Hub location problems in transportation networks

In this paper we propose a 4-index formulation for the uncapacitated multiple allocation hub location problem tailored for urban transport and liner shipping network design. This formulation is very tight and most of the tractable instances for MIP solvers are optimally solvable at the root node. While the existing state-of-the-art MIP solvers fail to solve even small size instances of problem, our accelerated and efficient primal (Benders) decomposition solves larger ones. In addition, a very efficient greedy heuristic, proven to be capable of obtaining high quality solutions, is proposed. We also introduce fixed cost values for Australian Post (AP) dataset.     

A tabu search heuristic for redesigning a multi-echelon supply chain network over a planning horizon

This paper addresses the problem of redesigning a supply chain network with multiple echelons and commodities. The problem belongs to a comprehensive class of network redesign problems previously introduced in the literature. Redesign decisions comprise the relocation of existing facilities to new sites under an available budget over a finite time horizon, the supply of commodities by upstream facilities, the inventory levels at storage facilities, and the flow of commodities through the network. The problem is modeled as a large-scale mixed-integer linear program. Feasible solutions are obtained by using a tabu search procedure that explores the space of the facility location variables. The latter prescribe the time periods in which changes in the network configuration occur. They are triggered by the setup of new facilities, which operate with capacity transferred from the existing facilities, and by closing the latter upon their entire relocation. As the problem is highly constrained, infeasible solutions with excess budget are allowed during the course of the search process. However, such solutions are penalized for their infeasibility. Computational experiments on realistically sized randomly generated instances indicate that this strategic oscillation scheme used in conjunction with tabu search performs very well.     

Multi-period layout planning for hospital wards

Layout planning for hospitals is a long-term decision. Nevertheless, medical and organizational factors change over time. For example, demand for different-sized bed rooms varies based on medical requirements and patient preferences. In this paper, we consider the planning of ward layouts over multiple periods using different approaches. The fixed ward layout models aim at minimizing either the number of demand violations or costs for installing fixed patient rooms. In contrast, the variable ward layout model allows for layout adaptations to satisfy demand. Thus, additional costs for the movement of walls have to be considered. The application of the different approaches as a decision support tool for hospital planners is explained. Hence, it can be derived in which settings the costs for adapting a layout do not exceed the benefits of such a change. Computational experiments demonstrate the applicability of the models for realistic instances.     

Multidimensional Competition and Corporate Disclosure

In this paper, we argue that the influence product market competition exerts on disclosure is defined by the combined effect of the incentives and disincentives to disclose raised by the multiple competition dimensions. We distinguish between firm‐ and industry‐level competition measures, and we hypothesize that the former raises agency and proprietary costs, whereas the latter creates incentives to disclose either to fulfil the owners’ need for information to monitor managers or to deter the entrance of new competitors in the industry. Our research design allows for non‐monotonic relationships between competition and disclosure as well as for interactions between competition dimensions. Using a sample of US manufacturing companies, we gather evidence that is consistent with our hypotheses. First, we find an inverted U‐shape relationship between corporate disclosure and a firm's abnormal profitability, which is suggestive of firms being reluctant to disclose when they are underperforming (outperforming) their rivals because of the fear of unveiling agency conflicts (raising proprietary costs). Second, we observe a U‐shape relationship between corporate disclosure and industry profitability, although this U design evolves to approximate a rising function as the protection provided by entry barriers increases.