4,317 research outputs found
From quantum monodromy to duality
For N\!=\!2 SUSY theories with non vanishing \beta-function and a one dimensional quantum moduli, we study the representation on the special coordinates, of the group of motions on the quantum moduli defined by \Gamma_W\!=\!Sl(2;Z)\!/\!\Gamma_M, with \Gamma_M the quantum monodromy group. \Gamma_W contains both the global symmetries and the strong-weak coupling duality. The action of \Gamma_W on the special coordinates is not part of the symplectic group Sl(2;Z). After coupling to gravity, namely in the context of non-rigid special geometry, we can define the action of \Gamma_W as part of Sp(4;Z). To do that requires singular gauge transformations on the "scalar" component of the graviphoton field. In terms of these singular gauge transformations the topological obstruction to strong-weak duality can be interpreted as a \sigma-model anomaly, indicating the possible dynamical role of the dilaton field in S-duality
Evolución en la enseñanza de la ciencia: una introducción para maestros
PDF de 41 páginas con gráficos y figuras a color. M.ª José Gómez Díaz es Coordinadora de El CSIC en la Escuela. VACC-CSIC
José María López Sancho es Director de El CSIC en la Escuela. IFF-CSIC
Esteban Moreno Gómez es director de los recursos WEB del programa El CSIC en la Escuela.Exponemos brevemente las últimas líneas de investigación centradas en cuestionarios de evaluación
diagnóstica referentes a la NOS (Nature of Science). Utilizamos esta exposición para meditar acerca
de las líneas fundamentales que definen la verdadera naturaleza de la ciencia que debemos aprender
y transmitir a nuestros alumnos de acuerdo con sus características.
El concepto de NOS se deriva de la forma en la que los científicos construyen el conocimiento
científico y en sus características. Nosotros iremos un paso más allá en cuanto a abstracción: nos
apoyamos en el modelo de conocimiento de Piaget que, como veremos, coincide exactamente con el
esquema introducido por Kuhn para explicar la construcción del conocimiento de las comunidades
científicas.Peer reviewe
Nanocrystalline cathodes for PC-SOFCs based on BCZY
Perovskites based on BaCeO3-δ exhibit the highest proton conductivity among this class of materials, however, they are susceptible to hydration and carbonation in presence of water vapor and CO2 [1]. In contrast, the chemical stability of BaZrO3-based protonic conductors is better, but they require sintering temperatures as high as 1700 ºC and suffer from high intrinsic grain boundary resistance, limiting the final performance. Partial substitution of Zr for Ce in Ba(Ce0.9-xZrx)Y0.2O3-δ allows obtaining electrolytes with both high proton conductivity and good chemical stability.
The performance of a PC-SOFC at low temperatures depends significantly on the ohmic resistance of the electrolyte, although it can be lowered by reducing the electrolyte thickness. Another important limiting factor is the increase of the cathode polarization resistance due to the thermally activated nature of the oxygen reduction reaction. For this reason, it is essential to obtain high efficiency cathodes operating at reduced temperatures.
In this work, BaCe0.6Zr0.2Y0.2O3-δ (BCZY) powders were prepared by freeze-drying precursor method. These powders were mixed with a Zn-containing solution as sintering additive in order to obtain dense pellets with submicrometric grain size at only 1200 ºC. After that, La0.6Sr0.4Co0.8Fe0.2O3 nanocrystalline electrodes were deposited symmetrically onto dense pellets BCZY by conventional spray-pyrolysis [3]. The structure, microstructure and electrochemical properties of these electrodes have been examined by XRD, FE-SEM and impedance spectroscopy. The stability of these electrodes at intermediate temperatures was evaluated as a function of time.
These nanocrystalline cathodes exhibit a substantial improvement of the electrode polarization resistance with respect to the same materials prepared by screen-printing method at high sintering temperatures, e.g. 0.7 and 3.2 cm2 at 600 ºC for LSCF cathodes prepared by spray-pyrolysis and screen-printing method respectively (Figure). An anode supported cell with composition LSCF/BCZY/NiO-BCZY was also prepared to test the electrochemical performance.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
870 micron continuum observations of the bubble-shaped nebula Gum 31
We are presenting here a study of the cold dust in the infrared ring nebula
Gum 31. We aim at deriving the physical properties of the molecular gas and
dust associated with the nebula, and investigating its correlation with the
star formation in the region, that was probably triggered by the expansion of
the ionization front. We use 870 micron data obtained with LABOCA to map the
dust emission. The obtained LABOCA image was compared to archival IR,radio
continuum, and optical images. The 870 micron emission follows the 8 micron
(Spitzer), 250 micron, and 500 micron (Herschel) emission distributions showing
the classical morphology of a spherical shell. We use the 870 micron and 250
micron images to identify 60 dust clumps in the collected layers of molecular
gas using the Gaussclumps algorithm. The clumps have effective deconvolved
radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume
densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the
clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21
K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass
distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to
M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for
the stellar IMF in the solar neighborhood, suggesting that the clumps are not
direct progenitors of single stars/protostars. The mass-radius relationship for
the 41 clumps detected in the 870 microns emission shows that only 37% of them
lie in or above the high-mass star formation threshold, most of them having
candidate YSOs projected inside. A comparison of the dynamical age of the HII
region with the fragmentation time, allowed us to conclude that the collect and
collapse mechanism may be important for the star formation at the edge of Gum
31, although other processes may also be acting.Comment: 15 pages, 10 figures. Accepted for publication in A&
Ictiólogos de la Argentina : Ricardo Gerónimo Perrotta
Fil: López, Hugo Luis. División Zoología Vertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Ponte Gómez, Justina. División Zoología Vertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Hansen, Jorge E.
Dibujantes de la Argentina: Edmundo Maristany.
En esta colección de la Serie Documentos presentamos a los dibujantes y artistas que pasaron por nuestra institución, lo que representa una tarea nada fácil.
Sin embargo, con las imperfecciones del caso, iniciamos este trabajo esperando que, en un futuro próximo, esta iniciativa sea continuada dentro de las diferentes Divisiones que conforman la estructura de nuestro Museo.
En este primer artículo mostramos algunas de las imágenes que pudimos rescatar de Edmundo Maristany, una figura polifacética, ya que, entre sus logros se encuentra el descubrimiento de un cometa que hoy lleva su nombre y el escrito de sonetos publicados en la década del cincuenta.
A través de sus dibujos de vertebrados, sabemos que trabajó para el Dr. Emiliano Mac Donagh en el Museo de La Plata y para el Dr. Carlos Marelli en el Jardín Zoológico de nuestra ciudad
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