耦合地理模拟与优化的城镇开发边界划定

研究目的:城镇开发边界划定是典型耦合空间模拟和优化的复杂地理问题,当前划定方法的科学性和系统性还有待加强,引入地理模拟优化系统理论以期提供更好的辅助规划成果。研究方法:在回顾城镇开发边界相关概念及划定方法的基础上,提出基于地理模拟优化系统(GeoSOS)的城镇开发边界划定方法,并以珠江三角洲重点优化开发区域为例对城镇开发边界进行了划定。研究结果:基于GeoSOS的多目标空间优化方法界定了研究区的生态、农业和城镇空间,并通过城镇扩展数量和农业生态双重约束的CA模型预测未来城镇扩展格局,最终利用形态学方法划定城镇开发边界。研究结论:基于GeoSOS的划定方法能够优化这三类空间,并基于底线约束预测未来规划期的城镇扩展格局,从而划定城镇开发边界,为划定实践工作提供科学依据和有利支撑。     

Data center supply chain configuration design: A two-stage decision approach

Data centers are special-purpose facilities that enable customers to perform cloud based real-time online transactions and rigorous computing operations. Service levels of data center facilities are characterized by response time between query and action, which to a large extent depends on data center location and data travel distance. Another aspect of service level is resource up-time availability, which is determined by data center configuration. Data center location and configuration decisions are, therefore, of great significance to ensure uninterrupted operations in customers of manufacturing and service industries relying on cloud-based computing resources. In this study, following a grid-based location approach, we present two mixed integer linear programming models for capacitated single-source data center location-allocation problems. The first model provides optimal locations, capacities and configurations of data centers, and allocation of demands to open facilities when there is no existing facilities in the region. Our second model considers the decision problem of meeting new demand when the existing demand is met by the already opened facilities. We term these newly arrived demand as replication demand, which results either from emergence of new users of existing customers at distant locations in the future, or as a means of increasing data resilience by creating data replication as a backup. To solve the decision problem for meeting primary and replication demand optimally, we propose a two-stage decision algorithm. The algorithm provides optimal locations, capacities and configurations for new data centers, capacity addition decisions to the existing facilities and subsequent allocation of demands. Both models and solution algorithm are implemented using AMPL programming language and solved with CPLEX solver. The models are found to be scalable and capable to provide high quality solutions in reasonable time.     

On the existence of a strictly strong Nash equilibrium under the student-optimal deferred acceptance algorithm

This study analyzes a preference revelation game in the student-optimal deferred acceptance algorithm in a college admission problem. We assume that each college's true preferences are known publicly, and analyze the strategic behavior of students. We demonstrate the existence of a strictly strong Nash equilibrium in the preference revelation game through a simple algorithm that finds it. Specifically, (i) the equilibrium outcome from our algorithm is the same matching as in the efficiency-adjusted deferred acceptance algorithm and (ii) in a one-to-one matching market, it coincides with the student-optimal von Neumann–Morgenstern (vNM) stable matching. We also show that (i) when a strict core allocation in a housing market derived from a college admission market exists, it can be supported by a strictly strong Nash equilibrium, and (ii) there exists a strictly strong Nash equilibrium under the college-optimal deferred acceptance algorithm if and only if the student-optimal stable matching is Pareto-efficient for students.     

设施农业对农田排涝模数影响

[目的]研究设施农业发展对农田设计排涝模数的影响。[方法]以天津市西青区一处封闭农田为对象,进行了农田排涝现场观测试验。在现场观测数据的基础上,构建了超渗—蓄满垂向耦合产流模型,用Sobol'法进行参数敏感性分析,甄别出模型的敏感性参数,并将SCE-UA算法与人工率定相结合对模型参数进行率定。利用水量平衡条件、地下水位相对变化量以及土壤含水量变化量对模型的模拟精度进行评价,并与单一超渗产流模型、单一蓄满产流模型进行对比,进一步验证所建模型的适用性。最后针对不同重现期下的设计暴雨,利用耦合产流模型推求产水量,进而给出相应设计排涝模数。[结果]模型各项评价指标的相对误差在20%之内,Nash系数在0.6以上,模拟精度高;与单一超渗模型和蓄满模型相比,有效性分别提高了0.869和0.912,因此所建立的超渗—蓄满垂向耦合模型是合理有效的。在3年、5年、10年和20年一遇的重现期下,设计排涝模数与原排涝模数相比均有所增加,增大幅度分别为16.44%、8.63%、7.50%和3.77%。通过降雨趋势分析,基准期与评价期的降雨没有显著线性变化趋势,相较于降雨,设施农业占比增加对农田设计排涝模数有更大的影响。[结论]在设施农业迅速发展背景下,重新修订农田小区排涝模数是必要的,对有效控制农田洪涝灾害有重要现实意义。     

Online Principal Component Analysis in High Dimension: Which Algorithm to Choose?

