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See detailEarly detection of university students in potential difficulty
Hoffait, Anne-Sophie ULiege; Schyns, Michael ULiege

Conference (2015, February)

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by ... [more ▼]

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by early identifying students who have a high probability to face difficulties if nothing is done, the Universities might develop adapted methods to attack the problem with more emphasis where it is more needed and when it is still possible. Thus we want to develop a decision tool able to identify these students to help them. For that, we consider three standard datamining methods: logistic regression, artificial neural networks and decision trees and focus on early detection, i.e. before starting at the University. Then, we suggest to adapt these three methods as well as the classification framework in order to increase the probability of correct identification of the students. In our approach, we do not restrict the classification to two extreme classes, e.g. failure or success, but we create subcategories for different levels of confidence: high risk of failure, risk of failure, expected success or high probability of success. The algorithms are modified accordingly and to give more weight to the class that really matters. Note that this approach remains valid for any other classification problems for which the focus is on some extreme classes; e.g. fraud detection, credit default... Finally, simulations are conducted to measure the performances of the three methods, with and without the suggested adaptation. We check if the factors of success/failure we can identify are similar to those reported in the literature. We also make a ``what-if sensitivity analysis''. The goal is to measure in more depth the impact of some factors and the impact of some solutions, e.g., a complementary training or a reorientation. [less ▲]

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See detailDoc'Data: mesure de la persévérance au doctorat à l'Université de Liège
Aerts, Stéphanie ULiege; Haesbroeck, Gentiane ULiege; Schyns, Michael ULiege

Report (2015)

Le Conseil du Doctorat a parmi ses missions celle d’accompagner les doctorants dans leur parcours et de mettre en place des actions en vue de favoriser la réussite. Cependant, pour réellement mesurer ... [more ▼]

Le Conseil du Doctorat a parmi ses missions celle d’accompagner les doctorants dans leur parcours et de mettre en place des actions en vue de favoriser la réussite. Cependant, pour réellement mesurer l’impact des actions mises en oeuvre dans cette optique, il faut d’abord pouvoir quantifier le taux de réussite. Or, mesurer le taux de réussite dans les études de 3ème cycle n’est pas une démarche évidente. De nombreux raccourcis de raisonnement sont tentants mais mènent à des résultats très variables et incorrects. Le but de ce document est de présenter les difficultés inhérentes au calcul d’un taux de réussite et de proposer quelques procédures appropriées. Dans un premier temps, les chances (ou, d’un point de vue plus formel, les probabilités) de réussite et d'abandon des doctorants sont modélisées en fonction du nombre d’années d’inscription et en tenant compte de caractéristiques du doctorant comme son genre, sa nationalité, son âge au moment de l’inscription, son statut professionnel... L'analyse descriptive et exploratoire est ensuite confirmée par l’application d’une analyse de survie avec risques compétitifs. [less ▲]

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Peer Reviewed
See detailThe Airline Container Loading Problem with Pickup and Delivery
Lurkin, Virginie ULiege; Schyns, Michael ULiege

Conference (2014, November 09)

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints. The originality of our approach is ... [more ▼]

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints. The originality of our approach is to allow multi-trips with pickup and delivery at some intermediate locations. The objective is to minimize the economic and environmental costs including the impact of the intermediate operations. We resort to an integer linear model. Numerical experiments have been performed using a standard B\&C library. Heuristics are developed to speed up the process. [less ▲]

Detailed reference viewed: 35 (5 ULiège)
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See detailEarly detection of university students in potential difficulty : a case study
Hoffait, Anne-Sophie ULiege; Schyns, Michael ULiege

Conference (2014, November)

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by ... [more ▼]

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by early identifying students who have a high probability to face difficulties if nothing is done, the Universities might develop adapted methods to attack the problem with more emphasis where it is more needed and when it is still possible. Thus we want to develop a decision tool able to identify these students to help them. For that, we consider three standard datamining methods: logistic regression, artificial neural networks and decision trees and focus on early detection, i.e. before starting at the University. Then, we suggest to adapt these three methods as well as the classification framework in order to increase the probability of correct identification of the students. In our approach, we do not restrict the classification to two extreme classes, e.g. failure or success, but we create subcategories for different levels of confidence: high risk of failure, risk of failure, expected success or high probability of success. The algorithms are modified accordingly and to give more weight to the class that really matters. Note that this approach remains valid for any other classification problems for which the focus is on some extreme classes; e.g. fraud detection, credit default... Finally, simulations are conducted to measure the performances of the three methods, with and without the suggested adaptation. We check if the factors of success/failure we can identify are similar to those reported in the literature. We also make a ``what-if sensitivity analysis''. The goal is to measure in more depth the impact of some factors and the impact of some solutions, e.g., a complementary training or a reorientation. [less ▲]

