "Cationic Polymers and Naturally Occurring Vaults as Vectors for Delivery of Therapeutic Molecules" by Dr. Muri Han, David Geffen School of Medicine, University of California, Los Angeles Wednesday, 11/5/2008, 4:00 PM-5:00 PM
A carrier molecule, vector, facilitates the delivery of therapeutic drugs, proteins, and/or nucleic acids into the target sites in effective and safe ways. The vector should be easy to be modified in order to improve the stability, and to facilitate the transportation of therapeutic materials. A variety of non-viral vectors have received much attention in the past decade ; 1) Polyplexes are formed by the electrostatic interaction between plasmid DNA and polycations. They have been designed to condense pDNA and to facilitate their cellular uptake in order to achieve effective gene delivery based on their versatility and ease of modification. Among such modifications, PEGylation of therapeutic particles is widely used to mask particles from the phagocytic system. PEG-block-polycation copolymers having the N-(2-aminoethyl)-2-aminoethyl group in the side chain (PEG-b-P[Asp(DET)]) were developed, which show high transfection efficiencies and low cytotoxicity. 2) Vaults are naturally occurring 13-MDa ribonucleoprotein particles with a highly conserved structure composed of three different proteins: major vault protein (MVP), vault poly (ADP-ribose) polymerase (VPARP) and telomerase-associated protein 1 (TEP1). Recombinant vaults can be engineered by expressing MVP using the baculovirus system. Vaults have several advantages as a delivery system including low immunogenicity and structural stability. The hollow vault particle is able to encapsulate sequestered materials within the central cavity using a targeting peptide derived from the VPARP protein. The vault shell is a dynamic structure which can disassemble into halves in response to low pH. Considering the low pH of the endosome compartment, dissociation of vaults may allow the intracellular release of molecules. Sponsored by: WPI Physics Department, Dr. Izabela Stroe
Physics Colloquium, "A Comparative Study of General Finite Element Techniques in Atomistic-to-Continuum Coupling" by Dr. Peter W. Chung, U.S. Army Research Laboratory Monday, 9/15/2008, 4:00 AM-5:00 AM
It is well known that continuum based techniques such as Lagrangian or Eulerian numerical methods, which use constitutive relations that do not account for the atomistic structure, are invalid beyond the scope of their calibration. In regions containing dislocations, mobile defects, or nonlinear material, these numerical methods have to be modified to capture important phenomena. Yet they remain useful for dealing with field variations that occur slowly relative to atomic spacings. Molecular dynamics (MD), on the other hand, is an excellent means for modeling interactions on an atomic scale as well as predicting the response when sub-micron scale phenomena occur. However, MD can be computationally expensive beyond relatively small sample sizes. Therefore, to alleviate these problems multiscale methods have been developed in recent years to couple the continuum and atomistic scales together. After a brief introduction of motivational problems currently being considered at the U. S. Army Research Laboratory, we show a comparative study of the quality of interpolation that best suits continuum methods in regions at and near the interface with a molecular dynamics region. We specifically examine interpolation functions prominent in general finite element methods and meshless methods - Bubnov-Galerkin, partition of unity, and moving least squares - and assess their ability to capture a travelling wave through a discrete/continuum interface and a graded finite element mesh (increasing element size away from the MD region). Within the interface region, where the continuum and atomistic scales overlap, the displacements on the continuum are dictated by the atomistic results generated from MD. The results of our study show that using simple changes to the interpolation quality of fields in the continuum, namely using partition of unity interpolation functions, produces accurate results compared to finite elements and moving least squares interpolation functions. For example, we demonstrate the effectiveness of partition of unity shape functions by simulating a Gaussian wave propagating throughout a 1D domain with a harmonic potential between neighbouring atoms. As the wave moves through the atomistic-continuum interface and through the graded mesh, the effectiveness of the partition of unity shape functions are clearly seen. In spite of the higher computational costs, the improvement in accuracy appears beneficial in practice. The presentation will conclude with a discussion of open issues related to the problem from the point of view of phonon transport and the on-going development of numerical methods that can adequately represent the physics through modeling methods representing multiple scales. Sponsored by: WPI Physics Department, Izabela Stroe
Physics Colloquium, "Microflyidic Devices for Single Cells," by Dr. Amy Rowat, Harvard University Monday, 4/28/2008, 4:00 PM-5:00 PM
We have developed microfluidic tools for studying populations of single cells. We encapsulate individual cells using polydimethylsiloxane (PDMS) devices. Cells are trapped either in chambers as wide as a single cell and long enough to contain many generations of cells, or in 15 micron droplets of a water-in-oil emulsion generated in PDMS microfluidic devices. In the chambers, cells are maintained under constant flow conditions, and divide for many generations. All progeny deriving from the single cell are contained in the chamber, facilitating studies of gene expression, stress response, and DNA repair as a function of cell genealogy and replicative age. Drops of a water-in-oil emulsion also function to isolate single cells over the experimental timecourse. We have developed a device to immobilize drops, allowing us to track single cell growth, and to quantify levels of secreted enzymes that rapidly attain high concentrations due to the small drop volume. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Department Ph.D Defense, "Resonance Production and Nuclear Fragmentation for Space Radiation," by Ryan B. Norman, WPI Physics Department Graduate Student Thursday, 4/17/2008, 10:00 AM-11:00 AM
Space radiation and its effects on human life and sensitive equipment are of concern to a safe exploration of space. Radiation fields are modified in quality and quantity by intervening shielding materials. The modification of space radiation by shielding materials is modeled by deterministic transport codes using the Boltzmann transport equation. Databases of cross sections for particle production are needed as input for transport codes. A simple model of nucleon-nucleon interactions is developed and used to derive differential and total cross sections. The validity of the model is verified for proton-proton elastic scattering and applied to Δ-resonance production. Additionally, a comprehensive validation program of the nucleus-nucleus fragmentation cross section models NUCFRG2 and QMSFRG is performed. A database of over 300 experiments was assembled and used to compare to model fragmentation cross sections. Sponsored by: WPI Physics Department
Physics Faculty Search Candidate, "Precision Condensed Matter Measurements Applied to Biology" by Dr. Izabela Stroe, National High Magnetic Field Laboratory-Los Alamos National Laboratory Thursday, 4/10/2008, 4:00 PM-5:00 PM
I describe three experimental techniques, resonant ultrasound spectroscopy (RUS), relaxation calorimetry (RC), and dielectric relaxation spectroscopy (DRS). All are used extensively in condensed matter physics, and also are successfully applied to biological systems, proteins and DNA. These techniques have a common theme-they all probe normal modes of vibration. RUS probes mechanical oscillator strength (phonons), DRS probes the low-frequency sum of all the infrared-active oscillator strengths, and RHC probes entropy from all types of vibrational modes. RUS measures the mechanical resonances of a material to determine all elastic constants at once. Its accuracy and high sensitivity can be useful in investigating the hydration and dehydration of protein crystals. The RC that we developed at LANL improves accuracy and reduces noise by eliminating digitization artifacts present in all commercial calorimeters. Originally developed for high temperature superconductors, we describe here its application to DNA melting. DRS, another popular condensed matter technique, measures the dielectric response of a system and is sensitive to the dynamics and hydration properties of proteins. We recently studied protein-solvent interactions of horse myoglobin (Mb) in glycerol/H2O mixtures with DRS from 40Hz-110MHz and showed that the Myoglobin (Mb)-related process is associated with the conformational uctuations of the whole Mb protein. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Nanomagnets: Long-Range Order, Wide-Range Applications" by Dr. Mark Tuominen, NSF Center for Hierarchical Manufacturing, UMASS Amherst Monday, 4/7/2008, 4:00 PM-5:00 PM
From data storage to generators to sensors, ferromagnetic materials play a vital role in modern technology one that is continuously evolving. Recent techniques for producing nanoscale ferromagnets are changing the way magnetic materials and components are designed and leading to new functional paradigms: rings, clusters, spin-polarized current devices, nanostructured composites and more. This presentation will discuss some of key experimental approaches in the development to advance nanomagnetic technologies and the underlying Physics behind these applications. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Snakes on a Plane" by Dr. David Hu, Courant Institute of Mathematical Sciences, New York University Monday, 3/31/2008, 4:00 PM-5:00 PM
Snakes propel themselves over land using a variety of techniques, including sidewinding, lateral sinuous slithering and a unidirectional accordion-like mode. We explore these friction-based propulsion mechanisms through a combined experimental and theoretical investigation. Particular attention is given to classifying the gaits of snakes according to Froude number and the relative magnitudes of the frictional forces in the tangential and normal directions. In a simple kinematic model, we prescribe the waveform of the snake and calculate its motion as required by the torque and force balances on its body. A key feature of our model is that it allows us to rationalize the snake's gait on the basis of speed and mechanical efficiency. We also provide a historical survey of our previous work on the propulsion of water-walking insects. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Case-Control Study of Lung-Cancer Risk from Residential Radon Exposure in Worcester County, MA," by Dr. Donald Nelson, Professor Emeritus of Physics at WPI Monday, 2/25/2008, 4:00 PM-5:00 PM
The risk of lung cancer from exposure to residential radon and its radioactive progeny has been thought to follow the Linear-No-Threshold hypothesis, that is, any amount is bad for a person and twice the amount is twice as bad. This has been difficult to establish because the risk at typical residential exposures is small and because of confounding factors, such as smoking. Individual North American case/control studies have been unable to establish the LNT relationship with the requisite statistical certainty, and a recently published pooling of those studies has also been unable to do so. During 199097 WPI in cooperation with the Fallon Health Maintenance Organization (lead researchers: Joel H. Popkin and Zenaida Popkin) undertook a case/control study of this risk. Our results have been analyzed by a Johns Hopkins University biostatistician, Richard E. Thompson. Forty-three IQP students were involved in the study over the seven years of data taking. The study enrolled 200 lung cancer cases and 397 controls matched in age and sex, all from the Fallon clientele. Each was administered a questionnaire concerning smoking habits, use of the house, job exposures to known or suspected carcinogens, etc. Multiple, year-long measurements of radon concentrations were made in each house. The risk was analyzed by conditional logistic regression by both stratifying the data with respect to radon concentration and by a natural cubic spline fitting technique, each of which let the data determine its own functional form. Smoking, years of residency, education, income, and exposure to known or suspected carcinogens were controlled for. Contrary to the LNT hypothesis, we found that small concentrations of radon typical of most houses (but not large concentrations) are actually protective with respect to lung cancer. Furthermore, over a portion of the exposure range the results are statistically significant, an unusual result for a study of this size.. Opposition to our non-LNT results not our methodology has delayed publication to the present time. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Faculty Search Candidate, "Bright Shining Nanosensor Platforms," by Dr. Jeffery Anker, Northwestern University Friday, 2/22/2008, 4:00 PM-5:00 PM
Fluorescent and plasmonic nanoparticles are increasingly used in cellular imaging applications because they fluorescence and scatter light so brightly that single nanoparticles can be observed over extended periods without bleaching. In addition, nanoparticles can act as a platform onto which many components can be loaded. By loading new components onto nanoparticle platforms, new properties are created with diverse applications. For example, using vapor deposition to coat a fluorescent nanosphere with a hemispherical half-shell of opaque metal breaks the nanosphere's optical symmetry so that it reflects and fluoresces light in an orientation-dependent manner. If the nanoparticle is magnetic, it aligns with an external magnetic and rotates to follow a rotating magnetic field. The particle blinks as it rotates through bright and dark orientations. The blinking signal from these magnetically modulated optical nanoprobes (MagMOONs) can be separated from unmodulated autofluorescence backgrounds. The blinking frequency provides a measure of the local viscosity, while the fluorescence spectrum provides a measure of the concentration of chemicals that interact with the fluorophores in the nanosensors. Plasmonic chemical nanosensors are another example of multifunctional nanoplatforms. In addition to serving as brightly scattering spatial labels, silver nanoprisms exhibit exquisite sensitivity to changes in local refractive index. When molecules adsorb to the nanoparticle surface, the resulting increase in local refractive index causes the nanoparticle extinction and scattering spectrum to redshift. Tracking this redshift in real-time facilitates the study of molecular binding kinetics and interactions. Overall, combinations of top-down and bottom-up nanofabrication processes provide control over nanoparticle optical, magnetic, and chemical properties allowing integration of features for a wide range of biomedical applications. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Phyisics Department Faculty Search Candidate, "Single Molecule Biophysics in Femtoliter Containers," by Dr. Lori S. Goldner, NIST Monday, 2/18/2008, 4:00 PM-5:00 PM
Biomolecular function can now be studied with unprecedented detail by optically observing the motion and conformational changes of single molecules. Typically, biomolecules or long-lived molecular complexes are tethered to a surface and studied on an individual basis utilizing the optical properties of attached dyes or nanoparticles. In contrast, more commonly-occurring short-lived complexes are not easily studied on an individual basis because each of the molecular components must be localized and yet permitted to interact in the observation region. I will demonstrate a new technique that uses aqueous nanodroplets as femtoliter "test tubes" to confine, study, and mix individual molecules. The nanodroplets can be manipulated, mixed and held immobile using optical tweezers. Confined molecules are studied by optical techniques that are sensitive to the fluorescence from a single dye molecule. I will discuss how single molecular-pair fluorescence resonance energy transfer can be used to study RNA antisense interactions or RNA/protein interactions, and how polarization anisotropy lifetime can be used to investigate the rotational dynamics of confined biomolecules. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Department Faculty Search Candidate, "Perturbed Dynamics of Soft Materials," by Dr. Chanjoong Kim, Harvard University Wednesday, 2/13/2008, 4:00 PM-5:00 PM
Soft matter is neither simple liquid nor crystalline solid, but in an in-between state, including bio materials, lipid membranes, liquid crystals, and colloidal suspensions. We are in fact familiar with soft matter from every-day life - paints, cheese, foams, or liquid crystal display - and are also made of soft matter. In contrast to hard condensed matter, soft matter is easily perturbed by a small stress, which also affects its dynamics and mechanical properties. I will discuss our recent findings on the perturbed dynamics of two soft materials; a colloidal glass and a gel. We find that diffusive behavior of colloidal particles is recovered by application of perturbation to a glassy system. These model systems may provide a valuable insight to the biological systems.
