On the use of JMAK theory to describe mechanical amorphization: a comparison between experiments, numerical solutions and simulations

The kinetics of amorphization during ball milling is generally analyzed using two different approaches: the classical Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory and Delogu and Cocco’s model for which a region deterministically transforms after it reaches a certain number of collisions. The application of JMAK analysis to the latter model predicts Avrami exponents to be higher than the experimental ones (typically close to one). We develop simulations based on the probabilistic character of the nucleation phenomenon and concave growth of the amorphous phase in the core of a nanocrystal. The predictions of our simulations are in good agreement with the low Avrami exponents and with the size evolution of the remaining crystallites found experimentally. From these values, the parameters involved in the simulated model (growth rate and probability of nucleation) can be estimated.AEI/FEDER-UE (Project MAT-2016-77265-R)Junta de Andalucía (Grupo PAI

Influence of Milling Time on the Homogeneity and Magnetism of a Fe70Zr30 Partially Amorphous Alloy: Distribution of Curie Temperatures

In this work, the mechanically alloyed Fe70Zr30 (at. %) composition has been used to study the influence of milling time on its homogeneity and magnetic properties. The microstructure and Fe environment results show the formation of an almost fully amorphous alloy after 50 h of milling in a mixture of pure 70 at. % Fe and 30 at. % Zr. The soft magnetic behavior of the samples enhances with the increase of the milling time, which is ascribed to the averaging out of the magnetocrystalline anisotropy as the crystal size decreases and the amorphous fraction increases. The formation of a non-perfectly homogenous system leads to a certain compositional heterogeneity, motivating the existence of a distribution of Curie temperatures. The parameters of the distribution (the average Curie temperature, T C ¯ , and the broadening of the distribution, ∆ T C ) have been obtained using a recently reported procedure, based on the analysis of the approach towards the saturation curves and the magnetocaloric effect. The decrease of ∆ T C and the increase of T C ¯ with the milling time are in agreement with the microstructural results. As the remaining α-Fe phase decreases, the amorphous matrix is enriched in Fe atoms, enhancing its magnetic response.AEI/FEDER-UE Project MAT 2016-77265-

Fischer-Tropsch synthesis in microchannels

Different metallic supports (aluminum foams of 40ppi, honeycomb monolith and micromonolith of 350 and 1180cpsi, respectively) have been loaded with a 20%Co-0.5%Re/γ-Al2O3 catalyst by the washcoating method. Layers of different thicknesses have been deposited onto the metallic supports. The catalytic coatings were characterized measuring their textural properties, adhesion and morphology. These structured catalysts have been tested in the Fischer-Tropsch synthesis (FTS) and compared with a microchannel block presenting perpendicular channels for reaction and cooling. The selectivity depends on the type of support used and mainly on the thickness of the layer deposited. In general, the C5+ selectivity decreased at increasing CO conversion for all of the systems (powder, monoliths, foams and microchannels block). On the other hand, the selectivity to methane increased with the thickness of the catalytic layer due to the higher effective H2/CO ratio over the active sites resulting from the higher diffusivity of H2 compared with CO in the liquid products filling the pores. The C5+ selectivity of the microchannels reactor is higher than that of the structured supports and the powder catalyst.Ministerio de Ciencia e Innovación MAT2006-12386-C05, ENE2009-14522-C0

Estudio magnetoestructural y cinético de las transiciones de fase en estado sólido de aleaciones metaestables basadas en Fe

Esta tesis se centra en el análisis de las transformaciones de fase en estado sólido que exhiben ciertas aleaciones metaestables basadas en Fe. Para ello se ha analizado la evolución estructural y magnética que experimentan diferentes sistemas durante las transiciones que presentan, así como su cinética. En primer lugar, se han analizado aleaciones amorfas binarias y tipo FINEMET, utilizadas como precursores para el desarrollo de aleaciones nanocristalinas. La comparación sistemática de los resultados obtenidos a través de diferentes técnicas de caracterización ha permitido analizar tanto el proceso de amorfización mecánica como las fases resultantes del proceso de desvitrificación. Para su caracterización cinética se ha desarrollado un modelo a partir de la teoría clásica de cristalización asumiendo varios procesos simultáneos. Este modelo permite la descripción de los procesos de desvitrificación que dan lugar a varias fases y se ha extendido a un conjunto de múltiples microprocesos para la descripción del proceso de nanocristalización. En segundo lugar, se ha evaluado la estabilidad de la transformación martensítica en sistemas Heusler Ni-Fe-Ga obtenidos por enfriamiento rápido. Aunque ésta técnica de producción permite la obtención de muestras metaestables monofásicas de la fase modulada 14M a temperatura ambiente, la transformación martensítica es especialmente sensible a la temperatura y la presión hidrostática. La alta velocidad de crecimiento de la fase austenita impide que la transformación martensítica sea descrita mediante la teoría clásica de cristalización, mostrándose que realmente responde a un proceso autocatalítico de primer orden. Finalmente, varios factores experimentales que pueden afectar a una correcta caracterización magnética de los sistemas estudiados han sido evaluados a partir de datos experimentales y cálculos numéricos. En particular, el análisis de la respuesta teórica de sistemas heterogéneos ha permitido proporcionar una serie de ecuaciones simples con las que estimar los parámetros de la distribución de temperaturas de transición

Infraestructura de datos espaciales en medio ambiente y acceso a la información ambiental en Andalucía. El canal de la red de información ambiental de Andalucía.

