共查询到20条相似文献，搜索用时 31 毫秒
1.
生长地层记录了大量的构造变形和沉积历史信息,主要形成于逆冲-褶皱造山带前陆盆地边缘,在前陆盆地生长构造(如生长逆断裂-褶皱带)翼部或顶部与褶皱构造变形同期沉积的地层,是构造运动与沉积作用同时进行的产物,在构造横剖面上,整个生长地层序列在褶皱翼部具有楔形几何状态。根据其形成方式的不同,可以分为断层转折褶皱作用和断层传播褶皱及滑脱褶皱作用等。生长地层的最终形态受各种地质作用影响,其中主要因素是构造变形、沉积速率和侵蚀作用,三者之间在生长地层形成过程中通常具有“复合”作用。通过生长地层的详细研究,可以建立同构造生长地层模式,而广泛应用于确定前陆逆冲-褶皱带与相应地层的时代、变形速率,分析与逆冲推覆断层相关的褶皱几何形态,以及建立动力学模式等。生长地层的野外识别一般可从褶皱翼部和枢纽变化、翼部同沉积楔体、地层产状和厚度变化以及区域资料收集对比等几方面来综合分析,同时采用多模式、多手段的室内分析将是研究生长地层最为有效的方法,也是今后的重点发展方向。通过对生长地层的识别标志和模式的进一步认识,初步分析了六盘山山前宁夏固原寺口子剖面,认为寺口子盆地为逆冲-褶皱造山带前陆磨拉石盆地,其内可能存在有生长地层和生长不整合,但需 相似文献
2.
目的:探讨韧带样纤维瘤（DF）的CT、MRI表现及其诊断价值。方法:回顾性分析经病理证实的16例DF患者的临床及影像学资料,16例中7例行CT平扫与增强,7例行MRI平扫与增强,2例同时行CT、MRI检查。结果:16例DF均为单发,包括腹外型7例,腹壁型5例,腹内型4例。边界不清14例,边界清晰2例。呈浸润性生长13例,膨胀性生长3例。病灶与肌肉长轴平行9例。CT表现:9例平扫呈稍低密度,未见出血、坏死及钙化,增强扫描飘带样强化7例,6例延迟扫描均呈渐进性持续强化。MRI表现9例均见T2WI抑脂条带状低信号,未见出血、坏死,增强扫描均呈明显不均匀强化、延迟呈渐进性持续强化。“蟹足样”浸润周围组织5例;“筋膜尾征”4例。结论:DF的CT和MRI表现具有一定的特征,综合分析这些特点对其诊断及鉴别诊断具有重要价值。CT和MRI可清晰评估DF边缘和范围,有助于术前制定手术计划。 相似文献
3.
结构健康监测系统设计标准化评述与展望 总被引：4，自引：1，他引：3
阐述了结构健康监测的概念和内涵。详细介绍了结构健康监测系统的功能、组成和应用现状。结构健康监测系统设计标准化能够促进健康监测的应用和发展,具有重要的工程意义。对世界范围内相关研究进展进行了综述和评价。强调在我国建立监测系统设计标准的重要性,并提出了相应的说明和建议。设计标准可以分为总则、外观检查与无损检测、传感器的选择与布置、信息采集与处理系统、通信与传输系统、损伤识别和评估系统、应用实例等7部分。结构健康监测系统设计标准的实现将有力地推动健康监测的研究。 相似文献
4.
A series of major geological and biological events which altered the evolutionary processes of whole biosphere occurred during the earth history. Establishing a high-resolution stratigraphic framework and timescale is essential to understand their tempo and causes. High-resolution biostratigraphy remains the most useful approach and forms the basis of dividing the chronostratigraphic system and making the inter-continental and regional correlation. China possesses nearly complete strata from Ediacaran to Quaternary covering wide palaeogeographic regions and containing abundant well-preserved fossils. Traditional biostratigraphy based on sytematic palaeontology of various fossil groups have played an important role in establishing the GSSPs and improving the International and Chinese Stratigraphic Charts. 11 out of 72 establised GSSPs are located in China.Recently, more high-precision geochronology, chemostratigraphy, cyclostrtatigraphy have been applied for stratigraphy and correlation and important advances have been made in some periods. This volume invited Chinese palaeontologists and stratigraphers to summarize the progresses of stratigraphy and timescale from Ediacaran to Quaternary and intercontinental and regional correlation during the last two decades. 相似文献
5.
