AMIRKABIR
Year:2003 | Volume:14 | Issue:54-D|Papers Count:5

Consider a two-echelon repairable inventory system consisting of a centeral depot and Multiple stocking centers. There are two kinds of defective, type A defects must be repaired at centeral depot, and type B defects at stocking centers. The centers provide parts replacement service to customers and the depot fills center replenishment orders on a FCFS basis. Type A defects that are received at the centers are passed to the depot for repair and depot inventory replenishment. For this system, existing models (for exemple, METRIC model) usually assume that the depot replenishment lead times (DRLTs) (for type A defects) are i.i.d., which however, does not fit well into the service part logistics system, that motivated this research. Because the DRLTs consist of ti,e sum of repair times, defective return times and transportation times, they are different across stocking centers which are located globally. We study the impact of such center dependent DRLTs on system performance. We show that for such system. using the i.i.d. DRLT assumption introduces errors in estimating system performance.

In this paper a new metric (called Exponentially Metric) is introduced on functions from a metric space X into another metric space Y.Exponentially metric can be defined on a large set of functions (called Exponentially Bounded Functions) enjoying interesting properties similar to uniform metric. Some results concerning the exponentially meric are proved.

The competitive and social context in which companies compete is changing. As a result managers must reevaluate their attitudes and approaches to suppliers who are competing. Specially they have to plan a new strategy for selecting their suppliers, and generate a new strong relationship with their loyal suppliers. In this research, the problem of suppliers selection and its development problem will be considered.Based on variety of different condition of suppliers selections for a large number of items and various method of supplying, it would need to do a lot of comparison. In order to achieve different goals with qualitative and quantitative criterias, it is possible to have a multi objective mathematical programming, it has considered several scenarios by sensivity analysis of the model. A numerical example is given to show the results. Finally, the special structure of the model being used, and its extension have been asked througll further research for the fuzzy situation.

In this paper, with emphasis on scheduling of head of crews for coach trains, a crew scheduling problem is presented in a network form with task arcs. To solve the problem, a meta heuristic algorithm based on grouping evolutionary algorithm is developed. The grouping evolutionary algorithm contains two search methods which generate offspring from a parent chromosome; one of these methods is based on a logic constraints heuristic algorithm, and the other one is relied on branch and bound approach. Computational results showed that combining grouping evolutionary algorithm and branch and bound approach generates good solutions, and for the problems that we knew their optimal solutions accomplish optimal outcomes. It is also shown that the algorithm provides goods results for large scale real world problems.

In order to overcome the problems of traffic, socioeconomic, as well as ecological ones, especially in big cities, there is a need for an equipped system to promote the public transportation. Since the urban bus network is the crucial part of the public transportation in developing countries, optimal design of the bus network aiming to improve the countries condition of public transportation enjoys its high importance.Route network design is the single most important planning step in the urban bus transit planning process. This is because the route structure designed with invariably affect both frequency setting and bus and crew sheduling, and also due to the fact that operators have the least flexibility in altering the routes.In this paper, beside defining an innovative way for solving the problem of route finding, a method based on the branch and bound technique is presented. This method is applied to a case study network and results are presented.