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See detailModeling in Air Transportation: Cargo Loading and Itinerary Choice
Lurkin, Virginie ULg

in 4OR : Quarterly Journal of the Belgian, French and Italian Operations Research Societies (2016)

This is a summary of the author's PhD thesis supervised by Michael Schyns and defended on April 29, 2016 at the University of Li\`ege, Belgium. We examine two problems as part of this dissertation. The ... [more ▼]

This is a summary of the author's PhD thesis supervised by Michael Schyns and defended on April 29, 2016 at the University of Li\`ege, Belgium. We examine two problems as part of this dissertation. The first is a cargo loading problem. The second problem we examine involves the estimation of itinerary choice models that include price variables and correct for price endogeneity using a control function that uses several types of instrumental variables. [less ▲]

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See detailModeling in Air Transportation: Cargo Loading and Itinerary Choice
Lurkin, Virginie ULg

Doctoral thesis (2016)

We examine two problems as part of this dissertation. The first is a cargo loading problem. The aim is to load a set of containers and pallets into a cargo aircraft that serves multiple airports. Our work ... [more ▼]

We examine two problems as part of this dissertation. The first is a cargo loading problem. The aim is to load a set of containers and pallets into a cargo aircraft that serves multiple airports. Our work is the first to model cargo transport as a series of trips consisting of several legs at the end of which pickup and delivery operations might occur. This problem is crucial for airlines because in an attempt to reduce their costs, most airlines prefer to load as many containers as possible, even if all the loaded containers do not have the same final destination. Our results demonstrate that it is possible to quickly find near optimal or excellent feasible loading plans, and that our approach leads to substantial savings with respect to typical manual approaches currently used in practice. The second problem we examine involves the estimation of itinerary choice models that include price variables and correct for price endogeneity using a control function that uses several types of instrumental variables. The motivation for developing these models is to demonstrate the importance of accounting for price endogeneity and to estimate different price sensitivities as a function of advance purchase periods. This is important as the airline industry can use our results to incorporate different customer segments as revealed through high-yield and low-yield booking curves when evaluating the profitability of airline schedules. Results based on Continental U.S. markets for May 2013 departures showed that models that fail to account for price endogeneity overestimate customers' value of time and result in biased price estimates and incorrect pricing recommendations. The advanced models estimated (nested logit and ordered generalized extreme value (OGEV) models) are shown to outperform the baseline multinomial logit model with regard to statistical tests and behavioral interpretations. Additionally, results show that price sensitivities vary as a function of advance purchase periods, with those purchasing high-yield products being less price sensitive than those purchasing low-yield products (across any advance purchase periods) and those purchasing closer to departure being less price sensitive. Results also indicate that inter-alternative competition is strong for itineraries that share similar departure times. Finally, as part of the itinerary choice model developed in this dissertation, we estimate highly refined departure time of day preferences. Results are intuitive and show that departure time of day preferences vary across many dimensions including the length of haul, direction of travel, number of time zones crossed, departure day of week, and itinerary type (i.e., outbound, inbound, and one-way itineraries). To the best of our knowledge, these curves represent the most refined publicly-available estimates of airline passengers' time of day preferences. [less ▲]

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See detailModeling inflorescence development in tomato
Périlleux, Claire ULg; Lobet, Guillaume ULg; Tocquin, Pierre ULg

Conference (2015, June)

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See detailModeling information sharing in animal health surveillance with social network analysis
Delabouglise, Alexis; Dao Thi, Hiep; Nguyen Tien, Thanh et al

Poster (2014, May 08)

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See detailModeling inter-laminar failure in composite structures: illustration on an industrial case study
Bruyneel, Michaël ULg; Delsemme, Jean-Pierre; Jetteur, Philippe et al

in Applied Composite Materials (2009), 16

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See detailModeling lactation curves and estimation of genetic parameters for first lactation test-day records of French Holstein cows.
Druet, Tom ULg; Jaffrezic, F.; Boichard, D. et al

in Journal of Dairy Science (2003), 86(7), 2480-90

Several functions were used to model the fixed part of the lactation curve and genetic parameters of milk test-day records to estimate using French Holstein data. Parametric curves (Legendre polynomials ... [more ▼]

