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《The Australian geographer》1991,22(2):178-184
Significant elements of the Australian landscape date from Mesozoic or earlier times. Australia did not separate completely from other Gondwanan components until Early Tertiary times and these Mesozoic and older elements can therefore be regarded as Gondwanan. During the separation and northern drift of the continent and particularly in Late Jurassic and earlier Cretaceous times the sea invaded and spread across much of the erstwhile landmass. The associated sediments not only covered and preserved much of the pre‐existing land surface, but they also augmented the effects of thalassostatic loading of the basins, causing further subsidence. Hinge lines developed near the coastal zones of the times, so that subsidence of the basins caused adjacent land masses to rise. Many old land surfaces have been re‐exposed at the former oceanic margins, but epigene forms are preserved high in the relief on the uplifted blocks. They survive partly because, as Crickmay (1976) suggested, rivers effectively erode at and near their channels; the divides remain untouched. A reinforcement effect also operates because the valleys are wet sites, the interfluves dry. Hence weathering and erosion proceed apace in the former while the latter are stable, allowing palaeoforms to survive. 相似文献
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高精度时间间隔测量技术与方法 总被引：31，自引：0，他引：31
时间间隔测量技术,尤其是高精度的时间间隔测量技术意义重大。不论是电信通讯、芯片设计等工程实践,还是原子物理、天文观测实验等理论研究,以及激光测距、卫星定位等航天军事技术,都离不开高精度的时间间隔测量技术。经过几十年的研究,目前已经有多种测量方法。在阐明插值原理之后,依次介绍了直接计数法、扩展法、时间幅度转换法、游标法、抽头延迟线法和差分延迟线法等主要方法。然后对影响测量的几个因素,包括非线性和不定态作了讨论。针对这些不良影响,还探讨了一些提高精度和稳定度的方法,比如非线性校正、PLL(Phase Lock Loop)和DLL (Delay Lock Loop)技术。最后,对时间间隔测量技术的前景作了展望。 相似文献
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Application of grey theory-based model to prediction of land subsidence due to engineering environment in Shanghai 总被引：7，自引：0，他引：7
Yi-Qun Tang Zhen-Dong Cui Jian-Xiu Wang Li-Ping Yan Xue-Xin Yan 《Environmental Geology》2008,55(3):583-593
Land subsidence is a common geological hazard. The long-term accumulation of land subsidence in Shanghai has caused economic
loss to the city. Since the 1990s, the engineering structures have become a new cause of land subsidence. Many factors affect
the process of land subsidence. Although such a process cannot be explicitly expressed by a mathematical formula, it is not
a “black box” whose internal structure, parameters, and characteristics are unknown. Therefore, the grey theory can be applied
to the prediction of land subsidence and provides useful information for the control of land subsidence. In this paper, a
grey model (GM) GM (1, 1) with unequal time-intervals was used to predict the subsidence of a high-rise building in the Lujiazui
area of Shanghai, and the results were compared with the monitored data. The prediction of subsidence was also corroborated
by laboratory tests and the results were compared with measured data and the predicted data by the adaptive neuro-fuzzy inference
system (ANFIS). It is found that the GM (1, 1) with unequal time-intervals is accurate and feasible for the prediction of
land subsidence. 相似文献
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地面沉降是目前常见的地质灾害之一,其长期的积累给城市带来巨大的经济损失,成为制约城市发展的主要因素。进入20世纪90年代以来,工程环境效应诱发的沉降已经成为上海地面沉降的新趋势,对于外荷载引起的地面沉降过程而言,影响因素较多,既无法用明确的数学关系式表达,又非黑箱那样内部结构、参数和特征一无所知,因此可将灰色预测理论应用于地面沉降的预测。针对监测和观测时间的非等时性,本文应用非等时距灰色理论模型对上海陆家嘴地区某高层建筑的沉降进行预测,并和实际监测沉降量进行了比较;对室内模型试验进行沉降预测,并和实验观测数据以及自适应神经网络系统(ANFIS)预测结果进行了比较。研究发现,对于工程环境效应引起的地面沉降,应用非等时距灰色理论模型进行沉降预测是可行、精确的。 相似文献
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Latin America has long played a key role in the global provision of natural resources. Most of the continent's economies are net exporters of low-value, primary products and importers of manufactured goods at a high price. This pattern of specialised trade has highly negative consequences for economic development, the environment, and the local population’s wellbeing. Yet to date, little empirical evidence has been collected on Latin America’s total contribution to the rest of the world's regions in historical perspective. Applying the Material Flow Accounting methodology, this paper estimates the physical and monetary trade of 16 Latin American economies between 1900 and 2016. Our results show that: (i) yearly net exports of materials went from 4 Mt to 610 Mt between 1900 and 2016, and greatly accelerated since the World War II. (ii) Latin America is a net exporter of most types of materials (fossil fuels, non-energy minerals and biomass), so it harbours socio-environmental problems associated with different types of extractivism. (iii) Different regional export patterns exist: Andeans export subsoil (mining and energy carriers) while the rest export soil (land-based products). The countries with the lowest net exports are the smallest in size and with the highest population density. (iv) Europe and the USA have historically received most of the imports, but since the end of the twentieth century, the Southeast Asia region is the biggest importer of materials from Latin America. (v) The price received for exported material is much lower than the price paid for imported material; and (vi) various historical periods can be differentiated regarding the relationship between economic growth and physical trade balance. 相似文献
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Unequal exchange theory posits that economic growth in the “advanced economies” of the global North relies on a large net appropriation of resources and labour from the global South, extracted through price differentials in international trade. Past attempts to estimate the scale and value of this drain have faced a number of conceptual and empirical limitations, and have been unable to capture the upstream resources and labour embodied in traded goods. Here we use environmental input-output data and footprint analysis to quantify the physical scale of net appropriation from the South in terms of embodied resources and labour over the period 1990 to 2015. We then represent the value of appropriated resources in terms of prevailing market prices. Our results show that in 2015 the North net appropriated from the South 12 billion tons of embodied raw material equivalents, 822 million hectares of embodied land, 21 exajoules of embodied energy, and 188 million person-years of embodied labour, worth $10.8 trillion in Northern prices – enough to end extreme poverty 70 times over. Over the whole period, drain from the South totalled $242 trillion (constant 2010 USD). This drain represents a significant windfall for the global North, equivalent to a quarter of Northern GDP. For comparison, we also report drain in global average prices. Using this method, we find that the South’s losses due to unequal exchange outstrip their total aid receipts over the period by a factor of 30. Our analysis confirms that unequal exchange is a significant driver of global inequality, uneven development, and ecological breakdown. 相似文献
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实际海面受风浪的影响是个随机起伏的复杂曲面.一个随机起伏的自由表面对地震波形成相当复杂的散射,进而影响波场在靶区的二次照明与成像结果;此外,起伏海面具有小尺度随机起伏的特性,难以用贴体网格等处理大尺度起伏地表的常规方法和技术对其进行逼近和处理.鉴于此,利用不等距有限差分法实现小尺度起伏海面的波场自由表面边界条件,以此进行正演、波场照明分析;利用逆时偏移（Reverse Time Migration,RTM）进行起伏海面下的成像并对成像结果进行分析.不同模型的试算结果表明：起伏海面引起的复杂散射使靶区地下照明不均匀、成像界面发生弯曲和畸变,从而降低成像结果的分辨率和信噪比. 相似文献
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