1,721,137 research outputs found
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
Doughnut-shaped beam generation in solid-state and fibre lasers
No full textThis thesis focuses on developing new techniques for generating doughnut-shaped beams with a radial polarization state or a vortex phase front.An all-fibre-based pump beam conditioning element based on a tapered capillary fibre has been developed to provide a ring-shaped pump beam for end-pumped solid-state lasers. This unique pumping scheme provides a simple, efficient and robust approach for generating the doughnut-shaped first higher-order Laguerre-Gaussian (LG01) mode due to its optimized spatial overlap for the LG01 mode. However, the analysis of mode composition shows the doughnut-shaped LG01 mode is apt to be a ‘hybrid’ mode consisting of TEM01 modes with orthogonal orientations and LG01 modes with opposite handedness of helical phase front at axial modes with different frequencies. A novel mode selection element consisting of two nanoscale thickness aluminium strips has been developed by exploiting the fact that the standing wave intensity distribution for the LG01+ and LG01- modes inside a laser resonator are different. This scheme has been demonstrated for the first time in a diode-pumped Nd:YAG laser to generate an LG01 mode with controllable handedness of helical phase front at output powers ~1 W. Using the ring-shaped pumping scheme, direct generation of a radially-polarized beam has been successfully demonstrated in a Nd:YAG laser by exploiting the fact that the radially-polarized and azimuthally-polarized beams have slightly different spatial overlaps with the ring-shaped pump beam due to bifocusing within the laser crystal, thus resulting in a different threshold for each mode.The ring-shaped pumping scheme also provides flexibility in transverse mode selection and a significant reduction in adverse thermal lensing effects, offering the prospect of power scalability in end-pumped lasers. 14 W of linearly-polarized TEM00 mode output with a beam quality factor (M2) <1.1 and 16 W of linearly-polarized doughnut-shaped LG01 mode with M2<2.2 were obtained in a Nd:YVO4 laser with a slope efficiency of 53% and 55%, respectively. The results showed a reduction in thermal lens strength by approximately 30% compared with traditional fibre-coupled laser diode end pumping.Furthermore, I have investigated extracavity conversion to radial polarization in both 1µm and 2µm regimes using continuously space-variant lambda/4 or lambda/2 waveplates (also called S-waveplates), fabricated by a recently developed femtosecond writing technique. In the one-micron wavelength regime, the lambda/2 S-waveplate can transform a linearly polarized Gaussian beam into a radially polarized beam with a conversion efficiency of ~75% and M2 of 2.7, whilst the lambda/4 S-waveplate can transform a circularly polarized LG01 mode into radial polarization with a conversion efficiency of ~86% and M2 of 2.9. The S-waveplate has a much better performance in longer wavelength regime due to reduced Rayleigh scattering. We demonstrate highly efficient conversion (~86%) to radial polarization in the 2µm band with wavelength tuning from 1950nm to 2100nm by using a 2µm lambda/2 S-waveplate. The resulting radially polarized beam had a M2 of 2.1 and a maximum polarization extinction ratio (PER) of 17.5dB at 2050nm with a variation of less than 3dB over the full wavelength range.I finally exploited the lambda/2 S-waveplate as an intracavity polarization-controlling element to directly excite radially-polarized TM01 mode operation in an Yb-doped fibre laser. The laser yielded ~32W of output power with a radially-polarized TM01 mode output beam at 1040nm with a slope efficiency of 66% and polarization purity of 95%. Moreover, I have demonstrated a simple technique for selectively generating the fundamental LP01 mode and the next higher order doughnut-shaped LP11 mode with a vortex phase front in an Yb-doped fibre laser. This approach exploits the difference in polarization behaviour of individual transverse modes due to transverse variation of birefringence in a few-moded fibre, allowing robust mode discrimination through the use of an appropriately aligned intracavity polarizing element. The laser yielded ~36W of output power for both transverse modes with slope efficiency of 74% and a mode purity of 95%
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
Polarization-dependent transverse mode selection in an Yb-doped fiber laser
No full textA simple technique for selectively generating the fundamental LP01 and the next higher order donut-shaped LP11 mode with vortex phase front in a cladding-pumped few-moded ytterbium-doped fiber laser is reported. Our approach exploits the difference in polarization behavior of individual transverse modes due to transverse variation of birefringence in a few-mode fiber allowing robust mode discrimination through the use of an appropriately aligned intracavity polarizing element. The laser yielded ~36 W of output power for both transverse modes with corresponding slope efficiency of 74% with respect to absorbed pump power and a mode purity of 98% for the donut-shaped LP11 mode
Cladding-pumped Yb-doped fiber laser with vortex output beam
No full textA simple technique for selectively generating a donut-shaped LP11 mode with vortex phase front in a cladding-pumped ytterbium-doped fiber laser is reported. The laser yielded 36W of output with a slope efficiency of 74%
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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