Dissertations / Theses on the topic 'Relativistic processe'
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Glass, John T. "Relativistic ion-atom collision processes." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282153.
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Dunkel, Jörn. "Relativistic Brownian motion and diffusion processes." kostenfrei, 2008. http://d-nb.info/991318757/34.
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Jaroschek, Claus. "Critical Kinetic Plasma Processes In Relativistic Astrophysics." Diss., lmu, 2005. http://nbn-resolving.de/urn:nbn:de:bvb:19-46601.
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Jamil, Omar. "A theoretical study of relativistic jets and accretion processes." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/161189/.
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The following work explores different aspects of the disc:jet connection in X-ray binaries. There is a detailed description of a new jet model (iShocks) that is used, firstly, to address the re-energization problem in the conical jet geometries. The adiabatic energy losses suffered by conical jets are successfully countered to reproduce the canonical flat/inverted synchrotron spectrum associated with compact radio jets. The iShocks model uses discrete packets of plasma, or shells, to simulate a jet. The shell collisions give rise to the shocks that are used to re-energize the emitting electrons. Multiple internal shocks, all along the jet, are shown to be necessary to achieve sufficient re-acceleration. The flat/inverted spectrum (ranging from the infra-red to the radio) is successfully reproduced and the high frequency break for such a spectrum is shown to be correlated with the jet power: vb ∼ L0.6 W. While the flat-spectrum synchrotron flux is also correlated with the jet power via: Fv ∼ L1.4 W. Both these correlations are in agreement with the previous analytical predictions. Themodel is also used to explore themassive ejections scenario in the source GRS 1915+105. Various iShocks set-ups are used to model the data that display the flaring behaviour observed in different frequencies (IR-mm-radio). The X-ray binary timing properties are also investigated with the aide of the iShocks model. In particular, the optical/X-ray correlations are the focus of the present study. These correlations have been observed to show some interesting behaviours, such as: the optical lagging the X-rays, and the optical emission showing awareness of the X-ray emission in the form of pre-cognition dips. A number of these correlations are successfully reproduced by translating the simulated X-ray light curves into the jet parameters used as the input for the iShocks model. In addition to relativistic jets, a study of the electron-positron pair processes is also included in the present work. The electron-positron pair annihilation is implemented in an existing Comptonization code (simulating the corona) to explore the possibility of masking an annihilation line from the X-ray binary sources. The results show that radiative processes such as inverse Compton scattering and bremsstrahlung radiation, in addition to thermal line broadening, can be very effective in making the e−/e+ annihilation line indistinguishable from the rest of the high energy spectrum.
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Postavaru, Octavian [Verfasser]. "Strong-field relativistic processes in highly charged ions / Octavian Postavaru." Heidelberg : Universitätsbibliothek Heidelberg, 2010. http://d-nb.info/1024909743/34.
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Chen, Guo-Xin. "Relativistic close coupling calculations for fundamental atomic processes in astrophysics." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078938510.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxvi, 249 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Anil K. Pradhan, Dept. of Astronomy. Includes bibliographical references (p. 237-249).
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Melzani, Mickaël. "Reconnexion magnétique non-collisionelle dans les plasmas relativistes et simulations particle-in-cell." Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0946/document.
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L'objectif de cette thèse est l'étude de la reconnexion magnétique dans les plasmas non-collisionels et relativistes. De tels plasmas sont présents dans divers objets astrophysiques (MQs, AGNs, GRBs...), où la reconnexion pourrait expliquer la production de particules et de radiation de haute énergie, un chauffage, ou des jets. Une compréhension fondamentale de la reconnexion n'est cependant toujours pas acquise, en particulier dans les plasmas relativistes ion-électron. Nous présentons d'abord les bases de la reconnexion magnétique. Nous démontrons des résultats particuliers à la physique des plasmas relativistes, concernant par exemple la distribution de Maxwell-Jüttner. Ensuite, nous réalisons une étude détaillée de l'outil numérique utilisé : les simulations particle-in-cell (PIC). Le fait que le plasma réel contienne beaucoup plus de particules que le plasma PIC a des conséquences importantes (collisionalité, relaxation, bruit) que nous décrivons. Enfin, nous étudions la reconnexion magnétique dans les plasmas ion-électron et relativistes à l'aide de simulations PIC. Nous soulignons des points spécifiques : loi d'Ohm (l'inertie de bulk dominante), zone de diffusion, taux de reconnexion (et sa normalisation relativiste). Les ions et les électrons produisent des lois de puissance, avec un index qui dépend de la vitesse d'Alfvén et de la magnétisation, et qui peut être plus dur que dans le cas des chocs non-collisionels. De plus, les ions peuvent avoir plus ou moins d'énergie que les électrons selon la valeur du champ guide. Ces résultats fournissent une base solide à des modèles d'objets astrophysiques qui, jusque là, supposaient a priori ces résultatsThe purpose of this thesis is to study magnetic reconnection in collisionless and relativistic plasmas. Such plasmas can be encountered in various astrophysical objects (microquasars, AGNs, GRBs...), where reconnection could explain high-energy particle and photon production, plasma heating, or transient large-scale outflows. However, a first principle understanding of reconnection is still lacking, especially in relativistic ion-electron plasmas. We first present the basis of reconnection physics. We derive results relevant to relativistic plasma physics, including properties of the Maxwell-Jüttner distribution. Then, we provide a detailed study of our numerical tool, particle-in-cell simulations (PIC). The fact that the real plasma contains far less particles than the PIC plasma has important consequences concerning relaxation times or noise, that we describe. Finally, we study relativistic reconnection in ion-electron plasmas with PIC simulations. We stress outstanding properties: Ohm's law (dominated by bulk inertia), structure of the diffusion zone, energy content of the outflows (thermally dominated), reconnection rate (and its relativistic normalization). Ions and electrons produce power law distributions, with indexes that depend on the inflow Alfvén speed and on the magnetization of the corresponding species. They can be harder than those produced by collisionless shocks. Also, ions can get more or less energy than the electrons, depending on the guide field strength. These results provide a solid ground for astrophysical models that, up to now, assumed with no prior justification the existence of such distributions or of such ion/electron energy repartition
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Tardif, Camille. "Etude infinitésimale et asymptotique de certains flots stochastiques relativistes." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00703181.
