Tesis sobre el tema "Trou noir de Vaidya"
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Coudray, Armand. "Asymptotic behaviour of zero rest-mass fields on radiative space-times". Electronic Thesis or Diss., Brest, 2024. http://www.theses.fr/2024BRES0026.
Texto completoThis thesis adresses two distinct subjects. The first part examines the asymptotic behavior of scalar waves in the Vaidya spacetime, describing a spherical white hole evaporating via emission of isotropic dust. The analysis focuses on the regularity of conformal scalar waves at the isotropic boundary (past and future) of the compactified spacetime, depending on the initial data of the conformal field. Additionally, we construct the conformal scattering operator, demonstrating its ability to encode the entire field evolution in the compactified spacetime.These findings rely on energy inequalities and vector field methods.The second part centers on analyzing incoming isotropic curves in the purely radiative Robinson-Trautman spacetimes of type D. In contrast to a previous study on Vaidya’s metric, these curves do not form the past horizon due to the solution’s geometry. The final chapter categorizes these curves, revealing a behavior akin to that observed in Vaidya’s spacetime
Denis, Vivien. "Amortissement vibratoire de poutre par effet Trou Noir Acoustique". Thesis, Le Mans, 2014. http://www.theses.fr/2014LEMA1011/document.
Texto completoVibration damping of mechanical structures plays an important role in the design of many industrial systems. Classical methods for reducing vibrations using viscoelastic layers glued to the structure usually result in added mass on the treated structure, which may be prohibitive in the transportation industry for ecological and economical reasons. The "Acoustic Black Hole" (ABH) effect is a lightweight passive vibration technique: the flexural waves propagating in a beam extremity tapered with a power law profile are efficiently dissipated if an absorbing layer is placed where the thickness is minimum.A preliminary study experimentally confirms the potential of ABH as an efficient strategy for vibration damping: a modal analysis shows that the ABH significantly increases the Modal Overlap Factor (MOF) of the beam, thus reducing the resonant behaviour of the structure. An analysis based on a wave approach clearly shows that the reflection coefficient of an ABH termination has small values. Further investigations, including a two dimensional numerical model of the structure developed in order to understand its behaviour, show that the increase of MOF can be explained partly by an increase of the modal density and mostly by a high damping of a number of modes of the structure due to energy localisation in the tapered region. It is shown that the ABH beam possesses two-dimensional local modes. A waveguide model of an ABH termination with tip imperfection, which cannot be avoided in practice, shows that incident energy is scattered on local modes and that imperfections enhance the damping effect
Laurent, Philippe. "VERS UNE SIGNATURE DES SYSTEMES BINAIRES COMPORTANT UN TROU NOIR". Habilitation à diriger des recherches, Université Paris-Diderot - Paris VII, 2009. http://tel.archives-ouvertes.fr/tel-00683273.
Texto completoClavel, Maïca. "Activité du trou noir supermassif au centre de la Galaxie". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112170/document.
Texto completoSagittarius A⋆ is the supermassive black hole at the Galactic center. Due to its proximity, this specimen is an excellent laboratory to study the accretion processes occurring around black holes and to constrain the duty cycle of these objects. Sgr A* is currently extremely faint and despite the detection of daily flares, its luminosity remains at least eight orders of magnitude below its Eddington luminosity, making this specimen one of the least luminous known supermassive black holes. The radiative processes responsible for the daily variations of its luminosity have not been clearly identified yet. We present the results of a multi-wavelength campaign observing Sgr A* simultaneously in X-rays and in the near-infrared, using the XMM-Newton observatory and the VLT/NACO instrument. We studied the spectral variability of Sgr A* using the infrared data we obtained through a spectro-imaging technique. Uncertainties linked to the systematic errors are still large but the first tests applied seem to show that the spectral index of Sgr A* could depend on the black hole luminosity. On longer timescales, we demonstrate that Sgr A* experienced a higher level of activity in the recent past. Indeed, echoes of its past activity can be detected in the molecular material surrounding the black hole. They are traced by a strong signal in the iron fluorescence line at 6.4 keV. We achieved a complete and systematic study of this variable emission detected from the central molecular zone, using Chandra and XMM-Newton observatories. Our results confirm that Sgr A* experienced intense flares in the past few centuries, with a luminosity at least six orders of magnitude higher than its current one. In particular, we highlight for the first time the existence of two distinct transient events of relatively short duration, which are probably due to catastrophic events. These results are the first step needed to include Sgr A*’s activity into a broader understanding of the galactic nuclei
Luminet, Jean-Pierre. "Effets de marée : rupture explosive d’étoiles par un trou noir géant". Paris 7, 1985. http://www.theses.fr/1985PA077061.
Texto completoTrap, Guillaume. "Etude du trou noir massif central de la Galaxie et de son environnement". Phd thesis, Université Paris-Diderot - Paris VII, 2011. http://tel.archives-ouvertes.fr/tel-00862003.
Texto completoErbin, Harold. "Trous noirs en supergravité N = 2". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066367/document.
Texto completoThe most general black hole solution of Einstein–Maxwell theory has been discovered by Plebański and Demiański in 1976.This thesis provides several steps towards generalizing this solution by embedding it into N = 2 gauged supergravity.The (bosonic fields of the) latter consists in the metric together with gauge fields and two kinds of scalar fields (vector scalars and hyperscalars); as a consequence finding a general solution is involved and one needs to focus on specific subclasses of solutions or to rely on solution generating algorithms. In the first part of the thesis we approach the problem using the first strategy: we restrict our attention to BPS solutions, relying on a symplectic covariant formalism. First we study the possible Abelian gaugings involving the hyperscalars in order to understand which are the necessary conditions for obtaining N = 2 adS4 vacua and near-horizon geometries associated to the asymptotics of static black holes.A preliminary step is to obtain covariant expressions for the Killing vectors of symmetric special quaternionic-Kähler manifolds. Then we describe a general analytic solutions for 1/4-BPS (extremal) black holes with mass, NUT, dyonic charges and running scalars in N = 2 Fayet–Iliopoulos gauged supergravity with a symmetric very special Kähler manifold. In the second part we provide an extension of the Janis–Newman algorithm to all bosonic fields with spin less than 2, to topological horizons and to other dimensions. This provides all the necessary tools for applying this solution generating algorithm to (un)gauged supergravity, and interesting connections with the N = 2 supergravity theory are unravelled
Enríquez, de Salamanca Isabel. "Etude la matiere autour d'un trou noir massif dans les noyaux actifs des galaxies". Paris 7, 1995. http://www.theses.fr/1995PA077253.
Texto completoGhanem, Sari. "Équations de Maxwell et de Yang-Mills sur des Espaces-Temps Courbes avec un Trou Noir". Paris 7, 2014. http://www.theses.fr/2014PA077125.
