Heterolocalism: an alternative model of the sociospatial behaviour of immigrant ethnic communities   总被引：2，自引：0，他引：2  

Zelinsky W  Lee BA 《International journal of population geography : IJPG》1998,4(4):281-298

"This paper evaluates critically the applicability of the well-known assimilation and pluralist models to the contemporary ethnic landscape of the U.S.... We then consider an alternative model, labelled heterolocalism, which suggests that members of certain newly arrived groups may be able to sustain their identity as an ethnic community despite immediate or rapid spatial dispersion. The applicability of the heterolocal perspective to non-metropolitan and transnational phenomena is evaluated in subsequent sections of the paper."  相似文献   

Observations and origin of Rayleigh-wave amplitude anomalies   总被引：1，自引：0，他引：1  

S. van der Lee 《Geophysical Journal International》1998,135(2):691-699

This is a report of observations of amplitude anomalies of fundamental-mode Rayleigh waves ( R 1) between periods of 17 and 100  s. The anomalies are with respect to amplitudes predicted by Rayleigh-wave excitation for a reference earth model and catalogued centroid earthquake source parameters, such as are used in large-scale waveform inversions. The observations indicate that the amplitude anomalies are consistent for nearby recordings of the same event, while there is no obvious relation between the observed anomalies and the paths travelled by the waves. This is in contrast to Rayleigh-wave phase anomalies, which are consistent for similar propagation paths, and hence form the input in many inversions for along-path structure. The observations in this paper show that a similar inversion of intermediate-period amplitude anomalies for along- and near-path structure is not warranted without eliminating source effects, since the amplitude anomalies are dominated by scattering off near-source earth structure and by possible uncertainties in the source parameters. Sensitivity kernels that take the coupling between the moment tensor and displacement field into account demonstrate that Rayleigh-wave amplitude sensitivity is largest near the source. This report argues that the interaction between source-radiated Rayleigh waves and near-source earth structure may not be ignored in amplitude inversion procedures.  相似文献   

Effect of hydrologic management on marsh surface sediment deposition in coastal Louisiana     

Denise J. Reed  Nina De Luca  A. Lee Foote 《Estuaries and Coasts》1997,20(2):301-311

High rates of coastal land loss in Louisiana have prompted efforts to maintain or restore coastal wetland habitats, and structural management of marsh hydrology is one of a number of approaches that has been adopted. The aim of this study was to determine the effect of hydrologic management measures on marsh-surface sediment deposition in the Mississippi deltaic plain. Four impoundments, ranging in size from 50 ha to 177 ha and similarly sized control sites were included in the study. At each site, marsh-surface sediment traps were collected approximately biweekly for 3.5 yr to measure changes in sediment deposition. There was no significant difference in sediment deposition between any of the impoundment and control sites during the premanagement period. The results show no significant difference in marsh-surface sediment deposition between management year 1992–1993 and management year 1994–1995, but management year 1993–1994 had significantly lower sediment deposition than either the first or the last year of the study. Management year 1992–1993 showed the highest sediment deposition when it was assessed across all basins, areas, and sites, and this high rate of deposition is accounted for by the impact of Hurricane Andrew. For all management years there were significant differences between impoundment and control sites, with control sites showing higher rates of marsh surface sediment deposition than impoundments. No clear pattern was identified concerning the influence of various types of hydrologic management on rates of sediment deposition. This reduction in sediment deposition indicated that the areas under management in this study are receiving insufficient inorganic sediment deposition to keep pace with sea-level rise.  相似文献   

Decomposition of saltmeadow cordgrass (Spartina patens) in Louisiana coastal marshes     

A. Lee Foote  Kathleen A. Reynolds 《Estuaries and Coasts》1997,20(3):579-588

In Louisiana, plant production rates and associated decomposition rates may be important in offsetting high rates of land loss and subsidence in organic marsh soils. Decomposition ofSpartina patens shoot and leaf material was studied by using litter bags in mesohaline marshes in the Barataria and Terrebonne basins of coastal Louisiana.Spartina patens decomposed very slowly with an average decay constant of 0.0007, and approximately 50% of the material remained after 2 years in the field. Material at the Barataria site decomposed faster than did Terrebonne material with trend differences apparent during the first 150 days. This difference might be explained by the higher content of phosphorus in the Barataria material or a flooding period experienced by the Barataria bags during their first 10 days of deployment. Nitrogen and carbon content of the plant material studied did not differ between the two basins. We detected no consistent significant differences in decomposition above, at, or below sediment/water level. BecauseS. patens is the dominant plant in these marshes, and because it is so slow to decompose, we believe thatS. patens shoots are an important addition to vertical accretion and, therefore, marsh elevation.  相似文献   

Effects of alternative cloud radiation parameterizations in a general circulation model     