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Nous étudions certains processus de Lévy à valeurs dans les groupes d'isométries respectifs des espace-temps de Minkowski, de De Sitter et de Anti-De-Sitter. Le groupe d'isométries est vu comme le fibré des repères de l'espace-temps et les processus de Lévy considérés se projettent sur le fibré unitaire en un processus markovien relativiste ; c'est-à-dire que les trajectoires dans l'espace-temps sont de genre temps et que le générateur est invariant par les isométries. Dans la première partie nous adaptons pour les diffusions hypoelliptiques générales un résultat de Ben Arous et Gradinaru concernant la singularité de la fonction de Green hypoelliptique. Nous déduisons de cela un critère d'effilement de Wiener local pour les diffusions relativistes dans le groupe de Poincaré, groupe des isométries de l'espace-temps de Minkowski. Dans les deux dernières parties nous nous intéressons au comportement asymptotique du flot stochastique associé à ces processus de Lévy dans les différents groupes d'isométries. Sous une condition d'intégrabilité de la mesure de Lévy nous calculons explicitement les coefficients de Lyapounov des processus dans le groupe de Poincaré. Nous effectuons un travail similaire pour les espace-temps de De Sitter et Anti-De-Sitter en nous limitant au cas des diffusions. Nous explicitons de plus la frontière de Poisson pour la diffusion dans le groupe d'isométries de l'espace-temps de De Sitter.
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Fitoussi, Thomas. "Les cascades électromagnétiques cosmologiques comme sondes du milieu intergalactique." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30235/document.
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Cette thèse vise à étudier le phénomène dit de " cascades électromagnétiques cosmologiques ". Ces cascades sont typiquement générées dans le milieu intergalactique par l'absorption de rayons gamma sur les photons du fond optique / UV et par la production de paires électron / positron associés. Ces leptons eux-mêmes interagissent avec les photons du fond diffus cosmologique via diffusion inverse Compton pour produire de nouveaux rayons gamma qui eux même peuvent s'annihiler, générant à partir d'un unique photon primaire toute une gerbe de photons et de particules secondaires. D'un point de vue observationnel, le développement de cette cascade introduit trois effets : une déformation du spectre à haute énergie, un retard temporel dans l'arrivée des rayons gamma et une extension de la taille apparente de la source. Les cascades électromagnétiques cosmologiques ont commencé à être étudiées dans les années soixante. Mais ce n'est qu'à partir des années 2010 avec l'arrivée du satellite Fermi (entre autres) et des observations dans la bande au GeV et au TeV que la discipline a explosé. Le phénomène est particulièrement important. D'une part il altère le spectre observé des sources rendant difficile la compréhension de la physique de ces dernières. D'autre part les cascades se développant dans le milieu extragalactique, elles sont très sensibles à la composition de ce dernier (fond diffus de photons, champ magnétique). Or ce milieu étant très ténu, il est difficile à étudier. Les cascades deviennent alors une formidable sonde pour accéder à sa compréhension et pouvoir en comprendre l'origine qui remonte au commencement de l'Univers. Pourtant les cascades cosmologiques sont un phénomène complexe faisant intervenir des interactions difficiles à modéliser (sections efficaces complexes) et le transport de particules dans un Univers en expansion (cosmologie). Face à cette complexité les expressions analytiques sont vite limitées et le passage au numérique devient inévitable. Dans le cadre de cette thèse un code de simulation Monte Carlo a donc été développé visant à reproduire aussi précisément que possible le phénomène des cascades. Ce code a été testé et validé en le confrontant aux expressions analytiques. Grâce à ce code, le rôle des différents paramètres physiques impactant le développement de la cascade a été étudié de manière systématique. Cette étude a permis de mieux comprendre la physique du phénomène. En particulier, l'impact des propriétés du milieu extragalactique (fond diffus extragalactique, champ magnétique extragalactique) sur les observables a été mis en évidence. Finalement, une seconde étude a été menée pour mesurer la contribution des cascades au fond gamma extragalactique. Des travaux récents montrent qu'une grande partie de l'émission diffuse à très haute énergie provient de sources ponctuelles non résolues (blazars en particulier). Ces sources gamma (résolues et non résolues) doivent en principe initier des cascades qui peuvent contribuer au fond diffus. En partant d'une modélisation de l'émission des blazars à différents redshifts, l'absorption et la contribution des cascades ont alors été calculées à l'aide du code Monte Carlo. Les résultats montrent que la contribution des cascades au fond gamma extragalactique pourrait violer les limites Fermi mais l'excès doit encore être confirméThis thesis aims at studying "cosmological electromagnetic cascades". These cascades are initiated by the absorption of very high energy gamma-rays through gamma-gamma annihilation with optical / UV background photons of the intergalactic medium. In this interaction, electron/positron pairs are produced. The newly created leptons interact with photons of the Cosmological Microwave Background producing new gamma-rays through inverse Compton scattering which can also annihilate producing a cascade of secondary particles from a single primary photon. Observationally, the development of this cascade has three effects : the observed high energy spectrum is altered, observed photons arrive with a time delay with respect to primary photons and the source appears extended. Cosmological