Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
Peer Reviewed
See detailModelling the early phases of bone regeneration around an endosseous oral implant
Amor, N.; Geris, Liesbet ULg; Vander Sloten, J. et al

in Computer Methods in Biomechanics & Biomedical Engineering (2009), 12(4), 459-468

The objective of this study was to see whether a mathematical model of fracture healing was able to mimic bone formation around an unloaded screw-shaped titanium implant as it is well-believed that both ... [more ▼]

The objective of this study was to see whether a mathematical model of fracture healing was able to mimic bone formation around an unloaded screw-shaped titanium implant as it is well-believed that both processes exhibit many biological similarities. This model describes the spatio-temporal evolution of cellular activities, ranging from mesenchymal stem cell migration, proliferation, differentiation to bone formation, which are initiated and regulated by the growth factors present at the peri-implant site. For the simulations, a finite volume code was used and adequate initial and boundary conditions were applied. Two sets of analyses have been performed, in which either initial and boundary condition or model parameter values were changed with respect to the fracture healing model parameter values. For a number of combinations, the spatio-temporal evolution of bone density was well-predicted. However reducing cell proliferation rate and increasing osteoblast differentiation and osteogenic growth factor synthesis rates, the simulation results were in agreement with the experimental data. [less ▲]

Detailed reference viewed: 12 (2 ULg)
Full Text
Peer Reviewed
See detailModelling The Effect Of Temperature, Water Activity And Solute On The In Vitro Growth Of The Biocontrol Yeast Pichia Anomala Strain K
Lahlali, R.; Bajji, M.; Serrhini, Mn. et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2008), 12(4),

Detailed reference viewed: 24 (1 ULg)
Full Text
Peer Reviewed
See detailModelling the effects of the current policy measures in agriculture: an unique model from field to regional scale in Walloon region of Belgium
Sohier, Catherine ULg; Degre, Aurore ULg

in Environmental Science & Policy (2010), 13(2010), 754-765

Diffuse nutrient loss from agriculture into the soil, groundwater and surface water affects their quality. Different policies are in force throughout the European Union aiming for their limitation. They ... [more ▼]

Diffuse nutrient loss from agriculture into the soil, groundwater and surface water affects their quality. Different policies are in force throughout the European Union aiming for their limitation. They were implemented through action plans on a regional scale. Hydrological modelling can be a powerful method for efficiently evaluating their effectiveness. In order to be useful whatever the action and for every reporting unit (whole Region, water bodies, nitrate vulnerable zones, fields...) the model must be physically based, it must simulate water and nutrient fluxes in the root zone and the vadose zone as well as being geographically flexible. This paper presents such a model and its application in the context of Wallonia (Southern part of Belgium). It also presents a calculation of what water and nutrient flows could be under a given climatic scenario until 2015. In Belgium, water quality depends upon Regions. Wallonia implemented the European Nitrate Directive through two action plans the first in 2002 and the second in 2007. These actions plans were modelled and compared to a scenario without any modification in the farmers’ practices. The modelling showed the need for two indicators: nitrate concentration under the root zone as fast indicator of the actions’ efficiency and transfer time from surface to groundwater table. The first action plan hardly modified farmers’ field practices and consequently it did not impact water quality. The second action plan had more impact (reduction up to 10 mg/l NO3 under the root zone). It was mainly due to catch crop introduction in the nitrate vulnerable zone, if they are followed by a reduction of the mineral fertilisation (not mandatory). Our results show that new actions are necessary. We show where and to what extent they have to be implemented. Nevertheless, the greatest variation in nitrate leaching from the root zone seems to be dependent on the weather, more than the action plans. Particularly the rainy period between 1998 and 2002 had a huge impact on nitrogen flows. Our hydrological modelling is showed to be a powerful tool of nitrogen management in a still uncertain climatic evolution context. Finally, we showed that patience and perseverance will be necessary to reach the targets of the WFD in the Walloon context. The map of transfer time shows that 8% of the groundwater bodies need over 15 years to be impacted by mitigation measures. [less ▲]

Detailed reference viewed: 60 (24 ULg)
Full Text
See detailModelling the evolution of climate and sea level over the third millennium (MILMO)
Fichefet, Thierry; Driesschaert, Emmanuelle; Goosse, Hugues et al

Report (2007)

