Dissertations / Theses on the topic 'Black hole structure'
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Riedel, Gårding Elias. "Quantum structure of holographic black holes." Thesis, KTH, Fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284694.
Full textVi studerar ett fritt skalärt kvantfält i BTZ-rumtiden som en modell av AdS/CFT-dualiteten för svarta hål och visar huvudstegen i beräkningen av Bogolyubov-koefficienter mellan moder på olika sidor av maskhålet. Som bakgrund redogör vi för BTZ-geometrin i standard-, Kruskal- och Poincarékoordinater, holografisk renormering av den duala fältteorin och kanonisk kvantisering i krökt rumtid.
Ryle, Wesley Thomas. "Investigation of Fundamental Black Hole Properties of AGN through Optical Variability." Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/phy_astr_diss/25.
Full textBellisardi, Federico. "Study of gaseous structures in axisymmetric rotation in presence of a black hole." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18422/.
Full textLee, Chih Yun. "Funding the Black Hole: The Ineffectiveness of the Current Retirement Plan Structure and Future Solutions." Scholarship @ Claremont, 2013. http://scholarship.claremont.edu/cmc_theses/629.
Full textLeng, Julien. "Controlling flexural waves using subwavelength perfect absorbers : application to Acoustic Black Holes." Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1027/document.
Full textThe 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
Cochet, Some Claire. "Numerical characterization of boson stars and Kerr Black holes." Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC094.
Full textThe Galactic Center is an interesting place to test possible effects of strong gravity regime. Whereas it is generally believed that the compact object located at the Galactic Center, named Sgr A*, is a rotating black hole, some alternative models can also explain the current observations. This work is centered on one of these other objects, which is the Boson Star. Rotating boson stars are numerical solutions of the coupled Einstein-Klein-Gordon system, so these equations are written within the 3+1 formalism and then a numerical code capable of solving them with the Kadath library has been developed. Several kinds of boson stars with different potentials are presented : free fields an self-interacting fields, with quartic and sextic potentials, and different values of the rotational quantum number. Then two different ways of comparing this spacetime to Kerr's are presented. One way was to compute timelike geodesics in this geometry and study them. For that the ray-tracing code Gyoto is used to integrate numerically the geodesic equations for several types of boson stars. A peculiar type of orbits has been identifyed: the zero-angular-momentum ones which is called pointy-petal orbits thanks to their shape. These orbits pass very close to the center and are qualitatively different from orbits around a Kerr black hole. Another way to compare Kerr to any stationary and asymptotically flat metric given in its 3+1 form was to us a the characterization of the Kerr spacetime given by the Simon-Mars tensor. This tensor has the property of being identically zero for a vacuum and asymptotically flat spacetime if and only if the latter is locally isometric to the Kerr spacetime. The idea was to build a scalar with this tensor, and a scalar which is an invariant quality factor. Then, write it in 3+1 form to be able to compute it with numerical codes such as Kadath. Computing this scalar provides a simple way of comparing locally a generic (even non vacuum and non analytic) stationary spacetime to Kerr, therefore measure its 'non-Kerness". As an illustration, this invariant quality factor is evaluated for numerical solutions of the Einstein equations generated by boson stars and neutron stars, and for analytic solutions of the Einstein equations such as Curzon Chazy spacetime
Bowyer, E. P. "Experimental investigation of damping structural vibrations using the acoustic black hole effect." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10983.
Full textBergstedt, Viktor. "Spacetime as a Hamiltonian Orbit and Geroch's Theorem on the Existence of Fermions." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-432488.
Full textAllmän relativitetsteori har i över hundra år legat i teoretiska fysikens framkant. Det är möjligt att lösningarna på öppna problem som kvantiseringen av gravitation går att finna i en utvidgning av allmän relativitetsteori – och kanske uppenbarar sig denna utvidgning bara ur en alternativ formulering av teorin. I den här uppsatsen formuleras allmän relativitetsteori och dess Einsteinekvationer som ett begynnelsevärdesproblem, genom vilket rumtiden kan betraktas som rummets historia. Vi visar att rummets rörelseekvationer är Hamiltons ekvationer med tvångsvillkor. Enligt partikelfysiken bör fermioner kunna finnas till i rumtiden. Härom kan vi åberopa Gerochs sats, enligt vilken rumtider som har en Hamiltonsk formulering också medger fermioner. Vi redogör för huvuddragen i beviset av Gerochs sats.
Kawamuro, Taiki. "X-ray Studies on Nucleus Structures of Mass Accreting Supermassive Black Holes and Luminosity Function of Tidal Disruption Events." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225404.
