Can the Type-IIB axion prevent Pre-big Bang inflation?

We look at the possibility of superinflationary behavior in a class of anisotropic Type-IIB superstring cosmologies in the context of Pre-big Bang scenario and find that there exists a rather narrow range of parameters for which these models inflate. We then show that, although in general this behavior is left untouched by the introduction of a Ramond-Ramond axion field through a SL(2,R) rotation, there exists a particular class of axions for which inflation disappears completely. Asymptotic past initial conditions are briefly discussed, and some speculations on the possible extension of Pre-big Bang ideas to gravitational collapse are presented.Comment: harvmac, epsf. 3 figures include

Chirality transfer from Graphene Quantum Dots

Chiral graphene quantum dots were prepared by acidic exfoliation and oxidation of graphite, dialysis, and esterification with enantiomerically pure (R) or (S)‐2‐phenyl‐1‐propanol. Circular dichroism studies support the formation of supramolecular aggregates with pyrene molecules, where a transfer of chirality occurs from the chiral graphene quantum dots to the pyrene

Actitudes e intereses de los alumnos en el ámbito de la ciencia y la tecnología

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Large N limit of Extremal Non-supersymmetric Black Holes

The large N limit of extremal non-supersymmetric Type-I five-dimensional string black holes is studied from the point of view of D-branes. We find that the agreement between the D-brane and the black-hole picture is due to an asymptotic restoration of supersymmetry in the large $N$ limit in which both pictures are compared. In that limit Type-I string perturbation theory is effectively embedded into a Type-IIB perturbation theory with unbroken supersymmetric charges whose presence guarantees the non-renormalization of mass and entropy as the effective couplings are increased. In this vein, we also study the near-horizon geometry of the Type-I black hole using D5-brane probes to find that the low energy effective action for the probe is identical to the corresponding one in the auxiliary Type-IIB theory in the large N limit.Comment: 25 pages, harvmac, typos corrected and references adde

La vocación científica y tecnológica: predictores actitudinales significativos

Este estudio presenta un análisis empírico acerca de los factores afectivos y actitudinales relacionados con la ciencia y tecnología que influyen sobre la vocación científica en alumnos adolescentes que acaban la educación obligatoria; también se analiza la elección de una carrera científica y las expectativas de un trabajo en ciencia y tecnología para actuar sobre ellos mejorando la educación científica. Las actitudes relacionadas con la ciencia comprenden un amplio conjunto de variables sobre imagen de la ciencia, preservación del medio ambiente, actitudes hacia la ciencia escolar, experiencias extraescolares y expectativas sobre el trabajo futuro, de las cuales se extraen los predictores significativos respecto a la vocación mediante un análisis de regresión lineal múltiple en una muestra de estudiantes del último curso de la educación secundaria obligatoria. Los resultados demuestran que las variables actitudinales tienen una alta capacidad predictiva global de la vocación, la carrera y la expectativa de trabajo y descubre un conjunto amplio y diverso de predictores significativos. El gusto por estudiar ciencia destaca tanto por su universalidad como por su alta capacidad predictiva; otros indicadores significativos encontrados son las creencias sobre la capacidad de la ciencia escolar para mejorar las oportunidades de carrera y abrir perspectivas a nuevos y excitantes trabajos, trabajar con máquinas o herramientas, hacer o inventar algo y usar un equipo de ciencias. Finalmente, se discuten las implicaciones de estos resultados para mejorar la educación científica y tecnológica desde la perspectiva de promover vocaciones científicas.Palabras clave: vocación científica y tecnológica; educación científica y tecnológica; currículo científico; carreras científicas y tecnológicas; expectativas laborales.The scientific and technological vocation: significant attitudinal predictors of scientific and technological vocationThis study presents an empiric analysis about the influence of related-to-science-and-technology affective and attitudinal factors on the science and technology vocation and its two components, scientific studies and job expectations. The aim is the identification of the significant factors that influence the science and technology vocational choice as a mean to improve science education according to the findings. The related-to-science-and-technology attitudes embrace a wide array of variables on the image of science, the preservation of the environment, attitudes toward school science, out-of-school experiences and expectations on the future work, which are entered as independent variables in a multiple lineal regression analysis to extract the significant predictors for the scientific vocation by means of a lineal multiple regression analysis on a sample of last grade secondary compulsory education. The results show the high predictive power of the attitudinal variables on vocation, career, and job expectations and finds a wide and diverse set of significant predictors. The liking for the school science is the most universal and powerful predictor; other significant predictors are the beliefs on the power of school science to widen career opportunities and to open ways toward new and exciting jobs for students, working with machines or tools, making or inventing something and using science kits. Finally, the implications of the findings to improve the scientific and technological education from the vocational view are discussed.Key Words: scientific and technological vocation; science and technological education; science curriculum; scientific and technological studies; job expectations

Open String Thermodynamics and D-Branes

We study the thermodynamics of open superstrings in the presence of $p$-dimensional D-branes. We get some finite temperature dualities relating the one-loop canonical free energy of open strings to the self-energy of D-branes at dual temperature. For the open bosonic string the inverse dual temperature is, as expected, the dual length under T-duality, $4\pi^{2}\alpha^{'}/\beta$. On the contrary, for the $SO(N)$, type-I superstring the dual temperature is given by $\beta$-duality, $2\pi^{2}\alpha^{'}/\beta$. We also study the emergence of the Hagedorn singularity in the dual description as triggered by the coupling of the D-brane to unphysical tachyons as well as the high temperature limit.Comment: 16 pages, harvmac (b), epsf, 2 figures included. Minor changes; discussion in section 4 has been expanded and two footnotes and a reference adde

Comparison of a proprioceptive training program on stable base and unstable base

El objetivo de este estudio fue comparar dos programas de entrenamiento propioceptivo sobre base estable (G1) y base inestable (G2). Durante 5 semanas, 18 jugadores de fútbol profesional se sometieron a un programa de entrenamiento propioceptivo, 9 formaron el G1 y 9 G2. Se aplicó el Standard Excursion Balance Test (Test de Estrella) antes y después de la intervención. Los resultados intragrupo mostraron diferencias significativas en las variables ANT.IZDO; ANTLAT.IZDO; POST.D y ANTMED.D (p<0,005) para el G1 y ANT.D; ANT.IZDO; POSTMED.D; POSTMED.IZDO Y MED.D (p <0,005) para el G2. No se hallaron evidencias significativas entre el entrenamiento en base estable y base inestable para la mejora del equilibrio y la estabilidadThe aim is to compare two proprioceptive training programs on a stable (G1) and an unstable (G2) base in terms of balance and stability. During a 5 week period, 18 professional football players underwent a proprioceptive training program, 9 in G1 and the other 9 in G2. The Standard Excursion Balance Test was applied before and after the intervention program. Significant intragroup differences were found in the variables LEFT FRONT, ANTEROLATERAL LEFT (ANTLAT.LEFT), BACK RIGHT and ANTEROMEDIAL RIGHT (ANTMED.RIGHT) (p<0,005) for the G1, and FRONT RIGHT, FRONT LEFT, POSTMED.RIGHT, POSTMED.LEFT and MED.RIGHT (p <0,005) for G2. We conclude that there are no significant differences between the unstable base training and training stable base regarding improvement in balance and stabilit