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Search Results: 1 - 10 of 1654 matches for " Rivas Mercury "
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Hidratación de los cementos de aluminatos de calcio. Parte II: Efecto de las adiciones de sílice y alumina
Rivas Mercury, J. M.,de Aza, A. H.,Turrillas, X.,Pena, P.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 2003,
Abstract: The present work is a literature review on the hydration process of calcium aluminate cements with high alumina contents with alumina and microsilica additions. The main hydrations products of these materials are described as function of temperature. Their reaction mechanisms, studied through different methods and techniques by several authors are discussed. The products of dehydration at high temperatures are also described. El presente trabajo es una revisión sobre el proceso de hidratación de los cementos de aluminatos de calcio, de alto contenido en alúmina, con adiciones de microsílice y alumina. En el se describen los principales productos de hidratación de estos materiales. Así mismo se exponen los mecanismos de reacción que han sido establecidos por distintos autores utilizando técnicas diversas. Finalmente se describe el proceso de deshidratación térmica de estos materiales.
Hidratación de los cementos de aluminatos de calcio (Parte I)
Rivas Mercury, J. M.,de Aza, A. H.,Turrillas, X.,Pena, P.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 2003,
Abstract: The present work is a literature review on the hydration process of calcium aluminates cements with high alumina contents. The main hydration products of these materials are described as function of the water/solid ratio and temperature. Their reaction mechanisms, studied by several authors and also their typical microstructure are discussed. El presente trabajo es una revisión sobre el proceso de hidratación de los cementos de aluminatos de calcio de alto contenido en alúmina. En el se describen los principales productos de hidratación de estos materiales en función de las relaciones de agua/sólidos y temperatura. Se exponen los mecanismos de reacción que han sido establecidos por distintos autores en la literatura y se describe la microestructura típica de estos materiales.
Estudio por difracción de rayos X de la hidratación de mezclas de CaAl2O4 - Humo de silice
Rivas-Mercury, J. M.,Turrillas, X.,de Aza, A. H.,Rodríguez, M. A.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 2007,
Abstract: The influence of the amorphous silica on the mechanism of hydration of the calcium monoaluminate (CaAl2O4) has been studied at ambient temperature with a water/solids ratio of 0.5. The evolution of the hydrated phases, formed in the first instants of the reaction, has been studied by laboratory X ray diffraction with a time resolution of 36 min. The integration of selected diffraction peaks of the phases: Ca2Al2O5 8H2O (Ca2Al2(OH)10 3H2O), CaAl2O4 and Ca4Al2(OH)12(CO3) 5H2O, has allowed to establish the kinetics of the reaction. This way, it has been shown that the amorphous silica causes a drastic decrease in the period of induction of the hydration and accelerates the formation of the metastable crystalline hydrates Ca2Al2(OH)10 3H2O and Ca4Al2(OH)12(CO3) 5H2O. These results have been confirmed by Thermogravimetry, Differential Thermal Analysis and Scanning Electric Microscopy. The hydration mechanism proposed confirms previous data of Nuclear Magnetic Resonance of Solids (RMN) of 29Si of the authors of this paper. Se ha estudiado la influencia del humo de sílice sobre el mecanismo de hidratación del monoaluminato de calcio (CaAl2O4) a temperatura ambiente y con una relación agua/sólidos de 0,5. La evolución de las fases hidratadas, que se forman en los primeros instantes de la reacción, se ha estudiado por difracción de rayos X de laboratorio con una resolución temporal de 36 min. La integración de picos de difracción seleccionados de las fases: Ca2Al2O5 8H2O (Ca2Al2(OH)10 3H2O), CaAl2O4 y Ca4Al2(OH)12(CO3) 5H2O, ha permitido establecer la cinética de la reacción. Así, se ha puesto de manifiesto que el humo de sílice provoca una drástica disminución en el periodo de inducción de la hidratación y acelera la formación de los hidratos cristalinos metaestables Ca2Al2(OH)10 3H2O y Ca4Al2(OH)12(CO3) 5H2O. Estos resultados se han confirmado por Termogravimetría, Análisis Térmico Diferencial y Microscopía Electrónica de Barrido. El mecanismo de hidratación propuesto se apoya en datos previos de Resonancia Magnética Nuclear de Sólidos (RMN) de 29Si de los autores de este artículo.
