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921.
Jean Ndzié Ewodo 《Journal of statistical physics》2001,104(5-6):1253-1272
In this paper, we study the propagation of acoustic waves in a layered random medium. Using the time-reversed method, we prove the space-time refocusing effect and the stabilization for acoustic signals. This work is a generalization of ref. 4 and 7 in the three-dimensional case. 相似文献
922.
在风速为6~30m/s的范围内,许多研究表明可近似认为热线探针的偏角因子K1和倾角因子K2不随风速变化,倾角θ对K1及偏角ψ对K2也近似认为没有影响,一般采用k1≈0.2,K2≈1.02.然而在极低风速下,特别是1m/s以下,由于热线的传热机理发生变化,所以K1和K2也出现了显著的变化.本文对单丝探针和双丝探针方向特性进行了探讨性的研究,实验表明,风速小于3m/s时,K1和K2随速度发生变化,且θ对K1以及ψ对K2都有影响.当取ψ和θ为90°时,K1和K2在整个角度范围内计算速度的误差较小. 相似文献
923.
924.
925.
For solving complex flow field with multi-scale structure higher order accurate schemes are preferred. Among high order schemes
the compact schemes have higher resolving efficiency. When the compact and upwind compact schemes are used to solve aerodynamic
problems there are numerical oscillations near the shocks. The reason of oscillation production is because of non-uniform
group velocity of wave packets in numerical solutions. For improvement of resolution of the shock a parameter function is
introduced in compact scheme to control the group velocity. The newly developed method is simple. It has higher accuracy and
less stencil of grid points 相似文献
926.
本文详细考察了大孔聚苯乙烯型吸附树脂对不同大小吸附质分子的吸附动力学行为,当吸附过程为粒扩散控制时,树脂孔径与分子尺寸的相对大小不仅决定了粒扩散速度的大小,也影响了粒扩散的控制机制.随着吸附质分子尺寸的增加,决定粒扩散速度的控速步骤也逐渐由表面扩散转向孔扩散。此外,还利用建立的扩散方程,测定了树脂吸附不间大小的吸附质时的粒扩散常数B和有效粒扩散系数De。 相似文献
927.
A method for the study of the steady-state nonlocal electron kinetics in radially and axially inhomogeneous cylindrical plasmas is presented. The method is based on the solution of the relevant space-dependent kinetic equation for the electron velocity distribution using the two-term expansion. A three-dimensional initial boundary value problem for the isotropic distribution component with the total energy as the evolution variable of the kinetic problem has to be treated. The technique is applied to analyze the electron kinetics in a cylindrical DC column plasma under impact of a space-independent axial field and a radially increasing radial field. Particularly, the spatial relaxation of the electron gas in axial direction in response to a disturbance of the axial homogeneity is investigated. A detailed analysis of the spatially resolved energy balance is given. Considerable modification of the results with respect to those obtained by earlier studies of axially homogeneous DC column plasmas, as well as of relaxation processes in one spatial dimension, has been found. 相似文献
928.
运用Monte-Carlo轨迹法研究了Kr(1Sg)+HF(X1Σ+;ν=1,2,3;J=4)→Kr(1Sg)+HF(X1Σ+,ν',J')的碰撞过程,从而分析Kr原子对HF基频和泛频的影响。研究表明:在初始相对平动能Et≤251.0kJ/mol时,Kr原子能够减少产生基频的粒子数反转,增加产生泛频特别是ν'=2能级的粒子数反转,并且,Kr原子有较强的弛豫高转动态(J'≥4)的能力,因此,Kr原子对HF泛频激光在提高光强和增强大气传输能力方面均有 较大的改善。 相似文献
929.
Ultrafine aluminum nitride (AlN) powders were obtained by chemical vapor deposition via AlCl3–NH3–N2 system operated at various temperatures and at a same 200 cm3/min flow rate of NH3 and N2, respectively. It has been shown that when the reaction temperature of AlCl3 and NH3 was above 600°C, then crystalline AlN powder can be formed; whereas, amorphous AlN was obtained with NH4Cl if reacted in a lower-temperature zone of the reaction chamber. The amorphous AlN powder was heat treated at 1400°C under NH3 and N2 atmosphere for 2 h, then the crystalline phases of the obtained powder belong to a single phase of AlN; a mixture of AlN and Al2O3 and only AlON, respectively. On the other hand, if crystalline AlN powder is heat treated at 1400°C under N2 atmosphere for 2 h, the crystalline phases were composed of the major phase of AlN and a minor phase of Al2O3. The morphology, particle size and agglomerate size of the AlN powder were strongly dependent on the heat-treatment temperature. The particle size of AlN powder increases from 28.1 to 45.0 nm, as the heat treatment temperature increases from 800 to 1400°C. 相似文献
930.
A spatially and temporally local analysis is provided for unsteady, oblique shock waves, in which the flow is assumed to
be two-dimensional or axisymmetric. Three unsteady parameters, in a laboratory frame, are viewed as the known independent
variables. These are the upstream Mach number, the shock Mach number, and the angle of the shock relative to the instantaneous
upstream velocity. Other steady and unsteady parameters, such as the velocity turn angles and downstream Mach numbers, are
evaluated in closed form, in terms of these three quantities. Trends are assessed, and a sensitivity analysis is provided.
It is suggested that the theory may find application in converting a shock capturing algorithm, at an early time during the
computational process, into a shock fitting algorithm.
Received 30 April 1999 / Accepted 29 November 1999 相似文献