旋转盘腔流场速度与压力的实验研究

本文描述一个旋转盘腔流场的实验研究。该盘腔由一个旋转盘，一个静止盘及静止的外围屏组成．实验表明在盘腔的两个盘面上都有边界层形成，在边界层中，流体除有切向速度外，还有沿径向的二次流存在。在边界层外的核心区中径向速度为零。一般来说，静盘边界层比转盘边界层向紊流转捩地要早。另外，压力的测量表明，在半径较大的区域中压力分布可由“流体以恒角速度旋转”的假设所得的结果近似。     

用跃变旋转矢量研究滑动摩擦空气阻尼弹簧振子

运用跃变旋转矢量法,即通过旋转矢量的起点、长度和相位的变化规律对受到空气弱阻尼作用和滑动摩擦力作用的弹簧振子的振动进行了研究.讨论了在滑动摩擦力作用下空气阻尼为临界阻尼和欠阻尼情况下的弹簧振子的运动,根据阻尼和初值情况得出不同的振动曲线.并对弹簧振子4种相图和相图旋转矢量进行了比较.     

利用阻尼振动测量气垫导轨阻尼系数的新思路

利用气垫导轨上两根弹簧连接滑块做阻尼振动的模型,通过求解阻尼振动方程推算得到了滑块运动的最大速度衰减式,从而求得气垫导轨的阻尼系数.此外,从品质因数的角度推算阻尼系数的计算式,在阻尼很小时,该方法可视为最大速度衰减法的近似.通过气垫导轨阻尼振动实验,测量振幅、周期和光电门遮光时间等物理量,利用最大速度衰减和品质因数法得出阻尼系数的值非常接近.进一步对做阻尼振动的滑块拍摄视频,通过慢放视频得到其振动过程中振幅的衰减值,利用最大振幅衰减法计算出阻尼系数,所得结果与上述两种方法的数值符合较好,从另一个角度证明了本文提出的最大速度衰减法和品质因数法测阻尼系数的可靠性,该类方法在实验中易于操作、实践性强、所得结论可靠,为气垫导轨阻尼系数的测量提供了一种新的思路.     

轴向通流旋转盘腔中流动与传热数值研究

本文采用三维N-S非定常计算方法对旋转盘腔中的流动与传热进行了数值研究.数值计算结果表明;下游盘的Nu数径向分布与实验结果吻合较好,上游盘趋势吻合但数值上有一定差别;旋转盘腔中流体的整体转动速度小于旋转圆盘的转动速度.进一步计算结果表明,重力的影响大小与整体流态转速相对坐标系转速的比值密切相关,该相对转速越大影响越小,反之越大.     

基于时域BLT的多导体传输线串扰响应分析

当传输线上通有电压和电流信号时,会在其周围的传输线上产生串扰响应。采用时域BLT方程建立多导体传输线对多导体传输线的串扰模型,分析了不同数目和不同频率正弦波集总电压源激励下的多导体受扰线终端负载串扰电压响应特性。研究结果表明,受扰线终端负载上的串扰电压响应主要频点的个数与集总电压源的个数相同,响应频点与集总电压源的频率相等,响应幅值与相应电压源离受扰线的间距有关。     

基于时域BLT的多导体传输线串扰响应分析

当传输线上通有电压和电流信号时,会在其周围的传输线上产生串扰响应。采用时域BLT方程建立多导体传输线对多导体传输线的串扰模型,分析了不同数目和不同频率正弦波集总电压源激励下的多导体受扰线终端负载串扰电压响应特性。研究结果表明,受扰线终端负载上的串扰电压响应主要频点的个数与集总电压源的个数相同,响应频点与集总电压源的频率相等,响应幅值与相应电压源离受扰线的间距有关。     

一个描述Josephson振动阻尼效应的场方程

在GPE方程的基础上添加了一个耗散项-12γcψ,用来分析双势阱模型的Josephson振荡中的阻尼现象,并得出:凝聚态粒子总数及 Josephson振动的振幅随时间呈指数衰减.     

