Mass segregation in young stellar clusters

We investigate the evolutionary effect of dynamical mass segregation in young stellar clusters. Dynamical mass segregation acts on a time-scale of order the relaxation time of a cluster. Although some degree of mass segregation occurs earlier, the position of massive stars in rich young clusters generally reflects the cluster's initial conditions. In particular, the positions of the massive stars in the Trapezium cluster in Orion cannot be due to dynamical mass segregation, but indicate that they formed in, or near, the centre of the cluster. Implications of this for cluster formation and for the formation of high-mass stars are discussed.     

An integrated wavelet concept of physical geodesy

For the determination of the earth's gravity field many types of observations are nowadays available, including terrestrial gravimetry, airborne gravimetry, satellite-to-satellite tracking, satellite gradio-metry, etc. The mathematical connection between these observables on the one hand and gravity field and shape of the earth on the other is called the integrated concept of physical geodesy. In this paper harmonic wavelets are introduced by which the gravitational part of the gravity field can be approximated progressively better and better, reflecting an increasing flow of observations. An integrated concept of physical geodesy in terms of harmonic wavelets is presented. Essential tools for approximation are integration formulas relating an integral over an internal sphere to suitable linear combinations of observation functionals, i.e. linear functionals representing the geodetic observables. A scale discrete version of multiresolution is described for approximating the gravitational potential outside and on the earth's surface. Furthermore, an exact fully discrete wavelet approximation is developed for the case of band-limited wavelets. A method for combined global outer harmonic and local harmonic wavelet modelling is proposed corresponding to realistic earth's models. As examples, the role of wavelets is discussed for the classical Stokes problem, the oblique derivative problem, satellite-to-satellite tracking, satellite gravity gradiometry and combined satellite-to-satellite tracking and gradiometry. Received: 28 February 1997 / Accepted: 17 November 1997     

L1估计的分布及统计性质

推导了Ｌ１估计的密度函数,讨论了Ｌ１估计的统计性质,证明Ｌ１估计是无偏估计,同时还证明Ｌ１估计优于ＬＳ估计。     

格运算的扩张定理与落影函数定理

讨论了格上可测结构的封闭性以及此结构上落影函数的有关问题。指出并证明了逐次扩张与同时扩张的充要条件 ,以及落影函数与模糊集的关系     

三维空间实体间拓扑关系的矩阵描述

三维空间实体及其间拓扑关系的语义描述和形式化表达是三维ＧＩＳ空间数据建模的重要理论基础。在ｋ－维流形的三维空间实体形式化描述方法的基础上,根据三维空间实体的可剖分性,采用顾及维数的九元组描述框架,研究用于构成三维实体的ｋ－单纯形（０≤ｋ≤３）之间的拓扑空间关系,继而研究三维实体间的拓扑空间关系。     

高温高压下水的剪切粘滞度的平衡分子动力学计算

本项工作用ＴＩＰ４Ｐ模型对水分子进行了平衡分子动力学模拟。根据Ｇｒｅｅｎ－Ｋｕｂｏ理论,计算了温度从６５２Ｋ到８１４Ｋ,密度从０．５３６０ｇ／ｃｍ３到０．８６３８ｇ／ｃｍ３六个不同温度和密度水的剪切粘滞度,并和实验值进行了对比。在所计算的温度和密度范围,平衡分子动力学计算结果与实验值的平均绝对值差别为１５％,好于使用非平衡分子动力学方法获得的粘滞度值。平衡分子动力学的方法将是获得地学中高温高压下流体输运性质的重要途径。     

统一分布下的LP估计抗差测度

本文根据定位参数Ｍ估计理论,导出了ＬＰ估计的影响函数,分析了ＬＰ估计的抗差能力,同时还推导了ＬＰ估计的渐近效率,综合抗差能力和效率,分析了ＬＰ估计的优劣性,明确指出,用现测数据中含有粗差扰动的数据和Ｐ为（１,１．２５）的ＬＰ估计进行处理,结果较优,效率较高。     

Accounting for Estimation Optimality Criteria in Simulated Annealing

This paper presents both estimation and simulation as optimization problems that differ in the optimization criteria, minimization of a local expected loss for estimation and reproduction of global statistics (semivariogram, histogram) for simulation. An intermediate approach is proposed whereby an initial random image is gradually modified using simulated annealing so as to better match both local and global constraints. The relative weights of the different constraints in the objective function allow the user to strike a balance between smoothness of the estimated map and reproduction of spatial variability by simulated maps. The procedure is illustrated using a synthetic dataset. The proposed approach is shown to enhance the influence of observations on neighboring simulated values, hence the final realizations appear to be better conditioned to the sample information. It also produces maps that are more accurate (smaller prediction error) than stochastic simulation ignoring local constraints, but not as accurate as E-type estimation. Flow simulation results show that accounting for local constraints yields, on average, smaller errors in production forecast than a smooth estimated map or a simulated map that reproduces only the histogram and semivariogram. The approach thus reduces the risk associated with the use of a single realization for forecasting and planning.     

Closed Form Solutions of the Two-Dimensional Turning Bands Equation

The turning bands method generates realizations of isotropic Gaussian random fields by means of appropriately summed line processes. For two-dimensional simulations the relation between the isotropic correlation function of the random field and the correlation function to be simulated along the lines is given by an integral equation of Abel type. We present closed form solutions of this integral equation for almost all two-dimensional correlation models encountered in practice and discuss their numerical implementation. As an additional benefit, our tables and illustrations serve as a concise guide to correlation models useful in geostatistics.