A new three-dimensional Earth system model of intermediate complexity was developed. This model, named LOVECLIM, consists of five major components representing the atmosphere (ECBilt), the ocean and sea ... [more ▼]

A new three-dimensional Earth system model of intermediate complexity was developed. This model, named LOVECLIM, consists of five major components representing the atmosphere (ECBilt), the ocean and sea ice (CLIO), the terrestrial biosphere (VECODE), the oceanic carbon cycle (LOCH) and the Greenland and Antarctic ice sheets (AGISM). It also includes a global glacier-melt algorithm which is run in off-line mode. It is worth mentioning that there are very few models of this type worldwide. ECBilt is a quasi-geostrophic atmospheric model with 3 levels and a T21 horizontal resolution. It includes simple parameterisations of the diabatic heating processes and an explicit representation of the hydrological cycle. Cloud cover is prescribed according to present-day climatology. CLIO is a primitive-equation, free-surface ocean general circulation model coupled to a thermodynamic–dynamic sea-ice model. Its horizontal resolution is 3° × 3°, and there are 20 levels in the ocean. VECODE is a reduced-form model of vegetation dynamics and of the terrestrial carbon cycle. It simulates the dynamics of two main terrestrial plant functional types (trees and grassland) at the same resolution as that of ECBilt. LOCH is a comprehensive model of the oceanic carbon cycle that takes into account both the solubility and biological pumps. The version utilised here has the same resolution as the one of CLIO, which greatly facilitates the coupling between both models. Finally, AGISM is composed of a three-dimensional thermomechanical model of the ice sheet flow, a visco-elastic bedrock model and a model of the mass balance at the ice–atmosphere and ice–ocean interfaces. The Antarctic ice-sheet module also contains a model of the ice-shelf dynamics to enable interactions with the ocean and migration of the grounding line. For both ice sheets, calculations are made on a 10 km × 10 km resolution grid with 31 sigma levels. The performance of LOVECLIM was assessed by conducting ensemble simulations over the last few centuries. Starting from different initial conditions, the model was integrated from year 1500 AD up to year 2000 AD with solar irradiance, volcanic activity, tropospheric ozone amount, greenhouse-gas (including CO2) concentrations and sulphate-aerosol load evolving with time according to reconstructions. Over the last 140 years, the model simulates a global surface warming ranging from 0.33°C to 0.43°C, with a mean value of 0.38°C. This value is about 0.15°C lower than the observed one. A detailed analysis of the results has revealed the model behaves reasonably well at mid- and high latitudes. By contrast, at low latitudes, the agreement between the model results and observational estimates is less good, especially in the Southern Hemisphere. In those regions, LOVECLIM significantly underestimates the warming and the climate variability observed during the last few decades. The coarse resolution of the model and the simplified representation of the atmospheric dynamical and physical processes seem to be the two major candidates responsible for this deficiency. Regarding the Greenland ice sheet, we found a slightly increasing ice volume during the period 1700–2000 AD. This trend is largely explained as a residual response to the late Holocene forcing, in particular to the Little Ice Age cooling after year 1500 AD. The effect is not particularly large, however, amounting to only 1.2 cm of global sea-level rise over the entire period. The growing trend stabilizes during the 20th century, with almost no net effect on ice volume. Only during the last decades of the 20th century, the ice volume begins to decrease in response to the imposed warming. We also found the Antarctic ice sheet to be retreating slowly at a rate equivalent to a global sea-level rise of about 1.7 cm during the 20th century. This evolution is mostly due to a long-term background trend of +2.6 cm, mitigated by about 0.9 cm from slightly rising accumulation rates over the same period. The ongoing dominance of past climatic changes on the contemporary ice-sheet evolution is a fine illustration of the inertia encountered when studying the response of large continental ice sheets. In this case, it mainly results from an ongoing grounding-line retreat in West Antarctica following rising sea levels since the Last Glacial Maximum. As far as mountain glaciers and small ice caps are concerned, their area and volume are found to reach a maximum in the late 19th century corresponding to the Little Ice Age, but this maximum and the