Physics Faculty Search Candidate, "Dynamics of Intramolecular Contact Formation in Islet Amyloid Polypeptied (IAPP)", by Dr. Sara Vaiana, NIH Wednesday, 2/6/2008, 4:00 PM-5:00 PM
Measuring the dynamical properties of unfolded chains in solution, and in particular of amyloid forming peptides, is of key importance to understand the first elementary steps in folding, misfolding and aggregation. Protein misfolding and aggregation is at the basis of a vast class of diseases (including Alzheimer's and type II Diabetes) called amyloid diseases, where aggregates of specific structure, called amyloid fibrils, are formed. In type II Diabetes a peptide called human islet amyloid polypeptide (hIAPP) forms amyloid fibrils inside the b-cells of the pancreas (where insulin is produced) contributing to b-cell death and consequent impairment of insulin production. In order to understand aggregation it is critical to know what the constituents are. As an example I will present a study of IAPP, where we have directly compared an aggregating variant (hIAPP) to a non-aggregating variant (rIAPP), in their monomeric states. Before aggregating into highly ordered amyloid fibrils the hIAPP monomer is known to be unstructured. This poses the fundamental question of how to parameterize an unstructured chain. We do this by measuring the rates of intra-molecular end-to-end contact formation using tryptophan triplet quenching by cystine. We find a significant chain collapse in aqueous solvent for both peptides, and the appearance of kinetic traps that slow down chain dynamics. Interestingly rIAPP shows an increased chain stiffness with respect to hIAPP. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Department Faculty Search Candidate, "Flagella and Swimming Bacteria", by Dr. Nicholas Darnton, Amherst College Wednesday, 1/30/2008, 4:00 PM-5:00 PM
Many bacteria swim by rotating flagella. The swimming cell is an ideal candidate for a physicist's approximation: it is very nearly a prolate spheroid (the cell body) pushed by a simple helical propeller (the flagellum). Moreover, since the motion occurs at low Reynolds number it can be solved analytically. Unfortunately, most bacteria, including common pathogens such as Escherichia coli and Salmonella, have several flagella that operate simultaneously. This slightly more complicated problem - propulsion by several interacting flagella - has not been solved satisfactorily, either analytically or numerically. I will summarize the simple physics of swimming cells and of the flagellar rotary motor, and point out as-yet-unresolved issues involving interacting flagella, such as the unknown mechanism that causes flagella to bundle. From high-speed video of fluorescently labeled bacteria, we have attempted a complete force-balance accounting of swimming cells. We find that, contrary to physical intuition, adding flagella does not allow a cell to swim faster. In light of this conclusion, I will offer some ideas as to the purpose of having multiple flagella. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "The Domino Effect and the Flagellar Motor" by Dr. Greg Huber, UCONN Monday, 1/28/2008, 4:00 PM-5:00 PM
The flagellar motor of bacteria is a nearly-stoichiometric rotary molecular machine, perhaps the most elaborate engineered by evolution. It harnesses the chemical energy associated with a proton gradient for its rotation (typically hundreds of Hz), while, at longer time scales, stochastically switching between clockwise (CW) and counterclockwise (CCW) rotations. And while the switching of the rotational direction of the flagellar motor plays a crucial role in bacterial chemotaxis, its mechanism remains poorly understood. Here, I'll present recent work on the switch statistics of the flagellar motor of Caulobacter crescentus. I'll show how the interval distribution of the CW and CCW rotation provides insight into the switching, and describe a model that combines first-passage-time theory and dynamic binding to explain the switching mechanism. The model accounts for the motor's dependence on CheYp concentration, and predicts that dynamic binding of CheYp to the switch-complex proteins is the key to the signal amplification of the motor. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Surface Fluctuations on Polymer Films" by Dr. Ophelia K.C. Tsui, Boston University Monday, 1/21/2008, 4:00 PM-5:00 PM
Classical phase transition theory predicts that a homogeneous system is unstable against spontaneous phase-separation into an inhomogeneous structure if the second derivative of its free energy, G, as a function of the order parameter, h0, is negative. However, this prediction a result of the mean-field formalism is expected to fail if the fluctuations in the system order parameter due to thermal fluctuations are larger than the average order parameter, which occurs either when |h0 hsp|/hsp 0 (where hsp is the order parameter such that G(hsp) = 0) or when the dimension of the system is less than six. This prediction is well attested in three-dimensional (3D) systems, where the effects of fluctuations are usually found to be important only when h0 is within a few % from hsp. No experimental study has been performed on 2D systems, where the effects of fluctuations is stronger. Here, we use polystyrene films deposited on oxide coated silicon as a model 2D system to study the effect of fluctuations on the stability of a system for which the order parameter, h0, is the film thickness. We examine the temporal growth of surface capillary waves on this system of films with different h0. For the most unstable film (where h0 is within 98.8% from hsp), the data fits well to the mean-field theory. But as h0 is increased slightly such that h0 is within 97.7% from hsp, the mean-field theory demonstrates marked disagreement with experiment. We verify that the deviations are caused by large-amplitude fluctuations on the film surface due to stochastic thermal noises. Our results thus show that the stability of a low dimensional system can be easily compromised by spontaneous fluctuations, and cannot be predicted at all by the mean-field theory. We thank the support of NSF through project no. DMR 0706096. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Wonderful Speaker Series, "Small-Particles-Big Qulestions" by Dr. Ulrich Heintz, Boston University Monday, 12/3/2007, 4:00 PM-5:00 PM
Dr. Heintz will present recent findings from the accelerator at Fermilab and tell us about the smallest particles: the W Boson, the Top Quark as well as the Technicolor/Z'Search. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Fundamental Physics Through Astrophysics", Dr. Christopher Stubbs, Harvard University Monday, 11/12/2007, 4:00 PM-5:00 PM
We now have persuasive evidence for physics beyond the standard model, from astrophysical observations. The motion of luminous stars and gas in galaxies and galaxy clusters imply the existence of dark matter, which is probably made of something other than protons, neutrons, and electrons. More recently the convergence of multiple lines of evidence that indicate an accelerating expansion of the Universe points to new physics ("Dark Energy") at the troublesome interface between gravity and quantum mechanics. I will describe projects our group has undertaken to address the Dark Energy problem, including bouncing laser pulses off the moon and looking for exploding stars halfway across the Universe. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Photonic Crystal Defect Mode Analysis" by John Albrecht, Air Force Research Laboratory, Wright-Patterson Air Force Base-Ohio Monday, 11/5/2007, 4:00 PM-5:00 PM
Photonic crystals, in this case periodic structures of dielectrics, can be used to control light propagation through geometric features and dielectric contrast. An especially attractive application for photonic crystals is to construct localized electromagnetic modes by introducing defects in the periodic structure. These confined modes could be used as optical resonators, laser cavities being the most obvious application. In this seminar, I will discuss a theoretical approach for calculating the photonic structure of defects in 2D photonic crystals. The central feature of this approach is the construction of a basis set of local vector Wannier functions from the perfect crystal eigenstates. It has been proposed[1] that this basis be used to expand photonic crystal defect states analogous to the famous expansion in linear combinations of atomic orbitals of the electronic structure of the ideal silicon vacancy[2]. These approaches rely on a small number of basis states local to the defect region. Here, we replace the Fourier expansion of the perfect crystal by a real-space description in vector finite-elements. This method allows the computation of the Wannier basis on the same grid used to compute the perfect structure and results in a straightforward defect eigenvalue problem. I will present results [3] that verify the eigenmodes of the crystal and examine the physics of selected defect modes. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Comet Acoustic Surface Sounding Experiment Within the European ROSETTA Mission" by W. Arnold, Fraunhofer-Institute for Nondestructive Testing (IZFP), Saarbrucken, Germany Friday, 11/2/2007, 3:00 PM-4:00 PM
Comets are thought to contain pristine material from the time of the formation of the planets. The Comet Acoustic Surface Sounding Experiment (CASSE) is an instrument of the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME) within the Rosetta mission built in international European co-operation. The Rosetta mission spacecraft was launched in April 2004. The spacecraft itself carries a number of experiments and also a lander called Philae which will land on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of SESAME are to measure mechanical and electrical properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface. Most of the sensors are mounted within the six soles of the landing gear feet, in order to provide good contact with or proximity to the cometary surface. CASSE is designed to obtain data on the elastic properties of the comet surface by measuring the time-of-flight of surface P- and S-wave signals around 1 kHz. The sounding experiments to be performed are also used to obtain information on the structure of the comet material by means of backscattering. The sounding signals are generated by piezo-composites mounted in the lander-soles. The piezo-composites were built by the IZFP. This contribution discusses the concept and the scientific and engineering aspects of the CASSE experiment. In particular the construction of the transducers and the expected scenario of wave propagation on a comet surface will be discussed, as well as the inversion of the data in order to obtain the wanted quantities, in particular elasticity and porosity. Some of the concepts for the inversion of the data are lent from NDE of porous materials. In highly attenuating fine-grained sand the obtainable signal-to-noise ratio of piezo-composites of the CASSE instrument was evaluated. Data which were used in the design of CASSE were also obtained by measurement of sound attenuation and sound velocity in comet-analog material which is a watery suspension of minerals, mostly olivine injected via spray guns into a dewar vessel, filled with liquid nitrogen (LN2) and producing a fluffy ice/mineral mixture. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Menagerie of Viruses: Diverse Chemical Sequences or Simple Electrostatics?", by Professor M. Muthukumar, UMASS Amherst Monday, 10/29/2007, 4:00 PM-5:00 PM
The genome packing in hundreds of viruses is investigated by analyzing the chemical sequences of the genomes and the corresponding capsid proteins, in combination with experimental facts on the structures of the packaged genomes. A universal model, based simply on non-specific electrostatic interactions, is able to predict the essential aspects of genome packing in diversely different viruses, such as the genome size and its density distribution. Our result is in contrast to the long-held view that specific interactions between the sequenced amino acid residues and the nucleotides of the genome control the genome packing. Implications of this finding in the evolution and biotechnology will be discussed. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Swarming bacteria: a self-propelled 2D gas", by Professor Nicholas Darton, Amherst College Monday, 10/8/2007, 4:00 PM-5:00 PM
Under appropriate conditions of wetness and temperature, many commonly studied bacteria form a thin, highly dynamic layer that quickly grows to cover an agar plate. This phenomenon, known as swarming, enables rapid colonization of a rich medium. Swarmer cells are phenotypically distinct from vegetative cells they are longer, more highly flagellated, and more motile and some of the genes that govern swarm differentiation have been identified. The edge of a swarm colony is an extensive monolayer of billions of constantly moving cells. Formally, this should be described by the two-dimensional statistical mechanics of a self-propelled gas, sometimes known as 'boid' theory. Versions of this theory predict phase transitions and the emergence of long-range symmetry-breaking order. We are currently measuring the statistical properties of cell motion in Escherichia coli swarm monolayers, and comparing them to the better-known statistics of cell swimming in bulk (3D) fluid. To date, we have high-magnification data covering the motion of individual cells, but we have seen coherent motions over length scales of more than two orders of magnitude limited only by our ability to make large, homogeneous swarms. I will discuss our observed short-range anisotropic velocity correlation function as a combination of nematic liquid crystal order and self-propulsion.
