Article (Scientific journals)
Recovery management for a dial-a-ride system with real-time disruptions
Paquay, Célia  ; Crama, Yves  ; Pironet, Thierry 
2020 • In European Journal of Operational Research, 280, p. 253-269
The problem considered in this work stems from a non-profit organization in charge of door-to-door passenger transportation for medical appointments. Patients are picked up at home by a driver and are then dropped at their appointment location. They may also be driven back home at the end of their appointment. Some patients have specific requirements, e.g., they may require an accompanying person or a wheelchair. Planning such activities gives rise to a so-called dial-a-ride problem. In the present work, it is assumed that the requests assigned to the drivers have been selected, and the transportation plan has been established for the next day. However, in practice, appointment durations may vary due to unforeseen circumstances, and some transportation requests may be modified, delayed or canceled during the day. The aim of this work is to propose a reactive algorithm which can adapt the initial plan in order to manage the disruptions and to take care of as many patients as possible in real-time. The plan should be modified quickly when a perturbation is observed, without resorting to major changes which may confuse the drivers and the patients. Several recourse procedures are defined for this purpose. They allow the dispatcher to temporarily delete a request, to insert a previously deleted request, or to permanently cancel a request. Simulation techniques are used to test the approach on randomly generated scenarios. Several key performance indicators are introduced in order to measure the impact of the disruptions and the quality of the solutions.
Article (Scientific journals)
A Comprehensive Comparison of Word Embeddings in Event & Entity Coréférence Resolution.
Poumay, Judicaël  ; Ittoo, Ashwin 
2021 • In Findings of the Association for Computational Linguistics
Article (Scientific journals)
Using meaning instead of words to track topics
Poumay, Judicaël  ; Ittoo, Ashwin 
2022 • In Natural Language Processing and Information Systems
The ability to monitor the evolution of topics over time is extremely valuable for businesses. Currently, all existing topic tracking methods use lexical information by matching word usage. However, no studies has ever experimented with the use of semantic information for tracking topics. Hence, we explore a novel semantic-based method using word embeddings. Our results show that a semantic-based approach to topic tracking is on par with the lexical approach but makes different mistakes. This suggest that both methods may complement each other.
Article (Scientific journals)
Cycle Selections
Baratto, Marie  ; Crama, Yves 
In press • In Discrete Applied Mathematics
We introduce the following cycle selection problem which is motivated by an application to kidney exchange problems. Given a directed graph, a cycle selection is a subset of arcs forming a union of directed cycles. A related optimization problem, the Maximum Weighted Cycle Selection problem can be defined as follows: given a weight for each arc, find a cycle selection which maximizes the total weight. We prove that this problem is strongly NP-hard. Next, we focus on cycle selections in complete directed graphs. We provide several ILP formulations of the problem: an arc formulation featuring an exponential number of constraints which can be separated in polynomial time, four extended compact formulations, and an extended non compact formulation. We investigate the relative strength of these formulations. We concentrate on the arc formulation and on the description of the associated cycle selection polytope. We prove that this polytope is full-dimensional, and that all the inequalities used in the arc formulation are facet-defining. Furthermore, we describe three new classes of facet-defining inequalities and a class of valid inequalities. We also consider the consequences of including additional constraints on the cardinality of a selection or on the length of the associated cycles.
Article (Scientific journals)
Une audience virtuelle pour l’entrainement de la fluence de parole lors d’une prise de parole en public : Etude pilote
Menjot, Pauline; Remacle, Angélique  ; Schyns, Michael  et al.
