声波在水-多孔介质海底界面上的反射与透射     

彭临慧  赵燕鹏  郁高坤 《中国海洋大学学报(自然科学版)》2007,37(4):671-675

声波在海底界面的反射和透射是海底散射、海底混响、海底目标探测的重要问题。利用Biot多孔介质声传播理论对声波在水-多孔海底界面上的反射和透射进行了分析,具体给出反射声波的反射系数,3种透射声波的透射系数以及声能透射系数随入射波入射角和频率(10~40 kHz)的变化关系,分析了各种透射波对透射声能的贡献。多孔海底介质参数分别采用Stoll和Chotiros给出的2组参数进行理论计算。  相似文献   

Megalodicopia hians in the Monterey submarine canyon: Distribution,larval development,and culture     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(2):215-222

The exclusively deep-sea ascidian family Octacnemidae comprises several genera in which the oral siphon has hypertrophied to form two large lips which create an “oral hood” capable of capturing motile prey. Megalodicopia hians is typical of this carnivorous family and has been reported to prey upon small epibenthic crustaceans. Distribution of M. hians in the Monterey Canyon system (36°45′N, 122°00′W) (California) was determined with remotely operated vehicles. M. hians was found sparsely to depths of at least 3800 m throughout the canyon; however, abundance was greatest within the oxygen-minimum zone (400–800 m). Eggs, sperm, and recently fertilized embryos were obtained repeatedly from adults returned to the laboratory in vivo, indicating that this species free-spawns routinely. Overall egg diameter (ovum plus chorion, plus follicle cells) was 175–190 μm—considerably smaller than previously reported for this species. Embryonic development at temperature and oxygen concentrations equivalent to the oxygen-minimum zone was 2–4 d and, embryos gave rise to typical phlebobranch “simple” tadpole larvae. Larval period was extremely variable, and settlement/metamorphosis occurred up to 3 months post-hatching. These results are discussed within the context of settlement-site selection and fertilization ecology of the species.  相似文献   

Political risk assessment of five East Asian ports—the viewpoints of global carriers     

《Marine Policy》2005,29(4):291-298

This study develops a port-to-port comparative political risk assessment and conducts a case study of the political environment evaluations of five East Asian ports: Hong Kong, Singapore, Busan, Kaohsiung and Shanghai. This system approach consists of political risk factor identification, risk measurement and assessment processes using the three methods of Delphi, analytic hierarchy process and Ward's clustering. Fifteen high-ranking managers from five leading global carriers present their viewpoints for analysis. The empirical case concluded that political risk was a strong indictor for the business environments of the host ports. Jointly, the micro-risks resulting from the port development and management policies were considered to be more significant than the macrorisks from the integrated political and economics conditions. Political risks of the five host ports were assessed as ranging from 0.17 to 0.38, so these ports were considered to be politically secure for the global carrier business. Finally, the five ports were statistically clustered into three groups to signify the differences in their political environments.  相似文献   

基于活动目录的通用授权管理平台的设计与实现     

唐瑞春  毛健  徐建良  任丽婕 《中国海洋大学学报(自然科学版)》2006,36(6):1013-1018

考虑应用系统中如何安全、高效的进行统一的人员管理及权限管理问题,研究基于微软活动目录构建通用中间件并以WebService方式发布的解决方案。具体内容包括把活动目录作为统一的人员库;构建通用授权管理平台统一管理用户在不同的软件系统中的角色和权限;该管理平台以WebService的方式向其它的应用系统提供接口。文中示例表明该方案切实可行,应用范围广。  相似文献   

煤矿区地质环境与地质灾害遥感集成监测系统的关键技术     

杜培军  ;陈云浩  ;曹金亮  ;王润福 《测绘软科学研究》2008,(5):14-20

面向“数字矿山”应用系统的需要,在分析煤矿区地质环境和地质灾害特点及其在遥感监测理论依据的基础上,提出了煤矿区地质环境与地质灾害遥感集成监测系统的技术思路和体系结构,强调各种监测技术手段、不同时空尺度、不同数据源和不同主题信息的集成,并针对这一集成系统实现与应用中的多目标遥感信息处理、环境传感器网络应用、遥感监测数据与专题分析模型的集成、数据质量控制等关键问题进行了探讨。  相似文献   