Full textDeng, Jie. "Vibroacoustic modeling of acoustic blackhole applications in flat, curved andcomplex mechanical structures." Doctoral thesis, Universitat Ramon Llull, 2020. http://hdl.handle.net/10803/670666.
Full textLos agujeros negros acústicos en mecánica (conocidos por las siglas ABHs, del inglés Acoustic Black Holes) suelen estar formados por muescas en vigas y placas, el grueso de las cuales decae según una ley potencial. El efecto del ABH es el de ralentizar las velocidades de fase y de grupo de las ondas de flexión incidentes de tal modo que, en teoría, haría falta un tiempo infinito para que las ondas alcanzaran el centro del ABH, si el grueso de este último fuera exactamente cero. Sin embargo, en la práctica esto no es posible, aunque se puede conseguir una fuerte disipación colocando una capa de material amortiguador en el centro del ABH, donde se concentra la mayor parte de la energía de las ondas. En los últimos años, los ABHs no sólo se han explotado como método pasivo para reducir vibraciones estructurales y la consecuente emisión de ruido, sino que también se ha explorado su potencial para otras aplicaciones como la manipulación de ondas o la captación de energía. Esta tesis tiene tres objetivos principales. Así pues, tras una introducción general a los ABHs, el trabajo se ha dividido en tres grandes secciones. La primera aborda aplicaciones de los ABHs en vigas rectas y placas planas. Para empezar, se propone y analiza un voladizo piezoeléctrico con un acabado de ABH para capturar energía. A continuación, se presentan ABHs en forma de anillo para aislar puntos de excitación externos en placas planas y así evitar la transmisión de vibraciones. Finalmente, se contemplan configuraciones periódicas de matrices de ABHs para colimar haces de ondas de flexión y concentrar su energía en zonas predeterminadas de una placa. La segunda parte de la tesis propone nuevos diseños de ABHs para estructuras con curvatura. Estas son muy habituales en los sectores naval, aeronáutico e industrial, por lo que merece la pena investigar si los ABH pueden dar buenos resultados en algunos casos. La sección comienza analizando la inclusión de ABHs en vigas circulares y se ve como estos dan pie a la aparición de fenómenos típicos de sistemas periódicos. Seguidamente se propone un ABH anular para reducir las vibraciones en conductos cilíndricos. En concreto, se tratan los casos de un conducto simplemente soportado con un ABH anular, y el de un conducto con ABH, soportes periódicos y rigidificadores. Para finalizar la sección, se investigan los efectos de los ABH anulares en la radiación acústica del conducto teniendo en cuenta el nivel de potencia acústica, la eficiencia de radiación y la intensidad supersónica. La tercera parte de la tesis es más corta que las anteriores y simula el aislamiento de una placa con múltiples ABHs, en el rango de media y alta frecuencia. A tal efecto se emplea el método del análisis estadístico de distribución modal de energía (SmEdA: statistical modal energy distribution analysis). En esta sección, la estructura con ABHs ya no se analiza como un elemento individual, sino que se acopla a dos cavidades de aire formando parte de un sistema mecánico más complejo. A lo largo de la tesis se utiliza repetidamente el método de expansión gaussiana (GEM: Gaussian expansión method). Por GEM entendemos tomar funciones gaussianas como base para resolver ecuaciones diferenciales en derivadas parciales en el marco del método de Rayleigh-Ritz. El GEM se parece mucho a los enfoques de ondículas, pero ofrece algunas ventajas en el caso de condiciones de contorno periódicas. Al principio de la tesis se expone un breve repaso del GEM y, cuando es necesario, se aborda su reformulación para un problema particular en el capítulo correspondiente.
