Surface magnetism in ZnO/Co3O4 mixtures

We recently reported the observation of room temperature ferromagnetism in mixtures of ZnO and Co3O4 despite the diamagnetic and antiferromagnetic character of these oxides respectively. Here we present a detailed study on the electronic structure of this material in order to account for this unexpected ferromagnetism. Electrostatic interactions between both oxides lead to a dispersion of Co3O4 particles over the surface of ZnO larger ones. As a consequence, the reduction of Co+3 to Co2+ at the particle surface takes place as evidenced by XAS measurements and optical spectrocopy. This reduction allows to xplain the observed ferromagnetic signal within the well established theories of magnetism.Comment: Accepted in Journal of Applied Physic

Tillage effects on weed seed bank with wheat monoculture and rotational

El banco de semillas de malas hierbas presente en el suelo es una demostración de la existencia de una comunidad de malas hierbas y está vinculado a las fases de crecimiento de un ecosistema. Las prácticas agronómicas pueden ocasionar cambios en el banco de semillas de los suelos agrícolas. Nuestro objetivo fue comparar la influencia del laboreo de conservación (mínimo laboreo y siembra directa) frente al laboreo convencional, sobre la densidad y riqueza específica del banco de semillas persistente de un suelo agrícola, en parcelas con dos sistemas de cultivo: monocultivo y rotación de trigo de invierno. Se tomaron muestras de suelo en parcelas con los tres sistemas de laboreo, a 3 profundidades: 0-7 cm, 7-15 cm y 15-30 cm. Los resultados obtenidos en este estudio mostraron que el efecto acumulativo del laboreo en parcelas con trigo en monocultivo no tuvo efectos en la densidad de semillas, aunque sí en su distribución, cuantificadas mayoritariamente a mayor profundidad (P3). Por otro lado, se observó una clara influencia del laboreo y la profundidad en la densidad y riqueza específica del banco de semillas de tipo persistente del suelo, en las parcelas con rotación de trigo. Nuestros resultados confirman que una variedad de cultivos puede ir asociada a una mayor variedad de especies de malas hierbas presentes en el banco de semillas del suelo.The weed seedbank into the soil is a demonstration of the existence of a weed community and it is linked to ecosystem growth phases. Agronomic practices can cause changes in the seed bank of agricultural soils. Our objective was to compare the influence of conservation tillage (mínimum tillage and direct seeding) with conventional tillage on weed seed density and species richness of persistent seedbank, with two cropping systems: wheat monoculture and wheat rotation. Soil samples were taken in plots with three tillage systems, at 3 depths: P1 (0-7 cm), P2 (7-15cm) and P3 (15-30 cm). The results of this study showed that cumulative effects of tillage systems, in wheat monoculture plots, had no effect on seed density, and the seed species were concentrated in deepest section of soil (P3). On the other hand, we observed a clear influence of tillage and depth on weed density and species richness of the persistent weed seed bank in wheat rotation plots. Our results confirm that a variety of crops could be associated to a variety of weed species present into soil seedbank

Insights into the room temperature magnetism of ZnO/Co3O4 mixtures

The origin of room temperature (RT) ferromagneticlike behavior in ZnO-based diluted magnetic semiconductors is still an unclear topic. The present work concentrates on the appearance of RT magnetic moments in just mixed ZnO/Co3O4 mixtures without thermal treatment. In this study, it is shown that the magnetism seems to be related to surface reduction of the Co3O4 nanoparticles, in which, an antiferromagnetic Co3O4 nanoparticle (core) is surrounded by a CoO-like shell. This singular superficial magnetism has also been found in other mixtures with semiconductors such as TiO2 and insulators such as Al2O3

Maxwellian Neutron Spectrum generation and Stellar Cross-Section measurements: measurement of the 197Au(n,γ) MACS

