Impact of replenishment rules with endogenous lead times on supply chain performance

This text summarizes the PhD thesis of Robert Boute, obtained at the Katholieke Universiteit Leuven (Belgium) under supervision of Marc Lambrecht. This doctoral dissertation in the field of Supply Chain Management demonstrates that significant cost reductions can be obtained for both the retailer and the manufacturer when they align their replenishment policy. Such a collaboration strategy goes far beyond “information sharing”. In this summary, we present the research model, the general outline of the thesis and the methodology used. The PhD thesis, written in English, is available from the author upon request.      

Operations research methods in preventing domino accidents in the chemical process industry

This text summarizes the results related to Operations research contained in the PhD thesis defended by the author in June 2006 under the supervision of Karel Soudan at the Universiteit Antwerpen in Belgium. The thesis is written in English and is available from the author upon request (Reniers in shaping an integrated cluster safety culture in the chemical process industry, 415 p, 2006a). This work investigates the optimization of major accident precautions in the chemical process industry. An integrated cluster safety culture is shaped by developing three separate capabilities (procedural, human, and technological) and by both integrating and optimizing them using the well-known Deming loop. The technological (Operations research) part develops a cluster management decision support system. The latter tool offers prevention planning guidance in taking adequate precaution measures to overcome complex domino effect risks.      

Exact and heuristic methodologies for scheduling in hospitals: problems, formulations and algorithms

This text summarizes the PhD thesis defended by the author in January 2006 under the supervision of Professor Erik Demeulemeester at the Katholieke Universiteit Leuven. The thesis is written in English and is available from the author’s website (http://www.econ.kuleuven.be/jeroen.belien). In this research we propose a number of exact and heuristic algorithms for various scheduling problems encountered in hospitals. The emphasis lies on the design of new methodologies as well as on the applicability of the algorithms in real-life environments. The main contributions include a new decomposition approach for a particular class of staff scheduling problems, an extensive study of master surgery scheduling algorithms that aim at leveling the resultant bed occupancy and an innovative method for integrating nurse and surgery scheduling.      

Analysis of discrete-time queueing systems with priority jumps

This text is a summary of the author’s PhD thesis supervised by Herwig Bruneel and Joris Walraevens, and defended on 5 March 2009 at Ghent University. The thesis is written in English and is available from the author upon request. The work deals with several priority scheduling disciplines with so-called priority jumps. An efficient priority scheduling discipline is of great importance in modern telecommunication devices. Static priority scheduling achieves maximum service differentiation between different types of traffic, but may have a too severe impact on the performance of lower-priority traffic. Introducing priority jumps aims for a more gradual service differentiation. In the thesis, we propose several (types of) jumping mechanisms, and we analyse their effect on the performance of a discrete-time queueing system.     

A theorem of Nachbin-Shirota type for algebras

This work was written while the author was preparing his dissertation at the University of Paderborn (Germany). He is indebted to DAAD for the support and to the supervising professors K. D. Bierstedt and M. Oudadess. He would also like to thank professor J. Schmets (Belgium) for his interest in the work.     

The generation of stable project plans

This text summarises the PhD thesis that Roel Leus presented to obtain the degree of Doctor in Applied Economics at the Katholieke Universiteit Leuven, in September 2003. The promotor of the thesis was professor Willy Herroelen. The thesis is written in English and is available from the authors website. The goal of the thesis was to provide recommendations for the detailed scheduling of multi-project organisations, when a certain degree of uncertainty exists about a number of characteristics of the project. Up till now, the majority of the literature on project scheduling has consisted of deterministic models for planning a single project: both the uncertainty aspect as well as the intrinsic difficulty of coordination of a portfolio of projects have been largely ignored.Received: October 2003, MSC classification: 09B35, 90B36     

