Materias primas de la Luna para emprender la colonización espacial

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Determinación de sulfuros de hierro en pizarras para cubiertas del noroeste de España

The most important production of roofing slates in the world is quarried from the Ordovician formations of the Truchas Syncline, which have the largest amount of working quarries. Roofing slates, sometimes, have crystallized iron sulphides such as pyrite, pyrrhotite and other minerals. These iron sulphides oxidise and stain the tiles when are exposed to atmospheric conditions, so much oxidized how much more inclined is the roof. Galician quarrymen distinguish between harmless pyrite (i.e., resistant cubes of pyrite) and damaging pyrite (i.e., other alterable metallic minerals such as pyrrhotite, chalcopyrite, marcasite and arsenopyirite). An improved identification method is proposed using both methods (a) chemical element ratios of samples under electron microprobes and (b) quantitative determination of the iron sulphides in the slate measuring the oxidized areas by digital camera. The analysed Fe/S ratios, in an XY plot, of seventy metallic samples, define three separated zones: pyrite, pyrrhotite and iron oxi-hydroxides. Quantitative determination of iron sulphides in the slate tile were performed by sinking the tile horizontally for six hours in oxygen peroxide (3% diluted) and capturing the oxidation areas with a magnetic camera and analysing the bitmap images with Sigma-Scan 5 software. The proposed method is faster than the Spanish UNE norm (UNE-EN- 12326-2 Sept.2000), which requires thermal strike cycles for a month. The necessary use of heavy analytical equipment such as electron microprobes can be facilitated by installing it in the Slate Technological Centre of Sobradelo de Valdeorras (Orense) or by using a simple optical stereoscopic zoom microscope to classify the iron minerals.Las formaciones ordovícicas del Sinclinal de Duchas concentran la mayor producción mundial de pizarra para cubiertas y el mayor número de canteras en producción. Las pizarras para cubiertas muchas veces contienen sulfuros de hierro cristalizados en forma de pirita, pirrotina y oíros minerales. Bajo condiciones atmosféricas, este tipo de sulfuros se oxida en las superficies y mancha las placas colocadas, tanto más cuanto más inclinado sea el tejado. Los productores de pizarra distinguen bien entre piritas inofensivas (es decir, cubos de pirita resistentes) y piritas oxidables (es decir, otros minerales metálicos rápidamente oxidables como pirrotina, calcopirita, marcasita y arsenopirita). Se propone una combinación de dos métodos: (a) una rutina de identificación más objetiva utilizando proporciones de elementos analizados por microsonda electrónica y (b) una determinación cuantitativa de áreas de sulfuros oxidados en planos de exfoliación (001) de pizarra mediante registro fotográfico digital. Las relaciones obtenidas Fe/S de setenta muestras metálicas se representan en un gráfico XY y se definen bien tres zonas diferentes: pirita, pirrotina y oxi-hidróxidos de hierro. La determinación cuantitativa de sulfuros de hierro en la placa de pizarra fue llevada a cabo sumergiéndola seis horas horizontalmente en agua oxigenada y después registrando las oxidaciones con una cámara fotográfica digital y analizando los resultados con programa comercial de análisis de imagen (SigmaScan v.5). El método propuesto es mejor y más rápido que la norma Española UNE vigente (UNE-EN-12326-2), que supone varios ciclos de choques térmicos durante un mes. El inconveniente del uso obligado de una microsonda electrónica podría paliarse instalando una en el Centro Tecnológico de la Pizarra de Sobradelo de Valdeorras (Orense) o utilizando una lupa binocular moderna para reconocer los minerales de hierro

Protocol for assessing the effectiveness of protective coatings for roofing slate

España es líder mundial en producción de pizarras de techar; la producción supera las 600.000 toneladas de pizarra de gran calidad, suponiendo más de 300 millones de euros. La aplicación de la pizarra con productos protectores permite comercializar placas más oxidables reduciendo escombreras y problemas ambientales. El presente protocolo sirve para evaluar estos nuevos productos protectores que empiezan a utilizarse en el sector pizarrero. Se propone una combinación de tres ensayos tecnológicos junto con un cuestionario visual para otorgar índices de calidad. Cada ensayo está orientado para clarificar una propiedad importante en el uso de la pizarra de techar: (i) Ciclo térmico para determinar el grado de oxidación de los sulfuros de hierro; (ii) Exposición al gas SO2 para conocer su comportamiento en ambientes urbanos ácidos; (iii) Exposición a la niebla salina y rayos UV para evaluar la eficacia de la capa protectora frente a la corrosión salina y la radiación solaroduction, quarriying more than 600,000 tons of slate of great quality and generating around 300 euros million in sales each year. However, an enormous quantity of slate plates is considered as a low quality product or discarded every year as waste. The application of protective products on roofing slate tiles helps to commercialise slate with higher oxidation rates, reducing wastes and environmental problems. The present protocol serves to evaluate the new protective products that are now used by slate producers. A combination of three technological tests is proposed here, along with a visual questionnaire to grant quality indices. Each test is oriented to clarify critical properties for the future use of the roofing slate, as follows: (i) Thermal cycles were used to determine the oxidation rate of iron sulphides; (ii) Slate behaviour in acid urban atmospheres was interpreted by exposition of slate tiles to SO2 gas; (iii) Effectiveness of the protective layer under saline corrosion and solar radiation was obtained by exposition to saline fog and UV-irradiationFinancial support was provided by the project “Development of a new methodology to protect the roofing slate from oxidation” sponsored by Dirección Xeral de I+D de la Consellería de Industria de la Xunta de Galicia. Thanks are also due to projects S-0505/MAT/000094 of author J.G.Guinea and CGL2004-03564/BTES

