Search results for "méthodes"
showing 10 items of 77 documents
Méthodes géometriques en mécanique spatiale et aspects numériques
2005
We present in this thesis two research projectson the optimal control of the space vehicles.In the first, we have dealt with the orbit transferproblem. We study the minimum time control of a satellite that we want to reach a geostationary orbit. Our contribution is of two kinds. Geometric, first, since we study the controllability of the system together with the geometry of the transfer (structure of the command) by means of geometric control without state constraint tools (minimum principle). Then we present shootingalgorithm and homotopy method. These approaches allow the numerical resolution of problems with strong or low thrust satellites.The second project concerns to the calculation o…
Energy minimization of single input orbit transfer by averaging and continuation
2006
AbstractThis article deals with the transfer between Keplerian coplanar orbits using low propulsion. We focus on the energy minimization problem and compute the averaged system, proving integrability and relating the corresponding trajectories to a three-dimensional Riemannian problem that is analyzed in details. The geodesics provide approximations of the extremals of the energy minimization problem and can be used in order to evaluate the optimal trajectories of the time optimal and the minimization of the consumption problems with continuation methods. In particular, minimizing trajectories for transfer towards the geostationary orbit can be approximated in suitable coordinates by straig…
Méthodes récursives
2001
PUF, Paris
Les extentes de la principauté savoyarde (fin XIIIe-fin XVe siècle): étude d'une source et de ses apports à la connaissance des structures agraires d…
2002
Ghislain Brunel, Olivier Guyotjeannin, Jean-Marc Moriceau; International audience
« Apprendre à apprendre » : quels enjeux pour les apprenants et les enseignants ?
2019
International audience
Multifunctionality: refocusing a spreading, loose and fashionable concept for looking at sustainability?
2008
International audience; The notion of agriculture's Multifunctionality (MF) emerged in the 1980s. It then followed two trajectories since the 1990s: a conflicting period linked to its use in the international trade negotiations on the one hand, a spreading in terms of meaning, use and geographically on the other hand. Specific meanings appeared in connection with policy making, at national or international levels, or through the involvement of new disciplines. Yet, very few authors discuss the implication of the chosen meaning on their findings. To explore and take advantage of using this word and to deliver it from its controversial use in international trade negotiations, it is absolutely…
Nodulating symbiotic bacteria and soil quality
2005
Chapitre 9 : Plant microbe interactions and soil quality Partie : 9-2; International audience
Evaluation agroécologique de systèmes de culture en zone tropicale humide : Cas de la mise en valeur agricole d'une savane herbacée acide (Plaine des…
2013
Dans les régions tropicales humides, concilier intensification agricole et protection des ressources naturelles est un défi majeur et difficile à relever. Dans les savanes acides du nord-est laotien, des systèmes de culture de semis direct sur couverture végétale (SCV), basés sur les trois principes du non-labour, d’une couverture permanente du sol, et sur la pratique de rotations culturales diversifiées, sont proposés comme alternative technique à l’intensification agricole conventionnelle basée sur le labour. Si ces systèmes ont connu une diffusion importante et rapide dans les grandes agricultures mécanisées, leur diffusion reste néanmoins à ce jour limitée en contexte de petite agricult…
Dynamique et assemblage des communautés adventices : Approche par modélisation statistique
2011
To develop solutions for a productive and sustainable agriculture, principles, theories, andmethods of ecology may contribute to understand the biological processes governing the agroecosystem.The present case study was based on data collected by a network of observatories of weeds covering the whole of France (‘Biovigilance Flore’) and aimed at establishing forrules governing the assemblage and dynamics of weed communities in fields grown with annual crops. We particularly studied the possible relationships between species within acommunity, as well as the relationships between communities and their environment. Analyses were based on species abundances to take account of their effect on c…
Stock de semences versus relevé de flore : comment mesurer les évolutions de la flore adventice liées à des modifications de systèmes de culture ?
2019
Le suivi des changements de la composition adventice est une préoccupation majeure lors de la mise en place de nouveaux systèmes de culture. Il se pose toutefois des questions sur la méthodologie à mettre en place pour ce type de travail. L’étude du stock de semences qui représente en théorie la flore potentielle, semble s’imposer comme la façon la plus évidente de caractériser les communautés de mauvaises herbes. Toutefois cette méthode est lourde à mettre en place et nécessite un nombre d’échantillons important. La flore adventice d’une centaine de parcelles conduites en semis direct sous couvert a été étudiée au travers de deux méthodes : un relevé de flore réalisé au printemps et un éch…