2021 • In Les cahiers de l'ASELF, 18 (2), p. 13-18
Contexte : Prendre la parole face à une audience est un défi pour beaucoup. Elle est considérée comme l’une des activités les plus craintes. L’anxiété liée à la prise de parole en public a un impact sur les performances de communication, notamment sur la fluence de parole. La littérature met en évidence les bénéfices d’un entrainement ciblant les compétences communicationnelles liées à cette activité. Néanmoins, son implémentation dans des situations proches du monde réel reste complexe. Par conséquent, la réalité virtuelle pourrait être un outil novateur et pertinent pour ce type d’entrainement. Objectifs : Cette étude vise à valider l’utilisation d’une audience virtuelle pour l’entrainement de la prise de parole en public en évaluant sa capacité à susciter des réactions émotionnelles (en termes d’anxiété) et comportementales (en termes de disfluences). Méthodologie : Huit participants ont réalisé une présentation orale dans trois conditions : 1) face à un public réel (Vivo_Public), 2) devant un public virtuel (Virtuo_Public) et 3) dans une salle de conférence virtuelle sans public (Virtuo_Vide). Les disfluences et le niveau d’anxiété des participants ont été analysés. Le vécu de l’immersion dans l’environnement virtuel a quant à lui été évalué au moyen d’un questionnaire portant sur le sentiment de présence et les cybermalaises. Résultats : Les réactions comportementales, le sentiment de présence satisfaisant et l’absence de cybermalaises suggèrent que cet environnement virtuel est un outil prometteur pour l’entrainement à la prise de parole en public. Conclusion : Cette étude est la première étape d’un projet à long terme. Elle a permis de mettre en évidence les éléments positifs de cette audience virtuelle ainsi que ceux nécessitant une amélioration. D’autres études sont toutefois nécessaires pour améliorer cet environnement et confirmer statistiquement sa validité écologique.
Article (Scientific journals)
Time-Dependent Stochastic Vehicle Routing Problem with Random Requests: Application to online police patrol management in Brussels
Saint-Guillain, Michael; Paquay, Célia  ; Limbourg, Sabine 
2020 • In European Journal of Operational Research
The Static and Stochastic Vehicle Routing Problem with Random Requests (SS-VRP-R) describes realistic operational contexts in which a fleet of vehicles has to serve customer requests appearing dynamically. Based on a probabilistic knowledge about the appearance of requests, the SS-VRP-R seeks a priori sequences of vehicle relocations, optimizing the expected responsiveness to the requests. In this paper, an existing computational framework, based on recourse strategies, is adapted to meet the objectives of the SS-VRP-R. The resulting models are applied to a real case study of the management of police units in Brussels. In this context, the expected average response time is minimized. To cope with the reality of the urban context, a time-dependent variant is also studied (TD-SS-VRP-R) in which the travel time between two locations is a function that depends on the departure time at the first location. Experiments confirm the contribution and the adaptability of the recourse strategies to a real-life, complex operational context. Provided an adequate solution method, simulation-based results show the high quality of the a priori solutions designed, even when compared to those designed by field experts. Finally, the experiments provide evidence that there is no potential gain in considering time-dependency in such an operational context.
Article (Scientific journals)
Covid-19: contribution of clinical characteristics and laboratory features for early detection of patients with high risk of severe evolution
Sepulchre, Edith  ; Pittie, Guillaume; Stojkovic, Violeta et al.
2022 • In Acta Clinica Belgica, 77 (2), p. 261-267
The aim of this study was to identify early clinical and laboratory predictive factors of a severe coronavirus disease 2019 (COVID-19). The study revealed clinical and laboratory features able to predict high risk of ICU requirement, or even death, at admission time. These results provide a potential tool for patient’s triage in a context of pandemic.
Article (Scientific journals)
The time-consistent dial-a-ride problem
Tellez Sanchez, Oscar Augusto  ; Vercraene, Samuel; Lehuédé, Fabien et al.
2021 • In Networks
In the context of door-to-door transportation of people with disabilities, service quality considerations such as maximum ride time and service time consistency are critical requirements. To identify a good trade-off between these considerations and economic objectives, we define a new variant of the multiperiod dial-a-ride problem called the time-consistent dial-a-ride problem. A transportation planning is supposed to be time consistent if for each passenger, the same service time is used all along the planning horizon. However, considering the numerous variations in transportation demands over a week, designing consistent plan for all passengers can be too expensive. It is therefore necessary to find a compromise solution between costs and time-consistency objectives. The time-consistent dial-a-ride problem is solved using an epsilon-constraint approach to illustrate the trade-off between these two objectives. It computes an approximation of the Pareto front, using a matheuristic framework that combines a large neighbourhood search with the solution of set partitioning problems. This approach is benchmarked on time-consistent vehicle routing problem literature instances. Experiments are also conducted in the context of door-to-door transportation for people with disabilities, using real data. These experiments support managerial insights regarding the inter-relatedness of costs and quality of service.
