3,791 research outputs found

    Discontinuities in the level density of small quantum dots under strong magnetic fields

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    Exact diagonalization studies of the level density in a six-electron quantum dot under magnetic fields around 7 T (``filling factor'' around 1/2) are reported. In any spin-polarization channel, two regimes are visible in the dot excitation spectrum: one corresponding to interacting quasiparticles (i.e. composite fermions) for excitation energies below 0.4 meV, and a second one for energies above 0.4 meV, in which the level density (exponentially) increases at the same rate as in the non-interacting composite-fermion model.Comment: Accepted in Phys. Rev.

    Crossover between the Dense Electron-Hole Phase and the BCS Excitonic Phase in Quantum Dots

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    Second order perturbation theory and a Lipkin-Nogami scheme combined with an exact Monte Carlo projection after variation are applied to compute the ground-state energy of 6‚ȧN‚ȧ2106\le N\le 210 electron-hole pairs confined in a parabolic two-dimensional quantum dot. The energy shows nice scaling properties as N or the confinement strength is varied. A crossover from the high-density electron-hole phase to the BCS excitonic phase is found at a density which is roughly four times the close-packing density of excitons.Comment: Improved variational and projection calculations. 17 pages, 3 ps figures. Accepted for publication in Int. J. Mod. Phys.

    Elastic and inelastic breakup of deuterons with energy below 100 MeV

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    We present calculations of deuteron elastic and inelastic breakup cross sections and angular distributions at deuteron energies below 100 MeV obtained using the post-form DWBA approximation. The elastic breakup cross section was extensively studied in the past. Very few calculations of inelastic breakup have been performed, however. We also analyze the angular momentum - energy distributions of the cross section for formation of the compound nucleus after inelastic breakup.Comment: 7 page

    Dispersive spherical optical model of neutron scattering from Al27 up to 250 MeV

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    A spherical optical model potential (OMP) containing a dispersive term is used to fit the available experimental database of angular distribution and total cross section data for n + Al27 covering the energy range 0.1- 250 MeV using relativistic kinematics and a relativistic extension of the Schroedinger equation. A dispersive OMP with parameters that show a smooth energy dependence and energy independent geometry are determined from fits to the entire data set. A very good overall agreement between experimental data and predictions is achieved up to 150 MeV. Inclusion of nonlocality effects in the absorptive volume potential allows to achieve an excellent agreement up to 250 MeV.Comment: 13 figures (11 eps and 2 jpg), 3 table

    ‚ÄėRural transnationalism‚Äô: The return to the mobility of moroccans employed in the agriculture sector during the economic crisis

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    La crisis econ√≥mica en Espa√Īa se ha traducido en un cambio de ciclo migratorio. En este contexto han surgido nuevas l√≠neas tem√°ticas en los estudios sobre las migraciones. Uno de los nuevos objetivos es analizar las estrategias de los inmigrados para hacer frente a la crisis. En el caso de los marroqu√≠es, la agricultura ha pasado a ser un refugio ante la p√©rdida de trabajo en otros sectores. Nuestro estudio revela que este regreso a la agricultura se ha traducido a menudo en una vuelta a la movilidad geogr√°fica, la cual adquiere adem√°s una dimensi√≥n territorial transnacional rural porque abarca tanto a distintos municipios agr√≠colas espa√Īoles como marroqu√≠esThe economic crisis in Spain has been translated into a change of migratory cycle. In this context new thematic lines have arisen in the study of migrations. One of the new aims is to analyze the strategies of the immigrated ones to face the crisis. In the case of Moroccans, the agriculture has happened to be a refuge before the loss of jobs in other sectors. Our study highlights that this return to the agriculture has also become a return to geographical mobility. This mobility also acquires a rural transnational territorial dimension as it covers different rural Spanish as well as Moroccan municipalitie

    Notes on unrest among Moroccan youth: Migrant projects and internal mobility in Morocco as a prelude to international migration

