1,721,144 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
Finite size effects in surface emitting Terahertz quantum cascade lasers
Full text linkWe analyze surface-emitting distributed feedback resonators for Terahertz quantum cascade lasers fabricated from double-metal waveguides. We explain the influence on resonances and surface-emission properties of the finite length and width of the gratings in connection with absorbing boundary conditions, and show that, contrary to the infinite case, the modes on either side of the photonic band-gap have finite surface losses. The lateral design of the resonator is shown to be important to avoid transverse modes of higher order and anti-guiding effects. Experimental findings are indeed in excellent agreement with the simulations. Both modeling and fabrication can easily be applied to arbitrary gratings, of which we discuss here a first interesting example. (c) 2009 Optical Society of Americ
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
Frequency manipulation of THz bound-to-continuum quantum-cascade lasers
No full textThe laser emission frequencies of existing designs are controlled by uniform thickness transformations. Experimental results from a total of ten wafers are presented demonstrating a predictable shift in the emission wavelength concurrent with an anticipated alteration in electrical transport. Wafers based on a design around 2.9 THz produced a frequency shift of 0.35 THz. Furthermore, a 2.5% thickness reduction in our 2-THz design saw a 0.1-THz frequency shift and changes in electrical transport predicted by simulations
THz quantum cascade designs for optimized injection
No full textWe report two different terahertz (THz) quantum cascade lasers based on bound-to-continuum transitions emitting at 2.8 and 3.8 THz. Novel design approaches have been explored with the purpose of optimizing the electron injection process. Both devices show large current dynamic ranges with output powers of several tens of mW, offering ample scope for future improvements. (C) 2007 Elsevier B.V. All rights reserved
Tuning a distributed feedback laser with a coupled microcavity
Full text linkWe show that a distributed-feedback terahertz quantum cascade laser can be tuned with a coupled microcavity by anti-crossing of the respective eigenfrequencies. In this proof-of-concept experiment, a tuning range of 20 GHz is obtained, in good agreement with a simple finite element model, which shows that the tuning is determined by the coupling strength between the resonators. The concept could be applied to any laser cavity, but becomes progressively more attractive the lower the emission frequency. (c) 2010 Optical Society of Americ
High peak power femtosecond pulse passively mode-locked vertical-external-cavity surface-emitting laser
No full textWe report a passively mode-locked vertical-external-cavity surface-emitting laser (VECSEL) producing 335-fs near-transform-limited pulses at a repetition rate of 1 GHz with an average output power of 120 mW at a center wavelength of 999 nm. The VECSEL was optically pumped with a power of 1.85 W at a wavelength of 830 nm. The peak power of the output pulses was 315 W.<br/
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