铁路沿线山岬对电波传播特性影响分析

利用波导分析理论及介质表面阻抗的概念,分析了电波在非理想表面的山岬中的传播特性．同时,对频率为９００ ＭＨｚ 的电波在非理想表面的矩形山岬内的传播特性进行了理论计算与分析．计算分析结果表明,环境媒质的相对介电常数对电波传播特性的影响较其它环境参数对电波传播特性的影响要明显得多．非理想表面介质增加了电波传播能量的损耗,缩短了纵向传播距离．在传播的横截面上,水平方向的电场衰减呈现波动分布．     

Perceiving distance accurately by a directional process of integrating ground information

By itself, the absolute distance of an object cannot be accurately judged beyond 2-3 m (refs 1-3). Yet, when it is viewed with reference to a flat terrain, humans accurately judge the absolute distance of the object up to 20 m, an ability that is important for various actions. Here we provide evidence that this is accomplished by integrating local patches of ground information into a global surface reference frame. We first show that restricting an observer's visual field of view to the local ground area around the target leads to distance underestimation, indicating that a relatively wide expanse of the ground surface is required for accurate distance judgement. Second, as proof of surface integration, we show that even with the restricted view, the observer can accurately judge absolute distance by scanning local patches of the ground surface, bit by bit, from near to far, but not in the reverse direction. This finding also reveals that the surface integration process uses the near-ground-surface information as a foundation for surface representation, and extrapolation to the far ground surface around the target for accurate absolute distance computation.     

线型聚能装药射流形成过程的数值模拟

聚能射流形式过程的研究对于正确认识射流侵彻理论具有重要的意义。根据线型聚能药的结构特点,利用DYNA3D显式有限元程序对线型聚能射流的形成过程进行了数值模拟。模型探讨了线型聚能装药爆炸的诸多重要物理特性,如药型罩的压垮、射流形成和拉伸以及体杵体的“体缩”现象。还分析了线型聚能射流形成过程中速度、密度、温度等参数的分布特性,得出了射流有逆向速度梯度和杵体存在“体缩”现象听结论,其结果与现有的理论分成果基本一致。     

区域前兆台网的管理

简要介绍了广东前兆台网“十五“项目的部署情况。根据国家地震前兆台网中心的工作要求,制定了相应的区域前兆台网中心和台站的规章制度,对中心和台站进行规范化管理。该工作仍在不断改进和完善中,目的是要按质、按量、按时地提供前兆数据。     

Study on crustal, lithospheric and asthenospheric thickness beneath the Qinghai-Tibet Plateau and its adjacent areas

Based on the results of pure dispersions of Rayleigh wave tomography in the Qinghai-Tlbet Plateau and its adjacent areas, tsklng S wave velocities from previous linear inversion as the initial model, using the simulated annealing algorithm, a nonlinear simultaneous inversion has been carried out for S wave velocity and thickness of different layers, including the crust, the lithosphere and the asthenosphere. The results indicate： The crustal thickness shows strong correlation with geology structures sketched by the sutures and major faults. The crust is very thick in the Qinghal-Tibet Plateau, varying from 60 km to 80 kin. The Ilthospherlc thickness in the Qinghai-Tibet Plateau Is thinner （130-160 kin） than Its adjacent areas. And two blocks can be recognized, divided by an NNE strike boundary running between 90°E-92°E inside the plateau. Its asthenosphere is relatively thick, varies from 150 km to 230 kin, and the thickest area is located in the western Qiangtsng. India has a thinner crust （32-38 kin）, a thicker lithosphere of 190 km and a rather thin asthenosphere of only 60 kin. Sichuan and Tarlm basins have the crust thickness less than 50 kin. Their Iithospheres are thicker than the Qinghai-Tibet Plateau, and their asthenospheres are thinner. A discussion has been made on the character and formation mechanism of the typical crust-mantle transition zone in the western Qiangtsng block.     

从“革命”到“革命”：建国以来教育主题词的演变——以“革命教育”到“教育革命”的转换为例

建国前30年，党和国家推行以革命为主题的教育，主要是出于在夺取政权的基础上为巩固政权服务的目的；改革开放30余年，教育领域的改革与革命，体现出教育为经济发展服务、为人的全面发展服务的要求。教育从“革命”到“革命”的演变伴随着中华民族从寻求民族生存到追求大国崛起的历程。反映了民族与国家最大利益至上的要求。     

古田山自然保护区药用植物资源及其综合评价

浙江古田山国家级自然保护区有较丰富的药用植物资源,根据实地调查并结合有关资料统计,保护区内有药用种子植物770种(包括种以下分类单位),隶属136科463属,按其药用功能划分为理气活血类、清热解表类、凉血止血类、祛风除湿类、利水渗湿类、化痰止咳类、收敛固涩类等11类.保护区药用植物科的构成比较集中,菊科、蔷薇科、豆科、百合科、唇形科、禾本科、茜草科、毛茛科、玄参科、大戟科等22个大科共含246属444种,占保护区药用植物总属数和总种数的53.13%和57.66%;属的构成相对分散,悬钩子属、珍珠菜属、蓼属、卫矛属、薯蓣属、铁线莲属、景天属、胡枝子属、菝葜属等22个大属共含135种,占总种数的17.53%.保护区有一定数量的特有及珍稀濒危保护药用植物,有中国特有属药用植物12种,珍稀濒危保护药用植物21种.对该地区药用植物资源的保护和合理利用提出了一些参考性建议.     

我国房地产市场现状分析和对策研究

从分析我国房地产市场存在的问题入手,提出了启动我国房地产市场的若干对策.     

任意波形发生器设计中TMS320VC5509A的应用与探讨

简要阐述了DDS技术的基本原理,介绍了一种由TMS320VC5509A DSP控制器为核心的任意波形发生器。详细叙述了该波形发生器的硬件设计原理及软件设计方法。本设计具有结构简单、性能稳定、生成波形精度高及可扩展性好等优点。     

A new complex Duffing oscillator used in complex signal detection

In view of the fact that complex signals are often used in the digital processing of certain systems such as digital communication and radar systems,a new complex Duffing equation is proposed.In addition,the dynamical behaviors are analyzed.By calculating the maximal Lyapunov exponent and power spectrum,we prove that the proposed complex differential equation has a chaotic solution or a large-scale periodic one depending on different parameters.Based on the proposed equation,we present a complex chaotic oscillator detection system of the Duffing type.Such a dynamic system is sensitive to the initial conditions and highly immune to complex white Gaussian noise,so it can be used to detect a weak complex signal against a background of strong noise.Results of the Monte-Carlo simulation show that the proposed detection system can effectively detect complex single frequency signals and linear frequency modulation signals with a guaranteed low false alarm rate.