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排序方式: 共有1351条查询结果,搜索用时 15 毫秒
1.
2.
《Diamond and Related Materials》2005,14(10):1588-1591
X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with submicron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties of MicroElectroMechancial Systems (MEMS). This investigation examined the local strain induced by irradiating a polycrystalline diamond thin film with a dose of 2 × 1017 H+/cm2 protons. Preliminary results indicate that a measurable strain, on the order of 10− 3, was introduced into the film near the End of Range (EOR) region of the protons. 相似文献
3.
During experiments on the MSL-1 (first microgravity science laboratory) mission of the space shuttle (STS-83 and STS-94, April
and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the
nondeforming droplet, the resultant magnetohydrodynamic (MHD) flow inside the drop can be inferred from motion of impurity
particulates on the surface. In the experiments, subsequent to melting, Joule heating produces a continuous reduction of viscosity
of the fluid resulting in an acceleration of the flow with time. These observations indicate formation of a pair of co-rotating
toroidal flow structures inside the spheroidal drop that undergo flow instabilities. As the fluid temperature rises, the amplitude
of the secondary flow increases, and beyond a point, the tracers exhibit noncoherent chaotic motion signifying emergence of
turbulence inside the drop. Assuming that the observed laminar-turbulent transition is shear-layer type, the internal structure
of the toroidal loops is used to develop a semiempirical correlation for the onset of turbulence. Our calculations indicate
that the suggested correlation is in modest agreement with the experimental data, with the transition occurring at a Reynolds
number of 600. 相似文献
4.
CHING-HUA Su YI-GAO Sha S. L Lehoczky F. R Szofran D. C Gillies S. D Cobb R. N Scripa 《Journal of Materials Science》1997,32(14):3765-3768
A series of Hg0.84Zn0.16 Te crystal ingots have been grown from pseudobinary melts by the Bridgmam–Stockbarger type directional solidification using
a Marshall Space Flight Center/Space Science Laboratory heat-pipe furnace and the ground control experiment laboratory furnace
of the crystal growth furnace which was flown on the first United States Microgravity Mission. A number of translation rates
and a series of hot- and cold-zone temperatures were employed to assess the influence of growth parameters on the crystal
properties for the purpose of optimizing the in-flight growth conditions.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
5.
《Materials Letters》2007,61(11-12):2191-2194
Porous TiO2 films with both mesoporosity and macroporosity were fabricated by a templated sol–gel method for applications, such as dye-sensitized solar cells (DSC), photocatalysis and catalysis. With the incorporation of differently sized pores, the resultant structures exhibit high surface areas and possess interpenetrating aligned pore channels, which are believed to be beneficial for applications where diffusion of reactants to interior surface can be rate limiting. Both liquid and solid TiO2 precursors can be applied for large area coating in this process. Almost crack-free films were produced by templated coating of pre-synthesized TiO2 nanoparticles. The measured specific surface area and porosity of synthesized films were in the range of 33–137 m2/g and 61–80%, respectively, depending on the size of the selected template. 相似文献
6.
7.
J.S Walker P DoldA Cröll M.P VolzF.R Szofran 《International Journal of Heat and Mass Transfer》2002,45(23):4695-4702
This paper treats the steady axisymmetric flow and mass transport in a cylindrical liquid bridge between the melting end of a feed rod and the solidifying end of an alloyed semiconductor crystal. There is a strong, uniform, steady, axial magnetic field. The surface tension depends on the temperature and the concentration of the species, while variations of the concentration occur because one species is rejected into the liquid during solidification. The thermocapillary and solutocapillary convections tend to cancel over part of the liquid bridge. For certain parameter ranges, there are two different stable solutions: one where the concentration gradient along the free surface leads to dominance by the solutocapillary convection and one where the mass transport due to the thermocapillary convection makes the concentration gradient along the free surface small, so that the thermocapillary convection is dominant. 相似文献
8.
William F. Kaukler 《Metallurgical and Materials Transactions A》1988,19(11):2625-2630
An interfluid meniscus oscillates within a cylindrical container when suddenly released from earth's gravity and taken into
a microgravity environment. Oscillations damp out from energy dissipative mechanisms such as viscosity and interfacial friction.
Damping out of the oscillations by the latter mechanism is affected by the nature of the interfacial junction between the
fluid-fluid interface and the container wall. Perfluoromethylcyclohexane and isopropanol in glass were the materials used
for the experiment. The wetting condition of the fluids against the wall changes at the critical wetting transition temperature.
This change in wetting causes a change in the damping characteristics.
This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research”
presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25–29, 1988, under the auspices of the ASM/MSD
Thermodynamic Data Committee and the Material Processing Committee. 相似文献
9.
The electromagnetic fields and currents associated with an infinite four parallel wire transmission line are analyzed through the use of the spatial Fourier transform method. The near and far electromagnetic fields and currents that are associated with frill and gap voltage excitations are analyzed by the Fourier transform method. Possible VHF compact range applications of a four parallel wire antenna system are discussed, including the possibility of simulating an off-axis EM plane wave by the appropriate adjustment of the exciting voltage phase on each of the four parallel wires. Comparisons of Fourier transform method solutions with method-of-moments solutions and finite-difference-time-domain solutions are made for an infinite four parallel wire antenna system 相似文献
10.
The permeability and lag time for a heterogeneous diffusion system, in which the diffusivity and partition coefficient for the diffusant are dependent on position, are formulated in terms of a linear asymptotic analysis. A repeated integration of the diffusion equation is used to obtain the time dependence of the total solute release into the receiver, Q(t). The asymptotic form of Q(t) is linear in time. The slope, and intercept of this linear asymptote with the time axis, respectively, give formulas for the steady-state permeability and lag time. These formulas are then applied to diffusion systems of multiple laminates, consisting of a series of different homogeneous slabs. Thus, for the first time, a concise treatment of diffusion in multiple laminates is obtained. The formulas are also applied to periodic laminates, consisting of a series of identical slabs, but with position-dependent diffusivity and partition coefficient. We found that the lag time can be well approximated by (nh))2/(6Deff), where n and h are, respectively, the number and thickness of individual lamella, and Deff is an effective diffusivity, for which a relation in terms of the local property distributions is obtained. This approximation becomes more accurate with increasing number of lamellae. At n = 5, the relative error is already within 4%. Finally a procedure is discussed for readily obtaining the lag time for periodic structures consisting of a serial repetition of a multi-laminate. 相似文献