Search results for " statistiques"
showing 10 items of 22 documents
Morphological characterisation of soil structure in tilled fields: from a diagnosis method to the modelling of structural changes over time
2004
Characterisation of soit structure within the tilled layer of cultivated fields is crucial because the importance of this soil characteristic on the biological, chemical and physical properties of the soil and its repercussions on water cycle, root growth and functioning. We present in this paper a method for field characterisation of soil structure. This method, practised since the 1970s, was designed for field diagnosis of the effects of cropping systems on soil structure. It is based on a stratification of the observation face of a pit dug perpendicular to the direction of tillage and traffic: spatial compartments are distinguished, according to the nature of the mechanical stresses they…
Adapter localement les prévisions climatiques saisonnières : désagrégation stochastique et interpolation spatiale.
2013
6 pages; International audience; Un panorama est fait des méthodes de descente d’échelles permettant de passer de prévisions climatiques saisonnières de large-échelle à des séries locales journalières. L’exemple des générateurs stochastiques de temps est appliqué à la prévision des récoltes de sorgho au Kenya, dans le cadre du programme ANR PICREVAT. Une méthode d’interpolation spatiale des paramètres des générateurs est testée, pour obtenir des séries journalières de précipitations en tout point du territoire. Les séries générées sont utilisées en entrée du modèle agronomique SARRA-H.
Climatic gradients along the windward slopes of Mount Kenya and their implication for crop risks. Part 2 : crop sensitivity.
2016
16 pages; International audience; Mount Kenya is an equatorial mountain whose climatic setting is fairly simple (two rainy seasons in March–May, the Long Rains, and October–December, the Short Rains) though concealing significant spatial variations related to elevation and aspect (part I, Camberlin et al., 2014). This part II is dedicated to the sensitivity of sorghum yields to climate variability in space and time, with a focus on the intra-seasonal characteristics of the rainy seasons. To that aim we use the crop model SARRA-H calibrated for the region and fed with rainfall, temperature, wind speed, humidity and solar radiation data over the period 1973–2001 at three stations located on t…
Timing and patterns of the ENSO signal in Africa over the last 30 years: insights from normalized difference vegetation index data.
2014
Abstract A more complete picture of the timing and patterns of the ENSO signal during the seasonal cycle for the whole of Africa over the three last decades is provided using the normalized difference vegetation index (NDVI). Indeed, NDVI has a higher spatial resolution and is more frequently updated than in situ climate databases, and highlights the impact of ENSO on vegetation dynamics as a combined result of ENSO on rainfall, solar radiation, and temperature. The month-by-month NDVI–Niño-3.4 correlation patterns evolve as follows. From July to September, negative correlations are observed over the Sahel, the Gulf of Guinea coast, and regions from the northern Democratic Republic of Congo…
Analyse et Estimations Spectrales des Processus alpha-Stables non-Stationnaires
2006
In this work a new spectral representation of a symmetric alpha-stable processes is introduced. It is based on a covariation pseudo-additivity and Morse-Transue's integral with respect to a bimesure built by using pseudo-additivity property. This representation, specific to S$\alpha$S processes, is analogous to the covariance of second order processes. On the other hand, it generalizes the representation established for stochastic integrals with respect to symmetric alpha-stable process of independent increments. We provide a classification of non-stationary harmonizable processes; this classification is based on the bimesure structure. In particular, we defined and investigated periodicall…
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…
La gestion des betteraves adventices résistantes à un herbicide: une approche par simulation
2007
National audience; Les variétés de betteraves sucrières génétiquement modifiées (GM) résistantes à un herbicide sont, a priori, intéressantes dans des champs fortement infestés par la betterave adventice. Cependant, la montée à fleurs de ces betteraves GM peut entraîner l’apparition d’individus résistants, via la dispersion de pollen. Nous avons développé et utilisé le modèle GENESYS-Betterave pour simuler, à l’échelle d’une petite région agricole, l’impact des pratiques culturales sur la dispersion du transgène. Il permet d'identifier des stratégies pour contrôler les adventices et limiter l'apparition de populations résistantes en zone de production de betterave sucrière. L’utilisation de…
Le décolonialisme, c'est 50,4%
2021
International audience
A unifying framework for specifying generalized linear models for categorical data
2013
International audience; In the context of categorical data analysis, the case of nominal and ordinal data has been investigated in depth while the case of partially ordered data has been comparatively neglected. We first propose a new specification of generalized linear models (GLMs) for categorical response variables which en- compasses all the classical models such as multinomial logit, odds proportional or continuation ratio models but also led us to identify new GLMs. This unifying framework makes the different GLMs easier to compare and combine. We then define the more general class of partitioned conditional GLMs for categorical re- sponse variables. This new class enables to take int…
Vers une ontologie des risques et des catastrophes : le modèle conceptuel
2009
ACTI; International audience; Nous présentons une réflexion sur la construction d'une ontologie formalisée du domaine des risques et des catastrophes. L'objectif est de revenir sur les concepts essentiels permettant de caractériser le risque, l'accident, la catastrophe et les notions associées, et d'organiser ces concepts entre eux par des relations. Nous présentons donc le modèle conceptuel du domaine des risques et des catastrophes, modèle réalisé à partir des diagrammes de classe d'UML(Unified Modelling Language). Si l'exercice semble a priori simple, la prise en compte de la représentation des différents types d'acteurs concernés complexifie notablement ce que recouvrent le risque et la…