1,720,985 research outputs found
High-voltage high-frequency arbitrary waveform multilevel generator for dielectric barrier discharge2014 International Symposium on Power Electronics, Electrical Drives, Automation and Motion
No full textA high-voltage high-frequency arbitrary waveform voltage generator able to supply a wide range of plasma reactors
is proposed in this paper. The generator structure is based on the cascaded H-bridge multilevel topology, including 24 H-bridge basic modules with the capability of 49 output voltage levels. The individual H-bridge dc supply (600V) is provided by a flyback converter fed by a low-voltage (12V) dc battery. In this way, the input isolation of the ±15kV maximum output voltage is realized in a simple and effective manner, and a portable device is obtained. The generator has been tested by supplying a DBD plasma actuator with different voltage waveforms, up to 20 kHz, pointing out a wide and interesting set of results in terms of output plasma currents
Schlieren imaging in a dielectric barrier discharge actuator for airflow control
No full textThe operation of a surface dielectric barrier discharge actuator for airflow control has been experimentally investigated. The actuator is constituted by an electrode pair separated by a dielectric Teflon sheet. Several ac supply conditions have been utilized. An electrohydrodynamics interaction was induced in still air, and several fluid-dynamic regimes were obtained. Visualization of the plasma boundary layer during the discharge ignition phase and during the steady state regime was obtained by utilizing a Schlieren diagnostic technique. The vortex morphology and propagation velocities at all supply conditions utilized have been evaluated. Velocity profiles perpendicular to the actuator surface, obtained from Pitot tube measurements, and line intensity profiles, determined by means of Schlieren imaging, have been determined for the steady regime operation. The integral along a line perpendicular to the actuator surface of the light intensity of the Schlieren image has been calculated. The profile obtained is in good agreement with the Pitot velocity profile in all the supply conditions investigated. Numerical simulations were also performed. The calculations confirm the relation between the flow velocity distribution in the boundary layer and the gas density distribution, which is the cause of the Schlieren image
Electrohydrodynamic interaction induced by a dielectric barrier discharge
No full textIn the present work an experimental investigation on the electrohydrodynamic (EHD) interaction effect, induced by means of a dielectric barrier discharge on a one atmos-phere subsonic air flow, is described. The air flow is obtained in an open circuit blowing wind tunnel at different air speeds. A plane plasma panel equipped with a dielectric dis-charge barrier system is immersed in the flow. A single phase sinusoidal power supply system, a superposition of a single phase sinusoidal system with a DC voltage supply, and a three phase symmetrical power supply configuration are considered. Electric, fluid dynamic and spectroscopic diagnostic techniques are utilized. Pitot probe meas-urements are performed in the boundary layer on the plasma panel surface. Schlieren imaging is done to visualize the plasma sheath. Vibrational and rotational temperatures are evaluated by means of spectroscopic techniques. The force induced on the flow by the dielectric barrier discharge acts on the ions of the non-neutral sheath ahead of the plasma filament traveling on the panel surface. This causes a reduction of the time in-terval during which the force is active. The EHD effect and the momentum transfer to the gas flow in the boundary layer are reduced when the flow speed grows. An increase of the supply frequency and of the supply voltage causes an increase of the momentum transfer. In these experiments no significant increase of the efficiency of EHD effect is observed when utilizing the superposition of a DC voltage to a single phase power supply or a three phase power supply
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
Magnetohydrodynamics Interaction Over an Axisymmetric Body in a Hypersonic Flow
No full textThe magnetohydrodynamics interaction around a conical test body in a hypersonic argon flow is experimentally
investigated. The hypersonic flow is realized in the high-enthalpy arc-heated wind tunnel of Alta Società per Azioni(S.p.A.) (Pisa, Italy) at Mach 6. The aim of experimental activity is to produce an experimental data base to be used for the validation of numerical codes for the analysis of the magnetohydrodynamics interaction. The magnetohydrodynamics interaction is obtained in the shock layer of the conical test body at the exit of the hypersonic nozzle. The electrical configuration realized allows one to enhance the effect of the magnetohydrodynamics
interaction on the plasma parameters. This is done using the Hall field to generate the magnetohydrodynamics
interaction and by short-circuiting the Faraday current inside the plasma of the shock layer. The magnetic flux density is produced by an array of three magnets located in the test body. Tests are performed at three different stagnation pressures. Fluid-dynamic, electrical, and optical observations have been done. The experiment showed a considerable effect of the magnetohydrodynamics interaction on the values of the quantities measured
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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