Resolución de enigmas geológicos e históricos utilizando técnicas gemológicas avanzadas: Caso del ópalo noble de Franco Dávila (1772)

The large precious opal weighting 33 grams fitted in a silver jewel and exposed to visitors at the Museo Nacional de Ciencias Naturales (MNCN) is well documented in: (i) its own mounting (1772), (ii) at the 775 document of the Archive of the MNCN and (iii) the 395 specimen described in the of Pedro Franco Dávila catalogue. The X-ray diffractogram (XRD) performed onto the opal block is very similar to other opals of volcanic origin containing varied amounts of cristobalite, tridymite and amorphous silica. The Raman spectrum shows a band peaked at 242, 343 and 416 cm-1 associated with O-Si-O stretching groups; other spectral band peaked at 780 and 819 cm-1 corresponding to vibration of symmetrical O-Si-O rings of 3 and 4 link members, plus other minor bands. The Raman spectrum is also very similar to those observed in Mexican opals of volcanic origin containing an spectral band of stretching nodes v1 (OH) at 3233, 3393, 3511, 3628 cm-1 related to OH groups with hydrogen bonds of isolated silanol groups. The interferometric confocal dual microscope 3D (MCI3D), which is a nondestructive facility of high resolution and LED technology reveals the geometry of graver tools on the silver jewel and the computed tomography X-ray highlights the opal cutting as a squared princess type and silver chloride infillings of a crack probably caused by a shock on a corner. Under the scanning electron microscope we observed barite, sealed veins of silica rich in Mn and opal with high contents of Al and K which, along with the historical data, the piece can be attributed to the historical site of opals hosted in Slovakia andesite rocks, this data explains the optical light behavior in the cabochon. The silver jewel has large amounts of Hg and AgCl indicating amalgam method. In addition the natural AgS2 phases probably come from Nueva España (year 1772) in full production of silver in such time. The association of new analytical non-destructive techniques combines the preservation of samples together with significant analytical data allowing us to deduce genetic mineral processes, provenances and manufacturing techniques of materials. These facilities allow the characterization, interpretation, conservation and enhancement of cultural and archaeological heritage.Un gran ópalo noble de 33 gramos engastado en montura de plata dorada está expuesto al público en el Museo Nacional de Ciencias Naturales (MNCN). Esta pieza histórica está documentada en su propia montura (año 1772), en el legajo 775 del Archivo del Museo y en la muestra 395 del Catálogo de muestras de Pedro Franco Dávila. Su patrón de difracción de rayos X (DRX) es muy parecido al de otros ópalos de origen volcánico y contiene cantidades variables de cristobalita, tridimita y sílice amorfa. El espectro Raman muestra una banda con picos a 242, 343 y 416 cm-1 asociados a deformaciones O-Si-O; otra con picos a 780 y 819 cm-1 de vibraciones de tensión simétricas O-Si-O de anillos de 3 y 4 eslabones y otras menores. El espectro Raman es similar a los de ópalos mexicanos de origen volcánico y muestra una banda con nodos de tensión v1 (OH) a 3233, 3393, 3511, 3628 cm-1 relacionados con grupos OH con enlaces de hidrógeno con grupos silanoles aislados. Mediante microscopía dual confocal interferométrica 3D (MCI3D), que es una técnica no destructiva de alta resolución y tecnología LED, se desvela la geometría de grabado del buril sobre la montura mientras que la tomografía computerizada de rayos X destaca la talla cuadrada de tipo carre-princesa y los rellenos de AgCl de una fisura. Bajo microscopia electrónica de barrido ambiental (MEBA) se han observado baritinas, filoncillos de sílice enriquecida en Mn y elevados contenidos de Al y K. Estos datos, junto con la información histórica sugieren que la pieza procede de los yacimientos históricos de ópalos encajados en andesitas de Eslovaquia y explican la compleja óptica del cabujón. El marco de Ag tiene Hg y AgCl que indican su extracción por amalgama; además tiene Ag2S que podría provenir de Nueva España, entonces (año 1772) en plena producción de plata. La asociación de varias técnicas analíticas no-destructivas preserva la integridad de esta pieza histórica aportando datos analíticos significativos que permiten deducir procesos genéticos de minerales, procedencias y técnicas de manufactura de materiales. Todo ello facilita la caracterización, interpretación, conservación y valorización del patrimonio cultural y arqueológico

