On alternative mixed integer programming formulations and LP-based heuristics for lot-sizing with setup times

We address the multi-item, capacitated lot-sizing problem (CLSP) encountered in environments where demand is dynamic and to be met on time. Items compete for a limited capacity resource, which requires a setup for each lot of items to be produced causing unproductive time but no direct costs. The problem belongs to a class of problems that are difcult to solve. Even the feasibility problem becomes combinatorial when setup times are considered. This difculty in reaching optimality and the practical relevance of CLSP make it important to design and analyse heuristics to nd good solutions that can be implemented in practice. We consider certain mixed integer programming formulations of the problem and develop heuristics including a curtailed branch and bound, for rounding the setup variables in the LP solution of the tighter formulations. We report our computational results for a class of instances taken from literature

Conceptual design of an e-marketplace for small and medium enterprises in the Turkish machinery industry

This paper reports on the results of a study carried out in the Turkish machinery industry. The purpose of the study was to identify the benefits the sector can seize from e-business and to develop a conceptual framework for potential e-business applications. We analysed the current state of e-business use in the machinery industry in order to understand the future requirements and application opportunities and to come up with a conceptual e-business design that would suit both the needs and the characteristics of the sector. The study included those companies, which are members of the Machine Manufacturers’ Association (MMA) in Turkey. Information about the existing applications and future requirements was obtained from the results of a survey conducted among the member companies. Statistically adequate number of responses was obtained to make the results representative of the machine industry. Web sites of the member companies were also reviewed for further information gathering. Results indicated that most of the companies are Small and Medium Enterprises(SME) and it would be better for them to carry out certain operations through an e-market specifically designed for the sector. The proposed conceptual e-market design is based on the characteristics of the industry emerging from the survey

Drift or shift? Continuity, change, and international variation in knowledge production in OR/MS

With the aim of contributing to the debate around OR/MS as a discipline, this study provides a historical comparative investigation of publicly available knowledge production in the field. The empirical investigation is based on a content analysis of 300 randomly selected articles from six major journals in the field. We have found: (1) since the late 1950s to the present day there has been no significant change in the types of published research in OR/MS in North America; (2) from the late 1950s to the present day, there have been significant differences in types of published research in OR/MS internationally. The imputed imbalance between theory and applications in published work had already occurred in the early stages of the development of OR/MS in North America and has since remained very much the same. Furthermore, research in the United Kingdom has been distinctly different from that dominant in North America and elsewhere. There are also indications that outside North America and the United Kingdom there is an emerging turn towards applications-oriented research. Over the last two or three decades there has been a significant increase overall in the share of articles published by academic authors

Toward the Physical Internet—Logistics Service Modularity and Design Implications

The Physical Internet (PI) is a modularization of logistics services: standardized protocols, full interoperability and standardized packaging, PI‐containers, and encapsulated freight. The PI‐containers are a core component of the PI; however, previous PI studies have not addressed those containers’ repositioning, despite its importance and effect on the PI network efficiency. In this paper, we analyze how the PI‐containers’ design and characteristics will determine the containers’ flows in a domestic network context. The flows are studied strategically using a linear programming model minimizing flow imbalances between hubs and simulating the effect of PI‐container compatibility. The model is tested using inter‐regional freight data from Sweden, and the results are framed using modularity theory. Our analysis reveals that PI‐container compatibility in terms of forward and reverse flows determines whether PI presents increased or decreased empty runs compared with the existing conventional logistics system. Departing from modularization theory, we discuss our results, emphasizing not only the importance of keeping synergistic specificity low but also how the characteristics will affect the urgency of technology use. Our implications are important to supply chain managers and policymakers for the future research on the Physical Internet, PI‐container repositioning and routing, and packaging design.This accepted article is published as Sternberg, H.S. and Denizel, M. (2020), Toward the Physical Internet—Logistics Service Modularity and Design Implications. J Bus Logist. November 202; doi:10.1111/jbl.12261. Posted with permission. </p

Addressing endogeneity in the causal relationship between sustainability and financial performance

The existing empirical literature on the relationship between corporate sustainability performance and corporate financial performance casts doubt on the direction of this relationship although more studies point out a direction from sustainability to performance. Literature also presents a gap in addressing the mechanism(s) of the relationship that hinders the convergence of the empirical findings and only recently the question of causality is being addressed with modern econometric techniques. We argue that due to the potential endogeneity problem in the relationship, an empirical strategy without a theoretical base may result in inconclusive or misleading conclusions. We address the potential endogeneity problem in the relationship and identify the possible causes of this endogeneity as: (i) firm level heterogeneity in financial returns, (ii) the relationship between firm's productivity level and the marginal cost of sustainability initiatives, and (iii) measurement error. We implement Instrumental Variable (IV) technique to overcome these biases. Our results present empirical evidence to support the hypothesis that corporate sustainability is positively related (possibly causally) with corporate financial performance. We further find that sustainability initiatives are more costly for companies that are more productive; thus, they have less incentive to invest. Finally, measurement error in the sustainability metrics does not play a crucial role.This accepted article is published as Soytas, M.A., Denizel, M., Usar, D.D., Addressing endogeneity in the casual relationship between sustainability and financial performance. International Journal of Production Economics, 210(April 2019);56-71. Doi: 10.1016/j.ijpe.2019.01.016. Posted with permission.</p