Several functions were used to model the fixed part of the lactation curve and genetic parameters of milk test-day records to estimate using French Holstein data. Parametric curves (Legendre polynomials, Ali-Schaeffer curve, Wilmink curve), fixed classes curves (5-d classes), and regression splines were tested. The latter were appealing because they adjusted the data well, were relatively insensitive to outliers, were flexible, and resulted in smooth curves without requiring the estimation of a large number of parameters. Genetic parameters were estimated with an Average Information REML algorithm where the average information matrix and the first derivatives of the likelihood functions were pooled over 10 samples. This approach made it possible to handle larger data sets. The residual variance was modeled as a quadratic function of days in milk. Quartic Legendre polynomials were used to estimate (co)variances of random effects. The estimates were within the range of most other studies. The greatest genetic variance was in the middle of the lactation while residual and permanent environmental variances mostly decreased during the lactation. The resulting heritability ranged from 0.15 to 0.40. The genetic correlation between the extreme parts of the lactation was 0.35 but genetic correlations were higher than 0.90 for a large part of the lactation. The use of the pooling approach resulted in smaller standard errors for the genetic parameters when compared to those obtained with a single sample. [less ▲]

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See detailModeling leucine's metabolic pathway and knockout prediction improving the production of surfactin, a biosurfactant from Bacillus subtilis
Coutte, François; Niehren, Joachim; Dhali, Debarun et al

in Biotechnology journal (2015), 10(8), 1216-1234

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See detailModeling Lymphangiogenesis in a three-dimensional culture system
Bruyere, Françoise; Melen-Lamalle, Laurence; Blacher, Silvia ULg et al

in Nature Methods (2008), 5(5), 431-437

Unraveling the molecular mechanisms of lymphangiogenesis is hampered by the lack of appropriate in vitro models of three-dimensional (3D) lymph vessel growth which can be used to exploit the potential of ... [more ▼]

Unraveling the molecular mechanisms of lymphangiogenesis is hampered by the lack of appropriate in vitro models of three-dimensional (3D) lymph vessel growth which can be used to exploit the potential of available transgenic mice. We developed a potent reproducible and quantifiable 3D-culture system of lymphatic endothelial cells, the lymphatic ring assay, bridging the gap between 2D-in vitro and in vivo models of lymphangiogenesis. Mice thoracic duct fragments are embedded in a collagen gel leading to the formation of lymphatic capillaries containing a lumen as assessed by electron microscopy and immunostaining. This assay phenocopies the different steps of lymphangiogenesis, including the spreading from a preexisting vessel, cell proliferation, migration and differentiation into capillaries. Our study provides evidence for the implication of an individual matrix metalloproteinase, MMP-2, during lymphangiogenesis. The lymphatic ring assay is a robust, quantifiable and reproducible system which offers new opportunities for rapid identification of unknown regulators of lymphangiogenesis. [less ▲]

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See detailModeling medium-scale TEC structures observed by Belgian GPS receivers network
Kutiev, Ivan; Marinov, Pencho; Fidanova, Stefka et al

in Advances in Space Research (2009), 43

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See detailModeling Microbial Cross-contamination in Quick Service Restaurants by Means of Experimental Simulations With Bacillus Spores
Baptista Rodrigues, Ana Lúcia ULg; Crevecoeur, Sébastien ULg; Dure, Remi et al

Poster (2010)

Cross contamination has been frequently mentioned as being in the origin of a wide range of food borne outbreaks. Handling of food is one of the ways through which cross contamination may occur. For many ... [more ▼]

Cross contamination has been frequently mentioned as being in the origin of a wide range of food borne outbreaks. Handling of food is one of the ways through which cross contamination may occur. For many different reasons, quick service restaurants are particularly at risk. Due to its importance, cross contamination via the hands should be taken into consideration when carrying out a quantitative risk assessment. The main goal of this study was to determine transfer rates of bacteria to and via the hands, reduction rates of two hand sanitizing procedures and to apply the results to a quantitative microbial risk assessment model. According to our results, handling of a portion of raw minced meat contaminated at 4.104 cfu leads to the presence of 24 cfu on both hands, 3 cfu on ready-to-eat product (RTE) manipulated with unwashed hands, 1 cfu on RTE manipulated with wiped hands and absence on RTE manipulated with washed hands. This study provides adequate quantitative data for quantitative microbial risk assessment. [less ▲]