Physics Colloquium, "Approaching and Leaving Metastability" by Professor Harvey Gould, Physics Department, Clark University Monday, 10/1/2007, 4:00 PM-5:00 PM
I will discuss the approach to metastable equilibrium in the Ising model using a cluster representation and find that the system is still changing at the microscopic level even after the mean values of various global quantities have ceased to change. I then will discuss the nature of nucleation in both Ising models and supercooled Lennard-Jones liquids. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Ordering and Flocking in a Collection of Fluidised Rods" by Professor Narayanan Menon, Physics Department, UMASS, Amherst Monday, 9/24/2007, 4:00 PM-5:00 PM
I will discuss experiments that study the ordering of fluidised rod-like grains into orientationally ordered states and compare these to the phases of equilibrium liquid crystalline systems. The most dramatic phenomena in the system, however, are associated with the motions of the rods rather than their order. These nonequilibrium effects include persistent vortices and large-scale swirling. Most importantly, the population of rods shows giant, persistent density fluctuations, which I will discuss in the context of recent ideas of the flocking and swarming of active, or self-propelled, particles. Sponsored by: WPI Physics Department, Dr. Stephan Koehler
Physics Colloquium, "Atomic Scale Friction and Microscale Machines: These Squeaky Wheels will get no Grease" by Professor Jacqueline Krim, North Carolina State University, Physics Department Monday, 4/30/2007, 4:00 PM-5:00 PM
There is widespread belief that the future is likely to be dominated by MEMS (Micro-Electro-Mechanical Systems) and/or NEMS (Nano-Electro-Mechanical Systems) devices, which will be used in such diverse applications as gas and pressure sensors, accelerometers, chemical analytic ``microlaboratories'', and airborne ``nanosatellites''. Because MEMS devices must react to mechanical signals, many employ construction topologies that require physical motion and the concomitant lubrication which prevents heating/melting and wear of the device. It is well established however that the macroscopic laws governing friction and wear are inapplicable at the molecular scale. The need to carry out new and fundamental research relevant to the development of optimal, or even operational submicron-scale mechanical systems is therefore increasingly important. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloqium, M.S thesis presentation, "Mori Projected Dynamics On a Quantum System", by Rachel Nasto, WPI Physics Department Graduate Student Thursday, 4/26/2007, 4:00 PM-5:00 PM
In this thesis we discuss Mori Projected Time Dynamics in a quantum mechanical system. As a precursor to calculating the time derivative of a mixed state of the system we examine the derivation of the Mori-Zwanzig formalism. We consider the exact calculation of the time derivative of a mixed state. We then calculate the same time evolution using Mori Theory and compare the two results. From the general calculation of the Mori Equation we were able to perform a series of simple tests to compare Mori Theory to the known result. We discovered that in each of the four simple cases the Mori Equation and the direct calculation of the time evolution give the same result, but in the more complicated situations the two calculations differed. This result leads us to believe that the Mori Equation is an accurate way of calculating the derivative of a mechanical variable in a quantum system. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department, Ph.D. Dissertation, "Summing the Infinite Ladder", by Frank Dick, WPI Physics Department Graduate Student Monday, 4/23/2007, 4:00 PM-5:00 PM
In quantum field theory, the Dyson scattering matrix is a perturbation expansion in the interaction Hamiltonian that generates an infinite series of Feynman diagrams. A holy grail of QFT is to sum the series. The Bethe-Salpeter equation (BSE) sums all diagrams in what is known as the ladder approximation, but is restricted to elastic scattering processes. As part of my research, I developed a generalized Bethe-Salpeter equation (GBSE) to handle inelastic processes in the ladder approximation. The GBSE, formulated using quantized scalar field theory introduces a systematic method for analyzing families of coupled reactions. A formalism is developed centered around the amplitude matrix M' defined for a given Lagrangian. M' gives the amplitudes of a family of reactions that arise from the Lagrangian. The formalism demonstrates how these amplitudes, to 2nd order, segregate into independent groups of coupled BSEs. A proof is given of the equivalence of the series of ladder diagrams generated by M' and the S-matrix. The GBSE formalism is applied to the coupled BSE (CBSE) of Faassen and Tjon, showing that the CBSE is missing a coupling channel, and in the expansion, under counts ladder diagrams. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Atomoptics and Atomtronics", by James Stickney, WPI Physics Department - Graduate Student Monday, 4/16/2007, 4:00 PM-5:00 PM
The invention of the laser in the early 1960s caused a revolution in modern optics. Lasers found applications in medicine, telecommunications, information storage, and, perhaps most importantly, precision measurements. The state of matter known as Bose-Einstein condensate (BEC) is the matter-wave equivalent of laser light. Because they are much more sensitive, it is believed that BEC-based "atomoptical" devices will eventually replace many current laser-based devices used in precision measurements. BEC based devices that are analogous to electronic devices may also be possible. In an "atomtronic" device, the atoms in the BEC play the role of the electrons in an electronic circuit. In this presentation, the current state of BEC-based devices will be discussed, with particular emphasis how atom-atom interactions affect their operation. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Optical Cooling in High Power Solid State Lasers", by Dr. Richard S. Quimby, Physics Deparartment, WPI Monday, 4/2/2007, 4:00 PM-5:00 PM
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "Colloidal Interactions and Controlled Self-Assembly in Ordered Soft and Biomolecular Materials," by Dr. Ivan Smalyukh, University of Illinois, Urbana Monday, 3/5/2007, 4:00 PM-5:00 PM
Self-assembly of colloidal particles and molecules into ordered structures is a fascinating phenomenon of both fundamental and applied interest. This lecture will demonstrate that the self-assembly phenomena in elastic liquid crystal (LC) media are particularly rich and can be controlled. In LCs the embedded spherical particles can cause elastic distortions of either dipolar or quadrupolar symmetry because of the anisotropic molecular interactions at the colloid-LC interfaces. I will show that the surface treatment of the colloidal particles and the LC confinement determine the nature of inter-particle interactions as well as the formation of colloidal structures. For example, the particles with the dipolar elastic distortions interact similar to the electrostatic dipoles and form chains along the far-field LC director. The particles with tangential surface anchoring and quadrupolar elastic distortions aggregate into chains directed at about 30 degrees to the average orientation of the LC molecules far from the spheres. When the elasticity-mediated colloidal interactions between particles take place at the surfaces of anisotropic fluids, the particle arrangements strongly depend on the boundary conditions at the confining surfaces and can vary from linear chains to hexagonal colloidal structures. Moreover, both in the LC bulk and at the surfaces, the inter-particle interactions and the structures are strongly altered by adding tiny amounts of chiral additives, resulting in twisted colloidal chains and spirals. I will show that even live biological cells (such as Pseudomonas aeruginosa) can be orientationally ordered when placed into the elastic liquid-crystalline matrices of DNA biopolymers. The particle motions are monitored using video-rate optical imaging and the interactions are explored using laser tweezers. The inter-particle colloidal forces exhibit rich angular and distance dependencies, consistent with the symmetry of the elastic distortions around the particles. The experimental observations are modeled considering the LC elastic properties and correctly reproduce the experimentally measured parameters. These findings impinge broadly on understanding of phenomena as diverse as colloidal interactions in anisotropic media and biofilm formation in the presence of extracellular biopolymers, as well as demonstrate the possibility of controlled colloidal self-assembly into tunable photonic crystal structures. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "Particulate Flows" by Dr. Stephan Koehler, Emory University Monday, 2/26/2007, 4:00 PM-5:00 PM
Foams and granular materials are two fundamental model systems of complex fluids studied by soft condensed matter physicists. A common feature is their cellular structure, which consists of bubbles and grains respectively. Their particle sizes exceed microns, and therefore at rest these materials are jammed, athermal systems. The packing and shearing of these cellular elements and their micro-scale interactions lead to fascinating macroscopic continuum-type behaviors. Familiar examples include foam drainage of freshly-poured beer and the sudden onset of granular flow causing landslides. The mechanical properties of these complex fluids span a large dynamical range of continuum behavior and include elasticity, viscosity and plasticity. I will compare and contrast behaviors of foams and granular materials based upon various experiments performed in my lab. I will discuss the similarity between Darcy flow through soils and foam drainage in the limit of large surface viscosity. Moreover, foams and granular particles have similar rheological behaviors, which depend on pressure between particles, shearing rates and shearing displacements. For example, both systems are prone to shear band formation, and have a finite yield stress. I will conclude with recent experimental results for self-propulsion that were inspired by sand-swimming animals such as desert vipers and lizards. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "From Imaging to Therapy: The Physics of Gas Bubbles for Medical Applications of Ultrasound," by Dr. Elisabetta Sassaroli, Dept. of Radiology, Brigham & Women's Hospital and Harvard Medical School Wednesday, 2/21/2007, 4:00 PM-5:00 PM
Gas bubbles powerfully influence the acoustics in tissues and liquids. This presentation gives an introduction to the physics of gas bubbles, focusing primarily on biomedical applications. In a sound field of sufficient amplitude, bubbles oscillate nonlinearly and emit harmonic and subharmonic components of the driving frequency. In practice, microscopic bubbles are injected into the blood stream to increase the echo from blood, in particular at the level of the microcirculation. As the pressure is further increased, bubbles may undergo inertial cavitation. Inertial cavitation is characterized by the sudden expansion and then rapid collapse of the bubble. Bubble collapse can generate shock waves and shear, which can produce erosion and bioeffects. There is clear evidence that the permeability of the cell membrane to large molecules is increased when suspensions of cells are exposed to ultrasound in the presence of microbubbles. The understanding of bubble acoustical behavior in a confined geometry is essential for their control and exploitation when injected into the blood stream. Experimental and numerical modeling of microbubble behavior in micron-sized tubes and tunnels embedded in gel will be presented Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Department Faculty Search Candidate, "Colloids in action: Microscopic insights into clogging and jamming", by Dr. Daniel Blair, Harvard University Monday, 2/12/2007, 4:00 PM-5:00 PM
Suspensions of colloidal particles are astounding model systems used to study a variety of fundamentally important problems in soft matter physics. The versatility of colloids is due in large part to the increasing sophistication of their synthesis, and the relative simplicity of their interactions. This talk will discuss recent experimental results on two soft-matter topics that utilize colloidal particles; clogging during flow and jamming in glasses. I will first present results from microfluidic studies of clogging in model porous media. By using simple imaging techniques, and a minimal geometric model, I will describe the physical origins of clogging in microfluidic devices. These results demonstrate that the aggregation of micron sized particles, in a low Reynolds number flow, is dominated by single particle interactions. In the second half of the talk, I will discuss the microscopic response of colloidal glasses to a macroscopically applied compressive stress. Using time resolved laser scanning confocal microscopy, I identify and track the motion of thousands of colloidal particles in real space over very long times. With this technique, and ideas garnered from metallic glasses, the complete local strain tensor for each particle is determined. I will demonstrate that highly localized, correlated shear and compression transformations are necessary for colloidal glasses to approach a maximally jammed state. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Faculty Candidate Colloquium,"Fingers and Holes in Shear Thickening Fluids" by Dr. Robert Deegan, Bristol,UK Monday, 2/5/2007, 4:00 PM-5:00 PM
The simplest models of matter posit a linear relationship between the stress and deformation, as for example in Hooke's law. However, many useful and important fluids (such as, shampoos, industrial slurries, geophysical fluids, polymeric melts) exhibit a nonlinear response to stress. I will discuss the behaviour of shear thickening fluids subjected to vertical vibrations in the context of pattern forming systems. I will show that a mixture of cornflour/water or glass beads/water vibrated above a critical acceleration (approximately 10 g) is unstable to perturbations. At low accelerations a small indentation of the fluid surface will grow until it reaches the bottom of the container, forming a circular hole. At higher accelerations the rim of the hole becomes unstable and develops an upward growing tongue. At even higher accelerations, the entire layer writhes in a disordered manner. The mechanism for these instabilities is unknown. I will present experimental correlations between these instabilities and the fluid's rheological proprieties.
Wonderful Speaker Series, "Dripping, Jetting, Drops and Wetting: the Magic of Microfluides" by Dr. David Weitz, Department of Physics, Harvard University Monday, 1/15/2007, 4:00 PM-5:00 PM
This talk will discuss some of the new opportunities that arise by precisely controlling fluid flow and mixing using microfluidic devices. I describe studies to elucidate mechanisms of drop formation and use these to create new fluid structures that are difficult to achieve with any other method. I also show how the exquisite control afforded by the microfluidic devices provides the enabling technology to use droplets as nanoreactors to qualitatively increase the rate of combinatorial screening of chemical reactions.
