Computational implementation of the Kubo formula for the static conductance: application to two-dimensional quantum dots

Kubo formula is used to get the d.c conductance of a statistical ensemble of two-dimensional clusters of the square lattice in the presence of standard diagonal disorder, a uniform magnetic field and random magnetic fluxes. Working within a one-band tight-binding approach the calculation is quite general. The shape of the cluster is rectangular with ideal leads attached to opposite corners. Both geometrical characteristics and physical parameters can be easily selected. The output is just the conductance of a system of given parameters or a statistical ensemble of conductances measured for different disorder realizations.Comment: 14 pages, one table, no figures, RevTeX styl

Análisis técnico económico de tres explotaciones lecheras en Girardot.

Ganado de leche-Ganadería lecheMaestría en CienciasMaestrí

Free initial wave packets and the long-time behavior of the survival and nonescape probabilities

The behavior of both the survival S(t) and nonescape P(t) probabilities at long times for the one-dimensional free particle system is shown to be closely connected to that of the initial wave packet at small momentum. We prove that both S(t) and P(t) asymptotically exhibit the same power-law decrease at long times, when the initial wave packet in momentum representation behaves as O(1) or O(k) at small momentum. On the other hand, if the integer m becomes greater than 1, S(t) and P(t) decrease in different power-laws at long times.Comment: 4 pages, 3 figures, Title and organization changed, however the results not changed, To appear in Phys. Rev.

Using the Biocheck.UGent™ scoring tool in Irish farrow-to-finish pig farms : Assessing biosecurity and its relation to productive performance

Background: Biosecurity is one of the main factors affecting disease occurrence and antimicrobial use, and it is associated with performance in pig production. However, the importance of specific measures could vary depending on the (national) context. The aim of this study was to describe the biosecurity status in a cohort of Irish pig farms, to investigate which of those biosecurity aspects are more relevant by using the Biocheck.UGent™ scoring system, and to study the impact of such aspects on farm performance. Results: External biosecurity score was high compared to most countries due to the characteristics of the Irish pig sector (i.e. purchasing only semen and breeding gilts on farm). The internal biosecurity score was lower and had greater variability among farms than other EU countries. Using multivariable linear regression, the biosecurity practices explained 8, 23, and 16% of variability in piglet mortality, finisher mortality, and average daily gain, respectively. Three clusters of farms were defined based on their biosecurity scores (0 to 100) using principal components and hierarchical clustering analysis. Scores for clusters 1, 2 and 3 were (mean ± SD) 38 ± 7.6, 61 ± 7.0 and 66 ± 9.8 for internal and 73 ± 5.1, 74 ± 5.3 and 86 ± 4.5 for external biosecurity. Cluster 3 had lower piglet mortality (P = 0.022) and higher average daily gain (P = 0.037) when compared to cluster 2. Conclusions: Irish farms follow European tendencies with internal biosecurity posing as the biggest liability. Our results suggest that practices related to the environment and region, feed, water and equipment supply, and the management of the different stages, need to be addressed in lower performing farms to improve productive performance. Further studies on the economic impact of these biosecurity practices including complementary data on herd health, gilt rearing, piglet management, vaccination and feeding strategies are needed

Mixing aggression intensity is associated with age at first service and floor type during gestation, with implications for sow reproductive performance

peer-reviewedAggression resulting from mixing to establish a dominance hierarchy is a major welfare concern for group-housed sows. The associated stress can negatively impact aspects of reproductive performance. Objectives of this study were to investigate associations between 1) age at first service (AFS) and mixing aggression intensity in first parity sows, 2) mixing aggression intensity and reproductive performance within and between parity one and parity two, and 3) mixing aggression intensity, floor type during gestation and reproductive performance. Gilts (n =160, hereafter referred to as sows) were mixed into stable groups of eight unfamiliar individuals approximately 4 days after artificial insemination, housed on fully slatted concrete (CON; n =80) floor uncovered or covered with rubber slat mats (RUB; n =80), and followed through two parities. Skin lesions (SLMIX; a proxy for the intensity of mixing aggression), were scored post mixing in each parity according to severity (0=no lesions to 5=severe lesions) on five body regions (ear, neck, hindquarter, rump, and belly) on the left and right sides, and at the tail/anogenital region. Total SLMIX score was calculated for each sow. Data on reproductive performance traits were acquired retrospectively from farm records for both parities. Two analyses were performed: 1) data from each parity were analysed separately and 2) SLMIX score in parity one was used to predict reproductive performance in parity two. Lower AFS was associated with a lower SLMIX score in parity one (P =0.031). There was no association between SLMIX score and reproductive performance in parity one, while sows with higher SLMIX score in parity two had a higher proportion of piglets dead during lactation (P =0.027) and a longer cycle length (P =0.003) in parity two. Sows with higher SLMIX scores in parity one had more non-productive days (P <0.001) in parity two. Concrete sows had a higher SLMIX score than RUB sows in parity one (P =0.015), but not in parity two. In addition, CON sows had a higher proportion of piglets born dead (P =0.013) compared with RUB sows in parity two. Mixing aggression has a negative influence on reproductive performance within parities, and it may also have a long-term negative carry-over effect on reproductive performance in subsequent parities. Serving gilts at younger ages could help to minimize the intensity of aggression at mixing, while housing on rubber flooring has beneficial implications for their reproductive performance