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See detailModeling microdamage behavior of cortical bone
Donaldson, Finn; Ruffoni, Davide ULg; Schneider, Philipp et al

in BIOMECHANICS AND MODELING IN MECHANOBIOLOGY (2014), 13(6), 1227-1242

Bone is a complex material which exhibits several hierarchical levels of structural organization. At the submicron-scale, the local tissue porosity gives rise to discontinuities in the bone matrix which ... [more ▼]

Bone is a complex material which exhibits several hierarchical levels of structural organization. At the submicron-scale, the local tissue porosity gives rise to discontinuities in the bone matrix which have been shown to influence damage behavior. Computational tools to model the damage behavior of bone at different length scales are mostly based on finite element (FE) analysis, with a range of algorithms developed for this purpose. Although the local mechanical behavior of bone tissue is influenced by microstructural features such as bone canals and osteocyte lacunae, they are often not considered in FE damage models due to the high computational cost required to simulate across several length scales, i.e., from the loads applied at the organ level down to the stresses and strains around bone canals and osteocyte lacunae. Hence, the aim of the current study was twofold: First, a multilevel FE framework was developed to compute, starting from the loads applied at the whole bone scale, the local mechanical forces acting at the micrometer and submicrometer level. Second, three simple microdamage simulation procedures based on element removal were developed and applied to bone samples at the submicrometerscale, where cortical microporosity is included. The present microdamage algorithm produced a qualitatively analogous behavior to previous experimental tests based on stepwise mechanical compression combined with in situ synchrotron radiation computed tomography. Our results demonstrate the feasibility of simulating microdamage at a physiologically relevant scale using an image-based meshing technique and multilevel FE analysis; this allows relating microdamage behavior to intracortical bone microstructure. [less ▲]

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See detailModeling milk urea of Walloon dairy cows in management perspectives.
Bastin, Catherine ULg; Laloux, Laurent; Gillon, Alain ULg et al

in Journal of Dairy Science (2009), 92(7), 3529-40

The aim of this study was to develop an adapted random regression test-day model for milk urea (MU) and to study the possibility of using predictions and solutions given by the model for management ... [more ▼]

The aim of this study was to develop an adapted random regression test-day model for milk urea (MU) and to study the possibility of using predictions and solutions given by the model for management purposes. Data included 607,416 MU test-day records of first-lactation cows from 632 dairy herds in the Walloon Region of Belgium. Several advanced features were used. First, to detect the herd influence, the classical herd x test-day effect was split into 3 new effects: a fixed herd x year effect, a fixed herd x month-period effect, and a random herd test-day effect. A fixed time period regression was added in the model to take into account the yearly oscillations of MU on a population scale. Moreover, first autoregressive processes were introduced and allowed us to consider the link between successive test-day records. The variance component estimation indicated that large variance was associated with the random herd x test-day effect (48% of the total variance), suggesting the strong influence of herd management on the MU level. The heritability estimate was 0.13. By comparing observed and predicted MU levels at both the individual and herd levels, target ranges for MU concentrations were defined to take into account features of each cow and each herd. At the cow level, an MU record was considered as deviant if it was <200 or >400 mg/L (target range used in the field) and if the prediction error was >50 mg/L (indicating a significant deviation from the expected level). Approximately 7.5% of the MU records collected between June 2007 and May 2008 were beyond these thresholds. This combination allowed for the detection of potentially suspicious cows. At the herd level, the expected MU level was considered as the sum of the solutions for specific herd effects. A herd was considered as deviant from its target range when the prediction error was greater than the standard deviation of MU averaged by herd test day. Results showed that 6.7% of the herd test-day MU levels between June 2007 and May 2008 were considered deviant. These deviations seemed to occur more often during the grazing period. Although theoretical considerations developed in this study should be validated in the field, this research showed the potential use of a test-day model for analyzing functional traits to advise dairy farmers. [less ▲]