Texto completoIn this thesis, we take a systematic study of global regularity of the Maxwell equations and of the Yang-Mills equations on curved black hole space-times. In the first chapter, we write the proof of the non-blow up of the Yang-Mills curvature on arbitrary curved space-times using the Klainerman-Rodnianski parametrix combined with suitable Grönwall type inequalities. While the Chruściel-Shatah argument requires a control on two derivatives of the Yang-Mills curvature, we can get away by controlling only one derivative instead, and write a new gauge independent proof on arbitrary, fixed, sufficiently smooth, globally hyperbolic, curved 4-dimensional Lorentzian manifolds. In it's sequel, we study the Maxwell equations in the domain of outer-communication of the Schwarzschild black hole. We show that if we assume that the middle components of the non-stationary solutions of the Maxwell equations verify a Morawetz type estimate supported on a compact region in space around the trapped surface, then we can prove uniform decay properties for the components of the Maxwell fields in the entire exterior of the Schwarzschild black hole, including the event horizon, by making only use of Sobolev inequalities combined with energy estimates using the Maxwell equations directly. This proof does not pass through the scalar wave equation on the Schwarzschild black hole, does not need to separate the middle components for the Maxwell fields, and would then be in particular useful for the non-abelian case of the Yang-Mills equations where the separation of the middle components cannot occur. The last chapter is an opening to different problems in partial differential equations
Del, Santo Melania. "Observations of black hole binaries in the integral era : binaires à trou noir à l'ère d'INTEGRAL". Toulouse 3, 2005. http://www.theses.fr/2005TOU30052.
Texto completoAn X-ray binary is a system containing a compact object (black hole, neutron star or white dwarf) accreting material from a companion star. The matter falling on the compact object is an emitter of X and even soft-gamma radiation. Searching and studying these objects, either transient or persistent, is one of the main goal of INTEGRAL, the in-orbit ESA mission devoted to X-ray and gamma-ray astrophysics. Scans of the Galactic plane and deep exposures of the Galactic Centre are performed periodically by INTEGRAL in the framework of the Core Programme guaranteed time. These regions are well known to be rich of X-ray binaries. Thanks to its unprecedented combined spatial resolution (12' FHM) and sensitivity, the IBIS/ISGRI telescope on board INTEGRAL provides high resolution images and good quality spectra in the energy range 15-600 keV. The work reported in this thesis is divided in two different parts which are linked to the status of the IBIS instrument during the different stages of its operation. In the first part, on-ground and in-flight calibration activities of the IBIS telescope are described. Observations of the Crab have been used in order to improve the spectral response matrix of the instrument; sensitivity and imaging capabilities have been accurately tested with several pointings of the Cyg X-1 region. In order to give an idea of the IBIS scientific performances, among the several results of the first year of observations, I briefly report on two key results I have been contributing: the first IBIS source catalogue and the origin of the Galactic diffuse emission between 20 and 100 keV, explained as being mainly due to the emission of previously unresolved Galactic point sources. The second part concerns data analysis and interpretation of three black hole binaries observed with INTEGRAL and simultaneously with two other X-ray satellites, namely XMM-Newton and RXTE. I present in this thesis the spectral evolution and luminosity variation of two transient black hole candidates, XTE J1720-318 and IGR J17464-3213, observed during their 2003 outburst activities. .
Marcel, Grégoire. "Etude des cycles d'hystérésis dans les binaires X à trou noir : application à l'objet GX 339-4". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY042/document.
Texto completoThe hysteresis behavior of X-ray binaries during their outbursts remains a mystery. In this work, we developed the paradigm proposed in Ferreira et al. (2006) where the disk material accretes in two possible, mutually exclusive, ways. In the standard accretion disk (SAD, Shakura et Sunyaev 1973) mode, the dominant local torque is due to MHD turbulence that transports radially the disk angular momentum. In the jet-emitting disk (JED, Ferreira et Pelletier 1995) mode, magnetically-driven jets carry away mass, energy and all the angular momentum from the disk. Within our framework, the transition from one mode to another is related to the magnetic field distribution, an unknown yet.In this thesis, I have developped a two-temperature plasma code able to compute the thermal balance at each radius for a large ensemble of disk parameters, as well as the self- consistent global emitted spectrum. The radiative cooling term and related spectrum (comptonized bremsstrahlung and synchrotron emission) are obtained using the Belm code (Belmont et al. 2008 ; Belmont 2009). Heating processes are analytical and due only to accretion, while advection is properly taken into account, carrying outside-in the memory of the outer thermal states.Using this code, we have shown that a JED extending along the entire disk nicely repro- duces hard states up to 0.5 Eddington luminosities (Marcel et al. 2018a). It was also shown that JEDs produce a natural hysteresis cycle. However, the global luminosity of the cycle is insufficient and the inevitable presence of jets in JEDs advocates for an inner SAD configuration in soft states.Based on these results, the code was enhanced to solve hybrid configurations with an internal JED and an external SAD, separated by a given transition radius rJ. Playing on both rJ and the accretion rate mdot, we have shown that X-ray observations of typical cycles can be completely covered. Using a simple synchrotron model similar to that of Heinz et Sunyaev (2003), the radio flux produced by the jets can be estimated, showing two important features. First, all radio observations can be covered by our model. Second, the radio flux and X- ray spectral coverages are consistents : parameter sets that reproduce best each spectral state also account for a consistent associated radio flux. For illustration, 5 canonical states from GX 339-4 have been reproduced in X-ray spectral shape and associated radio fluxes (Marcel et al. 2018b).Finaly, using a simple fitting procedure on X-ray spectral shape, the 2010-2011 cycle from GX 339-4 has been reproduced. Strikingly, the co-evolution of rJ and mdot seems to be in adequacy with initial theoretical expectations (Esin et al. 1997). Moreover, the estimated radio flux evolution being close to observations, we decided to use those within the fitting procedure. Adding radio fluxes constraints in the procedure allowed us to reproduce both the associated X-ray spectral shape and radio fluxes with excellent agreement. This is, to our knowledge, the first time that such an accretion-ejection cycle is reproduced. Those results, as well as discussions and implications will be soon submitted
Michel, Yann. "Aspects des trous noirs extrémaux en supergravité et théorie des cordes". Paris 6, 2008. http://www.theses.fr/2008PA066486.
Texto completoGoutéraux, Blaise. "Solutions de Trou Noir aux Équations d'Einstein en Présence de Matière et Modifications de la Gravitation en Dimensions Supplémentaires". Phd thesis, Université Paris Sud - Paris XI, 2010. http://tel.archives-ouvertes.fr/tel-00608494.
Texto completoRitter, Patxi. "Ondes gravitationnelles et calcul de la force propre pour un astre compact en mouvement autour d'un trou noir supermassif". Phd thesis, Université d'Orléans, 2013. http://tel.archives-ouvertes.fr/tel-00920959.
Texto completoAimar, Nicolas. "Astrophysique extrême avec GRAVITY : sursauts énergétiques aux abords de l'horizon des événements du trou noir central de la Galaxie". Electronic Thesis or Diss., Université Paris sciences et lettres, 2023. http://www.theses.fr/2023UPSLO006.
