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Search Results: 1 - 10 of 462077 matches for " Lejeune A. "
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Distribution of Lutra maculicollis in Rwanda : ecological constraints
Lejeune A.,Frank A.
IUCN Otter Specialist Group Bulletin , 1990,
Abstract: The study of 10 rwandese lakes, where there are still quite important populations of Lutra maculicollis, has pointed out a few characteristics of the habitat favorable to the survival of these populations. The ecological constraints for the survival of these populations are: the abundance of small fishes, the continuity of the lake side vegetation, the absence of crocodiles and pollution by pesticides, and the low level of predation by man.
Trehalose as a stress marker of the physiological impact of mixing on yeast production: scale-down reactors and mini-bioreactors investigations
Lejeune, A.,Delvigne, F.,Thonart, P.
Biotechnologie, Agronomie, Société et Environnement , 2010,
Abstract: Trehalose is a reserve carbohydrate produced by Saccharomyces cerevisiae under stress conditions and used as a cryoprotectant during freeze drying. So the cellular content of trehalose is an important parameter to control in industrial context. Scale-down reactors have been used to produce Saccharomyces cerevisiae. These reactors permit to mimic the hydrodynamic conditions experienced by cells during large scale production. Three types of scale-down reactors have been tested, differing by the geometry of the non-mixed part and the recirculation flow rate. The results show that cells cultivated in scale-down reactors produced less trehalose compared to the reference reactor. These results are completed by the study of the expression of the TPS2 promoter coupled with a green fluorescent protein (GFP). TPS2 is a gene coding for a subunit of the enzymatic complex responsible of trehalose synthesis. This strain was produced in mini-bioreactors which are shake flasks equipped with a dissolved oxygen probe. This approach allows using trehalose, or related enzymes, as a cellular marker of the stress encountered by yeast in industrial process.
Dynamics of many-particle fragmentation in a Cellular Automaton model
A. Lejeune,J. Perdang,J. Richter
Physics , 2003, DOI: 10.1103/PhysRevE.67.046214
Abstract: A 3D Cellular Automaton model developed by the authors to deal with the dynamics of N-body interactions has been adapted to investigate the head-on collision of two identical bound clusters of particles, and the ensuing process of fragmentation. The range of impact energies is chosen low enough, to secure that a compound bound cluster can be formed. The model is devised to simulate the laboratory set-up of fragmentation experiments as monitored by 4pi detectors. The particles interact via a Lennard-Jones potential. At low impact energies the numerical experiments following the dynamics of the individual particles indicate a phase of energy sharing among all the particles of the compound cluster. Fragments of all sizes are then found to evaporate from the latter cluster. The cluster sizes, measured in our set-up by simulated 4pi detectors, conform to a power law of exponent around 2.6.
Nuclear Matter EOS with a Three-body Force
A. Lejeune,U. Lombardo,W. Zuo
Physics , 2001, DOI: 10.1016/S0370-2693(00)00211-2
Abstract: The effect of a microscopic three-body force on the saturation properties of nuclear matter is studied within the Brueckner-Hartree-Fock approach. The calculations show a decisive improvement of the saturation density along with an overall agreement with the empirical saturation point. With the three-body force the symmetry energy turns more rapidly increasing with density, which allows for the direct URCA process to occur in $\beta$-stable neutron star matter. The influence of the three-body force on the nuclear mean field does not diminish the role of the ground state correlations.
Constitution d'une génothèque destinée l'identification des génomes mitochondriaux et recherche de nouvelles séquences mitochondriales chez les végétaux supérieurs
Lejeune B,de Souza A Pereira,Haouazine N,Jubier MF
Genetics Selection Evolution , 1994, DOI: 10.1186/1297-9686-26-s1-s81
Mise au point d' un modele cartographique pour la description des stations forestieres en Ardenne belge
Claessens H.,Lejeune P.,Cuvelier M.,Dierstein A.
Biotechnologie, Agronomie, Société et Environnement , 2002,
Abstract: Development of a cartographic mdel for the forest site types delineation in the Belgian Ardenne. The paper presents an original method dealing with the forest site types delineation. The suggested method consists in integrating a typological key in a GIS aiming at producing a thematic map that describes forest site types. Data used are the soil map of Belgium (digitized at the scale 1:20,000) and a digital elevation model built from a topographic map (scale 1:10,000). The typological key is mainly based on the methodology used by Thill et al. (1988) in the site types system for central Ardenne, the potential vegetation map of Sougnez and Dethioux (1975) and the ecoregion map of Delvaux and Galoux (1962). In that respect, site types are closely linked to the soil map and the phytosociological classification. So, they can be connected to the afforestation guide and different phytosociological and autecological studies concerning forest species. It is then possible to map the potential habitats or the site potentialities related to tree species. The key is valid for the Ardenne ecoregion located in Southern Belgium (elevation higher than 300 m). It has to be validated through an intensive use in the field, taking into account its imprecision linked to the types of collected data, chieffly those being digitized. The integration of such a tool in a SIG can be considered as an original way in terms of integrated forest management or forest sites description in the context of the project ""Natura 2000"" launched by the European Union. The study has been carried out within the framework of an experimental integrated management project concerning the Saint-Hubert forest (17,000 ha).