Physics Colloquium, "Casimir Forces and New Principles for Understanding the Wetting of Liquids" by Dr. Rafael Garcia, Physics Department, WPI Monday, 12/11/2006, 4:00 PM-5:00 PM
Despite the fact that during the last century there has been a lot of research into wetting and the properties of liquids, many things are not known and discoveries, potentially of great importance to science, technology and society, continue to be made about how, why and when liquids wet solid surfaces. During the last 20 years, we have seen the discovery of thermodynamic Casimir effects, triple point wetting, prewetting and critical wetting, to name a few. The wetting of a liquid droplet on a solid surface is universally characterized by its contact angle, the angle between the liquid surface and the solid surface. For a liquid which completely wets a surface (contact angle of zero), the wetting is characterized by the thickness of the adsorbed film. New experimental research at WPI is focused on discovering the principles necessary for predicting how the wetting of polar liquids and liquid crystals changes as we vary the temperature. Being investigated are water, nitrous oxide and the cigar-shaped n-alkylcyanobisphenyl liquid crystals. Despite the ordinary nature of these materials, preliminary data demonstrate a variety of extraordinary behaviors not anticipated by theory. Our goal is to try to confirm and understand these phenomena within the framework of Cheng-Cole-Saam-Treiner approximation for the difference between the liquid-solid and gas-solid surface tensions. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "High-power, Low-noise 1.5-m Slab-coupled Optical Waveguide Amplifiers (SCOWAs) and their Applications", by Dr. Paul W. Juodawlkis, MIT Monday, 12/4/2006
The slab-coupled optical waveguide amplifier (SCOWA) is a new class of semiconductor optical gain medium that was invented at MIT Lincoln Laboratory. The SCOWA architecture enables devices having Watt-level optical output power, low internal loss (~ 0.5 cm-1), and large (> 5 x 5 m) symmetric fundamental-mode operation. In this talk, we will review the SCOWA operating principles and describe applications of the SCOWA technology ranging from high-power semiconductor optical amplifiers (SOAs), to monolithic and ring-cavity mode-locked lasers, to single-frequency external cavity lasers. The talk will also begin with a brief overview of MIT Lincoln Laboratory. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Why Do Silos Fail and Hourglasses Tick?" by, Dr. Bulbul Chakraborty, Brandeis University Monday, 10/30/2006, 4:00 PM-5:00 PM
Materials as diverse as molecular liquids, foams and granular matter experience a transition from a fluid-like state to a solid-like state characterized only by a sudden arrest of their dynamics. These sudden arrests are difficult to predict and lead to catastrophic events such as the buckling of grain silos. Numerous experiments and simulations indicate the appearance of large-scale dynamical heterogeneities and an associated growing dynamical length scale. In colloids near the glass transition, for example, fast-moving particles were observed to be spatially correlated with a characteristic cluster size that increased as the glass transition was approached. In granular materials, spatial structures have been directly observed in experiments on flowing systems. Several questions naturally arise: (1) Are dynamical heterogeneities a necessary precursor to dynamical arrest of the jamming kind? (2) Do these heterogeneities and their mesoscopic scale lead to any kind of universal dynamical behavior irrespective of significant differences in microscopic dynamics? (3) Do static structures such as force chains observed in jammed granular packings emerge out of dynamical heterogeneities? In this talk I will address these questions through the analysis of a simple model that focuses on the essential effects of driving and dissipation in a flowing granular system. Sponsored by: physics Dept., Dr. Stephen Jasperson
Physics Colloquium, "New Materials for Sprintronic Applications" by Dr. Don Heiman, Northeastern University Monday, 10/9/2006, 4:00 PM-5:00 PM
Devices for spin-electronic applications are expected to benefit from new materials and unique device structures. With that goal in mind, my research group is currently focusing on two main areas: making new semiconductors which are ferromagnetic; and fabricating novel ferromagnetic metals which are compatible with semiconductors. I will briefly review spintronic mechanisms and devices, followed by discussion of our current work on the MBE fabrication of GaAs-based ferromagnetic materials. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Special Physics Colloquium, "Medical Physics as a Career" by Dr. Alex Cardenas, Department of Radiation Oncology, Lehigh Valley Hospital, Allentown, PA Friday, 10/6/2006, 4:00 PM-5:00 PM
This talk will give an overview of careers in medical physics based on the speakers own experience. He graduated with a B.S. in Physics from WPI in 1996, then received a Ph.D. in nuclear physics from Purdue University, following which he entered the field of medical physics. The talk will be informal, with plenty of opportunities for questions from the audience. All are invited. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Colloquium, "Photoluminescence Competitiveness in GaAs/AlGaAs Single Heterojuction", by Dr. Abdellah Dakhama, Physics Department, WPI Monday, 9/25/2006, 4:00 PM-5:00 PM
Near-field photoluminescence using a near-field scanning optical microscope (NSOM) has been a valuable tool in studying excitons in GaAs-based quantum wells. The resolution that is beyond the diffraction limit revealed striking, new results that cannot be captured by far-field photoluminescence. We report low temperature near-field photoluminescence imaging of the electron density in a modulation doped GaAs/AlGaAs single heterojunction with a spatial resolution of 100 nm. We discovered an unusual competitiveness in the photoluminescence between the first electron subband to first heavy-hole subband transition and the second electron subband to first heavy-hole subband transition. We attribute this competitiveness to the fluctuations in the electron density which results from fluctuations in the donor (Si) density. NSOM is itself a technique that is still under research and development. Our goal is not limited to just imaging the surface topography but extends to imaging physical properties of buried quantum structures. In the first part of the talk we will discuss the experimental setup used for near-field scanning photoluminescence experiments. In the second part we will present our results for a two-dimensional electron gas. Finally, preliminary results from near-field scanning fluorescence will be briefly discussed. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Colloquium, "Structure and Dynamics of Nano-colloidal Silica Gel Dispersion", By Dr. Germano Iannacchione, Physics Department, WPI Monday, 9/18/2006, 4:00 PM-5:00 PM
This talk presents a study on the structure and the dynamics of a nano-colloidal silica gel dispersed in an organic solvent (octylcyanobiphenyl, 8CB) as a function of silica density by x-ray intensity fluctuation spectroscopy (XIFS). The silica density of the dispersed aerosil gel samples ranged from 0.03 to 0.20 g cm-3 and the autocorrelation of the silica scattering were probed over the q range from 0.03 to 0.15 nm-1 (corresponding to length scales from 42 to 209 nm) at a constant room temperature at which 8CB is in the smectic-A phase. The gel structure has a fractal dimension in this density range of df ~ 2.15. The time autocorrelation functions of the gels show clear density-dependent and complex dynamics. The gel relaxation times are very long and become bimodal with nonergodic character for densities from 0.10 to 0.16 g cm-3. In this same density range, the fluctuation contrast (strength) is a minimum while the relaxation time becomes independent of wavevector. Together, these results indicate that there is a narrow silica density range for these gels in which the dynamics changes dramatically. This suggests a complex phase diagram for the dynamics of aerosil gels as a function of densification. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium, "Baked Alaska: Inhomogeneous Phases of Bosons Trapped in an Optical Lattice," by Dr. Courtney Lannert, Wellesley University Monday, 5/1/2006, 4:00 PM-5:00 PM
Abstract: Recent work with bosonic atoms at ultra-low temperatures in an optical lattice has opened new avenues for exploring the superfluid and Mott-insulating phases of bosons. The presence of the (usually harmonic) confining trap in the experimental set-up is likely to cause complications that are either a nuisance or a boon, depending on one's perspective. Adopting the latter state of mind, we can see how, when properly designed, these experiments might create novel spatially-inhomogeneous phases. I will describe some recent work on the Mott-insulating and superfluid regions present in these systems. The stability of the Mott phases is an important consideration. I will describe a proposed experiment for spatially resolving the spatial structure of the system and some unique physics associated with the superfluid regions. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "Atomic Scale Friction and Microscale Machines: These Squeaky Wheels Will Get No Grease", by Prof. Jacqueline Krim, N. Carolina University Physics Department Sunday, 4/30/2006, 4:00 PM-5:00 PM
There is widespread belief that the future is likely to be dominated by MEMS (Micro-Electro-Mechanical Systems) and/or NEMS (Nano-Electro-Mechanical Systems) devices, which will be used in such diverse applications as gas and pressure sensors, accelerometers, chemical analytic ``microlaboratories'', and airborne ``nanosatellites''. Because MEMS devices must react to mechanical signals, many employ construction topologies that require physical motion and the concomitant lubrication which prevents heating/melting and wear of the device. It is well established however that the macroscopic laws governing friction and wear are inapplicable at the molecular scale. The need to carry out new and fundamental research relevant to the development of optimal, or even operational submicron-scale mechanical systems is therefore increasingly important. Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Physics Colloquium and Ph.D. Defense, "Reciprocity Between Emission and Absorption for Rare Earth Ions in Glass", by Rodica Martin, WPI Physics Graduate Student Tuesday, 4/25/2006, 9:00 AM-10:00 AM
The McCumber theory allows optical emission cross section spectra to be determined from measured absorption spectra, and vice versa. The present work is a detailed study of the range of validity of the McCumber theory, focusing particularly on those aspects that most critically affect its applicability to transitions of rare earth ions in glasses. When the various possible sources of systematic error are properly accounted for, we find in all cases an excellent agreement between the calculated and the measured cross section spectra. This suggests that at room temperature, the McCumber theory is not limited to crystalline hosts, as has been asserted in the literature, but describes quite well the reciprocity between emission and absorption for the broader transitions of rare earths in glassy hosts. At lower temperatures, however, discrepancies are observed, and our results suggest that the McCumber theory must be used with caution for temperatures below 200 K. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "A New Approach to Diffusion Analysis for Multicomponent Systems", by Dr. L. R. Ram-Mohan, WPI Physics Department Monday, 4/24/2006, 4:00 PM-5:00 PM
--Local Averages of Diffusion Coefficients and the Transfer Matrix Method-- The diffusion of matter from one region into another is a universal phenomenon occurring in gases, liquids and solids. In metallic alloys, we can study diffusion by putting two alloys together and allowing the components of one alloy to diffuse into the other alloy at high temperature, and then quenching the system to freeze the diffusion. We can then experimentally determine the concentration profiles. Such diffusion under controlled conditions gives us information about the diffusion process and the stability of the interface. This has wide applications in the welding of metals and similar industrial processes. Until recently, the diffusion coefficients could not be determined in a reliable manner in multicomponent diffusion, such as ternary or quaternary diffusion. They are functions of composition, making diffusion an intrinsically nonlinear process. I will present a new method of determining the diffusion coefficients developed recently, and show how the concentration profiles can be reconstructed, given the diffusion coefficients, using a transfer-matrix method (TMM). The TMM developed by me is applicable to any number of diffusion components. I will also mention the directions in research we are pursuing. We are close to being able to predict the diffusion path in a diffusion couple given the end compositions. Diffusion in three- and four-component systems already displays a rich variety of complex phenomena. I will illustrate these with examples. We are starting on an investigation of grain boundary diffusion and triple junction diffusion in macroscopic and nanoscopic systems. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium, "Fascination of Diamonds," by Dr. A. K. Ramdas, Purdue University, Department of Physics Monday, 4/17/2006, 4:00 PM-5:00 PM
Laymen and Scientists alike have had a longstanding fascination for diamond, thanks to its hypnotizing appeal as a gemstone and its unique physical properties. Its incomparable hardness makes it the best abrasive; it exceeds the thermal conductivity of even copper at room temperature; it is a perfect electrical insulator, unless it is boron doped when its resistivity is reduced by orders of magnitude. Even superconductivity has been reported very recently in such specimens. It is a material with the largest atomic density. These and many other striking properties have commanded the attention of scientists like Newton, Lavoisier, Humphrey Davy, Einstein, Lawrence and William Bragg. A short account of the extraordinary aspects of the genesis and, in modern times, the laboratory synthesis of diamond will be followed by illustrative examples from the Brillioun, Raman, and Infrared researches of my collaborators and me.
