Center for Soft Matter and Biological Physics Seminars

Spring 2018

Organizer: Vinh Nguyen

These meetings occur on Mondays from 4:00pm to 5:00pm in Robeson 304.
Refreshments are served before the semnars (unless otherwise indicated)

January 2018
January 15

Monday 4:00pm
304 Robeson Hall
(poster)

Martin Luther King Holiday. No Seminar Scheduled.

January 22

Monday 4:00pm
304 Robeson Hall
(poster)

Physics Faculty Search. No CSB Seminar Scheduled

January 29

Monday 4:00pm
304 Robeson Hall
(poster)

Physics Faculty Search. No CSB Seminar Scheduled.

February 2018
February 5

Monday 4:00pm
304 Robeson Hall
(poster)

Physics Faculty Search. No CSB Seminar Scheduled

February 12

Monday 4:00pm
304 Robeson Hall
(poster)

Physics Faculty Search. No CSB Seminar Scheduled.<./b>

February 19

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Dr. Michael Cooney ( NASA Langley Research Center )

MEDLI2, ARCSTONE and Broadband Photodetectors for measuring radiative flux

Dr. Michael Cooney engineer in the Electronic Systems Branch, will discuss three projects he currently supports. The first is a space flight project, the Mars Entry Descent and Landing Instrumentation 2 (MEDLI2). MEDLI2 will extend and enhance the dataset from the MEDLI mission, which flew on the Mars Science Laboratory (MSL) in 2012 and was the first instrument to characterize Mars’ aero-thermal environment. MEDLI2 is scheduled to fly on the MARS 2020 mission. The second project is ARCSTONE, a lunar spectral reflectance instrument in response to the 2007 and 2017 Earth Science Decadal Surveys. Instrument intercalibration is a vital tool to maintain consistent datasets across various instruments and ensure historical continuity. The Moon is considered to be an excellent exoatmospheric calibration source, however the accuracy of the Moon as an absolute reference is limited to 5-10%. An orbiting spectrometer flying on a small satellite in low Earth orbit will provide lunar spectral reflectance with accuracy sufficient to establish an SI-traceable absolute lunar calibration standard for past, current, and future Earth weather and climate sensors. The final project is a research activity in partnership with Virginia Tech to develop broadband photodetectors for measuring radiative flux in response to the Earth Science Decadal survey. Existing Earth science radiation budget instruments rely on radiometers with relatively difficult custom manufacturing processes and slow readout speed. To provide a lower cost future mission options, photon based photosensors have the possibility to lower mission cost while enabling new mission architectures.

Host: Vinh Nguyen

February 19

Monday 5:00pm
304 Robeson Hall
Special Seminar
(poster)

Dr. Michael Cooney ( NASA Langley Research Center )

Job/Internship Possibilities at NASA Langley

Host: Vinh Nguyen

February 26

Monday 4:00pm
304 Robeson Hall
CM Seminar Only
(poster)

Prof. Sumanta Tewari (Clemson University)

"TBD"

Host: Ed Barnes

March 2018
March 5

Monday 4:00pm
304 Robeson Hall
(poster)

Spring Break Week and APS March Meeting. No Seminar Scheduled.

March 12

Monday 4:00pm
"Canceled and Rescheduled"
Joint CM Seminar
(poster)

Weigang Liu (Department of Physics, Virginia Tech)

"A study of the complex Ginzburg-Landau equation: analytical and numerical results"

Rescheduled for March 14, 2018

Host: Uwe Tauber

March 14

Wednesday 4:00pm
400 Hahn Hall, North
Joint CM Seminar
(poster)

Weigang Liu (Department of Physics, Virginia Tech)

"A study of the complex Ginzburg-Landau equation: analytical and numerical results"

The complex Ginzburg-Landau equation (CGLe) is a stochastic partial differential equation that describes a remarkably wide range of physical systems: coupled non-linear oscillators subject to external noise near a Hopf bifurcation instability; spontaneous structure formation in non-equilibrium systems, e.g., in cyclically competing populations; and driven-dissipative Bose-Einstein condensation, realized in open systems on the interface of quantum optics and many-body physics. We employ the perturbative field-theoretic renormalization group method to analytically investigate the universal critical behavior near the continuous non-equilibrium phase transition in the complex Ginzburg–Landau equation with additive white noise. We show that to first order in the dimensional expansion about the upper critical dimension, the initial-slip exponent in the complex Ginzburg–Landau equation is identical to its equilibrium model A counterpart. In our second project, we have employed a finite-difference method to numerically solve the noisy complex Ginzburg-Landau equation on a two-dimensional domain with the goal to investigate the coarsening dynamics following a quench from a strongly fluctuating defect turbulence regime to a long-range ordered phase. We study the spatio-temporal behavior characterized by the spontaneous creation and annihilation of topological defects (spiral waves). We check our simulation results against the known dynamical phase diagram in this non-equilibrium system, tentatively analyze the coarsening kinetics following sudden quenches between different phases, and have begun to characterize the ensuing aging scaling behavior. Moreover, we are currently extracting the activation energy barrier for the nucleation process of the stable spiral wave structures.

