Crossing the phantom divide in an interacting generalized Chaplygin gas

Unified generalized Chaplygin gas models assuming an interaction between dark energy and dark matter fluids have been previously proposed. Following these ideas, we consider a particular relation between dark densities, which allows the possibility of a time varying equation of state for dark energy that crosses the phantom divide at a recent epoch. Moreover, these densities decay during all the evolution of the Universe, avoiding a Big Rip. We find also a scaling solution, i.e. these densities are asymptotically proportional in the future, which contributes to the solution of the coincidence problem.Comment: Improved version, 10 pages, 4 figures, References adde

Hermenêutica da pergunta pedagógica: Aprendizagem mediada pela prática da liberdade a partir da perspectiva de Freire

El ser humano se aproxima al mundo mediante la dialéctica de pregunta y respuesta para construir socialmente la realidad mediante la práctica de la libertad. En este contexto, el estudio se realizó con el objetivo de exponer el análisis hermenéutico de la pregunta pedagógica como instrumento pedagógico para el aprendizaje mediado por la práctica de la libertad desde la perspectiva de Freire. Desde el campo de la investigación filosófica se desarrollaron tres etapas (construcción del horizonte de comprensión, destructiva y constructiva) para proyectar la tradición educativa de Vigotsky y Ausubel hacia la hermenéutica de la pregunta y confrontar el aporte de la pedagogía de la pregunta de Freire. Los resultados obtenidos recuperan la pregunta inicial, mediadora y esencial situándolas en relación con la estructura y horizonte de la pregunta. El acto de preguntar se rehabilita como práctica de la libertad al mediar el aprendizaje desde el pensamiento crítico y creativo.The man approaches the world through the dialectic of question and answer to socially construct reality by practicing freedom. In this context, the study was conducted with the aim of exposing the hermeneutical analysis of the pedagogical question as an educational tool for learning through practice of freedom from the perspective of Freire. From the field of philosophical inquiry three stages (construction horizon of understanding, destructive and constructive) were developed to project the educational tradition of Vygotsky and Ausubel hermeneutics to question and confront the contribution of pedagogy Freire's question. The results obtained recover the initial question, mediator and essential placing them in relation to the structure and horizon of the question. The act of asking is rehabilitated as a practice of freedom to mediate learning from the critical and creative thinkingO ser humano aproxima-se ao mundo mediante a dialética de pergunta e resposta para construir socialmente a realidade mediante a prática da liberdade. Neste contexto, o estudo realizou-se com o objetivo de expor a análise hermenêutica da pergunta pedagógica como instrumento pedagógico para a aprendizagem mediada pela prática de liberdade a partir da perspectiva de Freire. Do campo da investigação filosófica desenvolveram-se três etapas (construção do horizonte de compreensão, destrutiva e construtiva) para projetar a tradição educativa de Vigotsky e Ausubel para a hermenêutica da pergunta e confrontar a contribuição da pedagogia da pergunta de Freire. Os resultados obtidos recuperam a pergunta inicial, mediadora e essencial situando-as em relação com a estrutura e horizonte da pergunta. O ato de perguntar reabilita-se como prática da liberdade ao mediar a aprendizagem a partir do pensamento crítico e criativ

Towards SDp-brane Quantization

The quantum mechanical analysis of the canonical hamiltonian description of the effective action of a SDp-brane in bosonic ten dimensional Type II supergravity in a homogeneous background is given. We find exact solutions for the corresponding quantum theory by solving the Wheeler-deWitt equation in the late-time limit of the rolling tachyon. The probability densities for several values of p are shown and their possible interpretation is discussed. In the process the effects of electromagnetic fields are also incorporated and it is shown that in this case the interpretation of tachyon regarded as ``matter clock'' is modified.Comment: 15 pages, 3 eps figures, revtex

Biodiversity of Bacteriocin-Producing Lactic Acid Bacteria from Mexican Regional Cheeses and their Contribution to Milk Fermentation

The aim of this work was to examine the biodiversity of bacteriocin-producing lactic acid bacteria from homemade cheeses produced in Veracruz (México) and assess their contribution as adjunct cultures in dairy products. Ninety-three presumptive bacteriocinogenic strains were detected by direct antagonism assays and 29 of them were active against Enterococcus faecalis NRRL-B537, Listeria innocua 062 AST, or Listeria monocytogenes ATCC19115 by the well diffusion test using cell-free supernatants, adjusted to pH 6.0 to exclude inhibition by organic acids. Positive isolates were identified by partial sequencing of the 16s rDNA as Pediococcus acidilactici (four isolates), Enterococcus faecium (17 isolates), Lactobacillus plantarum (six isolates) and Lactobacillus fermentum (two isolates). RAPD-PCR discriminated seven groups with a 50% similarity and revealed the presence of the same isolates. The coding genes for the synthesis of plantaricin EF, plantaricin JK, plantaricin N, plantaricin NC8 and the inducing peptide plantaricin A were detected by PCR in L. plantarum. Similarly, enterocin P and pediocin PA-1 genes were amplified from Enterococcus and Pediococcus genomic DNA, respectively. Overall, co-culturing of bacteriocin producing Lactobacillus and Pediococcus strains with the dairy starter Lactococcus lactis IPLA947 did not interfere with milk acidification. Lactose consumption, acidification rate and production of lactic acid were unchanged. Nonetheless, higher levels of acetic acid, ethanol and succinic acid were detected depending on the strain. Our results demonstrate the diversity of bacteriocinogenic species in homemade Mexican cheeses which may be used as adjunct cultures to enhancing safety of this well-appreciated cheese while providing a richer range of metabolites.This work was supported by Tecnológico Nacional de México (5486.14.15-P), the Mexican National Council for Science and Technology (Consejo Nacional de Ciencia y Tecnología -CONACYT) and partially by the Ministry of Economy and Competitiveness of Spain (MINECO) through grant BIO2013-46266-R. Funding by GRUPIN14-139 Plan de Ciencia, Tecnología e Innovación 2013-2017 (Principado de Asturias, Spain), supported by FEDER EU funds, is also acknowledged. S. Portilla-Vázquez held a CONACYT fellowship as well as an i-COOP mobility grant COOPA20015 funded by Consejo Superior de Investigaciones Científicas (CSIC), Spain.Peer reviewe

Temperature-dependent properties of 147-and 309-atom iron-gold nanoclusters

The properties of several Au-N and AuN-xFex nanoclusters are obtained by means of classical molecular dynamics calculations. In particular we study the configurations Au-147, Au134Fe13, Au-309, and Au254Fe55, which correspond to icosahedral magic numbers, for both the gold and the iron. We investigate the melting and freezing processes, atomic diffusion, hardness, vibration spectra, and specific heat of these nanoclusters. All the data obtained point toward the stability of the AuN-xFex system, with the gold atoms on the outside of the iron core