The Sun City Wars: Chapter 3     

《Urban geography》2013,34(7):627-648

A revealing indicator of social fragmentation in metropolitan America is the proliferation of common interest developments (CIDs), communities defined by restrictive covenants, deed restrictions, community associations, and citizens groups that wield substantial political influence and power. In Phoenix, large-scale retirement communities represent a conspicuous form of CID, populated by Anglo, middle, and upper-middle class elderly migrants who display high levels of political organization and participation. We present a case study of heated conflict between retirees in Sun City West—who see themselves as separate from the larger metropolitan region—and surrounding communities in the Dysart School District. The conflict is fraught with age, social class, and cultural tensions and evolves around seniors wielding political muscle in defeating school funding measures, controlling the Dysart governing board, and seeking to de-annex themselves out of the district to avoid paying school taxes. We argue that political conflict between advantaged seniors and neighboring working class Latino communities is symptomatic of troubling divisions across urban social space in America, raising thorny questions about the nature and scale of community, political representation and power, and fostering the public good in the face of "secession of the successful" from the larger polity.  相似文献   

PREDICTING ABOVE-GROUND NET PRIMARY PRODUCTIVITY OF TROPICAL RAINFORESTS FROM EVAPOTRANSPIRATION DATA     

Stanley R. Herwitz  Steven M. Friedland 《自然地理学》2013,34(1):18-25

The relationship between above-ground net primary productivity (ANPP) and actual evapotranspiration (AE) has been previously shown by Rosenzweig (1968) to be significant for a variety of mainly temperate terrestrial ecosystems. Our study of ANPP and AE data from the humid tropics showed that AE remains a useful predictor of ANPP in tropical rainforest environments. However, we also noted that 80% of the tropical rainforest data points were depressed below Rosenzweig's original regression line. We attribute these lower-than-predicted ANPP values to transpiration losses and rainfall interception losses that do not result in a corresponding production of biomass.  相似文献   

基于3S技术的雅江县植被类型调查与分析     

刘中正  彭培好  周正坤 《地理空间信息》2013,11(2):78-79

使用TM遥感影像,借助GIS软件进行了影像的处理和解译;制作了植被类型图,计算主要植被类型的面积及其变化情况;分析了3S技术在植被调查中的优势,并调查了植被动态变化,为植被恢复模式的建立提供了依据。  相似文献   

牙轮钻头动静耦合碎岩机理及旋挖成桩应用          下载免费PDF全文

阮强  宋武超  水俊峰 《探矿工程》2013,40(10):49-50

总结了在不同高温状态下冷却、不同加载速率及随机裂隙发育状态下花岗岩动态抗拉力学特性的变化规律;结合牙轮钻头孔底碎岩过程,分析了动静载荷耦合作用下岩石破碎的载荷一侵深特性曲线,认为动、静载荷耦合作用的加载点（即动载的施加点）应是在静载处于卸载阶段;并根据加载能量大小讨论了不同动静耦合工况下产生的岩石破裂深度及破碎体积,表明通过一定范围内增大静载荷及冲击力、预加静压对岩石进行预应力损伤、加载一卸载一加载的破碎循环模式,有利于高效碎岩及裂纹的发育。嵌岩桩基础工程实践表明,通过改造牙轮钻头等钻具结构形式及布齿方式,利用动静耦合加载方式及对钻头冷却处理,可实现牙轮钻头在微风化花岗岩高效钻进的目的,为牙轮钻头的旋挖钻进成桩应用提供了重要的技术支撑。  相似文献   

青海野马泉矿区地层破碎程度评价及钻井液体系研究     

刘鹏  王道宽  乌效鸣  赵珊珊 《探矿工程》2013,40(11):5-9

为了评价和分析青海野马泉矿区地层的破碎情况,提出了破碎比表面、破碎块度、岩石空隙率、岩石崩解率、岩石完整性系数、岩石抗压强度6个破碎程度的评价指标,运用模糊数学评价体系并结合岩石破碎程度指标建立了破碎地层的分类标准,结合野马泉矿区钻探现场,将破碎地层分为了5类。对于破碎地层研究出具有针对性的钻井液体系。  相似文献   

