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Search Results: 1 - 10 of 20162 matches for " Alexander Valladares "
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A New Approach to the Computer Modeling of Amorphous Nanoporous Structures of Semiconducting and Metallic Materials: A Review
Cristina Romero,Juan C. Noyola,Ulises Santiago,Renela M. Valladares,Alexander Valladares,Ariel A. Valladares
Materials , 2010, DOI: 10.3390/ma3010467
Abstract: We review our approach to the generation of nanoporous materials, both semiconducting and metallic, which leads to the existence of nanopores within the bulk structure. This method, which we have named as the expanding lattice method, is a novel transferable approach which consists first of constructing crystalline supercells with a large number of atoms and a density close to the real value and then lowering the density by increasing the volume. The resulting supercells are subjected to either ab initio or parameterized—Tersoff-based—molecular dynamics processes at various temperatures, all below the corresponding bulk melting points, followed by geometry relaxations. The resulting samples are essentially amorphous and display pores along some of the “crystallographic” directions without the need of incorporating ad hoc semiconducting atomic structural elements such as graphene-like sheets and/or chain-like patterns ( reconstructive simulations) or of reproducing the experimental processes ( mimetic simulations). We report radial (pair) distribution functions, nanoporous structures of C and Si, and some computational predictions for their vibrational density of states. We present numerical estimates and discuss possible applications of semiconducting materials for hydrogen storage in potential fuel tanks. Nanopore structures for metallic elements like Al and Au also obtained through the expanding lattice method are reported.
Demandas formativas para la concepción de la superación del profesor-tutor de enfermería, en la universidad de las ciencias médicas cubana / Training Needs for Transcending Nursing Professor-TutorConception at the Cuban University of Medical Sciences
Alexander Mendoza Jacomino,Iliana Artiles Olivera,Javier Torres Valladares
Revista Electrónica Educare , 2010,
Abstract: Recibido 27 de julio de 2010 Aceptado 31 de agosto de 2010 Corregido 25 de noviembre de 2010 Resumen. En el siglo XXI crece el interés por elevar la calidad de los sistemas educativos, lo que plantea la urgencia de profesionalizar el rol del docente, mientras se hace patente la necesidad de una superación apoyada en la autogestión del aprendizaje, por lo que se requiere que estas actividades constituyan modelos de la práctica pedagógica. Partiendo de los presupuestos que enfatizan el cambio hacia acciones de superación por consenso y no directivas, como generalmente se ha hecho, y desde el enfoque histórico cultural, es que se introduce un visón de la superación profesional del enfermero, el cual trasciende la trasmisión de conocimientos, hacia un desarrollo de sus necesidades educativas diagnosticadas. Abstract. In the twenty-first Century the concern to increase the quality of educational systems has grown considerably, urging us to professionalize teacher capabilities and to work continued education all along their professional careers. This, in turn, is based on the self-management of learning and also on activities directed to the professional development of true models of pedagogical practice. Departing from the assumption that calls for a change in the way professional development is understood, which emphasizes the need to move towards a model that would deal with the issue on an agreed-upon way-rather than a directive one, as it has traditionally happened- a new vision as to the way that professional development should be conducted is herein presented, namely that of Psycho-pedagogical Counseling, which goes from the mere transmission of knowledge onto the development of competencies according to the needs that have been identified by those taking part in the process.
