1,722,250 research outputs found
Thickness-dependent native strain in graphene membranes visualized by Raman spectroscopy
No full textSince graphene, a representative 2-dimensional crystal, has an extreme surface-to-volume ratio, its various material properties are known to be susceptible to various interactions with environment. Its high stretchability, in particular, allows graphene to conform well to external perturbation, which leads to modifications of its electronic, magnetic and chemical properties. In this work, we report a Raman spectroscopic strain metrology and visualize the native strain induced by the van der Waals interactions of mechanically exfoliated graphene of varying thickness with supporting silica substrates. Using freestanding graphene as a strain-free and charge-neutral reference, we quantified the resulting strain with a resolution of 0.02% and found that its spread decreases as increasing the number of layers finally reaching the detection limit for the thickness of similar to 30 layers. The spatially resolved strain maps revealed that the native strain is randomly distributed and that both of compression and expansion are also randomly generated. The current optical analysis can serve as a highly sensitive and efficient strain metrology tool for graphene samples in a wide range of thickness and can be extended to other 2dimensional crystal systems. (C) 2016 Elsevier Ltd. All rights reserved.1194Nsciescopu
Direction-Controlled Chemical Doping for Reversible G-Phonon Mixing in ABC Trilayer Graphene
Full text linkNot only the apparent atomic arrangement but the charge distribution also defines the crystalline symmetry that dictates the electronic and vibrational structures. In this work, we report reversible and direction-controlled chemical doping that modifies the inversion symmetry of AB-bilayer and ABC-trilayer graphene. For the "top-down'' and "bottom-up'' hole injection into graphene sheets, we employed molecular adsorption of electronegative I-2 and annealing-induced interfacial hole doping, respectively. The chemical breakdown of the inversion symmetry led to the mixing of the G phonons, Raman active E-g and Raman-inactive E-u modes, which was manifested as the two split G peaks, G(-) and G(+). The broken inversion symmetry could be recovered by removing the hole dopants by simple rinsing or interfacial molecular replacement. Alternatively, the symmetry could be regained by double-side charge injection, which eliminated G(-) and formed an additional peak, G(o), originating from the barely doped interior layer. Chemical modification of crystalline symmetry as demonstrated in the current study can be applied to other low dimensional crystals in tuning their various material properties.open1136Ysciescopu
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
Two-stage multi-intent detection for spoken language understanding
No full textThis paper presents a system to detect multiple intents (MIs) in an input sentence when only single-intent (SI)-labeled training data are available. To solve the problem, this paper categorizes input sentences into three types and uses a two-stage approach in which each stage attempts to detect MIs in different types of sentences. In the first stage, the system generates MI hypotheses based on conjunctions in the input sentence, then evaluates the hypotheses and then selects the best one that satisfies specified conditions. In the second stage, the system applies sequence labeling to mark intents on the input sentence. The sequence labeling model is trained based on SI-labeled training data. In experiments, the proposed two-stage MI detection method reduced errors for written and spoken input by 20.54 and 17.34?% respectively. ? 2016, Springer Science+Business Media New York.11sciescopu
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
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