Events Archive

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.
Oct
06
2010
"Neutron Stars: Cosmic laboratories for theoretical and computational physics" by Kostas Kokkotas
Neutron stars were discovered accidentally in 1967 although their existence was predicted 65 years earlier.  These exotic objects are the remnants from the deaths of massive stars, a death marked by one of the most spectacular pyrotechnic events in the cosmos, a supernovae explosion. Neutron stars have a solid crust overlying a sea of neutrons that can flow without friction (superfluidity). Their unique, yet not fully understood, internal structure, together with their immense gravitational field, makes them the perfect laboratory where the physics of the macro-cosmos meets microphysics phenomena. Explosive thermonuclear processes on neutron stars and their colossal...
May
26
2010
Strands of Superconductivity at the Nanoscale
Superconducting circuitry can now be fabricated at the nanoscale by depositing suitable materials on to single molecules, such as DNA or carbon nanotubes. I shall discuss various themes that arise when superconductivity is explored in this new regime, including the thermal passage over and quantum tunneling through barriers by the superconducting condensate, as well as the hormetic impact that magnetism can have on nanosuperconductivity. I shall also describe circuits that realize nanoscale superconducting quantum interference devices, exploring their sensitivity to magnetic fields and spatial patterns of supercurrent. These features hint at possible uses of nanoscale superconducting...
May
05
2010
Atomic and molecular strong-field physics at ultrafast x-ray sources
X-ray science is undergoing one of its greatest revolutions to date with the construction of intense x-ray free electron lasers in Stanford, USA (LCLS), Hamburg, Germany (XFEL), and Harima Science Garden City, Japan (SCSS). These are vast, several-hundred-million dollar machines that will provide x-ray pulses that are many million times brighter than current sources. Similarly groundbreaking are the emerging attosecond light sources based on intense, pulsed lasers; they are relatively inexpensive laboratory-size instruments. These two emerging radiation sources will enable radically new research and have unnumbered potential applications in materials science, chemistry, biology, AMO,...
Mar
25
2009
Twistor Theory, Then and Now
Twistor theory is now over 45 years old. In December 1963, I proposed the initial ideas of this scheme, based on complex-number geometry, which presents an alternative perspective to that of standard 4-dimensional space-time, for the basic arena in which (quantum) physics takes place. Over the succeeding years, there were numerous intriguing developments. But many of these were primarily mathematical, and there was little interest expressed by the physics community. Things changed rather dramatically, in December 2003, when E.Witten produced a 99-page article initiating the subject of “twistor-string theory” this providing a novel approach to high-energy scattering...
Mar
24
2009
Aeons Before the Big Bang?
There is much impressive observational evidence, mainly from the cosmic microwave background (CMB), for an enormously hot and dense early stage of the universe referred to as the Big Bang. Observations of the CMB are now very detailed, but this very detail presents new puzzles of various kinds, one of the most blatant being an apparent paradox in relation to the second law of thermodynamics. The hypothesis of inflationary cosmology has long been argued to explain away some of these puzzles, but it does not resolve some key issues, including that raised by the second law. In this talk, I describe a quite different proposal, which posits a succession of universe aeons prior to our...

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