工业CT中机械径跳投影数据仿真

在工业X射线CT检测系统中,当对某一物体进行检测的时候,系统中的载物台机架会进行不断的旋转,在旋转过程中,机架将会伴随有机械径跳,径跳会影响到探测器接收到的光子数,最后对投影数据有一定的影响,进而影响重建出的物体图像。本文主要分析了载物台机架发生机械径跳的原因,以及径跳对探测器接收X射线光子的影响;在对以上原因进行分析的基础上,提出了在考虑CT机架径跳时的CT投影公式,并对这一投影进行仿真。     

围岩稳定性评价的投影寻踪权重-属性区间识别模型

围岩的稳定性评价是一个复杂的不确定系统问题。采用粒子群算法优化投影寻踪方法,并结合属性区间识别理论,建立了围岩稳定性评价的投影寻踪权重-属性区间识别模型。选取5个围岩稳定性影响因子作为评价指标,通过构造属性测度区间函数计算单指标属性测度区间,利用基于粒子群优化的投影寻踪确定各评价指标的权重以计算综合属性测度区间,应用置信度准则和评分准则对围岩的稳定性进行属性识别。实例研究表明,该模型能有效的解决围岩稳定性评价问题,且评价结果科学可靠;评价模型采用投影寻踪确定权重,避免了权重确定中的主观性和随意性,保证了评价工作的客观性和准确性。     

遥感植物地球化学方法的研究进展

近些年来随着遥感技术的不断发展,在植被覆盖区的金属矿床的探查中,遥感植物地球化学方法得到了越来越广泛的应用。文章从理论、技术和应用三个方面对遥感植物地球化学方法的发展进行阐述,并指出目前存在的问题。其中使用定量化的手段提取植物地球化学信息是未来的必由之路。然而在定量化的过程中,光谱尺度效应和空间尺度效应是两个重要的影响模型精度的因素。针对这个问题,文章提出两种解决方案来减小光谱尺度效应的影响,然而这两种方法的可操作性以及可靠性还需要进一步探讨。最后,文章对遥感植物地球化学方法的发展前景进行阐述,并指出在以后定量模型的建立中可以引入支持向量机、投影追踪等机器学习的方法。     

等距离球面高斯投影

针对传统高斯投影直接基于等角横切圆柱投影而带来的不能直接用球面坐标换算等问题,研究了一种运用等距离球面进行投影的高斯投影,即等距离球面高斯投影。借助等距离纬度正反解公式,推导了等距离球面高斯投影的正反解公式,分析了其经纬线变形情况;基于投影公式,计算和分析了等距离球面高斯投影的长度变形、角度变形、面积变形及子午线收敛角等参数;最后与传统高斯投影进行比较,说明了该投影的可用性。     

长江口海平面上升预测及其对滨海湿地影响

选择吴淞站和吕四站2个验潮站数据,通过统计学方法进行长江口海平面上升预测,从而构建了一套长江口地区较完备的海平面上升情景库：以2013年为基准年份,其最佳预测值的范围在2030年、2050年、2100年分别为50~217 mm,118~430 mm,256~1215 mm。以此情景库为基础,探究海平面上升变化对长江口滨海湿地的影响,结果表明：随着海平面上升值的增加,长江口滨海湿地的面积不断减少;在基于验潮站数据作趋势外推得到的情景下,湿地面积减少较平缓,而在考虑全球变暖背景的情景下,湿地面积减少迅速;且不论在何种情景下,时间尺度越大,湿地减少的面积越大。     

中国地磁基本场模式建立方法探讨

利用７０年代的地磁资料，讨论了测点密度和测点坐标变换对建立中国地磁基本场模式的影响。结果表明，只选用分布较均匀的２００个左右的测点建立基本场模式是可行的；对测点的球面坐标进行Ｍｅｒｃａｔｏｒ投影变换是必要的，可以显著减小模式的场值分布在边界附近出现的畸变现象；３阶到５阶模式均主要反映正常的基本磁场分布，而５阶模式效果最好     

On integration of a cyclic soil plasticity model

Performance of three classes of explicit and implicit time‐stepping integrators is assessed for a cyclic plasticity constitutive model for sands. The model is representative of an important class of cyclic plasticity models for soils and includes both isotropic and nonlinear kinematic hardening. The implicit algorithm is based on the closest point projection method and the explicit algorithm follows a cutting‐plane integration procedure. A sub‐stepping technique was also implemented. The performance of these algorithms is assessed through a series of numerical simulations ranging from simulations of laboratory tests (such as triaxial and bi‐axial compression, direct shear, and cyclic triaxial tests) to the analysis of a typical boundary value problem of geotechnical earthquake engineering. These simulations show that the closest point projection algorithm remains stable and accurate for relatively large strain increments and for cases where the mean effective stress in a soil element reaches very small values leading to a liquefaction state. It is also shown that while the cutting plane (CP) and sub‐stepping (SS) algorithms provide high efficiency and good accuracy for small to medium size strain increments, their accuracy and efficiency deteriorate faster than the closest point projection method for large strain increments. The CP and SS algorithms also face convergence difficulties in the liquefaction analysis when the soil approaches very small mean effective stresses. Copyright © 2001 John Wiley & Sons, Ltd.     

