A neighbor decay cellular automata approach for simulating urban expansion based on particle swarm intelligence

Simulation and quantitative analysis of urban land use change are effective ways to investigate urban form evolution. Cellular Automata (CA) has been used as a convenient and useful tool for simulating urban land use change. However, the key issue for CA models is the definition of the transition rules, and a number of statistical or artificial intelligence methods may be used to obtain the optimal rules. Neighborhood configuration is a basic component of transition rules, and is characterized by a distance decay effect. However, many CA models do not consider the neighbor decay effect in cellular space. This paper presents a neighbor decay cellular automata model based on particle swarm optimization (PSO-NDCA). We used particle swarm optimization (PSO) to find transition rules and considered the decay effect of the cellular neighborhood. A negative power exponential function was used to compute the decay coefficient of the cellular neighborhood in the model. By calculating the cumulative differences between simulation results and the sample data, the PSO automatically searched for the optimal combination of parameters of the transition rules. Using Xiamen City as a case study, we simulated urban land use changes for the periods 1992–1997 and 2002–2007. Results showed that the PSO-NDCA model had a higher prediction accuracy for built-up land, and a higher overall accuracy and Kappa coefficient than the urban CA model based on particle swarm optimization. The study demonstrates that there exist optimal neighborhood decay coefficients in accordance with the regional characteristics of an area. Urban CA modelling should take into account the role of neighborhood decay.     

基于RPC模型的ZY-3正射纠正研究

采用基于RPC模型进行ZY-3影像正射纠正处理时,当使用全局布点控制方案时控制点增加到12个以上后,对整景影像的纠正精度影响不明显,且由于选取多个高精度的控制点非常困难,而有时控制点的增加并不一定能带来精度的提高。本文通过采用几种不同的控制点布设方案对同一景ZY-3影像进行正射纠正,并对几种方案的纠正成果进行了精度比较和分析,从而进一步证实了选择合适的控制点布设方案和控制点数量大大提高ZY-3影像的纠正质量和纠正效率。     

火星探测器行星际定轨两种数据处理方案比较

计算了由于形状、姿态和表面性质不准确导致火星探测器行星际定轨存在较大光压模型误差时,两种不同定轨方案(方案1只估计光压系数,方案2同时估计光压系数和随机加速度)对光压模型误差的补偿效果。在方案2中建立了高斯马尔科夫模型表征光压模型导致的加速度误差,并选取了合适的随机模型参数。仿真分析表明方案2可以有效补偿光压模型误差,避免滤波发散,提高定轨精度。     

一种基于复共线性分析的RPC参数优选法

推导了求解有理多项式系数(RPC)的严密误差方程,从分析误差方程设计矩阵列向量间的复共线性着手,提出了一种去相关的RPC参数优选方法。对一景SPOT-5 HRG 1A级影像进行实验,结果表明,当地面控制点稀疏时,通过优选20~30个RPC参数,可以很好地消除参数间的相关性,有效消除有理函数模型(RFM)在地形拟合中出现的振荡现象,可明显提高RPC参数求解和RFM的影像几何处理精度。当地面控制点足够多时,利用此方法优选的RPC参数进行地形拟合的结果与用常规最小二乘法求解的78个RPC参数实施地形拟合的结果完全一致。     

双排弹性桩隔振屏障对平面SH波的多重散射

提出了一种新的求解任意排列、任意半径的弹性桩对平面SH波的多重散射的理论方法,以解决以往假设单重散射的计算方法中不考虑桩列作为整体屏障从而忽略桩间相互干涉关系的不足,并且可用于分析多排弹性桩对平面SH波的散射性状。在数值计算分析中讨论了散射重数,排间距,桩土剪切模量比,桩数等对双排弹性桩屏障隔离效果的影响,从而对实际工程中利用排桩进行振动污染的治理和屏障隔振设计提出了重要的理论依据。     

On geometric design considerations and control methodologies for absorbing wavemakers

This paper investigates the effects that geometry and control have on the absorption characteristics of wavemakers. It presents the hydrodynamic coefficients for piston and bottom hinged flap wavemakers and also for two novel wavemaker profiles. Absorption efficiencies are presented for wavemakers using one, two and three control coefficients for reactive control. This is then used to analyse the absorption efficiency of each of the different wavemakers based upon the geometry and the control strategy used. It is shown that the amount of absorption for a given paddle differs greatly depending on the choice of control coefficients used to implement complex conjugate control. Increased absorption can be achieved over a broader bandwith of frequencies when the geometry of the wavemaker is optimised for one specific frequency.     

东北地区近40年干燥指数变化趋势及其气候敏感性

基于东北地区91个站点1971～2008的常规气象资料,应用Mann-Kendall方法分析了区内近40年干燥指数的变化趋势,并基于Penman-Monteith公式计算了干燥指数对各气象要素的敏感性系数,分析了气候变化影响下,干燥指数气候敏感系数的变化规律。研究表明：（1）东北地区近40年来干燥指数以0.06/10a...     

新疆艾比湖生态脆弱区生态服务价值对土地利用变化的响应

以干旱区生态脆弱区新疆艾比湖区域为研究对象,运用GIS手段和生态经济学的方法,采用Costanza生态系统服务价值计算公式,并参照谢高地等人的中国陆地生态系统服务单位面积价值,探讨了艾比湖区域1990—2007年土地利用和生态系统服务价值的变化特征。结果表明:1990—2007年间,艾比湖区域土地利用处于发展阶段,土地利用程度呈增大趋势;1990,2001和2007年艾比湖区域生态服务价值分别为53.63,63.01和56.96亿元,呈波动性变化;研究区生态系统的服务性功能远大于生产性功能。2001—2007年间研究区生态系统服务价值下降速度较快,作为艾比湖湿地自然保护区的核心部分,生态系统服务价值具有退化的趋势,需要加强管理,控制人类活动的影响强度。     

Discontinuous deformation analysis with second‐order finite element meshed block

The discontinuous deformation analysis (DDA) with second‐order displacement functions was derived based on six‐node triangular mesh in order to satisfy the requirement for the accurate calculations in practical applications. The matrices of equilibrium equations for the second‐order DDA were given in detail for program coding. By close comparison with widely used finite element method and closed form solutions, the advantages of the modified DDA were illustrated. The program coding was carried out in C++ environment and the new code applied to three examples with known analytical solutions. A very good agreement was achieved between the analytical and numerical results produced by the modified DDA code. Copyright © 2006 John Wiley & Sons, Ltd.