Apprentissage dynamique du nombre d'états d'un modèle de markov caché à observations continues : Application au tri de formulaires

Dans le cadre de la reconnaissance automatique de types de formulaires avec champs manuscrits et sans aucun signe de référence, basée sur une description de la structure physique du formulaire, nous sommes amenés à représenter un formulaire par un modèle de Markov caché pseudo-2D (PHMM). Ce modèle est constitué d'un graphe de super-états. A chaque super-état on associe un modèle de Markov caché secondaire (HMM) dont les observations sont continues. Nous exposons pourquoi la méthode classique des k-moyennes est mal adaptée à notre problème, puis nous détaillons une nouvelle méthode générale qui prend mieux en compte la réalité physique des états, en les situant dans l'espace de représentation des caractéristiques, et en les construisant dynamiquement par agrégation progressive des séquences d'observations. Ce n'est qu'à la fin du processus d'agrégation que le nombre d'états du modèle stochastique initial est connu

Marge de stabilité des systèmes linéaires : une extension du critère de Routh-Hurwitz

Nous exposons une condition nécessaire et suffisante, portant sur les coefficients d'un polynôme, qui permet de localiser les racines de celui-ci relativement à un secteur angulaire du plan complexe, ce qui généralise le champ de validité du théorème de Routh-Hürwitz qui est limité au cas du demi-plan gauche. Ce résultat théorique permet d'étendre le critère de stabilité absolue de Routh-Hürwitz, utilisé notamment pour le réglage du gain des systèmes asservis linéaires, au cas où l'on souhaite préserver une marge de stabilité réglable, les pôles de la fonction de transfert étant alors situés à l'intérieur du secteur angulaire qui définit la zone de stabilité

Performance of Small Cluster Surveys and the Clustered LQAS Design to estimate Local-level Vaccination Coverage in Mali

<p>Abstract</p> <p>Background</p> <p>Estimation of vaccination coverage at the local level is essential to identify communities that may require additional support. Cluster surveys can be used in resource-poor settings, when population figures are inaccurate. To be feasible, cluster samples need to be small, without losing robustness of results. The clustered LQAS (CLQAS) approach has been proposed as an alternative, as smaller sample sizes are required.</p> <p>Methods</p> <p>We explored (i) the efficiency of cluster surveys of decreasing sample size through bootstrapping analysis and (ii) the performance of CLQAS under three alternative sampling plans to classify local VC, using data from a survey carried out in Mali after mass vaccination against meningococcal meningitis group A.</p> <p>Results</p> <p>VC estimates provided by a 10 × 15 cluster survey design were reasonably robust. We used them to classify health areas in three categories and guide mop-up activities: i) health areas not requiring supplemental activities; ii) health areas requiring additional vaccination; iii) health areas requiring further evaluation. As sample size decreased (from 10 × 15 to 10 × 3), standard error of VC and ICC estimates were increasingly unstable. Results of CLQAS simulations were not accurate for most health areas, with an overall risk of misclassification greater than 0.25 in one health area out of three. It was greater than 0.50 in one health area out of two under two of the three sampling plans.</p> <p>Conclusions</p> <p>Small sample cluster surveys (10 × 15) are acceptably robust for classification of VC at local level. We do not recommend the CLQAS method as currently formulated for evaluating vaccination programmes.</p

Collateral damage? Small-scale fisheries in the global fight against IUU fishing

© 2020 The Authors. Fish and Fisheries published by John Wiley & Sons Ltd Concern over illegal, unreported and unregulated (IUU) fishing has led to a number of policy, trade and surveillance measures. While much attention has been given to the impact of IUU regulation on industrial fleets, recognition of the distinct impacts on small-scale fisheries is conspicuously lacking from the policy and research debate. In this paper, we outline three ways in which the application of IUU discourse and regulation undermines small-scale fisheries. First, the mainstream construction of “illegal,” “unreported” and “unregulated” fishing, and also the categorical use of “IUU” in an all-inclusive sense, disregards the diversity, legitimacy and sustainability of small-scale fisheries practices and their governing systems. Second, we explore how the recent trade-related measures to counter IUU fishing mask and reinforce existing inequalities between different sectors and countries, creating an unfair burden on small-scale fisheries and countries who depend on them. Third, as IUU fishing is increasingly approached as “organized crime,” there is a risk of inappropriately targeting small-scale fisheries, at times violently. Reflecting on these three trends, we propose three strategies by which a more sensitive and ultimately more equitable incorporation of small-scale fisheries can be supported in the global fight against IUU fishing

Localisation de points caracteristiques dans un dessin: Application a la reconnaissance du chinois multiposte

Nous présentons une méthode de reconnaissance statistique des caractères chinois multipolices, qui peut être transposée à tout dessin au graphisme complexe. Les noeuds et des extrémités, extraits sur le squelette du caractère lissé, constituent les éléments caractéristiques de chaque classe . Une première classification est effectuée selon un indice de complexité, somme pondérée du nombre de noeuds et d'extrémités. Les coefficients de pondération sont choisis de telle sorte qu'une jonction intempestive entre une extrémité et le corps d'une branche ne modifie pas la valeur de l'indice. Une sous-classification est faite ensuite par comparaison entre les coordonnées des points caractéristiques de la forme et du modèle. Cependant, aucun élément retenu ne permet d'étiqueter ces points: il est donc nécessaire de faire une mise en correspondance entre les points du caractère inconnu et ceux du caractère modèle, en minimisant la distance. Le degré de ressemblance est calculé à l'aide d'un coefficient de similarité, qui décroît avec la distance. Des essais ont été effectués sur une base de données d'un millier de caractères environ, pour les plus faibles valeurs du coefficient de complexité. Le taux de reconnaissance est supérieur à 96 %