新疆阿舍勒盆地泥盆纪火成岩与构造-岩浆演化   总被引：1，自引：0，他引：1  

孟贵祥  汤贺军  刘鸿佑  秦继华  吴晓贵  李成文 《地质学报》2022,96(2):445-464

阿舍勒泥盆纪火山盆地是阿尔泰西南缘重要的矿集区,产出我国著名的火山成因块状硫化物型(VMS)矿床——阿舍勒铜矿.其内部发育的火山岩和侵入岩地球化学特征记录了阿舍勒盆地的构造岩浆演化和成岩、成矿作用过程,但其形成构造背景和成岩成矿机制一直存在争论.本文报道了阿舍勒矿集区萨尔朔克铜金多金属矿区深部英云闪长岩的LA-MC-I...  相似文献   

Community structure of epibenthic meiofauna in the St. Lucia Estuarine Lake (South Africa) during a drought phase     

D. Pillay  R. Perissinotto 《Estuarine, Coastal and Shelf Science》2009

The St. Lucia Estuary is Africa's largest estuarine system. It is a major component of the iSimangaliso (formerly Greater St. Lucia) Wetland Park, which was declared a World Heritage Site in 1999. The system has been severely affected by drought conditions which have culminated in the mouth of the system being cut off from the Indian Ocean since June 2002, for a period of almost five years. This study aimed to document the dynamics of meiofauna of the system during a drought phase, since (1) the effects of droughts on estuaries are poorly documented and understood and (2) because studies of meiofauna have never been undertaken in this system before. Meiofauna samples as well as physico-chemical data were collected at representative sites in February, April, August and October 2005. The drought had a major effect on the estuary, resulting in the development of hypersaline conditions (maximum 126 at Hells Gate), and to the complete evaporation of pelagic habitats, especially in the northern regions. The meiofauna of the St. Lucia Estuary was statistically separated into two distinct spatial clusters under drought conditions. The first cluster comprised sites in the Narrows and the southern region of South Lake, while the second comprised sites in the northern regions of South Lake and False Bay. Meiofauna of cluster 1, which was least affected by the drought, comprised nematodes, polychaetes, copepods, amphipods and ostracods, all of which accounted for 97% of meiofauna in this cluster. Cluster 2 on the other hand, which was more severely affected by the drought, was dominated by nematodes and copepods, which cumulatively contributed 97% to meiofauna in this group. Taxonomic richness and diversity of meiofauna were positively correlated with water depth, while abundance was inversely correlated with water temperature. The major effects of low water levels on the meiofauna of the system occurred through a negative impact on diversity and taxonomic richness, resulting in assemblages dominated by taxa most physiologically suited to such conditions. Secondly, at the peak of the drought, there was discontinuous water flow in the St. Lucia Estuary, resulting in parts of the northern and southern regions of the system being fragmented. This could have prevented the spread of meiofaunal taxa between the different basins of the system, and also explains the spatial separation of meiofauna into distinct clusters within the estuary.  相似文献   

