Fourier变换光谱仪信噪比测量方法研究

对一种测量计算Fourier变换光谱仪信噪比的方法进行了修正.讨论了该方法与传统信噪比测量方法之间的关系,发现采用本修正方法计算的信噪比较传统方法计算的信噪比高约1.5倍,并通过计算机模拟和理论分析给予证明.讨论了Fourier变换光谱仪的主要误差源,特别提出在设计Fourier变换光谱仪时,为了避免零光程差采样位置的变化引起的复原光谱强度失真,采样频率应适当高于Nyquist频率.     

用EWB仿真软件研究傅里叶合成波形失真原因

针对某周期电信号傅里叶分析仪合成方波时出现的合成波形严重畸变的现象，采用EWB软件仿真方波的合成，查找波形失真的原因．设计“移相补偿电路”，纠正“左右不对称失真”和“幅度失真”．     

超声光衍射强度的一组解析表达式

对光垂直入射于声波传播方向,而在声-光衍射谱中只有零级和正、负一级光的特定条件下,本文应用简正波方法推导了该三级衍射光(n=0,n=+1和n=-1)强度的解析表达式。该表达式与Nath从Raman-Nath方程出发所给出的结果是一致的。文中,应用数值计算方法,在1≤Q≤10的范围内,给出了该表达式能成立的条件。     

落球加速运动的路程

导出了落球法测粘度的二级半公式，误差≤0．022％．由于定义了雷诺数的零级近似R一级近似RI，使公式和计算大为简化．如果误差≤0．1%能满足要求，在R0≤0．005时可采用零级近似，0．005＜R0≤0．123时采用一级近似，R00.123时才采用二级半近似．     

平板在任意周期表面热扰动作用下的非Fourier热传导的求解与分析

分析了平板前表面遭受任意周期热扰动这类非Fourier传热情形下的温度响应. 采用双曲型热传导方程描述平板表面温度急速变化时的热传导问题. 为求解此类方程, 首先 利用分离变量法和Duhamel积分原理, 得到了平板前表面遭受突变热流和简谐热流两种情况下的解析解.然后, 在此基础上应用Fourier级数展开法和叠加原理, 获得了平板前表面热流任意周期变化时非Fourier热传导下温度场的解析表达式. 利用得到的解析表达式进行数值模拟, 分析了不同热松弛时间、 不同时刻和不同位置对温度响应的影响, 讨论了非Fourier热传导模型所给出的温度响应与Fourier热传导模型的差别. 这种方法能够处理许多在生产实际中具有周期边界条件的非Fourier热传导问题. 关键词： 非Fourier 热传导 周期变化 温度响应 平板     

无限深方势阱的求解中存在的一普遍错误

许多量子力学和近代物理教课书中,在求一维无限深方阱中粒子的能级及其对应的波函数时,取区间0≤x≤L内,势为零,其他区域,势为无穷大。在阱内,不含时的薛定谔方程是这里K=2mE/h2≥0,m是粒子的质量,E是粒子的能量。波函数　(x)遵从这条伴(0)=(L)=0。 在此问题的标准处理中,写出(1)的通解,其形式是其中A=A(K), B=B(K)。在x=0,边界条件要求B=0.因为这两个任意常数至少有一个不为零,在x=L处,这条件要求K=n/L,这里。的可能值是0,±1,±2,…….n取负值仅导致波函数符号的改变,而这在物理上无关紧要,因此可以弃掉。 n=0的值必须弃去,在标准处…     

多孔和复合媒质直流电导率的计算方法(Ⅰ)——应用于周期性多孔媒质

我们发展了一种计算多孔和复合媒质直流电导率的第一性原理方法。本文具体讨论周期性多孔媒质直流电导率的理论计算。我们用幂级数展开法、Fourier级数展开高斯消去法和Fourier级数展开迭代法计算了许多二维多孔媒质的有效电导率,并采用改进的迭代法计算了Sierpinski地毯的直流电导率的临界指数。所有结果都与最新的实验结果符合相当好。 关键词：     

ZnS/ZnSe周期性迭层介质中光的反射特性分析

基于光在多层介质中的传输理论,对ZnS/ZnSe周期迭层介质结构中光的反射特性作了分析和计算,由得到的Bragg反射率与光波长的关系曲线,发现当ZnS/ZnSe的折射率改变时,其Bragg反射率曲线将发生平移,平移的方向与Δn为“正”或“负”有关.据此,提出了利用ZnS/ZnSe的光学非线性特性,可能研制出光控“开关”或“光逻辑门”,用于光计算和光互连.     

IM－DD SCM光波系统的非线性分析

本文在简要分析了激光器非线性机理的基础上,采用计算机模拟及数学归纳的方法,着重分析了IM-DDSCM光纤通信系统中各种非线性失真项的数目、幅度及其抑制方法,归纳出了落入各个信道中的各种非线性失真项的数目的数学表达式,推导出了非线性失真项的功率之和的计算公式;通过对计算结果的比较得知,激光器P-I曲线的非线性是影响系统非线性失真的主要因素,指出了利用预失真的方法补偿激光器P-I曲线非线性的影响。     

Y_1Ba_2Cu_3O_(7-δ)的氧离子缺位数,氧空穴数变化与结构相变的关系

在空气、氮气、真空(10^(-3)乇)、氧气等气氛条件下,利用高温 X 射线动态跟踪法和 TG-DTA测定了 Y_1Ba_4Cu_3O_(7-δ)的结构和氧缺位量随温度的变化,注意到不同气氛对超导体中晶格氧和吸附氧的动态平衡的影响;测得氧缺位量δ与晶体结构转变之间的关系.根据文献[11]关于Cu-O 间电子转移的结论,计算出 Cu-O_2层中 O 的平均空穴数 n_h 与结构变化的对应关系.O≤δ≤0.25,0.25≥n_h≥0.125为正交超导相的稳定区,氧的空穴浓度为(1.44—0.72)x10^(21)/cm^30.25≤δ<0.5,0.125≥n_k>0为正交、四方相的转变过渡区;0.5≤δ≤1,n_h=0为四方非超导相的稳定区.因此,除了四方非超导结构区氧负离子取2价外,其它情况氧负离子也不总是取负2价.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.