Calculation of the electrostatic potential of the diode system based on a sharp-edged field cathode

A mathematical model of a diode system based on a sharp-edged field cathode is presented. The surface of the sharp-edged cathode is simulated by two infinitely thin spherical segments, while the anode is modeled by a single infinitely thin spherical segment. The region occupied by the cathode is a lens (lune-shaped region). The problem of the electrostatic potential distribution in the entire domain occupied by the system is solved.     

Resonantly enhanced strip-line technique to measure microwave permeability of thin films

The sensitivity of a reflective single-port strip-line technique is increased by 10-20 times by amplification of a measured reflectivity response at a set of resonance frequencies. The resonant behavior is organized by connecting the strip cell to a network analyzer through a capacitor with a long coaxial cable. The capacitance defines the amplification; the cable length defines the resonance frequencies. S-parameters of the coaxial-to-strip junction and the field inhomogeneity inside the cell are accounted for by a reference measurement of sample with known constitutive parameters. Two methods for permeability calculation are suggested. The fist method is based on the comparison of Lorentzian parameters of resonance reflectivity curves. The second method is based on numerical solution of Fresnel's equation. The enhancement is essential at low-frequency part of the band, where the cell reflectivity is close to unity and the sensitivity of non-resonant technique is poor. The technique sensitivity is estimated by permeability measurements of Al stripes with different cross-section.     

Enhancement of an Instability by Internal Feedbacks in a Plasma

The electron-ion instability is excited in counterstreaming ion beams and plasma system. The instability is a new type of standing oscillations whose wavelength is given by D/n, where D is the distance between boundaries and n is an integer. The amplitude is controlled by a difference between the velocities of the beams, which changes the phase of a feedback loop. The internal feedback is caused by a reflected wave and by a coupling between the boundaries. Temporal evolution of the instability is measured and is found to agree with numerical solutions of the Van der Pol equation including a feedback term. A measured growth rate is proportional to the square of the oscillation amplitude.     

Boson Mean Field Theory of Effective Holon-Holon Interaction in the RVB Model

The RVB model is investigated by a mean field theory, in which the holon is expressed by a fermion operator, and the spinon by a boson operator. The effective holon-holon interaction by exchanging the spinons is derived for T≠0. It is found that the interaction is attractive.     

Stochastic Dynamics of Reduced Wave Functions and Continuous Measurement in Quantum Optics

The stochastic dynamics of open quantum systems interacting with a zero temperature environment is investigated by employing a formulation of quantum statistical ensembles in terms of probability distributions on projective Hilbert space. It is demonstrated that the open system dynamics can consistently be described by a stochastic process on the reduced state space. The physical meaning of reduced probability distributions on projective Hilbert space is derived from a complete, orthogonal measurement of the environment. The elimination of the variables of the environment is shown to lead to a piecewise deterministic process in Hilbert space defined by a differential Chapman-Kolmogorov equation. A Hilbert space path integral representation of the stochastic process is constructed. The general theory is illustrated by means of three examples from quantum optics. For these examples the microscopic derivation of the stochastic process is given and the general solution of the differential Chapman-Kolmogorov equation is constructed by means of the path integral representation.     

Synthesis and characterization of palladium nanoislands on the silicon surface

Samples representing a system of Pd nanoparticles on a Si surface is obtained. The metal is deposited onto the substrate by thermal evaporation in vacuum. The system of nanoparticles is formed using a thin screen located at an angle to the substrate and by vacuum annealing of ultrathin continuous palladium films. The chemical composition of the deposited substance is studied by Auger electron spectroscopy. The size and topology of the islands on the surface is established by scanning electron microscopy.     

