12,978 research outputs found
Superfluid Optomechanics: Coupling of a Superfluid to a Superconducting Condensate
We investigate the low loss acoustic motion of superfluid He
parametrically coupled to a very low loss, superconducting Nb, TE
microwave resonator, forming a gram-scale, sideband resolved, optomechanical
system. We demonstrate the detection of a series of acoustic modes with quality
factors as high as . At higher temperatures, the lowest
dissipation modes are limited by an intrinsic three phonon process. Acoustic
quality factors approaching may be possible in isotopically purified
samples at temperatures below 10 mK. A system of this type may be utilized to
study macroscopic quantized motion and as an ultra-sensitive sensor of
extremely weak displacements and forces, such as continuous gravity wave
sources
Ultra-high Q Acoustic Resonance in Superfluid 4He
We report the measurement of the acoustic quality factor of a gram-scale,
kilo-hertz frequency superfluid resonator, detected through the parametric
coupling to a superconducting niobium microwave cavity. For temperature between
400mK and 50mK, we observe a temperature dependence of the quality
factor, consistent with a 3-phonon dissipation mechanism. We observe Q factors
up to , consistent with the dissipation due to dilute He
impurities, and expect that significant further improvements are possible.
These experiments are relevant to exploring quantum behavior and decoherence of
massive macroscopic objects, the laboratory detection of continuous wave
gravitational waves from pulsars, and the probing of possible limits to
physical length scales.Comment: 5 pages, 2 figure
Results from new fungus-tolerant grapevine varieties for Organic Viticulture
Two red and three white new fungus-tolerant grape varieties were tested within a period of five years. REGENT, RONDO, JOHANNITER and Gf 48-12 show a better wine quality than PINOT NOIR or SILVANER and can be recommended for Organic Viticulture as well as for the conventional viticulture to reduce copper and fungicide applications
Quasiclassical approach to the spin-Hall effect in the two-dimensional electron gas
We study the spin-charge coupled transport in a two-dimensional electron
system using the method of quasiclassical (-integrated) Green's functions.
In particular we derive the Eilenberger equation in the presence of a generic
spin-orbit field. The method allows us to study spin and charge transport from
ballistic to diffusive regimes and continuity equations for spin and charge are
automatically incorporated. In the clean limit we establish the connection
between the spin-Hall conductivity and the Berry phase in momentum space. For
finite systems we solve the Eilenberger equation numerically for the special
case of the Rashba spin-orbit coupling and a two-terminal geometry. In
particular, we calculate explicitly the spin-Hall induced spin polarization in
the corners, predicted by Mishchenko et al. [13]. Furthermore we find universal
spin currents in the short-time dynamics after switching on the voltage across
the sample, and calculate the corresponding spin-Hall polarization at the
edges. Where available, we find perfect agreement with analytical results.Comment: 9 pages, 6 figure
Comparison of secondary flows predicted by a viscous code and an inviscid code with experimental data for a turning duct
A comparison of the secondary flows computed by the viscous Kreskovsky-Briley-McDonald code and the inviscid Denton code with benchmark experimental data for turning duct is presented. The viscous code is a fully parabolized space-marching Navier-Stokes solver while the inviscid code is a time-marching Euler solver. The experimental data were collected by Taylor, Whitelaw, and Yianneskis with a laser Doppler velocimeter system in a 90 deg turning duct of square cross-section. The agreement between the viscous and inviscid computations was generally very good for the streamwise primary velocity and the radial secondary velocity, except at the walls, where slip conditions were specified for the inviscid code. The agreement between both the computations and the experimental data was not as close, especially at the 60.0 deg and 77.5 deg angular positions within the duct. This disagreement was attributed to incomplete modelling of the vortex development near the suction surface
Anomalous dynamics of cell migration
Cell movement, for example during embryogenesis or tumor metastasis, is a
complex dynamical process resulting from an intricate interplay of multiple
components of the cellular migration machinery. At first sight, the paths of
migrating cells resemble those of thermally driven Brownian particles. However,
cell migration is an active biological process putting a characterization in
terms of normal Brownian motion into question. By analyzing the trajectories of
wildtype and mutated epithelial (MDCK-F) cells we show experimentally that
anomalous dynamics characterizes cell migration. A superdiffusive increase of
the mean squared displacement, non-Gaussian spatial probability distributions,
and power-law decays of the velocity autocorrelations are the basis for this
interpretation. Almost all results can be explained with a fractional Klein-
Kramers equation allowing the quantitative classification of cell migration by
a few parameters. Thereby it discloses the influence and relative importance of
individual components of the cellular migration apparatus to the behavior of
the cell as a whole.Comment: 20 pages, 3 figures, 1 tabl
Determination of |V_us| from hadronic tau decays
The recent update of the strange spectral function and the moments of the
invariant mass distribution by the OPAL collaboration from hadronic tau decay
data are employed to determine |V_us| as well as m_s. Our result,
|V_us|=0.2208\pm0.0034, is competitive to the standard extraction of |V_us|
from K_e3 decays and to the new proposals to determine it. Furthermore, the
error associated to our determination of |V_us| can be reduced in the future
since it is dominated by the experimental uncertainty that will be eventually
much improved by the B-factories hadronic tau data. Another improvement that
can be performed is the simultaneous fit of both |V_us| and m_s to a set of
moments of the hadronic tau decays invariant mass distribution, which will
provide even a more accurate determination of both parameters.Comment: 6 pages. Invited talk given by E.G. at the XXXXth Rencontres de
Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy,
5-12 Mar 200
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