1,721,130 research outputs found
Large Amplitude Solitons And Double Layers In Multicomponent Dusty Plasmas
No full textSupposing that the constituents of dusty plasmas are inertialess electrons, inertialess ions, and an admixture of negatively and positively charged inertial dust grains, and employing the nonlinear multi-fluid dusty plasma equations and Poisson's equation, we have derived dynamical equations for small amplitude nonlinear dust-acoustic waves, as well as the energy integral of a classical particle with a modified Sagdeev potential for large amplitude disturbances. The energy integral is analyzed both analytically and numerically to demonstrate the existence of rarefactive and compressive electrostatic potentials which travel faster than the effective dust-acoustic velocity. Compressive dust-acoustic potential exist only when there is a significant fraction of positively charged dust grains. Furthermore, the four-fluid dusty plasma system also admit double layers.84181183Rao, N.N., Shukla, P.K., Yu, M.Y., (1990) Planet. Space Sci., 38, p. 543Shukla, P.K., (1992) Physica Scripta, 45, p. 510Shukla, P.K., Rahman, H.U., (1996) Phys. Plasmas, 3, p. 430Shukla, P.K., (1999) Phys. Lett., A252, p. 340Barkan, A., Merlino, R.L., D'Angelo, N., (1995) Phys. Plasmas, 2, p. 3563Merlino, R.L., Barkan, A., Thompson, C., D'Angelo, N., (1998) Phys. Plasmas, 5, p. 1607Prabhakara, H.R., Tanna, V.L., (1996) Phys. Plasmas, 3, p. 3176Morfill, G., Thomas, H., Zuzic, M., (1997) Advances in Dusty Plasma, pp. 99-142. , (edited by P. K. Shukla, D. A. Mendis and T. Desa), World Scientific, SingaporeNakamura, Y., Odagiri, T., Tsukabayashi, I., (1997) Plasma Phys. Control Fusion, 39, p. 105Nakamura, Y., Tsukabayashi, I., (1984) Phys. Rev. Lett., 52, p. 2356Watanabe, S., (1984) J. Phys. Soc. Japan, 53, p. 950Tajiri, M., Tuda, M., (1985) J. Phys. Soc. Japan, 54, p. 19Sheridan, T.E., (1998) J. Plasma Phys., 60, p. 17Shukla, P.K., (1994) Phys. Plasmas, 1, p. 1362Sagdeev, R.Z., (1966) Reviews of Plasma Physic, pp. 23-91. , (edited by M. A. Leontovich), Consultants Bureau, New YorkSakanaka, P.H., Shukla, P.K., Theory of Solitons and Double Layers in Multicomponent Dusty Plasmas, , in preparatio
Modelling electronegative complex plasma systems
No full textThe control of the generation and assembly of the electronegative plasma-grown particles is discussed. Due to the large number of elementary processes of particle creation and loss, electronegative complex plasmas should be treated as open systems where the stationary states are sustained by various particle creation and loss processes in the plasma bulk, on the walls, and on the dust grain surfaces. To be physically self-consistent, ionization, diffusion, electron attachment, recombination, dust charge variation, and dissipation due to electron and ion elastic collisions with neutrals and fine particles, as well as charging collisions with the dust, must be accounted for
Self-organized And Chaotic States In Nonuniform Dusty Magnetoplasmas With Sheared Flows
No full textIt is well known that sheared plasma flows can be built up both in astrophysical environments as well as in laboratory dusty plasmas. Our objective here is to understand the coupling of velocity gradient energy to electrostatic and electromagnetic waves in nonuniform dusty magnetoplasma. For this purpose, we employ the multi-fluid dusty plasma model and derive the relevant nonlinear equations for low-frequency (in comparison with the ion gyrofrequency) waves in the presence of sheared plasma flows. Linear dispersion relations are derived and analyzed. It is found that both the electrostatic and electromagnetic waves are driven by sheared plasma flows. Furthermore, the newly derived mode coupling equations provide the possibility of self-organized and chaotic states in dusty plasmas. The results of our investigation should be helpful in understanding the properties of dusty plasma microturbulence when sources and sinks are simultaneously present.75158160Shukla, P.K., Vanna, R.K., Krishan, V., McKenzie, J.F., (1993) Phys. Rev., E47, p. 750Goertz, C.K., (1989) Rev. Geophys., 27, p. 271De Angelis, U., (1992) Physica Scripta, 45, p. 465Shukla, P.K., (1996) The Physics of Dusty Plasma, pp. 107-121. , (Edited by P. K. Shukla, D. A. Mendis and V. W. Chow) World Scientific, SingaporeLorenz, E.N., (1964) J. Atmos. Sci., 20, p. 130Stenflo, L., (1996) Phys. Lett., A212, p. 224Mirza, A.M., Shukla, P.K., (1997) Phys. Lett., A229, p. 31
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
A New Approach to the Coronal Heating Problem
No full textThe heating of the solar corona is discussed within both frameworks of kinetic and fluid drift wave theory. It is shown that the basic ingredient necessary for the heating is the presence of the background density gradients in the direction perpendicular to the magnetic field vector. These gradients are a source of free energy for the electrostatic instabilities. Strongly growing modes are found for some typical coronal plasma parameters. The instabilities a) imply the presence of electric fields that can accelerate the plasma particles in both the perpendicular and the parallel direction with respect to the magnetic field vector, and b) can stochastically heat ions. The stochastic heating i) is due to the electrostatic nature of the waves, ii) is more effective on ions than on electrons, iii) acts predominantly in the perpendicular direction, iv) heats heavier ions more efficiently than lighter ions, and v) may easily provide a drift wave heating rate that is orders of magnitude above the value that is presently believed to be sufficient for heating the solar corona.sponsorship: Center for Plasma Astrophysics
LMCC, Leuven Mathematical Modeling and Computational Science Centrestatus: Publishe
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
The Problem of Coronal Heating
No full textThe inhomogeneous coronal plasma is a perfect environment for fast growing drift waves. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities like the density, magnetic field and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (both in the presence of collisions and without it) and within the two-component kinetic descriptions (due to purely kinetic effects). Some aspects of these phenomena are investigated here. In particular the analysis of the particle dynamics within the growing wave is compared with the corresponding fluid analysis. While both of them predict the stochastic heating, the threshold for the heating obtained from the single particle analysis is higher. The explanation for this effect is given. Also, the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic and electromagnetic regimes. The electromagnetic regime implies the coupling of the gradient-driven drift wave with the Alfvén wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the electrostatic regime is characterized by stronger growth rates, as compared with the electromagnetic perturbations. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfvén waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field. On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above the value presently accepted as necessary for a sustainable coronal heating. The vertical stratification and the very long wavelengths along the magnetic loops imply that a drift-Alfvén wave, propagating as a twisted structure along the loop, in fact occupies regions with different plasma-β and, therefore, may have different (electromagnetic-electrostatic) properties, resulting in different heating rates within just one or two wavelengths. © 2010 American Institute of Physics.sponsorship: The results presented here are obtained in the framework of the projects G.0304.07 (FWO-Vlaanderen), C 90347 (Prodex), GOA/2009-009 (K.U.Leuven). Financial support by the European Commission through the SOLAIRE Network (MTRN-CT-2006- 035484) is gratefully acknowledged. (European Commission through SOLAIRE Network|MTRN-CT-2006- 035484, G.0304.07, C 90347, GOA/2009-009)status: Publishe
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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