Effect of graded triple delta-doped sheets on the performance of GaAs based dual channel pseudomorphic high electron mobility transistors

The characteristics of InGaP/InGaAs/GaAs dual channel pseudomorphic high electron mobility transistors (DCPHEMTs) with different graded triple delta-doped sheets are investigated and experimentally demonstrated. Based on a two-dimensional simulator of ATLAS, the band diagrams, electron densities and DC characteristics of studied devices are comprehensively analyzed. Due to the use of properly graded triple delta-doped sheets, good pinch-off and saturation characteristics, improved transport properties and wide current swing are obtained. For comparison, a practical DCPHEMT with good device performances is fabricated as well. It is found that the simulated data are in good agreement with experimental results.     

湍流信号分析中小波基的对比和选取

采用小波分析处理湍流脉动信号时,不同的小波基往往会带来不同的分析结果.为了尽可能准确地提取湍流流动的多尺度特征,研究并建立湍流信号处理中适宜小波基选取的合理方法是十分必要的.基于湍流时频特性,结合信息熵理论,建立了以品质因数和特征谱熵值为评价指标的小波基选取方法.以计算分析三组不同湍流信号的小波基为例,结果进一步验证了...     

不同湍流模型对热等离子体射流模拟的影响

本文应用大气压等离子体射流传热与流动的三维数学模型,在相同初始条件下,计算得到了采用不同湍流模型时氩等离子体射流对称轴线上的温度、速度及空气质量分数分布,并与文献中同等条件下的实验结果进行了比较,结果表明采用标准κ-ε模型和Realizableκ-ε模型时与实验结果相差较大,而采用RNGκ-ε湍流模型时模拟结果与实验数...     

带通道插件管道流磁流体动力学效应的数值模拟

采用二维完全发展流模型对聚变反应堆包层带通道插件和压力平衡槽隙的矩形磁流体管流的MHD效应进行数值模拟,分析速度分布,MHD压降随哈德曼数以及通道插件的电导率的变化规律.与无插件磁流体管流相比,带绝缘通道插件管流MHD压降显著降低,MHD压降随哈德曼数的增加而减小,通道插件材料的电导率增加MHD压降系数减小.压力平衡槽隙处的回流与通道插件的电导率有关.在宏观上计算结果与实验结果和简化理论结果一致.     

Stationary turbulent closure via the Hopf functional equation

Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow.     

The effect of a coriolis force on Taylor-Couette flow

Taylor-Couette flow subject to a Coriolis force is studied experimentally and numerically. In the experiment, the Couette apparatus is mounted on a turntable with the axis of the cylinders orthogonal to the rotation vector of the turntable. The Coriolis force stabilizes the fluid against the onset of Taylor vortices and alters the velocity fields, both above and below the transition from the initial flow. At small dimensionless turntable frequencies, the transition yields time-independent Taylor vortices which are tilted with respect to the cylinder axis. At larger there is a direct transition to turbulence. We determine the first-order correction to the classical Couette initial flow, to account for the effects of the Coriolis force, by expanding in powers of. We present numerical results for the axial velocity (the only nonvanishing correction term to order) in the infinite-cylinder approximation.     

计及风和湍流的热晕及其相位补偿的数值研究

本工作用包括热晕、湍流和风等效应的等压近似下四维激光传输程序，数值计算了激光大气传输中的整束热畸变效应及其理想相位补偿，得到了各种情况下的激光大气传输畸变图象，并分析了热晕和湍流的相互作用。另外，还讨论了时、空步长的选取原则。     

The WKBZ mode approach to sound propagation in range-independent ocean channels

I.IntroductionThenorma1-modeapproachcangiveanexactso1utiontotheacousticfie1dinastratifiedmedium,soitisoftenusedtocomparewithotherapproximatemethodssuchasraytheory,parabo1icequationl'](PE)methodandGaussianbeam[21approach,andtakenasacriteriontochecktheaccuracyofapproximatemeth0dsl3J.Themodeapproachmayalsobeextendedtorange-dcpendente..i,onmentsl4.5l.Thoughtherearemanynumerica1propagationcodesbasedonthemodeapproachI'],theconventionalmodeapproachisawkwardtoapplyt0'higherfrequencya-ndbroadbandprop…     

透平级S_2流面内的反问题湍流计算

本文发展了应用湍流流函数方程计算湍流流场的方法。计算了扭曲叶片Ｓ２流面的湍流流场．在非正交曲线坐标可压湍流方程组中包含了以无量纲形式表示的能量方程，熵方程和Ｋ－ε湍流模型方程。固壁边界上采用了壁函数方程。通过计算得到了透平级内部的湍流流动合理的收敛解。此方法可以通过调节子午通道的形状及环量的大小分布来防止流动中负速度的出现，为高效透平级的设计提供了一种新的途径。