土-结构动力相互作用的振动台试验研究综述   总被引：1，自引：1，他引：0  

李振宝  李晓亮  唐贞云  纪金豹 《震灾防御技术》2010,5(4):439-450

本文从土-结构动力相互作用振动台试验过程中所涉及的结构模型动力相似设计、模型土体的模拟及土体边界条件的模拟三个方面,回顾了近几年来土-结构动力相互作用振动台试验研究的发展历程与现状,重点描述了试验过程中为了更好地反映震动条件下土与结构动力相互作用的机理,学者们所采取的办法和措施。并在此基础上,介绍了一种新的研究土-结构动力相互作用的振动台试验技术。最后,总结了传统的土箱-振动台试验存在的不足,并与这种新的试验技术进行了对比,提出了对于这种新的试验方法仍需要进一步研究和解决的问题。  相似文献   

A critical review of approaches to aquatic environmental assessment   总被引：1，自引：0，他引：1  

Foden J  Rogers SI  Jones AP 《Marine pollution bulletin》2008,56(11):1825-1833

As demands on aquatic resources increase, there is a growing need to monitor and assess their condition. This paper reviews a variety of aquatic environmental assessments, at local, national, international and global scales and finds confusion in the terminology used to describe assessments. In particular the terms 'ecosystem' and 'integrated' are often misused resulting in lack of clarity. Therefore, definitions of some assessment terminology are suggested, consolidating existing proposals and simplifying future applications. A conclusion from the review is that a new classification system is required. The categorisation system proposed builds on preliminary work of the International Council for the Exploration of the Sea (ICES). Assessment classification is based on the environmental components considered, methodologies and nature of the linkages between components, and the inclusion or exclusion of socio-economic factors. The assessment terminology and categorisation system provided could in future simplify the way that assessments are defined and used to inform development of management strategies.  相似文献   

An overview of physical and ecological processes in the Rio de la Plata Estuary     

E. Marcelo Acha  Hermes Mianzan  Raúl Guerrero  José Carreto  Diego Giberto  Norma Montoya  Mario Carignan 《Continental Shelf Research》2008

The Rio de la Plata is a large-scale estuary located at 35°S on the Atlantic coast of South America. This system is one of the most important estuarine environments in the continent, being a highly productive area that sustains valuable artisanal and coastal fisheries in Uruguay and Argentina. The main goals of this paper are to summarize recent knowledge on this estuary, integrating physical, chemical and biological studies, and to explore the sources and ecological meaning of estuarine variability associated to the stratification/mixing alternateness in the estuary. We summarized unpublished data and information from several bibliographic sources. From study cases representing different stratification conditions, we draw a holistic view of physical patterns and ecological processes of the stratification/mixing alternateness. This estuary is characterized by strong vertical salinity stratification most of the time (the salt-wedge condition). The head of the estuary is characterized by a well-developed turbidity front. High turbidity constrains their photosynthesis. Immediately offshore the turbidity front, water becomes less turbid and phytoplankton peaks. As a consequence, trophic web in the estuary could be based on two sources of organic matter: phytoplankton and plant detritus. Dense plankton aggregations occur below the halocline and at the tip of the salt wedge. The mysid Neomysis americana, a key prey for juvenile fishes, occurs all along the turbidity front. A similar spatial pattern is shown by one of the most abundant benthic species, the clam Mactra isabelleana. These species could be taken advantage of the particulate organic matter and/or phytoplankton concentrated near the front. Nekton is represented by a rich fish community, with several fishes breeding inside the estuary. The most important species in terms of biomass is Micropogonias furnieri, the main target for the coastal fisheries of Argentina and Uruguay. Two processes have been identified as producing partially stratified conditions: persistent moderate winds (synoptic scale), or low freshwater runoff (interannual scale). Less frequently, total mixing of the salt wedge occurs after several hours of strong winds. The co-dominance of diatoms (which proliferate in highly turbulent environments) and red tides dinoflagellates and other bloom taxa (better adapted to stratified conditions), would indicate great variability in the turbulence strength, probably manifested as pulses. Microplankton and ichthyoplankton assemblages defined for the stratified condition are still recognized during the partially mixed condition, but in this case they occupy the entire water column: vertical structure of the plankton featuring the stratified condition become lost. Bottom fish assemblages, on the contrary, shows persistence under the different stratification conditions, though the dominant species of the groups show some variations. Summarizing, the Río de la Plata Estuary is a highly variable environment, strongly stratified most of the time but that can be mixed in some few hours by strong wind events that occur in an unpredictable manner, generating stratification/partially mixed (less frequently totally mixed) pulses all along the year. At larger temporal scales, the system is under the effects of river discharge variations associated to the ENSO cycle, but their ecological consequences are not fully studied.  相似文献   

中日地理学者的论文写作年龄对比分析   总被引：1，自引：1，他引：0  

刘云刚  刘冠娜 《地理学报》2009,64(8):1019-1024

以2000年以来的《地理学报》中英文版论文为例,分析了中国地理学者的论文写作年龄特征,包括平均写作年龄、论文写作主体年龄段、高峰期年龄等等,并以日本《地理学评论》为参照,分析了体制环境因素对地理学者论文写作年龄和周期的影响。结果表明,中国地理学母语论文的写作主体是40岁左右年龄段的学者,而英文论文的写作主体是35岁左右年龄段的学者。中国地理学者的母语平均写作年龄要高于日本,但英文论文作者的平均年龄则低于日本,这种差异反映了中日两国在科研管理制度及理念上的不同。在概括分析了两者差异后提出了对中国地理学的学科发展建议。  相似文献   

