Momentum-sector-selective metal-insulator transition in the eight-site dynamical mean-field approximation to the Hubbard model in two dimensions

We explore the momentum-sector-selective metal insulator transitions recently found in the eight - site dynamical cluster approximation to the two-dimensional Hubbard model. The phase diagram in the space of interaction and second-neighbor hopping is established. The initial transitions from Fermi-liquid like to sector-selective phases are found to be of second order, caused by the continuous opening of an energy gap whereas the other transitions are found to be of first order. In the sector-selective phase the Fermi surface regions which are not gapped are found to have a non-Fermi-liquid self-energy. We demonstrate that the phenomenon is not caused by the Van Hove divergence in the density of states. The sector-selective and insulating phases are characterized by a cluster spin correlation function that is strongly peaked at the commensurate antiferromagnetic wave vector $(\pi,\pi)$ but the model has no nematic instability. Comparison to dynamical mean-field studies on smaller clusters is made

Three form potential in (special) minimal supergravity superspace and supermembrane supercurrent

This contribution begins the study of the complete superfield Lagrangian description of the interacting system of D=4 N=1 supergravity (SUGRA) and supermembrane. Firstly, we review a 'three form supergravity' by Ovrut and Waldram, which we prefer to call 'special minimal supergravity'. This off-shell formulation of simple SUGRA is appropriate for our purposes as the supermembrane action contains the so-called Wess-Zumino term given by the integral over a three form potential in superspace, C3. We describe this formulation in the frame of Wess--Zumino superfield approach, showing how the basic variations of minimal SUGRA are restricted by the conditions of the existence of a three-form potential C3 in its superspace. In this language the effect of dynamical generation of cosmological constant, known to be characteristic for this formulation of SUGRA, appears in its superfield form, first described by Ogievetsky and Sokatchev in their formulation of SUGRA as a theory of axial vector superfield. Secondly, we vary the supermembrane action with respect to the special minimal SUGRA superfields (basic variations) and obtain the supercurrent superfields as well as the supergravity superfield equations with the supermembrane contributions.Comment: 18 pages, no figures. V2: Important references added. The abstract and presentation have been changed to reflect the overloop with that. Submitted to the QTS7 Proceedings. J. Phys. style use

First case of highly pathogenic H5N1 avian influenza virus in Spain

<p>Abstract</p> <p>Background</p> <p>The H5N1 strain of avian influenza virus has been involved in severe mortality in domestic poultry, and has also been found in different species of wildlife in Europe. The Basque Country avian influenza surveillance program began sample collection and processing the fall of 2005.</p> <p>Results</p> <p>Here we report the first confirmation of the presence of highly pathogenic H5N1 strain in a Great Crested Grebe (<it>Podiceps cristatus</it>) found dead in a pond near Vitoria in the Basque Country on the North of Spain. Regarding the survey for generic influenza type A virus, we have obtained positive results in about 8% of more that 3500 birds examined.</p> <p>Conclusion</p> <p>We think that the self-limiting nature of our finding and others proves that certain regions have ecological, geographical and climatological features that make it difficult for the H5N1 virus to spread <abbrgrp><abbr bid="B1">1</abbr></abbrgrp> and cause disease at least in the large scale scenario that has been worrying human and animal health authorities during the last years.</p

The Noncommutative Supersymmetric Nonlinear Sigma Model

We show that the noncommutativity of space-time destroys the renormalizability of the 1/N expansion of the O(N) Gross-Neveu model. A similar statement holds for the noncommutative nonlinear sigma model. However, we show that, up to the subleading order in 1/N expansion, the noncommutative supersymmetric O(N) nonlinear sigma model becomes renormalizable in D=3. We also show that dynamical mass generation is restored and there is no catastrophic UV/IR mixing. Unlike the commutative case, we find that the Lagrange multiplier fields, which enforce the supersymmetric constraints, are also renormalized. For D=2 the divergence of the four point function of the basic scalar field, which in D=3 is absent, cannot be eliminated by means of a counterterm having the structure of a Moyal product.Comment: 15 pages, 7 figures, revtex, minor modifications in the text, references adde

Shuttle Mechanism for Charge Transfer in Coulomb Blockade Nanostructures

Room-temperature Coulomb blockade of charge transport through composite nanostructures containing organic inter-links has recently been observed. A pronounced charging effect in combination with the softness of the molecular links implies that charge transfer gives rise to a significant deformation of these structures. For a simple model system containing one nanoscale metallic cluster connected by molecular links to two bulk metallic electrodes we show that self-excitation of periodic cluster oscillations in conjunction with sequential processes of cluster charging and decharging appears for a sufficiently large bias voltage. This new `electron shuttle' mechanism of discrete charge transfer gives rise to a current through the nanostructure, which is proportional to the cluster vibration frequency.Comment: 4 pages, 4 figure

Parvovirus Equino-Hepatitis (EqPV-H): un nuevo virus contaminante de productos biológicos de origen veterinario

