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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
151

Numerical simulations of instabilities in general relativity

Kunesch, Markus January 2018 (has links)
General relativity, one of the pillars of our understanding of the universe, has been a remarkably successful theory. It has stood the test of time for more than 100 years and has passed all experimental tests so far. Most recently, the LIGO collaboration made the first-ever direct detection of gravitational waves, confirming a long-standing prediction of general relativity. Despite this, several fundamental mathematical questions remain unanswered, many of which relate to the global existence and the stability of solutions to Einstein's equations. This thesis presents our efforts to use numerical relativity to investigate some of these questions. We present a complete picture of the end points of black ring instabilities in five dimensions. Fat rings collapse to Myers-Perry black holes. For intermediate rings, we discover a previously unknown instability that stretches the ring without changing its thickness and causes it to collapse to a Myers-Perry black hole. Most importantly, however, we find that for very thin rings, the Gregory-Laflamme instability dominates and causes the ring to break. This provides the first concrete evidence that in higher dimensions, the weak cosmic censorship conjecture may be violated even in asymptotically flat spacetimes. For Myers-Perry black holes, we investigate instabilities in five and six dimensions. In six dimensions, we demonstrate that both axisymmetric and non-axisymmetric instabilities can cause the black hole to pinch off, and we study the approach to the naked singularity in detail. Another question that has attracted intense interest recently is the instability of anti-de Sitter space. In this thesis, we explore how breaking spherical symmetry in gravitational collapse in anti-de Sitter space affects black hole formation. These findings were made possible by our new open source general relativity code, GRChombo, whose adaptive mesh capabilities allow accurate simulations of phenomena in which new length scales are produced dynamically. In this thesis, we describe GRChombo in detail, and analyse its performance on the latest supercomputers. Furthermore, we outline numerical advances that were necessary for simulating higher dimensional black holes stably and efficiently.
152

Att vara eller att inte vara personlig? : En kvantitativ studie om influencermarknadsföring på Instagram

Boström, Isabella, Hasselqvist Haglund, Josefin January 2018 (has links)
Influencermarknadsföring är en ny sorts marknadsföringsstrategi som har förändrat dynamiken i hur företag arbetar idag. Många företag använder sig av mediapersonligheter, så kallade influencers, på sociala medier för att göra reklam för sina produkter. Syftet med denna studie är att undersöka om det finns ett samband mellan influencers användning av ett personligt budskap i marknadsföringen av en produkt på Instagram och dennes följares varumärkesattityd och köpintention. Ett personligt budskap definieras enligt teori om emotionell marknadsföring och storytelling. En analysmodell utvecklas med inspiration från Lutz och MacKenzies (1989) modell om attitydbildning kring ett marknadsföringsobjekt. En digital enkätundersökning genomförs med ett personligt/opersonligt fokus där cirka hälften av de 160 respondenterna svarar på enkäten med ett personligt fokus och resterande svarar på samma enkät med ett opersonligt fokus. Syftet med denna indelning är att jämföra huruvida det finns en statistiskt signifikant skillnad mellan de två grupperna. Två av sex formulerade hypoteser om trovärdighet och attityd i relation till influencern och Instagram-inlägget samt varumärkesattityd och köpintention kan accepteras enligt undersökningens resultat.
153

Využití online marketingu ve vybraném sportovním e-shopu / The Use of online marketing in chosen sports e-shop

Procházková, Petra January 2019 (has links)
Title: The Use of online marketing in chosen sports e-shop Objectives: The objective of this thesis is to evaluate the use of online marketing in chosen sports e-shop Kolo-park.cz. The objective is to evaluate the use and settings of individual online marketing channels with emphasis on evaluating settings and structure of PPC campaigns. Then recommend suitable settings and structure of individual online marketing channels on the grounds on data analysis and also suggest new strategy of online marketing channels on the basis of framework See-Think-Do-Care, Methods: Methods used in this thesis: observation of online marketing area, monitoring and synthesis, analysis of PPC campaigns, analysis of e-mailing campaigns, analysis of commodity comparators settings, SEO analysis and analysis of social media. Next used methods were monitoring and synthesis. Results: The result contains recommendation to improve the structure and settings of online marketing channels/tools to achieve better results of Kolo-park.cz online marketing activities. The result is a new created strategy of individual online marketing tools/channels on the basis of framework See-Think-Do-Care. Audience, targeting, relevant content and the way how to measure online marketing activities depending on customer's buying cycle is defined...
154

AdS/CFT duality involving deformed PP-waves from the Lunin-Maldacena background

Smolic, Milena 13 August 2008 (has links)
ABSTRACT WOULD NOT LOAD ON DSpace
155

GPPZ and the Holographic Triforce against Scalars

Vaduret, Jean-François January 2019 (has links)
We use gauge-invariant cosmological perturbation theory to compute one-point functions of active and inert scalar fields of the GPPZ RG-flow in AdS5. Linearized Einstein equations are computed and made gauge-invariant for D-dimensional Euclidean domain-wall geometry. We briefly review the procedure of holographic renormalization for the GPPZ RG-flow in AdS5 to get different one-point functions. The source-dependant vev of the operator dual to the ∆ = 3 active scalar field in the GPPZ solution is computed and agrees with literature. We also find the source-dependant one-point function of the operator dual to the ∆ = 3 inert scalar.
156

Duality symmetries in string-inspired supergravity: T-dualities and the gauge/gravity correspondence

Whiting, Catherine Ann 01 May 2015 (has links)
Motivated by the AdS/CFT correspondence, new supersymmetric solutions to Type IIB and Type IIA supergravity are presented. These solutions contain $AdS_5$ or $AdS_4$ factors and are generated using T-duality symmetries of supergravity. The technique used to generate these solutions consists of performing a series of non-Abelian and Abelian T-dualities, sometimes with coordinate shifts in-between, to Freund-Rubin type seed backgrounds. An added bonus of the gauge fixing procedure inherent in non-Abelian T-Duality is the freedom to generate backgrounds with extra free parameters, some examples of which are presented. Aspects of the dual field theories of these new solutions are analyzed using holography techniques. The supersymmetry of these new backgrounds is also discussed. In addition to supergravity backgrounds with AdS, the study of generalized Calabi-Yau manifolds in the context of flux compactifications is briefly reviewed. The particular case of the resolved cone over $Y^{p,q}$ and its admission of generalized SU(3) structure solutions is examined. Contrary to geometries with $AdS$ factors, whose field theory duals are conformal field theories, these types of geometries can be phenomenologically interesting to study, as their gauge theory duals are minimally supersymmetric and confining, thus they could someday help aid our understanding of strongly-coupled QCD (Quantum Chromodynamics).
157

Applications of the holographic principle in string theory

Button, Bradly Kevin 01 July 2014 (has links)
The holographic principle has become an extraordinary tool in theoretical physics, most notably in the form of the Anti-deSitter Conformal Field Theory (AdS/CFT) correspondence, in which classical gravitational degrees of freedom in N-dimensions are related quantum field theory degrees of freedom in N − 1 dimensions in the limit of a large number of fields. Here we present an account of the AdS/CFT correspondence, also known as the gauge/gravity duality, from its origins in the large N 'tHooft expansion, up to Maldacena's proposal that type IIB string theory in the presences of D-branes at low energy is dual to an N = 4, d = 4, U(N) super Yang-Mills on AdS5 × S5 . We begin with an extensive review of (super)string theory including D-branes. We then present the general formulation of the AdS/CFT in the supergravity background of AdS5 × S5 , along with several examples of how it is used in terms of the identification of bulk fields with operators on the bound- ary of a CFT. We move on to discuss two applications of the gauge/gravity duality. The first is the application of the holographic gauge/gravity correspondence to the QCDk-string. The second applies the AdS/CFT formalism to a Kerr black hole solution embedded in 10-dimensional heterotic sting theory. These two applications of the holographic gauge/gravity duality comprise the original work presented here. We follow with summaries and discussions of the background material, the original work, and future investigations.
158

Mesure de l'angle gamma du triangle d'unitarité avec le détecteur BaBar

Derkach, D. 25 June 2010 (has links) (PDF)
Dans cette thèse nous présentons des études sur les mésons B effectués en utilisant les données enregistrées par l'expérience Babar auprès de PEP-II à SLAC. D'abord nous présentons la recherche des désintégrations B+→D+K(*)0. Ces modes de désintégration sont intéressants car il s'agit de processus d'annihilation qui fournit des informations importantes sur la dynamique de la désintégration des mésons beaux et les éléments de la matrice CKM, Vij. Les résultats obtenus sur ces modes de désintégration peuvent être utilisés dans des ajustements phénoménologiques. Cela permet de traduire les mesures sur les amplitudes chargées B+→D+K(*)0 en estimations sur les amplitudes B0→D0K(*)0 supprimées par Vub. L'analyse expérimentale est effectuée en utilisant plusieurs modes de désintégration du méson D chargé. Nous n'avons obtenu aucune évidence significative de signal et les limites supérieures sur les rapports d'embranchement suivants ont été établies. Dans la deuxième partie de la thèse nous présentons des études sur la violation de CP dans le système des mésons B et en particulier la mesure de l'angle γ du Triangle d'Unitarité. L'angle γ est la phase relative entre les éléments Vub et Vcb de la matrice CKM. Un paramètre crucial qui détermine la sensibilité à γ est le rapport r entre les amplitudes de transition b→u et b→c. Dans cette thèse nous présentons une analyse du canal de désintégration des mésons B: B+→D0K+. Ces désintégrations sont étudiées en utilisant la méthode ADS et le méson neutre D est reconstruit dans son état final Kππ0. En combinant cette analyse avec une analyse similaire qui utilise l'état final Kπ des D0 le rapport r et l'angle γ ont été déterminés.
159

Kommunikationsgränssnitt mot GP&C transponder / Communication interface to a GP&C transponder

Johansson, Anders January 2002 (has links)
<p>Examensarbetet som beskrivs i denna rapport handlar om en ny teknik för att förbättra säkerheten för flygplan i luften och i närheten av flygplatser. Denna teknik benämns ADS-B (Automatic Dependent Surveillance Broadcast), och är tänkt att göra det möjligt för piloter att själva få information om trafik i närområdet. Nuvarande system baserar sig i huvudsak på visuella observationer från flygledare i kontrolltorn samt radarspaning omkring flygplatserna. Med det nuvarande systemet kommer det att bli både dyrt och svårt att upprätthålla en acceptabel nivå på flygsäkerheten när trafiken ökar. </p><p>Arbetet har bedrivits i AerotechTelubs regi i Linköping samt med hjälp ifrån företaget Sectra Wireless Technologies AB. Huvuddelen av arbetet inriktar sig på implementerandet av C-funktioner för att hantera kommunikationen och sammankopplandet av ett tidigare skapat system, för grafikvisning, med en transponder som hanterar ADS-B (tillverkad av Sectra). Målet med detta var att göra förberedande arbete åt AerotechTelub som de förhoppningsvis kommer att kunna använda i ett eventuellt kommande projekt. Rapporten tar upp några standarder som hör till konceptet GP&C (Global Positioning & Communication), samt beskriver de delar som ligger till grund för programmets funktion. </p><p>Examensarbetet har resulterat i ett demonstrationsprogram för att visa hur en lösning av problemet kan se ut. Det har tyvärr inte gått att säkerställa om programmet fungerar till fullo, men genom simuleringar och andra tester har huvuddelen av programmets funktioner gått att verifiera.</p>
160

Characterisation of a data transmission link / Characterisation of a data transmission link

Johansson, Christian, Karlsson, Marcus January 2004 (has links)
<p>This report is the result of a Master Thesis work that has been performed between October 2003 and March 2004. The purpose of the work was to evaluate a part of the signal chain in a product of Micronic Laser Systems AB. The evaluation was performed to obtain the characterisation for the signal chain, such as impedances and crosstalk. </p><p>The work started with a literature study in order to refresh and increase the knowledge that was needed before the practical work. Then measurements, computer aided simulations and comparisons between these were performed. </p><p>Measurements were performed using TDR (Time Domain Reflectometry). The results showed the impedance levels along the signal chain. This was interesting since it showed how well the different parts in the system are matched. Unmatched parts result in reflections that disturb the transmitted signal and contribute to crosstalk, which also was measured. </p><p>Simulations were done using ADS (Advance Design System), a tool from Agilent Technologies Inc. A substantial part of the simulation work was to build models of the real system. These models have been used for simulation. The simulation results were then compared to the measurement results. </p><p>The results show that the system can be better matched concerning the channel impedance. There are large variations in impedance levels along the signal chain, resulting in signal reflections. Another effect studied is crosstalk between channels. Measurements and simulations showed the presence of crosstalk but it seems to be a minor problem in the current machine.</p>

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