1,283,485 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
Man-vehicle systems research facility advanced aircraft flight simulator throttle mechanism
The Advanced Aircraft Flight Simulator is equipped with a motorized mechanism that simulates a two engine throttle control system that can be operated via a computer driven performance management system or manually by the pilots. The throttle control system incorporates features to simulate normal engine operations and thrust reverse and vary the force feel to meet a variety of research needs. While additional testing to integrate the work required is principally now in software design, since the mechanical aspects function correctly. The mechanism is an important part of the flight control system and provides the capability to conduct human factors research of flight crews with advanced aircraft systems under various flight conditions such as go arounds, coupled instrument flight rule approaches, normal and ground operations and emergencies that would or would not normally be experienced in actual flight
Finite size scaling as a cure for supercell approximation errors in calculations of neutral native defects in InP
The relaxed and unrelaxed formation energies of neutral antisites and
interstitial defects in InP are calculated using ab initio density functional
theory and simple cubic supercells of up to 512 atoms. The finite size errors
in the formation energies of all the neutral defects arising from the supercell
approximation are examined and corrected for using finite size scaling methods,
which are shown to be a very promising approach to the problem. Elastic errors
scale linearly, whilst the errors arising from charge multipole interactions
between the defect and its images in the periodic boundary conditions have a
linear plus a higher order term, for which a cubic provides the best fit. These
latter errors are shown to be significant even for neutral defects. Instances
are also presented where even the 512 atom supercell is not sufficiently
converged. Instead, physically relevant results can be obtained only by finite
size scaling the results of calculations in several supercells, up to and
including the 512 atom cell and in extreme cases possibly even including the
1000 atom supercell.Comment: 13 pages, 11 figures. Errata in tables I and III correcte
van Vleck determinants: geodesic focussing and defocussing in Lorentzian spacetimes
The van Vleck determinant is an ubiquitous object, arising in many physically
interesting situations such as: (1) WKB approximations to quantum time
evolution operators and Green functions. (2) Adiabatic approximations to heat
kernels. (3) One loop approximations to functional integrals. (4) The theory of
caustics in geometrical optics and ultrasonics. (5) The focussing and
defocussing of geodesic flows in Riemannian manifolds. While all of these
topics are interrelated, the present paper is particularly concerned with the
last case and presents extensive theoretical developments that aid in the
computation of the van Vleck determinant associated with geodesic flows in
Lorentzian spacetimes. {\sl A fortiori} these developments have important
implications for the entire array of topics indicated. PACS: 04.20.-q,
04.20.Cv, 04.60.+n. To appear in Physical Review D47 (1993) 15 March.Comment: plain LaTeX, 18 page
Ionic and Electronic Conductivity of Nanostructured, Samaria-Doped Ceria
The ionic and electronic conductivities of samaria doped ceria electrolytes, Ce_(0.85)Sm_(0.15)O_(1.925−δ), with nanometric grain size have been evaluated. Nanostructured bulk specimens were obtained using a combination of high specific-surface-area starting materials and suitable sintering profiles under conventional, pressureless conditions. Bulk specimens with relatively high density (≥92% of theoretical density) and low medium grain size (as small as 33 nm) were achieved. Electrical A.C. impedance spectra were recorded over wide temperature (150 to 650°C) and oxygen partial pressure ranges (0.21 to 10^(−31) atm). Under all measurement conditions the total conductivity decreased monotonically with decreasing grain size. In both the electrolytic and mixed conducting regimes this behavior is attributed to the high number density of high resistance grain boundaries. The results suggest a possible variation in effective grain boundary width with grain size, as well as a possible variation in specific grain boundary resistance with decreasing oxygen partial pressure. No evidence appears for either enhanced reducibility or enhanced electronic conductivity upon nanostructuring
Energy levels of a parabolically confined quantum dot in the presence of spin-orbit interaction
We present a theoretical study of the energy levels in a parabolically
confined quantum dot in the presence of the Rashba spin-orbit interaction
(SOI). The features of some low-lying states in various strengths of the SOI
are examined at finite magnetic fields. The presence of a magnetic field
enhances the possibility of the spin polarization and the SOI leads to
different energy dependence on magnetic fields applied. Furthermore, in high
magnetic fields, the spectra of low-lying states show basic features of
Fock-Darwin levels as well as Landau levels.Comment: 6 pages, 4 figures, accepted by J. Appl. Phy
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