Gender of large river deltas and parasitizing rivers 总被引：1，自引：0，他引：1
Deltas are the most dynamic part of large rivers and the characteristics of deltas reflect the basic nature of morphodynamics,ecology and anthropogenic influence.The authors investigated many deltas of... 相似文献
6.
Arid alluvial fan and fluvial dry wash surfaces in Stonewall Flat, Nevada, USA, are characterized using surface geomorphic surveys, soil pits, botanical line surveys, and varnish microlamination dating techniques. Active and abandoned washes, and active fan surfaces are dominated by primary geomorphic processes of high‐energy sedimentation from flash floods. These surfaces are characterized by bar and swale topography, a lack of stone pavements, soil horizons, and rock varnish. Younger terraces and slightly older intermediate fan surfaces are in transition from primary sedimentation processes to lower energy secondary surface‐modifying processes of sheet wash and eolian transport and deposition. These surfaces are characterized by faint to no bar and swale topography, incipient to moderately well‐developed pavements and soil horizons, and abundant coppices. Old and stable fan surfaces are dominated by lower energy secondary processes and manifest well‐developed pavements, soils, and sparse coppices around widely distributed shrubs. Varnish microlamination dating yields ages of 13·15 ka for intermediate fan surfaces and 25·55 to 86·75 ka for stable fan surfaces. Plant communities co‐developing with these surfaces affect and are affected by both primary and secondary geomorphic fan processes. Relatively active surfaces contain few woody species. Co‐dominance of shrubs and annuals with abundant annuals between the shrubs is characteristic of surfaces transitional from primary processes to secondary processes. Stable surfaces dominated by secondary processes are characterized by woody perennials, with long‐lived woody species inhabiting the oldest surfaces. Feedback mechanisms between early botanical communities and eolian deposition affect coppice and pavement development. In turn, these surface features control both the composition and distribution of botanical communities on older, more stable surfaces. Published 2012. This article is a U.S. Government work and is in the public domain in the USA. 相似文献
7.
长江流域历史水旱灾害分析 总被引：2，自引：1，他引：1
长江流域有丰富和长期的水旱灾害史料,最早的水灾和旱灾记载有2000余年的历史,经过系统整理和分析的历史水旱灾害资料有1000余年的旱涝型年表和500余年的旱涝分布图集.在以上资料基础上,对长江流域历史水旱灾害的地域分布特性和时间变化规律进行了初步分析:500余年历史水旱灾害的地域分布显示,流域水旱灾害总体特征是水灾重于旱灾,各级水旱灾害频率的地域分布极不均匀,存在着显著的灾害多发和少发地带,它们与自然地理环境、水系特征、气候条件和社会经济条件等因素有关;1000余年旱涝型年表分析表明,长江流域洪涝和干旱频次在时间上的非均匀分布并非完全随机,表现出多种时间尺度的年际变化特征,其中主要表现为约100a上下的大干湿气候期变化及40a左右的小旱涝期振动. 相似文献
8.
Tiffany A. Schriever M. W. Cadotte D. Dudley Williams 《Aquatic Sciences - Research Across Boundaries》2014,76(1):131-143
Ecosystem functioning is influenced by the flow of nutrients, detritus, and organisms. Variation in these flows, like that found in temporary ecosystems, affects temporal and spatial patterns of community diversity and secondary production. We evaluated the influence of hydroperiod and ecosystem size on the bi-directional flow of subsidies from intermittent ponds and surrounding forests by quantifying litter deposition and the abundance and biomass of emerging insects and amphibians. In addition, we assessed whether amphibian and insect diversity influenced the magnitude of cross-habitat resource flux. We found substantial spatial and temporal variation in the magnitude, composition, and timing of cross-habitat resource subsidies. Overall, deposition into ponds far exceeded biomass exported via insect and amphibian emergence. We found a negative association between resource flux and the diversity of amphibians and insects. Different species groups contributed to flux patterns unequally, with insects having higher diversity but lower flux compared to amphibians. Organismal flux varied among ponds with amphibians having the highest flux in the shortest hydroperiod pond and insect flux was highest from an intermediate hydroperiod pond. This work reveals how variation in pond size and permanence affects species diversity and ecosystem flows. Species composition played a major role in flux differences across ponds. Further, given the general lack of research and conservation prioritization of temporary ponds, uncovering how these ponds contribute to cross-habitat linkages is necessary to develop fully integrated management strategies. 相似文献
9.
