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排序方式: 共有214条查询结果,搜索用时 156 毫秒
151.
Max Ledbetter 《Ecological modelling》1979,7(4):289-310
A computer simulation model of oceanic Langmuir circulations illustrates the role of these vortical water movements as physical forcing mechanisms affecting the horizontal and vertical distributions of planktonic organisms. The diel migration of omnivorous and herbivorous zooplankton (approximately by literature values for the swimming speeds of Meganyctiphanes norvegica and Calanus finmarchicus, respectively) and the sinking of phytoplankton interact with the Langmuir cells, resulting in a spatially heterogeneous community. The patchy distributions, in turn, affect the prey—predator interactions in this simple food web. Situations involving threshold and non-threshold feeding strategies as well as constant and changing circulations are investigated. The simulations are restricted to twilight and nocturnal events. 相似文献
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Making humanitarian relief networks more effective: operational coordination, trust and sense making 总被引:6,自引:0,他引:6
Stephenson M 《Disasters》2005,29(4):337-350
Effective coordination of humanitarian assistance activities remains elusive. This paper briefly addresses some of the reasons for what is widely perceived as a coordination dilemma in humanitarian affairs and argues for a new conceptualisation of the issue. Rather than continue to request that more authority be vested in a single organisation to secure coordination through top-down control, it contends that it may be timely to consider whether relief agencies involved in an emergency should be reconceived as social networks and efforts made to achieve changes in their organizational cultures that encourage operational coordination across institutional lines. Since such labours imply the need to trust, this article explores what forms of trust might be employed to promote improved coordination among relief institutions and how those relationships could themselves be conceptualised. Finally, while acknowledging that coordination is not costless, it suggests that its effective pursuit may be advantageous even in scenarios where aid organisations balk at cooperating to secure it. 相似文献
156.
Michel Potier Jocelyne Cousineau Lorraine Michaud Max Zolinger Serge B. Melançon Louis Dallaire 《黑龙江环境通报》1986,6(6):429-436
The intestinal microvilli of fetal origin in human amniotic fluid were purified by Ca2+ precipitation of contaminating organelles followed by differential centrifugation of microvillar membranes. In the purified preparation, the specific activity of the microvillar marker-enzymes maltase and sucrase increased about 77-fold over that in cell-free amniotic fluid. Significant contamination of the purified preparation by endoplasmic reticulum (microsomes) and lysosomes was ruled out on the basis of a low content of the marker enzymes glucose-6-phosphatase (microsomes) and acid phosphatase (lysosomes). Amniotic fluid microvilli contain typical enzymes of the fetal intestine including maltase, sucrase, trehalase, alkaline phosphatase and γ-glutamyltransferase, and their morphology by electron microscopy resembles that of vesiculated intestinal microvilli. Prenatal detection of genetic diseases due to a deficiency of a protein expressed in these membranes or associated to abnormal microvilli seems feasible. 相似文献
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Hajo Holzmann Axel Munk Max Suster Walter Zucchini 《Environmental and Ecological Statistics》2006,13(3):325-347
We introduce a new class of circular time series based on hidden Markov models. These are compared with existing models, their
properties are outlined and issues relating to parameter estimation are discussed. The new models conveniently describe multi-modal
circular time series as dependent mixtures of circular distributions. Two examples from biology and meteorology are used to
illustrate the theory. Finally, we introduce a hidden Markov model for bivariate linear-circular time series and use it to
describe larval movement of the fly Drosophila.
Received: September 2003 / Revised: March 2004 相似文献