Long-lived protoplanetary disks in multiple systems: the VLA view of HD 98800

The conditions and evolution of protoplanetary disks in multiple systems can be considerably different from those around single stars, which may have important consequences for planet formation. We present Very Large Array (VLA) 8.8 mm (34 GHz) and 5 cm (6 GHz) observations of the quadruple system HD 98800, which consists of two spectroscopic binary systems (Aa-Ab, Ba-Bb). The Ba-Bb pair is surrounded by a circumbinary disk, usually assumed to be a debris disk given its $\sim$10 Myr age and lack of near infrared excess. The VLA 8.8 mm observations resolve the disk size (5-5.5 au) and its inner cavity ($\approx$3 au) for the first time, making it one of the smallest disks known. Its small size, large fractional luminosity, and millimeter spectral index consistent with blackbody emission support the idea that HD 98800 B is a massive, optically thick ring which may still retain significant amounts of gas. The disk detection at 5 cm is compatible with free-free emission from photoionized material. The diskless HD 98800 A component is also detected, showing partial polarization at 5 cm compatible with non-thermal chromospheric activity. We propose that tidal torques from Ba-Bb and A-B have stopped the viscous evolution of the inner and outer disk radii, and the disk is evolving via mass loss through photoevaporative winds. This scenario can explain the properties and longevity of HD 98800 B as well as the lack of a disk around HD 98800 A, suggesting that planet formation could have more time to proceed in multiple systems than around single stars in certain system configurations.Comment: 14 pages, 4 figures, 3 tables; Submitted to ApJ May 14 2018; Accepted to ApJ August 3 2018. This version fixes a mistake in the reported position angle. The order of the figures has been changed to match that of the references in the tex

Evolución geoquímica de las rocas gabroicas de Galicia durante su meteorización

[Resumen] Se realiza un estudio de la evolución geoquímica de las rocas gabroicasdel macizo de Monte Castelo (La Coruña) en el curso de su meteorización .En medios bien drenados se produce una fuerte pérdida de bases, y en menor medida de Si, ya desde las primeras fases de la alteración, por el, contrario, en tos medios donde la hidromorfia es permanente la lixiviación de bases decrece, la movilidad del Si se aproxima a la del Al y se incrementa la del Fe y el Mn.[Abstract] This paper is a study of the geochemical evolution of the gabbroic rocks of Monte Castelo (La Coruña) in the progress of their üJeathering •In üJell drained envirorunents there are an intense l03S of bases and, in a minor level, of Si, even in the first phases of the üJeathering; but in hydromorphic énvironments , the leach of bases decreases ; the movitity of Si comes near of the Al and that of Fe and Mn increases

Geochemical and Volcanological Criteria in Assessing the Links between Volcanism and VMS Deposits: A Case on the Iberian Pyrite Belt, Spain

VMS deposits in the Iberian Pyrite Belt (IPB), Spain and Portugal, constitute the largest accumulation of these deposits on Earth. Although several factors account for their genetic interpretation, a link between volcanism and mineralization is generally accepted. In many VMS districts, research is focused on the geochemical discrimination between barren and fertile volcanic rocks, these latter being a proxy of VMS mineralization. Additionally, the volcanological study of igneous successions sheds light on the environment at which volcanic rocks were emplaced, showing an emplacement depth consistent with that required for VMS formation. We describe a case on the El Almendro–Villanueva de los Castillejos (EAVC) succession, Spanish IPB, where abundant felsic volcanic rocks occur. According to the available evidence, their geochemical features, εNd signature and U–Pb dates suggest a possible link to VMS deposits. However, (paleo)volcanological evidence here indicates pyroclastic emplacement in a shallow water environment. We infer that such a shallow environment precluded VMS generation, a conclusion that is consistent with the absence of massive deposits all along this area. We also show that this interpretation lends additional support to previous models of the whole IPB, suggesting that compartmentalization of the belt had a major role in determining the sites of VMS depositionThis research is supported by the research project “Caracterización y datación isotópicas de rocas ígneas y sistemas hidrotermales en la Faja Pirítica Ibérica Española” (BTE2003-04354, Plan Nacional I+D) Careful revisions by anonymous reviewers have importantly contributed to improve this work and are acknowledged with than

Closed-form solutions for the piezoresistivity properties of short-fiber reinforced composites with percolation-type behavior

