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This Week at Physics

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Events During the Week of September 30th through October 7th, 2012

Monday, October 1st, 2012

Special Seminar
Tunneling spectroscopy of many-body effects in a two-dimensional electron gas of near-surface delta-doped layer
Time: 11:30 am
Place: 5310 Chamberlin
Speaker: Sergey Dizhur, Institute of Radioengineering & Electronics, Russian Academy of Science
Abstract: The Al/delta-GaAs tunnel junctions with different subbands spectra in the 2D electron system (2DES) of delta-layer were studied. In each of the junctions subband energies Ei in 2DES can be changed by the diamagnetic shift or by the persistent tunnelling photoconductivity (PTPC) effect. The change of tunnelling conductance at the LO-phonon emission threshold was investigated. The negative change of conductance (electron reflection) was observed for tunnelling in two subband (empty E1 and occupied E0), when intersubband LO-phonon emission into 2DES was possible. The crossover of the zero point in conductance change was found when the energy difference E1F between E1 and the Fermi level EF in 2DES becomes more then LO-phonon energy. In the case the usual inelastic LO-phonon-assisted processes dominate and the new (inelastic) channel is added to the elastic one (positive change).

The obtained results show that the reflection of electrons is related to a new subband being involved in the tunneling process and to the emission of LO-phonons under electron transitions from this subband to the ground state in the 2DES region.
Host: McDermott
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Plasma Physics (Physics/ECE/NE 922) Seminar
Neutronics of ARIES and ITER: Progress and Challenges
Time: 12:00 pm
Place: 1310 Sterling Hall
Speaker: Laila El-Guebaly, University of Wisconsin-Madison
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Tuesday, October 2nd, 2012

Chaos & Complex Systems Seminar
Mitochondrial proteins, pathways and pathogenesis
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Dave Pagliarini, UW Department of Biochemistry
Abstract: Mitochondria are ubiquitous, tiny metabolic machines that live inside nearly all of our cells. Collectively, the make up ~10% of our body weight, and consume ~90% of the oxygen that we breath. They are best known for their role as "power plants" that transform different fuel sources into the universal cellular energy currency, ATP. However, their physiological functions are much more diverse, and their dysfunction leads to a wide spectrum of human disorders ranging from cancer to neurodegeneration. My group studies the composition and biogenesis of these organelles, and how defects in specific mitochondrial proteins gives rise to human disorders. To do so, we leverage a broad range of techniques including mass spectrometry-based proteomics, chemical genetics and mouse physiology.
Host: Sprott
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High Energy Seminar
Updated results from the T2K long baseline neutrino experiment
Time: 3:00 pm
Place: 4274 Chamberlin
Speaker: Kendall Mahn, TRIUMF
Abstract: An unresolved problem in the Standard Model is the observed presence
of matter and lack of corresponding antimatter in the universe. To
explain the matter-antimatter asymmetry, Sakharov suggested three
conditions had to be met: that baryon number is violated, CP violation
and that matter and antimatter are out of thermal equilibrium. A
sufficient source of CP violation could be from new physics in the
quark sector, or in the lepton sector within neutrino mixing.

The conversion of muon neutrinos to electron neutrinos, nue
appearance, is sensitive to CP violation between the light neutrinos,
which can be related to CP violation of a hypothetical heavy neutrino
in the early universe to meet Sakharov's conditions. However, nue
appearance is also dependant on precision measurements of other mixing
parameters, including Dm2(32), theta(23) and theta(13). The
Tokai-To-Kamioka (T2K) long baseline neutrino experiment is designed
to precisely measure muon neutrino disappearance (Dm2(32), theta(23))
and nue appearance. The experiment uses a beam of muon neutrinos
generated at the J-PARC facility in Tokai-mura, Japan, which is
sampled by two near detectors, ND280 and INGRID, before reaching the
Super-Kamiokande detector, 295km away. Since the March 2011
earthquake, T2K has recovered, resumed and updated the nue appearance
analysis with an increased data set corresponding to 3.01e20 protons
on target (at 15.5 kW x 10^7 s). This seminar will highlight T2K's
incredible recovery and analysis improvements, and discuss prospects
for future neutrino-based searches for CP violation in the lepton
sector.
Host: Karsten Heeger
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Wednesday, October 3rd, 2012