electromagnetic cascades start to being studied in the early sixties. But it is during the 2010's with the Fermi satellite and GeV to TeV observations that the field has really started to being explored. In the fast evolving backgound of gamma-ray astronomy, understanding the cascade physics has become a crucial stake. First the observed spectrum from a distant source is altered, which directly affects the modelling of high energy sources. Secondly, the cascades develop in the extragalactic medium and are very sensitive to its composition (background light, magnetic field). This medium is hard to study because it is extremely thin. Hence the cosmological cascades are a formidable probe to access its comprehension and its origin coming from the very beginning of our Universe. Yet the cosmological cascades are a complex phenomenon which involves complicated interactions (complex cross sections) and transport of particles in an expanding Universe. Analytical expressions are rapidly limited and numerical computations are required. In this thesis a Monte Carlo simulation code has been developed aiming at reproducing the cosmological cascades. This code has been tested and validated against analytical expressions. With the simulation code, a systematic study of the parameters impacting the development of the cascade has been led. This study allows a better understanding of the cascade physics. Especially, the impact of the intergalactic medium properties (extragalactic background light, extragalactic magnetic field) on the observables has been highlighted. Finally, a second study has been done to measure the contribution of cascades to the extragalactic gamma ray background. Recent works show that a great part of the diffuse emission at very high energy is explained by unresolved sources (blazars in particular). These gamma sources (resolved and unresolved) must in principle initiate cosmological cascades which can also contribute to the extragalactic gamma ray background. Starting from a modeling of the blazars at different redshifts, absorption and contribution of the cascades have been estimated with the simulation code. The results show that the contribution of the cascades might violate the Fermi limits but the excess must be confirmed
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Lundman, Christoffer. "Photospheric emission from structured, relativistic jets : applications to gamma-ray burst spectra and polarization." Doctoral thesis, KTH, Partikel- och astropartikelfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-136178.
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The radiative mechanism responsible for the prompt gamma-ray burst (GRB) emission remains elusive. For the last decade, optically thin synchrotron emission from shocks internal to the GRB jet appeared to be the most plausible explanation. However, the synchrotron interpretation is incompatible with a significant fraction of GRB observations, highlighting the need for new ideas. In this thesis, it is shown that the narrow, dominating component of the prompt emission from the bright GRB090902B is initially consistent only with emission released at the optically thick jet photosphere. However, this emission component then broadens in time into a more typical GRB spectrum, which calls for an explanation. In this thesis, a previously unconsidered way of broadening the spectrum of photospheric emission, based on considerations of the lateral jet structure, is presented and explored. Expressions for the spectral features, as well as polarization properties, of the photospheric emission observed from structured, relativistic jets are derived analytically under simplifying assumptions on the radiative transfer close to the photosphere. The full, polarized radiative transfer is solved through Monte Carlo simulations, using a code which has been constructed for this unique purpose. It is shown that the typical observed GRB spectrum can be obtained from the photosphere, without the need for additional, commonly assumed, physical processes (e.g. energy dissipation, particle acceleration, or additional radiative processes). Furthermore, contrary to common expectations, it is found that the observed photospheric emission can be highly linearly polarized (up to $\sim 40 \, \%$). In particular, it is shown that a shift of $\pi/2$ of the angle of polarization is the only shift allowed by the proposed model, consistent with the only measurement preformed to date. A number of ways to test the theory is proposed, mainly involving simultaneous spectral and polarization measurements. The simplest measurement, which tests not only the proposed theory but also common assumptions on the jet structure, involves only two consecutive measurements of the angle of polarization during the prompt emission.QC 20131204
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Leonardi, Andrea. "La visualizzabilità dei processi fisici: dalla meccanica quantistica non relativistica alla gravità quantistica." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23939/.
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Per la fisica classica, la visualizzabilità era un aspetto implicito e scontato della teoria, un approccio intuitivo e naturale allo studio dei fenomeni.
Nei primi del ‘900, l’esplicitazione della visualizzabilità entrava in contrasto con i nuovi risultati teorici e sperimentali portando Heisenberg a proporre una rivoluzione epistemologica: la fisica microscopica non può e non deve essere visualizzabile.
A partire dal termine della Seconda guerra mondiale, le redini della fisica teorica passavano ai fisici statunitensi e il loro approccio epistemologicamente più morbido ripropone la visualizzabilità dei fenomeni fisici come una caratteristica soggettiva e intersoggettiva degli stessi fisici, riscontrabile nel successo dei diagrammi di Feynman.
