An efficient metaheuristic for integrated scheduling and staffing IT projects based on a generalized minimum cost flow network

Scheduling IT projects and assigning the project work to human resources are an important and common tasks in almost any IT service company. It is particularly complex because human resources usually have multiple skills. Up to now only little work has considered IT‐specific properties of the project structure and human resources. In this article, we present an optimization model that simultaneously schedules the activities of multiple IT projects with serial network structures and assigns the project work to multiskilled internal and external human resources with different efficiencies. The goal is to minimize costs. We introduce a metaheuristic that decomposes the problem into a binary scheduling problem and a continuous staffing problem where the latter is solved efficiently by exploiting its underlying network structure. For comparison, we solve the mixed–binary linear program with a state–of–the–art commercial solver. The impacts of problem parameters on computation time and solution gaps between the metaheuristic and the solver are assessed in an experimental study. Our results show that the metaheuristic provides very favorable results in considerable less time than the solver for midsize problems. For larger problems, it shows a similar performance while the solver fails to return feasible solutions. © 2012 Wiley Periodicals, Inc. Naval Research Logistics 59: 111–127, 2012     

Optimal inventory control policy for periodic‐review inventory systems with inventory‐level‐dependent demand

We consider a setting in which inventory plays both promotional and service roles; that is, higher inventories not only improve service levels but also stimulate demand by serving as a promotional tool (e.g., as the result of advertising effect by the enhanced product visibility). Specifically, we study the periodic‐review inventory systems in which the demand in each period is uncertain but increases with the inventory level. We investigate the multiperiod model with normal and expediting orders in each period, that is, any shortage will be met through emergency replenishment. Such a model takes the lost sales model as a special case. For the cases without and with fixed order costs, the optimal inventory replenishment policy is shown to be of the base‐stock type and of the (s,S) type, respectively. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012     

广义A-调和张量的反向H?lder型不等式

基于微分形式A-调和方程的反向Hlder型不等式,是研究其解可积性的重要工具。本文将A-调和方程推广到拟线性方程的情形,在一定的条件下获得方程解的反向Hlder型不等式,所得结果可以退化到经典的情形,为研究此类调和方程的正则性与可积性奠定了基础。     

支持广义多方案分析仿真的异地克隆研究

仿真克隆可以提高并行离散事件仿真的效率和并行性,方便快捷地对仿真中的多种可能性进行分析、比较和评估.给出广义多方案分析仿真概念,介绍仿真克隆的相关概念,分析当前仿真克隆方法的不足,提出提高广义多方案分析仿真整体运行效率的异地克隆概念.基于检查点与恢复方法,在动态并行仿真引擎中实现了异地克隆.利用Phold测试程序对异地克隆方法的效率进行测试,测试结果表明,异地克隆可以提高多方案分析仿真系统整体运行效率.     

组网雷达的改进粒子滤波算法

针对现代战争中有源雷达容易受到干扰和反辐射导弹的摧毁,以及无源雷达隐蔽性高,只能测量方位角度,测量精度小等特点,提出利用集中式有源雷达系统与无源雷达系统协同组网对目标进行跟踪。但是在实际环境中,噪声属性以及有源雷达,无源雷达接收信号的特点决定了组网雷达需要应用非线性滤波技术对信号进行处理。传统的非线性技术包括卡尔曼滤波、扩展卡尔曼滤波(EKF)或无迹卡尔曼滤波(UKF)等方法。非线性近似过程带来的误差相对较大,而且均要求观测噪声和过程噪声为独立或相关的高斯白噪声。而粒子滤波避免了传统非线性滤波方法的缺陷,但是存在粒子退化,于是用EKF和UKF在每一时刻更新粒子,用更新的粒子及其协方差构造重要性函数,然后重采样。仿真实验表明这两种改进粒子滤波方法有很好的效果。     

电视制导系统抗干扰性能评估

提出了一种空地电视制导导弹图像传输系统抗干扰评估的总体框架,建立了电磁干扰条件下系统的抗干扰评估的空间模型。而后基于有限状态机理论,建立了电视制导导弹图像识别模态转换模型,详细讨论了典型干扰对电视图像数据链的影响。最后,应用计算机仿真技术,得到制导系统在不同信噪比条件下导弹的最大作用距离和图像干扰效果。     

SAR卫星偏航导引补偿效果分析

通过建立"SAR卫星—地球—目标点"几何模型,得到多普勒中心频率的精确值;简化模型,求得卫星的偏航导引规律;分析简化前后两模型,从而得出偏航导引的补偿效果。     

低功率霍尔推力器阳极供气环工程设计关键参数仿真

为了提高低功率霍尔推力器放电通道内中性原子分布均匀性,采用有限元方法对阳极供气环关键结构参数进行优化研究。针对双腔式阳极供气环结构,重点分析了缓冲腔容积比以及缓冲腔隔板导流小孔数量等关键参数对阳极供气均匀性的影响。研究结果表明:随着缓冲腔容积比的增大,阳极供气环出气孔差异率先快速减小后趋于稳定,其中当容积率k=1.0时,平均差异率和最大差异率分别为1.77%和3.79%;隔板间导流小孔数量从8增加到14时,出气孔差异率呈现浴盆曲线特性,其中导流孔数量为10时,平均差异率和最大差异率分别为1.8%和3.8%。研究结果可为霍尔推力器阳极供气环工程设计提供理论支撑。     

Insurgency by the numbers I: A reconsideration of the ecology of communist success in jiangxi province,China

Theorizing about Taliban operations in Afghanistan has its limits and it is possible that Kabul-centric strategies do not adequately address the unique circumstances of each region in the country. How exactly has the Taliban gone about attaining its objectives in Kandahar province and how have those approaches evolved since 2002? And how have the Taliban adapted to coalition forces' attempts to compete with the insurgency and stamp it out? The answers to these questions are critical in the formulation of any counterinsurgency approach to Afghanistan.