形体细胞的MCEM模型及其光散射分布特征

针对光散射细胞微粒测量中真实形体细胞的取向对测量结果的影响问题，基于Rayleigh-Debye-Gans理论和双椭球核式(CEM)模型在应用中的差异，建立了CEM的修正模型(MCEM)，根据此模型系统讨论了细胞在不同入射角变化情况下其光散射强度分布所产生的变化，得到了不同入射角下有核细胞光散射强度分布与有核细胞相关物理特征量的动态响应关系；此外，对有核细胞光散射强度分布进行拟合，得到了有核细胞光散射强度分布函数。误差分析表明：拟合结果可有效地应用于真实细胞光散射测量中的数值反演计算。     

数字示波器测量RLC谐振特性

使用数字存储示波器测量RLC电路的幅频和相频特性,既能更清晰地观察信号相位变化及其物理含意,还可充分发挥其特色功能并采用离散傅里叶变换准确得到信号幅值和相位.由于使用比数字电桥更灵活的扫频设置可以消除测量频率点限制,而外置取样电阻则提高了理解I-V法测量原理的实在感.     

噪声信号特征量分布函数相似特性的研究

应用高速数据采集卡,记录悬浮颗粒计数光电传感器本底噪声信号序列值,研究噪声信号独立特征量, 如信号幅度极值、上升沿幅值、下降沿幅值、极值时序间隔,以及特征量乘积值等统计分布规律. 结果表明,上述独立特征量均能够与以自然数l为自变量的对数正态分布函数高度符合, 噪声信号特征量统计分布呈现出高度相似特征.基于这种统计相似性,还可推出噪声信号不同特征量对应的统计自变量之间的幂函数变换关系.噪声信号特征量统计分布函数相似性可理解为噪声信号集合统计分形特性的一种表现.     

可变温条件下材料表面的双向反射分布函数测量

基于双向反射分布函数单一参考测量法的测量原理,研制了一套测量温度最高可达500℃的双向反射分布函数测量系统。系统利用转角装置来实现不同角度位置的变换,用加热炉对试样进行加热,采用模糊PID控制器进行温度的控制。在25℃～500℃的温度范围内,对铜表面的双向反射分布函数进行了测量实验,光源采用可见光波长0.6328μm,功率约8mW的He-Ne激光器,选用Si1336-5BK光电探测器。实验表明：随着试样表面温度的升高,铜表面的BRDF测量值发生了改变;在温度上升或下降到同一温度时,铜表面的BRDF测量值不同。最后,对实验现象的形成机理进行了深入分析。上述实验结论对材料表面空间反射特性的研究具有重要意义。     

200—350nm合肥同步辐射光谱分布测量

英国国家物理实验室传递标准光源ＭｇＦ２窗口氘灯为标准，测量了２００－３５０ｎｍ合肥同步辐射光谱分布。结果表明，在实验误差范围内，测量结果与依Ｓｃｈｗｉｎｇｅｒ理论计算值具有较好的一致性，２００ｎｍ处偏差为６％，２４０ｎｍ处为１．５％。     

表征液态金属结构双体分布函数的讲授方法

双体分布函数是表征液态金属结构的重要方法,对理解液态结构具有重要的作用。本文根据分布函数能够完整地描述随机变量统计规律的内涵,并且决定随机变量其他概率特征的基本属性,结合双体分布函数简洁的数学表达和抽象的物理表征,在课程教学过程中,从双体分布函数的物理意义入手,介绍了实验中测量双体分布函数的手段,同时讲解了计算模拟中双体分布函数的统计方法,并以液态金属Nb和液态Ni-Zr合金的前沿科技成果为例,分析了不同有序度双体分布函数的曲线特征,讲授了其中物理过程与数学模型的内在联系。以典型案例将双体分布函数与液态结构变化的知识同步传授,形象且深刻地讲解了双体分布函数在液态金属结构中的表征过程。     

统计优化迭代法测量质子交换波导折射率分布

提出了一种用于拟合测量渐变波导的折射率分布的新的理论处理。该方法把统计优化手段导入循环迭代法 ,可适用于费米函数这一类曲线变化范围大、且有多个自变量的函数。实验上用焦磷酸质子交换制备了LiNbO3波导样品 ,用该方法对退火后的折射率分布作了测量拟合 ,折射率拟合值与实验值的均方差为± 8.2× 10 - 4。     

基于多波长激光吸收光谱技术的气体浓度与温度二维分布遗传模拟退火重建研究

利用可调谐半导体激光吸收光谱技术实现气体浓度温度二维分布重建.设计了气体浓度温度二维分布重建测量系统,采用四路波分复用技术以减少投影光路布置数量和增加气体吸收测量信息.针对于图像重建过程中建立的非线性投影方程组,将遗传算法与模拟退火算法相结合进行求解,在实现全局最优搜索基础上提高算法搜索效率.建立燃烧环境下H2O浓度温度二维分布模型,借助于近红外波段1.3—1.5μm范围内4条H2O气体吸收谱线,利用数值模拟计算方法进行了气体分布重建,重建结果与模型符合得很好.通过在投影数据中添加不同比例的随机误差,考察其对气体分布重建结果的影响.研究表明,气体浓度分布重建结果对于投影误差不敏感,而增加投影误差幅值将导致温度分布重建均方误差增大。     

