Spectral type, temperature and evolutionary stage in cool supergiants

In recent years, temperature scales in cool supergiants (CSGs) have been disputed, and the possibility that spectral types (SpTs) do not depend primarily on temperature has been raised. We explore the relations between different observed parameters and the capability of deriving accurate intrinsic stellar parameters from them through the analysis of the largest spectroscopic sample of CSGs to date from SMC and LMC. We explore possible correlations between different observational parameters, also making use of near- and mid-infrared colours and literature on photometric variability. Direct comparison between the behaviour of atomic lines (Fe I, Ti I, and Ca II) in the observed spectra and synthetic atmospheric models provides compelling evidence that effective temperature is the prime underlying variable driving the SpT sequence in CSGs. However, there is a clear correlation between SpT and luminosity, with later ones tending to correspond to more luminous stars with heavier mass loss. The population of CSGs in the SMC is characterised by a higher degree of spectral variability, early spectral types (centred on type K1) and low mass-loss rates (at least as measured by dust-sensitive mid-infrared colours). The population in the LMC displays less spectroscopic variability and later spectral types. The distribution of spectral types is not single-peaked. Instead, the brightest CSGs have a significantly different distribution from less luminous objects, presenting mostly M subtypes (centred on M2), and increasing mass-loss rates for later types. In conclusion, the observed properties of CSGs in the SMC and the LMC cannot be described correctly by standard evolutionary models. The very strong correlation between spectral type and bolometric luminosity, supported by all data from the Milky Way, cannot be reproduced at all by current evolutionary tracks.Comment: 25 pages, 24 figure

Analysis of the Behaviour of Biofuel-Fired Gas Turbine Power Plants

The utilisation of biofuels in gas turbines is a promising alternative to fossil fuels for power generation. It would lead to significant reduction of CO2 emissions using an existing combustion technology, although significant changes seem to be needed and further technological development is necessary. The goal of this work is to perform energy and exergy analyses of the behaviour of gas turbines fired with biogas, ethanol and synthesis gas (bio-syngas), compared with natural gas. The global energy transformation process (i.e. from biomass to electricity) has also been studied. Furthermore, the potential reduction of CO2 emissions attained by the use of biofuels has been determined, considering the restrictions regarding biomass availability. Two different simulation tools have been used to accomplish the aims of this work. The results suggest a high interest and the technical viability of the use of Biomass Integrated Gasification Combined Cycle (BIGCC) systems for large scale power generation

A wide family of singularity-free cosmological models

In this paper a family of non-singular cylindrical perfect fluid cosmologies is derived. The equation of state corresponds to a stiff fluid. The family depends on two independent functions under very simple conditions. A sufficient condition for geodesic completeness is provided.Comment: 7 pages, RevTeX

Estrategia didáctica para favorecer la formación y el desarrollo de la competencia para gestionar el conocimiento matemático en los estudiantes universitarios

Nota: Artículo derivado de tesis doctoral de igual título aprobada en mayo de 2009.La investigación tuvo como objeto el proceso docente-educativo de la matemática en la carrera de Ingeniería en Sistemas de Computación de la Universidad APEC (UNAPEC). Estuvo orientada al diseño de una estrategia didáctica para favorecer la formación y el desarrollo de la competencia para gestionar el conocimiento matemático en los estudiantes, la que se sustenta en un modelo teórico que se explica a partir de tres subsistemas que permiten develar las relaciones que se dan en el proceso de formación y desarrollo de la competencia declarada en el contexto del proceso docente-educativo (PDE) de la matemática. Para determinar la factibilidad y pertinencia se realizó la ejemplificación y valoración de la estrategia didáctica a través del método de expertos, y la constatación empírica a través de un pre-experimento pedagógico. La novedad científica está dada al develar las relaciones existentes entre los subsistemas que componen el modelo y expresan la concepción de la competencia para gestionar el conocimiento matemático