Texto completoThe Milky Way, like presumably all structured galaxies, harbors a supermassive black hole at its core, approximately 4.3 million times the mass of the Sun, named Sagittarius A* (Sgr A*). Its size, determined by its mass, and its proximity of about 8.3 kpc make it the black hole with the largest angular size in the sky (~50 μas), making it the ideal target for studying this type of object. Black holes are the most compact objects in the Universe, with an extreme gravitational field near their event horizon. Describing these objects and their immediate environment requires taking into account General Relativity, introduced in 1915 by Albert Einstein .For over 20 years, Sgr A* and its environment have been the subject of numerous observation campaigns at various wavelengths (radio, IR, X-rays). Tracking the orbits of S-stars within one arcsecond around Sgr A* has provided evidence for certain effects predicted by General Relativity, such as Schwarzschild precession. X-ray and NIR observations have shown that Sgr A* exhibits significant variability in the emitted flux from the accretion flow. The advent of adaptive optics and optical interferometry, particularly with the four large telescopes of the VLTI and the GRAVITY instrument, have revealed an orbital motion of the origin of three flares observed in 2018.Numerous models have been proposed to explain the flares of Sgr A*, but the observation of orbital motion has strongly constrained these models. Among them, the analytical hot spot model is widely used with varying degrees of complexity and assumptions. In parallel with the development of analytical models, numerous simulations of accretion around black holes have been studied, with a particular focus on the phenomenon of magnetic reconnection, which appears as a plausible scenario to explain the origin of the flares of Sgr A*.In this thesis, we study different models for the flares of Sgr A* using the ray-tracing code Gyoto, ranging from an analytical hot spot model with intrinsic variability to a semi-analytical model based on magnetic reconnection. The first model is very useful for understanding the effects of Relativity (Special and General) on observables (astrometry and light curves), as well as the influence of intrinsic variability on them. The second model is motivated by a specific physical phenomenon, magnetic reconnection, and is constructed based on the results of numerical simulations. In this model, the azimuthal velocity is free to be super-Keplerian, due to the dragging of the reconnection site by the magnetic field lines. This property constitutes an observational constraint of the 2018 flares observed by GRAVITY that previous models failed to explain. Additionally, we also study the impact of modeling the quiescent state combined with the flares on the observables. Its contribution in astrometry calculations results in a shift between the position of the black hole and the center of the apparent orbit, which is another conclusion from the observations of the 2018 flares.In addition to astrometry and light curves, GRAVITY has measured the polarization of the 2018 flares. The Gyoto ray-tracing code is now capable of calculating the polarization of images. The new version of the code has been validated by comparing the results with another ray-tracing code, ipole.The model based on magnetic reconnection shows very promising results and can be further improved to account for polarization, as well as the multi-wavelength properties of the flares of Sgr A*
Cordier, Bertrand. "Etude du centre galactique dans le domaine des rayons y de faible énergie à partir des observations pratiquées par le télescope spatial SIGMA". Paris 7, 1992. http://www.theses.fr/1992PA077318.
Texto completoChuard, Dimitri. "Echos X dans la zone moléculaire centrale. Une histoire de l'activité du trou noir galactique au cours du dernier millénaire". Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC214.
Texto completoLike most massive galaxies, the Milky Way hosts a supermassive black hole at its centre. In contrast with active galaxies, the luminosity of its radiative counterpart — the source Sagittarius A* — is almost nine orders of magnitude below the Eddington limit. However, there are several indications that the black hole may have been more active in the past. In particular, the giant clouds located within the central molecular zone reflect X-rays emitted during the most recent outbursts. The study we present here focuses on these light echoes that are key to probing the past activity of the Galactic nucleus over the past thousand years. Using the X-ray observatories Chandra and XMM-Newton, we confirm the reflection origin of the non-thermal, diffuse emission from the molecular complex Sagittarius C. The localisation of each bright clump is made possible by the use of Monte Carlo-simulated reflection spectra, notably the rayflX model we specifically designed for the study of the reflection phenomenon and its time behaviour. Considering eight clouds from the main molecular complexes of the Galactic central regions, this work provides with a high confidence level the first quantitative evidence that Sgr A* experienced two powerful outbursts, whose age, duration and luminosity can be estimated. These results place new constraints on the black hole duty cycle and pave the way for a tomographic reconstruction of the matter distribution at the Galactic centre
Ritter, Patxi. "Ondes gravitationnelles et calcul de la force propre pour un astre compact en mouvement autour d'un trou noir super-massif". Thesis, Orléans, 2013. http://www.theses.fr/2013ORLE2038/document.
Texto completoThis thesis focuses on modelling the gravitational waves and the relativistic motion associated to Extreme Mass Ratio Inspiral (EMRI) systems. These systems consist of a stellar mass compact object gravitationally captured by a super-massive black hole. In black hole perturbation theory, we further develop a numerical method which computes waveforms generated by a point mass particle orbiting a Schwarzschild black hole. The Regge-Wheeler-Zerilli wave equation is solved in time domain. The gauge invariant solution is related to the polarisation modes, the energy and the angular momentum carried by the gravitational waves. In reaction to the energy and the moment lost, the trajectory is modified all along. In the MiSaTaQuWa formalism, we compute the self-force acting upon a point particle which is initially at rest, and then falling into a Schwarzschild black hole. We show how this quantity is defined in the Regge-Wheeler gauge by using the mode-sum regularisation technique. We take into account the self-force effect on the motion of the particle by using an iterative and osculating orbit method conceived herein. We quantify the orbital deviation with respect to the geodesic motion, but also the perturbed wave forms and the associated radiated energy
Van, Aelst Karim. "Rotating black holes in the cubic Galileon theory". Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7043.
Texto completoThe present project falls within the wide effort conducted to study theories of gravitation, notably by modelling the physics of compact objects like black holes. The long-term objective of this approach is to determine all theories that are either incompatible with observations, or theoretically inconsistent. The first part of the manuscript thus presents the essential concepts and principles that are common to all these theories, and introduces some of these theories which connect to the project. In the second part, the actual contribution of the project is exposed: comparing rotating black holes of the cubic Galileon theory with the Kerr family of the general theory of relativity. The latter was developed by Albert Einstein more than a century ago, while the cubic Galileon is a much more recent theory.First, the rotating black holes are constructed numerically. Then, the properties of the orbits around them are investigated, in particular their stability. Finally, the images of a simple model of accretion disk orbiting the black holes are simulated. Such orbits and images directly relate the observations realized by instruments like GRAVITY or the Event Horizon Telescope, which monitor supermassive black holes. The present project thus allows to identify possible tensions between the predictions of the cubic Galileon theory and observational data on black holes
Cuenca, Jacques. "VIBRATIONS DE FLEXION DE PLAQUES MINCES: APPROCHES ONDULATOIRES - Modèle des vibrations de plaques polygonales basé sur la méthode des sources image - Absorption passive de vibrations par l'effet de trou noir acoustique". Phd thesis, Université du Maine, 2009. http://tel.archives-ouvertes.fr/tel-00442260.
Texto completoCuenca, Jacques. "Wave models for the flexural vibrations of thin plates : model of the vibrations of polygonal plates by the image source method : vibration damping using the acoustic black hole effect". Le Mans, 2009. http://cyberdoc.univ-lemans.fr/theses/2009/2009LEMA1011.pdf.
Texto completoFlexural vibrations of thin structures are strongly related to sound radiation and structural damage, for which they deserve careful attention in many domains of science and engineering. Two aspects of crucial importance are the development of accurate tools for the prediction and analysis of vibrations and efficient vibration damping. In the first part of the thesis, a model of the flexural vibrations of thin convex polygonal plates based on the image source method is presented. The developed approach allows to predict the vibrations of individual plates and plate assemblies of arbitrary convex polygonal geometry and having arbitrary boundary conditions. The method is particularly suitable for mid- and high-frequency dynamics, in that its accuracy is improved with an increase in frequency or structural damping. A tool for estimating the Young's modulus and structural damping ratio of highly damped flat panels is also proposed. The second part of the thesis concerns vibration damping using the acoustic black hole effect. It is weel-known that a flexural wave travelling in a thin plate or beam slows down in a zone of decreasing thickness. Thus, if the thickness decreases sufficiently smoothly to zero, the wave stops travelling, without being reflected back. Such is the principle of the so-called acoustic black hole effect. A model of the flexural vibrations of such profile is proposed, allowing to determine optimal geometrical and material properties in order to maximise vibration damping. Simulated and measured responses show a reduction of vibration level up to 20 decibels
Grisé, Fabien. "Sources X ultra-lumineuses: étude optique détaillée de deux contreparties et de leurs environnements : Deux exemples contre la présence d'un trou noir de masse intermédiaire". Université Louis Pasteur (Strasbourg) (1971-2008), 2008. https://publication-theses.unistra.fr/public/theses_doctorat/2008/GRISE_Fabien_2008.pdf.