La Consejería de Medio Ambiente de la Junta de Andalucía ha puesto en marcha un sistema para poder cumplir adecuadamente los requisitos derivados de la normativa vigente en dos vertientes que están muy relacionadas: la del acceso a la información ambiental y la de las Infraestructuras de Datos Espaciales. Ambas vertientes, que vienen definidas por sendas Directivas, han condicionado la solución establecida que pasa por la creación mediante el desarrollo normativo adecuado de un instrumento, la Red de Información Ambiental de Andalucía (REDIAM). Esta red se ha dotado de una plataforma en entorno web, el Canal de la Red de Información Ambiental de Andalucía, en la que confluyen elementos constitutivos de una Infraestructura de Datos Espaciales (IDE) con otros de obtención y acceso al dato como es el de de solicitud de información ambiental o la descarga directa, y con elementos de navegación que pretenden facilitar al público en general el acceso a este conjunto de servicios y productos. Puesto en explotación el 29 de enero de 2009, hoy podemos hacer balance del uso que ha registrado en su primer año.The Ministry of Environment of the Junta de Andalucía has launched a system to carry out the requirements under current regulations in two areas which are closely related: access to environmental information and Spatial Data Infrastructures. Both sides, which are defined by EU Directives, have conditioned the solution through the developing an appropriate regulatory instrument, the Environmental Information Network of Andalusia (REDIAM). This network has set up a web-based platform, the Andalusian Environmental Information Network Channel, which combines elements of a Spatial Data Infrastructure (SDI) with other elements of data collection and access like the environmental information request or direct download, and navigation elements that are intended to facilitate the general public access to the package of services and products. Having been put into operation on January 29, 2009, today we can assess the use it has registered in its first year

¿Qué investigación didáctica en el aula de física se publica en España? Una revisión crítica de la última década para el caso de educación secundaria

Se presenta un estudio exploratorio y descriptivo sobre la investigación didáctica publicada en España durante la última década relativa a la enseñanza de la física en educación secundaria. Al centrar la atención en aquellos estudios que analizan algún aspecto del proceso de enseñanza-aprendizaje en el aula, se obtiene que estos constituyen una minoría en el conjunto de la bibliografía consultada. Se encuentra también que la autoría de profesorado de secundaria en los estudios sobre didáctica de la física consultados es relativamente baja. Asimismo, en los estudios predomina un enfoque de la enseñanza de la física orientado por contenidos disciplinares que no sintonizan con los planteamientos basados en el desarrollo de competencias. Todo ello revela cierta distancia entre investigación y práctica en la enseñanza de la física.An explorative and descriptive study about educational research concerning physics teaching in secondary education, published in Spain during the last decade, is presented. When focusing on those studies oriented towards the analysis of some aspects of the teaching/learning processes within classroom, it is found that they constituted a minority in the frame of the consulted literature. It is also found that the number of studies on physics education authored by secondary teachers is relatively low. Likewise, an approach to physics teaching guided by disciplinary contents is predominant in these studies, which is not in tune with those approaches based on the development of competences. All this reveals a certain disconnection between research and practice in physics education

A comparative study of magnetic and electrical properties of BiFeO3 mutiferroic ceramics sintered by electric field assisted-methods: Spark plasma sintering and flash sintering

Please click Additional Files below to see the full abstract

Effect of reactive flash sintering on the magnetic and hyperfine parameters of SrFe12O19 ceramic permanent magnets

Please click Additional Files below to see the full abstract

Mono and bimetallic Cu-Ni structured catalysts for the water gas shift reaction

The water-gas shift (WGS) reaction over structured Cu, Ni, and bimetallic Cu-Ni supported on active carbon (AC) catalysts was investigated. The structured catalysts were prepared in pellets form and applied in the medium range WGS reaction. A good activity in the 180-350 °C temperature range was registered being the bimetallic Cu-Ni:2-1/AC catalyst the best catalyst. The presence of Cu mitigates the methanation activity of Ni favoring the shift process. In addition the active carbon gasification reaction was not observed for the Cu-containing catalyst converting the active carbon in a very convenient support for the WGS reaction. The stability of the bimetallic Cu-Ni:2-1/AC catalyst under continuous operation conditions, as well as its tolerance towards start/stop cycles was also evaluated.Ministerio de Economía y Competitividad ENE2013-47880-C3-2-

Integral field spectroscopy of M1-67. A Wolf-Rayet nebula with LBVN appearance

This work aims to disentangle the morphological, kinematic, and chemical components of the nebula M1-67 to shed light on its process of formation around the central Wolf-Rayet (WR) star WR124. We have carried out integral field spectroscopy observations over two regions of M1-67, covering most of the nebula in the optical range. Maps of electron density, line ratios, and radial velocity were created to perform a detailed analysis of the two-dimensional structure. We studied the physical and chemical properties by means of integrated spectra selected over the whole nebula. Photoionization models were performed to confirm the empirical chemical results theoretically. In addition, we analysed infrared spectroscopic data and the MIPS 24micron image of M1-67 from Spitzer. We find that the ionized gas of M1-67 is condensed in knots aligned in a preferred axis along the NE-SW direction, like a bipolar structure. Both electron density and radial velocity decrease in this direction when moving away from the central star. From the derived electron temperature, Te~8200 K, we have estimated chemical abundances, obtaining that nitrogen appears strongly enriched and oxygen depleted. From the last two results, we infer that this bipolarity is the consequence of an ejection of an evolved stage of WR124 with material processed in the CNO cycle. The infrared study has revealed that the bipolar axis is composed of ionized gas with a low ionization degree that is well mixed with warm dust and of a spherical bubble surrounding the ejection at 24micron. Taking the evolution of a 60 Mo star and the temporal scale of the bipolar ejection into account, we propose that the observed gas was ejected during an eruption in the luminous blue variable. The star has entered the WR phase recently without apparent signs of interaction between WR-winds and interstellar material.Comment: Accepted for publication in section 6 of Astronomy and Astrophysics. The official date of acceptance is 15/03/2013. 17 pages, 14 figures and 8 table