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
Agenda: http://www.physics.wisc.edu/twap/agendas/2719.pdf
Minutes: http://www.physics.wisc.edu/twap/minutes/2719.pdf
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Thursday, October 4th, 2012

R. G. Herb Condensed Matter Seminar
No Herb Seminar -- Atomic Seminar held at this time
Time: 10:00 am
Place: 5310 Chamberlin
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Atomic Physics Seminar
Atom Interferometry in an inductively coupled ring trap
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Jonathan Pritchard, University of Strathclyde, Glasgow
Abstract: Atom interferometry offers a number advantages to the field of precision metrology overt over optical interferometers due to the sensitivity of atoms to external electromagnetic fields and inertial forces. Utilising a circular waveguide has the further benefit of providing a strong common-mode rejection between paths and rotational sensitivity via the Sagnac effect, whilst also permitting longer interaction times compared to optical sensors. We present the first demonstration of a novel inductively coupled ring trap for cold atoms to create a circular waveguide of radius 5 mm. A uniform, ac magnetic field induces current in a copper ring, which creates an opposing magnetic field that is time-averaged to produce a smooth cylindrically symmetric ring trap. This resolves the issue of perturbations due to electrical connections and benefits from averaging out corrugation of the potential due to current meandering. A laser-cooled atomic sample is used to characterise the loading efficiency and adiabaticity of the magnetic potential, achieving a vacuum-limited lifetime in the trap. This technique is suitable for creating scalable toroidal waveguides for applications in matterwave interferometry, with a large enclosed area and long interaction times. Development of a second generation apparatus to utilise the ac ring trap for Sagnac interferometry with Bose (87Rb) and Fermi (40K) quantum degenerate gases is described.
Host: Saffman
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Astronomy Colloquium
Probing the Gas Around Galaxies and Black Holes
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Aleks Diamond-Stanic, UC San Diego
Abstract: Our understanding of galaxy evolution centers around questions of how gas gets into galaxies, how it participates in star formation and black hole growth, and how it is returned to its galactic
surroundings via feedback. I will present results on the relationship between gas that forms stars and gas that accretes onto supermassive black holes, and the nature of feedback that is capable of removing gas from galaxies. These results have important implications for how radiation, momentum, and kinetic energy from stars and black holes regulate the cold gas supply in
galaxies. I will also discuss prospects for characterizing the physical properties of gaseous outflows and inflows using existing and future facilities.
Host: Christy Tremonti
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Graduate Introductory Seminar
High Energy Phenomenology String Theory & Theoretical Cosmology
Time: 5:45 pm
Place: 2223 Chamberlin Hall
Speaker: Bai, Barger, Chung, Everett, Hashimoto, Shiu, UW Madison
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Friday, October 5th, 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:
    http://cmb.physics.wisc.edu/journal/index.html
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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Theory Seminar (High Energy/Cosmology)
Three Exceptions for Thermal Dark Matter with Enhanced Annihilation to Gamma Gamma
Time: 2:00 pm
Place: 5280 Chamberlin
Speaker: Hai-Bo Yu, University of Michigan
Abstract: Recently, there have been hints for dark matter (DM) annihilation in the galactic center to one or more photon lines. In order to achieve the observed photon line flux, DM must have a relatively large effective coupling to photons, typically generated radiatively from large couplings to charged particles. When kinematically accessible, direct annihilation of DM to these charged particles is far too large to accommodate both the DM relic density and constraints from the observed flux of continuum photons from the galactic center, halo and dwarf galaxies. We discuss three exceptions to these obstacles, generating the observed line signal while providing the correct relic density and evading photon continuum constraints. The exceptions are (i) coannihilation, where the DM density is set by interactions with a heavier state that is not populated today, (ii) forbidden channels, where DM annihilates to heavier states that are kinematically blocked today, but open in the early Universe, and (iii) asymmetric DM, where the relic density is set by a primordial asymmetry. We build simple models to realize these scenarios.
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Physics Department Colloquium
No Colloquium


"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-10-01.pdf

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