Stochastic simulation of spatially correlated geo-processes

In this study, developments in the theory of stochastic simulation are discussed. The unifying element is the notion of Radon projection in Euclidean spaces. This notion provides a natural way of reconstructing the real process from a corresponding process observable on a reduced dimensionality space, where analysis is theoretically easier and computationally tractable. Within this framework, the concept of space transformation is defined and several of its properties, which are of significant importance within the context of spatially correlated processes, are explored. The turning bands operator is shown to follow from this. This strengthens considerably the theoretical background of the geostatistical method of simulation, and some new results are obtained in both the space and frequency domains. The inverse problem is solved generally and the applicability of the method is extended to anisotropic as well as integrated processes. Some ill-posed problems of the inverse operator are discussed. Effects of the measurement error and impulses at origin are examined. Important features of the simulated process as described by geomechanical laws, the morphology of the deposit, etc., may be incorporated in the analysis. The simulation may become a model-dependent procedure and this, in turn, may provide numerical solutions to spatial-temporal geologic models. Because the spatial simlation may be technically reduced to unidimensional simulations, various techniques of generating one-dimensional realizations are reviewed. To link theory and practice, an example is computed in detail.     

BOOK REVIEWS

Book Reviewed in this article: Geographical Aspects of Health and Disease in India . Rais Akhtar and A.T.A. Learmonth , eds . Antarctic Treaty System: An Assessment . Proceedings of a Workshop at Beardmore South Field Camp, Antarctica. American Electoral Mosaics . J. Clark Archer and Fred M. Shelley . Kompas op Suidwes-Afrika/Namibie . W.S. Barnard , ed . Jerusalem in the 19th Century: The Old City . Yehoshua Ben -Arieh . The World as a Total System . Kenneth E. Boulding . A Social History of Housing 1815–1985, Second Ed . John Burnett . Human Migration . W.A.V. Clark . Regional Population Projection Models . Andrei Rogers . The State of Population Theory: Forward from Malthus . David Coleman and Roger Schofield , eds . Imagining Tomorrow: History, Technology and the American Future . Joseph C. Corn , ed. Swidden Agriculture in Indonesia: The Subsistence Strategies of the Kalimantan Kantú . Michael R. Dove . Glacial Geologic Processes . David Drewry . Physics of Desertification . Farouk El -Baz and M.H.A. Hassan , eds . Housing the Homeless . Jon Erickson and Charles Wilhelm , eds . Settlement Patterns in Missouri: A Study of Population Origins, with a Wall Map . Russel L. Gerlach . Desert Development: Man and Technology in Sparselands . Yehuda Gradus , ed . Nuclear Winter. The Evidence and Risks . Owen Greene , Ian Percival and Irene Ridge . The Take-off of Suburbia and the Crisis of the Central City . Günter Heinritz and Elisabeth Lichtenberger , eds . Regional Input-Output Analysis . Geoffrey J. D. Hewings . Spatial Transportation Modeling . Christian Werner . The Atlas of Georgia . Thomas W. Hodler and Howard A. Schretter , eds . Latin America. 5th ed . Preston E. James and C.W. Minkel . Applied Remote Sensing . C.P. Lo . Localities, Class, and Gender . The Lancaster Regionalism Group . Urban Social Movements: The City after Castells . Stuart Lowe . Politics and Method . Doreen Massey and Richard Meegan , eds . Land Use . A. S. Mather . The Kingdom of Coal . Donald L. Miller and Richard E. Sharpless . The Presidio and Militia on the Northern Frontier of New Spain, A Documentary History, Vol. 1: 1570–1700 . Thomas H. Naylor and Charles W. Polzer , S.J., comps . and eds . Nuclear Power: Siting and Safety . Stan Openshaw . The Central African Republic: The Continent's Hidden Heart . Thomas O'Toole . Environmental and Dynamic Geomorphology . Márton Pécsi , ed . Remote Sensing Principles and Interpretation . Floyd F. Sabins , Jr . Acid Rain and Friendly Neighbors: The Policy Dispute between Canada and the United States . Jurgen Schmandt and Hilliard Roderick , eds . Earth's Changing Surface: An Introduction to Geomorphology . M.J. Selby . International Migration: The Female Experience . Rita J. Simon and Caroline B. Brettell , eds . On Geography and Its History . D.R. Stoddart . Transportation Networks: A Quantitative Approach . D. Teodorovic . Processes in Physical Geography . R.D. Thompson , A.M. Mannion , C.W. Mitchell , M. Parry , J.R.G. Townshend . Imaging Radar for Resources Surveys . J.W. Trevett . Dominance and Affection: The Making of Pets . Yi -Fu Tuan . Capturing the Horizon. The Historical Geography of Transportation since the Transportation Revolution of the Sixteenth Century . James E. Vance , Jr . Nations at Risk: The Impact of the Computer Revolution . Edward Yourdon .     

减小测区的长度变形

论述了测量工作中的长度变形种类以及减小长度变形的方法，然后通过一实例说明如何减小长度变形，得出几点结论，有较好的参考价值。