An update on the cost of net-trawling operations in the Gulf of Mexico     

Mark J. Kaiser  Jimmie Martin 《Marine Policy》2009

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Modeling Local Tidal Constituents Using TOPEX/POSEIDON SSH for the Malaysian Marine Region     

Muhammad Nur J. P. Vella  Sahrum Ses  Majid Kadir  Koji Matsumoto 《Marine Geodesy》2013,36(2):99-106

A new Local Ocean Tide Model, has been produced for the Exclusive Economic Zone (EEZ) of Malaysia, which incorporates some of the latest TOPEX/POSEIDON data for the years 1992 to 1998. Local tide gauge data are used as a comparison, along with another leading Global Ocean Tide Model, Ori96. The leading diurnal and semidiurnal constituents M₂, S₂, N₂, K₁, O₁, P₁ and Q₁ are reproduced using TOPEX/POSEIDON Sea Surface Heights (SSH) in a response analysis type least squares derivation following Munk and Cartwright (1966).  相似文献   

海洋浮游桡足类摄食纤毛虫的研究   总被引：1，自引：0，他引：1  

张武昌  陈雪  李海波  丰美萍  于莹  赵苑  肖天 《海洋与湖沼》2014,45(4):764-775

20世纪60年代起,人们发现了许多有关桡足类摄食纤毛虫的直接或间接的证据。20世纪70年代,有人在实验室内培养纤毛虫并开展桡足类对其清滤率的研究,结果表明桡足类对纤毛虫的清滤率为0.1—58.1mL/(ind.·h)。桡足类对纤毛虫的摄食方式有多种,包括伏击摄食和通过游泳过滤海水中的纤毛虫等。有的纤毛虫有逃避摄食的行为。20世纪80年代末,自然状况下桡足类群体对自然饵料中纤毛虫的摄食得到了研究,结果表明桡足类对纤毛虫的清滤率多数情况下低于40mL/(ind.·h)。实验室内和自然海区的研究都表明,与浮游植物相比,桡足类倾向于选择摄食纤毛虫。根据现场测定的清滤率和桡足类丰度估计自然海区桡足类对纤毛虫的摄食压力的大部分研究结果表明,桡足类群体对纤毛虫生物量的摄食压力大约为每天5%。这些自然海区的研究多集中在近岸区域,需要加强对大洋浮游桡足类摄食纤毛虫的研究。  相似文献   

冲绳海槽末次冰期、全新世沉积物化学元素分布特征   总被引：1，自引：0，他引：1  

李凤业  何丽娟  史玉兰 《海洋科学》1996,20(5):55-59

根据测定冲绳海槽０８０、０８２两岩芯中放射性同位素和化学元素的垂种布，基于＾２３０Ｔｈ／＾２３２Ｔｈ放射性活度比值，确定了末次冰期和全新世之间确切地层年代。测得资料表明，在全新世和晚更新世期间沉积物中元素丰度有很大的变化，反映了冲绳海槽在不同历史时期沉积环境的变迁和物质来源的差异。  相似文献   

Grazing on microcystin-producing and microcystin-free phytoplankters by different filter-feeders: implications for lake restoration     

Luis M. Dionisio Pires  Babette M. Bontes  Larysa Samchyshyna  Jacco Jong  Ellen Van Donk  Bas W. Ibelings 《Aquatic Sciences - Research Across Boundaries》2007,69(4):534-543

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含裂纹故障多自由度齿轮系统的动力学分析     

马锐  陈予恕 《东北石油大学学报》2012,(3):110-114,12

为探讨齿轮系统裂纹故障的非线性动力学机理,研究含裂纹故障的四自由度齿轮系统的动力学特性,考虑时变啮合刚度及非线性间隙的影响,建立含裂纹故障的齿轮四自由度啮合耦合动力学模型,分析裂纹故障对系统啮合刚度的影响;采用谐波平衡法给出系统的解析解,分析裂纹故障及齿轮系统参数对齿轮传动系统的动力学行为的影响.结果表明,裂纹故障能够引起齿轮系统的幅值跳跃、分岔现象和系统共振,从而为齿轮箱的设计及裂纹故障的诊断提供依据.  相似文献   

Design estimates of surface wave interaction with compliant deepwater platforms     

J. M. Niedzwecki  J. W. van de Lindt  J. H. Gage  P. S. Teigen 《Ocean Engineering》2000,27(8)

The extreme behavior of surface waves as they encounter and pass compliant deepwater platforms is an important class of problems for offshore engineers attempting to specify the platform deck elevation. In this study analytical expressions for the probability density and cumulative distribution functions that utilize empirical coefficients in an attempt to accurately model surface wave runup and airgap problems are presented. The analysis focuses upon interpreting the tails of the measured data histograms using two parameter Weibull distribution models. The appropriate empirical constants, assumed to be solely dependent upon the significant wave height, were evaluated and compared for all the test data. Based upon a small select set of data, for a mini-TLP and two Spar platforms, the airgap problem was found to be adequately modeled using a Rayleigh distribution. Further, for the seven seastates analyzed, the Weibull shape parameter was nearly constant and the data confirmed that the exclusive fit of the scale parameter assuming dependence only on the significant wave height was a reasonable approach for modeling the wave runup. Finally, by combining these models with a Poisson return model for each storm the associated reliability estimates for various deck heights were estimated.  相似文献   

Woodlands in England: an appreciation of Hilda Annie Wilcox     

Brian K. Roberts 《The Geographical journal》2000,167(2):163-173

In 1933 two maps reconstructing the woodlands of England were published by Hilda A. Wilcox: one of these, woodland 'deduced from early literature', is re-assessed in this paper. The distribution it shows is compared with a recently constructed map of national woodland, created as part of an English Heritage project, and based on the analysis of the Domesday Book by Sir Clifford Darby and his co-workers, together with the results of investigations by numerous place-name scholars. In spite of differences in detail, the two maps are in remarkably close accord. This conclusion is used as the basis for a brief synoptic analysis of the distribution of cleared land and woodland in the centuries preceding 1086, and touching even the Roman period. The recent computer-based reconstruction, drawing upon published, sound and accepted sources, and supported by the earlier and wholly independent work by scholars such as Rackham and Thirsk, provides a national picture of fundamental importance to the historical geography of the English environment.  相似文献   

民用机场净空保护锥形面范围的计算确定     

方学东  郝斌 《测绘科学》2010,35(2):132-133

针对民用机场净空管理过程中锥形面范围难以准确确定,主要采用手工方式绘制障碍物限制面图进行管理的问题,给出了净空管理过程中受城市建设影响较大的、形状最为复杂的锥形面范围,导出了锥形面边界的计算方法,并确定了围限锥形面的各关键点坐标,为采用计算机自动判定障碍物是否落入锥形面奠定了理论基础。  相似文献   

城市地铁控制网稳定性分析及应用   总被引：3，自引：2，他引：1  

张广伟  李鹏  宫辉 《测绘科学》2008,33(4)

城市地铁控制网是城市地铁工程的基准,是工程施工质量安全的保障,其稳定与否直接影响到联系测量及贯通误差的计算。本文研究了控制网的稳定性分析方法,结合北京地铁五号线某段控制网,利用两期平面观测数据对控制网进行稳定性分析,保证了隧道的安全贯通。  相似文献