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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)

Detailed reference viewed: 18 (2 ULg)
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 Middle Miocene fluctuations in ocean biological productivity, ocean carbon isotopic composition and atmospheric CO2 level
Jacquemin, Ingrid ULg; François, Louis ULg; Diester-Haass, Liselotte et al

Conference (2011, April 05)

The Middle Miocene (17.5-13.5 Ma) is characterized by high frequency fluctuations in the seawater delta13C record with six distinct delta13C maxima linked to Earth orbital cycles (mainly the 400 kyr ... [more ▼]

The Middle Miocene (17.5-13.5 Ma) is characterized by high frequency fluctuations in the seawater delta13C record with six distinct delta13C maxima linked to Earth orbital cycles (mainly the 400 kyr eccentricity cycle). These fluctuations are negatively correlated with the delta18O variations and, on the other hand, marine data show that the ocean productivity tends to be higher during warmer periods. However, on the long term, these three indicators show a different relationship: the productivity does not show any major trend, while a positive excursion of the delta13C is observed (the so-called Monterey event) and is accompanied by a warming, i.e., a decrease in the delta18O. The question of the long-term trend has already been addressed in a previous study (Diester-Haass et al., Paleoceanography, 24, PA1209, 2008), where the positive excursion in delta13C was explained by the storage in sediments of organic carbon from continental origin. In the current study we hypothesize that the short-term (400 kyr cycle) fluctuations of the marine delta13C are mainly linked to sea level and marine productivity changes and not to changes in the terrestrial environment, explaining the different relationship between the isotopic indicators for this shorter as compared to the longer timescale. We test this hypothesis by using a global geochemical box model representing the carbon, alkalinity, phosphorus and oxygen cycles and coupled to an energy balance climate model. The model is forced with sea level fluctuations associated with the observed variations of ocean delta18O. We first evaluate the changes in continental weathering associated with these sea level fluctuations and the related climate change. The model shows that these changes in weathering cannot explain the observed amplitude of marine productivity and ocean delta13C variations over the 400 kyr eccentricity cycle. We then test the assumption that these high frequency delta13C variations were the result of a change in the turnover rate of the oceans, with higher upwelling rates and higher productivity during warmer periods. Results of model sensitivity tests indicate that this hypothesis is plausible, since it leads to approximately correct amplitudes and phases of the oceanic productivity and delta13C signals. Thus, the following picture emerges that, in the Middle Miocene, the short-term fluctuations in oceanic delta13C are driven by ocean circulation and productivity changes, while the trends at longer timescales are linked to a change in the burial rate of continental organic carbon. From this picture, the model is able to provide a geochemical history of the Middle Miocene ocean-atmosphere system consistent with the marine delta13C record. In this reconstructed history, the atmospheric CO2 level only shows small variations, with a slight decrease from the Lower Miocene (about 310 ppmv at 19 Ma) to the Middle Miocene (280 ppmv at 16 Ma) followed by a small increase thereafter (310 to 320 ppmv near 12 Ma). This history is relatively consistent with the marine 13C isotopic proxies for atmospheric CO2. [less ▲]

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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 mortality of Hylotrupes bajulus (L.) larvae exposed to anoxic treatment for disinfestation of wooden art objects
de Streel, Géraud; Henin, Jean-Marc; Bogaert, Patrick et al

in Wood Science & Technology (2016)

Experiments were conducted to quantify the effect of several variables on the mortality of insects exposed to an anoxic treatment in order to generate a model linking mortality to these variables. This ... [more ▼]

Experiments were conducted to quantify the effect of several variables on the mortality of insects exposed to an anoxic treatment in order to generate a model linking mortality to these variables. This study aims to explore the possible interest of using such a model to determine the characteristics of treatment (especially duration) needed to guarantee insect mortality with a given level of probability. Trials were performed on Hylotrupes bajulus larvae, which is a widespread species known for its high tolerance to anoxic conditions. The studied variables are the initial mass of the larvae, the treatment temperature (21, 30 and 40 C), the treatment duration (four durations for each temperature tested) and whether the larva is held in wood or in a petri dish (directly exposed to anoxic atmosphere) during the experiment. It was found that, while the last variable is not correlated with mortality, treatment duration and temperature are significantly and positively correlated with it. Larvae with higher body mass were also shown to have a better resistance to the treatment. Based on these results, a model including insect initial mass, treatment temperature and duration, together with the interaction between these two variables, was determined. This relatively simple model appeared to be a useful tool in overcoming the difficulty in defining the modalities for anoxic treatment in order to reach a given level of mortality. [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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See detailModelling the North Sea hydrodynamics in a management perspective
Djenidi, Salim ULg; Delhez, Eric ULg; Martin, Géraldine ULg et al

in Bulletin de la Société Royale des Sciences de Liège (1996), 65

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See detailModelling the Phenomenon of Galloping in Overhead Lines
Lilien, Jean-Louis ULg; Ponthot, Jean-Philippe ULg

in Revue de la Société Royale Belge des Electriciens (1987), 103(12), 5-19

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See detailModelling the plastic anisotropy of metals
Habraken, Anne ULg

in Archives of Computational Methods in Engineering (2004), 11

This work is an overview of available constitutive laws used in finite element codes to model elastoplastic metal anisotropy behaviour at a macroscopic level. It focuses on models with strong links with ... [more ▼]

