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: Population & Finite element method. The organization has 895 authors who have published 1430 publications receiving 21712 citations.

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 article, 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.

Optimisme et pessimisme comparatifs consécutifs à l'exposition à plusieurs messages menaçants

Abstract: The aim was to investigate whether comparative optimism or CO (i.e. general tendency to believe that negative events are less likely to others than for self) is a compatible clue or not with adoption of preventive behaviours. Sixty-three smokers have read one and five prevention messages followed by recommendations. Presence or non-appearance of pictures (vividness) and positive or negative framing were manipulated. Five illustrated (high vividness) messages and positively framed messages showed CP (health risks were more likely for self than for others), whereas the same messages without pictures (low vividness) generated CO. Presenting five messages strengthened the relationship between CO (or CP), and behavioural intention. Presenting a single message triggered negative affects whereas five messages elicited coping response highly correlated to CO (or CP). It is valuable to present positively framed messages five times to enhance their efficacy. The role of CO within tobacco prevention is discussed.

Design and Validation of an All-Dielectric Metamaterial Medium for Collimating Orbital-Angular-Momentum Vortex Waves at Microwave Frequencies

Abstract: Vortex waves have potential applications in wireless communication, because of their advantages in improving channel-transmission efficiency. However, the peculiar divergence of vortex waves seriously limits their propagation distance for communication. Thus the authors propose an innovative method for collimating vortex waves at microwave frequencies, based on transformation optics. Their all-dielectric device can reduce the divergence angle of vortex waves over a wide bandwidth, and collimate vortex beams with multiple modes.

Predicting failure using conditioning on damage history: demonstration on percolation and hierarchical fiber bundles.

Abstract: We formulate the problem of probabilistic predictions of global failure in the simplest possible model based on site percolation and on one of the simplest models of time-dependent rupture, a hierarchical fiber bundle model. We show that conditioning the predictions on the knowledge of the current degree of damage (occupancy density $p$ or number and size of cracks) and on some information on the largest cluster improves significantly the prediction accuracy, in particular by allowing one to identify those realizations which have anomalously low or large clusters (cracks). We quantify the prediction gains using two measures, the relative specific information gain (which is the variation of entropy obtained by adding new information) and the root mean square of the prediction errors over a large ensemble of realizations. The bulk of our simulations have been obtained with the two-dimensional site percolation model on a lattice of size $L\ifmmode\times\else\texttimes\fi{}L=20\ifmmode\times\else\texttimes\fi{}20$ and hold true for other lattice sizes. For the hierarchical fiber bundle model, conditioning the measures of damage on the information of the location and size of the largest crack extends significantly the critical region and the prediction skills. These examples illustrate how ongoing damage can be used as a revelation of both the realization-dependent preexisting heterogeneity and the damage scenario undertaken by each specific sample.