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.     

Concentration of competing retail stores

The geographical concentration of stores that sell similar commodities is analyzed using a two-dimensional spatial competition model. A higher concentration of stores attracts more consumers with taste uncertainty and low price expectations (a market-size effect), while it leads to fiercer price competition (a price-cutting effect). Our model is general enough to allow for the coexistence of multiple (possibly) asymmetric clusters of stores. We provide sufficient conditions for the nonemptiness of equilibrium store location choices in pure strategies. Through numerical examples, we illustrate the trade-off between the market-size and price-cutting effects, and provide agglomeration patterns of stores in special cases.     

Unemployment and Economic Policy in Denmark in the 1930s

Abstract

The paper examines Danish unemployment and the employment policy in the 1930s. The unemployment data indicate that though the unemployment increased dramatically the rate of unemployment remained low. The official Danish unemployment records definitely underestimated the actual unemployment in the early 1930s, but the discrepancy was hardly as big as some scholars have suggested. The paper furthermore points out that the rather atypical rise in the Danish unemployment from the mid-1930s can be attributed to a rise in the natural rate of unemployment due to an improved unemployment insurance coverage and a more comprehensive registration of the unemployment. The second part of the paper deals with the Danish employment policy. Unemployment remained high on the political agenda, but the employment problem never became the main target for the economic policy. An active employment policy was constrained by the problems of the balance of payments and the political disagreements in parliament. While the macroeconomic policy did help to stabilize the economy and the employment, the number of measures directly targeting the labour market was small, and they seldom gave rise to much job creation.     

Valuing Pre-Commercial Genetic Resources: A Maximum Entropy Approach

Genetic improvement has been a major contributor to agricultural productivity in the United States, but many questions about the economics of crop breeding, such as the value of pre-commercial germplasm, remain unanswered. This study estimates the marginal value of poorly characterized materials contained in the U.S. national germplasm system. Within the search theoretic framework, we apply a maximum entropy method to estimate the probability and the expected level of improvement in pest susceptibility relative to its best previously observed level. The results indicate that the lower-bound estimate of benefit is significantly higher than the upper-bound cost of conserving an accession.     

Modeling and optimization of a container drayage problem with resource constraints

This paper investigates the problem faced by firms that transport containers by truck in an environment with resource constraints. The considered area is export-dominant. As a result, there are three types of container movements as inbound full, outbound full, and inbound empty movements. Both the time windows at the terminal and at the customers’ places and the operation times are considered. Empty containers are also regarded as separate transportation resources besides trucks. The total operating time including waiting time of all the trucks in operation is minimized. The problem is first formulated as a directed graph and then mathematically modeled based on the graph. It falls into a multiple traveling salesman problem with time windows (m-TSPTW) with resource constraints. An algorithm based on reactive tabu search (RTS) is developed to solve the problem. A number of randomly generated examples indicate that the algorithm can be applied to the real world.     

B2C电子商务中带退货的多配送站点车辆路径优化问题研究

研究了一个带退货的多配送站点车辆路径优化问题,建立了求解该问题的0-1整数规划模型,以实现各个配送站点在给他们客户配送货物的同时,沿途取回这些客户的退货,以节约运输成本的目的。设计了一种新的解的表示方法和邻域变换,以此为基础构造出直接求解多配送站点车辆路径优化问题的禁忌搜索算法,在该禁忌搜索算法中首先通过一个启发式算法求得了0-1整数规划模型的一个较好的初始可行解,从而提高了禁忌搜索算法的收敛速度及性能,最后通过例子对禁忌搜索算法及其性能进行了说明。     

基于禁忌搜索的物流配送中心选址方法研究

物流配送中心选址问题在物流网络规划中占有非常重要的地位,选址的合理与否直接关系到配送中心未来的发展。针对企业选址的一般要求,以配送中心总成本最小为目标,构造了一种物流配送中心选址模型。该模型较接近现实情况,同时,给出了求解该模型的禁忌搜索算法和简单算例。     

飞机发动机吊装实训平台安全性论证

以理论力学,材料力学,机械设计基础为理论依据,通过对发动机在安装状态和在吊装状态时的受力分析,计算论证了飞机发动机吊装实训平台的安全性。并且经过实践检验和无损检测的鉴定,进一步证明了飞机发动机吊装实训平台的安全可靠性。     

基于“会诊式”推理控制策略的智能型搜索引擎的研究

随着Internet和网络技术的发展,搜索引擎给人们带来的很大便利。本文分析了传统搜索引擎的缺点,探讨了"会诊式"推理控制策略的结构和特点,研究了基于"会诊式"推理控制策略的智能型搜索引擎的特征,并给出其实现技术。     

浅论一种新的检查算法

利用平均步长的方法,查找给定值的结点位置,使用C语言描述其算法,讨论了该算法的平均检索长度,与其他算法比较,得出了该算法的优劣结论。