2020 Discussion Meetings

Prof. William Ducker (Chemical Engineering, Virginia Tech)

"A Surface Coating that Inactivates SARS-CoV-2"

Host: Vinh Nguyen

No CSB Meeting

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No CSB Meeting

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Tiffany Roach (Biological Science, Virginia Tech)

"Adaptor Functions of TOM1 in Health and Disease"

Host: Vinh Nguyen

Prof. Sohan Kale Mechanical Engineering, Virginia Tech)

" From Active-gel Theory of Actomyosin Cortex to Dynamic Vertex Models of Epithelial Mechanics"

Epithelial tissues are cohesive cellular sheets of adherent cells that line organs surfaces and cavities in our bodies. These bio-interfaces act as physical barriers against pathogens, regulate chemical transport, and compartmentalize our bodies into different functional units. Epithelial sheets maintain their mechanical integrity under dynamic conditions with mechanical loading of varied magnitudes and at wide range of loading rates. Moreover, various morphogenetic modules have revealed that epithelia can be shaped into functional 3D structures under the action of active internal and passive external forces. At intermediate timescales of seconds to minutes, epithelial mechanics is governed by the architecture and dynamics of cytology-skeletal structures, especially by the active-viscoelastic rheology of the actomyosin cortex. Even in this seemingly simple regime with frozen junction-al network, a rich phenomenology of epithelial behaviors governed by cortical dynamics has been recently discovered. Yet, a connection between cortical rheology and theoretical tissue-scale models of epithelia has been lacking. For instance, in vertex models of epithelial, phenomenological work functions governing the vertex dynamics are used that often lack a direct connection to the dynamic sub-cellular processes. We address this gap through a formulation based on Onsager's variation-al principle which allows us to coarse-grain active-gel models of the actomyosin cortex to tissue-scale vertex models. The tissue-scale rheology naturally emerges from the coupling between cell shapes and activity, visco elasticity, and turnover of the cortex. This modeling approach provides a unifying framework to capture epithelial phenomenology at different loading rates, including 'reinforcement' and 'fluidization' responses following sudden stretch and un-stretch, solid and complex-fluid creep responses, transient flattening and stable folding of compression-induced folds in suspended epithelial sheets, pulsatile cellular oscillations, and active-super-elasticity. While encapsulating these epithelial phenomenology, the formulation also provides a common sub-cellular origin for seemingly disconnected tissue-scale behaviors. Bio: Dr. Sohan Kale is an Assistant Professor in the Department of Mechanical Engineering at Virginia Tech. The overarching theme of the research in his ‘Mechanics of Living Materials Lab’ is to develop robust and high-fidelity models for complex bio-chemo-mechanical cellular and multicellular behaviors relevant in physiology, pathological conditions, and bio-engineering applications. The research employs diverse set of topics and techniques from computational mechanics, soft matter, non-equilibrium processes, inverse problems, and homogenization. Dr. Kale received his MS and PhD in Mechanical Engineering from University of Illinois at Urbana-Champaign in 2017. Following that, he was a postdoctoral scholar at UPC-Barcelona in the Mathematical and Computational Modeling (Lacan) group. He is a recipient of the Outstanding Dissertation Award from the Mechanical Engineering department and Mavis Future Faculty Fellow award from the college of engineering at UIUC.

Host: Vinh Nguyen

Prof. Michel Pleimling (Physics, Virginia Tech)

"Dynamic Phase Transitions in the Ising Ferromagnet: Bulk and Surface Phase Diagrams"

