Modificaciones producidas por tratamiento térmico en las propiedades fisicoquímicas de los silicatos de la serie isomorfa montmorillonita-beidelita. I.

68 páginas, 21 figuras, 29 tablas, 64 referencias.[ES]: Continuando investigaciones de uno de nosotros publicadas en trabajos anteriores, se ha realizado un extenso estudio por métodos químicos, fisicoquímicos y difracción de rayos X, acerca de la influencia de la naturaleza del material, cationes de cambio y temperatura de tratamiento sobre la deshidratación reversible e irreversible de la montmorillonita. Las muestras de montmorillonita saturadas con cationes de campo electrostático intenso y gran capacidad de polarización (Li+, Mg++, Zn++, Ce+++. H+) se deshidratan irreversiblemente por calentamiento a temperaturas inferiores a las de eliminación de los OH reticulares. Las muestras saturadas con cationes de campo electrostático débil (Ba++, K+, Rb+) se deshidratan reversiblcmente en las mismas condiciones de tratamiento). La deshidratación irreversible de las muestras de la primera clase citada se debe a la fijación de las láminas por los cationes de cambio deshidratados, alcanzándose una situación estructural semejante a la de las micas. Paralelamente estas muestras experimentan una fuerte reducción en el número de cationes cambiables y en la capacidad de retención de etilenglicol. Se estudia la dependencia de estas reducciones con la temperatura, grado de deshidratación, clase de cationes cambiables y otros factores. Las muestras saturadas con cationes de la segunda clase citada no sufren por el indicado tratamiento reducción alguna sensible en su capacidad de hidratación, número de cationes cambiables ni retención de etilenglicol. La retención de etilenglicol por la montmorillonita depende, como su capacidad de hidratación, de la naturaleza de los cationes de cambio. Las muestras saturadas con los cationes Mg++, Zn++, Ba++, Ce+++, Li+, H+, forman solvatos conteniendo dos capas monomoleculares de glicol entre las láminas del silicato, con un espaciado (001) de 17 A. Las muestras saturadas con los cationes K + o Rb+ dan solvatos conteniendo una sola capa monomolecular de glicol entre las láminas, con un espaciado (001) de 13,2 A. La totalidad de los diagramas de rayos X de las muestras investigadas serán discutidos en otra publicación independiente.[EN]: As a continuation to investigations published in some previous works a extensive study by chemical, physicochemical and X-Ray difractions methods about reversible and irreversible dehydration of montmorillonite, has been carried out. The influence of matherial, exchangeable calions and temperature on the irreversible dehydration and other properties of the montmorillonite have been considered. Samples of montmorillonite saturated with cations having an intense electrostatic field (Li+, Mg++, Zn++, Ce+++, H+) show irreversible dehydration by thermal treatment at temperatures below to those producing the loss of the reticular OH. On the contrary, samples saturated with voluminous cations having a small electrostatic field (Ba++, K+, Rb+, etc.) show reversible dehydration by the same treatment. The relationship of the exchangeable cations to temperature and intensity of the irreversible dehydration, has been studied. Irreversible dehydration produces the fixation of the sheets by interaction with the partially dehydrated exchangeable cations. By this mean, a structural situation like as the micas is reached. Irreversible dehydration of the above mentioned samples reduces strongly the amount of exchangeable cations and the ethylene glicol retention capacity. The relationship of these reductions to temperature of thermal treatment, dehydration grade of the samples, king of exchangeable cations and other factors, are briefly discussed. Samples showing reversible dehydration reduce neither the amount of exchangeable cations nor the ethylene glicol retention. Ethylene glicol retention by montmorillonite depends -as the hydration capacity- on the kind of the exchangeable cations. Adsorption complexes formed by Mg++, Zn++, Ba++, Ce+++, Li+, or H+ montmorillonites, contain two monomolecular layers of ethylene glicol between the structural sheets of the clay mineral. Complexes formed by K+ or Rb+ montmorillonites, contain one monomolecular layer of ethylene glicol belween the structural sheets. These conclusions are confirmed by X-Ray and ethylene glicol retention dates. X-Ray diffractions diagrams of all thermal treated and original samples will be considered in another work.Peer reviewe