广义参量Wigner分布函数:一种新的信号双域表示方法

本文基于分数傅里叶变换的概念,提出了由三个广义参量p1、p2和p3所表征的Wigner分布函数-广义参量Wigner分布函数,然后对其性质进行了讨论,并指出广义参量Wigner分布函数也属于一般的Cohen双线性类,而部分相干光场的互谱密度、传统的Wigner分布函数以及分数Wigner分布函数都可以作为广义参量Wigner分布函数在其广义参量取特殊值时的特例而得到,表明广义参量Wigner分布函数具有比传统的Wigner分布函数更强的信号表征能力.     

基于衍射层析理论的弱散射单颗粒粒径反演方法

衍射层析理论揭示了物体的散射场分布与物体的散射势之间存在傅里叶变换关系。基于衍射层析理论,提出一种反演未知折射率的浮游植物及其它弱散射颗粒粒径的方法。利用单波长、大角度范围内的散射光分布信息,通过傅里叶变换得到颗粒散射势的二次投影函数,进而获得颗粒粒径。进行数值仿真实验,并针对不同的测量角度范围、测量角度分辨率进行比较分析,结果表明:本文所开发的粒径反演算法可以通过测量大角度散射光分布,在适度噪声存在的情况下,准确反演与入射光波长相比拟的单个弱散射球形颗粒粒径。这一方法可用于测量未知折射率的浮游植物及其它微小颗粒粒径。     

Resonant excitation of single-pulse nuclear spin echo in magnetically ordered media

An analytical expression for a single-pulse nuclear echo signal in magnetically ordered materials has been obtained taking into account inhomogeneous broadening of the spectroscopic transition and non-uniform distribution of the enhancement factor. The signal has been shown to result from superimposing the nuclear magnetic moment oscillations of the same amplitude and phase that arise upon termination of a radio-frequency pulse. The cause for the effective suppression of oscillations of nuclear magnetic moments in the initial phase of the free precession signal has been determined analytically. The single-pulse echo signal amplitude has been found as a function of the external variable magnetic field strength, the exciting pulse duration, the inhomogeneous NMR line broadening, and the distribution width of the enhancement factor. The results have been compared with experimental data observed in a Co₂MnSi ferromagnetic polycrystalline sample. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 387–394, May–June, 2009.     

Choosing the amplitude interval for a proportional counter at a low signal level

A procedure is described for choosing the optimum pulse amplitude interval for a proportional counter when the useful signal level is comparable with the natural background level. It is shown that the optimum interval for counter pulses having a Gaussian amplitude distribution function corresponds to 1.4σ. The application of the procedure is demonstrated in a test example with processing of the iron K _α x-ray spectrum. Zh. Tekh. Fiz. 68, 126–127 (May 1998)     

悬浮颗粒散射脉冲信号群的统计分形特性

将PCI-9812高速数据采集卡与激光尘埃粒子计数光电传感器结合,对空气中悬浮颗粒群产生的散射脉冲信号数随幅度的统计分布p(l)进行高分辨率的测定.实验数据表明,在大样本条件下,脉冲信号集合整体及不同脉宽信号子集的p(l)函数在幅度定义域(V0,VM)内均以很高的精度满足对数正态分布形式,即该随机脉冲信号群具有统计分形(自相似)特征.进一步理论研究表明,p(l)函数具有非线性缩放不变性;且当统计参数满足(lnl-lnl)2lnl时,该函数与幂函数l-(1-ε)表现出几何相似性,其中ε1.     

Effect of thermal nonlinearity in high-absorption media on the parameters of the photoacoustic signal detected by the gas microphone method: The fundamental and second harmonics

A perturbation theory is put forward that describes the effect of thermal nonlinearity due to the temperature dependence of the thermophysical parameters of high-absorption systems with a low thermal conductivity on the parameters of the photoacoustic signal detected by the gas microphone technique. It is found that the dependence of the photoacoustic signal amplitude on incident beam intensity I ₀ stems from the dependence of the illuminated surface temperature on I ₀. This dependence is a complicated function instead of being a simple quadratic function as was expected. In the limiting cases (μ_sβ ? 1 and μ_sβ ? 1), this contribution to the photoacoustic signal amplitude is described by simple expressions, which are convenient for determining the thermal coefficients of the thermophysical parameters of the medium. It is found that the thermal nonlinearity significantly affects the photoacoustic signal phase in the frequency region meeting the condition μ_sβ ～ 1. In the above limiting cases, its effect is insignificant. A theory of generation of the photoacoustic signal second harmonic is proposed. The second harmonic is related to the temperature dependence of the thermophysical parameters of the buffer gas and sample. It is shown that the amplitude of the signal is a quadratic function of the incident beam intensity and varies with its frequency as ω^?3/2 for μ_sβ ? 1 and ω^?5/2 for μ_sβ ? 1.     

