Variation in low food access areas due to data source inaccuracies

Several spatial measures of community food access identifying so called “food deserts” have been developed based on geospatial information and commercially-available, secondary data listings of food retail outlets. It is not known how data inaccuracies influence the designation of Census tracts as areas of low access. This study replicated the U.S. Department of Agriculture Economic Research Service (USDA ERS) food desert measure and the Centers for Disease Control and Prevention (CDC) non-healthier food retail tract measure in two secondary data sources (InfoUSA and Dun & Bradstreet) and reference data from an eight-county field census covering 169 Census tracts in South Carolina. For the USDA ERS food deserts measure accuracy statistics for secondary data sources were 94% concordance, 50–65% sensitivity, and 60–64% positive predictive value (PPV). Based on the CDC non-healthier food retail tracts both secondary data demonstrated 88–91% concordance, 80–86% sensitivity and 78–82% PPV. While inaccuracies in secondary data sources used to identify low food access areas may be acceptable for large-scale surveillance, verification with field work is advisable for local community efforts aimed at identifying and improving food access.     

深圳服装业空间演化及影响因素分析

基于服装企业点状数据,采用核密度、标准差椭圆、热点探测和Ripley's K函数相结合的点模式空间分析方法,对比研究了1995、2000、2005和2010年深圳服装企业空间分布特征,进而利用负二项回归模型检验主要区位的影响因素,结果表明：深圳服装业随时间演变,核密度高值区域日渐明朗,整体呈现集中分布态势,标准差椭圆面积有所收缩,热点区域在扩大,西部热点区倾向北移,中部热点区得到进一步强化,集聚特征呈现“先增后减”趋势,集聚范围逐年扩大;负二项回归结果表明：产业集聚、区域协作和制度因素对服装业空间演化有着显著影响,其中产业集聚和制度因素影响逐渐加强,而区域协作在城市产业发展中寻求着空间动态平衡。深圳服装业空间演化惯性效应突出,因企业对集聚经济内在需求和区位环境等外部需求产生的路径依赖,约束了产业后续空间演化的各项特征。     

华北冬小麦—夏玉米两熟区干旱特征分析

研究华北冬小麦—夏玉米主要生长季的干旱时空特征,可为全球气候变暖背景下制定抗旱减灾对策提供理论依据。利用华北5省（市）64个气象台站1961——2010年逐日降水资料,以降水负距平或降水量表征的干旱指标,通过经验正交分解法提取了冬小麦、夏玉米全生育期和关键生长阶段的特征向量和时间系数,分析了干旱频率、站次比及干旱强度的变化特征,并通过构建冬小麦夏玉米轮作期综合干旱指数,探讨了华北地区农业干旱的总体状况。结果表明：EOF分解的前4个模态提取了60%以上作物干旱的主要时空分布信息,冬小麦主要生长季收敛效果优于夏玉米;冬小麦全生育期、苗期及拔节—抽穗期干旱的高强度中心主要分布在冀中南、豫北及鲁西北地区,而灌浆—成熟期干旱则以豫东为中心;夏玉米全生育期干旱的高强度中心主要位于冀南和鲁北地区,初夏旱以冀北大部为高强度区,而卡脖旱以豫西和鲁南为高强度区。从时间系数和区域干旱强度及站次比的时间变化趋势看,冬小麦全生育期干旱、灌浆—成熟期干旱及夏玉米初夏旱、卡脖旱均表现为递减趋势,但未通过显著性检验,而冬小麦播种期、拔节—抽穗期干旱,以及夏玉米全生育期干旱为不显著的递增趋势。整个冬小麦—夏玉米轮作期干旱威胁较高的地区主要位于京津局部、冀中南、豫北和鲁北等地区。     

岳麓山及其周围地区空气负离子变化初探

采用美国进口的空气离子测量仪，在岳麓山及其周围地区，于不同时间测定了其空气负离子含量，并用相关的评价方法进行评价。其结果表明：(1)岳麓山空气负离子含量和空气清洁度，先随海拔高度的升高而增加，到150m处左右达到最大，然后又逐渐降低，发生明显的垂直变。(2)岳麓山空气负离子和空气清洁度在下雨前后明显不同，下雨后山上的空气负离子含量显著增加，空气的清洁程度也明显提高。(3)岳麓山上非景点区的空气负离子含量和空气清洁度要高于景点区。(4)不同功能区的空气负离子含量和空气清洁度差别显著，其大小依次为：河岸＞风景区＞商业广场＞办公室＞交通干线＞车站广场。     

