Events Archive

May
25
2011
5th Southeast Meeting on Soft Materials
This workshop brings together researchers with an interest in soft materials, fluids, and biophysics to discuss their work and explore partnerships. All participants may present a sound bite (a few minutes).  The day will include breakfast, lunch, and coffee. Registration is free, but required. Invited Speakers include M. Cristina Marchetti (Keynote Speaker, Syracuse University), Paul Goldbart (Georgia Tech), Juana Mendenhall (Morehouse College), Elisa Riedo (Georgia Tech), Susanne Ullrich (University of Georgia). Location: Georgia Tech, Marcus Nanotechnology Building, Room 1116Registration...
May
24
2011
"From Lattice QCD to Graphene and Ultracold Fermi Gases"
Obtaining a priori information on strongly interacting many-fermion systems remains a challenging problem in theoretical physics. A promising way forward is the use of Monte Carlo simulations, which are non-perturbative and take full account of quantum fluctuations. A famous example is Lattice QCD, which aims to elucidate the interactions between quarks and gluons at low energies, where QCD is strongly coupled. I will provide an updateon the application of such methods to closely related problems in condensed matter and atomic physics, highlighting modern computational and algorithmic developments. Specific examples include graphene and strongly coupled ultracold Fermi gases.
May
19
2011
"Discrete breathers and the anomalous decay of luminescence"
Some years ago an anomaly was noted in the decay of luminescence in certain doped alkali halides. The anomaly was eventually explained using a factor of a billion slowdown in lattice relaxation, a remarkable stretching of time scales. This slowdown was found to be caused by the creation of a ‘breather’ in the neighborhood of the dopant. Discrete breathers are nondispersive classical excitations that are known to be significant in many natural systems. In the talk I focus on the occurrence of breathers in doped alkali halides. Several more general properties of breathers have arisen from this study, among them is the quantum breather...
Apr
21
2011
"Coupled quantized harmonic oscillators" by Kenton Brown
In theory, quantum computers can solve certain problems much more efficiently than classical computers. This possibility has motivated experimental efforts to construct devices that manipulate quantum bits (qubits) in a variety of physical systems. One such system is composed of atomic ions confined by electric fields in a rf Paul trap. The motions of such ions can be modeled to a very good approximation as harmonic oscillators, and with suitable laser cooling techniques they can be cooled to the harmonic oscillator ground state. When trapped within the same potential minimum, ions interact strongly via the Coulomb force, thereby enabling multiple-qubit quantum gates that are...
Apr
20
2011
"Hydrodynamic Analogues of Quantum Systems" by John W.M. Bush
Yves Couder and coworkers have recently reported the results of a startling series of experiments in which droplets bouncing on a fluid surface exhibit wave-particle duality and, as a consequence, several dynamical features previously thought to be peculiar to the microscopic realm, including single-particle diffraction, interference, tunneling and quantized orbits. We explore this fluid system in light of the Madelung transformation, whereby Schrodinger's equation is recast in a hydrodynamic form. Doing so reveals a remarkable correspondence between bouncing droplets and subatomic particles, and provides rationale for the observed macroscopic quantum behaviour. New experiments are...
Apr
19
2011
"Thermal Conductivity, from Quark Matter to Cold Atoms" by Jingyi Chao
I briefly review the formation of color superconductivity which happens in compact stars. Below the temperature scale set by the gap in the quark spectrum, transport properties are determined by collective modes. We compute the thermal conductivity, $\kappa$, of color-flavor locked (CFL) quark matter in the frame of kinetics theory. We present and compare the result with previous estimates. We also conclude a CFL quark matter core ofthe compact star becomes isothermal on a timescale of a few seconds.  Moreover, we compute the thermal conductivity and sound attenuation length of a dilute Fermi gas, which help us comment on the possibility of extracting the shear viscosity of...
Apr
12
2011
"Relaxation of high-energy quasiparticles in a one-dimensional Bose liquid" by Prof. Michael Pustilnik
In this talk we will discuss a relaxation of high-energy quasiparticles in a weakly interacting one-dimensional Bose liquid. Unlike in higher dimensions, the rate is a nonmonotonic function of temperature. Moreover, it turns out that the inelastic scattering due to deviations from the integrability occurs at a much higher rate than three-body recombination processes, which is the main mechanism of losses in cold-atom-based realizations of 1D Bose liquids.
Apr
12
2011
"How Size and Strain Determine the Strength of Soft Materials" by Daniel Blair
Soft and biological materials often exhibit disordered and  heterogeneous microstructure. In most cases, the transmission and distribution of stresses through these complex materials reflects their inherent heterogeneity. We are developing a set of techniques that provide the ability to apply to quantify the connection between microstructure and local stresses.  We subject soft and biological materials to precise deformations while measuring real space information about the distribution and redistribution of stress. Using our custom confocal rheometer platform we can determine the role of shear stress in a variety...
Apr
12
2011
"Navier-Stokes solver using Green's functions" by Divakar Viswanath (Joint Physics & Math Seminar)
The incompressible Navier-Stokes equations provide an adequate physical model of a variety of physical phenomena. However, when the fluid speeds are not too low, the equations possess very complicated solutions making both mathematical theory and numerical work challenging. If time is discretized by treating the inertial term explicitly, each time step of the solver is a linear boundary value problem. We show how to solve this linear boundary value problem using Green's functions, assuming the channel and plane Couette geometries. The advantage of using Green's functions is that numerical derivatives are replaced by numerical integrals. However, the...
Apr
11
2011
"Towards optimal prediction of chaotic signals" by Divakar Viswanath
Abstract:  Suppose that x(t) is a signal generated by a chaotic system and that the signal has been recorded in the interval [0,T]. We ask: What is the largest value t_f such that the signal can be predicted in the interval (T,T+t_f] using the history of the signal and nothing more? We show that the answer to this question is contained in a major result of modern information theory proved by Wyner, Ziv, Ornstein, and Weiss. All current algorithms for predicting chaotic series assume that if a pattern of events in some interval in the past is similar to the pattern of events leading up to the present moment, the...

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