Events at Physics |
Events During the Week of April 5th through April 12th, 2009
Monday, April 6th, 2009
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Experiments on Turbulence and Zonal Flows in TJ-K
- Time: 12:05 pm
- Place: 3345 Engineering Hall
- Speaker: Prof. Uli Stroth, University of Stuttgart-Germany
- Plasma Theory Seminar
- Instability-Enhanced Collisional Effects Near Plasma Boundaries:Langmuir's Paradox and Bohm's Criterion
- Time: 4:00 pm
- Place: 514 ERB
- Speaker: Scott Baalrud, UW-Madison, CPTC
Tuesday, April 7th, 2009
- Chaos & Complex Systems Seminar
- A search for the simplest chaotic partial differential equation
- Time: 12:05 pm
- Place: 4274 Chamberlin
- Speaker: Charlie Brummitt, UW Department of Physics
- Abstract: A search for the simplest chaotic partial differential equation (PDE) concludes that the Kuramoto-Sivashinsky equation is likely the simplest chaotic PDE. We enumerate all of the equations with one quadratic or cubic nonlinearity that are "simpler" than the Kuramoto-Sivashinsky equation and test them for chaos, but none appear to be chaotic. Nevertheless, the search finds a strikingly simple PDE that is chaotic in the discrete limit of finitely many, coupled ordinary differential equations (ODEs). Analysis of this finite system indicates why the chaos vanishes in the limit of infinitely many ODEs.
- Astronomy Colloquium
- Massive Star Clusters in the Milky Way: The known and the known unkowns
- Time: 3:45 pm - 5:00 pm
- Place: 6515 Sterling Hall
- Speaker: Margaret Hanson, University of Cincinnati Physics Dept
- Abstract: The GLIMPSE survey of the Spitzer Space Telescope has provided unprecedented views to study the stellar population of the inner plane
of the Milky Way galaxy. Numerous groups have used this survey to identify new massive stellar cluster candidates. Follow up study of
these candidates indicate about half are true, bound clusters (theknown). The remaining are 'false positives': high density fields of unassociated stars, mimicking a true cluster. What is not so easy to estimate is the number of 'false negatives' from present surveys. These are clusters which exist, but are not detected in current searches (known unknowns). A cluster might not be detected because the core is not concentrated enough, it is highly extinguished, or there may be significant biases in the selection criteria used. In order to derive critical characteristics of the Milky Way's massive cluster population, such as the cluster mass function and cluster lifetimes, one must estimate the characteristics of stellar clusters that are presently missed by current surveys. Our group has taken on this daunting task to constrain the known unknowns via a sophisticated stellar cluster image simulation tool, MASSCLEAN, we've developed. I will present our preliminary efforts that make the first attempt to understand the biases of current searches, provide guidance on preparing more effective searches and our goal of ultimately estimating the characteristics of the massive cluster population of the entire Milky Way galaxy.
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- Host: Prof John Gallagher
Wednesday, April 8th, 2009
- No events scheduled
Thursday, April 9th, 2009
- Passover
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Simple Atom, Extreme Nucleus: Laser Trapping and Probing of Helium-8
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Zheng-Tian Lu, Argonne National Laboratory an University of Chicagod
- Abstract: Helium-8 (8He) is the most neutron-rich matter to have been synthesized on the Earth: it consists of two protons and six neutrons, and remains stable for an average of 0.2 seconds. It is often viewed as a 4He core with four additional neutrons orbiting at a relatively large distance, forming a halo. Because of its intriguing properties, 8He has the potential to reveal new aspects of the fundamental forces among the constituent nucleons. We have recently succeeded in laser trapping and cooling this exotic helium isotope, and have performed precision laser spectroscopy on individual trapped atoms. Based on the atomic frequency differences measured along the isotope chain 3He - 4He - 6He - 8He, the nuclear charge radius of 8He has now been determined for the first time. Comparing this result with the values predicted by a number of nuclear structure calculations, we test theoretical understanding of the nuclear forces in the extremely neutron-rich environment. Moreover, this method of capturing and probing atoms of rare isotopes is also applied to experiments that test fundamental symmetries and to applications of ultrasensitive trace analysis.
