Search results for "VARIATION"
showing 10 items of 2124 documents
Tracking in Presence of Total Occlusion and Size Variation using Mean Shift and Kalman Filter
2011
International audience; The classical mean shift algorithm for tracking in perfectly arranged conditions constitutes a good object tracking method. However, in the real environment it presents some limitations, especially under the presence of noise, objects with varying size, or occlusions. In order to deal with these problems, this paper proposes a reliable object tracking algorithm using mean shift and the Kalman filter, which was added to the traditional algorithm as a predictor when no reliable model of the object being tracked is found. Experimental work demonstrates that the proposed mean shift Kalman filter algorithm improves the tracking performance of the classical algorithms in c…
Discovering human mobility from mobile data : probabilistic models and learning algorithms
2020
Smartphone usage data can be used to study human indoor and outdoor mobility. In our work, we investigate both aspects in proposing machine learning-based algorithms adapted to the different information sources that can be collected.In terms of outdoor mobility, we use the collected GPS coordinate data to discover the daily mobility patterns of the users. To this end, we propose an automatic clustering algorithm using the Dirichlet process Gaussian mixture model (DPGMM) so as to cluster the daily GPS trajectories. This clustering method is based on estimating probability densities of the trajectories, which alleviate the problems caused by the data noise.By contrast, we utilize the collecte…
Quelques thèmes en l'analyse variationnelle et optimisation
2014
In this thesis, we first study the theory of [gamma]-limits. Besides some basic properties of [gamma]-limits,expressions of sequential [gamma]-limits generalizing classical results of Greco are presented. These limits also give us a clue to a unified classification of derivatives and tangent cones. Next, we develop an approach to generalized differentiation theory. This allows us to deal with several generalized derivatives of set-valued maps defined directly in primal spaces, such as variational sets, radial sets, radial derivatives, Studniarski derivatives. Finally, we study calculus rules of these derivatives and applications related to optimality conditions and sensitivity analysis.
Variational Bethe ansatz approach for dipolar one-dimensional bosons
2020
We propose a variational approximation to the ground state energy of a one-dimensional gas of interacting bosons on the continuum based on the Bethe Ansatz ground state wavefunction of the Lieb-Liniger model. We apply our variational approximation to a gas of dipolar bosons in the single mode approximation and obtain its ground state energy per unit length. This allows for the calculation of the Tomonaga-Luttinger exponent as a function of density and the determination of the structure factor at small momenta. Moreover, in the case of attractive dipolar interaction, an instability is predicted at a critical density, which could be accessed in lanthanide atoms.
Temporal dynamics of arable weeds communities assembly : interactions between farming practices and ecological processes across crop sequences
2018
Understanding how farming practices affect weed community assembly in arable fields is a core challenge of agro-ecology. Weeds are supposed to share particular ecological characteristics that allow them to colonize arable fields despite environmental constrains exert by farming practices. In addition, interactions between ecological processes operating during a cropping season (eg: abiotic filtering) and at the scale of crop succession (eg: temporal dispersal) are supposed to drive weed community assembly in arable fields. These two hypotheses have been tested in my phD work.First, we compared a pool of weed species to a pool of non-weed herbaceous plants based on several functional traits …
Variations de la phénologie végétale et relations avec la variabilité pluviométrique et la croissance démographique dans le nord du Cameroun.
2009
International audience; La variabilité des précipitations dans le Nord du Cameroun (entre 6°N-13°N et 12°E-16°E), au cours de la période 1982-2002 et leur relation avec l'évolution de la phénologie végétale et la croissance démographique est étudiée. Dans un premier temps, l'on présente le cycle annuel et la variabilité interannuelle des pluies à partir des données de 31 stations inégalement réparties sur la région. L'évolution du couvert végétal et la densité de la population sont ensuite présentées à partir de synthèses bimensuelles d'indice de végétation normalisée (NDVI) à 8km de résolution d'une part, et de données de densité de population de 79 unités administratives d'autre part. Afi…
Dissolved silica in the Garonne River waters : changes in the weathering dynamics
2000
The major ion chemistry of the Garonne River is indicative of seasonal variations in the weathering dynamics of the drainage basin. Using the geochemical model MEGA for calculation of the contribution of atmospheric CO2 to the total bicarbonate fluxes exported by the Garonne River allows estimations of the concentrations of the major dissolved elements that originate from silicate- and carbonate-rock weathering. The molecular ratio SiO2/Al2O3 was calculated for the 1989–1992 period to identify the main type of weathering in the Garonne River, and montmorillonite was shown to be the major mineral occurring in the weathering products. The seasonal variations of the SiO2/Al2O3 ratio also showe…
Medicago species affect the community composition of arbuscular mycorrhizal fungi associated with roots
2007
National audience; The symbiosis between plants and arbuscular mycorrhizal fungi (AMF) is ancient and involves 80% of terrestrial plant families. The symbiotic association between AMF and plants was described to be non specific. However, AMF were reported to influence plant community diversity and productivity. On the other way, the effect of plant genotypes belonging to closely related species on AMF diversity has not been explored so far. The aim of this work was to assess the impact of four different Medicago species, M. laciniata, M. murex, M. polymorpha and M. truncatula cv. Jemalong J5, on the composition of AM fungal community, when cultivated in a silty-thin clay soil (Mas d’Imbert,…
Microbial Community Structure and Density Under Different Tree Species in an Acid Forest Soil (Morvan, France)
2005
Overexploitation of forests to increase wood production has led to the replacement of native forest by large areas of monospecific tree plantations. In the present study, the effects of different monospecific tree cover plantations on density and composition of the indigenous soil microbial community are described. The experimental site of "Breuil-Chenue" in the Morvan (France) was the site of a comparison of a similar mineral soil under Norway spruce (Picea abies), Douglas fir (Pseudotuga menziesii), oak (Quercus sessiflora), and native forest [mixed stand dominated by oak and beech (Fagus sylvatica)]. Sampling was performed during winter (February) at three depths (0-5, 5-10, and 10-15 cm…
Guinean and sahelian rainfall anomaly indices at annual and monthly scales (1933-1990)
1994
The annual and monthly rainfall variability in north tropical Africa are analysed by principal component analysis in order to detect the main coherent modes. The Sahel constitutes the first mode, although it is divided close to 1O"W into an Atlantic section and a Continental section. The Guinean zone is less coherent, and is divided into distinct modes. The subequatorial area never formed a distinct mode. Rainfall variability for the coherent areas is constructed from rainfall anomaly indices (RAI), based on the coherent areas, and a rainfall typology taking into account the spatial pattern of the rainfall anomaly fields and the intensity of the anomaly. Their evolution (mainly since 1950) …