Texto completoUltraluminous X-ray sources (ULXs) are objects emitting above the Eddington limit of a 10 solar masses black hole while not being located at the nucleus of their host galaxy. Despite two decades of X-ray observations, the precise nature of ULXs remains a mystery. Indeed, these accreting binary systems became the ideal candidates for the famous intermediate mass black holes (IMBHs), but direct proofs are missing. This thesis relies on optical data of unprecedented exposure time that was taken by ground-based telescopes of the 8+ meter class and by the Hubble space telescope. My study follows a multi-wavelength approach that is essential in present astrophysics. Observations of two of the most luminous ULXs known revealed lots of information, such as a secure spectroscopic indentification of their optical counterparts by detecting an HeII emission line in the continuum. The photometry of the environment of these sources has permitted to link ULXs to young and small stellar associations and to estimate an upper mass limit for the donor star in these systems. Photometric variability on different time scales has been observed and is interpreted as being linked to stochastic variations of the accretion disk. For the first time, a shift in the radial velocity of the HeII line has been detected, which has encouraged an attempt to determine a radial velocity curve of a ULX. Such a curve would permit to discriminate unambiguously the black hole class to which it belongs. For the moment, only an upper limit on the black hole mass has been found, being compatible with less than 50 solar masses. The presence of a high mass black hole is hence unlikely. The stellar environment in which these objects are located also pleads for small mass black holes rather than the intermediate mass ones. Finally, these ULXs distinguish themselves by the presence of large nebulae around them; spectroscopy of these ionised bubbles reveals an important contribution due to shocks and a second contribution by photoionization that is still to be quantified precisely. In any case, the ejection of jets and/or winds by the ULX itself seems to be the only way to shape these nebulae of a very unusual size
Grisé, Fabien Pakull Manfred W. Motch Christian. "Sources X ultra-lumineuses : étude optique détaillée de deux contreparties et de leurs environnements deux exemples contre la présence d'un trou noir de masse intermédiaire /". Strasbourg : Université Louis Pasteur, 2008. http://eprints-scd-ulp.u-strasbg.fr:8080/1097/01/GRISE_Fabien_2008-restrict.pdf.
Texto completoZouari, Samuël. "Étude de l'origine de l'émission à très haute énergie au centre de notre galaxie et connexion possible avec Sgr A*, notre plus proche trou noir super-massif". Electronic Thesis or Diss., Université Paris Cité, 2023. http://www.theses.fr/2023UNIP7120.
Texto completoAt the Centre of our Galaxy lies a supermassive black hole named Sgr A*. The HESS experiment has been observing the region in very high energy gamma rays, and has detected a compact source HESS J1745-290, compatible in position with the black hole, as well as a diffuse emission, interpreted as a proof of an excess of energetic particles, freshly injected by a PeVatron. The key to understanding the origin of the diffusion emission is the establishment of an association between Sgr A* and the central source : its possible extension, its spectral behaviour and its possible time variations. Indeed, there are two objects compatible with the position of HESS J1745-290, which could theoretically emit very high energy gamma rays : Sgr A* and the pulsar nebula G359,95. This thesis will investigate these questions from a theoretical perspective and then through the analysis of the many data HESS has gather on the Galactic Centre (GC). This work will also allow to offer prospects for the first years of CTA observing the GC. By using gamma ray emission model relying on the interaction between cosmic rays and molecular clouds, and by incorporating a spatial description of the target gas, we were able to model the temporal evolution of the gamma ray flux at TeV energies from a injection spectrum of protons, a hypothesis on their diffusion speed and a particle injection scenario (2 massive flares 100 and 200 years ago). We find that the flux variations corresponding to our assumptions are of the order of 10 to 15% during the HESS observation period. With regard to the analysis of HESS data we begin with the practical application of the spectro-morphological analysis (or 3D analysis) recently developed for HESS, applied to the Galactic Center. This allows us to obtain the first intrinsic spectrum of the HESS J1745-290 source, i.e separated from any contribution from the diffuse emission. We also re-estimate of the amplitude of the systematic errors of HESS on the spectral parameters, using in particular the new numerical tools developed within the framework of the python library gammapy. The separation of the contributions from HESS J1745-290 and the diffuse emission is what allows us to better study the temporal evolution of the central source. Indeed, monitoring a source over fifteen years is made difficult by the many changes (instrumental, climatic, etc.) experienced by the HESS system. We therefore use the diffuse emission as a reference to monitor more precisely the intrinsic variations of the HESS J1745-290 source. However, we do not observe any sign of variability over the period 2004-2019. To estimate the sensitivity of HESS to temporal variations, and in order to determine the evolution scenarios that we can already exclude, we simulated HESS data, using the response functions of the instrument and different models of temporal evolution. We find that the variation in flux of HESS J1745-290 over a single year is detectable if it is greater than 30%. Then, for a linear decrease in flux between 2004-2019, HESS is able to detect it if it is greater than 30% over 16 years. We deduce that the particle injection model developed previously is not excluded by the observations of HESS. Finally, using predictive instrument functions for CTA, we were able to make predictions about CTA's performance with respect to the observation of HESS J1745-290 : we determine that CTA will have sufficient angular resolution to determine whether this gamma source is associated with Sgr A* or G359.95-0.4. In addition, CTA's sensitivity to low flux variations will confirm or invalidate the temporal evolution scenario studied in our work
Smolderen, Alison. "Cinquante nuances de noir. Problèmes de diagnostic en archéologie du feu: études de cas du Bassin Mosan belge au MIS 3". Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/223857.
Texto completoDoctorat en Histoire, histoire de l'art et archéologie
info:eu-repo/semantics/nonPublished
Djahel, Soufiene. "Secure routing and medium access protocols in wireless multi-hop networks". Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10094/document.
Texto completoWhile the rapid proliferation of mobile devices along with the tremendous growth of various applications using wireless multi-hop networks have significantly facilitate our human life, securing and ensuring high quality services of these networks are still a primary concern. In particular, anomalous protocol operation in wireless multi-hop networks has recently received considerable attention in the research community. These relevant security issues are fundamentally different from those of wireline networks due to the special characteristics of wireless multi-hop networks, such as the limited energy resources and the lack of centralized control. These issues are extremely hard to cope with due to the absence of trust relationships between the nodes.To enhance security in wireless multi-hop networks, this dissertation addresses both MAC and routing layers misbehaviors issues, with main focuses on thwarting black hole attack in proactive routing protocols like OLSR, and greedy behavior in IEEE 802.11 MAC protocol. Our contributions are briefly summarized as follows. As for black hole attack, we analyze two types of attack scenarios: one is launched at routing layer, and the other is cross layer. We then provide comprehensive analysis on the consequences of this attack and propose effective countermeasures. As for MAC layer misbehavior, we particularly study the adaptive greedy behavior in the context of Wireless Mesh Networks (WMNs) and propose FLSAC (Fuzzy Logic based scheme to Struggle against Adaptive Cheaters) to cope with it. A new characterization of the greedy behavior in Mobile Ad Hoc Networks (MANETs) is also introduced. Finally, we design a new backoff scheme to quickly detect the greedy nodes that do not comply with IEEE 802.11 MAC protocol, together with a reaction scheme that encourages the greedy nodes to become honest rather than punishing them
Grould, Marion. "Études d'effets relativistes au Centre Galactique à l'aide de simulations d'observations d'orbites d'étoiles par l'instrument GRAVITY". Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEO013/document.
