7,764 research outputs found

    Phase diagram of soft-core bosons in two dimensions

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    The low temperature phase diagram of Bose soft disks in two dimensions is studied by numerical simulations. It is shown that a supersolid cluster phase exists, within a range of the model parameters, analogous to that recently observed for a system of aligned dipoles interacting via a softened potential at short distance. These findings indicate that a long-range tail of the interaction is unneeded to obtain such a phase, and that the soft-core repulsive interaction is the minimal model for supersolidity

    Un océano, dos móviles y cuatro generaciones: interactividad familiar a partir de lives de portugués lengua de herencia en Instagram

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    Este trabalho traz um relato de experiência sobre o impacto de lives do Instagram na interatividade de quatro gerações de uma mesma família durante a pandemia do COVID-19, entre março e junho de 2020, no Brasil, onde se encontravam um casal de bisavós e a avó, e na Catalunha (Espanha), onde se encontravam a mãe e a filha. Propõe-se uma perspectiva situada de produção de conhecimento, já que as pesquisadoras, avó e mãe, participam da experiência relatada. O ponto de partida é a necessidade de adaptar aulas presenciais de português língua de herança (PLH) a um formato on-line. A professora e sua filha passam a apresentar uma live semanal no Instagram, que chega a uma audiência mais ampla, incluindo seus familiares. Este formato desencadeia trocas de conhecimento e afetivas e permite refletir sobre a inclusão de idosos em práticas sociais mediadas por novas tecnologias e sobre novas formas de se relacionar a partir delas.Se presenta un relato de experiencia sobre el impacto de lives de Instagram en la interactividad de cuatro generaciones de una misma familia en la pandemia del COVID-19, entre marzo y junio de 2020, en Brasil, donde se encontraban una pareja de bisabuelos y la abuela, y Cataluña (España), donde se encontraban la madre y la hija. Se propone una perspectiva situada de producción de conocimiento, pues las investigadoras, abuela y madre, participan de la experiencia relatada. El punto de partida es la necesidad de adaptar clases de portugués lengua de herencia (PLH) a un formato on-line. La profesora y su hija empiezan a presentar una live semanal en Instagram que alcanza una audiencia más amplia, incluyendo a sus familiares. Este formato desencadena intercambios de conocimiento y de afectos, y permite reflexionar sobre la inclusión de personas mayores en prácticas sociales mediadas por nuevas tecnologías y sobre nuevas formas de relacionarse a partir de ellas

    C/O white dwarfs of very low mass: 0.33-0.5 Mo

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    The standard lower limit for the mass of white dwarfs (WDs) with a C/O core is roughly 0.5 Mo. In the present work we investigated the possibility to form C/O WDs with mass as low as 0.33 Mo. Both the pre-WD and the cooling evolution of such nonstandard models will be described.Comment: Submitted to the "Proceedings of the 16th European White Dwarf Workshop" (to be published JPCS). 7 pages including 13 figure

    Analytical expressions for the charge-charge local-field factor and the exchange-correlation kernel of a two-dimensional electron gas

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    We present an analytical expression for the static many-body local field factor G+(q)G_{+}(q) of a homogeneous two-dimensional electron gas, which reproduces Diffusion Monte Carlo data and embodies the exact asymptotic behaviors at both small and large wave number qq. This allows us to also provide a closed-form expression for the exchange and correlation kernel Kxc(r)K_{xc}(r), which represents a key input for density functional studies of inhomogeneous systems.Comment: 5 pages, 3 figure

    Analisi basata sugli sforzi locali della resistenza a fatica di giunzioni incollate di materiali compositi

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    Il lavoro prende spunto dai risultati di un’analisi sperimentale del comportamento a fatica di giunzioni incollate di materiali compositi laminati di elevato spessore formati da strati di unidirezionale e di tessuto di fibra di carbonio. I giunti sono stati realizzati in modo tale da saggiare l’influenza della lunghezza di sovrapposizione (da 25,4 mm a 110,8 mm), della forma del giunto (con e senza rastremazione), e della composizione degli aderendi (sostituzione di uno degli aderendi in composito con uno in acciaio). Mediante analisi 2D elastiche con il metodo degli elementi finiti sono state ricavate le distribuzioni degli sforzi all’interno dello strato di adesivo, al fine di individuare un parametro utile alla descrizione del comportamento a fatica in termini di sforzi locali - numero di cicli a rottura. Il ruolo della fase di propagazione viene discusso alla luce di osservazioni dell’avanzamento della frattura, condotta su alcuni dei giunti testati

    Competing effects of Mn and Y doping on the low-energy excitations and phase diagram of La1−y_{1-y}Yy_{y}Fe1−x_{1-x}Mnx_xAsO0.89_{0.89}F0.11_{0.11} iron-based superconductors

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    Muon Spin Rotation (μ\muSR) and 19^{19}F Nuclear Magnetic Resonance (NMR) measurements were performed to investigate the effect of Mn for Fe substitutions in La1−y_{1-y}Yy_{y}Fe1−x_{1-x}Mnx_xAsO0.89_{0.89}F0.11_{0.11} superconductors. While for y=0y = 0 a very low critical concentration of Mn (x=0.2x = 0.2%) is needed to quench superconductivity, as yy increases the negative chemical pressure introduced by Y for La substitution stabilizes superconductivity and for y=20y= 20% it is suppressed at Mn contents an order of magnitude larger. A magnetic phase arises once superconductivity is suppressed both for yy=0 and for y=20y= 20%. Low-energy spin fluctuations give rise to a peak in 19^{19}F NMR 1/T11/T_1 with an onset well above the superconducting transition temperature and whose magnitude increases with xx. Also the static magnetic correlations probed by 19^{19}F NMR linewidth measurements show a marked increase with Mn content. The disruption of superconductivity and the onset of the magnetic ground-state are discussed in the light of the proximity of LaFeAsO0.89_{0.89}F0.11_{0.11} to a quantum critical point.Comment: 8 pages, 9 figure

    Isotopic Composition of Fragments in Nuclear Multifragmentation

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    The isotope yields of fragments, produced in the decay of the quasiprojectile in Au+Au peripheral collisions at 35 MeV/nucleon and those coming from the disassembly of the unique source formed in Xe+Cu central reactions at 30 MeV/nucleon, were measured. We show that the relative yields of neutron-rich isotopes increase with the excitation energy in multifragmentation reaction. In the framework of the statistical multifragmentation model which fairly well reproduces the experimental observables, this behaviour can be explained by increasing N/Z ratio of hot primary fragments, that corresponds to the statistical evolution of the decay mechanism with the excitation energy: from a compound-like decay to complete multifragmentation.Comment: 10 pages. 4 Postscript figures. Submitted to Physical Review C, Rapid Communicatio
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