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See detailModeling Neuronal Adaptation in the Brain: Integrating Receptor Signaling and Electrophysiology
Vadigepalli, R.; Fey, Dirk ULg; Schwaber, James S

in 2nd Conference on Foundations of Systems Biology in Engineering, Stuttgart, Germany (2007)

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See detailModeling of 3-D losses and deviations in a throughflow analysis tool
Simon, Jean-Francois; Nicks, Alain; Paris, Nicolas et al

in Proceedings of the 8th International Symposium for Experimental and Computational Aerothermodynamics of Internal Flow (2007, July)

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See detailModeling of 3-D losses and deviations in a throughflow analysis tool
Simon, Jean-Francois; Léonard, Olivier ULg

in Journal Of Thermal Science (2007), 16(3), 208-214

This contribution is dedicated to the modeling of the end-wall flows in a throughflow model for turbomachinery applications. The throughflow model is based on the Euler or Navier-Stokes equations solved ... [more ▼]

This contribution is dedicated to the modeling of the end-wall flows in a throughflow model for turbomachinery applications. The throughflow model is based on the Euler or Navier-Stokes equations solved by a Finite-Volume technique. Two approaches are presented for the end-wall modeling. The first one is based on an inviscid formulation with dedicated 3-D distributions of loss coefficient and deviation in the end-wall regions. The second approach is directly based on a viscous formulation with no-slip boundary condition along the annular end-walls and blade force modification in the region close to the end-walls. The throughflow results are compared to a series of 3-D Navier-Stokes calculations averaged in the circumferential direction. These 3-D calculations were performed on the three rotors of a low pressure axial compressor, for a series of tip clearance values. [less ▲]

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See detailModeling of 3-D stranded inductors with the magnetic vector potential formulation and spatially dependent turn voltages of reduced support
Dular, Patrick ULg; Gyselinck, Johan

in IEEE Transactions on Magnetics (2004), 40(2, Part 2), 1298-1301

An alternative method is developed to take three-dimensional stranded inductors into account with the magnetic vector potential magnetodynamic formulation. The definition of the turn voltages as a ... [more ▼]

An alternative method is developed to take three-dimensional stranded inductors into account with the magnetic vector potential magnetodynamic formulation. The definition of the turn voltages as a continuous spatially dependent quantity of reduced support enables us to simplify the turn circuit relations, relating currents and turn voltages. The continuous extension of these relations for all the wire turns then reduces the bandwidth in the system matrix in comparison with the usual method. The voltage of each turn is, moreover, directly known and, hence, does not require a postprocessing. [less ▲]

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See detailModeling of a continuous rotary reactor for carbon nanotube synthesis by catalytic chemical vapor deposition
Pirard, Sophie ULg; Bossuot, Christophe; Pirard, Jean-Paul ULg

in AIChE Journal (2009), 55

The modeling of carbon nanotube production by the CCVD process in a continuous rotary reactor with mobile bed was performed according to a rigorous chemical reaction engineering approach. The geometric ... [more ▼]

The modeling of carbon nanotube production by the CCVD process in a continuous rotary reactor with mobile bed was performed according to a rigorous chemical reaction engineering approach. The geometric, hydrodynamic, physical and physicochemical factors governing the process were analyzed in order to establish the reactor equations. While the study of the hydrodynamic factor suggests a co-current plug-flow approximation, the physical factor mainly deals with the phenomena of transport and the transfer of mass, which can be neglected. Concerning the physicochemical factor, the modeling is based on knowledge of the expression of the initial reaction rate, and takes into account catalytic deactivation as a function of time, according to a sigmoid decreasing law. The reactor modeling allows obtaining the evolution of partial pressure, carbon nanotube production and catalytic deactivation along the reactor for given initial operating conditions. The comparison between experimental and calculated production highlights a very good fit of data. (c) 2009 American Institute of Chemical lEngineers AIChE J, 55: 675-686, 2009 [less ▲]

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