排序方式： 共有11条查询结果，搜索用时 31 毫秒
1.
Cluster correspondence analysis examines the spatial autocorrelation of multi-location events at the local scale. This paper
argues that patterns of cluster correspondence are highly sensitive to the definition of operational neighborhoods that form
the spatial units of analysis. A subset of multi-location events is examined for cluster correspondence if they are associated
with the same operational neighborhood. This paper discusses the construction of operational neighborhoods for cluster correspondence
analysis based on the spatial properties of the underlying zoning system and the scales at which the zones are aggregated
into neighborhoods. Impacts of this construction on the degree of cluster correspondence are also analyzed. Empirical analyses
of cluster correspondence between paired vehicle theft and recovery locations are conducted on different zoning methods and
across a series of geographic scales and the dynamics of cluster correspondence patterns are discussed.
相似文献
2.
A full particle simulation study is carried out on a perpendicular collisionless shock with a relatively low Alfven Mach number (MA = 5). Recent self-consistent hybrid and full particle simulations have demonstrated ion kinetics are essential for the non-stationarity of perpendicular collisionless shocks, which means that physical processes due to ion kinetics modify the shock jump condition for fluid plasmas. This is a cross-scale coupling between fluid dynamics and ion kinetics. On the other hand, it is not easy to study cross-scale coupling of electron kinetics with ion kinetics or fluid dynamics, because it is a heavy task to conduct large-scale full particle simulations of collisionless shocks. In the present study, we have performed a two-dimensional (2D) electromagnetic full particle simulation with a “shock-rest-frame model”. The simulation domain is taken to be larger than the ion inertial length in order to include full kinetics of both electrons and ions. The present simulation result has confirmed the transition of shock structures from the cyclic self-reformation to the quasi-stationary shock front. During the transition, electrons and ions are thermalized in the direction parallel to the shock magnetic field. Ions are thermalized by low-frequency electromagnetic waves (or rippled structures) excited by strong ion temperature anisotropy at the shock foot, while electrons are thermalized by high-frequency electromagnetic waves (or whistler mode waves) excited by electron temperature anisotropy at the shock overshoot. Ion acoustic waves are also excited at the shock overshoot where the electron parallel temperature becomes higher than the ion parallel temperature. We expect that ion acoustic waves are responsible for parallel diffusion of both electrons and ions, and that a cross-scale coupling between an ion-scale mesoscopic instability and an electron-scale microscopic instability is important for structures and dynamics of a collisionless perpendicular shock. 相似文献
3.
SELFE: A semi-implicit Eulerian–Lagrangian finite-element model for cross-scale ocean circulation 总被引：1，自引：0，他引：1
Unstructured-grid models grounded on semi-implicit, finite-volume, Eulerian–Lagrangian algorithms, such as UnTRIM and ELCIRC, have enjoyed considerable success recently in simulating 3D estuarine and coastal circulation. However, opportunities for improving the accuracy of this type of models were identified during extensive simulations of a tightly coupled estuary–plume–shelf system in the Columbia River system. Efforts to improve numerical accuracy resulted in SELFE, a new finite-element model for cross-scale ocean modeling. SELFE retains key benefits, including computational efficiency of existing semi-implicit Eulerian–Lagrangian finite-volume models, but relaxes restrictions on grids, uses higher-order shape functions for elevation, and enables superior flexibility in representing the bathymetry. Better representation of the bathymetry is enabled by a novel, “localized” vertical grid that resembles unstructured grids. At a particular horizontal location, SELFE uses either S coordinates or SZ coordinates, but the equations are consistently solved in Z space. SELFE also performs well relative to volume conservation and spurious oscillations, two problems that plague some finite-element models. This paper introduces SELFE as an open-source code available for community use and enhancement. The main focus here is on describing the formulation of the model and on showing results for a range of progressively demanding benchmark tests. While leaving details to separate publications, we also briefly illustrate the superior performance of SELFE over ELCIRC in a field application to the Columbia River estuary and plume. 相似文献
4.