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Peer Reviewed
See detailThe Airline Container Loading Problem with Pickup and Delivery
Lurkin, Virginie ULiege; Schyns, Michael ULiege

in Airline Group of the Intl Federation of Operational Research Soc ( AGIFORS ) (Ed.) 54th AGIFORS Annual Proceedings 2014 (2014, October 19)

The present paper looks into the problem of optimizing the loading of a set of containers and pallets into cargo aircraft serving multiple airports. Due to the pickup and delivery operations occurring at ... [more ▼]

The present paper looks into the problem of optimizing the loading of a set of containers and pallets into cargo aircraft serving multiple airports. Due to the pickup and delivery operations occurring at intermediate airports, this problem is simultaneously a weight and balance problem and a sequencing problem. Our objective is to minimize fuel and handling operations costs. This problem is shown to be NP-hard. We resort to a mixed integer linear program. On the basis of a professional partner's real-world data, TNT Airways, we perform numerical experiments using a standard B&C library. This approach yields better solutions than traditional manual planning, which results in substantial cost savings. [less ▲]

Detailed reference viewed: 92 (16 ULiège)
See detailA 'price balance statistic' for optimizing pricing strategies: a better estimation of elasticities and cross-elasticities
Lurkin, Virginie ULiege; Schyns, Michael ULiege; Garrow, Laurie A. et al

Conference (2014, May 16)

Demand forecasting, price optimization and capacity controls form three major tools of revenue management. Over the past few decades, each discipline has generated a great deal of research but has ... [more ▼]

Demand forecasting, price optimization and capacity controls form three major tools of revenue management. Over the past few decades, each discipline has generated a great deal of research but has typically been studied separately from the others. Yet, better understanding their relationship gives an airline the opportunity to increase its profitability. In prior work, Tim Jacobs and colleagues introduced a macro-level metric known as the ‘Price Balance Statistic (PBS)’ for evaluating the quality of a given pricing strategy and guiding a search algorithm to identify an optimal alignment between pricing structure, scheduled capacity and RM controls using marginal revenue principles. The aim of our work is to incorporate additional modeling improvements to the PBS. The current model formulation uses price elasticity as input parameters and assumes perfect independency between the different fare classes. However, in reality, a passenger demand fluctuates between classes based on differences in prices. We propose to use instrumented variable linear regression methods to obtain parameter estimates for price elasticities and cross-elasticities. This modification incorporates accurate price elasticities but also the impact of a change in one fare class on another through the cross-elasticities. [less ▲]

Detailed reference viewed: 51 (12 ULiège)
Peer Reviewed
See detailA 'price balance statistic' for optimizing pricing strategies: a better estimation of elasticities and cross-elasticities
Lurkin, Virginie ULiege; Schyns, Michael ULiege; Garrow, Laurie A. et al

Conference (2014, May 15)

Demand forecasting, price optimization and capacity controls form three major tools of revenue management. Over the past few decades, each discipline has generated a great deal of research but has ... [more ▼]

Demand forecasting, price optimization and capacity controls form three major tools of revenue management. Over the past few decades, each discipline has generated a great deal of research but has typically been studied separately from the others. Yet, better understanding their relationship gives an airline the opportunity to increase its profitability. In prior work, Tim Jacobs and colleagues introduced a macro-level metric known as the ‘Price Balance Statistic (PBS)’ for evaluating the quality of a given pricing strategy and guiding a search algorithm to identify an optimal alignment between pricing structure, scheduled capacity and RM controls using marginal revenue principles. The aim of our work is to incorporate additional modeling improvements to the PBS. The current model formulation uses price elasticity as input parameters and assumes perfect independency between the different fare classes. However, in reality, a passenger demand fluctuates between classes based on differences in prices. We propose to use instrumented variable linear regression methods to obtain parameter estimates for price elasticities and cross-elasticities. This modification incorporates accurate price elasticities but also the impact of a change in one fare class on another through the cross-elasticities. [less ▲]

