Another Look at the Chemical Relationships in the Dissolved Phase of Complex River Systems

Large rivers are a major pathway for the erosion products of continents to reach the oceans. The riverine transport of dissolved and particulate materials is generally related to a large number of interactions involving climate, hydrological, physico-chemical and biological aspects. Consequently, the investigation of large rivers allows the erosion processes at a global scale to be addressed, with information about biogeochemical cycles of the elements, weathering rates, physical erosion rates and CO₂ consumption by the acid degradation of continental rocks. Today, good databases exist for the major dissolved ions in the world’s largest rivers. Since concentration of ions in river waters has to be considered in a compositional context, it is necessary to study the implications of considering the simplex, with its proper geometry, as the natural sample space. Using the additive (alr) or the isometric (ilr) log-ratio transformations, a composition can be represented as a real vector; but only in the second case can these coordinates be mapped onto orthogonal axes. Using data related to the dissolved load of some of the most important rivers in the world, the relationships among the major ions frequently used in molar ratio mixing diagrams have been investigated with alternative tools. Following the balances approach, an investigation of the properties of aqueous solutions of electrolytes that are often treated in terms of equilibrium constants is undertaken. The role played by the source—rain water, weathering of silic, carbonatic and evaporitic rocks, pollution—from which elements and chemical species can potentially be derived, has been checked through an investigation of a probabilistic model able to describe the relationships among the different components that contribute to the chemical composition of a river water sample.     

A spatial co-location mining algorithm that includes adaptive proximity improvements and distant instance references

Spatial co-location pattern mining is employed to identify a group of spatial types whose instances are frequently located in spatial proximity. Current co-location mining methods have two limitations: (1) it is difficult to set an appropriate proximity threshold to identify close instances in an unknown region, and (2) such methods neglect the effects of the distance values between instances and long-distance instance effects on pattern significance. This paper proposes a novel maximal co-location algorithm to address these problems. To remove the first constraint, the algorithm uses Voronoi diagrams to extract the most related instance pairs of different types and their normalized distances, from which two distance-separating parameters are adaptively extracted using a statistical method. To remove the second constraint, the algorithm employs a reward-based verification based on distance-separating parameters to identify the prevalent patterns. Our experiments with both synthetic data and real data from Beijing, China, demonstrate that the algorithm can identify many interesting patterns that are neglected by traditional co-location methods.     

Voronoi Diagrams and Spatial Analysis of Crime

A range of spatial analyses are used in the field of crime mapping, such as kernel density estimation, Ripley's K-function, and spatial autocorrelation, but there is limited use of Voronoi diagrams (VDs). The goal of this article is to contribute to the spatial analysis of crime through the use of VDs. We use four years of commercial robbery data from Campinas, Brazil, and employ several VD techniques: (1) We analyze crime concentrations through the properties of VDs—area and number of vertices—and coverage curve; (2) we introduce a new crime geovisualization with VD in three dimensions; and (3) we apply a network VD technique to crime analysis. The results demonstrate associations between these VD techniques and the ability of the researcher to recognize crime patterns associated with crime concentration, crime along pathways, and the highly regularized distribution of crime in limited areas spatially.     

克服双重约束的面目标位置聚类方法

面目标的聚集模式识别是空间聚类研究的重要方向之一,但因多边形几何信息和空间障碍阻隔的双重约束,目标的位置相似性难以快速而准确地计算。扩展点目标多尺度聚类方法,通过构建面目标的强度函数计算目标与邻近目标的位置聚集程度,提出了有效作用于双重约束下的面目标位置聚类法,并以判断相邻尺度下同一面目标类的强度函数阈值相等作为算法的收敛条件。经试验分析与比较发现,算法无须自定义参数,能够识别密度不均、任意形状分布,以及"桥"链接的面目标集群,同时能够准确判断障碍约束对面目标簇的阻隔和划分。     

