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This Week at Physics

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Events During the Week of April 15th through April 22nd, 2012

Monday, April 16th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
Kinetic Turbulence in Space and Astrophysical Plasmas: Theoretical, Numerical, and Experimental Investigations
Time: 12:05 pm
Place: 2535 Engineering Hall
Speaker: Prof. Greg Howes, University of Iowa
Abstract: In many turbulent space and astrophysical plasma environments, the
dissipation of the turbulence, and consequent conversion of turbulent
fluctuation energy to plasma heat, occurs at scales on which the plasma
dynamics is collisionless. Direct access to the near Earth solar wind provides a
unique opportunity to confront our understanding of the dynamics of kinetic
plasma turbulence, and its dissipation via collisionless damping mechanisms,
with in situ spacecraft measurements. Significant effort has recently been
focused on employing the gyrokinetic formalism to study the dissipation of
turbulence in the solar wind, taking advantage of sophisticated numerical
techniques developed for use in the fusion community. Here I will report on
some of the most recent successes of this effort, in particular the first threedimensional,
nonlinear gyrokinetic simulation of plasma turbulence resolving
scales from the ion to electron gyroradius with a realistic mass ratio, where all
damping is provided by resolved physical mechanisms. Complementing this
theoretical and numerical research program are experiments on the Large
Plasma Device (LAPD) at UCLA to measure the nonlinear interactions between
counterpropagating Alfven waves, the fundamental building block of Alfvenic
plasma turbulence.
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Condensed Matter Theory Group Seminar
Multiparticle Quantum Walks and the Graph Isomorphism Problem
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Kenny Rudinger, UW-Madison
Abstract: We investigate the quantum dynamics of particles on graphs ("quantum walk"), with the aim of developing quantum algorithms for determining whether or not two graphs are isomorphic. We investigate such walks on strongly regular graphs (SRGs), a class of graphs with high symmetry. We explore the effects of particle number and interaction range on a walk's ability to distinguish non-isomorphic graphs. We numerically find that both non-interacting three-boson and three-fermion continuous time walks have the same distinguishing power on a dataset of 70,712 pairs of SRGs, each distinguishing over 99.6% of the pairs. We also find that increasing to four non-interacting particles further increases distinguishing power on this dataset. While increasing particle number increases distinguishing power, we prove that any walk of a fixed number of non-interacting particles cannot distinguish all SRGs.
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Tuesday, April 17th, 2012

Chaos & Complex Systems Seminar
Towards quantifying biological complexity: Lessons from circadian rhythms
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Amir Assadi, UW Department of Mathematics
Abstract: Computational complexity has been the subject of intensive research with rewarding theoretical and practical accomplishments. ShannonaEuroTMs mathematical formalism to quantify and study digitized information has provided a powerful framework for applications to science and engineering. In biology, the analog nature of the system observables and aEurooesignal-encodingaEuro pose a formidable challenge to draw biologically insightful parallels between the digital information theory and the analog theory of biological information, even if such a theory could potentially be developed.<br>
We provide an outline of a systematic program that aims to better understand the phenomena generally recognized as the culprit to aEurooebiological complexityaEuro, namely, variation of phenotypic traits within a single genotype. A quantitative theory of phenotypic variation leads to the theory of biological complexity at DNA level; which is as a central question in theoretical biology, and sheds new light on the evolution of diversity of life.<br>
We use the physics approach to extract the hints from a data set of gene expression time-series (courtesy of the Chory Lab, Salk Institute), regarded as observations from a complex dynamical system in the ground state and subject to various perturbations. We provide a sketch of the steps to compute variations at the very first molecular stage past the DNA. In parallel to KolmogrovaEuroTMs theory of computational complexity, we propose a multi-scale multi-resolution theory to elucidate ideal measures of the most efficient description of computations initiated at the genome level, leading to the phenotypic observables. We discuss an application to aEurooequantifying phenotypic plasticityaEuro and formulate new hypotheses regarding the DNA-level sources and molecular mechanisms of plasticity. These results are obtained via massively parallel and distributed computation, which offer exciting new research problems of their own. <br>
Host: Sprott
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Wednesday, April 18th, 2012

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
Agenda: http://www.physics.wisc.edu/twap/agendas/2288.pdf
Minutes: http://www.physics.wisc.edu/twap/minutes/2288.pdf
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Thursday, April 19th, 2012