Il ventesimo secolo si chiude con l’impressione che la visualizzabilità stia invece scomparendo a favore di una visione del mondo priva di quei filtri mentali che, fin dall’antichità, furono ritenuti necessari per far sì che la nostra mente possa comprendere la realtà che ci circonda.
Il terzo e ultimo capitolo, infine, propone un tentativo di visualizzazione dei fondamenti della teoria quantistica a partire dai legami matematici e formali della stessa con la meccanica classica.
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Lefa, Eva [Verfasser], and Felix A. [Akademischer Betreuer] Aharonian. "Non-thermal Radiation Processes in Relativistic Outflows from AGN / Eva Lefa ; Betreuer: Felix A. Aharonian." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1180607813/34.
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Plotnikov, Illya. "Ondes de choc relativistes." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00961589.
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La formation et l'activité des objets compacts, tels que Trous Noirs ou étoiles à Neutrons, s'accompagne couramment d'éjection de matière ionisée sous forme de jets à la vitesse proche de celle de la lumière (vitesses relativistes). Se propageant dans le milieu environnant, par exemple Milieu Interstellaire, ces jets conduisent inéluctablement à la formation d'ondes de choc relativistes. Une forte turbulence magnétique et une population d'électrons accélérés sont requises afin de tenir compte de l'émission radiative non-thermique de ces chocs. L'approche naturelle de ce problème, décrivant de manière auto-consistante la structure du choc non-collisionnel, est celle de la physique cinétique des plasmas en régime relativiste. L'aspect essentiel de cette approche est l'étude du précurseur du choc, sous forme d'un faisceau de protons très énergétiques. Un ensemble d'instabilites plasma y prend lieu et dissipe l'energie du choc sous forme de micro-turbulence électromagnétique, électrons chauffés et particules accélérées. Ce cadre conceptuel emmène à reconsidérer le processus de transport de particules charges autour du choc. Deux études indépendantes, effectuées pendant la thèse, montrent que les lois de diffusion en aval et amont du choc se mettent sous une forme concise, en loi de puissance en fonction de l'énergie des particules et de l'intensité de la micro-turbulence magnétique. Les lois de diffusion, dérivées à l'aide des simulations Monte-Carlo et analytiquement, chiffrent l'énergie maximale des protons accélérés au choc à 10^15 eV, si le facteur de Lorentz du choc est très grand devant 1. Cette limite se situe loin de l'énergie maximale des Rayons Cosmique et rend les chocs relativistes comme accélérateurs de particules inefficaces aux énergies les plus extrêmes. Le rayonnement, issu de l'accélération des électrons, atteint plusieurs GeV et corrobore l'idée que les chocs externes des Sursauts Gamma peuvent émettre à de telles énergies. L'approche alternative de l'étude des chocs, simulations Particle-In-Cell, m'as permis d'étudier la formation, structuration et évolution des chocs modérément relativistes dans une géométrie spatiale 1D. L'auto-reformation du front d'un choc perpendiculaire, connue dans le régime non-relativiste, persiste dans le régime moyennement relativiste et exhibe un front de choc non-stationnaire. A magnétisation basse, les électrons sont préchauffés dans le pied du choc par l'instabilité de Buneman entre protons réfléchis et électrons incidents, mais leur température en aval du choc reste plus faible que celle des protons. A magnétisation croissante, l'instabilité Maser Synchrotron devient essentielle dans la structuration du front de choc, avec émission d'un fort précurseur électromagnétique a partir du front de choc. Dans ce cas les électrons se mettent en équipartition avec les protons. Ces simulations 1D ne montrent pas d'évidence d'accélération des particules et des simulations 2D (3D) sont nécessaires.
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Souza, Rubin Assis da Silveira. "A decisão judicial e a filosofia relativista de Hans Kelsen: uma abordagem hermenêutica." reponame:Repositório Institucional da UFSC, 2015. https://repositorio.ufsc.br/xmlui/handle/123456789/132983.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Jurídicas, Programa de Pós-Graduação em Direito, Florianópolis, 2015.Made available in DSpace on 2015-05-19T04:09:08Z (GMT). No. of bitstreams: 1 333234.pdf: 1646853 bytes, checksum: c89773cdd60d0aa569ac7cca678d83e4 (MD5) Previous issue date: 2015
A presente dissertação tem como tema central a proposta da abordagem hermenêutica da decisão judicial em Hans Kelsen considerando seu relativismo filosófico. No primeiro momento expõe a concepção de decisão judicial no autor e as suas reformulações conceituais no decorrer das suas obras - as passagens do formalismo normativista das primeiras obras até o ceticismo de regras na Teoria geral das normas. Também propõe a dissolução entre as leituras formalistas e realistas através da possibilidade de uma leitura realista moderada. Após expõe a filosofia relativista do autor e seu resultado na exclusão dos elementos da moralidade do conceito de direito. Finalmente deduz regras de interpretação a partir de uma visão abrangente das obras do autor. O objetivo da dissertação, nesse sentido, é analisar a dinâmica da criação normativa pelo judiciário, a discricionariedade daí resultante e a possibilidade de interpretar os vários sentidos das normas sem recorrer a qualquer moralismo para tal.