Texto completoDecades of studies have demonstrated the presence of a compact object of several million solar masses at the center of the Galaxy. Nowadays, the assumption is that this compact object is probably a supermassive black hole described by general relativity. The second generation instrument at the Very Large Telescope Interferometer, GRAVITY, is expected to better constrain the nature of this central object. By using its astrometric accuracy of about 10 microarcseconds, it will probe spacetime in strong gravitational fields by observing stars and gas located near the compact object.During my PhD I have developed a stellar-orbit model in order to interpret the future GRAVITY observations. By using this model it will be possible to extract the central black hole candidate parameters and relativistic effects. To implement the model, I used the ray-tracing code GYOTO developed at Observatoire de Paris. This code allows computing star and photon trajectories obtained in the vicinity of a compact object. It is thus possible to simulate apparent positions of stars orbiting the Galactic Center by computing relativistic images.My work started by validating the photon trajectories computed in GYOTO. By doing tests in both weak- and strong-deflection limits, I have shown that the GYOTO code is highly qualified to simulate GRAVITY observations. Indeed, the error made on the photon trajectories is inferior to 10^-2 microarcsecond, even when integrating over large distances.Then, I was interested in studying a star called S2 that contributed to importantly constrain the mass of the central object. This star is the second closest star to the Galactic Center and has an orbital period of about 16 years. Nowadays, we do not know whether closer-in stars will be discovered by GRAVITY. It is thus important to extract as much information as possible from this star. In particular, I have estimated the minimal observation times needed to detect relativistic effects by using astrometric and spectroscopic measurements of S2. To do so, I have developed different stellar-orbit models taking into account a certain number of relativistic effects. The more accurate model is obtained by using the ray-tracing code GYOTO and considering all relativistic effects. However, as the S2 star is sufficiently far from the compact object, this model neglects certain gravitational lensing effects such as the secondary images and the primary images amplification. Besides, I was also interested in the possibility of constraining the angular momentum of the central black hole candidate with the S2 star. In particular, I have shown that with a model which does not use ray-tracing, the norm and the direction of the angular momentum can be constrained with an uncertainty of about 0.1 and 20 degrees, respectively, by using observations obtained during three periods of S2 and with accuracies reaching 10 microarseconds and 10 km/s.Since closer-in stars could be detected by GRAVITY, I have developed a more accurate stellar-orbit model taking into account the lensing effects neglected in the previous model. However, in order to minimize the computing time required by this model, I determined a volume in which it is possible to neglect both the secondary images and the primary images amplification.Finally, I have studied the impact of different components of the Solar System on astrometric positions measured by GRAVITY. This study has shown that those measurements are deviated by an amount of a few microarcseconds by the gravitational perturbation generated by the Sun. However, those apparent positions are shifted by several hundred microarcseconds by the aberration effect due to the movement of the Earth with respect to the Galactic Center. It is thus necessary to take into account this effect in future interpretations of GRAVITY observations
Rodriguez, Jérôme. "Études spectro-temporelles de microquasars en rayons X : oscillations quasi-périodiques et couplage accrétion-éjection". Paris 6, 2002. http://www.theses.fr/2002PA066320.
Texto completoRolland, Loïc. "Etalonnage des caméras de l'expérience d'astronomie γ H. E. S. S. Et observations du Centre Galactique au-delà de 100 GeV". Paris 6, 2005. http://www.theses.fr/2005PA066106.
Texto completoGrandclément, Philippe. "Étude numérique de binaires d'étoiles à neutrons et de trous noirs". Paris 7, 2001. http://www.theses.fr/2001PA077200.
Texto completoShen, Dawei. "Problèmes de stabilité en relativité générale". Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS014.
Texto completoThis thesis is devoted to study the stability of particular solutions to Einstein vacuum equations: the Minkowski spacetime and Kerr black holes. More precisely, this thesis contains four main results. The first result concerns the stability of Minkowski spacetime outside an outgoing null cone and contains a generalization of the result of Klainerman-Nicolo. The second result shows the global nonlinear stability of the Minkowski space under the assumption of minimal decay on the initial data generalizing a result of Bieri. The third result provides a new proof of Kerr stability in external regions, obtained by Caciotta-Nicolo. The common feature of these three works is the application of the r^p-weighted estimate method introduced by Dafermos-Rodnianski, as an alternative to the vectorfield method, to obtain control of the curvature terms. The last result provides a construction of GCM hypersurfaces, which is a part of a sequence of five works (the four others are due to Klainerman-Szeftel and Giorgi-Klainerman-Szeftel) establishing Kerr stability for small angular momentum
Lamy, Frédéric. "Theoretical and phenomenological aspects of non-singular black holes". Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC203/document.
Texto completoThe issue of singularities in General Relativity dates back to the very first solution to the equations of the theory, namely Schwarzschild's 1915 black hole. Whether they be of coordinate or curvature nature, these singularities have long puzzled physicists, who managed to better characterize them in the late 60's. This led to the famous singularity theorems applying both to cosmology and black holes, and which assume a classical behaviour of the matter content of spacetime summarized in the so-called energy conditions. The violation of these conditions by quantum phenomena supports the idea that singularities are to be seen as a limitation of General Relativity, and would be cured in a more general theory of quantum gravity. In this thesis, pending for such a theory, we aim at investigating black hole spacetimes deprived of any singularity as well as their observational consequences. To that purpose, we consider both modifications of General Relativity and the coupling of Einstein's theory to exotic matter contents. In the first case, we show that one can recover the static spherically symmetric non-singular black holes of Bardeen and Hayward in principle in mimetic gravity, and implicitly by a deformation of General Relativity's hamiltonian constraint in an approach based on loop quantum gravity techniques. In the second case, we stay inside the framework of General Relativity and consider effective energy-momentum tensors associated with a fully regular rotating Hayward metric and with a dynamical spacetime describing the formation and evaporation of a non-singular black hole. For the latter, we show that all models based on the collapse of ingoing null shells and willing to describe Hawking’s evaporation are doomed to violate the energy conditions in a non-compact region of spacetime. Lastly, the theoretical study of the rotating Hayward metric comes with numerical simulations of such an object at the center of the Milky Way, using the ray-tracing code Gyoto and mimicking the known properties of the accretion structure of Sgr A*. These simulations allow exhibiting the two very different regimes of the metric, with or without horizon, and emphasize the difficulty of asserting the presence of a horizon from strong-field images as the ones provided by the Event Horizon Telescope
Xiang, Shuyang. "Sur la dynamique des fluides dans le domaine de communication extérieur d'un espace-temps de Schwarzschild". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066179/document.
