7 results on '"Prieels, René"'
Search Results
2. Neutron-Induced Fission Cross Sections of Nuclei in the Vicinity of 208Pb at Incident Energies below 60 MeV.
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Ryzhov, Igor V., Tutin, Gennady A., Eismont, Vilen P., Mitryukhin, Andrey G., Oplavin, Valery S., Soloviev, Sergey M., Meulders, Jean-Pierre, El Masri, Youssef, Keutgen, Thomas, Prieels, René, and Nolte, Ralf
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NEUTRONS ,PARTICLES (Nuclear physics) ,NEUTRON beams ,NEUTRAL beams ,NUCLEAR physics ,PHYSICS - Abstract
Neutron-induced fission cross sections of 205Tl, 204, 206, 207, 208Pb, and 209Bi have been measured at incident energies of 32.8, 45.3, and 59.9 MeV. The measurements were performed at the Louvain-la-Neuve neutron beam facility using the 7Li (p, n) reaction as neutron source. Fission fragments were detected with a multi-section Frisch-gridded ionization chamber (MFGIC). Neutron fluence measurements were based on the 238U(n, f) reaction. The neutron fluence monitoring procedure was asserted by crosscheck measurement, in which the 59.9-MeV neutron beam fluence was simultaneously determined with the MFGIC and with a fission chamber monitor calibrated relative to a proton-recoil telescope. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
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- 2005
- Full Text
- View/download PDF
3. Radiation damage induced by neutrons in CMS silicon sensors
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Forton, Eric, UCL - SC/PHYS - Département de physique, Tavernier, Stefaan, Hartmann, Frank, Piotrzkowski, Krzysztof, Lemaître, Vincent, Delbar, Thierry, Prieels, René, and Grégoire, Ghislain
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Silicon ,Damage ,Radiation ,CMS ,Sensors ,Detectors and Experimental Techniques - Abstract
Les expériences conduites auprès du futur accélérateur LHC au CERN nécessitent la construction des détecteurs les plus grands et les plus complexes jamais conçus. En particulier, le trajectographe de la collaboration CMS utilisera uniquement des détecteurs micropiste silicium et ce, en très grandes quantités. Ce dernier dépend donc de manière capitale de la qualité de toute la production des senseurs et la collaboration CMS a ainsi décidé de mettre en place un vaste programme de contrôle de cette qualité. Cette thèse présente une partie des travaux réalisés à l'UCL dans ce cadre. La discussion porte en particulier sur résistance aux radiations des senseurs en silicium, testée de manière routinière à Louvain-la-Neuve. Le texte débute par une présentation du détecteur CMS et des dégâts radiatifs subits par les détecteurs micropiste silicium. Les dispositifs expérimentaux mis en place auprès des cyclotrons et dans le laboratoire de l'institut de Physique nucléaire sont ensuite détaillés. Finalement, les résultats des tests systématiques sont résumés, et discutés au regard des critères posés par la collaboration (PHYS 3)--UCL, 2006
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- 2014
4. On the assimilation of ice velocity and concentration data into large-scale sea ice models
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Dulière, Valérie, UCL - SC/PHYS - Département de physique, Fichefet, Thierry, van Yperseele, Jean-Pascal, Timmermann, Ralph, Goosse, Hugues, Deleersnijder, Eric, Garric, Gilles, Prieels, René, and Defrance, Pierre
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Sea ice ,Data assimilation ,Astrophysics::Earth and Planetary Astrophysics ,Twin experiments ,Physics::Atmospheric and Oceanic Physics ,Physics::Geophysics - Abstract
Data assimilation into sea ice models designed for climate studies has started about 15 years ago. In most of the studies conducted so far, it is assumed that the improvement brought by the assimilation is straightforward. However, some studies suggest this might not be true. In order to elucidate this question and to find an appropriate way to further assimilate sea ice concentration and velocity observations into large-scale sea ice models, we analyze here results from a number of twin experiments (i.e. experiments in which the assimilated data are model outputs) carried out with first a simplified model of the Arctic sea ice pack then with NEMO-LIM2, a primitive equation ocean general circulation model coupled to LIM (Louvain-la-Neuve sea ice model). Our objective is to determine to what degree the assimilation of ice velocity and/or concentration data improves the global performance of the model and, more specifically, reduces the error in the computed ice thickness. A simple scheme is used, and outputs from a control run and from perturbed experiments without and with data assimilation are thoroughly compared. Our results indicate that, under certain conditions depending on the assimilation weights and the type of model error, the assimilation of ice velocity data enhances the model performance. The assimilation of ice concentration data also helps in improving the model results, but it has to be handled with care because of the strong link between ice concentration and ice thickness. Therefore, we show that one should conserve the ice thickness (not the ice volume) when ice concentration data are assimilated into the model. We also demonstrate that one should assimilate sea ice concentration and velocity data simultaneously. Finally, we give some concrete keys in order to choose which observational data set to assimilate. (PHYS 3)--UCL, 2007
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- 2007
5. Soil-vegetation-atmosphere interactions in the West African monsoon / Interactions entre le sol, la végétation et l'atmosphère dans la mousson ouest-africaine
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Vanvyve, Emilie, UCL - SC/PHYS - Département de physique, Prieels, René, van Ypersele de Strihou, Jean-Pascal, Gallée, Hubert, Berger, André, Schayes, Guy, Hall, Nicholas, and Cornet, Alain
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Climatology ,Rainfall ,Monsoon ,Biosphere ,Afrique de l'Ouest ,West Africa ,Précipitations ,Climatologie ,Mousson ,Modèle climatique régional ,Regional climate model ,Biosphère - Abstract
