A first-principles study of superconductivity on RbH by doping without applied pressure

The structural, electronic, lattice dynamics, electron-phonon coupling, and superconducting properties of the alkali-metal hydride RbH, metalized through electron-doping by the construction of the solid-solution Rb$_{1-x}$Sr$_x$H, are systematically analyzed as a function of Sr-content within the framework of density functional perturbation and Migdal-Eliashberg theories, taking into account the effect of zero-point energy contribution by the quasi-harmonic approximation. For the entire studied range of Sr-content, steady increments of the electron-phonon coupling constant and the superconducting critical temperature are found with progressive alkaline-earth metal content through electron-doping, reaching the values of $\lambda=1.92$ and $T_c=51.3(66.1)$~K with $\mu^*$=0.1(0). The steady rise of such quantities as a function of Sr-content is consequence of the metallization of the hydride as an increase of density of states at the Fermi level is observed, as well as the softening of the phonon spectrum, mainly coming from H-optical modes. Our results indicate that electron-doping on metal-hydrides is an encouraging alternative to look for superconductivity without applied pressure.Comment: 8 pages, 6 figure

The alkaline reaction of FEBEX bentonite: a contribution to the study of the performance of bentonite/concrete engineered barrier system

Desde 1997, el desarrollo de dos proyectos de la Unión Europea, Effects of Cement On CLAY barrier performance (ECOCLAY, 1997-2000) y ECOCLAY phase II (2000-2003), ha permitido abordar la investigación del efecto de la pluma alcalina inducida por la lixiviación del hormigón sobre la bentonita. Ambos materiales forman parte de un concepto de barrera compuesta de hormigón y bentonita, en el contexto del almacenamiento de residuos a una profundidad dada. El grupo de geoquímica aplicada a las arcillas de la Universidad Autónoma de Madrid (UAM) ha participado en ambos proyectos, y ha conseguido aportar experiencia y cono¬cimiento al estudio del comportamiento de la bentonita de referencia española (FEBEX) bajo condiciones de elevada alcalinidad. Este artículo ofrece una síntesis del trabajo desarrollado, mencionando las lecciones aprendidas sobre la reactividad alcalina de la bentonita, y su enfoque práctico hacia el análisis del comportamiento de uno de los conceptos de referencia, el almacenamiento de residuos en formaciones arcillosas. Se han seleccionado las principales contribuciones científicas a este respecto, a juicio de los autores: (1) la naturaleza particular de los productos generados en la reacción alcalina de la bentonita FEBEX (zeolitas, arcillas magnésicas y geles de silicato aluminato cálcico hidratado (CASH)); (2) la aproximación mediante mineralogía cuantitativa al ritmo de reacción de la montmorillonita FEBEX a pHs elevados, y (3) la validación experimental de la reactividad alcalina de la bentonita a partir de experimentos en columna

Mineral phases in metakaolin-portlandite pastes cured 15 years at 60 °C. New data for scientific advancement

One of the problems addressed by the scientific community in connection with cement matrix hydration is the evolution of hydrated phases under certain, primarily temperature-related, curing conditions. Such conditions are of utmost importance when the cement generates metastable hydrated phases that develop into stable phases, inducing substantial physical-mechanical changes in the matrix. One such instance arises during the pozzolanic reaction between metakaolinite and calcium hydroxide at 60 °C when metastable hexagonal phases co-exist with cubic stable phases. Such processes are well understood in the short and medium term (<5 years). Evolution at longer curing times has not been studied, however. This paper describes the evolution of the initial (stable and metastable) mineral phases in the metakaolinite / Ca(OH) reaction toward a zeolite-like phase after 15 year curing at 60 °C. An understanding of such mineralogical changes is scientifically significant, given their direct impact on the engineering properties of cement-based matricesThe authors thank the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund (ref: RTI2018-097074-B-C21/C22

The deterioration and environmental impact of binary cements containing thermally activated coal mining waste due to calcium leaching

Calcium-leaching processes can potentially degrade the structure of a concrete matrix. This problem is studied here through the progressive dissolution of Ca2+ in both ordinary Portland cement pastes (C-0) and binary cement blends (C-20) containing 20% thermally Activated Coal Mining Waste (ACMW).1 A series of accelerated tests are conducted that involve the immersion of these cement pastes in a 6 M ammonium nitrate solution at a temperature of 20  C for 7 and for 21 days. A rise in paste porosity was observed, due to increased capillary pore sizes of between 5 and 0.1 μm. In the case of the 20% ACMW pastes (C-20), calcium leaching decreased, probably as a consequence of the pozzolanic effect of the ACMW, while potassium and magnesium leaching increased, due to the presence of the phyllosilicates in the ACMW. The paste compounds most affected by leaching were Ca(OH)2, C6AS3H32, and C4AC¯H12. In general terms, it can be concluded that the incorporation of ACMW into binary cements slightly reduces the calcium leaching phenomena. Concerning the environmental impact assessment, the substitution of 20% OPC by ACMW reduced CO2 emissions by as much as 12% and improved energy efficiency by using approximately 19% fewer fossil resources.This research was developed in the framework of the MATCON Associated Unit (CSICTecnalia, Madrid, Spain) with the support of the Spanish Ministry of Economy and Competitiveness (Project Ref. MAT2012-37005-CO3-01/02/03) and the European Regional Development Fund (MINECO/FEDER) (Project Ref.BIA2015-65558-C3- 1,2,3-R. The authors are also grateful to the Sociedad Anónima Hullera Vasco-Leonesa and to the Spanish Cement Institute (IECA) for providing us with raw materials

