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See detailModelling the hydrogeological environment for disposal of wastes in low permeability sediments
Dassargues, Alain ULg

Scientific conference (1996, November 07)

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See detailModelling the hydrological response of an urban watershed Diachronic analysis of the effects of land use changes on storm runoff generation in the Upper Bukit Timah basin, Singapore
Cesar, Emilie ULg

Master's dissertation (2011)

This work consisted in the modelling of the rainfall-runoff relationships in the Upper Bukit Timah catchment in Singapore, in order to highlight the impacts of urbanisation on hydrology. The SWMM model, a ... [more ▼]

This work consisted in the modelling of the rainfall-runoff relationships in the Upper Bukit Timah catchment in Singapore, in order to highlight the impacts of urbanisation on hydrology. The SWMM model, a one-dimensional physically based model especially developed for urban areas, was mainly used. The parameters encoded into the model were determined by different means and several methods were used for their determination in order to assess their influence on the modelling.Using the final adjustment of the SWMM model, a diachronic analysis was performed in order to present the effects of urbanisation on runoff. [less ▲]

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See detailModelling the impact of benthic filter-feeders on the composition and biomass of river plankton
Descy, Jean-Pierre; Everbecq, Etienne ULg; Gosselain, Véronique ULg et al

in Freshwater Biology (2003), 48(3), 404-417

1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a ... [more ▼]

1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton (Stephanodiscus, Cyclotella -like, large diatoms, Skeletonema and non-siliceous algae) to model filter-feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus -like and Keratella -like rotifers. 2. According to density estimates from field surveys (Bachmann V. et al. (1995) Hydroecologie Appliquee, 7, 185, Bachmann V. & Usseglio-Polatera P. (1999) Hydrobiologia, 410, 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers. 3. The simulations suggest a significant impact of benthic filter-feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton. 4. A daily carbon balance for a typical summer shows the effect of benthic filter-feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches. [less ▲]

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See detailModelling the impact of wind turbines on the visual attractivity of landscapes at a regional scale
Van Rompaey, A.; Vanderheyden, V.; Schmitz, Serge ULg

in European Wind Energy Conference & Exhibition : Brussels Expo 31 March-3 April 2008 (2008)

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See detailModelling the influence of activation-induced apoptosis of CD4+ and CD8+ T-cells on the immune system response of a HIV-infected patient
Stan, Guy-Bart; Belmudes, Florence ULg; Fonteneau, Raphaël ULg et al

in IET Systems Biology (2008), 2(2), 94-102

On the basis of the human immunodeficiency virus (HIV) infection dynamics model proposed by Adams, the authors propose an extended model that aims at incorporating the influence of activation-induced ... [more ▼]

On the basis of the human immunodeficiency virus (HIV) infection dynamics model proposed by Adams, the authors propose an extended model that aims at incorporating the influence of activation-induced apoptosis of CD4+ and CD8+ T-cells on the immune system response of HIV-infected patients. Through this model, the authors study the influence of this phenomenon on the time evolution of specific cell populations such as plasma concentrations of HIV copies, or blood concentrations of CD4+ and CD8+ T-cells. In particular, this study shows that depending on its intensity, the apoptosis phenomenon can either favour or mitigate the long-term evolution of the HIV infection. [less ▲]

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See detailModelling the Influence of Climate on Black Grouse Population Dynamics in Lüneburger Heide (North Germany)
Loneux, Michèle ULg; Lütkepohl, Manfred; Wübbenhorst, Jann et al

in PLUMMER, Ron (Ed.) European Conference Black Grouse Endangered species (2005, December)

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See detailModelling the injection of a tracer in a well: a new mathematical and numerical approach.
Brouyère, Serge ULg

in Dassargues, Alain (Ed.) Tracers and Modelling in Hydrogeology (2000)

A new mathematical approach is proposed to model the injection of a tracer in a well for field tracer tests. It is based on the water and tracer mass budget integrated over the injection well, for the ... [more ▼]

