- 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.
Search results
Showing 301 to 310 of 312 (0.024 seconds)| 301 |
The Schur complement and H-matrix theory / Шуров комплемент и теорија Х-матрица / Šurov komplement i teorija H-matricaNedović Maja 19 October 2016 (has links)
<p>This thesis studies subclasses of the class of H-matrices and their applications, with<br />emphasis on the investigation of the Schur complement properties. The contributions<br />of the thesis are new nonsingularity results, bounds for the maximum norm of the<br />inverse matrix, closure properties of some matrix classes under taking Schur<br />complements, as well as results on localization and separation of the eigenvalues of<br />the Schur complement based on the entries of the original matrix.</p> / <p>Докторска дисертација изучава поткласе класе Х-матрица и њихове примене,<br />првенствено у истраживању својстава Шуровог комплемента. Оригиналан допринос<br />тезе представљају нови услови за регуларност матрица, оцене максимум норме<br />инверзне матрице, резултати о затворености појединих класа матрица на Шуров<br />комплемент, као и резултати о локализацији и сепарацији карактеристичних<br />корена Шуровог комплемента на основу елемената полазне матрице.</p> / <p>Doktorska disertacija izučava potklase klase H-matrica i njihove primene,<br />prvenstveno u istraživanju svojstava Šurovog komplementa. Originalan doprinos<br />teze predstavljaju novi uslovi za regularnost matrica, ocene maksimum norme<br />inverzne matrice, rezultati o zatvorenosti pojedinih klasa matrica na Šurov<br />komplement, kao i rezultati o lokalizaciji i separaciji karakterističnih<br />korena Šurovog komplementa na osnovu elemenata polazne matrice.</p>
|
| 302 |
Antenna Implants and Feasibility of Performance Limitations : AStudy of Radiation Efficiency on Electrically Small Antenna Implants with Finite Conductivity and Size / Antennimplantat och rimlighetsbedömning av dess prestandabegränsningar : En studie gällande effektivitet för elektriskt små antennimplant av realistisk konduktivitet och storlekAlgarp, Erik January 2022 (has links)
Antenna implants are used to establish a telemetry link to enable wireless data transfer, suitable for telemedicine and other medical applications. Inbody environments with water-based tissues lead to severe power absorption, making signal strength and radiation efficiency challenging yet central performance aspects of antenna implants. Fundamental performance limits exist regarding radiation efficiency; however, these limits consider theoretically ideal Hertzian dipoles. A semi-analytical model is used to evaluate the feasibility of previously determined fundamental bounds and the optimal dipole solution, both with respect to physical necessities of finite material conductivity and antenna size. This study uses a spherical model to represent a simplified in-body environment with various phantom compositions. Furthermore, the study focuses on implants operating within the Medical Implant Communication System (MICS) frequency band, but models and methods are not restricted to the considered frequency. The work contributes to the field of implantable antennas in several aspects; evaluating the feasibility of fundamental bounds, establishing more realistic performance limits, and determining the optimal dipole solution with respect to radiation efficiency. Other findings are presented in related areas, particularly concerning conductor loss and evaluation of the impedance for antennas inside a high-loss phantom. Moreover, the work presents a suggested method to measure electrically small magnetic dipole antennas. Methods and models are documented in a substantial theoretical derivation, and findings are verified using independent methods. Neglecting necessary antenna aspects like finite size and conductivity can lead to faulty conclusions on implant performance. Providing a more realistic performance target helps predict the performance of realistic antenna designs. Ultimately, increased knowledge of implanted antennas simplifies the design process to achieve high-performance implants. / Antennimplant används för att etablera en telemetrilänk som möjliggör trådlös dataöverföring, exempelvis användbart inom telemedicin och andra medicinska tillämpningar. Vattenbaserade kroppsmiljöer resulterar i kraftig absorption, vilket implicerar att signalstyrka samt strålningseffektivit blir utmanande men även centrala prestanda egenskaper för antennimplnatat. Det existerar fundamentala prestandabegränsningar för strålningseffektivitet, men dessa gränser är etablerade med hänsyn till teoretiskt ideala elementära dipoler. En semi-analytisk modell används för att utvärdera rimligheten av tidigare begränsningar samt den optimala dipolen, bägge med hänsyn till nödvändiga aspekter som ändlig konduktivitet och antennstorlek. Denna studie använder en sfärisk modell för att representera en simplifierad kroppslig miljö med olika vävnadskompositioner. Studien fokuserar på antennimplantat inom frekvensbandet dedikerat för Medical Implant Communication System (MICS) enheter, men modeller och metoder är typiskt inte begränsade inom omnämnt band. Arbetet bidrar till området för implanterbara antenner i flera aspekter; att utvärdera rimligheten av fundamentala gränser, fastställa mer realistiska prestandagränser samt bestämma den optimala dipolen med avseende på strålningseffektivitet. Andra resultat presenteras inom relaterade aspekter som metallförlust och utvärdering av en antenns last eller ingångs impedans inuti sfäriska och kroppsliga miljöer. Dessutom presenteras en metod för att mäta elektriskt små magnetiska dipoler. Metoder och modeller är dokumenterade eller demonstrerade via härledning, och centrala resultat har verifieras med oberoende metoder. Att förbise nödvändiga aspekter som ändlig storlek och konduktivitet kan leda till felaktiga slutsatser gällande prestanda. Däremot, att fastställa en mer realistisk gräns bidrar till att förutsäga prestandan i realistiska tillämpningar. I slutändan så resulterar ökad kunskap i en simplifierad designprocess som underlättar i strävan till att uppnå högpresterande antennimplantat.
