1,720,961 research outputs found
Formation of current sheets in structurally stable and structurally unstable magnetic configurations with two null lines
No full textThe nonlinear dynamics of magnetoacoustic and Alfven Mt-ID perturbations in structurally unstable magnetic configurations with two null lines (X-lines) is studied both analytically and numerically. It is shown that these perturbations cause the electric current to evolve nonlinearly in such a manner that a structurally unstable configuration of the magnetic field transforms into a structurally stable configuration. Such a transformation is forbidden in ideal magnetohydrodynamics but can occur in the process of magnetic field line reconnection. The final magnetic configuration to which the system evolves is shown to contain no separatrices connecting the null lines. (C) 2000 MAIK "Nauka/Interperiodica"
Three-dimensional MHD simulations of forced magnetic reconnection
No full textResults are presented from MHD simulations of three-dimensional flows of a high-conductivity plasma in the vicinity of a null point of a magnetic field. The excitation of an electric current at the boundary of the computation region results in self-consistent plasma flows and change in the structure of the magnetic field. Generally, in the vicinity of a null point, an MHD singularity arises that manifests itself in the formation of locally plane current sheets. It is shown that the current sheet can be oriented either along the separatrix surface of a magnetic configuration or perpendicular to it, except for axisymmetric configurations (or close to them), when the excitation of an electric current in the direction orthogonal to the separatrix surface does not lead to the formation of a current sheet. (C) 2001 MAIK "Nauka/Interperiodica"
Current sheet formation in three-dimensional magnetic configurations
No full textThe formation of electric current sheets in a high-conductivity three-dimensional plasma configuration is studied in the neighborhood of the critical points of the magnetic field. First, with the help of a Clebsch variable representation, the propagation of magnetohydrodynamic (MHD) waves in azimuthally symmetric current-free configurations is investigated. Exact solutions of the MHD equations that describe the self-similar evolution of a magnetic configuration near a critical point are presented. Then, the nonlinear plasma evolution is simulated with an MHD code. The excitation of an electric current at the boundary of the computational region results in a self-consistent plasma flow and in the change of the structure of the magnetic field. No electric current sheet is formed when both the equilibrium configuration and the perturbations are azimuthally symmetric. (C) 2002 American Institute of Physics
Phase-locked ions and foil transparency in the radiation pressure acceleration regime
No full textThe transverse expansion of a thin foil accelerated in the RPDA regime can be exploited in order to increase the ion energy and the acceleration efficiency at the expense of decreasing the number of accelerated particles. In the relativistic regime, the ions become phase-locked with respect to the electromagnetic wave. The use of an optimal laser pulse shape makes it possible to keep the expanding foil opaque to the laser radiation. This provides a new approach in order to enhance the energy of laser accelerated ions significantly. (C) 2010 Elsevier B.V. All rights reserved
Unlimited Ion Acceleration by Radiation Pressure
No full textThe energy of ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region resulting in an increase in the ion energy and in the ion longitudinal velocity. In the relativistic limit, the ions become phase locked with respect to the electromagnetic wave resulting in unlimited ion energy gain
Dependence of the ion energy on the parameters of the laser pulse and target in the radiation-pressure-dominated regime of acceleration
No full textWhen the dominant mechanism for ion acceleration is the laser radiation pressure, the conversion efficiency of the laser energy into the energy of relativistic ions may be very high. Stability analysis of a thin plasma layer accelerated by the radiation pressure shows that Raleigh-Taylor instability may enhance plasma inhomogeneity. In the linear stage of instability, the plasma layer decays into separate bunches, which are accelerated by the radiation pressure similarly to clusters accelerated under the action of an electromagnetic wave. The energy and luminosity of an ion beam accelerated in the radiation-pressure-dominated regime are calculated
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
- …