An interesting type of non-equilibrium criticality is encountered when kinetic ferromagnets are subjected to a periodically oscillating magnetic field. When increasing the frequency of the field, a phase transition takes place between a dynamically disordered phase at low frequencies, where the ferromagnet is able to follow the changes of the field, and a dynamically ordered phase at high frequencies, where the magnetic system does not have time to adjust to the magnetic field before it changes its orientation. In this talk I discuss the bulk and surface properties of this dynamic phase transition. For bulk systems this non-equilibrium phase transition belongs to the universality class of the equilibrium three-dimensional Ising model. We find, however, that the non-equilibrium surface exponents do not coincide with those of the equilibrium critical surface. Whereas the resulting non-equilibrium surface phase diagram strongly resembles the corresponding equilibrium phase diagram, with an ordinary transition, an extraordinary transition and a surface transition, for weak surface couplings the non-equilibrium surface does not order. These results indicate that our understanding of the role played by surfaces in non-equilibrium systems, and more specifically at non-equilibrium phase transitions, is far from being complete.

Host: Vinh Nguyen

Fall Semester Exams (No CSB Meeting)

Host: Vinh Nguyen

University & Graduate Commencement Ceremonies
No CSB Meeting

Holiday (No Classes)

Prof. Uwe Tauber (Physics, Virginia Tech)

"Introduction to Critical Phenomena and the Renormalization Group, Part 1"

Host: Vinh Nguyen

Prof. Uwe Tauber (Physics, Virginia Tech)

"Introduction to Critical Phenomena and the Renormalization Group, Part 2"

Host: Vinh Nguyen

Prof. Uwe Tauber (Physics, Virginia Tech)

"Introduction to Critical Phenomena and the Renormalization Group, Part 3"

Host: Vinh Nguyen

Shengfeng Cheng (Physics, Virginia Tech)

"A Coupled two-species model for the pair contract process with diffusion"

Host: Vinh Nguyen

Ruslan Mukhamadiarov (Physics, Virginia Tech)

"Temperature Interfaces in the Katz-Lebowitz Spohn Driven Lattic Gas"

Host: Vinh Nguyen

Binghan Liu (Physics, Virginia Tech)

"Molecular Dynamics Modeling of Liquid-Liquid Mixtures"

Host: Vinh Nguyen

Priyanka (Physics, Virginia Tech)

"Effect of Control on One Dimensional Surface Growth Processes"

Host: Vinh Nguyen

Prof. Vinh Nguyen (Physics, Virginia Tech)

"Monte Carloray-trace diffraction method for studying Fresnel zone plate lens andphoton-sieve"

Host: Vinh Nguyen

Chengyuan Wen (Physics, Virginia Tech)

Molecular Dynamics Simulations of DNA

Host: Vinh Nguyen

No Discussion Meeting (Physics Faculty Meeting)

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No Discussion Meeting (Physics Faculty Meeting)

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Dr. Abhishek Singh (Physics, Virginia Tech)

"Insights into Hydration Dynamics at Sub-picosecond Timescales"

The liquid state of water is a very complex system due to hydrogen bonding characteristics. Water forms a transient tetrahedral network with neighboring molecules with a life time of the order of picoseconds. The presence of biomolecules in water matrix distorts the H-bond network and makes the water dynamics slower as a results of hydrogen bonding between biomolecule and water. The electrostatic field exerted by a biomolecules gradually weakens as a function of intermolecular distance between biomolecule and water. This results in hydration layers at the surface of a biomolecule, with hydration water molecules having distinct temporal characteristics. I will talk about some of our recent results on the aqueous solutions of DNA, studied employing an extended megahertz-terahertz frequency domain spectroscopy. Based on the spatio-temporal behavior, water molecules in the aqueous DNA solutions can be classified as tightly-, loosely bound, and bulk water. I will further discuss effective medium approximation at terahertz frequencies for such systems.

Host: Vinh Nguyen

No Discussion Meeting

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No Discussion Meeting (Tenure Track Physics Faculty Meeting)

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No Discussion Meeting (Physics Faculty Meeting)

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No Discussion Meeting (Due to COVID-19)

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No Discussion Meeting (Due to COVID-19)

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"Exam Day" (No Meeting)

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"University Commencement "(No Meeting)