Monte Carlo simulation of recrystallization

A Monte Carlo computer simulation technique, in which a continuum system is modeled employing a discrete lattice, has been applied to the problem of recrystallization. Primary recrystallization is modeled under conditions where the degree of stored energy is varied and nucleation occurs homogeneously (without regard for position in the microstructure). The nucleation rate is chosen as site saturated. Temporal evolution of the simulated microstructures is analyzed to provide the time dependence of the recrystallized volume fraction and grain sizes. The recrystallized volume fraction shows sigmoidal variations with time. The data are approximately fit by the Johnson-Mehl-Avrami equation with the expected exponents, however significant deviations are observed for both small and large recrystallized volume fractions. Under constant rate nucleation conditions, the propensity for irregular grain shapes is decreased and the density of two sided grains increases

HCO3- enrichment causes cytosolic NO3- efflux in Posidonia oceanica leaf cells

Posidonia oceanica is a seagrass, the only group of vascular plants to colonize the marine environment. Seawater is an extreme yet stable environment, characterized by high salinity, alkaline pH and low availability of essential nutrients, such as nitrate or phosphate. In addition, in aquatic environments the supply of CO2 for the photosynthesis is limited by diffusion and therefore many aquatic plants use HCO3- as the inorganic carbon source for photosynthesis. Previous results have shown that Na+ -dependent transport systems operate on the plasma membrane of P. oceanica mesophyll leaf cells for the high-affinity NO3-, Pi or amino acids uptake. Also, a direct transport of HCO3- driven by H+ has been found in this species that provides inorganic carbon for photosynthesis and could be a significant component of a carbon concentrating mechanism in this species. Interestingly, this HCO3- direct uptake caused the efflux of chloride from the cytosol, probably through S-type anion channels, pointing that other anions could also be removed from the cytosol. This hypothesis could be relevant in the case of NO3-, since the decrease of cytosolic NO3- in response to HCO3- enrichment could limit N-assimilation. Here we analyse the effect of HCO3- increase on NO3- uptake and cytosolic homeostasis in P. oceanica. Enrichment of natural seawater with 3 mM HCO3- evokes the on-going decrease of cytosolic NO3-, from 5.7 ± 0.2 to 4.8 ± 0.7 mM after 40 min of treatment. The incubation of P. oceanica leaf pieces in 3 mM HCO3- NSW causes an initial increase of NO3- concentration in the medium. Maximum efflux (21 nmol NO3- gFM-1 min-1) occurs within the first minute of incubation. Then, external NO3- is depleted from the medium at lower net uptake rate than the value observed in non HCO3- -enriched natural seawater. These results fit the hypothesis that HCO3- enrichment causes the nitrogen loose and could impair nitrogen assimilation promoting N biomass impoverishment.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Spanish MINECO, projects BFU2017-85117-R and BIO2016-81957-RED

Na+-dependent NO3- uptake in leaf cells of the seagrass Posidonia oceanica (L.) Delile

Posidonia oceanica (L.) Delile is an endemic Mediterranean seagrass of recognized ecological significance and, as other seagrasses, this species has secondarily adapted to live in the marine environment. In this alkaline medium with a high Na+ concentration (0.5 M), the high inwardly directed electrochemical potential gradient for sodium is used in the seagrass Zostera marina to energize the uptake of nitrate1 and phosphate that usually occur at concentration below 10 µM. Here we summarize several evidences for the operation of a sodium-dependent high-affinity nitrate transport system at the plasma membrane of the mesophyll leaf cells of P. oceanica. Leaf cells of P. oceanica possess a H+-ATPase as a primary pump, exhibit a plasma membrane potential (Em) of -174 ± 10 mV and show reduced Na+ permeability. The addition of micromolar nitrate concentrations induces membrane depolarizations that show saturation kinetics. Curve fitting of the values renders a semisaturation constant (Km) of 21.3 ± 6.6 μM and a maximum depolarization (Dmax) of 7 ± 1 mV. In dark conditions, Dmax decreases by fifty percent but no significant effect is observed on the Km value. On the other hand, nitrate induced depolarizations show sodium dependence. The depolarizations induced by 100 µM NO3- in media containing increasing Na+ concentrations (from 0 to 250 mM) show saturation kinetics, rendering a Km value of 16 ± 5 mM Na+. Moreover, the depolarization induced by 100 µM NO3- is accompanied by a simultaneous increase of cytosolic sodium, measured by Na+-sensitive microelectrodes, of 0.4 ± 0.2 mM above the resting cytosolic sodium concentration (17 ± 2 mM). Finally, nitrate uptake rates, measured in depletion experiments, decreases by 50% and 80% in dark conditions and in the absence of Na+, respectively, compared with control conditions (0.5 M Na+ and light). All together, these results strongly suggest that NO3- uptake in P. oceanica leaf cells is mediated by a high-affinity nitrate carrier that uses Na+ as the driving ion. 1 Rubio et al. (2005). J. Exp. Bot, 412: 613-622. Project Funding: CTM 2011-30356. (MEC)Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Effect of elevated inorganic carbon on the cytosolic homeostasis of NO3- in the marine angiosperm Posidonia oceanica (L.) Delile

