Events Archive

Dec
09
2010
"2D turbulence - Where do we stand?" by Robert Ecke
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
2010
"Nearly perfect flows" by Wendy Zhang
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
2010
"Multiple Time Scale Dynamics in Chemical Oscillators" by Chris Scheper
(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
2010
"Condensed Matter Physics Opportunities in Semiconductor Nanowires from Bottom-up" by Xuan Gao
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
2010
"Turbulence: a stroll through 61,506 dimensions" by Predrag Cvitanovic
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
2010
"Advanced Polymeric Materials for Electronic Applications" by Elsa Reichmanis
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
2010
"Epitaxial Graphene: Designing a New Electronic Material" by Walt deHeer
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
2010
"Theoretical investigations of the rheology of fluid membranes" by George Biros
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...
Oct
20
2010
"Normal Modes and Density of States of Disordered Colloidal Solids" by Mohammad Islam
The normal modes and the density of states (DOS) of any material provide a basis for understanding its thermal and mechanical transport properties. In perfect crystals, normal modes take the form of planewaves, but they can be complex in disordered systems. I will show our recent experimental measurement of the normal modes, the DOS and dynamical structure factor (DSF) in disordered colloidal solids: disordered colloidal crystals composed of thermally sensitive micron‐sized hydrogel particles at several different particle volume fractions, φ. Particle positions are tracked over long times using optical microscopy and particle tracking algorithms in a single two dimensional (2D) [111]...
Oct
13
2010
Black holes in the centers of galaxies
The massive black holes found at the centers of most nearby galaxies, including our own, are believed to be the ashes of the fuel that powered quasars early in the history of the universe. I will review the observational evidence for these objects and describe some of the exotic dynamical phenomena that originate in their vicinity, including hypervelocity stars, resonant relaxation, phase transitions, and lopsided stellar disks.

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