X射线荧光光谱法测定黄金首饰金含量不确定度的评定

黄金首饰的表层元素经X射线激发,发射出特征X射线荧光能量光谱线.不同元素的能量光谱线与其含量存在着特定的线性关系.能量色散X射线荧光光谱仪通过采用脉冲高度分析器和配套的相关软件将不同能量的脉冲分开,找出相应的元素,测量相应元素的具体含量值.通过X射线荧光光谱仪对黄金首饰的金含量测出的一系列测量值,依据GB/T18043-2013对黄金首饰样品金含量的不确定度进行计算.对采用的黄金标准物质运用最小二乘法建立数学模型,以标准值为x,3次测量值的平均值为y,找出线性关系方程.通过标准物质的运用,当置信因子k=2时,最终分别计算出18K金样品、足金样品金含量的扩展不确定度.     

基于规范及实测风谱的苏通大桥抖振响应对比研究

复核结构设计是桥梁结构健康监测系统的主要功能之一。以世界第一大跨斜拉桥——苏通大桥为工程背景,采用实测风谱对大桥设计阶段基于规范谱所进行的抖振分析进行验证。首先采用非线性最小二乘法对桥址区实测强风紊流功率谱密度函数进行拟合,获得实测谱曲线,并分别以该实测拟合谱和规范谱为目标谱分别模拟桥址区三维脉动风场。然后采用上述两种风场,基于ANSYS对苏通大桥进行非线性时域抖振响应分析。两种分析结果的对比表明:与实测谱相比,基于规范谱所得的主梁抖振响应情况不一,但主塔抖振响应均偏于保守;两种抖振响应的PSD曲线整体趋势基本一致。分析结果可为该桥的风致抖振性能评价提供研究信息,同时对其他类型结构的抗风设计具有重要的参考价值。     

空心包体式钻孔三向应变计测试技术探讨

探讨了澳大利亚CSIRO型空心包体式钻孔三向应变计的测量技术,重点介绍了测量元件应变片的布置形式和利用围压加载试验成果修正原始解除应变实测值的方法。对解除应变实测值的修正提出了具体方法,由修正后的解除应变推算的地应力实测值更精确。在三峡工程永久船闸开挖完成后岩体应力动态变化测量中,具体分析了测量元件应变片黏贴部位和角度的误差所引起的地应力实测值的误差,具体实施了对解除应变实测值的修正,实测的岩体应力动态变化更符合工程实际情况。     

小波变换在瞬变电磁勘探中的应用

根据瞬变电磁接收信号的频率范围可将地质体响应的有用信号和干扰信号分离,利用小波变换对接收的瞬变电磁信号进行多分辨率分析,通过分解与重构,将干扰信号去除,从中提取有效信号,就得到去噪后的信号。实例的结果表明:该方法对去除瞬变电磁晚期信号的噪声干扰有较好的效果。     

Digital Void Velocimeter

The paper describes the principle of measuring digitally the flow velocity of local voids, and discusses the accuracy of this method. It is shown that the spectrum of local void velocities can be determined reliably with digital values.

The measurement errors of void velocity u_g (m/sec) are within about ±9% in cases when the probes have detector head lengths of 0.8~1.0mm, and head diameters of 0.1 mmφ, when the voids have a flow velocity in the range of 0.2 m/sec≤u_g ≤1.2 m/sec and a radius of curvature of void of 2mm≤R≤16mm.     

A posteriori estimate of the random response of a dynamic system with autocorrelated additive noises

The signal recorded during the measurement of a mechanical system response is a mixture of a useful signal and random noises. On the one hand, these noises enter the investigated system directly, and on the other hand they are added to the signal during its transmission to the measuring device and its further processing. Thus, the measured signals are a stochastic function of the response and, consequently, provide only indirect, but the only information of the actual response of the investigated system. The problem is to determine most accurately the actual response of the investigated system by virtue of known outputs from the measuring system. As such a problem is not sufficiently determined in a general case, but it can be solved as an optimum estimate of actual response. It is coming to light, however, that in the meaning of the minimum mean square deviation of actual response and of this estimate the optimum a posteriori first stochastic moment of the response is conditioned by the measured signals. This article describes the principal characteristics of the mutually influenced investigated system and the measuring system. After a short analysis of the principal variant of the problem, assuming that all noises entering the system are Gaussian white noises, principal attention is afforded to the cases when the noises are described by more complicated autocorrelation functions. Cross correlation of noises, which are considered as additive only, is neglected.     

