应变组合的地质意义及其分解实例

以分析递进变形序列为主线,论述了主有限应变和增量应变的内部旋转所组合的应变扇形区的空间展布。结合发育于剪切带中的一个微细粒浸染型金矿的找矿实际,指出该理论的野外应用方法。     

Composite suspended sediment particles in river systems: their incidence,dynamics and physical characteristics

Most of the existing data on the effective particle size characteristics of fluvial suspended sediment derive from instantaneous sampling methods that may not be representative of the overall suspended sediment loads. This presents difficulties when there is a need to incorporate effective particle size data into numerical models of floodplain sedimentation and sediment‐associated contaminant transfer. We have used a field‐based water elutriation apparatus (WEA) to assemble a large (36 flood) database on the time‐integrated nature of the effective and absolute particle size characteristics of suspended sediment in four subcatchments of the River Exe basin of southwest England. These catchments encompass a wide range of terrains and fluvial environments that are broadly representative of much of the UK and temperate, low relief northwest Europe. The WEA provides important data on the physical characteristics of composite particles that are not attainable using other methods. This dataset has allowed, for the first time, detailed interbasin comparisons of the time‐integrated particle size characteristics of suspended sediment and reliable estimates of the contribution of five effective size classes to the mean annual suspended sediment load of the study catchments. The suspended sediment load of each river is dominated by composite rather than primary particles, with, for example, almost 60% (by mass) of the sediment load of the River Exe at Thorverton transported as composite particles > 16 µm in size. All the effective size classes contain significant clay components. A key outcome of this study is the recognition that each catchment has a distinctive time‐integrated effective particle size signature. In addition, the time‐integrated effective particle size characteristics of the suspended loads in each of the catchments display much greater spatial variability than the equivalent absolute particle size distributions. This indicates that the processes producing composite particles vary significantly between these catchments, and this has important implications for our understanding of the dynamics of suspended sediment properties. Copyright © 2007 John Wiley & Sons, Ltd.     

Conflation and aggregation of spatial data improve predictive models for species with limited habitats: A case of the threatened yellow-billed cuckoo in Arizona,USA

Riparian vegetation provides important wildlife habitat in the southwestern United States, but limited distributions and spatial complexity often leads to inaccurate representation in maps used to guide conservation. We test the use of data conflation and aggregation on multiple vegetation/land-cover maps to improve the accuracy of habitat models for the threatened western yellow-billed cuckoo (Coccyzus americanus occidentalis). We used species observations (n = 479) from a state-wide survey to develop habitat models from 1) three vegetation/land-cover maps produced at different geographic scales ranging from state to national, and 2) new aggregate maps defined by the spatial agreement of cover types, which were defined as high (agreement = all data sets), moderate (agreement ≥ 2), and low (no agreement required). Model accuracies, predicted habitat locations, and total area of predicted habitat varied considerably, illustrating the effects of input data quality on habitat predictions and resulting potential impacts on conservation planning. Habitat models based on aggregated and conflated data were more accurate and had higher model sensitivity than original vegetation/land-cover, but this accuracy came at the cost of reduced geographic extent of predicted habitat. Using the highest performing models, we assessed cuckoo habitat preference and distribution in Arizona and found that major watersheds containing high-probably habitat are fragmented by a wide swath of low-probability habitat. Focus on riparian restoration in these areas could provide more breeding habitat for the threatened cuckoo, offset potential future habitat losses in adjacent watershed, and increase regional connectivity for other threatened vertebrates that also use riparian corridors.     