Abstract : The central theme of this thesis is the hermeneutic approach of the court decision in Hans Kelsen considering his philosophical relativism. In the first chapter exposes his conception of court decision and his conceptual reformulations - the normative formalism and the legal realism. Also proposes the moderate realism as a possible reading. After, in the second chapter, exposes the philosophical relativism and the exclusion of the morality elements of the concept of law. Finally deduces interpretation rules from a full view of the author's works. The aim of the thesis is analyze the dynamics of the normative creation by the judiciary, his discretionary consequences and the interpretation of the various sense of the norms without any moralism.
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Moriyama, Kotaro. "New methods for probing black-hole space-time based on infalling gas clouds." Kyoto University, 2018. http://hdl.handle.net/2433/232254.
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Alexander, K. D., T. Laskar, E. Berger, C. Guidorzi, S. Dichiara, W. Fong, A. Gomboc, et al. "A Reverse Shock and Unusual Radio Properties in GRB 160625B." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626042.
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We present multi-wavelength observations and modeling of the exceptionally bright long gamma-ray burst GRB 160625B. The optical and X-ray data are well fit by synchrotron emission from a collimated blastwave with an opening angle of theta(j) approximate to 3 degrees.6 and kinetic energy of E-K approximate to 2 x 10(51) erg, propagating into a low-density (n approximate to 5 x 10(-5) cm(-3)) medium with a uniform profile. The forward shock is sub-dominant in the radio band; instead, the radio emission is dominated by two additional components. The first component is consistent with emission from a reverse shock, indicating an initial Lorentz factor of Gamma(0) greater than or similar to 100 and an ejecta magnetization of R-B approximate to 1-100. The second component exhibits peculiar spectral and temporal evolution and is most likely the result of scattering of the radio emission by the turbulent Milky Way interstellar medium (ISM). Such scattering is expected in any sufficiently compact extragalactic source and has been seen in GRBs before, but the large amplitude and long duration of the variability seen here are qualitatively more similar to extreme scattering events previously observed in quasars, rather than normal interstellar scintillation effects. High-cadence, broadband radio observations of future GRBs are needed to fully characterize such effects, which can sensitively probe the properties of the ISM and must be taken into account before variability intrinsic to the GRB can be interpreted correctly.
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DIltz, Christopher S. "Time Dependent Leptonic and Lepto-Hadronic Modeling of Blazar Emission." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1459506010.
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Venter, Christo. "The effect of general relativistic frame dragging on millisecond pulsar visibility for the H.E.S.S. telescope / C. Venter." Thesis, North-West University, 2004. http://hdl.handle.net/10394/215.
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It has been noted by several authors that General Relativistic frame dragging in rotating
neutron stars is a first order effect which has to be included in a self-consistent model of pulsar
magnetospheric structure and associated radiation and transport processes. To this end, I
undertook the present study with the aim of investigating the effect of General Relativity
(GR) on millisecond pulsar (MSP) visibility.
I developed a numerical code for simulating a pulsar magnetosphere, incorporating the
GR-corrected expressions for the electric potential and field. I included curvature radiation
(CR) due to primary electrons accelerated above the stellar surface, as well as inverse Compton
scattering (ICS) of thermal X-ray photons by these electrons. I then applied the model to
PSR J0437-4715, a prime candidate for testing the GR-Electrodynamic theory, and examined
its visibility for the H.E.S.S. telescope. I also considered the question of whether magnetic
photon absorption would take place for this particular pulsar. In addition, I developed a
classical model for comparison with the GR results.
I found that the typical electron energies and associated CR photon energies are functions
of position above the polar cap (PC). These energies are also quite smaller in the GR case
than in the classical case due to the different functional forms of the GR and classical electric
fields. I found the CR energy cut-off to be ~ 4 GeV compared to the well-known classical
value of ~ 100 GeV. Since the H.E.S.S. energy threshold is ~ 100 GeV, it seems as though
the CR component will not be visible, contrary to wide-held opinion. However, the ICS
component seems to be well in excess of the H.E.S.S. energy threshold and is expected to be
visible. I also found that no pair production will take place for PSR J0437-4715.
Hopefully, forthcoming H.E.S.S. observations will provide validation of these results.
KEY WORDS: General relativistic frame dragging, GR electrodynamics, millisecond pulsar
visibility, non-thermal radiation processes, pair production, H.E.S.S., individual pulsars:
PSR J0437-4715.Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.
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Johannsen, Tim. "Testing General Relativity in the Strong-Field Regime with Observations of Black Holes in the Electromagnetic Spectrum." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/238893.
