1,720,959 research outputs found
A software tool for thermal simulation and rating evaluation of high power silicon devices
No full textHigh reliable high power diode for welding applications
No full textLong-term power cycling of high power diodes for welding application is presented. The devices are packaged in an ultra-slim flat package, which allows very high heat sinking capability and rating current. Tests with different operating conditions were carried out and the results compared with the few data available in literature. Our devices show very good lifetime, especially considering that all tests were terminated without any performance degradation. Finally a thermo-electrical model of the device was built and will be used for both validation of lumped element thermal models and evaluation of new design solutions
A new silicon resistor technology for very high power snubbers
No full textIn this work we developed press-pack silicon resistors for current ratings of thousands of amperes. Many prototypes were fabricated (with various resistance values) and characterized, using low-voltage (< 100 V) fast-pulsed (i.e., isothermal) measurements to tune a two-dimensional electro-thermal numerical model. The simulations then provided us with a description of the resistor behavior under high-voltage and high-current conditions that were unattainable by our measurement set-up. The decrease of carrier mobility with electric field causes a non-linear I-V relationship whereby the resistance is lower at low fields and higher at high fields. This feature is useful in snubber applications, where the resistor is used as a current-limiting element during the discharge of the capacitor: the resistance is maximum at the onset of the discharge phase, when current must be limited, then its value decreases with the voltage drop, thus speeding up the transient. The simulations also allowed us to study the temperature dependence of the resistance. We observed a non-monotonic behavior, with an increase of the resistance with temperature due to carrier scattering, followed by a rapid decrease due to thermal generation of excess carriers. These press-packed resistors represent a promising solution for snubber application in stacks with high-power diodes or GTOs, very large currents being allowed by the outstanding heat-sinking capabilities of the press-pack
Finite Element Design of Water Heat Sinks for Press-Pack IGBTs
No full textIn the power electronics market the keywords for an evaluation of fluid heat sinks are "pressure drop" and "thermal resistance". Nevertheless the devices that have to be cooled, especially the chips contained in the presspack IGBTs, require a uniform distribution of the surface temperatures in order to withstand a large number of thermal cycles. For this reason the commonplace concept of "thermal resistance" that does not take into consideration the non-uniformities cannot be satisfactory. In this work, because of its complexity, we don't present any new project solutions nor any new prototypes. On the contrary our aim is to show the importance of a complete 3D modeling as a support in the modem designing of fluid heat sinks in order to produce really efficient products
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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