Detailed reference viewed: 96 (17 ULiège)
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See detailEarly detection of university students in potential difficulty
Hoffait, Anne-Sophie ULiege; Schyns, Michael ULiege

Conference (2014, January)

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by ... [more ▼]

Rate of success in the first year at University in Belgium is very low regarding other foreign universities. The University of Liege, as other Universities, has already taken different initiatives. But by early identifying students who have a high probability to face difficulties if nothing is done, the Universities might develop adapted methods to attack the problem with more emphasis where it is more needed and when it is still possible. Thus we want to develop a decision tool able to identify these students to help them. For that, we consider three standard datamining methods: logistic regression, artificial neural networks and decision trees and focus on early detection, i.e. before starting at the University. Then, we suggest to adapt these three methods as well as the classification framework in order to increase the probability of correct identification of the students. In our approach, we do not restrict the classification to two extreme classes, e.g. failure or success, but we create subcategories for different levels of confidence: high risk of failure, risk of failure, expected success or high probability of success. The algorithms are modified accordingly and to give more weight to the class that really matters. Note that this approach remains valid for any other classification problems for which the focus is on some extreme classes; e.g. fraud detection, credit default... We check if the factors of success/failure we can identify are similar to those reported in the literature. We also make a ``what-if sensitivity analysis''. The goal is to measure in more depth the impact of some factors and the impact of some solutions, e.g., a complementary training or a reorientation. [less ▲]

Detailed reference viewed: 25 (2 ULiège)
See detailA constructive heuristic for the three dimensional Bin Packing Problem with transportation constraints
Paquay, Célia ULiege; Schyns, Michael ULiege; Limbourg, Sabine ULiege

Conference (2014)

The aim of this work is to propose a Relax-And-Fix heuristic to build a good initial solution to the 3D BPP. First, a mathematical formulation has been developed taking into account several types of ... [more ▼]

The aim of this work is to propose a Relax-And-Fix heuristic to build a good initial solution to the 3D BPP. First, a mathematical formulation has been developed taking into account several types of constraints such as the stability and fragility of the boxes to pack, their possibility to rotate, the weight distribution inside the bins and their special shapes. Since this model contains a lot of integer variables, we have decided to apply the Relax-and-Fix method. We have selected several sets of variables to be the branching variables and carried out some tests. [less ▲]

Detailed reference viewed: 143 (6 ULiège)
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See detailThe Airline Container Loading Problem with Pickup & Delivery and Multi Doors
Schyns, Michael ULiege; Lurkin, Virginie ULiege

in 53rd AGIFORS Annual Proceedings 2013: Annual Symposium and Study Group Meeting (2013, August)

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints, including the management of ... [more ▼]

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints, including the management of several doors. The originality of our approach is to allow multi-trips with pickup and delivery at some intermediate locations. The objective is to minimize the economic and environmental costs including the impact of the intermediate operations. We resort to an integer linear model. Numerical experiments have been performed using a standard B&C library. The cost impact is measured. The Airline Group of the International Federation of Operational Research Societies, composed of professionals and academics, has awarded us the price of the "Best technical presentation" for this work. [less ▲]

Detailed reference viewed: 140 (42 ULiège)
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Peer Reviewed
See detailThe Airline Container Loading Problem with Pickup and Delivery
Lurkin, Virginie ULiege; Schyns, Michael ULiege

Conference (2013, July 02)

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints. The originality of our approach is ... [more ▼]

We address the problem of allocating containers into predefined positions of a carrier, in this case aircraft, under several realistic structural and safety constraints. The originality of our approach is to allow multi-trips with pickup and delivery at some intermediate locations. The objective is to minimize the economic and environmental costs including the impact of the intermediate operations. We resort to an integer linear model. Numerical experiments have been performed using a standard B\&C library. Heuristics are developed to speed up the process. [less ▲]

Detailed reference viewed: 146 (21 ULiège)
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Peer Reviewed
See detailA branch and price approach for an airport vehicle routing problem
Schyns, Michael ULiege

Conference (2013, July)