|
| 303 |
A practical-theological investigation of the nineteenth and twentieth century "faith theologies"King, Paul Leslie 11 1900 (has links)
This thesis is a study of nineteenth and twentieth century faith theology and praxis, seeking to
determine a balanced, healthy faith that is both sound in theology and effective in practice, Part
1 presents a history and sources of Faith Teaching and Practices. It first looks
historically at the roots of later faith teaching and practice by presenting a sampling of
teachings on faith from early church fathers, reformers, mystics, and Pietists. These form the
foundation for the movements of faith in the nineteenth and early twentieth centuries-the classic
faith teaching, followed by the modern faith movement and leaders.
Part 2 deals with the foundational issues of faith teaching and practice: the relationship of faith
to the supernatural, the concept of the inheritance of the believer and the practice of claiming
the promises of God, the nature of faith, and the authority of the believer and its inferences for
faith praxis.
Part 3 investigates seven major theological issues of faith teaching and practice: faith as a law
and force, the object and source of faith, the relationship of faith and the will of God,
distinguishing between a logos and a rhema word of God, the concepts of revelation and
sense knowledge, the doctrine of healing in the atonement, the question of evidence of the baptism
in the Holy Spirit.
Part 4 examines major practical issues of faith teaching and practice about which controversy
swirls: positive mental attitude and positive confession; issues of discernment in acting upon
impressions, voices, revelations, and "words from the Lord;" questions of faith regarding sickness
and healing, death, doctors and medicine; the relationships between sickness, suffering, healing,
and sanctification; and prosperity.
Part 5 reflects upon these issues and comes to final conclusions regarding: the role of
hermeneutics in determining faith theology and praxis, how to handle unanswered prayers and
apparent failures of faith, the seeming paradox and tension between claiming one's inheritance and dying to self, a summary of practical conclusions for exercise of healthy faith, and final conclusions and recommendations on developing a sound theology and practice of faith for the twenty-first century. / Philosophy, Practical & Systematic Theology / D.Th. (Practical Theology)
|
| 304 |
Stabilised finite element approximation for degenerate convex minimisation problemsBoiger, Wolfgang Josef 19 August 2013 (has links)
Infimalfolgen nichtkonvexer Variationsprobleme haben aufgrund feiner Oszillationen häufig keinen starken Grenzwert in Sobolevräumen. Diese Oszillationen haben eine physikalische Bedeutung; Finite-Element-Approximationen können sie jedoch im Allgemeinen nicht auflösen. Relaxationsmethoden ersetzen die nichtkonvexe Energie durch ihre (semi)konvexe Hülle. Das entstehende makroskopische Modell ist degeneriert: es ist nicht strikt konvex und hat eventuell mehrere Minimalstellen. Die fehlende Kontrolle der primalen Variablen führt zu Schwierigkeiten bei der a priori und a posteriori Fehlerschätzung, wie der Zuverlässigkeits- Effizienz-Lücke und fehlender starker Konvergenz. Zur Überwindung dieser Schwierigkeiten erweitern Stabilisierungstechniken die relaxierte Energie um einen diskreten, positiv definiten Term. Bartels et al. (IFB, 2004) wenden Stabilisierung auf zweidimensionale Probleme an und beweisen dabei starke Konvergenz der Gradienten. Dieses Ergebnis ist auf glatte Lösungen und quasi-uniforme Netze beschränkt, was adaptive Netzverfeinerungen ausschließt. Die vorliegende Arbeit behandelt einen modifizierten Stabilisierungsterm und beweist auf unstrukturierten Netzen sowohl Konvergenz der Spannungstensoren, als auch starke Konvergenz der Gradienten für glatte Lösungen. Ferner wird der sogenannte Fluss-Fehlerschätzer hergeleitet und dessen Zuverlässigkeit und Effizienz gezeigt. Für Interface-Probleme mit stückweise glatter Lösung wird eine Verfeinerung des Fehlerschätzers entwickelt, die den Fehler