On the stereochemical composition of poly(vinyl chloride) (PVC) and polypropylene (PP): a phenomenological study

The number of mmr‐ and rrm‐based structures which occur necessarily whenever an isotactic or a syndiotactic sequence breaks off respectively; the extent to which they are isolated or are extended to atactic sequences, and the fact that the mmr repeating sequence, especially when it takes the GTTG^?TT conformation, is shorter and exhibits greater local free volume than rrm, mmm and rrr sequences, are shown to be the stereochemical composition determining structures in poly(vinyl chloride) (PVC) and polypropylene (PP) polymers. These structures, as analyzed by ¹³C NMR spectroscopy and probability calculations, have been determined as a function of the overall tacticity for one series of samples prepared by bulk polymerization at temperatures varying from ?50 °C to 70 °C, and one series of samples prepared by polarity‐based fractionation of a commercial polymer. Using this approach, the stereochemical composition of the samples could be identified. The results are of interest to understand the changes in the physical properties as shown in earlier and current work for both series of polymers. © 2003 Society of Chemical Industry     

基于短波测量数据的信道模型聚类方法

提出了一种使用减法聚类有效分类离散随机信道参数的方法．在青岛北京链路的信道测量数据基础上,使用该方法将短波信道测量计算出的信道参数分别进行一维和多维聚合分类,得到在特定链路、时间上,某频率对应的典型信道参数和信道模型,为短波频谱管理中的频率打分提供精确量化依据．     

Scaled consensus for MASs with compound noises over Markovian switched topologies

This article aims to address the stochastic scaled consensus issue in almost surely and mean square sense of stochastic multiagent systems (SMASs) with compound noises in a Markovian switching setting. At first, based on stochastic approximation technique and nearest-neighbor interaction rules, the stochastic scaled consensus controller is built for SMASs in presence of multiplicative and additive noise by designing a time-varying gain. Meanwhile, some consensus criterions of SMASs are addressed if the union of the graph and time-varying gain fulfill some mild requirements. Furthermore, the scaled consensus means that the agents' state variables tend to a prescribed proportion rather than the common value, so this behavior can be seen as non-convergent behavior. The difference with most of excellent literatures is that the coexistence of noncooperative behavior and multiplicative noise generates that it is not easy to transform the multiplicative noise term into the form of an error equation, which means that the Lyapunov methods cannot be directly utilized in our article. To cope with this, we first demonstrate the boundedness for each agent's state, and hence the convergence can be achieved. Finally, in order to reveal the efficiency of our proposed protocol, the corresponding example is given in the simulation part.     

Multiple models decentralized coordinated control of doubly fed induction generator

In this paper, a multiple model optimal tracking control (MOTC) design method for the double fed induction generator (DFIG) using correlative measured technique is proposed. The DFIG is represented by a third-order model, where electro-magnetic transients of stator are neglected. By using the correlative measured technique, the correlative measured matrix (CMM) of wind power system is obtained firstly. Then, a nonstandard state space equation of DFIG is obtained with the correlative measured vectors (CMVs), which reflect interactions between the DFIGs and grid. In order to cope with nonlinearities and continuous variation in the operating points, a multiple model design method is proposed in the discrete domain. The obtained control law, synthesized by using Bayesian probability, only depends on the local measured parameters. Hence, the MOTC can be regarded as a decentralized coordinated control, which can simplify the control structure and improve the transient stability of DFIG. To illustrate the effectiveness of the proposed MOTC strategy, simulations on a hybrid wind thermal power (HWTP) system are performed. The results show that the proposed MOTC strategy can provide acceptable performance throughout the whole operating region. Comparing to the conventional PID control, transient stability, damping, and fault ride-through capability of DFIG with the proposed MOTC design method have been improved effectively.