ensuing 20th century glacier retreat are not very pronounced. Over the last hundred years, the model simulates an ice loss equivalent to only 0.89 cm of sea-level rise. This value is at the lower end compared to other assessments. One reason is the low total ice volume assumed by the global glacier-melt algorithm (about 20 cm of total sea-level rise, a factor 2.5 less than previous estimates). A second reason is the prescribed global ice mass balance for the 1961–1990 reference period, which is also at the lower end of other simulations. For the 20th century, LOVECLIM explains about 7.6 cm of sea-level rise. The bulk of that value, about 4.7 cm, comes from thermal expansion of the World Ocean. The Antarctic and Greenland ice sheets combined lead to a sea-level rise of 2 cm, and glaciers and ice caps are responsible for about 0.9 cm of sea-level rise. These numbers are similar to those that have been derived for the IPCC Third Assessment Report (TAR) for the same components except for the lower glacier contribution as found here. Over the industrial era, the net uptake of carbon by the ocean simulated by LOVECLIM is within the range of current estimates, although at the lower end of this range. It should be noted that a detailed evaluation of the performance of the terrestrial carbon-cycle module was impossible to perform given the very wide range of available data. Experiments with interactive atmospheric CO2 concentration were also carried out with LOVECLIM forced by CO2 emissions from fossil fuel burning and land-use change. Interestingly enough, the atmospheric CO2 level computed by the model in year 2000 AD compares relatively well with the observed one. A series of climate-change projections were then conducted over the 21st century. In these experiments, LOVECLIM was driven by changes in greenhouse-gas (including CO2), tropospheric ozone and sulphate-aerosol concentrations following the IPCC SRES scenarios B1, A1B and A2. In year 2100 AD, the model predicts a globally averaged, annual mean surface warming of 1°C, 1.4°C and 1.8°C for scenarios B1, A1B and A2, respectively, and an associated increase in precipitation of 3.6%, 5.1% and 6.6%, respectively. In agreement with studies performed with climate general circulation models (CGCMs), a weakening of the Atlantic meridional overturning circulation (MOC) is noticed in all runs. At the end of the 21st century, the decrease in the maximum value of the annual mean meridional overturning streamfunction below the surface layer in the Atlantic basin, which is an index of the MOC intensity, reaches 19% for scenario B1, 21% for scenario A1B and 27% for scenario A2. In our model, as in the majority of CGCMs, this decrease is caused more by changes in surface heat flux than by changes in surface freshwater flux. Under the forcing scenario A1B, LOVECLIM simulates a global sea-level rise of 31.3 cm in year 2100 AD. As for the 20th century, the most important contributor is the oceanic thermal expansion (+18.8 cm), followed by the contributions from the Greenland ice sheet (+5.2 cm), glaciers and ice caps (+3.8 cm) and the Antarctic ice sheet (+3.5 cm). The total rise is equivalent to a quadrupling of the sea-level rise simulated for the 20th century. Our sea-level value is somewhat lower than the central estimate for the same four components of about 40 cm in the IPCC TAR predictions. This can be explained by the low climate sensitivity of LOVECLIM, and hence the lower global temperature rise, which mostly affects the largest contribution of thermal expansion of the World Ocean. Another difference with the IPCC TAR predictions is the positive contribution from Antarctica of several cm of sea-level rise. That is in contrast to most other simulations showing a growing ice sheet and a negative contribution to global sea level of typically between -5 and -20 cm. The IPCC TAR also found a generally larger contribution from mountain glaciers and small ice caps. Our glacier-volume loss is smaller because of the lower initial glacier volume assumed by the glacier-melt algorithm. The total projected sea-level rise for the 21st century is only slightly affected by the scenario itself. For the range of SRES scenarios used by LOVECLIM, the total sea-level rise is found to vary between +22 and +35 cm by year 2100 AD. The much larger range of between +9 and +88 cm obtained for the IPCC TAR arose mainly from the inclusion of model uncertainties, and not from the greenhouse-gas-forcing scenarios employed. As expected, climate change impacts the air–sea CO2 exchange in the model by lowering the solubility and hence the net uptake of carbon by the ocean. The effect is however rather modest at the century time-scale given the moderate increase in