der primalen Variablen und ihres Gradienten beschränkt und so starke Konvergenz der Gradienten sichert. Der verfeinerte Fehlerschätzer konvergiert schneller als der Fluss- Fehlerschätzer, und verringert so die Zuverlässigkeits-Effizienz-Lücke. Numerische Experimente mit fünf Benchmark-Tests der Mikrostruktursimulation und Topologieoptimierung ergänzen und bestätigen die theoretischen Ergebnisse. / Infimising sequences of nonconvex variational problems often do not converge strongly in Sobolev spaces due to fine oscillations. These oscillations are physically meaningful; finite element approximations, however, fail to resolve them in general. Relaxation methods replace the nonconvex energy with its (semi)convex hull. This leads to a macroscopic model which is degenerate in the sense that it is not strictly convex and possibly admits multiple minimisers. The lack of control on the primal variable leads to difficulties in the a priori and a posteriori finite element error analysis, such as the reliability-efficiency gap and no strong convergence. To overcome these difficulties, stabilisation techniques add a discrete positive definite term to the relaxed energy. Bartels et al. (IFB, 2004) apply stabilisation to two-dimensional problems and thereby prove strong convergence of gradients. This result is restricted to smooth solutions and quasi-uniform meshes, which prohibit adaptive mesh refinements. This thesis concerns a modified stabilisation term and proves convergence of the stress and, for smooth solutions, strong convergence of gradients, even on unstructured meshes. Furthermore, the thesis derives the so-called flux error estimator and proves its reliability and efficiency. For interface problems with piecewise smooth solutions, a refined version of this error estimator is developed, which provides control of the error of the primal variable and its gradient and thus yields strong convergence of gradients. The refined error estimator converges faster than the flux error estimator and therefore narrows the reliability-efficiency gap. Numerical experiments with five benchmark examples from computational microstructure and topology optimisation complement and confirm the theoretical results.
|
| 305 |
A practical-theological investigation of the nineteenth and twentieth century "faith theologies"King, Paul Leslie 11 1900 (has links)
This thesis is a study of nineteenth and twentieth century faith theology and praxis, seeking to
determine a balanced, healthy faith that is both sound in theology and effective in practice, Part
1 presents a history and sources of Faith Teaching and Practices. It first looks
historically at the roots of later faith teaching and practice by presenting a sampling of
teachings on faith from early church fathers, reformers, mystics, and Pietists. These form the
foundation for the movements of faith in the nineteenth and early twentieth centuries-the classic
faith teaching, followed by the modern faith movement and leaders.
Part 2 deals with the foundational issues of faith teaching and practice: the relationship of faith
to the supernatural, the concept of the inheritance of the believer and the practice of claiming
the promises of God, the nature of faith, and the authority of the believer and its inferences for
faith praxis.
Part 3 investigates seven major theological issues of faith teaching and practice: faith as a law
and force, the object and source of faith, the relationship of faith and the will of God,
distinguishing between a logos and a rhema word of God, the concepts of revelation and
sense knowledge, the doctrine of healing in the atonement, the question of evidence of the baptism
in the Holy Spirit.
Part 4 examines major practical issues of faith teaching and practice about which controversy
swirls: positive mental attitude and positive confession; issues of discernment in acting upon
impressions, voices, revelations, and "words from the Lord;" questions of faith regarding sickness
and healing, death, doctors and medicine; the relationships between sickness, suffering, healing,
and sanctification; and prosperity.