A new mathematical approach is proposed to model the injection of a tracer in a well for field tracer tests. It is based on the water and tracer mass budget integrated over the injection well, for the different injection steps (tracer injection, water flush and tracer behaviour after the injection). This physical approach deals with well-bore mixing and dilution effects, local distortion of the flow field around the injection well, back-diffusion of the tracer in the injection well after the injection, and tracer capture in the well bore. A numerical solution (finite differences over time) is proposed and implemented in a three-dimensional finite element flow and transport simulator (SUFT3D). A radially converging tracer test is computed to illustrate the adequacy and usefulness of this new mathematical concept to model field results. [less ▲]

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See detailModelling the interaction of the deep ocean and the shelf and coastal seas
Nihoul, Jacques ULg; Djenidi, Salim ULg

in Journal of Marine Systems (1992), 3(4-5), 307-308

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See detailModelling the Ionosphere over Europe: Investigation of NeQuick Formulation
Bidaine, Benoît ULg; Warnant, René ULg

Poster (2008, November 18)

The modelling of the Total Electron Content (TEC) plays an important role in global satellite navigation systems (GNSS) accuracy, especially for single-frequency receivers, the most common ones ... [more ▼]

The modelling of the Total Electron Content (TEC) plays an important role in global satellite navigation systems (GNSS) accuracy, especially for single-frequency receivers, the most common ones constituting the mass market. For the latter and in the framework of Galileo, the NeQuick model has been chosen for correcting the ionospheric error contribution. It has been designed to calculate the electron density at a given point of the ionosphere according to the time conditions and the solar activity. This electron density can be integrated along the path from the receiver to the considered satellite to provide the TEC. For Galileo, a parameter Az (“effective ionisation level”) will be provided to the model as solar activity information and will be daily updated by the ground stations. Since NeQuick was chosen for Galileo purpose, a new version of the model has been released. It involves simplifications in the representation of the bottomside as well as a unique formula for a key parameter of the topside formulation previously defined through two equations, each one used for six months of the year. Hence we decided to investigate consecutive improvements and remaining weaknesses of this new formulation. To this extent, we take benefit of various ionosphere data from several European stations (Chilton in UK, Dourbes in Belgium, El Arenosillo and Roquetes in Spain, Pruhonice in Czech Republic) where ionosonde and GPS TEC data are available for different solar activity levels. These data allow us to study NeQuick representation of the ionosphere at mid-latitudes. We investigate the difference between GPS-derived vTEC and corresponding values from NeQuick for the latest years (between solar maximum in 2000 and minimum in 2007) in order to observe the temporal dependencies towards Universal Time, season and solar activity. We use ionosonde data to constrain the model so that we can concentrate on its formulation of the profile only. We especially highlight the improvements from the second version of NeQuick and show the critical importance of the topside formulation. [less ▲]

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See detailModelling the Ionosphere over Europe: Investigation of NeQuick Formulation
Bidaine, Benoît ULg; Warnant, René ULg

Conference (2008, November 18)

The modelling of the Total Electron Content (TEC) plays an important role in global satellite navigation systems (GNSS) accuracy, especially for single-frequency receivers, the most common ones ... [more ▼]

The modelling of the Total Electron Content (TEC) plays an important role in global satellite navigation systems (GNSS) accuracy, especially for single-frequency receivers, the most common ones constituting the mass market. For the latter and in the framework of Galileo, the NeQuick model has been chosen for correcting the ionospheric error contribution. It has been designed to calculate the electron density at a given point of the ionosphere according to the time conditions and the solar activity. This electron density can be integrated along the path from the receiver to the considered satellite to provide the TEC. For Galileo, a parameter Az (“effective ionisation level”) will be provided to the model as solar activity information and will be daily updated by the ground stations. Since NeQuick was chosen for Galileo purpose, a new version of the model has been released. It involves simplifications in the representation of the bottomside as well as a unique formula for a key parameter of the topside formulation previously defined through two equations, each one used for six months of the year. Hence we decided to investigate consecutive improvements and remaining weaknesses of this new formulation. To this extent, we take benefit of various ionosphere data from several European stations (Chilton in UK, Dourbes in Belgium, El Arenosillo and Roquetes in Spain, Pruhonice in Czech Republic) where ionosonde and GPS TEC data are available for different solar activity levels. These data allow us to study NeQuick representation of the ionosphere at mid-latitudes. We investigate the difference between GPS-derived vTEC and corresponding values from NeQuick for the latest years (between solar maximum in 2000 and minimum in 2007) in order to observe the temporal dependencies towards Universal Time, season and solar activity. We use ionosonde data to constrain the model so that we can concentrate on its formulation of the profile only. We especially highlight the improvements from the second version of NeQuick and show the critical importance of the topside formulation. [less ▲]

