广州地理信息空间基础体系建设     

杨光  方锋  王红新 《国土资源信息化》2006,(5):9-12

高质量、强现势性的城市空间数据的获取、更新和使用问题已成为当前“数字广州”建设中的瓶颈。广州地理信息空间基础体系概念的提出具有较强的前瞻性和现实意叉,其目的是在广州市建立完善的空间信息采集与应用体系,并确保信息的完整性、可靠性和现势性,从而为广州城市建设、管理等各类信息平台提供服务。本文对其中的关键技术和具体实施进行了研究。  相似文献   

The effects of extremely wet planting conditions on maize and soybean yields     

Daniel W. Urban  Michael J. Roberts  Wolfram Schlenker  David B. Lobell 《Climatic change》2015,130(2):247-260

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东海黑潮表层盐度分布特征及其影响因素     

任惠茹  康建成  李卫江  安琰  张建平  王甜甜 《热带海洋学报》2011,(5)

利用美国国家海洋大气管理局2007年发布的全球海域温、盐数据库资料,美国地球物理数据中心2006年发布的海底地形数据库资料以及日本海洋科学与技术机构2003年发布的1997—2002年东海地区月平均降水量资料,研究东海黑潮表层盐度的月季分布特征,并分析其影响因素。结果表明,东海黑潮表层盐度存在明显的月季变化特征。总体而言,12月至次年3月表层盐度高,6—9月表层盐度低,4、5月和10、11月为过渡阶段;表层盐度高值分布在东海黑潮主段靠近东边界一侧;6—9月入口段的表层盐度高于出口段的表层盐度,其他月份入口段的表层盐度低于出口段的表层盐度。东海黑潮表层盐度主要受表层温度、降水、径流的影响。冬、春、秋季的表层盐度分布在黑潮主段靠近陆架一侧区域受表层温度影响大;降水对东海黑潮表层盐度产生局部小范围的影响,时间主要集中在1月和6—8月份,区域分布在低纬25°N以南和30°N附近。长江冲淡水夏季对东海黑潮表层盐度的影响大于其他季节对东海黑潮表层盐度的影响,7月长江径流量达到最大值时,对应的黑潮扇形区的盐度最低。  相似文献   

Factors Influencing Helophyte Distribution in Lakes (Eastern Poland)     

Joanna Sender  Urban  Danuta  Różańska-Boczula  Monika  Garbowski  Magda 《Water Resources》2020,47(2):315-324

Water Resources - The aim of the study was to show which morphometric traits of lakes influence the development of the rush zone of lakes and how buffer zone management influences analyzed features...  相似文献   

Planetary Systems     

Pawel Artymowicz 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):313-316

The past decade brought direct evidence of the previously surmised exoplanetary systems. A variety of planetary system types exist: those around pulsars, around both young and old main-sequence stars (as evidenced by planetesimal disks of the Beta Pictoris-type), and the mature giant exoplanets found in radial velocity surveys. The surprising diversity of the exoplanetary systems is addressed by several theories of their origin. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Improved moraine age interpretations through explicit matching of geomorphic process models to cosmogenic nuclide measurements from single landforms     

Patrick J. Applegate  Nathan M. Urban  Klaus Keller  Thomas V. Lowell  Benjamin J.C. Laabs  Meredith A. Kelly  Richard B. Alley 《Quaternary Research》2012,77(2):293-304

The statistical distributions of cosmogenic nuclide measurements from moraine boulders contain previously unused information on moraine ages, and they help determine whether moraine degradation or inheritance is more important on individual moraines. Here, we present a method for extracting this information by fitting geomorphic process models to observed exposure ages from single moraines. We also apply this method to 94 ¹⁰Be apparent exposure ages from 11 moraines reported in four published studies. Our models represent ¹⁰Be accumulation in boulders that are exhumed over time by slope processes (moraine degradation), and the delivery of boulders with preexisting ¹⁰Be inventories to moraines (inheritance). For now, we neglect boulder erosion and snow cover, which are likely second-order processes. Given a highly scattered data set, we establish which model yields the better fit to the data, and estimate the age of the moraine from the better model fit. The process represented by the better-fitting model is probably responsible for most of the scatter among the apparent ages. Our methods should help resolve controversies in exposure dating; we reexamine the conclusions from two published studies based on our model fits.  相似文献   

Changing patterns of residential and workplace segregation in the Stockholm metropolitan area     

Szymon Marcińczak  Tiit Tammaru  Magnus Strömgren  Urban Lindgren 《Urban geography》2013,34(7):969-992

