Melting behavior of large disordered sodium clusters

The melting-like transition in disordered sodium clusters Na_N, with N=92 and 142 is studied by using a first-principles constant-energy molecular dynamics simulation method. Na_142, whose atoms are distributed in two (surface and inner) main shells with different radial distances to the center of mass of the cluster, melts in two steps: the first one, at approx. 130 K, is characterized by a high intrashell mobility of the atoms, and the second, homogeneous melting, at approx. 270 K, involves diffusive motion of all the atoms across the whole cluster volume (both intrashell and intershell displacements are allowed). On the contrary, the melting of Na_92 proceeds gradually over a very wide temperature interval, without any abrupt step visible in the thermal or structural melting indicators. The occurrence of well defined steps in the melting transition is then shown to be related to the existence of a distribution of the atoms in shells. Thereby we propose a necessary condition for a cluster to be considered rigorously amorphouslike (totally disordered), namely that there are no space regions of the cluster where the local value of the atomic density is considerably reduced. Na_92 is the only cluster from the two considered that verifies this condition, so its thermal behavior can be considered as representative of that expected for amorphous clusters. Na_142, on the other hand, has a discernible atomic shell structure and should be considered instead as just partially disordered. The thermal behavior of these two clusters is also compared to that of icosahedral (totally ordered) sodium clusters of the same sizes.Comment: LaTeX file. 7 pages with 12 picture

Structures and Stabilities of Doubly-charged (MgO)nMg2+ (n=1-29) Cluster Ions

Ab initio perturbed ion plus polarization calculations are reported for doubly-charged nonstoichiometric (MgO)nMg2+ (n=1-29) cluster ions. We consider a large number of isomers with full relaxations of the geometries, and add the correlation correction to the Hartree-Fock energies for all cluster sizes. The polarization contribution is included at a semiempirical level also for all cluster sizes. Comparison is made with theoretical results for neutral (MgO)n clusters and singly-charged alkali-halide cluster ions. Our method is also compared to phenomenological pair potential models in order to asses their reliability for calculations on small ionic systems. The large coordination-dependent polarizabilities of oxide anions favor the formation of surface sites, and thus bulklike structures begin to dominate only after n=24. The relative stabilities of the cluster ions against evaporation of a MgO molecule show variations that are in excellent agreement with the experimental abundance spectra.Comment: Final version accepted in Journal of Chemical Physics; 8 pages plus 8 figures (6 GIFs and 2 PSs). The main difference with respect to the original submission is the inclusion of coordination-dependent polarizabilities for oxide anions. That results in substantial changes in the result

Producción científica venezolana: apuntes sobre su pérdida de liderazgo en la región latinoamericana

Se analiza la evolución de la producción y colaboración científicas de Venezuela, país que se ha caracterizado por su pérdida de liderazgo en los últimos años. El universo de análisis lo constituyen 1.117 revistas iberoamericanas de acceso abierto de la base de datos redalyc.org, con más de 250 mil artículos en un periodo de 10 años (2005-2014). La caída de la ciencia venezolana se aprecia desde bases de corriente principal (en Scopus, a través del SJR, presentó 1.857 artículos en 2005, representaba el 3.4% de la región. En 2014 tuvo 1.592 artículos, representaba el 1.44% de la región. Es decir, tuvo una caída del 14.27%), así como desde Redalyc (donde contaba con 875 artículos en 2005 y representaba el 5.5% de la región; en 2014 tuvo 791 artículos, representando el 3.0% de la región. La caída es del 9.6%); base de datos que permite apreciar además una alta tasa de concentración en la producción científica y editorial de Venezuela, así como un comportamiento endógeno en términos de producción y colaboración

La Recuperación del Observador en la Construcción del Dato

Although in last decades the interpretative character of social sciences has been emphasized, that doesn?t mean there is an absence -and sometimes not even a lack of consolidation- of quantitative character researches. Is in this sense that we consider of great importance to get the discussion around the measuring issue back, but this time with a constructivist approach that does not consider the qualitative research as a permanent opposite of the quantitative one, and vice versa, having as a starting point that the main issue is not datum itself, but its construction. In this sense, we attempt to approach to the datum role and construction, in their modality of analytical constructions that are as abstracts as the qualitative ones. Summarizing, the issue is if the person, in singular and plural, is a part of the so called knowledge. As we are assuming an affirmative answer, it is necessary to argument and present the reasons that have led us to this conclusion, and to restart the discussion about its implications in the methodological, technical and discursive construction levels of social sciences. It is intended to situate the discussion on datum construction in an epistemological level, giving particular emphasis to the problem of construction-correspondence, facing those perspectives which have reduced it to its clearly technical level, which sees the problem as a mere correspondence between preciseness and accuracy. Likewise, it is intended to underline the necessity of keeping a constant epistemological vigilance during every research process. As a complement to this remarks, we present an example taking some studies about poverty and marginality in Mexico and Latin America as a basis, where the different ways in which indicators are constructed, and the variety of outputs that result from them are analyzed; this exercise allows to clearly identify the primacy of theory over observation, and at the same time it allows to find one of the reasons for divergence between the researches, and between these and the management programs