Single-pulse nuclear echo signals in magnetically ordered media

An analytical expression for the amplitude of a single-pulse nuclear echo signal generated in magnetically ordered materials is obtained taking into account the inhomogeneous broadening of the spectroscopic transition and the inhomogeneous distribution of the gain with an average value of greater than unity. It is shown that, in this signal, summation of the oscillations of nuclear magnetic moments with equal amplitudes and phases occurs at each instant of time. The cause of the effective suppression of the nuclear magnetic moment oscillations in the initial portion of the free precession signal is revealed analytically. The dependence of the amplitude of the one-pulse echo signal on the strength of an external alternating magnetic field, the pulse duration, and the width of the gain distribution is determined. The results obtained are compared with the experimental data for a Co₂MnSi ferromagnetic polycrystalline sample.     

Influence of structural interfaces on the statistics of corrosion microcracks

The amplitude distributions of acoustic emission signals generated during the formation of corrosion microcracks in loaded welded joints connecting two corrosion-resistant steel tubes are studied. For acoustic emission signal amplitudes of less than 0.6 mV and a microcrack concentration of ～10 mm^?3, the distribution density of the signal amplitudes is described by a gamma function. For acoustic emission signal amplitudes exceeding 1.0 mV and a microcrack concentration of greater than or equal to 10² mm^?3, the distribution density of the amplitudes exhibits two maxima, whose shape is described by a Gaussian function. The mean amplitudes of acoustic emission signals differ by a factor of 3. The change in the amplitude distribution of acoustic emission signals is explained by the effect exerted by the weld-metal interface on the microcrack formation.     

Optical-Information Transfer Through Perturbing Media and Determination of the Transfer Function

A version of the solution of the problem of simultaneous determination of the structure and characteristics of a two-dimensional signal and of two-dimensional complex transfer or instrumental functions is considered. The solution is based on measurements of four independent intensity distributions for spectral representation of a signal: I_sr(W_x, W_y) for a signal subjected to the transfer function, I_smrn(W_x, W_y) for a signal affected by additional specially produced modulation and the transfer function, I_srn(W_x, w_y) for a signal of the form I_sr(W_x, W_y) with a certain additional modulation at the output, and /₅mm(w_x,u/_y) for a signal of the form I_smr(W_x, W_y) with a certain additional modulation at the output. The intensity distributions obtained in the work make it possible to calculate the amplitude and phase components of the signal being analyzed and the transfer function. Additional modulations should provide visualization of phase information in one form or another.Linear amplitude modulation, which represents a particular form of spatial modulation, is analyzed. For this case, concrete expressions making it possible to calculate the amplitude and phase characteristics of the spectra of the signal being analyzed and the transfer function and, therefore, the characteristics of both the signal itself and the transfer function are obtained.     

Laser induced thermal desorption of carbon monoxide from Fe(110) surfaces

Thermal desorption of CO is induced by bombarding an Fe(110) surface with pulses of a neodymium glass laser. The maximum amplitude of the desorption signal is recorded by a mass spectrometer as a function of the laser pulse intensity and of the CO coverage for both single pulses and sequences of pulses. Since the half width of the laser pulses is only 30 ns the shape of the desorption signal is mainly determined by the time-of-flight of the desorbed particles. There is strong evidence that the latter obey a Maxwell-Boltzmann distribution of temperature T_d, identical in the low temperature range with the maximum surface temperature T_s. Above T_s = 600 K, however, T_d is smaller than T_s. The experimental observations are analyzed successfully with the first order rate equation for desorption.     

Improving the signal amplitude of meandering coil EMATs by using ribbon soft magnetic flux concentrators (MFC)

This paper presents a new method of improving the ultrasonic signal amplitude from a meander line EMAT by using soft magnetic alloy ribbon (Fe₆₀Ni₁₀V₁₀B₂₀) as a magnetic flux concentrator (MFC). The flux concentrator is a thin soft amorphous magnetic material (Fe₆₀Ni₁₀V₁₀B₂₀) which is very sensitive to a small flux change. The MFC is used with the EMAT to improve the signal amplitude and it was observed that the peak signal amplitude increases by a factor of two compared to the signal without MFC. Two dimensional numerical models have been developed for the EMAT with MFC to quantify the improvement of the received signal amplitudes. Model calculations and experiments have been carried out for a wide range of ultrasonic frequencies (500 kHz-1 MHz) in different materials.