1,721,004 research outputs found
Polarization-insensitive tunable multiple electromagnetically induced transparencies analogue in terahertz graphene metamaterial
No full textA graphene-based metamaterial structure composed of multilayer graphene/dielectric stacking configuration is proposed, which achieves multiple analogue of electromagnetically induced transparencies (EIT) effect at terahertz frequencies. Using the phase-coupling scheme, a theoretical model is established to study the EIT-like effect of the proposed structure, and the theoretical calculations coincide well with the numerical simulated results. By varying the Fermi energy level of the graphene, the EIT-like windows can be dynamically tuned in a wide range of terahertz spectra. Particularly, since the symmetry of the structure, the EIT-like effect is polarization-insensitive and can be performed very well in a large incident angles, nearly 80 degrees for both transverse electric and transverse magnetic waves. The proposed structure has potential applications in tunable terahertz chip-integrated optical devices, especially for dynamic multi-band filters, sensors, modulators and nonlinear devices. (C) 2016 Optical Society of Americ
Suppression of the fluctuation effect in terahertz imaging using homomorphic filtering
No full textTo suppress the fluctuation effect due to laser power instability and terahertz radiation fluctuation, a homomorphic filtering method is proposed to process the terahertz images obtained from a pulsed terahertz raster scanning imaging system. The physical model of homomorphic filtering for terahertz imaging is established. The mathematical expressions are given with the specific physical meaning in accordance with the imaging principle. To demonstrate the effectiveness of the method, a homomorphic filtering experiment based on two raw terahertz images selected from the literature using a continuous-wave (CW) terahertz source is also performed. The effect of the method is compared with those described in the literature, and the advantages of homomorphic filtering are discussed. The pulsed- and CW-terahertz image processing results both show that in addition to suppressing the fluctuation effect, the method can also enhance target imaging
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
太赫兹场驱动半导体超晶格的极化波包运动与光吸收谱
No full textUnder the one-dimensional tight-binding miniband and contact interaction approximation, the extended semiconductor Bloch equation is employed to investigate the optical absorption spectra and evolution of the polarization wavepacket in semiconductor superlattices driven by a terahertz field, after the excitation by a femtosecond laser pulse. Under a direct current (DC) bias, the optical absorption spectrum changes from the absorption band in the case of zero field into a series of equal-distant peaks, so-called Wannier-Stark ladder, with the energy distance being proportional to the field strength. The Wannier-Stark ladder is the counterpart (in the frequency domain) of the periodic oscillation of electrons and holes in real space and in momentum space, i.e. Bloch oscillation. Under a THz alternating current (AC) field, the absorption spectrum also consists of a series of peaks, called dynamical Stark ladder, however, the energy distance is equal to the photon energy of the applied THz field and is independent on the field strength. Furthermore, the absorption edge is shifted. When a DC field and a THz field present simultaneously, the absorption edge does not shift, and the spectrum becomes richer. But the complicated features can be interpreted and identified by the combination of the Wannier-Stark ladder and the dynamical Stark ladder. The ratio of the Bloch frequency to the frequency of THz field and the ratio of field strength of the THz field to the frequency of THz field are two determinant quantities. If the ratio of the Bloch frequency to the frequency of THz field is an integer n, then n-order harmonic wave of THz photon is generated in one Bloch frequency. If the ratio of the Bloch frequency to the frequency of THz field is a fraction, then dynamical fractional Stark ladder is formed. On the contrary to this, the ratio of field strength of the THz field to the frequency of THz field determines the spatial extension of the polarization wavepacket
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
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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