Conductance as a Function of the Temperature in the Double Exchange Model

We have used the Kubo formula to calculate the temperature dependence of the electrical conductance of the double exchange Hamiltonian. We average the conductance over an statistical ensemble of clusters, which are obtained by performing Monte Carlo simulations on the classical spin orientation of the double exchange Hamiltonian. We find that for electron concentrations bigger than 0.1, the system is metallic at all temperatures. In particular it is not observed any change in the temperature dependence of the resistivity near the magnetical critical temperature. The calculated resistivity near $T_c$ is around ten times smaller than the experimental value. We conclude that the double exchange model is not able to explain the metal to insulator transition which experimentally occurs at temperatures near the magnetic critical temperature.Comment: 6 pages, 5 figures included in the tex

Análisis semicuantitativo del calcio y fósforo en el esmalte y la dentina

Existe una serie de características comunes asociadas al proceso biológico de formación de los tejidos calcificados a pesar de que los productos finales sean estructuralmente distintos. La presente investigación tiene como propósito determinar si la ratio Ca/P ratio es la misma para los tejidos calcificados dentales tanto del feto como del adulto y si dicha ratio es diferente al valor de la ratio Ca/P de la hidroxiapatita pura calculada por estequiometría. Se escogió como material de observación el esmalte y la dentina, en muestras de fetos humanos y en un total de 30 ratas adultas de raza Wistar y 20 dientes humanos sanos. Las observaciones se llevaron a cabo por medio de Microscopia Electrónica de Barrido y Microanálisis por separación de energía de rayos X. Los valores totales de la ratio Ca/P para el esmalte oscilaron en un intervalo de 0,9 y 1,2, con una media que se encuentra entre 1,07 y 1,08. Los valores totales de la ratio Ca/P para la dentina oscilan entre 1,03 y 1,12 y la media entre 1,07 y 1,075. No se encontraron diferencias estadísticamente significativas entre esmalte fetal y adulto ni entre la dentina fetal y adulta. Aún no pudiendo definir la existencia de precursores específicos en los tejidos calcificados del diente (esmalte y dentina), nuestros resultados sugieren que no toda la cristalización de estos tejidos corre a cargo de la hidroxiapatita sino que deben haber otros compuestos que expliquen la disminución del valor de la ratio Ca/P en las muestras estudiadas

Análisis semicuantitativo del calcio y fósforo en los tejidos calcificados de la mandíbula

El objetivo de nuestra investigación es realizar un estudio microanalítico semicuantitativo del calcio y el fósforo en los tejidos calcificados de la mandíbula. Dentro de este estudio se pretende calcular el valor de la ratio Ca/P por métodos semicuantitativos y compararlo con los valores estequiométricos de la ratio Ca/P de la hidroxiapatita referidos en la literatura; conocer los valores de la ratio Ca/P obtenidos para el tejido condroide, el hueso lamelar, el hueso fibrorreticular y el cartílago calcificado en las muestras fetales, por una parte, y adultas, por otra; y si existen o no diferencias significativas en la proporción Ca/P obtenidos para feto y adulto. El análisis morfológico de los tejidos calcificados fue realizado por medio de Microrradiografía Electrónica de Barrido (MEB) por electrones retrodispersados (Backscattering), y los resultados permiten afirmar que la ratio obtenida por análisis semicuantitativo mediante dispersión de rayos X de los tejidos calcificados (condroide, hueso lamelar y fibrorreticular) se encuentra más próxima a 1, y que no existen diferencias significativas entre las muestras fetales y de adulto en los tejidos analizados

Ultra-fast propagation of Schr\"odinger waves in absorbing media

We identify the characteristic times of the evolution of a quantum wave generated by a point source with a sharp onset in an absorbing medium. The "traversal'' or "B\"uttiker-Landauer'' time (which grows linearly with the distance to the source) for the Hermitian, non-absorbing case is substituted by three different characteristic quantities. One of them describes the arrival of a maximum of the density calculated with respect to position, but the maximum with respect to time for a given position becomes independent of the distance to the source and is given by the particle's ``survival time'' in the medium. This later effect, unlike the Hartman effect, occurs for injection frequencies under or above the cut-off, and for arbitrarily large distances. A possible physical realization is proposed by illuminating a two-level atom with a detuned laser

CdsH contributes to the replication of salmonella typhimurium inside epithelial cells in a cysteine-supplemented medium

Indexación ScopusSalmonella Typhimurium is a facultative, intracellular pathogen whose products range from self-limited gastroenteritis to systemic diseases. Food ingestion increases biomolecules’ concentration in the intestinal lumen, including amino acids such as cysteine, which is toxic in a concentration-dependent manner. When cysteine’s intracellular concentration reaches toxic levels, S. Typhimurium expresses a cysteine-inducible enzyme (CdsH), which converts cysteine into pyruvate, sulfide, and ammonia. Despite this evidence, the biological context of cdsH’s role is not completely clear, especially in the infective cycle. Since inside epithelial cells both cdsH and its positive regulator, ybaO, are overexpressed, we hypothesized a possible role of cdsH in the intestinal phase of the infection. To test this hypothesis, we used an in vitro model of HT-29 cell infection, adding extra cysteine to the culture medium during the infective process. We observed that, at 6 h post-invasion, the wild type S. Typhimurium proliferated 30% more than the ∆cdsH strain in the presence of extra cysteine. This result shows that cdsH contributes to the bacterial replication in the intracellular environment in increased concentrations of extracellular cysteine, strongly suggesting that cdsH participates by increasing the bacterial fitness in the intestinal phase of the S. Typhimurium infection. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.https://www.mdpi.com/2076-2607/8/12/201