Article (Scientific journals)
A stakeholder oriented approach to the optimization of transports of people with disabilities
Tellez Sanchez, Oscar Augusto  ; Daguet, Laurent; Lehuédé, Fabien et al.
2020 • In Supply Chain Forum: An International Journal, 21 (2), p. 93-102
Article (Scientific journals)
Using i* and UML for Blockchain Oriented Software Engineering: Strengths,Weaknesses, Lacks and Complementarity
Vingerhoets, Anne Sofie; Heng, Samedi  ; Wautelet, Yves
2021 • In Complex Systems Informatics and Modeling Quarterly, 26
New blockchain-based projects do appear every day. The technology has indeed been popularized by cryptocurrencies but is now gaining interest in various domains and new types of applications are evaluated constantly. Understanding the impact of blockchain adoption on the organization and the internals of blockchain-related behavior nevertheless remains a challenge for managers but also for IT professionals. This article studies how two existing organizational and software modeling languages can be fit to document a blockchain development project in Supply Chain Management (SCM) at its earliest stages. These two frameworks are i* on the one side and the Unified Modeling Language (UML) use case and sequence diagrams on the other side. The real life project used as a case study in this application is ‘Farm-to-Fork’ where a blockchain solution for the Supply Chain (SC) of farm animals is developed. The application of the frameworks is intended to identify their strengths and weaknesses. An extension of i* is proposed to deal with blockchain privacy issues as well as laws and norms. We finally point to the complementarity of i* and UML use case and sequence diagrams in a Blockchain-Oriented Software Engineering (BOSE) context. The i* framework indeed supports early requirements to understand the impact of the project on stakeholders while UML use case and sequence diagrams support the late requirements and the design by depicting the use of blockchain and some of its behavioral mechanisms.
Article (Scientific journals)
Gleaning Insight from Antitrust Cases Using Machine Learning
Massarotto, Giovanna; Ittoo, Ashwin 
2021 • In Stanford Computational Antitrust, 1
Article (Scientific journals)
AI algorithms, price discrimination and collusion: a technological, economic and legal perspective
Gautier, Axel  ; Ittoo, Ashwin  ; Van Cleynenbreugel, Pieter 
2020 • In European Journal of Law and Economics, 50 (3), p. 405-435
Article (Scientific journals)
The Impact of Virtual Reality Exposure on Stress Level and Sense of Competence in Ambulance Workers
Chaabane, Sourour  ; Etienne, Anne-Marie  ; Schyns, Michael  et al.
2021 • In Journal of Traumatic Stress
Virtual reality (VR) exposure is one of the tools used in clinical psychology to treat anxiety dis-orders. It is also used to enhance the resilience of soldiers by confronting them with virtual combat environments. Increasing their resilience could strengthen them against the negative consequences of trauma exposure or the suffering experienced by people they rescued. Most studies focused on military and emergency medical staff but none has so far investigated ambu-lance workers’ experience (AW) while they are daily confronted with traumatic situations. The current study aims to assess the impact of a single VR exposure session on AW’ competence and stress. Forty participants were randomly assigned to either a VR immersion (experimental group, N = 20) or an audio immersion (control group, N = 20) of a shooting attack situation. The main hypotheses were that VR would lead to a decrease of anxiety, as measured by visual analogue scales, as well as an increase in the sense of competence compared to the control situa-tion. Results showed a significant reduction in the fear in both groups. Besides, results revealed an increase of the sense of competence after the VR immersion, and a reduction of the tension in the control group, even if these differences did not reach statistical significance’s level (p = 0.06). Although our hypotheses were only partially confirmed, since beneficial effects of either VR and the audio description on stress were observed, findings suggested that VR exposure could be a useful way to increase the resilience of the AW.
Article (Scientific journals)
Competing risks proportional-hazards cure model and Generalized Extreme Value regression: an application to bank failures and acquisitions in the United States.
