1,721,148 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
Electronically-Coupled Phase Boundaries in α-Fe2O3/Fe3O4 Nanocomposite Photoanodes for Enhanced Water Oxidation
No full textPhotoelectrochemical (PEC) water splitting reactions are promising for sustainable hydrogen production from renewable sources. We report here, the preparation of α-Fe2O3/Fe3O4 composite films via a single-step chemical vapor deposition of [Fe(OtBu)3]2 and their use as efficient photoanode materials in PEC setups. Film thickness and phase segregation was controlled by varying the deposition time and corroborated through cross-section Raman spectroscopy and scanning electron microscopy. The highest water oxidation activity (0.48 mA/cm2 at 1.23 V vs RHE) using intermittent AM 1.5 G (100 mW/cm2) standard illumination was found for hybrid films with a thickness of 11 μm. This phenomenon is attributed to an improved electron transport resulting from a higher magnetite content toward the substrate interface and an increased light absorption due to the hematite layer mainly located at the top surface of the film. The observed high efficiency of α-Fe2O3/Fe3O4 nanocomposite photoanodes is attributed to the close proximity and establishment of 3D interfaces between the weakly ferro- (Fe2O3) and ferrimagnetic (Fe3O4) oxides, which in view of their differential chemical constitution and valence states of Fe ions (Fe2+/Fe3+) can enhance the charge separation and thus the overall electrical conductivity of the layer
Anisotropy control in magnetic nanostructures through field-assisted chemical vapor deposition
No full textChemical vapor deposition of iron pentacarbonyl (Fe(CO)(5)) in an external magnetic field (B = 1.00 T) was found to significantly affect the microstructure and anisotropy of as-deposited iron crystallites that could be transformed into anisotropic hematite (α-Fe(2)O(3)) nanorods by aerobic oxidation. The deterministic influence of external magnetic fields on CVD deposits was found to be substrate-independent as demonstrated by the growth of anisotropic α-Fe columns on FTO (F:SnO(2)) and Si (100), whereas the films deposited in the absence of the magnetic field were constituted by isotropic grains. TEM images revealed gradual increase in average crystallite size in correlation to the increasing field strength and orientation, which indicates the potential of magnetic field-assisted chemical vapor deposition (mfCVD) in controlling the texture of the CVD grown thin films. Given the facet-dependent activity of hematite in forming surface-oxygenated intermediates, exposure of crystalline facets and planes with high atomic density and electron mobilities is crucial for oxygen evolution reactions. The field-induced anisotropy in iron nanocolumns acting as templates for growing textured hematite pillars resulted in two-fold higher photoelectrochemical efficiency for hematite films grown under external magnetic fields (J = 0.050 mA cm(−2)), when compared to films grown in zero field (J = 0.027 mA cm(−2)). The dark current measurements indicated faster surface kinetics as the origin of the increased catalytic activity
Interplay of thickness and photoelectrochemical properties in nanostructured α-Fe<inf>2</inf>O<inf>3</inf> thin films
No full textNanostructured Fe2O3 thin films were grown by plasma enhanced-chemical vapor deposition (PE-CVD) from Ar/O2 plasmas for photoelectrochemical (PEC) water splitting applications. Iron oxide coatings were deposited on fluorine-doped tin oxide (FTO) substrates at 300°C under optimized conditions, and subsequently annealed ex-situin air at 650°C. Structural and compositional analyses confirmed the formation of pure alpha-Fe2O3 (hematite), free from other crystalline iron oxide phases. Controlled variations of the deposition time enabled tuning ofthe thickness and nanoaggregate sizesin the resulting deposits and, correspondingly, their current-voltage characteristics. A maximum photocurrent density close to1mA cm-2was achieved at 1.23 V vs. the Reversible Hydrogen Electrode (RHE), without the need of any oxygen evolution catalyst orover/underlayer. The present findingsrevealed the key role played by the engineering of Fe2O3-based nanomaterials, resulting ultimately in a lowered carrier diffusion length, and in an optimal diffusion of tin from FTO into thinner layers. These features offer an amenable opportunity for harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogenin a carbon-neutral fashion
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
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Fluid-structure interactions in microstructures
Full text linktextRadio-frequency microelectromechanical systems (RF MEMS) are widely used for contact actuators and capacitive switches. These devices typically consist of a metallic membrane which is activated by a time-periodic electrostatic force and makes periodic contact with a contact pad. The increase in switch capacitance at contact causes the RF signal to be deflected and the switch thus closes. Membrane motion is damped by the surrounding gas, typically air or nitrogen. As the switch opens and closes, the flow transitions between the continuum and rarefied regimes. Furthermore, creep is a critical physical mechanism responsible for the failure in these devices, especially those operating at high RF power. Simultaneous and accurate modeling of all these different physics is required to understand the dynamical membrane response in these devices and to estimate device lifetime and to improve MEMS reliability. It is advantageous to model fluid and structural mechanics and electrostatics within a single comprehensive numerical framework to facilitate coupling between them.