Host: Uwe Tauber

March 19

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Chengyuan Wen (Department of Physics, Virginia Tech)

"Evaporation of Liquids and Solutions"

Evaporation of a liquid is a ubiquitous phenomenon. It drives the water cycle and can be used for cooling. It is also a useful tool for materials fabrication such as evaporation-induced self-assembly of colloidal particles and thin-film deposition via spin coating. In the first part of this talk, we will present million-atom scale molecular dynamics (MD) simulations of the evaporation process of water. An enhancement of water density near the liquid-vapor interface is found during fast evaporation. The temperature profiles based on both translational and rotational degrees of freedom are calculated at different stages of evaporation and evaporative cooling of the liquid-vapor interface is observed, which accounts for the higher water density at the interface. The velocity distribution of water molecules in the vapor phase during evaporation is also computed at various distances relative to the interface and fit to the Maxwell-Boltzmann distribution. Results indicate that local thermal equilibrium holds in the liquid phase, though the whole system is driven out of equilibrium. In the second part of this talk, we will focus on evaporating behavior of polymer solutions. In particular, polyelectrolyte solutions show rich physical behavior because of electrostatic interactions. We use MD simulations to study the evaporation of a solution of polyanionic chains (sodium polystyrene sulfonate). The polymers are represented by MARTINI-type bead-spring chains. Water is included as an explicit solvent and described with a model taking into account polarization effects. Counterions and salts are also explicitly included as mobile single beads. Our results show that the polyelectrolyte chains form layered structures with alternating polymer-rich and counterion-rich layers, indicating that one-pot evaporation technique may be developed to fabricate multilayer polyelectrolyte films that are currently mainly produced via a layer-by-layer deposition process. We will discuss the effects of polymer concentration, salt concentration, and evaporation rate on the structure of the resulting film. Finally, we will also briefly discuss our recent study of the evaporation of polymer solutions containing both polyanionic and polycationic chains.

Host: Shengfeng Cheng

March 26

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Xiangwen Wang (Department of Physics, Virginia Tech)

"Data-driven modeling of heavy-tailed distributions and scaling laws in human dynamics"

Studying human behavior is of fundamental importance in many social applications. Yet, it remains a challenging problem due to the high complexity of human activities. In recent years, advances in information technology have resulted in the collection of vast amounts of human activity logs, thus enabling the quantitative modeling of human behavior. Using a variety of metrics like probability distributions, we prove the wide existence of heavy-tailed distributions and scaling laws in human behavior. In human online searches we describe the search behavior as a foraging process that takes place on the semi-infinite line. A pairwise power-law distribution respectively exponential distribution is reported for step-lengths in long-range respectively short-range displacements, indicating that the search process is a combination of Brownian-motion local phases and truncated-Levy-flight relocation phases. These results are confirmed through the analysis of mean squared displacements. In human online gambling, we view the net change of income of each player as a random walk and find that the win/loss distributions follow power laws with exponential cut-offs. The mean squared displacement of these net income random walks exhibits a transition between a super-diffusive and a diffusive regime. We present a model that allows to reproduce this behavior and identify the key features needed for observing this transition. For human movements in both real and virtual spaces, heavy-tailed step-lengths are also reported.

Host: Michel Pleimling

April 2018
April 2

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Ali Charkhesht (Department of Physcis, Virginia Tech)

"Probing collective motions and hydration dynamics of bio-molecules"

Studying dynamics of proteins in their biological milieu such as water is interesting because of their strong absorption in the terahertz range that contain information on their global and sub-global collective vibrational modes (conformational dynamics) and global dynamical correlations among solvent water molecules and proteins. In addition, water molecules dynamics within protein solvation layers play a major role in enzyme activity. However, due to the strong absorption of water in the gigahertz-to-terahertz frequencies, it is challenging to study properties of the solvent dynamics as well as conformational changes protein in water. In response, we have developed a highly sensitive megahertz-to-terahertz dielectric spectroscopy system to probe the hydration shells as well as large-scale dynamics of these biomolecules. . Thereby, we have deduced the conformation flexibility of proteins and compare the hydration dynamics around proteins to understand the effects of surface-mediated solvent dynamics, relationships among different measures of interfacial solvent dynamics, and protein-mediated solvent dynamics based on the complex dielectric response from 50 MHz up to 2 THz by using the system we developed. Comparing these assets of various proteins in different classes helps us shed light on the macromolecular dynamics in a biologically relevant water environment.

