1,721,005 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Optical phase conjugation in fiber-optic transmission systems
Get PDFAs the data rate of long-haul transmission links is increased, the design and realization of the transmission link becomes more difficult. As a result, more sophisticated methods are required to improve the transmission quality. The robustness of a transmission link can be increased and its structure greatly simplified by the use of mid-link optical phase conjugation (OPC). OPC is a promising technology to compensate for deterministic, phase related impairments (i.e. the Kerr effect and chromatic dispersion) in long-haul transmission systems. This thesis assesses the regenerative capabilities of OPC for the compensation of distortions that occur in modern transmission systems. The focus of the research is on transmission systems where OPC is employed to compensate for both chromatic dispersion and nonlinear impairments. The dispersion map (i.e. the dispersion as a function of the transmission distance) of such a transmission system is completely different from that of a conventional transmission system. The accumulated dispersion along the link of an OPCbased transmission system is significantly higher than that of a conventional transmission system. We investigated the influence of the dispersion map of OPC on nonlinear impairments using the non return-to-zero amplitude-shift-keying (NRZ-ASK) modulation format. As a result, it is shown that the peak powers that occur in the OPC transmission system are at a 10-Gbit/s/channel data rate significantly higher than the peak powers that occur in a conventional transmission system. The higher peak powers in the OPC based transmission system lead to an increased self-phase modulation (SPM) penalty. Through phase conjugation most of the SPM impairments are compensated for. However, when multiple wavelength division multiplexed (WDM) channels at narrow channel spacing are used for transmission, cross-phase modulation (XPM) is the dominating transmission impairment. Although XPM is principally a deterministic distortion, it must be treated as non-deterministic due to the dispersion of the transmission link. With simulations and experiments we show that because of this, the XPM compensation through OPC is marginal. At a 40 Gbit/s data rate, the peak powers that occur in the OPC-based transmission system are similar to those that occur in the conventional transmission system. In 40 Gbit/s WDM transmission systems the influence of XPM is relatively low. These transmission systems are rather limited by intra-channel nonlinear impairments such as SPM, intrachannel XPM (IXPM) and intrachannel FWM (IFWM). We show experimentally that in this case, the performance of the OPC transmission system is better than that of the conventional transmission system. When OPC is used to compensate for the chromatic dispersion, the OPC must be placed in the middle of the transmission link. This technique is often referred to as "midlink OPC". However, in some transmission links it is not possible to place the OPC exactly in the middle. Therefore, several configurations with a transmission length of 700 km to 900 km were assessed where the OPC was placed 100 km from the middle of the transmission link. In this experiment practically no bit-error ratio (BER) degradation was observed in the off-center configuration. Recently, strong interest has been shown in phase-shift keying modulation (PSK) formats such as differential phase-shift-keying (DPSK). DPSK’s main advantages over ASK are that it is more robust to narrowband optical filtering and has a 3 dB higher sensitivity in combination with balanced detection. However, unlike ASK signals PSK signals can be distorted by nonlinear phase noise (NPN). For long-haul transmission systems, the impact of NPN is so severe that the performance of DPSK is in some cases even worse than that of ASK. The impact of nonlinear phase noise is studied for 10.7-Gbit/s DPSK in an 800-km transmission link. In this experiment it is shown that impairments due to nonlinear phase noise can be significantly reduced using optical phase conjugation. The dependence of the location of the OPC within the transmission link is assessed as well. Allowing a penalty of 1 decade in BER from the optimum, the OPC-unit can be varied over a wide range, from nearly 1/3 to 2/3 of the transmission link. The combination of mid-link OPC is assessed with 21.4-Gbit/s return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) in an ultra long-haul transmission experiment. Error-free transmission after FEC is realized over 10,200 km for all 22 WDM channels. In this experiment, a single OPC-unit is used in the middle of the link to compensate for an accumulated chromatic dispersion of over 160,000 ps/nm. Along the transmission line, the dispersion accumulates in this experiment to more than 80,000 ps/nm. This is significantly higher than the maximum accumulated dispersion in the conventional transmission system (approximately 3,000 ps/nm). The high accumulated dispersion results in an extreme overlap of the pulses along the transmission line. With this experiment we show that despite the high dispersion, the feasible transmission distance of the OPC based transmission system is 44% greater than that obtained in the conventional transmission system. By doubling the data rate and keeping the 50-GHz channel spacing, a 0.8-bit/s/Hz spectral efficient WDM transmission system is realized. At 42.8-Gbit/s RZ-DQPSK, transmission over 5,000 km was realized with mid-link OPC. Compared to the feasible transmission distance obtained at 21.4-Gbit/s, the feasible transmission distance is reduced by about 50%. This reduction of transmission distance with 50% corresponds to the 3-dB OSNR penalty that is present between 21.4-Gbit/s and 42.8-Gbit/s RZ-DQPSK in the back-toback configuration. For the conventional transmission system, a greater reduction in the feasible transmission distance (factor of 2.4) is measured due to increased penalties that result from a combination of self phase modulation and nonlinear phase noise. Comparing the feasible transmission distance of the OPC to the conventional transmission system an improvement of 60% is observed in this experiment
Ultrafast optical signal processing applying electroabsorption modulators as a pulse source and four-wave mixing in semiconductor optical amplifiers as a gating device
No full textkoamabayili/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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