水生态系统是人类赖以生存的基础,近年来气候变化和水资源开发、水体污染、过度捕捞等人类活动导致水生态系统严重受损,水生态系统的保护和修复已成为全球面临的重大挑战。科学合理的水生态评价方法是实现水生态系统稳定、健康和可持续管理的基本保障,也是目前我国各相关管理部门高度重视的关键问题,多个部门围绕水生态评价展开了积极探索与实践。本文系统回顾了水生态评价方法的发展历程并阐释了水生态评价的内涵,梳理了常用的水生态评价方法,明晰了各方法的基本理念和应用场景,分析了各方法的优点和不足,提出了基于生态完整性的水生态健康评价方法,最后对目前我国水生态评价需进一步完善的工作进行了展望。本文以期与相关领域研究者和管理者在水生态评价理论和方法方面进行探讨,为我国水生态考核工作提供理论支持。 相似文献
10.
Geomorphological investigations in the Russian Altai Mountains provide evidence for the extent and timing of Late Quaternary glaciations and aeolian sediments. Infrared optically stimulated luminescence (IR-OSL) and thermoluminescence (TL) dating of aeolian sediments from the central part of the Russian Altai were carried out on silty and sandy sediments that cover fluvial and glacio-fluvial terraces. Most samples from loess, loess-like sediments and sandy loess taken from different terrace sequences within the Altai Mountains provide IRSL ages suggesting a main aeolian deposition period between 25 and 15 ka. These data are consistent with those from the adjacent Mongolian Altai. Sand and silt layers within moraines yielded IRSL age estimates between 22 and 19 ka and correlate to the ice margins of the Last Glacial Maximum. Aeolian dune sands overlying or neighbouring the loess-like sediments and the fluvial terraces at some places provide evidence for Late Glacial (around 15 ka) and Early Holocene (around 9 ka) aeolian activity. The youngest sand sheets gave deposition ages of about 1.5 ka. These sediments covered graves and are related to overgrazing. They provide evidence for the significant human impact on the environment. Fluvial sediments, including silt and sandy gravel intermingled with charcoal, yielded contradicting radiocarbon and luminescence ages. IRSL age estimates obtained for the silty layers range from 19 to 18 ka and are significantly older than the radiocarbon ages, which gave sub-recent ages between 1170 and 910 BP. These data indicate fluvial sedimentation of debris and mudflows in a period of deforestation and strong soil erosion related to mining activities during the 9th and 10th century. 相似文献
11.
R. J. Watters D. R. Zimbelman S. D. Bowman J. K. Crowley 《Pure and Applied Geophysics》2000,157(6-8):957-976
—Catastrophic edifice and sector failure occur commonly on stratovolcanoes worldwide and in some cases leave telltale horseshoe-shaped calderas. Many of these failures are now recognised as having resulted from large-scale landsliding. These slides often transform into debris avalanches and lahars that can devastate populations downstream of the volcano. Research on these phenomena has been directed mainly at understanding avalanche mechanics and travel distances and related socioeconomic impacts. Few investigations have examined volcanic avalanche source characteristics. The focus of this paper is to 1) describe a methodology for obtaining rock strengths that control initial failure and 2) report results of rock mass strength testing from Mount Rainier and Mount Hood. Rock mass and shear strength for fresh and hydrothermally altered rocks were obtained by 1) utilizing rock strength and structural information obtained from field studies and 2) applying rock mechanics techniques common in mining and civil engineering to the edifice region. Rock mass and intact rock strength differences greatly in excess of one order of magnitude were obtained when comparing strength behavior of fresh and completely altered volcanic rock. The recognition and determination of marked strength differences existing on the volcano edifice and flank, when combined with detailed geologic mapping, can be used to quantify volcano stability assessment and improve hazard mitigation efforts. 相似文献
12.
