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.

Active metasurface for reconfigurable reflectors

Abstract: Metasurfaces relying solely on passive unit cells printed on a dielectric substrate present limited characteristics due to their intrinsic dispersions. A metasurface composed of active unit cells incorporating voltage-controlled varactor diodes, where the dispersion responses of the cells can be tailored, is proposed to overcome the limitations of passive metasurfaces. Two functionalities are numerically and experimentally demonstrated from the active metasurface used as an electronically reconfigurable reflector. First, we show that anomalous reflection properties can be produced within a broad frequency range and second, we show that the direction of the reflected beam can be scanned within an angular range.

The Economics of Private Institutions * An Introduction to the Dynamics of Institutional Frameworks and to the Analysis of Multilevel Multi-type Governance

Abstract: Summary: Private institutions are complementary, both to contracts and the public and general institutions of a society, in that they allow agents to collectively coordinate (and so benefit from economies of scale , from learning effects, and from management of externalities), while avoiding over high maladaptation costs (since they can be adapted to the specificities of a category of transactions or of a community). They depend on a principle of voluntary adhesion. Their members agree to comply ex-post with a private order. Exit can therefore hinder enforcement, potentially calling for reinforcement by public institutions. From a dynamic perspective, private institutions are the driving force of changes to institutional frameworks. They are set up to complete (or bypass) existing institutional frameworks. With the passing of time, an increasing number of economic agents can “adopt” a given private institution, making its order less negotiated and increasingly mandatory. In line with the BarzelNorth study of property rights, we believe private institutions have an impact both on the costs of creating coordination rules and on the enforcement costs of these rules. Therefore, we reveal, both in static and dynamic, firstly, the rationale behind the creation of private institutions (or a private collective order), secondly, how agents prefer to rely on a combination of various coordination devices, that compensating for each other’s weaknesses, to settle their coordination problems by minimizing transaction costs.

Versatile Airy-Beam Generation Using a 1-Bit Coding Programmable Reflective Metasurface

Abstract: The Airy beam, known to present particular unique features, such as diffraction-free, self-healing, and self-bending, has attracted considerable interest in recent years. Here, an electronically controlled reflective coding metasurface is exploited to generate and dynamically manipulate the Airy beam over a wide frequency band in the microwave regime. By judiciously controlling the external dc bias voltage applied to the programmable metasurface, two distinct control states, ``0'' and ``1'', are engineered as digital codes for \ensuremath{-}\ensuremath{\pi}/2 and +\ensuremath{\pi}/2 phase responses, respectively. The programmable binary-phase-coding metasurface enables the generation and active reshaping of the Airy beam to be numerically simulated and experimentally validated. Moreover, the metasurface allows the bandwidth limitation of passive counterparts to be overcome and is able to modulate electromagnetic waves over a broad frequency range, spanning from 9 to 12 GHz, to realize diffraction-free Airy beams.

Effect of COVID-19-Related Home Confinement on Sleep Quality, Screen Time and Physical Activity in Tunisian Boys and Girls: A Survey.

Abstract: COVID-19 home confinement has led to a stressful situation for children around the world and affected their lifestyle. The present study aimed to investigate the effect of these restrictions on sleep quality, screen time (ST) and physical activity (PA) in Tunisian children with a special focus on gender differences. An online survey was launched in April 2020. Questions were presented in a differential format, with expected responses related to "before" and "during" confinement. Participants (52 boys and 48 girls, age: 8.66 ± 3.3 years) responded to the Pittsburgh Sleep Quality Index (PSQI), the digital media use, and the Ricci and Gagnon sedentary behavior questionnaires. Findings revealed that COVID19 home confinement had a negative effect on all the considered parameters (p < 0.05). Significant effects of gender were found on sleep disturbances (p = 0.016, np2 = 0.05), subjective sleep quality (p < 0.01, np2 = 0.07), global score of PSQI (p = 0.01, np2 = 0.01) and nocturnal and global screen time (p < 0.001, np2 = 0.09) with poorer sleep and higher screen time in girls compared to boys during home confinement. A significant correlation was shown between Global ST and PSQI score (r = 0.39, p < 0.001). Programs of PA for children and sensitization campaigns against the use of screens have been deemed urgent with special focus oriented to girls.