Addressing Grand Energy Challenges through Advanced Materials, by Mildred Dresselhaus, MIT Dept. of Physics Monday, 4/10/2006, 4:00 PM-5:00 PM
Advanced materials, utilizing nanostructures to provide new materials properties and opportunities for the independent control of materials structures and properties, offer new promise for addressing some of the grand energy challenges facing our future. This talk will review opportunities opened up at the nanoscale, with materials of reduced dimensionality and enhanced surface-to-volume ratio. Some examples of research accomplishments and opportunities at the nanoscale will be described, with special attention given to the potential of advanced materials and nanoscience to have an impact on addressing grand challenges related to a sustainable energy supply for the 21st century and beyond. Sponsored by: Rafael Garcia
The End of the Solar System by Prof. John Belcher, Massachusetts Institute of Technology, Astrophysics Division Wednesday, 4/5/2006, 5:00 PM-6:00 PM
The Voyager spacecraft, after a 30 year journey, are finally at the boundaries of the solar system and approaching entry into the local interstellar medium. We will review some of the outstanding science accomplishments of this mission to the outer planets, and what is to come as they explore regions beyond the influence of the sun. Sponsored by: Rafael Garcia
Physics Colloquium, "Ballistic Electro Photonics," by Dr. V. Narayanamurti, Harvard University Monday, 4/3/2006, 4:00 PM-5:00 PM
The ballistic transport of hot electrons in semiconductors has long been a subject of interest. Over the last decade enormous progress has been made in the study of such transport using tunneling-based hot electron (or hole) injectors. In this talk, I will present several exciting new results which have broad implications for the study of new semiconductor nanostructures that feature the transport of spin. These are: (1) the development of Ballistic Electron Emission Luminescence (BEEL), a technique which allows the simultaneous monitoring of electron transport and luminescence for quantum dot structures placed below the surface; (2) the demonstration of several new types of hot electron based devices, such as spin valve photodiodes and avalanche spin valve transistors; and (3) exciting new studies of transport and luminescence in semiconductor nanowires such as ZnON and GaN. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "Some Secrets in the Life of Escherichia Coli," by Dr. Howard Berg, Harvard University Wednesday, 3/22/2006, 5:00 PM-6:00 PM
Flagellated bacteria swim by rotating long, thin, helical filaments that arise at different points on the cell surface. Each filament is driven at its base by a rotary motor only 45 nm in diameter made from about 20 different kinds of parts. Control of the direction of rotation of such motors is the basis for the chemotactic response, i.e., for the ability of cells to swim up spatial gradients of chemical attractants. I will review the history of this subject, tell you about some of the physics that E. coli knows, and outline the signal transduction pathway that links chemoreceptors to flagella. I will describe some of the methods (fluorescence, FRET, BRET) that we have used to probe this remarkable molecular system. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "Atomic Force of Biological Structures", by Dr. Bryan D. Huey, UCONN, Institute of Materials Science Monday, 2/27/2006, 4:00 PM-5:00 PM
Atomic Force Microscopy provides an opportunity to map topography as well as local properties at the nanoscale. During this presentation, careful experiments of local mechanical properties will be described for two distinct systems: ceramic ferroelectric thin films, and living hamster cells. In each case, assessing the mechanical response as a function of position reveals important details about spatial variations of the sample properties. With respect to PZT ferroelectric thin films, the piezoelectric hysteresis has been found to vary in the vicinity of grain boundaries, due to built in strain resulting from the local microstructure of this anisotropic material as supported by complimentary electron beam diffraction and 2-d finite element modeling. For biological structures, the mechanics of individual cells are shown to vary depending on their health as well as exposure to quantum dots. By recording the vibration spectrum of cell membranes, sounds emanating from a cell can also be heard and will be played during the seminar. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "A New Approach to Diffusion Analysis for Multicomponent Systems", by Dr. L. Ramdas Ram-Mohan, WPI Physics Department Monday, 2/20/2006, 4:00 PM-5:00 PM
The diffusion of matter from one region into another is a universal phenomenon occurring in gases, liquids and solids. In metallic alloys, we can study diffusion by putting two alloys together and allowing the components of one alloy to diffuse into the other alloy at high temperature, and then quenching the system to freeze the diffusion. We can then experimentally determine the concentration profiles. Such diffusion under controlled conditions gives us information about the diffusion process and the stability of the interface. This has wide applications in the welding of metals and similar industrial processes. Until recently, the diffusion coefficients could not be determined in a reliable manner in multicomponent diffusion, such as ternary or quaternary diffusion. They are functions of composition, making diffusion an intrinsically nonlinear process. I will present a new method of determining the diffusion coefficients developed recently, and show how the concentration profiles can be reconstructed, given the diffusion coefficients, using a transfer-matrix method (TMM). The TMM developed by me is applicable to any number of diffusion components. I will also mention the directions in research we are pursuing. We are close to being able to predict the diffusion path in a diffusion couple given the end compositions. Diffusion in three- and four-component systems already displays a rich variety of complex phenomena. I will illustrate these with examples. We are starting on an investigation of grain boundary diffusion and triple junction diffusion in macroscopic and nanoscopic systems. Undergraduate and graduate students are encouraged to attend. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "The History of the Universe in One Hour', by Dr. Max Tegmark, MIT Physics Department Wednesday, 2/15/2006, 5:00 PM-6:00 PM
With a cosmic flight simulator, we'll take a scenic journey through space and time. After exploring our local Galactic neighborhood, we'll travel back 13.7 billion years back to explore the Big Bang itself and how state-of-the-art measurements are transforming our understanding of our cosmic origin and ultimate fate. If you have questions about dark matter, dark energy, black holes, parallel universes or other things cosmological, this will be a great opportunity to ask them! Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "Acoustic Amplification from Coherent Quantum Condensation in Superfluid He-4", by Dr. Fred Ellis, Weslyan University, Department of Physics Monday, 2/13/2006, 4:00 PM-5:00 PM
The atoms of superfluid helium are in a macroscopic state of coherent quantum de Broglie waves. Vapor atoms evaporating from, or condensing into, the superfluid do so while preserving the macroscopic phase structure of the coherent quantum waves. This remarkable process in superfluids is the matter equivalent of the laser.. The physics of this process and progress on an experiment to demonstrate this equivalence by the stimulated amplification of acoustic waves in superfluid films will be described. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "New Forms of Quantum Matter Near Absolute Zero Temperature", by Dr. Wolfgang Ketterle, Physics Department, MIT Monday, 2/6/2006, 4:00 PM-5:00 PM
Why do physicists freeze matter to extremely low temperatures? Why is it worthwhile to cool to temperatures which are more than a million times lower than that of interstellar space? This lecture will discuss new forms of matter, which only exist at extremely low temperatures. Low temperatures open a new door to the quantum world where particles behave as waves and march in lockstep. In 1925, Einstein predicted such a new form of matter, the Bose-Einstein condensate, but it was realized only in 1995 in laboratories at Boulder and at MIT. More recently, Bose-Einstein condensates of molecules and fermion pairs have been created and may show behavior similar to electrons in superconducting materials. A new form of high-temperature superfluidity has been discovered. In the future, we hope to use ultracold gases to create designer matter, i.e. to realize new forms of matter in the laboratory which have been discussed as model systems for many-body phenomena, but have not been observed in nature. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Physics Colloquium, "How to Find Splice Junctions in mRNA", by Dr. Daniel Aalberts, Williams College Monday, 1/30/2006, 4:00 PM-5:00 PM
Before being translated into proteins, messenger RNA is processed in the nucleus. The spliceosome directs precursor mRNA to remove intervening sequences (introns), and to splice the remaining expressed sequences (exons) back together to form mature mRNA. The alternation of coding and noncoding regions makes eukaryotic genes difficult to predict from primary sequence alone, so the ability to correctly identify the intron-exon boundaries is also crucial to gene finding efforts. Splicing is done with great specificity, even though the apparent splicing signals are rather weak. Methods from statistics have proven most effective to identify the splice sites, but we know that cells don't perform Hidden Markov calculations. Cells use thermodynamics. I will present results of our thermodynamic model of splice site recognition. I will then discuss how statistical-mechanical scaling ideas led us to improve upon statistics methods. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "A Known Unknown: Directly Detecting the Missing Mass of the Universe",Dr. Richard Gaitskell, Brown University Physics Department Wednesday, 11/30/2005, 5:00 PM-6:00 PM
The majority of the mass of the Universe is still unidentified. Many different astrophysics and cosmological measurements support the hypothesis that Cold Dark Matter dominates the gravitational behavior of galaxies and galactic clusters. I will discuss the interpretation of existing data, and focus on a number of experiments that are being conducted deep underground to directly detect a new type of dark matter particle: one which arises naturally from the extension of existing particle physics theories. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
"Extrasolar Planets in Binary Star Systems", By Dr. Matthew Muterspaugh, MIT Center for Research Monday, 11/28/2005, 4:00 PM-5:00 PM
Ten years ago, there was a revolution in astronomy as planets orbiting sunlike stars were first discovered in large numbers. Their properties have introduced many changes to the way in which we understand planet formation and evolution, and provide context for our own solar system. Many of the systems now known occur in environments once thought to be incompatible with planet formation. Several planets have now been discovered orbiting stars that have additional distant stellar companions. I will present recent results from planet searches targeting systems are known to contain stellar companions in much closer orbits, in which the second star may have significant gravitational effects on the planet system during formation. These searches probe the extent to which these interactions enhance or prohibit planet formation, and provide constraints on the timescales on which planet formation can happen. I will conclude by discussing similar results from the study of systems with three or more stars. Sponsored by: WPI Physics Department
Colloquium, "Rapid Movements in the Plant Kingdom: Nature's Weapons of Mass Reproduction", by Dr. Dwight Whitaker, Williams College Monday, 11/21/2005, 4:00 PM-5:00 PM
While most people might think that rapid movements in biological systems are limited to the muscle driven motion of animals, this is not the case. A number of plant species have developed mechanisms to quickly transfer stored elastic energy into kinetic energy. The most famous of these cases is the closing of the Venus flytrap, which happens in a timescale of less that 0.1 s. However there are a number of other plants, which have devised methods for moving even faster. We have used a high-speed video camera to capture the sub-millisecond actions of the bunchberry flower, Sphagnum moss, and a several other local plant species. Through video analysis and measurements of elastic properties we have been able to model these explosive movements whose quickness matches or exceeds any recorded motion in the animal kingdom. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: "Playing with Virtual Photons: Measurement and Design of Long-Range QED Forces and Torques and Their Application in Nanomechanics", by Dr. Federico Capasso, Harvard University Monday, 10/31/2005, 4:00 PM-5:00 PM
High precision measurements of the Casimir force between metallic surfaces using Micro/Nanomechanical Systems (MEMS/NEMS), along with attempts to tune them using hydrogen switchable mirrors, have clearly demonstrated the skin-depth effect on these forces as well as have elucidated a counterintuitive aspect of the underlying Lifshitz- Dzyaloshinskii-Pitaevski theory. Nonlinear Casimir oscillators have been implemented which could find use as nanometric position sensors. Calculations of the expected mechanical torque between birefringent plates induced by quantum fluctuations will be discussed along with a proposed experiment to observe it. The scheme utilizes repulsive QED forces between plates separated by a liquid of suitable dielectric constant, which creates a virtually frictionless bearing. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium" DNA in a tight squeeze: The physics of viral infection and gene regulation", by Dr. Jane' Kondev, Physics Department, Brandeis University Wednesday, 10/26/2005, 5:00 PM-6:00 PM
DNA in cells and viruses finds itself packed into a tight space, occupying a volume much smaller that the volume it adopts free in solution. This state of confinement places important constraints on a variety of biological processes, such as viral infection, gene expression, and DNA recombination. Quantitative experimental techniques such as laser tweezers, cryo-electron microscopy and fluorescence microscopy have recently begun to probe the confined state of DNA, both in live cells and in the test tube. In this talk I will describe this emerging experimental landscape and outline the theoretical challenges it poses. The particular examples I will focus on will be provided by DNA packing in viruses and gene regulation in bacteria where physics models can be used to propose a new generation of quantitative biology experiments. Sponsored by: WPI Physics Dept., Dr. Rafael Garcia
Wonderful Speaker Series, " How Einstein Rocked the World of Physics in 1905: A 100 Year Celebration", by Dr. Phil Deutchman, Emeritus Professor, University of Idaho Wednesday, 10/5/2005, 4:00 PM-5:00 PM
The presentation, aimed at the undergraduate and general audiences, will be a discussion (mathematics kept to a minimum) of Einsteins five papers that rocked the world of physics. There will be a gentle introduction, with visual examples, to the basic ideas contained in each paper and the emphasis will be on the impact each paper had on the field of physics. Phils hope is to convey the pleasure and excitement of these ideas to the audience and to marvel at how Albert Einstein could have produced work of such profusion, profundity and prescience in such a short period of time. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "Analogies, Categories, Language and Physics", by Dr. Leslie Atkins, Dartmouth College Wednesday, 9/28/2005, 4:00 PM-5:00 PM
In the field of education, lines between disciplines are getting blurry. In order to understand how one learns physics, many researchers are not only drawing on the traditional fields related to education (such as cognitive science and psychology), but also fields ranging from linguistics to animal behavior to art history. My research (which, broadly, is interested in discourse in science) focuses on how students and scientists use analogy and categorization in physics, and this work has been informed by many of those disciplines. In this talk, I will outline some of the ways in which we understand mind and language and how these are brought to bear on how we understand science and learning. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium, "Building a Better Snail: Lubrication and Adhesive Locomotion", by Dr. Annette Peko Hosoi, MIT Monday, 9/19/2005, 4:00 PM-5:00 PM
Many gastropods, such as slugs and snails, crawl via an unusual mechanism known as adhesive locomotion. We investigate this method of propulsion using two mathematicalmodels, one for direct waves and one for retrograde waves. We then test the effectiveness of both proposed mechanisms by constructing two mechanical crawlers. Each crawler uses a different mechanical strategy to move on a thin layer of viscous fluid. The first uses a flexible flapping sheet to generate lubrication pressures in a Newtonian fluid which in turn propel the mechanical snail. The second generates a wave of compression on a layer of Laponite, a non-Newtonian, finite- yield stress fluid with characteristics similar to those of snail mucus. This second design can climb smooth vertical walls and perform an inverted traverse. Sponsored by: free
Wonderful Speaker Series, "From Rocks to Brains- Using Physics and Nuclear Magnetic Resonance to Characterize Structure", by Dr. Karl Helmer, WPI Biomedical Engineering Wednesday, 9/7/2005, 4:00 PM-5:00 PM
Nuclear Magnetic Resonance imaging has become a standard tool in medicine because it provides a non-invasive window into the body. It can provide contrast between normal and pathological tissue and measure changes in physiological parameters such as blood flow. In some cases, the onset of pathology results in a change in tissue structure. I use the diffusion of water in tissue to probe changes in tissue structure that are the results of diseases such as stroke and cancer. This work grew out of my experience in characterizing the pore structure of rocks using similar methods. In this talk, I will give some background on these types of problems (inverse problems), show what kind of information can be measured, discuss the complexities of building physically-relevant models, and show results from both rocks and biological tissue that will convince you that the two are not so far apart. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: "Using the Atomic Force Microscope to Quantify Adhesion of a Few Asperity Contacts" by Graduate Student, Erik Thoreson Monday, 8/29/2005, 4:00 PM-5:00 PM
