Institut für Theoretische Physik
Start / Aktuell
April  2014
Seminarraum Astrophysik (SR 17, F 05.104)
SFB 963
SFB 963 Seminar

Niels Clausen
Institute for Geophysics, Georg-August-Universität Göttingen

Elliptical instability of compressible flows in ellipsoids

The elliptical instability is due to a parametric resonance of two inertial modes in a fluid velocity field with elliptical streamlines. This flow is a simple model of the motion in a tidally deformed, rotating body. The elliptical instability typically leads to three-dimensional turbulence. The associated turbulent dissipation together with the dissipation of the large scale mode may be important for the synchronization process in stellar and planetary binary systems. We use the anelastic approximation to include compressibility for the calculation of the growth rates of the elliptical instability in a slightly elliptically deformed sphere. In addition, the influence of the Coriolis force and viscosity are taken into account. We use our results to examine the possibility that the elliptical instability appears in Jupiter, the binary star system V636 Centauri and the Earth.

Kontakt: Schleicher
Seminarraum Astrophysik (SR 17, F 05.104)
SFB 963
SFB 963 Seminar

Dr. Warrick Ball
Institut für Astrophysik Göttingen

Correcting stellar oscillations for near-surface effects

Oscillation frequencies of stellar models are known to show ystematic differences with observations, owing to poor modelling of the near-surface layers. These deviations prevent the exploitation of accurate space-based results from Kepler and CoRoT. In this talk, I assess two methods for correcting the frequencies. I first examine a recently-proposed Bayesian method and show that it is potentially heavily biased. Second, I present a new, theoretically-motivated, parametrization of the surface effect that fits the known differences between observed and modelled solar frequencies better than current commonlyused models. I show early tests for bias, and preliminary results of fitting a real star, HD 52265.

Kontakt: Schleicher
Sitzungssaal Mathematik
Theoretische Physik
Graduiertenkolleg 1493

Jan Schlemmer

Deformed Quantum Field Theories and Thermal

Kontakt: K.-H. Rehren
MPI für Sonnensystemforschung

Damian Fabbian

3D MHD simulations and non-LTE spectra: modern tools for studying the Sun's composition and irradiance

Kontakt: Sami Solanki
Seminarraum 11, C3.101
SFB 1073
SFB Seminar

Dr. Bernd Gotsmann
IBM Research, Zurich

Heat generation and dissipation in nanosystems

Self-heating degrades the performance of devices for logic, storage and energy conversion. Reduced thermal conductance in nano-structures has become a limiting factor towards increasing density, performance and reliability of many scaled CMOS devices. Other devices, however, may even benefit from the reduced thermal conductance, for example in thermoelectric energy converters or thermally assisted switching in various data storage schemes. The technological need for characterization of scaled nano-devices is not paralleled with the availability of methods to measure heat flux and temperature on small scales. To measure local temperature and conductance variation we therefore focus on developing measurement tools. These are based on scanning a thermometer across the sample surface region of interest, so called scanning thermal microscopy (SThM), measuring thermal properties directly through self-heating, and measuring directly the heat-flux through molecular 1D-structures. In SThM, a heater-sensor with a sharp tip is scanned across a sample surface to measure the spatial distribution of thermal conductance or temperature of a sample with a resolution down to ~10 nm. We discuss demonstrations of sensitivity and lateral resolution for both thermometry and conductance measurements using examples of graphene and organic layers and self-heated nanowires. It is shown that the surface roughness of tip and sample have critical influence on the measured thermal transport of the tip-surface contact. MEMS-based heater-sensors have been used since about a decade to measure thermal transport in nanowires, and tubes. A remaining challenge is the correlation of electrical and thermal transport properties of samples. We fabricated extremely sensitive MEMS devices to simultaneously measure thermal conductivity, electrical conductivity and thermopower. Results of a full thermoelectric characterization of single InAs nanowires are presented.

Kontakt: Prof. Konrad Samwer

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