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Abstract It is suggested that reverse currents seen in recent numerical reconnection experiments (Biskamp, 1986; Forbes and Priest, 1983) are caused by the choice of outflow boundary conditions. The specification of the normal velocity at the outflow boundary may result in a mismatch in velocity at the diffusion region which is manifested as a spike of reverse current. 相似文献
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The study examines the various sociospatial features of immigrant populations in two transnationally-linked ethnic enclaves in terms of how they may facilitate and constrain the politics of growth and development. In recent decades, the growing ethnic enclave economies of Koreatown and Monterey Park have witnessed the emergence of progrowth ethnic interest groups comprised of immigrant capitalists, entrepreneurs, developers, and organizations, who are playing key roles in politically spearheading (re)development projects in the Los Angeles metropolitan area. Our aim is to understand how the sociospatial, entrepreneurial, and residential layout of these host municipalities set the context for the politics of growth in these ethnic enclave economies based on an analysis of GIS spatial mapping, 2000–2010 census data, and other secondary sources. The data suggests that Korean and Chinese elite face different political opportunities and challenges because of their different sociospatial characteristics—the former based on their greater entrepreneurial influence and weak electoral impact and the latter on their stronger political presence as residents. 相似文献
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Maria Potouroglou Emma J. Kenyon Angie Gall Kevan J. Cook James C. Bull 《Marine pollution bulletin》2014
Interaction between biotic and abiotic drivers of dynamics is an important topic in ecology. Despite numerous short-term studies, there is a paucity of evidence about how environmental structure modifies dynamics in marine systems. We quantified Zostera marina flowering and non-flowering shoot density annually from 1996 to 2012 around the Isles of Scilly, UK, parameterizing a population dynamic model. Flowering is structured in time and space, with temperature and flowering positively associated at some locations only. We found no evidence that flower production contributes to seagrass density but ‘patchiness’ was positively associated with flowering in the previous year. With evidence of substantial overwinter survival, findings support the hypothesis that local populations are maintained largely through vegetative reproduction but sexual reproduction may contribute to colonisation of vacant habitat. This long-term study (1) tests validity of shorter-term investigations, (2) quantifies interaction between biotic and abiotic factors and (3) promotes seagrass as a model ecosystem. 相似文献
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Understanding the interactions of climate, physical erosion, chemical weathering and pedogenic processes is essential when considering the evolution of critical zone systems. Interactions among these components are particularly important to predicting how semiarid landscapes will respond to forecasted changes in precipitation and temperature under future climate change. The primary goal of this study was to understand how climate and landscape structure interact to control chemical denudation and mineral transformation across a range of semiarid ecosystems in southern Arizona. The research was conducted along the steep environmental gradient encompassed by the Santa Catalina Mountains Critical Zone Observatory (SCM-CZO). The gradient is dominated by granitic parent materials and spans significant range in both mean annual temperature (>10 °C) and precipitation (>50 cm a?1), with concomitant shift in vegetation communities from desert scrub to mixed conifer forest. Regolith profiles were sampled from divergent and convergent landscape positions in five different ecosystems to quantify how climate-landscape position interactions control regolith development. Regolith development was quantified as depth to paralithic contact and degree of chemical weathering and mineral transformation using a combination of quantitative and semi-quantitative X-ray diffraction (XRD) analyses of bulk soils and specific particle size classes. Depth to paralithic contact was found to increase systematically with elevation for divergent positions at approximately 28 cm per 1000 m elevation, but varied inconsistently for convergent positions. The relative differences in depth between convergent and divergent landscape positions was greatest at the low and high elevation sites and is hypothesized to be a product of changes in physical erosion rates across the gradient. Quartz/Plagioclase (Q/P) ratios were used as a general proxy for bulk regolith chemical denudation. Q/P was generally higher in divergent landscape positions compared to the adjacent convergent hollows. Convergent landscape positions appear to be collecting solute-rich soil–waters from divergent positions thereby inhibiting chemical denudation. Clay mineral assemblage of the low elevation sites was dominated by smectite and partially dehydrated halloysite whereas vermiculite and kaolinite were predominant in the high elevation sites. The increased depth to paralithic contact, chemical denudation and mineral transformation are likely functions of greater water availability and increased primary productivity. Landscape position within a given ecosystem exerts strong control on chemical denudation as a result of the redistribution of water and solutes across the landscape surface. The combined data from this research demonstrates a strong interactive control of climate, landscape position and erosion on the development of soil and regolith. 相似文献
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Angie Carter 《社会与自然资源》2019,32(8):893-910
Women own or co-own approximately half of the farmland in Iowa, United States, yet researchers are only beginning to study these landowners’ social relationships in relation to their land. This study analyzes qualitative data collected in Iowa through a series of meetings hosted by the Women, Food and Agriculture Network (WFAN). I find that social control through exclusion constrains women landowners’ access to information about and implementation of conservation. Specifically, I identify how women landowners experience the social processes of boundary maintenance and othering in land management. These processes create barriers to conservation adoption and maintain gendered agricultural landscapes. The women who participated in WFAN’s conservation programs express their experience of and resistance to dominant narratives as they attempt to create landscape change. These findings highlight the importance of further study of inequality processes and their relation to control of farmland if conservation goals are to be met. 相似文献
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I. D. L. Foster A. J. Albon K. M. Bardell J. L. Fletcher T. C. Jardine R. J. Mothers M. A. Pritchard S. E. Turner 《地球表面变化过程与地形》1991,16(4):341-356
Sediments left by coastal flooding have been observed worldwide and have been variously ascribed to the action of storm surges and tsunami waves. To date, no study has attempted to unequivocally establish on stratigraphical, sedimentological, and palaeoecological grounds the means by which these two different processes might be distinguished in coastal sedimentary sequences. This paper examines the evidence for historical storm surges and tsunamis and shows that both high magnitude events have been documented over the past 250 years in southwest England. Sand layers of varying thickness are present within Holocene lagoonal and peat sequences of several shallow lakes of the Scilly Isles. Detailed analysis of Big Pool, St Agnes, indicates that the basal peats date from around 1000 BP. Within the basal peats are numerous thin sand layers. Above the basal peat is an extensive sand layer 15 to 40 cm thick. The base of this latter layer probably dates from the early to mid 18th century. Particle size, grain surface morphology, diatom, and mineral magnetic studies are used to try and determine the most likely mode of deposition. The results of all analyses are inconclusive, but the weight of evidence suggests that the increasing frequency of thin sand layers in the upper part of the basal peat may be related to the increasing frequency and intensity of Atlantic storms during the Little Ice Age superimposed upon a rising sea level. The thick sand layer may have been deposited by the tsunami wave generated by the Lisbon earthquake of November 1,1755. Due to the difficulties in distinguishing depositional processes in coastal environments known to have been affected by storm surges and tsunami waves, it is suggested that generally accepted sedimentological techniques are inadequate for discriminating depositional processes in coastal environments. 相似文献
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