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Search Results: 1 - 10 of 19844 matches for " André Buldgen "
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Croissance juvénile et comportement physiologique d'Andropogon gayanus Kunth var. bisquamulatus en conditions de stress hydrique
André Buldgen
Biotechnologie, Agronomie, Société et Environnement , 1997,
Abstract: Seedling growth and physiological behaviour of Andropogon gayanus Kunth cv. bisquamulatus in water stress conditions.Several studies carried on the physiology of Andropogon gayanus Kunth cv. bisquamulatus were conducted in Belgium in a wind tunnel simulating climatic conditions close to those prevailing during the rainy season in Sahelo-Sudanese region. The first experiments simulated water supply of 15, 20 and 25 mm at the outset of a caryopse sowing in a sandy soil. The observations were focused on daily evaporation losses, seedling emergencies, their growth and the mortality evolution. Results show that an initial soil water reserve of 25 mm, i.e. about 22.5 % in volume in the upper layer, is necessary to ensure the seedling survival during a period of 15 days after emergence. After 27 days, 95 % of the seedlings were still clive. With an initial soil water reserve of 13.5 or 18 % in volume (15 and 25 mm treatment respectively), mortalities occur already 4 to 6 days after sowing and increase vert' rapidly over a 10 day period. Whatever the initial water reserve mat' be, seedling losses occur systematically for a soil water reserve under or equal to 5 mm (4.5 % in volume). Two subsequent experiments were also conducted in order to analyse the photosynthetic parameters and the water status of 6 plants of Andropogon gayanus in the rainy and the dry seasons and during two drying cycles imposed in the rainy season. The first experiment shows that the hydric potentiel is -0.44 MPa during the rainy season and louver than -1 MPa during the dry season. The stomacal conductance is high (more than 1 cm . s-1) during both seasons, but the rate of photosynthesis decreases by half (from 19.8 to 10.9 graoles CO2 . m-2 . s-1) during the dry season. When the graminea endures a drought period in the rainy season, the physiological parameters evolve slowly until the soil water reserve reaches.
Intensification agricole en région sahélo-soudanienne. 2. Productivité et risques économiques
Marc Piraux,André Buldgen,Patrick Steyaert,Abdoulaye Dieng
Biotechnologie, Agronomie, Société et Environnement , 1997,
Abstract: Intensification of farming in the Sahelian-Sudanese region. 2. Productivity and economic risks.his second part concerns the analysis of land productivity and labour results within a traditional farming system and two improved systems experimented on a site in the center-west part of the Senegalese groundnut basin. Intensified farming systems associate farming and livestock and use motorized or draft cultivation (oxen) as means of mechanization. Results show that intensification systematically increases crop yields and gives rise to larger amounts of by-products fitting well for use as animal feed. Furthermore, yields stabilize with soil fertility improvement. The economic risk linked to intensification strongly depends on the climatic context. A 400 mm annual rainfall appears as a threshold to insure a net increase of land and labour productivity, justifying an intensification operation that combines plowing, liming material, organic and minerai fertilizer applications. In the climatic risk zone like that where the experimentation took place, the diversification of farming activity increases and stabilizes income. Therefore, productions as cassava or bissap and the integration of a perennial forage crop offer interesting development perspectives. The constraints limiting the adoption of intensified and diversified farming systems are linked to market conditions, time-labour feasibility, soil fertility management and institutional context. To minimize the risks, tactical adjustments are also analyzed.
Intensification agricole en région sahélo-soudanienne. 1. Itinéraires techniques dans un contexte à risques
Marc Piraux,André Buldgen,Patrick Steyaert,Abdoulaye Dieng
Biotechnologie, Agronomie, Société et Environnement , 1997,
Abstract: Intensification of farming in the Sahelian-Sudanese region. 1. Crop management sequence in a risk context.An experimentation carried out in a station during five consecutive years compared the traditional farming system of the Senegalese groundnut basin to two modernized systems, based on a close synergy between agriculture and livestock productions: a system intensified by draught cultivation (oxen) and a system using heavy motorization. The experimentation, implemented at a real farm scale, has taken place in pedo-climatic conditions representative of the region. By producing manure and an important work force, livestock strongly contributes to the success of farming activities. Results show that the suggested intensification models have a beneficial effect on the soil fertility. Several technical options are put forward aiming at a reduction of the risks linked to climatic hazards. Among the main adjustments considered in the modernized systems, we can mention: crop diversification, rotation between cereals and short duration crops ("bissap", black-eyed cowpeas), planned minerai fertilizer application and judicious selection of growing season and soil tilling procedures. Results provide interesting technical references for setting up development programs
Nutritional and environmental consequences of dietary fibre in pig nutrition: a review
Bindelle J.,Leterme P.,Buldgen A.