Nanoscale and macroscale adhesion data have given seemingly inconsistent results. Despite the importance of bridging the gap between the two regimes, little experimental work has been done, presumably due to the difficulty of the experiment needed to determine how small amounts of surface roughness might influence adhesion data lying in between the two scales. We observed that the pull-off (adhesion) force was independent of the radius of the AFM (Atomic Force Microscope) tip, which was contrary to all continuum-mechanics model predictions. In this talk, I will derive how the cantilever and tip parameters contribute to the measured pull-off force, show that applying a simple correction to the experimental data results in agreement with continuum mechanics, and demonstrate how the AFM probes were calibrated. Although much work is still needed, the work presented here should progress the understanding of adhesion data lying between the nanoscale and macroscale. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Special Speaker, "Radiation Protection for Space Missions" by Dr. Ram Tripathi, NASA Langley Research Center Tuesday, 8/23/2005, 4:00 PM-5:00 PM
Protecting astronauts and electronics from the harmful effects of space radiation is becoming critically important for long duration missions such as space stations and Lunar and Martion missions. This talk will discuss the latest developments in this field and will also focus on the relavant nuclear physics issues that remain unresolved. Sponsored by: WPI Physics Department, Dr. John Norbury
Wonderful Speaker Series; The Physics of Brass Musical Instruments, or, what do horn players do with their right hands, anyway? by, Prof. Brian Holmes, San Jose State University Wednesday, 4/13/2005, 3:00 PM-4:00 PM
A brass instrument such as a trumpet consists of a cup-shaped mouthpiece, a conical lead pipe, a cylindrical section (including valves) and a flared bell. By building a trumpet, I will demonstrate the acoustical significance of these parts. In the days before valves, horn players learned to augment their supply of notes by moving their right hands in the bell. Even though this technique is obsolete, the hand is acoustically necessary in the modern horn. I will explain the underlying physics. I conclude with a performance of Beethoven's horn sonata, played on a valveless horn. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: Research Opportunities in the Physics Department, Presented by the Physics Faculty Monday, 4/11/2005, 4:00 PM-5:00 PM
WPI Physics Faculty Research Interests Monday, 4/11/2005, 4:00 PM-5:00 PM
Principally for the benefit of physics undergraduates, but also for members of other departments, the faculty of the Physics Department will provide short descriptions of their research, IQP, and MQP interests. The tentative order of the presentations, each less than five minutes including questions, is: Drs.,Aravind, Burnham, Garcia, Iannacchione, Norbury, Phillies, Quimby, Zozuyla. Sponsored by: WPI Physics Department
Colloquium: World Year of Physics 2005 Lecture: "Einstein's Boxes", by Dr. Travis Norsen, Marlboro College Monday, 4/4/2005, 4:00 PM-5:00 PM
Everyone knows that Albert Einstein was uncomfortable with the "orthodox" interpretation of quantum theory, and was never willing to accept its allegedly radical implications. Most physicists dismiss Einstein's obstinateness, attributing it to his being past his scientific prime by the time quantum theory came around, and to his simply being unable to fully comprehend and assess the new ideas. But this turns out to be a complete myth. More careful historical analysis shows that the dismissal of Einstein's ideas is largely based on a failure to understand what Einstein's objections actually were. In this talk I will attempt to clarify those objections, by focusing on a little-known thought experiment -- "Einstein's Boxes" -- which permits a streamlined version of the more widely-known EPR argument for the incompleteness of quantum mechanics, due to Einstein, Podolsky and Rosen. We will also connect up Einstein's objections to orthodox quantum theory with more recent work in the foundations of physics such as Bell's Theorem and its empirical tests. It will be argued that, although Einstein's specific vision of an alternative to QM isn't viable, his criticism of the orthodox interpretation nevertheless plays a major role in determining what sorts of views are viable. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
SPS Seminar, "Calculating the Ising Density of States", by Professor Louis Colonna-Romano Wednesday, 3/23/2005, 3:30 PM-4:30 PM
In statistical mechanics, much of our knowledge comes from the study of model systems. One of the most important models is the Ising model because it is relative simple and it has a phase transition. In this model, spins must be in one of two allowed states (up or down), are fixed on a lattice and interact only with their nearest neighbors. Even in this simple model, little can be solved exactly and approximate methods must be used. As an example, we calculate the density of states using the recently-developed Wang-Landau algorithm and consider the efficiency of this approach for Ising models of different dimensions. The density of states, the number of configurations that have a particular energy, can be used to calculate most thermodynamic quantities. Sponsored by: WPI Physics Department
Graduate Seminar: "Fermi's Virtual Photons" by Frank Dick, WPI Graduate Student Wednesday, 3/9/2005, 3:30 PM-4:30 PM
In 1924, at the age of 23, Enrico Fermi published a method to simplify the analysis of relativistic heavy ion collisions. The electromagnetic field surrounding a relativistic ion looks to a nearby "observer ion" very much like a passing pulse of EM radiation, brief but intense. According to Fermi "this time-dependent electromagnetic field can be replaced by the field of radiation with a corresponding frequency distribution". He called this "aquivalente strahlung", equivalent radiation. The spectrum of these photons can be calculated from the kinematics of the collision process, and the subsequent dynamics of the observer ion can be effectively treated as the interaction of the ion with the EM pulse. The method was extended 10 years later by C. Weizsacker and E. Williams, and is now called the Weizsacker-Williams Method (WWM) or Equivalent Photon Approximation (EPA). WWM continues to be extended, and finds widespread use in high energy physics. Prof. Norbury has applied the method to analyze the effects of the heavy ion component of space radiation, the production of pions in proton-proton collisions, and in investigations of new phenomena, such as the production of Higgs bosons by photon-photon interactions. Sponsored by: WPI Physics Department
SPS Seminar; "The World Year of Physics 2005: Einstein and Brownian Motion", by Dr. Germano Iannacchione, WPI Wednesday, 3/2/2005, 3:30 PM-4:30 PM
The year 2005 celebrates the centennial of the miraculous year 1905 in which Albert Einstein published five papers that changed the world. While we may be familiar with the ideas of relativity and the quantum nature of light that were introduced, this talk will focus on the work explaining Brownian Motion. Einstein's theoretical treatment of Brownian Motion via the molecular-kinetic view of heat marks a milestone in the development of statistical mechanics. This talk presents the historical perspective of this phenomena, Einstein's approach, and the ramification to modern physics. Sponsored by: WPI Physics Department, Dr. Iannacchione
Colloquium: Particle-Based Computational Techniques for Modeling Charge Transport in Nanoscale Devices and Biological Channels, by Dr. Shela Aboud, WPI Monday, 2/28/2005, 4:00 PM-5:00 PM
Particle-based methods have long demonstrated success in simulating the electrical properties of semiconductor devices. These approaches are based on a semi-classical description of the charge transport through the use of an ensemble of "computational" particles. The time and/or space averages of the quantities carried by these particles then yield the macroscopic properties of the system. Particle-based approaches provide an excellent probe to analyze the microscopic behavior of complex systems, such as electron devices, and are important in the development of the next generations of nanoelectronic devices. In this talk, a fast and efficient particle-based simulation approach is presented, which represents the state-of-the-art in semi-classical semiconductor modeling capabilities. The simulation tool is then used to model and characterize several high performance field-effect transistors. This simulation tool has also been extended to model ionic charge transport through complex protein structures in biological systems. The focus of this work is to model the flux of ions through ion channels, which are a class of proteins responsible for controlling the flow of ions into and out of biological cells. Ion channels are also interesting for their possible application in hybrid bioelectronic sensors ntegrated with existing semiconductor technologies. Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Graduate Seminar: "The Art of the Hubble" by Anne Adamczyk, WPI Physics Graduate Student Wednesday, 2/23/2005, 3:30 PM-4:00 PM
Hubble Space Telescope, the first space based optical telescope, is noted for providing beautiful and often bizarre color images of the galaxies,planets, and nebula. Take a peak behind the scenes to discover how Hubble actually makes images. Hubble has changed the way the public sees astronomy. The pictures truly are art. The five science instruments its cameras, spectrographs, and fine guidance sensors, work together or individually to capture light from the cosmos, convert it into digital data and transmit it back to Earth. These instruments bring stunning images from the farthest reaches of space. Find out about the inner workings of this telescope. The periodic maintenance and upgrading of Hubble has clearly been the key to its success as one of the premier scientific facilities in human history. The contributions Hubble has made and still can make to science and public understanding of the heavens is worth the cost of a fourth servicing mission. Sponsored by: WPI Physics Department
Colloquium: "Controversial Precision-Final Results from the Muon g-2 Experiment at BNL" by Dr. Robert Carey, BU Monday, 2/14/2005, 4:00 PM-5:00 PM
The muon g-2 experiment at Brookhaven National Laboratory is a 0.55 parts per million measurement of the muon's anomalous magnetic moment. Our final result represents a 13-fold improvement over those made at CERN in the late 60s and 70s, provides a stringent test of the Standard Model and serves as a probe of physics at the TeV scale. In the talk, I will explain how, with the help of a few fundamental insights, a value of the anomaly can be extracted from the detection of decay-electrons in our muon storage ring. I will explain our schemes for minimizing statistical and systematic errors, present our recently published number from the 2001 run, and shed light on the controversy surrounding its interpretation. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: "Prospects for Hard X-ray Astronomy" by Dr. Tomohiko Narita, College of the Holy Cross Monday, 2/7/2005, 4:00 PM-5:00 PM
The hard X-ray band, from 10-600 keV, is a relatively unexplored part of the spectrum for the study of astrophysical processes. Black holes and the Gamma-ray bursts that are believed to accompany their birth emit most of their power in the hard X-ray band. This band is also key for study of the obscured universe, particularly the obscured massive black holes in the centers of galaxies, which are invisible in the soft X-ray and optical wavebands. We are currently fabricating a prototype hard X-ray telescope using an array of Cadmium-Zinc-Telluride detectors. We report on our progress and also illustrate the concept for a future space mission. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
SPS Event: "Looking at Blue Lights from Red Stars and What Happens When Good Optics Go Bad", by Carol Carveth, WPI Physics Student Wednesday, 2/2/2005, 3:30 PM-4:00 PM
In the early days of Astronomy the idea was to study the way stars look. The development of spectroscopy has started to drive out the study of the appearance of stars as "serious" science, but since spectra seem to vary widely between stars, reasons behind certain spectroscopic features are still unknown. A study of the Ca II K absorption line in Red Giant stars was started this past spring at McDonald Observatory. In 1997 the Hobby Eberly Telescope was opened for the first time atop Mount Folkes in Fort Davis, TX. Since then the reflectivity of the silvered mirrors has dropped significantly. Three years ago mirror coating samples were placed in different spots around McDonald Observatory, and identical samples were kept in a desicator. Total Reflectivities and Scattering values were compared for each mirror using a Cary 100 Spectrophotometer which the Observatory obtained for the purpose. Sponsored by: Society of Physics Students
Colloquium: An Optical Vortex Coronagraph by Dr. David Palacios Monday, 1/31/2005, 4:00 PM-5:00 PM
A coronagraph is a device used to block light from a star so nearby objects may be seen. Bernard Lyot first used such a device in 1939 to block the intense glare of the sun so that the solar corona could be imaged. Similarly, an optical vortex coronagraph opens a dark window in the glare of a distant star so nearby terrestrial sized planets and exo-zodiacal dust may be detected. An optical vortex may be characterized as a dark core of destructive interference in a beam of spatially coherent light. This dark core may be used as a filter to attenuate a coherent beam of light so an incoherent background signal may be detected. Applications of such a filter include: eye and sensor protection, forward-scattered light measurement, and the detection of extra-solar planets. An optical vortex coronagraph may hold several advantages over other techniques presently being developed at JPL for the Terrestrial Planet Finder Mission. These advantages include: broadband nulling, nearly on-axis planet detection, and low aberration sensitivity. During this talk I will discuss the nulling properties of an optical vortex coronagraph. I will also provide both experimental and numerical results demonstrating the versatility of an optical vortex coronagraph. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Graduate Seminar, "Reciprocity Between Absorption and Emission", by Rodica Martin, WPI Physics Graduate Student Wednesday, 1/26/2005, 3:30 PM-4:00 PM
When designing optical amplifiers, accurate knowledge of the emission cross-section is required. Unfortunately, emission spectra are not always easy and straightforward to obtain. McCumber theory is a generalization of Einstein A and B coefficients for broadband transitions used to predict emission cross-sections from measured absorption spectra. Although widely used, the theory is still controversial when applied to broad transitions of the rare earths. Experimental studies have been performed to investigate the accuracy of the method for a number of rare earth doped samples. Sponsored by: WPI Physics Graduate Students
Colloquium: Atom Optics in the Presence of Gravity by Dr. Timothy Roach, College of the Holy Cross Monday, 1/24/2005, 4:00 PM-5:00 PM
Slow, laser-cooled atoms are the basis for many experiments on matter wave optics because of their relatively large deBroglie wavelength. The earth's gravity presents challenges to experimental design, however. For example, during the transfer of low momentum atoms from a source (e.g., MOT or BEC) to an optical element, the momentum increase due to gravity is orders of magnitude larger than the thermal momentum. As a complement to our ongoing experiments with magnetic diffraction gratings, we have analyzed how gravity influences the results of various experimental diffraction geometries. We will present a model of how gravity affects the fringe resolvability and compare this to experimental results of several research groups. We will also report on progress on our current round of diffraction experiments with laser-cooled rubidium atoms. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "Protection of Astronauts from Cosmic Radiation", by Dr. John Norbury, Physics Department Head, WPI Wednesday, 1/19/2005, 11:00 AM-12:00 PM
The two most important medical problems that astronauts face on long duration space missions are the effects of microgravity and radiation due to cosmic rays. The radiation comes from three separate sources, namely geomagnetically trapped particles, energetic solar particles and Galactic cosmic rays. The talk will review these radiations and discuss research relevant to the general space radiation problem. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: An Optical Vortex Coherence Filter, by Dr. David Palacios Monday, 1/17/2005, 4:00 PM-5:00 PM
Sponsored by: WPI Physics Dept., Dr. Garcia
SPS event: High-Resolution AC-Calorimetry by RF-Field Heating for Complex Fluids by Saimir Barjami Wednesday, 12/15/2004, 3:30 PM-4:30 PM
A new, high-resolution, modulation calorimetric technique using Radio Frequency or Dielectric heating of the sample, has been developed for the study of complex fluids. This powerful method is sensitive to both the heat capacity and permittivity of organic liquids. The employment of this calorimeter on dispersions of aerosils in the liquid crystal octylcyanobiphenyl (8CB) is described. There is no enhancement of the dielectric permittivity through SmA to N transition in the disordered liquid crystal at the studied density consistent with recent NMR work, suggesting decoupling of the nematic and smectic order parameters. Sponsored by: WPI Physics Department, Dr. Germano Iannacchione
SPS speaker, Summer Job Opportunities in Physics, by Deanna Wolfson Wednesday, 12/8/2004, 3:30 PM-4:30 PM
The presentation will be an overview of summer job opportunities in physics. The talk will focus on NSF-funded Research Experience for Undergrads. It will include the opportunities and benefits of REUs, as well as the process for applying for one. Non-REU job opportunities will also be discussed.