Beretta, Alessandro  ; Heuchenne, Cédric  ; Restaino, Maria-Luisa
2022 • In Journal of Applied Statistics
Article (Scientific journals)
penPHcure: Variable Selection in Proportional Hazards Cure Model with Time-Varying Covariates
Beretta, Alessandro  ; Heuchenne, Cédric 
2021 • In R Journal, 13 (1), p. 116-129
Article (Scientific journals)
One-sided variable sampling interval EWMA control charts for monitoring the multivariate coefficient of variation in the presence of measurement errors
Nguyen, Quoc Thong  ; Ginger-Bosh, Vincent; Tran, Kim Duc et al.
2021 • In International Journal of Advanced Manufacturing Technology, 115 (5-6), p. 1821-1851
Article (Scientific journals)
Monitoring the Coefficient of Variation using Variable Sampling Interval CUSUM control charts
Tran, Phuong Hanh  ; Heuchenne, Cédric 
2021 • In Journal of Statistical Computation and Simulation, 91 (3), p. 501-521
Article (Scientific journals)
Monitoring coefficient of variation using one-sided run rules control charts in the presence of measurement errors
Tran, Phuong Hanh  ; Heuchenne, Cédric  ; Nguyen, Huu Du et al.
2021 • In Journal of Applied Statistics, 48 (12), p. 2178- 2204
We investigate, in this paper, the effect of the measurement error (ME) on the performance of Run Rules control charts monitoring the coefficient of variation (CV) squared. The previous Run Rules CV chart in the literature is improved slightly by monitoring the CV squared using two one-sided Run Rules charts instead of monitoring the CV itself using a two-sided chart. The numerical results show that this improvement gives better performance in detecting process shifts. Moreover, we will show through simulation that the precision and accuracy errors do have a negative effect on the performance of the proposed Run Rules charts. We also find out that taking multiple measurements per item is not an effective way to reduce these negative effects. The proposed Run Rules control charts can be applied in the anomaly detection area.
Article (Scientific journals)
How do Volatility Regimes Affect the Pricing of Quality and Liquidity in the Stock Market ?
Bazgour, Tarik  ; Heuchenne, Cédric  ; Hübner, Georges  et al.
2021 • In Studies in Nonlinear Dynamics and Econometrics, 25 (1)
This paper shows how stock market volatility regimes affect the cross-section of stock returns along quality and liquidity dimensions. We find that, during crisis periods, low quality and low liquidity stocks experience relatively higher losses than predicted in normal times, while high quality and high liquidity stocks experience rather relatively lower losses. These findings lend strong support to the presence of cross-market and within-market flight-to-quality and to-liquidity episodes during crisis periods. During low volatility periods, however, low quality and low liquidity stocks earn relatively larger returns, while high quality and high liquidity stocks yield lower returns; suggesting that low volatility conditions benefit junk and illiquid stocks but not quality and liquid stocks. Finally, our results reveal that liquidity-level dominates liquidity-beta in explaining stock returns across the different market volatility regimes.
Article (Scientific journals)
The nonparametric location-scale mixture cure model
Chown, Justin; Heuchenne, Cédric  ; Van Keilegom, Ingrid
2020 • In TEST, 29, p. 1008-1028
We propose completely nonparametric methodology to investigate location-scale modeling of two-component mixture cure models that is similar in spirit to accelerated failure time models, where the responses of interest are only indirectly observable due to the presence of censoring and the presence of long-term survivors that are always censored. We use nonparametric estimators of the location-scale model components that depend on a bandwidth sequence to propose an estimator of the error distribution function that has not been considered before in the literature. When this bandwidth belongs to a certain range of undersmoothing bandwidths, the proposed estimator of the error distribution function is root-n consistent. A simulation study investigates the finite sample properties of our approach, and the methodology is illustrated using data obtained to study the behavior of distant metastasis in lymph-node-negative breast cancer patients. © 2019, Sociedad de Estadística e Investigación Operativa.
Article (Scientific journals)
Monitoring process variation using modified EWMA
Saghir, Aamir; Aslam, Muhammad; Faraz, Alireza  et al.