Host: Vinh Nguyen

April 6

"Special Seminar"
Friday, 2:30pm
210 Robeson Hall
Colloquium
(poster)

Prof. Jeff Chen (Department of Physics & Astronomy, University of Waterloo)

"The Onsager model for liquid crystals "

The Onsager model in liquid crystal theory holds the status of the Ising model for phase transitions. They both take a different view from the phenomenological Landau-de Gennes model [liquid crystals] and Landau model [phase transitions] by relating the microscopic properties to the physical world. Identifiable molecular parameters are used in the Onsager model, allowing direct interpretation of experiments and computer simulation results. While the original model was proposed 70 years ago to deal with the bulk isotropic-nematic transition, adding geometric frustrations gives the model a new life. In this talk, the solutions of the model for a number of confined systems of current interest, which display topological defects due to the frustrations between geometry and the nematic ordering field, are presented.

Host: Shengfeng Cheng

April 9

Monday 4:00pm
304 Robeson Hall

(poster)

Mengsu Chen

Exploring quantum many-body systems via lattice model and exact diagonalization

The quantum many-body problem of solving Schrodinger equation of a large number of interacting microscopic particles is generally considered impossible to tackle analytically. Numerical simulations becomes the essential tools to study these systems, especially at the strongly correlated regime. We used exact diagonalization (ED), the only unbiased numeric method, to study the newly proposed interaction-induced states such as fractional Chern insulators (FCI), topological Mott insulators (TMI), emergent kinetics on various quantum lattice model describing many physic systems including 2D materials and optical lattices. We study quantum phase transitions between different parameter regimes of Hamiltonian, and exotic properties such as fractional charges, spontaneous time-reversal symmetry breaking in these phases.

Host: Vito Scarola

April 16

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Professor Mark Dykman ( Physics, Michigan State University)

"Time-translation symmetry breaking in vibrational Floquet systems"

A periodically driven system has discrete time-translation symmetry with the period of the driving. Its quantum dynamics is described in terms of the Floquet states. Generally, if the system is in a Floquet state, its dynamical variables oscillate with the period of the driving. Recently much interest have attracted systems where the time symmetry is broken, the “time crystal” effect. Nonlinear oscillators, including Nano mechanical systems and modes in electromagnetic cavities, provide an ideal platform for studying this effect. We will show how the symmetry breaking occurs in an individual oscillator in the quantum coherent regime. We will then discuss the classical and quantum phase transitions to the broken-symmetry state in systems of coupled oscillators.

Host: Uwe Tauber

April 23

Monday 4:00pm
304 Robeson Hall
CM Seminar Only
(poster)

Sriram Ganeshan (Stony Brook, New York)

"Odd Surface waves in two-dimensional in-compressible fluids"

In everyday fluids, the viscosity is the measure of resistance to the fluid flow and has a dissipative character. Avron, Seiler, and Zograf showed that viscosity of a quantum Hall (QH) fluid at zero temperature is non-dissipative. This non-dissipative viscosity (also known as ‘odd’ or ‘Hall’ viscosity) is the antisymmetric component of the total viscosity tensor and can be non-zero for parity violating fluids. I will discuss free surface dynamics of a two-dimensional incompressible fluid with the odd viscosity (not quite quantum Hall hydro). For the case of incompressible fluids, the odd viscosity manifests itself through the free surface (no stress) boundary conditions. We first find the free surface wave solutions of hydrodynamics in the linear approximation and study the dispersion of such waves. As expected, the surface waves are chiral.  In the limit of vanishing shear viscosity and gravity, we derive effective nonlinear Hamiltonian equations for the surface dynamics, generalizing the linear solutions to the weakly nonlinear case.  In a small surface angle approximation, the equation of motion results in a new class of non-linear chiral dynamics which we dub as chiral Burgers equation. I will briefly discuss how this program can be extended to the free surface of quantum Hall hydrodynamics.


Host: Ed Barnes

April 27

"Special Seminar"
Friday, 2:30pm
210 Robeson Hall
Colloquium
(poster)

Prof. Timothy Halpin-Healy (Department of Physics, Columbia University)

"Within & Beyond the Realm of KPZ "

We discuss significant events in the recent Renaissance triggered by the enigmatic and elusive, but reach stochastic nonlinear PDE of Kardar, Parisi & Zhang, * a celebrated equation whose reach far exceeds its grasp, touching such diverse phenomena as non-equilibrium stochastic growth, optimal paths in ill-condensed matter, the dynamics of driven lattice gases, as well as the extremal statistics of random matrix eigenvalues. *J. Stat. Phys. 160, 794 (2015).

