Transport coefficients, spectral functions and the lattice

Transport coefficients are determined by the slope of spectral functions of composite operators at zero frequency. We study the spectral function relevant for the shear viscosity for arbitrary frequencies in weakly-coupled scalar and nonabelian gauge theories at high temperature and compute the corresponding correlator in euclidean time. We discuss whether nonperturbative values of transport coefficients can be extracted from euclidean lattice simulations.Comment: 25 pages with 7 eps figures, discussion improved, acknowledgement added; to appear in JHE

QuickXsort: Efficient Sorting with n log n - 1.399n +o(n) Comparisons on Average

In this paper we generalize the idea of QuickHeapsort leading to the notion of QuickXsort. Given some external sorting algorithm X, QuickXsort yields an internal sorting algorithm if X satisfies certain natural conditions. With QuickWeakHeapsort and QuickMergesort we present two examples for the QuickXsort-construction. Both are efficient algorithms that incur approximately n log n - 1.26n +o(n) comparisons on the average. A worst case of n log n + O(n) comparisons can be achieved without significantly affecting the average case. Furthermore, we describe an implementation of MergeInsertion for small n. Taking MergeInsertion as a base case for QuickMergesort, we establish a worst-case efficient sorting algorithm calling for n log n - 1.3999n + o(n) comparisons on average. QuickMergesort with constant size base cases shows the best performance on practical inputs: when sorting integers it is slower by only 15% to STL-Introsort

Caracterización de la raza criolla colombiana Blanco Orejinegro (BON), 4. Heterosis del crecimiento predestete de BON, Cebú y sus cruces con Charolais y Santa Gertrudis.

Se analizaron las características de crecimiento predestete y los valores de heterosis individual (hi) y materna (hm) de las progenies resultantes del apareamiento de vacas BON, Cebú (C) y cruzadas F1 BONxC y CxBON con toros BON, C, Charolais (Ch) y Santa Gertrudis (SG). De los registros de 508 terneros nacidos entre 1977 y 1983 en el Centro de Investigación El Nus (Ant.) localizado a 800 m.s.n.m., 2200 mm de precipitación anual, 23 grados centígrados de temperatura media y 87 por ciento de humedad relativa. Las características de crecimiento estudiadas y los valores promedios de los terneros BON y C, con los correspondientes valores de hi, expresada en porcentajes de las diferencias en comportamiento de los híbridos BONxC y CxBON con respecto al promedio del comportamiento de los animales puros, fueron: peso al nacimiento (PN), 26.9 kg y 12.4 por ciento, ganancias diarias de nacimiento al destete (PD), 580 g y 14.1 por ciento, peso al destete (PD) a los 8 meses de edad, ajustado a 240 días, 166.2 kg y 13.6 por ciento, y calificación de la muscularidad de los cuartos posteriores al destete (CD), 50.3 puntos y 9.4 por ciento. Estos valores de hi fueron significativos (P menor que 0.01). Los terneros BON pesaron al nacer 2.8 kg (P menor que 0.05) más que los C (28.5 vs 25.7), ganaron 45 g menos por día (557 vs 602 g/dia) y pesaron 8 kg menos al destete (162.2 vs 170.2 kg) (P menor que 0.01) y recibieron 4.7 puntos menos (P menor que 0.01) en la CD (47.9 vs 52.6). Los valores de hm definida como la ventaja o desventaja de utilizar una madre cruzada y estimada de las diferencias de las progenies de las vacas cruzadas F1 (BONxC y CxBON) y de las de sus progenitoras puras BON y C apareadas todas ellas con toros Ch y SG fueron, excepto la CD, significativos (P menor que 0.05) positivos. Los valores medios de las características en los dihíbridos ChxBON, CHxC, SGxBON y SGxC, y los correspondientes valores de hm fueron:;PN, 27.5 kg y 9.3 por ciento, GDPD, 656 g/día y 9.3 por ciento, PD, 184.8 kg y 9.2 por ciento y CD, 50.4 puntos y 4.4 por cientoGanado de carne-Ganadería carn

