Institut Universitaire de France

About: Institut Universitaire de France is a education organization based out in Paris, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 1905 authors who have published 9042 publications receiving 309878 citations.

Thickness dependence of the Josephson ground States of superconductor-ferromagnet-superconductor junctions.

Abstract: We report the first experimental observation of the two-node thickness dependence of the critical current in Josephson junctions with a ferromagnetic interlayer. Nodes of the critical current correspond to the transitions into the pi state and back into the conventional 0 state. From the experimental data the superconducting order parameter oscillation period and the pair decay length in the ferromagnet are extracted reliably. We develop a theoretical approach based on the Usadel equations taking into account the spin-flip scattering. Results of numerical calculations are in good agreement with experiments.

Radiatively efficient accreting black holes in the hard state: the case study of H1743-322

Abstract: In recent years, much effort has been devoted to unravelling the connection between the accretion flow and the jets in accreting compact objects. In the present work, we report new constraints on these issues, through the long-term study of the radio and X-ray behaviour of the black hole candidate H1743−322. This source is known to be one of the ‘outliers’ of the universal radio/X-ray correlation, i.e. a group of accreting stellar-mass black holes displaying fainter radio emission for a given X-ray luminosity than expected from the correlation. Our study shows that the radio and X-ray emission of H1743−322 are strongly correlated at high luminosity in the hard spectral state. However, this correlation is unusually steep for a black hole X-ray binary: b ∼ 1.4 (with Lradio ∝ L b ). Below a critical luminosity, the correlation becomes shallower until it rejoins the standard correlation with b ∼ 0.6. Based on these results, we first show that the steep correlation can be explained if the inner accretion flow is radiatively efficient during the hard state, in contrast to what is usually assumed for black hole X-ray binaries in this spectral state. The transition between the steep and the standard correlation would therefore reflect a change from a radiatively efficient to a radiatively inefficient accretion flow. Finally, we investigate the possibility that the discrepancy between ‘outliers’ and ‘standard’ black holes arises from the outflow properties rather than from the accretion flow.

The Redistributive State and Conflicts in Africa

Abstract: This article argues that ethnic problems are only one aspect of political violence in Africa, while violent conflicts must be considered a failure of the state to perform some of its fundamental tasks. State formation in Africa is a transition process starting from an institutional endowment of ethnic division. Ethnic capital in Africa ensures the provision of many of the services that a modern state has taken over in rich countries, e.g. security, education, norms of behaviour. Few African states can deliver all these services adequately, and must go through an initial phase of federation of ethnic groups before they can provide a credible substitute for ethnic capital. The system of redistribution within and among groups is the key to creating the solidarity links between them, and its breakdown is liable to trigger political violence. A formal game-theoretic model is presented which brings out the impact of redistribution on rebellious activity, as well as the crucial role of the ability of the government to commit credibly to its expenditure policy. Without this, there is no redistribution taking place in equilibrium, and large amounts of resources are invested in warring. Civil wars, or other forms of political violence, are thus an integral part of the political economy of Africa.

Recent Progress on Titanium Dioxide Nanomaterials for Photocatalytic Applications.

Abstract: Environmental and energy problems have drawn much attention owing to rapid population growth and accelerated economic development For instance, photocatalysis, "a green technology", plays an important role in solar-energy conversion owing to its potential to solve energy and environmental problems Recently, many efforts have been devoted to improving visible-light photocatalytic activity by using titanium dioxide as a photocatalyst as a result of its wide range of applications in the energy and environment fields However, fast charge recombination and an absorption edge in the UV range limit the photocatalytic efficiency of TiO2 under visible-light irradiation Many investigations have been undertaken to overcome the limitations of TiO2 and, therefore, to enhance its photocatalytic activity under visible light The present literature review focuses on different strategies used to promote the separation efficiency of electron-hole pairs and to shift the absorption edge of TiO2 to the visible region Current synthesis techniques used to elaborate several nanostructures of TiO2 -based materials, recent progress in enhancing visible photocatalytic activity, and different photocatalysis applications will be discussed On the basis of the studies reported in the literature, we believe that this review will help in the development of new strategies to improve the visible-light photocatalytic performance of TiO2 -based materials further

Exact spectrum of planar N=4 supersymmetric Yang-Mills theory: Konishi dimension at any coupling.

Abstract: We compute the full dimension of the Konishi operator in planar N=4 super Yang-Mills theory for a wide range of couplings, from weak to strong coupling regime, and predict the subleading terms in its strong coupling asymptotics. For this purpose we solve numerically the integral form of the AdS/CFT Y-system equations for the exact energies of excited states proposed by us and A. Kozak.