BEGIN:VCALENDAR CALSCALE:GREGORIAN VERSION:2.0 METHOD:PUBLISH PRODID:-//Drupal iCal API//EN X-WR-TIMEZONE:America/New_York BEGIN:VTIMEZONE TZID:America/New_York BEGIN:DAYLIGHT TZOFFSETFROM:-0500 RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU DTSTART:20070311T020000 TZNAME:EDT TZOFFSETTO:-0400 END:DAYLIGHT BEGIN:STANDARD TZOFFSETFROM:-0400 RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU DTSTART:20071104T020000 TZNAME:EST TZOFFSETTO:-0500 END:STANDARD END:VTIMEZONE BEGIN:VEVENT SEQUENCE:1 X-APPLE-TRAVEL-ADVISORY-BEHAVIOR:AUTOMATIC 234806 20260416T135901Z DTSTART;TZID=America/New_York:20260501T140000 DTEND;TZID=America/New_York:2 0260501T163000 URL;TYPE=URI:https://www.wpi.edu/news/calendar/events/physi cs-graduate-student-joshua-dickies-phd-dissertation-defense Physics Graduate Student Joshua Dickie’s Ph.D. Dissertation Defense ABSTRACTThe Active River\nCharacterizing Active Fluid Response to External Shear and Geometric Confinement\nActive fluids are a class of soft matter systems capable of self-propulsion through the conversion of microscopic energy sources into mechanical motion. These materials are ubiquitous in nature; for example, the cytoplasm of eukaryotic cells can be described as a form of active fluid which converts chemical energy (ATP) into the mechanical motion known as cytoplasmic streaming. Cytoplasmic streaming is a phase of coherent active fluid which transports proteins within the cell far more efficiently than diffusion alone. When eukaryotic cells move through their environment, they experience external shear, which then affects their cytoplasm. Despite the ubiquity of this interaction, active fluid’s response to external shear has been relatively unexplored. Therefore, to understand the interplay between internal and external shear we use a biologically derived model active fluid system, microtubule kinesin-based active fluid, to probe the behavior.\n\n\nImage\n \n\n\n\nUtilizing our active fluid system, we demonstrate that the response of active fluid to external shear is influenced by geometric confinement. Specifically, we examine three distinct geometries: a thin slab-like confinement, a toroidal confinement, and a connected tor oidal confinement. Across these configurations, the behavior of the active fluid ranges from resisting externally applied shear to cooperating with it, resulting in a diverse set of dynamical responses. Slab-like geometrie s were found to suppress the influence of shear until the externally appli ed stress became comparable to the internally generated stress at ~1.5mPa. Above this critical point, the system’s flow structure became water-lik e with the correlation length matching the inactive, passive fluid system and fluid dynamics dominated by the external driving force.\nToroidal geom etries, which can form coherent transport phases, were instead found to pr omote cooperation with external forcing even at low driving speeds of (~50 µm/s). It was found that under external forcing the local active fluid n etwork is reoriented by the external shear. This reorientation then propag ates across the entire interlinked network, exceeding the length scales ac cessible in passive fluid systems, and reversing the direction of flow. Fu rther examination of the interconnected toroidal system found it capable o f self-correcting behavior. When a notch or ratchet is inscribed into the wall of a toroidal system, it had previously been shown that the spontaneo us flow direction in a toroidal system would be directed by the ratchets o rientation. This work expands upon these previous results, showing if the fluid is driven against its preferred orientation the ratchets can reverse the flow after driving has ceased.\nThese results suggest that the compet ition between internally generated active stress and externally applied sh ear depends on confinement geometries. By leveraging the role of geometry in active fluid response to external stimuli, its flow phases can be progr ammed and externally controlled, allowing novel microfluidic chips with se lf-correcting flow dynamics after mechanical forcing. More broadly this wo rk can connect to cellular systems, demonstrating that geometry influences the behavior of active fluids, such as cytoplasm, in the presence of mech anical shear. Understanding how geometry influences the interaction betwee n internally and externally generated stress can provide new control mecha nisms for systems which are driven by force-sensitive self-organization.\n Advisor: Kun-Ta Wu\nCommittee Members:\nChair:Qi WenMember:Robert Pelcovit sMember:Kun-Ta WuMember:Germano Iannachione\nJoin Zoom Meetinghttps://wpi. zoom.us/j/92311530319\nMeeting ID: 923 1153 0319\nOne tap mobile+164693138 60,,92311530319# US+13017158592,,92311530319# US (Washington DC)\nDial by your location•+1 646 931 3860 US• +1 301 715 8592 US (Washington DC)� � +1 305 224 1968 US• +1 309 205 3325 US• +1 312 626 6799 US (Chicago) • +1 646 876 9923 US (New York)• +1 360 209 5623 US• +1 386 347 5053 US• +1 507 473 4847 US• +1 564 217 2000 US• +1 669 444 9171 US• + 1 669 900 6833 US (San Jose)• +1 689 278 1000 US• +1 719 359 4580 US� � +1 253 205 0468 US• +1 253 215 8782 US (Tacoma)• +1 346 248 7799 US (Houston)\nMeeting ID: 923 1153 0319\nFind your local number:https://wpi.z oom.us/u/adEgh7Oahp\nJoin by SIP•92311530319@zoomcrc.com\nJoin by H.323� �� 144.195.19.161 (US West)• 206.247.11.121 (US East)• 159.124.15.191 (Amsterdam Netherlands)• 159.124.47.249 (Germany)• 159.124.104.213 (Au stralia Sydney)• 159.124.74.212 (Australia Melbourne)• 159.124.168.213 (Canada Toronto)• 159.124.196.25 (Canada Vancouver)• 170.114.194.163 (Japan Tokyo)• 147.124.100.25 (Japan Osaka)\nMeeting ID: 923 1153 0319\n END:VEVENT END:VCALENDAR