Biotechnologie, Agronomie, Société et Environnement , 2008,
Abstract: Despite its negative impact on performances because of lower protein and energy digestibility, increasing attention has been paid in the past decade to dietary fibre in swine nutrition due to its multiple functionalities. The present review examines the influence of dietary fibre on the digestive processes and the consequences on pig protein and energy nutrition, health concerns and environmental issues. Dietary fibre is defined as the plant polysaccharides that are resistant to digestive secretions and are potentially available for bacterial fermentation in the intestines of single-stomached animals. Resistant starch is also considered as a dietary fibre. The short-chain fatty acids released by bacteria contribute to the host energy supply and both regulate the composition of the flora and the growth of epithelial cells, especially in the case of butyrate. The bacterial growth supported by the fermentation induces a shift of N excretion from urine to faeces. Beside the fermentability, the physical properties of dietary fibre such as the water-holding capacity, the viscosity and the solubility influence the digestion, the satiety and the transit time. In relationship with the mechanisms of dietary fibre interaction with the digestive processes exposed in this review, the opportunities and treats of dietary fibre inclusion in swine rations for intensified and for more extensive tropical production systems are discussed. Dietary fibre is indeed a possible means to reduce nitrogen losses of production units and to improve pig intestinal health and animal welfare. Finally, the potential role of in vitro fermentation methods to investigate the fate of dietary fibre in the digestive system is discussed.
Factors affecting intake by grazing ruminants and related quantification methods: a review
Decruyenaere V.,Buldgen A.,Stilmant D.
Biotechnologie, Agronomie, Société et Environnement , 2009,
Abstract: The aim of this review is to discuss the factors affecting intake of grazing ruminants and its main quantification methods. Level of intake depends on many factors linked, for instance to the gut capacity, to the animal’s requirements covering, or to the forage quality. The post-ingestive feedback of the intake, the morphological characteristics of grazed plants and the environment such as climate, characteristics of feed resources, are also factors of interest to explain some intake variations. Intake is a multi-factorial phenomenon. There are few studies on the estimation of that parameter. Methods and techniques developed to measure intake are often laborious and expensive, sometimes unrepresentative of the true grazing conditions and often lacking of accuracy. Currently, the n-alkanes, natural markers presents in the plants, appear as one of the best way to predict at the same time intake and digestibility of ingested diet. However, the method remains hard to apply for long periods and in free ranging schemes. If sufficiently robust databases and calibrations are developed, Near Infrared Spectroscopy (NIRS) appears as an interesting technique to predict rapidly intake and digestibility of grazed grass. Particularly, NIRS applied to faeces appears promising as related in recent studies. It could be considered as a good alternative for assessing the diet, in quantity and in quality, of grazing or ranging ruminants.
Simplified Analytical Method for Estimating the Resistance of Lock Gates to Ship Impacts
Lo c Buldgen,Hervé Le Sourne,Philippe Rigo
Journal of Applied Mathematics , 2012, DOI: 10.1155/2012/763849
Abstract: The present paper is concerned with the design of lock gates submitted to ship impacts. In this paper, a simplified analytical method is presented to evaluate the resistance of such structures under collision. The basic idea is to assume that the resistance is first provided through a local deforming mode, corresponding to a localized crushing of some impacted structural elements. For consecutive larger deformations, the resistance is then mostly provided through a global deforming mode, corresponding to an overall movement of the entire gate. For assessing the resistance in the case of the local deforming mode, the structure is divided into a given number of large structural entities called “superelements.” For each of them, a relation between the resistance of the gate and the penetration of the striking ship is established. However, as some results are already available in the literature, this subject is not treated extensively in this paper. On the contrary, the calculation of the resistance of the gate provided through the global mode is detailed and the strategy to switch from local to global deformation is highlighted. Finally, we propose to validate our developments by making a comparison between results obtained numerically and those predicted by the present analytical approach.
Some suitable grasses and legumes for ley pastures in Sudanian Africa: the case of the Borgou region in Benin
Adjolohoun S.,Bindelle J.,Adandédjan C.,Buldgen A.