In this work, we develop a single unified finite volume method based numerical framework to study this multi-physics problem in RF MEMS. Our objective required us to develop structural solvers, fluid flow solvers, and electrostatic solvers using the finite volume method, and efficient mechanisms to couple these different solvers. A particular focus is the development of flow solvers which work efficiently across continuum and rarefied regimes. A number of novel contributions have been made in this process. Structural solvers based on a fully implicit finite volume method have been developed for the first time. Furthermore, strongly implicit fluid flow solvers have also been developed that are valid for both continuum and rarefied flow regimes and which show an order of magnitude speed-up over conventional algorithms on serial platforms. On parallel platforms, the solution techniques developed in this thesis are shown to be significantly more scalable than existing algorithms. The numerical methods developed are used to compute the static and dynamic response of MEMS. Our results indicate that our numerical framework can become a computationally efficient tool to model the dynamics of RF MEMS switches under electrostatic actuation and gas damping.Mechanical Engineerin
Porous silicon nanowires for hydrogen generation: mechanism and photocatalytic studies
Full text linkDie Wasserstofferzeugung von SiNWs in wässriger Lösung wurde im Rahmen der vorliegenden Doktorarbeit systematisch untersucht. Sie enthält die Bewertung der Wasserstofferzeugung in Abhängigkeit von der Vornatur des Siliziumwafers: () verschiedene Siliziumleitfähigkeitstypen (n-und p-Typ) und Dotierungsgrad (hoch-und niedrigdotiert) von SiNWs; (II) SiNWs-Dekoration mit AgNPs oben, in der Mitte und unten, realisiert durch die Anwendung von drei Silberabscheidungsmethoden: stromlose Silberabscheidung (ELD), Silberspiegelreaktion (MR) und native AgNPs. Die atomare, elektronische Struktur und Zusammensetzung von SiNWs und die Oberflächenveränderung während der Wasserstofferzeugung wurden im Detail untersucht. Auch die Einflussfaktoren der Wasserstofferzeugung wie SiNWs Oberflächen- und Lochfänger wurden untersucht. Darüber hinaus hat diese Arbeit versucht, den Mechanismus der Wasserstofferzeugung auf der Grundlage von SiNWs.Hydrogen generation of SiNWs in water-based solution was systematically investigated in the frame of presented Ph.D. thesis. It contains the evaluation of hydrogen generation depending on the pre-nature of silicon wafer: (Ι) different silicon conductivity types (n- and p-type) and doping level (highly and lowly doped) of SiNWs; (II) SiNWs decoration with AgNPs at the top, in middle and at the bottom, realized by applying three silver deposition methods: electroless silver deposition (ELD), silver mirror reaction (MR) and native AgNPs. The atomic, electronic structure and composition of SiNWs and the surface change during the hydrogen generation have been studied in detail. The influencing factors of hydrogen generation such as SiNWs surface and hole scavagers have also been investigated. Moreover, this thesis aimed at revealing the mechanism of hydrogen generation based on SiNWs
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
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