The community morphology of skilled migration: the changing role of voluntary and community organisations (VCOs) in the grounding of British migrant identities in Paris (France)     

Sam Scott 《Geoforum》2007,38(4):655-676

Research into skilled migrant communities tends to emphasize the grounding of identities through transnationalism and mobility. Less research has been conducted into how skilled migrants actually ground their identities within the city through everyday social networks. The paper addresses this imbalance by examining the changing significance of British voluntary and community organisations (VCOs) in Paris, France. Combining qualitative and quantitative data, findings show local migrant networks to be important focal points for the British even though migrants’ lives may increasingly be transnational in orientation. The research also shows that in situ social networks are evolving. Specifically, traditional forms of elite expatriate communality are not as omnipotent as they once were, with the popularity of some high-profile British VCOs in Paris declining over recent decades. The paper argues that the link between social dynamism and communal morphology helps explain this shift: as British middle-class lifestyles have fragmented, and as the British migrant population in Paris has grown in scale and scope, so the range of VCOs and associated informal networks has grown. Whilst some skilled migrants still embed within traditional expatriate organisations, Britishness is increasingly grounded elsewhere; both within the city through alternative social networks, and located beyond the city through transnational ties.  相似文献   

中国石炭纪生物礁造礁群落演化   总被引：5，自引：3，他引：2  

巩恩普  关广岳 《地质论评》1998,44(2):160-164

中国石炭纪造礁群落是弗拉斯期—法门期生物绝灭事件后新兴起的。该群落在早期演化过程中经历了形成、发展、完善和衰落的过程,构成一个群落演化旋回。晚期又开始新一轮的旋回,群落的二分性十分显著。显然,石炭纪造礁群落代表一个不连续的演化过程。  相似文献   

Monitoring vegetation dynamics in semi-arid African rangelands: Use and limitations of Earth observation data to characterize vegetation structure     

N.M Trodd  A.J Dougill 《Applied geography (Sevenoaks, England)》1998,18(4):315-330

Vegetation community structure is a key indicator of long-term vegetation change in semi-arid ecosystems. This study uses ground-based spectral measurements and a canopy reflectance model to investigate the potential of Earth observation data to characterize variations in vegetation structure along a grazing gradient in the eastern Kalahari, Botswana. Despite differences in the bidirectional reflectances of soil, plant litter, bush and grass canopies towards the end of a dry season, it is unlikely that Earth observation data can be used to estimate vegetation structure at this time. This is due to an ambiguity in the relationship between spectral reflectance and vegetation structure caused primarily by the limited dimensionality of reflectance data. Variations in canopy architecture cause differences in the level of inter-canopy shadowing but the net effect—lower reflectance with an increase in bush cover—parallels the darkening effects of any vegetation cover on relatively bright sandy soils in semi-arid environments. These results highlight the continued need for long-term ground-based ecological monitoring in conjunction with satellite-based monitoring of changes in vegetation cover.  相似文献   

Assessment of Man-made and Natural Hazards in the Surroundings of Hydropower Projects under Construction in the Beas Valley of Northwestern Himalaya     

Sanjeev Sharma Jagdish C. Kuniyal J. C. Sharma 《山地科学学报》2007,4(3):221-236

Mountain ecosystem,on the earth,has plenty of natural resources. In Himachal Pradesh all the rivers are snowfed and therefore rich in water resources. These resources have been supporting enough for the generation of electricity through introducing hydropower projects since the last decade. However,every developmental activity has its own negative impacts on the surrounding environment. Due to the fragile nature of topography and delicacy of ecology of the Himalaya,it results in lot of disturbances because of high degree of human interferences like construction of major hydropower projects. The increased extent of geological hazards,such as landslides,rock fall and soil erosion,have mainly due to alike developmental interventions in the natural ecosystem. So understanding and analysing such impacts of the hydropower projects have mainly been on the environment in various forms but natural hazards have been frequent ones. The present study,therefore,focuses mainly on the Parbati Stage Ⅱ (800 MW) and the Parbati Stage Ⅲ (520 MW) hydropower projects; both of which fall within the Kullu district of Himachal Pradesh. Based on the perception survey of the local communities,the existing land use pattern,status of total acquired land of the residents by hydropower projects,frequent natural hazards and resultant loss to the local communities due to upcoming construction of hydropower projects surrounding to the Parbati Stage Ⅱ and Ⅲ have been analysed in the paper. Also,the preventive measures to mitigate these adverse impacts have been suggested to strengthen these projects in eco-friendly manner in the mountain context.  相似文献   

加拿大海盆北部营养盐限制作用研究   总被引：1，自引：1，他引：0  

李宏亮  陈建芳  高生泉  卢勇  金海燕  白有成  庄燕培  张海生 《海洋学报》2015,37(11):147-154

利用2008年夏季中国第三次北极科学考察获得的营养盐、叶绿素a、温度和盐度等数据资料,结合现场营养盐添加实验的结果讨论西北冰洋加拿大海盆北部营养盐对浮游植物生长的限制作用。结果表明:由于融冰水稀释作用,加拿大海盆B80站约20m深度存在较强的盐跃层,阻碍了水体上下混合。较低浓度的溶解无机氮(DIN)和硅酸盐(分别为0.31μmol/L和0.94μmol/L)以及严重偏离Redfield比值的N/P、N/Si比值(分别为0.42和0.32)表明加拿大海盆表层水体存在N和Si限制。根据现场营养盐加富实验各培养组叶绿素a浓度变化、营养盐吸收总量差异和浮游植物种群结构,进一步表明氮是北冰洋海盆首要限制营养盐,而Si则抑制了硅质生物的生长。同时,较小的硝酸盐半饱和常数(Ks)证明即使在营养盐充足的情况下北冰洋海盆浮游植物生长速率也处于较低水平。计算得到各培养组营养盐吸收比例(N/P比值)均大于Redfield比值,可能是培养实验过程中以微型、微微型浮游植物为主,硅藻等小型浮游植物为辅造成的。  相似文献   

南海北部自由生活海洋线虫的群落结构和生物多样性     

刘晓收  许嫚  张敬怀  刘丹  李肖 《海洋学报(英文版)》2015,34(6):77-85

A quantitative study on the community structure and biodiversity of free-living marine nematodes and their relationship with environmental factors in the northern South China Sea were carried out based...  相似文献   

江苏近岸紫菜养殖筏架区定生绿藻群落结构及其受控因素   总被引：3，自引：1，他引：2  

李艳  肖洁  丁兰平  王宗灵  宋伟  方松  范士亮  李瑞香  张学雷 《海洋学报(英文版)》2015,34(8):93-99

基于2010年10月至2011年4月对苏北紫菜养殖筏架区定生绿藻及环境因素调查数据,分析研究了紫菜筏架上定生绿藻种群结构和数量变化及重要环境因子对其的影响并估算了调查区绿藻总生物量.结果表明,筏架上定生绿藻种类有浒苔(Ulva prolifera)、盒管藻(Capsosiphon groenlandicus)、缘管浒苔(Ulva linza)、肠浒苔(Ulva intestinalis)、条浒苔(Ulva clathrata)和扁浒苔(Ulva compressa).绿藻生物量变化呈倒抛物线型,4月份为主高峰14898吨,11月份为次高峰2034吨,2月份最低,仅为729吨,3-4月份绿藻几乎呈暴发性增长.种类多样性随季节变化有很大差异,养殖筏架刚入海的9、10月份,绿藻种类丰富,生物多样性高;12月至笠年2月,尽管生物量很低,但仍是多种并存;3-4月份随着生物量的猛增,种类多样性降至最低,盒管藻优势地位明显,生物量比例最大能到80%,浒苔比例呈指数增长,达20%～40%.水温对绿藻生物量及种类演替有直接调控作用,在水温< 10℃时,绿藻即能快速生长;而盐度作用不明显.开展紫菜筏架上定生绿藻群落动态变化及其生物量的估算,为追溯南黄海大规模绿潮发源地提供佐证,为绿潮预防和治理提供基础数据支撑.  相似文献   