国内外城市群研究的回顾与展望   总被引：24，自引：0，他引：24  

林先扬  陈忠暖  蔡国田 《热带地理》2003,23(1):44-49

城市群的存在是区域城市化与城市区域化的重要表现,它作为区域城市化高级阶级性现象,是集聚与扩散共同作用的产物.经济全球化与区域经济一体化必然要求重视和加强城市群的发展,当今城市群的发展深刻影响着国家的国际竞争力,对国家持续稳定发展具有重大意义.城市群越来越成为学者关注的焦点,对它的研究与探索是城市研究领域的新拓展,它有助于人们在更广阔的视野中把握城市的发展.文中简要回顾了国外城市群研究阶段与主要成果与观点,着重对我国城市群研究进行回顾与评述,进一步探讨了城市群研究的新趋向,以利于推动我国城市群研究的深入开展  相似文献   

钍的光度分析新进展   总被引：2，自引：0，他引：2  

杨乡珍 《铀矿地质》1992,8(3):184-189

  相似文献   

浅成热液成矿系统模型研究评述   总被引：6，自引：0，他引：6  

张德会 《地球科学进展》1996,11(6):563-568

目前国内外矿床模型研究的一个明显发展势是研制成矿系统的地质成因模型，即建立具有一定的成因联系的不同矿种的矿系列成因模型。分析了近年来浅成热液矿床概念，分类、成模型式研究进展，评述了浅成热液矿床矿系统研究现状，并对我国此类矿床的研究提出建议。  相似文献   

异重流研究进展综述   总被引：1，自引：0，他引：1  

唐武  王英民  仲米虹  田建华  邹梦君 《海相油气地质》2016,(2):47-56

基于国内外文献分析,从与经典浊流对比的角度,厘定了异重流的概念,探讨了异重流的形成机制、异重岩的结构特征以及异重流发育过程的模式。异重流是一种低密度准稳定的沉积物重力流。异重岩纵向剖面上通常由一个向上变粗和一个向上变细的沉积单元组成。异重流的形成与流体悬浮负载浓度密切相关,它的演化过程受气候条件、构造活动、沉积物供给以及相对海(湖)平面变化的控制,其中,气候条件最为重要。  相似文献   

Towards end-to-end models for investigating the effects of climate and fishing in marine ecosystems   总被引：2，自引：0，他引：2  

M. Travers  Y.-J. Shin  S. Jennings  P. Cury 《Progress in Oceanography》2007,75(4):751-770

End-to-end models that represent ecosystem components from primary producers to top predators, linked through trophic interactions and affected by the abiotic environment, are expected to provide valuable tools for assessing the effects of climate change and fishing on ecosystem dynamics. Here, we review the main process-based approaches used for marine ecosystem modelling, focusing on the extent of the food web modelled, the forcing factors considered, the trophic processes represented, as well as the potential use and further development of the models. We consider models of a subset of the food web, models which represent the first attempts to couple low and high trophic levels, integrated models of the whole ecosystem, and size spectrum models. Comparisons within and among these groups of models highlight the preferential use of functional groups at low trophic levels and species at higher trophic levels and the different ways in which the models account for abiotic processes. The model comparisons also highlight the importance of choosing an appropriate spatial dimension for representing organism dynamics. Many of the reviewed models could be extended by adding components and by ensuring that the full life cycles of species components are represented, but end-to-end models should provide full coverage of ecosystem components, the integration of physical and biological processes at different scales and two-way interactions between ecosystem components. We suggest that this is best achieved by coupling models, but there are very few existing cases where the coupling supports true two-way interaction. The advantages of coupling models are that the extent of discretization and representation can be targeted to the part of the food web being considered, making their development time- and cost-effective. Processes such as predation can be coupled to allow the propagation of forcing factors effects up and down the food web. However, there needs to be a stronger focus on enabling two-way interaction, carefully selecting the key functional groups and species, reconciling different time and space scales and the methods of converting between energy, nutrients and mass.  相似文献   

Geographical and temporal variation in levels of organochlorine contaminants in marine mammals   总被引：1，自引：0，他引：1  

Aguilar A  Borrell A  Reijnders PJ 《Marine environmental research》2002,53(5):425-452

The interpretation of the spatial and temporal patterns of variation in organochlorine concentrations in marine mammal populations is complex because of the lack of wide-scale, long-term surveys. Therefore the results from several surveys must be combined and this causes undesired heterogeneity due to differences in the sampling and analytical techniques used and in the biological characteristics of the individuals sampled. Moreover, information is not homogeneously distributed in either space or in time. Most research is concentrated in western Europe, northern America and certain areas of Asia, while it is extremely limited or non-existent in Africa and most regions of the southern hemisphere. Marine mammals from the temperate fringe of the northern hemisphere, particularly fish-eating species which inhabit the mid-latitudes of Europe and North America, show the greatest organochlorine loads; noteworthy are the extremely high levels found in the Mediterranean Sea and certain locations on the western coasts of the United States. Concentrations in the tropical and equatorial fringe of the northern hemisphere and throughout the southern hemisphere are low or extremely low. The polar regions of both hemispheres showed the lowest concentrations of DDTs and PCBs, although levels of HCHs, chlordanes and HCB were moderate to high in the cold waters of the North Pacific. During recent decades, concentrations have tended to decrease in the regions where pollution was initially high but they have increased in regions located far from the pollution source as a consequence of atmospheric transport and redistribution. It is expected that the Arctic and, to a lesser extent, the Antarctic, will become major sinks for organochlorines in the future; this process may already be significant for some compounds such as HCB and HCHs. Effort should be devoted to both assessment of organochlorine trends in the now highly polluted populations of the temperate fringe of the northern hemisphere and to the implementation of long-term monitoring of marine mammal populations inhabiting polar regions.  相似文献