Events

## SMARTech Video Archive

Oct

07

In the framework of the Fitzhugh-Nagumo kinetics and the oscillatory recovery in excitable media, we present a new type of meandering of the spiral waves, which leads to spiral break up and spatiotemporal chaos. The tip of the spiral follows an outward spiral-like trajectory and the spiral core expands in time. This type of destabilization of simple rotation is attributed to the effects of curvature and the wave-fronts interactions in the case of oscillatory damped recovery to the rest state. This model offers a new route to and caricature for cardiac fibrillation, and when we apply the feedback resonant drift method, for defibrillation all wave activity gets eliminated at the...

Oct

05

Gamma-ray bursts have been detected at photon energies up to tens of GeV, and there are reasons to believe that the sources emit at least up to TeV energies, via leptonic or/and hadronic mechanisms. I review some recent developments in the GeV photon phenomenology in the light of Fermi observations, as well as recent related theoretical work. I discuss then the expected production of gravitational waves, the possibility of accelerating cosmic rays resulting in high energy neutrinos, and recent observational constraints.

Sep

29

We are going to present new results related to the dynamics and the associated instabilities of strong magnetic fields in neutron stars. The results are the first of their kind in general relativistic magneto-hydrodynamics (GR-MHD). We verify and extend earlier Newtonian results produced using either perturbation theory or Newtonian MHD codes. Finally, we will present estimations of the possibility that the giant flares observed in magnetars can be associated with significant emission of detectable gravitational waves.

Sep

28

"From Cardiac Cells to Genetic Regulatory Networks"

R. Grosu, G. Batt, F. Fenton, J. Glimm, C. Le Guernic, S.A. Smolka, and E. Bartocci

A fundamental question in the treatment of cardiac disorders, such as tachycardia and fibrillation, is under what circumstances does such a disorder arise? To answer to this question, we develop a multiaffine hybrid automaton (MHA) cardiac-cell model, and restate the original question as one of identication of the parameter ranges under which the MHA model accurately reproduces the disorder. The MHA model is obtained from the minimal cardiac model of Fenton by first bringing it into the form of a canonical, genetic regulatory...

Sep

28

Particle scattering processes at experiments such as the Large Hadron Collider at CERN are described by scattering amplitudes. In quantum field

theory classes, students learn to calculate amplitudes using Feynman diagram methods. This is a wonderful method for a process like electron +

positron -> muon^- + muon^+, but it is a highly challenging for a process like gluon+gluon -> 5 gluons, which requires 149 diagrams even at the leading order in perturbation theory. It turns out, however, that the result for such gluon scattering processes is remarkably simple, in some cases it is just a single term! This has lead to new methods for...

Sep

27

We study wetting and filling of patterned surfaces by a nematic liquid crystal. We focus on three important classes of periodic surfaces: saw-toothed, sinusoidal and stepwise, which have been considered in the literature as promising candidates to develop less-consuming zenithal bistable switches for practical applications. For saw-toothed substrates, geometry induces the nucleation of disclination lines on the wedges and apexes of the substrate, so the nematic surface free energy density develops an elastic contribution which scales as qlnq (with q being the wavenumber associated with the substrate periodicity). This leads to a large departure from...

Sep

21

Bose-Einstein condensates (BECs) have revolutionized atomic physics, a revolution which, sixteen years after their discovery, shows little sign of stopping. The attention of the quantum gases community has increasingly shifted from studies of broad features of the many-body condensed state to more specific realizations based upon control of spin state, trapping geometry, dimensionality and temporal behavior. In many regards quantum gases have no direct counterpart in condensed matter, although many parallels do exist, and these serve to guide efforts at the interface between disciplines....

Sep

12

As a student of numerical relativity who planned to work the rest of his life in academia, I had never envisioned the possibility of finding myself working in the commercial sector. The perception exists that opportunities to do novel research or to direct one's own career path are limited in industry, but I have found that this is largely not true. Rather, different constraints on your time and resources are imposed, with different challenges and rewards. In this talk, I will describe how I came to find myself leading the development of a cloud-scale information extraction and retrieval application for a customer within the Intelligence Community, share my experiences working with...

Sep

07

Measuring an event in time seems to require a shorter one. As a result, the development of a technique for measuring ultrashort laser pulses—the shortest events ever created—has been particularly difficult. We have, however, developed simple methods for fully characterizing these events, that is, for measuring a pulse's intensity and phase vs. time. One involves making an optical spectrogram of the pulse by using nonlinear optic. The mathematics involved is equivalent to the two-dimensional phase-retrieval problem—a problem that’s solvable because the Fundamental Theorem of Algebra fails for polynomials of two variables. We call...

Sep

01

We'll look at two novel experiments that are looking for ultrahigh energy neutrinos in the Antarctic ice. ANITA is a balloon-borne experiment which has twice flown over Antarctica making observations of ultrahigh energy cosmic rays and neutrinos. ARA is a new englacial project, under construction at the South Pole with similar goals. Both utilize the Askaryan Effect, coherent radio Cherenkov emission from particle cascades in matter, for neutrino detection.

Aug

29

Photons do not interact strongly in nature, and have thus been relegated to a role as a tool rather than an object of study in condensed matter physics.

However, in cavity quantum electrodynamics, the strong interaction of light with a single atom can lead to strong atom-mediated photon-photon

interactions, even when the light and atomic transitions are not resonant. Recent theoretical proposals have predicted phase transitions in arrays of

these cavities, demonstrating that complex matter-like phenomena can emerge from a sea of interacting photons.

I will present our recent measurements demonstrating strong photon-photon interactions in superconducting cavity QED...

Aug

24

As Goodyear discovered, when he first vulcanized rubber in 1839, a viscous liquid of macromolecules becomes an unusual, utterly random, solid, provided that enough chemical bonds are introduced between the molecules. Perhaps surprisingly, given the randomness of their architectures, solids formed by the vulcanization process exhibit a number of rather simple and universal features -- both structural and elastic -- that are not exhibited by the apparently simpler, crystalline solids. In this colloquium, I shall give an overview of current approaches to the physical properties of vulcanized matter and other random-network-forming media, paying special attention to...

Jun

23

Two important advances have occurred in recent years which have brought us closer to the goal of observing and interpreting gravitational waves from coalescing compact objects: the successful construction and operation of a world-wide network of ground-based gravitational-wave detectors and the impressive success of numerical relativity in successfully simulating the merger phase of Binary Black Hole (BBH) coalescence. The aim of the Numerical INjection Analysis (NINJA) project is to study the sensitivity of gravitational-wave analysis pipelines to numerical simulations of waveforms and foster close collaboration between numerical relativists and data analysts. NINJA-1 was a huge...

May

25

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 1116

Registration...