Estimated population mixing by country and risk cohort for the HIV/AIDS epidemic in Western Europe     

Richard Thomas 《Journal of Geographical Systems》2001,3(3):283-301

 This paper applies a compartmental epidemic model to estimating the mixing relations that support the transfer of HIV infection between risk populations within the countries of Western Europe. To this end, a space-time epidemic model with compartments representing countries with populations specified to be at high (gay men and intravenous drug injectors ever with AIDS) and low (the remainder who are sexually active) risk is described. This model also allows for contacts between susceptible and infectious individuals by both local and international travel. This system is calibrated to recorded AIDS incidence and the best-fit solution provides estimates of variations in the rates of mixing between the compartments together with a reconstruction of the transmission pathway. This solution indicates that, for all the countries, AIDS incidence among those at low risk is expected to remain extremely small relative to their total number. A sensitivity analysis of the low risk partner acquisition rate, however, suggests this endemic state might be fragile within Europe during this century. The discussion examines the relevance of these mixing relationships for the maintenance of disease control. Received: 4 May 2000 / Accepted: 9 July 2000  相似文献   

Late Pleistocene-Holocene paleolimnology of three north-western Russian lakes     

Natalya N. Davydova  Dmitry A. Subetto  Valentina I. Khomutova  Tatyana V. Sapelko 《Journal of Paleolimnology》2001,26(1):37-51

The vegetation history and development of three different types of lakes, lakes Valday, Kubenskoye and Vishnevskoye (northwest of the East European Plain) were reconstructed using paleolimnological techniques. Watershed vegetation demonstrates a close connection with climate fluctuations: gradual expansion of the southern broad-leaved trees to the North during the Holocene with the maximum extent during the climate optimum (8000–5000 BP); and their subsequent retreat afterwards; followed by the extension of spruce during the cold and dry Subboreal time; and dominance of pine-spruce-birch forests in the Subatlantic time. The Late Pleistocene and Holocene climate changes resulted in lake-level fluctuations and other ecosystem changes. Valday Lake was formed ca. 12,500 BP as an oligotrophic, deep water basin. The lake level decreased during the dry Boreal, then increased again during the humid Atlantic period. The large shallow Kubenskoye Lake was formerly a part of an ice margin lake, which was then separated (ca. 13,000 BP) and developed into the Sukhona Basin with an outflow to the northwest. During the Atlantic, the outflow direction changed to the east. As a result, the ancient Sukhona Lake disappeared and Kubenskoye Lake formed in its modern size and shape. Vishnevskoye Lake, on the Karelian Isthmus, was formed at the beginning of the Preboreal after the disappearance of the Baltic Ice Lake. It was flooded by waters of the Boreal Ancylus transgression of the Baltic Basin and had become a small eutrophic lake by the time.  相似文献   

Summer and winter regimes of runoff generation and soil erosion on cultivated loess soils (The Netherlands)     

F. J. P. M. Kwaad 《地球表面变化过程与地形》1991,16(7):653-662

Monthly runoff and soil loss data of three fallow experimental plots are presented, comprising a summer and following winter season. The fallow plots were only tilled once, at the end of April. Summer runoff appeared to be controlled by rainfall intensity and conforms to the Horton model of overland flow generation. Winter runoff was primarily controlled by rainfall amount and conforms to the saturation or storage control model of runoff generation. Summer runoff volume was one fourth of winter runoff volume. Summer soil loss was twice as high as winter soil loss and was caused by high intensity, high energy rainfall. Winter soil loss was due to detachment limited erosion, caused by low intensity, low energy rainfall. Mean sediment concentration of winter runoff was one seventh of that of summer runoff. Implications for runoff and erosion of climatic change, involving increased rainfall amounts or intensities in summer or winter, are given.  相似文献   

Late Cretaceous lithoevents in the Bohemian Cretaceous Basin, Czechoslovakia     

J. Vale ka  V. Sko ek 《Cretaceous Research》1991,12(6)

Facies evolution and vertical changes within the Late Cretaceous sequence of the Bohemian Cretaceous Basin reveal fluctuations of intra- and extrabasinal circumstances. Evidence of periodic oscillations is recognized and two categories of aperiodic event indications are distinguished according to their significance and lateral persistence. Several lithoevents may be related to eustatic changes, while others indicate the independent evolution of the basin, influenced by epeirogenetic movements of segments of the Bohemian Massif.  相似文献   

