What can we learn about changing ethnic diversity from the distributions of mixed-race individuals?     

William A. V. Clark  Eva K. Andersson  Bo Malmberg 《Urban geography》2018,39(2):263-281

It is hypothesized that self-defined mixed-race persons live in residentially mixed areas in the largest metropolitan areas in California. The hypothesis is tested by examining the distribution of mixed-race persons among ethnically and racially diverse and nondiverse neighborhoods in the San Francisco and Los Angeles Metropolitan Areas. The research confirmed that mixed-race individuals are more likely to live in areas with ethnic diversity and that the tendency is greater for the mixed-race population in the San Francisco–Oakland Metropolitan Areas than in the Los Angeles Metropolitan Area. Mixed-race individuals live in neighborhoods which are diverse with mixes of all four major ethnic and racial groups, and in “well-off” (but not the most affluent) neighborhoods. The study also shows that the mixed-race population is youthful. The association of mixed-race individuals and racially integrated neighborhoods will have important implications for the evolving nature of spatial integration in California specifically, and the United States more generally.  相似文献   

黄土孢粉分析的新途径——筛滤分析法   总被引：7，自引：0，他引：7  

李小强  周杰  A.R. Ashraf  Eva Wacker 《中国沙漠》1999,19(4):399-402

黄土-古土壤序列在全球古气候、古环境研究中占有不可替代的重要地位,而其中的孢粉是黄土高原生态环境演化过程中保存的直接生物学证据,它对建立黄土高原降水或湿度状况的时空变化特征,认识季风变迁的过程、规律以及未来发展趋势等具有重要的意义。随着黄土研究工作的不断深入,作为直接生物学证据的孢粉研究相对薄弱。其中最困扰的因素是从黄土中提取孢粉极其困难,分析技术上始终未能找到一个突破口,因此需要一种分析效果好、快捷、成本低的分析方法以获得大量高精度的孢粉数据。筛滤分析法正是为了适应黄土研究的需要而设计的一种新型的黄土孢粉分析方法。筛滤分析法利用真空状态下的气压差使样品在水中完全悬浮跳动,样品得到充分的冲洗并促使孢粉与其它无机质与有机质分离。相对真空的状态减少了微细颗粒对极为细小的网眼的阻塞,重力作用促使水及各类颗粒不断冲击筛网,使粒径小于10μm的物质较容易被过滤到聚水容器中,而孢粉与较少的大颗粒物质则被隔离在筛网之上,这使我们很容易用重液浮选出干净、清晰的孢粉底样。筛滤分析法与常规的黄土孢粉分析相比,具有以下特点:①大大降低了分析样品的重量及药品的消耗,一般仅需样品30 g左右,是常规分析法用量的1/6~1/8。②整个分析流程短, 12个样品一个流程仅需3~4 d。③筛滤分析法使孢粉几乎全部被隔离在筛网上而丢失极少,提高了黄土孢粉研究精度。④筛滤分析法几乎不破坏孢粉的结构,孢粉底样干净、清晰。使用筛滤分析法共分析耀县全新世黄土剖面69块孢粉样品,均发现数量不等的孢粉。孢粉底样干净、杂质少,结构清楚。共统计孢粉14978粒,分属27个科属,这些科属包括了黄土高原主要的孢粉类型。从孢粉结果可以初步确定,在全新世时期,位于黄土高原南缘的耀县地区,草本植物占全部孢粉总量的93.6%,而乔木植物仅占孢粉总量的4.7%。在整个剖面中没有出现乔木植物含量超过30%,可以认为在黄土高原的全新世时期是以草原植被为主,并无森林生长。  相似文献   

Digital mapping of coastal boulders – high-resolution data acquisition to infer past and recent transport dynamics     

Fabian Boesl  Max Engel  Rodrigo C. Eco  JaN B. Galang  Lia A. Gonzalo  Francesca Llanes  Eva Quix  Helmut Brückner 《Sedimentology》2020,67(3):1393-1410

Coastal boulder fields provide clues to long-term frequency-magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour-intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists who are not specialists in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of sub-metre resolution (from Pléiades and WorldView-3 imagery) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon-generated waves. During the investigated events, boulders with a-axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a-axes and b-axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultra-high-resolution data, and have the potential to not only improve the results of satellite image analysis, but also those from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a-axes and b-axes including their orientation, while precise values for c-axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder-specific Structure from Motion-based three-dimensional models. Battery power, flight speed and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks, field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating, recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre-scale, or documentation of fine-grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre-scale and to better understand the hydrodynamics of extreme-wave events on a fringing reef coastline.  相似文献   

How Well Does Chlorophyll Explain the Seasonal Variation in Phytoplankton Activity?     

