X射线荧光光谱法检验橡胶鞋底的研究

建立一种简便快速、灵敏准确、无损的检验橡胶鞋底物证的分析方法,为侦查破案提供线索、指明方向,为证实犯罪提供科学的依据。利用能量色散型X射线荧光光谱仪,电压为45 kV,电流为40 A,功率为1.8 kW,样品量为1.5 cm1.5 cm,测试时间60 s。对不同品牌、不同种类的40个橡胶鞋底样品中的无机元素进行定性和半定量分析,并考查了该方法的重现性。依据样品中所含元素的种类及含量的不同,可以对不同品牌、同一品牌不同种类的橡胶鞋底样品进行区分。同时,利用SPSS聚类分析-重心法作为类间定义距离,对橡胶鞋底样品进行分类,样品的聚类效果很好。试验结果表明:利用该方法检验橡胶鞋底样品简便快速、结果准确可靠、重现性好、无需制样且无损检材,可用于公安机关实际办案。     

X射线荧光光谱结合多元统计学检验纸张灰烬

为了实现对案件现场残留的纸张灰烬样品快速、准确地检验与认定,采用X射线荧光光谱法(XRF)结合多元统计学的系统聚类和主成分分析法测定32个不同来源、不同用途的纸张灰烬,进行了理论分析和实验验证.结果表明,根据样品所含元素种类和含量的不同,可以准确地将样本进行区分;同时,将32个样本分为五大类,两种分析方法所得到的分类结...     

X射线荧光光谱结合深度学习算法可视化检验食品包装纸

为了实现对案件现场常见食品包装纸的快速分类及认定,提出一种基于X射线荧光光谱(XRF)结合深度学习算法的食品包装纸可视化检验方法.首先,采用XRF检验44个不同来源的食品包装纸样本中的无机元素,并根据主要构成元素的含量,对其进行人工分类和系统聚类分析.其次,分别使用主成分分析和t分布随机邻域嵌入两种降维算法处理数据以检...     

软X射线成像光学技术的发展

成像光学系统的基本性能的要求是分辩率。根据成像原理,分辩率受光波衍射的限制。提高衍射极限分辩率的途径之一是减小波长。X射线光学成像是在这一指导思想下开始研究的,电子光学成像也是这样。而且这两种成像技术的研究,在历史上几乎是同时并进的。1895年伦琴发现X射线,1897年J.J汤姆逊证实了电子的存在;1923年康普顿证明了掠入射条件下射线在抛光金属表面可以像可见光一样反射、聚焦,1926年H。布希等证明了旋转对称静电场和静磁场可以使电子束偏折、聚焦和成     

X射线荧光层析

X射线荧光层析技术是利用内壳层电子跃迁所发出荧光辐射,来测定样品中的元素含量,获取样品内部的结构信息。Wolter型掠入射镜装置的元素灵敏度可以达到100个原子／cm^3,空间分辨率达到微米量级。结合康普顿散射和吸收层析进行成像可使其图像质量得到进一步的提高。而当获得了物体的投影数据以后,可采用各种重建算法来使物体得以准确重现。介绍了几种常用的重建算法,并就其特点进行了比较。     

早期的X射线光学：—采访Albert V.Baez

早期的Ｘ射线光学──采访ＡｌｂｅｒｔＶ．ＢａｅｚＡｌｂｅｒｔＶｉｎｉｃｉｏＢａｅｚ：在德鲁大学获得数学和物理学士学位，在锡拉丘斯大学获得数学硕士学位。二战后，他在ＰａｕｌＫｉｒｋｐａｔｒｉｃｋ领导下从事教学和指导研究生的工作。Ｂａｅｚ和Ｋｉｒｋｐａｔ...     

硬X射线相位衬度成像的实验研究

介绍了硬X射线(类同轴)相位衬度成像的工作原理及其实验研究结果。X射线波长为0．08860nm,样品为未经任何处理的飞蛾，记录介质为X射线胶片。胶片经处理以后，用光学显微镜读出，可以看出样品的许多细节,尤其在折射率突变处。而同样条件下基于吸收衬度机制的硬X射线吸收成像，由于是弱吸收样品．没有观察到任何图像。     

宽带高斯型功率谱噪声信号相关特性分析

宽带噪声雷达具有良好的抗干扰和低截获性能.传统的窄带相关函数由于忽略了运动目标的多普勒色散效应而无法准确分析宽带信号的相关特性.本文以宽带噪声调频雷达测量高速目标为研究背景,推导了宽带相关函数均值的解析表达式,并对其进行了仿真验证.在此基础上分析得出,当多普勒色散积较大时宽带相关函数具有双峰特性,并揭示了其产生原因,指出了双峰位置与多普勒色散积及相对带宽之间的关系.为宽带高斯谱噪声雷达的分辨力和检测性能分析以及系统的参数设计提供了理论基础.     

