1,721,013 research outputs found
Monte Carlo methods for stationary solutions of general-relativistic Vlasov systems: Collisionless accretion onto black holes - Wolfram Mathematica packages
No full textA collection of 5 Wolfram Mathematica packages supplementing the article: Patryk Mach, Adam Cieślik, Andrzej Odrzywołek, "Monte Carlo methods for stationary solutions of general-relativistic Vlasov systems: Collisionless accretion onto black holes," arXiv:2310.07872
Accretion of the Vlasov gas onto a Kerr black hole: Wolfram Mathematica notebooks
No full textWolfram Mathematica notebooks supplementing the articles:
Patryk Mach, Mehrab Momennia, Olivier Sarbach, Accretion of a Vlasov gas by a Kerr black hole, arXiv:2508.04783 (2025);
Patryk Mach, Mehrab Momennia, Olivier Sarbach, Bondi-type accretion onto a Kerr black hole in the kinetic regime, arXiv:2508.20189 (2025)
Wolfram Mathematica package supplementing the article: Adam Cieślik, Andrzej Góźdź, Patryk Mach, Aleksandra Pȩdrak, Włodzimierz Piechocki, "Semiclassical causal geodesics: Minkowski spacetime case"
No full textThe Wolfram Mathematica package illustrates an integral quantization method based on the Heisenberg-Weyl group, applied to the motion of relativistic spinless particles. We provide numerical calculations of transition amplitudes between coherent states, a numerical implementation of quantum random walks, as well as sample interference patterns in the double-slit experiment
Kerr Geodesics in Terms of Weierstrass Elliptic Functions
No full textWe provide a code package written in Wolfram Mathematica to calculate the motion of test particles around a Kerr black hole. The novel analytical solutions describe both timelike and null geodesics. They are parameterized explicitly by constants of motion -- the energy, the angular momentum, and the Carter constant -- and initial coordinates. A single set of formulas is valid for all null and timelike geodesics, irrespectively of their radial and polar type. This uniformity has been achieved by applying a little-known result due to Biermann and Weierstrass, regarding solutions of a certain class of ordinary differential equations. Different from other expressions in terms of Weierstrass functions, our solution is explicitly real for all types of geodesics. In particular, for the first time the so-called transit orbits are now expressed by explicitly real Weierstrass functions. In addition to the code package itself a description and demonstration file is also available
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
Gravitační zdroje v blízkosti černých děr
No full textČerné díry patří mezi nejzajímavější objekty ve vesmíru. Jsou-li izolované a stacionární, jejich gravitační pole je popsáno jednoduchou Kerrovou(-Newmanovou) metrikou. As- trofyzikální černé díry však nebývají izolované; ve skutečnosti se o nich dozvídáme právě prostřednictvím jejich interakce s okolím. Gravitační pole se tím pádem liší od Kerrova(- Newmanova). Tato práce zkoumá vliv okolní hmoty na gravitační pole černých děr. Ve stacionárním (nebo statickém) a axiálně symetrickém případě odvodíme několik analyt- ických modelů popisujících černou díru obklopenou diskem nebo prstencem. Statickou "superpozici" takových zdrojů vyřešíme přesně, v některých případech dokonce odvodíme metriku v uzavřeném tvaru. Kromě základních fyzikálních vlastností výsledných polí an- alyzujeme též kvazinormální módy (QNM) skalárního pole v takové geometrii. Výsledky naznačují jisté univerzální chování QNM, což může pomoci odlišit efekty způsobené okolní hmotou od efektů plynoucích z modifikovaných teorií gravitace. Ve stacionárním pří- padě použijeme perturbační teorii v tetrádovém formalismu. Díky zavedení Debyeova potenciálu nalezneme elektromagnetické pole prstence kolem rotující černé díry. Práci zakončíme podrobným popisem analogického přístupu ke gravitačním perturbacím. 1Black holes are among the most intriguing objects in the Universe. When isolated and stationary, they are described by the simple Kerr(-Newman) metric. However, astro- physical black holes are seldom isolated; in fact, we can only know of them through their interaction with the environment. Consequently, the actual gravitational field differs from the Kerr(-Newman) ideal. This thesis investigates the influence of the environment on the gravitational field of black holes. In the stationary (or static) and axially symmet- ric setting, we derive several analytical models describing a black hole surrounded by a disc or ring. The static problem is solved exactly, yielding the metric in closed form in some cases. Besides the basic physical properties of the results, we analyze the scalar- field quasinormal modes in such a deformed black-hole geometry. Our findings indicate a universal behaviour of the QNM response, which may help in distinguishing the envi- ronmental effects from those of modified theories of gravity. In the stationary case, we employ perturbation theory in the tetrad formalism. By introducing the Debye potential, we find the electromagnetic field of a ring source on the rotating black-hole background. We conclude with a discussion of similar treatment of gravitational perturbations. 1Institute of Theoretical PhysicsÚstav teoretické fyzikyMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
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
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