2020 • In Quality and Reliability Engineering International, 36 (1), p. 328-339
A new control chart, namely, modified exponentially weighted moving average (EWMA) control chart, for monitoring the process variance is introduced in this work by following the recommendations of Khan et al.15 The proposed control chart deduces the existing charts to be its special cases. The necessary coefficients, which are required for the construction of modified EWMA chart, are determined for various choices of sample sizes and smoothing constants. The performance of the proposed modified EWMA is evaluated in terms of its run length (RL) characteristics such as average RL and standard deviation of RL. The efficiency of the modified EWMA chart is investigated and compared with some existing control charts. The comparison reveals the superiority of proposal as compared with other control charts in terms of early detection of shift in process variation. The application of the proposal is also demonstrated using a real-life dataset. © 2019 John Wiley & Sons, Ltd.
Article (Scientific journals)
Inference for monotone single-index conditional means: a Lorenz regression approach.
Heuchenne, Cédric  ; Jacquemin, Alexandre
2022 • In Computational Statistics and Data Analysis
Article (Scientific journals)
Goodness-of-fit tests for censored regression based on artificial data points
Gonzalez, Wenceslao González; Heuchenne, Cédric  ; Sanchez, César Sánchez et al.
2020 • In TEST, 29, p. 599-615
Suppose we have a location-scale regression model where the location is the conditional mean and the scale is the conditional standard deviation; the response is possibly right-censored, the covariate is fully observed, and the error is independent of the covariate. We propose new goodness-of-fit testing procedures for the conditional mean and variance based on an integrated regression function technique which uses artificial data points. We obtain the weak convergence of the resulting processes and study their finite sample behavior via simulations. Finally, we analyze a data set about unemployment in Galicia. © 2019, Sociedad de Estadística e Investigación Operativa.
Article (Scientific journals)
Estimation from cross-sectional data under a semiparametric truncation model
Heuchenne, Cédric  ; De uña Alvarez, Jacobo; Laurent, Géraldine
2020 • In Biometrika, 107 (2), p. 449-465
Article (Scientific journals)
The impact of axle weight constraints on the deployment of a mixed-fleet in vehicle routing decisions
Pollaris, Hanne; Janssens, Gerrit K; Braekers, Kris et al.
2021 • In IJTTE. International Journal for Traffic and Transport Engineering, 11 (3)
A vehicle routing problem (VRP), using a mixed fleet of vehicles, with sequence-based pallet loading and axle weight constraints is introduced. The effect of the integration of axle weight constraints in a Fleet Size and Mix VRP is analyzed by comparing the problem with and without axle weight constraints. A vehicle fleet of 30-foot and 45-foot trucks, consisting of a tractor and a semi-trailer, is considered. Two scenarios are analyzed with different objective functions. In the first scenario, the objective aims to minimize total distance while in the second scenario the objective aims the minimization of total transport costs. An Iterated Local Search metaheuristic algorithm is used to solve the problem. The results indicate that the impact of axle weight constraints on the solution cost of a vehicle routing problem depends on the fleet composition. Therefore, decisions on the deployment of a mixed-size fleet may be influenced by the integration of axle weight constraints.
Article (Scientific journals)
A matheuristic for solving inventory sharing problems
Achamrah, Fatima Ezzahra; Riane, Fouad; Di Martinelly, Christine et al.
2022 • In Computers and Operations Research
In this paper, we addressed a two-level supply chain in which a company manufactures products and sells them through its point of sale network. The problem of concern is a multi-product, multi-vehicle inventory sharing routing problem. We formulated it as a mixed-integer linear programming problem. We also designed a two-phase matheuristic that integrates mathematical modelling strengthened with relevant derived valid inequalities and hybridisation of sophisticated metaheuristics: Genetic Algorithm and Simulated Annealing. We tested 660 best known instances designed for the single and multi-vehicle inventory routing problem, and the results showed that the matheuristic outperformed the best known algorithms regarding computational times and enhanced 156 solutions for large instances. Extra experiments were conducted on a set of data specially designed for the multi-product multi-vehicle inventory sharing routing problem. Computational results highlighted the benefits of sharing inventory on the overall supply chain. Finally, a sensitivity analysis was conducted, which revealed the extent to which inventory sharing among different points of sale can be cost-effective by the savings it brings to reduce lost sales and inventory holding.
