The nonsymmetric pressure tensor in polyatomic fluids

Nonequilibrium molecular dynamics calculations are used to show that polyatomic fluids can support antisymmetric stress. In a homogeneous system where the time dependence of vorticity is a step function, it is shown that the rate at which intrinsic angular velocity approaches its steady-state value ( = 1/2 × u) is determined by the magnitude of the antisymmetric part of the pressure tensor.     

Effects of multi-Schell beams on orbital angular momentum of entangled signal photons in low-order turbulence aberration channels

We model the detection and crosstalk probability of orbital angular momentum (OAM) states of the entangled signal photon in the Kolmogorov channels of the low-order turbulence aberrations and by the Rytov approximation. The results show that lower OAM mode number of signal photons and larger sub-beam number of multi-Gaussian Schell-model pump beam, the less susceptible of the detection probability of the signal photon to spatial coherence of source and turbulence aberrations is achieved. The maximum crosstalk probability is decrease as the decreasing of the sub-beam number of multi-Gaussian Schell-model. Enlarging OAM difference value or decreasing sub-beam number of multi-Gaussian Schell-model pump beam results in a lower crosstalk probability of the OAM of entangled signal photons.     

Quantitative assessment of motion correction for high angular resolution diffusion imaging

Several methods have been proposed for motion correction of high angular resolution diffusion imaging (HARDI) data. There have been few comparisons of these methods, partly due to a lack of quantitative metrics of performance. We compare two motion correction strategies using two figures of merit: displacement introduced by the motion correction and the 95% confidence interval of the cone of uncertainty of voxels with prolate tensors. What follows is a general approach for assessing motion correction of HARDI data that may have broad application for quality assurance and optimization of postprocessing protocols. Our analysis demonstrates two important issues related to motion correction of HARDI data: (1) although neither method we tested was dramatically superior in performance, both were dramatically better than performing no motion correction, and (2) iteration of motion correction can improve the final results. Based on the results demonstrated here, iterative motion correction is strongly recommended for HARDI acquisitions.     

光电成像导引察打一体无人机命中精度计算分析

针对采用电视或红外成像导引方式的自毁式侦察打击一体化无人机,在落点偏差正态分布假定下,根据相对目标的以圆概率误差（CEP）表示的命中精度的定义,忽略无人机滚转影响,对CEP与落点系统偏差和标准偏差的关系进行数学描述。结合系统工作原理和俯冲攻击流程,建立CEP和基于视频图像的跟踪导引系统和随机角误差及导引盲距（即最短有效导引距离）间的数学方程,并利用Mathcard数学软件举例计算分析。此方法可以用于依据给定CEP和导引盲距分解确定跟踪导引角误差参数,也可基于导引盲距和跟踪导引角误差预测CEP指标是否能够实现。     

基于光纤陀螺的转台周期性误差抑制方法

为抑制测角系统周期性测量误差对光电跟踪系统速度平稳性和成像效果的影响,采用光纤陀螺系统建立误差模型和误差补偿器,对系统进行误差补偿控制。首先,对测角系统测量结果中含有周期性误差的机理进行分析,建立了周期性测角误差的数学模型;其次,采用高精度光纤陀螺建立了一套基于傅里叶理论的角度测量误差模型采集系统,并通过七个步骤提取了测角误差模型的具体表达式;然后,根据提取的测角误差表达式,分四个步骤对系统周期性误差进行补偿控制。最后,通过跟踪成像实验来验证控制补偿的有效性。实验结果表明,跟踪速度误差的最大值降低到0.04 ()/s,比未补偿控制时降低了8倍左右,满足光学成像系统速度误差小于0.1 ()/s的要求,条纹成像效果得到了明显改善。     

Evolution of coercivity and its angular dependence in CoFe nanostructures subjected to field cooling

Evolution of coercivity and its angular dependence in CoFe nanostructures subjected to field cooling has been investigated in this work. Spherical CoFe grains with an average diameter of 30 nm were grown on a silicon substrate using electron beam evaporation. Further, the as‐deposited sample was subjected to field cooling. The morphology and topography of the sample before and after field cooling were characterized by atomic force microscopy and SEM. Magnetic force microscopy indicated that there is a good uniformity of magnetization throughout the sample after field cooling. Vibrating sample magnetometer measurements indicate that the coercivity in CoFe nanostructures is dependent on shape of the nanostructures. Copyright © 2013 John Wiley & Sons, Ltd.     

圆柱型阵机载雷达杂波抑制新方法

圆柱型阵天线相对于常规的平面阵天线具有空间全方位扫描、搜索跟踪方式灵活和波束方向性好等优点。该文首先从圆柱型阵机载雷达杂波协方差矩阵特征值分布和杂波功率谱距离向分布两个方面分析了圆柱型阵列与均匀平面阵列之间的区别,得到杂波功率谱随距离变化的结论。然后根据圆柱型阵机载雷达杂波分布特点提出了两种不同的杂波抑制方法,它们能够很好地解决圆柱型阵机载雷达杂波距离向分布非均匀的问题。最后通过仿真实验验证了该文方法的正确性。     

脉动热管的毛细管结构和尺度效应实验研究

脉动热管的毛细管结构变化如何影响其性能是研究者关注的问题.本文对毛细管截面为正方形和正三角形,水力直径范围为1 mm左右的回路型脉动热管的传热性能进行了实验研究.结果表明,角管脉动热管的倾角变化时,底加热明显优于顶加热;三角形截面脉动热管的热阻比正方形截面脉动热管的热阻更低.脉动热管在水力直径为1.5 mm时比1mm时的性能要好.实验研究为理论分析打下了基础.