Renormalized Kaluza-Klein theories

Using six-dimensional quantum electrodynamics ($QED_6$) as an example we study the one-loop renormalization of the theory both from the six and four-dimensional points of view. Our main conclusion is that the properly renormalized four dimensional theory never forgets its higher dimensional origin. In particular, the coefficients of the neccessary extra counterterms in the four dimensional theory are determined in a precise way. We check our results by studying the reduction of $QED_4$ on a two-torus.Comment: LaTeX, 36 pages. A new section added; references improved, typos fixe

ESTIMACIÓN BAYESIANA EN EL MODELO DE RIESGOS ADITIVOS

En el "análisis de supervivencia", se estudia el comportamiento de variables que miden el tiempo hasta la ocurrencia de cierto evento de interés, por ejemplo, en medicina puede interesar el tiempo hasta la remisión de determinada enfermedad. Dada la naturaleza del estudio, es usual la presencia de "datos censurados", es decir, en estos casos, se mide la variable durante cierto período de tiempo, durante el cual no se ha observado el evento de interés. En este contexto, se define la "función de riesgo", que se puede expresar en función de las expresiones de las funciones de densidad de probabilidad y de distribución acumulada de la variable en cuestión. Se suelen caracterizar los distintos modelos acorde a la expresión que toma su función de riesgo, siendo el más conocido el modelo de riesgos proporcionales de Cox [1]. Como alternativas, suelen aparecer otros modelos. Uno de ellos es en el cual basamos nuestro estudio: el modelo de riesgos aditivos (o AHM) [1]. Estos modelos (Cox, Aalen) son semi-paramétricos, ya que constan de una componente paramétrica y una no paramétrica. En el caso de AHM, Lin & Ying [3] abordaron el problema de la estimación de la componente paramétrica del modelo. En nuestro trabajo, tratamos a este modelo mediante un enfoque Bayesiano para ambas componentes, basándonos en las ecuaciones descriptas por Lin & Ying para la componente paramétrica. En el caso de la componente no paramétrica, proponemos, extendiendo lo expuesto el año anterior (Riddick, Álvarez [4]), un proceso a priori conjunto, optando por un proceso Gamma. Para ilustrar la eficacia del método, exponemos los resultados obtenidos mediante simulaciones, y en un conjunto de datos asociados a la medicina

Size-dependent photoacclimation of the phytoplankton community in temperate shelf waters (southern Bay of Biscay)

Shelf waters of the Cantabrian Sea (southern Bay of Biscay) are productive ecosystems with a marked seasonality. We present the results from 1 yr of monthly monitoring of the phytoplankton community together with an intensive sampling carried out in 2 contrasting scenarios during the summer and autumn in a mid-shelf area. Stratification was apparent on the shelf in summer, while the water column was comparatively well mixed in autumn. The size structure of the photoautotrophic community, from pico-to micro-phytoplankton, was tightly coupled with the meteo-climatic and hydrographical conditions. Over the short term, variations in the size structure and chlorophyll content of phytoplankton cells were related to changes in the physico-chemical environment, through changes in the availability of nutrients and light. Uncoupling between the dynamics of carbon biomass and chlorophyll resulted in chlorophyll to carbon ratios dependent on body size. The slope of the size dependence of chlorophyll content increased with increasing irradiance, reflecting different photoacclimation plasticity from pico-to micro-phytoplankton. The results have important implications for the productivity and the fate of biogenic carbon in this region, since the size dependence of photosynthetic rates is directly related to the size scaling of chlorophyll content.Versión del edito

Quantum corrections to Higher-Dimensional Theories

This is a non-technical summary of the subtleties of quantum corrections on extra-dimensional theories: should one first renormalize and then mode expand, or first expand in four-dimensional modes and then renormalize?Comment: 9 pages, based on a talk at IRGAC 2006, Barcelon

An approach to dynamic line rating state estimation at thermal steady state using direct and indirect measurements