A new analytical formulation for the modeling of piezoresistive fiber-reinforced composites with percolation-type behavior is presented in this work. Firstly, we develop a closed-form solution of the electrical conductivity of oriented short-fiber reinforced composites by using generalized spherical harmonics series expansions of a Mori-Tanaka (MT) model. Piezoresistive effects are accounted for by means of three distinct mechanisms, namely filler reorientation, volume expansion, and breakage/formation of conductive paths. Then, this solution is used to derive simple analytical formulas to estimate the linear piezoresistivity coefficients. To illustrate the potentials of the proposed formulation, numerical results and discussion are presented on its application to the modeling of the piezoresistive composites doped with carbon nanotubes (CNTs). The presented formulation is also inlaid in a standard 3D finite element code to simulate the electromechanical response of full-scale CNT-based structural elements. The reported results demonstrate the capabilities of the proposed formulation to link the microstructural properties of short-fiber composites with the macroscopic response of structural systems with extraordinarily fast computation times and accuracy.A new analytical formulation for the modeling of piezoresistive fiber-reinforced composites with percolation-type behavior is presented in this work. Firstly, we develop a closed-form solution of the electrical conductivity of oriented short-fiber reinforced composites by using generalized spherical harmonics series expansions of a Mori-Tanaka (MT) model. Piezoresistive effects are accounted for by means of three distinct mechanisms, namely filler reorientation, volume expansion, and breakage/formation of conductive paths. Then, this solution is used to derive simple analytical formulas to estimate the linear piezoresistivity coefficients. To illustrate the potentials of the proposed formulation, numerical results and discussion are presented on its application to the modeling of the piezoresistive composites doped with carbon nanotubes (CNTs). The presented formulation is also inlaid in a standard 3D finite element code to simulate the electromechanical response of full-scale CNT-based structural elements. The reported results demonstrate the capabilities of the proposed formulation to link the microstructural properties of short-fiber composites with the macroscopic response of structural systems with extraordinarily fast computation times and accuracy

¿Qué preguntas formulan los estudiantes a partir de la lectura de un texto sobre los dispositivos de seguridad domiciliaria?

En este trabajo presentamos un estudio sobre la formulación de preguntas que realizan estudiantes de nivel secundario, cuando leen un texto ilustrado que se refiere a dispositivos de seguridad domiciliaria. Las preguntas son utilizadas para evaluar la comprensión. Hemos categorizado el corpus de preguntas obtenido en relación con los niveles de representación cognitiva y según se refieran a objetos, procesos y mecanismos causales. Comprobamos que cuando los estudiantes detectan obstáculos en la comprensión formulan preguntas y en éstas ha primado el interés por conocer los elementos de la situación física, las ventajas de los dispositivos y las relaciones causales

Mine soil caracterization in the coal mine dumps of As Pontes (NW Spain) during its reclamation

[Resumen] Se evalúa el estado nutritivo, condiciones de acidez y elementos potencialmente tóxicos para las plantas en los suelos de mina generados en la escombrera de la Mina Puentes (La Coruña), en actual proceso de restauración ambiental. Para ello se estudia la capacidad de intercambio catiónico, la acidez actual y potencial y la fracción metálica teóricamente biodisponible (extraída con DPTA). Los resultados muestran un amplio rango de variación en los parámetros analizados. La calidad de material original, en concreto el contenido en S, determina los niveles de acidez actual y potencial. La CICe es, en general, baja pero no significativamente diferente de los suelos naturales de la zona. La secuencia de extracción de metales con DPTA es: Fe> >Mn> >Cu>Ni~fZn~Pb>Co>>Cd, siendo la acidez del medio el parámetro fundamental que condiciona su movilización.[Abstract] Acidity, nutrient availability and potential toxicity in the coal mine dump of As Pontes (NW Spain) are evaluated. Then, cationic exchange capacity, actual and potenctial acidity and available heavy metals (DPTA extracted) are analized. Results show a wide variability of the spoil materials. Sulfur level in the spoils explains the different actual and potential acidity conditions. Cationic exchange capacity is low ( >Mn> >Cu>Ni~~Zn~Pb>Co>>Cd and the system acidity explains its mobilization

Meteorización de las granulitas de Cabo Ortegal

[Resumen] Se realiza el estudio químico y mineralógico del proceso de alteración, en medios sustractivos, de las granuli tas de Cabo Ortegal, la precipi tación media anual supera los 1.300 mm. y las temperaturas medias mensuales extremas son 23ºC y 4,7ºC. Durante el proceso de meteorizaciór se origina una fuerte pérdida de Ca, Na y Mg y,en menor proporción, de Si con acumulación relativa de Fe y Al. Como productos de alteración aparecen filosilicatos 1:1 dioctaédricos, gibbsita, oxihidróxidos de hierro y micas y cloritas degradadas. La edafogénesis es de tipo fermonosialítico con una tendencia ferralítica, al menos en sus fases iniciales.[Abstract] This paper is a chemical and mineralogical study about the weathering process, in subtr&ctive environments, of the granul i tes in Cabo Ortegal. The mean annual precipitation is over 1.300 mm. and the mean monthly extreme temperatures are 23ºC and 4,7ºC . In the process of weathering there is an intense 10S8 of Ca, Na and Mg and, in a minar level , of Si, with a relative accumulation of Fe and Al. Proqucts of the weathering are 1: 1 dioctahedral phyllosilicates, gibbsi teiron oxyhydroxides and degraded micas and chlorites. The pedogenesis is of fermonosialli tic type wi th a ferrallitic tendence, in the first phases at least