Interrelation between the pseudogap and the incoherent quasi-particle features of high-Tc superconductors

Using a scenario of a hybridized mixture of localized bipolarons and conduction electrons, we demonstrate for the latter the simultaneous appearance of a pseudogap and of strong incoherent contributions to their quasi-particle spectrum which arise from phonon shake-off effects. This can be traced back to temporarily fluctuating local lattice deformations, giving rise to a double-peak structure in the pair distribution function, which should be a key feature in testing the origin of these incoherent contributions, recently seen in angle-resolved photoemission spectroscopy (ARPES).Comment: 4 pages, 3 figures, to be published in Phys. Rev. Let

Whole genome sequencing of experimental hybrids supports meiosis-like sexual recombination in Leishmania

Hybrid genotypes have been repeatedly described among natural isolates of Leishmania, and the recovery of experimental hybrids from sand flies co-infected with different strains or species of Leishmania has formally demonstrated that members of the genus possess the machinery for genetic exchange. As neither gamete stages nor cell fusion events have been directly observed during parasite development in the vector, we have relied on a classical genetic analysis to determine if Leishmania has a true sexual cycle. Here, we used whole genome sequencing to follow the chromosomal inheritance patterns of experimental hybrids generated within and between different strains of L. major and L. infantum. We also generated and sequenced the first experimental hybrids in L. tropica. We found that in each case the parental somy and allele contributions matched the inheritance patterns expected under meiosis 97–99% of the time. The hybrids were equivalent to F1 progeny, heterozygous throughout most of the genome for the markers that were homozygous and different between the parents. Rare, non-Mendelian patterns of chromosomal inheritance were observed, including a gain or loss of somy, and loss of heterozygosity, that likely arose during meiosis or during mitotic divisions of the progeny clones in the fly or culture. While the interspecies hybrids appeared to be sterile, the intraspecies hybrids were able to produce backcross and outcross progeny. Analysis of 5 backcross and outcross progeny clones generated from an L. major F1 hybrid, as well as 17 progeny clones generated from backcrosses involving a natural hybrid of L. tropica, revealed genome wide patterns of recombination, demonstrating that classical crossing over occurs at meiosis, and allowed us to construct the first physical and genetic maps in Leishmania. Altogether, the findings provide strong evidence for meiosis-like sexual recombination in Leishmania, presenting clear opportunities for forward genetic analysis and positional cloning of important genes.</div

Jets, knots and tails in planetary nebulae: NGC 3918, K 1-2 and Wray 17-1

We analyze optical images and high-resolution, long-slit spectra of three planetary nebulae which possess collimated, low-ionization features. NGC 3918 is composed of an inner, spindle-shaped shell mildly inclined with respect to the plane of the sky. Departing from the polar regions of this shell, we find a two-sided jet expanding with velocities which increase linearly with distance from 50 to 100 km/s. The jet is probably coeval with the inner shell (with the age of approximately 1000 D yr, where D is the distance in kpc), suggesting that its formation should be ascribed to the same dynamical processes which also shaped the main nebula, and not to a more recent mass loss episode. We discuss the formation of the aspherical shell and jet in the light of current hydrodynamical and magnetohydrodynamical theories. K 1-2 is a planetary nebula with a close binary nucleus which shows a collimated string of knots embedded in a diffuse, elliptical shell. The knots expand with a velocity similar to that of the elliptical nebula (25 km/s), except for an extended tail located out of the main nebula, which linearly accelerates up to 45 km/s. We estimate an inclination on the line of the sight of 40 degres for the string of knots; once the orientation of the orbit is also determined, this information will allow us to test the prediction of current theories of the occurrence of polar jets from close binary systems. Wray 17-1 has a complex morphology, showing two pairs of low-ionization structures located in almost perpendicular directions from the central star, and embedded in a large, diffuse nebula. The two pairs show notable similarities and differences, and their origin is very puzzling.Comment: 20 pages plus 10 figures. ApJ recently published (ApJ 523, 721 (1999)