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General relativity has been tested by many experiments, which, however, almost exclusively probe weak spacetime curvatures. In this thesis, I create two frameworks for testing general relativity in the strong-field regime with observations of black holes in the electromagnetic spectrum using current or near-future instruments. In the first part, I design tests of the no-hair theorem, which uniquely characterizes the nature of black holes in terms of their masses and spins in general relativity and which states that these compact objects are described by the Kerr metric. I investigate a quasi-Kerr metric and construct a Kerr-like spacetime, both of which contain an independent parameter in addition to mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric has to be zero. I show that already moderate changes of the deviation parameters in either metric lead to significant modifications of the observed signals. First, I apply this framework to the imaging of supermassive black holes using very-long baseline interferometry. I show that the shadow of a black hole as well as the shape of a bright and narrow ring surrounding the shadow depend uniquely on its mass, spin, inclination, and the deviation parameter. I argue that the no-hair theorem can be tested with observations of the supermassive black hole Sgr A*. Second, I investigate the potential of quasi-periodic variability observed in both galactic black holes and active galactic nuclei to test the no-hair theorem in two different scenarios. Third, I show that the profiles of relativistically broadened iron lines emitted from the accretion disks of black holes imprint the signatures of deviations from the Kerr metric. In the second part, I devise a method to test the predicted evaporation of black holes in the Randall-Sundrum model of string theory-inspired braneworld gravity through the orbital evolution of black-hole X-ray binaries and obtain constraints on the size of the extra dimension from A0620-00 and XTE J1118+480. I predict the first detection of orbital evolution in a black-hole binary.
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Vega, Garcia Laura [Verfasser], A. [Gutachter] Eckart, and J. A. [Gutachter] Zensus. "Space VLBI studies of internal structure and physical processes in extragalactic relativistic jets / Laura Vega Garcia ; Gutachter: A. Eckart, J. A. Zensus." Köln : Universitäts- und Stadtbibliothek Köln, 2018. http://d-nb.info/1180601572/34.
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Patel, Gayatri. "How 'universal' is the United Nations' universal periodic review process? : an examination from a cultural relativist perspective." Thesis, University of Leicester, 2016. http://hdl.handle.net/2381/37501.
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This thesis explores the United Nations’ human rights monitoring mechanism, the Universal Periodic Review (UPR) process. The aim of the UPR process is to peer review states’ human rights records through an interactive dialogue session. One of the core elements of the review process is its claim of universality, which is based on two grounds: first, the universal applicability of the process, and second, the normative claim of universalism that is embedded in the operation of the process. Focusing on the second claim of universalism, I challenge the normative claim of universality of the process using the theories of cultural relativism. I ask whether, and to what extent, member states adopt positions that affiliate with the cultural relativist perspective during the interactive dialogue stage in the UPR process. Guided by the theoretical framework of this investigation, I selected three women’s rights categories as the focus of this investigation: women’s rights to health, women’s rights under private and family law and violence against women. The findings of this investigation reveal that there was evidence of states introducing arguments from a form of cultural relativism to challenge universality of international women’s rights. The foundations of this investigation are laid down in the first three chapters of this thesis, which broadly provide details of the UPR process, define the theoretical framework and justify the research methods adopted for this study. Chapters 4, 5 and 6 of this thesis present, analyse and discuss the findings of this research project. Drawing upon the findings, this thesis provides two main conclusions. First, that the extent to which the universality of human rights is promoted is contingent on the states participating in the review and the human rights issue being discussed. Second, an unchecked challenge of universalism expressed by some states from a form of cultural relativism threatens not only the creditability of the UPR process, but could potentially question the very infrastructure of international human rights norms.
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Wang, Xiang-Peng [Verfasser], and Bernd [Akademischer Betreuer] Kniehl. "Inclusive charmonium production via Upsilon decayand break-down of non-relativistic QCD factorization in double quarkonia processes / Xiang-Peng Wang ; Betreuer: Bernd Kniehl." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/1162621842/34.
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Beerwerth, Randolf [Verfasser], Stephan [Gutachter] Fritzsche, J. Gutachter] Bieron, and Tomas [Gutachter] [Brage. "Electron correlation in relativistic multiconfiguration calculations of isotope shift parameters, hyperfine coupling constants and atomic processes / Randolf Beerwerth ; Gutachter: Stephan Fritzsche, J. Bieron, Tomas Brage." Jena : Friedrich-Schiller-Universität Jena, 2019. http://d-nb.info/1206542586/34.
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Souza, Ulisses Gulart de. "Medida da produção de hádrons estranhos e estudo do processo de hadronização em colisões entre íons pesados relativísticos." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-01122014-141659/.
Full textAbstract:
O principal objetivo de experimentos envolvendo colisões de íons pesados relativísticos é estudar a matéria nuclear sob condições extremas de temperatura e densidade. Sob tais condições, acredita-se que a matéria transite para um novo estado no qual quarks e glúons deixem de estar confinados, o plasma de quarks e glúons (PQG). A produção de partículas estranhas é uma importante ferramenta para a caracterização desse novo estado. O aumento da produção dessas partículas já era considerado como sendo um possível sinal para a existência do plasma de quarks e glúons mesmo antes da obtenção dos primeiros resultados experimentais do RHIC. Nesse trabalho, é feita a determinação da produção das partículas estranhas neutras K0s , e em colisões Cu+Cu ap sNN = 62:4 GeV, utilizando o intervalo de rapidez y < j0:75j. Em seguida, esses dados são comparados a modelos teóricos (estatístico -termodinâmicos, coalescência e core-corona) para entender o processo de produção dessas partículas em colisões de íons pesados relativísticos.The main goal of relativistic heavy ion collisions is to study nuclear matter under extreme conditions of temperature and density. It is under these conditions that it is believed that a phase transition to a new state of matter where quarks and gluons are no loger conned takes place, the so called Quarks and Gluon Plasma. Strange particle production is an important tool for the characterization of this new state of matter. Strangeness enhancement was considered as a possible evidence for the formation QGP even before the rst RHIC experimental results. In this thesis, it is determined a production of neutral strange particles K0 s and in Cu+Cu collisions at p sNN = 62:4 GeV, using a rapidity range y < j0:75j. These data are compared to theoretical models (statistical-thermodynamic, coalescence and core-corona) in order to understand the hadronization process in relativistic heavy ions collisions.
