1,721,254 research outputs found
Experimental investigation of plasma dynamics in dc and short-pulse magnetron discharges
No full textThe spatiotemporal evolution of the electron energy distribution function (EEDF) and of plasma parameters such as the electron density, the electron temperature and the plasma and floating potentials has been investigated using spatially and temporally resolved single Langmuir probe measurements in dc and mid-frequency, short-pulse magnetron discharges with a repetition frequency of 10 kHz and a duty cycle of 10%. In the pulsed discharge of the short duty cycle, a peak electron temperature higher than 10 eV was observed near the cathode fall region during the early phase of the pulse-on, which is about three times higher than the steady-state value of the electron temperature in the dc discharge. The temporal evolution of the measured EEDFs showed the initial efficient electron heating during the early phase of the pulse-on and the subsequent relaxation of electron energy by the inelastic collisions and the diffusive loss. The high-energy electrons generated during the pulse-on phase diffused the downstream region toward the grounded substrate, resulting in a bi-Maxwellian EEDF consisting of the background low-energy electrons and the high-energy electrons. The results of the spatially and temporally resolved probe measurements will be presented and the enhanced efficiency of the electron heating in the short-pulse discharge will be explained on the basis of the global model of a pulsed discharge
Temporal evolution of electron energy distribution function and plasma parameters in the afterglow of drifting magnetron plasma
No full textThe temporal behaviour of the electron energy distribution function (EEDF) and the plasma parameters such as electron density, electron temperature and plasma and floating potentials in a mid-frequency pulsed do magnetron plasma are investigated using time-resolved probe measurements. A negative-voltage do pulse with an average power of 160 W during the pulse-on period, a repetition frequency of 20 kHz and a duty cycle of 50% is applied to the cathode of a planar unbalanced magnetron discharge with a grounded substrate. The measured electron energy distribution is found to exhibit a bi-Maxwellian distribution, which can be resolved with the low-energy electron group and the high-energy tail part during the pulse-on period, and a Maxwellian distribution only with low-energy electrons as a consequence of initially rapid decay of the high-energy tail part during the pulse-off period. This characteristic evolution of the EEDF is reflected in the decay characteristics of the electron density and temperature in the afterglow. These parameters exhibit twofold decay represented by two characteristic decay times of an initial fast decay time tau(1), and a subsequent slower decay time tau(2) in the afterglow when approximated with a bi-exponential function. While the initial fast decay times are of the order of 1 mu s (tau(T1) - 0.99 mu s and tau(N1) similar to 1.5 mu s), the slower decay times are of the order of a few tens of microseconds (tau(T2) similar to 7 mu s and tau(N2) similar to 40 mu s). The temporal evolution of the plasma parameters are qualitatively explained by considering the formation mechanism of the bi-Maxwellian electron distribution function and the electron transports of these electron groups in bulk plasma
Measurements of electron energy distribution functions and electron transport in the downstream region of an unbalanced dc magnetron discharge
No full textIn this study, electron energy distribution functions (EEDFs) are measured using a Langmuir probe in conjunction with the ac superposition method in the downstream region of a planar and unbalanced magnetron argon discharge and the effects of an anode sheath boundary on the discharge characteristics are investigated. The potential of the anode sheath can be controlled by applying a dc voltage to the substrate, and the nonlinear behaviour of the plasma potential with respect to the dc substrate voltage causes the distinctive evolution of the potential of the anode sheath. It is found that when the potential of the anode sheath reaches a specific value, which is related to the threshold energies of argon for the inelastic collisions, an outstanding EEDF transition from a bi-Maxwellian distribution to a single Maxwellian distribution occurs. We introduce the concept of the total electron bounce frequency as an indicator of how the electron collisions such as the electron-electron collision and the inelastic collisions affect the EEDF features as the potential of the anode sheath changes. This result provides the decisive clue to explaining the appearance of the bi-Maxwellian distribution in magnetron discharges. The results of the spatially resolved measurements of EEDF and plasma characteristics are also presented. From these results, we will discuss the electron transport in the downstream region in detail
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
Comparison of excitation tenperature and electron temperature in low pressure argon plasma
No full textVariations 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
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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