欧洲景观生态学研究展望   总被引：21，自引：1，他引：21  

郭旭东  刘国华  陈利顶  傅伯杰 《地球科学进展》1999,14(4):353-357

随着土地利用变化的加剧以及社会经济体制的改变，欧洲传统景观生态学近切需要改革和创新。如何保持景观生态学在未来社会中的重要地位并发挥它解决实际问题的作用是摆在欧洲景观生态学家面前的迫切课题。介绍了欧洲景观生态学目前的研究热点，对未来欧洲景观生态学的发展趋势、研究框架和主要研究领域进行了展望，以期对中国景观生态不的发展有所借鉴。  相似文献   

Late Maastrichtian cephalopods,dinoflagellate cysts and foraminifera from the Cretaceous–Paleogene succession at Lechówka,southeast Poland: Stratigraphic and environmental implications     

《Cretaceous Research》2016

The Lechówka section comprises the most complete Cretaceous–Paleogene (K-Pg) boundary succession in Poland and is among 29 sites worldwide with the youngest ammonite record. Here, cephalopods (ammonites and nautilids), organic-walled dinoflagellates (dinocysts) and foraminifera from the uppermost Maastrichtian interval are studied. In terms of ammonite biostratigraphy, the upper Maastrichtian Hoploscaphites constrictus crassus Zone is documented up to a level 120 cm below the K-Pg boundary. There is no direct, ammonite-based evidence of the highest Maastrichtian H. constrictus johnjagti Zone. However, the predominance of the dinocyst marker taxon Palynodinium grallator suggests the presence of the equivalent of the uppermost Maastrichtian Thalassiphora pelagica Subzone, which is correlatable with the H. c. johnjagti ammonite Zone. The planktonic foraminiferal assemblage is coeval with that from the H. c. johnjagti Zone as well. These data indicate that the top of the Maastrichtian at Lechówka is complete within the limits of biostratigraphic resolution, albeit slightly condensed. The dinocyst and foraminiferal assemblages are dominated by taxa that are characteristic of high-energy, marginal marine environments. A reduction in test size among the calcareous epifaunal benthic foraminifera is observed at a level 50 cm below the K-Pg boundary, which is possibly related to environmental stress associated with Deccan volcanism.  相似文献   

Review of the Late Cretaceous-early Paleogene crocodylomorphs of Europe: Extinction patterns across the K-PG boundary     

《Cretaceous Research》2016

Although the European dinosaur succession during the latest Cretaceous and its relationship with the Cretaceous-Paleogene (K-Pg) mass extinction has been the focus of recent work, other continental vertebrates, such as crocodylomorphs, have received less attention. The European continental record of crocodylomorphs in general, and of eusuchians in particular, is relatively dense through the Maastrichtian until the K-Pg boundary. Traditionally it has been argued that continental crocodylomorphs were minimally impacted by the K-Pg extinction, but they were substantially affected in Europe with the disappearance of endemic eusuchians such as Hylaeochampsidae, Allodaposuchus and their close relatives, and non-eusuchians such as Doratodon or Theriosuchus. Despite extensive sampling in Danian continental deposits, only scarce fragmentary crocodylomorph remains have been cited. It is not until the late Paleocene and Eocene that a recovery in continental crocodylomorphs is observed. The presence of taxa such as planocraniids, the alligatoroids Diplocynodon and Hassiacosuchus, and stem crocodyloids during this period provide the first reliable continental records of Crocodylia in Europe and is best explained by post-extinction immigration from Asia or North America. By contrast, marine forms such as Thoracosaurus are found on both sides of the K-Pg boundary in Europe. The adaptation of these marine animals to different environments, from shallow seas to more transitional or fluvial environments, could be the key to their success and survival across the K-Pg boundary, as seen in other marine crocodylomorph clades such as Dyrosauridae.  相似文献   

Sedimentology,structure and age estimate of five continental slope submarine landslides,eastern Australia     

S. Clarke  T. Hubble  J. Webster  D. Airey  E. De Carli  C. Ferraz 《Australian Journal of Earth Sciences》2016,63(5):631-652