Wan-Ho Lee  Richard C. J. Somerville 《Annales Geophysicae》1996,14(1):107-114

Using the National Center for Atmospheric Research (NCAR) general circulation model (CCM2), a suite of alternative cloud radiation parameterizations has been tested. Our methodology relies on perpetual July integrations driven by ±2 K sea surface temperature forcing. The tested parameterizations include relative humidity based clouds and versions of schemes involving a prognostic cloud water budget. We are especially interested in testing the effect of cloud optical thickness feedbacks on global climate sensitivity. All schemes exhibit negative cloud radiation feedbacks, i.e., cloud moderates the global warming. However, these negative net cloud radiation feedbacks consist of quite different shortwave and longwave components between a scheme with interactive cloud radiative properties and several schemes with specified cloud water paths. An increase in cloud water content in the warmer climate leads to optically thicker middle- and low-level clouds and in turn negative shortwave feedbacks for the interactive radiative scheme, while a decrease in cloud amount leads to a positive shortwave feedback for the other schemes. For the longwave feedbacks, a decrease in high effective cloudiness for the schemes without interactive radiative properties leads to a negative feedback, while no distinct changes in effective high cloudiness and the resulting feedback are exhibited for the scheme with interactive radiative properties. The resulting magnitude of negative net cloud radiation feed-back is largest for the scheme with interactive radiative properties. Even though the simulated values of cloud radiative forcing for the present climate using this method differ most from the observational data, the approach shows great promise for the future.  相似文献   

An experimentally verified model for calcite precipitation in veins     

Young-Joon Lee  John W. Morse  David V. Wiltschko 《Chemical Geology》1996,130(3-4):203-215

Calcite is commonly found as a vein-filling mineral in rocks. However, the factors controlling its deposition are complex and not well understood in quantitative terms. In order to advance our understanding of the processes involved, we have refined the model for calcium carbonate mass transport in subsurface carbonate rocks of Morse and Mackenzie (1993) and developed a new experimental technique to test it. This technique uses a flow-through reactor that simulates a vein opening. Agreement was observed between model predictions and experimental observations for the deposition of calcite in synthetic veins. The influences of surface area to solution volume ratio, solution saturation state with respect to calcite, and flow velocity were well predicted by the model.

The model predicts that in order to have a fairly uniform deposition of calcite within a vein, solution flow must be quite rapid (tens to thousands of cm h⁻¹) or the solution must be only slightly supersaturated with respect to calcite. A low degree of solution supersaturation demands what may be unreasonably large volumes of solution flow to achieve vein filling for the vein configuration we have studied.  相似文献   

SIMULATING REGIONAL SYSTEMS: A SYSTEM DYNAMICS APPROACH     

Colllin Lee 《地理学报(英文版)》1996,(2)

I.IntroductionTheuseofquantitative111odeIstodevelopUnderstanding,prePareforecastsandexplorepolicyoptionsinthecontextofurbanandroponaldevelpl11entremainsapopularaCtivlty,althouglrathermoresointheacadel11iccol11n1unitythanintl1epIanningprofession.However,thehistoryoftheapplicationoffon11aln1odelstopolicyproblemsdoesnotproducegreatconfidence.objeCtiveevaluationoftheuseofl11odelsinpolicyn1akingiscomplicatedbythefaCtthat,asafonl1ercolleagueoncesaid,con1puter111odeIsarelikecl1ildrenfmostpeopleten…  相似文献   

Sediment indicators of meromixis: comparison of laminations, diatoms, and sediment chemistry in Brownie Lake, Minneapolis, USA     

B. Tracey  N. Lee  V. Card 《Journal of Paleolimnology》1996,15(2):129-132

Meromixis has several powerful effects on lakes, yet there is no single definitive sediment indicator of meromixis. In this study three sediment indicators of meromixis were compared in Brownie Lake, Minneapolis, Minnesota, a small eutrophic lake that became meromictic around 1925. The results show that in Brownie the onset of laminations and changes in the iron to manganese ratio most likely occurred before the development of permanently anoxic bottom water and that changes in the diatom assemblage occurred later, most likely only when meromixis was well developed.This is the 11th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.  相似文献   

Pore-Pressure Rise, Frictional Strength, and Fault Slip: One-Dimensional Interaction Models     

Tien-Chang Lee 《Geophysical Journal International》1996,125(2):371-384

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Coherent eddies and temperature structure functions for three contrasting surfaces. Part I: Ramp model with finite microfront time     

Wenjun Chen  Michael D. Novak  T. Andrew Black  Xuhui Lee 《Boundary-Layer Meteorology》1997,84(1):99-124

Air temperature time series within and above canopies reveal ramp patternsassociated with coherent eddies that are responsible for most of thevertical transport of sensible heat. Van Atta used a simple step-changeramp model to analyse the coherent part of air temperature structurefunctions. However, his ocean data, and our own measurements for aDouglas-fir forest, straw mulch, and bare soil, reveal that even withoutlinearization his model cannot account for the observed decrease of thecubic structure function for small time lag. We found that a ramp model inwhich the rapid change at the end of the ramp occurs in a finite microfronttime can describe this decrease very well, and predict at least relativemagnitudes of microfront times between different surfaces. Averagerecurrence time for ramps, determined by analysis of the cubic structurefunction with the new ramp model, agreed well with values determined usingthe Mexican Hat wavelet transform, except at lower levels within theforest. Ramp frequency above the forest and mulch scaled very well withwind speed at the canopy top divided by canopy height. Within the forest,ramp frequency did not vary systematically with height. This is inaccordance with the idea that large-scale canopy turbulence is mostlygenerated by instability of the mean canopy wind profile, similar to aplane mixing layer. The straw mulch and bare soil experiments uniquelyextend measurements of temperature structure functions and ramp frequencyto the smallest scales possible in the field.  相似文献