Principal component analysis (PCA) is a method of choice for dimension reduction. In the current context of data explosion, online techniques that do not require storing all data in memory are indispensable to perform the PCA of streaming data and/or massive data. Despite the wide availability of recursive algorithms that can efficiently update the PCA when new data are observed, the literature offers little guidance on how to select a suitable algorithm for a given application. This paper reviews the main approaches to online PCA, namely, perturbation techniques, incremental methods and stochastic optimisation, and compares the most widely employed techniques in terms statistical accuracy, computation time and memory requirements using artificial and real data. Extensions of online PCA to missing data and to functional data are detailed. All studied algorithms are available in the  package onlinePCA on CRAN.     

两台可重排平行机覆盖问题的最优在线算法

讨论了一个可重排平行机半在线排序问题.设有两台同型平行机,加工速度相同,工件以列表在线方式依次到达,当且仅当当前工件安排后,下一个工件才到达,目标是使两台机器中的较小负荷最大化.进一步在所有工件预排完毕后,允许重排任意k个工件.提出竞争比为3/2的最优算法H,且该算法只需重排一个工件.     

基于改进FAHP Entropy赋权法的丘区耕地整理潜力评价

[目的]我国西南丘陵地区耕地资源有限,其后备资源和耕地整理潜力的研究显得尤为重要,耕地整理潜力评价是耕地后备资源整理开发的基础性工作。[方法]文章提出改进FAHP-Entropy赋权法,该赋权法不仅兼顾FAHP-Entropy赋权法和改进AHP-Entropy赋权法的优点,而且其兼容度大于FAHP-Entropy等赋权法的兼容度,证明改进FAHP-Entropy赋权法的稳健性、优越性。在此基础上,以西南丘陵地区盐亭县为例,建立针对丘区耕地潜力评价指标体系,结合综合评价法研究盐亭县各乡镇耕地整理潜力综合指数。[结果]采用ArcGIS软件对耕地潜力综合指数进行插值分级,得出盐亭行政区域内耕地潜力等级分布情况;同时,以耕地整理潜力综合指数为依据采用Matlab软件构建耕地潜力三维DEM模型,并基于三维DEM模型在4个主方向进行剖分分析,探讨耕地潜力在剖分方向与地域之间的微观特性。[结论]在ArcGIS综合指数插值分级、耕地潜力三维DEM模型剖分等基础上,将盐亭县耕地划分为4个耕地整理潜力开发区。该研究将为盐亭县等西南丘陵地区耕地后备资源整理开发等提供理论支撑。     

Optimizing flight equencing and gate assignment considering terminal configuration and walking time

Operating airline hub-and-spoke networks (HSN) rather than direct flights among city pairs may significantly reduce supplier cost; however, passengers' travel time may significantly increase due to increased transfer and in-flight time. The costs considered in this study are hub-related and incurred by passengers and aircraft (i.e., passenger transfer, flight dwelling, and gate occupancy). The objective is to minimize the total cost by optimizing flight sequence (i.e., arrivals and departures) and gate assignment, while considering transfer speed, transfer demand, flight size, gate size and terminal configuration. A real-world HSN whose hub airport (HA) is located at Xianyang International Airport (XIY) in Xi'an, China is analyzed. The optimized solutions and their relations to various model parameters are explored.     

翼尖尖点散射特性分析

为解决机翼翼尖等弱散射源所带来的雷达散射截面(RCS)贡献问题，针对典型机翼设计了几种不同的机翼翼尖方案，建立了典型翼尖数值模型。利用基于多层快速多极子算法（MLFMA）的FEKO软件，计算、分析不同方案翼尖外形在不同频段、不同方位角下的RCS量级，并优选出对机翼RCS贡献最低的翼尖外形方案。计算结果表明，针对典型机翼，从翼尖到翼根方向上15%处顺气流直切的翼尖外形方案，其翼尖尖点所带来的RCS贡献最小。     

自适应变步长的动量项盲源分离方法

针对传统盲源分离算法采用单一步长而无法同时兼顾收敛速度与稳态性以及动量因子选取的问题，介绍了一种盲源分离优化方法。该方法依据自然梯度算法(Natural Gradient Algorithm，NGA)的收敛条件，通过输出信号建立一种新的表示信号分离程度的度量指标，通过此度量指标构造非线性单调函数，使步长与动量因子参数自适应调节，从而可以合理、准确地选择参数。仿真表明了在平稳和非平稳环境下所提分离指标的正确性，且该指标可有效监测信号分离程度；针对步长及动量因子参数选取所设计的优化策略能够有效地缓解固定值对算法性能的约束，在有无噪声的情况下，均获得了优良的分离效果。