The marine angiosperm Posidonia oceanica is a mediterranean endemism of great ecological significance. As other marine plants, P. oceanica has adapted secondarily to the marine environment and develop anew different mechanisms to colonize it. Among others, this plant has developed a plasma membrane system for the direct uptake of bicarbonate. In this work we have developed both NO3- and Cl- selective microelectrodes for the continuous monitoring of the intracellular (cytosolic) NO3- and Cl-. In the light, leaf mesophyll cells show a cytosolic NO3- concentration of 5.7±0.2 mM (n=10), while in the dark cytosolic NO3- raises up to 8.7±1.1 mM; these values are in the range of concentrations quoted for Arabidopsis thaliana (Cookson et al., 2005). The enrichment of natural seawater (NSW) with 3 mM NaHCO3 caused a decrease of the cytosolic NO3- concentration of 1 mM and a decrease of the cytosolic concentration of Cl- of 3.5 mM. The saturation of NSW with 1000 µL CO2 L-1 produced a lower diminution of the cytosolic NO3- (0.3 mM). In the presence of 0.1 mM of the plasma membrane permeable inhibitor of the carbonic anhydrase (EZ) the diminution of cytosolic NO3- caused by the same concentration of CO2 was much lower, 0.1 mM. The addition of inorganic carbon, either HCO3- or CO2, has an effect on the cytosolic mechanisms for anionic homeostasis, one of which is the opening of the slow anion channels. These channels are permeable to NO3- and Cl- and could elicit the efflux of these ions. In P. oceanica, the response in the presence of EZ points out that the inorganic carbon species that cause the NO3-/Cl- efflux is HCO3-. This effect could contribute to plant biomass N dilution observed in elevated CO2. References: Cookson et al. 2005. Plant Physiology 138, 1097–1105.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Coupled equations for Kähler metrics and Yang-Mills connections

We study equations on a principal bundle over a compact complex manifold coupling a connection on the bundle with a Kahler structure on the base. These equations generalize the conditions of constant scalar curvature for a Kahler metric and Hermite-Yang-Mills for a connection. We provide a moment map interpretation of the equations and study obstructions for the existence of solutions, generalizing the Futaki invariant, the Mabuchi K-energy and geodesic stability. We finish by giving some examples of solutions.Comment: 61 pages; v2: introduction partially rewritten; minor corrections and improvements in presentation, especially in Section 4; added references; v3: To appear in Geom. Topol. Minor corrections and improvements, following comments by referee

Modelo de ISING en 3-d. aplicación a sensores magnéticos

El modelo de Ising es un problema de física estadística que tiene solución exacta en dos dimensiones, para el caso de tres dimensiones es preciso utilizar procedimientos de simulación. En este trabajo se ha utilizado un método de Monte Carlo para estudiar el comportamiento del sistema en distintas situaciones, siendo de especial interés el estudio del paso por la transición de fase a la temperatura crítica (Temperatura de Curie, Tc). Se ha estudiado la cinética de los dominios magnéticos, considerando la estructura de los dominios desde el punto de vista de la energía, y en consecuencia, hemos tenido en cuenta la energía de canje que tiende a mantener alineados los espines de los electrones en los materiales ferromagnéticos. Este término contribuye a hacer mayor el espesor de la pared, por la tendencia a que los espines de los átomos vecinos se mantengan alineados. Se ha considerado el ferromagnetismo desde el punto de vista cuántico y basado en las propiedades de simetría de las funciones de onda de los electrones, que se manifiestan en variaciones de la energía electrostática de un sistema en función de la orientación de sus espines. Se han estudiado los efectos de histéresis que resultan al aplicar un campo magnético externo a la red y la orientación de los espines de la misma a lo largo de su evolución. Para la determinación de las propiedades de los materiales ferromagnéticos se utiliza el ciclo de histéresis aunque algunas de las propiedades magnéticas, como la dirección de anisotropía, no pueden ser deducidas directamente de esta manera. Se utilizan distintos métodos para la determinación de la anisotropía de las muestras. El acoplamiento entre la magnetización en zonas próximas a la superficie y la magnetización en zonas internas de la muestra puede ser utilizado para obtener un ciclo de histéresis, que permita obtener sensores magnéticos adaptados a las medidas que se quieran realizar. Mediante el control del campo coercitivo y la susceptibilidad se abre una línea de investigación para el desarrollo de sensores magnético

Manejo de la producción equina e impacto ambiental: el caso de establecimientos en Buenos Aires (Argentina)

La producción equina en Buenos Aires (Argentina) es de 512847 cabezas. El manejo de la producción equina es un factor importante para la minimización de los efectos ambientales. Este manejo incluye la implementación de buenas prácticas. El objetivo de este trabajo es caracterizar los establecimientos de producción equina en Buenos Aires en cuanto a su manejo y evaluar el posible impacto ambiental que pueden generar. Se han caracterizado 16 establecimientos según las fuentes de abastecimiento de agua, cantidad y profundidad de los pozos, raza, sistema productivo, tipo y gestión de camas, tipo de alimentación, prácticas veterinarias, suplementos dietarios utilizados, y manejo de la alimentación. Este trabajo es el primer estudio sobre los efectos ambientales de la producción equina en Argentina.Equine production in Buenos Aires (Argentina) is 512847 heads. The equine production management is an important factor for the minimization of environmental effects. This management includes the implementation of good practices. The aim of this paper is to characterize the equine production paddocks in Buenos Aires in terms of their management, and to evaluate the possible environmental impact they may generate. Sixteen paddocks have been characterized according to the sources of water supply, quantity and depth of the wells, breed, productive system, type and management of beds, type of feed, feeding practices, supplementation, other ration components and management. These are the first studies on environmental effects of equine production in Argentine.Fil: Vaccaro, Mariana Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Unidad Ejecutora de Investigaciones en Producción Animal. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Unidad Ejecutora de Investigaciones en Producción Animal; ArgentinaFil: García Liñeiro, José Alberto. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias; ArgentinaFil: Fernandez Cirelli, Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Unidad Ejecutora de Investigaciones en Producción Animal. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Unidad Ejecutora de Investigaciones en Producción Animal; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Centro de Estudios Transdisciplinarios del Agua; Argentin

Habitar en la ceguera. Casas, atmósferas y paisajes perceptivos a los ojos de algunos maestros del siglo XX