Article (Scientific journals)
Solving inventory routing with transshipment and substitution under dynamic and stochastic demands using genetic algorithm and deep reinforcement learning
Achamrah, Fatima Ezzahra; Riane, Fouad; Limbourg, Sabine 
2021 • In International Journal of Production Research
In this paper, we investigate a two-level supply chain consisting of a company which manufactures a set of products and distributes them via its central warehouse to a set of customers. The problem is modelled as a dynamic and stochastic inventory routing problem (DSIRP) that considers two flexible instruments of transshipment and substitution to mitigate shortages at the customer level. A new resolution approach, based on the hybridisation of mathematical modelling, Genetic Algorithm and Deep Reinforcement Learning is proposed to handle the combinatorial complexity of the problem at hand. Tested on the 150 most commonly used benchmark instances for single-vehicle-product DSIRP, results show that the proposed algorithm outperforms the current best results in the literature for medium and large instances. Moreover, 450 additional instances for multi-products DSIRP are generated. Different demand distributions are examined in these experiments, namely, Normal distribution, Poisson distribution for demand occurrence, combined with demands of constant size; Stuttering Poisson distribution and Negative Binomial distribution. In terms of managerial insights, results show the advantages of promoting inventory sharing and substitutions on the overall supply chain performance.
Article (Scientific journals)
An iterative two-stage heuristic algorithm for a bilevel service network design and pricing model
Tawfik, Christine Maher Fouad  ; Gendron, Bernard; Limbourg, Sabine 
2021 • In European Journal of Operational Research
Building upon earlier research, we revisit a bilevel formulation of service design and pricing for freight networks, with the aim of investigating its algorithmic aspects. The model adds substantial computational challenges to the existing literature, as it deals with general integer network design variables. An iterative heuristic algorithm is introduced, based on the concepts of inverse optimization and neighbourhood search. The procedure alternates between two versions of restricted formulations of the model while inducing promising changes into the service assignments. The approach has proven a high performance for all of the considered real-world instances. Its efficiency rests on its ability to deliver results within a close proximity to those obtained by the exact solver in terms of quality, yet within a significantly smaller amount of time, and to land feasible solutions for the large-sized instances that could not be previously solved. In line with the sustainable transport goals, a deeper observation of the transport management side highlights the strategy of the algorithm favouring freight consolidation and achieving high load factors.
Article (Scientific journals)
Cost and Environmental Impacts of a Mixed Fleet of Vehicles
Fraselle, Justin  ; Limbourg, Sabine  ; Vidal, Laura 
2021 • In Sustainability, 13 (9413)
Urban parcel delivery is increasingly restricted by regulations limiting access to certain heavy or high emitting vehicles to reduce emissions and noise pollution in cities. Cargo bikes represent an alternative solution that enables deliveries with low environmental impact, but they may represent a higher economic cost and come with constraints like battery autonomy or small loading capacity. As a transport scheme relying on bikes for the last miles with fewer externalities, it is regarded as an environmentally friendly choice, and economic sustainability is assessed. This paper aims to present the environmental and economic aspects of different delivery means of transport in European urban areas. Life cycle assessment (LCA) methodology is selected to analyse the environmental impact of several vehicles, allowing us to quantify the emissions according to the loading factor. The electricity mix is an important parameter and makes the results vary according to the country studied. For the economic aspect, the cost price allows us to quantify the operational cost of each means of transport. A trade-off can thus be made between the two.
