A circular passive synthetic array: an inverse problem approach     

Yen  N. 《Oceanic Engineering, IEEE Journal of》1992,17(1):40-47

Based on the general concept of the inverse acoustic radiation problem, the temporal scanning of a stationary acoustic field along a closed contour is used to simplify the measurement approach for obtaining information on source directionality. The mathematical formulation is derived from a model of the two-dimensional acoustic field. The formulation of the inverse problem is also investigated to establish a methodology for improving the angular resolution of the array processing. The fundamental relationship between the sound sources and the circular passive synthetic array is explored, utilizing existing mathematical methods, in order to develop the processing algorithm. Other subjects of practical interest, such as directional ambiguity, effect of Doppler frequency, interference noise, and processing gain are discussed. It is concluded that the results can be used to establish guidelines for engineering design and deployment of this type of synthetic array, and to further exploit the new array signal processing technique  相似文献   

Effect of spatial variation characteristics on contouring of design storm depth     

Ke‐Sheng Cheng  Chiang Wei  Yen‐Ben Cheng  Hui‐Chung Yeh 《水文研究》2003,17(9):1755-1769

The ordinary kriging method, a geostatistical interpolation technique, was applied for developing contour maps of design storm depth in northern Taiwan using intensity–duration–frequency (IDF) data. Results of variogram modelling on design storm depths indicate that the design storms can be categorized into two distinct storm types: (i) storms of short duration and high spatial variation and (ii) storms of long duration and less spatial variation. For storms of the first category, the influence range of rainfall depth decreases when the recurrence interval increases, owing to the increasing degree of their spatial independence. However, for storms of the second category, the influence range of rainfall depth does not change significantly and has an average of approximately 72 km. For very extreme events, such as events of short duration and long recurrence interval, we do not recommend usage of the established design storm contours, because most of the interstation distances exceed the influence ranges. Our study concludes that the influence range of the design storm depth is dependent on the design duration and recurrence interval and is a key factor in developing design storm contours. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

A perturbation theory for Love waves in anelastic media     

G. Madja  R. C. Y. Chin  F. E. Followill 《Geophysical Journal International》1985,80(1):1-34

Summary. We give a systematic formulation and a rigorous justification of a perturbation technique for the computation of the eigenvalues and eigenfunctions of Love waves (and toroidal oscillations by an appropriate change for variables) in an anelastic medium with a constitutive law modelling geophysical media of current interest such as the Kelvin—Voigt Solid, the Maxwell Solid, the Standard Linear Solid, and the Standard Linear Solid with a continuous spectrum of relaxation times. We develop expressions relating the eigenvalues of eigenfunctions for Love waves in a continuously varying vertically stratified anelastic half-space to the corresponding elastic eigenvalues and eigenfunctions. Analytically, our correspondence principle has the form of a regular perturbation expansion in terms of a parameter for both the eigenvalues and eigenfunctions. The identification of ɛ is motivated by the dissipativity principle of viscoelasticity theory. Moreover, we show that our correspondence principle applies respectively only in the high and low frequency range for the Maxwell and Kelvin—Voigt Solids. Outside of the applicable range of frequencies, our correspondence principle yields no useful information. For the family of Standard Linear Solids it is uniformly applicable for all non-zero frequencies.
We also derive an explicit formula to estimate the radius of convergence of our perturbation expansions. This estimate of the radius of convergence for each eigenvalue and eigenfunction is functionally defined by the constitutive model for the anelastic medium. The estimate is frequency dependent and depends on the separation distance between the eigenvalue and the remainder of the spectrum of the corresponding elastic problem.  相似文献   

The relationship between poverty and fertility in some less developed countries     

Chin Ptc 《Singapore journal of tropical geography》1985,6(2):139-152

The author investigates the extent to which both absolute and relative poverty affect population growth in developing countries. Aggregate data from U.N. sources for 26 countries at various stages of the fertility transition are used. The results indicate that the most significant steps in reducing fertility would be more effective provision of basic human needs and reforms in land tenure. The need to distinguish between absolute and relative poverty in formulating population policies is noted.  相似文献   

A new efficient 3D non-hydrostatic free-surface flow model for simulating water wave motions     

