New perspectives on the politics of development in Africa     

Claire Mercer  Giles Mohan  Marcus Power 《Geoforum》2003,34(4):417-418

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Sediment records of phosphorus-driven shifts to phytoplanktondominance in shallow Florida lakes     

William F. Kenney  Matthew N. Waters  Claire L. Schelske  Mark Brenner 《Journal of Paleolimnology》2002,27(3):367-377

Primary producer community structure (PPCS) in shallow lakes isinfluenced by phosphorus (P) load and water column P concentration.Theoretically PPCS may shift between phytoplankton and macrophyte states withintermediate P loading, but phytoplankton dominate when P loading exceeds acritical threshold. We analyzed sediment cores from five shallow, eutrophiclakes (size range: 0.6 to 125 km²) that arephytoplankton dominated to determine whether the development of the currentstate was associated stratigraphically with an increase in sediment total P(TP) and a shift in PPCS. We used sponge biogenic silica(BSi_Sponges) concentrations and total carbon to total nitrogenratios (TC:TN) as proxies for macrophyte abundance and sediment organic mattersource, respectively. Three stratigraphic groups of sediments were identifiedwith k-means cluster analysis. These samples were grouped by increasing TPconcentrations and decreasing age and identified as macrophyte, transitionaland phytoplankton sediments. Results show that as P loading increased in thelate 19th and early 20th centuries, the lakes producedsediments with an increasing contribution from phytoplankton. Four of our lakesmay represent a subset of shallow lakes because of their large size (30 to 125km²) and relatively rapid historic P enrichment. Inthese Florida lakes, PPCS shifted to phytoplankton dominance with nopaleolimnological record of lake-wide alternating stable states or of lake-widephytoplankton dominance before anthropogenic P enrichment.  相似文献   

Comment on “A High-Resolution Sea-Surface Temperature Record from the tropical South China Sea (16,500–3000 yr B.P.)” by Steinke et al.     

Claire Waelbroeck  Stephan Steinke 《Quaternary Research》2002,57(3):432

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The impact of pyrite variability, dispersive transport and precipitation of secondary phases on the sulphate release due to pyrite weathering     

Claus Kohfahl  Paul L. Brown  Claire M. Linklater  Kai Mazur  Parviz Irannejad  Asaf Pekdeger 《Applied Geochemistry》2008,23(12):3783-3798

The objective of this study was to investigate the impact of flow, transport and geochemical parameters in the unsaturated and saturated zones on the release of SO₄ from overburden lignite spoil piles into the adjacent lake. A vertical one-dimensional model was set up using the reactive transport simulator SULFIDOX in order to account for the unsaturated zone. The SULFIDOX model was calibrated for effective diffusion using measured O₂ in the gas phase and SO₄ concentrations in the liquid phase from the unsaturated zone of the heap. The results show high sensitivity to O₂ supply and initially present gypsum, but the inclusion of secondary mineral precipitation in equilibrium is of minor importance for the results. To account for the transport of released SO₄ from the saturated zone into the surface water, scenarios were performed by using SULFIDOX results as input concentration for a two-dimensional vertical model set up with PROCESSING MODFLOW and MT3D. These scenarios indicate a rising discharge of SO₄ into the adjacent lake due to continued pyrite weathering for 80 a. Results are highly sensitive to dispersivity, whereas the spatial variability of pyrite distribution did not show any influence on the results. The consideration of initially present gypsum shows a major effect on the modelled SO₄ release.  相似文献   

Consumer involvement in fair trade and local food systems: delegation and empowerment regimes     

Sophie Dubuisson-Quellier  Claire Lamine 《GeoJournal》2008,73(1):55-65

Today, various types of fair trade systems propose new forms of relationships between producers and consumers. If several studies have provided accurate understandings of consumers’ motivations to buy fair trade products, the specific kinds of consumer involvement that are emphasized in those systems remain partly unknown. In France, controversies about the regulation and organization of fair trade with producers from Southern countries has led to broader debates about how consumers can best express their solidarity with producers. In these debates local food networks are often portrayed as good examples of fair trade and as having potential to redefine the role of the consumer in the marketplace (or in commercial relations). Based on examination of the type of mechanisms used to enrol consumers in local and fair trade networks, we have distinguished two main kinds of consumers’ involvement. The first one may be called “delegation” and is based on market mechanisms. The second one is called “empowerment” and is based on contractual mechanisms between consumers and producers and on the construction of collective choices. This latter kind of consumer involvement points out the capacity of alternative food networks to empower consumers in a more broadly political sense.

