Transportation cost changes with statewide school district consolidation

This article studies the relationship between school district size and bus transportation costs, and estimates the change in such costs when a statewide policy of consolidation is pursued. To explore this relationship, we develop a multiple-objective model and solution procedure that combines a geographic aggregation and bus routing heuristic to generate consolidation scenarios. The heuristic was developed to explicitly consider efficiency, effectiveness, and equity objectives, and can be applied in both urban and rural states. The scenarios will generate average statewide bus transportation costs. As applied to the State of Iowa, within the legislature's proposed range of consolidation of 500-1000 students, it was found that transportation operational and capital cost increases range from 0.6 to 10.6 percent and 0.7 to 7.7 percent, respectively.     

A survey on pickup and delivery problems

This paper is the first part of a comprehensive survey on pickup and delivery problems. Basically, two problem classes can be distinguished. The first class, discussed in this paper, deals with the transportation of goods from the depot to linehaul customers and from backhaul customers to the depot. This class is denoted as Vehicle Routing Problems with Backhauls (VRPB). Four subtypes can be considered, namely the Vehicle Routing Problem with Clustered Backhauls (VRPCB – all linehauls before backhauls), the Vehicle Routing Problem with Mixed linehauls and Backhauls (VRPMB – any sequence of linehauls and backhauls permitted), the Vehicle Routing Problem with Divisible Delivery and Pickup (VRPDDP – customers demanding delivery and pickup service can be visited twice), and the Vehicle Routing Problem with Simultaneous Delivery and Pickup (VRPSDP – customers demanding both services have to be visited exactly once). The second class, dealt with in the second part of this survey, refers to all those problems where goods are transported between pickup and delivery locations. These are the Pickup and Delivery Vehicle Routing Problem (PDVRP – unpaired pickup and delivery points), the classical Pickup and Delivery Problem (PDP – paired pickup and delivery points), and the Dial-A-Ride Problem (DARP – passenger transportation between paired pickup and delivery points and user inconvenience taken into consideration). Single as well as multi vehicle versions of the mathematical problem formulations are given for all four VRPB types, the corresponding exact, heuristic, and metaheuristic solution methods are discussed.      

非静止轨道卫星系统考虑通信中断的服务质量分析

基于Globalstar和Odyssey两个Walker delta星座,建立星间链路网络,重点分析网络中的不同轨道间星间链的动态特性,特别是与星上跟瞄系统密切相关的俯仰角、方位角和链路长度变化,为卫星网络路由提供依据.对传统的卫星路由策略作了改进,利用卫星系统的冗余覆盖的特性,选择不同策略下的最优路径.针对用户不能忍受通信中断的情况,提出考虑消除中断的路由策略,进行服务质量的分析比较.同时也比较在消除中断的路由策略下,LEO同MEO网络差异之处.消除通信中断是以其它QoS性能下降为代价.     

汽车零部件入厂物流优化问题研究现状与趋势

汽车零部件入厂物流优化问题一直是汽车物流研究领域的难点和热点。由于零部件入厂物流在总物流成本中的较大占比,所以至今以来国内外学者不断提出多种汽车零部件入厂物流优化问题和解决方法以降低物流成本费用。为了进一步梳理国内外研究现状,对取货模式分类、管理、运作、优化等入厂物流取货模式问题进行了总结分析,并重点介绍了当下的热点取货模式——循环取货(Milk-run)。然后从需求拆分、成本目标优化等角度对车辆路径优化进行较为全面的综述,最后对本领域一些新的研究方向进行了展望。     

A hybrid population heuristic for the heterogeneous vehicle routing problems

The heterogeneous vehicle routing problem (HVRP) plays an important role in supply chain logistics. Two variants of HVRP are treated in this paper: one with fixed and variable costs (HVRPFD), and the other with only variable cost (HVRPD). A hybrid population heuristic that is able to solve both variants is proposed, in which a population of solutions are progressively evolved by crossovers and local searches. Computational results on a set of eight benchmark test problems from literature show that the proposed heuristic produces excellent solutions in short computing times.     

New batch construction heuristics to optimise the performance of order picking systems

Two new batch construction heuristics called K-means Batching (KMB) and Self-organisation Map Batching (SOMB) are developed and verified by simulation experiments. Both KMB and SOMB have a preferment of superior performance in total travel distance and average picking vehicle utility, and even a conspicuous improvement in total CPU running time. Besides, this paper investigates the overall performance of order picking systems integrating storage assignment, order batching and picker routing to find the optimal policy combinations under different order types. The sensitivity analysis is performed to distinguish the relative importance of the various strategies to enhance the performance of operations management.     

浅析LEO卫星网络中的QoS路由问题

LEO卫星网络能够提供全球覆盖,为任何地点的用户提供适时应用服务。然而由于LEO的高速运动,LEO卫星网络的网络拓扑一直处于动态变化的过程中。文中首先分析了在这种动态变化的网络环境中QoS路由面临的新问题,接着提出了解决这些问题的几点考虑。     

一种保证QoS的组播网络设计

给出了一种利用建立一系列本地策略(优先级策略、收发数据速率调整策略、路由选择策略、组播管理策略等)的网络主机来分摊控制管理组播系统的设计，保证了组播系统拥有良好的服务质量。     

从旧货价值挖掘二手市场发展潜力的探究

二手市场作为社会主义市场经济的一部分,一直不为消费者和政府管理者所关注,在任其发展的过程中,商铺数量、商品种类、从业人员等等日益增多,其中的问题也逐渐浮现,亟待解决,一个集约化、流程化管理、规范化的二手市场,不仅方便居民的生活,而且对于地区城市的发展举足轻重。     

机场地面保障服务车辆协同调度和仿真优化

为实现大型机场地面保障服务高效化、智能化运行管理,通过研究多航班、多种地服车辆、多车场、带容量时间窗的复杂车辆路径规划问题,构建地服资源协同调度模型。结果表明：根据航班到达规律和机位分布情况,基于分解的高维进化算法求解效果较好,得到车辆使用数少、行驶距离短、超出时间窗惩罚函数最小和任务均衡的四维多目标优化问题的调度优化方案;通过Anylogic仿真软件验证,可实现机位占用情况、车辆使用情况动态分配和监控。