Sedimentological and accelerator mass spectrometry (AMS) ¹⁴C data provide estimates of the structure and age of five submarine landslides (～0.4–3 km³) present on eastern Australia's continental slope between Noosa Heads and Yamba. Dating of the post-slide conformably deposited sediment indicates sediment accumulation rates between 0.017 m ka^–1 and 0.2 m ka^–1, which is consistent with previous estimates reported for this area. Boundary surfaces were identified in five continental slope cores at depths of 0.8 to 2.2 m below the present-day seafloor. Boundary surfaces present as a sharp colour-change across the surface, discernible but small increases in sediment stiffness, a slight increase in sediment bulk density of 0.1 g cm^–3, and distinct gaps in AMS ¹⁴C ages of at least 25 ka. Boundary surfaces are interpreted to represent a slide plane detachment surface but are not necessarily the only ones or even the major ones. Sub-bottom profiler records indicate that: (1) the youngest identifiable sediment reflectors upslope from three submarine landslides terminate on and are truncated by slide rupture surfaces; (2) there is no obvious evidence for a post-slide sediment layer draped over, or burying, slide ruptures or exposed slide detachment surfaces; and (3) the boundary surfaces identified within the cores are unlikely to be near-surface slide surfaces within an overall larger en masse dislocation. These findings suggest that these submarine landslides are geologically recent (<25 ka), and that the boundary surfaces are either: (a) an erosional features that developed after the landslide, in which case the boundary surface age provides a minimum age for the landslide; or (b) detachment surfaces from which slabs of near-surface sediment were removed during landsliding, in which case the age of the sediment above the boundary surface indicates the approximate age of landsliding. While an earthquake-triggering mechanism is favoured for the initiation of submarine landslides on the eastern Australian margin, further evidence is required to confirm this interpretation.  相似文献   

鄂尔多斯盆地东南部长6成岩作用及其对孔隙的影响     

范萌萌  李文厚  袁珍 《地质通报》2016,35(203):448-453

应用薄片鉴定、扫描电镜、X-衍射等方法分析鄂尔多斯盆地东南部长6储层岩性特征、成岩作用及其对储层孔隙的影响。结果表明,研究区长6储层以长石砂岩和岩屑质长石砂岩为主,砂岩颗粒多为磨圆度中等-好,分选性中等,其成岩阶段主要处于中成岩A期。主要成岩作用有压实作用、胶结作用、溶蚀作用、交代作用、其中压实作用和胶结对储层孔隙空间起破坏作用,使储层孔隙分别减少了原始孔隙的68.8%和16.90%;而后期的溶蚀作用对储层孔隙空间起建设作用,使储层孔隙增加了原始孔隙3.67%,为油气聚集空间贡献了一定的作用。  相似文献   

Environmental and resource footprints in a global context: Europe’s structural deficit in resource endowments     

《Global Environmental Change》2016

The European Union (EU) has proposed in its Resource-efficiency roadmap a ‘dashboard of indicators’ consisting of four headline indicators for carbon, water, land and materials. The EU recognizes the need to use a consumption-based (or ‘footprint’) perspective to capture the global dimension of resources and their impacts. In this paper, we analyse how the EU’s footprints compare to those of other nations, to what extent the EU and other major economies of the world rely on embodied resource imports, and what the implications are for policy making based on this comparison. This study is the first comprehensive multi-indicator comparison of all four policy relevant indicators, and uses a single consistent global Multi-Regional Input Output (MRIO) database with a unique and high level of product detail across countries. We find that Europe is the only region in the world that relies on net embodied imports for all indicators considered. We further find that the powerful economies of China and others in the Asia-Pacific already dominate global resource consumption from a footprint perspective, while they still haven’t reached the prosperity of developed countries. Competition for resources is hence likely to increase, making Europe even more vulnerable. A hot spot analysis suggests that final consumption of food, transport and housing are priorities for reduction efforts along the life cycle. Further, countries with a similar Human Development Index can have very different footprints, pointing at societal organisation at macro-level as option for improvement. This points at options for countries for lowering their footprint, becoming less dependent on embodied imports, while maintaining a high quality of life.  相似文献