The climate of West Africa is characterised by a monsoonal system that brings rainfall onto the subcontinent during an annual rainy season. From the late 60's to the mid-90's, rainfall levels significantly below average were observed, which brought severe socio-economic implications. The causes of the uncharacteristically long drought period, and indeed the mechanisms underpinning West African climate were poorly understood at the time, but have since attracted growing attention from the scientific community. Amongst the factors identified as critical is the interaction between the Earth surface and the atmosphere. To investigate these interactions over West Africa we have adopted an approach based upon regional climate modelling, an internationally recognised discipline enabling the representation of past and future climates, and the study of specific meteorological mechanisms. Using the regional climate model MAR, we have carried out simulations of the West African climate for the years 1986, 1987, and 1988. To improve the accuracy with which the model represents the biosphere, a new dataset describing the local vegetation was incorporated and a new scheme for the representation of roots implemented. A measure of the internal variability inherent to all results produced with this, and other such models, was determined. Subsequently, the influence of soil moisture anomalies on the model behaviour was investigated. The latest version of the model was validated by comparing it to observational data for selected years. Our results have prooven the ability of the improved MAR to simulate the West African climate, its monsoon and its spatial and temporal behaviour and provide strong evidence of its suitability for further investigation of the surface-atmosphere interactions over West Africa. (PHYS 3)--UCL, 2007
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- 2007
6. Reconstruction of the 1979-2005 Greenland ice sheet surface mass balance using satellite data and the regional climate model MAR
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Fettweis, Xavier, UCL - SC/PHYS - Département de physique, Nauts, André, Fichefet, Thierry, Lefebre, Filip, Schayes, Guy, van Lipzig, Nicole, Prieels, René, Gallée, Hubert, and van Ypersele, Jean-Pascal
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Ice sheet ,Satellite ,Climate ,Snow ,Greenland ,Mass balance ,Microwave ,Model ,Melt - Abstract
In order to improve our knowledge on the current state and variability of the Greenland ice sheet surface mass balance (SMB), a 27-year simulation (1979-2005) has been performed with the coupled atmosphere-snow regional model MAR. This simulation reveals an increase in the main factors of the SMB which are, on the one hand, the snowfall (+ 1.6 ± 1.8 km3 yr-1) in winter and on the other hand, the run-off (+ 4.2 ± 1.9 km3 yr-1) in summer. The net effect of these two competing factors leads to a SMB loss rate of - 2.7 ± 3.0 km3 yr-1, which has a significance of 87%. The melt extent derived from the passive microwave satellite data since 1979 also shows this trend. The melt water supply has increased because the Greenland ice sheet has been warming up by + 0.09 ± 0.04 °C yr-1 since 1979. This warming comes from a uniform increase of downward infra-red radiation which can not be explained by the natural variability. These changes result very likely from the global warming induced by human activities. As a result, it seems that: i) increased melting dominates over increased accumulation in a warming scenario, ii) the Greenland ice sheet has been significantly losing mass since the beginning of the 1980's by an increasing melt water run-off as well as by a probable increase of iceberg discharge into the ocean due to the "Zwally effect" (the melt water-induced ice sheet flow acceleration) and iii) the Greenland ice sheet is projected to continue to lose mass in the future. The Greenland ice sheet melting could have an effect on the stability of the thermohaline circulation (THC) and the global sea level rise. On the one hand, increases in the freshwater flux from the Greenland ice sheet (glacier discharge and run-off) could perturb the THC by reducing the density contrast driving it. On the other hand, the melting of the whole Greenland ice sheet would account for a global mean sea level rise of 7.4 m. (PHYS 3)--UCL, 2006
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- 2006
7. Climate change over the next millennia using LOVECLIM, a new Earth system model including the polar ice sheets
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Driesschaert, Emmanuelle, UCL - SC/PHYS - Département de physique, van Ypersele, Jean-Pascal, Kageyama, Masa, Huybrechts, Philippe, Goosse, Hugues, Berger, André, Prieels, René, and Fichefet, Thierry
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Abrupt event ,Changements climatiques ,Climate change ,Ice sheets ,LOVECLIM ,Calottes glaciaires ,Evénements abruptes - Abstract
A new Earth system model of intermediate complexity, LOVECLIM, has been developed in order to study long-term future climate changes. In particular, LOVECLIM includes an interactive Greenland and Antarctic ice sheet model (AGISM) as well as an oceanic carbon cycle model (LOCH). Those climatic components can have a great impact on future climate. However, most studies investigating future climate changes do not take them into account. The few studies in recent literature assessing the impact of polar ice sheets on future climate draw very different conclusions, which shows the need for developing such a model. The aim of this study is to analyse the possible perturbations of climate induced by human activities over the next millennia. A particular attention is given to the evolution of the oceanic thermohaline circulation. A series of numerical simulations have been performed with LOVECLIM over the next millennia using various forcing scenarios. The global equilibrium warming computed by the model ranges from 0.55°C to 3.75°C with respect to preindustrial times. The model does not simulate a complete shut down of the oceanic thermohaline circulation but a transient weakening followed by a quasi-recovering at equilibrium. In most of the projections, the Greenland ice sheet undergoes a continuous reduction in volume, leading to an almost total disappearance in the most pessimistic scenarios. The impact of the Greenland deglaciation on climate has been assessed through sensitivity experiments. The removal of the Greenland ice sheet is responsible for a regional amplification of the global warming inducing a total melt of Arctic sea ice in summer. The freshwater flux from Greenland generates large salinity anomalies in the North Atlantic Ocean that reduce the rate of North Atlantic Deep Water formation, slowing down the oceanic thermohaline circulation. (PHYS 3)--UCL, 2005
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- 2005
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