1,722,203 research outputs found
Nanoscale triboelectrification of two-dimensional chemical vapor deposited transition metal dichalcogenides
No full textTriboelectrification, a contact-induced electrification where a material becomes electrically charged after brought into contact with a dissimilar one via friction [1], is an available, stable and efficient method to realize the mechanical-to-electrical energy conversion. Until now, this phenomenon has been investigated for insulators like polymers and silicon dioxide, and zero-bandgap semiconductor like graphene. For semiconductors with non-zero bandgaps, transition metal dichalcogenides have been paid much attention due to their distinctive optical, electrical and mechanical properties, and it has been reported that the performance of triboelectric nanogenerators can be dramatically enhanced by introducing single-layer MoS2 into the friction layer as the triboelectric electron-accepter layer [2], but the theories behind are still poorly understood, so the aim of this investigation is to fill this research gap. With this aim in mind, high-quality MoS2, WS2, MoSe2, and WSe2 nanoflakes were synthesized by chemical vapor deposition method and their triboelectric properties were characterized with atomic force microscopy and Kelvin force microscopy. Due to the various work functions of these four materials in reference to the conductive Pt-coated tip, the electrons are transferred from the samples to the tip during triboelectrification in the case of WS2, MoSe2, and WSe2 whereas MoS2 exhibits an opposite transfer direction. The densities of tribo-charges are different for these four materials but they can be modified by applying diverse biases to the conductive tip during the rubbing process. Impressively, these tribocharges, tunneling to the interlayer between the nanoflakes and the underlying insulating substrate, show more than two orders of magnitude longer lifetime than conventional triboelectrification, and MoS2 owns the longest lifetime while WSe2 has the shortest among these four materials. In addition, the diffusion processes of WS2 and MoSe2 are alike thanks to their similar work functions. The surface-adsorbed water molecules from the atmosphere can act as carrier trappers to affect the surface potential and charge distribution of 2D materials given the interaction with the environment nearby, but heat treatment can efficiently solve this problem. Besides, a positive correlation between the layer number and resistance to charge dissipation was observed, and there also exists the transfer of materials during the frictional process, which can be utilized for tuning the triboelectric properties of the rubbed material. On these basis, applicable fields consisting of bandgap modification as well as tunable antenna have been investigated. For the bandgap modification, the in situ effect of strain was investigated and it exhibits that the bandgap decreases monotonically with the increase of applied force. The reason behind is the reduction of orbital overlapping and hybridization due to the weakened atomic bonds when localized strain appears. In addition, while the bandgap of MoS2 is almost unchanged when an external perpendicular electric field is applied because of the very subtle band structure deformation, the bandgap of bilayer MoS2 can be modified via the electric field generated by the underlying tribo-charges, and applying positive and negative biases has different effects on the bandgap thanks to the spontaneous polarization along the direction perpendicular to the nanoflakes plane. Meanwhile, a MoSe2- based triboelectrically-controlled tunable antenna was proposed to apply to the upcoming 5G base station. As the tribo-charges can tunnel through the MoSe2 nanoflakes and localize at the interlayer to act as a bias voltage, the conductive/insulating states MoSe2 can be controlled, which results in the adjustable working frequency band from 28 GHz to around 38 GHz. In the meantime, a stable gain (less than 0.1 dBi variation in the whole range) is achieved for this omnidirectional antenna. Additionally, a unidirectional radiation can be reached with a metallic reflector placed at the back of the tunable antenna, and a broad beamwidth can still remain. Due to the long-term preservation of the tribo-charges, no extra bias is needed in this case and the energy can be saved to a large extent
Eurographics/ ACM SIGGRAPH Symposium on Computer Animation 2024 - CGF 43-8: Frontmatter
No full textComputer Graphics Forum43
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
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
Orophyllus guttatus Xie, Wang & He 2021, sp. nov.
No full textOrophyllus guttatus Xie, Wang & He sp. nov. Figs. 5A–G Material examined: Holotype: 1 male, CHINA, Guangxi Prov., Maoershan (110.48°E, 25.88°N), 11-viii-2020 coll. Xie Hui-Cong (ECNU). Description. Male individuals are similar to Orophyllus supeciliarilamellatus sp. nov. (Figs. 5A–F), but differs in a dark spot at the base of the subgenital plate (Fig. 5G). Female unknown. Measurements (in mm): Male: SZ 42.51, PR 6.24, FW 34.43. Etymology: Species name guttatus means patches in the middle of subgenital and preceding plates. Distribution: Guangxi.Published as part of Xie, Hui-Cong, Wang, Han-Qiang, Li, Kai & He, Zhu-Qing, 2021, Taxonomy of genus Orophyllus Beier, 1954 (Orthoptera: Tettigoniidae: Pseudophyllinae), pp. 147-159 in Zootaxa 4990 (1) on page 154, DOI: 10.11646/zootaxa.4990.1.9, http://zenodo.org/record/498301
Triboelectrification of two-dimensional chemical vapor deposited WS<sub>2</sub> at nanoscale
No full textTriboelectric properties of chemical vapor deposited WS2 nanoflakes have been characterized in nano-range by atomic force microscopy (AFM) and Kelvin force microscopy (KFM). The triboelectric process is dependent on the thickness of WS2 nanoflakes, and it is sensitive to the adsorbates like water molecules, as well as transferred Pt from the tip on the sample. The density of tribo-charge can be modified by applying various biases to the conductive Pt-coated tip during the frictional process. Tunneling of the tribo-charge into the gap between WS2 and the underlying substrate results in a long lifetime, which is about 100 times longer than conventional triboelectric charges. Moreover, we observe a positive correlation between the layer number and resistance to charge dissipation. Our finding can become the driving force for a new category of two-dimensional (2D) WS2 triboelectrically controllable nanodevices
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
Nanotribology of transition metal dichalcogenide flakes deposited by chemical vapour deposition: The influence of chemical composition and sliding speed on nanoscale friction of monolayers
No full textWe present nanoscale frictional analysis of three commonly used transition metal dichalcogenide (TMD) monolayers, WS
2, MoSe
2 and WSe
2, deposited by chemical vapour deposition (CVD). The monolayers were characterised by Raman spectroscopy, photoluminescence spectroscopy (PL), and X-ray spectroscopy (XPS), to determine the composition of the coating and confirm monolayer structure. Nanoscale frictional analysis was performed by atomic force microscopy (AFM). Load-dependent frictional behaviour was measured at different sliding speeds to quantitatively assess friction on each sample. All samples experienced low nanoscale friction, with the lowest friction observed on WSe
2. The friction was independent of sliding speed within the analysed range. Furthermore, monolayer TMDs significantly increase the operational load range by at least one order of magnitude when compared to SiO
2 substrate.
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