Search results for "sampling"
showing 10 items of 788 documents
Extrapolation des inventaires de biodiversité incomplets : comment estimer au mieux le nombre d’espèces manquantes et prévoir l’effort additionnel d’…
2016
While approaching or even reaching total completeness remains the idealgoal of any species inventory, incomplete samplings are deemed to become more often the rule, that are significantly more difficult to cope with (such as (micro-) invertebrates, for example).However, once post-operated appropriately, incomplete samplings may provide farmore data than it would seem and it is indeed possible to obtain valuable extra information froma reliable mode of extrapolation of the so-called Species Accumulation Curve.In fact, numerous tools designed for the exploitation of incomplete samplings havealready been proposed in the literature but the concern, with these numerous different tools, isprecise…
Probability and algorithmics: a focus on some recent developments
2017
Jean-François Coeurjolly, Adeline Leclercq-Samson Eds.; International audience; This article presents different recent theoretical results illustrating the interactions between probability and algorithmics. These contributions deal with various topics: cellular automata and calculability, variable length Markov chains and persistent random walks, perfect sampling via coupling from the past. All of them involve discrete dynamics on complex random structures.; Cet article présente différents résultats récents de nature théorique illustrant les interactions entre probabilités et algorithmique. Ces contributions traitent de sujets variés : automates cellulaires et calculabilité, chaînes de Mark…
Exact simulation of diffusion first exit times: algorithm acceleration
2020
In order to describe or estimate different quantities related to a specific random variable, it is of prime interest to numerically generate such a variate. In specific situations, the exact generation of random variables might be either momentarily unavailable or too expensive in terms of computation time. It therefore needs to be replaced by an approximation procedure. As was previously the case, the ambitious exact simulation of exit times for diffusion processes was unreachable though it concerns many applications in different fields like mathematical finance, neuroscience or reliability. The usual way to describe exit times was to use discretization schemes, that are of course approxim…
Weeds sampling for map reconstruction: a Markov random field approach
2012
In the past 15 years, there has been a growing interest for the study of the spatial repartition of weeds in crops, mainly because this is a prerequisite to herbicides use reduction. There has been a large variety of statistical methods developped for this problem ([5], [7], [10]). However, one common point of all of these methods is that they are based on in situ collection of data about weeds spatial repartition. A crucial problem is then to choose where, in the eld, data should be collected. Since exhaustive sampling of a eld is too costly, a lot of attention has been paid to the development of spatial sampling methods ([12], [4], [6] [9]). Classical spatial stochastic model of weeds cou…
The impact of urban contamination on antibioresistance in microbial communities from periphyton and sediments
2020
International audience; Since the early 20's antibiotics have been massively produced and consumed for the benefit of bothhuman and animal health. Nevertheless, antibiotics have also reached the aquatic environmentthrough diffuse sources (e.g. veterinary treatment, contaminated manure application...) and throughwastewater. Consequently, antibiotics concentrations between the ng/L and μg/L range are regularlydetected in surface water and those molecules have also been found in sediments and aquatic biota.The ubiquitous presence of antibiotics exerts a selective pressure on microbial communities leading tothe acquisition and dissemination of antibioresistance in the environment. While both an…
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…
Échantillonnage adaptatif optimal dans les champs de Markov, application à l’échantillonnage d’une espèce adventice
2012
This work is divided into two parts: (i) the theoretical study of the problem of adaptive sampling in Markov Random Fields (MRF) and (ii) the modeling of the problem of weed sampling in a crop field and the design of adaptive sampling strategies for this problem. For the first point, we first modeled the problem of finding an optimal sampling strategy as a finite horizon Markov Decision Process (MDP). Then, we proposed a generic algorithm for computing an approximate solution to any finite horizon MDP with known model. This algorithm, called Least-Squared Dynamic Programming (LSDP), combines the concepts of dynamic programming and reinforcement learning. It was then adapted to compute adapt…
Assessing environmental noise exposure: does the size of the neighbourhood matter?
2013
International audience; In environmental epidemiology, studies rely on the quantification of subject'sexposures in a surface defined as the subject exposure area. For outdoor exposure, this area is often considered as the subject's neighbourhood. But, depending on the authors, the size and the nature of this neighbourhood differs, making difficult to compare results. In order to study the impact of the sampling surface on the noise exposure values affected to a subject, a high definition environmental noise model has been builton a middle-sized French city. Outdoor neighbourhood noise indices were computed at 10,394 residential buildings, using eight different sizes of buffers defined by di…
Développement et évaluation d'une méthode fondée sur la PCR temps réel pour la caractérisation des bioaérosols : application au groupe des actinomycè…
2013
Actinomycetes are ubiquitous bacteria and some can be potentially pathogen for Humans in the air of some working areas. It’s notably the case in composting plants where bacteria concentrations can reach high values. Workers exposure to these inhalable bioaerosols can be source of various diseases (hypersensitivity pneumonitis notably). Although this problem is admitted, bibliography reveals a lack of knowledge about risk assessment: currently, none global method for bioaerosols sampling and analysis is standardized. So much that neither dose-effects relationship for most of these bacteria, nor Threshold Limit Value exists. Traditional methods, that are used, have some drawbacks (concentrati…
Ecomic - RMQs : Cartographie de la diversité microbienne des sols à l'échelle de la France
2009
aeres : C-AFF; National audience; no abstract