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This Week at Physics

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Events During the Week of April 14th through April 21st, 2013

Monday, April 15th, 2013

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:30 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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Tuesday, April 16th, 2013

Chaos & Complex Systems Seminar
The Ascaris nervous system - a simple nervous system. Hah!
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Tony Stretton, UW Department of Zoology
Abstract: Numerically, nematodes have very simple nervous systems. The female parasitic nematode Ascaris suum has only 298 neurons, and the hermaphroditic free-living Caenorhabditis elegans has 302. A. suum is large (ca 35 cm), and has large neurons suitable for electrophysiological recording. We assembled a functional circuit from the morphological synapses, scored by electron microscopy, and the physiological properties of the neurons and their synapses. The predicted activity of this circuit matched that actually recorded from neurons in dissected preparations that were opened to allow microelectrode penetration. However, it differed dramatically from the activity recorded from these same neurons in semi-intact behaving preparations. Something was missing from the circuit description. We have now shown that there are numerous neuropeptides (at least 250) present in A. suum, and the ones we have sequenced have potent activity on individual neurons. We think that they were washed out of the dissected preparations, thus losing their modulatory activity on individual neurons. For peptide identification, initially peptides were purified by HPLC and sequenced by Edman degradation. Now we are using mass spectrometry, which has speeded up the discovery process more than one hundred-fold. In particular, we are now dissecting single identified neurons and subjecting them to MALDI-TOF MS and tandem MS for sequence determination. All neurons examined so far contain peptides. Most contain previously unknown peptides, and the unknown peptides often outnumber the known peptides. This is a powerful method of peptide discovery. It has the distinct advantage that it simultaneously solves the identity and the cellular expression of the peptide. It also has the advantage that it identifies the peptide actually expressed by a particular neuron, rather than relying on predictions from cDNA or genomic DNA sequences, and on reporter constructs for expression patterns. Neuropeptides are processed from precursor proteins, and the rules of the proteolytic cleavage are not yet robust enough for accurate prediction of processing.
Host: Sprott
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Wednesday, April 17th, 2013

No events scheduled

Thursday, April 18th, 2013

Astronomy Colloquium
"Profiling Massive Black Holes through Stellar Tidal Disruption"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Enrico Ramirez-Ruiz, UC Santa Cruz
Abstract: A star interacting with a massive black hole cannot be treated as a point mass if its gets o close to the black hole that it becomes vulnerable to tidal distortions and even disruption. When a rapidly changing tidal force starts to compete with a staraEuroTMs self-gravity, the material of the star responds on a complicated way. This phenomenon poses an as yet unmet challenge to computer simulations. The art of modeling the tidal disruption of stars by massive black holes forms the main theme of my talk. Detailed simulations should tell us what happen when stars of diinotEuroerent types get tidally disrupted, and what radiation a distant observer might detect as the observational signature of such events.
Host: Prof Elena D'onghia
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Friday, April 19th, 2013

Theory Seminar (High Energy/Cosmology)
Gravity Duals of Dynamical Supersymmetry Breaking
Time: 2:15 pm
Place: 5280 Chamberlin Hall
Speaker: William Cottrell, University of Wisconsin-Madison
Abstract: The AdS/CFT correspondance allows one to study supersymmetry breaking in field theory from the perspective of a gravitational dual. In one scenario, supersymmetry breaking is implemented on the gravity side by inserting antibranes into an otherwise supersymmetric geometry. However, it has been argued that the full backreaction of such a perturbation generates unacceptable singularities and potentially eliminates this class of models. We study these issues in the context of an A_{8} geometry, dual to the ABJM theory of M2 branes. We find that upon inserting anti M2 branes, the perturbative sugra analysis does indeed yield singularities, though we argue that these are smoothed out in the full quantum corrected geometry.
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Physics Department Colloquium
Breaking Barriers with Maxwell's Demon
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Mark Raizen, University of Texas at Austin
Abstract: In 1871, James Clerk Maxwell proposed a mythical creature that could regulate the motion of gas-phase particles by controlling a gate. This creature was called Maxwell's demon by Lord Kelvin, and remained a vigorous topic of debate for over 130 years. The demon seemed to violate the Second Law of Thermodynamics, though it was later shown that in principle, information entropy saves us from that catastrophe. In this talk, I will describe how we have now realized Maxwell's demon in the laboratory with a self-acting one-way wall, and how it enables the control of matter with light. In particular, I will discuss how Maxwell's demon is being used to break the barriers of Laser Cooling, Isotope Separation and Nanoscience.
Host: Saffman
Poster: http://www.physics.wisc.edu/twap/posters/2013/2810.pdf
Video: https://vod.physics.wisc.edu/media/2013_04_19.m4v
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2013/2013-04-15.pdf

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