国家测绘档案目录数据库升级迁移技术研究及实践北大核心CSCD

针对国家测绘档案目录数据分类多及历史原因造成的数据库欠缺整体规范性、无规范化空间定位索引等问题,为提高测绘档案的管理和服务效率,通过深入分析国家测绘档案目录数据特点、选取试验数据,规范化处理测绘档案目录数据、制作空间定位索引数据,采取渐进式测绘档案目录升级技术方案,在测绘档案业务管理系统开发建设的同时,顺利地实现了历史测绘档案目录数据的迁移和升级,避免了以往系统先建成而目录数据尚未完成迁移改造对测绘档案业务工作的影响。     

多尺度地图空间居民地语义相似度计算方法

地图综合的本质是一种空间相似变换,制图者在相似原则的指导下实施概括,读图者从包含相似性的地图中形成心象地图、重构现实世界。因此,多尺度地图空间中的相似关系研究非常重要。然而,由于相似的可计算性差,且其计算的目的在于揭示更深层次的信息,地图综合中相似关系尤其是语义相似关系的研究相对较少。针对这一问题,本文以语义功能区约束下的大比例尺街区式居民地合并（1∶1750至1∶4000）为例,基于匹配距离模型计算建筑物合并中的语义相似度,得到语义相似度在关键比例尺节点的值,并对结果进行分析、评价。试验表明,语义功能区约束下的建筑物合并符合读图者的地图认知需求,本文所述方法有助于地图更好地发挥信息传输载体的作用。     

考虑桩-土体系渐进破坏的单桩承载特性研究

针对目前桩基承载特性确定时未考虑桩-土体系渐进变形过程的现状,采用现场试验和理论分析等手段对考虑桩-土体系渐进破坏的单桩承载特性展开研究。首先,利用现场试验数据对侧阻和端阻的软化特性展开深入探讨,提出了侧阻和端阻软化模型,明确了模型中各参数取值方法,并验证了其合理性。同时,根据提出的侧阻和端阻软化模型,建立了一种可考虑桩-土体系渐进破坏的单桩承载特性的迭代算法。算例分析表明,计算获得的破坏性单桩承载特性与实测值有较好的一致性,且可反映侧阻和端阻的破坏特性。实际工程中,结合单桩承载特性分析算法,可根据单桩的实际受力特点灵活选用不同形式的侧阻和端阻荷载传递函数来分析不同桩顶荷载水平下的单桩受力特性。     

农村土地调查基本农田上图方法

土地是人类赖以生存和社会发展的物质基础,耕地是农业生产最基本、不可替代的生产资料。基本农田调查是农村土地调查最为重要的一个部分,基本农田上图工作对于政府部门制定土地政策、优化土地结构、保护耕地、提高耕地质量具有十分重要的意义。本文从基本农田概念的引入、基本农田上图技术流程、基本农田保护块上图以及图件编制、数据汇总几个方面阐述了农村土地调查基本农田的上图方法。     

洛川黄土地层渗透性与孔隙性的关系

本文用逐步回归分析方法对洛川黄土孔隙性诸要素进行了变量筛选,选出了影响渗透系数的孔隙要素,并建立了随机数学模型,定量解决了影响渗透系数的孔隙多少和孔隙形状问题,初步确定出了洛川黄土地层透水性与孔隙性的关系。     

Estimation of snow ablation under a dust layer covering a wide range of albedo

Ablation processes of snow under a thin dust cover are complicated compared with those under a thick cover, mainly owing to the effects of aggregation (redistribution) of dust particles on the conditions of surface melting. Aggregation of dust particles causes the snow surface to brighten after the initial dust configuration, thus affecting the relationship between initial dust concentration and surface albedo. In order to estimate snow ablation rate under a thin dust cover, we used a composite energy balance model in which the surface albedo is taken as a measured input variable. The estimated results of snow ablation agreed reasonably well with the observation, considering the measurement errors inherited in the snow depressions. Comparison of the two cases, that is, one considering the aggregation of dust particles (observation: albedo variable) and the other without aggregation (assumption: albedo constant), showed that the ablation rates were noticeably lower on the former case. This suggests that the aggregation of dust particles induces a reduction of snow ablation. Copyright © 2002 John Wiley & Sons, Ltd.     

车载激光扫描数据分类支持下的路面数据提取

车载激光扫描系统可以快速采集道路及两旁的建筑物、植被、电杆等地物的点云数据,而点云数据的分类提取是车载激光扫描系统应用的关键。本文选用全景激光移动测量系统获取的激光点云数据,分析了路面点云数据的特征,采用渐进格网法进行了路面点云数据的提取研究;通过试验区的实例验证,取得了较好的分类效果。