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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.
Pełny tekst źródłaThis 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
Ritter, 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.
Pełny tekst źródłaGrandclément, Philippe. "Étude numérique de binaires d'étoiles à neutrons et de trous noirs". Paris 7, 2001. http://www.theses.fr/2001PA077200.
Pełny tekst źródłaGrosjean, Daniel. "Aspects de la recherche de coalescences binaires avec le détecteur Virgo". Phd thesis, Chambéry, 2007. http://tel.archives-ouvertes.fr/tel-00184887.
Pełny tekst źródłaLa 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.
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.
Pełny tekst źródłaThis 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
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.
Pełny tekst źródłaIn 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
Leng, Julien. "Controlling flexural waves using subwavelength perfect absorbers : application to Acoustic Black Holes". Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1027/document.
Pełny tekst źródłaThe 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
Aoudia, Sofiane. "Capture des étoiles par les trous noirs et ondes gravitationnelles". Nice, 2008. http://www.theses.fr/2008NICE4103.
Pełny tekst źródłaSiellez, Karelle. "Les systèmes binaires compacts comme sources de multimessagers : taux, distribution, émissions". Thesis, Nice, 2015. http://www.theses.fr/2015NICE4055.
Pełny tekst źródłaThe 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
Foucaud, Simon. "Propagation d'ondes dans un guide inhomogène : application à la cochlée". Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0027/document.
Pełny tekst źródłaThe 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
Denis, Vivien. "Amortissement vibratoire de poutre par effet Trou Noir Acoustique". Thesis, Le Mans, 2014. http://www.theses.fr/2014LEMA1011/document.
Pełny tekst źródłaVibration 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
Gourgoulhon, Eric. "Étoiles à neutrons, étoiles de quarks, trous noirs et ondes gravitationnelles". Habilitation à diriger des recherches, Université Paris-Diderot - Paris VII, 2003. http://tel.archives-ouvertes.fr/tel-00004260.
Pełny tekst źródłaEuvé, Léo-Paul. "Interactions ondes-courant-obstacle : application à la physique des trous noirs". Thesis, Poitiers, 2017. http://www.theses.fr/2017POIT2280/document.
Pełny tekst źródłaThe aim of the PhD is the observation the Hawking radiation in the laboratory, this astounding prediction of the English astrophysicist Stephen Hawking made in 1974: black holes are not black. In other words, they do not absorb anything within reach but emit a radiation. In addition to the complications of the fact that these celestial objects are thousands of light years away, this radiation is so weak that it would be like trying to hear a whisper in a rock concert. But William Unruh, in 1981, proposed a solution: to use hydrodynamic systems which have the same mathematical equations as in astrophysics. More precisely, in our case, we use the correspondence between the propagation of light in the vicinity of a black hole and surface waves propagation on a inhomogeneous countercurrent (due to the presence of a submerged obstacle). For this, a thorough understanding of the surface waves physics is necessary (variable bathymetry, vorticity, non-linearities ...). On the technical side, a free surface measurement method has been developed and optimized
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.
Pełny tekst źródłaClavel, Maïca. "Activité du trou noir supermassif au centre de la Galaxie". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112170/document.
Pełny tekst źródłaSagittarius 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
Iguaz, Juan Joaquim. "Un conte de trous noirs primordiaux : des aspects cosmologiques aux recherches astrophysiques". Electronic Thesis or Diss., Chambéry, 2023. http://www.theses.fr/2023CHAMA023.
Pełny tekst źródłaPrimordial Black Holes (PBHs) can form in the very early universe and can be associated to numerous cosmological and astrophysical signatures. In this thesis we explore the physics related to PBHs since its possible formation at the earliest stages of the universe to the possible signatures of a population of PBHs in our own galaxy. I present here a fascinating story with PBHs as the only and main character and playing the roles of: Dark Matter (DM), coalescing objects detected by LIGO/Virgo, and Supermassive Black Holes (SMBHs). After an introduction, the bulk of the thesis is divided into three main chapters organized chronologically: In the first chapter, I discuss the possible formation of PBHs during the preheating phase that immediately follows inflation. In the second chapter, I present a discussion on the implications of early universe phenomena, most notably the quantum chromodynamics (QCD) phase transition and electron-positron annihilation, on the mass distribution of PBHs forming at these epochs; I then analyze the constraints on this scenario from a number of observations: the specific pattern in cosmic microwave background (CMB) anisotropies induced by accretion onto PBHs, CMB spectral distortions, gravitational wave searches, and direct counts of SMBHs at high redshift. Finally, in the last chapter, I study the evaporation of light PBHs via Hawking evaporation and its possible observable signatures on the measured galactic and isotropic gamma ray fluxes. No PBH signal is detected and we set the strongest limit on PBH DM in the mass range under study. A discussion of further research directions concludes the thesis, while technical results are reported in some appendices
Luminet, Jean-Pierre. "Effets de marée : rupture explosive d’étoiles par un trou noir géant". Paris 7, 1985. http://www.theses.fr/1985PA077061.
