3,185 research outputs found
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
Theoretical Studies in Solar Cell Physics
Paper VI is excluded from the dissertation until it will be published.In this thesis, we develop analytical models with the purpose of expanding knowledge and gaining understanding of some of the internal mechanisms that limit the efficiency of single-junction solar cells. We focus on three distinct topics: fundamental energy losses, the temperature sensitivity of single-junction solar cells and the effect of the series resistance on the maximum power point. The thesis is divided in two parts. The first part reviews basic solar cell physics topics and introduces some more advanced concepts to provide the reader with the necessary background to understand the attached papers. The latter constitute the second part of the thesis.publishedVersio
Díaz Marsá, M.: "Modificaciones. Ontología crítica y antropología política en el pensamiento de Foucault"
Analytical Modeling of the Maximum Power Point with Series Resistance
This paper presents new analytical expressions for the maximum power point voltage, current, and power that have an explicit dependence on the series resistance. An explicit expression that relates the series resistance to well-known solar cell parameters was also derived. The range of the validity of the model, as well as the mathematical assumptions taken to derive it are explained and discussed. To test the accuracy of the derived model, a numerical single-diode model with solar cell parameters whose values can be found in the latest installment of the solar cell efficiency tables was used. The accuracy of the derived model was found to increase with increasing bandgap and to decrease with increasing series resistance. An experimental validation of the analytical model is provided and its practical limitations addressed. The new expressions predicted the maximum power obtainable by the studied cells with estimated errors below 0.1% compared to the numerical model, for typical values of the series resistance.publishedVersio
Andreev-Coulomb Drag in Coupled Quantum Dots
The Coulomb drag effect has been observed as a tiny current induced by both
electron-hole asymmetry and interactions in normal coupled quantum dot devices.
In the present work we show that the effect can be boosted by replacing one of
the normal electrodes by a superconducting one. Moreover, we show that at low
temperatures and for sufficiently strong coupling to the superconducting lead,
the Coulomb drag is dominated by Andreev processes, is robust against details
of the system parameters and can be controlled with a single gate voltage. This
mechanism can be distinguished from single-particle contributions by a sign
inversion of the drag current.Comment: 6 pages, 4 figures, supplemental material; published versio
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