Eric Sembrat's Test Bonanza

For thousands of years people are using glass transition process and glasses in their everyday life. For hundreds of years researchers are studying the glass transition phenomenon. However, understanding the microscopic mechanism underlying the tremendous slowing down of structural relaxation remains one of the main challenges in the current condensed matter physics.

This talk will present an overview of intriguing puzzles of the glass transition phenomena and new ideas generated recently in this field. The mechanism of the steep temperature dependence of structural relaxation time or viscosity remains the central question of the glass transition. Although most of the researchers agree on importance of cooperativity/heterogeneity in dynamics of glass-forming systems, recent studies reveal no clear correlation of dynamic heterogeneity to the sharp slowing down of the structural relaxation.

The mechanism of decoupling of molecular diffusion from structural relaxation (viscosity) in glass-forming liquids, i.e. breakdown of classical Debye-Stokes-Einstein relationship, still has no clear explanation. A tight connection between molecular dynamics on picosecond time scale and structural relaxation on time scale of seconds and hours remains an intriguing puzzle and thus far found no reasonable explanation. We will discuss those and other important issues in the field and will formulate some general ideas describing mechanism of the glass transition.

The last part of the talk focuses on application of the ideas developed in the field of the glass transition to challenging problems in energy and bio technologies. In particular, we will discuss novel ideas for developing advanced polymer electrolytes for energy storage applications and a role of the glass transition in biology and in preservation of biological molecules and organisms.

The theoretical physicist Walter Kohn was awarded one-half the 1998 Nobel Prize for Chemistry for his mid-1960's creation of an approach to the many-particle problem in quantum mechanics called density functional theory (DFT). DFT establishes that the ground state charge density provides a complete description of ALL the properties of any atom, molecule, or solid. This was a breakthrough (both conceptually and computationally) because it had been presumed previously that the vastly more complicated many-electron wave function was essential for this purpose. In this talk, I present a biographical sketch of Kohn's unusual educational experiences and the events in his professional career which led him to create DFT. A coda explains how the chemists came to award "their" Nobel prize to a card-carrying physicist.

Contact Person: Della Phinisee, della@cc.gatech.edu

One of the deepest and most controversial questions of our time is that of the origin of life. In this lecture a hypothesis is presented, according to which the temperature gradients existing deep in the earth (which leads to plate tectonics and the formation of undersea thermal vents), also led to the origin and evolution of life around those vents. Movies and data will be shown of experiments in which various stages of this scenario are presented: how thermal gradients led to plate tectonics, to DNA possible amplification in the thermal vents, and to huge increase of molecular concentration in the early soup. In this scenario the Carnot cycle, at the origin of the first industrial revolution, might have also be relevant at the origin of life.

The syntax of theoretical physics and modern finance is deceptively similar, but the semantics is very different. I present a short introduction to the principles of modern finance, and compare and contrast the field to physics.

After a general introduction to the Lagrangian of QCD (Quantum Chromodynamics) and its symmetries, I will present the QCD Sum Rules approach for studying hadronic properties. This will be generalized to a finite temperature scenario, where we expect that phase transitions like deconfinement and/or chiral symmetry restorations should occur. In particular we will present our results for the rho meson spectrum, reconstructed from the dimuon spectrum in heavy ion collisions, and for charmonium resonances which could survive beyond the critical temperature. I will try to avoid technical details, emphasizing the physical and general aspects of our approach.

Note: This is a WEBINAR

The theory of Lagrangian Coherent Structures (LCSs) has advanced significantly over recent years, and now covers both hyperbolic and elliptic material surfaces in unsteady flow. Parabolic (i.e., jet-type) LCSs have, however, remained outside the reach of the theory, despite their significance in oceanic and atmospheric transport.

Here I discuss a new variational approach to general shearless transport barriers in two-dimensional unsteady flows, which covers both hyperbolic and parabolic LCSs. I also describe a computational implementation of this new theory, and show applications to model flows and geophysical data sets.

Intrinsically disordered proteins (IDPs), which form over a third of human proteins, challenge the structure-function paradigm because they function without ever folding into a unique three-dimensional structure. A particularly fascinating example of IDP function is the gating mechanism of the nuclear pore complex (NPC). The NPC is a large macromolecular structure that gates nanoscale pores in the nuclear envelope and controls all nucleo-cytoplasmic traffic such as the import of proteins from the cytoplasm and the export of RNA from the nucleus. The NPC forms a highly selective barrier composed of a large number of IDPs that fill the pore and potentially interact with each other and the cargo.

However, despite numerous studies, the actual structure of the complex within the nuclear pore and its mechanism of operation are poorly understood primarily because of the disordered nature of these proteins. I will present our “bottom-up” approach to understanding the higher-order architecture formed by these proteins using coarse-grained simulations and polymer brush theory. Our results indicate that different regions or “blocks” of an individual NPC protein can have distinctly different forms of disorder and properties and our bioinformatic analysis indicates that this appears to be a conserved feature across all of eukarya. Furthermore, this block structure at the individual protein level is critical to the formation of a unique higher-order polymer brush architecture. Our results indicate that there exist transitions between distinct brush morphologies, which can be triggered by the presence of cargo with specific surface properties which points to a novel form of gated transport in operation within the nuclear pore complex. Insights into this system can potentially be applied to the design of bio-mimetic filters that can achieve highly regulated transport across biological or in vitro membranes.

Bio:

Ajay Gopinathan is currently an Associate Professor and Chair of the Physics Graduate Group at UC Merced. He received his Ph.D in Physics in 2003, from the University of Chicago, working under the supervision of Tom Witten on various problems in soft condensed matter physics including crumpling, colloids and polymers. Following this, he was a joint postdoctoral fellow at UCLA and UCSB with Andrea Liu and Phil Pincus working on biopolymers with a focus on actin dynamics. His current research involves using theoretical and computational methods to understand biological transport at the molecular, cellular and multicellular scales. Examples include understanding cooperative behavior in molecular motor-driven intracellular transport; the role of membrane pore geometry and environment in gated transport through nuclear pores; actin based cellular motility; bacterial cell division and collective motility; optimal foraging in groups and swarming in the presence of behavioral heterogeneity and in disordered environments. Honors include the James S. McDonnell Foundation 21^st Century Science Initiative Award, the George E. Brown, Jr. award and the UC Merced Chancellor's award.

We utilize electroconvecting liquid crystal samples as a test bed from non-equilibrium driven systems. I will discuss results from the application of a novel mathematical analysis that incorporates time-delay embedding and diffusion maps to elucidate the underlying geometry in this system. This analysis permits the discrimination of different dynamical states from empirical data and is used to demonstrate multistability in this system. In addition we investigate the effects of an abrupt transition to defect turbulence on the structure and energy flow in this system.