Influence of Ca/Si ratio on the microstructure and properties of blended cements elaborated with kaolinite based waste

ICCC 2015, Beijing, China, 13~16 October 2015; http://iccc2015.csp.escience.cn/dct/page/1To reduce the environmental impact of cement industries, cementitious materials are added to the manufacture of eco-efficient cements, focusing in industrial wastes. In this paper metakaolinite (MK) based industrial wastes have been mixed with cement in order to study the effect of the chemical composition of the raw material in both microstructural and mechanical properties of the pastes. Frattini test was also determined. The selected metakaolin based industrial wastes were previously activated for two hours at temperatures around 600ºC to transform the inert waste into a cementing material. The industrial wastes materials used were coal mining and paper sludge. The second one was mixed with fly ash (50/50 w/w) in order to evaluate the performance of ternary blended cements. The mixtures were prepared with OPC and both 6 and 20% of activated industrial waste (coal mining and paper sludge + fly ash). Prismatic samples (1x1x6 cm) were prepared with water/cement ratio of 0.5 and cured 28 days. After this time, mineralogical composition of the samples was determined by XRD as well as mechanical properties (compressive and flexural strength, total porosity, etc). Besides, portlandite and ettringite, both monocarboaluminate and C4AH13 have been formed in the samples after 28 days of hydration. It can be observed that C4AH13 decreases as Ca/Si ratio decreases; with the opposite behaviour for the monocarboaluminate. From the mechanical properties, porosity decreases from 1 to 28 days of curing as compressive strength increases.To the Ministry of Economy and Competiveness by the financial support (MAT2012-37005-C03-01-02-03).Peer Reviewe

Potasio en algunos suelos argentinos : II- extractantes y ensayo de Neubauer

p.173-179En el presente trabajo los autores intentan completar el panorama logrado en uno anterior (Villa y Mizuno. 1974). Para el estudio comparativo de extractantes se añadió la solución de EDTA, efectuándose con las muestras de suelos ensayos de Neubauer con 50 y 100 g de las mismas, para un mejor conocimiento de la dinámica del potasio en los suelos estudiados. La utilización de extractantes diversos, combinados con ensayos de Neubauer con 50 y 100 g suelo, abre un campo promisorio para un mejor conocimiento del potasio del suelo

The first Hochschild cohomology group of a schurian cluster-tilted algebra

Given a cluster-tilted algebra B we study its first Hochschild cohomology group HH1(B) with coefficients in the B-B-bimodule B. We find several consequences when B is representation-finite, and also in the case where B is cluster-tilted of type Ã.Fil: Assem, Ibrahim. University of Sherbrooke; CanadáFil: Redondo, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Matemática Bahía Blanca. Universidad Nacional del Sur. Departamento de Matemática. Instituto de Matemática Bahía Blanca; Argentin

Effects of varnish on the color of chromatic reintegrations

El estudio muestra en qué grado dos técnicas pictóricas, acuarela y pigmentos aglutinados al barniz (Gamblin), utilizadas en la reintegración cromática de obras arte, experimentan un cambio de color tras ser barnizadas. El método de trabajo ha consistido en aplicar dos tipos de barniz, mate y brillante, sobre diferentes muestras de color de cada una de las dos técnicas pictóricas analizadas. El análisis colorimétrico realizado sobre las muestras barnizadas y el estudio comparativo de los resultados obtenidos permiten conocer hasta qué punto se produce un cambio de color sobre cada una de ellas y qué parámetro claridad, croma o tono es el que tiene mayor influencia en el cambio.The study shows to what extent two painting techniques, watercolor and varnish painting (Gamblin), used in chromatic reintegration of artworks, experience color change after being varnished. The working method has consisted of applying two types of varnish, matte and shiny, over different color samples of each painting techniques analyzed. The colorimetric analysis made on every sample and the comparative study of the obtained results have allowed knowing to what degree color change occurs in each sample and which parameter, brightness, chroma, or hue, is the one with the greatest influence on the change.Depto. de Pintura y Conservación-RestauraciónFac. de Bellas ArtesTRUEpu