1,721,002 research outputs found
Anisotropic optical properties of single-crystal GdBa2Cu3O7-delta
No full textThe optical spectrum of reduced-T(c) GdBa2Cu3O7-delta has been measured for polarizations parallel and perpendicular to the ab plane. The sample was an oxygen-deficient single crystal with a large face containing the c axis. The polarized reflectance from this face was measured from 20-300 K in the spectral region from 30-3000 cm-1, with 300 K data to 30 000 cm-1. Kramers-Kronig analysis was used to determine the spectral dependence of the ab and the c components of the dielectric tensor. The optical properties are strongly anisotropic. The ab-plane response resembles that of other reduced-T(c) materials whereas the c axis, in contrast, shows only the presence of several phonons. There is a complete absence of charge carrier response along c above and below T(c). This observation allows us to set an upper limit to the free-carrier spectral weight for transport perpendicular to the CuO2 planes
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
The Far Infrared Absorption Spectrum of Silicon and Germanium Under High Optical Excitation
No full textA study has been conducted, at low temperatures, of the far infrared absorption spectrum of silicon and germanium under high optical excitation. This work presents the first experimental observation of the absorption of both the gas of indirect excitons and the electron-hole drops (EHD) in silicon. Using the strength of the exciton absorption, a study of the coexistence of the exciton gas with the EHD was undertaken. For germanium, the absorption spectra produced by excitons and the behaviour of the exciton transitions in the presence of a small magnetic field were measured. The experimental excitonic absorption spectra in both silicon and germanium are compared with the results of the effective mass Hamiltonian model and it is found that the results of this model account well for the observed structure in both materials. A model for the response of the exciton levels to an externally applied magnetic field was developed. The comparison of the experimental results provided a check on the identification of the observed transitions between lS to 2P exciton states in germanium. The absorption spectrum produced by EHD is silicon is compared with a calculated spectrum using the Mie theory for the absorption of radiation by small particles. The calculation included both interband and intraband transitions for the valence bands. The agreement with the experiment is good and justifies an estimate of the value of the electron-hole density inside the drops in silicon. As a result of the study of the coexistence of the exciton gas with the EHD, estimates could be done for the radius of the drops in silicon.Doctor of Philosophy (PhD
Far-infrared Absorption by Excitons in Germanium at High Concentrations
Full text linkThe dependence on frenuency of the photo-ionization cross~section of indirect excitons in germanium (at concentrations corresponding to "isolated" excitons) was found to be v⁻¹.⁵. A dependence of v⁻².⁷ had been expected, by comparison with the hydrogen theory previously thought applicable. No adequate replacement theory exists. A probable explanation might lie in the Lucovsky model of impurities in semiconductors, which predicts the correct frequency dependence, assuming an enhanced interparticle potential at small separations. This central cell correction was justified in excitons because the dielectric constant of the material varies with the election- hole separation. The - 1.5 power was found to decrease slowly as concentration increased. The main observation at concentrations of 2x10¹⁴ cm⁻³ and above was a new, strongly absorbing, component of non excitonic character in the absorption spectrum between 1 and 2 meV, peaking at 1.5 meV with a FWHM of ~ 1 meV. The peak grew at the 1.5th power of the exciton peaks, having a fairly sharp onset between 4 and 5.5°K and a very small temperature dependence above that range. This peak was interpreted in terms of an electron-hole plasma analogous to ordinary electron-hole fluid, which appeared in the form of drops in the high density exciton cloud. A double peaked phase diagram was constructed, in qualitative agreement with some theoretical predictions, and experimental results obtained by workers using the recombination luminescence technique, some of whom attribute their results to the formation of biexcitons.Master of Science (MS
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