Pooling of repairable spare parts: A study on inventory policies

This is a summary of the most important results presented in the author's PhD thesis (Wong 2004). This thesis, written in English, was defended on 14 June 2004 at the Katholieke Universiteit Leuven (Belgium) and supervised by Dirk Cattrysse and Dirk Van Oudheusden. A copy is available from the author upon request. It presents a number of modeling and solution approaches for investigating how the use of pooling contributes to the goal of increased service performance and reduced cost in the context of repairable spare parts inventory management. MSC classification: 47N10, 90B05, 91A80     

A solution approach of production planning problems based on compact formulations for single-item lot-sizing models

We survey the main results presented in the authors PhD Thesis presented in June 2003 at the Université catholique de Louvain and supervised by Y. Pochet and L. A. Wolsey. The dissertation is written in English and is available from the author. In the first part of the thesis, we investigate the complexity and the polyhedral structure of various extensions of the uncapacitated single-item lot-sizing problem (Barany et al. 1984). In particular, we study models involving fixed charges on stocks, constant capacity and backlogging, and lower bounds on production. We describe algorithms, extended formulations, (facet-defining) valid inequalities and separation algorithms. Emphasis is placed on compact (i.e. of polynomial size) exact extended formulations. In a second part, we show how such extended reformulations for single-item problems can help to improve the solution of much more general production planning problems.Received: August 2003,     

Modeling, simulation and optimization in logistics

This text summarizes the PhD thesis defended by the author in March 2009 under the supervision of Pasquale Legato at the University of Calabria, Italy. The thesis is written in English and is available for download at the following URL: . It aims to explore friendly Operations Research tools for modeling and simulation of logistics processes, with particular interest for mathematical programming models combined with stochastic simulation tools. In particular key assignment and scheduling problems that arise in maritime container terminals are explored. Initially it is presented a study on different modeling paradigms devoted to the representation of logistical processes and the formalization of problems with complex scheduling/assignment constraints. Successively an IP model for managing the assignment of a pool of rail-mounted gantry cranes to berthed vessels is proposed. Then, according to a functional integration approach, a second model centered on the intra-ship scheduling of vessel container bulks to the assigned cranes is further formulated. Finally a simulation-based optimization approach is investigated and the effectiveness of recent search methods is evaluated by comparison with a commercial solver.     

Suitability and managerial implications of a Master Surgical Scheduling approach

Operating room (OR) planning and scheduling is a popular and challenging subject within the operational research applied to health services research (ORAHS). However, the impact in practice is very limited. The organization and culture of a hospital and the inherent characteristics of its processes impose specific implementation issues that affect the success of planning approaches. Current tactical OR planning approaches often fail to account for these issues. Master surgical scheduling (MSS) is a promising approach for hospitals to optimize resource utilization and patient flows. We discuss the pros and cons of MSS and compare MSS with centralized and decentralized planning approaches. Finally, we address various implementation issues of MSS and discuss its suitability for hospitals with different organizational foci and culture.     

Design of axisymmetric sandwich plates for alternative loads

The minimal-weight design of sandwich plates whose rigidplastic face sheets obey the Tresca yield condition and which are subjected to two alternative loads is systematically determined by the method of stress variation. It is shown that, when the loads are unidirectional, the general solution for a certain class of edge conditions consists of five fundamentally different designs. The totality of optimal design solutions is depicted in the form of a design chart. A comprehensive example is presented to illustrate the method.This paper is based in part upon a dissertation submitted by the first author to The University of Iowa in partial fulfillment of requirements for the PhD Degree.     

Varieties of interlaced bilattices

The paper contains some algebraic results on several varieties of algebras having an (interlaced) bilattice reduct. Some of these algebras have already been studied in the literature (for instance bilattices with conflation, introduced by M. Fitting), while others arose from the algebraic study of O. Arieli and A. Avron??s bilattice logics developed in the third author??s PhD dissertation. We extend the representation theorem for bounded interlaced bilattices (proved, among others, by A. Avron) to unbounded bilattices and prove analogous representation theorems for the other classes of bilattices considered. We use these results to establish categorical equivalences between these structures and well-known varieties of lattices.     

