2,585 research outputs found

    Slave spin cluster mean field theory away from half-filling: Application to the Hubbard and the extended Hubbard Model

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    A new slave-spin representation of fermion operators has recently been proposed for the half-filled Hubbard model. We show that with the addition of a gauge variable, the formalism can be extended to finite doping. The resulting spin problem can be solved using the cluster mean-field approximation. This approximation takes short-range correlations into account by exact diagonalization on the cluster, whereas long-range correlations beyond the size of clusters are treated at the mean-field level. In the limit where the cluster has only one site and the interaction strength UU is infinite, this approach reduces to the Gutzwiller approximation. There are some qualitative differences when the size of the cluster is finite. We first compute the critical UU for the Mott transition as a function of a frustrating second-neighbor interaction on lattices relevant for various correlated systems, namely the cobaltites, the layered organic superconductors and the high-temperature superconductors. For the triangular lattice, we also study the extended Hubbard model with nearest-neighbor repulsion. In additionto a uniform metallic state, we find a (3)×(3)\sqrt(3) \times \sqrt(3) charge density wave in a broad doping regime, including commensurate ones. We find that in the large UU limit, intersite Coulomb repulsion VV strongly suppresses the single-particle weight of the metallic state.Comment: 10 pages, 11 figures, submitted to PR

    Causes and Consequences of Thyroid Dysfunction throughout Life: a population-based and genetic approach

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    __Abstract__ Adequate thyroid hormone (TH) levels are essential for normal growth and differentiation, for the regulation of energy metabolism, and for the physiological function of virtually all human tissues. This is illustrated by the well-known effects of hypo- and hyperthyroidism. In addition, more recent studies show that also minor variation in serum TH levels, even within the normal range, can have important effects on clinical endpoints, such as bone mineral density, atrial fibrillation, metabolic syndrome (3) and cardiovascular mortality

    CRITICAL ANALYSIS AND DIGITAL RECONSTRUCTIONS OF ALBERTI'S ARCHITECTURES BY THE USE OF 3D MORPHOMETRIC INTEGRATED SURVEY DATABASE

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    Since 2005, DIAPReM Centre of the Department of Architecture of the University of Ferrara, in collaboration with the "Centro Studi Leon Battista Alberti" Foundation and the Consorzio Futuro in Ricerca, is carrying out a research project for the creation of 3D databases that could allow the development of a critical interpretation of Alberti's architectural work. The project is primarily based on a common three-dimensional integrated survey methodology for the creation of a navigable multilayered database. The research allows the possibility of reiterative metrical analysis, thanks to the use of a coherent data in order to check and validate hypothesis by researchers, art historians and scholars on Alberti's architectural work. Coherently with this methodological framework, indeed, two case studies are explained in this paper: the church of San Sebastiano in Matua and The Church of the Santissima Annunziata in Florence. Furthermore, thanks to a brief introduction of further developments of the project, a short graphical analysis of preliminary results on Tempio Malatestiano in Rimini opens new perspectives of research

    Supersolidity, entropy and frustration

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    We study the properties of t-t'-V model of hard-core bosons on the triangular lattice that can be realized in optical lattices. By mapping to the spin-1/2 XXZ model in a field, we determine the phase diagram of the t-V model where the supersolid characterized by the ordering pattern (x,x,-2x') ("ferrimagnetic" or SS A) is a ground state for chemical potential \mu >3V. By turning on either temperature or t' at half-filling \mu =3V, we find a first order transition from SS A to the elusive supersolid characterized by the (x,-x,0) ordering pattern ("antiferromagnetic" or SS C). In addition, we find a large region where a superfluid phase becomes a solid upon raising temperature at fixed chemical potential. This is an analog of the Pomeranchuk effect driven by the large entropic effects associated with geometric frustration on the triangular lattice.Comment: 4 pages, igures, LaTe

    A continuous-time solver for quantum impurity models

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    We present a new continuous time solver for quantum impurity models such as those relevant to dynamical mean field theory. It is based on a stochastic sampling of a perturbation expansion in the impurity-bath hybridization parameter. Comparisons to quantum Monte Carlo and exact diagonalization calculations confirm the accuracy of the new approach, which allows very efficient simulations even at low temperatures and for strong interactions. As examples of the power of the method we present results for the temperature dependence of the kinetic energy and the free energy, enabling an accurate location of the temperature-driven metal-insulator transition.Comment: Published versio
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