Texto completoThis thesis is devoted to fluid dynamics evolving in the domain of outer communication of a Schwarzschild black hole. In the first chapter, we formulate the initial value problem of the relativistic Euler model within a class of weak solutions with bounded variation, possibly containing shock waves. We then introduce a version of the random choice method founded on the global steady state solutions and the generalized Riemann problem and we establish a global-in-time existence theory for the initial value problem within the proposed class of weakly regular fluid flows. In the second chapter, we consider the relativistic Burgers model. We have introduced a version of the total variation which is decreasing with respect to time in the Cauchy problem. We also use the generalized characteristics to prove the nonlinear stability of a piecewise steady state solution. In the third chapter, we present some numerical methods based on the Schwarzschild geometry and study numerically the nonlinear stability of steady state solutions and the asymptotic behavior of a general solutions. The proposed schemes provide a numerical tool capable to preserve exactly the equilibria and allow us to analyse the evolution of fluids with the geometry effects
Foucaud, Simon. "Propagation d'ondes dans un guide inhomogène : application à la cochlée". Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0027/document.
Texto completoThe cochlea is the organ of hearing for humans and mammals. It is often modelled as an inhomogeneous waveguide. A travelling wave propagates along the fluid structure coupled waveguide. The mechanical impedance of the structure is varying and provides a frequency place relation. The asymptotic method Wentzel-Kramers-Brillouin allows to solve for the basilar membrane vibration. The evanescents modes are taken into account to provide a better representation compared to the numerical models. As a second step, the finite elements method is used to solve for the transversal modes while the WKB Approximation deals with the longitudinal propagation. The first flexural mode of the basilar membrane is shown. The second propagative mode reveals a shearing motion of the tectorial membrane which can help stimulating the hair cells. An over-size artificial cochlea is designed and built. Thanks to an acoustic black hole, used as a anechoic end, travelling waves are observed on this device. Reflected waves are attenuated and the interferences with incident waves reduced. Mode coupling could be applied not only to evanescent modes but also to propagatives ones. Perspectives for the adaptation of the WKB method to fluid structure inhomogeneous waveguides, and particularly to the immersed acoustic black hole, seem to be very promising
Mathieu, Franck. "L’errance psychique des sujets SDF : le manteau cloacal, l’effondrement scénique et la séduction". Thesis, Lyon 2, 2011. http://www.theses.fr/2011LYO20066.
Texto completoThis work concerns the psychic life of the populations without fixed residence, excluded or the seriously precarious subjects. In spite of the various profiles strewing this public, the wandering is not an epiphenomenon occurring around psychiatric pathologies but a major, singular psychic disease non-reducible with other nosographic entities. It is a psychodynamic configuration which takes its origin in incapacity to place itself in the primary object, i.e. to feel contained in its concern and its function of daydream, creating a « black hole » into which unceasingly the subject is likely to fall. The defensive mechanisms associated with this psychodynamic have effects on the externality: the externality is a prism where space, the body, the sensoriality and the object are articulated. So usually, the externality functions in a quiet way. But in the psychic wandering it appears noisy and symptomatic so that various spaces which constitute the externality mix. To analyze these mixings up of the externality, the clinical investigation was carried out on the fields of the great exclusion by the participation in psychiatry-precariousness mobile teams and Samu Social, but also by the creation of therapeutic group into social structures. Presentation of the clinical practices and the work of social accompaniment aiming to make emerge a durable and safe bond belonged to the concerns of this research. At the end of this work, two concepts are proposed: the Cloacal Coat, which can be defined as an anesthetic and stimulative psychic envelope in a search for contact with the primary object; and the Scenic Collapse, which attempt to force by the use of the sensoriality and a certain form of seduction, a « psychic residence » in the object
Meliani, Zakaria. "Modélisation de vents et de jets relativistes". Phd thesis, Université Paris-Diderot - Paris VII, 2004. http://tel.archives-ouvertes.fr/tel-00008067.
Texto completoAklouche, Omar. "Réduction des niveaux vibratoires d'un panneau au moyen de trous noirs acoustiques structurés en réseau périodique : conception d'une méta-plaque". Thesis, Le Mans, 2017. http://www.theses.fr/2017LEMA1030/document.
Texto completoThe "Acoustic Black Hole" (ABH) is a passive device of reducing vibrations of structures without increasing their mass. It consists in a local thinning of the structure, coated with a thin layer of viscoelastic material. The ABH effect results from the local increase in vibratory magnitude, which strongly solicits the coating, giving rise to local significant damping. A detailed analysis of the mechanisms of dissipation of the ABH is carried out : the scattering of bending waves by an ABH is studied when the latter is inserted in an infinite thin plate. It is shown that the coating induces a significant local damping, allowing to significantly increase the global damping. The ABH is especially effective at high frequencies(HF), it is periodized on a plate to take advantage of the band gaps effect at low frequencies (LF). Two lattices (square and triangular) are studied numerically by the PWE method and experimentally by measuring vibratory mobilities. The results show that the plate is damped at the same time in LF by the lattice effect and in HF by the ABH effect
Bacon, Philippe. "Graphes d'ondelettes pour la recherche d'ondes gravitationnelles : application aux binaires excentriques de trous noirs". Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC113/document.
Texto completoIn december 2015 the LIGO detectors have first detected a gravitational wave emitted by a pair of coalescing black holes 1.3 billion years ago. Many more observations have been realised since then and heralded gravitational waves as a new messenger in astronomy. The latest detection is the merge of two neutron stars whose electromagnetic counterpart has been followed up by many observatories around the globe. These direct observations have been made possible by the developpement of advanced data analysis techniques. With them the weak gravitational wave inprint in detectors may be recovered. The realised work during this thesis aims at developping an existing gravitational wave detection method which relies on minimal assumptions of the targeted signal. It more precisely consists in introducing an information on the signal phase depending on the astrophysical context. The first part is dedicated to a presentation of the method. The second one presents the results obtained when applying the method to the search of stellar mass binary black holes in simulated Gaussian noise data. The study is repeated in real instrumental data collected during the first run of LIGO. Finally, the third part presents the method applied in the search for eccentric binary black holes. Their orbit exhibits a deviation from the quasi-circular orbit case considered so far and thus complicates the signal morphology. This third analysis establishes first results with the proposed method in the case of a poorly modeled signal
Grosjean, Daniel. "Aspects de la recherche de coalescences binaires avec le détecteur Virgo". Phd thesis, Chambéry, 2007. http://tel.archives-ouvertes.fr/tel-00184887.
Texto completoLa sensibilité actuelle du détecteur a été atteinte après une période de mise en route de l'interféromètre marquée par différentes campagnes de prises de données. L'analyse dans le contexte d'une recherche de systèmes binaires d'étoiles à neutrons des données recueillies depuis août 2005 s'est concentrée sur la notion de qualité de données et a conduit à développer des méthodes d'exclusion d'événements liés à un fonctionnement anormalement bruyant de l'interféromètre. La compréhension de ces sources de bruit a parfois permis d'en améliorer le fonctionnement.
La méthode d'analyse utilisée pour la recherche de systèmes binaires d'étoiles à neutrons peut s'avérer mal adaptée au cas de systèmes binaires plus massifs comportant un ou deux trous noirs. Après avoir clarifié ce point, nous envisageons dans le contexte du détecteur Virgo fonctionnant à sensibilité nominale différentes solutions pour une recherche performante de tels systèmes. Il s'agit d'une part de l'utilisation d'une famille de calques de détection, dont on confirme les performances. D'autre part, on s'intéresse à l'utilisation de calques spécifiquement adaptés à la description de l'évolution de systèmes binaires de trous noirs. Certains aspects techniques nécessaires à la mise en oeuvre d'une recherche utilisant ces solutions sont discutés.
