Spatial statistics: Marks,maps, and shapes

ABSTRACT

Spatial statistics is concerned with phenomena unfolding in space and possibly also evolving in time, expressing a system of interactions whereby an observation made at a (spatiotemporal) location is informative about observations made at other locations. In general, the interactions are best described probabilistically, rather than deterministically. Spatial scales range from the microscopic (for example, when describing interactions between molecules of a liquid) to planetary (for example, when studying the Earth’s ozone layer) or even larger; temporal scales are similarly varied.

Marks indicate objects whose spatial locations are influenced by the presence and nature of other objects nearby: trees of the same or different species in a grove, molecules in a liquid, or galaxies throughout the universe. The statistical models are (marked) spatial point processes.

Maps describe the variability of the values of a property across a geographical region. The Ising model of ferromagnetism describes collective properties of atoms arranged in a regular lattice. When mapping the prevalence or the incidence of a disease at the level of counties or parishes, the observations are associated with subsets of a region whose spatial relations are meaningful. Many maps are drawn based on observations made at a finite set of locations distributed either regularly or irregularly throughout a 2D or 3D spatial domain. For example, the mass fraction of uranium in soils and surface sediments across Colorado. Gaussian random functions are a model of choice for such quantities, possibly after re-expression.

Shapes arise owing to modulated interactions between surface elements anchored to points in space — “generators” in the nomenclature of Ulf Grenander’s pattern theory. Probability distributions on spaces of generators and on spaces of interactions between them can then be used to describe variations on patterns and to fit shape models.     

长兴电厂粉煤灰的微量元素含量及其安全性评价——长兴电厂粉煤灰综合利用对策研究之二

利用VF-320型X射线荧光光谱仪(XRFS)对长兴电厂粉煤灰中有毒、有害微量元素及放射性元素含量进行了测试。结果表明,大部分微量元素及放射性元素都有在细粒径粉煤灰中富集的趋势。该电厂粉煤灰中有毒、有害元素的含量不高,只要施用量不超过8654kg/亩(129810kg/公顷),用作土壤改良剂或肥料,不会对农作物造成危害;若用于生产建材,只要将掺量控制在总量44%内,建材制品的放射性防护也是安全的。     

Fischer-Tropsch synthesis with an iron catalyst: Incorporation of ethene into higher carbon number alkanes

Tracer studies with C labeled ethene show that for synthesis over a doubly promoted iron catalyst at 7 atm and ca. 60% CO conversion, higher carbon number products are formed from ethene initiation. About 10% of the added ethene (ethene/CO 0.02) is incorporated into C ₅ ⁺ products and that ca. 85% of the ethene that is incorporated does so by initiating chain growth.     

The Level of Trace Elements in Tripoli City Groundwater

Abstract

Groundwater samples from different regions of Tripoli city (Libya) were analyzed for environmental control purposes. The concentrations of several trace elements (As, B, Ba, Be, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Sb, Sr, and Zn) were determined by means of ICP‐OES and AAS methods. The obtained results were also compared with the European and Canadian standards, as well as with the Egyptian ground, Nile, and drinking water concentrations. As a result, the detected elements were classified into three different groups. The first group of elements, (Na and Sr) was found to have high concentrations. The second group of elements, (Ba, B, Ca, Cr, Cu, K, Li, Mg, and Zn) had comparable concentrations. The third group of elements, (As, Cd, Fe, Mn, and Sb), showed low concentrations. The observed high concentrations of some elements, in particular Sr, and the lower concentrations of the others, such as Fe and Mn are relevant to their levels in Tripoli city soils. In addition to the above elements, some inorganic ions, (NH₄ ⁺, NO₂ ^?, and NO₃ ^?) were also detected using ion chromatography (IC). The elevated concentration of NO₃ ^? is mainly due to various industrial activities, the use of fertilizers, and/or pollution from sewage. The concentration of the other inorganic ions, (NH₄ ⁺, NO₂ ^?) was found to be within the international standard limits. The natural radioactivity in the samples has also been investigated using γ‐spectrometry and was found to be very low.     

冷凝氡源的α能谱特性与活度计算方法研究

基于中国计量科学研究院建立的小立体角氡绝对测量装置,研究了冷凝氡源的α能谱随冷凝室内真空压力和冷指温度的变化特性,介绍了在少量杂质气体不可避免地被引入冷凝室、导致氡源能谱分辨率变化的情况下,如何计算冷凝氡源活度的方法.实验结果表明:氡源冷凝之后,杂质气体随时间逐渐增加会导致能谱分辨力变差,根据氡与子体衰变特性所建立的计算方法计算氡活度,得到连续5h的重复测量结果的一致性在0.45％以内,这对氡源活度的国际比对及量值传递具有重要意义.     

核辐射测井中的Monte Carlo数值模拟

数值模拟技术为核辐射测井的研究提供了新的思想方法和工作方法,大大提高核辐射测井的研究水准.在核辐射测井的数值模拟技术中,Monte Carlo模拟技术是应用最为成功的技术之一.本文根据多年的核辐射测井研究得出,Monte Carlo数值模拟技术可以应用于核辐射测井基本物理问题,方法的可行性、仪器物理设计、新应用方法和算法研究、测井解释模型建立、校正图版制作等方面.Monte Carlo数值模拟技术为核辐射测井方法的研究带来崭新空间.     

γ射线探伤作业中的安全防护

以崖城13-1气田陆地处理厂工程施工为例,介绍用γ射线探伤所应采取的防护措施,以确保操作人员的安全。     

Experimental Verification Study for System for Prediction of Environmental Emergency Dose Information: SPEEDI, (II)

The performance of a computational model to simulate an accidental release of radioactivity into the atmosphere was evaluated by data sets from field tracer experiments over an isolated mountain. This model consists of a mass-consistent model for wind-fields and a particle random-walk model for atmospheric dispersion.

Model simulations of tracer concentrations were compared with observed values from twelve experiments. The computed results agree reasonably with observed concentration patterns and achieve an agreement within a factor of 10 for 50% of the samples.     

塔设备故障诊断γ射线扫描检测技术的开发

长岭炼油化工有限责任公司和石油大学(北京)共同研制开发的用于工艺塔故障诊断的γ射线扫描检测系统由硬件和软件两部分组成，其中硬件包括射线源、探测器、移动机构、射线扫描仪及计算机，软件有数据采集和系统控制软件。该系统在工业应用中快速、准确地诊断出了精馏塔运行中存在的一些故障，如浮阀掉落故障、液泛故障和雾沫夹带故障等，为优化操作条件、延长操作周期和设备检修提供了科学依据。     

Uncertainty in radon measurements with CR39 detector due to unknown deposition of Po

Uncertainty in radon measurements using the CR39 solid-state nuclear track detector in chambers is introduced by the unknown fraction f₁ of ²¹⁸Po that deposited onto the inner chamber walls. This uncertainty was estimated for cylindrical chambers with different size in the present study. It was found that the uncertainty increased with the chamber height and radius. For short chambers with a height H=2 cm the uncertainty was less than 5%, while in tall chambers with H=7 cm it could be up to 17%. The radial track density on the CR39 detector inside the diffusion chamber was also found to be dependent on the fraction f₁. In this work, some examples of this dependence are shown.