27,995 research outputs found
Statistics of turbulent fluctuations in counter-rotating Taylor-Couette flows
The statistics of velocity fluctuations of turbulent Taylor-Couette flow are
examined. The rotation rate of the inner and outer cylinder are varied while
keeping the Taylor number fixed to
(). The azimuthal velocity component of the flow
is measured using laser Doppler anemometry (LDA). For each experiment
datapoints are acquired and carefully analysed. Using extended
self-similarity (ESS) \cite{ben93b} the longitudinal structure function
exponents are extracted, and are found to weakly depend on the ratio of the
rotation rates. For the case where only the inner cylinder rotates the results
are in good agreement with results measured by Lewis and Swinney \cite{lew99}
using hot-film anemometry. The power spectra shows clear -5/3 scaling for the
intermediate angular velocity ratios , roughly -5/3 scaling for , and no clear scaling law can be found for
(inner cylinder rotation only); the local scaling exponent of the spectra has a
strong frequency dependence. We relate these observations to the shape of the
probability density function of the azimuthal velocity and the presence of a
neutral line
Quantum oscillations of spin current through a III-V semiconductor loop
We have investigated the transport of spin polarization through a classically
chaotic semiconductor loop with a strong Rashba spin-orbit interaction. We
found that if the escape time of a particle is long enough, the configuration
averaged spin conductance oscillates strongly with the geometric spin phase. We
predict a sizable rotation of spin polarization along its flowing path across
the loop from the injector to the collector. We have also discovered a
quantized universal spin relaxation in a 2D reservoir connected to such a
semiconductor loop.Comment: 4 pages, 1 figur
Cryogenic Sapphire Oscillator using a low-vibration design pulse-tube cryocooler: First results
A Cryogenic Sapphire Oscillator has been implemented at 11.2 GHz using a
low-vibration design pulse-tube cryocooler. Compared with a state-of-the-art
liquid helium cooled CSO in the same laboratory, the square root Allan variance
of their combined fractional frequency instability is for integration times s, dominated by
white frequency noise. The minimum for the two
oscillators was reached at s. Assuming equal contributions from
both CSOs, the single oscillator phase noise at 1 Hz offset from the carrier.Comment: 5 pages, 5 figures, accepted in IEEE Trans on Ultrasonics,
Ferroelectrics and Frequency Contro
Turbulence strength in ultimate Taylor-Couette turbulence
We provide experimental measurements for the effective scaling of the
Taylor-Reynolds number within the bulk , based
on local flow quantities as a function of the driving strength (expressed as
the Taylor number Ta), in the ultimate regime of Taylor-Couette flow. The data
are obtained through flow velocity field measurements using Particle Image
Velocimetry (PIV). We estimate the value of the local dissipation rate
using the scaling of the second order velocity structure
functions in the longitudinal and transverse direction within the inertial
range---without invoking Taylor's hypothesis. We find an effective scaling of
, (corresponding
to for the dimensionless
local angular velocity transfer), which is nearly the same as for the global
energy dissipation rate obtained from both torque measurements
() and Direct Numerical Simulations
(). The resulting Kolmogorov length
scale is then found to scale as
and the turbulence intensity as . With both the local dissipation rate and the local
fluctuations available we finally find that the Taylor-Reynolds number
effectively scales as Re in the
present parameter regime of .Comment: 15 pages, 8 figures, J. Fluid Mech. (In press
Generation of spin current and polarization under dynamic gate control of spin-orbit interaction in low-dimensional semiconductor systems
Based on the Keldysh formalism, the Boltzmann kinetic equation and the drift
diffusion equation have been derived for studying spin polarization flow and
spin accumulation under effect of the time dependent Rashba spin-orbit
interaction in a semiconductor quantum well. The time dependent Rashba
interaction is provided by time dependent electric gates of appropriate shapes.
Several examples of spin manipulation by gates have been considered. Mechanisms
and conditions for obtaining the stationary spin density and the induced
rectified DC spin current are studied.Comment: 10 pages, 3 figures, RevTeX
Dancing with the Dragon Heads: Enforcement, Innovations and Efficiency of Contracts between Agricultural Processors and Farmers in China
Contractual breaches are very common in developing countries such as China. In order to prevent breaches of contract, the contractual designs between farmers and agricultural processors (Dragon Head Firms) in China are innovating in two ways: organizational innovations and contractual innovations. Due to contractual innovations, simple price-quantity contracts are evolving into complex cooperation contracts. Using data for over 500 state key processors in 2003 from the Chinese Ministry of Agriculture, we construct econometric models to study contractual choices, contract intensity, and their impacts on sales and profits for agricultural processors in China. The results indicate that capital and the number of contracted farmers are endogenous to contract choices. Processors are more likely to use cooperation contracts compared with price-quantity contracts as the number of contracted farmers increases, because the costs of coordinating, monitoring and enforcing price-quantity contracts may increase dramatically under these circumstances . On the other hand, contract types are not important for the number of contracted farmers, the intensity of contracts, or sales and profits for processors. The results also indicate that the elasticity of profits with respect to capital is 0.52, which implies that the returns to investing in the food processing industry are relatively high in China.Agribusiness,
Bosonic Super Liouville System: Lax Pair and Solution
We study the bosonic super Liouville system which is a statistical
transmutation of super Liouville system. Lax pair for the bosonic super
Liouville system is constructed using prolongation method, ensuring the Lax
integrability, and the solution to the equations of motion is also considered
via Leznov-Saveliev analysis.Comment: LaTeX, no figures, 11 page
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