太湖水系结构特点及其功能的变化 总被引：20，自引：8，他引：12
太源水系上游为树状排列的河流,下游为扇形排水系统,全区江河湖海相贯通,受海潮和江流的作用,下游水系多变,防洪抗灾能力脆弱。近年来,虽经治理,该水系仍出现了“中雨大灾”,水资源不足及水质污染突出等一系列功能性的变化。 相似文献
13.
A review is presented of dynamical and physical properties of asteroids. Discovery methods are discussed and some distributions of the orbital elements and the absolute magnitudes are presented as are properties of planet-crossing asteroids, Hildas and Trojans. Various observational methods such as polarimetry, radar and occultations are briefly introduced and lightcurve data are more extensively described. Asteroid taxonomy in the Barucci classifiction is thoroughly discussed as are asteroid spins and shapes and the origin and the evolution of these bodies. Space missions to asteroids and space observations of asteroids are also introduced. 相似文献
14.
A Permanent Multilevel Monitoring and Sampling System in the Coastal Groundwater Mixing Zones 
下载免费PDF全文
下载免费PDF全文 To study the spatial and temporal variability of water dynamics and chemical reactions within the coastal groundwater mixing zones (CGMZs), high‐resolution periodical and spatial groundwater sampling within CGMZs is needed. However, current samplers and sampling systems may require heavy driving machines to install. There is also possible contamination from the metal materials for current samplers and sampling systems. Here, a permanent multilevel sampling system is designed to sample coastal groundwater within CGMZs. This cost‐effective system consists of metal‐free materials and can be installed easily. The system is tested in Po Sam Pai and Tingkok, Tolo Harbor and Hong Kong. Major ions, nutrients, stable isotopes and radium and radon isotopes were analyzed and the data provided scientific information to study the fresh‐saltwater interface fluctuations, and temporal variations and spatial heterogeneity of geochemical processes occurred within CGMZs. The reliable spatial and temporal data from the sampling system demonstrate that the system functions well and can provide scientific data for coastal aquifer studies. 相似文献
15.
结合小束源和Fourier传播子，应用Fourier传播子进行面向目标的小束源照明和成像.小束源的合成通过小波束变换中的小束函数获得，而Fourier传播子进行波场外推，完成小束源的波传播.小束源具有空间位置和方向的双局部特性，对于照明和成像，它更加灵活，并有更多的控制方法.通过照明分析，选择面向目标的有效照明小束源，进行部分小束源偏移，可以提供更好的成像质量和计算效率.作为数值试验，我们选用Fourier有限差分传播子，对 Marmousi模型和二维SEG-EAGE盐丘模型的数据，试验了小束源对目标结构的方向照明和成像.获得的结果表明，结合小束源和Fourier传播子进行面向目标的照明和成像是切实有效的. 相似文献
16.
根据1984-1985年地震测深资料,论述了攀西地区的深部地质特征。该区地壳厚50-60km;具高、低速相间的多层结构及断块构造;五个主要速度界面中,界面R4稳定且清晰,为上、下地壳的分界面,R6稳定并有较强的能量反射,为壳、幔之间的界面（莫霍面）,莫霍面沿构造带北深南浅（56-50km）,横穿构造带西深东浅（60-48km）。构造带内的上地壳较薄,纵横速度变化均较大,而下地壳较厚,速度较均匀,上地壳底部的低速层,在构造带内较带外薄而浅,Pn速度较低,为7.54-7.80km/s,属壳-幔过渡带,厚13-22km。小江、四开、安宁河及金河等断裂为超壳型或壳内断裂,多为逆冲断层。该构造带的各种深部特征表明它为大陆高原型年轻构造带。 相似文献
17.
18.