Jorge Luis Borges confessed, on more than one occasion, that his modest blindness was not the dramatic darkness that common sense believes but rather a refuge that, in his case, was built in a slow twilight. At the end of his speech to receive the Honoris Causa degree from the Faculty of Philosophy and Letters of the University of Chile, the Argentine writer spoke about the gradual parting of his sight and the pleasant sensation of entering a new, richer, deeper, and more creative living space. Relying on blindness as an introspective landscape, as a habitable space where fantasy meets realism, it is in this context that the essay proposes to inhabit, with thought, a weightless and infinite domestic space. Other artists achieved it - Groussac, Monet, Homer, Joyce, Herzog, Pallasmaa, and Italo Calvino - turning this kind of induced blindness into an intimate and creative room in which to settle at the end of their lives. Professor Yeager introduces this story, making us ascend to the heavens in search of an inspiring, black, and profound space. The house dreamed by Manuel Parra and Danilo Veras leads us away from the light to discover ourselves in a unique sensory experience. From the hand of the master Lewerentz, this essay will bring together some architectural experimentations with a singular dark box, an asphalt and black environment: black box in Lund. Living in blindness suggests a revision of our perceptual field, imaginatively inhabiting these introspective places where laws seem to have disappeared. Blindness, as Borges mentioned in that speech, makes the body join the space to dream of a new, more poetic, and creative dwelling (Figure 1).Jorge Luis Borges confesó, en más de una ocasión, que su modesta ceguera no era la dramática oscuridad que el sentido común cree, sino mas bien un refugio que en su caso se fue construyendo en un lento crepúsculo. Al finalizar su discurso de recepción del grado Honoris Causa de la Facultad de Filosofía y Letras de la Universidad de Chile, el escritor argentino narraba la lenta despedida de su vista y la sensación placentera de entrar en un nuevo espacio habitable más rico, profundo y creativo. Confiando en la ceguera como paisaje introspectivo, como espacio habitable donde se da cita a la fantasía con el realismo, es en este contexto que, el ensayo propone habitar con el pensamiento un espacio doméstico ingrávido e infinito. Otros artistas lo consiguieron - Groussac, Monet, Homero, Joyce, Herzog, Pallasmaa e Italo Calvino- convirtiendo esta especie de ceguera inducida en una habitación íntima y creativa, en la cual acomodarse al final de sus vidas. El profesor Yeager introduce este relato haciéndonos ascender a los cielos en busca de un espacio inspirador, negro y profundo. La casa soñada por Manuel Parra y Danilo Veras, nos aleja de la luz para descubrirnos a nosotros mismos en una experiencia sensitiva única. De la mano del maestro Lewerentz se dará cita en este ensayo a algunas experimentaciones arquitectónicas con una singular caja oscura, un medioambiente asfáltico y negro: black box en Lund. Habitar en la ceguera nos sugiere una revisión de nuestro campo perceptivo, habitando con la imaginación estos lugares introspectivos en los que las leyes parecen haber desaparecido. La ceguera, como afirmaba Borges en aquel discurso, hace que el cuerpo se una al espacio para soñar con un nuevo habitar más poético y creativo (Figura 1).Jorge Luis Borges confessou, em mais de uma ocasião, que sua modesta cegueira não era a escuridão dramática que o senso comum acredita que fosse, mas sim um refúgio que, no seu caso, foi construído em um lento crepúsculo. No final de seu discurso para receber o título Honoris Causa da Faculdade de Filosofia e Letras da Universidade do Chile, o escritor argentino relatou a lenta despedida de sua visão e a agradável sensação de entrar em um novo espaço habitável, mais rico, mais profundo e mais criativo. Confiando na cegueira como uma paisagem introspectiva, como um espaço habitável onde a fantasia se encontra com o realismo, é nesse contexto que o ensaio propõe habitar com o pensamento um espaço doméstico leve e infinito. Outros artistas conseguiram isso - Groussac, Monet, Homer, Joyce, Herzog, Pallasmaa e Italo Calvino - transformando esse tipo de cegueira induzida em um cômodo íntimo e criativo no qual se instalaram no final de suas vidas. O professor Yeager apresenta essa história fazendo-nos subir aos céus em busca de um espaço inspirador, negro e profundo. A casa sonhada por Manuel Parra e Danilo Veras nos afasta da luz para nos descobrirmos em uma experiência sensorial única. Das mãos do mestre Lewerentz, este ensaio reunirá algumas experiências arquitetônicas com uma singular caixa escura, um ambiente asfáltico e negro: black box em Lund. Habitar na cegueira sugere uma revisão de nosso campo perceptivo, habitando com a imaginação esses lugares introspectivos nos quais as leis parecem ter desaparecido. A cegueira, como Borges afirmou naquele discurso, faz com que o corpo se junte ao espaço para sonhar com um novo habitar, mais poético e criativo (Figura 1)