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See detailModelling the Ligurian Sea ecosystem by means of a 1D couled physical-biogeochemical model. Improvement of model results using sequential data assimilation
Raick, C.; Soetaert, K.; Grégoire, Marilaure ULg

in Geophysical Research Abstracts (2005), 7

A 1D coupled physical-biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version 1D) developed ... [more ▼]

A 1D coupled physical-biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version 1D) developed at the GHER (University of Liège, Belgium). The ecosystem model contains nineteen state variables describing the carbon and nitrogen cycles of the pelagic food web. Silicate is considered as a potential limiting nutrient of diatoms’ growth. The aggregation model described in Kriest and Evans (2000) is used to evaluate the sinking rate of particulate detritus. The model is forced at the air-sea interface by the METEO France meteorological data. The DYFAMED time series data of year 2000 are used to calibrate and validate the biological model (Raick et al., 2005). By combining the numerical model and the available observations, data assimilation techniques are useful to improve the state estimation of the ocean. A Singular Fixed Extended Kalman filter (Pham et al., 1998) has been implemented in this way. Twin experiments are first performed to choose the suitable experimental protocol, which is then applied to perform real data assimilation experiments using DYFAMED data (Raick et al., submitted). To be coupled in a 3D environment, the ecosystem model is too complex. Our ongoing work is to perform a simplification, by studying simplified structures in comparison with the original ecosystem model. The advantage of deriving a simplified model from the complex one, is that we would be able to identify the most important processes of the Ligurian Sea ecosystem. [less ▲]

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See detailModelling the magnetic field of the B-type N-rich star ζ Cassiopeiae
Briquet, Maryline ULg; Neiner, Coralie

Diverse speeche and writing (2012)

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See detailModelling the Marine Environment.
Djenidi, Salim ULg

Report (1990)

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See detailModelling the medium-scale TEC structures, observed by Belgian GPS receiver network
Kutiev, Ivan; Marinov, P.; Fidanova, S. et al

Conference (2007)

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See detailModelling the Mid-latitude Ionosphere: Assessment of the NeQuick Model using GPS TEC and Ionosonde Data
Bidaine, Benoît ULg

Master of advanced studies dissertation (2007)

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding ... [more ▼]

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding 100 m. At first approximation, ionospheric effects depend mainly on the total content in free electrons of the ionosphere ("total electron content", TEC) defined as the integral of the electron density on the path between the satellite and the receiver. The modelling of the latter parameter reveals thus itself critical in particular for single frequency receivers, the most common ones constituting the mass market. In the framework of GALILEO, the European system in development, the NeQuick model has been chosen to this extent. Computing monthly median electron densities as a basis, it will be integrated into a global algorithm providing the users with daily updated information and allowing them to calculate TEC and thus to mitigate the ionospheric effects. In order to reach the specified correction level, the model itself and its latest evolutions as well as its use for GALILEO are investigated. Different situations have to be considered e.g. different latitude regions and the results can be compared to various data sets. As a first step in a thorough analysis, we take benefit of ionosonde and GPS TEC data from the Dourbes Geophysical Observatory (Belgium) to study the mid-latitudes. Constraining the model with ionosonde measurements, we first investigate the difference between GPS-derived vertical TEC (vTEC) for Dourbes station and corresponding values from NeQuick for the latest years (for solar maximum in 2002 and minimum in 2006). With this approach, we reach residual errors of about 20% RMS for 2002 and 30% for 2006 keeping in mind that TEC values are far lower in this low solar activity year. Through a focusing process, we identify then gradually best and worst months and days for which we observe the evolution between two versions of NeQuick. We highlight among others improvements from the latest modification in the topside formulation which appears clearly in the electron density profiles examined at the end of the assessment. [less ▲]

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See detailModelling the Middle Miocene climate with PLASIM and CARAIB
Henrot, Alexandra ULg

Scientific conference (2010, October)

