1,720,962 research outputs found
Wavelength selective photoexcitation of picosecond acoustic-phonon pulses in a triple GaAs/Al<sub>0.3</sub>Ga<sub>0.7</sub>As quantum well structure
No full textUltrashort coherent phonon-pulse generation and detection is investigated in a GaAs–Al0.3Ga0.7As quantum well structure containing three wells of different widths using an optical pump and probe method. The pump photon energy is tuned to the region of the hh1–e1 transition energies of the wells and the probe photon energy is chosen for detection of the phonon pulses that reach the sample surface. By studying the dependence of the probe reflectance change on the pump photon energy, we demonstrate the possibility of wavelength-selective excitation of picosecond acoustic-phonon pulses in quantum wells.<br/
Acoustic phonon generation and detection in GaAs/Al0.3Ga0.7As quantum wells with picosecond laser pulses
Full text linkPicosecond acoustic-phonon pulse generation and detection is investigated in a sample containing three GaAs/Al0.3Ga0.7As quantum wells of different thickness with an interferometric optical pump and probe technique. The pump photon energy is tuned through the hh1-e1 transitions of each well and the probe photon energy is chosen to allow the detection of the phonon pulses at the sample surface. The phonon pulse shapes are explained with a model that relates the carrier wave functions to the acoustic strain, and the acoustic strain to the detected optical reflectance and phase changes
Picosecond acoustics in semiconductor quantum wells
No full textPicosecond acoustic phonon pulses are generated with ultrashort laser pulses in a sample containing three GaAs-Al0.3Ga0.7As quantum wells of different thickness. The pump photon energy is tuned through the hh1-e1 transitions of each well (1.44 - 1.64 eV) and the probe photon energy is chosen to allow detection of the phonon pulses at the sample surface (3.06 eV). Transient optical reflectance and phase changes are recorded as a function of the delay time between the pump and probe light pulses using an interferometric technique. The transition between the valence and conduction sublevels of the wells is observed to strongly influence the pump-photon-energy dependence of the acoustic phonon pulse generation. The data are analyzed with a model that relates the carrier wavefunctions in the quantum wells to the acoustic strain through the deformation potential, and the acoustic strain to the transient optical reflectance and phase
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
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