- Host: Karsten Heeger
- R. G. Herb Condensed Matter Seminar
- Coulomb drag in quantum circuits
- Time: 4:00 pm
- Place: Chamberlin 5310
- Speaker: Alex Kamenev, University of Minnesota
- Abstract: The talk will review experimental and theoretical works on Coulomb drag in coupled 2d electron systems. Recent experiments have demonstrated drag phenomena in quantum confined geometries and suggested that drag is a convenient tool to measure a quantum shot noise. I shall discuss the theory and implications of these studies.
- Host: Maxim Vavilov
Friday, April 10th, 2009
- Good Friday
- Special Astronomy Colloquium Talk
- Positron Annihilation Radiation from the Center of our Galaxy
- Time: 12:00 pm - 1:00 pm
- Place: 6515 Sterling Hall
- Speaker: Nidhal Guessoum, American University of Sharjah,
- Abstract: The staggering rate of positron production and annihilation in the
Galaxy (1043 e+/s) has been established for three decades now but has yet to find a convincing explanation, especially after the INTEGRAL satellite (launched in 2002) produced a radiation map showing the emission to be mostly coming from the galactic bulge (Knodlseder et al. 2004, Weidenspointner et al. 2008). While the physics of the annihilation of positrons has now mostly been understood (Guessoum, Jean, Gillard 2005), the origin and propagation of those positrons remain an unsettled question, although good progress has been made lately with interesting models and constraints presented.<br>
In this seminar I first review the current knowledge of that
positron-electron annihilation radiation, with what the spectroscopic analysis and the spatial mapping tell us about the media of annihilation (mainly) and to some extent about the sources of positrons. I explain the physical processes which the positrons undergo during their long lives and highlight the role of the interstellar gas, dust, and organic molecules. I then focus on the Galactic Center (with its supermassive black hole) and its potential contribution to explaining part, if not all, of the annihilation radiation observed at least in the Galactic bulge. Several specific proposals have recently been made for the production of positrons by the GC?s SMBH, and they will be critically reviewed on the basis of:a) the positrons? propagation away from the central compact source, given their initial kinetic energy; b) the constraint from direct annihilation emission in flight produced by relativistic positrons; c) estimates of the rates of positron production and other plausibility considerations. Finally, I briefly highlight the important issue of positron propagation from their production site(s), for which the specific physical process is uncertain (collisional or diffusional) and the conditions of the region (density, temperature, and magneticfield distributions) are complex.
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I conclude with some pointers for near-future research on the problem. - Theory/Phenomenology Seminar
- Light Higgsino-LSP Scenario in the BMSSM
- Time: 2:30 pm - 3:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Jeonghyeon Song, Konkuk University, Seoul, Korea
- Abstract: The modest addition of the dimension-5 term lambda(H_u.H_d)^2/M to the superpotential of the Minimal Supersymmetric Standard Model (MSSM) originated from physics beyond the MSSM (BMSSM) has a significant impact on the scenario of the Higgsino-dominated neutralino state being the lightest supersymmetric particle (LSP). It increases the mass difference between the LSP and the lighter chargino as well as that between the LSP and the second-lightest neutralino. This enhances the LHC discovery potential of the chargino and neutralino decays, producing more energetic charged leptons or pions than the decays without the BMSSM corrections. Furthermore, the coannihilation between the lighter chargino or second-lightest neutralino and the LSP is reduced substantially such that the LSP mass does not have to be very heavy. Consequently, an almost pure Higgsino LSP with its mass ~100 GeV in the BMSSM can account for all the relic density of cold dark matter in the Universe unless tan(beta) is too large.
- Host: F. Petriello
- Physics Department Colloquium
- What's so Cool about Ultra-Cold Neutrons
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: Brad Filippone, Caltech
- Abstract: Ultra-Cold Neutrons (UCN) are neutrons with small enough kinetic energy that they can be trapped in material bottles or by modest magnetic fields. With kinetic energies below 300 nano eV, UCN are ideal for studying the fundamental properties of the neutron. Precision studies of neutron decay can explore physics beyond the Standard Electroweak Model. In addition, highly sensitive searches for an Electric Dipole Moment of the neutron probe possible new sources of CP violation (Charge-conjugation and Parity) which could be responsible for the dominance of matter over antimatter observed in the Universe.
- Host: Ramsey-Musolf