1,721,209 research outputs found
Thermodynamics of photovoltaics
No full textA solar cell is a thermodynamic engine working between two heat reservoirs, one at high temperature T 1 (= the temperature of the Sun = 5762 K) and one at low temperature T 2 (= the temperature of the Earth = 288 K). Its electric current consists of two parts: the light current, strongly dependent on T 1, and the dark current, strongly dependent both on T 2 and on material constants and technology parameters
Interfacing reversible pass-transistor CMOS chips with conventional restoring CMOS circuits
No full textImportant progress has been made recently in the prototyping of reversible (quantum) digital circuits, proving that digital reversible dual-line pass-transistor technology may be used for applications in reversible linear computation. This raises new questions regarding the compatibility of this new technology with existing standard switching CMOS technology. The greatest difficulty is brought by the difference of signal shape used by the two technologies. Whereas standard switching CMOS circuits make use of rectangular pulses, dual-line pass-transistor reversible circuits use adiabatic triangular or trapezoidal ones. This work proposes a simple technical solution that allows interfacing digital reversible pass-transistor with conventional CMOS switching technology represented here by a Xilinx FPGA embedded on a commercial Spartan-3E board. All the proposed solutions have successfully been tested, allowing the FPGA to practically drive a reversible chip
Statistical thermodynamic foundation for photovoltaic and photothermal conversion. IV. Solar cells with larger-than-unity quantum efficiency revisited
No full textA detailed balance solar energy conversion model offering a single treatment of both photovoltaic and photothermal conversion is expounded. It includes a heat rejection mechanism. The effect of multiple impact ionizations on the solar cell efficiency is reconsidered by including the constraints dictated by the first law of thermodynamics (which already exist in the model) and it improves of course the solar cell efficiency. However the upper bound efficiencies previously derived are too optimistic as they do not take into consideration the necessary increase in solar cell temperature. The cell efficiency operating under unconcentrated radiation is a few percent lower than in the ideal case (i.e., with perfect cooling). Wider band gap materials are recommended for those applications where the cell cooling is not effective. The best operation of naturally ventilated cells is under unconcentrated or slightly concentrated solar radiation. Increasing the (forced) ventilation rate allows an increase of the optimum concentration ratio. Additional effects such as the radiation reflectance and radiative pair recombination efficiency are also considered. A sort of threshold minimum band gap depending on the last effect is emphasized: materials with band gaps narrower than this threshold are characterized by very low cell efficiency
Statistical thermodynamic foundation for photovoltaic and photothermal conversion III: application to hybrid solar convertors
No full textThis article considers different optimized applications of hybrid (i.e., combined) solar converters (which are devices to generate simultaneously electrical power, mechanical power, and, possibly, thermal energy). A theoretical model proposed recently by the authors is used. An improved model to evaluate upper bounds for the efficiency of photovoltaic converters is elaborated. Its predictions are used to discuss the performance of hybrid converters. It follows that band gap materials are appropriate for these combined converters
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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