sea-surface temperature simulated by LOVECLIM. In addition, we do not observe any significant change in the oceanic biology at the global scale during the 21st century. The picture is a bit different regarding the terrestrial biosphere. Both the climate and fertilization effects strongly increase the carbon uptake in VECODE. A number of experiments with interactive atmospheric CO2 concentration were also carried out over the 21st century. Contrary to other modelling studies, LOVECLIM predicts lower atmospheric CO2 levels at the end of the 21st century when the effect of climate change on the carbon cycle is accounted for in the model. The warming enhances the net uptake of carbon by the terrestrial biosphere which more than offsets the reduction in oceanic uptake resulting from the solubility decrease. Finally, we have thoroughly analysed the model response to a range of stabilized anthropogenic forcings over the next millennia. For the variety of forcing scenarios considered, LOVECLIM simulates a globally averaged, annual mean surface warming ranging between 0.55°C and 3.75°C and an associated decrease in Arctic and Antarctic sea-ice extent. However, no simulation predicts an entirely ice-free Arctic Ocean during summertime at the millennium time-scale. In the most pessimistic case, a small ice pack of about 0.5×106 km2 persists. Our results also suggest that it is very likely that the volume of the Greenland ice sheet will largely decrease in the future. After 1000 years of model integration, the ice volume is reduced by more than 20% when the radiative forcing is higher than 6.5 W m-2. Moreover, for a radiative forcing greater than 7.5 W m-2, the ice sheet melts away in less than 3000 years. Note that the ice-sheet disintegration might be even more rapid if processes responsible for the widespread glacier acceleration currently observed in Greenland were taken into consideration in the model. We also found that the freshwater flux from the melting Greenland ice sheet into the neighbouring oceans, which peaks in the most extreme scenario tested at 0.11 Sv (1 Sv = 10^6 m3 s-1) and remains above 0.1 Sv during three centuries, is not large enough to trigger a shutdown of the Atlantic MOC in our model, in contrast to some other models. Those models are however more responsive to freshwater perturbations than ours. Besides, we showed that climate feedbacks play a crucial role in the ice-sheet evolution and that the Greenland deglaciation considerably enhances the greenhouse-gas-induced warming over Greenland and the central Arctic. This stresses the importance of incorporating the two-way interactions between the Greenland ice sheet and climate in climate- and sea-level-change projections at the millennial time-scale. For the Antarctic ice sheet, the response is much less drastic than for the Greenland ice sheet. For instance, after 3000 years of 4×CO2 forcing (∼7.7 W m-2), the Antarctic grounded ice volume and area are reduced in our model by only 8% and 4%, respectively. For a sustained radiative forcing of 8.5 W m-2 (the highest forcing scenario considered in our study), LOVECLIM predicts a global sea-level rise of 7.15 m by year 3000 AD. Most of it is due to melting of the Greenland ice sheet (+4.25 m), followed by melting of the Antarctic ice sheet (+1.42 m), thermal expansion (+1.29 m) and the contribution from mountain glaciers and small ice caps (+0.19 m). Our results show that it will be very difficult to limit the eventual sea-level rise to less than 1 m after 1000 years, unless the atmospheric CO2 concentration can be stabilized to less than twice its pre-industrial level. Such a goal can only be reached by emission reductions far larger than any policy currently pursued. Concerning the carbon cycle, the experiments carried out with LOVECLIM highlight the opposite responses of the terrestrial and oceanic carbon reservoirs to climate change. We also found that, when anthropogenic CO2 emissions cease, the terrestrial biosphere becomes a weak carbon source, while the ocean continues to be a sink. It should be mentioned that no dramatic change in the global marine productivity is observed in our simulations. This arises from the fact that the modifications of the oceanic properties that affect this productivity (stratification, meridional overturning, …) are rather moderate. The effects of climate change are however not negligible. In particular, the decrease in sea-ice extent predicted by the model results in a longer growing season and a larger nutrient uptake (especially silica) in polar regions. As a result, by the end of the 23rd century, silica concentrations in the upper 100 m of the Southern Ocean drop by as much of 30% for the most extreme forcing scenarios. [less ▲]