基于多方位DEM地形晕渲的黄土地貌正负地形提取

以陕北绥德县韭园沟流域5 m分辨率DEM数据为基础,在数字地形分析、多元统计和数据挖掘方法的基础上,提出利用多方位DEM地形晕渲、坡度等多元指标,以主成分分析消除多重共线性和约减维数,并以Logis-tic回归模型提取黄土高原正、负地形的方法。研究结果表明:模型提取精度为82.1%,Kappa统计量为0.629;模型在6个不同流域测试样本上正、负地形的平均精度分别为77.6%,84.9%,加权平均精度为81.3%,模型具有较好的一致性和泛化能力,正、负地形提取效果良好。     

Occurrence of negative epsilon in seismic hazard analysis deaggregation,and its impact on target spectra computation

This paper investigates circumstances behind the occurrence of negative ε (the normalized difference between the spectral acceleration of a recorded ground motion and the median response predicted by a ground motion prediction equation) in probabilistic seismic hazard deaggregation. Negative ε values are of engineering interest because of their impact on the conditional mean spectrum (CMS), which is a proposed alternative to the uniform hazard spectrum (UHS) as a target spectrum for ground motion selection. In the case where target ε values from deaggregation are positive, the CMS calculation produces relatively lower response spectra than the UHS. Positive target ε values occur almost universally in active seismic regions at long return periods of engineering interest, but the possibility of negative target ε values is important because in the case of negative target ε, some relationships between the CMS and UHS would reverse. This paper describes the calculation of target ε, performs parametric studies to determine when negative ε values occur in deaggregation, and investigates the potential impact on target spectrum calculation and ground motion selection. The case studies indicate that special seismicity models and certain ground motion prediction equations have the most significant effect on ε values and a combination of these characteristics in Eastern North America creates the most likely situation for negative target ε to occur. CMS results are nonintuitive when the target ε is negative, but it is not clear that this is a common practical concern because negative target ε occurs only in well‐constrained areas. Copyright © 2011 John Wiley & Sons, Ltd.     

负摩阻力的概念与案例分析

负摩阻力在岩土工程领域中占有重要的地位，在工程实践中特别是桩基工程中，负摩阻力日益受到重视。近几年全国注册土木工程师专业案例考试中不断有关于负摩阻力的试题出现，只有正确地理解负摩阻力的概念，深刻领会《建筑桩基技术规范》（JGJ94—94）的相关规定，明确负摩阻力产生的条件，掌握负摩阻力及下拉荷载的计算步骤，在注册考试中合理应用计算公式得到正确的结果。通过对三个关于负摩阻力案例的分析，明确了各种类型习题的关键所在，为以后的应试和工程实践打下良好的基础。     

新一轮区域规划若干问题探讨

对新规划理念与方法的应用、区域规划的空间尺度选择与规划重点、区域协调发展的空间管治分区与功能定位、空间发展模式的多样性选择以及各种规划间的关系如何衔接等问题进行探讨,认为新一轮区域规划应革新理念,坚持以“科学发展观”为指导思想,借鉴“反规划”方法,实行弹性规划期限;以县域规划作为基本规划单元,开展村镇小区域规划和城市群大区域规划;合理确定空间管治的分区与功能定位,选择多样性空间发展模式,完善区域规划体系,以理顺各种规划关系并提高规划的总体效用。     

考虑东北航线的亚欧LNG运输发展潜力研究

北极海冰的加速消融为北极航线的开发利用带来了机遇,北极地区的经济价值凸显。北极东北航线为亚欧间的LNG运输提供了新的运输通道。为使亚欧间的LNG运输更为经济合理,基于海运里程和单船必要运费率两方面比较通过北极东北航线、苏伊士运河航线、好望角航线进行跨亚欧LNG运输的经济性。在此基础上,采用负指数网络配流方法计算不同路径的配流比例,研究东北航线的亚欧间LNG运输发展潜力。结果表明,整体而言,采用东北航线进行跨亚欧LNG运输的海运里程更短,单船必要运费率更低,配流比例更高,其中,日本袖浦使用东北航线的经济性最为显著。将跨亚欧LNG运输通道的经济性分析和交通分配相结合,为亚洲地区更为经济合理地进行LNG运输提供参考。