This project has been initiated by a main European freight airport. The goal is to optimize the aircraft refueling process which relies on a given set of trucks. The underlying process can be defined as a ... [more ▼]

This project has been initiated by a main European freight airport. The goal is to optimize the aircraft refueling process which relies on a given set of trucks. The underlying process can be defined as a vehicle routing problem with capacity and time windows. We resort to a branch and price approach for which we first analyze the impact of different parameters on the performance of the algorithm. Due to the stochastic nature of the demand and time windows in this context, we are also working on a priori (split delivery) and a posteriori (efficient re-optimization) measures. [less ▲]

Detailed reference viewed: 93 (5 ULiège)
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See detailAutomatic Aircraft Cargo Load Planning with Pick-up and Delivery
Lurkin, Virginie ULiege; Schyns, Michael ULiege

Conference (2013, March 15)

This research aims to develop a new mixed integer linear program to solve the containers assignment problem when pickup and deliveries are considered. Given a pool of ULDs and an aircraft with multiple ... [more ▼]

This research aims to develop a new mixed integer linear program to solve the containers assignment problem when pickup and deliveries are considered. Given a pool of ULDs and an aircraft with multiple destinations, we want to obtain a loading plan determining at which positions the ULDs must be assigned in order to minimize simultaneous the quantity of fuel consumed and the number of re-handles. The loading plan should also ensure a number of structural, safety and manoeuvrability constraints. The model has been tested on real instances and provides encouraging results. [less ▲]

Detailed reference viewed: 188 (31 ULiège)
See detailAutomatic Aircraft Cargo Load Planning with Pick-up and Delivery
Lurkin, Virginie ULiege; Schyns, Michael ULiege

Conference (2013, February 07)

This research aims to develop a new mixed integer linear program to solve the containers assignment problem when pickup and deliveries are considered. Given a pool of ULDs and an aircraft with multiple ... [more ▼]

This research aims to develop a new mixed integer linear program to solve the containers assignment problem when pickup and deliveries are considered. Given a pool of ULDs and an aircraft with multiple destinations, we want to obtain a loading plan determining at which positions the ULDs must be assigned in order to minimize simultaneous the quantity of fuel consumed and the number of re-handles. The loading plan should also ensure a number of structural, safety and manoeuvrability constraints. The model has been tested on real instances and provides encouraging results. [less ▲]

Detailed reference viewed: 178 (22 ULiège)
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Peer Reviewed
See detailAutomatic Cargo Load Planning: Special shipments
Kleyntssens, Thomas ULiege; Limbourg, Sabine ULiege; Schyns, Michael ULiege

in ILS 2012 Proceedings (2012, August 28)

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. Indeed, loading the aircraft so the gross weight is less than the maximum allowable is not enough. This ... [more ▼]

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. Indeed, loading the aircraft so the gross weight is less than the maximum allowable is not enough. This weight must be distributed to keep the centre of gravity within specified limits. Moreover, an aircraft has usually several cargo compartments with specific contours and structural limitations such as floor loading, combined load limits and cumulative load limitations. Finally, some shipments are particularly restrictive to transport, like dangerous goods, live animals and perishable goods. This paper is concerned with the incorporation of these latter constraints in a mixed integer linear program for the problem of loading a set of Unit Loading Devices and bulk into an aircraft. Experimental results show that our method achieves optimal solutions within only few seconds. [less ▲]

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See detailThree dimensional Bin Packing Problem applied to air cargo
Paquay, Célia ULiege; Schyns, Michael ULiege; Limbourg, Sabine ULiege

in ILS 2012 Proceedings (2012, August 26)

Deciding whether a set of three dimensional boxes can be packed into a container is a NP-hard problem. Mathematical models have been developed, however, only few studies take into account constraints ... [more ▼]

Deciding whether a set of three dimensional boxes can be packed into a container is a NP-hard problem. Mathematical models have been developed, however, only few studies take into account constraints encountered in real-world applications such as the stability or the fragility of the cargo. Moreover, despite the importance of this issue in air transport, the literature is almost silent on constraints related to the distribution of the weight inside a container. This paper is concerned with the formulation of the three dimensional palletization which includes the main constraints met in the air cargo industry. [less ▲]

Detailed reference viewed: 154 (21 ULiège)