Acoustic black holes (ABHs) in mechanics usually consist of geometrical indentations on beams and plates having a power-law decreasing thickness profile. An ABH slows down the phase and group velocity of incident flexural waves in such a way that, ideally, it would take an infinite amount of time for them to reach the ABH center, if the latter had an exact zero thickness. Though this is not possible in practice, strong wave dissipation can be achieved by placing a damping layer at the central region of the ABH, where most vibration energy concentrates. In recent years, ABHs have been not only exploited as a passive means for structural vibration and noise reduction, but its potential for other applications like wave manipulation or energy harvesting have been also explored. The objective of this thesis is threefold. Therefore, after an initial overview the work is divided into three main parts. The first one deals with ABH applications on straight beams and flat plates. To start with, an ABH piezoelectric bimorph cantilever for energy harvesting is proposed and analyzed. Then, ring-shaped ABH indentations are suggested as a means of isolating external excitation points in flat plates and prevent vibration transmission. Finally, periodic ABH array configurations are contemplated to collimate flexural wave beams and focus energy at desired plate locations. The second part of the thesis proposes new ABH designs for curved structures. The latter are very common in the naval, aeronautical and industrial sectors so it is worth investigating if ABHs could function for them. The section starts analyzing the embedding of ABHs on circular beams and how this results in the appearance of typical phenomena of periodic systems. After that, an annular ABH is proposed to reduce vibrations in cylindrical shells. The cases of a simply supported shell with an annular ABH indentation and of a periodic simply supported ABH shell with stiffeners are considered. To finish the section, the effects of annular ABHs on sound radiation are investigated in terms of sound power level, radiation efficiency and supersonic intensity. The third part of the thesis is shorter than the previous ones and is devoted to analyzing the transmission loss of a plate with multiple ABH indentations, in the mid-high frequency range. Statistical modal energy distribution analysis is used for that purpose. Here, the ABH plate is not taken as an individual structure but coupled to two air cavities, thus being part of a more complex mechanical system. Throughout the thesis repeated use is made of the Gaussian expansion method (GEM). The GEM refers to taking Gaussian functions as the basis for solving partial differential equations in the framework of the Rayleigh-Ritz method. The GEM closely resembles wavelet approaches but offers some advantages in the case of periodic boundary conditions. A brief overview of the GEM is exposed at the beginning of the thesis and, when necessary, its reformulation for a particular problem is tackled in its corresponding chapter.
Mancino, Antonio. "On the structural and dynamical properties of a new class of galaxy models with a central BH." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18722/.
Full textFlayac, Hugo. "Nouvelles tendances dans les condensats d'exciton-polaritons spineurs : défauts topologiques et structures de basse dimensionnalité." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2012. http://tel.archives-ouvertes.fr/tel-00822148.
Full textBelletête, Jonathan. "Structure et interactions de bulles d'espace-temps en relativité générale." Thèse, 2012. http://hdl.handle.net/1866/8597.
Full textWe analyze space-time bubbles of finite thickness in general relativity. We use the energy conditions to restrict their structures. In the case of static, spherically symmetric bubbles, we get a set of four differential inequalities. If the effective gravitational potential is taken of a particular form, we show that they can be further reduced to a set of two differential inequalities. We then parameterize the bubble's wall in a particular way, simplifying the inequalities, and easing the application of boundary conditions on our solutions. We then treat four different cases of bubbles that all have a Schwarzschild de Sitter exterior. We show that in the limit where the thickness of the bubble's wall goes to zero, we recover the standard results. Lastly, we treat gravitational waves propagating in a dilute gas of non-interacting space-time bubbles.
Veselý, Jiří. "Nabité částice v prostoročasech s elektromagnetickým polem." Master's thesis, 2017. http://www.nusl.cz/ntk/nusl-365177.
Full text(7887968), Siddharth Nair. "Nonlocal Acoustic Black Hole Metastructures: Achieving Ultralow Frequency and Broadband Vibration Attenuation." Thesis, 2019.
Find full textTsai, Yu-Dai, and 蔡育岱. "The phase structure of Kerr-AdS black holes." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/70956247064091140866.
Full text國立清華大學
物理系
101
The phase structure of Kerr-AdS black holes is studied at three different temperatures, $T_{c1}$, $T_{c2}$ and $T_L$. At $T_{c1}$, a second order phase transition is identified to be in the same universality class as the van der Waals liquid-gas system. We derive the critical exponents ($\alpha$, $\beta$, $\gamma$, $\delta$)=(0, $\frac{1}{2}$, 1, 3) associated to this phase transition, and discuss the free energy and the scaling symmetry near the critical point. $T_L$ is the lowest temperature under which a Kerr-AdS black hole could reduce to a Schwarzschild-AdS black hole, and this temperature correspond to the critical temperature determined in the Hawking-Page phase transition. $T_{c2}$ is the temperature which separates the stable and partially unstable isotherms. Along with $T_{c2}$, we found an asymptotic value of angular momentum $\Omega_0$ = $1/l$ as $J$ goes to infinity. This asymptotic value reminisces us the minimal value of the molecule volume $V_0$ in the van der Waals liquid-gas system.
Du, Song Ming. "Fundamental Physics Through Gravitational Waves: From No-Hair Theorem to Quantum Structures of Black Holes." Thesis, 2019. https://thesis.library.caltech.edu/11315/1/songming_du_2018_thesis.pdf.