A guided tour of new results on “Trade execution in illiquid markets”

We give an overview of the dissertation “Trade execution in illiquid markets: Optimal stochastic control and multi-agent equilibria” (Schöneborn, PhD thesis, TU Berlin, 2008). The dissertation focuses on two questions in the field of optimal trade execution strategies: First, how should traders best sell an illiquid asset position if they want to maximize the expected utility of liquidation proceeds? And second, in a situation where one market participant needs to liquidate a position, what is the effect of other market participants obtaining advance information of this impending liquidation?     

Trust-region algorithms for derivative-free optimization and nonlinear bilevel programming

We briefly describe the contents of the authors PhD thesis (see Colson 2003) discussed on July 2003 at the University of Namur (Belgium) and supervised by Philippe L. Toint. The contributions presented in this thesis are the development of trust-region methods for solving two particular classes of mathematical programs, namely derivative-free optimization (DFO) problems and nonlinear bilevel programming problems. The thesis is written in English and is available via the author.Received: July 2003, AMS classification: 65D05, 90C30, 90C56, 90C59     

A branch-and-price approach for integrating nurse and surgery scheduling

A common problem at hospitals is the extreme variation in daily (even hourly) workload pressure for nurses. The operating room is considered to be the main engine and hence the main generator of variance in the hospital. The purpose of this paper is threefold. First of all, we present a concrete model that integrates both the nurse and the operating room scheduling process. Second, we show how the column generation technique approach, one of the most employed exact methods for solving nurse scheduling problems, can easily cope with this model extension. Third, by means of a large number of computational experiments we provide an idea of the cost saving opportunities and required solution times.     

Solving scheduling problems from high-level models

This is the summary of the author??s PhD thesis supervised by Yves Deville and Pascal Van Hentenryck, and defended on 25 May 2010?at the Université catholique de Louvain in Louvain-la-Neuve. The thesis is written in English and is available from the author, or downloadable from http://becool.info.ucl.ac.be/files2/thesis-monette.pdf. This work is about the gap between high-level modelling of scheduling problems and its efficient resolution. We propose to automatically classify models of scheduling problems, and to apply an appropriate search algorithm. Thanks to the strong separation between model and search, we propose also a simple way to create hybrid algorithms. A second part of the thesis deals with Constraint Programming approaches for two scheduling problems: The one-machine non-preemptive problem and the Just-In-Time Job-Shop problem. All parts are accompanied by experimental results showing their practicality.     

Performances improvement of the column generation algorithm: application to vehicle routing problems

We survey the main results obtained by the author in his PhD dissertation supervised by Anass Nagih and Lucas Létocart. It was defended in December 2008 at The Computer Science lab of the Paris-Nord University (L.I.P.N.), Villetaneuse, France. The thesis is written in French and is available from . Column generation algorithms are instrumental in many areas of applied optimization, where linear programs with an enormous number of variables need to be solved. Although successfully used in many applications, this method suffers from well-known “instability” issues that somewhat limit its efficiency. This work focuses on accelerating strategies in a column generation scheme; on the first iterations using diversification, on the last iterations using reoptimization and on the overall GC scheme using an improving technique to solve the pricing problems (dynamic programming with blocs). The effectiveness of these approaches is validated on the Vehicle Routing Problem with Time Windows.     

Methods to solve multi-skill project scheduling problem

This is a summary of the author’s PhD thesis supervised by P. Martineau and E. Néron and defended on 28 November 2006 at the Université François-Rabelais de Tours. The thesis is written in French, and is available upon request from the author. This work deals with the problem of scheduling a project. The activities of this project requires skills that may not be mastered by all persons involved. First of all, the problem is defined in the introduction part. Then we propose different methods to solve it: lower bounds in part 2, different heuristics and meta-heuristics in part 3, and finally a branch-and-bound procedure in the last part.