海南岛三亚珊瑚礁区大型底栖动物群落特征   总被引：5，自引：1，他引：4  

董栋  李新正  王洪法  张宝琳  寇琦  甘志彬  许鹏 《海洋科学》2015,39(3):83-91

为了解海南省三亚市3个典型珊瑚礁区的底栖生物群落现状,并依此反映该区域珊瑚礁生态系统的健康现状和受扰动程度,作者于2011年11月22日~23日在海南岛三亚西岛、鹿回头和亚龙湾3个珊瑚礁自然保护区内采用潜水方法采集底栖动物,并对分析群落的物种组成、优势类群、丰度、生物量、Shannon-Wiener指数、物种丰富度指数和物种均匀度指数以及生物量/丰度比较曲线特征等进行研究。结果共获得三亚珊瑚礁大型底栖动物166种,优势类群为甲壳动物,优势种为珊瑚铠甲虾(Galathea coralliophilus)。调查区底栖动物平均栖息丰度为566.29个/m2,平均生物量为82.146 g/m2;Shannon-Wiener指数、物种丰富度指数和均匀度指数的平均值分别为3.0581、7.9116和0.8494。其中亚龙湾的上述3项指数均高于其他两个采样地点。生物量/丰度比较曲线表明亚龙湾的底栖群落最稳定,受扰动程度最小。  相似文献   

2013年春季崂山湾浮游植物群落及其环境控制   总被引：4，自引：0，他引：4  

乔芮  栾青杉  王俊  袁伟  崔毅  孙坚强 《海洋科学》2015,39(7):13-21

2013 年春季(3、4、5 月)对崂山湾海域浮游植物群落及其理化环境进行了3 个航次的调查研究。共鉴定浮游植物40 属75 种, 硅藻是调查区主要的浮游植物类群; 浮游植物细胞丰度平均为1.27×10⁶个/m³,3 月份的平均丰度显著高于4、5 月份(P<0.01); 优势种主要为冰河拟星杆藻(Asterionopsis glacialis)、加拉星平藻(Asteroplanus karianus)、密联角毛藻(Chaetoceros densus)和夜光藻(Noctiluca scintillans), 浮游植物群落演替明显, 由3 月份硅藻控制逐步过渡到4、5 月份硅/甲藻共同控制; 相对较低的硝酸盐水平是导致4、5 月份浮游植物丰度显著低于3 月份的主要原因; 物种–环境数据的冗余分析(RDA)结果显示, 温度、硝酸盐含量是控制崂山湾春季浮游植物分布的重要环境因子。  相似文献   

BJ-RUC产品在小区供暖供回水温度预报的应用研究   总被引：1，自引：1，他引：0  

李迅  冯涛  丁德平  谢庄 《气象》2015,41(2):234-239

利用气象部门快速更新的BJ-RUC(Beijing-Rapid UpdateCycle)数值预报系统获得的24 h逐时的室外温度预报资料,应用能量平衡原理,建立建筑物热损失方程和供热量方程,从而推导出室外温度和室内温度、供水、回水温度的预报模型。用此模型对2010年3月1—15日期间的供、回水温度进行预报模拟,与北京市海园物业供热单位实况值进行对比分析。检验结果表明,该模型模拟的室内温度与设计要求的室内温度(20℃)之间的均方根误差为0.25℃,海园物业室内温度监测点数值与20℃之间的均方根误差为1.53℃。模拟的供、回水温度与海园物业监测点供水温度的均方根误差分别为3.69℃和3.80℃。  相似文献