Detailed reference viewed: 39 (3 ULg)
See detailModelling the evolution of domestic wastes landfills.
Thonart, Philippe ULg; Dumont, M.; Destain, Jacqueline ULg et al

Poster (1995, February)

Detailed reference viewed: 4 (0 ULg)
Full Text
Peer Reviewed
See detailModelling the Excavated damage zone around an underground gallery- Coupling mechanical, thermal and hydraulical aspects
Charlier, Robert ULg; Chambon, René; Li, Xiang Ling et al

in Management and Disposal of Radioactive Waste Euradwast’08 (2008)

A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed in clay around underground excavations. The stress perturbation around ... [more ▼]

A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed in clay around underground excavations. The stress perturbation around the excavation could lead to a significant increase of the permeability, related to diffuse and/or localized crack propagation in the material. Further the drainage and the heating of disposal will modified the size and the structure of the damage zone. The main objective of the study is to model these processes at small and large scale in order to assess their impacts on the performance of radioactive waste geological repositories. This paper concerns more particularly the thermo-hydro-mechanical modelling of a hollow cylinder experiment performed in Boom Clay and the hydro-mechanical modelling of a long term dilatometer experiment performed in Opalinus Clay at Mont Terri Rock Laboratory in Switzerland. This study shows that simple models already permit to reproduce the behaviours observed experimentally. [less ▲]

Detailed reference viewed: 104 (26 ULg)
Full Text
Peer Reviewed
See detailModelling the excavation damaged zone in Callovo-Oxfordian claystone with strain localization
Pardoen, Benoît ULg; Collin, Frédéric ULg; Levasseur, Séverine ULg et al

Conference (2012, October)

Gallery excavation in clayey rocks induces stress perturbations that trigger damage propagation. The excavation process creates then the so-called excavation damaged zone in which properties are modified ... [more ▼]

Gallery excavation in clayey rocks induces stress perturbations that trigger damage propagation. The excavation process creates then the so-called excavation damaged zone in which properties are modified. The prediction of the extension and especially of the fracturing structure in this zone remains a crucial issue in the context of underground storage. Since strain localization in shear band mode is frequently observed in experimental works, the excavation damaged zone can be modeled by considering the development of strain localization bands. A hydro-mechanical modelling of a gallery excavation is performed. The numerical results exhibit an excavation damaged zone extension similar to the in situ measurements and provides information about the rock state within this zone. [less ▲]

Detailed reference viewed: 32 (14 ULg)
Full Text
Peer Reviewed
See detailModelling the excavation damaged zone in claystone with strain localisation using coupled second gradient model and the influence of gallery ventilation
Pardoen, Benoît ULg; Levasseur, Séverine ULg; Collin, Frédéric ULg

Conference (2013, July 09)

Drilling of galleries induces stress perturbations that trigger damage propagation in the surrounding medium. The excavation process creates then the so-called excavation damaged zone around the galleries ... [more ▼]

Drilling of galleries induces stress perturbations that trigger damage propagation in the surrounding medium. The excavation process creates then the so-called excavation damaged zone around the galleries. The prediction of the extension and of the fracture structure within this zone remains nowadays a major issue especially in the context of underground storage. Since localised deformation in shear band mode is frequently observed in experimental works, the excavation damaged zone can be modelled by considering the development of shear strain localisation bands. To correctly model this behaviour, an enhanced model with a regularisation method is required. In underground structures, air ventilation inside the galleries induces a rock-atmosphere interaction that may lead to drainage and to rock desaturation close to the gallery wall. Such desaturation may influence the damage zone structure and needs to be studied. A hydro-mechanical modelling of a gallery excavation including air ventilation is thus performed and the numerical results provide information about the damaged zone extension, the strain localisation bands pattern and the influence of rock desaturation. [less ▲]

Detailed reference viewed: 42 (16 ULg)
Full Text
See detailModelling the fracture generation in EDZ
Charlier, Robert ULg; Chambon, René; Al-Holo, Sama et al

in Report of the Swiss Geological Survey (2007), 2

Detailed reference viewed: 56 (10 ULg)
Full Text
Peer Reviewed
See detailModelling the Fringing of the FORS2 CCD
Walsh, J. R.; Kuntschner, H.; Jehin, Emmanuel ULg et al

in Kaufer, A. (Ed.) The 2007 ESO Instrument Calibration Workshop (2008)

Thinned CCD detectors display fringing which arises from the interference of multiply reflected light in the layers of the CCD. If the layer construction - the thicknesses and refractive indexes of the ... [more ▼]