Room temperature ferromagnetic-like behavior in Mn-implanted and post-annealed InAs layers deposited by Molecular Beam Epitaxy

We report on the magnetic and structural properties of Ar and Mn implanted InAs epitaxial films grown on GaAs (100) by Molecular Beam Epitaxy (MBE) and the effect of Rapid Thermal Annealing (RTA) for 30 seconds at 750C. Channeling Particle Induced X- ray Emission (PIXE) experiments reveal that after Mn implantation almost all Mn atoms are subsbtitutional in the In-site of the InAs lattice, like in a diluted magnetic semiconductor (DMS). All of these samples show diamagnetic behavior. But, after RTA treatment the Mn-InAs films exhibit room-temperature magnetism. According to PIXE measurements the Mn atoms are no longer substitutional. When the same set of experiments were performed with As as implantation ion all of the layers present diamagnetism without exception. This indicates that the appearance of room-temperature ferromagnetic-like behavior in the Mn-InAs-RTA layer is not related to lattice disorder produce during implantation, but to a Mn reaction produced after a short thermal treatment. X-ray diffraction patterns (XRD) and Rutherford Back Scattering (RBS) measurements evidence the segregation of an oxygen deficient-MnO2 phase (nominally MnO1.94) in the Mn-InAs-RTA epitaxial layers which might be on the origin of room temperature ferromagnetic-like response observed.Comment: 16 pages, 5 figures. Acepted in J. Appl. Phy

La trama secundaria de “Casa con dos puertas, mala es de guardar”

Este artículo revisa la relación entre la trama principal y la línea argumental secundaria en la comedia calderoniana “Casa con dos puertas, mala es de guardar”. Se centra en la imbricación de la historia central, los amores de los protagonistas, Marcela y Lisardo, y la relación sentimental de Laura y Félix, que se da en un segundo plano. El autor llega a la conclusión de que la línea de acción secundaria tiene una estructura dramática más compleja que la primera. Destaca así el desarrollo más dinámico de esta trama, la presencia de más elementos de ambigüedad y contradicción en el comportamiento de los personajes, la mayor complejidad del enredo producido por los celos, y, por último, un mayor número de expectativas dramáticas. González García vincula la riqueza constructiva de la pieza, en la que lo secundario pasa a ocupar el primer plano, con uno de los rasgos centrales de la estética manierista, el descentramiento del motivo principal

Strategies to introduce gender perspective in Engineering studies: a proposal based on selfdiagnosis.

Gender inequality in STEM careers is a global problem and avoid bias in education can be a solution. This paper presents a framework for inclusion of gender perspective in engineering courses. The methodology followed in its design was divided into two phases: the developed of different educational innovation projects and a co-creation workshop. Several instruments have been created and validated, such as questionnaires, canvas model and rubrics. The framework includes elements such as the self-diagnosis and redefinition of curriculum, contents and practices, specific learning outcomes and gender and sex balanced methods and learning environments for equity

Wide therapeutic time window for nimesulide neuroprotection in a model of transient focal cerebral ischemia in the rat