Full textIn general relativity, black hole is the simplest macroscopic object in the universe: any black hole can be completely described by its mass, charge and angular mo- mentum. However, such a simple picture might be changed if the gravitational field equations are modified or quantum effects are taken into consideration. These additional hairs of black hole, if exist, may provide valuable information to reveal the deepest mystery of the universe: quantum theory of gravity.
In this thesis, we try to relate the hypothetical extra hairs of black hole with the ob- servational evidence as gravitational waves – another prediction of general relativity and are recently detected. In Chapter I, we provide a pedagogical introduction to the black hole hairs introduced by modified gravity and quantum mechanics, and lay out a mathematical framework to describe the gravitational wave emission with the existence of near-horizon quantum hair. In Chapter II we show that in scalar-tensor theory of gravity, the formation process of a black hole from gravitational collapse is accompanied with the emission of scalar hair. This mechanism gives rise to a scalar type memory effect of gravitational wave, which does not exist in general relativity. This phenomenon can further be used to study the parameter space of the scalar-tensor theory. In Chapter III, we find the scalar gravitational memory effect from stellar collapses provide the strongest sources for the stochastic gravita- tional wave background with scalar polarization in Brans-Dicke theory. The energy density spectrum for this background is provided and its model dependencies are studied. In Chapter IV, we provide a Green’s function method to study the echoes, which are the gravitational waves reflected by the quantum hair near the event hori- zon of a black hole. In Chapter V, we build phenomenological models to describe the near-horizon quantum hair and predict its implication to the binary black hole stochastic gravitational wave background. Our study indicates that the existence of the quantum hair will significantly increases such a background and pins down the most relevant model parameter to be the area under the effective potential. Further, we also demonstrate that the result is rather robust against the uncertainties about the nature of the near-horizon quantum hair. In the end, a field theory based treatment to the gravitational waves in general relativity is provided as the appendix.
Vikaeus, Anton. "The information paradox - Horizon structures and its effects on the quasinormal mode gravitational radiation from binary merger ringdowns : Gravitational echoes from reflective near horizon structures." Thesis, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-325840.
Full textGlass, Lisa Anne. "The Central regions of early-type galaxies in nearby clusters." Thesis, 2012. http://hdl.handle.net/1828/4188.
Full textGraduate
Araneda, Bernardo Gabriel. "Simetrías ocultas, twistors, y estabilidad de campos lineales en agujeros negros." Doctoral thesis, 2018. http://hdl.handle.net/11086/6424.
Full textEn el marco del problema de estabilidad de agujeros negros, esta tesis trata diversos aspectos de las ecuaciones de campos libres sin masa sobre espacio-tiempos curvos, con énfasis en espacios algebraicamente especiales que contienen agujeros negros como soluciones particulares. El enfoque central es el estudio de la posible correspondencia entre campos escalares y campos de spin superior, y de la existencia y origen de simetrías ocultas y ciertos mecanismos asociados a la teoría de twistors. Encontramos fórmulas explícitas de esta correspondencia, y mostramos que el patrón de simetrías subyacente se entiende desde el punto de vista de la covariancia conforme y la existencia de estructuras complejas en el espacio-tiempo. Analizamos también aspectos de estabilidad de los campos en el caso de agujeros negros estáticos asintóticamente anti-de Sitter. Estudiamos espacio-tiempos tanto de cuatro como de altas dimensiones.
In the context of the black hole stability problem, this thesis deals with several aspects of the massless free field equations on curved spacetimes, with emphasis on algebraically special spaces that contain black hole solutions as particular cases. The main approach is the study of the possible correspondence between scalar fields and higher spin fields, and of the existence and origin of hidden symmetries and certain mechanisms associated to twistor theory. We find explicit formulas for this correspondence, and we show that the underlying symmetry pattern is understood from the point of view of conformal covariance and the existence of complex structures on the spacetime. We also analyze aspects of the stability of the fields in the case of asymptotically anti-de Sitter static black holes. We study spacetimes of both four and higher dimensions.
Ngwenya, Kingsman. "Somali immigrants and social capital formation : a case study of spaza shops in the Johannesburg township of Cosmo City." Diss., 2017. http://hdl.handle.net/10500/23364.
Full textThe aim of this research is to assess the impact social capital has had on Somali businesses. It argues against the perception that Somali business expertise is derived solely from the principles of economics. It argues that social capital plays a pivotal role in shaping the Somali spirit of entrepreneurship. The role of social capital in the creation of Somali human and financial capital is examined. This thesis, being a qualitative study, used semi-structured, unstructured interviews and direct observation as data collection methods.
Sociology
M.A. (Sociology)