电磁场本征值问题及其研究现状

从理论上给出了电磁场本征值问题的定义及分类,阐述了研究目的和意义,着重介绍了电磁场本征值问题的最新研究方法、研究现状以及各种方法的具体应用范围,并讨论了各种方法的优缺点.     

自闭症谱系障碍者面孔加工障碍的成因——来自不同理论的解释

通过分析自闭症谱系障碍者面孔加工障碍的相关理论,揭示该群体面孔加工障碍的形成原因。首先,自闭症谱系障碍者在面孔加工中对社会刺激感知异常,对面孔缺乏兴趣,忽视面孔;在特定条件下回避眼睛,依靠嘴部进行面孔识别。相关理论有:社交动机假说、眼睛威胁假说和嘴部信息补偿假说。其次,自闭症谱系障碍者面孔加工能力不足,面孔加工相关脑区存在功能损伤、加工策略可能异常。相关理论有:加工策略异常假说、社会脑假说。最后,根据自闭症谱系障碍者面孔加工障碍的形成原因,提出教学启示。     

X射线荧光光谱法分析石灰石中SiO2和CaO

文章介绍采用压片法制样,X射线荧光光谱法分析石灰石中CaO和SiO₂,通过自制标准试样,根据产地不同分别建立工作曲线,克服了压片法的基体效应和矿物效应,分析准确度和精密度进一步提高,分析周期短,时效性好。     

Er~(3+):Y_(0.5)Gd_(0.5)VO_4晶体生长和缺陷研究

采用液相法合成了多晶材料,用高温提拉法(CZ法)生长出Er3 :Y0.5Gd0.5VO4晶体.用ICP光谱法测定晶体中Er3 离子含量为1.25 at%,分凝系数为1.06.采用热磷酸腐蚀晶片,在偏光显微镜下对晶体的(010)、(001)面上的缺陷进行了观察,可明显观察到位错线、生长层和包裹物.由此得出,Er3 :Y0.5Gd0.5VO4晶体的主要缺陷是位错、生长层和包裹物等.     

Time-frequency channel modeling and estimation of multi-carrier spread spectrum communication systems

In wireless communications, the channel is typically modeled as a random, linear, time-varying system that spreads the transmitted signal in both time and frequency due to multi-path propagation and Doppler effects. Estimated channel parameters allow system designers to develop coherent receivers that increase the system performance. In this paper, we show how time-frequency analysis can be used to model and estimate the time-varying channel of a multi-carrier spread spectrum (MCSS) system using a complex quadratic sequence as the spreading code. We will show that for this spreading code, the effects of time delays and Doppler frequency shifts, caused by the mobility of environment objects, can be combined and represented effectively as time shifts. The discrete evolutionary transform (DET), as a time-frequency analysis method, enables us to estimate the effective time shifts via a spreading function and to use them to equalize the channel. Using the effective time shifts, the time-varying channel can be represented simply as linear-time invariant system by embedding the Doppler shifts that characterize the time-varying channel into effective time shifts. The channel parameters are used to estimate the data bit sent. To illustrate the performance of the proposed method we perform several simulations with different levels of channel noise, jammer interference, and Doppler frequency shifts.     

激光甲烷传感器及其交叉干扰实验研究

基于激光光谱吸收的原理,研究了激光甲烷传感器的测量原理和系统设计,开展了实验室环境下水汽、一氧化碳和二氧化碳等气体对甲烷测量结果的交叉干扰,给出了实验数据并进行了相关分析。实验证明激光甲烷传感器具有测量准确,稳定性高,抗气体交叉干扰等特性。     

通讯扩频序列混合并行捕获预检测积分时间和判决门限最优设计

论文以低轨卫星信道为例，给出一种适用于大频偏条件下突发通信系统直接扩频序列混合并行捕获结构，分析了预检测积分时间和判决门限对平均捕获时间的影响，提出了在门限信噪比下以平均捕获时间最小为原则的预检测积分时间和判决门限参数最优设置方案。     

提高CaAl2O4:Eu2+,Nd3+荧光粉发光亮度的优化设计

为了进一步提高CaAl2O4：Eu^2＋，Nd^3＋荧光粉的发光性能，通过掺杂制备了发光性能更好的（Ca1-xSrx）Al2O4：Eu^2＋,Nd^3＋、（Ca1-wxZrx）Al2O4：Eu^2＋，Nd^3＋和CaA12O4：Eu^2＋，Nd^3＋，Ce^3＋荧光粉。     

Performance analysis of a spreading sequence estimator for spread spectrum transmissions

Direct sequence spread spectrum transmissions (DS-SS) are now widely used for secure communications, as well as for multiple access. They have many interesting properties, including low probability of interception. Indeed, DS-SS transmitters use a periodical pseudo-random sequence to modulate the baseband signal before transmission. A receiver which does not know the sequence cannot demodulate the signal.In this paper, we propose a new method which can estimate the spreading sequence in a noncooperative context. The method is based on eigenanalysis techniques. The received signal is divided into windows, from which a covariance matrix is computed. We show that the sequence can be reconstructed from the two first eigenvectors of this matrix, and that useful information, such as desynchronisation time, can be extracted from the eigenvalues.The main achievement of the present paper is a performance analysis of the proposed spreading sequence estimation procedure. An analytical approach is first considered owing to matrix perturbation theory and Wishart matrix properties. Then, complementary Monte Carlo simulations are performed to show the effectiveness of the proposed method.     

山东大磨曲家矿区成矿元素多重分形特征

通过矩方法,以无序数据集中不同品位级次内的频率为测度,研究了胶东大磨曲家金矿矿体及玲珑花岗岩、胶东群等近矿围岩的Au、Ag、As等主要成矿元素分布的广义谱曲线（Dq-q）和多重谱曲线（f（α）-α）特征.在权重-0.2≤q≤1.6时,结果显示矿体与近矿围岩中成矿元素品位分布的广义谱和多重谱特征存在明显的区别.矿体中三种成矿元素的广义谱曲线近似直线,而多重谱曲线的宽度较小,显示成矿元素品位级次密集,较为均匀,接近简单分形;近矿围岩中广义谱曲线弯曲明显,多重谱曲线的宽度较大,显示近矿围岩中元素品位级次范围较宽,相对不均匀.同时,矿体中多重谱曲线f（α）的极值所对应的α比近矿围岩中的小,代表最或然子集的品位增加,指示成矿元素在矿体中富集.多重分形分析显示矿体中的成矿元素较近矿围岩中变得更为富集而均匀.