Effect of different approaches to decouple the dependence of nuclei-liquid surface energy on size and temperature
Freitas, Mara Cristina;Costa, Dalmo Inácio Galdez;Cabral, Aluísio Alves;Gomes, Adalto Rodrigues;Mercury, José Manuel Rivas;
Materials Research , 2009, DOI: 10.1590/S1516-14392009000100013
Abstract: tests involving the classical nucleation theory (cnt) often disregard the size dependence of surface energy. thus, the surface energy of critical nuclei is assumed to be a macroscopic quantity that depends only on the temperature of a flat surface. however, because the size of critical nuclei changes with temperature, σcl(t) should be described as a function of both temperature and size of critical nuclei. the present work examines the temperature dependence of macroscopic surface energy, decoupling it from the size dependent part. tolman, rasmussen and vogelsberger's equations are used to decouple the dependence of surface energy on size, using experimental data for the following silicate glasses li2o.2sio2 (ls2) and na2o.2cao.3sio2 (n1c2s3). these equations are successful in obtaining a decrease in σcl(t), in agreement with theoretical predictions. for all the values of δ , tolman's equation produces the lowest values of σcl(t). nevertheless, they are very close to the liquid/vapor surface energy (σlv), which contradicts the stefan's rule (i.e. σcl/σ lv << 1). therefore, it is demonstrated that the assumption of the curvature dependence of surface energy does not suffice, per se, to explain the discrepancy between the experimental and theoretical values of nucleation rates.
Influencia del contenido de lodo rojo (residuo de bauxita) en las propiedades físico-mecánicas de materiales cerámicos conformados por extrusión
José Manuel Rivas Mercury,Laécio Gomes Galdino,Ant?nio Ernandes Macedo Paiva,Aluísio Alves Cabral Junior
Revista Latinoamericana de Metalurgia y Materiales , 2009,
Abstract: En el presente trabajo se ha estudiado la influencia de adiciones de Lodo Rojo (LR) en concentraciones variables de 45-65 %-p, en las propiedades físico-mecánicas de materiales cerámicos conformados por extrusión de mezclas de arcillas + LR. Los materiales obtenidos se trataron térmicamente en el intervalo de 750-1.050 oC con tiempo de reacción de una 1 h para determinación de las propiedades cerámicas: Módulo de Ruptura (MOR), Absorción de Agua (AA), Retracción Linear (RLAq). Las fases cristalinas presentes de los materiales de partida, así como de los materiales después del tratamiento térmico fueron determinadas por Difracción de rayos (DRX) método de polvos, mientras que su microestructura por Microscopia Electrónica de Barrido (MEB). Los resultados han puesto de manifiesto que es posible utilizar este material como materia prima para la fabricación de ladrillos y tejas, los cuales presentaron buenas propiedades físico-mecánicas, superando las especificaciones de las Normas NBR 6113 y 6220 de la Asociación Brasile a de Normas Técnicas (ABNT) para la fabricación de materiales estructurales. At the present work was studied the influence of Red Mud additions in the concentration range of 45-65 % w/w on the physical-mechanical properties of ceramic materials made with extruded clay + red mud mixtures. All ceramics material obtained were thermal treated in temperature range of 750-1050 oC, with 1 h of dwell time, and their mechanical properties like: Flexural strength (MOR), Water Absorption, Linear shrinkage before and after firing was measure. The crystalline phases of the raw materials and sintered materials were analyzed by X ray Diffraction and the micro structure by Scanning Electron Microscope (SEM). The results pointed out that it is possible to produce heavy clay products like roof tile and clay bricks with physical-mechanics properties higher than the specifications of the Brazilian technical standard (ABNT) for heavy clay products.
Influencia del contenido de lodo rojo (residuo de bauxita) en las propiedades físico-mecánicas de materiales cerámicos conformados por extrusión
Rivas Mercury,José Manuel; Gomes Galdino,Laécio; Ernandes Macedo Paiva,Ant?nio; Alves Cabral Junior,Aluísio; Sim?es Angélica,R?mulo;
Revista Latinoamericana de Metalurgia y Materiales , 2009,
Abstract: at the present work was studied the influence of red mud additions in the concentration range of 45-65 % w/w on the physical-mechanical properties of ceramic materials made with extruded clay + red mud mixtures. all ceramics material obtained were thermal treated in temperature range of 750-1050 oc, with 1 h of dwell time, and their mechanical properties like: flexural strength (mor), water absorption, linear shrinkage before and after firing was measure. the crystalline phases of the raw materials and sintered materials were analyzed by x ray diffraction and the micro structure by scanning electron microscope (sem). the results pointed out that it is possible to produce heavy clay products like roof tile and clay bricks with physical-mechanics properties higher than the specifications of the brazilian technical standard (abnt) for heavy clay products.
