Microscopic approaches for nuclear Many-Body dynamics: applications to nuclear reactions

These lecture notes are addressed to PhD student and/or researchers who want a general overview of microscopic approaches based on mean-field and applied to nuclear dynamics. Our goal is to provide a good description of low energy heavy-ion collisions. We present both formal aspects and practical applications of the time-dependent Hartree-Fock (TDHF) theory. The TDHF approach gives a mean field dynamics of the system under the assumption that particles evolve independently in their self-consistent average field. As an example, we study the fusion of both spherical and deformed nuclei with TDHF. We also focus on nucleon transfer which may occur between nuclei below the barrier. These studies allow us to specify the range of applications of TDHF in one hand, and, on the other hand, its intrinsic limitations: absence of tunneling below the Coulomb barrier, missing dissipative effects and/or quantum fluctuations. Time-dependent mean-field theories should be improved to properly account for these effects. Several approaches, generically named "beyond TDHF" are presented which account for instance for pairing and/or direct nucleon-nucleon collisions. Finally we discuss recent progresses in exact ab-initio methods based on the stochastic mean-field concept.Comment: 55 pages. Lecture given at the "Joliot Curie" school, Maubuisson, september 17-22, 2007. A french version is available at http://www.cenbg.in2p3.fr/heberge/EcoleJoliotCurie/coursannee/cours/CoursSimenel.pd

Partially resummed perturbation theory for multiple Andreev reflections in a short three-terminal Josephson junction

In a transparent three-terminal Josephson junction, modeling nonequilibrium transport is numerically challenging, owing to the interplay between multiple Andreev reflection (MAR) thresholds and multipair resonances in the pair current. An approximate method, coined as "partially resummed perturbation theory in the number of nonlocal Green's functions", is presented that can be operational on a standard computer and demonstrates compatibility with results existing in the literature. In a linear structure made of two neighboring interfaces (with intermediate transparency) connected by a central superconductor, tunneling through each of the interfaces separately is taken into account to all orders. On the contrary, nonlocal processes connecting the two interfaces are accounted for at the lowest relevant order. This yields logarithmically divergent contributions at the gap edges, which are sufficient as a semi-quantitative description. The method is able to describe the current in the full two-dimensional voltage range, including commensurate as well as incommensurate values. The results found for the multipair (for instance quartet) current-phase characteristics as well as the MAR thresholds are compatible with previous results. At intermediate transparency, the multipair critical current is much larger than the background MAR current, which supports an experimental observation of the quartet and multipair resonances. The paper provides a proof of principle for addressing in the future the interplay between quasiparticles and multipairs in four-terminal structures.Comment: 18 pages, 10 figures, improvements in the presentation, Eur. Phys. J. B in pres

La mobilité comme modalité de l'ancrage : enrichir l'évaluation de la durabilité des espaces périurbains

This paper proposes to deepen the relationship between mobility and tethering in peri-urban spaces, and provide new methodological avenues, capable of contributing to the build-up of key knowledge elements, that we feel are crucial in a company's capacity to implement their own sustainability requirements. These key knowledge elements are primarily based on the results stemming from research entitled "Peri-urbanism testing models for living; peri-urban viability, in theory and in practice". The aim of this research was to assess, at least potentially, the sustainability of periurban spaces, which have seen recent development, as they have benefited from a growing trend towards removing space and time restrictions, through the generalisation of mobility, at the centre of many societal issues today.La présente contribution se propose d'approfondir les relations entre mobilité et ancrage dans les espaces périurbains et d'apporter pour ce faire de nouvelles pistes méthodologiques susceptibles de contribuer à la construction d'éléments de connaissance qui nous semblent déterminants pour la capacité des sociétés à mettre en oeuvre les conditions de leur durabilité. Ces éléments de connaissance reposent principalement sur les résultats obtenus dans le cadre d'une recherche: " Le périurbain à l'épreuve des modèles d'habiter, la viabilité périurbaine entre théorie(s) et pratique(s) ". L'objectif de cette recherche était d'évaluer la durabilité, au moins potentielle, d'espaces -- périurbains -- dont les formes de développement récentes, parce qu'elles ont bénéficié d'un mouvement d'affranchissement croissant des contraintes de l'espace et du temps grâce à la généralisation de la mobilité, cristallisent un grand nombre d'enjeux sociétaux

Coupling an annotated corpus and a lexicon for state-of-the-art POS tagging

International audienceThis paper investigates how to best couple hand-annotated data with information extracted from an external lexical resource to improve POS tagging performance. Focusing on French tagging, we introduce a maximum entropy conditional sequence tagging system that is enriched with information extracted from a morphological resource. This system gives a 97.7% accuracy on the French Treebank, an error reduction of 23% (28% on unknown words) over the same tagger without lexical information. We also conduct experiments on datasets and lexicons of varying sizes in order to assess the best trade-off between annotating data vs. developing a lexicon. We find that the use of a lexicon improves the quality of the tagger at any stage of development of either resource, and that for fixed performance levels the availability of the full lexicon consistently reduces the need for supervised data by at least one half

Beyond 5G Wireless Localization with Reconfigurable Intelligent Surfaces

5G radio positioning exploits information in both angle and delay, by virtue of increased bandwidth and large antenna arrays. When large arrays are embedded in surfaces, they can passively steer electromagnetic waves in preferred directions of space. Reconfigurable intelligent surfaces (RIS), which are seen as a transformative "beyond 5G" technology, can thus control the physical propagation environment. Whereas such RIS have been mainly intended for communication purposes so far, we herein state and analyze a RIS-aided downlink positioning problem from the Fisher Information perspective. Then, based on this analysis, we propose a two-step optimization scheme that selects the best RIS combination to be activated and controls the phases of their constituting elements so as to improve positioning performance. Preliminary simulation results show coverage and accuracy gains in comparison with natural scattering, while pointing out limitations in terms of low signal to noise ratio (SNR) and inter-path interference.Comment: Accepted in IEEE ICC 2020. The IEEE Xplore version had a problem with Figure 1, which is fixed her

La « manipulation » dans la communication

Toute communication produit des effets : elle manipule « au sens instrumental du terme. Dès lors, aussitôt que l’on communique l’on manipule, et c’est bien cet axiome fondamental qui doit être posé à la base de toute étude exhaustive en la matière, et notamment des recherches en communication « persuasive », soit celles qui traitent à la fois de l’« efficacité » et de l’« efficience » de la communication, c’est-à-dire à la fois des effets voulus sur autrui par l’auteur d’un message et de ceux que celui-ci n’a pas « consciemment » recherchés. Ainsi l’essai qui tente de distinguer argumentation et rhétorique n’apparaît pas parfaitement satisfaisant dans la mesure où toute communication d’arguments s’établit sur le substrat d’une « relation » implicite qui conditionne l’échange, et que « fond » et « forme » sont indissolublement liés.Every communication produces effects: it « manipulates » in the instrumental acceptance of the word. Thus, as soon as we communicate we manipulate, and this is indeed this basic « axiome » that must be put at the very base of any extensive study in this field, and particularly as far as « persuasive communication » is concerned, that is to say studies regarding at the same time « efficiency » and « effectiveness » in communication, that is to say both the effects meant on somebody by the person uttering the message and those he didn’t knowingly mean, therefore, attempting to distinguish between argumentation and rhetoric doesn’t seem to be rotally satisfying in the extent that every communication of arguments establishes on the basis of an implicit « relationship » which the exchange depends on, and « content » and « form » are very closely linked