Stephane Descloux Thibault Datry Pierre Marmonier 《Aquatic Sciences - Research Across Boundaries》2013,75(4):493-507
Streambed colmation by fine sediment, e.g. the deposition, accumulation and storage of fines in the substrate, is a major environmental concern throughout the world. Nevertheless, the ecological effects of streambed colmation on both benthic and hyporheic invertebrate assemblages have rarely been considered simultaneously. We studied a continuum of a naturally increasing percentage of fine sediment in three temperate rivers and hypothesized that the increasing percentage of fine sediment would decrease both benthic and hyporheic invertebrate densities and diversities, and reduce the similarities between them. To test these hypotheses, we first compared heavily, moderately and lightly clogged reaches located in downwelling areas and sampled invertebrates in the benthic zone and at 3 different depths (10, 30 and 50 cm) in the hyporheic zone. Secondly, we modified the sediment grain size distribution experimentally by increasing the percentage of fine sediment and using artificial substrates. The increasing colmation halved the hyporheic taxonomic richness and reduced benthic and hyporheic densities to a third. Some taxa were found in both zones, mainly in high colmation (e.g. Baetidae) or low colmation contexts (e.g. Orthocladiinae, Cyclopoida and Harpacticoida). The dissimilarity between benthic and hyporheic fauna (only at ?50 cm) was significantly higher in heavily clogged reaches than in moderately and lightly clogged ones, suggesting reduced vertical exchange of invertebrates or differential impacts between zones. The total abundance, taxonomic richness, percentage of EPT taxa and densities of most organisms observed using the artificial substrates decreased linearly with the increasing percentage of fine sediment in the experiment. Only the Ephemeroptera Caenis spp. and Heptageniidae disappeared above 30 and 50 % of fine sediment, respectively, suggesting that the response to increasing colmation are strongly taxon-specific. High amount of fine sediments within the substrate significantly decreased habitat quality for benthic and hyporheic invertebrates and thus limit the production of streams and their capacity to recover after disturbance. Moreover, the use of hyporheic invertebrates seems more relevant than benthic invertebrates to assess the effect of colmation and thus could be tested in future research as indicators. 相似文献
19.
双程波方程逆时深度偏移是复杂介质高精度成像的有效技术,但其结果中通常包含成像方法引起的噪音和假象,一般的滤波方法会破坏成像剖面上的振幅,其中的假象也会给后续地质解释带来困扰.将波场进行方向分解然后实现入射波与反射波的相关成像能够有效地消除这类成像噪音,并提高逆时偏移成像质量.波传播方向的分解通常在频率波数域实现,它会占用大量的存储和计算资源,不便于在沿时间外推的逆时深度偏移中应用.本文提出解析时间波场外推方法,可以在时间外推的每个时间片上实现波传播方向的显式分解,逆时深度偏移中利用分解后的炮检波场进行对应的相关运算,实现成像噪音和成像信号的分离.在模型和实际数据上的测试表明,相比于常规互相关逆时偏移成像结果,本文方法能够有效地消除低频成像噪音和特殊地质构造导致的成像假象. 相似文献
20.
目的:探究食管胃结合部癌病理型别的能谱CT鉴别诊断效果。方法:回顾性分析2015年1月至2018年1月期间我院收治的116例食管胃结合部癌患者的临床资料,其中64例为腺癌,52例为鳞癌。高分化27例,中分化45例,低分化44例。所有患者均行能谱CT扫描。比较腺癌和鳞癌患者动脉期和静脉期肿块内统一ROI碘浓度（IC）、有效原子序数（Eff-Z）、水浓度（WC）、能谱曲线斜率（λHU）,并比较不同分化程度患者动脉期和静脉期肿块内IC、Eff-Z、WC、λHU。分析能谱CT对食管胃结合部癌病理型别和分化程度的鉴别诊断效能。对腺癌和鳞癌患者动脉期和静脉期能谱CT的IC、Eff-Z、WC、λHU比较,结果:①两组患者动脉期和静脉期的WC比较差异无统计学意义（P>0.05）。②两组患者动脉期和静脉期的IC、Eff-Z、λHU比较差异具有统计学意义（P<0.05）,腺癌患者动脉期和静脉期的IC、Eff-Z、λHU均高于鳞癌患者。静脉期IC、Eff-Z、λHU具有较高的诊断效能,静脉期Eff-Z诊断效能最佳,AUC为0.97,以8.72为阈值时,鉴别敏感度为88.90％,特异度为94.70％。结论:能谱CT多参数定量分析对食管胃结合部癌病理类型具有较高的诊断价值。 相似文献