Maren Moltke Lyngsgaard  Stiig Markager  Katherine Richardson  Eva Friis Møller  Hans Henrik Jakobsen 《Estuaries and Coasts》2017,40(5):1263-1275

The seasonal variation in phytoplankton activity is determined by analysing 1385 primary production (PP) profiles, chlorophyll a (Chl) concentration profiles and phytoplankton carbon biomass concentrations (C) from the period 1998–2012. The data was collected at six different stations in the Baltic Sea transition zone (BSTZ) which is a location with strong seasonal production patterns with light as the key parameter controlling this productivity. We show that the use of Chl as a proxy for phytoplankton activity strongly overestimates the contribution from the spring production to annual pelagic carbon flow. Spring (February and March) Chl comprised 16–30% of the total annual Chl produced, whereas spring C was much lower (8–23%) compared to the annual C. Spring PP accounted for 10–18% of the total annual PP, while the July–August production contributed 26–33%, i.e. within the time frame when zooplankton biomass and grazing pressure are highest. That is, Chl failed in this study to reflect the importance of the high summer PP. A better proxy for biomass may be C, which correlated well with the seasonal pattern of PP (Pearson correlation, p < 0.05). Thus, this study suggests to account for the strong seasonal pattern in C/Chl ratios when considering carbon flow in coastal systems. Seasonal data for PP were fitted to a simple sinusoidal wave model describing the seasonal distribution of PP in the BSTZ and were proposed to present a better parameterizaton of PP in shallow stratified temperate regions than more commonly applied proxies.  相似文献   

Application of diffracted wave analysis to time‐lapse seismic data for CO2 leakage detection     

Faisal Alonaizi  Roman Pevzner  Andrej Bóna  Mohammad Alshamry  Eva Caspari  Boris Gurevich 《Geophysical Prospecting》2014,62(2):197-209

Time‐lapse seismic analysis is utilized in CO₂ geosequestration to verify the CO₂ containment within a reservoir. A major risk associated with geosequestration is a possible leakage of CO₂ from the storage formation into overlaying formations. To mitigate this risk, the deployment of carbon capture and storage projects requires fast and reliable detection of relatively small volumes of CO₂ outside the storage formation. To do this, it is necessary to predict typical seepage scenarios and improve subsurface seepage detection methods. In this work we present a technique for CO₂ monitoring based on the detection of diffracted waves in time‐lapse seismic data. In the case of CO₂ seepage, the migrating plume might form small secondary accumulations that would produce diffracted, rather than reflected waves. From time‐lapse data analysis, we are able to separate the diffracted waves from the predominant reflections in order to image the small CO₂ plumes. To explore possibilities to detect relatively small amounts of CO₂, we performed synthetic time‐lapse seismic modelling based on the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) Otway project data. The detection method is based on defining the CO₂ location by measuring the coherency of the signal along diffraction offset‐traveltime curves. The technique is applied to a time‐lapse stacked section using a stacking velocity to construct offset‐traveltime curves. Given the amount of noise found in the surface seismic data, the predicted minimum detectable amount of CO₂ is 1000–2000 tonnes. This method was also applied to real data obtained from a time‐lapse seismic physical model. The use of diffractions rather than reflections for monitoring small amounts of CO₂ can enhance the capability of subsurface monitoring in CO₂ geosequestration projects.  相似文献   

Illicit Drugs in the Environment: Occurrence,Analysis, and Fate Using Mass Spectrometry     

Eva Pocurull 《洁净——土壤、空气、水》2012,40(11):1307-1307

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Standing proud: a response to ‘Soil‐erosion models: where do we really stand?’ by Smith et al.     

