Manifold embedding for curve registration

We focus on the problem of finding a good representative of a sample of random curves warped from a common pattern f. We first prove that such a problem can be moved onto a manifold framework. Then, we propose an estimation of the common pattern f based on an approximated geodesic distance on a suitable manifold. We then compare the proposed method to more classical methods

Méthodes d'estimations statistiques et apprentissage pour l'imagerie agricole

Nous disposons de séries temporelles d'indices associés à chaque pixel d'une image satellite. Notre objectif est de fournir au plus tôt une information fiable sur les estimations de surfaces en culture à partir de l'information attachée à chaque pixel et caractérisée par la courbe qui lui est associée. Il s'agira donc dans un premier temps de caractériser la variabilité spatiale associée à ces pixels et de déterminer une segmentation spatiale qui permette d'homogénéiser les données par classe. Dans un second temps l'extraction de l'information utile tiendra compte de la structure des courbes caractéristiques de la nature des pixels de l'image. L'étape finale consistera à déterminer la méthode adéquate d'estimation pour une prédiction des surfaces en cultures.We have to provide reliable information on the acreage estimate of crop areas. We have time series of indices contained in satellite images, and thus sets of curves. We propose to segment the space in order to reduce the variability of our initial classes of curves. Then, we reduce the data volume and we find a set of meaningful representative functions that characterizes the common behavior of each crop class. This method is close to the extraction of a "structural mean". We compare each unknown curve to a curve of the representative base and we allocate each curve to the class of the nearest representative curve. At the last step we learn the error of estimates on known data and correct the first estimate by calibration

Sperm whale ship strikes in the Pelagos Sanctuary and adjacent waters: assessing and mapping collision risks in summer

International audienceCollisions with large vessels potentially present a major conservation issue for sperm whales in the Pelagos Sanctuary in the northwestern Mediterranean Sea. The exact numbers and locations of ship strikes remain largely unknown at present. In this study, sightings of sperm whales in summer (June–September) were gathered for the period between 1998 and 2008 from nine French and Italian organisations, together covering an area of more than 68,000km. Working on a regular grid of 0.1° × 0.1° latitude/longitude cells, approximate surface density of the whales was calculated using kriging methods. A database of shipping lanes of ferries and merchant vessels was assembled, and traffic density was mapped (kilometres travelled per cell). The data was overlayed and multiplied, using ArcGis, to create a relative density surface map of sperm whales correlated with the relative density of maritime traffic. Several maps of collision risk were drawn up according to the speed class of the vessels. Of living animals that had been photo-identified, 9% had scars attributed to ship strike. Results show that sperm whales are at high risk from merchant vessels along the French and Italian continental coasts and at risk from conventional ferries on the east side of the islands of Corsica and Sardinia. It was calculated that 74 animals could be in a ship strike risk situation during the summer period in the Pelagos Sanctuary. Based on these results, mitigation measures already in place were reviewed and new measures to reduce ship strike risk are suggested

Big Data et Santé publique : plus que jamais, les enjeux de la connaissance

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Etiology of neonatal seizures and maintenance therapy use: a 10-year retrospective study at Toulouse Children’s hospital

International audienceBACKGROUND:No guidelines exist concerning the maintenance antiepileptic drug to use after neonatal seizures. Practices vary from one hospital to another. The aim of this study was to investigate etiologies and to report on the use of maintenance antiepileptic therapy in our population of full-term neonates presenting neonatal seizures.METHODS:From January 2004 to October 2014, we retrospectively collected data from all full-term neonates with neonatal seizures admitted to the Children's Hospital of Toulouse, France.RESULTS:Two hundred and forty-three neonates were included (59% males, 48% electroencephalographic confirmation). The frequencies of etiologies of neonatal seizures were: hypoxic-ischemic encephalopathy (HIE) (n = 91; 37%), ischemic infarction (n = 36; 15%), intracranial hemorrhage (n = 29; 12%), intracranial infection (n = 19; 8%), metabolic or electrolyte disorders (n = 9; 3%), inborn errors of metabolism (n = 5; 2%), congenital malformations of the central nervous system (n = 11; 5%), epileptic syndromes (n = 27; 12%) and unknown (n = 16; 7%). A maintenance therapy was prescribed in 180 (72%) newborns: valproic acid (n = 123), carbamazepine (n = 28), levetiracetam (n = 17), vigabatrin (n = 2), and phenobarbital (n = 4). In our cohort, the choice of antiepileptic drug depended mainly on etiology. The average duration of treatment was six months.CONCLUSIONS:In our cohort, valproic acid was the most frequently prescribed maintenance antiepileptic therapy. However, the arrival on the market of new antiepileptic drugs and a better understanding of the physiopathology of genetic encephalopathies is changing our practice.TRIAL REGISTRATION:Retrospectively registered. Patient data were reported to the "Commission Nationale Informatique et Libertés" under the number 2106953

A robust algorithm for template curve estimation based on manifold embedding

International audienceThe problem of finding a template function that represents the common pattern of a sample of curves is considered. To address this issue, a novel algorithm based on a robust version of the isometric featuring mapping (Isomap) algorithm is developed. When the functional data lie on an unknown intrinsically low-dimensional smooth manifold, the corresponding empirical Frechet median function is chosen as an intrinsic estimator of the template function. However, since the geodesic distance is unknown, it has to be estimated. For this, a version of the Isomap procedure is proposed, which has the advantage of being parameter free and easy to use. The feature estimated with this method appears to be a good pattern for the data, capturing the inner geometry of the curves. Comparisons with other methods, with both simulated and real datasets, are provided