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Events on Thursday, September 16th, 2010

R. G. Herb Condensed Matter Seminar
A Macroscopic Mechanical Resonator Driven by Mesoscopic Electrical Backaction
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Alex Rimberg, Dartmouth College
Abstract: We have recently discovered that the driven classical dynamics of a macroscopic mechanical object can be dominated by the quantum statistical fluctuations of tunneling electrons, i.e., by shot noise. Furthermore, coupling between the object and the electrons modifies the electron-electron correlations, resulting in strongly super- and sub-Poissonian current noise. In particular, we have found that a GaAs-based quantum point contact (QPC) can be viewed as a macroscopic mechanical oscillator (a normal mode of the host crystal) whose position is continuously monitored by a mesoscopic electrical detector (the QPC). Furthermore, electrons tunneling through the QPC cause the host crystal to vibrate by means of quantum mechanical backaction. This effect is similar to Brownian motion, in which the motion of a grain of pollen in water is determined by the classical equilibrium statistical fluctuation of molecules. In our case, however, the motion of the oscillator is determined by the quantum non-equilibrium statistical fluctuations of tunneling electrons. Furthermore, the size disparity between the oscillator (a semiconducting chip containing 10^20 atoms) and the source of the fluctuations driving them (fundamental subatomic particles) is truly extreme, and provides a dramatic example of interaction between the quantum and classical worlds.
Host: Mark Eriksson
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Astronomy Colloquium
Finding Dark Galaxies From Their Tidal Imprints
Time: 3:30 pm
Place: 4421 Sterling Hall Same Location
Speaker: Sukanya Chakrabarti, UC Berkeley
Abstract: Characterizing the ubiquitous dark matter in the universe has proven to be one of the most challenging problems in modern astrophysics. If the dynamical impact of dark-matter dominated dwarf galaxies on the outskirts of galactic disks can be deciphered, we may be able to infer and characterize cold dark matter sub-structure in a fundamentally new way. I show how one can analyze observed disturbances in the outer gas disks of spiral galaxies to quantitatively characterize galactic companions without requiring knowledge of their optical light. This method, which I call "Tidal Analysis", allows one to determine the mass and relative position (in radius and azimuth) of galactic companions from analysis of observed disturbances in gas disks. I will first demonstrate the validity of this method by applying it to local spirals with known optical companions to provide a proof of principle. I will then review my earlier work on the Milky Way that prompted the development of this method. Specifically, analysis of observed disturbances on the outskirts of the Milky Way disk favor a 1:100 mass ratio perturber with a close pericentric approach. I will conclude by discussing ongoing work on developing scaling relations between observed HI maps and satellite mass, and our plans for the near-future which include testing the Tidal Analysis method on large samples to determine its statistical viability.
Host: Bob Benjamin/Barb Whitney
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Precision Gravity and Effective Field Theories
Time: 4:00 pm
Place: 4274 Chamberlin
Speaker: Andreas Ross, University of Wisconsin at Madison/Argonne National Laboratory
Abstract: The effective field theory description yields a systematic treatment of gravitational bound states such as binary systems. Gravitational waves emitted from binaries are one of the prime event candidates at direct detection experiments such as LIGO, VIRGO etc. Due to the multiple scales involved in the binary problem, an effective field theory treatment yields many advantages in perturbative calculations. My talk will review the setup of the effective field theory framework and report on recent progress in gravitational wave phenomenology.
Host: Michael Ramsey-Musolf
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Graduate Introductory Seminar
Biophysics Seminar
Time: 5:30 pm
Place: 2223 Chamberlin Hall
Speaker: Coppersmith, Gilbert
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