Influence of advection on scales of ecological studies in a coastal equilibrium flow     

Ingrid Hillmer  Jörg Imberger 《Continental Shelf Research》2007

Spatial patterns are generated as a result of the coupling between biogeochemical and physical processes and the ability to capture and reproduce patchiness is crucial for the better comprehension of an ecosystem and its response to external perturbations. A 1D reaction–diffusion–advection equation is used to investigate the formation of patterns and relevant time and spatial scales and thus define an approach for the determination of a critical domain size that allows differentiation of the role of local and internal cycling from advective fluxes across the open boundaries in a shallow coastal ecosystem. By using a 3D numerical model, in conjunction with an extensive field data set, it is shown that domain sizes must be larger than this critical value in order to capture the patterns generated within the system. For smaller domains, the evolution of the system is controlled by transport processes across the boundaries misleading the interpretation of the internal ecological dynamics. The study of the influence of boundary fluxes on ecological patchiness was motivated by the need to define the size of the domain necessary for the assessment of the impact of a sewage outflow on a coastal regime.  相似文献   

Source parameters and stress release of seismic sequences occurred in the Friuli-Venezia Giulia region (Northeastern Italy) and in Western Slovenia     

Gianni Bressan  Stefano Kravanja  Gianlorenzo Franceschina   《Physics of the Earth and Planetary Interiors》2007,160(3-4):192-214

The source parameters of the major events of a swarm and of two seismic sequences, occurred in the Friuli area (Northeastern Italy) and in Western Slovenia, were estimated. The Claut swarm (C96) occurred since the end of January to June 1996, with a M_D 4.3 major shock and it appears composed of three sub-sequences. The two sequences are the Kobarid sequence (K98) started on April 12, 1998 with a M_D 5.6 mainshock and the M.te Sernio (S02) sequence caused by the February 14, 2002 earthquake (M_D = 4.9). Acceleration and velocity data recorded by the local seismic network of the Istituto Nazionale di Oceanografia e di Geofisica Sperimenale (OGS) and corrected for attenuation, were employed to estimate seismic moments and radiated energies. Source dimensions were inferred from the computed corner frequencies and the stress release was estimated from the Brune stress drop, the apparent stress and the RMS stress drop. On the whole, seismic moments range from 1.7 × 10¹² to 1.1 × 10¹⁷ N m, and radiated energies are in the range 10⁶–10¹³ J. Brune stress drops are scattered and do not show any evidence of a self-similarity breakdown for sources down to 130 m radius. The radiated seismic energy scales as a function of seismic moment, with a slope of the scaling relation that decreases for increasing seismic moments.The mechanism of stress release was analyzed by computing the ɛ parameter of Zuniga [Zuniga, R., 1993. Frictional overshoot and partial stress drop. Which one? Bull. Seismol. Soc. Am. 83, 939–944]. The K98 and S02 sequences are characterized by a wide range of the ɛ parameter with stress drop mechanism varying from partial locking to overshoot cases. The ɛ values of the C96 swarm are more homogeneous and close to the Orowan's condition. The radiated seismic energy and the ratio of stress drop between mainshock and aftershocks appear different among the analyzed cases. We therefore investigated the relationship between the stress parameters of the main shock and the energy radiated by the aftershock sequences. For this purpose, we also estimated the source parameters of two other sequences occurred in the area, with mainshocks of M_D 4.1 and 5.1, respectively. We found a positive correlation between the Brune stress drop of the mainshock and the ratio between the radiated energy of the mainshock and the summation of the energies radiated by the aftershocks.  相似文献   

Fractal approaches in investigating the time dynamics of self-potential hourly variability     

Luciano Telesca  Gerardo Colangelo  Vincenzo Lapenna  Maria Macchiato 《International Journal of Earth Sciences》2005,94(2):285-300

Fractal tools have been used to investigate the time dynamics of hourly self-potential data, recorded during the year 2001 by five geoelectrical stations located in one of the most seismic areas of southern Italy. Scaling behaviour has been revealed by means of different statistics: the Lomb Periodogram method, the Detrended Fluctuation Analysis, the Higuchi analysis and the mean distance spanned within the time L. The values of the scaling exponents estimated by means of these methods indicate that the temporal fluctuations of the geoelectrical signals are not typical of purely random stochastic processes (i.e. white noise), but evidence the presence of long-range correlations. Furthermore, it is found that these correlations are linear.  相似文献   

Scaling organization in the dynamics of blocks-and-faults systems     

Peter Shebalin  Alexandre SolovievJean-Louis Le Mouël 《Physics of the Earth and Planetary Interiors》2002,131(2):141-153

Some elements of the model of scaling organization of fracture tectonics (SOFT) are incorporated into the model of block structure dynamics (BSD). The resulting new model permits to obtain a power law relationship between earthquake energy and fault area with an exponent 3/2, as for observed seismicity. This is an important advantage of the new model in comparison with the BSD model, in which this dependence is generally linear.  相似文献   

Strain-dependent rheology and the memory of plasticine     

Martin P. J. Schpfer  Gernold Zulauf 《Tectonophysics》2002,354(1-2)

