A coupled mode examination of irregular waveguides including the continuum spectrum

Summary. A coupled mode theory is used to examine surface wave propagation in a laterally inhomogeneous acoustic waveguide. The theory is developed from the equations of motion for the pressure and velocity fields. The presence of lateral inhomogeneities in the form of varying layer thickness causes coupling among the discrete modes of the waveguide and radiation to the continuum. Expressions for the coupling coefficients among all mode types including coupling to the continuum spectrum are derived. The coupling coefficients are proportional to the horizontal derivative of the function describing the interface between layers of constant material properties but varying thickness. The coupled mode equations are solved in approximation for the case of a sinusoidal boundary and a sloping boundary. The results for radiation losses due to interaction with the irregular boundary of the waveguide are presented in analytical form, which clearly show the primary physical effects on the wavefield of the interaction. The far field amplitude of the scattered modes, excited by the interaction of some incident signal with a weak boundary irregularity, is modulated by the spatial Fourier transform of the irregularity.     

WOMEN'S WORLDS AT THE AMERICAN GEOGRAPHICAL SOCIETY*

ABSTRACT. For much of the twentieth century, women in the United States found it difficult to obtain university positions in geography. Opportunities existed in other types of institutions, however, including the American Geographical Society (ags ). This article addresses ways in which the Society's mission intersected with its historical context from 1895 to 1970 to create niches for women in editorial and library work. It explores the women's origins, their perspectives and experiences with the ags , and the significance of their contributions to the discipline. It suggests the potential of a gendered social approach for enriching understanding of the histories of geographical institutions.     

岩土层含水量分层监测系统的研究及应用

开发为地质灾害预测预报所需用的岩土层含水量和渗透力测试仪,并和气候雨量、地质灾害成灾规律联系起来,是我国地质灾害监测预报发展的趋势。岩土层含水量分层监测系统是采用TDR（Time Domain Refiectometry）技术原理、方法研制的仪器,通过波导棒探针发射的电磁波射入岩土层,测量电磁波脉冲从波导棒的起点传播到接收末端的反射电压值,此反射电压值与岩土体本身含水量介电常数有函数关系,经过计算转换为测点岩土体积含水量,实时测量和采集地质灾害岩土层含水量和渗透力参数。介绍了该监测系统的基本原理、主要技术参数、监测工艺技术方法以及现场应用情况。     

介质加载折叠波导行波管的线性分析

提出了一种介质加载折叠波导慢波结构,给出了该结构中存在电子注时慢波互作用的热色散方程,在介电常数ε_r=1的特殊情况下该方程即简化为普通折叠波导的小信号工作方程.在给定慢波结构尺寸的基础上,分析比较了介质加载对放大器小信号增益特性的影响,结果表明:"弱加载"(介质厚度d/a<0.1)时,无需重新设计慢波结构的参数,只需适当调整工作电压和电流就可以满足原有设计要求,而且和未加载时相比增益特性更为平坦,降低的电子注阻抗也有利于电子效率的提高.考虑到     

锥形空心银波导的聚焦特性

利用时域有限差分(FDTD)方法数值演示了一种能光学引导和聚焦激光的锥形空心银波导,数值模拟结果表明这种锥形空心银波导能把激光聚焦成一个极小的、直径只有1 μm、强度高度局域性的光斑.对锥形波导能光学引导和聚焦激光的物理机理作了分析和探索,并进一步探讨了激光倾斜入射、波导几何结构对锥形波导聚焦特性造成的影响,这些研究结果对于锥形光学的应用、快点火或产生高能带电粒子中锥靶结构的最佳设计具有重要的参考价值.     

Liquid waveguide capillary cell for the spectrophotometric determination of nanomolar iodate concentrations in marine waters

A new spectrophotometric method based on a liquid waveguide capillary cell for an enhanced detection was developed to measure nanomolar iodate concentrations. This method has a detection limit and precision of 1–2 nmol/L, which is equivalent to 10% that of conventional methods, a recovery of 97.7%–104.0%, and a working range of 10–120 nmol/L. Water samples were collected from three estuaries and one coastal ocean for testing, and the proposed technique detected as low as 11 nmol/L and 18 nmol/L ...     

一种条形二进制编码标尺的数字水准仪系统设计与实验

目前,世界上极少数的公司垄断了数字水准仪的生产,他们的专利保护主要集中在电子读数原理和标尺编码结构上。本文在此背景下,提出了一种新的基于二进制编码的标尺编码方案。该方案将使用的刻度标尺横线进行二进制编码,水准仪部分采用面阵CCD采集标尺图像,利用快速数字图像处理算法进行水平中心定位读数。理论分析和实验表明,该设计具有可行性,在标尺不同位置和椒盐噪声点数小于60 K的时候有着100%的识别率。     

基于WOA13数据的海区位置对北大西洋声波导影响分析

应用WOA13季节平均数据和BELLHOP模型,在季节、声源频率等因素确定的情况下,分10 m表面声源和250 m水下声源,分析北大西洋冬季东、西部海区的声波导情况。在给出不同海区位置的声速场和声波导具体信息的基础上,研究其规律:最小声速值和声道轴深度由直布罗陀海峡向外递减扩散,表层声速值和声速梯度由南向北递减,声跃层存在于低纬度海区,混合层在低纬度通常在100 m以内,在高纬度增加至100 m以上。10 m深度表面声源的汇聚区反转深度随纬度增加逐渐减少,西部海区深于东部海区;西部海区的汇聚区跨度大于东部海区,东西部跨度最大值出现在25°N和15°N,传播损失基本一致。250 m水下声源的汇聚区反转深度浅于10 m深度表面声源时,同样是西部海区大于东部海区,汇聚区跨度呈低-高-低规律,东西部跨度最大值出现在35°N和25°N;东部海区25°N以南、西部海区15°N以南,不同接收深度上的传播损失差异较大,以北差异较小。同时简要叙述了声影区对目标探测的影响。     

脊波导激励腔的实验研究

在理论和实验的基础上 ,对近截止脊波导微波谐振腔进行了分析和设计 ,通过合理选择脊波导的截面尺寸和腔端结构 ,可以实现场的单模传输和场沿纵向的均匀分布 ,并在不同的工作气体气压下 ,给出了放电实验结果     

基于人才梯队建设的地勘单位职工培训研究——以山东省物化探勘查院为例

培训作为人力资源开发的重要组成部分,是一个组织拥有持续竞争力的源泉。组织的发展除了要积极引进人才外,还可以通过教育与培训达到提高人才素质,实现发展目标的目的。地勘行业20世纪90年代曾经历发展低谷,导致地质人才大量转移和流失,造成了目前普遍存在专业技术队伍年龄结构的“断层”。针对这一问题,以山东省物化探勘查院为例,针对地勘单位如何从自身实际出发,依托全面、有效的职工培训来盘活现有人力资源、打造人才梯队,实现可持续发展的问题,提出相应对策。