A contour-based approach for clods identification and characterization on a soil surface

International audienceBecause the surface micro-topography has a large impact on soil properties, numerous studies have focused on surface roughness, soil height changes, and soil cloddiness characterization. Usually, feature parameters are estimated from soil measurement samples, based on statistics characterizing the surface as a whole. Now, the shortcoming of such a global approach is that it fails to detect local soil height changes and non-stationarities. The present study introduces a new method to identify and characterize the clods on a seedbed surface Digital Elevation Model (DEM). It is based on an a priori model of the clods, namely objects presenting closed elevation contours with high gradient values. Our clod segmentation method was assessed with the help of a soil scientist on the two kinds of tilled soil surfaces which were considered in this study: an artificial surface made in the laboratory to have a controlled roughness, and an actual seedbed surface made in an experimental field. In both cases results were evaluated in terms of sensitivity and specificity, and showed the performance of the method. We also study the impacts of the main parameters of the method and the computer time. Its main limitations are that it fails to identify the small clods (diameter smaller than 7 mm in this study) and the clods embedded within another piece of relief, such as a greater clod or a hollow border. Then, we show how results can be used to compute clod parameters: mapping of clods provided as output of our algorithm and clod shape measurements. Finally, an application to study soil heights changes with rainfall is provided

Estimation de l'évapotranspiration des couverts végétaux par inversion de modèles de télédétection

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Estimating the characteristics of vegetation canopies with airborne radar measurements

International audiencePossible use of synthetic aperture radars (SAR) for monitoring agricultural canopies is investigated in this paper. Data have been acquired on the Orgcval watershed during the AGRISCATT'88 campaign. Four radar experiments were carried out with the airborne scattcrometer ERASME (C and X bands, HH and VV polarizations, multi-incidence angles). Simultaneous ground measurements (soil moisture, leaf area index, water content of the canopy) were conducted on 11 wheat fields. Backscattering coefficients of the canopies arc interpreted in the framework of semi-empirical ‘water-cloud’ models. A simple paramctrization of the angular effect of soil roughness is introduced, allowing the simultaneous use of multi-incidence angle radar data. With a unique set of parameters for each radar configuration ‘ frequency and polarization’ the water-cloud model appears to describe adequately the backscattering of all the fields, over the range of incidence angles. It is shown that in this case, attenuation is the dominant effect of the vegetation and an inversion algorithm is proposed for estimating the water content of vegetation. This algorithm requires measurements at two different incidence angles and various combinations of radar configurations are then tested

How useful are hemoglobin concentration and its variations to predict significant hemorrhage in the early phase of trauma? A multicentric cohort study

Abstract Background The diagnostic value of hemoglobin (Hb) for detecting a significant hemorrhage (SH) in the early phase of trauma remains controversial. The present study aimed to assess the abilities of Hb measurements taken at different times throughout trauma management to identify patients with SH. Methods All consecutive adult trauma patients directly admitted to six French level-1 trauma centers with at least one prehospital Hb measurement were analyzed. The abilities of the following variables to identify SH (≥ 4 units of red blood cells in the first 6 h and/or death related to uncontrolled bleeding within 24 h) were determined and compared to that of shock index (SI): Hb as measured with a point-of-care (POC) device by the prehospital team on scene (POC-Hbprehosp) and upon patient’s admission to the hospital (POC-Hbhosp), the difference between POC-Hbhosp and POC-Hbprehosp (DeltaPOC-Hb) and Hb as measured by the hospital laboratory on admission (Hb-Labhosp). Results A total of 6402 patients were included, 755 with SH and 5647 controls (CL). POC-Hbprehosp significantly predicted SH with an area under ROC curve (AUC) of 0.72 and best cutoff values of 12 g/dl for women and 13 g/dl for men. POC-Hbprehosp < 12 g/dl had 90% specificity to predict of SH. POC-Hbhosp and Hb-Labhosp (AUCs of 0.92 and 0.89, respectively) predicted SH better than SI (AUC = 0.77, p < 0.001); best cutoff values of POC-Hbhosp were 10 g/dl for women and 12 g/dl for men. DeltaPOC-Hb also predicted SH with an AUC of 0.77, a best cutoff value of − 2 g/dl irrespective of the gender. For a same prehospital fluid volume infused, DeltaPOC-Hb was significantly larger in patients with significant hemorrhage than in controls. Conclusions Challenging the classical idea that early Hb measurement is not meaningful in predicting SH, POC-Hbprehosp was able, albeit modestly, to predict significant hemorrhage. POC-Hbhosp had a greater ability to predict SH when compared to shock index. For a given prehospital fluid volume infused, the magnitude of the Hb drop was significantly higher in patients with significant hemorrhage than in controls

Applicability of the active microwave remote sensing method in water resources : the Agriscatt'88 airborne campaign on the Orgeval watershed

The results of the French part of Agriscatt'88, the airborne European campaign, are presented and discussed. Field operations were conducted concurrently. Statistical analysis shows that the best results are obtained when estimating soil water content with the C-band. Spatial variability of the radar signal was studied on the watershed scale using the variogram function. The plot seems to constitute a coherent unit, the soil water content characteristics of which can be evaluated using active microwave remote sensing. / On décrit et on présente les résultats de la partie française de la campagne européenne aéroportée Agriscatt'88. Des opérations-vérité sur le terrain ont été menées simultanément ; l'analyse statistique montre que l'on obtient les meilleurs résultats pour l'évaluation de l'humidité du sol avec la bande C. La variabilité spatiale du signal radar a été étudiée à l'échelle du bassin versant en utilisant la fonction du variogramme. La parcelle semble constituer une entité cohérente dont les caractéristiques d'humidité du sol peuvent être évaluées par la télédétection par microondes actives