Status of medium-sized ungulate populations in 2010, at the Nazinga Game Ranch, Burkina Faso (Western Africa)
Marchal, A.,Lejeune, P.,Bouché, P.,Ouédraogo, M.
Biotechnologie, Agronomie, Société et Environnement , 2012,
Abstract: The present study consists of analyzing the raw data collected from the annual line-transect foot count of medium-sized ungulates, carried out at the Nazinga Game Ranch (NGR), Burkina Faso (Western Africa), in both 2001 and 2010. The annual census focused on the seven main medium-sized ungulates, namely (in alphabetical order), the Bushbuck (Tragelaphus scriptus), the Common Warthog (Phacochoerus africanus), the Defassa Waterbuck (Kobus ellipsiprymnus), the Grimm's Duiker (Sylvicapra grimmia), the Oribi (Ourebia ourebi), the Roan Antelope (Hippotragus equinus) and the Western Hartebeest (Alcelaphus buselaphus). The census also focused on illegal anthropogenic activities. The wildlife populations were quantitatively analyzed through an estimation of their absolute density via the distance sampling method and through their evolution over the last decade using two relative density indexes, namely the Kilometric Abundance Index (KAI) and a spatial distribution index. These indexes were also used to measure the evolution of illegal activities over the same period. Both the wildlife observations and the anthropogenic observations were mapped using the Kernel method. Following an increasing trend in their population between 2001 and 2010, both the Roan Antelope and the Western Hartebeest reached an estimated density of 4.7 individuals per km2, while the Defassa Waterbuck reached 2.4 individuals per km2. Following an inverse trend over the same period, the Bushbuck, the Grimm's Duiker and the Oribi reached an estimated density of 0.4 individuals per km2. As for the Common Warthog, its estimated density of 2.5 individuals per km2 seemed to remain unchanged during that decade. A comparison between wildlife observations and anthropogenic observations reveals a high decrease in animal densities in the north, east and west peripheral borders of the NGR and a flagrant extension of the proportion of the ranch being subjected to illegal activities (poaching, cattle herding, etc.).
Phase space characteristics of fragmenting nuclei described as excited disordered systems
J. Richert,D. Boose,A. Lejeune,P. Wagner
Physics , 1996, DOI: 10.1016/S0375-9474(96)00468-X
Abstract: We investigate the thermodynamical content of a cellular model which describes nuclear fragmentation as a process taking place in an excited disordered system. The model which reproduces very well the size distribution of fragments does not show the existence of a first order phase transition.
Microscopic three-body force for asymmetric nuclear matter
W. Zuo,A. Lejeune,U. Lombardo,J. F. Mathiot
Physics , 2002,
Abstract: Brueckner calculations including a microscopic three-body force have been extended to isospin asymmetric nuclear matter. The effects of the three-body force on the equation of state and on the single-particle properties of nuclear matter are discussed with a view to possible applications in nuclear physics and astrophysics. It is shown that, even in the presence of the three-body force, the empirical parabolic law of the energy per nucleon vs isospin asymmetry $\beta=(N-Z)/A$ is fulfilled in the whole asymmetry range $0\le\beta\le 1$ up to high densities. The three-body force provides a strong enhancement of symmetry energy increasing with the density in good agreement with relativistic approaches. The Lane's assumption that proton and neutron mean fields linearly vary vs the isospin parameter is violated at high density in the presence of the three-body force. Instead the momentum dependence of the mean fields is rather insensitive to three body force which brings about a linear isospin deviation of the neutron and proton effective masses. The isospin effects on multifragmentation events and collective flows in heavy-ion collisions are briefly discussed along with the conditions for direct URCA processes to occur in the neutron-star cooling.
Interplay of Three-Body Interactions in the EOS of Nuclear Matter
W. Zuo,A. Lejeune,U. Lombardo,J. F. Mathiot
Physics , 2002, DOI: 10.1016/S0375-9474(02)00750-9
Abstract: The equation of state of symmetric nuclear matter has been investigated within Brueckner approach adopting the charge-dependent Argonne $V_{18}$ two-body force plus a microscopic three-body force based on a meson-exchange model. The effects on the equation of state of the individual processes giving rise to the three-body force are explored up to high baryonic density. It is found that the major role is played by the competition between the strongly repulsive $(\sigma, \omega)$ exchange term with virtual nucleon-antinucleon excitation and the large attractive contribution due to $(\sigma, \omega)$ exchange with $N^*(1440)$ resonance excitation. The net result is a repulsive term which shifts the saturation density corresponding to the only two-body force much closer to the empirical value, while keeping constant the saturation energy per particle. The contribution from $(\pi, \rho)$ exchange 3BF is shown to be attractive and rather small. The analysis of the separate three-body force contributions allows to make a comparison with the prediction of Dirac-Brueckner approach which is supposed to incorporate via the {\it dressed} Dirac spinors the same virtual nucleon-antinucleon excitations as in the present three-body force. The numerical results suggest that the three-body force components missing from the Dirac-Brueckner approach are not negligible, especially at high density. The calculation of the nuclear mean field and the effective mass shows that the three-body force affects to a limited extent such properties.
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