Article (Scientific journals)
Spare parts inventory routing problem with transshipment and substitutions under stochastic demands
Achamrah, Fatima Ezzahra; Riane, Fouad; Limbourg, Sabine 
2022 • In Applied Mathematical Modelling, 101, p. 309–331
We study a two-level spare parts supply chain in which a manufacturer supplies a central warehouse (CW) with original equipment manufacturer (OEM) and replacement or pattern parts (PP). The CW, distantly located from the manufacturer, distributes both OEM parts and PP to a given number of depots facing stochastic demands. The demand for spare parts is intermittent, exhibiting an infrequent rate and extreme dispersal over time periods. Along with lateral transshipment, PP can be used as substitutes for the OEM parts to sidestep shortage at depots. Assuming that emergency shipments are significantly longer and more expensive, we aim at underlining the relative effectiveness of such a new spare parts inventory management policy. A mixed-integer linear programming model is proposed to solve the inventory routing problem with transshipment and substitution under stochastic demands. The objective is to minimise costs of holding inventory, transportation which includes regular shipment and transshipment, substitution and lost sales. To solve the problem, Sample Average Approximation method is used. Based on empirical goodness-of-fit tests, three demand patterns are studied: Poisson distribution, stuttering Poisson distribution and negative binomial distribution. The model is tested on well-known benchmark instances generated for multi-product multi-vehicle IRP. Computational experiments highlight the benefits of promoting transshipment and substitution on the overall supply chain performance. Results also suggest insights, which are of interest to professionals who are willing to develop new decision support models for the most efficient management of such items.
Article (Scientific journals)
Le retournement territorial au prisme de l'optimisation des chaines logistiques agricoles dans le département du Bourgou au Bénin : cas du maïs et du soja
Lihoussou, Messan; Limbourg, Sabine 
2021 • In Annales de l’Université de Parakou : Lettres, arts et sciences humaines, 4 (1), p. 59-74
Le processus du retournement territorial permet d’étudier les changements de modèles au niveau des populations concernées. Cette contribution vise à analyser ce processus mais sous un angle nouveau, celui de l’organisation des chaines logistiques agricoles à travers l’utilisation des entrepôts modernes de stockage. Pour y arriver, cette recherche s’appuie sur des enquêtes de terrain en décembre 2019 et janvier 2020 (observation directe, focus group et enquêtes avec questionnaire) auprès de 287 producteurs et productrices des huit communes du Borgou. Les données collectées à l’aide des smartphones sont traitées grâce aux logiciels SPSS 21.0 et RStudio. Les résultats montrent que l’utilisation des magasins pour le stockage des récoltes du maïs et du soja améliore la rentabilité des activités paysannes, le regain local, le rayonnement socioéconomique et contribue à une structuration des territoires intérieurs. Les entrepôts modernes agricoles sont des outils déterminants de l’accès au marché et du retournement territorial.
Article (Scientific journals)
An Artificial-Immune-System-Based Algorithm Enhanced with Deep Reinforcement Learning for Solving Returnable Transport Item Problems
Achamrah, Fatima Ezzahra; Riane, Fouad; Sahin, Evren et al.
2022 • In Sustainability, 14 (10), p. 5805
This paper proposes a new approach, i.e., virtual pooling, for optimising returnable transport item (RTI) flows in a two-level closed-loop supply chain. The supply chain comprises a set of suppliers delivering their products loaded on RTIs to a set of customers. RTIs are of various types. The objective is to model a deterministic, multi-supplier, multi-customer inventory routing problem with pickup and delivery of multi-RTI. The model includes inventory-level constraints, the availability of empty RTIs to suppliers, and the minimisation of the total cost, including inventory holding, screening, maintenance, transportation, sharing, and purchasing costs for new RTIs. Furthermore, suppliers with common customers coordinate to virtually pool their inventory of empty RTIs held by customers so that, when loaded RTIs are delivered to customers, each may benefit from this visit to pick up the empty RTI, regardless of the ownership. To handle the combinatorial complexity of the model, a new artificial-immune-system-based algorithm coupled with deep reinforcement learning is proposed. The algorithm combines artificial immune systems’ strong global search ability and a strong self-adaptability ability into a goal-driven performance enhanced by deep reinforcement learning, all tailored to the suggested mathematical model. Computational experiments on randomly generated instances highlight the performance of the proposed approach. From a managerial point of view, the results stress that this new approach allows for economies of scale and cost reduction at the level of all involved parties to about 40%. In addition, a sensitivity analysis on the unit cost of transportation and the procurement of new RTIs is conducted, highlighting the benefits and limits of the proposed model compared to dedicated and physical pooling modes.