Estudo do comportamento térmico e propriedades físico-mecanicas da lama vermelha
Mercury, J.M. Rivas;Galdino, L.G.;Vasconcelos, N.S.L.S.;Paiva, A.E.M;Cabral, A.A.;Angélica, R.S.;
Matéria (Rio de Janeiro) , 2010, DOI: 10.1590/S1517-70762010000300007
Abstract: the present work studied the thermal behavior, the evolution of the crystalline phases with temperature and the ceramic properties of the red mud (bauxite tailing) from an aluminium industry of the maranhao state. the research was carried out by simultaneous thermal analysis (tg-dta), optical dilatometry up to 1350 oc, while the evolution of the crystalline phases was performed by x-ray diffraction analysis upon heating between 750 to 1150 oc. physical-mechanical properties, like specific surface area, particle size distribution, plastic limit (pl), liquid limit (ll), plasticity index (pi), flexural strength, water absorption (wa), linear shrinkage after firing (ls) and the apparent porosity (ap) were also determined at the same range of temperature. the following major crystalline phases were detected: hematite, sodalite, and anatase at 750 < t < 850 oc; and hematite, nepheline and sodalite at 950 < t < 1150 oc. the technological experiments indicated that red mud can be used for the processing of structural ceramic materials, since it is an inert material between 870-950 oc and presents highest water absorption and lowest shrinkage and flexural strength. at 950 < t < 1350 oc, red mud presented a high shrinking of almost 5 to 50 % with total fusion at 1350 oc, due to the presence of feldspathoids phases in its mineral composition.
Dos enfoques clásicos para el estudio de la estratificación social y de las clases sociales
Ricardo Rivas Rivas
Espacio Abierto , 2008,
Abstract:
Evolutionary models for insertions and deletions in a probabilistic modeling framework
Elena Rivas
BMC Bioinformatics , 2005, DOI: 10.1186/1471-2105-6-63
Abstract: Probabilistic models of substitution events are well established, but there has not been a completely satisfactory theoretical framework for modeling insertion and deletion events.I have developed a method for extending standard Markov substitution models to include gap characters, and another method for the evolution of state transition probabilities in a probabilistic model. These methods use instantaneous rate matrices in a way that is more general than those used for substitution processes, and are sufficient to provide time-dependent models for standard linear and affine gap penalties, respectively.Given a probabilistic model, we can make all of its emission probabilities (including gap characters) and all its transition probabilities conditional on a chosen divergence time. To do this, we only need to know the parameters of the model at one particular divergence time instance, as well as the parameters of the model at the two extremes of zero and infinite divergence.I have implemented these methods in a new generation of the RNA genefinder QRNA (eQRNA).These methods can be applied to incorporate evolutionary models of insertions and deletions into any hidden Markov model or stochastic context-free grammar, in a pair or profile form, for sequence modeling.Probabilistic models are widely used for sequence analysis [1]. Hidden Markov models (HMMs) are a very large class of probabilistic models used for many problems in biological sequence analysis such as sequence homology searches [2-4], sequence alignment [5], or protein genefinding [6-8]. Stochastic context-free grammars (SCFGs) are another class of probabilistic models used for structural RNAs for problems such as RNA homology searches [9-13], RNA structure prediction [14,15], and RNA genefinding [16].Sequence similarity methods based on HMMs or SCFGs can take the form of profile or pair models and are very important for comparative genomics. These probabilistic methods for sequence comparison assume a certai
La docencia desde la investidura académica y la impostura fraudulenta
Rivas,Pedro;
Educere , 2009,
Abstract: the following text is a brief summary of reflections that aims to restore teaching conceived from a teaching invested in an authority that comes from the desire of knowing and the contribution of transforming the other, as it is transformed in itself into a pedagogic act of taking in a stream of dignified and respectful communication. this memorial attempts to highlight that the educational act directed by a teaching that overcomes routine and daily life and makes the learning subject visible will transcend in the search and achievement of integral development in the scholars. in order to be achieved, this purpose finds some obstacles in the practice when the intention of exercising teaching without authority and training is perverted. this disfiguration is turned into an impostor and fraudulent teaching because it is done from deceiving and deception.
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