Part 5 reflects upon these issues and comes to final conclusions regarding: the role of
hermeneutics in determining faith theology and praxis, how to handle unanswered prayers and
apparent failures of faith, the seeming paradox and tension between claiming one's inheritance and dying to self, a summary of practical conclusions for exercise of healthy faith, and final conclusions and recommendations on developing a sound theology and practice of faith for the twenty-first century. / Philosophy, Practical and Systematic Theology / D.Th. (Practical Theology)
|
| 306 |
Estimation de canal à évanouissements plats dans les transmissions sans fils à relais multibonds / Flat fading channel estimation for multihop relay wireless transmissionsGhandour-Haidar, Soukayna 12 December 2014 (has links)
Cette thèse traite de l'estimation d'un canal de communication radio-mobile multi-bond. La communication entre l'émetteur et le récepteur est ainsi faite par l'intermédiaire de relais (de type « Amplify and-Forward ») en série. Les différents éléments (émetteurs, relais, récepteurs) peuvent être fixes ou mobiles. Chaque lien de communication (chaque bond) est modélisé par un canal de Rayleigh à évanouissements plats, avec un spectre Doppler issu de deux environnements possibles de diffusion : en deux dimensions (2D, amenant le spectre en U de Jakes), ou en trois dimensions (3D, amenant un spectre Doppler plat). L'objectif majeur de la thèse est l'estimation dynamique du canal global issue de la cascade des différents liens. A cette fin, la cascade de canaux est approchée par une modèle auto-régressif du premier ordre (AR (1)), et l'estimation est réalisée à l'aide d'un algorithme standard, le filtre de Kalman. La méthode couramment utilisée dans la littérature pour fixer le paramètre du modèle AR(1) est basée sur un critère de « corrélation matching » (CM). Cependant, nous montrons que pour des canaux à variations lentes, un autre critère basé sur la minimisation de la variance asymptotique (MAV) de la sortie du filtre de Kalman est plus approprié. Pour les deux critères, CM et MAV, cette thèse donne une justification analytique en fournissant des formules approchées de la variance d'estimation par le filtre de Kalman, ainsi que du réglage optimal du paramètre du modèle AR(1). Ces formules analytiques sont données en fonctions des fréquences Doppler et du rapport signal sur bruit, pour les environnements de diffusion 2D et 3D, quel que soit le nombre et le type de bonds (fixe-mobile ou mobile-mobile). Les résultats de simulations montrent un gain considérable en termes de l'erreur quadratique moyenne (MSE) de l'estimateur de canal bien réglé, en particulier pour le scénario le plus courant de canal à évanouissements lents. / This thesis deals with the estimation of the multihop Amplify-and-Forward relay communications. The various objects (transmitter, relays, receivers) can be fixed or mobile. Each link is modeled by a flat fading Rayleigh channel, with a Doppler spectrum resulting from two-dimensional (2D, leading to the U-shape Dopller spectrum) or three-dimensional (3D, leading to a flat Doppler spectrum) scattering environments. The cascade of channel hops is approximated by a first-order autoregressive (AR(1)) model and is tracked by a standard estimation algorithm, the Kalman Filter (KF). The common method used in the literature to tune the parameter of the AR(1) model is based on a Correlation Matching (CM) criterion. However, for slow fading variations, another criterion based on the off-line Minimization of the Asymptotic Variance (MAV) of the KF is shown to be more appropriate. For both the CM and MAV criteria, this thesis gives analytic justification by providing approximated closed-form expressions of the estimation variance in output of the Kalman filter, and of the optimal AR(1) parameter. The analytical results are calculated for given Doppler frequencies and Signal-to-Noise Ratio for both scattering environments, whatever the number and type of transmission hops (Fixed-to-Mobile or Mobile-to-Mobile). The simulation results show a considerable gain in terms of the Mean Square Error (MSE) of the well tuned Kalman-based channel estimator, especially for the most common scenario of slow-fading channel.
|
| 307 |
Automaty v rozhodovacích procedurách a výkonnostní analýze / Automata in Decision Procedures and Performance AnalysisFiedor, Tomáš Unknown Date (has links)
Tato práce se věnuje vylepšení současného stavu formalní analýzy a verifikace založené na automatech a zaměřené na systémy s nekonečnými stavovými prostory. V první části se práce zabývá dvěma rozhodovacími procedurami pro logiku WS1S, které jsou založené na korespondenci mezi formulemi logiky WS1S a konečnými automaty. První metoda je založena na tzv. antiřetězcích, ale, je limitována pouze na formule v prenexním normálním tvaru. Následně je tento přístup zobecněn na libovolné formule, jsou zavedeny tzv. jazykové termy a na jejich základě je navržena nová procedura, která pracuje za běhu a zpracovává tyto termy "líným" způsobem. Abychom získali efektivní rozhodovací proceduru, je dále navržena sada optimalizací (přičemž některé nejsou limitovány pouze pro naše přístupy). Obě metody jsou srovnány s ostatními nástroji implementujícími různé známé rozhodovací procedury. Získané výsledky jsou povzbuzující a ukazují, že použitelnost logiky WS1S je možno rozšířit na širší třídu formulí. V druhé části se práce zabývá analýzou mezí zdrojů programů manipulujících s haldou. Je zde navržena nová třída tzv. tvarových norem založených na délkách cest mezi význačnými místy na haldě, které jsou automaticky odvozovány z analyzovaného programu. Na základě této třídy norem je dále navržen kalkul, který je schopen přesně odvodit změny odvozených normů a použít je k vygenerování odpovídající celočíselné reprezentace vstupního programu, která je následně využita pro následovanou dedikovanou analýzou mezí zdrojů. Tato metoda byla implementována nad analýzou tvaru založenou na tzv. lesních automatech, implementovanou v nástroji Forester, a dále byl použit dobře zavedený analyzátor mezí zdrojů, implementovaný v nástroji Loopus. V experimentální evaluaci bylo ukázáno, že je opravdu takto získán silný analyzátor, který je schopen odvodit meze programů, které ještě nikdy plně automatizovaně odvozené nebyly.
