Events at Physics |
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 - 5:10 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
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
Friday, January 15th, 2010
- No events scheduled