The End of a Centralized Open Access Project and the Beginning of a Community-Based Sustainable Infrastructure for Latin America: Redalyc.org after Fifteen Years The Open Access ecosystem in Latin America

The Latin American region has an ecosystem where the nature of publication is conceived as the act of making public, of sharing and not as the publishing industry. International, national and institutional contexts have led to a redefinition of a project—Redalyc.org—that begun in 2003 and that has already fulfilled its original mission: give visibility to knowledge generated in Latin America and promote quality of scientific journals. Nevertheless, it is mandatory to be transformed from a Latin American platform based in Mexico into a community-based regional infrastructure that continues assessing journals quality and providing access to full-text in benefit of journals visibility and free access to knowledge. A framework that generates technology in favor of the empowerment and professionalization of journal editors, making the editorial task in open access sustainable and that allows Redalyc to sustain itself collectively. This work describes the first Redalyc's model, presents the problematic in course and the new business model Redalyc is designing and adopting to operate on

A Semantic Model for Selective Knowledge Discovery over OAI-PMH Structured Resources

This work presents OntoOAI, a semantic model for the selective discovery of knowledge about resources structured with the OAI-PMH protocol, to verify the feasibility and account for limitations in the application of technologies of the Semantic Web to data sets for selective knowledge discovery, understood as the process of finding resources that were not explicitly requested by a user but are potentially useful based on their context. OntoOAI is tested with a combination of three sources of information: Redalyc.org, the portal of the Network of Journals of Latin America and the Caribbean, Spain, and Portugal; the institutional repository of Roskilde University (called RUDAR); and DBPedia. Its application allows the verification that it is feasible to use semantic technologies to achieve selective knowledge discovery and gives a sample of the limitations of the use of OAI-PMH data for this purpose

Patrones de internacionalización en psicología desde la revista interamericana de psicología

Con 50 años de trayectoria, la Revista Interamericana de Psicología (RIP) se ha consolidado como un órgano central de debate y ha posibilitado un intercambio de ideas cada vez más global en la psicología. Observando el papel central de la RIP en el desenvolvimiento de la disciplina, el presente escrito traza una hoja de ruta de la revista, con énfasis en el impacto que ha tenido en la configuración de la comunidad de psicología. El escrito parte de un enfoque distinto desde el cual analizar el papel de la RIP: tendencias de publicación, colaboración, uso, Índice de Esfuerzo Editorial e Índice de Internacionalización; y arroja como resultado estándares altos de internacionalización. En ello se considera el periodo 2005-2015 y se recurre a Redalyc.org como fuente de información

La legitimación de la Ciencia social en las bases de datos científicas más importantes para América Latina

Se analizan desde la Sociología de la ciencia tres ejes de su campo. El primero, rescata la epistemología de la producción científica social. El segundo, trata la construcción de la legitimidad de los científicos a través de sus publicaciones. El tercero, refiere el estudio de los indicadores más importantes para América Latina generados por la Cienciometría. Se concluye que la incorporación de las Tecnologías de Información y Comunicación son canales a través de los cuales se legitiman los resultados de investigación, productividad y visibilidad entre las comunidades científicas

Teachers’ satisfaction as indicator of education system performance

We investigate the potential trade-off between some teacher characteristics, particularly teachers’ satisfaction, and different measures of pupils’ performance, in order to optimize the outputs of the Spanish education system. Our contribution to the existing literature is twofold: on the one hand, we provide estimates on the balance between teachers’ effectiveness and 4th grade students’ performance in Spain, by using recent survey data (TIMSS, 2011); on the other hand we implement a novel methodology which allows optimizing simultaneously a set of indicators on the outputs of the educational system. These analyses provide empirical evidence of the importance of investing in teacher satisfaction as a motivation mechanism for improving national educational achievement.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This research has been partially supported by the Andalusian Regional Ministry of Innovation, Science and Enterprise (PAI group SEJ-532). We also acknowledge the research funding provided by Andalucía-Tech (Universidad de Malaga),the Research Plan of the University of Malaga (Capacity Building Programme I+D+i of Universities 2014-2015, FEDER Funds) and by the Ministry of Economy and Competitiveness of Spain (Research Project ECO2014-56397-P). Luis Alejandro Lopez-Agudo also acknowledges the research training provided by the “Programa de Doctorado en Economía y Empresa de la Universidad de Malaga”