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    El periple migratori dels immigrats marroquins a Espanya durant la passada d√®cada es va iniciar, molt sovint, abans de creuar la frontera. En molts casos, va ser just aquesta primera experi√®ncia migrat√≤ria al Marroc la que va constituir el desencadenant definitiu a l‚Äôhora de prendre la decisi√≥ d‚Äôemigrar a l‚Äôestranger, expressi√≥, a m√©s, del desassossec de gran part de la joventut marroquina davant les oportunitats que els ofereix la seva societat. En aquest article, hi analitzem els projectes migratoris de partida d‚Äôuna mostra de joves marroquins immigrats a Andalusia, fent un √®mfasi especial en aquells casos en qu√® es detecta una estreta articulaci√≥ entre l‚Äôemigraci√≥ a l‚Äôestranger i les migracions internes al Marroc. Per aix√≤ ens servim d‚Äôuna investigaci√≥ emp√≠rica realitzada en cinc municipis andalusos de les prov√≠ncies de C√≤rdova i Granada.El periplo migratorio de los inmigrados marroqu√≠es en Espa√Īa durante la pasada d√©cada se inici√≥, muy a menudo, antes de cruzar la frontera. En muchos casos, fue justo esta primera experiencia migratoria en Marruecos la que constituy√≥ el desencadenante definitivo a la hora de tomar la decisi√≥n de emigrar al extranjero, expresi√≥n adem√°s del desasosiego de gran parte de la juventud marroqu√≠ ante las oportunidades que les ofrece su sociedad. En este art√≠culo, analizamos los proyectos migratorios de partida de una muestra de j√≥venes marroqu√≠es inmigrados en Andaluc√≠a, haciendo especial hincapi√© en aquellos casos en los que se detecta una estrecha articulaci√≥n entre la emigraci√≥n al extranjero y las migraciones internas en Marruecos. Para ello, nos servimos de una investigaci√≥n emp√≠rica realizada en cinco municipios andaluces de las provincias de C√≥rdoba y Granada que ha utilizado m√©todos cuantitativos y cualitativos.The migratory journey of Moroccan immigrants in Spain during the past decade began, very often, before crossing the border. In many cases it was just this first migration experience in Morocco which was the factor that finally triggered the decision to migrate abroad, and it was also the expression of the unease of Moroccan youth in the face of the opportunities being offered by society. In this paper we analyze the starting points of migratory projects from a sample of young Moroccan immigrants in Andalusia, with particular emphasis on those cases where close links between migration abroad and internal migration in Morocco have been detected. For this we employ empirical research conducted in five municipalities of the Andalusian provinces of Cordoba and Granada

    Apuntes sobre el desasosiego entre la juventud marroquí : proyectos migratorios y movilidad interna en Marruecos como antesala de la inmigración internacional

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    El periplo migratorio de los inmigrados marroqu√≠es en Espa√Īa durante la pasada d√©cada se inici√≥, muy a menudo, antes de cruzar la frontera. En muchos casos, fue justo esta primera experiencia migratoria en Marruecos la que constituy√≥ el desencadenante definitivo a la hora de tomar la decisi√≥n de emigrar al extranjero, expresi√≥n adem√°s del desasosiego de gran parte de la juventud marroqu√≠ ante las oportunidades que les ofrece su sociedad. En este art√≠culo, analizamos los proyectos migratorios de partida de una muestra de j√≥venes marroqu√≠es inmigrados en Andaluc√≠a, haciendo especial hincapi√© en aquellos casos en los que se detecta una estrecha articulaci√≥n entre la emigraci√≥n al extranjero y las migraciones internas en Marruecos. Para ello, nos servimos de una investigaci√≥n emp√≠rica realizada en cinco municipios andaluces de las provincias de C√≥rdoba y Granada que ha utilizado m√©todos cuantitativos y cualitativos.El periple migratori dels immigrats marroquins a Espanya durant la passada d√®cada es va iniciar, molt sovint, abans de creuar la frontera. En molts casos, va ser just aquesta primera experi√®ncia migrat√≤ria al Marroc la que va constituir el desencadenant definitiu a l'hora de prendre la decisi√≥ d'emigrar a l'estranger, expressi√≥, a m√©s, del desassossec de gran part de la joventut marroquina davant les oportunitats que els ofereix la seva societat. En aquest article, hi analitzem els projectes migratoris de partida d'una mostra de joves marroquins immigrats a Andalusia, fent un √®mfasi especial en aquells casos en qu√® es detecta una estreta articulaci√≥ entre l'emigraci√≥ a l'estranger i les migracions internes al Marroc. Per aix√≤ ens servim d'una investigaci√≥ emp√≠rica realitzada en cinc municipis andalusos de les prov√≠ncies de C√≤rdova i Granada.Le p√©riple migratoire des Marocains immigr√©s en Espagne durant la derni√®re d√©cennie a commenc√©, tr√®s souvent, bien avant de traverser la fronti√®re. Dans beaucoup de cas, une premi√®re exp√©rience migratoire √† l'int√©rieur du Maroc a √©t√© le principal facteur de d√©clenchement pour prendre la d√©cision d'√©migrer √† l'√©tranger, ce que nous pouvons consid√©rer comme une expression du malaise d'une grande partie de la jeunesse marocaine. Dans cet article nous analysons les projets de d√©part d'un √©chantillon de jeunes marocains ayant √©migr√© en Andalousie, en portant une attention particuli√®re pour les parcours o√Ļ nous avons d√©tect√© une articulation √©troite entre l'√©migration √† l'√©tranger et les migrations internes au Maroc. Pour cela, nous pr√©sentons les r√©sultats obtenus dans le cadre d'une recherche empirique r√©alis√©e dans cinq communes d'Andalousie. La m√©thodologie a utilis√© des m√©thodes quantitatives (une enqu√™te) et qualitatives (une s√©rie d'entretiens semi-structur√©s).The migratory journey of Moroccan immigrants in Spain during the past decade began, very often, before crossing the border. In many cases it was just this first migration experience in Morocco which was the factor that finally triggered the decision to migrate abroad, and it was also the expression of the unease of Moroccan youth in the face of the opportunities being offered by society. In this paper we analyze the starting points of migratory projects from a sample of young Moroccan immigrants in Andalusia, with particular emphasis on those cases where close links between migration abroad and internal migration in Morocco have been detected. For this we employ empirical research conducted in five municipalities of the Andalusian provinces of Cordoba and Granada
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