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Faßhauer, Elke [Verfasser], and Markus [Akademischer Betreuer] Pernpointner. "Investigation of Relativistic Effects in Electronic Decay Processes in Small and Large Noble Gas Clusters by Ab Initio and New Simulation Approaches / Elke Faßhauer ; Betreuer: Markus Pernpointner." Heidelberg : Universitätsbibliothek Heidelberg, 2014. http://d-nb.info/1179925459/34.
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Tomei, Niccolò. "GRMHD simulations of thick accretion disks in the Event Horizon Telescope era: the role of the mean-field dynamo mechanism." Doctoral thesis, 2022. http://hdl.handle.net/2158/1264722.
Full textAbstract:
The baryonic matter of the Universe is found almost entirely in the form
of plasma, or ionized gas where the moving charges interact with each other
through the self-generated currents and the related magnetic fields within a
highly material conductive. The energy contained in the plasma in terms of
the magnetic field is usually comparable to the kinetic and/or thermal energy
of the plasma itself, and many violent observed phenomena are attributable to
the sudden release of magnetic energy (e.g. flares and coronal mass ejection in
the Sun, gamma ray bursts, gamma flare in magnetars, relativistic jets in active
galactic nuclei).
Since the Universe may not have formed magnetized, a natural question one
needs to answer is what processes can lead to a weak magnetic field, from zero
initial fields. Battery-like mechanisms are needed to create primordial extra-
galactic fields, which may be amplified to higher values by plasma advection,
rotation and collapse to values appropriate for stellar magnetism, up to B ∼ 1012
G, the field of a standard neutron star, a value required to power the surrounding
young supernova remnant. Most of these batteries lead to field strengths
much weaker than the observed field. So some way of amplifying the field is
required.
Magnetic fields of small scale and large scale components are observed in
various astrophysical settings. This thesis work is focused on the investigation
of the amplification mechanisms of magnetic fields in system of gas rotating
around a supermassive black hole, following the renewed interest given by the
recent imaging of the M87 black hole at millimetre wavelengths by the Event
Horizon Telescope (EHT).
In most cases an amplification of the magnetic fields may occur also by instabilities
capable of converting kinetic energy into magnetic energy. A very
efficient and ideal process is the magneto-rotational instability (MRI) that provided
a local mechanism, effcient for a wide range of magnetic field strength,
which leads to a growth on dynamical time-scales of linear perturbations and
naturally develops MHD turbulence. The only necessary condition for its onset
is the presence of a differentially rotating fluid threaded by a weak magnetic
field. However, the amplification of the magnetic field is a non-ideal process
due to the non-linear coupling of small-scale velocity and magnetic field fluctuations,
possibly caused by the MRI. The result of this correlation leads to the
creation of an electromotive force capable of amplifying magnetic fields. This
process is known as mean-field dynamo and has been applied to a large number
of astrophysical contexts.
Currently, GRMHD simulations of MRI-induced accretion on to rotating
black holes are being receiving considerable attention due to the success of the
EHT collaboration, capable of imaging the emission and the shadow around the
event horizon of a black hole for the very first time. The aim of this thesis
work is to provide an alternative numerical accretion modelling to the ideal one
in which the initial magnetic field has a well-defined poloidal structure and an
intensity not exactly negligible. The mean-field dynamo allows us to investigate
the possibility of producing poloidal field necessary for the development of MRI
and the launch of jets even starting from the most unfavorable condition, that
is an initial toroidal field with extremely lower magnetization than those used
in ideal GRMHD simulations.
In this work we have investigated, for the first time by means of non-ideal
axisymmetric GRMHD simulations, the mean-field dynamo process operating
in thick accretion disks around black holes, in the fully non-linear regime. Combined
with the differential rotation of the disk, the dynamo process is able to
produce an exponential growth of any initial seed magnetic field up to the values
required to explain the observations,when the instability tends to saturate
even in the absence of artificial quenching effects. Before reaching the final saturation
stage we observe a secondary regime of exponential growing, where the
magnetic field increases more slowly due to accretion, which is modifying the
underlying equilibrium. In the stationary state characterized by the saturation
of the magnetic field growth, the dynamo is able to remove the angular momentum
and trigger the accretion. Finally, we show that it is possible to reproduce
the main diagnostics present in the literature by starting from very unfavorable
initial configurations, such as a purely toroidal magnetic field with negligible
magnetization. In parallel, we present the contribution to the code Comparison
Project that aims to compare ideal GRMHD solutions for the evolution of a
magnetized accretion flow in two distinct regimes where turbulence is promoted
by the magnetorotational instability.
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(8803361), Yonggang Luo. "Radiative Processes in Relativistic Astrophysical Plasmas." Thesis, 2020.
