1,721,062 research outputs found
Relation between dynamic and thermodynamic stability of relativistic stellar clusters with cutoff and gas spheres in a spherical box
No full textGalaxy clusters in presence of dark energy
No full textWe solve the equation of the equilibrium of the gravitating body, with a polytropic equation of state of the matter P = K rho^gamma, in the frame of the newtonian gravity, with non-zero cosmological constant Lambda. We consider here the cases with n = 1; 3, gamma = 1 + 1/n. For each n, the non-dimensional equation of the static equilibrium has a family of solutions, instead of only one solution of the Emden equation at Lambda = 0. The equilibrium state exists only for the central density rho_0 greater or equal than rho_c. There are no static solutions at rho_0 < rho_c. We show, that the presence of dark energy decrease a dynamic stability of the configuration. We apply our results for the analysis of a possibility of existence of equilibrium states of cluster of galaxies in the present universe with non-zero Lambda
Selfgravitating gas spheres in a box and relativistic clusters: relation between dynamical and thermodynamical stability
Full text linkWe derive a variational principle for the dynamical stability of a cluster as a gas sphere in a box. Newtonian clusters are always dynamically stable, and for relativistic clusters, the relation between dynamical and thermodynamical instabilities is analyzed. The boundaries between dynamically and thermodynamically stable and unstable models are found numerically for relativistic stellar systems with different cutoff parameters. A criterion based on the binding energy curve is used for determination of the boundary of dynamical stability
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
Stability of dense stellar clusters against relativistic collapse
No full textStability of dense stellar clusters against relativistic collapse is investigated by approximate methods, similar to the static criteria of stellar stability. The equilibrium models with Maxwellian distribution function with cutoff, studied by Zel'dovich & Podurets (ZP) (1965), have been considered. Three new methods for stability investigation are considered. They give only approximate results about the stability, because adiabatic perturbations of the collisionless Maxwellian model lead to complicated non-Maxwellian distribution, which cannot be written analytically. However, these results are more precise than those of ZP, obtained from consideration of the sequence of Maxwellian models with different temperature. The coincidence of the temperatures in the critical point, T = 0.223 mc^2 leads us to believe that these methods, although approximate, provide rather relatively good precision not worse than 0.001
Spherically symmetric relativistic stellar clusters with anisotropy and cutoff energy in momentum distribution. I. The Newtonian regime
No full textWe construct numerical models of spherically symmetric Newtonian stellar clusters with anisotropic distribution functions. These models generalize solutions obtained earlier for isotropic Maxwellian distribution functions with an energy cutoff and take into account distributions with different levels of anisotropy
Stability of the dense stellar clusters - II
No full textStability of dense stellar clusters to relativistic collapse is investigated by an approximate method, similar to static criteria of stellar stability. The equilibrium models with Maxwellian distribution function with cutoff, studied by Zel'dovich and Podurets (ZP), have been considered
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