Dynamic line rating has emerged as a solution for reducing congestion in overhead lines, allowing the optimization of power systems assets. This technique is based on direct and/or indirect monitoring of conductor temperature. Different devices and methods have been developed to sense conductor temperature in critical spans. In this work, an algorithm based on WLS is proposed to estimate temperature in all ruling spans of an overhead line. This algorithm uses indirect measurements - i.e. weather reports and/or downscaling nowcasting models as inputs as well as direct measurements of mechanical tension, sag and/or conductor temperature. The algorithm has been tested using typical atmospheric conditions in Iceland along with an overhead line´s real design, showing robustness, efficiency and the ability to minimize error in measurements.Fil: Alvarez, David L.. Universidad Nacional de Colombia; ColombiaFil: Faria da Silva, F.. Aalborg Universitet; DinamarcaFil: Mombello, Enrique Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; ArgentinaFil: Bak, Claus Leth. Aalborg Universitet; DinamarcaFil: Rosero, Javier A.. Universidad Nacional de Colombia; ColombiaFil: Ólason, Daníel Leó. Landsnet; Islandi

Modeling of the binodal curve of ionic liquid/salt aqueous systems

Ionic Liquid-based Aqueous Two Phase Systems (ILATPS) are an innovative technique to separate biomolecules that combines the advantages of liquid–liquid extraction and hydrophilic ionic liquids. Most ILATPS are based on ionic liquids and conventional inorganic salts, and the phase envelope, described by the binodal curve, is usually modeled by empirical equations that are used to determine the phase compositions and assess the ionic liquid recyclability. However, these empirical equations may provide a poor extrapolation ability or low accuracy at the extreme regions of the binodal curve or suffer from problems of convergence. Therefore, the aim of this work is the analysis of the binodal curve equations, comparing the models reported in the literature to describe ILATPS and proposing alternative equations to improve accuracy or to reduce the mathematical complexity. For this purpose, a database compiling binodal experimental data of 100 ILATPS has been built, so that the analysis could make it possible to obtain representative conclusions for all these systems. Several models were developed, and different statistical criteria were used to assess the advantages and disadvantages of each one of these models for the binodal curve. The results show that, when accuracy is critical, a proposed model with just an additional parameter reduced more than 25% the residual mean squared error (RMSE) with respect to the commonly used equation, without losing the statistical significance of the parameters. For complex problems where an explicit equation in both the concentration of ionic liquid and of salt is needed, the use of an explicit model developed with 3 adjusted parameters that kept high accuracy (R2 > 0.996 and RMSE < 0.66) is proposed. Finally, the analysis also revealed that a fitting method based on the minimization of relative errors is recommended to increase the accuracy of the binodal curve at high salt concentrations, which is the crucial region for assessing the recyclability of the ionic liquid.This work was developed in the scope of the project CICECO Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement. The authors also acknowledge FCT for the Post-doctoral grant SFRH/BPD/79263/2011 of S.P.M. Ventura

Neolignanos en hojas de virola calophylla (warb)*

De las hojas de Virola Calophylla (Mynsticaceae) se aislaron e identificaron dos neolignanos nuevos, calophyn y calophyllin, y dos neolignanos conocidos, ácido meso-dihidroguaiarético y austrobailignano-6. Las estructuras fueron establecidas por métodos espectroscópicos

Early Cerebral Hemodynamic, Metabolic, and Histological Changes in Hypoxic–Ischemic Fetal Lambs during Postnatal Life

The hemodynamic, metabolic, and biochemical changes produced during the transition from fetal to neonatal life may be aggravated if an episode of asphyxia occurs during fetal life. The aim of the study was to examine regional cerebral blood flow (RCBF), histological changes, and cerebral brain metabolism in preterm lambs, and to analyze the role of oxidative stress in the first hours of postnatal life following severe fetal asphyxia. Eighteen chronically instrumented newborn lambs were randomly assigned to either a control group or the hypoxic–ischemic (HI) group, in which case fetal asphyxia was induced just before delivery. All the animals were maintained on intermittent positive pressure ventilation for 3 h after delivery. During the HI insult, the injured group developed acidosis, hypoxia, hypercapnia, lactic acidosis, and tachycardia (relative to the control group), without hypotension. The intermittent positive pressure ventilation transiently improved gas exchange and cardiovascular parameters. After HI injury and during ventilatory support, there continued to be an increased RCBF in inner regions among the HI group, but no significant differences were detected in cortical flow compared to the control group. Also, the magnitude of the increase in TUNEL positive cells (apoptosis) and antioxidant enzymes, and decrease of ATP reserves was significantly greater in the brain regions where the RCBF was not higher. In conclusion, our findings identify early metabolic, histological, and hemodynamic changes involved in brain damage in premature asphyxiated lambs. Such changes have been described in human neonates, so our model could be useful to test the safety and the effectiveness of different neuroprotective or ventilation strategies applied in the first hours after fetal HI injury