Colloquium, Non-Lithographic fabrication of superlattices for nanometric electro-magnetic-optic applications, by Dr. Jianyu Liang Monday, 12/6/2004, 4:00 PM-5:00 PM
Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Lateral Superlattices for Nanometric Electro-Magnetic-Optic Applications by Dr. Jianya Liang Monday, 12/6/2004, 4:00 PM-5:00 PM
Exploiting materials of dimension less than 100 nm for potential applications has been proved a fascinating enterprise. However, efforts so far have concentrated on individual nanostructures. The collective behaviors of nanostructures in a large ensemble remain largely unexplored. As the first step into the nano realm, investigation of isolated nanostructures and characterization of individual nanodevices are of great importance and naturally of strong appeal to researchers. Yet more challenging and probably of greater impact is the assembly and manipulation of multiple nanostructures into integrable functional units. It is both desirable and timely to seek for ways to advance both the fabrication capabilities and the science explorations beyond the realm of individual nanostructures. In this talk, a non-lithographic technique that utilizes highly ordered anodized aluminum oxide (AAO) porous membrane as a template will be introduced as a general fabrication means for the formation of an array of vastly different 2-dimensional lateral superlattices. The fact that material systems as different as metals, semiconductors, and carbon nanotubes can be treated with the same ease attest to the generality of this nano-fabrication approach. The original AAO membranes determine the uniformity, packing density, and size of the nanostructures. The flexibility of using a variety of materials, the accurate control over fabrication process, and the command over AAO template attributes give us the freedom of engineering various physical properties determined by the shape, size, composition, and doping of the nanostructures. A fundamentally new nanoheteroepitaxial growth method based on the as fabricated semiconductor nanostructures will also be presented. Employing this approach, high quality semiconductor thin films and quantum dots have been successfully grown by molecular beam epitaxy on nanopatterned semiconductor substrates. Optical and structural characterizations have shown that the novel nanomaterial platform realized by this unique non-lithographic technique is powerfully enabling a broad range of applications. Sponsored by: WPI Physics Department, Dr. N. A. Burnham
Colloquium: Physics of Red Blood Cell Shapes by Dr. Ranjan Mukhopadhyay, Clark University Monday, 11/29/2004, 4:00 PM-5:00 PM
A mature human red blood cell normally assumes the shape of a flattened biconcave disc. However, under a variety of chemical or physical treatments, the cell undergoes a quasi-universal sequence of reversible shape transformations. Since a red blood cell has no internal structure, its shape is encoded in the mechanical properties of its membrane. Using a simple physical model we show how the full sequence of shapes can be driven by variation in a single control parameter. Our predicted shapes are in surprisingly detailed agreement with observations. Our results make it possible to use shape transformations as a quantitative tool to probe the physics and biochemistry of cell membranes. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: Data and Modeling of Dendrites Subject to a Step Change in Pressure, by Dr. Matthew B. Koss , College of the Holy Cross Monday, 11/22/2004, 4:00 PM-5:00 PM
Current theories and models of dendritic growth generally couple diffusion effects in the melt with the physics of the interface. Data and subsequent analysis of the tip growth speed and radii of thermal succinonitrile dendrites in the near-convection free, on-orbit, free-fall environment demonstrate that these theories yield predictions that are reasonably in agreement with the results of experiment. However, data and analysis for assessing the interfacial physics component of theory are not sufficiently detailed or definitive. To study fundamental aspects of dendritic interface stability we subject thermal dendrites, growing under steady-state conditions, to a rapid change in pressure. This leads to a rapid change in thermal driving force from the corresponding change in both the equilibrium melting temperature due to the Clapeyron effect, and a change in the far-field temperature due to adiabatic temperature changes in the bulk liquid and solid. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Wonderful Speaker Series, "The Accelerating Universe", by Dr. Robert Kirshner, Harvard University Wednesday, 11/17/2004, 3:30 AM-4:30 AM
Observations of exploding stars halfway across the observable universe show that cosmic expansion is not slowing down, as expected due to gravity. It is speeding up. We attribute this to the effect of "Dark Energy." Quantitative estimates of the expected vacuum energy for gravitation miss the observed amount by 10^120! This points to a deep theoretical problem right at the heart of physics. At present, the only evidence for the dark energy is from astronomical observations. This talk will describe Dark Energy as an idea, show the astronomical evidence from supernovae, and describe future work to learn more about this strange new component that makes up 2/3 of the mass-energy of the Universe. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
Colloquium: Nanomechanics: Quantum and Other Aspects by Dr. Raj Mohanty, Boston University Monday, 11/15/2004, 4:00 PM-5:00 PM
Engineered nanomechanical systems offer exiciting prospects for studying a variety of phenomena of fundamental and technical interests. Recent technological advances have made it possible to create mechanical structures that can move over a billion times in a second. If cooled to sub-kelvin temperatures, such nanomechanical oscillators enter the quantum regime of mechanical motion, becoming text-book quantum "mechanical" oscillators. Experimental realization of motion in the quantum regime will prospect the ground for a new direction for studies of quantum measurement and quantum computation. I will describe the recent experiments in our group, which demonstrate the first observation of mechanical motion in the quantum regime with the fastest-moving manmade structures. In addition, I will discuss the prospect of classical nanomechanical computation with memory elements created by nanomechanical silicon beams, reminiscent of Babbage's original idea of analytical computing. This technology has the potential to supercede the current memory technologies in both speed and density. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
COLLOQUIUM: From Atoms to Quantum Computers: The Classical and Quantum Faces of Matter, by Dr. Antonio Castro Neto, Boston University Monday, 11/8/2004, 4:00 PM-5:00 PM
In this seminar I am going to discuss the problem of the transition from a quantum to a classical description of the world. I will argue that this transition can be better studied and understood in condensed matter systems where many particles interact with each other and the environment that surround them. I will show that the understanding of the classical/quantum duality has direct consequences in basic science as well as emerging technologies. Sponsored by: WPI Physics Department, Dr. Garcia
Wonderful Speaker:"Physics and the Boundary of a Boundary" by Professor Khin Maung Maung, Hampton University Wednesday, 11/3/2004, 3:30 PM-4:30 PM
There is one geometrical principle behind Maxwell's Equations of Electromagnetism, Yang-Mill's Equations of Quantum Chromodynamics and Einstein's Equations of General Relativity. The geometrical theme behind all this is that boundary of a boundary is zero. These ideas will be presented in an elementary manner and anyone with a little knowledge of calculus and matrices will be able to follow. Sponsored by: WPI Physics Department, Dr. John Norbury
Colloquium: "Investigating structural properties of carbon nanotubes using inelastic light scattering" by Dr. Wolfgang Bacsa, Solid State Physics Laboratory, University of Toulouse, France Monday, 11/1/2004, 4:00 PM-5:00 PM
Carbon nanotubes have properties characteristic of molecules and yet they are macroscopic in their length. For single shell carbon nanotubes all atoms are located at the surface. The combination of these and other unique characteristics makes nanotubes an extraordinary material. Structural properties of carbon nanotubes such as helicity and response to external pressure can be explored using inelastic light scattering. Recent results will be summarized after giving an introduction on nanotubes and inelastic light scattering.
GPSO Event: Dielectric Spectroscopy of Liquid Crystals by Florentin Cruceanu Wednesday, 10/27/2004, 3:30 PM-4:30 PM
I will review the progress to date in constructing a high-resolution, narrow-band, dielectric spectrometer suitable for phase transition studies of fluids and solids. Background on the theory of the technique and experimental details will be given. Initial studies on the phase behavior of the liquid crystal octylcyanobiphenyl (8CB) will be presented as well as some preliminary results on a nano-colloidal dispersion of an aerosil gel in 8CB. Future directions will also be discussed. Sponsored by: WPI Physics Department
Colloquium:Quantum Entaglement and its Ramifications by Dr. A.K. Rajagopal Monday, 10/11/2004, 4:00 PM-5:00 PM
Walter Arnold.Naval Research Labs, Washington, D.C. QUANTUM ENTANGLEMENT AND ITS RAMIFICATIONS. After a quick review of ideas of classical bits (cbit) leading to modern conveniences such as telephone, TV, Computer technology etc, a discussion of quantum bits (qubits) is given. This discussion includes a review of quantum mechanics superposition principle and uncertainty relations whose implications for qubits are explored. Consideration of two qubits in detail will be shown to lead to new features, most importantly, entanglement. Several applications of this (encryption, no copying, teleportation, computing) are briefly discussed. Considerations of continuous variables where light sources play the role of qubits will be touched upon. Sponsored by: Dr. L. R. Ram-Mohan, WPI Physics Department
GPSO Event: Ellipsometric measurements of packaged samples to detect changes to die surfaces through packaging and correlation with MEMS performance, by Erika Shutte Wednesday, 10/6/2004, 3:00 PM-3:30 PM
Reliability and performance of low-g accelerometers are closely linked to sensor surface characteristics. Surface film changes after packaging of only a few angstroms have altered performance and wear life in inertial MEMS, but standard characterization techniques cannot measure nanometer films on packaged die. To meet the need for sensor surface characterization of packaged devices, we installed micro-spot optics on a manual ellipsometer and developed a sample preparation and test protocol to measure die surface films after packaging. Experiments were conducted to characterize the effects of outgassing from die attach materials, the influence of a diphenyl siloxane coating, and the packaging process. This presentation will outline the equipment, calibration, and measurement protocol developed to ensure reliable thickness data in the 10A range, then results from our studies of packaging variants will be discussed. Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Calibrated AFM measurements to detect changes in die surfaces after packaging, by Erik Thoreson Wednesday, 10/6/2004, 3:30 PM-4:00 PM
If moving micro- or nanostructures touch, recovery requires that restoring forces overcome the surface adhesive forces. To study restoring forces, we have calibrated cantilever probes for an Autoprobe M5 AFM (Atomic-Force Microscope) from Veeco, so that the work of adhesion can be determined to an accuracy of about 13% 1,2 . This presentation will provide an overview of the AFM, describe how to calibrate the AFM, and show our results for the calibrated works of adhesion between AFM tips (less than 1 m radius tip, 2 m, 12 m, and 120 m) and unpatterned silicon die that were solder-sealed in 5 mm x 5 mm LCC (Leadless Ceramic Chip Carrier) packages. Two sample variables were examined; four die attach conditions (no attachment, silicone, polyimide silicone, and silver glass) and two surface conditions (with and without a few angstroms of vapor-deposited diphenylsiloxane). All measurements were made at a relative humidity of 24.5 1.5 % and a temperature of 22.5 1.9 C. Sponsored by: WPI Physics Department, Dr. Nancy Burnham
Colloquium: Wetting Transitions of Liquids on Solid Surfaces by Milton W. Cole Monday, 10/4/2004, 4:00 PM-5:00 PM
Milton W. Cole, Penn State University, Physics Department. Water beads up to form little droplets on a teflon frying plan. In contrast, water films spread uniformly across other surfaces. What determines this differing behavior? The answer to this question can be understood in simple physical terms, as described in this talk. Also discussed is a remarkable wetting phase transition that has been in seen for various liquid films and surfaces. At low temperature, these liquids bead up while at high temperature they spread. This transition is observed in both equilibrium studies and flow measurements. Although thie transition is predicted to occur for water, such a transition has never been studied in the laboratory. The talk will feature a movie demonstrating the behavior. Sponsored by: Dr. Rafael Garcia, WPI Physics Dept.
