Physics Colloquia Fall 2012

(usually Fridays 2:00 PM in SE 319)

Titles link to the abstracts.

Date Speaker Title
Sep 7
 Jonathan Engle
(FAU)
Sep 14
 Luc Wille
(FAU)
Sep 21
 Armin Fuchs
(FAU)
Oct 5
 Theodora Leventouri
(FAU)
Oct 12
 Konstantin Yakunin
(FAU)
Oct 19
 Sukanya Chakrabarti
(FAU)
Nov 2
 Sam Falkner
(FAU)
Nov 9
 Chris Beetle
(FAU)
Nov 16
 Wolfgang Tichy
(FAU)
   

Colloquium Abstracts

Spin-foams: Key classic results and recent developments.
Jonathan Engle (FAU), Sep 7
In general relativity, the space-time metric is not a fixed background structure, but is dynamical, acting on, and reacting to, matter. A quantum theory of gravity should thus be a quantum field theory in which there is no fixed background space-time metric, a so-called "background independent QFT". Such a QFT is necessarily very different in structure from all previously studied QFTs. In this colloquium, we discuss background independent QFT and the general boundary approach to quantum mechanics. A specific example of such a QFT is loop quantum gravity (LQG). The path integral formulation of LQG, spin-foams, has enabled a number of valuable calculations of the semiclassical limit of the theory, as well as making tantalizing connections with Regge calculus. We show how spin-foams can be used to calculate a "graviton propagator" for LQG, and we note how the resulting graviton propagator is consistent with both Newtonian gravity and linearized general relativity in appropriate approximations. We also discuss recent developments in analyzing the semiclassical limit of spin-foams more generally, which has led to a proposed correction of the dynamics.
 
Kuramoto meets Darwin: Synchronization in Evolving Populations
Luc T. Wille (FAU), Sep 14
Numerous systems in Nature consist of interacting oscillatory units each with its own natural frequency. It is well known that, depending on the spread of frequencies and the coupling strength, such ensembles may exhibit synchronized behavior. Huygens was the first to notice that two pendulum clocks back to back end up swinging in phase regardless of initial conditions. Ever since, synchronization has been observed in a great many situations, ranging from cardiac rhythms to flashing fireflies. The simplest model to describe such behavior is that due to Kuramoto: it consists of a phase oscillator and a sinusoidal coupling in the phase difference. In the mean-field limit this author showed a transition to a synchronized state as the coupling strength is increased. This model has been generalized in numerous ways including changes in dimensionality and interaction type. However, till now the question of how synchronizing systems evolve in Nature has not been addressed. Clearly, since the behavior is so ubiquitous there must be some evolutionary pressure that favors synchronizing units. This talk will report the results of Genetic Algorithm (GA) simulations of oscillator populations that are initially non-synchronizing but whose offspring evolves towards synchronizing behavior. Oscillators are ranked according to their ability to synchronize, with those that earn a higher ranking being able to pass on their genetic information to the next generation. This procedure is repeated for thousands of generations until the system settles on a steady state. It is found that both cross-over and point mutations need to be included in the GA to achieve rapid convergence. The approach towards a globally synchronous state may be classified through a series of reverse bifurcations. These findings may be experimentally testable. Parts of this work were performed in collaboration with Aaron M. Ganz.
 
Segmentation of alpha-EEG and its Application to Dual Brain Dynamics in Social Coordination
Armin Fuchs (FAU), Sep 21
Since the notion of "microstates" as sequences in spatiotemporal EEG signals was introduced by Lehman and colleagues in the seventies of the last century, a variety of procedures has been used to determine data segments where the underlying sources do not change during a certain time span. Even though some event related microstates have been identified (see http://www.scholarpedia.org/article/EEG_microstates for a brief review), their behavioral relevance remains an open question. Here we introduce a new approach for the segmentation of signals in the so-called alpha-band, i.e. EEG in the frequency range between 8 and 12Hz, based on the rotating wave approximation and the velocity of the slowly varying amplitude in a 60-dimensional space. This procedure is applied to EEG recordings where two subjects interact while the brain activity of both is measured simultaneously.
 
Physiological Apatites: From bulk to nano structures
Theodora Leventouri (FAU), Oct 5
An overview of our research on physiological multi- substituted Apatites will be presented.
 
Core-Collapse Supernova: from 2D to 3D.
Konstantin Yakunin (FAU), Oct 12
Core-collapse supernova simulations have made remarkable progress in the past decade. This progress is possible by made of more sophisticated numerical scheme for neutrino transport, improved microphysics, and the proper treatment of hydrodynamic instabilities. New features of the gravitational-wave signals were discovered, our understanding of supernova nucleosynthesis, origin of pulsar kicks and explosion asymmetries was significantly improved.This talk presents the results of four ongoing 2D models being performed by the ORNL-FAU collaboration as well as status of the developing 3D models.
 
Dark Matter, Dark Galaxies Continued
Sukanya Chakrabarti (FAU), Oct 19
Continuing work to characterize the darkest galaxies and the density profile of dark matter in spiral galaxies.
 
Multiple Scattering Theory
Samuel Faulkner (FAU), Nov 2
Multiple scattering theory has proved to be a very powerful technique for calculating the electronic states in condensed matter. The basic principles will be explained, as well as some recent applications.
 
Simulations of compact-object binaries
Wolfgang Tichy (FAU), Nov 16
In order to describe compact objects such as black holes or neutron stars one needs to consider full General Relativity. Since for the case of a binary systems no known analytical solutions exist, we turn to numerical relativity simulations to find answers. In this talk we describe how one can reformulate Einstein's original equations so that we can perform computer simulations. We also show some recent results about the inspiral and merger of both black holes and neutron stars. Of particular interest is the fact that such systems can produce gravitational waves that are strong enough to be observed in detectors such as LIGO.