Maxwellian-averaged cross-sections (MACS) are needed as an input for the models of stellar s- and r-processes nucleosynthesis. MACS can be obtained from activation measurements, irradiating a sample with the neutron field generated by the 7Li(p,n)7Be reaction at 1912 keV proton energy. At this energy, the neutron energy spectrum is close (R2≤0.9) to a Maxwellian one of kT=25 keV. However, it was shown that shaping the energy of the incident proton beam is possible to generate a neutron field with an energy spectrum much closer to a real Maxwellian (R2>0.995), therefore avoiding or minimizing corrections in the MACS calculation. We show a preliminary result of an experiment performed at JRC-IRMM (Geel) to confirm our method. We have measured the MACS30 (kT=30 keV) of the 197Au(n,γ) reaction, at CNA (Seville). We obtained 612 mb, in good agreement with the latest measurements

SPH simulations of thixo-viscoplastic fluid flow past a cylinder

Thixotropic materials are complex fluids that display time-dependent viscosity and/or yield-stress response upon the application of a fixed deformation, while recovering their original structured-state when the deformation is discontinued. Thixotropic effects are presents in many different systems and applications, ranging from food products, such as ketchup, to metals, such as molten aluminum. In this work we present a first attempt to simulate the rheological properties of thixo-viscoplastic flows using a Smoothed Particle Hydrodynamic (SPH) method. The study set up is a 2D flow around a circular cylinder as well as a simple shear flow between parallel plates to validate our numerical results. SPH solutions are compared with simulations performed using the open-source Finite Volume Method solver RheoTool, based on OpenFOAM. The viscoplastic model used in this work is the Papanastasiou model combined with a recently developed microstructural one, in order to include thixotropy. In this thixo-viscoplastic framework, we analyze the flow properties in terms of yield-fronts, streamlines and structure-parameter fields at different Bingham and Thixotropy numbers, through microstructural thixotropic and yield-stress parameters variation. Obtained results show an important novelty: an asymmetry in the thixo-viscoplastic flow around the cylinder

The competitive ability of weed communities in selected crucifer oilseed crops under different water and nitrogen

Durante los años 2012 y 2013, se llevó a cabo un experimento en el centro de la península cuyo objetivo fue el estudio de la flora arvense en 3 especies de “Brassica” (“B. carinata”, “B. juncea” y “B. nigra”). Las malas hierbas se evaluaron con 2 niveles de riego, con y sin aporte de agua, y con tres dosis de fertilización diferentes: 0, 75 y 150 kg N ha-1. El establecimiento del cultivo de las tres especies de “Brassica” varió en función del año. Las escasas lluvias de 2012 redujeron la densidad y biomasa de la flora arvense en comparación con el año 2013 en el que la pluviometría fue mayor. Los resultados sugieren que la especie “B. nigra” no estaba bien adaptada a nuestras condiciones climáticas continentales, mostrando un rendimiento más bajo que el resto de los cultivares. Por otro lado, la infestación de malas hierbas fue menor en todas las parcelas donde se cultivaba “B. carinata”.A field study was undertaken to examine the interaction and relationships between weeds and three “Brassica” species (“B. carinata”, “B. juncea” and “B. nigra”) grown in 2012 and 2013. We evaluated the weed density, fresh and dry biomass of weeds with 2 water regimes: with and without irrigation, and three different doses of fertilization: 0, 75 and 150 kg N ha-1. Crop establishment of “Brassica” species varied significantly each year. Lower rainfall in 2012 led to lower density, fresh and dry biomass of weeds compared to 2013. The results confirmed that “B. nigra” was not well adapted to our continental climatic conditions, and thus the yield was lower than the other cultivars. The lowest weed infestation occurred in plots where “B. carinata” was grown in all cases