Plasticine and plasticine-like materials have been widely used as analogue materials for experimental deformation, but not many workers have conducted detailed investigations on their rheology. The physical properties of Beck's green and black plasticine, a modelling material made in Gomaringen, Germany, and plasticine/oil mixtures were investigated by means of uniaxial compression and relaxation tests. Beck's plasticine is a non-Newtonian fluid characterised by strain rate-dependent plastic yielding and strain hardening. Strain hardening is more pronounced at low strain rates leading to an increase of both stress exponent and viscosity. The addition of oil leads to an increase of the stress exponent and a decrease in viscosity. The strain dependence of viscosity decreases with increasing oil content. Compression tests on preflattened plasticine were also conducted in order to study possible ‘strain memory’ of the materials. Preflattened plasticine is characterised by a later onset of yielding and an increase in both stress exponent and viscosity. Our results suggest that Beck's green and black plasticine is a suitable analogue material for modelling rocks that deform by dislocation creep and exhibit pronounced strain hardening. Nevertheless, plane strain modelling of boudinage has verified analytical solutions for the dominant wavelength at viscosity contrasts of approximately 1.5 and 2.5.  相似文献   

CATCHMENT-WIDE, SECTIONAL AND LOCAL ASPECTS IN SEDIMENT TRANSPORT MODELLING AND MONITORING     

Helmut M.HABERSACK Research Assistant  Institute for Water Management  Hydrology  Hydraulic Engineering  Universitaet fuer Bodenkultur  Muthgasse  Vienna  Austria 《国际泥沙研究》1997,(3)

1.INTRODUCTIONOVerthelastdecadesmuchprogresshasbeenmadeconcerningsedimenttransPOrtmodellingandmonitoring.Thedifferelltiationincatchmeflt-tvide,sectionalandlocalaspectsreflectsthefactthatmanysedimenttransportandpredictionmodelsaredealingwithspecialpartsofriverSystems,mainlydifferinginscale.Overthepastyears,scaleissuesinhydrologyhaverapidlyincreasedinimportance(BLoSCHL,1996).Onalargescaletheapplicationoffractals,self-similarityanalysistolandscapeorganizationandoptimalchannelnetlvorks(O…  相似文献   

论工程地质模型涵义、意义、建模与应用   总被引：10，自引：7，他引：10  

许兵 《工程地质学报》1997,5(3):199-204

本文重点论述了工程地质模型。阐明了工程地质模型的概念与涵义、阐述了建模的依据与方法；探讨了其应用的范畴与要点；尤其充分论述了工程地质模型的学科意义与深远影响。工程地质模型是条件研究的归宿, 是分析、计算与评论的基础。  相似文献   

黑河流域陆地—大气相互作用研究的几点思考   总被引：4，自引：2，他引：2  

高艳红  程国栋 《地球科学进展》2008,23(7):779-784

陆地和大气之间是相互作用、相互影响的,不仅陆面分布与地表过程对大气变化有着响应过程,而且陆面物理过程、地表特征分布对大气过程也有着重要影响。我国西北地区地形分布极不均匀,是水资源变化和气候变化的敏感区与脆弱地区。这里,由于海拔高度起伏造就了以水为主线的上游山区冰雪、冻土—中游森林、绿洲—下游戈壁荒漠的多个自然景观带共存的内陆河流域,是开展陆—气相互作用研究的理想场所。文章集中黑河流域水循环过程、冰雪/冻土与大气相互作用、降水异质性、人类活动影响以及尺度等问题,阐述了流域研究现状以及研究热点,指出发挥各学科优势,将大尺度的大气过程与中间尺度和小尺度的陆面水文/生态过程结合,建立流域尺度大气—水文—生态过程真正的双向耦合模式,不仅研究气候变化对陆面水文、生态的影响,同时探讨陆面小尺度过程对大气的反馈机理,探索流域尺度的水循环过程和驱动机理,为水资源合理利用提供理论基础。  相似文献   

Catalyzing sustainability pathways: Navigating urban nature based solutions in Europe     

《Global Environmental Change》2022

The notion that pathways can be identified and followed towards more sustainable futures has become an increasingly prevalent idea across the science and policy of global environmental change. Focusing on the debate within literatures on socio-technical systems, we find that pathways are often tied to the concept of scaling up such that they are dependent on trajectories which extend from the geographically small to large scale or from singular incidences to widespread adoption. Building on relational approaches to scaling, in this paper we argue that sustainability pathways need to be conceived as emerging from the catalytic interaction of multiple and overlapping efforts to change the status quo. We suggest that pathways can be conceptualized as being composed of ‘stepping stones’: bundles of related interventions that seize or create opportunities to build momentum for the implementation of innovations, the form of which is not predetermined. Drawing on 243 interviews, participant observation, and document analysis examining urban nature-based solutions across six European countries and the EU, we identify 20 stepping stones that can be used to accelerate the uptake of urban NBS in European cities. In the case of urban NBS in Europe, we find that the capacity of stepping stones to generate catalytic change strongly depends on how they interact with one another. We illustrate that pathways are not given but rather assembled through key interventions that collectively generate the capacities and momentum needed to overcome inertia and generate new socio-material orders in which such interventions are normalized as mainstream responses to sustainability challenges.  相似文献   

基于城市流空间的城市群变形结构识别——以长江三角洲城市群为例   总被引：10，自引：7，他引：3  

王钊  杨山  龚富华  刘帅宾 《地理科学》2017,37(9):1337-1344

全球化、信息化时代,城市群空间结构在城市流的作用下发生剧烈的变形。基于长三角城市流的测度和关系矩阵构建,通过流要素分析、多维尺度分析,从“节点-联系-格局”3个方面识别流空间下城市群变形结构。研究表明：流空间下城市中心性层级特征变化明显,中间层级的城市数量大幅增加;局域范围内城市流网络仍受地理空间距离的制约,但高等级城市流具有跨地理空间流动特征;中心城市和边缘城市呈“异化”发展趋势,表现为中心城市的集聚组团以及边缘城市的分散偏离。  相似文献