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.

Omega-bianisotropic metasurface for converting a propagating wave into a surface wave

Abstract: Although a rigorous theoretical ground on metasurfaces has been established in the recent years on the basis of the equivalence principle, the majority of metasurfaces for converting a propagating wave into a surface wave are developed in accordance with the so-called generalized Snell's law being a simple heuristic rule for performing wave transformations. Recently, Tcvetkova et al. [Phys. Rev. B 97, 115447 (2018)] have rigorously studied this problem by means of a reflecting anisotropic metasurface, which is unfortunately difficult to realize, and no experimental results are available. In this paper, we propose an alternative practical design of a metasurface-based converter by separating the incident plane wave and the surface wave in different half-spaces. It allows one to preserve the polarization of the incident wave and substitute the anisotropic metasurface by an omega-bianisotropic one. The problem is approached from two sides: By directly solving the corresponding boundary problem and by considering the "time-reversed" scenario when a surface wave is converted into a nonuniform plane wave. Particularly, we reveal that an input surface wave plays an important role in the conversion process, influencing the conversion efficiency. To validate the theory, we develop a practical three-layer metasurface based on a conventional printed circuit board technology to mimic the omega-bianisotropic response at the microwave frequency range. The design is verified by full-wave three-dimensional numerical simulations and demonstrates high conversion efficiency. Obtained results are relevant independently of the frequency range and can be generalized to acoustics domain. It enables novel applications, from efficient excitation of waveguide modes in integrated photonic circuits to cloaking of large objects.

The Role of Brief Motivational Intervention on Self-Efficacy and Abstinence in a Cohort of Patients with Alcohol Dependence:

Abstract: OBJECTIVES: Brief interventions are effective in reducing heavy drinking in the general population but few studies examined whether it is also effective in alcohol dependent patients, and whether brief intervention increases self-efficacy. METHOD: One hundred and seven patients with alcohol-dependence were randomized in a controlled trial examining the efficacy of a brief motivational intervention on both self-efficacy level and days of abstinence. RESULTS: We found that brief motivational interventions had no effect on days of abstinence, nor on self-efficacy, but that high self-efficacy was consistently correlated with a longer period of abstinence, at all assessment-points. CONCLUSION: Self-efficacy appears to be a crucial prognosis factor, and is not influenced by brief motivational interventions. Other types of specific psychotherapy, probably more intensive, may be more efficient in alcohol-dependent patients than motivational interventions. Language: en

Modelling financial markets with agents competing on different time scales and with different amount of information

Abstract: We use agent-based models to study the competition among investors who use trading strategies with different amount of information and with different time scales. We find that mixing agents that trade on the same time scale but with different amount of information has a stabilizing impact on the large and extreme fluctuations of the market. Traders with the most information are found to be more likely to arbitrage traders who use less information in the decision making. On the other hand, introducing investors who act on two different time scales has a destabilizing effect on the large and extreme price movements, increasing the volatility of the market. Closeness in time scale used in the decision making is found to facilitate the creation of local trends. The larger the overlap in commonly shared information the more the traders in a mixed system with different time scales are found to profit from the presence of traders acting at another time scale than themselves.

Does the Entry Mode of Foreign Banks Matter for Bank Efficiency? Evidence from the Czech Republic,Hungary, and Poland

Abstract: This paper investigates the impact of specific modes of entry of foreign banks, i.e. greenfield investment versus merger and acquisition, on bank performance in three transition economies - the Czech Republic, Hungary, and Poland. We use stochastic frontier analysis to model and measure the cost efficiency of banks. We adopt a maximum likelihood approach to estimation in which the variance of the one-sided error term is modeled jointly with the cost frontier, thus enabling us to retrieve efficiency scores, as well as estimating the various determinants of X-inefficiency. We first find that foreign banks are generally more cost efficient than their domestic counterparts, a result that confirms those of the existing empirical literature. We then turn our focus to comparative performance of greenfield banks versus merger and acquisition banks (M&As), and of M&As versus domestic banks. The results show that on average, M&As are surpassed in terms of efficiency by greenfields banks, but no cost efficiency difference is apparent between M&As and domestic banks. However, we find a strong age effect with respect to M&As which suggests that the evolution of M&As' efficiency follows an inverse U-shape, that means M&As tend to get more inefficient following the acquisition, but approximately 4 years and a haft later, their efficiency starts to improve.