116,201 research outputs found
Investigation of Micro Porosity Sintered wick in Vapor Chamber for Fan Less Design
Micro Porosity Sintered wick is made from metal injection molding processes,
which provides a wick density with micro scale. It can keep more than 53 %
working fluid inside the wick structure, and presents good pumping ability on
working fluid transmission by fine infiltrated effect. Capillary pumping
ability is the important factor in heat pipe design, and those general
applications on wick structure are manufactured with groove type or screen
type. Gravity affects capillary of these two types more than a sintered wick
structure does, and mass heat transfer through vaporized working fluid
determines the thermal performance of a vapor chamber. First of all, high
density of porous wick supports high transmission ability of working fluid. The
wick porosity is sintered in micro scale, which limits the bubble size while
working fluid vaporizing on vapor section. Maximum heat transfer capacity
increases dramatically as thermal resistance of wick decreases. This study on
permeability design of wick structure is 0.5 - 0.7, especially permeability (R)
= 0.5 can have the best performance, and its heat conductivity is 20 times to a
heat pipe with diameter (Phi) = 10mm. Test data of this vapor chamber shows
thermal performance increases over 33 %.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
First-principles calculations of a high-pressure synthesized compound PtC
First-principles density-functional method is used to study the recently
high-pressure synthesized compound PtC. It is confirmed by our calculations
that the platinum carbide has a zinc-blende ground-state phase at zero pressure
and the rock-salt structure is a high-pressure phase. The theoretical
transition pressure from zinc-blende to rock-salt is determined to be 52GPa.
Furthermore, our calculation shows the possibility that the experimentally
synthesized PtC by Ono et al. under high pressure condition might undergo a
transition from rock-salt structure to zinc-blende after the pressure quench to
ambient condition.Comment: A revised versio
Distributed Stochastic Optimization over Time-Varying Noisy Network
This paper is concerned with distributed stochastic multi-agent optimization
problem over a class of time-varying network with slowly decreasing
communication noise effects. This paper considers the problem in composite
optimization setting which is more general in noisy network optimization. It is
noteworthy that existing methods for noisy network optimization are Euclidean
projection based. We present two related different classes of non-Euclidean
methods and investigate their convergence behavior. One is distributed
stochastic composite mirror descent type method (DSCMD-N) which provides a more
general algorithm framework than former works in this literature. As a
counterpart, we also consider a composite dual averaging type method (DSCDA-N)
for noisy network optimization. Some main error bounds for DSCMD-N and DSCDA-N
are obtained. The trade-off among stepsizes, noise decreasing rates,
convergence rates of algorithm is analyzed in detail. To the best of our
knowledge, this is the first work to analyze and derive convergence rates of
optimization algorithm in noisy network optimization. We show that an optimal
rate of in nonsmooth convex optimization can be obtained for
proposed methods under appropriate communication noise condition. Moveover,
convergence rates in different orders are comprehensively derived in both
expectation convergence and high probability convergence sense.Comment: 27 page
Volumetric pattern analysis of airborne antennas
By blending together the roll and elevation plane high frequency solutions, a very efficient technique was developed for the volumetric pattern analysis of antennas mounted on the fuselage of a generalized aircraft. The fuselage is simulated by an infinitely long, perfectly conducting, elliptic cylinder in cross-section and a composite elliptic cylinder in profile. The wings, nose section, stabilizers, and landing gear doors may be modeled by finite flat or bent plates. Good agreement with accurate scale model measurements was obtained for a variety of airborne antenna problems
Temperature dependent third cumulant of tunneling noise
Poisson statistics predicts that the shot noise in a tunnel junction has a
temperature independent third cumulant e^2\I, determined solely by the mean
current I. Experimental data, however, show a puzzling temperature dependence.
We demonstrate theoretically that the third cumulant becomes strongly
temperature dependent and may even change sign as a result of feedback from the
electromagnetic environment. In the limit of a noninvasive (zero-impedance)
measurement circuit in thermal equilibrium with the junction, we find that the
third cumulant crosses over from e^2/I at low temperatures to -e^2/I at high
temperatures.Comment: 4 pages including 2 figure
Feedback of the electromagnetic environment on current and voltage fluctuations out of equilibrium
A theory is presented for low-frequency current and voltage correlators of a
mesoscopic conductor embedded in a macroscopic electromagnetic environment.
This Keldysh field theory evaluated at its saddle-point provides the
microscopic justification for our earlier phenomenological calculation (using
the cascaded Langevin approach). The nonlinear feedback from the environment
mixes correlators of different orders, which explains the unexpected
temperature dependence of the third moment of tunneling noise observed in a
recent experiment. At non-zero temperature, current and voltage correlators of
order three and higher are no longer linearly related. We show that a Hall bar
measures voltage correlators in the longitudinal voltage and current
correlators in the Hall voltage. We go beyond the saddle-point approximation to
consider the environmental Coulomb blockade. We derive that the leading order
Coulomb blockade correction to the n-th cumulant of current fluctuations is
proportional to the voltage derivative of the (n+1)-th cumulant, generalizing
to any n the earlier results for n=1,2.Comment: 12 pages, 8 figure
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