青藏高原腹地湖泊沉积对第四纪晚期古季风变化的响应   总被引：2，自引：0，他引：2  

胡东生  张华京  徐冰  李炳元  孔照辰  温景春 《干旱区地理》2006,29(4):483-489

通过对青藏高原腹地的综合科学考察和对中心钻孔岩芯剖面的最新研究,用层序地层学与年代地层学和气候地层学相结合的方法,分辨出可可西里地区湖泊沉积记录(孔深7.25 m)的第四纪晚期距今3万余年以来的古气候变化,沉积物磁化率等因子综合表征的高原古季风变化是波动发展的,发生在仙女木期地质环境事件中的季风活动具有强烈暴发的特点,是高原季风发展中的突变事件,而且地表热点效应对其起到了激发作用。综合分析的研究成果表明,它的变化频谱与激变因子及其运行机制是伴随着青藏高原地质效应的演变而发展的,为研究第四纪冰消期以来的气候变化提供了新的信息。  相似文献   

Development of a remotely sensed,historical land-cover change database for rural Chihuahua,Mexico     

《International Journal of Applied Earth Observation and Geoinformation》2005,7(3):232-247

The purpose of this article is to describe the development of a remotely sensed, historical land-cover change database for the northwestern quarter of Chihuahua, Mexico, The database consists of multi-temporal land-cover classifications and change detection images. The database is developed to facilitate future investigations that examine urban–rural linkages as possible drivers of rural land-use and land-cover changes. To develop the needed land-cover change database, this study uses the North American Landsat Characterization (NALC) MSS triplicates because of their temporal depth and spatial breadth. Challenges exist, however, to effective classification and change detection using the NALC triplicates, including illumination differences across multiple scenes and periods caused by topographic and solar variations and the lack of ground reference data for historic periods. Therefore, creation of the database is a four step process. First, extensive pre-processing is performed to enhance comparability of multi-date images. Pre-processing includes topographic correction, mosaic creation and multi-date radiance normalization. Second, ancillary sources of land-cover data are combined with visual interpretations of enhanced images to define reference pixels used to classify the images using the maximum likelihood algorithm. Third, classification accuracy is assessed. Fourth, post-classification change detection is performed. Results indicate significant image improvements after pre-processing that permit very good overall classification (86.26% classified correctly) and change detection. To conclude, findings are presented that indicate significant changes to arid grasslands/shrublands and forest resources in mountainous regions.  相似文献   

Water resources sustainability in a globalizing world: who uses the water?          下载免费PDF全文

Megan Konar  Tom P. Evans  Morgan Levy  Christopher A. Scott  Tara J. Troy  Charles J. Vörösmarty  Murugesu Sivapalan 《水文研究》2016,30(18):3330-3336

  相似文献   

Damage and Acoustic Emission Characteristics of Combined Rock Mass with Anchor Under Different Inclination Angles and Combination Modes     

Tang  Xinbao  Zhang  Qinghao  Zhou  Yan  Ma  Depeng 《Geotechnical and Geological Engineering》2021,39(8):5895-5906

Geotechnical and Geological Engineering - Soft and hard rock assemblages and anchor solids have important effects on rock mechanics properties under different inclinations and assemblages, so it is...  相似文献   

Nonhumans in the practice of development: Material agency and friction in a small-scale energy program in Indonesia     

《Geoforum》2016

We develop the outlines of a new approach to study the role of nonhumans in constituting ‘implementation’ and calculative–discursive practices in development projects and programs. Developing a framework around the concept of friction (material resistance or recalcitrance encountered in processes of transformation), we analyze an Energy Self-sufficient Village program in Indonesia. Focusing on specific projects and episodes within this program, we identify multiple distinctive instances of friction. These were driven by nonhumans’ (and humans’) resistance, as remolding of development beneficiaries’ practices was attempted by project administrators, government officials, entrepreneurs and by the (scientific) calculations embedded in their policies, strategies and models. In concluding, we distill four ways in which nonhumans relationally shape development practices: (a) by resisting representations and calculations produced by human actors, (b) by re-directing planned/expected courses of action, (c) through biophysical change to their weight or textures as they move in space and time, and (d) by mediating competition for resources. Overall, nonhumans play a central role in making and unmaking asymmetric relations of power in practice and by constituting practices that diverge from prior expectations, problematize linear understandings of ‘policy implementation’. Their material and discursive agency is multiple, manifesting differently in different relational settings, which highlights the importance of broadening the range of spokespersons who speak on behalf of nonhumans and whose voices can be considered reliable and true. Our study thus provides support to calls for pluralizing and democratizing development ‘expertise’ beyond the usual suspects in science, government and civil society.  相似文献