Enfin, le dernier aspect de la recherche de systèmes binaires abordé concerne l'analyse en réseau des données recueillies par les différents détecteurs mondiaux. En utilisant des données simulées, on montre que la définition d'un nouveau temps de référence pour les événements de coalescences permet d'améliorer la précision de reconstruction de la position des sources binaires.
Stadnicki, Yann. "Théorie de la diffusion dans un espace-temps de Reissner-Nordstrøm extrème pour des champs de Dirac (chargés et massifs) et de Maxwell". Bordeaux 1, 2008. http://www.theses.fr/2008BOR16022.
Texto completoChristodoulou, Marios. "Transition de géométrie en gravité quantique à boucles covariante". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0273.
Texto completoIn this manuscript we present a calculation from covariant Loop Quantum Gravity, of a physical observable in a non-perturbative quantum gravitational physical process. The process regards the transition of a trapped region to an anti--trapped region and is treated as a quantum geometry transition akin to gravitational tunneling. The physical observable is the characteristic timescale in which the process takes place. We start with a top--to--bottom formal derivation of the ansatz defining the amplitudes for covariant LQG, starting from the Hilbert-Einstein action. We then take the bottom--to--top path, starting from the EPRL ansatz, to the sum--over--geometries path integral emerging in the semi-classical limit, and discuss its close relation to the naive path integral over the Regge action. We proceed to the construction of wave--packets describing quantum spacelike three-geometries that include a notion of embedding in a Lorentzian spacetime. We derive a simple estimation for the amplitudes describing geometry transition and show that a probabilistic description for such phenomena emerges, with the probability of the phenomena to take place being in general non-vanishing.The Haggard-Rovelli spacetime, modelling the spacetime surrounding the geometry transition region for a black to white hole process, is formulated. We then use the semi--classical approximation to give a general estimation of amplitudes describing the process. We conclude that the transition is predicted to be allowed by LQG, with a crossing time that is linear in the mass. The probability for the process to take place is suppressed but non-zero
Siellez, Karelle. "Les systèmes binaires compacts comme sources de multimessagers : taux, distribution, émissions". Thesis, Nice, 2015. http://www.theses.fr/2015NICE4055.
Texto completoThe coalescence of compact binaries (two neutron stars or a neutron star and a black hole) emits gravitational waves and are thought to produce a short Gamma-Ray Burst (sGRB). With the second generation of gravitational waves detector, the detection in coincidence of both electromagnetic and gravitational emission will open a new window in astrophysics; the multimessenger area. It will allow the understanding of this phenomena, their progenitor and central engine. The goal of this thesis was to made an estimation of the coincident rate for different instruments, using two different method. The first one was based on the oberservations. Thus, I selected a sample of 31 sGRBs of known redshift based on specific criteria. After studying the spectral, temporal and host properties, I derived the isotropic local rate corrected from all known biases. This result was then applied to different satellites and gravitational detectors. After that I simulated this population to confirm this coincident rate with the Monte Carlo simulations. The difference between the two results is explained by a low-redshift population that can't be reproduce by the simulations, and was underestimated before. After tested different parameters for the model, I conclude that this non reproducible population of faint sGRBs at low redshift might be due to an other sort of progenitor. This thesis shows the feasibility of a coincident detection and the observational strategy that should be adopted. The understanding of our sample of sGRB is crucial in the preparation of this coincident detection
Bassi, Tiziana. "Accrétion et éjection dans les systèmes binaires X transitoires à trous noirs : le cas de GRS 1716-249". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30019.
Texto completoBlack hole transients (BHTs) are among the brightest X-ray sources in the Galaxy. Thanks to their high X-ray flux and short variability time scales they offer a unique opportunity to study the physics of the accretion under extraordinary physical conditions. These sources show episodic outbursts characterised by different X/gamma-ray luminosities, spectral shapes and timing properties. The aim of this thesis is the understanding of the geometry, mechanisms and physical processes playing a role in the bright black hole X-ray transient GRS 1716-249. I present the spectral and timing analysis of X-ray observations performed with the Neil Gehrels Swift Observatory on GRS 1716-249 during the 2016-2017 outburst. These data gave me the opportunity to study the evolution of physical parameters and geometry variation of the accreting matter through the spectral transitions during the whole outburst. I found that the accretion disc could have reached the inner stable circular orbit during the hard intermediate state, coherently with the truncated accretion disc scenario in which the disc moves closer to the compact object. Then, the radio monitoring performed during the outburst let me locate the source on the ever more populated radio-quiet branch on the radio/X-ray luminosity plane. Thereafter, focusing on the soft gamma-ray emission of the source, I observed a high energy excess, above 200 keV, in addition to the thermal Comptonisation spectrum. This component could be originate either through inverse Compton of the soft photons by non-thermal electrons in the corona, or from synchrotron emission of energetic electrons in the jet. First, I fitted the broad band X/gamma-ray spectrum of GRS 1716-249 with hybrid Comptonisation thermal/non-thermal models: eqpair and belm. Using belm I obtained an upper limit on the magnetic field intensity in the corona. Finally, I investigated the possible origin of this high energy excess as due to jet emission. To this aim, I computed the Spectral Energy Distribution of GRS 1716-249 with the multi-wavelength observations (from the radio band to gamma-rays) performed. I modelled the accretion flow with an irradiated disc plus Comptonisation model and the jet emission with the internal shock emission model (ishem). This model assumes that the jet velocity fluctuations are directly driven by the variability of X-ray timing proprieties of the accretion flow. Even though ishem reproduces the radio and soft gamma-ray data of GRS 1716-249, the results seems to disfavour the jet scenario for the excess above 200 keV, in favour of non-thermal Comptonisation process
Leng, Julien. "Controlling flexural waves using subwavelength perfect absorbers : application to Acoustic Black Holes". Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1027/document.
Texto completoThe vibration control adapted to light structures is a scientific and technological challenge due toincreasingly stringent economic and ecological standards. Meanwhile, recent studies in audible acoustics havefocused on broadband wave absorption at low frequencies by means of subwavelength perfect absorbers. Suchmetamaterials can totally absorb the energy of an incident wave. The generalisation of this method for applicationsin elastodynamics could be of great interest for the vibration control of light structures.This thesis aims at adapting the perfect absorption problem for flexural waves in 1D and 2D systems with localresonators using the critical coupling condition. A study of 1D systems with simple geometries is first proposed. Thisprovides methods to design simple resonators for an effective absorption of flexural waves. The 1D systems thenbecome more complex by studying the critical coupling of 1D Acoustic Black Holes (ABH). The ABH effect is theninterpreted using the concept of critical coupling, and key features for future optimisation procedures of ABHs arepresented. The critical coupling condition is then extended to 2D systems. The perfect absorption by the firstaxisymmetric mode of a circular resonator inserted in a thin plate is analysed. Multiple scattering by an array ofcircular resonators inserted in an infinite or semi-infinite 2D thin plate, called metaplate, is also considered to getclose to practical applications. Through this thesis, analytical models, numerical simulations and experiments areshown to validate the physical behaviour of the systems presented
Dubus, Guillaume. "Observations et modèles d’étoiles binaires X". Paris 7, 1998. http://www.theses.fr/1998PA077043.
Texto completoMokdad, Mokdad. "Champs de Maxwell en espace-temps de Reissner - Nordstr∫m- De Sitter : décroissance et scattering conforme". Thesis, Brest, 2016. http://www.theses.fr/2016BRES0060/document.