Pełny tekst źródłaFilloux, Charline. "Croissance et évolution des trous noirs supermassifs : simulations cosmologiques". Nice, 2009. http://www.theses.fr/2009NICE4107.
Pełny tekst źródłaThe presence of supermassive black holes in the centers of galaxies seems to be a well established fact and their masses are correlated with properties of their host galaxies. This thesis aim to bring some answers about the origin of these correlations, studying the coeval evolution of galaxies and supermassive black holes through cosmological simulations. The galaxy evolution is followed according to the star formation history and corresponding feedback mechanisms. Black holes grow from primordial 100 solar masses seeds that accrete matter mainly through a viscous gaseous disk. Our simulations indicate that the spherical accretion (Hoyle-Bondi accretion) is not efficient enough to produce very massive black holes but seeds are able to grow up to masses of 109 solar masses by accreting through a disk. In this case; the different correlations involving the black hole mass and the velocity dispersion, the stellar mass or the host halo mass are well reproduced. Our work indicates that these relations are strongly affected by the feedback either of supernovae or of black holes themselves. The present simulations indicate that the evolution of the aforementioned relations follow a hierarchical pattern, although some observations seem to suggest that seeds grow faster than their host halos. Finally, we have also investigated the emission of gravitational waves resulting from the capture of compact stars by supermassive black holes or by the coalescence of black holes during a merger of two galaxies
Le, Tiec Alexandre. "Coalescence de trous noirs en relativité générale & Le problème de la matière noire en astrophysique". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00521645.
Pełny tekst źródłaTrap, 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.
Pełny tekst źródłaErbin, Harold. "Trous noirs en supergravité N = 2". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066367/document.
Pełny tekst źródłaThe 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.
Pełny tekst źródłaNissanke, Samaya Michiko. "Aspects théoriques de la forme des ondes gravitationnelles pour les phases spiralante et de fusion des systèmes binaires compacts". Paris 7, 2006. http://www.theses.fr/2006PA077053.
Pełny tekst źródłaThis thesis is devoted to the theoretical prediction of the gravitational waveform for the inspiral and eventual merger of compact binaries, le. Systems of two black holes or neutron stars. Such waveforms are essential for detecting and measuring gravitational waves by ground-based and space-based laser interferometers. In developing theoretical waveform templates for such systems, the thesis addresses two important areas. Firstly, we study gravitational radiation reaction effects on isolated matter systems in the post-newtonian approximation of general relativity. The formalism is applied to the computation of the radiation reaction force in the equations of motion of a compact binary system at the 3. 5pn order in harmonic coordinates (in both a general frame and the centre-of-mass frame). Secondly, we propose astrophysically motivated freely specifiable initial datathat are in agreement with post-newtonian results for numerically modelling binary black hole mergers
Ghanem, 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.
Pełny tekst źródłaIn 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.
Pełny tekst źródłaAn 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.
Pełny tekst źródłaThe 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.
Pełny tekst źródłaGrüning, Pierre. "Développement et exploitation d'un simulateur électro-optique pour le futur détecteur spatial à ondes gravitationnelles eLISA". Sorbonne Paris Cité, 2015. https://theses.hal.science/tel-01307782.
Pełny tekst źródłaGravitational waves have been predicted by Einstein near a century ago. They are disturbances of space-time traveling at the speed of light and are carrying unique informations about their sources. These sources are various, form the Big Bang to massive objects like black holes. The effect of a gravitational wave is very tiny, the distance variation is at the order of picometer for a 1 million km distance. Thus, their detection is very challenging and needs very performant detectors. Te eLISA project is the first space based detector which aims to do gravitational wave astronomy and which will be made of a laser interferometer with 1 million km arms. Many noises will disturb this detector, this noises must be well known and reduced in order to reach the required sensitivity. The most important noise will corne from the laser itself. In a classic equal arm Michelson type interferometer, the laser frequency noise cancels. On eLISA the arm lengths are not constant because of the orbitography of the satellites. Thus a noise reduction algorithm called TDI will be applied on the measured data to reduce the noise level. The TDI technic must be tested in experimental conditions and this is the goal of this thesis which describes an electro-optical simulator, the LOT, aiming to simulate eLISA and noise reduction technics such as TDI. This thesis presents the hardware simulator and the experiences realized as well as the results we obtained
Goutéraux, 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.