John Wainwright  Anthony J. Parsons  Eva N. Müller  Richard E. Brazier  D. Mark Powell 《地球表面变化过程与地形》2010,35(11):1349-1356

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Response to Hairsine's and Sander's ‘Comment on “A transport‐distance based approach to scaling erosionrates”: Parts 1, 2 and 3 by Wainwright et al.’     

John Wainwright  Anthony J. Parsons  Eva N. Müller  Richard E. Brazier  D. Mark Powell 《地球表面变化过程与地形》2009,34(6):886-890

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A transport‐distance approach to scaling erosion rates: 1. Background and model development     

John Wainwright  Anthony J. Parsons  Eva N. Müller  Richard E. Brazier  D. Mark Powell  Bantigegne Fenti 《地球表面变化过程与地形》2008,33(5):813-826

The process basis of existing soil‐erosion models is shown to be ill‐founded. The existing literature builds directly or indirectly on Bennett's (1974) paper, which provided a blueprint for integrated catchment‐scale erosion modelling. Whereas Bennett recognized the inherent assumptions of the approach suggested, subsequent readings of the paper have led to a less critical approach. Most notably, the assumption that sediment movement could be approximated by a continuity equation that related to transport in suspension has produced a series of submodels that assume that all movement occurs in suspension. For commonly occurring conditions on hillslopes, this case is demonstrably untrue both on theoretical grounds and from empirical observations. Elsewhere in the catchment system, it is only partially true, and the extent to which the assumption is reasonable varies both spatially and temporally. A second ground‐breaking paper – that of Foster and Meyer (1972) – was responsible for subsequent uncritical application of a first‐order approximation to deposition based on steady‐state analysis and again a weak empirical basis. We describe in this paper an alternative model (Mahleran – Model for Assessing Hillslope‐Landscape Erosion, Runoff And Nutrients) based upon particle‐travel distance that overcomes existing limitations by incorporating parameterizations of the different detachment and transport mechanisms that occur in water erosion in hillslopes and small catchments. In the second paper in the series, we consider the sensitivity and general behaviour of Mahleran , and test it in relation to data from a large rainfall‐simulation experiment. The third paper of the sequence evaluates the model using data from plots of different sizes in monitored rainfall events. From this evaluation, we consider the scaling characteristics of the current form of Mahleran and suggest that integrated modelling, laboratory and field approaches are required in order to advance the state of the art in soil‐erosion modelling. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Vegetation patterns and diversity along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of northern Oman   总被引：1，自引：0，他引：1  

Katja Brinkmann  Annette Patzelt  Uta Dickhoefer  Eva Schlecht  Andreas Buerkert 《Journal of Arid Environments》2009,73(11):1035-1045

Little is known about the effects of grazing on vegetation composition on the Arabian Peninsula. The aim of this study therefore was to analyse the vegetation response to environmental conditions of open woodlands along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of Oman. The species composition, vegetation structure, grazing damage and several environmental variables were investigated for 62 samples using a nested plot design. Classification analysis and a Canonical Variate Analysis (CVA) were used to define vegetation types and to identify underlying environmental gradients. The relationship between environmental variables and diversity was analysed using correlation coefficients and a main-effects ANOVA. The plant species richness followed a unimodal distribution along the altitudinal gradient with the highest number of species at the intermediate altitudinal belt. The cluster analysis led to five vegetation groups: The Sideroxylon mascatense–Dodonaea viscosa group on grazed and the Olea europaea–Fingerhuthia africana group on ungrazed plateau sites at 2000 m a.s.l., the Ziziphus spina-christi–Nerium oleander group at wadi sites and the Moringa peregrina–Pteropyrum scoparium group at 1200 m a.s.l, and the Acacia gerrardii–Leucas inflata group at 1700 m a.s.l. The CVA indicated a clear distinction of the groups obtained by the agglomerative cluster analysis. The landform, altitude and grazing intensity were found to be the most important variables distinguishing between clusters. Overgrazing of the studied rangeland is an increasing environmental problem, whereas the plant composition at ungrazed sites pointed to a relatively fast and high regeneration potential of the local vegetation.  相似文献