1,721,020 research outputs found
Investigation of the exciton relaxation processes in poly(9,9-dioctylfluorene-co -benzothiadiazole):CsPbI1.5Br1.5nanocrystal hybrid polymer-perovskite nanocrystal blend
No full textThe combination of lead halide perovskite nanocrystals and conjugated polymer in a blend film opens the way to the realization of hybrid active layers with widely tunable optical and electrical properties. However, the interaction between the polymeric and the perovskite component of the blends is mainly unexplored to date. In this work we perform temperature-dependent photoluminescence and time resolved photoluminescence measurements in order to deeply investigate the photophysics of a poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT):CsPbI1.5Br1.5 nanocrystal hybrid film. Our results suggest that the primary interaction channel is charge transfer, both from F8BT to the NCs and from the NCs to F8BT, while Förster resonant energy transfer has no visible effects. Moreover, we show that the charge transfer is assisted by energy migration within the F8BT excited state distribution and that it is dependent on the local micromorphology of the film. Our work improves the current understanding of the polymer:perovskite NC interactions in hybrid films, and it is expected to be relevant for the development of hybrid organic-perovskite optoelectronic devices
Cavity Size and Temperature Dependence of Stimulated Emission in Single Zn1-xCdxSe/ZnSe Quantum-well Lasers
No full textRaman and Photoluminescence spectroscopy of polycarbonate matrices irradiated with different energy 28Si+ ions
No full textThe irradiation of a polycarbonate (PC) matrix with 28Si+ ions has been performed by selecting three different energies: 0.5 MeV, 1.0 MeV and 2.0 MeV. The comparative study of the modifications induced in the polymer as a function of the incident ion beam energy has been carried out in the range of fluences between 5 × 1013 ions cm-2 and 1 × 1015 ions cm-2. The changes induced in the structure of the matrix towards the production of conducting plastics for optoelectronics devices have been evaluated by Raman and Photoluminescence spectroscopy. The carbonization process of the polymer generates a network made of sp2-bonded graphitic clusters embedded in a sp3-bonded matrix. The amount of nanocrystalline-graphite with respect to amorphous-carbon increases as ion energy and fluence increase, in accordance with the increase of the sp2-order arrangement. With 0.5 MeV the modification process is at an initial stage so that the changes, in terms of structure and PL emission, are observed only for the highest fluence, while for 1.0 MeV it has been achieved a higher density of small cluster with an order and homogeneity even better than for 2.0 MeV. The irradiation process with a suitable set of experimental parameters allows tuning the PC emission from ∼510 nm (pristine matrix) up to ∼550-600 nm
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
- …