Biotechnologie, Agronomie, Société et Environnement , 2008,
Abstract: In Sudanian region of Africa, agricultural systems are under increasing pressure because of human and animal population growth, climate changes, extensive practises, decreasing prices for cash crops, etc. Possibilities of intensification in smallholder farming systems of the Borgou region in Benin are limited due to difficulties to pay for external inputs. Therefore, rural communities rely heavily on low input technologies to increase crop production and animal feed. Cultivated forages are of better-feed quality for ruminants compared to weed fallows. Their integration in cropping system through ley pastures has the potential to increase not only animal feed availability but also to improve soil fertility. This paper reviews some possible grass and legume species that can be used for that purpose with a special focus on the strengths and weaknesses of the species in terms of soil and climate suitability, forage production, nutritive value and soil fertility restoration. The choice of one or several among them as leys in pure stands or mixed forage crops must be taken carefully considering the balance between advantages and disadvantages of the species, the available financial and technical inputs and the adaptation to the local environment.
Bovine colostrum as a natural growth promoter for newly weaned piglets: a review
Boudry C.,Dehoux JP.,Portetelle D.,Buldgen A.
Biotechnologie, Agronomie, Société et Environnement , 2008,
Abstract: The aim of this review is to present the potential of bovine colostrum as growth promoter in piglet-weaner diet. The consequences of weaning on the growth performance, on the gastro-intestinal tract and on the metabolic and endocrine systems of the piglet are described in the first part of this review. The second part is dedicated to bovine colostrum, with a description of the actions due to its main growth promoters and antimicrobial factors. Finally, the reported effects of colostrum specific components or colostrum fractions on the growth performance and on the structure and function of the gastro-intestinal tract of piglets in the early postweaning period are presented. They show clearly the potential of bovine colostrum to reduce the growth-check related to the weaning of the piglet.
Using seismic inversions to obtain an internal mixing processes indicator for main-sequence solar-like stars
G. Buldgen,D. R. Reese,M. A. Dupret
Physics , 2015, DOI: 10.1051/0004-6361/201526390
Abstract: Determining accurate and precise stellar ages is a major problem in astrophysics. These determinations are either obtained through empirical relations or model-dependent approaches. Currently, seismic modelling is one of the best ways of providing accurate ages. However, current methods are affected by simplifying assumptions concerning mixing processes. In this context, providing new structural indicators which are less model-dependent and more sensitive to such processes is crucial. We build a new indicator for core conditions on the main sequence, which should be more sensitive to structural differences and applicable to older stars than the indicator t presented in a previous paper. We also wish to analyse the importance of the number and type of modes for the inversion, as well as the impact of various constraints and levels of accuracy in the forward modelling process that is used to obtain reference models for the inversion. First, we present a method to obtain new structural kernels and use them to build an indicator of central conditions in stars and test it for various effects including atomic diffusion, various initial helium abundances and metallicities, following the seismic inversion method presented in our previous paper. We then study its accuracy for 7 different pulsation spectra including those of 16CygA and 16CygB and analyse its dependence on the reference model by using different constraints and levels of accuracy for its selection We observe that the inversion of the new indicator using the SOLA method provides a good diagnostic for additional mixing processes in central regions of stars. Its sensitivity allows us to test for diffusive processes and chemical composition mismatch. We also observe that octupole modes can improve the accuracy of the results, as well as modes of low radial order.
Constraints on the structure of 16 Cyg A and 16 Cyg B using inversion techniques
G. Buldgen,D. R. Reese,M. A. Dupret
Physics , 2015,
Abstract: Constraining mixing processes and chemical composition is a central problem in stellar physics as their impact on stellar age determinations leads to biases in our studies of stellar evolution, galactic history and exoplanetary systems. In two previous papers, we showed how seismic inversion techniques could offer strong constraints on such processes by pointing out weaknesses in theoretical models. We now apply our technique to the solar analogues 16CygA and 16CygB, being amongst the best targets in the Kepler field to test the diagnostic potential of seismic inversions. The combination of various seismic indicators helps to provide more constrained and accurate fundamendal parameters for these stars. We use the latest seismic, spectroscopic and interferometric observational constraints in the litterature for this system to determine reference models independently for both stars. We carry out seismic inversions of the acoustic radius, the mean density and a core conditions indicator. We note that a degeneracy exists for the reference models. Namely, changing the diffusion coefficient or the chemical composition within the observational values leads to 5% changes in mass, 3% changes in radius and up to 8% changes in age. We use acoustic radius and mean density inversions to improve our reference models then carry out inversions for a core conditions indicator. Thanks to its sensitivity to microscopic diffusion and chemical composition mismatches, we are able to reduce the mass dispersion to 2%, namely [0.96, 1.0] M_sun, the radius dispersion to 1%, namely [1.188, 1.200] R_sun and the age dispersion to 3%, namely [7.0, 7.4] Gy, for 16CygA. For 16CygB, we can check the consistency of the models but not reduce independently the age dispersion. Nonetheless, assuming consistency with the age of 16CygA helps to further constrain its mass and radius.
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