The Spin Holonomy Group In General Relativity

It has recently been shown by Goldberg et al that the holonomy group of the chiral spin-connection is preserved under time evolution in vacuum general relativity. Here, the underlying reason for the time-independence of the holonomy group is traced to the self-duality of the curvature 2-form for an Einstein space. This observation reveals that the holonomy group is time-independent not only in vacuum, but also in the presence of a cosmological constant. It also shows that once matter is coupled to gravity, the "conservation of holonomy" is lost. When the fundamental group of space is non-trivial, the holonomy group need not be connected. For each homotopy class of loops, the holonomies comprise a coset of the full holonomy group modulo its connected component. These cosets are also time-independent. All possible holonomy groups that can arise are classified, and examples are given of connections with these holonomy groups. The classification of local and global solutions with given holonomy groups is discussed.Comment: 21 page

Suppression of SERK gene expression affects fungus tolerance and somatic embryogenesis in transgenic lettuce.

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Interaction anisotropy and random impurities effects on the critical behaviour of ferromagnets

The theory of phase transitions is based on the consideration of "idealized" models, such as the Ising model: a system of magnetic moments living on a cubic lattice and having only two accessible states. For simplicity the interaction is supposed to be restricted to nearest--neighbour sites only. For these models, statistical physics gives a detailed description of the behaviour of various thermodynamic quantities in the vicinity of the transition temperature. These findings are confirmed by the most precise experiments. On the other hand, there exist other cases, where one must account for additional features, such as anisotropy, defects, dilution or any effect that may affect the nature and/or the range of the interaction. These features may have impact on the order of the phase transition in the ideal model or smear it out. Here we address two classes of models where the nature of the transition is altered by the presence of anisotropy or dilution.Comment: 11 pages, 4 figures, To appear in Journal of Physics: Conference Serie

Towards evaluating the impact of recommender systems on visitor experience in physical museums

Recommender systems have been used in physical museums to improve visitor experience; yet to assess their impact empirically, researchers often rely on the user experience criteria alone. In this paper, we examine the multidimensionality of visitor experience, specifically the components and factors that shape it. We present a framework that is built on existing bodies of knowledge about visitor experience and that serves as a starting point to further evaluate the transformations caused by the integration of recommender systems in museums. We then conclude that current approaches to testing the impact of recommender systems on visitor experience should be expanded beyond evaluations of user satisfaction level to include the demonstrated aspects of visitor experience. This research aims to contribute to a more in-depth understanding of the differences between visitor and user experience types as well as to address the need for a more comprehensive set of guidelines to evaluate how recommender systems enhance visitor experience in physical museums

Fowl typhoid in Argentine Republic

Luego de un brote de Tifosis en un criadero con 100.000 aves en producción a jaula (50% Leghorn y 50% AA-Harco), un 8,38% de positivos (Harco) a la prueba de aglutinación rápida, son trasladados a tinglado individual y alojados igualmente en jaula. Luego de 50 coprocultivos negativos, los animales son reanalizados con la misma prueba 30~60-90 y 120 días después, comprobándose que dichos positivos disminuían del 100 al 32%, no habiéndose constatado en todo ese tiempo, diferencia con su lote similar. Transcurrido ese período, 30 animales son descargados con cepa virulenta, comprobándose que sólo el 1% muere por Tifosis, frente al lote testigo donde los insucesos son del 50% Estos hechos son analizados estadísticamente entendiendo que la prueba de aglutinación no debe aplicarse con el mismo criterio que para la pullorosis ya que, según los resultados, muestra un valor muy relativo. Se efectúan paralelamente, consideraciones inmunológicas sobre la posible importancia de la lg A en los mecanismos de defensa de las aves.After a Typhoid outbreak in a farm with 100.000 birds in production in cages (50% Leghorn and 50% AA-Harco), 8,38% of positive reactors to the quick agglutination test (Harco) were transferred to an individual house also in cages. After 50 negative coprocultures, the birds are again assayed by the same test 30-60-90 and 120 days after, finding that said positives decreased from 100 to 32%. No difference was noted during that period with the similar lot. After that time, 30 birds are challenged with a virulent strain and only 1% die of Typhoid; as compared with the control group where mortality was 50%. These facts are statistically analyzed finding that the agglutination test should not be used with the same criteria as for pullorum, since, according to the findings, its value is quite relative. At the same time, immunological considerations were effected on the possible importance of Ig G and Ig A in the defense mechanisms of birds against infections caused by enterobacteria.Facultad de Ciencias Veterinaria