Solving spin quantum-master equations with matrix continued-fraction methods: application to superparamagnets

We implement continued-fraction techniques to solve exactly quantum master equations for a spin with arbitrary S coupled to a (bosonic) thermal bath. The full spin density matrix is obtained, so that along with relaxation and thermoactivation, coherent dynamics is included (precession, tunnel, etc.). The method is applied to study isotropic spins and spins in a bistable anisotropy potential (superparamagnets). We present examples of static response, the dynamical susceptibility including the contribution of the different relaxation modes, and of spin resonance in transverse fields.Comment: Resubmitted to J. Phys. A: Math. Gen. Some rewriting here and there. Discussion on positivity in App.D3 at request of one refere

Phase diagram and influence of defects in the double perovskites

The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo O_6 is analyzed, with and without disorder due to antisites. In addition to an homogeneous half metallic ferrimagnetic phase in the absence of doping and disorder, we find antiferromagnetic phases at large dopings, and other ferrimagnetic phases with lower saturation magnetization, in the presence of disorder.Comment: 4 pages, 3 postscript figures, some errata correcte

Non Equilibrium Electronic Distribution in Single Electron Devices

The electronic distribution in devices with sufficiently small diemnsions may not be in thermal equilibrium with their surroundings. Systems where the occupancies of electronic states are solely determined by tunneling processes are analyzed. It is shown that the effective temperature of the device may be higher, or lower, than that of its environment, depending on the applied voltage and the energy dependence of the tunneling rates. The I-V characteristics become asymmetric. Comparison with recent experiments is made

Discontinuous transitions in double exchange materials

It is shown that the double exchange Hamiltonian, with weak antiferromagnetic interactions, has a rich variety of first order transitions between phases with different electronic densities and/or magnetizations. For band fillings in the range $0.3 \le x \le 0.5$, and at finite temperatures, a discontinuous transition between phases with similar electronic densities but different magnetizations takes place. This sharp transition, which is not suppressed by electrostatic effects, and survives in the presence of an applied field, is consistent with the phenomenology of the doped manganites near the transition temperature.Comment: three more variational ansatzs considere

Expression of spidroin proteins in the silk glands of golden orb-weaver spiders.

The expression of spidroins in the major ampullate, minor ampullate, flagelliform, and tubuliform silk glands of Trichonephila clavipes spiders was analyzed using proteomics analysis techniques. Spidroin peptides were identified and assigned to different gene products based on sequence concurrence when compared with the whole genome of the spider. It was found that only a relatively low proportion of the spidroin genes are expressed as proteins in any of the studied glands. In addition, the expression of spidroin genes in different glands presents a wide range of patterns, with some spidroins being found in a single gland exclusively, while others appear in the content of several glands. The combination of precise genomics, proteomics, microstructural, and mechanical data provides new insights both on the design principles of these materials and how these principles might be translated for the production of high-performance bioinspired artificial fibers.Ministerio de Innovación, Cultura y Deportes(Spain), Grant/Award Numbers: PGC2018‐097019‐B‐I00, PID2020‐116403RB‐I00;Instituto de Salud Carlos III,Grant/Award Number: CB16/11/00277;Comunidad de Madrid, Grant/Award Numbers:NEUROCENTRO‐B2017/BMD‐3760,Tec4Bio‐CM/P2018/NMT‐4443 Spiders were reared by Oscar Campos (Reptilmadrid S.L., Spain). The artwork was made by Carmen Calvo. This study was funded by Comunidad de Madrid (Spain) through grants NEUROCENTRO‐ B2017/BMD‐3760 and Tec4Bio‐CM/P2018/NMT‐4443. This study was also supported by Spanish Ministerio de Innovación, Cultura y Deportes (PGC2018‐097019‐B‐I00 and PID2020‐116403RB‐I00), and Instituto de Salud Carlos III (CIBER de Enfermedades Cardiovasculares (CB16/11/00277); Plataforma de Recursos Biomoleculares PRB3 (ProteoRed; PT17/0019/0003)). The CNIC is supported by the Instituto de Salud Carlos III (ISCIII), the Ministerio de Ciencia e Innovación and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV‐2015‐0505).S

Mechanical characterization of the human thoracic descending aorta Experiments and modelling

This work presents experiments and modelling aimed at characterising the passive mechanical behaviour of the human thoracic descending aorta. To this end, uniaxial tension and pressurisation tests on healthy samples corresponding to newborn, young and adult arteries are performed. Then, the tensile measurements are used to calibrate the material parameters of the Holzapfel constitutive model. This model is found to adequately adjust the material behaviour in a wide deformation range; in particular, it captures the progressive stiffness increase and the anisotropy due to the stretching of the collagen fibres. Finally, the assessment of these material parameters in the modelling of the pressurisation test is addressed. The implication of this study is the possibility to predict the mechanical response of the human thoracic descending aorta under generalised loading states like those that can occur in physiological conditions and/or in medical device application