Article (Scientific journals)
Designing unmanned aerial vehicle networks for biological material transportation - The case of Brussels
Dhote, jeremy; Limbourg, Sabine 
2020 • In Computers & Industrial Engineering
Unmanned Aerial Vehicles (UAVs) may solve, or at least reduce, the negative impacts of road transport such as accidents, pollution and congestion. The objective of this paper is to design UAV networks for biomedical material transportation in line with the Drone4Care project. Political, Economic, Social, Technological, Environmental, Legal (PESTEL) analysis provides an overview of the macro-environmental factors that should be considered. To identify the internal and external factors that are favourable and unfavourable to achieve this objective, Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis is also performed. The raised issues are translated into a number of quantifiable scenario elements containing the most plausible up-coming events that may impact the future of UAV networks. Four location models are developed and applied to the city of Brussels and its periphery with respect to the associated market in terms of biomedical product flows (blood units or medical samples that are transported between hospitals, laboratories, and blood transfusion centres). In the context of separate case studies of scenario-based analysis, the experiments show that the use of charging stations is useful to extend the mission ranges and to gain market share. The results also show the possibility of gradually implementing the bases without requiring any major changes such as closing a base.
Article (Scientific journals)
Towards a sustainable production of maize and soybean in the department of Borgou
Lihoussou, Messan; Limbourg, Sabine 
2022 • In Cleaner Logistics and Supply Chain, 4, p. 100039
In Benin, as in most sub-Saharan African countries, people continue to rely primarily on low-productivity agriculture for livelihood and employment. Producers are faced with significant logistical challenges whilst managing their harvest. We empirically investigated the situation of the producers of maize and soybean in the department of Borgou. This research is aligned with the United Nations’ Sustainable Development Goal 2, zero hunger, and 12, sustainable consumption and production. Workshops brought together delegates from producer groups of the Borgou department, researchers in agronomy and management, rural development technicians from the non-governmental organization named Eclosio and the regional union of maize and soybean producers of Borgou-Alibori. The exchanges led to the development of a survey questionnaire. Then, direct and personal interviews was conducted with maize and soybean producers in their preferred language based on the questionnaire. The main objective of this paper is to support strategic choices towards a sustainable production of maize and soybean in the department of Borgou. Results show the need to finance agricultural campaigns, use warehouses, and have a transparent and trustworthy space for farmers and buyers to negotiate fair prices.
Article (Scientific journals)
Recourse in Kidney Exchange Programs
Smeulders, Bart; Bartier, Valentin; Crama, Yves  et al.
2022 • In INFORMS Journal on Computing, 34 (2), p. 1191-1206
The problem to decide which patient-donor pairs in a kidney exchange program should undergo a crossmatch test is modelled as a two-stage stochastic optimization problem. We give an integer programming formulation of this so-called selection problem, and describe a solution method based on Benders decomposition. We extensively test various solution methods, and observe that the solutions, when compared to solutions found by recourse models, lead to an improvement in the expected number of transplants. We also investigate the computational efficiency of our approach as a function of different parameters, such as maximum cycle length and the presence of altruistic donors.
Article (Scientific journals)
Compact quadratizations for pseudo-Boolean functions
Boros, Endre; Crama, Yves  ; Rodriguez Heck, Elisabeth 
2020 • In Journal of Combinatorial Optimization, 39, p. 687-707
The problem of minimizing a pseudo-Boolean function, that is, a real-valued function of 0-1 variables, arises in many applications. A quadratization is a reformulation of this nonlinear problem into a quadratic one, obtained by introducing a set of auxiliary binary variables. A desirable property for a quadratization is to introduce a small number of auxiliary variables. We present upper and lower bounds on the number of auxiliary variables required to define a quadratization for several classes of specially structured functions, such as functions with many zeros, symmetric, exact k-out-of-n, at least k-out-of-n and parity functions, and monomials with a positive coefficient, also called positive monomials. Most of these bounds are logarithmic in the number of original variables, and we prove that they are best possible for several of the classes under consideration. For positive monomials and for some other symmetric functions, a logarithmic bound represents a significant improvement with respect to the best bounds previously published, which are linear in the number of original variables. Moreover, the case of positive monomials is particularly interesting: indeed, when a pseudo-Boolean function is represented by its unique multilinear polynomial expression, a quadratization can be obtained by separately quadratizing its monomials.