SUSY QM, symmetries and spectrum generating algebras for two-dimensional systems

We show in a systematic and clear way how factorization methods can be used to construct the generators for hidden and dynamical symmetries. This is shown by studying the 2D problems of hydrogen atom, the isotropic harmonic oscillator and the radial potential $A\rho^{2\zeta-2}-B\rho^{\zeta-2}$. We show that in these cases the non-compact (compact) algebra corresponds to so(2,1) (su(2))

Onset and Evolution of Southern Annular Mode-Like Changes at Centennial Timescale

The Southern Westerly Winds (SWW) are the surface expression of geostrophic winds that encircle the southern mid-latitudes. In conjunction with the Southern Ocean, they establish a coupled system that not only controls climate in the southern third of the world, but is also closely connected to the position of the Intertropical Convergence Zone and CO2 degassing from the deep ocean. Paradoxically, little is known about their behavior since the last ice age and relationships with mid-latitude glacier history and tropical climate variability. Here we present a lake sediment record from Chilean Patagonia (51°S) that reveals fluctuations of the low-level SWW at mid-latitudes, including strong westerlies during the Antarctic Cold Reversal, anomalously low intensity during the early Holocene, which was unfavorable for glacier growth, and strong SWW since ∼7.5 ka. We detect nine positive Southern Annular Mode-like events at centennial timescale since ∼5.8 ka that alternate with cold/wet intervals favorable for glacier expansions (Neoglaciations) in southern Patagonia. The correspondence of key features of mid-latitude atmospheric circulation with shifts in tropical climate since ∼10 ka suggests that coherent climatic shifts in these regions have driven climate change in vast sectors of the Southern Hemisphere at centennial and millennial timescales.Fil: Moreno, P.I.. Universidad de Chile; ChileFil: Vilanova, Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Villa-Martínez, R.. Universidad de Magallanes; ChileFil: Dunbar, R.B.. University of Stanford; Estados UnidosFil: Mucciarone, D.A.. University of Stanford; Estados UnidosFil: Kaplan, M.R.. Columbia University; Estados UnidosFil: Garreaud, R.D.. Universidad de Chile; ChileFil: Rojas, M.. Universidad de Chile; ChileFil: Moy, C.M.. University of Otago; Nueva ZelandaFil: De Pol-Holz, R.. Universidad de Magallanes; ChileFil: Lambert, F.. Pontificia Universidad Católica de Chile; Chil

Propiedades físicas y cristalinas del Cd1-x Znx Te (0 <= x <= 1)

El Cd1-xZnxTe (0 <= x <= 1) y el ZnTe son semiconductores de la familia II-VI, que se usan en forma monocristalina porque así poseen mejores propiedades estructurales y eléctricas. El CZT y el ZnTe deben poseer alta calidad cristalina y eléctrica para ser usados, el primero en detectores de rayos X y ?, y como sustratos ordenadores de películas epitaxiales aptas para la detección de la radiación IR y el segundo para la fabricación de diodos láser y emisores de luz de alta intensidad, ambos casos en el verde. En este trabajo el CZT se sintetizó por el método de Bridgman, bajo un gradiente de temperatura de 10ºC/cm a velocidades de 1, 66 mm/h y 3, 22 mm/h para diferentes concentraciones de Zn. Por otro lado, el ZnTe se sintetizó por transporte físico en fase vapor bajo un gradiente de temperatura de 6ºC/cm a una velocidad de 6mm/día. Por medio de revelado químico y microscopía electrónica de transmisión convencional TEM y de alta resolución (HRTEM) se estudió la calidad cristalina de ambos materiales. Se observó que los lingotes de CZT tenían una densidad de dislocaciones promedio similar en todos los lingotes crecidos en ambas velocidades y para todas las concentraciones mientras que el ZnTe mostró una menor densidad de dislocaciones. Las micrografías de TEM mostraron en todos estos materiales un orden estructural importante. Estas características indicaron que la calidad cristalina del CZT y del ZnTe era adecuada para fabricar dispositivos optoelectrónicos. También se midió la Conductividad Eléctrica, Difusividad Térmica, Calor Específico y Coeficiente Seebeck en función de la temperatura en estos materiales. Se analizó la influencia de las propiedades estructurales en sus propiedades físicas con el objeto de determinar la relación con los defectos cristalinos observados. Cd1-xZnxTe (0 = x = 1) and ZnTe are II-VI semiconductors, which are used in single crystalline structure to improve their crystalline and electrical properties. The CZT and ZnTe must possess high crystalline and electrical quality to be used, the first in x or ¿-ray detectors, and as substrates for suitable epitaxial films for detecting IR radiation and the second for the manufacture of laser diodes and high intensity light emitters, both cases in the green wavelengths. In this work CZT was synthesized by the Bridgman method employing a temperature gradient of 10ºC/cm at speeds of 1.66 mm/h and 3.22 mm/h for different Zn concentrations. Meanwhile ZnTe was synthesized by physical vapor transport employing a temperature gradient of 6ºC/cm at a speed of 6 mm/day. Chemical etching and low and high transmission electron microscopy (LRTEM and HRTEM) were employed to determine the crystalline quality of all materials. It was observed that CZT ingots had an average dislocations density similar in all ingots grown in both speeds and all concentrations while the ZnTe showed a lower dislocation density. HRTEM micrographs showed in all semiconductors an important structural order. These characteristics showed that the crystalline quality of CZT and ZnTe was suitable for manufacturing optoelectronic devices. Furthermore, Electrical Conductivity, Thermal Diffusivity, Specific Heat and Seebeck Coefficient were measured as temperature function in all these materials. The influence of structural properties in physical properties was analyzed in order to determine the relationship with the observed crystal defects

