Дисертації з теми "Hole dynamics"
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1
Chung, Hyeyoun. "Exploring Black Hole Dynamics." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:14226081.
Анотація:
This thesis explores the evolution of different types of black holes, and the ways in which black hole dynamics can be used to answer questions about other physical systems.
We first investigate the differences in observable gravitational effects between a four-dimensional Randall-Sundrum (RS) braneworld universe compared to a universe without the extra dimension, by considering a black hole solution to the braneworld model that is localized on the brane. When the brane has a negative cosmological constant, then for a certain range of parameters for the black hole, the intersection of the black hole with the brane approximates a Banados-Teitelboim-Zanelli (BTZ) black hole on the brane with corrections that fall off exponentially outside the horizon. We compute the quasinormal modes of the braneworld black hole, and compare them to the known quasinormal modes of the three-dimensional BTZ black hole. We find that there are two distinct regions for the braneworld black hole solutions that are reflected in the dependence of the quasinormal modes on the black hole mass. The imaginary parts of the quasinormal modes display phenomenological similarities to the quasinormal modes of the three-dimensional BTZ black hole, indicating that nonlinear gravitational effects may not be enough to distinguish between a lower-dimensional theory and a theory derived from a higher-dimensional braneworld.
Secondly, we consider the evolution of non-extremal black holes in N=4, d=2 supergravity, and investigate how such black holes might evolve over time if perturbed away from extremality. We study this problem in the probe limit by finding tunneling amplitudes for a Dirac field in a single-centered background, which gives the decay rates for the emission of charged probe black holes from the central black hole. We find that there is no minimum to the potential for the probe particles at a finite distance from the central black hole, so any probes that are emitted escape to infinity. If the central black hole is BPS in the extremal limit, then the potential is flat and so there is no barrier to the emission of probes. If the central black hole is non-BPS in the extremal limit, then there is a barrier to emission and we compute the decay rate, which depends both on the charge of the central black hole and the charges of the emitted black holes.
Finally, we consider the possibility that an extremal black hole, the end-point of the evolution of a non-extremal black hole through evaporation, may itself split into a multi-centered black hole solution through quantum tunneling, via a gravitational instanton analogous to the instanton for the symmetric double well in elementary quantum mechanics. We find a gravitational instanton that connects two vacuum states: one state corresponding to a single-centered extremal Reissner-Nordstrom (ERN) black hole configuration, and another state corresponding to a multi-centered ERN configuration. We evaluate the Euclidean action for this instanton and find that the amplitude for the tunneling process is equal to half the difference in entropy between the initial and final configurations.
2
Vaziri, Goudarzi Hamed. "Hole Dynamics in Films." Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS640.
Анотація:
L'éclatement du film océanique est un phénomène où un film liquide mince, représentant le chapeau de la bulle, éclate à la surface de l'océan, produisant des gouttelettes de film. Ce phénomène est crucial dans les échanges océan-atmosphère, en particulier dans le transfert de chaleur, de masse et de quantité de mouvement entre l'océan et l'atmosphère. L'éclatement du film implique une série de dynamiques complexes, telles que le drainage, la perforation, la rétraction du film et la désintégration en gouttelettes. La cicatrisation des trous (c’est-à-dire lorsqu’un trou est trop petit et se referme après sa nucléation) est un paramètre essentiel pouvant influencer la dynamique de l'éclatement du film, en particulier l'épaisseur du film lors de l'éclatement et, par conséquent, le budget liquide pour la production de gouttelettes de film. Cette étude approfondit la dynamique des trous dans les films liquides libres, avec des simulations numériques et des approches analytiques. Utilisant Basilisk, un solveur de flux à deux phases basé sur la méthode Volume-of-Fluid (VoF) et écrit en C, nous avons analysé finement le mécanisme de cicatrisation. Des simulations dichotomiques à maillage adaptatif haute résolution ont permis de déterminer le seuil de cicatrisation. Les approches analytiques ont été utilisées pour développer des hypothèses afin de prédire le seuil de cicatrisation d'un trou sur un film, qui ont été testées contre les résultats numériques. La dynamique critique du trou a été examinée, et des lois de puissance distinctes ont été identifiées pour la courbure de pointe afin d'illustrer le mécanisme moteur. Les variations du seuil de cicatrisation du trou avec d'autres paramètres du problème ont été examinées. Cette étude a d'abord été menée pour un film plat, découvrant que le seuil de cicatrisation est augmenté en augmentant le nombre de Laplace du film. Cet effet était prononcé pour des valeurs allant de 1 à 10000, coïncidant avec la gamme habituelle des nombres de Laplace de film observés pour les bulles éclatantes océaniques. Les effets observés ont également été élaborés, avec des explications physiques. Étant donné que la forme initiale exacte du trou s'est révélée influencer le seuil de cicatrisation, un examen a été effectué pour étudier cet effet sur la cohérence des résultats du changement du nombre de Laplace du film, pris comme exemple pour les autres. Il a été démontré que malgré les variations du seuil pour différentes formes, l'effet du changement du nombre de Laplace du film était indépendant de la forme du trou. Par conséquent, les résultats de la dichotomie se sont avérés indépendants du choix arbitraire de la forme du trou tout au long de l'étude. Une étude similaire a été menée pour un trou dans un chapeau de bulle après une étude détaillée de la dynamique de la bulle et de l'écoulement du gaz. Il a été découvert que l'écoulement de gaz subit un effet Venturi, où un écoulement plus fort, résultant de tailles de bulles plus petites ou de nombres de Laplace de gaz plus élevés, a été montré pour augmenter le seuil de cicatrisation. Une hypothèse a été développée pour prédire l'effet Venturi sur le seuil de cicatrisation, aboutissant à un terme de correction de Venturi qui prédit une dépendance de loi de puissance sur le diamètre de la bulle, ce qui correspondait aux résultats numériques. L'effet Venturi était significatif pour des valeurs élevées du nombre de Laplace du gaz, où le seuil de cicatrisation était doublé en augmentant la courbure moyenne du film d'un film plat à un chapeau de bulle avec une taille 20 fois l'épaisseur du chapeau de bulle. Ces résultats fournissent une compréhension complète du phénomène de cicatrisation des trous, en particulier dans l'éclatement du film océanique. Le présent travail offre également une base pour les futures études sur le phénomène d'éclatement du film impliquant des dynamiques complexes, y compris la cicatrisation des trousOceanic film bursting is a phenomenon in which a thin liquid film representing the cap of the bubble bursts at the surface of the ocean, producing film drops. The film bursting phenomenon is critical in ocean-atmosphere exchanges, particularly in transferring heat, mass, and momentum between the ocean and the atmosphere. The film bursting phenomenon comprises a series of complex dynamics, such as drainage, puncture, film retraction, and film disintegration into film drops. The hole healing (i.e., when a hole is too small and is closed after its nucleation) is a critical parameter that could impact the film bursting dynamics, particularly the film thickness at bursting and, thus, the liquid budget for the film drop production. The present work investigates the dynamics of holes in free liquid films, presenting a comprehensive understanding of the hole-healing phenomenon while focusing on the film bursting in the oceanic context. This was achieved through a combination of numerical simulations and analytical approaches. The numerical simulations were carried out using Basilisk. This robust and efficient two-phase flow solver is based on a Volume-of-Fluid (VoF) method and written using the C-programming language. The underlying mechanism for the hole-healing phenomenon was studied in detail. The dichotomy simulations for the determination of the healing threshold carried out in this work have used high-resolution mesh refinement. This was possible by using an adaptive mesh scheme provided by Basilisk. The analytical approaches were used to develop hypotheses to predict the healing threshold of a hole on a film, which were tested against numerical results. The critical dynamics of the hole are examined, and distinct power laws were identified for the tip curvature to illustrate the driving mechanism. The variations in the hole healing threshold with other problem parameters were examined. This study was first carried out for a flat film, discovering that the healing threshold is increased by increasing the film Laplace number. This effect was pronounced for values ranging from 1 to 10000, coinciding with the customary range of film Laplace numbers observed for oceanic bursting bubbles. The observed effects were also elaborated upon, along with physical explanations. Since the exact initial shape of the hole was shown to influence the healing threshold, an examination was carried out to study this effect on the consistency of the results from changing the film Laplace number, taken as an example for the other. It was shown that despite variations in the threshold for different shapes, the effect of changing the film Laplace number was independent of the hole shape. Therefore, the dichotomy results were shown to be independent of the arbitrary choice of the hole shape throughout the study. A similar study was carried out for a hole in a bubble cap after a detailed study of the bubble and gas outflow dynamics. It was discovered that the gas outflow undergoes a Venturi effect, where a stronger outflow, resulting from smaller bubble sizes or higher gas Laplace numbers, was shown to increase the healing threshold. A hypothesis was developed to predict the Venturi effect on the healing threshold, resulting in a Venturi correction term that predicted a power law dependency on the bubble diameter, which agreed with the numerical results. The Venturi effect was significant for high values of the gas Laplace number, where the healing threshold was doubled by increasing the film mean curvature from a flat film to a bubble cap with a size 20 times the bubble cap thickness. These findings provide a comprehensive understanding of the hole-healing phenomenon, particularly in oceanic film bursting. The present work also offers a foundation for future studies on the film-bursting phenomenon involving complex dynamics, including hole healing
3
Licht, David. "Effective Dynamics of Black Hole Horizons." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/671802.
Анотація:
In this thesis we present a new aspect pertaining to the effective field theory of general relativity in the limit of a large number D of dimensions. We demonstrate that the theory initially developed to capture the physics of asymptotically flat branes also contains a new family of localized solutions that can be identified with higher dimensional black holes such as the Schwarzschild-Thangerlini or the Myers-Perry black holes in the limit of a large number of spacetime dimensions. Using this technique we have explored several new aspects of these black hole solutions.
We show that the effective large D equations for the asymptotically flat brane also contain an analytic solution that is a gaussian blob (with the same topology as the flat membrane). The blob actually corresponds to a magnification of the geometry near the cap (north-pole) of the black hole. We calculate their (slow) quasi-normal spectrum, which captures the stability of Schwarzschild black holes and also the instability of ultraspinning Myers-Perry black holes.
Additionally we find novel class of rotating black bar solutions, that appear as stationary objects in the effective theory since they can not radiate gravitational waves which are decoupled from the effective theory.
We describe a method that allows to construct (Maxwell) charged solutions form every non- charged solution that the large D theory contains. Using this method we construct charged and rotating black holes in the Einstein-Maxwell theory.
Furthermore we explore the solutions that branch of from the (ultra-spinning) Myers-Perry (MP)
black hole and the non-linear extensions of the zero-modes of the analytically known black bar.
We study the evolution of higher dimensional black hole collisions by solving numerically the effective equations of motion. We demonstrate that in these collisions it is possible to form black holes with elongated horizons such as black bars and dumbbells. At high enough angular momentum the black bars and dumbbells can be so elongated that they are susceptible to a Greggory-Laflamme type instability, that leads to the a pinch off of the horizon towards a naked singularity. Accordingly this demonstrates a novel example of a violation of weak cosmic censorship in the quintessential process of general relativity: the collision of black holes.
Furthermore we study the evolution and decay of ultraspinning MP black holes, and observe remarkably rich structure in the intermediate states of the decay.
Lastly, we study how entropy production and irreversibility appear in the large D effective theory. With this tool we study how black hole entropy is generated in several highly dynamical processes, such as the fusion of black holes and the fission of unstable solutions into multiple black holes. We find the black hole fusion is highly irreversible, while fission which follows the decay of unstable black strings generates much less entropy. Additionally we describe how in processes that contain fusion and fission the intermediate state is quasi-thermalized.En esta tesis hemos presentado un nuevo aspecto perteneciente a la teoría efectiva de la relatividad general en el límite de un gran número de dimensiones. Hemos demostrado que la teoría desarrollada inicialmente para capturar la física de las branas asintóticamente planas también contiene una nueva familia de soluciones localizadas que pueden ser identificadas con agujeros negros de dimensiones más altas como los agujeros negros de Schwarzschild- Thangerlini o de Myers-Perry en el límite de gran D. Usando esta técnica hemos explorado varios aspectos nuevos de dichos agujeros negros. Encontramos una nueva clase de soluciones de barras negras giratorias, que aparecen como objetos estacionarios en la teoría efectiva Describimos un método que permite construir soluciones cargadas a partir de cada solución no cargada. Usando este método construimos agujeros negros cargados y giratorios en la teoría de Einstein-Maxwell. Estudiamos la evolución de las colisiones de agujeros negros en dimensiones superiores usando las ecuaciones efectivas. Demostramos que en estas colisiones es posible formar agujeros negros con horizontes alargados como barras negras o con forma de mancuernas. Con un momento angular lo suficientemente alto, las barras negras pueden ser tan alargadas que son susceptibles a una inestabilidad tipo Greggory-Laflamme, que lleva a una rotura del horizonte y a una singularidad desnuda. Por consiguiente, esto demuestra un ejemplo novedoso de una violación de la hipótesis de 'cosmic censorship' (censura cósmica). Además estudiamos la evolución y el decaimiento de los agujeros negros MP ultraspinning, y observamos una estructura notablemente rica en los estados intermedios del decaimiento.
4
Pacilio, Costantino. "Classical and quantum aspects of black hole dynamics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7532/.
Анотація:
Il contenuto fisico della Relatività Generale è espresso dal Principio di Equivalenza, che sancisce l'equivalenza di geometria e gravitazione. La teoria predice l'esistenza dei buchi neri, i più semplici oggetti macroscopici esistenti in natura: essi sono infatti descritti da pochi parametri, le cui variazioni obbediscono a leggi analoghe a quelle della termodinamica. La termodinamica dei buchi neri è posta su basi solide dalla meccanica quantistica, mediante il fenomeno noto come radiazione di Hawking. Questi risultati gettano una luce su una possibile teoria quantistica della gravitazione, ma ad oggi una simile teoria è ancora lontana.
In questa tesi ci proponiamo di studiare i buchi neri nei loro aspetti sia classici che quantistici. I primi due capitoli sono dedicati all'esposizione dei principali risultati raggiunti in ambito teorico: in particolare ci soffermeremo sui singularity theorems, le leggi della meccanica dei buchi neri e la radiazione di Hawking. Il terzo capitolo, che estende la discussione sulle singolarità, espone la teoria dei buchi neri non singolari, pensati come un modello effettivo di rimozione delle singolarità. Infine il quarto capitolo esplora le ulteriori conseguenze della meccanica quantistica sulla dinamica dei buchi neri, mediante l'uso della nozione di entropia di entanglement.
5
Wang, Xiaoya. "Theory of heavy-hole spin-echo dynamics." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123115.
Анотація:
In this work, we theoretically investigate hyperfine-induced effects on the spin-echo dynamics of a heavy hole in a quantum dot. We consider an in-plane applied magnetic field perpendicular to fluctuations arising from the hyperfine interaction, which drives the system into a motional averaging regime when the relevant (hole or nuclear) Zeeman energy scale exceeds the amplitude of hyperfine-induced fluctuations in the Overhauser field. For the parameters in Ref. [1], this system enters a motional averaging regime at moderate magnetic fields of the order of 1 T. In this regime, rapid spin precession about the external field effectively averages the out-of-plane fluctuations to zero, enabling the complete suppression of spin-echo envelope decay due to hyperfine coupling. We also predict the coherence dynamics to be strongly anisotropic, a property relevant to the discussion of electric-field-induced fluctuations currently limiting coherence times in single hole-spin experiments[2, 3]. More precisely, we find an alternative set of initialization and π-rotation axes which push the effects of electric-field-induced fluctuations out to very long timescales of the order of seconds for typical experimental parameters[2]. The anisotropy of this system also leads to counter-intuitive behaviour of the spin purity, an observable which quantifies the degree of spin-qubit polarization remaining after entangling with an environment for some time t. We find the spin purity to be maximally preserved when initializing along the hyperfine-induced fluctuations, in a superposition of Zeeman eigenstates. These results provide further evidence of the robustness of heavy-hole spin qubits, and pave the way for prolonging hole-spin coherence by optimizing the geometry of the system.Dans ce mémoire, nous étudions les effets de l'interaction hyperfine sur l'écho de spin d'un trou lourd localisé dans une boîte quantique. Nous considérons l'application d'un champ magnétique perpendiculaire aux fluctuations causéespar l'interaction hyperfine, qui entraîne le système dans un régime de moyenne motionnelle lorsque l'énergie Zeeman pertinente (du trou ou des noyaux nucléaires) dépasse l'amplitude des fluctuations dans le champ de Overhauser. Avec les paramètres utilisés dans la Réf. [1], le régime de moyenne motionnelle est atteint pour un champ magnétique de l'ordre de 1 T. Dans ce régime, la précession rapide du spin autour du champ magnétique externe a l'effet d'une moyenne sur les fluctuations hyperfines, ce qui permet la suppression complète de la décroissance de l'enveloppe du signal de l'écho de spin. Nous prédisons aussi une anisotropie présente dans la dynamique de cohérence qui serait pertinente à la discussion des fluctuations du champ électrique, fluctuations qui limitent les temps de cohérence dans des expériences actuelles[2, 3]. Plus précisément, nous trouvons des directions d'initialisation et de rotation qui repoussent les effets des fluctuations électriques jusqu'à des échelles de temps de l'ordre de plusieurs secondes pour des paramètres expérimentaux typiques[2]. L'anisotropie du système est également responsable d'un comportement inattendu de la pureté du spin, qui quantifie la polarisation restante du qubit de spin suivant l'enchevêtrement avec un environnement pendant un temps t. Nous montrons que la pureté du spin est préservée au maximum pour une initialisation parallèle aux fluctuations hyperfines, dans une superposition d'états propres Zeeman. Ces résultats fournissent une preuve supplémentaire du potentiel des qubits de spin de trou lourd, et permettent de prolonger leur cohérence en optimisant la géométrie du système.
6
Cáceres, Alejandro. "Electron dynamics in a black hole background." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614691.
7
Brunner and Michael. "Single hole dynamics in the t-J model." Phd thesis, Universitaet Stuttgart, 2000. http://elib.uni-stuttgart.de/opus/volltexte/2000/597/index.html.
8
De, Villiers Jean-Pierre. "Dynamics of cosmic strings in black hole spacetimes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0012/NQ34754.pdf.
9
Ziogas, Vaios. "Transport at strong coupling and black hole dynamics." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12683/.
Анотація:
In this thesis we study aspects of transport in strongly coupled quantum systems with broken translational symmetry. Using holographic duality, we also examine the associated dynamical problem in asymptotically Anti-de Sitter, spatially modulated black holes. More precisely, in chapter 2 we consider the transport of conserved charges in spatially inhomogeneous quantum systems with a discrete lattice symmetry. When the DC conductivities are finite, we derive a set of generalised Einstein relations, relating the diffusion constants of the conserved charges to the DC conductivities and static susceptibilities. We also develop a long-wavelength expansion in order to explicitly construct the heat and charge diffusive modes within hydrodynamics on curved manifolds. In chapter 3 we used analogous techniques to construct the thermoelectric diffusive quasinormal modes in a large class of black hole spacetimes that are holographically dual to strongly coupled field theories in which spatial translations are broken explicitly. These modes satisfy a set of constraints on the black hole horizon, from which we find that their dispersion relations are given by the generalised Einstein relations. In chapter 4 we define a boost incoherent current in spontaneously modulated phases, and we show that in holographic theories, its DC conductivity can be obtained from solving a system of horizon Stokes equations.
10
Brunner, Michael. "Single hole dynamics in the t-J model." [S.l.] : Universität Stuttgart , Fakultät Physik, 2000. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8473264.
11
Chimento, S. "BLACK HOLE DYNAMICS IN GENUINE AND FAKE GAUGED SUPERGRAVITY." Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/259452.
Анотація:
The goal of this thesis is to obtain and study new black hole solutions, both with and without supersymmetry, with a particular focus on multi-centered black holes in a cosmological background.
After a review of matter-coupled N=2 gauged supergravity in four dimensions and of the classification of its supersymmetric solutions, a new supersymmetric black hole solution is obtained, which is the first with nontrivial running hyperscalars.
Fake supergravity is a framework that allows to apply the methods used to classify supersymmetric solutions of supergravity also to theories without supersymmetry. A classification of fake supersymmetric solutions of a theory related to N=2, d=4 gauged supergravity is reviewed and used to construct dynamical solutions representing multiple black holes in a Friedmann-Lemaître-Robertson-Walker background. The physical properties of the single-centered case are then studied in some detail. More complicated solutions with rotation and NUT-charge, or with curved spatial slices, are obtained for a less general class of theories.
Finally a recipe to obtain multi-centered black holes in an arbitrary FLRW universe and in arbitrary dimension is presented. These spacetimes are a multi-centered generalization of the charged McVittie black hole and are sourced by a U(1) gauge field and by a charged perfect fluid. As a particular subcase, these solutions describe an arbitrary number of black holes in a background that is locally anti-de Sitter space in cosmological coordinates. Some physical properties of the single-centered asymptotically AdS black hole are studied, showing in particular that a generalized first law of black hole dynamics is satisfied.
12
Sargison, Jane Elizabeth. "Development of a novel film cooling hole geometry." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365427.
13
Mösta, Philipp. "Novel aspects of the dynamics of binary black-hole mergers." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2012/5982/.
Анотація:
The inspiral and merger of two black holes is among the most exciting and extreme events in our universe. Being one of the loudest sources of gravitational waves, they provide a unique dynamical probe of strong-field general relativity and a fertile ground for the observation of fundamental physics. While the detection of gravitational waves alone will allow us to observe our universe through an entirely new window, combining the information obtained from both gravitational wave and electro-magnetic observations will allow us to gain even greater insight in some of the most exciting astrophysical phenomena. In addition, binary black-hole mergers serve as an intriguing tool to study the geometry of space-time itself.
In this dissertation we study the merger process of binary black-holes in a variety of conditions. Our results show that asymmetries in the curvature distribution on the common apparent horizon are correlated to the linear momentum acquired by the merger remnant. We propose useful tools for the analysis of black holes in the dynamical and isolated horizon frameworks and shed light on how the final merger of apparent horizons proceeds after a common horizon has already formed. We connect mathematical theorems with data obtained from numerical simulations and provide a first glimpse on the behavior of these surfaces in situations not accessible to analytical tools.
We study electro-magnetic counterparts of super-massive binary black-hole mergers with fully 3D general relativistic simulations of binary black-holes immersed both in a uniform magnetic field in vacuum and in a tenuous plasma. We find that while a direct detection of merger signatures with current electro-magnetic telescopes is unlikely, secondary emission, either by altering the accretion rate of the circumbinary disk or by synchrotron radiation from accelerated charges, may be detectable. We propose a novel approach to measure the electro-magnetic radiation in these simulations and find a non-collimated emission that dominates over the collimated one appearing in the form of dual jets associated with each of the black holes. Finally, we provide an optimized gravitational wave detection pipeline using phenomenological waveforms for signals from compact binary coalescence and show that by including spin effects in the waveform templates, the detection efficiency is drastically improved as well as the bias on recovered source parameters reduced.
On the whole, this disseration provides evidence that a multi-messenger approach to binary black-hole merger observations provides an exciting prospect to understand these sources and, ultimately, our universe.Schwarze Löcher gehören zu den extremsten und faszinierensten Objekten in unserem Universum. Elektromagnetische Strahlung kann nicht aus ihrem Inneren entkommen, und sie bilden die kompaktesten Objekte, die wir kennen. Wir wissen heute, dass in den Zentren der meisten Galaxien sehr massereiche schwarze Löcher vorhanden sind. Im Fall unserer eigenen Galaxie, der Milchstrasse, ist dieses schwarze Loch ungefähr vier Millionen mal so schwer wie unsere Sonne. Wenn zwei Galaxien miteinander kollidieren, führt dies auch dazu, dass ihre beiden schwarzen Löcher kollidieren und zu einem einzelnen schwarzen Loch verschmelzen. Das Simulieren einer solchen Kollision von zwei schwarzen Löchern, die Vorhersage sowie Analyse der von ihnen abgestrahlten Energie in Form von Gravitations- und elektromagnetischen Wellen, bildet das Thema der vorliegenden Dissertation. Im ersten Teil dieser Arbeit untersuchen wir die Verschmelzung von zwei schwarzen Löchern unter verschiedenen Gesichtspunkten. Wir zeigen, dass Ungleichmässigkeiten in der Geometrie des aus einer Kollision entstehenden schwarzen Loches dazu führen, dass es zuerst beschleunigt und dann abgebremst wird, bis diese Ungleichmässigkeiten in Form von Gravitationswellen abgetrahlt sind. Weiterhin untersuchen wir, wie der genaue Verschmelzungsprozess aus einer geometrischen Sicht abläuft und schlagen neue Methoden zur Analyse der Raumzeitgeometrie in Systemen vor, die schwarze Löcher enthalten. Im zweiten Teil dieser Arbeit beschäftigen wir uns mit den Gravitationswellen und elektromagnetischer Strahlung, die bei einer Kollision von zwei schwarzen Löchern freigesetzt wird. Gravitationswellen sind Wellen, die Raum und Zeit dehnen und komprimieren. Durchläuft uns eine Gravitationswelle, werden wir in einer Richtung minimal gestreckt, während wir in einer anderen Richtung minimal zusammengedrückt werden. Diese Effekte sind allerdings so klein, dass wir sie weder spüren, noch auf einfache Weise messen können. Bei einer Kollision von zwei schwarzen Löchern wird eine grosse Menge Energie in Form von Gravitationswellen und elektromagnetischen Wellen abgestrahlt. Wir zeigen, dass beide Signale in ihrer Struktur sehr ähnlich sind, dass aber die abgestrahlte Energie in Gravitationswellen um ein Vielfaches grösser ist als in elektromagnetischer Strahlung. Wir führen eine neue Methode ein, um die elektromagnetische Strahlung in unseren Simulationen zu messen und zeigen, dass diese dazu führt, dass sich die räumliche Struktur der Strahlung verändert. Abschliessend folgern wir, dass in der Kombination der Signale aus Gravitationswellen und elektromagnetischer Strahlung eine grosse Chance liegt, ein System aus zwei schwarzen Löchern zu detektieren und in einem weiteren Schritt zu analysieren. Im dritten und letzen Teil dieser Dissertation entwickeln wir ein verbessertes Suchverfahren für Gravitationswellen, dass in modernen Laser-Interferometerexperimenten genutzt werden kann. Wir zeigen, wie dieses Verfahren die Chancen für die Detektion eines Gravitationswellensignals deutlich erhöht, und auch, dass im Falle einer erfolgreichen Detektion eines solchen Signals, seine Parameter besser bestimmt werden können. Wir schliessen die Arbeit mit dem Fazit, dass die Kollision von zwei schwarzen Löchern ein hochinteressantes Phenomenon darstellt, das uns neue Möglichkeiten bietet die Gravitation sowie eine Vielzahl anderer fundamentaler Vorgänge in unserem Universum besser zu verstehen.
14
Matía, Hernando Paloma. "Attosecond pump-probe methods for measurement of molecular hole dynamics." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/50155.
Анотація:
The generation of few-cycle pulses at near-infrared wavelengths is now a robust technology, as is their application to the efficient production of high-order harmonics in the extreme ultraviolet region with temporal confinement to hundreds of attoseconds. Recent years have seen considerable efforts directed to the study of electron dynamics in complex molecules in real time, with relevance to processes such as photosynthesis and radiation damage of proteins and DNA. This work describes the development of new and unique sources suited for the study of such dynamics, together with novel instrumentation and experimental methodology. This includes a pair of synchronised attosecond pulses at different photon energies in the VUV and XUV regions, which we have generated via high harmonic generation from a few-cycle NIR source and characterised with attosecond streaking. We have also explored the possibilities of sub-cycle control of these attosecond pulses by adding a second harmonic field to the high- harmonic generation process, and simultaneously characterised this second harmonic field with a novel characterisation technique known as ARIES, capable of waveform sampling at arbitrary optical wavelengths. In parallel, we have developed a few-cycle short-wavelength IR source for a UK user facility, to take advantage of the favourable wavelength scaling of the maximum photon energy achievable via high-harmonic generation. Using a commercial optical parametric amplifier and a hollow-core fibre compression system, we have generated sub-2-cycle pulses at 1750 nm, characterised via third-harmonic autocorrelation and a novel implementation of the dispersion scan technique. We have commissioned a beamline for attosecond pump-probe studies in the gas phase, including a purpose-built dual spectrometer with capabilities for simultaneous measurement of mass spectra of ions and velocity-map imaging of electrons. We have performed initial VUV-NIR pump-probe experiments on a small organic molecule, namely isopropanol, and identified a time- dependent signature as an IR-induced coupling. Finally, we have considered perspectives for future studies in attosecond pump-probe experiments with the demonstration of a two-VUV-photon process in helium performed with a moderate energy, high repetition rate attosecond source.
15
Casas, Roma Joan. "Deeper Down the Rabbit-Hole: Unfolding the Dynamics of Imagination Acts." Doctoral thesis, Universitat Oberta de Catalunya, 2018. http://hdl.handle.net/10803/565519.
Анотація:
Estudiem les dinàmiques dels actes d'imaginació des d'un punt de vista filosòfic, formal i aplicat. Partim de tres teories que identifiquen els mecanismes involucrats en els actes d'imaginació i mostrem que comparteixen una estructura semblant. Definim la lògica dels escenaris imaginaris, en què creem una capa per als actes d'imaginació sobre una lògica epistèmica per a un sol agent. Tot analitzant les propietats de la lògica, veiem que la manera com els mons imaginaris es desenvolupen està massa simplificada. Una anàlisi més profunda porta a la definició d¿una nova teoria especialment dissenyada per a les dinàmiques dels actes d'imaginació: el marc comú per als actes d'imaginació i el rombe de la imaginació. Partint d'aquesta nova teoria, definim la lògica dels actes d'imaginació, en què introduïm quatre algorismes diferents que comporten una representació molt més modular de la imaginació. Finalment, presentem la implementació del prototip d'un programa informàtic que captura els algorismes definits en la lògica anterior.Estudiamos las dinámicas de los actos de imaginación desde un punto de vista filosófico, formal y aplicado. Partimos de tres teorías que identifican los mecanismos involucrados en los actos de imaginación y mostramos que comparten una estructura similar. Definimos la lógica de los escenarios imaginarios, en la que creamos una capa para actos de imaginación partiendo de una lógica epistémica para un solo agente. Al discutir las propiedades de la lógica, vemos que el modo en que los mundos imaginarios se desarrollan está demasiado simplificado. Un análisis más profundo nos lleva a la definición de una nueva teoría especialmente diseñada para las dinámicas de los actos de imaginación: el marco común para actos de imaginación y el rombo de la imaginación. Partiendo de esta nueva teoría, definimos la lógica de los actos de imaginación, en la que introducimos cuatro algoritmos distintos que conllevan una representación mucho más modular de la imaginación. Finalmente, presentamos la implementación del prototipo de un programa informático que captura los algoritmos definidos en la lógica anterior.
We study the dynamics of imagination acts at a philosophical, formal and applied level. Our research is based on three theories that identify the mechanisms involved in imagination acts and show how all of them share a similar structure. We define the Logic of Imaginary Scenarios, in which we create a layer for imagination acts upon a single-agent epistemic logic. While discussing the properties of logic, we note that the way in which imaginary worlds are developed is oversimplified. A deeper analysis leads to the definition of a new theory especially suited for the dynamics of imagination acts, called the Common Frame for Imagination Acts, and the Rhombus of Imagination. With this new theory at hand, we define the Logic of Imagination Acts, in which we introduce four different algorithms that allow for a much more modular account of imagination. Finally, we provide an implementation of a computer programme prototype that captures the algorithms defined by our latter logic.
16
Brakel, Johannes Daniel. "Prediction of wellbore trajectory considering bottom hole assembly and drillbit dynamics /." Access abstract and link to full text, 1986. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/8624179.
17
Alcaraz, Barrera Rafael. "Topological and symbolic dynamics of the doubling map with a hole." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/topological-and-symbolic-dynamics-of-the-doubling-map-with-a-hole(b6f17b43-5285-4e35-883a-baf4708993bc).html.
Анотація:
This work motivates the study of open dynamical systems corresponding to the doubling map. In particular, the dynamical properties of the attractor of the doubling map when a symmetric, centred open interval is removed are studied. Using the arithmetical properties of the binary expansion of the points on the boundary of the removed interval, we study properties such as topological transitivity, the specification property and intrinsic ergodicity. The properties of the function that associates to each hole $(a,b)$ the topological entropy of the attractor of the considered dynamical system are also shown. For these purposes, a subshift corresponding to an element of the lexicographic world is associated to each attractor and the mentioned properties are studied symbolically.
18
Durham, Michael Glenn. "COMPARISON OF SQUARE-HOLE AND ROUND-HOLE FILM COOLING: A COMPUTATIONAL STUDY." Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4390.
Анотація:
Film cooling is a method used to protect surfaces exposed to high-temperature flows such as those that exist in gas turbines. It involves the injection of secondary fluid (at a lower temperature than that of the main flow) that covers the surface to be protected. This injection is through holes that can have various shapes; simple shapes such as those with a straight circular (by drilling) or straight square (by EDM) cross-section are relatively easy and inexpensive to create. Immediately downstream of the exit of a film cooling hole, a so-called horseshoe vortex structure consisting of a pair of counter-rotating vortices is formed. This vortex formation has an effect on the distribution of film coolant over the surface being protected. The fluid dynamics of these vortices is dependent upon the shape of the film cooling holes, and therefore so is the film coolant coverage which determines the film cooling effectiveness distribution and also has an effect on the heat transfer coefficient distribution. Differences in horseshoe vortex structures and in resultant effectiveness distributions are shown for circular and square hole cases for blowing ratios of 0.33, 0.50, 0.67, 1.00, and 1.33. The film cooling effectiveness values obtained are compared with experimental and computational data of Yuen and Martinez-Botas (2003a) and Walters and Leylek (1997). It was found that in the main flow portion of the domain immediately downstream of the cooling hole exit, there is greater lateral separation between the vortices in the horseshoe vortex pair for the case of the square hole. This was found to result in the square hole providing greater centerline film cooling effectiveness immediately downstream of the hole and better lateral film coolant coverage far downstream of the hole.M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering
19
Maureira, Fredes Cristián Danilo [Verfasser]. "Black hole binary systems : from dynamics to accretion / Cristián Danilo Maureira Fredes." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://d-nb.info/116930088X/34.
20
Blakely, Philip. "Numerical solutions of the general relativistic equations for black hole fluid dynamics." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/226111.
Анотація:
The aims of this thesis are to develop and validate a robust and efficient algorithm for the numerical solution of the equations of General Relativistic Hydrodynamics, to implement the algorithm in a computationally efficient manner, and to apply the resulting computer code to the problem of perturbed Bondi-Hoyle-Lyttleton accretion onto a Kerr black hole. The algorithm will also be designed to evolve the space-time metric, and standardised tests will be applied to this aspect of the algorithm. The algorithm will use up-to-date High-Resolution Shock-Capturing numerical schemes that have been developed for the stable and accurate solution of complex systems of equations. It will be built around the Adaptive Mesh Refinement and overlapping, curvilinear grid methodologies in order to extend these schemes to the efficient solution of two and three-dimensional problems. When implementing the algorithm, we will use previously written code libraries, where appropriate, to avoid excessive software development. We will validate the algorithm against standard test-cases for Special and General Relativistic Hydrodynamics, and for Einstein's equations for the evolution of the space-time metric. The methodologies we use will be tested to ensure that they lead to the stable and accurate numerical solution of these problems. Finally, the implemented algorithm will be applied to the problem of Bondi-Hoyle-Lyttleton flow onto a Kerr black hole in three dimensions. It will be validated against existing exact and numerical solutions of the problem, and then be used to perform an extensive parametric study of the problem, varying the spin of the black hole and the incident wind direction, and allowing for the perturbation of the fluid density upstream of the black hole. We will then analyze the results of the study, and present the complete set of results on a DVD accompanying this thesis.
21
Oberli, Solène. "Molecular double core hole spectroscopy : the role of electronic and nuclear dynamics." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS011/document.
Анотація:
Les propriétés de la matière peuvent être révélées en faisant interagir la matière avec la lumière. En particulier, les spectroscopies à rayons X sont largement utilisées pour étudier la structure électronique d'éléments isolés ou d'atomes et molécules dans un environnement donné, et sont spécifiques de la nature de l'élément. De telles capacités démontrent leur potentiel en terme d'analyse chimique. Le développement récent des lasers à électrons libres à rayons X (XFEL en anglais) permet de sonder la matière avec une résolution spatiale (angström) et temporelle (femtoseconde) hors de portée avec les lasers optiques et les sources synchrotron de troisième génération. Les caractéristiques uniques du rayonnement XFEL sont exploitées dans plusieurs domaines de recherche, comme la chimie, la physique et la biologie. En particulier, la spectroscopie de double trous a connu un nouvel essor avec l'apparition des XFELs. Les états double trous possèdent deux lacunes électroniques en couche interne. En régime XFEL, ces états sont produits principalement par l'absorption séquentielle de deux photons X d'une impulsion laser ultracourte (femtoseconde) et intense, avec la formation d'un état intermédiaire simplement ionisé. Au cours de cette thèse, nous avons étudié la formation de molécules doublement ionisées en couche de cœur, induite par l'absorption séquentielle de deux photons X d'une impulsion laser femtoseconde et intense. D'une part, nous mettons en évidence l'influence de la dynamique nucléaire sur les processus d'ionisation en couche de cœur. D'autre part, nous démontrons qu'un contrôle actif sur la compétition entre l'absorption de photon et le déclin Auger dans l'état intermédiaire simplement ionisé est possible en faisant varier la durée de l'impulsion laser. Afin d'atteindre ces objectifs, nous avons développé pour la première fois un modèle dépendant du temps et purement quantique, qui traite explicitement la dynamique nucléaire ainsi que l'absorption de photon, tandis que le déclin Auger est décrit de manière phénoménologique. Ce travail de recherche théorique ouvre la voie à une description complète de la formation de molécules doublement ionisées en couche de cœur en régime XFELProperties of matter can be revealed through its interaction with light. In particular, X-ray based spectroscopies are widely used to gain insight into the local electronic structure of isolated elements or atoms or molecules embedded in an environment, and are element specific. Such capabilities evidence their potential as tools for chemical analysis. The recent development of X-ray free electron laser (XFEL) allows to probe matter with spatial (angström) and temporal (femtosecond) resolutions out of reach so far with optical lasers or third generation synchrotron sources. The unique characteristics of XFEL radiation are exploited in several areas, such as chemistry, physics and biology. In particular, double core hole spectroscopy, whose sensitivity is considerably enhanced compared to conventional X-ray spectroscopies, is on the rise. Double core hole states, also referred as hollow states, are characterized by two electron vacancies in the inner shell(s). In the XFEL regime, the dominant pathway to produce them is the sequential absorption of two x-ray photons, where a singly core ionized species is produced in the intermediate step. In the present thesis, we tackle the study of double core hole state formation induced by the sequential absorption of two x-ray photons from an intense femtosecond laser pulse. On one hand, we bring forward the influence of the nuclear dynamics on core photoionization processes. On the other hand, we demonstrate that an active control over the competition between photoabsorption and Auger decay in the intermediate single core hole state is possible by varying the laser pulse duration. In pursuing these goals, we develop for the first time a time-dependent full quantum model treating both the photon absorption and the nuclear dynamics explicitly as well as the Auger decay phenomenologically. This purely theoretical work paves the road for a complete description of molecular double core hole state formation in th XFEL regime
22
Zhao, Yue. "Individual Business Initiation Process and Business Dynamics." Thesis, Uppsala universitet, Företagsekonomiska institutionen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183287.
Анотація:
Many relationship-based studies focus on how businesses are maintained and developed. However, little attention focused on individuals as business initiators and the consequent processes. This study will bridge this gap. A theoretical model with two cases will answer two questions -How individuals initiate business through personal network? -What is the consequent process? The studies demonstrate that individual do play a very important role when initiating a new business and they set in motion relationship-building processes that change the network structure. The contribution for research and management is clear. The netentrepruer is a new ‘actor’ and can be useful in future studies of business networks. Management can usefully become conscious of the possibilities they have in studying their network contacts before initiating new businesses. Managers should utilize managing individual’s networks as new competition strategies. This will modify the view of management strategy and also contribute to theory building.
23
Acharya, Khem. "Excitation energy transfer and charge separation dynamics in photosystem II: hole-burning study." Diss., Kansas State University, 2012. http://hdl.handle.net/2097/13600.
Анотація:
Doctor of PhilosophyDepartment of Chemistry
Ryszard J. Jankowiak
The constituents of oxygen-evolving photosystem II core complexes—antenna proteins (CP43 and CP47) and reaction center (RC)—have been the subject of many studies over the years. However, the various issues related to electronic structure, including the origin/composition of the lowest-energy traps, origin of various emission bands, excitation energy transfer (EET), primary charge separation (CS) processes and pigment site energies remain yet to be fully resolved. Exploiting our state-of-the-art techniques such as low-T absorption, fluorescence, and hole burning (HB) spectroscopies, we resolved some of the issues particularly related to CP47 and isolated RC protein complexes. For example, we demonstrated that the fluorescence origin band maximum (~695 nm) originates from the lowest-energy state ~693 nm of intact CP47. In intact CP47 in contrast to destablished protein complexes, the band (~695 nm) does not shift in the temperature range of 5–77 K unless hole-burning takes place. We also studied a large number of isolated RC preparations from spinach, and wild-type Chlamydomonas reinhardtii (at different levels of intactness), as well as its mutant (D2-L209H), in which the active branch pheophytin (PheoD1) has been genetically replaced with chlorophyll a (Chl a). We showed that the Qx-/Qy-region site-energies of PheoD1 and PheoD2 are ~545/680 nm and ~541.5/670 nm, respectively, in good agreement with our previous assignment [Jankowiak et al. J. Phys. Chem. B 2002, 106, 8803]. Finally, we demonstrated that the primary electron donor in isolated algal RCs from C. reinhardtii (referred to as RC684) is PD1 and/or PD2 of the special Chl pair (analogous to PL and PM, the special BChl pair of the bacterial RC) and not ChlD1. However, the latter can also be the primary electron donor (minor pathway) in RC684 depending on the realization of the energetic disorder. We further demonstrate that transient HB spectra in RC684 are very similar to P+QA - PQA spectra measured in PSII core, providing the first evidence that RC684 represent intact isolated RC that also possesses the secondary electron acceptor, QA. In summary, a new insight into possible charge separation pathways in isolated PSII RCs has been provided.
24
OLBRIGHT, GREGORY RICHARD. "FEMTOSECOND DYNAMICS AND NONLINEAR EFFECTS OF ELECTRON-HOLE PLASMA IN SEMICONDUCTOR DOPED GLASSES." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184091.
Анотація:
The following is a comprehensive study of transient and steady-state nonlinear optical properties of semiconductor microcrystals embedded in a glass matrix (semiconductor doped glass). Transient thermal effects which give rise to longitudinal excitation discontinuities (i.e., kinks) that arise from partial sample switching in increasing absorption optical bistability are observed in a doped glass. The transient thermal effects occur on time scales of a few hundred milliseconds. Femtosecond and nanosecond laser pulses are employed to measure time-resolved and steady-state transmission and differential transmission spectra. The measured spectra reveal several beautiful effects which are attributed to the many-particle effects of electron-hole plasma. The spectra reveal: bandgap renormalization, broadening of the tail states and screening of the continuum states, state filling (spectral hole burning), thermalization of nonthermal carrier population distributions, band filling due to carrier relaxation of the thermal and nonthermal distributions, direct electron-hole recombination and long lived (>>100 ps) tail states which are attributed to electron trapping. Absorption edge dynamics discussed in this dissertation span 15 orders of magnitude.
25
Gobat, Jason I. "The dynamics of geometrically compliant mooring systems." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88489.
Анотація:
Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2000.Includes bibliographical references (p. 255-264).
by Jason I. Gobat.
Ph.D.
26
Kell, Adam. "Energy transfer and exciton dynamics in photosynthetic pigment–protein complexes." Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32539.
Анотація:
Doctor of PhilosophyChemistry
Ryszard J. Jankowiak
The structure-function relationships of natural pigment–protein complexes are of great interest, as the electronic properties of the pigments are tuned by the protein environment to achieve high quantum yields and photon utilization. Determination of electronic structure and exciton dynamics in protein complexes is complicated by static disorder and uncertainties in the properties of system-bath coupling. The latter is described by the phonon profile (or spectral density), whose shape can only be reliably measured experimentally for the lowest energy state. Low-temperature, laser-based spectroscopies are applied towards model pigment–protein complexes, i.e., the Fenna-Matthews-Olson (FMO) and water-soluble chlorophyll-binding (WSCP) complexes, in order to study system-bath coupling and energy transfer pathways. Site-selective techniques, e.g., hole burning (HB) and fluorescence line narrowing, are utilized to overcome static disorder and reveal details on homogeneous broadening. In addition, excitonic calculations with non-Markovian lineshapes provide information on electronic structure and exciton dynamics. A new lognormal functional form of the spectral density is recommended which appropriately defines electron-phonon parameters, i.e., Huang-Rhys factor and reorganization energy. Absorbance and fluorescence spectral shifts and HB spectra reveal that samples of FMO may contain a subpopulation of destabilized proteins with modified HB efficiencies. Simulations of spectra corresponding to intact proteins indicate that the entire trimer has to be taken into account in order to properly describe fluorescence and HB spectra. The redshifted fluorescence spectrum of WSCP is described by uncorrelated energy transfer as opposed to previous models of excited state protein relaxation. Also, based on nonconservative HB spectra measured for WSCP, a mechanism of electron transfer between chlorophylls and aromatic amino acids is proposed.
27
Mishra, Nekkhil. "Investigation of hole cleaning parameters using computational fluid dynamics in horizontal and deviated wells." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5111.
Анотація:
Thesis (M.S.)--West Virginia University, 2007.Title from document title page. Document formatted into pages; contains x, 65 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 58-60).
28
Moffat, Varas Carlos F. "Ocean circulation and dynamics on the west Antarctic Peninsula continental shelf." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42104.
Анотація:
Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2007.Includes bibliographical references (p. 177-186).
Observations of current velocity, temperature, salinity and pressure from a 2-year moored array deployment and four hydrographic cruises conducted by the United States Southern Ocean GLOBEC program on the western Antarctic Peninsula continental shelf are used to characterize the ocean circulation and its connection to fresh water and heat fluxes on the shelf. Mean velocities on the shelf are of the order of 5 cm/s or less. Tidal motions are dominated by the M2 and S2 semi-diurnal tides and the 01 and K1 diurnal tides, although the tidal velocities are typically less than 2 cm/s. Near-inertial motions are relatively large, with current velocities as high as 26 cm/s. It is shown that Marguerite Trough, a large bathymetric feature connecting the shelf-break to Marguerite Bay, plays a critical role in determining the circulation. The mean flow is strongly steered in the along-slope direction, and the tidal currents also show increasing current polarization at depth in Marguerite Trough. At time-scales of 5 to 20 days, the observations show bottom-intensified motion in Marguerite Trough consistent with bottom-trapped topographic Rossby waves.
(cont.) The subtidal circulation in the trough has a significant wind-driven component in Marguerite Trough, with downwelling-favorable winds forcing cross-shelf flow on the northern side of the trough and along the shore on the outer shelf. Upwelling-favorable winds force roughly the opposite circulation. The cyclonic circulation on the trough helps advect blobs of salty, warm and nutrient-rich water across the shelf. These intrusions are small (;4 km) and frequent (4 events/month). Also, the Antarctic Peninsula Coastal Current (APCC), a coastal buoyant current which is described for the first time here. The APCC is a seasonal current which is only present during the ice-free season and is forced by freshwater fluxes associated with large glacier melt and precipitation rates in the region.
by Carlos F. Moffat Varas.
Ph.D.
29
You, Jhih-An [Verfasser], and Nina [Akademischer Betreuer] Rohringer. "Light-induced Electronic Hole Dynamics and Its Application / Jhih-An You ; Betreuer: Nina Rohringer." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2016. http://d-nb.info/1120623464/34.
30
Bittencourt, Gabriela Dornelles. "Influence of the Antarctic Ozone Hole and Atmospheric Dynamics on Ozone in Southern Brazil." Thesis, La Réunion, 2022. http://www.theses.fr/2022LARE0018.
Анотація:
Le printemps austral dans l'hémisphère sud présente des réductions temporaires de la teneur en ozone principalement dans la région antarctique connue sous le nom de trou d'ozone antarctique (AOH). Cependant, des études montrent une influence dans les régions de latitude moyenne, comme le sud du Brésil, où des jours avec des diminutions temporaires de la colonne d'ozone totale (COT) sont identifiés. L'objectif principal de cette thèse est d'étudier cette influence de l'AOH sur la région sud du Brésil, en utilisant les données de la colonne d'ozone totale et des profils verticaux qui aideront à identifier la hauteur préférentielle à laquelle ces diminutions se produisent dans le sud du Brésil, en plus à analyser le comportement dynamique de l'atmosphère lors de ces événements dans la période de 42 ans de données (1979-2020). La méthodologie utilisée comprend l'analyse des données quotidiennes moyennes de la colonne totale d'ozone à travers des instruments de surface (spectrophotomètre Brewer), des données satellitaires (TOMS et OMI), et de comparer les données de réanalyse de l'ECMWF-ERA5, pour l'identification des événements d'influence de l'AOH sur la région sud du Brésil. L'analyse du contenu vertical des données O3 du satellite TIMED/SABRE fournit des données quotidiennes de 15 a 105 km d'altitude et dispose de 17 années de profils O3 disponibles sur la période de 2002 à 2018. La validation de ces données était nécessaire, et pour cela le réseau SHADOZ de mesures de sondes d'ozone a été utilisé pour effectuer cette validation à travers la saison tropicale au Natal/RN comme référence. Cette validation a montré un bon accord entre les deux instruments, permettant l'utilisation de SABER pour l'analyse des événements d'influence AOH. À partir de là, 102 événements ont été identifiés qui ont influencé Santa Maria/RS avec une diminution temporaire de la teneur en O3 au cours de la période, et avec une chute moyenne entre 24 et 28,1 km d'altitude. Dans l'analyse dynamique, les champs stratosphériques ont montré une augmentation du tourbillon potentiel dans la moyenne des événements, principalement dans les mois de septembre et octobre. Dans la dynamique de la section verticale de l'atmosphère, la présence constante de jets stratosphériques et troposphériques dans la moyenne des événements, indique une forte influence que ces systèmes ont lors de l'occurrence des événements à effet secondaire AOH sur Santa Maria/RSThe austral spring in the Southern Hemisphere presents temporary reductions in ozone content mainly in the Antarctic region known as the Antarctic Ozone Hole (AOH). However, studies show an influence in mid-latitude regions, such as southern Brazil, where days with temporary decreases in the total ozone column (TCO) are identified. The main objective of this thesis is to investigate this influence of AOH on the southern region of Brazil, using data from the total ozone column and vertical profiles that will help to identify the preferential height at which these decreases occur in southern Brazil, in addition to analyzing the atmospheric dynamic behavior during these events in the period 42 years of data (1979 to 2020). The methodology used comprises the analysis of average daily data of the total column of ozone through surface instruments (Brewer Spectrophotometer), satellite data (TOMS and OMI), and to compare reanalysis data from the ECMWF-ERA5, for the identification of events of influence of the AOH on the southern region of Brazil. The analysis of the vertical content of O3 data from the TIMED/SABER satellite provides daily data from 15 to 105 km in height and has 17 years of O3 profiles available in the period from 2002 to 2018. The validation of these data was necessary, and for that the SHADOZ network of ozonesondes measurements was used to carry out this validation through the tropical season in Natal/RN as a reference. This validation showed a good agreement between the two instruments, enabling the use of SABER for the analysis of AOH influence events. From this, 102 events were identified that influenced Santa Maria/RS with a temporary decrease in O3 content during the period, and with an average drop between 24 - 28.1 km in altitude. In the dynamic analysis, the stratospheric fields showed an increase in the potential vorticity in the average of the events, mainly in the months of September and October. In the dynamics of the vertical section of the atmosphere, the constant presence of stratospheric and tropospheric jets in the average of the events, indicates a strong influence that these systems have during the occurrence of the AOH secondary effect events on Santa Maria/RS
A primavera austral no Hemisfério Sul apresenta reduções temporárias do conteúdo de ozônio principalmente na região Antártica conhecida como Buraco de Ozônio Antártico (AOH). Porém, estudos mostram uma influência sob regiões de médias latitudes, como o Sul do Brasil, onde são identificados dias com diminuições temporárias da coluna total de ozônio (CTO). Com isso, o objetivo principal dessa tese é investigar essa influência do AOH sobre a região sul do Brasil, utilizando dados da coluna total de ozônio e de perfis verticais que vão ajudar a identificar a altura preferencial em que essas diminuições ocorrem no sul do Brasil, além de analisar o comportamento dinâmico atmosférico durante esses eventos no período 42 anos de dados (1979 a 2020). A metodologia utilizado compreende a análise de dados médios diários da coluna total de ozônio através de instrumentos de superfície (Espectrofotômetro Brewer), dados de satélites (TOMS e OMI), e para comparação dados de reanálise do ECMWF-ERA5, para a identificação de eventos de influência do AOH sobre a região Sul do Brasil. A análise do conteúdo vertical de O3 dados do satélite TIMED/SABER disponibilizam dados diários de 15 a 110 km de altura e possuem 17 anos de perfis de O3 disponíveis no período de 2002 a 2018. A validação desses dados se fez necessária, e para isso foi utilizada a rede SHADOZ de medidas de ozonesondes para realizar essa validação através da estação tropical em Natal/RN como referência. Essa validação apresentou uma boa concordância entre os dois instrumentos, viabilizando o uso do SABER para as análises dos eventos de influência do AOH. A partir disso, foram identificados 102 eventos que influenciaram Santa Maria/RS com diminuição temporária no conteúdo de O3 durante o período, e com queda média entre 24 e 28,1 km de altitude. Nas análises dinâmicas os campos estratosféricos mostraram o aumento da vorticidade potencial na média dos eventos, principalmente nos meses de setembro e outubro. Na dinâmica do corte vertical da atmosfera a presença constante dos jatos estratosféricos e troposféricos na média dos eventos, indica forte influência que esses sistemas possuem durante a ocorrência dos eventos de efeito secundário do AOH sobre Santa Maria/RS
31
Jayne, Steven Robert. "Dynamics of global ocean heat transport variability." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/69203.
Анотація:
Thesis (Sc. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and Woods Hole Oceanographic Institution), 1999.Includes bibliographical references (p. 161-169).
A state-of-the-art, high-resolution ocean general circulation model is used to estimate the time-dependent global ocean heat transport and investigate its dynamics. The north-south heat transport is the prime manifestation of the ocean's role in global climate, but understanding of its variability has been fragmentary owing to uncertainties in observational analyses, limitations in models, and the lack of a convincing mechanism. These issues are addressed in this thesis. Technical problems associated with the forcing and sampling of the model, and the impact of high-frequency motions are discussed. Numerical schemes are suggested to remove the inertial energy to prevent aliasing when the model fields are stored for later analysis. Globally, the cross-equatorial, seasonal heat transport fluctuations are close to +4.5 x 1015 watts, the same amplitude as the seasonal, cross-equatorial atmospheric energy transport. The variability is concentrated within 200 of the equator and dominated by the annual cycle. The majority of it is due to wind-induced current fluctuations in which the time-varying wind drives Ekman layer mass transports that are compensated by depth-independent return flows. The temperature difference between the mass transports gives rise to the time-dependent heat transport. The rectified eddy heat transport is calculated from the model. It is weak in the central gyres, and strong in the western boundary currents, the Antarctic Circumpolar Current, and the equatorial region. It is largely confined to the upper 1000 meters of the ocean. The rotational component of the eddy heat transport is strong in the oceanic jets, while the divergent component is strongest in the equatorial region and Antarctic Circumpolar Current. The method of estimating the eddy heat transport from an eddy diffusivity derived from mixing length arguments and altimetry data, and the climatological temperature field, is tested and shown not to reproduce the model's directly evaluated eddy heat transport. Possible reasons for the discrepancy are explored.
by Steven Robert Jayne.
Sc.D.
32
Yusuf, Ahmed A. "The study of down-hole hydro-cyclone efficiency in oil wells using computational fluid dynamics." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4886.
Анотація:
Thesis (M.S.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains ix, 64 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 63-64).
33
Jackson, Rebecca H. (Rebecca Harding). "Dynamics of Greenland's glacial fjords." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104586.
Анотація:
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 165-172).
Glacial fjords form conduits between glaciers of the Greenland Ice Sheet and the North Atlantic. They are the gateways for importing oceanic heat to melt ice and for exporting meltwater into the ocean. Submarine melting in fjords has been implicated as a driver of recent glacier acceleration; however, there are no direct measurements of this melting, and little is known about the fjord processes that modulate melt rates. Combining observations, theory, and modeling, this thesis investigates the circulation, heat transport, and meltwater export in glacial fjords. While most recent studies focus on glacial buoyancy forcing, there are other drivers - e.g. tides, local wind, shelf variability - that can be important for fjord circulation. Using moored records from two major Greenlandic fjords, shelf forcing (from shelf density fluctuations) is found to dominate the fjord circulation, driving rapid exchange with the shelf and large heat content variability near the glacier. Contrary to the conventional paradigm, these flows mask any glacier-driven circulation in the non-summer months. During the summer, when shelf forcing is reduced and freshwater forcing peaks, a mean exchange flow transports warm Atlantic-origin water towards the glacier and exports glacial meltwater. Many recent studies have inferred submarine melt rates from oceanic heat transport, but the fjord budgets that underlie this method have been overlooked. Building on estuarine studies of salt fluxes, this thesis presents a new framework for assessing glacial fjord budgets and revised equations for inferring meltwater fluxes. Two different seasonal regimes are found in the heat/salt budgets for Sermilik Fjord, and the results provide the first time-series of submarine meltwater and subglacial discharge fluxes into a glacial fjord. Finally, building on the observations, ROMS numerical simulations and two analytical models are used to investigate the dynamics of shelf-driven flows and their importance relative to local wind forcing across the parameter space of Greenland's fjords. The fjord response is found to vary primarily with the width relative to the deformation radius and the fjord adjustment timescale relative to the forcing timescale. Understanding these modes of circulation is a step towards accurate modeling of ocean-glacier interactions.
by Rebecca H. Jackson.
Ph. D.
34
Donnay, Laura. "Symmetries and dynamics for non-AdS backgrounds in three-dimensional gravity." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/229439.
Анотація:
Dans cette thèse, nous étudions la structure asymptotique de la gravité à trois dimensions d’espace-temps avec et sans constante cosmologique.La première partie de la thèse présente en détails les propriétés fondamentales de la gravité à trois dimensions pour des espaces à constante cosmologique négative, ou espaces de types Anti-de Sitter (AdS). Nous introduisons le formalisme de Chern-Simons pour la gravité en utilisant la formulation dite du premier ordre pour cette dernière. Nous présentons également les conditions aux bords dites de Brown-Henneaux et le calcul associé de l’algèbre des charges de surface. Enfin, nous décrivons les étapes de la réduction du modèle de Chern-Simons à un modèle de Wess-Zumino-Witten puis à celui d’une théorie de Liouville. La relevance de cette théorie dans le calcul microscopique de l’entropie d’un trou noir à trois dimensions est également discutée.La seconde partie de la thèse contient les contributions originales. Tout d’abord, nous étendons l’analyse de la dynamique asymptotique de la supergravité à trois dimensions au cas d’une constante cosmologique nulle. Nous montrons que l’algèbre des charges de surface associée est une extension supersymétrique de l’algèbre BMS, et construisons la théorie bidimensionnelle située au bord de l’espace-temps qui possède cette symétrie. Le second résultat est l’obtention d’une symétrie de dimension infinie au voisinage de l’horizon d’événements d’un trou noir tridimensionnel non extrême. Troisièmement, nous discutions le cas d’une constante cosmologique positive et montrons l’existence d’une théorie de Liouville euclidienne duale à la gravité d’Einstein avec des conditions aux bords de Dirichlet dans le patch statique. Enfin, nous explorons un autre cadre dans lequel des symétries de dimension infinie apparaissent pour des espaces temps qui non sont pas du type Anti-de Sitter. Nous considérons pour cela des déformations de ces derniers, connus sous le nom d’espaces-temps Warped Anti-de Sitter. Nous montrons que ces déformations admettent une algèbre de surface donnée par une somme semi-direct entre une algèbre de Virasoro et une algèbre affine de Kac-Moody, avec extensions centrales non nulles. Nous montrons que les configurations du trou noir hôte des espaces-temps Warped s’organisent en termes de deux algèbres de Virasoro. Nous identifions les générateurs associés qui décrivent les représentations de la théorie duale et, en appliquant une formule de Cardy, nous prouvons qu’un calcul microscopique reproduit correctement l’entropie de ces trous noirs. Nous étendons ce résultat à des conditions aux bords plus générales qui incluent de nouvelles solutions associés à des degrés de liberté locaux, des gravitons massifs contenus dans le volume d’espace-temps.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
35
Mösta, Philipp [Verfasser], and Bernard [Akademischer Betreuer] Schutz. "Novel aspects of the dynamics of binary black-hole mergers / Philipp Mösta. Betreuer: Bernard Schutz." Potsdam : Universitätsbibliothek der Universität Potsdam, 2012. http://d-nb.info/1024613801/34.
36
Wittmer, Paul [Verfasser], and Carlo [Akademischer Betreuer] Ewerz. "Application of Black-Hole Physics to Vortex Dynamics in Superfluids / Paul Wittmer ; Betreuer: Carlo Ewerz." Heidelberg : Universitätsbibliothek Heidelberg, 2021. http://d-nb.info/1225484480/34.
37
Amavisca, Edward D. 1965. "Electron(hole)-phonon interaction in YBCO high temperature superconductor using quantum path integral molecular dynamics." Thesis, The University of Arizona, 1991. http://hdl.handle.net/10150/277899.
Анотація:
In this research, we have implemented an original technique to study the electronic properties of a single electron placed in YBa2 at 300K. Using a discretized extension of Feynman's Quantum Path Integral, we have been able to characterize effective electron-phonon interactions, and electron location site probability. We find that the electron stabilizes at oxygen vacant sites in the copper-oxygen chains. In the copper-oxygen planes, the electron is unstable and moves into the chain. Upon complementing the quantum electron to a positive charge thereby simulating a hole, we then find that the hole moves into favorable sites in the copper-oxygen planes. These sites are surrounded by four oxygens and two copper ions. Next, by decoupling the electron and hole from the lattice, we obtain effective electron-phonon and hole-phonon coupling constants on the order of 30. These results indicate that the next area of research is to move toward a multi-electron system and allow for further study of the electrons near the Fermi level. Some of the difficulties associated with multi-electron systems such as "exchange", are briefly discussed.
38
Bortolas, Elisa. "Dynamics of Single and Binary Black Holes in Galactic Nuclei." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3424973.
Анотація:
Galactic nuclei represent one of the most fascinating and dynamically richest regions of our Universe. They are often found to host at least one supermassive black hole (MBH) at their centre; in addition, observations suggest that MBHs frequently coexist with massive and extremely dense nuclear star clusters, making galactic nuclei ideal laboratories for the study of a broad range of exotic dynamical phenomena.
This thesis aims at providing new insights on the interplay between MBHs and their host environments by means of advanced numerical techniques. In particular, my work is relevant in the landscape of gravitational waves (GWs), as it explores the dynamical evolution of stellar compact objects and MBHs: these objects are expected to be promising GW sources detectable by present and future interferometers, as the forthcoming space-borne LISA observatory.
In this framework, Bortolas et al. (2017) investigates the impact of natal kicks on the distribution of compact objects in the Milky Way Galactic Centre (GC). My results show that supernova (SN) kicks typically either unbind neutron stars from the MBH, or set them on very eccentric orbits. In contrast, stellar black holes are not significantly affected by the kick: this, combined with mass segregation, would suggest a cusp of stellar relics to inhabit the GC innermost region, as supported by the recent detection of a cusp of accreting X-ray binaries near the MBH.
In addition, this thesis is the first to provide evidence that SN kicks may trigger extreme mass ratio inspirals (EMRIs), i.e. GW driven decays of stellar mass compact objects onto MBHs. In Bortolas & Mapelli (2019) I show that SN kicks effectively funnel infant black holes and neutron stars on low angular momentum orbits, promoting their GW decay onto the MBH. By applying this argument to the young stars in the GC, I predict up to 0.01% of SN kicks to induce an EMRI, meaning that LISA will detect up to a few SN-driven EMRIs from Milky-Way like galaxies every year.
A further relevant GW source for the LISA observatory is constituted by the coalescence of MBH binaries (BHBs). BHBs are expected to form in large numbers along the cosmic history, being a natural outcome of galaxy collisions. Their coupling in gas-poor galaxies can be described as a three-step process: a dynamical friction dominated phase, a migration phase induced by slingshot ejections of stars, and a GW driven inspiral leading to rapid coalescence. It has been pointed out that the slingshot-driven pairing may be ineffective if too few stars are scattered in the BHB vicinity, and the shrinking may come to a halt at roughly pc separation. However, there is circumstantial evidence that MBH pairs are rare and BHBs are likely to merge: this motivated a series of works aimed to solve the 'final pc problem'.
This thesis contributes to the forge of possible solutions in multiple ways. In Bortolas et al. (2018a), I explore the infall of a young massive star cluster onto a BHB. I show that a cluster approaching the BHB along a non-zero angular momentum orbit fails to enhance the BHB shrinking; in contrast, the same cluster free-falling onto the BHB considerably contributes to the BHB pairing, as the BHB separation shrinks by more than 10%. This suggests that several cluster infalls may effectively bring the BHB close to the regime at which GWs lead to a prompt coalescence.
A more general solution to the final pc problem is currently believed to reside in the non-sphericity (triaxiality) of the host galaxy. If the host galaxy is triaxial (e.g. as a result of a merger), large scale gravitational torques ensure that stars are continually scattered in the BHB vicinity. This assumption was initially validated via direct summation N-body simulations. However, the reliability of such simulations has been questioned due to the modest achievable number of particles (~1M). In fact, resolution limits enhance the amplitude of the BHB random walk, artificially boosting the BHB shrinking rate. In Bortolas et al. (2016), I numerically explore the significance of such spurious effect: I show that Brownian motion does not affect the evolution of BHBs in simulations including 1M particles or more, providing more reliability to the conclusion that BHBs effectively find their way to coalescence in non-spherical systems.
Finally, in Bortolas et al. (2018b) I explore the interplay between the BHB dynamics and the shape of its host system. My study suggests that no strong connection exists between the galaxy morphology and the BHB shrinking rate, which seems to depend only on the inner density slope of the host galaxy. Such result is particularly relevant for GW science, as the time needed for a BHB to reach its GW-emission stage can be assumed to scale only with the central density of the nucleus.
In conclusion, this thesis adds several pieces of information to our knowledge of GW sources in galactic nuclei, in preparation for the future of GW observations.
39
RAVIKUMAR, ABHILASH. "Electronic, spin dependent conductive properties of modified graphene." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2017. http://hdl.handle.net/10281/170813.
Анотація:
Nella prima parte della ricerca che presentiamo abbiamo considerato l’eccitazione di stati elettronici profondi di molecole organiche adsorbite sul grafene. Per tali sistemi abbiamo dedotto l’induzione o la soppressione di un momento di dipolo magnetico relativo alla banda di valenza di molecole sulla scala temporale del femtosecondo. Abbiamo considerato tre molecole organiche, prototipi di diversi tipi di legame con la superficie: la Piridina, la cui interazione con il substrato di grafene è dovuta principalmente a forze di van der Waals, il radicale di Piridina che viceversa si lega alla superficie in maniera covalente e il radicale di Picolina, che rappresenta una situazione intermedia. In tutti e tre i sistemi abbiamo studiato le proprietà elettroniche sia dello stato fondamentale che di quello ottenuto eccitando lo stato 1s dell’atomo di azoto. Nel primo caso, mentre la molecola fisisorbita mostra uno stato fondamentale non-magnetico le simulazioni numeriche indicano che dopo l’eccitazione di un elettrone proveniente da un stato profondo i restanti elettroni di valenza rilassano in una configurazione polarizzata in spin. Il magnetismo indotto dipende dall’efficienza del trasferimento di carica dal grafene, sulla scala temporale del femtosecondo. Nel caso invece di una molecola chemisorbita, lo stato fondamentale del sistema è magnetico, in cui sono presenti due stati dipendenti dallo spin all’interno del gap di energia e localizzati sul sito di adsorbimento. Al contrario del caso precedente, l’eccitazione elettronica permette l’ibridazione del LUMO della molecola con gli stati del grafene all’interno del gap, risultando in una configurazione non-magnetica.
Il passo successivo nella nostra analisi riguarda il legame tra il tempo di vita del trasferimento di carica in uno stato eccitato, creato a partire da livelli elettronici profondi di molecole adsorbite su grafene, e la modifica della struttura elettronica di tale interfaccia dovuta all’accoppiamento, di intensità variabile, con un substrato metallico. Abbiamo considerato la fotoemissione di un elettrone dallo stato 1s dell’azoto della molecola 1,10-bipiridina (C5H4N)2 adsorbita su un bilayer grafene/nickel(111) (BP/BLG/Ni) e su un substrato cresciuto per epitassia grafene/Ni(111) (BP/EG/Ni). Tramite simulazioni ab initio abbiamo osservato che il tempo caratteristico del trasferimento di carica durante il processo di eccitazione dipende fortemente dal tipo di interazione che si sviluppa tra il grafene ed il substrato di Ni sottostante. In entrambi i sistemi che abbiamo considerato, nello stato fondamentale il LUMO della molecola è fortemente accoppiato con la superficie. Nel caso del sistema BP/BLG/Ni, lo strato di grafene in contatto con il nickel è fortemente ibridizzato con il metallo, mentre lo strato superiore di grafene rimane sostanzialmente disaccoppiato. Il livello eccitato LUMO* della molecola ha la possibilità di ibridizzarsi con pochi livelli di grafene, intorno al punto di Dirac all’energia di Fermi. Per questo motivo il tempo di vita dello stato eccitato cresce significativamente (∼ 116 fs). Invece nel caso del sistema BP/EG/Ni la forte ibridizzazione del grafene con il sottostante substrato di nickel ne distorce significativamente la struttura elettronica, creando degli stati in prossimità del livello di Fermi. Questi livelli si possono accoppiare con il LUMO* della molecola, risultando in un tempo di vita sostanzialmente ridotto (∼ 33 fs). Abbiamo cercato delle conferme ai nostri risultati tramite misure sperimentali basate sul metodo della spettroscopia core-hole-clock. Il tempo caratteristico del trasferimento di carica che abbiamo ricavato è di ∼ 30 fs±5 fs per il sistema BP/BLG/Ni e ∼ 4 fs±1 fs per quello BP/EG/Ni. Questi risultati verificano le nostre previsioni teoriche, dimostrando l’effetto del substrato sulla dinamica del trasferimento di carica.The first part of research we present is the adsorption of core-excited organic molecules on graphene. We predict the induction or suppression of magnetism in the valence shell of physisorbed and chemisorbed organic molecules on graphene occurring on the femtosecond time scale as a result of core level excitations. We consider three organic molecules: Pyridine - whose interaction with graphene is mainly facilitated by van der Waals forces, Picoline radical - an intermediate case where there is a strong van der Waals interaction of the pyridine π ring with graphene but a covalent bonding of the molecule and pyri-dine radical - where the interaction is mainly by covalent bonding, and study the ground state and N 1s core excited state electronic properties for these systems. For physisorbed molecules, where the interaction with graphene is dominated by van der Waals forces and the system is non-magnetic in the ground state, numeri- cal simulations based on density functional theory show that the valence electrons relax towards a spin polarized configuration upon excitation of a core-level electron. The magnetism depends on efficient electron transfer from graphene on the femtosecond time scale. On the other hand, when graphene is covalently functionalized, the system is magnetic in the ground state showing two spin dependent midgap states localized around the adsorption site. At variance with the physisorbed case upon core-level excitation, the LUMO of the molecule and the mid gap states of graphene hybridize and the relaxed valence shell is not magnetic anymore. Next we discuss the interplay between the charge transfer lifetime of core excited organic molecules adsorbed on graphene and the modification of its electronic structure by a variable coupling with a metal substrate. Nitrogen 1s core electron of 1,10- bipyridine (C5H4N)2 is photoexcited and adsorbed on bilayer graphene/nickel(111) (BP/BLG/Ni) and epitaxially grown graphene/Ni(111) (BP/EG/ Ni). We predict from first principle calculations that the charge transfer time of core excited molecules depend strongly on the coupling of graphene to the underlying Ni substrate. In the ground state, the LUMO of the molecule is quite strongly coupled with the substrate in both the cases (BP/BLG/Ni and BP/EG/Ni). In the case of BP/BLG/Ni, the layer of graphene in contact with nickel substrate strongly hybridizes but the upper layer of graphene remains fairly decoupled. The excited molecular LUMO* finds very few states of graphene close to the Dirac point at the Fermi level to hybridize with. This leads to a decoupled molecular LUMO* and the lifetime increases significantly (∼ 116 fs). But in the case of BP/EG/Ni, the strong hybridization of graphene with the underlying nickel substrate significantly distorts the electronic structure of graphene generating states close to the Fermi level. The LUMO* of the molecule strongly couples with these states resulting in a substantially smaller lifetime (∼ 33 fs). We also find experimental evidence to confirm this trend by performing core-hole-clock spectroscopy. The resonant charge transfer lifetime we find is ∼ 30 fs±5 fs for the BP/BLG/Ni and ∼ 4 fs±1 fs for the BP/EG/Ni, thus clearly demonstrating the effect of substrate on the charge transfer dynamics of organic molecules on graphene.
40
Wacongne, Sophie. "Dynamics of the equatorial undercurrent and its determination." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/58533.
Анотація:
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1988.Includes bibliographical references (v.2, leaves 339-351).
This study focuses on the zonal weakening, eastern termination and seasonal variations of the Atlantic equatorial undercurrent (EUC). The main and most original contribution of the dissertation is a detailed analysis of the Atlantic EUC simulated by Philander and Pacanowski's (1986)general circulation model (GCM), which provides a novel description of the dynamical regimes governing various regions of a nonlinear stratified undercurrent. Only in a narrow deep western region of the simulation does one find an approximately inertial regime corresponding to zonal acceleration. Elsewhere frictional processes cannot be ignored. The bulk of the mid-basin model EUC terminates in the overlying westward surface flow while only a small fraction (the deeper more inertial layers) terminates at the eastern coast. In agreement with observations, a robust feature of the GCM not present in simpler models is the apparent migration of the EUC core from above the thermocline in the west to below it in the east. In the GCM, this happens because the eastward flow is eroded more efficiently by vertical friction above the base of the thermocline than by lateral friction at greater depths. This mechanism is a plausible one for the observed EUC. A scale analysis using a depth scale which decreases with distance eastwards predicts the model zonal transition between western inertial and eastern inertio-frictional regimes. Historical and recent observations and simple models of the equatorial and coastal eastern undercurrents are reviewed, and a new analysis of current measurements in the eastern equatorial Atlantic is presented. Although the measurements are inadequate for definitive conclusions, they suggest that Lukas' (1981) claim of a spring surge of the Pacific EUC to the eastern coast and a seasonal branching of the EUC into a coastal southeastward undercurrent may also hold for the Atlantic Ocean. To improve the agreement between observed and modelled strength of the eastern undercurrent, it is suggested that the eddy coefficient of horizontal mixing should be reduced in future GCM simulations.
by Sophie Huguette Claire Wacongne.
Ph.D.
41
Strasser, Carly Ann. "Metapopulation dynamics of the softshell clam, Mya arenaria." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43818.
Анотація:
Thesis (Ph. D.)--Joint Program in Biological Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2008.Includes bibliographical references.
In this dissertation, I explored metapopulation dynamics and population connectivity, with a focus on the softshell clam, Mya arenaria. I first worked towards developing a method for using elemental signatures retained in the larval shell as a tag of natal habitat. I designed and implemented an experiment to determine whether existing methods commonly used for fishes would be applicable to bivalves. I found that the instrumentation and setup I used were not able to isolate and measure the first larval shell of M. arenaria. In concert with developing this method for bivalves, I reared larval M. arenaria in the laboratory under controlled conditions to understand the environmental and biological factors that may influence elemental signatures in shell. My results show that growth rate and age have significant effects on juvenile shell composition, and that temperature and salinity affect larval and juvenile shell composition in variable ways depending on the element evaluated. I also examined the regional patterns of diversity over the current distribution of M. arenaria using the mitochondrial gene, cytochrome oxidase I (COI). I found minimal variability across all populations sampled, suggesting a recent population expansion in the Northwest Atlantic. Finally, I employed theoretical approaches to understand patch dynamics in a two-patch metapopulation when one patch is of high quality and the other low quality. I developed a matrix metapopulation model and compared growth rate elasticity to patch parameters under variable migration scenarios. I then expanded the model to include stochastic disturbance. I found that in many cases, the spatial distribution of individuals within the metapopulation affects whether growth rate is most elastic to parameters in the good or bad patch.
by Carly A. Strasser.
Ph.D.
42
Jacobs, Karen Marie. "Fire and vegetation history of the last 2000 years in Jackson Hole, Grand Teton National Park, Wyoming." Thesis, Montana State University, 2007. http://etd.lib.montana.edu/etd/2007/jacobs/JacobsK0507.pdf.
43
Wiesner, Karoline. "Electronic Structure and Core-Hole Dynamics of Ozone : Synchrotron-radiation based studies and ab-initio calculations." Doctoral thesis, Uppsala University, Department of Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3914.
Анотація:
The electronic structure of the ozone molecule O3 has been studied with spectroscopy techniques and computations. The investigation was focused on O3 in a core-hole state. The electronic configuration and the nuclear dynamics have been found to be highly correlated.
This electron correlation is mapped out for the two chemically different sites in the molecule: the central and the terminal oxygen. The energy difference between the corresponding core orbitals is 4.58 eV, which allows for site-selective core ionization and core excitation.
The influence of the core-hole site on the electronic structure is substantial, which is shown with ion and electron spectroscopy data and ab-initio quantum chemical computations. Moreover, the induced nuclear motion differs considerably for the two core-hole sites.
One of the core-excited states is proven to be ultra-fast dissociative. An analysis of the data with a formalism for two-body dissociation disclosed the localized character of core excitation. The symmetry-equivalent terminal-oxygen core orbitals do have very little overlap, so that a delocalized model for the core excitation becomes inadequate.
Moreover, core-excitation opens up a decay channel to a valence-ionized state that has not been observed with photoionization. The reason for this state to have low cross section for photoionization is illuminated with a CASSCF computation of the electronic configuration. The configuration of the state was found to be very distinct from the ground state configuration.
Another effect of configuration-interaction was found in MRCI computations of the core- ionized states. Several local minima with distinct electronic configurations could be identified.
44
Dean, Bruce H. "Variational results and solutions in gauge gravity and a bifurcation analysis of black hole orbital dynamics." Morgantown, W. Va. : [West Virginia University Libraries], 1999. http://etd.wvu.edu/templates/showETD.cfm?recnum=859.
Анотація:
Thesis (Ph. D.)--West Virginia University, 1999.Title from document title page. Document formatted into pages; contains ix, 223 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 214-223) and index.
45
Ghoma, Mohamed I. "The Effect of Wall Jet Flow on Local Scour Hole." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.
Анотація:
This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study.
In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations.
The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.
46
Kida, Shinichiro. "Eddy dynamics of [Beta] plumes." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/88447.
Анотація:
Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2003.In title on t.p., "[Beta]" appears as the Greek letter.
Includes bibliographical references (p. 81-84).
by Shinichiro Kida.
S.M.
47
Brownlee, Emily Fay. "Ciliate micrograzer dynamics of the New England shelf." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111223.
Анотація:
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Biology; and the Woods Hole Oceanographic Institution), 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 169-182).
Protists play important roles in grazing and nutrient recycling, but quantifying these roles has been hindered by difficulties in collecting, culturing, and observing these often-delicate cells. During long-term deployments at the Martha's Vineyard Coastal Observatory (MVCO) (Massachusetts, USA), Imaging FlowCytobot (IFCB) made it possible to study live cells in situ without the need to culture or preserve. IFCB records images of cells with chlorophyll fluorescence above a trigger threshold, so taxonomically resolved analysis of protists is limited to mixotrophs and herbivores, which have eaten recently. To overcome this limitation, I coupled a broad-application 'live cell' fluorescent stain with a modified IFCB so that protists which do not contain chlorophyll (such as consumers of unpigmented bacteria and other heterotrophs) can also be recorded. Staining IFCB (IFCB-S) revealed higher abundances of grazers than the original IFCB, as well as some cell types not previously detected. To analyze a 10-year time series of herbivorous ciliates at MVCO and address broad patterns of seasonality of major ciliate classes and their components, I employed a statistical model that estimates a seasonal density pattern and simultaneously accounts for and separates any annual-scale effects. I describe the seasonality of three functional groups: a phototrophic ciliate, a mixotroph, and a group of strict heterotrophs, and comment on potential drivers of these patterns. DNA sequencing has also contributed to the study of protist communities, providing new insight into diversity, predator-prey interactions, and discrepancies between morphologically defined species and genotype. To explore how well IFCB images can be used to detect seasonal community change of the class Spirotrichea, an important and numerous group, I used high-throughput sequencing (HTS), which does not discriminate between chlorophyll-containing cells and the rest of the community. I report on species and genera of ciliates for which morphotype and genotype displayed high congruency. In comparing how well temporal aspects of genotypes and morphotypes correspond, I found that HTS was critical to detect and identify certain ciliates occupying a niche associated with warmer temperatures. I further showed that when these types of analyses are combined with IFCB results, they can provide hypotheses about food preferences.
by Emily Fay Brownlee.
Ph. D.
48
Gatchell, Michael. "Molecular Hole Punching : Impulse Driven Reactions in Molecules and Molecular Clusters." Doctoral thesis, Stockholms universitet, Fysikum, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129523.
Анотація:
When molecules are excited by photons or energetic particles, they will cool through the emission of photons, electrons, or by fragmenting. Such processes are often thermal as they occur after the excitation energy has been redistributed across all degrees-of-freedom in the system. Collisions with atoms or ions may also lead to ultrafast fragmentation in Rutherford-like scattering processes, where one or several atoms can literally be knocked out of the molecule by the incoming projectile before the energy can be completely redistributed. The resulting fragmentation pathways can in such knockout processes be very different from those in thermal processes. This thesis covers extensive studies of collisions between ions/atoms and isolated Polycyclic Aromatic Hydrocarbon (PAH) molecules, isolated fullerene molecules, or clusters of these. The high stabilities and distinct fragmentation channels make these types of molecules excellent test cases for characterizing knockout-driven fragmentation and the reactions that these processes can lead to. I will present experimental measurements for a wide range of energies and compare them with my own molecular dynamics simulations and quantum chemical calculations. In this thesis, I present an in-depth study of the role of knockout in the energetic processing of molecules and clusters. The competition between knockout and thermally driven fragmentation is discussed in detail. Knockout-driven fragmentation is shown to result in exotic fragments that are far more reactive than the intact parent molecules or fragments from thermal processes. When such reactive species are formed within molecular clusters efficient molecular growth can take place on sub-picosecond timescales. The cluster environments are crucial here because they protect the newly formed molecules by absorbing excess energy. This is a possible pathway for the growth of large PAHs, fullerenes, and similar carbonaceous complexes found in, for instance, the interstellar medium.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 1: Submitted.
49
Ghoma, Mohamed Ibrahem. "The effect of wall jet flow on local scour hole." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.
Анотація:
This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study. In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations. The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.
50
Youngs, Madeleine Kendall. "Residual overturning circulation and its connection to Southern Ocean dynamics." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129068.
Анотація:
Thesis: Ph. D., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 135-145).
Over the last 20 years, our understanding of the meridional overturning circulation has improved, but primarily in a two-dimensional, zonally-averaged framework. In this thesis, I have pushed beyond this simplification and shown that the additional complexity of meanders, storm tracks, and other zonal asymmetries is necessary to reproduce the lowest-order behavior of the overturning circulation. First I examined the role of basin width for determining whether the Atlantic or Pacific oceans experience deep convection. I used a two layered model and a rectangular single-basin model to show that the basin width, in combination with scalings for the overturning circulation make the overturning relatively weaker in the wider basin, priming it for a convection shut down.
In addition to this large-scale work, I have examined Southern Ocean-like meanders using a hierarchy of idealized models to understand the role of bottom topography in determining how the large-scale circulation responds to climate change scenarios. These are useful because they preserve the lowest-order behavior, while remaining simple enough to understand. I tested the response of the stratification and transport in the Southern Ocean to changes in wind using a highly-idealized two-layer quasi-geostrophic model. In addition to showing that meanders are necessary to reproduce the behavior of the Southern Ocean, I found that strong winds concentrate the baroclinic and barotropic instabilities downstream of the bottom topography and weaken the instabilities elsewhere due to a form-drag process. With weak winds, however, the system is essentially symmetric in longitude, like a flat-bottomed ocean.
This result is consistent with observations of elevated turbulence down-stream of major topography in the Southern Ocean. My next study investigated a more realistic Southern Ocean-like channel, with and without bottom topography, and examined the three-dimensional circulation in order to understand where vertical transport occurs and develop a picture of the pathways taken by each individual water parcel. I found that the vertical transport happens in very isolated locations, just downstream of topography. Finally, I added a biogeochemical model to my simulations and found that carbon fluxes are enhanced near topography, again highlighting the role of zonal asymmetries.
by Madeleine Kendall Youngs.
Ph. D.
Ph.D. Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)