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DTSTART;TZID=America/New_York:20190813T103000
DTEND;TZID=America/New_York:20190813T120000
DTSTAMP:20260410T043540
CREATED:20190808T140550Z
LAST-MODIFIED:20190808T140550Z
UID:10006263-1565692200-1565697600@seasevents.nmsdev7.com
SUMMARY:MEAM Seminar: "Mechanical Models for DNA"
DESCRIPTION:We will discuss two complementary mechanical models for DNA that deal with\, respectively two problems: one\, phase transitions in a DNA molecule\, and two\, allosteric interactions between two ligands bound to DNA. \nExperimental studies on single molecules of DNA have reported a rich variety of cooperative structural transitions\, including coexistence of three phases\, when a torsionally constrained DNA molecule is pulled using magnetic or optical tweezers. Our objective is to examine the aforementioned structural transitions using ideas from statistical mechanics and the theory of elasticity. We use foundational concepts from the Zimm-Bragg helix-coil transition theory and merge them with ideas from the theory of fluctuating elastic rods to model the mechanics of DNA. Furthermore\, we use Poisson-Boltzmann to account for the electrostatic interactions between the ions and the negatively charged phosphate backbone of DNA. Using our model\, we calculate the force and torque corresponding to the over-stretching transition characterized by a 70% jump in the contour length of the molecule and examine the effect of salt concentration on this transition. \nIn the next part\, we present a mechanical model for computing the allosteric interaction energy between two ligands on DNA. This interaction is quantified by measuring the change in free energy as a function of the distance between the binding sites for two ligands. We show that trends in the interaction energy of two ligands binding to DNA can be explained using an elastic birod model which accounts for the elastic deformation of strands and base-pairs as well as the change in stacking energy due to perturbations in position and orientation of the bases caused by the binding of ligands. The strain fields produced by the ligands decay with distance from the binding site. The interaction energy of two ligands decays exponentially with the distance between them and oscillates with the periodicity of the double helix in quantitative agreement with experimental measurements. The trend in the computed interaction energy is similar to that in the perturbation of groove width produced by the binding of a single ligand which is consistent with molecular simulations. Our analysis provides a new framework to understand allosteric interactions in DNA and can be extended to other rod-like macromolecules whose elasticity plays a role in biological functions. \nThe results from our model are in agreement with multiple experiments documented in the literature and they generate new falsifiable predictions that can be experimentally tested.
URL:https://seasevents.nmsdev7.com/event/meam-seminar-mechanical-models-for-dna/
LOCATION:Room 337\, Towne Building\, 220 South 33rd Street\, Philadelphia\, PA\, 19104\, United States
ORGANIZER;CN="Mechanical Engineering and Applied Mechanics":MAILTO:meam@seas.upenn.edu
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190814T100000
DTEND;TZID=America/New_York:20190814T120000
DTSTAMP:20260410T043540
CREATED:20190730T155059Z
LAST-MODIFIED:20190730T155059Z
UID:10006253-1565776800-1565784000@seasevents.nmsdev7.com
SUMMARY:MEAM Doctoral Dissertation Defense: "Additive Manufacturing and Mechanical Properties of Cellulose Nanofibril Materials"
DESCRIPTION:Cellulose nanofibrils (CNFs) are a nanomaterial derived from plants that have high specific stiffness and strength\, can be made into optically transparent materials\, and are biodegradable. These properties make CNFs an attractive building block for bulk structural materials. However\, CNFs are typically produced in aqueous suspension at low CNF weight fractions (<1 wt.%)\, which makes manufacturing bulk CNF materials challenging due to long processing times and the development of significant residual stresses during drying. As a result\, applications of CNFs in structural materials are currently limited to thin films and their use as low concentration reinforcement in composite materials. The objective of this dissertation is to overcome current limitations in building neat CNF materials by using additive manufacturing approaches to print films from aqueous CNF solutions with controlled fiber orientation and to build bulk structures with mm-scale thicknesses and enhanced mechanical properties. \nThis dissertation reports the use of two additive manufacturing techniques\, direct ink writing and laminated object manufacturing\, to fabricate neat CNF thin films with controlled orientation and materials with millimeter-scale dimensions\, respectively. The orientation of the CNFs in the printed films and the mechanical properties of the films and laminated CNF materials were experimentally characterized. Orientation in the printed CNF films was found to be controlled by the drying mechanics\, and a correlation between orientation and stiffness was observed. The multi-ply CNF films and laminated bulk beams with thicknesses of up to 0.6 mm were found to have comparable stiffness and strength and increased toughness compared to single-layer CNF films. Key contributions of this dissertation include the development of a printing process to decrease the time to fabricate CNF films\, a demonstration and a mechanics-based understanding of the control of fiber orientation in printed CNF materials\, and a new process to realize bulk neat CNF materials with increased thickness and enhanced toughness.
