Determinación espectroquímica de impurezas en plata

Con el fin de verificar el grado de pureza de la plata empleada principalmente para la fabricación de fusibles, se ha aplicado el análisis espectroquímico por su gran sensibilidad y rapidez. Debido a la gran variedad en el diámetro de los alambres y ante la imposibilidad de disponer de los patrones standard para cada medida, fue necesario disolver la muestra y realizar el análisis sobre las sales (nitratos). Las muestras standard se prepararon por el mismo procedimiento, empleando sustancias de pureza espectroscópica (Johnson Matthey). Esta técnica de análisis nos permite determinar once elementos (Cu, Cd, Pb, Ni, Sn, Al, Zn, Pt, Pd, Ir, Au). Se utilizo un espectrógrafo Z-3 (Jobin-Yvon), fuente de excitación G.M.60 (de Durr) y densitómetro 21-051 (Jarrell-Ash).Because of its great sensitivity and time-saving characteristics spectrochemical analysis has "been applied to the purity control of silver to he used mainly in fuse manufacture. As wires differ widely in their diameters and it is almost impossible to obtain standards por each size, it was necessary to disolve the sample and analize the resulting salts (nitrates). Standard samples were prepared making use of the procedure on spectroscopically pure materials (Johnson Matthey). This analytical technique allows the determination of eleven elements, i.e. Cu, Cd, Pb, Ni, Sn, Al, Zn, Pt, Pd, Ir, Au. Instrumentation used includes Jobin-Yvon Z-3 spectrograph, Durr G.M.60 excitation source and Jarrell-Ash,model 21-051 densitometer

Estudios estadísticos de elementos traza en el basamento Igneo-Metamórfico de la Sierra de Quilmes

El conocimiento de los parámetros estadísticos de los elementos traza en rocas genéticamente asociadas es de fundamental importancia. En el campo de las rocas granitoídes, por ejemplo, el estudio de sus distribuciones es particularmente útil. En una secuencia de rocas graníticas la diferencia en composición de elementos mayoritarios entre las diferentes fases, es mínima; en cambio los tenores de elementos traza suelen diferir criticamente. En general, la variación relativa de elementos traza es mucho mayor que la de los elementos mayoritarios. Como consecuencia de ello, el grado de diferenciación y la acidez son mucho mejor indicados por la variación de aquéllos. A este respecto elementos como rubidio, estroncio, bario, cobalto y níquel, algunas de cuyas distribuciones se analizan en este trabajo, han resultado particularmente útiles como indicadores de diferenciación y del orden de intrusión de las diferentes fases que pueden componer un cuerpo complejo

Composición normativa y clasificación de rocas pelíticas

A normative classification oi pelitic rocks based on the proportion of major components (SiO" AI,O" Fe,O" MgO, Cao, Na,O, K,O, P,O. and CO,) is presented in this paper. The proposecl procedure includes two models of norm calculation: smectite present and smectite absent. In hoth models the content of K,O can he lIsed to determina te orthoclase  illite. The pelitic rack classificationis based upon the relative contentsin normative clay minerals,quartz and feldspars. Nine compositionalrock-types,which are clearlydefined in a triangulardiagramwere recognized. The importance of chemical compositionstudies in the interpretation of pelitic rocksis also discussed.Se da a conocer un método normativo de clasificación de rocas pelíticas basado en su composición química mayoritaria (SiO" ALO" Fe-..O",MgO, CaO, Na,O, K:O, P,O. y CO,). El procedimiento propuesto presenta dos modelos de norma, con o sin esmectita. En ambos modelos los contenjclos de K,O pueden ser asignados a Oltosa o a illita. La clasificación de las pelitas está basada en las proporciones normativas de argilominerales, cuarzo y fesdespatos. En ella se reconocen nueve variedades composicionales, las que se pueden representar en un diagrama triangular. Se discute el valor de los estudios qlÚmicos composicionales en la interpret'1ción genética de sucesiones y rocas pelíticas

Caracterización probabilística de vidrio mediante diferentes tipos de ensayos

El vidrio no puede ser tratado como un material estructural convencional desde el punto de vista de la resistencia mecánica. Su naturaleza, como material frágil, junto con la inevitable presencia de microfisuras en su superficie y las consecuencias de accidentes por posibles fallos, exigen métodos rigurosos que garanticen un cálculo seguro de los elementos estructurales de vidrio, cuya resistencia a rotura depende en gran medida del tamaño del elemento y del tipo de carga a la que está sometido. Por lo tanto, su cálculo debe basarse en conceptos probabilísticos y en criterios de mecánica de la fractura, en sustitución de un cálculo convencional de vidrio según tablas deducidas de programas experimentales y posterior aplicación del concepto de tensiones admisibles. Con el fin de analizar y comparar las características mecánicas de vidrios templados, termoendurecidos y recocidos, se realizó un amplio programa experimental de ensayos de flexión a cuatro puntos y de anillos concéntricos de pequeña superficie, seguido de un ajuste de los resultados mediante una función de distribución triparamétrica de Weibull. Glass cannot be handled as a conventional structural material from the point of view of the mechanical strength. Its nature as brittle material, together with the inevitable presence of micro-cracks on its surface and the consequences of eventual failures, demand rigorous methods to achieve a safe design for glass elements, whose stress resistance is very much dependent on the integrity of its surface, element size and loading pattern. Thus, its design must rely on probabilistic concepts and fracture mechanics criteria, substitutive of the conventional glass design based on charts derived from experimental programs and subsequent application of the admissible stress concept. In order to analyze and compare the strength characteristics of tempered, heat-strengthened and annealed glass, a large experimental programme based on four-point bending and coaxial double ring tests was performed and the results were fitted using a three-parameter Weibull cumulative distribution function