Find full textAbstract:
Synchrotron radiation and inverse Compton (IC) scattering are the two most essential radiation mechanisms in high energy astrophysics. Synchrotron radiation typically dominates lower energy emission, up to GeV, and IC scattering dominates higher energy gamma-ray emission. In this work, radiation codes are developed to calculate broadband synchrotron and IC spectra for relativistic astrophysical sources: Pulsar Wind Nebulae (PWNe) and Gamma-Ray Bursts (GRBs). Our robust radiation code takes into account varying intrinsic plasma properties (e.g., magnetic field evolution), various inverse Compton processes (synchrotron self-Compton and external Compton) while accounting for Klein-Nishina effects, as well as relativistic bulk motion of the emitting plasma.
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Dunkel, Jörn [Verfasser]. "Relativistic Brownian motion and diffusion processes / eingereicht von Jörn Dunkel." 2008. http://d-nb.info/991318757/34.
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Jaroschek, Claus H. [Verfasser]. "Critical kinetic plasma processes in relativistic astrophysics / vorgelegt von Claus H. Jaroschek." 2005. http://d-nb.info/978071425/34.
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Karmakar, Anupam [Verfasser]. "Theory and simulations of nonlinear and inelastic processes in relativistic laser plasma interactions / vorgelegt von Anupam Karmakar." 2008. http://d-nb.info/989798828/34.
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MacDonald, Nicholas Roy. "Order & disorder: a study of the flaring properties and polarized emission of blazars." Thesis, 2017. https://hdl.handle.net/2144/23367.
Full textAbstract:
Blazars are the most luminous persistent and enigmatic objects in the sky. They constitute a sub-class of active galactic nuclei (AGN) whose relativistic plasma jets are closely aligned to our line of sight. By monitoring the polarized emission of these jets and subsequently modeling flares in the high-energy emission, we are able to gain insight into the parsec-scale physics of the jets close to the central engines. My dissertation develops and augments several theoretical models of high-energy blazar emission.
The vast majority of gamma-ray flares detected in blazars are highly correlated with flares detected at longer wavelengths; however, a small subset of these gamma-ray flares appear to occur in isolation. These "orphan" gamma-ray flares challenge current models of blazar variability. I have developed a theoretical model of blazar emission to explain the origin of these orphan flares. This model invokes the presence of a sheath of plasma enshrouding the relativistic spine of the jet. The sheath supplies photons that are inverse-Compton scattered up to high energies by relativistic electrons contained within the jet, producing an orphan flare. This model is successfully applied to a number of such gamma-ray flares. In addition, I present stacked radio images that highlight the presence of jet sheaths in my sample of blazars.
Circular polarization (CP) has been detected in a number of blazar jets. CP is very sensitive to the underlying plasma content of the jet. A. Marscher has developed the Turbulent Extreme Multi-Zone (TEMZ) model for blazar emission consisting of thousands of individual cells of plasma that propagate relativistically across a standing shock in the jet. The turbulent nature of the magnetic field within the TEMZ grid naturally creates a birefringent environment in which CP emission can be produced. In order to investigate whether the TEMZ model can indeed produce CP, I have developed a numerical algorithm to solve the full Stokes equations of polarized radiative transfer. I apply this algorithm to ray tracing through the TEMZ model. I am able to demonstrate that TEMZ can reproduce CP at the levels present in blazars.
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Vieyro, Florencia Laura. "Efectos de partículas relativistas en el entorno de agujeros negros." Tesis, 2013. http://hdl.handle.net/10915/32866.
Full textAbstract:
En la presente Tesis se realiza un estudio de los procesos físicos que producen la emisión electromagnética y de neutrinos a altas energías en la vecindad de agujeros negros estelares que acretan materia.
Se estudia la inyección de partículas no térmicas en la corona de agujeros negros galácticos. Primero se caracteriza la región de interacción, detallando propiedades físicas básicas de los sistemas en estudio. Inicialmente se inyecta una población de electrones y protones relativistas, considerándose también la generación de partículas secundarias (piones, muones y pares electrón/positrón). Luego, se estiman los tiempos de enfriamiento por las diversas interacciones entre las partículas y los campos en la fuente. Una vez identificados los procesos radiativos más relevantes, se resuelve de manera auto-consistente el transporte de partículas masivas y de fotones. Este estudio se hace tanto para el estado estacionario, como para casos transitorios, como ser fulguraciones.
Además de la emisión electromagnética y de neutrinos de la fuente, se estudia el impacto de los neutrones creados en las interacciones hadrónicas sobre el medio circundante de la corona. En particular, se investiga la inyección de neutrones como posible mecanismo para cargar de bariones un jet inicialmente dominado magnéticamente.
Por último se hace una aplicación del método desarrollado para tratar el transporte de partículas relativistas en plasmas magnetizados, a las erupciones de rayos gamma. En este caso, se investiga la producción de neutrinos en el modelo de colapsar, abriéndose una nueva línea de trabajo.
Para todos los sistemas estudiados se hacen predicciones sobre la emisión a muy alta energía y la producción de neutrinos; estos resultados podrán ser contrastados en un futuro cercano con nuevos detectores de rayos gamma y de neutrinos (e.g., CTA, IceCube).
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Lötstedt, Erik [Verfasser]. "Laser-assisted second-order relativistic QED processes : Bremsstrahlung and pair creation modified by a strong electromagnetic wave field / presented by Erik Lötstedt." 2008. http://d-nb.info/989273636/34.
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