数字海图水深注记的自动选取

水深注记作为表示海底地形地貌特征的主要制图要素,它的正确选取对于保证航海安全、反映海底地貌起伏具有重要意义。针对传统的水深注记方法,该文提出一种顾及多重约束条件的水深注记选取方法。在总结水深注记综合约束条件基础上,以Vononoi图为支撑几何构造,对水深注记综合涉及的地形特征、空间分布特征、邻近特征3个方面的综合约束进行了形式化定义;借鉴人工选取的思想,在水深综合约束条件重要性排序的基础上,通过反映地形、空间分布、邻近关系等主体特征的重要水深的依次选取,以及背景水深的抽稀实现水深注记选取;最后以实测数据进行实验,验证该方法的有效性。     

Diagrammatic solutions for hydraulic head moments in 1-D and 2-D bounded domains

We present a diagrammatic method for solving stochastic 1-D and 2-D steady-state flow equations in bounded domains. The diagrammatic method results in explicit solutions for the moments of the hydraulic head. This avoids certain numerical constraints encountered in realization-based methods. The diagrammatic technique also allows for the consideration of finite domains or large fluctuations, and is not restricted by distributional assumptions. The results of the method for 1-D and 2-D finite domains are compared with those obtained through a realization-based approach. Mean and variance of head are well reproduced for all log-conductivity variances inputted, including those larger than one. The diagrammatic results also compare favorably to hydraulic head moments derived by standard analytic methods requiring a linearized form of the flow equation.     

Location-based anonymization: comparison and evaluation of the Voronoi-based aggregation system

Hospitals and health care organizations collect large amounts of detailed health care data that is in high demand by researchers. Thus, the possessors of such data are in need of methods that allow for this data to be released without compromising the confidentiality of the individuals to whom it pertains. As the geographic aspect of this data is becoming increasingly relevant for research being conducted, it is important for an anonymization process to pay due attention to the geographic attributes of such data. In this paper, a novel system for health care data anonymization is presented. At the core of the system is the aggregation of an initial regionalization guided by the use of a Voronoi diagram. We conduct a comparison with another location-based system of anonymization, GeoLeader. We show that our system is capable of producing results of a comparable quality with a much faster running time.     

障碍空间最大空隙的地图代数解法MA-MAXG(Ω)

对欧氏障碍空间最大空隙问题MAXG（Ω）进行了分析，并运用地图代数理论对其进行了阐述，利用距离变换和全形态图形Voronoi图生成并取其最大值点。实验表明，本文算法可无显著困难地扩展为三维与加权距离。     

基于二十面体剖分格网的球面实体表达与Voronoi图生成

在分析当前球面空间数据结构的基础上，讨论了利用Snyder等积投影在二十面体上建立球面空间基础剖分方式的思路，然后在初始投影面上采用六边形格网进行层次细分，获得多分辨率的全球铺盖。提出了基于六边形格网的三叶节点管理与瓦片编码的基本思路，确立了球面不同实体的六边形格网表达模式。在此基础上，提出了基于球面六边形铺盖的Voronoi图生成算法，实验验证了算法的正确性与效率。     

Subduction-related P–T path for eclogites and garnet glaucophanites from the Samaná Peninsula basement complex, northern Hispaniola

Eclogite and garnet glaucophanite lenses from the Punta Balandra unit of the Samaná basement complex (northern Hispaniola) preserve information of the early metamorphic and tectonic history of subduction in the Caribbean island-arc and its collision with the North America plate. For this reason, P–T paths were reconstructed from the interpretation of meso- and microfabrics, mineral assemblages and chemistry, with the aid of equilibrium phase diagrams calculated for specific bulk compositions in the CKNFMASH system and isopleths for selected solution end-members. The obtained results suggest that the subduction-related prograde path evolved from garnet-free and garnet-bearing lawsonite-blueschist facies, to phengite eclogite facies conditions at P=22–24 kbar and T=610–625°C, with a probable intermediate stage of low-P lawsonite eclogite facies. The subsequent retrograde P–T path entered the epidote-blueschist (garnet-free) facies and ended within the greenschist facies field, similar to the prograde evolution at low-P. Eclogites and garnet glaucophanites formed in a subduction zone in which oceanic lithosphere was subducted WSW/W beneath the Caribbean plate.