Texto completoWe study Maxwell fields on the exterior of Reissner-Nordstrom-de Sitter black holes. We start by studying the geometry of these spacetimes: we give the condition under which the metric admits three horizons and in this case we construct the maximal analytic extension of the Reissner-Nordstrom-de Sitter black hole. We then give a general description of Maxwell fields on curves spacetimes, their decomposition into spin components, and their energies. The first result establishes the pointwise decay of the Maxwell field in the exterior of a Reissner-Nordstrom-de Sitter black hole, as well as the uniform decay of the energy flux across a hyperboloid that recedes in the future. This chapter uses the vector fields methods (geometric energy estimates) in the spirit of the work of Pieter Blue. Finally, we construct a conformal scattering theory for Maxwell fields in the exterior of the black hole. This amounts to solving the Goursat problem for Maxwell fields on the null boundary of the exterior region, consisting of the future and past black hole and cosmological horizons. The uniform decay estimates of the energy are crucial to the construction of the conformal scattering theory
Vernier, Eric. "Non compact conformal field theories in statistical mechanics". Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0005/document.
Texto completoThe critical points of statistical mechanical systems in 2 dimensions or quantum mechanical systems in 1+1 dimensions (this also includes non interacting systems in 2+1 dimensions) are effciently tackled by the exact methods of conformal fieldtheory (CFT) and integrability, which have witnessed a spectacular progress during the past 40 years. Several problems have however escaped an exact understanding so far, among which the plateau transition in the Integer Quantum Hall Effect,the main reason for this being that such problems are usually associated with non unitary, logarithmic conformal field theories, the tentative classification of which leading to formidable mathematical dificulties. Turning to a lattice approach, andin particular to the quest for integrable, exactly sovable representatives of these problems, one hits the second dificulty that the associated CFTs are usually of the non compact type, or in other terms that they involve a continuum of criticalexponents. The connection between non compact field theories and lattice models or spin chains is indeed not very clear, and in particular it has long been believed that the former could not arise as the continuum limit of discrete models built out of acompact set of degrees of freedom, which are the only ones allowing for a systematic construction of exact solutions.In this thesis, we show that the world of compact lattice models/spin chains with a non compact continuum limit is much bigger than what could be expected from the few particular examples known up to this date. More precisely we propose an exact Bethe ansatz solution of an infinite family of models (the so-called $a_n^{(2)}$ models, as well as some results on the $b_n^{(1)}$ models), and show that all of these models allow for a regime described by a non compact CFT. Such models include cases ofgreat physical relevance, among which a model for two-dimensional polymers with attractive interactions and loop models involved in the description of coupled Potts models or in a tentative description of the quantum Hall plateau transition by somecompact geometrical truncation. We show that the existence of an unsuspected non compact continuum limit for such models can have dramatic practical effects, for instance on the output of numerical determination of the critical exponents or ofMonte-Carlo simulations. We put our results to use for a better understanding of the controversial theta transition describing the collapse of polymers in two dimensions, and draw perspectives on a possible understanding of the quantum Hall plateautransition by the lattice approach
Rihani, Mahran. "Maxwell's equations in presence of metamaterials". Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. https://theses.hal.science/tel-03670420.
Texto completoThe main subject of this thesis is the study of time-harmonic electromagnetic waves in a heterogeneous medium composed of a dielectric and a negative material (i.e. with a negative dielectric permittivity ε and/or a negative magnetic permeability μ) which are separated by an interface with a conical tip. Because of the sign-change in ε and/or μ, the Maxwell’s equations can be ill-posed in the classical L2 −frameworks. On the other hand, we know that when the two associated scalar problems, involving respectively ε and μ, are well-posed in H1, the Maxwell’s equations are well-posed. By combining the T-coercivity approach with the Mellin analysis in weighted Sobolev spaces, we present, in the first part of this work, a detailed study of these scalar problems. We prove that for each of them, the well-posedeness in H1 is lost iff the associated contrast belong to some critical set called the critical interval. These intervals correspond to the sets of negative contrasts for which propagating singularities, also known as black hole waves, appear at the tip. Contrary to the case of a 2D corner, for a 3D tip, several black hole waves can exist. Explicit expressions of these critical intervals are obtained for the particular case of circular conical tips. For critical contrasts, using the Mandelstam radiation principle, we construct functional frameworks in which well-posedness of the scalar problems is restored. The physically relevant framework is selected by a limiting absorption principle. In the process, we present a new numerical strategy for 2D/3D scalar problems in the non-critical case. This approach, presented in the second part of this work, contrary to existing ones, does not require additional assumptions on the mesh near the interface. The third part of the thesis concerns Maxwell’s equations with one or two critical coefficients. By using new results of vector potentials in weighted Sobolev spaces, we explain how to construct new functional frameworks for the electric and magnetic problems, directly related to the ones obtained for the two associated scalar problems. If one uses the setting that respects the limiting absorption principle for the scalar problems, then the settings provided for the electric and magnetic problems are also coherent with the limiting absorption principle. Finally, the last part is devoted to the homogenization process for time-harmonic Maxwell’s equations and associated scalar problems in a 3D domain that contains a periodic distribution of inclusions made of negative material. Using the T-coercivity approach, we obtain conditions on the contrasts such that the homogenization results is possible for both the scalar and the vector problems. Interestingly, we show that the homogenized matrices associated with the limit problems are either positive definite or negative definite
Itsieki, Putu Basey Jean de Dieu. "De la mémoire de l'histoire à la refonte des encyclopédies : médiations symboliques du roman francophone". Doctoral thesis, Université Laval, 2016. http://hdl.handle.net/20.500.11794/26873.
Texto completoThis research focuses on ten novels by Francophone authors: Monnè, outrages et défis, by Ahmadou Kourouma ; La mère du printemps and Naissance à l’aube, by Driss Chraïbi ; L’escargot entêté and Les 1001 années de nostalgie, by Rachid Boudjedra ; La déchirure and Le régiment noir, by Henry Bauchau ; Prochain épisode, Trou de mémoire, and L’antiphonaire, by Hubert Aquin. Beyond the socio-historical differences in their origins, the works show strong similarities both in writing and in their themes. Based – for the most part - on the life experience of the authors, they are rooted in the era or summon past events (invasions, colonization, wars, resistance) to produce an understanding of history. Through the device of metonymisation, the latter is embodied in an "I" hallucinated narrator, originally injured and psychologically broken down, desperately committed to writing in order to express his unhappiness and perhaps also to heal himself. Autobiography serves as a way to write history and it merges with the narrative, the discourse on the novel being written tending to become the object of the narrative. From another perspective, that of allegory, the texts show through older events, even experienced elsewhere, the patterns and figures that illustrate the cyclical nature and methods of building history, and reflect the resistance of the peoples and their survival strategies. Using a hermeneutic approach and also drawing upon the paradigm of "birth and death" in the light of which Pierre Nepveu understands Quebec literature, this analysis highlights the symbolic mediation at work in the novels. While featuring disinherited subjects (individual or collective) and the historical impasse, they propose ways to get around this. By showing that only false evidence and any "it-goes-without-saying " in imaginaries were originally selected and created in response to contingent needs, the fiction in the Francophone novel draws attention to a major principle in the regeneration of worlds : a tradition, a culture, a civilization is invented; specifically, it invents time and, conversely, time reinvents it.
Latulippe, Myriam. "Influence du trou noir supermassif central dans l’amas de galaxies MACS J1447.4+0827". Thèse, 2017. http://hdl.handle.net/1866/20312.
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