音叉振动阻尼系数的测定与研究

利用计算机的声卡采集音叉振动信号,研究了振动衰减过程中阻尼系数的大小,得出了阻尼系数不是常数,而是与音叉振幅成线性关系的初步结论,并用共振态下策动力振幅对音叉振幅的关系验证了这一结论.根据阻尼系数与振幅的关系解释了两种传统方法测量结果差别很大的原因.     

基于Phyphox的气垫导轨上弹簧振子的阻尼系数研究

组装ESP32开发板和超声波测距传感器,让装有Phyphox软件的智能手机通过蓝牙接收传感器的信号,研究弹簧振子在气垫导轨上做阻尼运动中不同挡板面积对阻尼系数的影响。实验结果显示,阻尼系数与挡板面积呈线性关系。     

图解法用于受迫振动实验的定量研究

用Origin科学作图,线性拟合得到自由振动下摆轮振幅θ与固有周期T₀的关系θ=10429-6525T₀,为后续实验图像的解析提供明确参考。分别使用逐差法和图解法处理阻尼振动和幅频特性的实验数据,得阻尼系数β为0.059 4 s^-1和0.061 0 s^-1。受迫振动幅频和相频特性曲线的拟合结果显示,当电机频率ω与摆轮固有频率ω₀相等时发生共振,振幅θ_r达144°,摆轮与强迫力的相位差φ_r为90°,很好验证了相关物理实验规律。解析共振处的特征参数,算出共振圆频率ω_r=3.985 9 s^-1,与系统固有频率ω₀(3.986 8s^-1)之间的相对误差仅0.023%,说明图解法用于《受迫振动》实验数据的定量分析与计算是非常成功的。     

Giant Hall effect in nonmagnetic granular metal films.

Nearly 3 orders of magnitude enhancement in the Hall coefficient is observed in Cu(x)-(SiO(2))(1--x) granular films. This large enhancement of the Hall coefficient not only is significantly larger than the prediction of the classical percolation theory, but also occurs at a metal concentration identified to be the quantum percolation threshold. Measurements of the electron dephasing length and magnetoresistance, plus the TEM characterization of microstructures, yield a physical picture consistent with the mechanism of the local quantum interference effect.     

Ab initio study on nonmetal and nonmagnetic metal atoms doped arsenene

The structural, electronic, and magnetic properties of arsenene doped with a series of nonmetals (B, C, F, N, and O) and nonmagnetic metals (Al, Ga, Li, Mg, and Na) are investigated using density functional theory. Magnetism is observed in the case of C. Among all the cases, the C-doped system is the most stable formed system. Hence, we study the ferromagnetic interaction in two-C-doped arsenene. Interestingly, both nonmagnetic (NM) and antiferromagnetic (AFM) states have been observed. As the increasing C?C distance, the magnetic coupling between the moments induced by two C is found to be AFM and the origin of the coupling can be attributed to the p?p hybridization interaction involving polarized electrons.     

Influence of nonmagnetic impurities on the kondo effect

The influence of scattering by nonmagnetic impurities is studied in perturbation theory. While the finite lifetime of the electrons in intermediate states due to scattering by nonmagnetic impurities does not lead to a change in the logT-behaviour of the third-order self-energy, certain vertex-corrections give rise to an additional term which varies like 1/√T at low temperatures. Similar correction terms are found to occur in the higher order self-energy contributions. Although these terms diverge more strongly atT=0 than the logarithmic contributions they are quite small at finite temperatures since they depend on the lifetime τ of the electrons through a factor of (? _F τ)^?5/2 (? _F Fermi energy). The possibility of observing these interference effects experimentally is discussed.     

