1,720,970 research outputs found
Analysis of the physical processes responsible for the degradation of deep-ultraviolet light emitting diodes
No full textThis paper reports an extensive analysis of the degradation of deep-ultraviolet light-emitting diodes
submitted to dc stress test. The study was carried out by means of combined electrical and optical
characterization techniques. Results described in the paper indicate that the following: i stress can
induce a significant decrease in the optical power emitted by the devices; ii optical power decrease
is more prominent at low measuring current levels, thus suggesting that degradation is related to an
increase in the concentration of defects; iii stress induces a significant increase in the green-yellow
parasitic emission of the devices; and iv stress causes a localized increase in the apparent charge
distribution profiles in the active region of the devices. Experimental evidence collected within this
work suggest that degradation is due to an increase in the defectiveness in the active layer of the
devices, with subsequent worsening of their radiative efficiency
Defect-related degradation of Deep-UV-LEDs
No full textWith this paper we describe an extensive analysis of the electro-optical degradation of deep ultraviolet
Light-Emitting Diodes emitting at 310 nm, submitted to accelerated stress test. The results obtained
within this study indicate that: (i) high current stress can induce a significant decrease in the optical
power emitted by the LEDs; (ii) optical power decrease is more prominent at low measuring current levels,
indicating that degradation is related to an increase in the concentration of defects, with subsequent
decrease in the radiative efficiency of the active layer; (iii) stress can induce a significant increase in the
operating voltage of the LEDs, due to the increase in the resistivity of the ohmic contacts or p-type semiconductor;
and (iv) after stress, LEDs show a significantly increased green parasitic emission. This result
suggest that stress induced an increase in the defectiveness of the active layer. Information on the location
of the degraded region is achieved by the analysis of the Apparent Charge Distribution curves
obtained by capacitance–voltage measurements
Carotid artery stenting: cerebral NMR-DW and histopathological analisis to stratify embolic risk
No full text
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
ESD characterization of multi-chip RGB LEDs
No full textIn this paper we present an extensive analysis of the failure mechanisms of RGB (multi-chip) LEDs submitted to ESD testing: the tests have been carried out on several commercially available LEDs of three different suppliers. In order to better understand the failure mechanisms, we have submitted LEDs to ESD tests under reverse and forward bias condition separately, by means of a Transmission Line Pulser (TLP). The experimental results indicate that: (i) red LEDs (based on AlInGaP) have an higher ESD robustness with respect to green and blue samples (based on InGaN), both under reverse and under forward bias test; (ii) TLP negative pulses with a current smaller than the failure threshold can induce a decrease of the leakage current in GaN-based LEDs, due to a partial annihilation of defective paths responsible for reverse conduction; (iii) typical failure mechanism of devices is represented by a catastrophic event, with short-circuiting of the junction. Moreover, some of the analyzed red LEDs had shown "soft" failure, with gradual increase of the leakage current and corresponding decrease of the optical power, even without a catastrophic damage. © 2013 Elsevier Ltd. All rights reserved
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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