Search

Abstract. In many computing and networking applications, arriving tasks have to be routed to one of many servers, with the goal of minimizing queueing delays. When the number of processors [...]

We study call routing policies for call centers with multiple call types and multiple agent groups. We introduce new weight-based routing policies where each pair (call type, agent group) is [...]

This paper presents an extension of the classical capacitated hub location problem with multiple assignments in which the amount of capacity installed at the hubs is part of the decision [...]

This paper presents a dynamic (or multi-period) hub location problem. It proposes a branch-and-bound algorithm that uses a Lagrangian relaxation to obtain lower and upper bounds at the nodes of [...]

This paper presents a branch-and-price algorithm for the capacitated hub location problem with single assignment, in which Lagrangean relaxation is used to obtain tight lower bounds of the restricted master [...]

Hub-and-spoke networks are widely applied in a variety of industries such as transportation, postal delivery, and telecommunications. Although they are designed to exploit economies of scale, hub-and-spoke networks are known [...]

Determining the pattern of links within a large social network is often problematic due to the labour-intensive nature of the data collection and analysis process. With constrained data collection capabilities it is often only possible to either make detailed observations of a limited number of individuals in the network, or to make fewer observations of a larger number of people. Previously we have shown how detailed observation of a small network can be used, which infer where in the network previously unconnected individuals are likely to fit, thereby attempting to predict network growth as new people are considered for inclusion. Here, by contrast, we show how social network topology can be inferred following a limited observation of a large network. Essentially the issue is one of inferring the presence of links that are missed during a constrained data collection campaign on the network. It is particularly difficult to infer network structures for those organizations that actively seek to remain covert and undetected. However, it is often very useful to know if two given individuals are likely to be connected even though limited surveillance effort yields no evidence of a link. Specifically, we show how a statistical inference technique can be used to successfully predict the existence of links that are missed during network sampling. The procedure is demonstrated using network data obtained from open source publications. Keywords: networks and graphs; defence studies; probability; forecasting

Hub location problems involve locating hub facilities and allocating demand nodes to hubs in order to provide service between origin-destination pairs. In this study, we focus on cargo applications of the hub location problem. Through observations from the Turkish cargo sector, we propose a new mathematical model for the hub location problem that relaxes the complete hub network assumption. Our model minimizes the cost of establishing hubs and hub links, while designing a network that services each origin-destination pair within a time bound. We formulate a single-allocation hub covering model that permits visiting at most three hubs on a route. The model is then applied to the realistic instances of the Turkish network and to the Civil Aeronautics Board data set. Keywords: hub location; hub cover; cargo applications; location; logistics

Hubs are critical elements of telecommunication and transportation networks because they play a vital role in mass traffic movement. The design of more reliable networks in hub-and-spoke systems is a [...]

When considering hub-and-spoke networks with multiple allocation, the classical models of the literature compute solutions with large discount factors for small flows on interhub connections. Addressing the economies of scale [...]

The solutions for hub network design problem, using integer programming, are presented.

Solutions for integer linear formulations of the multiple allocation hub location problem are presented.

Hub networks play an important role in many transportation and telecommunications systems. This paper introduces a new model called the hub arc location model. Rather than locate discrete hub facilities, this model locates hub arcs, which have reduced unit flow costs. Four special cases of the general hub arc location model are examined in detail. We provide motivation for the new models, and present examples and optimal solutions, using data for U.S. air passenger traffic. Results are used to compare optimal costs, hub locations, and hub arc locations with corresponding hub median optimal solutions. The results reveal interesting spatial patterns and help identify promising cities and regions for hubs. A companion paper (Campbell et al. 2005) presents integer programming formulations and solution algorithms for the new hub arc problems. It also provides details and computation times for these solution algorithms. Key words: hub arc location; hub location; network design, 1. Introduction Hub networks play an important role in many transportation and telecommunication systems. These networks provide connections between many origins and destinations via hub facilities that serve as switching, [...]

A companion paper (Campbell et al. 2005) introduces new hub arc location models and analyzes optimal solutions, with special attention to spatial pattens and relationships. This paper provides integer programming formulations and optimal solution algorithms for these problems. We describe two optimal solution approaches in detail and compare their performance, using standard hub location data sets. We present implementation details and show how algorithms can be fine tuned based on characteristics of the data. Key words: hub arc location; hub location; network design; integer programming formulations; algorithms, 1. Introduction This paper provides integer programming formulations and details of optimal solution algorithms for the hub arc location models presented in (Campbell et al. 2005). That paper provides motivation [...]

Formulations and solution approaches for multiple allocation hub location problems are discussed. A number of results that enable to develop preprocessing procedures and tightening constraints for existing mixed integer linear programming formulations are presented.

We study the hub coveting problem which, so far, has remained one of the unstudied hub location problems in the literature. We give a combinatorial and a new integer programming formulation of the hub coveting problem that is different from earlier integer programming formulations. Both new and old formulations are nonlinear binary integer programs. We give three linearizations for the old model and one linearization for the new one and test their computational performances based on 80 instances of the CAB data set. Computational results indicate that the linear version of the new model performs significantly better than the most successful linearization of the old model both in terms of average and maximum CPU times as well as in core storage requirements. Keywords: hub location; hub cover; location; combinatorial problems; integer programming

Mixed integer programming formulations for an alternative network design to help discount cost of flows are presented. Computational results comparing the models are given which confirm the effectiveness of the formulations.

This letter proposes a static synchronous series compensator switching functions model based on a 48-pulse voltage-source inverter in abc coordinates. The effectiveness and accuracy of the model are validated against simulations carried out in the professional computer program PSCAD/EMTDC. Index Terms--Static synchronous series compensator (SSSC), switching functions, voltage-source inverter (VSI).