Pełny tekst źródłaCordier, 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.
Pełny tekst źródłaChuard, 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.
Pełny tekst źródłaLike 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
Rihani, Mahran. "Maxwell's equations in presence of metamaterials". Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. https://theses.hal.science/tel-03670420.
Pełny tekst źródłaThe 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
Van, Aelst Karim. "Rotating black holes in the cubic Galileon theory". Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7043.
Pełny tekst źródłaThe 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.
Pełny tekst źródłaBouazizi, Abdelaziz. "Optimisation du couplage énergétique entre les micro-ondes et les composites époxy-noir de carbone". Toulouse, INPT, 1988. http://www.theses.fr/1988INPT005G.
Pełny tekst źródłaBouazizi, Abdelaziz. "Optimisation du couplage énergétique entre les micro-ondes et les composites époxy-noir de carbone". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37611896w.
Pełny tekst źródłaLimousin, Francois. "Etude de systèmes binaires d'objets compacts : étoiles à neutrons, étoiles de quarks étranges et trous noirs". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2005. http://tel.archives-ouvertes.fr/tel-00067971.
Pełny tekst źródłaUn effort est fait pour améliorer, rendre ces données initiales les plus réalistes possible d'un point de vue astrophysique. Nous avons ainsi construits les premières séquences de binaires d'étoiles de quarks étranges, et ce pour différentes équations d'état. Contrairement au cas d'étoiles à neutrons polytropiques, la séquence se termine par une instabilité dynamique. Nous avons également calculé des configurations de binaires d'étoiles à neutrons à l'aide d'une théorie sans onde allant au delà de l'approximation communément admise de métrique spatiale conformément plate. Les solutions obtenues devraient être plus précises et de meilleures conditions initiales que celles réalisées jusqu'alors. Nous avons enfin étudié, pour des systèmes d'un seul trou noir puis des trous noirs binaires, l'influence de conditions de bords aux horizons provenant du formalisme des horizons isolés et regroupnt des ingrédients de quasi-équilibre.
Limousin, François. "Etude de systemes binaires d'objets compacts : etoiles a neutrons, etoiles de quarks etranges et trous noirs". Paris 6, 2005. http://www.theses.fr/2005PA066524.
Pełny tekst źródłaCuenca, 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.
Pełny tekst źródłaFlexural 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.
Pełny tekst źródłaUltraluminous 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.
Pełny tekst źródłaPenillard, Anne. "Caractérisation du phosphore noir pour des applications optoélectroniques hyperfréquences". Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS019.
Pełny tekst źródłaThe research project conducted focuses on the optoelectronic and high frequency characterization of black phosphorus. The context of this project is the trend of downscaling and multi-physical coupling seen today in industrial electronics. The characterization carried out is directed for a specific application, the realisation of microwave photoswitch controlled by a laser optical excitation at 1.55 µm. For this purpose, during this PhD a production process of thin and large bi-dimensional layers of black phosphorus has been performed, along with the fabrication of characterization devices, and a discussion to determine suitable appendices for substrate, capping layer and metallization. The technological development is coupled with optical, electronic (DC) and radiofrequency characterizations of the bi-dimensional layers for the determination of inherent black phosphorus properties like the photogenerated carrier lifetime, the material permittivity, the resistivity and the mobility of the carriers. Those parameters are essential to understanding design and simulate high frequency optoelectronic devices on black phosphorus such as the microwave photoswitch controlled at 1.55 µm. The obtained results assert black phosphorus as a promising material for this kind of application. The first performances obtained with the use of bP as an active material for photoconductive switching are very encouraging and open the way for high frequency and high speed applications
Hartwig, Tilman. "Formation and growth of the first supermassive black holes". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066386/document.
