河套灌区不同尺度土壤氮含量的空间异质性分析

农业灌区土壤氮(N)是限制作物生长的主要因素,其空间异质性在不同尺度下会受气候、成土母质、土壤类型等自然因素及灌溉、耕作、不同土地利用方式等人为因素的综合制约。本研究以河套灌区永济灌域的土壤总氮(TN)含量为研究对象,分析2个尺度(L尺度:样点数为36个,采样深度0~<100 cm;M尺度:样点数为125,采样深度0~<20 cm)3种土地利用方式下(农田、林地、荒地)土壤TN的空间异质性。研究结果表明,不同土地利用方式下,土壤TN含量存在显著差异,林地和农田TN含量显著高于荒地,而不同种植类型的农田(玉米、小麦、向日葵)之间TN含量差异不显著;在M尺度上,灌域土壤TN半方差拟合效果较好,为球型模型,空间相关度为2.64%,远小于标准界限25%,表明随机性远小于结构性变异方差;在L尺度上,0~<20、20~<40 cm土层,半方差拟合为高斯模型,空间相关度分别为23.26%和22.30%,接近25%;40~<100 cm土层,半方差拟合为指数模型,空间自相关度为17.86%,3个土层空间自相关范围分别为240、240和30 m。可见,随着尺度的增加,空间相关性随之增加。2个尺度3层土壤,空间相关度均小于25%,TN在空间上主要受到自然因素的影响,如土壤母质、气候、地形等因素的影响较大,表层0~<40 cm土壤TN含量同时受到一定程度的人为因素干扰。

Probabilistic durability assessment approach of deteriorating RC bridges

A stochastic finite element computational methodology for probabilistic durability assessment of deteriorating reinforced concrete（RC） bridges by considering the time-and space-dependent variabilities is presented.First,finite element analysis with a smeared cracking approach is implemented.The time-dependent bond-slip relationship between steel and concrete,and the stress-strain relationship of corroded steel bars are considered.Secondly,a stochastic finite element-based computational framework for reliability assessment of deteriorating RC bridges is proposed.The spatial and temporal variability of several parameters affecting the reliability of RC bridges is considered.Based on the data reported by several researchers and from field investigations,the Monte Carlo simulation is used to account for the uncertainties in various parameters,including local and general corrosion in rebars,concrete cover depth,surface chloride concentration,chloride diffusion coefficient,and corrosion rate.Finally,the proposed probabilistic durability assessment approach and framework are applied to evaluate the time-dependent reliability of a girder of a RC bridge located on the Tianjin Binhai New Area in China.

喜马拉雅东部和西藏南部的分形和b值测绘

根据1993～2003年期间在分布于喜马拉雅东部和西藏南部32个地震台站记录的约1300次精定位的地震,确定了分形(相关)维数和b值。0.9的空间相关度表明,该地区地震更接近于成丛分布,而b值为1.02则表明该地区的地震活动高度活跃。此外,本文详尽地分析了频次—震级分布和分数维与深度的关系。分析结果表明,在喜马拉雅—青藏高原碰撞区,不同深度层次的构造变化,反映了这个地区存在高度的不均匀性和高度的变质作用。

Spatial Autocorrelation and Localization of Urban Development

A nonlinear analysis of urban evolution is made by using of spatial autocorrelation theory. A first-order nonlinear autoregression model based on Clark’s negative exponential model is proposed to show urban population density. The new method and model are applied to Hangzhou City, China, as an example. The average distance of population activities, the auto-correlation coefficient of urban population density, and the auto-regressive function values all show trends of gradual increase from 1964 to 2000, but there always is a sharp first-order cutoff in the partial auto- correlations. These results indicate that urban development is a process of localization. The discovery of urban locality is significant to improve the cellular-automata-based urban simulation of modeling spatial complexity.

A new measure for evaluating spatially related properties of traffic information credibility

With the wide applications of sensor network technology in traffic information acquisition systems,a new measure will be quite necessary to evaluate spatially related properties of traffic information credibility.The heterogeneity of spatial distribution of information credibility from sensor networks is analyzed and a new measure,information credibility function(ICF),is proposed to describe this heterogeneity.Three possible functional forms of sensor ICF and their corresponding expressions are presented.Then,two feasible operations of spatial superposition of sensor ICFs are discussed.Finally,a numerical example is introduced to show the calibration method of sensor ICF and obtain the spatially related properties of expressway in Beijing.The results show that the sensor ICF of expressway in Beijing possesses a negative exponent property.The traffic information is more abundant at or near the locations of sensor,while with the distance away from the sensor increasing,the traffic information credibility will be declined by an exponential trend.The new measure provides theoretical bases for the optimal locations of traffic sensor networks and the mechanism research of spatial distribution of traffic information credibility.

