大陆造山带地球化学研究：Ⅰ 岩石构造环境地球化学判别的改进   总被引：8，自引：1，他引：8  

张本仁 《西北地质》2001,34(3):1-17

本文讨论了如何改进岩石构造环境的地球化学判别方法及其应用于研究造山带构造演化的问题，在论述了岩石地球化学特征与形成构造环境关系实质的基础上，提出了优选判别指示元素，参数和方法的准则及应用实例；并提出采用岩套内岩类配套及相邻相造期岩套或岩石建造时空配套综合分析途径的建议，从解决某些岩石化学特征在反映构造环境方面存在的多解性问题，推动造山带构造演化细节的深入研究。  相似文献   

锥束CT图像重建算法   总被引：9，自引：0，他引：9  

王本  王革 《CT理论与应用研究》2001,10(2):1-8

随着螺旋多层面CT的出现，医用CT正在向着螺旋锥束CT转变，从螺旋锥束数据来重建图像有许多优点，但是这种成像方式在数学上比较复杂，技术实现也有相当的难度。本文介绍这一领域的重要成果，特别是近年文献中的基本思想，文中涉及及各种主要重算法，包括准确重建，近似重建和迭代重建算法，简言之，当数据是完整的，无噪音的，应选择准重建方法，当数据是有噪音的和／或受物体运动干扰，近似重建会有较好的性能，而当数据是不可靠的和被载截断时，迭代方法可以发挥作用，今后主要研究方向是对这些算法进行改进，比较它们的特性，并将其优点结合到一起。  相似文献   

Composite magnetic anisotropy fabrics: experiments, numerical models and implications for the quantification of rock fabrics   总被引：2，自引：0，他引：2  

Bernard A. Housen  Carl Richter  Ben A. van der Pluijm 《Tectonophysics》1993,220(1-4):1-12

Magnetic fabrics from rocks with multiple mineral-preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics. Our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and/or orientations of the individual mineral fabrics and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks. These criteria include:

1. (1) the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics, and

2. (2) the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases, as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases.

Composite magnetic fabrics are observed in the shales and slates of the Martinsburg Formation, Lehigh Gap, Pennsylvania. Modeling of the AMS (anisotropy of magnetic susceptibility) and ARMA (anhysteretic remanent magnetization anisotropy) behavior constrains the relative degree of anisotropy of the bedding-parallel and cleavage-parallel fabrics. In particular, ARMA model results allow a good estimate of magnetite fabric strength.

We conclude that, in the presence of composite magnetic fabrics, quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric. Such determinations require knowledge of the mineral(s) that are responsible for the measured magnetic fabric and their behavior during deformation.  相似文献   

Disaster vulnerability: Scale,power and daily life   总被引：13，自引：0，他引：13  

Ben Wisner  Henry R. Luce 《GeoJournal》1993,30(2):127-140

The author gratefully acknowledges the stimulation over a number of years of his co-authors in a project about to appear in 1994 under the title,At Risk: Natural Hazards, People's Vulnerability and Disasters, Routledge, London & New York — Piers Blaikie, Terry Cannon, and Ian Davis.Earlier versions of this paper were discussed by session on disasters organized by Tony Oliver-Smith at the annual meeting of the Society for Applied Anthropology, Memphis, March, 1992 and at the Famine and Food Systems Study Group of the International Geographical Union, convened at Tufts University, July, 1992, by John Field and Hans Bohle. My thanks as well to colleagues who participated in these two discussions.  相似文献   

U&z.sbnd;Th isotopic systematics at 13°N east Pacific Ridge segment     

D. Ben Othman  C.J. Alle&#x;gre 《Earth and Planetary Science Letters》1990,98(1)

Fresh basaltic glasses have been analyzed for U&z.sbnd;Th disequilibrium systematics as part of an extensive study on the East Pacific Rise (EPR) at 12°45′N. These samples are well described in terms of major and trace elements as well as in Nd, Pb and Sr isotopes. Our results show significant heterogeneities in the mantle source at a small scale, and show heterogeneities at larger scales also when compared to other EPR data.U and Th concentration and isotopic data rule out fractional crystallization as a main process and support a mixing model in agreement with the marble cake model developed by Alle`gre and Turcotte and constrained by trace elements and Nd, Sr and Pb isotopes on the same samples by Prinzhofer et al.Based on the high ( ²³⁰Th/²³²Th ) isotopic ratios on recent tholeiites especially the Th/U values inferred for their sources clearly show that the upper mantle Th/U has decreased with time.  相似文献   

Apparent lack of CYP1A response to high PCB body burdens in fish from a chronically contaminated PCB site     

Brammell BF  Price DJ  Birge WJ  Elskus AA 《Marine environmental research》2004,58(2-5):251-255