Pełny tekst źródłaSupermassive black holes reside in the centres of most massive galaxies and we observe correlations between their mass and properties of the host galaxies. Besides this correlation between a galaxy and its central black hole (BH), we see BHs more massive than one billion solar masses already a few hundred million years after the Big Bang. These supermassive BHs at high redshift are just the tip of the iceberg of the entire BH population, but they challenge our understanding of the formation and growth of the first BHs. Our improved method to calculate H2 self-shielding yields probabilities to form massive seed BHs that are more than one order of magnitude higher, than previously expected. We find that CR7 might be the first candidate to host such a direct collapse BH and we disprove the initially claimed existence of a massive metal-free stellar population in CR7. We calculate the merger rate density of binary BHs from the first stars and their detection rates with aLIGO. Our model demonstrates that upcoming detections of gravitational waves in the next decades will allow to put tighter constraints on the properties of the first stars and therefore on formation scenarios of the first BHs. We develop a 2D analytical model of active galactic nuclei-driven outflows to demonstrate that a more realistic disc profile reduces the amount of gas that is ejected out of the halo, compared to existing 1D models. The outflow prevents gas accretion on to the central BH for only about ∼1Myr, which permits almost continuous gas inflow in the disc plane. With this thesis, I contribute to a better understanding of the formation and growth of the first supermassive BHs
Zouari, 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.
Pełny tekst źródłaAt 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
Julié, Félix-Louis. "Sur le problème à deux corps et le rayonnement gravitationnel en théories scalaire-tenseur et Einstein-Maxwell-dilaton". Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC131/document.
Pełny tekst źródłaWith the birth of "gravitational wave astronomy" comes the opportunity to test general relativity and its alternatives in a strong field regime that had never been observed so far: that of the coalescence of a compact binary sytem. This thesis studies the problem of motion and gravitational radiation from such systems in modified gravities, by adapting some of the key analytical tools that were first developed in the context of general relativity. First, we show how to widen the "effective-one-body" (EOB) formalism to a large class of modified gravities, including, e.g., scalar-tensor theories. In the latter, the gravitational interaction is described by supplementing general relativity with a (massless) scalar degree of freedom. The corresponding two-body lagrangian being known at post-post-keplerian order, we build an associated EOB hamiltonian, which describes the motion of a test particle orbiting in effective external fields. This enables to simplify and resum the two-body dynamics; and hence, to explore the strong-field regime near merger. We then "tackle", for the first time, the analytical description of "hairy" binary black hole systems, and obtain their (EOB) gravitational waveform counterparts in Einstein-Maxwell-dilaton theories, which generalize scalar-tensor theories by means of a (massless) vector field. To that end, we derive the two-body lagrangian at post-keplerian order as well as the energy flux radiated at infinity at quadrupolar order. As in general relativity, our developments rely on the phenomenological description of the black hole’s trajectories as worldlines of point particles that are, in turn, described by a "skeleton" action generalizing that of general relativity. Finally, we develop a formalism based on Katz’ "superpotentials" to define the mass (as a nœther charge) of a black hole that is endowed with vector and scalar "hair". We then deduce the first law of thermodynamics, which is particularly suitable to describe its readjustments when interacting with a faraway companion. Black hole thermodynamics is lastly shown to be a powerful tool to interpret and discuss the scope of their "skeletonization"
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.
Pełny tekst źródłaDoctorat 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.
Pełny tekst źródłaWhile 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.
Pełny tekst źródłaDecades 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
Ben, Cheikh Harrek Zouhour. "Étude des ondes de spin dans des puits quantiques CdMnTe". Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20071/document.
Pełny tekst źródłaThis thesis focuses on the study of spin waves in n-doped CdMnTe quantum wells using respectively time-resolved Kerr rotation (TRKR) and four-wave mixing (FWM) techniques. We studied three high mobility samples with different characteristics.The TRKR technique gives access only to zero wave vector excitations, in our case the spin- flip wave q = 0 . We studied the anticrossing that appears between the spin -flip wave and the manganese spin -flip excitation. We studied the gap variation energy between these modes as function on the power excitation and the magnetic field. In particular, we have extended the measurements of mixed modes at lower Mn concentration (up 0.07 %) and contrary to what were expected; we found that the strong coupling regime persists at this concentration.We are then interested in determining the two dimensional electron gas spin polarization ζ, which can be deduced from the energy coupling between the mixed modes. We found that the measured polarization exceeds the theoretical polarization calculated taking into account the increased susceptibility by many-body effects. We also measured the electron spin relaxation time and we have shown that it is influenced by thermal effects inherent to optical pump-probe experiments on this time.In the second part of this thesis, we studied by FWM the damping and the dispersion of the non-zero wave vector spin waves for one of our samples. We have demonstrated that we can actually generate spin waves in femtosecond excitation and deted them by FWM. We found that the dispersion is lower than that observed in the Raman experiments. This low dispersion may be due to the strong excitation density used in the FWM experiments (typically three to four orders of magnitude higher than the Raman ones) and / or the fact that two waves of wave vector q and - q, having different dispersions are simultaneously probed in FWM
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.
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