Doo Yong Choi  Chin H. Wu   《Ocean Engineering》2006,33(5-6):587-609

A new three-dimensional, non-hydrostatic free surface flow model is presented. For simulating water wave motions over uneven bottoms, the model employs an explicit project method on a Cartesian the staggered gird system to solve the complete three-dimensional Navier–Stokes equations. A bi-conjugated gradient method with a pre-conditioning procedure is used to solve the resulting matrix system. The model is capable of resolving non-hydrostatic pressure by incorporating the integral method of the top-layer pressure treatment, and predicting wave propagation and interaction over irregular bottom by including a partial bottom-cell treatment. Four examples of surface wave propagation are used to demonstrate the capability of the model. Using a small of vertical layers (e.g. 2–3 layers), it is shown that the model could effectively and accurately resolve wave shoaling, non-linearity, dispersion, fission, refraction, and diffraction phenomena.  相似文献   

渤海海水中悬浮体的研究   总被引：29，自引：5，他引：29  

秦蕴珊  李凡 《海洋学报》1982,4(2):191-200

陆源悬浮体是边缘海海底沉积物的主要来源.所以,悬浮体(suspended matter)的调查研究是解决边缘海海底沉积作用的一个重要环节.当我们研究河口附近海域以及海底沉积物的通量平衡过程时,也必须对悬浮体的分布及其数量变化等进行调查.  相似文献   

海底可视技术在天然气水合物勘查中的应用     

张汉泉吴庐山  张锦炜 《地质通报》2005,24(2):185-188

海底可视技术是一种可以直观地对海底地形地貌、表层沉积物类型、生物群落等进行实时观察的调查手段。本文介绍了海底摄像、电视抓斗、深拖系统和ROV四种海底可视技术，并对海底可视技术在南海北部陆坡天然气水合物勘查中的应用进行阐述。利用海底可视技术，在南海北部陆坡发现了天然气水合物气体“冷泉”喷溢形成的自生碳酸盐岩和活动于天然气水合物冷喷溢口或渗流口周围的菌席、双壳类、管状蠕虫等化能自养生物群，圈定出该陆坡由天然气水合物气体“冷泉”喷溢形成的巨型碳酸盐岩面积达430km^2。  相似文献   

藏南江孜盆地北缘火山岩地球化学特征及其大地构造背景   总被引：3，自引：1，他引：3  

周志广刘文灿  梁定益王克友赵兴国  张爱平 《地质通报》2005,24(4):341-348

江孜盆地北缘火山岩可分为2个火山岩带，各带又有2个喷发旋回不同时代的火山岩具相似的岩石化学特征，表现为富钛、富铝、富钠、低钾的特点，属拉斑玄武岩系列，三叠纪和早白垩世火山岩的痕量元素具富集大离子不相容元素的特肛．稀土元素及其球粒陨石标准化配分型式显示其喷发构造背景为大陆裂谷环境。晚白垩世火山岩的痕量元素特征可分为富集大离子不相容元素、高场强元素和仅富集大离子不相容元素2种类型，上下层位的稀土元素特征和配分型式不同，喷发的构造环境分别为大陆裂谷环境和大洋环境。结合区域地质成果认为，雅鲁藏布江结合带在三叠纪和早白垩世时为大陆裂谷构造环境，晚白垩世早期为大陆裂谷向大洋演化的构造背景，晚期形成洋壳，其形成至少经历了4次脉动式的演化过程  相似文献   

藏北申扎地区奥陶纪鹦鹉螺类一新属（Variabioceras）   总被引：1，自引：0，他引：1  

程立人张以春  张予杰 《地质通报》2005,24(4):363-368

文中材料是采自西藏申扎县塔尔玛乡桥东—扎扛一带鹦鹉螺化石的一部分。描述了3属6种。其中有1个新属Variabioceras gen.nov．和3个新种V．typicum gen．etsp．nov．，V．zangbeiense gen．et sp．nov．，V．robustum gen．et sp．nov．  相似文献   

城市钻孔数据地下三维地质建模软件的实现   总被引：15，自引：1，他引：15  

李亦纲  曲国胜  陈建强 《地质通报》2005,24(5):470-475

介绍了基于钻孔数据的城市地下三维地质建模软件的实现过程，提出了基于钻孔数据三维地质建模的总体思路、钻孔数据管理和层序分层方法，还介绍了软件的模块组成及应用实例。建立的软件实现了对城市钻孔数据的三维建模、可视化分析和科学管理，具有丰富的二维成图和三维显示功能，实例的应用也说明本软件是分析城市第四系构造格架和演化的有力工具。  相似文献