基于遗传算法的金属辐射冷板换热性能优化研究

通过对金属辐射冷板传热数学模型的简化,得出影响辐射冷板换热性能的五个重要参数(冷水供回水平均温度、水流速度、管径、板厚、管间距)的数学描述。其次通过编写MATLAB遗传算法的金属辐射冷板目标函数优化代码,经遗传迭代求出辐射冷板换热性能目标函数的最值,及其对应的最优解组合。通过分析可知遗传算法能够有效的搜索到目标函数最优解,由于数学问题的提出是基于金属辐射冷板的基本原理,因此该算法具有一定的推广性,可用于多种形式的辐射冷板设计,能够有效、方便的提高辐射冷板的换热性能。     

Contact-induced magnetism in nanostructures based on chromium with nonmagnetic metal monolayers

Magnetic ordering is studied in Cr/X (1 ML) layer structures with monatomic layers (ML) of nonmagnetic metals (X = Sn, V, Ag, Au) incorporated into a chromium matrix. The mechanism associated with a redistribution of the charge and spin densities near the Cr/X interface and through which a spin-density wave (SDW) is induced and modified in these systems is analyzed. A semiphenomenological model is considered in detail in terms of which SDW structure near a single planar nonmagnetic defect can be described qualitatively using the Ginzburg-Landau functional. The spatial SDW configuration in a [Cr(t/X(1 ML)] superlattice is calculated, and the dependences of the SDW parameters on the temperature T, type of metal X, and superlattice period t are established. Based on the results of the study, experimental Mössbauer spectroscopy data are interpreted.     

金属挡板对平行线栅有界波模拟器的影响仿真研究

利用基于有限积分法的电磁场仿真软件CST仿真和分析了金属挡板对大型平行线栅有界波模拟器内部可用测试区和外部辐射电场分布的影响。首先建立了平行线栅有界波模拟器仿真模型,并依据GJB 8848证明了其合理性;而后重点分析了金属板对模拟器内部可用测试区电场分布的影响,并通过详实的数据列出了金属板位置、厚度、高度和长度等参数的具体作用效果;然后讨论了金属板对模拟器外部辐射电场的屏蔽效果;最后结合仿真结果提出金属挡板的设置应尽可能地远离模拟器,且有效反射面积越小越好,而对厚度无特别要求。     

New mechanism of the schoch effect in nonmagnetic dielectrics

A new type of a linear relation between the components of the magnetic field vector and those of the elastic strain tensor (a dynamic piezomagnetic interaction) is proposed. This relation is irrespective of the crystal symmetry and of the presence of a magnetic structure in the dielectric medium. This leads to anomalies in the reflection of a beam of shear bulk waves incident from the depth of the nonmagnetic dielectric medium on either its mechanically free surface or its slip boundary with a semibounded magnetic medium.     

Spin polarization of secondary electrons emitted from a nonmagnetic metal

We present the first angle-, energy-, and spin-resolved measurements of secondary electrons emitted from a Au(110) surface bombarded with unpolarized electrons. Both transversal components normal to and in the scattering plane, of the spin polarization vector exist. A simple two-step scattering process explains the observations, where the polarization is created via spin-orbit coupling in collisions of secondary electrons with ion-cores.     

Effects of nonmagnetic and magnetic impurities in the normal metal layer ofSNS junctions

The pair penetration depth into normal metal films containing various amounts of nonmagnetic or magnetic impurities is determined from the dependence of the critical current density on the normal metal film thickness in superconductor-normal metalsuperconductor junctions.     

The effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors

We investigated the effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors.A Lorentz-type magnetoresistance is obtained from spin-orbit coupling-dependent spin precession under the condition of a space-charge-limited current.The magnetoresistance depends on the initial spin orientation of the electron with respect to the hole in electron-hole pairs,and the increasing spin-orbit coupling slows down the change in magnetoresistance with magnetic field.The field dependence,the sign and the saturation value of the magnetoresistance are composite effects of recombination and dissociation rate constants of singlet and triplet electron-hole pairs.The simulated magnetoresistance shows good consistency with the experimental results.