Claire LamineEmail:

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Unbundled security services and urban fragmentation in post-apartheid Johannesburg     

Claire Bénit-Gbaffou 《Geoforum》2008,39(6):1933-1950

The paper questions the pluralization of policing devices and security agents across the Johannesburg metropolitan area, which has been accelerated and actually encouraged by public policies in the post-apartheid period. Are the various security initiatives and networks coordinated in a metropolitan security “system” – the regulation of which would need to be analysed – or does their development lead to urban fragmentation? Based on an analysis of an extensive documentation of security services, as well as a series of interviews with involved (street level) actors, different dimensions of potential urban fragmentation linked to security are examined: spatial fragmentation, with the development of road closures and their contestation; financial fragmentation, emblematised by business improvement districts encouraged by the municipality; and political fragmentation, as reflected by the analysis of the broader security policy framework. The paper argues that although the integrated vision of Johannesburg’s policing creates the basis for redistribution of resources and forms of policing regulation at a metropolitan level (in contrast with the apartheid period), the choice of neo-liberal urban policies, of which security strategies form a part, tends to encourage policing fragmentation, or in other words, the differential and unequal provision of security services according to place, income and race.  相似文献   

The circumstellar envelopes around three protostars in Taurus     

Claire J. Chandler  Mary Barsony  & Toby J. T. Moore 《Monthly notices of the Royal Astronomical Society》1998,299(3):789-798

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Distribution of sterol and fatty alcohol biomarkers in particulate matter from the frontal structure of the Alboran Sea (S.W. Mediterranean Sea)   总被引：1，自引：0，他引：1  

Imma Tolosa  Nathalie LeBlond  Claire Copin-Montgut  Jean-Claude Marty  Stephen de Mora  Louis Prieur 《Marine Chemistry》2003,82(3-4):161-183

Sterol and fatty alcohol biomarkers were analyzed in suspended and sinking particles from the water column (20–300 m) of the Almeria–Oran frontal zone to characterize the biogenic sources and biogeochemical processes. Diatom- and haptophyte-related sterols were predominant at all sites and vertical distributions of sterol, and fatty alcohol biomarkers in sinking particles were markedly different from suspended particles. In contrast to the relatively fresh sinking particles with elevated concentrations of phyto- and zooplanktonic sterols, suspended particles were extensively degraded with increasing depth and exhibited a more terrestrial and zooplanktonic signature with depth.Sterol and alcohol biomarkers distributions and δ¹³C values from the jet core and the associated gyre of Atlantic waters showed a decoupling between the sinking particles of 100- and 300-m depth, demonstrating the influence of lateral advection in the frontal zone. In contrast, vertical transport of the particulate organic matter in Mediterranean waters was interpreted from the similar isotopic and molecular composition at both depths. The high abundance of phytosterols and phytol below the euphotic zone at 100 m signified that downwelling of biomass occurred on the downstream side of the gyre. The high concentrations of phytosterols and POC, in combination with the high phytosterols/phytol ratio, indicated the accumulation of detrital plant material in the oligotrophic Mediterranean waters near the frontal zone.A higher contribution of phytol in the sinking particles collected during the night at the surface of the jet and at the upstream side of the gyre provided evidence of diel vertical zooplankton migration and important grazing by herbivorous zooplankton.Carbon isotope ratios of sterols confirmed that the 24-ethylcholest-5-en-3β-ol, commonly associated with terrestrial sources, was a substantial constituent of the phytoplankton in this area. However, the more δ¹³C depleted values obtained for this compound in suspended particles suggested that there was some terrestrial contribution that only becomes evident after degradation of the more labile marine organic matter.  相似文献   

The high temperature reaction zone of the Oman ophiolite: new field data,microthermometry of fluid inclusions,PIXE analyses and oxygen isotopic ratios     

Juteau  Thierry  Manac'h  Gilles  Moreau  Olivier  Lécuyer  Christophe  Ramboz  Claire 《Marine Geophysical Researches》2000,21(3-4):351-385

Marine Geophysical Research - The present study is focused on the so-called High Temprature Reaction Zone of the Oman ophiolite, a thin zone located between the roots of the sheeted dyke complex...  相似文献   

The Role of Contextual Info‐Marks in Navigating a Virtual Rural Environment          下载免费PDF全文

Adam Rousell  Claire Jarvis  Chris Brunsdon 《Transactions in GIS》2016,20(1):1-19

Navigation is a task performed in both large and small scale environments. Landmarks within an environment are of great benefit to these navigational tasks, but in large rural environments such landmarks may be sparse. It has been shown that landmarks need not be purely visual and that a change in context for a feature can make it become a landmark against its surroundings (such as being provided with significant meaning). Such meaning could be added through personal experience or by informing the observer via some form of communication. To investigate the effects of providing such contextual information on navigational performance, experiments were conducted in a large rural virtual environment where the delivery method of the information was varied between onscreen and PDA display. Users were instructed to perform a route tracing navigation task. In some instances users were presented with textual information about specific locations within the environment which appeared when they were in the vicinity of the location. Both quantitative and qualitative data were collected and analyzed, with results indicating that although the actual performance in the task was not significantly improved, users felt that their performance was better and the task easier when they were presented with the contextual information.  相似文献