Common-cause failure analysis of a k-out-of-n:G system with repairable units

A newly developed generalized expression for the mean time to failure of a k-out-of-n: G system composed of repairable units and subject to common-cause failures is presented. Also, reported are some special case system reliability and variance of time to failure formulas.     

乙醇对人血液荧光光谱的影响

本文用荧光光谱方法研究了血液和酒精的相互作用.乙醇对人血液的荧光强度的影响基本上分为两个阶段:第一阶段是加入微量乙醇,剂量从5μl/4ml至20μl/4ml的乙醇(白酒,体积分数56％);第二阶段是加入大量的乙醇,剂量从0.4ml/4ml至1.2ml/4ml.两个阶段酒精的剂量相差两个数量级.在不同的情况下荧光强度或波形都有所不同.作者借助光谱知识对这些实验结果做了分析和讨论.这对进一步研究酒精对人体伤害或者临床研究提供一些依据.     

Reliability of k-out-of-n nonrepairable systems with nonindependent components subjected to common shocks

This paper investigates the reliability of nonrepairable k-out-of-n systems with nonidentical components subjected to independent and common shocks. Some numerical examples are added to show how one can utilize the derived results to calculate the reliability for practical problems. The relationship between the failure rate of the system and that of its components is also investigated.     

Multidimensional cubic constellation with non-flat power spectrum

The author presents a multidimensional cubic constellation with a non-flat power spectrum. The objective is to maximise the rate for a fixed average energy, subject to certain constraints on the resulting power spectrum     

跳时脉位调制超宽带信号的功率谱密度分析

通过对时域信号的自相关时间均值函数做傅氏变换,推导出定周期跳时脉位调制超宽带脉冲序列的功率谱密度公式,形式更加简明;并分别在时域和频域进行仿真、分析,比较两种仿真结果,同时分析了跳时码周期和时延常数等参数对谱密度结构的影响,验证了推导结果与时域仿真的一致性。     

Advanced spectrum estimation methods for signal analysis in power electronics

Modern frequency power converters generate a wide spectrum of harmonic components. Large converters systems can also generate noncharacteristic harmonics and interharmonics. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present and the periodicity intervals are fixed, while periodicity intervals in the presence of interharmonics are variable and very long. A novel approach to harmonic and interharmonic analysis, based on the "subspace" methods, is proposed. Min-norm harmonic retrieval method is an example of high-resolution eigenstructure-based methods. The Prony method as applied for signal analysis was also tested for this purpose. Both high-resolution methods do not show the disadvantages of the traditional tools and allow exact estimation of the interharmonics frequencies. To investigate the methods several experiments were performed using simulated signals, current waveforms at the output of a simulated frequency converter, and current waveforms at the output of an industrial frequency converter. For comparison, similar experiments were repeated using the fast Fourier transform (FFT). The comparison proved the superiority of the new methods. However, their computation is much more complex than FFT.     

Determination of the composition of multicomponent chalcogenide semiconductors by X-ray fluorescence analysis

The composition of As _x (Ge _y Se_{1 ? y} )_{1 ? x} glassy alloys is quantitatively determined by measuring the X-ray fluorescence spectrum of a Ge_0.2As_0.4Se_0.4 reference alloy. The atomic fractions of arsenic, germanium, and selenium are calculated from the X-ray fluorescence spectra and the x _RFA = f(x) and y _RFA = f(y) dependences are plotted. These dependences make it possible to determine the composition of the glasses with an accuracy of ±0.0005 for x and y. This procedure is effective for finding the concentration of the tin impurity in Pb_{1 ? x} Sn _x Se crystalline solid solutions. However, it is impossible to determine the content of tellurium in Te _x (As _y Se_{1 ? y} )_{1 ? x} glassy alloys because the alloy components have significantly different X-ray fluorescence characteristics.     

Determination of the composition of binary chalcogenide glasses by X-ray fluorescence analysis

To quantitatively determine germanium, arsenic, sulfur, and selenium contents in As_{1 − x} S _x , Ge_{1 − x} S _x , As_{1 − x} Se _x , and Ge_{1 − x} Se _x glassy alloys by X-ray fluorescence analysis, a technique using standards was developed. This technique allows quantitative determination of the composition of these glasses with an accuracy of ±0.001 with respect to the parameter x.     

An algorithm for combined cell-site selection and power control tomaximize cellular spread spectrum capacity

There is much current interest in spread spectrum wireless mobile communications and in particular the issue of spread spectrum wireless capacity. We characterize spread spectrum cellular capacity and provide a combined power control, cell-site selection algorithm that enables this capacity to be achieved. The algorithm adapts users' transmitter power levels and switches them between cell-sites, and it is shown that the algorithm converges to an allocation of users to cells that is optimal in the sense that interference is minimized. The algorithm is decentralized, and can be considered as a mechanism for cell-site diversity and handover. We provide numerical examples to show how effectively the algorithm relieves local network congestion, by switching users in a heavily congested cell to adjacent, less congested cells