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See detailModelling the migration of a mid-Pleistocene erosion wave in the Ardennes (western Europe) drainage network: approach and first implications
Beckers, Arnaud ULg; Bovy, Benoît ULg; Demoulin, Alain ULg

Poster (2011, April)

Model parameterization through adjustment to field data is a crucial step in the modelling and the understanding of the drainage network response to tectonic or climatic perturbations. Using a data set of ... [more ▼]

Model parameterization through adjustment to field data is a crucial step in the modelling and the understanding of the drainage network response to tectonic or climatic perturbations. Using a data set of 18 knickpoints that materialize the migration of a 0.7-Ma-old erosion wave in the Ourthe catchment of northern Ardennes (western Europe) as a test case, we explore the impact of various data fitting on the calibration of the detachment-limited stream power model of river incision, from which a simple knickpoint celerity equation is derived. Our results show that statistical least squares adjustments (or misfit functions) based either on the stream-wise distances between observed and modelled knickpoint positions at time t = 0.7 Ma or on differences between observed (0.7 Ma) and modelled time at the actual knickpoint locations yield significantly different values for the m (more exactly, m/n) and K parameters of the model. As there is no physical reason to prefer one or the other approach, we suggest that an intermediate least rectangles adjustment might be the best compromise. In the Ourthe case, this leads to a m/n value lower than that obtained from the classical distance adjustment (0.79 against 0.86), leading to an increase in the non linear character of the dependence of knickpoint celerity on discharge. If we now recall that m/n = c(1-b) (Whipple & Tucker, 1999, JGR 104B: 17661-17674), where c and b are the exponents of the power law relations respectively linking discharge to drainage area and channel width to discharge, we can compare the calculated m/n value with that derived from field measurements of channel width, discharge and drainage area in the presently graded sections of the rivers. Such data taken from Petit et al. (2005, BSGLg 46: 37-50) allow us to derive m/n = 0.48 at equilibrium. As c may be considered constant, the higher m=n value obtained from the knickpoint retreat modelling must be ascribed to a lower b, i.e., to a channel narrowing associated with the transient phase of knickpoint migration. [less ▲]

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See detailModelling the migration of contaminants through variably saturated dual-porosity, dual-permeability chalk
Brouyère, Serge ULg

in Journal of Contaminant Hydrology (2006), 82(3-4), 195-219

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water ... [more ▼]

In the Hesbaye region in Belgium, tracer tests performed in variably saturated fissured chalk rocks presented very contrasting results in terms of transit times, according to artificially controlled water recharge conditions prevailing during the experiments. Under intense recharge conditions, tracers migrated across the partially or fully saturated fissure network, at high velocity in accordance with the high hydraulic conductivity and low effective porosity (fracture porosity). At the same time, a portion of the tracer was temporarily retarded in the almost immobile water located in the matrix. Under natural infiltration conditions, the fissure network remained inactive. Tracers migrated downward through the matrix, at low velocity in relation with the low hydraulic conductivity and the large porosity of the matrix. Based on these observations, Brouyere et al. (2004a) [Brouyere, S., Dassargues, A., Hallet, V, 2004a. Migration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation, J. Contain. Hydrol., 72 (1-4), 135-164, doi: 10.1016/j.conhyd.2003.10. 009] proposed a conceptual model in order to explain the migration of solutes in variably saturated, dual-porosity, dual-permeability chalk. Here, mathematical and numerical modelling of tracer and contaminant migration in variably saturated fissured chalk is presented, considering the aforementioned conceptual model. A new mathematical formulation is proposed to represent the unsaturated properties of the fissured chalk in a more dynamic and appropriate way. At the same time, the rock water content is partitioned between mobile and immobile water phases, as a function of the water saturation of the chalk rock. The groundwater flow and contaminant transport in the variably saturated chalk is solved using the control volume finite element method. Modelling the field tracer experiments performed in the variably saturated chalk shows the adequacy and usefulness of the new conceptual, mathematical and numerical model. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailModelling the Neritosphere
Djenidi, Salim ULg; Nihoul, Jacques ULg

in Sanchez-Arcilla, A.; Pastor, M.; Zienkiewicz, O. C. (Eds.) et al Proceedings of the 2nd International Conference on Computer Modelling in Ocean Engineering (1991)

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