351 research outputs found
Quasi-homogeneous black hole thermodynamics
Although the fundamental equations of ordinary thermodynamic systems are
known to correspond to first-degree homogeneous functions, in the case of
non-ordinary systems like black holes the corresponding fundamental equations
are not homogeneous. We present several arguments, indicating that black holes
should be described by means of quasi-homogeneous functions of degree different
from one. In particular, we show that imposing the first-degree condition leads
to contradictory results in thermodynamics and geometrothermodynamics of black
holes. As a consequence, we show that in generalized gravity theories the
coupling constants like the cosmological constant, the Born-Infeld parameter or
the Gauss-Bonnet constant must be considered as thermodynamic variables
Gowdy Cosmological Models in N=1 Supergravity
We investigate the canonical quantization of supergravity N=1 in the case of
a midisuperspace described by Gowdy cosmological models. The quantum
constraints are analyzed and the wave function of the universe is derived
explicitly. Unlike the minisuperspace case, we show the existence of physical
states in midisuperspace models. The analysis of the wave function of the
universe leads to the conclusion that the classical curvature singularity
present in the evolution of Gowdy models is removed at the quantum level due to
the presence of the Rarita-Schwinger field.Comment: 25 pages and 2 figure
Curvature as a Measure of the Thermodynamic Interaction
We present a systematic and consistent construction of geometrothermodynamics
by using Riemannian contact geometry for the phase manifold and harmonic maps
for the equilibrium manifold. We present several metrics for the phase manifold
that are invariant with respect to Legendre transformations and induce
thermodynamic metrics on the equilibrium manifold. We review all the known
examples in which the curvature of the thermodynamic metrics can be used as a
measure of the thermodynamic interaction
Geometrothermodynamic description of magnetic materials
We perform a statistical and geometrothermodynamic analysis of three
different models of magnetic materials, namely, the translational free model,
the spin model, and the mean-field model. First, we derive the fundamental
equation for each model, which is then used as input to compute the metrics of
the corresponding equilibrium spaces. Analyzing the corresponding
geometrothermodynamic curvatures, we conclude that they can be used to describe
thermodynamic interaction, stability conditions, and the phase transition
structure of the modeled substances. In all the cases, we reproduce their
well-known behavior close to the Curie temperature. Moreover, in the case of
the model with spin, we found a curvature singularity which corresponds to a
novel transition, where a particular response function diverges, indicating the
presence of second order phase transition, according to Ehrenfest
classification
Geometrothermodynamics of asymptotically anti - de Sitter black holes
We apply the formalism of geometrothermodynamics to the case of black holes
with cosmological constant in four and higher dimensions. We use a
thermodynamic metric which is invariant with respect to Legendre
transformations and determines the geometry of the space of equilibrium states.
For all known black holes in higher dimensions, we show that the curvature
scalar of the thermodynamic metric in all the cases is proportional to the heat
capacity. As a consequence, phase transitions, which correspond to divergencies
of the heat capacity, are represented geometrically as true curvature
singularities. We interpret this as a further indication that the curvature of
the thermodynamic metric is a measure of thermodynamic interaction.Comment: Section on statistical ensembles and new references adde
Simulación y evaluación de la confiabilidad de un proceso de sistema de producción
En el presente trabajo se estudia la confiabilidad y la supervivencia de datos en una empresa que comercializa equipos de tecnologÃa para desarrollar labores administrativas cotidianas.
Primero se realiza un preámbulo de la historia e importancia de la confiabilidad de aparatos o sistemas ya sea en el campo de la medicina o en el campo industrial; dando a conocer también algunos conceptos básicos de la teorÃa de la confiabilidad o supervivencia.
Luego se manifiestan los diversos modelos de supervivencia, y demás técnicas estadÃsticas y actuariales ligadas con este tipo de análisis.
Como paso siguiente se realiza un estudio de las técnicas para la estimación no paramétrica, apropiado para este análisis de los tiempos de falla o también denominados tiempos de supervivencia.
En la siguiente parte se realizarán los respectivos cálculos para estimar de forma paramétrica y no paramétrica la función de supervivencia de los datos obtenidos dentro de la empresa comercializadora de equipos con tecnologÃa. Por último, se realizarán las conclusiones obtenidas del desarrollo del estudio, junto con las respectivas recomendaciones para la obtención de mejoras para próximos análisis
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