Wonderful Speaker,"Physics of the Piano", by Dr. Nick Giordano, Purdue University Wednesday, 9/29/2004, 3:30 PM-4:30 PM
While a piano is a complicated mechanical device, it can presumably be described by physics at the level of freshman mechanics (i.e., field theory should not be required). In spite of this apparent simplicity, it is very difficult to use Newton's laws to calculate the sound produced by a piano. In this talk I will give a brief introduction to the physics of the piano, and describe a few of the interesting problems involved in constructing such a physical model of the instrument. I will then describe our attempts to calculate the sound produced by a piano from first principles; i.e., using F=ma. Sponsored by: WPI Physics Department, Dr. Rafael Garcia
GSPO, Overview of research Wednesday, 9/22/2004, 3:30 PM-4:30 PM
Sponsored by: Graduate Physics Student Organization
SPS Event, Vortex Cannon Wednesday, 9/15/2004, 3:30 PM-4:40 PM
Sponsored by: Society of Physics Students
Colloquium: Ongoing and Future Research and Teaching Collaborations Between WPI and MIT Lincoln Laboratory, by Dr. Bob O'Donnell Thursday, 9/2/2004, 4:00 PM-5:00 PM
Dr. Bob ODonnell. MIT Lincoln Laboratory. Beginning in 2002, WPI and MIT Lincoln Laboratory have developed an extensive collaborative effort. This talk will begin with a brief overview in MIT Lincoln Laboratory its mission an the nature of the research performed there. The WPI - MIT LL collabortive effforts (MQP, sponsored research, summer internships) will be described and it is hoped that this information will spark discussions, both at and after the meeting, that will lead to further joint efforts of this nature. Sponsored by: WPI Physics Department, Dr. John Norbury
Colloquium:Quantitative Contact Spectroscopy by Atomic-Force Acoustic Microscopy, by Dr. Walter Arnold Monday, 8/30/2004, 4:00 PM-5:00 PM
Walter Arnold, Fraunhofer-Institute for Nondestructive Testing, Bldg. 37, University D-66123 Saarbrücken, Germany.Quantitative Contact Spectroscoy by Atomic-Force Acoustic Microscopy. In Atomic Force Microscopy deflection of a micro-fabricated elastic beam with a sensor tip is used to generate high-resolution images of surfaces. Dynamic modes, where the cantilever is vibrated while the sample surface is scanned, are quite common allowing to obtain images whose contrast depend for example on the elasticity of the sample surface. However, quantitative determination of Young's modulus is still a challenge especially when stiff materials are encountered. Here, the evaluation of the cantilever vibration spectra at ultrasonic frequencies is discussed in order to discern local elastic indentation modulus quantitatively. Nano-crystalline magnetic and piezoelectric materials, nano-crystalline nickel, multi-domain piezoelectric ceramics, diamond-like carbon layers, polymeric materials, clay in rocks, crystalline silicon and other materials have been examined. Both the measurement procedures as well as the material physics underlying the data are discussed. The spatial resolution obtained is 10 nm and less. In the piezo-mode a sinusoidal voltage is applied between the sensor tip in contact with a piezoelectric sample. The ac-field at the tip generates a local vibration by the inverse piezoelectric effect. Selecting a frequency close to a resonance leads to an enhanced vibration of the cantilever and allows one to image the ferroelectric domain structure and to obtain information on the local piezoelectric constant. This technique has been applied to a large variety of thin films produced by combinational chemistry and to thin films forming a Schottky barrier on Si. Shear stiffness and friction phenomena can be investigated by evaluating the torsional or lateral resonances of AFM cantilevers. Both types of resonances are excited by a piezoelectric transducer placed below the sample which generates in-plane sample surface vibrations while the sensor tip is in contact with the sample. At low lateral surface vibration amplitudes the sensor tip remains in elastic contact with the sample surface, and the cantilever behaves like a linear oscillator with viscous damping and a certain set of resonances frequencies. If the surface vibration is increased above a critical amplitude, typically 0.2 nm for torsional resonances, the maximum of the resonance curves does not increase any more and the curves develop a plateau at their highest amplitude. Numerical simulations of a corresponding nonlinear oscillator driven by a dry friction element produced curve shapes as in the experiment. This led us to the conclusion that the plateaus in the resonance curves indicate the onset of stick-slip in the relative tip-sample oscillation. This is confirmed by the fact that the critical surface amplitude increases with increasing static cantilever load. Furthermore, for dry samples this amplitude is higher than for lubricated surfaces. Sponsored by: Dr. Nancy Burnham, WPI Physics Dept.
Progress towards SI traceable small force metrology, by Dr. Jon R. Pratt Monday, 4/26/2004, 4:00 PM-5:00 PM
Dr. Jon R. Pratt.NIST.Gaithersburg, Maryland. With all this scientific and technical activity focused on measuring seemingly imperceptible levels of force, it seems prudent to consider just how accurately such forces can be measured in terms of standard units. After all, within the International System of Units (SI) force is derived from the Kilogram, so that in order to derive an SI nanonewton we are presumably faced with the daunting task of subdividing the weight of a single Kilogram by ten orders of magnitude. Or are we? Recent experiments with the NIST Electrostatic Force Balance (EFB) have achieved agreement between an SI electrostatic force and an SI gravitational force of 10-5 N to within a few hundred pN/mN. This result suggests that a force derived from SI measurements of length, capacitance, and voltage provides a viable small force standard, circumventing the need to directly subdivide from the Kilogram. In this talk, we'll examine just what I mean by an SI traceable electricalforce, consider how one constructs an Electrostatic Force Balance as a practical realization of a nanonewton, and learn how such a balance has been used to calibrate the most sensitive of force measuring equipment, an AFM Sponsored by: Dr. Nancy Burnham
From Cathode to Counting House, a quick, dirty, and detailed expose of a Precision Nuclear Physics Experiment through the eyes on one harried PhD student, by Dr. Eric Clinton Monday, 4/19/2004, 4:00 PM-5:00 PM
Eric Clinton. Thomas Jefferson National Laboratory. The business of the Thomas Jefferson National Acclerator Facility is to make high energy electron and photon beams. These beams are used to make detailed measurements of nuclear and particles reactions that lead to a deeper understanding of the Standard Model of Physics. But what really goes on in this governement installation? How does a 6 GeV electron beam get acceration from .511 MeV to almost 2000 times its rest mass? How does this electron beam make a secondary beam of bremmstrahlung photons, and how in the name of Feynnman does a lowly, underpaid, overworked, misunderstood, alumnus of WPI plan to use that photon beam to make a Precision Measurement of the Neutral Pion Life- time Via the Primakoff Effect? Come find out April 19 when Eric Clinton, class of 1999, gives a whirlwind tour of Accelerator Physics and his PhD prospectus. Sponsored by: Dr. Germano Iannacchione
Discovery of Supersolidity in Helium, by Dr. Moses H. W. Chan Tuesday, 4/13/2004, 4:00 PM-5:00 PM
Moses Chan. Penn State Dept. of Physics. When liquid 4He is cooled below 2.176 K, it undergoes a phase transition-Bose-Einstein condensation-and becomes a superfluid with zero viscosity. Once in such a state, it can flow without dissipation even through pores of atomic dimensions. Although it is intuitive to associate superflow only with the liquid phase, it has been proposed theoretically that superflow can also occur in the solid phase of 4He. Owing to quantum mechanical fluctuations, delocalized vacancies and defects are expected to be present in crystalline solid 4He, even in the limit of zero temperature. These zero-point vacancies can in principle allow the appearance of superfluidity in the solid. However, in spite of many attempts, such a 'supersolid' phase has yet to be observed in bulk solid 4He. Here we report torsional oscillator measurements on solid helium confined in a porous medium, a configuration that is likely to be more heavily populated with vacancies than bulk helium. We find an abrupt drop in the rotational inertia of the confined solid below a certain critical temperature. The most likely interpretation of the inertia drop is entry into the supersolid phase. If confirmed, our results show that all three states of matter-gas, liquid and solid-can undergo Bose-Einstein condensation. Sponsored by: Dr. Rafael Garcia
High temperature superconductivity and strong correlation phyiscs, by Dr. Patrick Lee Monday, 4/5/2004, 4:00 PM-5:00 PM
Dr. Patrick Lee. MIT Physics Department. After 17 years of intense studies, a great deal is known about the high Tc superconductors. There is broad agreement that it should be understood in the context of strong correlation. By strong correlation we mean the repulsion between electrons is playing a crucial role and superconductivity arises as a result of adding carriers to what is called a Mott insulator. I shall explain some of the key concepts and review some experiments. Sponsored by: Dr. Rafael Garcia
Contradictions with Local Realism from Rotational Properties of Entangled States, by Dr. Walter E. Lawrence Monday, 3/29/2004, 2:00 PM-3:00 PM
Dr. Walter E. Lawrence Dartmouth College Department of Physics and Astronomy. A measurement on one member of an entangled pair of particles determines the state of the other. It is natural to ask whether rotation of one changes the state of the other. The answer to this question provides a new perspective on the nature of quantum entanglement and the nonlocality that comes with it. It also provides a way of predicting large numbers of measurements that produce absolute contradictions with local realism-measurements whose outcomes are certain (for which the system must be prepared in an eigenstate of the measurement operator), which nevertheless contradict the predictions of any local hidden Sponsored by: Dr. P.K. Aravind
The Electronic Kilogram, by David B. Newell Monday, 3/22/2004, 4:00 PM-5:00 PM
David B. Newell. National Institute of Standards and Technology. In the International System of Units (SI), the kilogram is the last base unit to be defined in terms of an artifact, a century-old platinum-iridium alloy cylinder. This talk will describe one effort towards a new definition of the kilogram in terms of invariant quantities, the NIST (National Institute of Standards and Technology) Electronic Kilogram project. The project uses a watt balance which measures the ratio of mechanical to electrical work, linking the meter, the artifact kilogram, and the second to the practical realizations of the ohm and the volt derived from the quantum Hall and the Josephson effects. In 1998, the NIST watt balance set an upper limit on the drift rate of the artifact kilogram of 2 x 108/yr (PRL Sept. 21, '98). By using the theoretical values for the Josephson and von Klitzing constants, the same results yield an SI determination of Planck's constant with a combined relative uncertainty of 8.7 x 10-8, the most accurate determination to date. Sponsored by: Dr. Nancy Burnham
Spin Fluctuations and High Temperature Superconductivity, by Robert Birgeneau Monday, 3/8/2004, 4:00 PM-5:00 PM
Dr. Robert Birgeneau University of Toronto Department of Physics. The most striking feature of high temperature superconductors is that they are created by doping planar antiferromagnetic copper oxide ceramics. It turns out that the magnetic behavior and the interplay between magnetism and superconductivity are remarkably rich and subtle. In this talk we will discuss recent experiments probing the static and dynamic spin fluctuations in various high-Tc materials. These experiments reveal new, interesting quantum many body behavior but the problem of the mechanism of high-Tc superconductivity remains open. Sponsored by: Dr. Rafael Garcia
Long-lived states of positronium in crossed electric and magnetic fields, by Janine Shertzer Monday, 3/1/2004, 4:00 PM-5:00 PM
Dr. Janine Shertzer College of the Holy Cross Department of Physics. Long-lived states of positronium in crossed electric and magnetic fields. Abstract Crossed electric and magnetic fields provide a unique way for stabilizing simple matter-antimatter systems. Theoretical calculations on positronium in crossed fields predict the existence of long-lived states in which the average positron-electron separation is several thousand Angstroms. These states are due to formation of a second attractive well in the potential for certain values of pseudomomentum and field strength. The near zero probability for positron-electron overlap suppresses direct annihilation processes resulting in excessively long lifetimes. Sponsored by: WPI Department of Physics
Nanomechanical Investigations Using Scanning Force Microscopy, by Dr. Udo D. Schwarz Monday, 2/23/2004, 4:00 PM-5:00 PM
Dr. Udo D. Schwarz Yale University Department of Mechanical Engineering. Nanomechanical Investigations Using Scanning Force Microscopy. Abstract The ability of the scanning force microscope to study the nanomechanics of materials down to the atomic scale is illustrated with two different examples. First, I will show how data acquired during the sliding of nanometer-sized tip-sample contacts provide new insight into the atomic origins of friction, which lead to a deeper understanding of Amontons and Coulombs phenomenological laws of friction. Interestingly, friction is on the nanometer scale proportional to the contact area, in opposition to the corresponding macroscopic law, whereas the macroscopically observed independence of friction from the sliding velocity remains approximately valid. In the second part of the talk, I will present an experimental set-up optimized for the operation in the so-called dynamic mode of scanning force microscopy at low temperatures and in ultrahigh vacuum. The instrument achieves a resolution comparable to the one of low-temperature scanning tunneling microscopes, but yields complementary information. Moreover, it provides atomic resolution even on insulating materials, which can otherwise not be investigated. In particular, I will introduce a method that allows the continuous measurement of the tip-sample interaction potential. Comparison of such data with model potentials gives access to a profound analysis of the interactions at and between surfaces, including nano-elastic and nano-contact mechanical effects.
Protection of Astronauts from Cosmic Radiation, by John Norbury Thursday, 2/19/2004, 11:00 AM-12:00 PM
Dr. John Norbury University of Wisconsin-Milwaukee Department of Physics. Protection of Astronauts from Space Radiation The two most important medical problems that astronauts face on long duration space missions are the effects of microgravity and radiation due to cosmic rays. The radiation comes from three separate sources, namely geomagnetically trapped particles, energetic solar particles and Galactic cosmic rays. The talk will review these radiations and discuss research relevant to the general space radiation problem. Sponsored by: WPI Department of Physics
Solid State Semiconductor Quantum Computing, by Vladimir Privman Monday, 2/16/2004, 11:00 AM-12:00 PM
Dr. Vladimir Privman NSF Center for Quantum Device Technology Clarkson University, Physics Department. Solid State Semiconductor Quantum Computing. An overview is presented of the ideas of quantum information and computing, with emphasis on their impact on recent solid-state research. The introduction is followed by survey of our groups work on evaluation of decoherence and relaxation in systems which are candidate for quantum computing implementations. Our results include investigations of interactions and decoherence in semiconductor heterostructures, with initial applications for quantum dots and for nuclear and donor-electron spins. Sponsored by: WPI Department of Physics
Freshman Physics, Ideas and Innovation, by Bill Goodhue Thursday, 2/12/2004, 11:00 AM-12:00 PM
Bill Goodhue, UMASS Lowell. As an experimentalist, the books most worn out on my bookshelf are those dealing with freshman physics. The material in those books has been a guiding force in my research; giving me many ideas, which I have developed, or help develop into practical semiconductor and optical devices. In this talk I'll show by example some of these devices and discuss my philosophy on research and teaching. Sponsored by: WPI Department of Physics
The Optical Amplifier Revolution, by John Zyskind Monday, 2/2/2004, 11:00 AM-12:00 PM
Sponsored by: WPI Department of Physics
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