Events Archive

Oct
19
2011
"What Sets the Maximum Spin Rate of Neutron Stars"
Neutron stars are observed to rotate as fast as 716 Hz. Astrophysicists believe that they are spun-up by accretion of matter and angular momentum in binary star systems. However, the "r-mode" instability of rotating neutron stars, which is driven by gravitational radiation reaction, appears to prevent spin up via accretion to rotation frequencies above about 350 Hz.
Oct
13
2011
Annual CRA Distinguished Lecture: "The Data and Compute-Driven Transformation of Modern Science"
We all know that modern science is undergoing a profound transformation as it aims to tackle the complex problems of the 21st Century.  It isbecoming highly collaborative; problems as diverse as climate change, renewable energy, or the origin of gamma-ray bursts require understandingprocesses that no single group or community alone has the skills to address. At the same time, after centuries of little change, compute, data, and network environments have grown by 9-12 orders of magnitude in the last few decades.  Moreover, science is not only compute-intensive but is dominated now by data-intensive methods.  This dramatic change in the culture and methodology of...
Oct
07
2011
Spatiotemporal chaos due to spiral waves core expansion and its elimination in excitable media
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
2011
"Gamma Ray Bursts: the high energy photon emission, and implications for gravitational waves, cosmic rays and neutrinos" by Peter Meszaros
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
2011
Magnetar Dynamics and Gravitational Waves
  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
2011
"From Cardiac Cells to Genetic Regulatory Networks"
"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
2011
"New Exciting Approaches to Particle Scattering Amplitudes"
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
2011
"Complex fluids at complex surfaces: simply complicated?" by Prof. Jose Manuel Romero
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
2011
"Spinor Bose-Einstein condensates and Quantum Antiferromagnetism"
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
2011
From Colliding Black Holes To Data Mining in the Cloud, a perspective from Industry
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...

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