1,721,007 research outputs found
Effect of symmetry in the many-particle Wigner funcion
Full text linkAn analysis of the Wigner function for identical particles is presented. Four situations have been considered. (i) The first is scattering process between two indistinguishable particles described by a minimum uncertainty wave packets showing the exchange and correlation effects in Wigner phase space. (ii) An equilibrium ensemble of N particles in a one-dimensional box and in a one-dimensional harmonic potential is considered second, showing that the reduced one-particle Wigner function, as a function of the energy defined in the Wigner phase space, tends to the Fermi-Dirac or to the Bose-Einstein distribution function, depending on the considered statistics. (iii) The third situation is reduced one-particle transport equation for the Wigner function, in the case of interacting particles, showing the need for the two-particle reduced Wigner function within the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy scheme. (iv) Finally, the electron-phonon interaction in the two-particle case is considered, showing coparticipation of two electrons in the interaction with the phonon bath
Exchange effects in the Wigner-function approach
No full textIn this paper, an analysis of the Wigner function (WF) for identical fermions is presented. Three situations have been analyzed. i) A scattering process between two indistinguishable electrons in minimum uncertainty wavepackets showing the exchange and correlation hole in Wigner phase space. ii) An equilibrium ensemble of N electrons in a box showing that the WF integrated over space assumes the shape of a Fermi distribution even for very small N. iii) The reduced one-particle transport-equation for the WF in the case of interacting electrons showing the first contribution to the BBGKY hierarchy
Roughness effect on electron transport through quantum wires
No full textIn the present work we study, by means of numerical simulations, the coherent propagation of electrons in quantum wires and focus on the effect of the introduction of roughness along the channel. We study the electron evolution both in single and coupled quantum wires in the case where the electron freely move through the channel and in the case where transport is assisted by surface acoustic waves. It has been shown that systems of coupled quantum wires can realize a complete set of quantum logic gates.However, its physical implementation is severely limited by the spreading of the wave packet and by the presence of interface roughness. Our results show that the potential of the surface acoustic wave succeeds in confining the electron wavefunction and in driving it along the channels also when interface roughness is introduced. This suggests that electron transport assisted by surface acoustic waves could be a very efficient way to realize quantum solid state devices
Electron decoherence in a semiconductor due to electron-phonon scattering
No full textIn the present work we study, by means of numerical simulations, the coherent propagation of electrons in quantum wires and focus on the effect of the introduction of roughness along the channel. We study the electron evolution both in single and coupled quantum wires in the case where the electron freely move through the channel and in the case where transport is assisted by surface acoustic waves. It has been shown that systems of coupled quantum wires can realize a complete set of quantum logic gates.However, its physical implementation is severely limited by the spreading of the wave packet and by the presence of interface roughness. Our results show that the potential of the surface acoustic wave succeeds in confining the electron wavefunction and in driving it along the channels also when interface roughness is introduced. This suggests that electron transport assisted by surface acoustic waves could be a very efficient way to realize quantum solid state devices
Wigner functions for identical particles
No full textIn this work the Wigner function approach to quantum transport developed for the single electron case is extended to a more complicated system for n indistingushable particles. In particular we study how the Monte Carlo tecnique and the Wigner paths method can be applyed to a single particle Wigner function defined for a system of n interacting particles. The numerical results are obtained for the case of a system of two particles under different conditions: two noninteracting fermions, two noninteracting bosons, two non interacting distinguishable particles and two interacting fermions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Elisabetta Barile. Littera antiqua scritture alla greca : notai e cancellieri copisti a Venezia nei primi decenni del Quattrocento. Venise : Istituto veneto di scienze, lettere ed arti, 1994. In-8°, 155 pages. (Memorie, Classe di scienze morali, lettere ed arti, 51.)
No full textElisabetta Barile. Littera antiqua scritture alla greca : notai e cancellieri copisti a Venezia nei primi decenni del Quattrocento. Venise : Istituto veneto di scienze, lettere ed arti, 1994. In-8°, 155 pages. (Memorie, Classe di scienze morali, lettere ed arti, 51.). In: Bibliothèque de l'école des chartes. 1996, tome 154, livraison 2. pp. 652-654
Elisabetta Barile. Littera antiqua scritture alla greca : notai e cancellieri copisti a Venezia nei primi decenni del Quattrocento. Venise : Istituto veneto di scienze, lettere ed arti, 1994. In-8°, 155 pages. (Memorie, Classe di scienze morali, lettere ed arti, 51.)
No full textElisabetta Barile. Littera antiqua scritture alla greca : notai e cancellieri copisti a Venezia nei primi decenni del Quattrocento. Venise : Istituto veneto di scienze, lettere ed arti, 1994. In-8°, 155 pages. (Memorie, Classe di scienze morali, lettere ed arti, 51.). In: Bibliothèque de l'école des chartes. 1996, tome 154, livraison 2. pp. 652-654
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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