Thinned CCD detectors display fringing which arises from the interference of multiply reflected light in the layers of the CCD. If the layer construction - the thicknesses and refractive indexes of the layers - is known, then the observed fringing can be accurately modelled and used to correct imaging and spectroscopic data for its effects. In practice the specifications on the actual deposited layer thicknesses may not be known to sufficient accuracy to predict the fringe behaviour. Thus calibration data, in the form of monochromatic flat fields, is required and can be modelled using the technique outlined by Malamuth et al. 2003, which has been applied to ACS CCDs. [less ▲]

Detailed reference viewed: 6 (0 ULg)
Peer Reviewed
See detailModelling the general circulation of shelf seas by 3Dk-ε models
Nihoul, Jacques ULg; Deleersnijder, Eric; Djenidi, Salim ULg

in Earth-Science Reviews (1989), 26(1-3), 163-189

One examines the modifications which must be made-and the limitations which must be set-to classicalk-ε models to extend their application to the simulation of marine mesoscale, synopticscale and ... [more ▼]

One examines the modifications which must be made-and the limitations which must be set-to classicalk-ε models to extend their application to the simulation of marine mesoscale, synopticscale and macroscale processes which compose the weather-like and general circulations of the sea. The case of the general circulation—for which sub-grid scale fluctuations include such semi-organized motions as tides and storm surges-is discussed in more detail. A 3Dk-ε model appropriate to the study of the general circulation in a shallow stratified sea is presented and illustrated with the results of a simulation of the general summer circulation in the Northern Bering Sea, made in the scope of the NSF ISHTAR (“Inner Shelf Transfer and Recycling”) Program. [less ▲]

Detailed reference viewed: 6 (1 ULg)
Full Text
Peer Reviewed
See detailModelling the Gibraltar Strait/Western Alboran Sea ecohydrodynamics
Skliris, Nikolaos; Beckers, Jean-Marie ULg

in Ocean Dynamics (2009), 59(3), 489-508

The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological ... [more ▼]

The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological database. A high-resolution model (~1 km) of the Gibraltar/Western Alboran region embedded within a coarse-resolution model of the West Mediterranean (~5 km) is implemented. The model seasonal climatology of the 3-D circulation and the flow characteristics at the Gibraltar Strait and the Alboran Sea are discussed, and their impact on the plankton ecosystem evolution is explored. An important ecohydrodynamic feature produced by the model is a permanent upwelling zone in the northwestern part of the Alboran Sea in agreement with observations. Model results show that both horizontal and vertical current intensity of the Atlantic Jet increases progressively at the strait to obtain maximum values in the northeastern Mediterranean entrance, inducing an upward displacement of the nitracline. The nutrient-rich water transport through the strait along with the generation of cyclonic vorticity in the northwestern Alboran Sea result in the accumulation of nutrients there and thus induce a permanent fertilisation of this area. [less ▲]

Detailed reference viewed: 92 (22 ULg)
Full Text
Peer Reviewed
See detailModelling the glacial-interglacial changes in the continental biosphere
François, Louis ULg; Delire, Christine; Warnant, Pierre ULg et al

in Global and Planetary Change (1998), 17

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to ... [more ▼]

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to drive the biosphere model are derived from results of the ECHAM2 General Circulation Model (GCM). Six model simulations (four under typical interglacial and two under typical glacial climatic conditions) were performed to analyse the roles of different environmental changes influencing the biospheric net primary productivity (NPP) and carbon stocks. The main differences between these simulations come from the adopted CO, levels in the atmosphere, the presence or absence of crops and from changing continental boundaries. The variation of the terrestrial carbon stocks since the LGM are estimated by comparing the pre-agricultural (280 ppm of CO2, no crops, modern climate) and the full glacial simulations (200 ppm of CO2, LGM climate reconstruction). Our model predicts a global NPP increase from 38 Gt C year(-1) to 53 Gt C year(-1) during the deglaciation, a substantial part of that change being due to CO, fertilization. At the same time, the terrestrial biosphere would have fixed between 134 (neglecting CO2 fertilization effects) and 606 Gt C. The treatment of both the C-3 and C-4 photosynthetic pathways in the CARAIB model enabled us further to reconstruct the partitioning between C, and C, plants. Following our experiments, 29.7% of the total biospheric carbon stock at the LGM was C-4 material, compared to an interglacial fraction of only 19.8%. The average biospheric fractionation factor was similar to 1.5 parts per thousand less negative at LGM than it is today. Considering an atmospheric delta(13)C 0.5 +/- 0.2 parts per thousand lower at LGM than at pre-industrial times, the 606 Gt C transfer would lead to a global ocean delta(13)C shift of roughly -0.41 parts per thousand, fully consistent with currently available data. For the smaller change of 134 Gt C obtained without the CO2 fertilization effect, this shift would only be on the order of -0.10 parts per thousand. (C) 1998 Elsevier Science B,V. All rights reserved. [less ▲]

