Safety and Efficacy of Magnetic Resonance-Guided Focused Ultrasound Surgery With Autofocusing Echo Imaging.

Objective: Magnetic resonance-guided focused ultrasound surgery (MRgFUS) lesioning is a new treatment for brain disorders. However, the skull is a major barrier of ultrasound sonication in MRgFUS because it has an irregular surface and varies its size and shape among individuals. We recently developed the concept of skull density ratio (SDR) to select candidates for MRgFUS from among patients with essential tremor (ET).

Cooling of electrons in a silicon inversion layer.

Low temperature cooling of two-dimensional electrons in silicon-metal-oxide semiconductor field effect transistors is studied experimentally and found to be more effective than expected from the bulk electron-phonon coupling in silicon. The extracted heat transfer rate to phonons depends cubically on electron temperature, suggesting that piezoelectric coupling, which is absent in bulk silicon, dominates over deformation potential. As a result, at 100 mK, electrons farther than approximately 100 microm from the contacts are mostly cooled by phonons.

Interband scattering and the "Metallic Phase" of two-dimensional holes in GaAs /AlGaAs.

The "metallic" characteristics of high density holes in GaAs/AlGaAs heterostructures are attributed to inelastic scattering between the two split heavy hole bands. Landau fan diagrams and weak field magnetoresistance are employed to measure the interband scattering rate. The inelastic rate is found to depend on temperature with an activation energy similar to that characterizing the longitudinal resistance.