This work is an overview of available constitutive laws used in finite element codes to model elastoplastic metal anisotropy behaviour at a macroscopic level. It focuses on models with strong links with the phenomena occurring at microscopic level. Starting from macroscopic well-known models such as Hill or Barlat’s laws, the limits of these macroscopic phenomenological yield loci are defined, which helps to understand the current trends to develop micro-macro laws. The characteristics of micro-macro laws, where physical behaviour at the level of grains and crystals are taken into account to provide an average macroscopic answer are described. Some basic knowledge about crystal plasticity models is given for non-specialists, so every one can understand the microscopic models used to reach macroscopic values. The assumptions defining the transition between the microscopic and macroscopic scales are summarized: full constraint or relaxed Taylor’s model, self-consistent approach, homogenisation technique. Then, the two generic families of micromacro models are presented: macroscopic laws without yield locus where computations on discrete set of crystals provide the macroscopic material behaviour and macroscopic laws with macroscopic yield locus defined by microscopic computations. The models proposed by Anand, Dawson, Miehe, Geers, Kalidindi or Nakamachi belong to the first family when proposals by Montheillet, Lequeu, Darrieulat, Arminjon, Van Houtte, Habraken enter the second family. The characteristics of all these models are presented and commented. This paper enhances interests of each model and suggests possible future developments. [less ▲]

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See detailModelling the Position Control of a Segment of the E-ELT using OOFELIE::Multiphysics Integrated FEM-based Approach
Nachtergaele, Philippe; Gamonal Rozas, Leonardo Alfredo ULg; Bruls, Olivier ULg

in Proceedings of the 13th International Conference on New Actuators (2012, June)

This paper presents the extension of a multiphysics software solution allowing to perform integrated simulation of multiphysics controlled systems. This enhancement relies on an innovative formulation of ... [more ▼]

This paper presents the extension of a multiphysics software solution allowing to perform integrated simulation of multiphysics controlled systems. This enhancement relies on an innovative formulation of time integration schemes allowing to take into account simultaneously, in an integrated FEM-based approach, the non linear structural response of a system and the controller dynamics. Interest and feasibility of this unified approach is illustrated through the Modelling of the position control of a segment of the primary mirror of the E-ELT (European Extremely Large Telescope), a highly representative application of complex multiphysics controlled systems. [less ▲]

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See detailModelling the potential of focal screening and treatment as elimination strategy for Plasmodium falciparum malaria in the Peruvian Amazon Region
Rosas-Aguirre, Angel; Erhart, Annette; Llanos-Cuentas, Alejandro et al

in Parasites & Vectors (2015), 8(1), 261

BACKGROUND:Focal screening and treatment (FSAT) of malaria infections has recently been introduced in Peru to overcome the inherent limitations of passive case detection (PCD) and further decrease the ... [more ▼]

BACKGROUND:Focal screening and treatment (FSAT) of malaria infections has recently been introduced in Peru to overcome the inherent limitations of passive case detection (PCD) and further decrease the malaria burden. Here, we used a relatively straightforward mathematical model to assess the potential of FSAT as elimination strategy for Plasmodium falciparum malaria in the Peruvian Amazon Region.METHODS:A baseline model was developed to simulate a scenario with seasonal malaria transmission and the effect of PCD and treatment of symptomatic infections on the P. falciparum malaria transmission in a low endemic area of the Peruvian Amazon. The model was then adjusted to simulate intervention scenarios for predicting the long term additional impact of FSAT on P. falciparum malaria prevalence and incidence. Model parameterization was done using data from a cohort study in a rural Amazonian community as well as published transmission parameters from previous studies in similar areas. The effect of FSAT timing and frequency, using either microscopy or a supposed field PCR, was assessed on both predicted incidence and prevalence rates.RESULTS:The intervention model indicated that the addition of FSAT to PCD significantly reduced the predicted P. falciparum incidence and prevalence. The strongest reduction was observed when three consecutive FSAT were implemented at the beginning of the low transmission season, and if malaria diagnosis was done with PCR. Repeated interventions for consecutive years (10 years with microscopy or 5 years with PCR), would allow reaching near to zero incidence and prevalence rates.CONCLUSIONS:The addition of FSAT interventions to PCD may enable to reach P. falciparum elimination levels in low endemic areas of the Amazon Region, yet the progression rates to those levels may vary substantially according to the operational criteria used for the intervention. [less ▲]

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See detailModelling the primary production interannual variability in the Ligurian Sea due to meteorological conditions with a 1D hydrodynamic/biological model
Lacroix, Geneviève; Nival, Paul; Djenidi, Salim ULg

in EOS : Transactions, American Geophysical Union (1998), 79

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