FCNC Top Quark Decays in Extra Dimensions

The flavor changing neutral top quark decay t -> c X is computed, where X is a neutral standard model particle, in a extended model with a single extra dimension. The cases for the photon, X= \gamma$, and a Standard Model Higgs boson, X = H, are analyzed in detail in a non-linear$R_\xi gauge. We find that the branching ratios can be enhanced by the dynamics originated in the extra dimension. In the limit where 1/R >> ->, we have found Br(t -> c \gamma) \simeq 10^{-10} for 1/R = 0.5 TeV. For the decay t -> c H, we have found Br(t -> cH) \simeq 10^{-10} for a low Higgs mass value. The branching ratios go to zero when 1/R -> \infty.Comment: Accepted to be published in the Europ. Phys. Jour. C; 16 pages, 2 figure

Charge disproportionation in YNiO3_{3} : ESR and susceptibility study

We present a study of the magnetic properties of YNiO$_{3}$ in the paramagnetic range, above and below the metal-insulator (MI) transition. The dc susceptibility, $\chi_{dc}$ (measured up to 1000 K) is a decreasing function of T for $T >$150 K (the N\'{e}el temperature) and we observe two different Curie-Weiss regimes corresponding to the metallic and insulator phases. In the metallic phase, this behaviour seems to be associated with the small ionic radius of Y% $^{3+}$. The value of the Curie constant for T$<$ T$_{MI}$ allows us to discard the possibility of Ni$^{3+}$ localization. An electron spin resonance (ESR) spectrum is visible in the insulator phase and only a fraction of the Ni ions contributes to this resonance. We explain the ESR and $\chi _{dc}$ behaviour for T $<$ T$_{MI}$ in terms of charge disproportionation of the type 2Ni$$ Ni$^{2+}$+Ni$^{4+},$ that is compatible with the previously observed structural transition across T$_{MI}$.Comment: 10 pages, 4 figures, submitted to Phys. Rev.

Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed Processes

A chromosphere is a universal attribute of stars of spectral type later than ~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae binaries) show extended and highly turbulent chromospheres, which develop into slow massive winds. The associated continuous mass loss has a significant impact on stellar evolution, and thence on the chemical evolution of galaxies. Yet despite the fundamental importance of those winds in astrophysics, the question of their origin(s) remains unsolved. What sources heat a chromosphere? What is the role of the chromosphere in the formation of stellar winds? This chapter provides a review of the observational requirements and theoretical approaches for modeling chromospheric heating and the acceleration of winds in single cool, evolved stars and in eclipsing binary stars, including physical models that have recently been proposed. It describes the successes that have been achieved so far by invoking acoustic and MHD waves to provide a physical description of plasma heating and wind acceleration, and discusses the challenges that still remain.Comment: 46 pages, 9 figures, 1 table; modified and unedited manuscript; accepted version to appear in: Giants of Eclipse, eds. E. Griffin and T. Ake (Berlin: Springer

A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses

We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants