1,721,091 research outputs found
Modified transmission and fluorescence in aperiodic and biomimetic photonic crystals
No full textComplete photonic bandgaps (PBGs) are more readily achieved in highly-symmetric photonic crystals (Ph Cs). Aperiodic crystals (quasicrystals) with arbitrarily high orientational order are promising candidates to lower the dielectric contrast necessary to open PBGs. This thesis in- vestigates the connection between the structural and optical properties of four PhC lattices by studying the effects on transmission and fluorescence spectra. In order of increasing structural isotropy these lattices are: hexagonal, Archimedean-like, Stampfli, and a biomimetic 'sunflower'. High structural isotropy is associated with weaker diffraction. The sunflower's Fourier spectrum is defined by a dense ring of weak reciprocal lattice vectors. Its local morphology, which is everywhere unique, continuously transforms between localised 4- or 6-fold symmetry. All other crystals are spatially uniform with pure point spectra. Although structurally similar to the Archimedean, the Starnpfli improves isotropy without sacrificing diffraction efficiency. TM gaps of high-contrast (~c = 8.61) rod-type PhCs are shown to be nearly independent of the lattice geometry by FDTD simulations. The primary gaps are sensitive to random rod sizes, which disrupts the coherent coupling between the individual rod resonances. Transmission spectra for TE polarisation or hole-type Ph Cs are more dependent on Bragg reflection due to weak or non-existent Mie resonances. In small samples, the TM gap is typically wider in less isotropic crystals. Much larger samples demonstrate the importance of structural isotropy and long-range interactions in low ~c PhCs. The sunflower's 21% TM gap is, to date, the widest TM PBG reported for ~c = 1. The Stampfli also supports a TE gap in the same range as its 14% TM gap, thus yielding a 4.6% absolute PBG. Further band diagram calculations on an 'approximant' of the sunflower reveal the presence of intrinsic dipolar and monopolar defect states. Microwave characterisation of rod-type samples (~c = 8.61) showed complete TM PBGs (> 60dB) with gap ratios ranging from 37.28% (hexagonal) to 25.85% (sunflower). Low-contrast samples (~c = 1.6) showed complete TM PBGs (> 30dB) with gap ratios rising from 10.37% (hexagonal) to an ambiguous value of either 10.48% or 20.95% for the sunflower due to the unusual spiral structuring of the transmission spectra. The Stampfli also supports a complete TE gap (> 10dB) that coincides with its 14.19% TM gap for a 3.55% absolute gap that, to the author's knowledge, represents the first conclusive demonstration of an absolute PBG for ~c = 1.6. A larger sunflower sample was shown to have an extremely large experimental (simulated) TM gap of 33.33% (23.16%), erroneously broadened by the non-parallel rods. A new approach to enhance the efficiency of up conversion pumping in RE-doped media is pro- posed based on PBG suppression of emission from intermediate levels. Preliminary results indi- cate that visible emission from hexagonal and sunflower PhC slabs in 0.2 wt% Er:GLSO pumped at 808nm is enhanced by up to 1.6x at 550nm, or up to 4.5x at 525nm. Subsequent analysis appears to rule out suppression of IR emission, and suggests modified thermal properties as the cause.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Tunable transmission in a graphene photonic crystal in mid-infrared
No full textOptical properties of Graphene have recently attracted enormous attention from investigators [1-5]. A significant amount of work is devoted to the calculation of optical conductivity ?(?) with the aim of probing the interaction of light with this material. These calculations take the electronic band structure of graphene as their starting point and most of them are restricted to the low frequency range where the electronic dispersion is linear in energy i.e
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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