Eric Sembrat's Test Bonanza

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

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.

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.

Hydrodynamics is the theory describing collective behaviors of fluids and gases. It has a very long history and is usually considered to belong to the realm of classical physics. In recent years, it has been found that, in many cases, hydrodynamics can manifest a purely quantum effect --- anomalies. We will see how this new appreciation of the interplay between quantum and classical physics has emerged, unexpectedly, through the idea of gauge/gravity duality, which originates in modern string theory. I will briefly mention the possible relevance of the new findings to the physics of the quark gluon plasma.

Striding bipedalism evolved over 230 million years ago in the ancestors of dinosaurs. Predatory dinosaurs (Theropoda) gave rise to tyrannosaurs and velociraptors, but also to birds, which survived the end-Cretaceous extinction. Fossilized skeletons and trackways offer unique, if static, evidence of ancient species. We seek to integrate data from living avians with the fossil record to understand theropods as living, moving organisms, as well as broader patterns of locomotor evolution along this lineage. I will first present a brief overview of X-ray Reconstruction of Moving Morphology, a 3-D method of skeletal motion analysis that we developed at Brown. I’ll then present animations, data, and questions from two studies using an XROMM approach. First, a six degree of freedom description of joint kinematics in guineafowl reveals a surprising amount of long-axis rotation at the hip and knee. Despite the limb’s superficially planar appearance, rotations about long bone axes are critical to maneuvering and steady locomotion in modern birds. When and why did this mechanism of 3-D limb control evolve? Second, we combine XROMM-based foot motion of birds walking through deformable substrates with Discrete Element Method (DEM) simulation to explore footprint formation. Modeling results from ‘virtual bedding planes’ show dramatic changes in track shape with depth, which could be easily misinterpreted if exposed as fossils. Linking DEM and XROMM techniques fosters a new perspective on the ‘birth’ of track morphology, the origin of footprint diversity, and inferences of trackmaker anatomy and behavior.

The concept of polariton is ubiquitous in the context of radiation-matter interaction. It refers to a generic quasi-particle resulting from the mixing of light with some kind of material excitation (e.g. a plasmon, phonon, or exciton). Cavity optomechanics offers an ideal system to study the coupling between trapped photons and the oscillations of a mechanical resonator. We can thus describe the coherent dynamics in terms of polaritonic excitations.

The role of dissipation mechanisms adds another layer of complexity to the problem. In particular, the photon and the mechanical phonon are coupled to reservoirs with different temperatures. This situation opens up the possibility to investigate thermodynamics at the quantum level as well as engineer heat engines at the nanoscale.

Coalescing binaries are among the most promising sources of gravitational waves for the advanced generation of ground based interferometers. Moreover they have been suggested as a possible progenitors of short gamma-ray bursts. The gravitational signal emitted in the late inspiral of such systems encodes the deformability properties of the neutron star, which depend on the behavior of matter in the stellar interior.

In this talk I will discuss how the detection of this signal can be used to extract information on the neutron star equation of state, and on the physics of the surrounding environment.

The history of drift-tube measurements of gaseous ion transport coefficients is reviewed, with an emphases on the contributions made by Dr. Gatland.  The use of experimental measurements of such coefficients in testing ion-neutral interaction potentials over wide ranges of internuclear separation is illustrated through recent tests of ab initio potentials.  Finally, the use of such data with recent theoretical advances is shown to have implications for ion-neutral reactions of importance in the ionosphere.

Entangled polymers have been thoroughly studied since the 1940s at least....or so we thought. In the last decade particle velocimetry and other imaging methods, combined with rheology, have shown that some dramatic instabilities can occur in strongly sheared well-entangled polymer melts. I will discuss how some of these new observations (such as various shear banding phenomena and `fracture') can be understood in terms of the 'Standard Model' for entangled polymers, and highlight some of the current controversies in the area.