Ageing of two 5kW PV arrays at the IES-UPM after 8 years of operation

This work analyses the degradation of two 5 kW PV arrays which are located on the roof of the Campus Sur of the Universidad Politécnica de Madrid. These systems were installed in March 2013 and they have been continuously monitored while they have been injecting power into the grid, storing at the same time its DC power and the operation conditions (effective irradiance and cell temperature). These variables allow to calculate their power at Standard Test Conditions over time and, consequently, the degradation rate for each PV array in these 8 years of operation. The linear degradations obtained are similar to the ones presented by other authors, but we have found that there is not apparent degradation in the first years of operation. Besides, it seems that shading could increase the degradation rates. These figures and phenomena can be useful for a better understanding of the actual behavior of PV systems in order to obtain more accurate energy predictions.This work has received funds from the European Union’s Horizon2020 research and innovation programme under Grant Agreement 787289. This work is part of the Project MADRID-PV2 (P2018/EMT-4308) funded by the Comunidad de Madrid with the support from FEDER Funds

A unified approach for a posteriori high-order curved mesh generation using solid mechanics

The paper presents a unified approach for the a posteriori generation of arbitrary high-order curvilinear meshes via a solid mechanics analogy. The approach encompasses a variety of methodologies, ranging from the popular incremental linear elastic approach to very sophisticated non-linear elasticity. In addition, an intermediate consistent incrementally linearised approach is also presented and applied for the first time in this context. Utilising a consistent derivation from energy principles, a theoretical comparison of the various approaches is presented which enables a detailed discussion regarding the material characterisation (calibration) employed for the different solid mechanics formulations. Five independent quality measures are proposed and their relations with existing quality indicators, used in the context of a posteriori mesh generation, are discussed. Finally, a comprehensive range of numerical examples, both in two and three dimensions, including challenging geometries of interest to the solids, fluids and electromagnetics communities, are shown in order to illustrate and thoroughly compare the performance of the different methodologies. This comparison considers the influence of material parameters and number of load increments on the quality of the generated high-order mesh, overall computational cost and, crucially, the approximation properties of the resulting mesh when considering an isoparametric finite element formulation

Centrally Administered Pertussis Toxin Inhibits Microglia Migration to the Spinal Cord and Prevents Dissemination of Disease in an EAE Mouse Model

Background: Experimental autoimmune encephalomyelitis (EAE) models are important vehicles for studying the effect of infectious elements such as Pertussis toxin (PTx) on disease processes related to acute demyelinating encephalomyelitis (ADEM) or multiple sclerosis (MS). PTx has pleotropic effects on the immune system. This study was designed to investigate the effects of PTx administered intracerebroventricularly (icv) in preventing downstream immune cell infiltration and demyelination of the spinal cord. Methods and Findings: EAE was induced in C57BL/6 mice with MOG35–55. PTx icv at seven days post MOG immunization resulted in mitigation of clinical motor symptoms, minimal T cell infiltration, and the marked absence of axonal loss and demyelination of the spinal cord. Integrity of the blood brain barrier was compromised in the brain whereas spinal cord BBB integrity remained intact. PTx icv markedly increased microglia numbers in the brain preventing their migration to the spinal cord. An in vitro transwell study demonstrated that PTx inhibited migration of microglia. Conclusion: Centrally administered PTx abrogated migration of microglia in EAE mice, limiting the inflammatory cytokine milieu to the brain and prevented dissemination of demyelination. The effects of PTx icv warrants further investigation and provides an attractive template for further study regarding the pleotropic effects of infectious elements such as PTx in th

Spin transport and spin torque in antiferromagnetic devices

Ferromagnets are key materials for sensing and memory applications. In contrast, antiferromagnets which represent the more common form of magnetically ordered materials, have found less practical application beyond their use for establishing reference magnetic orientations via exchange bias. This might change in the future due to the recent progress in materials research and discoveries of antiferromagnetic spintronic phenomena suitable for device applications. Experimental demonstration of the electrical switching and detection of the Néel order open a route towards memory devices based on antiferromagnets. Apart from the radiation and magnetic-field hardness, memory cells fabricated from antiferromagnets can be inherently multilevel, which could be used for neuromorphic computing. Switching speeds attainable in antiferromagnets far exceed those of ferromagnetic and semiconductor memory technologies. Here we review the recent progress in electronic spin-transport and spin-torque phenomena in antiferromagnets that are dominantly of the relativistic quantum mechanical origin. We discuss their utility in pure antiferromagnetic or hybrid ferromagnetic/antiferromagnetic memory devices