Detailed reference viewed: 25 (2 ULg)
See detailModelling the Global Riverine U Fluxes to the Oceans
Riotte, Jean; Goddéris, Yves; Chabaux, François et al

Conference (2005, May 21)

Mean U isotopic ratio of the ocean has remained roughly constant since about 600 kyrs (Henderson, 2001). This 1.14 value cannot be explained considering the present day value of the U riverine ratio (1.17 ... [more ▼]

Mean U isotopic ratio of the ocean has remained roughly constant since about 600 kyrs (Henderson, 2001). This 1.14 value cannot be explained considering the present day value of the U riverine ratio (1.17, Chabaux et al., 2001). However, the mean riverine ratio was calculated on half of the total continental runoff. Is this partial mean value really representative of the mean value? If yes, might this value have changed over a glacial-interglacial cycle ? We build up a numerical model calculating the flux of U transfer to the ocean through weathering. The spatial resolution of the model reaches 0.5°lat x0.5°long. Lithology is modified from Amiotte-Suchet et al. (2003). Weathering fluxes are estimated from simple parametric laws, calculating the flux of total dissolved solids from mean annual temperature and runoff. Soil PCO2 is used to estimate carbonate dissolution rates, and is calculated from a simulation of the Caraib model. Uranium fluxes are estimated proportional to the TDS flux, weighted by its abundance in the source rock. CO2 consumption through weathering is simultaneously computed. The 234U/238U ratio of the river is calculated according to a correlation existing between the measured 234U/238U and runoff, showing a decrease of this ratio with increasing runoff. The model is first validated over several large watersheds, including the Amazon, the Ganges-Brahmapoutra, the Mississippi, and the Congo rivers. Global runs are then performed, showing that the modelled mean global value is close to the measured partial mean of 1.17. We explore then possible variations of the modelled ratio at the last glacial maximum. Temperature and runoff fields are taken from LGM simulations of the ECHAM GCM. Extension of ice sheets is assumed to cut off part of the weathering fluxes, producing possible fluctuations in the riverine U isotopic ratio, as well as changes in the regional runoff pattern. [less ▲]

Detailed reference viewed: 14 (3 ULg)
Full Text
Peer Reviewed
See detailModelling the habitat suitability of cetaceans:Example of the sperm whale in the northwestern Mediterranean Sea
Praca, Emilie; Gannier, Alexandre; Das, Krishna ULg et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2009), (56), 648657

Cetaceans are mobile and spend long periods underwater. Because of this, modelling their habitat could be subject to a serious problem of false absence. Furthermore, extensive surveys at sea are time and ... [more ▼]

Cetaceans are mobile and spend long periods underwater. Because of this, modelling their habitat could be subject to a serious problem of false absence. Furthermore, extensive surveys at sea are time and money consuming, and presence–absence data are difficult to apply. This study compares the ability of two presence–absence and two presence-only habitat modelling methods and uses the example of the sperm whale (Physeter macrocephalus) in the northwestern Mediterranean Sea. The data consist of summer visual and acoustical detections of sperm whales, compiled between 1998 and 2005. Habitat maps were computed using topographical and hydrological eco-geographical variables. Four methods were compared: principal component analysis (PCA), ecological niche factor analysis (ENFA), generalized linear model (GLM) and multivariate adaptive regression splines (MARS). The evaluation of the models was achieved by calculating the receiver operating characteristic (ROC) of the models and their respective area under the curve (AUC). Presence–absence methods (GLM, AUC=0.70, and MARS, AUC=0.79) presented better AUC than presence-only methods (PCA, AUC=0.58, and ENFA, AUC=0.66), but this difference was not statistically significant, except between the MARS and the PCA models. The four models showed an influence of both topographical and hydrological factors, but the resulting habitat suitability maps differed. The core habitat on the continental slope was well highlighted by the four models, while GLM and MARS maps also showed a suitable habitat in the offshore waters. Presence–absence methods are therefore recommended for modelling the habitat suitability of cetaceans, as they seem more accurate to highlight complex habitat. However, the use of presence-only techniques, in particular ENFA, could be very useful for a first model of the habitat range or when important surveys at sea are not possible. [less ▲]

