Events Archive

Oct
31
2011
"Spintronics: Electrons, Spins, Computers and Telephones"
Albert Fert, Nobel Prize in Physics 2007 Joint colloquium between the School of Physics and MRSEC Spintronics exploits the influence of the electron spin orientation on electronic transport. It is mainly known for the “giant magnetoresistance” (GMR) and the large increase of the hard disc capacity obtained with read heads based on the GMR, but it has...
Oct
28
2011
Hybrid quantum computing
A quantum computer uses superposition states to accomplish tasks (e.g., database search and factoring of integers) more efficiently than any known classical computing strategy. In conventional registers for quantum information processing, quantum bits are associated with individual two-level quantum systems. Separate addressing and interaction with these systems permit one-bit gates, while an interaction between systems is neededto accomplish two-bit gates. The seminar will review recent theoretical proposals to implement quantum computing in collective excitation degrees of freedom in ensembles ofidentical quantum systems. In these proposals one does not address...
Oct
26
2011
"What are theory and experiment in climate research?"
Computational models of the Earth system lie at the heart of modern climate science. Concerns about their predictions have been illegitimately used to undercut the case that the climate is changing and this has put dynamical modelling in an awkward position. I will discuss ways that we, as a community, can contribute by highlighting some of the major outstanding questions that drive climate science, and I will outline their mathematical dimensions. I will put a particular focus on the issue of simultaneously handling the information coming from data and models, and argue that this balancing act will impact the way in...
Oct
25
2011
"Mechanics of Swimming Microorganisms"
At the small scale of a cell swimming in water, inertial effects are unimportant. Therefore, the motion of the fluid is governed by Stokes equations, which are linear. Nevertheless, there are many situations in which nonlinear effects are important. In this talk I will describe two such situations. The first is swimming in a viscoelastic material, which is motivated by the fact that many microorganisms move in non-Newtonian media such as mucus. I will present a simple model that shows how fading memory affects swimming speed. We will also present experimental results for a helix swimming in a viscoelastic fluid. The second situation I will consider is the...
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...

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