Institutionalization of Racial Inequality in Local Political Geographies

Municipalities create a local political geography that can institutionalize subordinate positions for minority groups. Most importantly, local governments determine which areas are incorporated into a municipality through annexation and which are excluded. Through these powers, local governments can diminish or deny minority political standing in local affairs, limit access to public services, and reduce the value of minority property. The boundaries are a component of racial residential segregation. Racially disparate application of local governments' power to shape local political geography creates barriers to equality that are difficult to discern on the ground, but which can be made visible by the mapping of spatial data. This study presents four cases where governmental decisions concerning a municipal boundary have institutionalized racial inequality, which is documented with maps created from public GIS data and other public records (e.g., City Council meeting minutes) as well as legal documents. This pattern of systematic exclusion of minority neighborhoods is receiving attention in the legal community, but studies in the social sciences have been limited.     

Mathematical Analysis of a Model of River Channel Formation

The study of overland flow of water over an erodible sediment leads to a coupled model describing the evolution of the topographic elevation and the depth of the overland water film. The spatially uniform solution of this model is unstable, and this instability corresponds to the formation of rills, which in reality then grow and coalesce to form large-scale river channels. In this paper we consider the deduction and mathematical analysis of a deterministic model describing river channel formation and the evolution of its depth. The model involves a degenerate nonlinear parabolic equation (satisfied on the interior of the support of the solution) with a super-linear source term and a prescribed constant mass. We propose here a global formulation of the problem (formulated in the whole space, beyond the support of the solution) which allows us to show the existence of a solution and leads to a suitable numerical scheme for its approximation. A particular novelty of the model is that the evolving channel self-determines its own width, without the need to pose any extra conditions at the channel margin.     

弹性波正演模拟中PML吸收边界条件的改进

在弹性波有限差分正演模拟中, 完全匹配层(PML) 吸收边界条件是使用广泛、吸收效果最好的吸收边界条件.在目前的两种PML实现方法中, 分裂形式的完全匹配层(SPML) 方法计算存储量大、编程实现复杂; 非分裂形式的完全匹配层(NPML) 方法计算效率低、计算过程复杂.针对传统PML吸收边界条件在实现过程中存在的问题, 推导出了一种简洁有效的非卷积实现的NPML吸收边界条件, 既不需要对场分量进行分裂, 也不需要做复杂的卷积运算.分析结果表明, 本文实现的NPML吸收边界条件不仅具有良好的吸收衰减性能, 而且计算方程简单, 编程实现容易, 占有内存更小.      

大陆盆地的聚敛-闭合过程研究:以塔里木盆地为例

印度与欧亚大陆第三纪以来碰撞汇聚,造成亚洲大陆内部强烈缩短变形。塔里木盆地如何发生相应的变形调节和应变分解,成为中亚板内构造的重要问题。塔里木陆块新生代以来被板内造山带及走滑断裂系环绕,盆地内部以刚性为特征,未发生强烈构造变形。区域大断裂与塔里木盆地的冲断、走滑构造边界共同作用,形成盆地边缘复杂的构造系。其新生代构造变形主要集中于盆地的构造边界上,4条构造边界显示差异性的运动特征和构造交切关系。盆地边缘构造带叠加并向盆内扩展,造成盆地总体上水平缩短,并发生应变分解。盆地内部发生沉积-构造分异,发育前陆盆地、前缘隆起、复合前陆盆地、拉分盆地等单元。其中,盆地西北缘及西南缘发生陆内俯冲,形成前陆盆地及前陆冲断带,对盆内构造演化有重要影响。区域构造研究表明,塔里木盆地新生代主要发生了4期区域构造变形,第三纪以来还发生顺时针旋转。大陆盆地构造边界上的运动组合、盆内不均匀阻挡和滑脱拆离,造成其变形扩展方式的差异,并影响盆内单元构造演化。因此,塔里木盆地是认识大陆盆地聚敛与闭合过程的天然实验室。     

Significance of ichnofossils to genetic stratigraphy--Examples from the Cretaceous of Alberta, Canada

Trace fossils represent both sedimentological and paleontological entities, representing a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition of various discontinuity types and to assist in their genetic interpretation. Ichnology may be employed to resolve surfaces of stratigraphic significance in two main ways: 1) through the identification of discontinuities using substrate-controlled ichnofacies, and 2) through careful analysis of vertical softground (penecontemporaneous) ichnologic successions (analogous to facies successions). Ichnological analysis is a valuable tool in genetic stratigraphic studies. Integrating the data derived from substrate-controlled ichnofacies with paleoecological data from vertical ichnologic successions greatly enhances the recognition and interpretation of a wide variety of stratigraphic surfaces. When this is coupled with conventional facies analysis and sequence stratigraphy, a powerful approach to the interpretation of the rock record is generated.     

Reconstructing fluvial bar surfaces from compound cross‐strata and the interpretation of bar accretion direction in large river deposits

The interpretation of fluvial styles from the rock record is based for a significant part on the identification of different types of fluvial bars, characterized by the geometric relationship between structures indicative of palaeocurrent and surfaces interpreted as indicative of bar form and bar accretion direction. These surfaces of bar accretion are the boundaries of flood‐related bar increment elements, which are typically less abundant in outcrops than what would be desirable, particularly in large river deposits in which each flood mobilizes large volumes of sediment, causing flood‐increment boundary surfaces to be widely spaced. Cross‐strata set boundaries, on the other hand, are abundant and indirectly reflect the process of unit bar accretion, inclined due to the combined effect of the unit bar surface inclination and the individual bedform climbing angle, in turn controlled by changes in flow structure caused by local bar‐scale morphology. This work presents a new method to deduce the geometry of unit bar surfaces from measured pairs of cross‐strata and cross‐strata set boundaries. The method can be used in the absence of abundant flood‐increment bounding surfaces; the study of real cases shows that, for both downstream and laterally accreting bars, the reconstructed planes are very similar to measured bar increment surfaces.     

惠民凹陷唐庄地区沙河街组层序地层和沉积相

针对研究区的区域地质概况,并借鉴了前人的研究成果,利用地震和测井资料识别出了三级层序边界,并对各层序进行了体系域划分,建立了研究区的等时地层格架。在此基础上,通过对岩芯和测井相的综合分析,以体系域为单位进行了沉积相的划分,建立了研究区的精细沉积相模型,并对沉积相的展布特征进行了分析。     

上海城市二氧化碳排放空间特征

构建上海1 km CO₂排放网格,分析市域（UB1）、市辖区（UB2）、建成区（UB3）和城区（UB4）4个城市范围的CO₂排放特征。上海市域CO2排放空间格局是以中心城区为核心,排放水平向外递减,形成了3个梯度。空间自相关分析表明,排放在空间上存在显著的集聚效应,部分地区高强度的经济活动和能源活动对周边区域的排放有显著影响。UB4是上海城市的最佳表征,2007年UB4内CO₂排放达到1.89亿t,人均排放12.04 t;UB4排放占UB1排放的75.40%,UB1人均排放比UB4人均排放高12%。上海城市化和工业化在空间上的高度重合,导致高排放源集聚于UB4内,形成UB4的高排放特征。个别网格的排放量已经占到区域或者城市总排放量的10%～20%;前10高和前100高排放网格,其累积排放总量分别占据了3个城市范围（UB1、UB3和UB4）总排放量的60%和80%以上。