Detailed reference viewed: 184 (17 ULg)
Full Text
Peer Reviewed
See detailModelling the Holocene migrational dynamics of Fagus sylvatica L. and Picea abies (L.) H. Karst
Lehsten, Lehsten; Dullinger, Stefan; Hülber, Karl et al

in Global Ecology and Biogeography (2014)

Aim: Vegetation dynamics and the competitive interactions involved are assumed to restrict the ability of species to migrate. But in most migration modelling approaches disturbance-driven succession and ... [more ▼]

Aim: Vegetation dynamics and the competitive interactions involved are assumed to restrict the ability of species to migrate. But in most migration modelling approaches disturbance-driven succession and competition processes are reduced to simple assumptions or are even missing. The aim of this study was to test a combination of a migration model and a dynamic vegetation model to estimate the migration of tree species controlled by climate, environment and local species dynamics such as succession and competition. Location: Europe. Methods: To estimate the effect of vegetation dynamics on the migration of European beech and Norway spruce, we developed a post-process migration tool (LPJ-CATS). This tool integrates outputs of the migration model CATS and the dynamic vegetation model LPJ-GUESS. The model LPJ-CATS relies on a linear dependency between the dispersal kernel and migration rate and is based on the assumption that competition reduces fecundity. Results: Simulating potential migration rates with the CATS model, which does not account for competition and disturbance, resulted in mean Holocene migra- tion rates of 435 ± 55 and 330 ± 95 m year−1 for the two species Picea abies and Fagus sylvatica, respectively. With LPJ-CATS, these mean migration rates were reduced to 250 ± 75 and 170 ± 60 m year−1 for spruce and beech, respectively. Moreover, LPJ-CATS simulated migration pathways of these two species that gen- erally comply well with those documented in the palaeo-records. Main conclusions: Our ‘hybrid’ modelling approach allowed for the simulation of generally realistic Holocene migration rates and pathways of the two study species on a continental scale. It suggests that competition can considerably modify spread rates, but also the magnitude of its effect depends on how close climate conditions are to the niche requirements of a particular species. [less ▲]

Detailed reference viewed: 33 (16 ULg)
Full Text
Peer Reviewed
See detailModelling the huge, Herschel-resolved debris ring around HD 207129
Löhne, T.; Augereau, J.-C.; Ertel, S. et al

in Astronomy and Astrophysics (2012), 537

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation ... [more ▼]

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation and evolution are linked to those of planetary bodies, they provide valuable information. The few well-resolved debris disks are even more valuable because they can serve as modelling benchmarks and help resolve degeneracies in modelling aspects such as typical grain sizes and distances. Here, we present an analysis of the HD 207129 debris disk, based on its well-covered spectral energy distribution and Herschel/PACS images obtained in the framework of the DUNES (DUst around NEarby Stars) programme. We use an empirical power-law approach to the distribution of dust and we then model the production and removal of dust by means of collisions, direct radiation pressure, and drag forces. The resulting best-fit model contains a total of nearly 10[SUP]-2[/SUP] Earth masses in dust, with typical grain sizes in the planetesimal belt ranging from 4 to 7 μm. We constrain the dynamical excitation to be low, which results in very long collisional lifetimes and a drag that notably fills the inner gap, especially at 70 μm. The radial distribution stretches from well within 100 AU in an unusual, outward-rising slope towards a rather sharp outer edge at about 170-190 AU. The inner edge is therefore smoother than that reported for Fomalhaut, but the contribution from the extended halo of barely bound grains is similarly small. Both slowly self-stirring and planetary perturbations could potentially have formed and shaped this disk. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

Detailed reference viewed: 34 (3 ULg)
Full Text
See detailModelling the hydrodispersive behaviour of variably saturated chalk
Brouyère, Serge ULg

Conference (2003, April 02)

The presentation dscribes the mathematical and numerical modelling of solute tracer experiments in variably saturated chalk

Detailed reference viewed: 9 (0 ULg)