103,582 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
Solving 1D Conservation Laws Using Pontryagin's Minimum Principle
This paper discusses a connection between scalar convex conservation laws and
Pontryagin's minimum principle. For flux functions for which an associated
optimal control problem can be found, a minimum value solution of the
conservation law is proposed. For scalar space-independent convex conservation
laws such a control problem exists and the minimum value solution of the
conservation law is equivalent to the entropy solution. This can be seen as a
generalization of the Lax--Oleinik formula to convex (not necessarily uniformly
convex) flux functions. Using Pontryagin's minimum principle, an algorithm for
finding the minimum value solution pointwise of scalar convex conservation laws
is given. Numerical examples of approximating the solution of both
space-dependent and space-independent conservation laws are provided to
demonstrate the accuracy and applicability of the proposed algorithm.
Furthermore, a MATLAB routine using Chebfun is provided (along with
demonstration code on how to use it) to approximately solve scalar convex
conservation laws with space-independent flux functions
Comment on ``Quantum Phase of Induced Dipoles Moving in a Magnetic Field''
It has recently been suggested that an Aharonov-Bohm phase should be capable
of detection using beams of neutral polarizable particles. A more careful
analysis of the proposed experiment suffices to show, however, that it cannot
be performed regardless of the strength of the external electric and magnetic
fields.Comment: 2 pages, latex file, no figure
Mitigating the Curse of Dimensionality: Sparse Grid Characteristics Method for Optimal Feedback Control and HJB Equations
We address finding the semi-global solutions to optimal feedback control and
the Hamilton--Jacobi--Bellman (HJB) equation. Using the solution of an HJB
equation, a feedback optimal control law can be implemented in real-time with
minimum computational load. However, except for systems with two or three state
variables, using traditional techniques for numerically finding a semi-global
solution to an HJB equation for general nonlinear systems is infeasible due to
the curse of dimensionality. Here we present a new computational method for
finding feedback optimal control and solving HJB equations which is able to
mitigate the curse of dimensionality. We do not discretize the HJB equation
directly, instead we introduce a sparse grid in the state space and use the
Pontryagin's maximum principle to derive a set of necessary conditions in the
form of a boundary value problem, also known as the characteristic equations,
for each grid point. Using this approach, the method is spatially causality
free, which enjoys the advantage of perfect parallelism on a sparse grid.
Compared with dense grids, a sparse grid has a significantly reduced size which
is feasible for systems with relatively high dimensions, such as the -D
system shown in the examples. Once the solution obtained at each grid point,
high-order accurate polynomial interpolation is used to approximate the
feedback control at arbitrary points. We prove an upper bound for the
approximation error and approximate it numerically. This sparse grid
characteristics method is demonstrated with two examples of rigid body attitude
control using momentum wheels
Do local manufacturing firms benefit from transactional linkages with multinational enterprises in China?
This paper examines the linkage effects of foreign direct investment (FDI) on firm-level productivity in Chinese manufacturing. It is found that FDI generates positive vertical linkage effects in Chinese manufacturing at both the national and regional levels, and limited positive horizontal spillovers at the regional level. While OECD firms gain from both vertical and (probably) horizontal linkages, Hong Kong, Macao and Taiwanese firms benefit only from backward linkage effects. In the domestic sector, in which we are most interested, both state-owned enterprises (SOEs) and non-SOEs are hurt by competition from foreign firms in the same industries. While SOEs gain from vertical linkages with foreign firms, non-SOEs are unable to do so. The patterns of productivity spillovers from FDI in Chinese manufacturing seem to be determined by one key factor – the technological capabilities of the firms involved. Important data limitations and policy implications of this research are discussed
The Transmission Property of the Discrete Heisenberg Ferromagnetic Spin Chain
We present a mechanism for displaying the transmission property of the
discrete Heisenberg ferromagnetic spin chain (DHF) via a geometric approach. By
the aid of a discrete nonlinear Schr\"odinger-like equation which is the
discrete gauge equivalent to the DHF, we show that the determination of
transmitting coefficients in the transmission problem is always bistable. Thus
a definite algorithm and general stochastic algorithms are presented. A new
invariant periodic phenomenon of the non-transmitting behavior for the DHF,
with a large probability, is revealed by an adoption of various stochastic
algorithms.Comment: 16 pages, 7 figure
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