33,150 research outputs found

    SPICE modelling of photoluminescence and electroluminescence based current-voltage curves of solar cells for concentration applications

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    Quantitative photoluminescence (PL) or electroluminescence (EL) experiments can be used to probe fast and in a non-destructive way the current-voltage (IV) characteristics of individual subcells in a multi-junction device, information that is, otherwise, not available. PL-based IV has the advantage that it is contactless and can be performed even in partly finished devices, allowing for an early diagnosis of the expected performance of the solar cells in the production environment. In this work we simulate the PL- and EL-based IV curves of single junction solar cells to assess their validity compared with the true IV curve and identify injection regimes where artefacts might appear due to the limited in-plane carrier transport in the solar cell layers. We model the whole photovoltaic device as a network of sub-circuits, each of them describing the solar cell behaviour using the two diode model. The sub-circuits are connected to the neighbouring ones with a resistor, representing the in-plane transport in the cell. The resulting circuit, involving several thousand subcircuits, is solved using SPICE

    Asymptotically anomalous black hole configurations in gravitating nonlinear electrodynamics

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    We analyze the class of non-linear electrodynamics minimally coupled to gravitation supporting asymptotically flat \textit{non Schwarzschild-like} elementary solutions. The Lagrangian densities governing the dynamics of these models in flat space are defined and fully characterized as a subclass of the set of functions of the two standard field invariants, restricted by requirements of regularity, parity invariance and positivity of the energy, which are necessary conditions for the theories to be physically admissible. Such requirements allow for a complete characterization and classification of the geometrical structures of the elementary solutions for the corresponding gravity-coupled models. In particular, an immediate consequence of the requirement of positivity of the energy is the asymptotic flatness of gravitating elementary solutions for any admissible model. The present analysis, together with the (already published) one concerning the full class of admissible gravitating non-linear electrodynamics supporting asymptotically flat \textit{Schwarzschild-like} elementary solutions, completes and exhausts the study of the gravitating point-like charge problem for this kind of models.Comment: 12 pages, 6 figures, revtex4, added extra paragraph in conclusions, added some references, added other minor changes, to published in Phys.Rev.

    Cooler and bigger than thought? Planetary host stellar parameters from the InfraRed Flux Method

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    Effective temperatures and radii for 92 planet-hosting stars as determined from the InfraRed Flux Method (IRFM) are presented and compared with those given by other authors using different approaches. The IRFM temperatures we have derived are systematically lower than those determined from the spectroscopic condition of excitation equilibrium, the mean difference being as large as 110 K. They are, however, consistent with previous IRFM studies and with the colors derived from Kurucz and MARCS model atmospheres. Comparison with direct measurements of stellar diameters for 7 dwarf stars, which approximately cover the range of temperatures of the planet-hosting stars, suggest that the IRFM radii and temperatures are reliable in an absolute scale. A better understanding of the fundamental properties of the stars with planets will be achieved once this discrepancy between the IRFM and the spectroscopic temperature scales is resolved.Comment: 15 pages, 4 figures. Accepted for publication in Ap

    Parallel imports, innovations and national welfare: The role of the sizes of the income classes and national markets for health care.

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    This paper shows that regardless of any intra-country income differences, parallel imports result in a lower level of health-care innovation but, contrary to popular as well as conventional theoretical wisdom, a lower price in the Third World compared to market-based discrimination. Despite such a lower price, however, parallel imports unambiguously make all buyers in the Third World worse off when intra-country income disparity exists. On the other hand, even discarding the MNC's profit, there will be cases in which the richer country prefers price discrimination as well. That is, in those cases, no countries will have any incentive under the welfare criterion to undo price discrimination, contrary to Richardso

    On the galactic chemical evolution of sulfur

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    Sulfur abundances have been determined for ten stars to resolve a debate in the literature on the Galactic chemical evolution of sulfur in the halo phase of the Milky Way. Our analysis is based on observations of the S I lines at 9212.9, 9228.1, and 9237.5 A for stars for which the S abundance was obtained previously from much weaker S I lines at 8694.0 and 8694.6 A. In contrast to the previous results showing [S/Fe] to rise steadily with decreasing [Fe/H], our results show that [S/Fe] is approximately constant for metal-poor stars ([Fe/H] < -1) at [S/Fe] = +0.3. Thus, sulfur behaves in a similar way to the other alpha elements, with an approximately constant [S/Fe] for metallicities lower than [Fe/H] = -1. We suggest that the reason for the earlier claims of a rise of [S/Fe] is partly due to the use of the weak S I 8694.0 and 8694.6 A lines and partly uncertainties in the determination of the metallicity when using Fe I lines. The S I 9212.9, 9228.1, and 9237.5 A lines are preferred for an abundance analysis of sulfur for metal-poor stars.Comment: Accepted by A&A, 12 pages. Full article with figures in A&
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