A proper generalized decomposition approach for high-order problems

En este artículo se desarrollan dos aproximaciones distintas para la resolución de problemas de alto orden mediante métodos de descomposición propia generalizada (PGD, del inglés Proper Generalized Decomposition ). La primera está basada en el uso de técnicas de colocación y polinomios de Chebyshev, mientras que la segunda se basa en el uso de polinomios de Hermite en el marco de una formulación de Galerkin. Ambas poseen ventajas e inconvenientes, que se analizan en detalle con la ayuda de distintos problemas clásicos de validación.In this paper two different approximations for the solution of high-order problems by proper generalized decompositions (PGD) are developed. The first one is based upon the use of collocation techniques, along with Chebyshev polynomials, while the second employs Hermite polynomials in a Galerkin framework. Both approaches having pros and cons, they are studied with the help of some classical benchmark tests.Peer Reviewe

The beginning of high mountain occupations in the Pyrenees. Human settlements and mobility from 10,500 cal BP to 4500 cal BP

During the last two decades, the archaeological research carried out in the Pyrenees challenged the traditional images of the past in this mountain area. The archaeological sequence of the range goes back and sites like Balma Margineda, treated until recently as an exception, now are seen as part of more global process. Actual data suggest that main valleys of the Pyrenean frequented by humans at the end of the last glacial period, with sites slightly over 1000 o.s.l. After the Younger Dryas, the human presence ascended to alpine and subalpine areas, in accordance with current archaeological data. The Neolisitation process was early in some hillsides, with intense remains of farming and pastoralism in many sites from dated in the second half of the 6th millennia cal BC. Human settlements like Coro Tracito, Els Trocs and El Sardo confirm the full introduction of agrarian activity in the central part of the Pyrenees between 5300 and 4600 cal BC. After 3500/3300 cal BC the indices oh sheepherding rises to alpine areas, with an abrupt increase of known archaeological sites in alpine areas, above the current timberline. This phenomena, as well as the signs of anthropic disturbance of the alpine environment in sedimentary sequences, suggests a more stable and ubiquitous human presence, probably largely associated with the development of mobile herding practices

Effect of Tuned Parameters on a LSA MCQ Answering Model

This paper presents the current state of a work in progress, whose objective is to better understand the effects of factors that significantly influence the performance of Latent Semantic Analysis (LSA). A difficult task, which consists in answering (French) biology Multiple Choice Questions, is used to test the semantic properties of the truncated singular space and to study the relative influence of main parameters. A dedicated software has been designed to fine tune the LSA semantic space for the Multiple Choice Questions task. With optimal parameters, the performances of our simple model are quite surprisingly equal or superior to those of 7th and 8th grades students. This indicates that semantic spaces were quite good despite their low dimensions and the small sizes of training data sets. Besides, we present an original entropy global weighting of answers' terms of each question of the Multiple Choice Questions which was necessary to achieve the model's success.Comment: 9 page

Obtención de jarabes glucosados por hidrólisis enzimática empleando almidón de sorgo CIAPR-132

La presente investigación está encaminada al estudio de la posible sustitución del maíz por el sorgo en la producción de jarabes glucosados para la industria alimenticia, considerando la evaluación de las potencialidades de dicho cereal. En este sentido se realizó un diseño experimental compuesto del tipo 2k, utilizando  el Software Statgraphics Centurion XV en elprocesamiento de los resultados del proceso desarrolladoen el laboratorio. Para ello se analizó la influenciade las variables independientes: concentración deenzima alfa amilasa (X1) en los niveles de 0,06 y 0,16%p/p, la concentración de enzima amiloglucosidasa(AMG) (X2) en los niveles de 0,18 y 0,375 %p/p ytiempo de sacarificación (X3) de 24 y 48 horas sobrelas variables respuestas °Brix y Azúcares ReductoresTotales (ART); además se determinó el rendimiento de cada experimento, obteniéndose los mejores resultados para la mayor concentración de enzima alfaamilasa, concentración de enzima AMG y tiempo de sacarificación en los menores valores. Los mejores resultados se obtuvieron para el Brix de 52,22 y ARTde 68,76%