Equine Parvovirus-Hepatitis (EqPV-H) is a new member of Parvoviridae family discovered 5 years ago. This virus was first identified in the serum and liver of a horse that died of equine serum hepatitis, also known as Theiler’s disease. This disease is one of the most common causes of acute hepatitis and liver failure in horses and has been frequently described after the administration of a biological product of equine origin. Several reports in recent years strongly suggest that EqPV-H is the etiologic agent of Theiler’s disease. The infection is usually asymptomatic, so infected horses can be healthy carriers and serve as reservoirs for infection to other horses. EqPV-H infection has been detected in America, Europe, Asia and Oceania, with a DNA prevalence of 3.2-19.8% and a seroprevalence of 15-34% in clinically healthy horses, reaching values of 90-100% in animals with Theiler’s disease. EqPV-H DNA has also been detected in commercial equine serum pools, revealing the risk of transmission by biological products that use this serum in their manufacturing process. Recently, the Center for Veterinary Biologics of the United States Department of Agriculture requires that all commercially licensed equine serum or plasma biologicals be tested and confirmed negative for EqPV-H. These sanitary restrictions could also be implemented in other countries. This article summarizes the published knowledge to date on EqPV-H, a focus of rapidly evolving research.El Parvovirus Equino-Hepatitis (EqPV-H) es un nuevo integrante de la familia Parvoviridae descubierto hace apenas 5 años. Este virus fue identificado en el suero e hígado de un caballo muerto por hepatitis sérica equina, también conocida como enfermedad de Theiler. Esta enfermedad es una de las causas más comunes de hepatitis aguda y falla hepática en caballos y se ha descripto frecuentemente luego de la administración de algún producto biológico de origen equino. Numerosos reportes en los últimos años sugieren fuertemente que el EqPV-H es el agente etiológico de la enfermedad de Theiler. Comúnmente la infección es asintomática por lo que los caballos infectados pueden ser portadores sanos y servir como reservorios para la infección de otros caballos. La infección por EqPV-H fue detectada en América, Europa, Asia y Oceanía, con una prevalencia de ADN del 3,2-19,8% y una seroprevalencia de 15-34% en caballos clínicamente sanos, alcanzando valores del 90-100% en animales con enfermedad de Theiler. Se ha reportado también la presencia de ADN de EqPV-H en lotes de suero equino comercial, evidenciando el riesgo de transmisión por productos biológicos que utilicen este insumo en su proceso de manufactura. Recientemente, el Centro de Biológicos Veterinarios del Departamento de Agricultura de Estados Unidos ha establecido que todos los productos biológicos de plasma o suero equino con licencia comercial deben ser analizados y resultar negativos para EqPV-H. Probablemente, estas restricciones sanitarias comiencen a implementarse en otros países. Este artículo resume el conocimiento publicado hasta la fecha sobre el EqPV-H, objeto de una investigación en rápida evolución

Heterogeneous-k-core versus Bootstrap Percolation on Complex Networks

We introduce the heterogeneous-$k$-core, which generalizes the $k$-core, and contrast it with bootstrap percolation. Vertices have a threshold $k_i$ which may be different at each vertex. If a vertex has less than $k_i$ neighbors it is pruned from the network. The heterogeneous-$k$-core is the sub-graph remaining after no further vertices can be pruned. If the thresholds $k_i$ are $1$ with probability $f$ or $k \geq 3$ with probability $(1-f)$, the process forms one branch of an activation-pruning process which demonstrates hysteresis. The other branch is formed by ordinary bootstrap percolation. We show that there are two types of transitions in this heterogeneous-$k$-core process: the giant heterogeneous-$k$-core may appear with a continuous transition and there may be a second, discontinuous, hybrid transition. We compare critical phenomena, critical clusters and avalanches at the heterogeneous-$k$-core and bootstrap percolation transitions. We also show that network structure has a crucial effect on these processes, with the giant heterogeneous-$k$-core appearing immediately at a finite value for any $f > 0$ when the degree distribution tends to a power law $P(q) \sim q^{-\gamma}$ with $\gamma < 3$.Comment: 10 pages, 4 figure

Casimir energy of a non-uniform string

The Casimir energy of a non-uniform string built up from two pieces with different speed of sound is calculated. A standard procedure of subtracting the energy of an infinite uniform string is applied, the subtraction being interpreted as the renormalization of the string tension. It is shown that in the case of a homogeneous string this method is completely equivalent to the zeta renormalization.Comment: 11 pages, REVTeX, no figures and table

Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays

We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum of the single G-type giant HR 9024 during a large flare. In analogy to solar X-ray observations, we interpret the observed Fe K$\alpha$ line as being produced by illumination of the photosphere by ionizing coronal X-rays, in which case, for a given Fe photospheric abundance, its intensity depends on the height of the X-ray source. The HETGS observations, together with 3D Monte Carlo calculations to model the fluorescence emission, are used to obtain a direct geometric constraint on the scale height of the flaring coronal plasma. We compute the Fe fluorescent emission induced by the emission of a single flaring coronal loop which well reproduces the observed X-ray temporal and spectral properties according to a detailed hydrodynamic modeling. The predicted Fe fluorescent emission is in good agreement with the observed value within observational uncertainties, pointing to a scale height $\lesssim 0.3$\rstar. Comparison of the HR 9024 flare with that recently observed on II Peg by Swift indicates the latter is consistent with excitation by X-ray photoionization.Comment: accepted for publication on the Astrophysical Journal Letter