Paris West University Nanterre La Défense

About: Paris West University Nanterre La Défense is a education organization based out in Paris, France. It is known for research contribution in the topics: Computer science & Politics. The organization has 895 authors who have published 1430 publications receiving 21712 citations.

Higher-order statistics for the detection of small objects in a noisy background application on sonar imaging

Abstract: An original algorithm for the detection of small objects in a noisy background is proposed. Its application to underwater objects detection by sonar imaging is addressed. This new method is based on the use of higher-order statistics (HOS) that are locally estimated on the images. The proposed algorithm is divided into two steps. In a first step, HOS (skewness and kurtosis) are estimated locally using a square sliding computation window. Small deterministic objects have different statistical properties from the background they are thus highlighted. The influence of the signal-to-noise ratio (SNR) on the results is studied in the case of Gaussian noise. Mathematical expressions of the estimators and of the expected performances are derived and are experimentally confirmed. In a second step, the results are focused by a matched filter using a theoretical model. This enables the precise localization of the regions of interest. The proposed method generalizes to other statistical distributions and we derive the theoretical expressions of the HOS estimators in the case of a Weibull distribution (both when only noise is present or when a small deterministic object is present within the filtering window). This enables the application of the proposed technique to the processing of synthetic aperture sonar data containing underwater mines whose echoes have to be detected and located. Results on real data sets are presented and quantitatively evaluated using receiver operating characteristic (ROC) curves.

Beamforming with metagratings at microwave frequencies: design procedure and experimental demonstration

Abstract: As opposed to metasurfaces, metagratings represent themselves sparse arrangements of scatterers. Established rigorous analytical models allow metagratings to overcome performance of metasurfaces in beam steering applications while handling less degrees of freedom. In this work we deal with reflective metagratings that have only as few as one degree of freedom (represented by a reactively loaded thin wire) per each propagating diffraction order. We present a detailed design procedure and fabrication of three experimental samples capable of establishing prescribed diffraction patterns. The samples are experimentally studied in an anechoic chamber dedicated to radar-cross-section bistatic measurements and results are compared with three-dimension full wave numerical simulations. We identify and analyze factors affecting operating frequency range of metagratings, suggest a strategy to increase the bandwidth.

Clustering the Winners: The French Policy of Competitiveness Clusters

Abstract: In 2005 the French government launched a policy of competitiveness clusters, giving subsidies for innovative projects managed locally and collectively by firms, research centers and universities. This paper proposes an ex-ante analysis of the outcome of the selection process that took place before the implementation of the subsidies program, in order to assess whether the policy ended up in choosing winners or losers. We first ask how the clusters have been selected, and then focus on the selection of firms within the clusters, using export and productivity as a measure of performance. Our main conclusion is that public authorities have chosen the winners during the two-step selection procedure. Export premium, beyond what individual characteristics would predict, is however most visible within the category of clusters having no international ambition, where heterogeneity among firms is the largest.