Results from several studies indicate that cyclooxygenase-2 (COX-2) is involved ischemic brain injury. The purpose of this study was to evaluate the neuroprotective effects of the selective COX-2 inhibitor nimesulide on cerebral infarction and neurological deficits in a standardized model of transient focal cerebral ischemia in rats. Three doses of nimesulide (3, 6 and 12 mg/kg; i.p.) or vehicle were administered immediately after stroke and additional doses were given at 6, 12, 24, 36 and 48 h after ischemia. In other set of experiments, the effect of nimesulide was studied in a situation in which its first administration was delayed for 3 to 24 h after ischemia. Total, cortical and subcortical infarct volumes and functional outcome (assessed by neurological deficit score and rotarod performance) were determined 3 days after ischemia. The effect of nimesulide on prostaglandin E2 (PGE2) levels in the injured brain was also investigated. Nimesulide dose-dependently reduced infarct volume and improved functional recovery when compared to vehicle. Of interest is the finding that neuroprotection conferred by nimesulide (reduction of infarct size and neurological deficits and improvement of rotarod performance) was also observed when treatment was delayed until 24 h after ischemia. Further, administration of nimesulide in a delayed treatment paradigm completely abolished PGE2 accumulation in the postischemic brain, suggesting that COX-2 inhibition is a promising therapeutic strategy for cerebral ischemia to target the late-occurring inflammatory events which amplify initial damage

Interaction Effects on the Magneto-optical Response of Magnetoplasmonic Dimers

The effect that dipole-dipole interactions have on the magneto-optical (MO) properties of magnetoplasmonic dimers is theoretically studied. The specific plasmonic versus magnetoplasmonic nature of the dimer's metallic components and their specific location within the dimer plays a crucial role on the determination of these properties. We find that it is possible to generate an induced MO activity in a purely plasmonic component, even larger than that of the MO one, therefore dominating the overall MO spectral dependence of the system. Adequate stacking of these components may allow obtaining, for specific spectral regions, larger MO activities in systems with reduced amount of MO metal and therefore with lower optical losses. Theoretical results are contrasted and confirmed with experiments for selected structures

S wave velocity structure below central Mexico using high-resolution surface wave tomography

Shear wave velocity of the crust below central Mexico is estimated using surface wave dispersion measurements from regional earthquakes recorded on a dense, 500 km long linear seismic network. Vertical components of regional records from 90 well-located earthquakes were used to compute Rayleigh-wave group-velocity dispersion curves. A tomographic inversion, with high resolution in a zone close to the array, obtained for periods between 5 and 50 s reveals significant differences relative to a reference model, especially at larger periods (>30 s). A 2-D S wave velocity model is obtained from the inversion of local dispersion curves that were reconstructed from the tomographic solutions. The results show large differences, especially in the lower crust, among back-arc, volcanic arc, and fore-arc regions; they also show a well-resolved low-velocity zone just below the active part of the Trans Mexican Volcanic Belt (TMVB) suggesting the presence of a mantle wedge. Low densities in the back arc, inferred from the low shear wave velocities, can provide isostatic support for the TMVB

A new approach for assessing natural patterns of flow variability and hydrological alterations: The case of the Spanish rivers

Ensuring water is available for human use usually requires dams and reservoirs that severely affect river ecosystems. Hydrological alteration by river damming represents one of the most prominent human impacts on freshwater ecosystems. This paper presents a methodological approach to assessing the natural patterns of flow variability and hydrological alterations in Mediterranean rivers. The methodology first defines the admissible range of flow variability under a natural flow regime. Then, the methodology measures the environmental impact of flow regulation according to the inferred hydrological alteration and classifies rivers into homogeneous groups according to the magnitude, frequency, duration and seasonality of the impacts. This paper applies the proposed methodology to thirty-three river segments below large reservoirs located in the three largest Spanish watersheds (Duero, Ebro and Tajo). For each segment, this study evaluates the general impoundment characteristics and geographical contexts and calculates the flow impacts and the divergence between the circulating flows and the reference area of admissible flow variability on a daily basis for the period 2000 2010. This assessment of dam regulation impacts provides a reference to plan measures for mitigating these impacts. The advantages of this flow regulation impact analysis over other analyses are discussed in terms of the implementation of environmental water costs as suggested by the European Water Framework Directive. This approach expands the current understanding of water environmental costs and represents a practical management tool for decreasing the environmental impacts of flow regulation and for increasing water-use efficiency. (c) 2018 Elsevier Lt