用信号处理技术及传播理论还原雷声频谱

以往关于雷声的研究都限于观测点雷声频域范围的探讨, 由于噪音和衰减因素的影响, 观测点的雷声频谱有很大失真. 针对在兰州地区观测的一次雷暴过程中的雷声信号, 利用数字信号处理技术,由观测点处的雷声音频信号得到频率谱,并对雷声频谱进行噪音分析; 然后结合声音在大气中传播的衰减理论, 分析了不同大气环境对声吸收的影响, 并推算出了声源附近的雷声频率谱. 关键词： 雷声频谱 信号处理 传播理论 峰值频率     

基于扩频码的单载波迭代频域均衡水声通信

单载波时域均衡在长时延扩展水声信道中计算量大,并对接收机参数的选择较为敏感,可靠性低,而正交频分复用信号峰均功率比高、对频率偏移敏感. 针对这些问题,提出基于扩频码的单载波块传输高速率水声通信方法和基于T/4分数间隔迭代频域均衡的接收机算法. 该接收机利用已知扩频码进行信道估计以及对由多普勒偏移引起的旋转相位进行估计,并通过一种低复杂度迭代频域均衡算法改善系统性能. 开展了湖上实验研究,结果表明在浅水1.8 km距离且复杂多径干扰条件下,利用BPSK/QPSK调制可实现10^-2–10^-4的误码率并达到1500–3000 bit/s的有效数据率. 关键词： 水声通信 单载波 频域均衡 迭代处理     

The C2π and the X2σ States of BaF

An extensive calculation was carried out using the precisely measured value of the Q-band heads and the following molecular constants for the C²π¹ ₂ and the X²σ states, which are responsible for the Green Band System of BaF, were determined.     

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Studies on the workability of precise seeders by means of labelling methods has been possible due to the solution of the following problems: labelling of seeds, radiation collimation of labelled seeds being sown, elaboration of measuring and registering systems as well as processing systems of a measuring signal. The developed method allows for precise, quick and fully objective evaluation of the studied seeders to be done under natural conditions.     

Analyse der Rückstoßprodukte in neutronenbestrahlten Phenylarsenverbindungen, 3. Mitteilung: Über die Bestimmung der Ausbeute an Diphenylarsen-Rückstoßprodukten

Für das in der 1. Mitteilung [1] beschriebene Trennverfahren zur Anfarbeitung bestrahlter Mono-, Di- und Triphenylarsenverbindungen sollte die Effektivität der chromatographischen Trennung an dem Kationenaustauscher KPS (6% DVB) mit Hilfe einer unabhängigen Methode überprüft werden. Außerdem sollten Hinweise über Art und Anzahl der nichtidentifizierten ?unbckanntcn Produkte“ erhalten werden, die gemeinsam mit den Diphenylarsen-Rüekstoßprodukten im NaOH-Eluat auftreten. Zu diesem Zweck wurde die von Siuda [2] vorgeschlagene papierelektrophoretische Trennung benutzt.     

Interfacial interaction in carbon fiber/thermoplastic composites

This work was undertaken in order to increase the understanding of the mechanism responsible for fiber/matrix interaction in carbon fiber/thermoplastic composite. From results of previous study on carbon fiber/PEEK composite, which suggested that the formation of the fiber/ matrix interaction was primarily related to a chemisorption mechanism, a study was done of the conditions required to obtain efficient fiber/matrix interaction in PA-12 and PP/carbon fiber composites. The interest in studying carbon fiber composite based on PP and PA-12 was that these two matrices are very different in terms of reactivity, polyamide having many more reactive groups than polypropylene. As expected, due to the non-reactive chemical structure of the polypropylene, fiber/matrix interaction in carbon fiber/PP composite occurred only when the matrix was thermally degraded, i.e. when the composite was molded at high temperature or under long residence time at the melt temperature. For the carbon fiber/PA-12 composite, strong fiber/matrix interaction occurred readily at relatively low molding temperature, i.e. well before thermal degradation of the matrix. It was also found that the short beam shear strength in these composites seems to evolve with molding temperature, and a maximum interfacial strength was observed at a molding temperature corresponding to the thermal degradation of the matrix. This indicates that although matrix degradation often results in strong reduction in the composite performance, some matrix degradation can be beneficial in terms of interfacial mechanical properties. Finally, this work demonstrated that while the formation of fiber/matrix interaction seems to be primarily related to a chemisorption mechanism, the contribution of interphase crystallinity to the interfacial strength is not negligible. In fact, interfacial crystallinity was found to be essential to ensure optimum interfacial strength.     

Two stage electrostatic separator for the recycling of plastics from waste electrical and electronic equipment

The aim of study was to evaluate the effectiveness of a new facility for recycling of plastics from granular waste electrical and electronic equipment. The installation consists of two sections, the products of a first tribo-aero-electrostatic separator being subsequently treated in two free-fall electrostatic separators. The tests were performed on a mixture of polycarbonate (PC) and polyamide (PA). Analysis of the purity of the products obtained was performed using a program of image processing in MATLAB. Products of very high purity (roughly 95% for both PC and PA) were obtained at a recovery rate higher than 70%.     

Temperature Measurement in Small-Scale Flows with Digital Moiré Deflectometry

Abstract

This article explores the potential of Moiré deflectometry for measuring the temperature field in quasi-two-dimensional small scale flows. The research shows that digital Moiré deflectometry combined with two-dimensional Fourier transform for phase map extraction constitutes a useful diagnostic tool for acquiring the fluid temperature with sufficient sensibility and spatial resolution in small two-dimensional or axisymmetric arrangements with negligible pressure variations. The results obtained in the thermal boundary layer of a flat plate are in good agreement with both thermocouple measurements and numerical results.     

加权总体最小二乘问题的解集和性质

本文讨论了加权总体最小二乘问题的等价解集，分析了加权总体最小二乘解与加权最小二乘问题的解之间的关系。推广了Ｇｏｌｕｂ和Ｖａｎ Ｌｏａｎ，Ｖａｎ Ｈｕｆｆｅｌ和Ｖａｎｄｅｗａｌｌｅ，及Ｗｅｉ的相应结果。