多层球对高斯波束散射的德拜级数研究

基于广义洛伦兹-米氏理论,利用多层球粒子散射系数的德拜级数展开公式,提出了一种新的研究多层球粒子对高斯波束散射的方法。计算结果与已有的广义洛伦兹-米氏理论算法的计算结果吻合得很好。利用该方法有效分离了折射率分布满足指数变化规律的多层球粒子对高斯波束散射的远区散射场中多阶彩虹的干涉强度分布。数值模拟了双层球的归一化双一阶彩虹强度分布以及各层的一阶彩虹艾里结构。最后分析讨论了高斯波束的入射位置和束腰半径对多层球单阶彩虹强度分布的影响。     

基于单片机的亥姆霍兹线圈磁场分布测量装置的研制

介绍了设计制作的基于AVR单片机的亥姆霍兹线圈磁感应强度分布测量装置。单片机统一协调和控制整个系统的工作,步进电机和丝杆控制霍尔元件的移动,A/D芯片将霍尔电压转换为数字信号,通过USB接口传输到上位机,上位机计算磁感应强度,并画出磁感应强度分布曲线。装置工作稳定,测量结果与理论值符合较好,可用于学生实验或演示实验中。     

数字散斑相关方法实现鼠标定位原理

在激光鼠标工作原理的基础上,利用数字散斑相关方法对激光鼠标的定位原理进行了研究。设计实验得到散斑场并用数码相机拍摄。用图像采集卡采集CCD扫描数散斑图像得到的图像,将图像数字化,分析数据得到了图像最优采样的像素单元和图像位移两个参量。基于两个参量,实验采集散斑图像在一定的轨迹运动下的散斑场,用Matlab软件模拟,并比较分析了实验和模拟结果。结果表明,用数字散斑相关方法可以实现激光鼠标的定位功能,并且分辨力可达到1μm,远高于市场上激光鼠标30μm的分辨力。     

声表面波在线性调频声栅上作Bragg衍射后的聚焦声场

本文应用准周期概念给出声表面波在线性调频声栅上Bragg衍射的透射函数。将一级衍射波的分布作为有限孔径内的已知分布。将求解透射区的一级声束的场分布问题作为求上述有限孔的衍射问题来处理。分析结果表明,对偏转声束来说,在Fresnel区存在一个Fraunhofer平面。线性调频声栅同时起两个作用:它既相当于一个等周期的声束偏转器,同时又是一个Fresnel透镜,在焦平面上的声场分布,是声栅出射平面上偏转声束幅度分布的Fourier变换。分析结果还表明:聚焦声轴随入射声波频率而平行移动。这一现象属首次发现,实验结果证实了上述理论分析预计。 关键词：     

紫外单光子成像系统的研究

搭建了紫外单光子成像系统,详细介绍了该系统的组成、工作原理和分辨率性能测试.由汞灯发出的紫外光经过大气散射、多块减光片得到了紫外单光子流.单光子直接打在微通道板上,微通道板产生的倍增电子由楔条形阳极收集,电荷灵敏前置放大器将阳极输出的电荷信号转变为电压信号,主放大器对前放信号进行滤波整形.利用高速数据采集卡连续采集主放大器的输出波形,通过软件对采集波形进行处理,采用图像处理技术得到了紫外单光子10min的计数图像,并对图像进行了畸变校正.此外,通过自己设计的分辨率板,测得该系统的分辨率可达150μm.该系统在极微弱光探测成像,生物发光,空间环境探测等方面具有广泛应用. 关键词： 单光子计数成像 阳极探测器 楔条形阳极 分辨率     

基于Labview的回波厚度测量系统

建立了基于Labview的回波厚度测量系统,用金属球撞击待测物体表面,产生脉冲声波,用换能器在待测物体表面接收物体内部多次反射的声波,用傅立叶变换计算出声波在物体内部的传输时间,就可得到待测物体的厚度。该测量方法具有成本低、设计新颖、物理思想清晰的特点,适合于发展为综合设计性大学物理实验项目。     

Individual,attractive defect centers in the SiO2-Si interface of μm-sized MOSFETs

In a micron-sized p-channel MOSFET, the alternate capture and emission of holes into a Coulomb-attractive defect center is analyzed by the random telegraph signal in the source-drain current. Anomalous switching is observed with a high channel conductance when the defect center is occupied, and a low channel conductance after re-emission. The rate constants show an inverse symmetry for capture and emission. The measured results are interpreted by a tunneling transfer of a hole bound in the channel at the attractive center to the defect center 2.4 nm deep in the oxide and vice versa. The energy offset of the two stable configurations can be linearly varied by the gate voltage. An excited state 40 meV above the ground state is observed for the defect level. The anomalous switching is caused by a mobility change rather than by a change in mobile charge carrier density. The tunneling transfer for Coulomb-attractive centers differs from the transfer observed for Coulomb-repulsive centers where activated emission is reported.     