Chronic exposure to organic contaminants such as polychlorinated biphenyls (PCBs) can lead to the development of resistance to these chemicals, a condition associated with reduced response of CYP1A1, a pollutant-inducible biomarker. We measured CYP1A activity (ethoxyresorufin o-deethylase, EROD) and PCB concentrations in feral fish from the Town Branch/Mud River system (Logan County, KY), a stream historically contaminated with PCBs and partially remediated. As a first step in evaluating the possible development of resistant populations in this system, we measured CYP1A expression and PCB body burdens in resident fish from sites we previously characterized as containing biologically significant levels of CYP1A inducing compounds. Mean PCB concentrations in edible flesh ranged from 75.2 to 16.7 microg/g in fish collected from Town Branch remediated sites and were relatively low (1.23 microg/g) in Town Branch reference site fish. However, hepatic CYP1A activity was similar among individuals of most species collected from reference and contaminated/remediated sites. The absence of elevated CYP1A levels in resident fish species despite the presence of significant PCB body burdens may indicate these fish have developed reduced sensitivity to CYP1A induction, a condition associated with acquired resistance to toxicants.  相似文献   

广西北海湾COD与水文生物要素及不同形态氮磷的关系   总被引：7，自引：3，他引：7  

韦蔓新  童万平  赖廷和  何本茂 《台湾海峡》2002,21(2):162-166

本文探讨了北海深COD值的分布特征及其与水文，生物要素及不同形态氮，磷含量的关系，结果表明；河流输入对本湾COD值的影响突出表现在春、夏季、冬季最小，秋季则以沿岸排废，排污影响为主，水文要素对COD值的分布起主导控制作用，生物化学作用仅占次要地位；春、夏、冬三个季度月COD值与氮含量的相关性较为显著，秋季则与磷含量的相关性较为显著。  相似文献   

养殖对虾细菌性红体病的初步研究   总被引：22，自引：2，他引：22       下载免费PDF全文

周永灿  张本  陈雪芬  钱家英 《海洋科学》2003,27(5):61-65

从海南琼山患红体病的养殖南美白对虾(Penaeus vannamei)的肝胰脏和肌肉中分离出2株细菌，经纯化培养后的人工感染结果表明，该2株菌均为引起对虾红体病的细菌性病原菌；根据对这2株菌的形态及生理生化特征检测结果，确定这2株菌分别为溶藻弧菌(Vibrioalginolyticus)和副溶血弧菌(V.parahaemolyticus)。药敏试验表明，氮霉素、链霉素和庆大霉素等7种抗生素对抑制这2种致病菌具有良好作用。  相似文献   

Postglacial relative sea‐level observations from Ireland and their role in glacial rebound modelling     

Anthony J. Brooks  Sarah L. Bradley  Robin J. Edwards  Glenn A. Milne  Ben Horton  Ian Shennan 《第四纪科学杂志》2008,23(2):175-192

The British Isles have been the focus of a number of recent modelling studies owing to the existence of a high‐quality sea‐level dataset for this region and the suitability of these data for constraining shallow earth viscosity structure, local to regional ice sheet histories and the magnitude/timing of global meltwater signals. Until recently, the paucity of both glaciological and relative sea‐level (RSL) data from Ireland has meant that the majority of these glacial isostatic adjustment (GIA) modelling studies of the British Isles region have tended to concentrate on reconstructing ice cover over Britain. However, the recent development of a sea‐level database for Ireland along with emergence of new glaciological data on the spatial extent, thickness and deglacial chronology of the Irish Ice Sheet means it is now possible to revisit this region of the British Isles. Here, we employ these new data to constrain the evolution of the Irish Ice Sheet. We find that in order to reconcile differences between model predictions and RSL evidence, a thick, spatially extensive ice sheet of ～600–700 m over much of north and central Ireland is required at the LGM with very rapid deglaciation after 21 k cal. yr BP. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

An overview of the Late Cretaceous-Eocene positive inversions and Oligo-Miocene subsidence events in the foreland of the Tunisian Atlas: Structural style and implications for the tectonic agenda of the Maghrebian Atlas system   总被引：4，自引：0，他引：4  

Sami Khomsi  Mohamed Ghazi Ben Jemia  Chokri Maherssi  Riadh Mezni 《Tectonophysics》2009,475(1):38-207

Structural interpretation of surface and subsurface data in the Eastern foreland basins of Tunisia, allows us to recognize positive inversion structures, i.e. related to compressional events, expressed and recorded in the Paleogene sedimentary pile of the Atlas domain. These episodes are followed by a period of relative tectonic quiescence during Oligocene-Early Miocene with development of extensional structures with slightly tilted panels, grabens and locally the development of listric normal faults branched at depth on “décollement” levels.Comparison of the seismic interpretations and field data collected along the South Atlas Front as well as in the Atlas belt, allows us to propose a tectonic scenario at the scale of Eastern Tunisia Atlas. In particular, we emphasise the role of the so-called “Atlas event” (Middle-Late Eocene), which was initially defined in Algeria but poorly outlined in Tunisia. We will show that the tectonic agenda defined in Eastern Tunisia is consistent with the one proposed elsewhere in the Maghreb allowing us to propose a unified view of the geodynamic evolution of the whole Atlas system during this period.The negative inversion recorded during Oligocene-Early Miocene along with the occurrence of synsedimentary normal faults are related to an increase of the subsidence rate in the frame of continuous shortening coeval to basin formation in the front of the Atlas. The whole Oligo-Miocene evolution results from two different mechanisms: flexuration in the front of the Atlas and the onset of the extension of the Pantelleria-Linosa-Malta rift system of central Mediterranean, which attained a climax stage later during Pliocene-Quaternary.  相似文献