URL:https://seasevents.nmsdev7.com/event/meam-doctoral-dissertation-defense-additive-manufacturing-and-mechanical-properties-of-cellulose-nanofibril-materials/
LOCATION:Room 337\, Towne Building\, 220 South 33rd Street\, Philadelphia\, PA\, 19104\, United States
ORGANIZER;CN="Mechanical Engineering and Applied Mechanics":MAILTO:meam@seas.upenn.edu
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190815T103000
DTEND;TZID=America/New_York:20190815T120000
DTSTAMP:20260410T043540
CREATED:20190801T194536Z
LAST-MODIFIED:20190801T194536Z
UID:10006254-1565865000-1565870400@seasevents.nmsdev7.com
SUMMARY:MEAM Seminar: “Delivering Expressive and Personalized Fingertip Haptic Cues”
DESCRIPTION:The importance of meaningful tactile experiences has become increasingly apparent in areas such as teleoperation\, education\, and gaming. As the applications of rendering haptic stimuli are growing\, so are the requirements of haptic interfaces\, in that the intended audience is becoming more diverse and the intended interactions are becoming more complicated. For the past few decades there has been a consistent effort to improve the range and realism of haptic cues\, yet typical haptic rendering continues to be one-size-fits-all and low-dimensional. To render increasingly realistic haptic cues\, we must focus on both expressiveness and personalization. \nIn this talk I will present work towards delivering more expressive and personalized fingertip haptic cues from the perspective of both mechanical design and rendering approach. I will first present the Fuppeteer\, a parallel continuum manipulator that can move a flat surface around the fingertip with six degrees of freedom. This wearable device can provide combinations of normal and shear forces across the user’s entire fingertip\, regardless of finger shape and size. We have evaluated system performance through force measurements and through a human-subject study. This talk will also feature ongoing development of algorithms for delivering personalized sensed cues\, independent of the specific haptic device and remote sensor used. I will discuss both geometric and data-driven approaches\, and I will provide preliminary measurements of the rendering error generated by each method.
URL:https://seasevents.nmsdev7.com/event/meam-seminar-delivering-expressive-and-personalized-fingertip-haptic-cues/
LOCATION:Room 337\, Towne Building\, 220 South 33rd Street\, Philadelphia\, PA\, 19104\, United States
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190816T100000
DTEND;TZID=America/New_York:20190816T113000
DTSTAMP:20260410T043540
CREATED:20190529T133703Z
LAST-MODIFIED:20190529T133703Z
UID:10006228-1565949600-1565955000@seasevents.nmsdev7.com
SUMMARY:CBE Doctoral Dissertation Defense: "Utilization of MEMS Techniques for the Fabrication of Scalable Energy Storage Devices"
DESCRIPTION:Committee Members: Sue Ann Bidstrup Allen\, Advisor; Raymond Gorte\, John Vohs and Mark Allen.
URL:https://seasevents.nmsdev7.com/event/cbe-doctoral-dissertation-defense-utilization-of-mems-techniques-for-the-fabrication-of-scalable-energy-storage-devices/
LOCATION:Glandt Forum\, Singh Center for Nanotechnology\, 3205 Walnut Street\, Philadelphia\, PA\, 19104\, United States
CATEGORIES:Doctoral,Student,Dissertation or Thesis Defense
ORGANIZER;CN="Chemical and Biomolecular Engineering":MAILTO:cbemail@seas.upenn.edu
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20190816T100000
DTEND;TZID=America/New_York:20190816T120000
DTSTAMP:20260410T043540
CREATED:20190722T204450Z
LAST-MODIFIED:20190722T204450Z
UID:10006243-1565949600-1565956800@seasevents.nmsdev7.com
SUMMARY:CBE Doctoral Thesis Defense: "Utilization of Mems Techniques for the Fabrication of Scalable Energy Storage Devices"
DESCRIPTION:Committee: Sue Ann Bidstrup Allen\, Advisor; Raymond Gorte\, John Vohs and Mark Allen
URL:https://seasevents.nmsdev7.com/event/cbe-doctoral-thesis-defense-utilization-of-mems-techniques-for-the-fabrication-of-scalable-energy-storage-devices/
LOCATION:Glandt Forum\, Singh Center for Nanotechnology\, 3205 Walnut Street\, Philadelphia\, PA\, 19104\, United States
CATEGORIES:Doctoral,Student,Dissertation or Thesis Defense
ORGANIZER;CN="Chemical and Biomolecular Engineering":MAILTO:cbemail@seas.upenn.edu
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