R. G. Herb Condensed Matter Seminar
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Craig Zaspel, University of Montana Western
Host: Huber
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Astronomy Colloquium
Infrared-luminous galaxies: their Evolution, Clustering and Fates
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Benjamin Weiner, Steward Observatory
Abstract: Infrared-luminous galaxies are powered by star formation or active
galactic nuclei, but emit much of their light as radiation reprocessed by dust into the far infrared. The most massive starbursts in both the local and high redshift universe are ultraluminous infrared galaxies(L_IR > 1012 Lsun). This class of galaxies was discovered by IRAS and studied extensively with Spitzer. However, it remains controversial what IR-luminous galaxies at z=1 are, and what they will evolve into. Are IR-luminous galaxies at high redshift mostly galaxy mergers, as they are at low redshift? Are ultraluminous IR galaxies strongly clustered, and can we infer whether they must evolve into cluster galaxies today? Is star formation in high-z IR-luminous galaxies centrally concentrated or spatially extended? I will discuss these questions using data from Spitzer/MIPS, HST, and the DEEP2 redshift survey. I will also show near-infrared slitless spectroscopy from the WFC3 instrument on Hubble, and its use as a probe of star-forming galaxies at high redshifts, with some application to measuring extinction and the spatial extent of star formation in high-z galaxies.
Host: Christy Tremonti
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Friday, April 20th, 2012

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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Special Physics History Lecture
Matter waves in Paris: the de Broglie you don't know
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Bruce R. Wheaton, Technology & Physical Science History Associates, Berkeley, CA
Abstract: IT IS WELL KNOWN that Louis de Broglie received the 1929 Nobel Prize for his audacious proposal six years earlier that atoms possess a wave component. Less well known is his motivation and justification for this concept. It occurred within the context of the first industrial electronics research laboratory in France, where numerous aspirants learned new techniques to be applied in French industries for process management, product sampling, lubrication studies, and a panoply of new control mechanisms. This Laboratoire francaise des rayons x was created after WWI in the fashionable 8th arrondissement of Paris by Louis' elder brother Maurice. Of distinctly noble status and possessing immense wealth, Maurice did this strictly as amateur and utilized his noblesse to form the necessary partnerships with recalcitrant French industrialists. But in the process, which led among many things to the first electron microscope intended for study of industrial procedure, Maurice and his student Alexandre Dauvillier rediscovered an enigma in the behavior of x-rays. When x-rays strike matter they release electrons whose velocities can easily be measured. The problem they found was that these velocities were virtually equal to the velocities of the cathode beam that produced the x-rays. As W. H. Bragg put it "it is as if a log falls in the sea, and the waves that result concentrate themselves on another log a thousand miles away sufficient to propel that log up into the air." To answer this conundrum, "little Louis" appealed to Einstein's theory of relativity and came up with his pilot wave hypothesis of matter in 1923. That it happened in the physics backwater of France owes much to the pragmatic atmosphere in his brother's lab where he could find nobody to test it because they were too busy trying to invent television.
Host: Sam Hokin
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Physics Department Colloquium
The Neutrino at Eighty - A remarkable journey and a feisty future
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: John Wilkerson, University of North Carolina
Abstract: Eighty years ago the neutrino was postulated by Pauli to explain the puzzling observations of nuclear beta decay. At the time many thought neutrinos would never be observed, but a quarter century later Reines and Cowan successfully detected their elusive signal. Following their discovery, a broad set of experiments were undertaken that culminated in the past decade with a remarkable transformation of our understanding of neutrino properties and the revelation that the standard model of particle interactions is incomplete. We have found that neutrinos morph from one species to another as they journey through matter and space. And based on these observations we know that neutrinos are not massless particles, but have tiny masses, being at least 250,000 times lighter than electrons. Even with such diminutive masses, neutrinos influence the largest scales of the cosmos. Today much remains unknown about neutrino properties. What do neutrinos "weigh?" -- Why are their masses so light compared to other particles? Are neutrinos and anti-neutrinos indistinguishable from one another (Majorana particles), indicating lepton number violation? A number of next-generation experiments aim to address these questions, but the reticent nature of neutrinos presents daunting challenges for experimentalists. The talk will focus on how nuclear beta decay and double beta decay serve as sensitive probes of neutrino properties.
Host: Heeger
Poster: http://www.physics.wisc.edu/twap/posters/2012/2298.pdf
Video: https://vod.physics.wisc.edu/media/2012_04_20.m4v
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-04-16.pdf

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