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当水平圆曲线给定半径和偏转角时，其余的５个曲线元素就可以直接计算，这５个元素切距，外矢矩，弦矩，弦长和曲线长，在一些实际问题中，半径和偏转角是未知的，而为了要放样曲线，就必须要有其它二个元素是已知的，这样有七种情况必须依靠已知的曲线元素来解算，然而，在这些情况中是不能直接进行未知元素的解算，本文提出一处方法，叫做迭代法，来解算各个未知元素，它和牛顿一拉夫逊法不一样，迭代法不要求转换计算，并用对曲线 相似文献
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在视距测量中，当视线较长、竖直角过大以及视线受阻时，常有必要观测1／2或1／4尺截值。此时若采用两倍1／2尺截值或四倍1／4尺截值的标准视距公式来计算水平距离和高差，则会产生相当大的偏差。本文导出了修正后的视距计算公式，该公式为实测1／2或1／4尺截值、竖直角以及有关仪器参数的显函数。这个公式是依据实际完整尺截值与实测部分尺截值之间的几何关系而得出的。非完整尺截值可以在下1／2或上1／2尺截值，或者是下、中下、中上或、1／4尺截值。这个仅对标准视距公式作局部改进的公式，可以很方便地供人工计算或在可编程序计算器上使用。 相似文献
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The epi-benthic dinoflagellate Ostreopsis cf. ovata Fukuyo has an increasingly global distribution. In Brazil there are reports of O. cf. ovata along the coast from 8°S to 27°S latitude and blooms have been registered on the Rio de Janeiro coastline. In the current study, an O. cf. ovata bloom is reported at Saint Paul's Rocks (0°55'10″N; 29°20'33″W), between the southern and northern hemispheres. The Archipelago is not inhabited and not subjected to eutrophication, due to isolation, and sustains a number of endemic species. Therefore, blooms of O. cf. ovata may potentially cause demise to trophic chains by affecting marine invertebrates and vertebrates. 相似文献
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The aim of this paper is to evaluate the current availability of port reception facilities within the North Sea area. The evaluation is based primarily on original survey data from the summer of 2001, supplemented by existing information from surveys conducted by the International Maritime Organization. The EU Directive on port reception facilities for ship-generated waste etc. (Directive 2000/59/EC) requires that all ports provide facilities to meet the needs of those vessels normally calling in at them. In order for the Directive to be implemented effectively, the physical availability of such facilities is vital. This paper audits the wide range of port types within the region and also outlines the wide range of vessel types using these ports, and their requirements for a range of facilities. On the basis of this analysis, conclusions are drawn about the extent to which the provision requirement of the Directive is already being met. 相似文献
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Dogwhelks Nucella lapillus became locally extinct on some shores adjacent to areas of high shipping/boating activity during the period of high tributyltin (TBT) contamination in the 1980s and early 1990s. However, the species has now re-colonised sites at which extinction occurred on the Isle of Cumbrae, the northeast coast of England, the Shetland Isles and southwest England. There have also been substantial declines in the severity of imposex on adjacent shores where the species has persisted during this period. Re-colonisation and recovery can be attributed to two measures: regulations prohibiting the use of TBT-based paints on vessels < 25 m in length and the development of slow-releasing, self-polishing copolymer paints. Nevertheless, the International Maritime Organisation has now imposed a total ban on the use of TBT-based paints as antifoulants. This is almost certain to result in the use of paints containing alternative biocides and there is widespread concern that there is relatively little information on which to assess their likely environmental impacts. They could cause substantial environmental damage. 相似文献