Structure of flow over alluvial bedforms: an experiment on linking field and laboratory methods

This paper presents results of a field study designed to examine the structure of flow over mobile and fixed bedforms in a natural stream and to compare the results with findings of previous laboratory studies within the framework of double time–space averaging approach. Measurements of turbulence were obtained in a small river in Illinois, USA, over a fine spatial grid of sampling points above a mobile sandy bedform and its artificially moulded replica. Flow structure over the artificial bedform is similar to that observed in laboratory studies, but is markedly different from the flow structure over natural bedforms. These differences are most pronounced in the roughness sublayer, whereas flow in the logarithmic layer over natural and artificial sand waves is fairly similar and exhibits spatial uniformity. The double time–space averaged distributions of turbulence statistics conform to the multilayer model of flow structure over bedforms. Mean velocity distributions indicate neither classical flow recirculation nor substantial reduction of velocities in the lee of bedform crests. However, vertical patterns of turbulence statistics over depth suggest that stacked wakes similar to those observed in laboratory studies exist above the bedforms. Thus, despite the absence of flow separation, wake development seems to be induced by the systematic influence of upstream bedforms on the vertical structure of turbulence. Copyright © 2006 John Wiley & Sons, Ltd.     

基于面向对象和规则的遥感影像分类研究

讨论了面向对象和规则的光学遥感影像分类方法。首先利用多尺度分割形成影像对象，建立对象的层次结构，计算对象的光谱特征、几何特征、拓扑特征等，利用对象、特征形成分类规则，并通过不同对象层间信息的传递和合并实现对影像的分类。并以北京城市土地利用分类为例，对该方法进行了验证。     

相空间地震波初至时刻拾取

提出了一种新的地震波初至时刻拾取的方法,即将原始时间序列信号映射到相空间当中,通过其相空间图的特征进行初至时刻的拾取。相对于非常耗时的传统方法,本方法使得运算速度提高,结果更加精确稳定。     

城市地质学发展前景展望

本文介绍了城市地质学的定义和研究内容,对国外、国内城市地质学发展历史进行了述评,对城市地质学的发展前景进行了展望。     

测高数据处理中网格化问题的探讨

本文从卫星测高数据处理中网距的选取、数据点的图形结构、网格算子等三个方面加以讨论,提出了频域中数据网格化的方法,最后利用两个周期的Topex/Poseidon卫星测高数据进行计算分析,得出了一些卫星测高数据网格化的经验。     

A GEOMETRIC ALGORITHM FOR TILTED-CAMERA PERSPECTIVE PROJECTION AND THE COMPARISON WITH EXTERNAL PERSPECTIVE PROJECTION

A geometric algorithm for Tilted-Camera Perspective（TCP）projec-tion is proposed in this paper based on the principle of perspective projection.Ac-cording to that,the difference between TCP projection and External Perspective（EXP）projection is analyzed.It is put forward prerequisites making these twoprojections were compatible,and some examples are given.     

长波辐射时空序列剖面中震兆特征的研究

做出了３２°～４０°Ｎ,８９°～１０５°Ｅ范围内各经纬度结点１９８９年７月～１９９６年１２月长波辐射（ＯＬＲ）月距平值曲线．将各结点的曲线图按经纬度排列起来,构成ＯＬＲ时空序列剖面图．根据对这些剖面图的分析,研究了强震前ＯＬＲ的变化特征．结果表明,强震前１～４个月震中附近结点ＯＬＲ曲线变化出现异常,表现为反向变化或振荡型．有的地震前异常的空间展布呈条带状．     

华中华东地区上空水汽平衡状况

华中华东地区,为我国纬度较低,涨岸线最长的地区。该区雨水资源,地表水资源量均居全国之首。其维系因子－空中水汽,业经本文计算,其年总蓄留量＋１９７７４．５４亿ｍ＾３,相当水深１３９７ｍｍ,为水资源总量的１．７６倍,全国第一。     

Opportunities, constraints and pluriactivity in rural Romania during the transition period; preliminary observations

This paper presents some initial implications of the changes brought about by recent economic transformations within the Romanian rural sector during the current transition period. As a case study of those trends, within the context of pluriactivity and constraints to rural development, it looks at some characteristics of agricultural production in the Subcarpathian region of the county of Valcea, an area where collectivisation, and thus its influences, had been partial and limited. The paper links micro and macro view points. At the micro level, it looks at the coping strategies, based on pluriactivity, adopted by rural households under changing economic conditions. At the macro level, the paper discusses some of the possible factors supporting as well as hindering rural welfare levels and agricultural development under current economic conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

MAP /GIS的简介及其在地质研究中的应用分析

本文概要介绍了MAP /GIS系统的构成、功能特点及适用范围,并着重分析了MAP /GIS系统中的空间分析和地图编辑功能在地质研究中的实际应用和发展前景,以便拓宽地质研究视野,为地质研究人员提供先进的信息处理、综合研究、 综合循环开发手段和工具,提高科研效率并促进地质科学的发展。