M.W. Dunlop R. Bingham P. Escoubet C. Shen R. Trines Z-Y. Pu S. Schwartz 《Planetary and Space Science》2011,59(7):630-638
The properties of plasmas (in space) are fundamentally governed by both ‘cross-scale’ coupling and comparative temporal behaviour operating over the micro-, meso-, and (MHD-) fluid regimes: for example, under conditions of turbulence, during magnetic reconnection and in shocks and other plasma boundaries. These themes map to a number of related and overlapping, phenomena, where known phenomena play different roles in each theme. Detailed understanding of fundamental plasma processes therefore requires analysis of both theoretical models (to distinguish the collisionless from the collisional regimes) and multi-scale measurements (suitable to address issues of stationarity). In particular, the investigation of phenomena requires analysis techniques which can distinguish and quantify temporal behaviour and the multi-scale spatial behaviour. The analysis of existing, multi-point data sets has led to a number of data co-ordination methods, such as the four spacecraft analysis tools developed for cluster, and we consider examples here. Advanced analysis concepts may be investigated with suitable considerations of measurement quality:adequate sampling of phenomena (for example, to extract the necessary information on the mechanisms operating) requires suitable spacecraft configurations and directly relates to the measurement quality achievable. A particular issue is how to resolve temporal behaviour across the spatial regimes, so that the data set is suitably coordinated. With the addition of theoretical modelling (in the context of particular phenomena) both the space and laboratory plasma regimes may be compared and we give an example of nonlinear wave coupling across spatial scales in this context. 相似文献
5.
The United Nations 2030 Agenda catalysed the development of global target-seeking sustainability-oriented scenarios representing alternative pathways to reach the Sustainable Development Goals (SDGs). Implementing the SDGs requires connected actions across local, national, regional, and global levels; thus, target-seeking scenarios need to reflect alternative options and tensions across those scales. We argue that the design of global sustainability-oriented target-seeking scenarios requires a consistent process for capturing multiple and contrasting perspectives on how to reach the goals, including the perspectives from multiple scales (e.g. local, national, regional) and geographic regions (e.g. the Global South). Here we propose a novel approach to co-design global target-seeking scenarios, consisting of (a) capturing global perspectives on pathways to the SDGs through a review of existing global scenarios; (b) a multi-stakeholder process to obtain multiple sub-global perspectives on pathways to sustainability; (c) an analysis of convergences, and crucially, divergences between global and regional perspectives on pathways to reach the SDGs, feeding into the design of new target-seeking scenario narratives. As a case study, we use the results of the 2018 African Dialogue on The World in 2050, discussing the future of agriculture and food systems. The identified divergent themes emerging from our analysis included urbanization, population growth, agricultural practices, and the roles of different actors in the future of agriculture. The results challenge some of the existing underlying assumptions of the current sustainability-oriented global scenarios (e.g. population growth, urbanisation, agricultural practices), indicating the relevance and timeliness of the proposed approach. We suggest that similar approaches can be replicated in other contexts to better inform the process of sustainability-oriented scenario co-design across scales, regions and cultures. In addition, we highlight the implications of the approach for scenario quantification and the evolution of modeling tools. 相似文献
6.
This study investigates the local social and fisheries impact of formal fisheries policies in Bahía de Kino, one of the most important fishing villages in terms of extraction of benthic resources in the Northern Gulf of California, Mexico. The paper focuses on cross-scale institutional interactions, describing how existing formal policies are functioning on the ground, how these policies interact with local arrangements, and how this interaction may affect the incentives of different actors towards sustainable fisheries. Besides providing lessons on how the performance of a local fishery could be improved, this paper addresses the question of whether the formal institutional structure of Mexican fishing regulations is effective in promoting responsible behavior by small-scale fishery stakeholders. It is argued that the design of the most widely used management tool to regulate access to marine resources throughout Mexico -the permit (licensing) system- provides the wrong incentives for sustainable-use. Granting secure rights to resources to those actively involved in the fishery is a necessary step for promoting sustainable fishing practices. 相似文献
7.