The benthic macrofauna of the St. Lucia Estuary during the 2005 drought year     

D. Pillay  R. Perissinotto 《Estuarine, Coastal and Shelf Science》2008

The St. Lucia Estuary is the largest estuarine system in Africa. The estuary is part of the Greater St. Lucia Wetland Park, which has been declared a World Heritage Site. This ecosystem has been subjected to severe drought conditions over the last four to five years, resulting in its mouth being closed off from the ocean in June 2002 for a period of over four years. The main aim of this study was to document the effects of the prevailing drought on the macrofauna of the system, since the last work on this benthic component had been undertaken over a decade ago, during a normal-to-wet phase. Macrofauna samples together with physico-chemical data were collected at representative sites in the Narrows, and the South and North lakes in February, April, August and October 2005. The drought exerted a strong influence on the system, leading to hypersaline conditions developing in its northern regions (maximum of 126 at Hell's Gate), and to the loss of aquatic habitat. Ordinations and clustering indicated that the macrofauna of the system could generally be separated into three clusters viz. (1) the Narrows and the southern portion of South Lake, (2) the northern half of South Lake, and (3) the North Lake–False Bay complex. Multivariate correlations indicated weak relationships between macrofaunal community structure and physico-chemical parameters. The distinction in macrofaunal assemblages between these clusters was probably caused by these habitats being physically separated at the peak of the drought, with no water flow between them, thereby preventing exchange of planktonic larvae and retarding colonisation of habitats. There was a northward decline in taxonomic richness and diversity of macrofauna in the system, which correlated positively with water depth and negatively with the biomass of microphytobenthos. It is evident that the drought structured macrofauna communities primarily through its effects on water depth and habitat fragmentation. The results of this investigation provide valuable information regarding the effects of droughts on estuarine–lake systems and the possible mechanisms by which they occur.  相似文献   

Use of the Connectivity of Runoff Model (CRUM) to investigate the influence of storm characteristics on runoff generation and connectivity in semi‐arid areas     

S. M. Reaney  L. J. Bracken  M. J. Kirkby 《水文研究》2007,21(7):894-906

Much attention has been given to the surface controls on the generation and transmission of runoff in semi‐arid areas. However, the surface controls form only one part of the system; hence, it is important to consider the effect that the characteristics of the storm event have on the generation of runoff and the transmission of flow across the slope. The impact of storm characteristics has been investigated using the Connectivity of Runoff Model (CRUM). This is a distributed, dynamic hydrology model that considers the hydrological processes relevant to semi‐arid environments at the temporal scale of a single storm event. The key storm characteristics that have been investigated are the storm duration, rainfall intensity, rainfall variability and temporal structure. This has been achieved through the use of a series of defined storm hydrographs and stochastic rainfall. Results show that the temporal fragmentation of high‐intensity rainfall is important for determining the travel distances of overland flow and, hence, the amount of runoff that leaves the slope as discharge. If the high‐intensity rainfall is fragmented, then the runoff infiltrates a short distance downslope. Longer periods of high‐intensity rainfall allow the runoff to travel further and, hence, become discharge. Therefore, storms with similar amounts of high‐intensity rainfall can produce very different amounts of discharge depending on the storm characteristics. The response of the hydrological system to changes in the rainfall characteristics can be explained using a four‐stage model of the runoff generation process. These stages are: (1) all water infiltrating, (2) the surface depression store filling or emptying without runoff occurring, (3) the generation and transmission of runoff and (4) the transmission of runoff without new runoff being generated. The storm event will move the system between the four stages and the nature of the rainfall required to move between the stages is determined by the surface characteristics. This research shows the importance of the variable‐intensity rainfall when modelling semi‐arid runoff generation. The amount of discharge may be greater or less than the amount that would have been produced if constant rainfall intensity is used in the model. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

地理探测器方法下甘肃白龙江流域景观破碎化与驱动因子分析   总被引：6，自引：0，他引：6  

张金茜  巩杰  柳冬青 《地理科学》2018,38(8):1370-1378

基于GIS技术、景观格局指数、主成分分析和地理探测器的方法,定量分析了1990~2014年甘肃白龙江流域的景观破碎化及其驱动因子。结果表明：1990~2014年甘肃白龙江流域景观破碎化程度先增加后降低;研究期间流域东南部的景观指数变化最为剧烈和复杂,主要是文县和武都区;人类干扰（人类活动强度和土地利用类型）和地形因子（高程、坡度和坡向）对景观破碎化空间分异的影响显著不同,其中人类干扰是景观破碎化空间分异的主要驱动因子。  相似文献