1,720,989 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
Adhesion and hardness of ZrN films sputtered on WC substrates
No full textZirconium nitride (ZrN) is a transition metal nitride widely studied to be used in different technological fields, like protective coatings and optoelectronics. High hardness, strong wear resistance, chemical stability and high corrosion resistance make transition metal nitride films suitable for tribological applications. For this kind of applications it is essential to evaluate and to control the film adhesion to the coated tool and its hardness properties. In this work ZrN films were RF-sputtered on WC–wt.10 % Co substrates using different assistance bias voltages (up to 20 V) applied during the film growth. The structural properties of the obtained coatings were analysed using x-ray diffraction (XRD) measurements. It was found that the substrate bias strongly influenced the incorporation of residual oxygen impurities in the films. A structural switch from the (200) to the (111) preferential crystal structure was detected with the increasing bias voltage. In addition, transmission electron microscopy (TEM) analyses showed some twinning features inside the deposited films. The film properties were correlated to the film adhesion, studied by scratch test, and to their wear resistance, carried out by ball-on-disc tribometry. The maximum obtained critical load was about 70 N and the wear rate was about 2.23*10^-6 mm3/Nm. Nanoindentation measurements is in progress in order to correlate them with the structural features and wear resistance properties of the grown films
Growth and characterization of TiAlN/AlN superlattices prepared by reactive magnetron sputtering
No full textMachining of aerospace materials is one of the major challenges of modern manufacturing. Application of nano-multi layered AlTiN/AlN PVD coatings to cemented carbide tooling results in a significant tool life improvement under conditions of cutting hard to machine alloys such as Ni-based Incone l 718 superalloy and Ti-based TiAl6V4 alloy [1]. TiAlN and AlN coatings were prepared using a reactive magnetron sputtering system from TiAl and Al targets. Structural characterization of the coatings using x-ray diffraction (XRD) revealed the B1 NaCl structure of TiAlN with a prominent reflection along the (111) plane and hexagonal wurtizite phase of AlN coatings. Subsequently, nanolayered multilayer coatings of TiAlN/AlN were deposited on silicon and WC-Co substrates at different modulation wavelengths (Λ) with a total thickness of approximately 1.0m. The modulation wavelengths were calculated from the x-ray reflectivity data using modified Bragg’s law. TiAlN/AlN multilayer coatings were textured along (111) for Λ<200 ? Study of thermal stability of the coatings in air indicated that the TiAlN/AlN multilayer coatings were stable up to 900°C in air. TiAlN/AlN multilayer coatings also exhibited improved wear resistance when compared to the substrate
Zinc oxide nanostructures grown by pulsed laser deposition
No full textWe report the use of PLD to grow different ZnO
nanostructures. Very different film morphologies have been
observed using different laser wavelengths to ablate the
target. The influence of substrate temperature and oxygen
background pressure on the film morphology has been investigated too. Smooth and rough films, hexagonal pyramids
and columns have been obtained by using a KrF excimer
laser (248 nm) for the target ablation, while hexagonal hierarchical structures and pencils have been obtained by using
ArF (193 nm). Photoluminescence and X-ray diffraction
measurements revealed the good quality of the samples, in
particular of those deposited using the ArF laser beam
Temperature dependence of the photoluminescence properties of colloidal CdSe/ZnS core/shell quantum dots embedded in a polystyrene matrix
Full text linkWe report on the temperature dependence of the photoluminescence sPLd spectrum and of the PL relaxation
dynamics for colloidal CdSe/ZnS core/shell quantum dots sQDsd embedded in an inert polystyrene matrix. We
demonstrate that the confinement energy in the QDs is independent of the temperature. The coupling with both
acoustic and optical phonons is also studied. Quantum confinement results in a strong increase of the exciton–
acoustic-phonon coupling constant, up to 71 microeV/K, and in a reduced exciton–longitudinal-optical (LO)-phonon coupling constant, down to 21 meV, with respect to bulk CdSe. In addition, we demonstrate that
the main nonradiative process that limits the quantum efficiency of the QD at room temperature is the thermal
escape from the dot assisted by scattering with four LO phonons. Thermally activated trapping in surface states
is also observed at low temperature, with an activation energy of about 15 meV
Förster energy transfer from blue emitting polymers to colloidal CdSe/ZnS core shell quantum dots
Full text linkWe have studied the interactions in the solid phase between a blue-light-emitting organic conjugated polymer {poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(9,ethyl-3,6-carbazole)]} and colloidal CdSe∕ZnS core shell quantum dots. We demonstrate by time resolved photoluminescence measurements that efficient Förster energy transfer takes place from the polymer acting as the donor and the CdSe∕ZnS dots, acting as the acceptors. A Förster radius of about 80±15 Angstrom is extracted from the analysis of the relaxation dynamics based on the solution of the donor-acceptor coupled rate equations. This value is in good agreement with the value extracted from the steady state spectra and indicates that efficient energy tranfer from a polymeric host to a nanocrystal guest can occur. Our results are relevant to the application of hybrid organic/inorganic systems to light-emitting devices
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
Optical gas sensing through nanostructured ZnO films with different morphologies
No full textWe report on nitrogen dioxide (NO(2)) sensing measurements by means of zinc oxide films presenting different morphologies. The variation in the photoluminescence emission of the films is employed as transduction mechanism to detect the presence of NO(2) gas molecules at room temperature. The significant role of film morphology on the sensing properties is presented and possible limits in the use of ZnO nanostructures for NO(2) detection at high gas concentration (>20 ppm) and low gas flow (50 ml/min), where a worsening of the sensor response is observed, are discussed. These features are ascribed to a likely incomplete reversibility of the NO(2) adsorption process and examined in connection with the mechanisms of interaction between NO(2) molecules and ZnO
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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