Fundamental Theories of Spatial Similarity Relations in Multi-scale Map Spaces

Similarity relation is one of the spatial relations in the community of geographic information science and cartography.It is widely used in the retrieval of spatial databases, the recognition of spatial objects from images, and the description of spatial features on maps.However, little achievements have been made for it by far.In this paper, spatial similarity relation was put forward with the introduction of automated map generalization in the construction of multi-scale map databases;then the definition of spatial similarity relations was presented based on set theory, the concept of spatial similarity degree was given, and the characteristics of spatial similarity were discussed in detail, in-cluding reflexivity, symmetry, non-transitivity, self-similarity in multi-scale spaces, and scale-dependence.Finally a classification system for spatial similarity relations in multi-scale map spaces was addressed.This research may be useful to automated map generalization, spatial similarity retrieval and spatial reasoning.

被光阑衍射的多色部分空间相干光的光谱异变和光谱开关

从空间-频率域部分空间相干光的传输理论出发,研究了被光阑衍射多色部分空间相干光远场的光谱异变和光谱开关。研究表明,与多色完全空间相干光的光谱异变仅由光阑衍射效应引起不同,多色部分空间相干光的光谱异变和光谱开关与光阑衍射、空间相关性和源光谱谱宽有关。作了详细的数值计算以说明多色部分空间相干光的光谱开关的特性。多色完全空间相干光可作为空间相关度β=1的特例而包含在理论模型之中。

杨氏实验远场的光谱位移和光谱开关

从部分相干光的传输定律出发 ,研究了杨氏双缝实验远场的光谱变化。指出杨氏实验中光谱开关在远场也会出现。缝的衍射和光的空间相干性是产生光谱开关的物理原因 ,增大缝参量ε和源的空间相关度Δ光谱开关效应越显著。作了详细的数值计算以说明远场光谱位移和光谱开关的特性 ,并与已有的工作进行了比较。

Spatio-temporal evolution of population and urbanization in the countries along the Belt and Road 1950–2050

This paper uses data for the period 1950-2050 compiled by the United Nations Population Division together with methods including spatial autocorrelation analysis, hie- rarchical cluster analysis and the standard deviational ellipse, to analyze the spatio-temporal evolution of population and urbanization in the 75 countries located along the routes of the Silk Road Economic Belt and the 21st-century Maritime Silk Road, to identify future popula- tion growth and urbanization hotspots. The results reveal the following： First, in 2015, the majority of Belt and Road countries in Europe, South Asia and Southeast Asia had high population densities, whereas most countries in Central Asia, North Africa and West Asia, as well as Russia and Mongolia, had low population densities; the majority of countries in South Asia, Southeast Asia, Central Asia, West Asia and North Africa had rapid population growth, whereas many countries in Europe had negative population growth; and five Belt and Road countries are in the initial stage of urbanization, 44 countries are in the acceleration stage of urbanization, and 26 are in the terminal stage of urbanization. Second, in the century from 1950 to 2050, the mean center of the study area＇s population is consistently located in the border region between India and China. Prior to 2000, the trajectory of the mean center was from northwest to southeast, but from 2000 it is on a southward trajectory, as the population of the study area becomes more concentrated. Future population growth hotspots are predicted to be in South Asia, West Asia and Southeast Asia, and hotspot countries for the period 2015-2030 include India, China, Pakistan and Indonesia, though China will move into nega- tive population growth after 2030. Third, the overall urban population of Belt and Road coun- tries increased from 22% in 1950 to 49% in 2015, and it is expected to gradually catch up with the world average, reaching 64% in 2050. The different levels of urbanization in different countries display significant spatial dependency, and in the hundred-year period under con-sideration, this dependency increases before eventually weakening. Fourth, between 2015 and 2030, urban population hotspots will include Thailand, China, Laos and Albania, while Kuwait, Cyprus, Qatar and Estonia will be urban ＂coldspots.＂ Fifth, there were 293 cities with populations over 1 million located along the Belt and Road in 2015, but that number Js ex- pected to increase to 377 by 2030. Of those, 43 will be in China, with many of the others located in India, Indonesia and the eastern Mediterranean.