The North Sea Regional Advisory Council (NSRAC) is the main forum through which fisheries interests are involved in Marine Spatial Planning (MSP) on the North Sea. The NSRAC is a relatively new and fragile forum involving various stakeholders. MSP confronts this group with a series of broader issues such as inter alia wind farms, transportation, and marine protected areas. The spatial focus involves both a reduction and a multiplication of the levels of geographical scale at which information for management must be resolved. The ongoing development of these institutions provides lessons about facilitating the evolution of cross-scale institutional linkages that strengthen adaptive, eco-system-based management. 相似文献
8.
Chanda L. Meek Amy Lauren Lovecraft Martin D. Robards Gary P. Kofinas 《Marine Policy》2008,32(6):1080-1089
Arctic coastal communities in the Bering Strait region of Alaska (USA) and Chukotka (Russia) share a close relationship with their natural environments that can be characterized as a social–ecological system. This system is complex, featuring changing ecosystem conditions, multiple jurisdictions, migratory animal populations, and several cultures. We argue that linkages between communities in both countries enhance the effectiveness of transborder polar bear and walrus conservation. We find that locally embedded bilateral institutions can provide effective management venues that persist despite slow or lacking processes of international law because they provide a better fit between rules for managing and the true system state. 相似文献
9.
Globalization has increased the speed and flow of people, information, and commodities across space, integrating markets and increasing interdependence of geographically dispersed places worldwide. Places historically driven by largely local forces and market demands are now increasingly affected by drivers at multiple scales. Trade is particularly important in driving these changes and more fish is now exported to international markets than ever before. When small-scale fisheries are integrated into global markets, local social–ecological systems change with potentially both positive and negative impacts on livelihoods, economics and ecology, but few studies systematically investigate how and why the outcomes of market integration vary from case to case.This paper systematically assesses multiple (social, ecological, economic and institutional) local effects of market integration in cases around the world by drawing on the global environmental change syndromes approach. Furthermore, we examine the factors contributing to the syndromes observed. Our analysis identifies three distinct social–ecological syndromes associated with international seafood trade. Results suggest that the presence of strong and well-enforced institutions is the principal factor behind the syndrome characterized by sustained fish stocks, while a combination of weak institutions, patron–client relationships, high demand from China and highly vulnerable target species explain the other two syndromes distinguished by declining stocks, conflict and debt among fishers.A key finding is that the factors emerging as important for explaining the different syndromes derive from different scales (e.g. local market structures vs distant market characteristics), indicating a need for multi-level governance approaches to deal with the effects of market integration. Furthermore, the meta-analysis shows that each syndrome encompasses fisheries from multiple continents. This suggests that the increasingly global nature of the seafood trade appears to be driving local dynamics by creating similar conditions for vulnerabilities in localities around the world, lending support to the notion of tele-connectivity across geographic space. 相似文献
10.
Steven J. Schwartz Timothy Horbury Christopher Owen Wolfgang Baumjohann Rumi Nakamura Patrick Canu Alain Roux Fouad Sahraoui Philippe Louarn Jean-André Sauvaud Jean-Louis Pinçon Andris Vaivads Maria Federica Marcucci Anastasios Anastasiadis Masaki Fujimoto Philippe Escoubet Matt Taylor Steven Eckersley Elie Allouis Marie-Claire Perkinson 《Experimental Astronomy》2009,23(3):1001-1015
Most of the visible universe is in the highly ionised plasma state, and most of that plasma is collision-free. Three physical
phenomena are responsible for nearly all of the processes that accelerate particles, transport material and energy, and mediate
flows in systems as diverse as radio galaxy jets and supernovae explosions through to solar flares and planetary magnetospheres.
These processes in turn result from the coupling amongst phenomena at macroscopic fluid scales, smaller ion scales, and down
to electron scales. Cross-Scale, in concert with its sister mission SCOPE (to be provided by the Japan Aerospace Exploration
Agency—JAXA), is dedicated to quantifying that nonlinear, time-varying coupling via the simultaneous in-situ observations
of space plasmas performed by a fleet of 12 spacecraft in near-Earth orbit. Cross-Scale has been selected for the Assessment
Phase of Cosmic Vision by the European Space Agency.
相似文献