1,720,977 research outputs found
Reliability analysis of Gan-Based LEDs for solid state illumination
No full textHigh-brightness, high-efficiency GaN-based LEDs have already found many applications, and are extremely
promising devices for solid-state lighting, including general illumination [1]. While reliability of LEDs is significantly
better in most aspects compared to traditional light sources, lumen maintenance remains one of the critical issues
concerning this new technology. Early reliability studies [2] observed a rapid loss of light output, severe degradation of
the transparent encapsulating material under blue and UV illumination and elevated temperatures; non-optimized
packaging also induced other reliability problems due to difficulties in thermal management. As the packaging
technology improves, the interest is focussing on failure modes and mechanisms related with the semiconductor
material and the die technology, which have been less investigated in the past.
This work presents the results of extensive high-current accelerated aging tests carried out on blue InGaN/GaN
LEDs packaged with the usual epoxy encapsulation (lamps) as well as mounted without encapsulation (chips), in order
to isolate the chip-related failure modes. As a result, 5 distinct failure modes were identified: (i) in encapsulated
devices, testing at high current levels and, consequently, at high junction temperatures, induces degradation of the
epoxy material in contact with the heated device surface, leading to the formation of an opaque layer on the device
surface; (ii) high current and temperature affect the semi-transparent ohmic contact on top of the device, leading to
increase in series resistance, with consequent current crowding effects that reduce the optical power; (iii) an increase
in doping of the p-type layer takes place, possibly due to decomposition of Mg complexes [3,4], and Mg reactivation;
(iv) Deep Level Transient Spectroscopy (DLTS) detects changes in the distribution of deep levels already present in
untreated devices, and also a generation of shallow traps; (v) both DLTS and photocurrent spectra indicate the
creation of extended defects in devices treated at high current density. Identification of the specific failure mechanisms
allows an accurate extrapolation of LED lifetime, and suggests specific actions for improving device reliability
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
Defect diagnostics of degradation mechanisms of GaN-based LEDs after accelerated DC current ageing
No full textDegradation mechanisms of GaN-based LEDs after accelerated DC current aging
No full textThis work presents the results of an extensive DC current aging and failure analysis carried out on blue InGaN/GaN LEDs which identify failure mechanisms related to package degradation, changes in effective doping profile, and generation of deep levels. DLTS and photocurrent spectra indicate the creation of extended defects in devices aged at very high current density
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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