Immigrant–native segregation is present in the spaces in which individuals from different ethnic/racial groups practice their everyday lives; interact with others and develop their ethnic, social and spatial networks. The overwhelming majority of academic research on immigrant segregation has focused on the residential domain, thus largely overlooking other arenas of daily interaction. The present study contributes to the emerging literature on immigrant residential and workplace segregation by examining changes in patterns of residential and workplace segregation over time. We draw our data from the Stockholm metropolitan region, Sweden’s main port of entry for immigrants. The results suggest a close association between residential and workplace segregation. Immigrant groups that are more segregated at home are also more segregated in workplace neighborhoods. More importantly, we found that a changing segregation level in one domain tends to involve a similar trend in the other domain.  相似文献   

Characterisation of rock aggregate breakage properties using realistic texture‐based modelling     

Hongyuan Liu  Per‐Arne Lindqvist  Urban Åkesson  Shaoquan Kou  Jan‐Eric Lindqvist 《国际地质力学数值与分析法杂志》2012,36(10):1280-1302

Realistic texture‐based modelling methods, that is microstructural modelling and micromechanical modelling, are developed to simulate the rock aggregate breakage properties on the basis of the rock actual microstructure obtained using microscopic observations and image analysis. The breakage properties of three types of rocks, that is Avja, LEP and Vandle taken from three quarries in Sweden, in single aggregate breakage tests and in inter‐aggregate breakage tests are then modelled using the proposed methods. The microstructural modelling directly integrates the microscopic observation, image analysis and numerical simulation together and provides a valuable tool to investigate the mechanical properties of rock aggregates on the basis of their microstructure properties. The micromechanical modelling takes the most important microstructure properties of rock aggregates into consideration and can model the major mechanical properties. Throughout this study, it is concluded that in general, the microstructure properties of rock aggregate work together to affect their mechanical properties, and it is difficult to correlate a single microstructure property with the mechanical properties of rock aggregates. In particular, for the three types of rock Avja, LEP and Vandle in this study, crack size distribution, grain size and grain perimeter (i.e. grain shape and spatial arrangement) show good correlations with the mechanical properties. The crack length and the grain size negatively affect the mechanical properties of Avja, LEP and Vandle, but the perimeter positively influences the mechanical properties. Besides, the modelled rock aggregate breakage properties in both single aggregate and inter‐aggregate tests reveal that the aggregate microstructure, aggregate shape and loading conditions influence the breakage process of rock aggregate in service. For the rock aggregate with the same microstructure, the quadratic shape and good packing dramatically improve its mechanical properties. During services, the aggregate is easiest to be fragmented under point‐to‐point loading condition, and then in the sequence of multiple‐point, point‐to‐plane and plane‐to‐plane loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Diurnal dynamics of streamflow in an upland forested micro‐watershed during short precipitation‐free periods is altered by tree sap flow          下载免费PDF全文

Jan Deutscher  Petr Kupec  Peter Dundek  Ladislav Holík  Martin Machala  Josef Urban 《水文研究》2016,30(13):2042-2049

Diurnal variations in streamflow are becoming acknowledged as a way of analysing how changing climatic conditions and land use affects watersheds but also as a way to understand watersheds as a whole. Yet not many studies from uplands below 900 mm mean annual precipitation zone are available from European countries. During the 2012 growing season, a sampling campaign took place in an upland forested micro‐watershed, Czech Republic (65 ha). Tree sap flow, rainfall and temperature were measured continuously, while streamflow at the discharge point and soil moisture were estimated from short‐term measurements. Short precipitation‐free periods lasting several days were identified for evaluation of trends in diurnal dynamics of both sap flow and streamflow. The results demonstrated that during these periods, the main factor altering streamflow was almost exclusively tree sap flow. A decrease in streamflow was observed during the day and an increase at night. The decline in sap flow after sunset was accompanied by a continuous increase in streamflow throughout the night up to its initial maximum in the morning. The amplitude in diurnal variations reached 18%. The observed time lag between the diurnal variations of sap flow and streamflow was approximately 2 h. Relatively low changes in diurnal dynamics of streamflow pointed out a strong regulatory role of the forest in buffering water discharge from the catchment. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Bias,variance and computational properties of Kijko’s estimators of the upper limit of magnitude distribution,M<Subscript>max</Subscript>     

Stanisław Lasocki  Paweł Urban 《Acta Geophysica》2011,59(4):659-673

It is often assumed in probabilistic seismic hazard analysis that the magnitude distribution has an upper limit M _max, which indicates a limitation on event size in specific seismogeneic conditions. Accurate estimation of M _max from an earthquake catalog is a matter of utmost importance. We compare bias, dispersion and computational properties of four popular M _max estimators, introduced by Kijko and others (e.g., Kijko and Sellevoll 1989, Kijko and Graham 1998, Kijko 2004) and we recommend the ones which can be the most fruitful in practical applications. We provide nomograms for evaluation of bias and standard deviation of the recommended estimators for combinations of sample sizes and distribution parameters. We suggest to use the bias nomograms to correct the M _max estimates. The nomograms of standard deviation can be used to determine minimum sample size for a required accuracy of M _max.  相似文献