New Approaches to the Computer Simulation of Amorphous Alloys: A Review
Ariel A. Valladares,Juan A. Díaz-Celaya,Jonathan Galván-Colín,Luis M. Mejía-Mendoza,José A. Reyes-Retana,Renela M. Valladares,Alexander Valladares,Fernando Alvarez-Ramirez,Dongdong Qu,Jun Shen
Materials , 2011, DOI: 10.3390/ma4040716
Abstract: In this work we review our new methods to computer generate amorphous atomic topologies of several binary alloys: SiH, SiN, CN; binary systems based on group IV elements like SiC; the GeSe 2 chalcogenide; aluminum-based systems: AlN and AlSi, and the CuZr amorphous alloy. We use an ab initio approach based on density functionals and computationally thermally-randomized periodically-continued cells with at least 108 atoms. The computational thermal process to generate the amorphous alloys is the undermelt-quench approach, or one of its variants, that consists in linearly heating the samples to just below their melting (or liquidus) temperatures, and then linearly cooling them afterwards. These processes are carried out from initial crystalline conditions using short and long time steps. We find that a step four-times the default time step is adequate for most of the simulations. Radial distribution functions (partial and total) are calculated and compared whenever possible with experimental results, and the agreement is very good. For some materials we report studies of the effect of the topological disorder on their electronic and vibrational densities of states and on their optical properties.
Las competencias en la educación científica. Tensiones desde el pragmatismo epistemológico
Valladares, Liliana;
Perfiles educativos , 2011,
Abstract: actually the focus on education by competences has become a matter of central interest in educational research because of its influence on many of the educational reforms. nevertheless the notion of competence, and particularly in scientific education, is still ambiguous and sets out many questions, not only for psychology, pedagogy and didactics, but also for the epistemology. this paper is a contribution to the understanding of the competences from the epistemological pragmatism. from this philosophical framework the author debates on three tensions within the relation between the competences and the process of knowledge: a) about the idea of knowledge; b) about the structure of competences; and c) about the role of the context. the author argües that in most of the definitions of competences the knowledge are reduced to their merely declarative aspect, instead of understanding it in a comprehensive way as actions.
A gênese da favela carioca. A produ??o anterior às ciências sociais
Valladares, Licia;
Revista Brasileira de Ciências Sociais , 2000, DOI: 10.1590/S0102-69092000000300001
Abstract: the article shows the role occupied by the favela and its residents in political and social debate during the first half of the 20th century. it highlights the production of knowledge generated by journalists, physicians, engineers and social workers in the period preceding the development of social sciences and the university in brazil. it proposes that the process of construction of social representation of the favela, begun at that time, should be analyzed as a periodization beginning at a different moment than the periodization which is traditionally accepted based on the relation of the favela to the state and the type of political regime in power at different historical moments. the author suggests a periodization that has its initial moment marked by a myth of origin, euclides da cunha's vision of the settlement of canudos in his book os sert?es. in this period the favela of rio de janeiro is discovered and described by transposing the duality of coastal versus bush country (sert?es) to the urban scene, through the opposition of city to favela. following the discovery period is a second period when the favela is transformed into a social and urban problem, followed by a third period, when the idea of administrating the problem takes the form of concrete policies and measures. a fourth period includes the production of official data and the transformation of a local phenomenon into a national reality. the article shows that the centenary favela corresponds to an almost centennial social representation, an important legacy that today's social science can not disregard.
La educación científica intercultural y el enfoque de las capacidades
Revista iberoamericana de ciencia tecnolog?-a y sociedad , 2011,
Abstract: this paper presents data related to the human development report of the indigenous people's lives and situation in mexico. this report reflects the social exclusion in which they live, particularly in the field of education and science education. the idea behind this paper is proposing the creation of an intercultural science education program as a strategy for expanding the capabilities of people to do and be what they have reason to value. intercultural science education is based on three conditions: 1) a pluralistic perspective of knowledge; 2) a socio-cultural perspective of education based on the achievement of competent performance on socially relevant situations; and 3) the conversion of the plurality of cognitive resources into real opportunities to improve people's lives and capabilities.
La política de Olivares y Portugal
Libros de la Corte.es , 2012,
Cambio global, un nuevo reto para la vieja Europa
F. Valladares
Ecosistemas , 2005,
GLOBIMED, una red temática sobre cambio global y biodiversidad en ecosistemas forestales mediterráneos
Fernando Valladares
Ecosistemas , 2003,
La ecología tras el legado de Margalef
F. Valladares
Ecosistemas , 2006,
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