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Events During the Week of January 10th through January 17th, 2010

Monday, January 11th, 2010

No events scheduled

Tuesday, January 12th, 2010

Astronomy Colloquium
"Magnetic Fields in the Cosmic-ray modified shocks"
Time: 3:30 pm
Place: 3425 Sterling Hall
Speaker: Andrey Beresynak, UW Madison Astronomy
Abstract: We propose a model for Diffusive Shock Acceleration (DSA) in which
stochastic magnetic fields in the shock precursor are generated
through purely fluid mechanisms of a so-called small-scale dynamo.
This contrasts with previous DSA models that considered magnetic
fields amplified through cosmic ray streaming instabilities; i.e.,
either by way of individual particles resonant scattering in the
magnetic fields, or by macroscopic electric currents associated with large-scale cosmic ray streaming. In our picture, the solenoidal velocity perturbations that amplify magnetic fields are produced through the interactions of the pressure gradient of the cosmic ray precursor and density inhomogeneities in the inflowing fluid.
Our estimates show that this mechanism provides fairly fast<br>
growth of magnetic field and is very generic. For supernovae shocks this mechanism is capable of generating upstream magnetic fields that are sufficiently strong for accelerating cosmic rays up to around $10^{16}$ eV.<br>
Host: UW Astronomy Dept
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Wednesday, January 13th, 2010

No events scheduled

Thursday, January 14th, 2010

R. G. Herb Condensed Matter Seminar
Charge sensing and excited state spectroscopy in a Si/SiGe quantum dot
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Madhu Thalakulam, UW-Madison
Abstract: Charge sensing with integrated point contacts is an essential component to the development of Si-based quantum dot spin qubits. Recently, we have shown that such charge sensing can be used to perform excited state spectroscopy in two complementary ways. In the first approach, pulsed gate voltages of increasing amplitude are applied to a gate. In the second approach, a non-zero dc source-drain bias is applied across the quantum dot. In neither case does measurable current flow through the dot. Instead, in both approaches excited states appear as sharp changes in time-averaged charge-sensing measurements performed with the integrated quantum point contact. The advantage of this approach is that it enables spectroscopy of quantum states when no transport is possible through the dot, which is a common situation for quantum dots in the one-electron limit. I will also present data demonstrating a Si/SiGe double quantum dot with exactly one-electron in each dot.
Host: Mark Eriksson
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Friday, January 15th, 2010

No events scheduled