Jan
31
Teaser:

The Fermi Large Area Telescope (LAT) has been successfully launched  from Cape Canaveral on 11 June 2008. It is exploring the gamma ray sky in the energy range from 20 MeV to over 300 GeV with unprecedeted sensitivity. One of the most exciting science questions that Fermi LAT will address is the nature of dark matter. Several theoretical models have been proposed that predict the existence of Weakly Interacting Massive Particles (WIMPs) that are excellent dark matter candidates. Fermi LAT investigates the existence of WIMPs indirectly, primarily...

Jan
28
Teaser:

It has recently become possible to compute precise equilibrium, traveling wave, and periodic orbit solutions to pipe and plane Couette flow at Reynolds numbers above the onset of turbulence. These invariant solutions capture the complex dynamics of unstable coherent structures in wall-bounded flows and provide a framework for understanding turbulent flows as dynamical systems. We present a number of weakly unstable equilibria, traveling waves, and periodic orbits of plane Couette flow and visualizations of their physical and state-space dynamics. What emerges is a picture of low-Reynolds turbulence as a walk among a set of weakly unstable invariant solutions...

Jan
26
Teaser:

Directed Migration of cells is vital to a wide array of biological processes: from the coordinated migration of cells during embryo development to the uncontrollable migration of a metastatic cancer.  We investigate directed cell migration in the model organism Dictyostelium aiming to understand the underlying biophysics of their motion, their direction, and the coordination among cell groups.   The problem of directed cell migration is often broken into three independent modules: a compass,...

Jan
25
Teaser:
The non-equilibrium current fluctuations, or shot noise, in ballistic graphene have received much attention since the seminal 2006 paper by Tworzydlo et al.  In that work, it was shown that shot noise can be generated even in a completely impurity-free sheet of graphene.  This result is surprising, as shot noise is expected to vanish in conductors without electron scattering.  The unexpected noise has been attributed to evanescent, that is, exponentially damped waves that backscatter electrons, even in clean graphene.  The predicted shot noise has been verified experimentally, but...
Jan
24
Teaser:

The cerebral cortex is a highly complex network comprised of billions of excitable nerve cells.  The coordinated dynamic interactions of these cells underlie our thoughts, memories, and sensory perceptions.  A healthy brain carefully regulates its neural excitability to optimize information processing and avoid brain disorders.  If excitability is too low, neural interactions are too weak and signals fail to propagate through the brain network.  On the other hand, high excitability can result in excessively strong interactions and, in some cases, epileptic seizures.  While it is commonly supposed that healthy neural excitability must...

Jan
21
Teaser:

12:15 in the M-Building, room 3201 A, for details see www.softmatter.gatech.edu/baglunch.html

Most industrial and biological materials exist, or are processed, in the form of multicomponent, microstructured fluids, and their ultimate function and use is dependent on the understanding of the optics,...

Dec
16
Teaser:

The discovery of neutrino oscillations has been one of the major advances in our understanding of particle physics in recent times, and we are still trying to fully understand them and the insights they may give to physics at very high energies and perhaps even into the matter-anti-matter asymmetry of the universe.  Long Baseline Neutrino Oscillation Experiments are becoming one of the main tools for the study of neutrinos.  The talk will briefly outline the history and physics of neutrino oscillations and long baseline experiments, and then discuss results from the current round of experiments - OPERA, MINOS, and now T2K.  I will then discuss...

Dec
09
Teaser:

Two dimensional turbulence is an idealization of real 3D systems with anisotropy caused by geometric confinement or body forcing.  I will review the current state of understanding of 2D turbulent flows including specific theoretical predictions, numerical simulation results and experimental realizations of quasi-2D turbulent systems.  Relevance to geophysical systems will be discussed.

Dec
08
Teaser:

In school, we learned that fluid flow becomes simple in two limits.  Over long lengthscales and at high speeds, inertia dominates and the motion can approach that of a perfect fluid with zero viscosity.  On short lengthscales and at slow speeds, viscous dissipation is important.  Fluid flows that correspond to the formation of a finite-time singularity in the continuum description involve both a vanishing characteristic lengthscale and a diverging velocity scale.  These flows can therefore evolve into final limits that defy expectations derived from properties of their initial states.  This talk focuses on 3 familiar processes that...

Dec
06
Teaser:

(Nonlinear Science Webinar)

Dynamical systems with multiple time scales have invariant geometric objects that organize the dynamics in phase space. The slow-fast structure of the dynamical system leads to phenomena such as canards, mixed-mode oscillations, and bifurcation delay. We'll discuss two projects involving chemical oscillators. The first is the analysis of a simple chemical model that exhibits complex oscillations. Its bifurcations are studied using a geometric reduction  of the system to a one-dimensional induced map. The second investigates the slow-fast mechanisms generating mixed-mode oscillations in a model of the Belousov-Zhabotinsky (BZ)...

Dec
01
Teaser:

Semiconductor nanowires synthesized in the bottom up approach have shown promising potential for a variety of applications in nanoelectronics, optoelectronics, biosensing and energy conversion. With the small length scale and a variety of material choices, nanowires also offer a versatile playground to explore mesoscopic and quantum physics. I will discuss our recent studies of magneto-transport phenomena in InAs and Bi2Se3 nanowires. In nanowires of InAs, a conventional low band-gap semiconductor, quantum interference and spin-orbit coupling lead to one-dimensional localization or anti-localization of electrons. For nanowires/ribbons of Bi2Se3, a 3D...

Nov
17
Teaser:

In the world of moderate Reynolds number, everyday turbulence of fluids flowing across planes and down pipes a velvet revolution is taking place. Experiments are almost as detailed as the numerical simulations, Numerical simulations are yielding exact numerical solutions that one dared not dream about a decade ago, and dynamical systems visualization of turbulent fluid's state space geometry is unexpectedly elegant.

We shall take you on a tour of this newly breached, hitherto inaccessible territory. Mastery of fluid mechanics is no prerequisite, and perhaps a hindrance: the talk is aimed at anyone who had ever wondered why - if no cloud is ever seen twice - we know a cloud when we...

Nov
10
Teaser:

Since the invention of the point contact transistor over 50 years ago, semiconductor technologies have become a ubiquitous mainstay of our Society.  Continued advancements in these technologies rely heavily on materials research spanning many areas including polymer and organic materials which play significant roles as sacrificial, passive and active layers in electronic and photonic devices.   The research outlined in this talk will identify fundamental materials parameters that will allow for the definition of materials architectures leading to sub-nanometer scale dimensional control of features for future semiconductor fabrication...

Nov
03
Teaser:

Graphene has been known for decades in many forms (exfoliated, epitaxial, isolated) and a number of its properties were measured or inferred from related materials, like graphite and carbon nanotubes. Yet, only recently was its potential as an electronic material recognized.  Epitaxial graphene on silicon carbide (EG) has played a pivotal role in this development: it was the first to be proposed as a platform for graphene-based electronics [1]; the first measurements on graphene monolayers were made on EG; and the graphene-electronic band structure was first measured on EG. The epitaxial graphene program, initiated in 2001 at the Georgia Institute...

Oct
27
Teaser:

Fluid membranes (vesicles) are area-preserving interfaces that resist bending. They are  models of cell membranes, intracellular organelles, and viral particles.  We are interested in developing simulation tools for dilute suspensions of deformable vesicles. These tools should be computationally efficient, that is, they should scale well as the number of vesicles increases.  For very low Reynolds numbers, as it is often the case in mesoscopic length scales, the Stokes approximation can be used for the background fluid.  We use a boundary integral...

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