Granular Rayleigh-Taylor instability: experiments and simulations

A granular instability driven by gravity is studied experimentally and numerically. The instability arises as grains fall in a closed Hele-Shaw cell where a layer of dense granular material is positioned above a layer of air. The initially flat front defined by the grains subsequently develops into a pattern of falling granular fingers separated by rising bubbles of air. A transient coarsening of the front is observed right from the start by a finger merging process. The coarsening is later stabilized by new fingers growing from the center of the rising bubbles. The structures are quantified by means of Fourier analysis and quantitative agreement between experiment and computation is shown. This analysis also reveals scale invariance of the flow structures under overall change of spatial scale.     

The transient response of a transversely isotropic cylinder under a laser point source impact

The transient response of a transversely isotropic cylinder under a laser point source impact is solved theoretically. The radial displacement generated by the laser under the ablation regime is numerically calculated by introducing Fourier series expansion and two-dimensional Fourier transform. The validity of this theoretical solution is demonstrated on a fiber reinforced composite cylinder with a strong anisotropy. Experimental displacements are detected at the cylinder surface by the laser ultrasonic technique, and are analyzed by the ray trajectories. Corresponding theoretical displacements are calculated numerically and compared to the experimental signals. Good agreement is found. The diffraction effect caused by the cusp is observed in both theory and experiment.     

一种基于LabVIEW的光谱仪设计

利用虚拟仪器开发软件LabVIEW设计了一台光谱仪,使用CCD一次接收整个光谱,同时利用LabVIEW高度集成化的模块进行显示、分析等处理,效率高,开发周期短,仪器使用方便,功能多且易于扩展.     

Dynamics of money

We present a dynamical many-body theory of money in which the value of money is a time dependent "strategic variable" that is chosen by the individual agents. The value of money in equilibrium is not fixed by the equations, and thus represents a continuous symmetry. The dynamics breaks this continuous symmetry by fixating the value of money at a level which depends on initial conditions. The fluctuations around the equilibrium, for instance in the presence of noise, are governed by the "Goldstone modes" associated with the broken symmetry. The idea is illustrated by a simple network model of monopolistic vendors and buyers.     

The steady state response of a damped circular plate driven at a diameter

The steady state response of a damped circular plate transversely or rotationally driven at a diameter is determined by the series-type method. With the reaction force or moment acting along a diameter of a circular plate regarded as an unknown harmonic load, the response of the plate to the load is expressed by the Green function. The force or moment distribution along the diameter is expanded into Fourier series with unknown coefficients, and the simultaneous linear equations for the coefficients are derived by the restraint condition on the diameter. The dynamic response of the plate is determined by solving the equations. The method is applied to circular plates driven by a sinusoidally varying transverse deflection or angular rotation at a diameter, and the steady state response of the plates is studied.     

二次彩虹法测量高折射率玻璃微珠折射率研究

基于米氏散射理论解释了激光照明下玻璃微珠的二次彩虹精细结构的成因,发现折射率的差异将直接影响二次彩虹精细结构的位置.对于实验中玻璃微珠半径变化引起二次彩虹精细结构间距变化的现象亦用米氏散射理论进行了模拟分析和实验研究.利用米氏散射的近似理论——艾里理论对玻璃微珠的折射率进行了测量.在对玻璃微珠二次彩虹精细结构所计算得到的折射率的统计分析基础上,通过校正测量误差后得到了玻璃微珠折射率的准确数据.     

Electron capture by charged impurities in semiconductors under conditions of spatial diffusion

The capture of electrons by charged impurities in semiconductors due to spatial diffusion is investigated theoretically. In a semiconductor, an electron either can be captured by the field of a charged impurity if this electron loses energy by emitting phonons or can be ionized from the trapping state if it acquires energy by absorbing phonons. The electron trapping is governed by a change in the distribution function of electrons in both coordinate and momentum space. The trapping coefficient is calculated under the condition where it is determined by the diffusion redistribution of the electron density in the field of a charged impurity.