1,720,962 research outputs found
Propagation of ultrastrong femtosecond laser pulses in PLASMON-X
No full textIn this work we present the derivation of the nonlinear equations
that describe the propagation of ultrashort laser pulses in a
plasma, in the PLASMON-X device, using a fully relativistic
hydrodynamic description for electrons. It is shown that for the
PLASMONX scheme used for the electron acceleration, it is
justified to use a stationary 1-D approximation in the electron
hydrodynamic equations, since the pulse width is sufficiently
bigger than the pulse length. Furthermore, with the laser power of TW and the initial spot size, the nonlinearity is sufficiently weak to allow for the power expansion in the nonlinear Poissons's equation, yielding a version of the nonlocal nonlinear Schr\"{o}dinger eqiation, with a periodic nonlocality. While in a one-dimensional limit the standard wakefield generation is obtained, our two-dimensional numerical studies, including the full nonlinear response, reveal the transverse collapse (or the self-focussing) of the pulse. Under
the typical operating conditions, the self-focussing is
sufficiently slow to allow the interaction between the laser pulse
and the accelerated electrons along an interaction length (in the
laboratory frame) that exceeds 1 m
Quantumlike description of the nonlinear and collective effects on relativistic electron beams in strongly magnetized plasmas
No full textA numerical analysis of the self-interaction induced by a relativistic electron/positron beam in the presence of an intense external longitudinal magnetic field in plasmas is carried out. Within the context of the Plasma Wake Field (PWF) theory in the overdense regime, the transverse beam-plasma dynamics is described by a quantumlike Zakharov system of equations in the long beam limit provided by the Thermal Wave Model (TWM). In the limiting case of beam spot size much larger than the plasma wavelength, the Zakharov system is reduced to a 2D Gross-Pitaevskii-type equation, where the trap potential well is due to the external magnetic field. Vortices, “beam halos” and nonlinear coherent states (2D solitons) are predicted
Self consistent thermal wave model description of the transverse dynamics for relativistic charged particle beams in magnetoactive plasmas
No full textA numerical analysis of the self-interaction induced by a relativistic electron/positron beam in the presence of an intense external longitudinal magnetic field in plasmas is carried out. Within the context of the Plasma Wake Field (PWF) theory in the overdense regime, the transverse beam-plasma dynamics is described by a quantumlike Zakharov system of equations in the long beam limit provided by the Thermal Wave Model (TWM). In the limiting case of beam spot size much larger than the plasma wavelength, the Zakharov system is reduced to a 2D Gross-Pitaevskii-type equation, where the trap potential well is due to the external magnetic field. Vortices, “beam halos” and nonlinear coherent states (2D solitons) are predicted
Self consistent nonlinear transverse quantum dynamics of a cold relativistic electron beam in a magnetized plasma
No full textA relativistic electron/positron beam travelling in a cold plasma in the overdense regime (n0>> nb) is the driver of large amplitude plasma oscillations that are generated by the Plasma
Wake Field excitation. The beam experiences the 3D effects of the wake field that it has produced by itself (self interaction). In the long beam limit, the transverse effects due to the self interaction (f.i., self focusing/defocusing) are dominant compared to the longitudinal ones. Here, ignoring the longitudinal beam dynamics, a theoretical investigation of the quantum transverse beam motion is carried out when a relativistic electron/positron beam is travelling along an external magnetic field. This is done by adopting a fluid model of a magnetized plasma describing the Plasma Wake Field excitation driven by the beam density and current. On the other hand, taking into account the quantum nature of the single particle of the beam, it is shown that the transverse electron/positron
dynamics is governed by a 2D Schrödinger equation in the form of the Gross-Pitaevskii equation. The latter accounts for the collective effects due to both the plasma wake field and the external magnetic field. The above set of equations governing the beam-plasma system (i.e., fluid plus 2D Schrödinger quations), is then reduced to a pair of coupled equations that can be thought as a quantum Zakharov system, leading in general to a 2D nonlocal and nonlinear Schrödinger equation. In the weakly focussed regime, the analysis of this equation is carried out, both analytically and numerically. Remarkably, the existence of quantum beam vortices is shown and the conditions for the self focusing and collapse that include the quantum nature of the beam particles are discussed
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
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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