Host: Uwe Tauber

April 30

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Prof. Juan Vanegas (University of Vermont)

"Mechanics at the nanoscale: Local stress calculations in Biomolecular systems"

The microscopic or local stress field provides a unique connection between molecular simulations and mechanics of materials at the nanoscale. Lateral stress profiles are routinely used to understand the mechanical behavior of liquid interfaces such as lipid membranes from molecular dynamics (MD) simulations. However, the 1-dimensional stress profiles are not adequate to understand the multidimensional mechanical state in complex asymmetrical systems such as membrane proteins or other macromolecular structures. Furthermore, the fact that the microscopic stress from MD simulations is not uniquely defined is a theoretical consideration that is most often ignored, which has acute practical consequences when atomistic models are considered. I will present our recent work on the development of objective 3D local stress calculations by way of expressions that satisfy balance of linear and angular momentum for force-fields with arbitrarily high many-body interactions. I will show how some definitions of the microscopic stress violate mechanical equilibrium through various examples including defective graphene, lipid membranes, and fibrous proteins. I will also demonstrate the use of the traction vector, computed from the microscopic stress, as a powerful tool to visualize the local balance of forces at an interface. Focusing on the bacterial mechanosensitive channel MscL, I will show how the traction vector allows identification of a unique association pattern of lipids at specific sites on the MscL surface that may mediate gating of the bacterial channel by membrane tension or other stimuli.


Host: Shengfeng Cheng

May 2018
May 7

Monday 4:00pm
304 Robeson Hall
(poster)

Final Exam Week. No Seminar Scheduled.

Center for Soft Matter and Biological Physics Seminars

Fall 2018

Organizer: Vinh Nguyen

These meetings occur on Mondays from 4:00pm to 5:00pm in Robeson 304.
Refreshments are served before the semnars (unless otherwise indicated)

August 2018
August 20

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Prof. Surita Bhatia (Stony Brook University, NY)

"TBD"

Host: Shengfeng Cheng

August 27

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

September 2018
September 3

Monday 4:00pm
304 Robeson Hall
(poster)

Labor Day "No CSB Seminar Scheduled"

Host:

September 10

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

September 17

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

September 24

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

October 2018
October 1

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

October 8

Monday 4:00pm
304 Robeson Hall

(poster)

Prof. David M. Leitner (University of Nevada, Reno )

"TBD"

Host:Vinh Nguyen

October 15

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

October 22

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

October 29

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

November 2018
November 5

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

November 12

Monday 4:00pm
304 Robeson Hall

(poster)

Shadi Esmaeili (Physics, Virginia Tech)

Host: Vinh Nguyen

November 19

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

November 26

Monday 4:00pm
304 Robeson Hall

(poster)

Shannon Serrao (Physics, Virginia Tech)


Host:

December 2018
December 3

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

December 10

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

December 17

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

Center for Soft Matter and Biological Physics Seminars

Spring 2019

Organizer: Vinh Nguyen

These meetings occur on Mondays from 4:00pm to 5:00pm in Robeson 304.
Refreshments are served before the semnars (unless otherwise indicated)

January 2019
January 21

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

"Martin Luther King holiday (No Classes-University Offices Closed)

Host:

January 28

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

February 2019
February 4

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

February 11

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

February 18

Monday 4:00pm
304 Robeson Hall

(poster)

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February 25

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

March 2019
March 1

Friday 2:30pm

Special Seminar

210 Robeson Hall
(poster)

Prof. Maikel Rheinstadter (McMaster University)

Host: Rana Ashkar

March 4

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

March 11

Monday 4:00pm
304 Robeson Hall

(poster)


Host:

March 18

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

March 22

Friday 2:30pm

Special Seminar

210 Robeson Hall
(poster)

Prof. Matt Helgeson (UC Santa Barbara)

Host: Rana Ashkar

March 25

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

April 2019
April 1

Monday 4:00pm
304 Robeson Hall

(poster)

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April 8

Monday 4:00pm
304 Robeson Hall

(poster)

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April 15

Monday 4:00pm
304 Robeson Hall

(poster)

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April 22

Monday 4:00pm
304 Robeson Hall

(poster)


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April 29

Monday 4:00pm
304 Robeson Hall

(poster)


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May 2019

May 6
Monday 4:00pm
304 Robeson Hall
(poster)

Host:

May 13

Monday 4:00pm
304 Robeson Hall
(poster)

Exam Week No Seminar

Host: