1,721,003 research outputs found
Electroluminescent characteristics of conjugated polymer/ionomer blend devices according to ionic contents
No full textFluorescent polymer and poly (sodium 4-styrenesulfonate) ionomer (PSS-ionomer) blends were used as emitting layers in polymer light-emitting diodes (LEDs). The two polymers were blended in the optimal ratio which shows the highest luminescent intensity due to dilution effect. We changed the ionic contents of ionomer from 5 mol% to 10 mol% with fixed optimal blended ratio. We obtained the narrow spectrum having high color purity in the blend system. The conjugated polymer/PSS-ionomer blend devices achieved a more enhanced luminescent efficiency as compared with that of the conjugated polymer/PS device due to polar groups in the PSS-ionomer, which enhance the electron injection from the cathode to the emitting molecules
Enhanced quantum efficiency in polymer light-emitting diode with polystryrene nanolayer
No full textWe report the effect of polystyrene nanolayer on electron injection in the polymer light-emitting diodes (PLEDs) in which hole is major charge carrier. Especially, when a similar to10 nm-thick polystyrene layer was employed, the device gave two orders of magnitude higher external quantum efficiency than that of the one without an insulating nanolayer This enhancement may result from the dramatic lowering of the effective barrier height for electron injection to the emitting layer
Effect of polymer-insulating nanolayers on electron injection in polymer light-emitting diodes
No full textWe report the effect of polymer-insulating nanolayers on electron injection in the polymer light-emitting diodes (PLEDs) in which a hole is the major charge carrier. Several different polymer nanolayers with varying dielectric constants were placed between the emitting layer and the aluminum cathode, and their influence on the device performance was investigated. The device with a nanolayer of lower dielectric constant demonstrated higher luminescence quantum efficiency. In particular, when a similar to10-nm-thick polystyrene layer was employed, the device gave approximately two orders of magnitude higher external quantum efficiency than that of the one without an insulating nanolayer. (C) 2004 American Institute of Physics
White light emission from a polymer bilayer by incomplete cascade energy transfer
No full textWhite light emission was obtained from a light-emitting diodes (LEDs) prepared from an immiscible polymer blend consisting of poly(9,9'-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (PDHFPPV) and poly(2-methoxy-5-(2'ethy-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV). An inefficient energy transfer between PDHFPPV and MEH-PPV was observed because the blends are partially miscible. More importantly, because the order of bandgap energy is PVK > PDHFPPV > MEH-PPV we observed pure and strong white emission from this PLEDs, which results from the efficient Forster-type energy transfer from PVK to PDHFPPV and the partial energy transfer from PDHFPPV to MEH-PPV. The ITO/(PVK/immiscible blend)/Li:Al devices showed more enhanced white-light output compared with that of the ITO/(immiscible blend)/Li:Al device. (c) 2005 Elsevier B.V. All rights reserved
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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