A random physical model of seismic ground motion field on local engineering site

This paper presents a random physical model of seismic ground motion field on a specific local engineering site.With this model,artificial ground motions which are consistent with realistic records at SMART-1 array on spatial correlation are synthesized.A two-scale modeling method of seismic random field is proposed.In large scale,the seismic ground motion field on bedrock surface is simplified to a two-dimensional spherical wave field based on the seismic point source and homogeneous isotropic media model.In small scale,the seismic ground motion field on the engineering site has a plane waveform.By introducing the physical models of seismic source,path and local site and considering the randomness of the basic physical parameters,the random model of seismic ground motion field is completed in a random functional form.This model is applied to simulation of the acceleration records at SMART-1 array by using the superposition method of wave group.

Characterization of spatial variability with observed responses:application of displacement back estimation

Soil spatial variability is difficult to evaluate due to insufficient test data.An alternative option is estimation by indirect methods such as inverse analysis.In this paper,two examples are presented to demonstrate the capability and accuracy of the probabilistic estimation method to characterize soil spatial variability with displacement responses.The first example is a soil slope subject to a surcharge load,in which the spatially varied field of the elastic modulus is estimated with displacements.The results show that estimations based on horizontal displacements were more accurate than those based on vertical displacements.The accuracy of the estimated field was substantially reduced by increasing variance of elastic modulus.However,the estimation was generally acceptable as the error was not more than 10%,even for the high variance case(COV^l.5).The accuracy of estimation was also affected by the type of covariance function and the correlation length.When the correlation length decreased,the accuracy of estimation was reduced.The second example is a validation of laboratory model tests where a horizontal load was applied on a layered ground.The estimated thicknesses of soil layers were close to those in the real situation,which demonstrates the capacity of the estimation method.

Shock wave standoff distance of near space hypersonic vehicles

The shock wave standoff distances of near space hypersonic vehicles, which execute missions mainly at the altitude of 25 km to 55 km, are vital in aerothermodynamic analysis. The implicit finite volume schemes are derived from axisymmetric Navier-Stokes equations for chemical equilibrium flow, and programmed in FORTRAN. Taking a sphere cone for example, the effects of Much numbers （from 22 to 36） on the shock wave standoffdistance and the average density behind the shock are simulated at different altitudes from 25km to 55km. The numerical results illustrate that the turning point of the standoff distance is corresponding to that of the average density with the variation of Mach numbers. Based on the numerical results, we propose a formula for shock wave standoff distance, which is the function of the radius of the blunt body, the Mach number and the altitude in the atmosphere. Compared with previous correlations, the new formula can overcome the drawbacks of larger relative errors and complex calculations of the average density.

Semi-linear Wave Equations with Effective Damping

The authors study the Cauchy problem for the semi-linear damped wave equation utt-△u＋b（t）ut=f（u）,u（0,χ）=u0（χ）,ut（0,χ）=u1（χ） in any space dimension n ≥ 1. It is assumed that the time-dependent damping term b（t）〉 0 is effective, and in particular tb（t） →∞ as t →∞. The global existence of small energy data solutions for｜f（u）｜≈｜u｜^p in the supercritical case of p 〉 1＋ 2/n and p ≤n/n-2 for n ≥ 3 is proved.

Exploiting a depth context model in visual tracking with correlation filter

Recently correlation filter based trackers have attracted considerable attention for their high computational efficiency. However, they cannot handle occlusion and scale variation well enough. This paper aims at preventing the tracker from failure in these two situations by integrating the depth information into a correlation filter based tracker. By using RGB-D data, we construct a depth context model to reveal the spatial correlation between the target and its surrounding regions. Furthermore, we adopt a region growing method to make our tracker robust to occlusion and scale variation. Additional optimizations such as a model updating scheme are applied to improve the performance for longer video sequences. Both qualitative and quantitative evaluations on challenging benchmark image sequences demonstrate that the proposed tracker performs favourably against state-of-the-art algorithms.