|
| 308 |
Direct guaranteed lower eigenvalue bounds with quasi-optimal adaptive mesh-refinementPuttkammer, Sophie Louise 19 January 2024 (has links)
Garantierte untere Eigenwertschranken (GLB) für elliptische Eigenwertprobleme partieller Differentialgleichungen sind in der Theorie sowie in praktischen Anwendungen relevant. Auf Grund des Rayleigh-Ritz- (oder) min-max-Prinzips berechnen alle konformen Finite-Elemente-Methoden (FEM) garantierte obere Schranken. Ein Postprocessing nichtkonformer Methoden von Carstensen und Gedicke (Math. Comp., 83.290, 2014) sowie Carstensen und Gallistl (Numer. Math., 126.1, 2014) berechnet GLB. In diesen Schranken ist die maximale Netzweite ein globaler Parameter, das kann bei adaptiver Netzverfeinerung zu deutlichen Unterschätzungen führen. In einigen numerischen Beispielen versagt dieses Postprocessing für lokal verfeinerte Netze komplett. Diese Dissertation präsentiert, inspiriert von einer neuen skeletal-Methode von Carstensen, Zhai und Zhang (SIAM J. Numer. Anal., 58.1, 2020), einerseits eine modifizierte hybrid-high-order Methode (m=1) und andererseits ein allgemeines Framework für extra-stabilisierte nichtkonforme Crouzeix-Raviart (m=1) bzw. Morley (m=2) FEM. Diese neuen Methoden berechnen direkte GLB für den m-Laplace-Operator, bei denen eine leicht überprüfbare Bedingung an die maximale Netzweite garantiert, dass der k-te diskrete Eigenwert eine untere Schranke für den k-ten Dirichlet-Eigenwert ist. Diese GLB-Eigenschaft und a priori Konvergenzraten werden für jede Raumdimension etabliert. Der neu entwickelte Ansatz erlaubt adaptive Netzverfeinerung, die für optimale Konvergenzraten auch bei nichtglatten Eigenfunktionen erforderlich ist. Die Überlegenheit der neuen adaptiven FEM wird durch eine Vielzahl repräsentativer numerischer Beispiele illustriert. Für die extra-stabilisierte GLB wird bewiesen, dass sie mit optimalen Raten gegen einen einfachen Eigenwert konvergiert, indem die Axiome der Adaptivität von Carstensen, Feischl, Page und Praetorius (Comput. Math. Appl., 67.6, 2014) sowie Carstensen und Rabus (SIAM J. Numer. Anal., 55.6, 2017) verallgemeinert werden. / Guaranteed lower eigenvalue bounds (GLB) for elliptic eigenvalue problems of partial differential equation are of high relevance in theory and praxis. Due to the Rayleigh-Ritz (or) min-max principle all conforming finite element methods (FEM) provide guaranteed upper eigenvalue bounds. A post-processing for nonconforming FEM of Carstensen and Gedicke (Math. Comp., 83.290, 2014) as well as Carstensen and Gallistl (Numer. Math., 126.1,2014) computes GLB. However, the maximal mesh-size enters as a global parameter in the eigenvalue bound and may cause significant underestimation for adaptive mesh-refinement. There are numerical examples, where this post-processing on locally refined meshes fails completely. Inspired by a recent skeletal method from Carstensen, Zhai, and Zhang (SIAM J. Numer. Anal., 58.1, 2020) this thesis presents on the one hand a modified hybrid high-order method (m=1) and on the other hand a general framework for an extra-stabilized nonconforming Crouzeix-Raviart (m=1) or Morley (m=2) FEM. These novel methods compute direct GLB for the m-Laplace operator in that a specific smallness assumption on the maximal mesh-size guarantees that the computed k-th discrete eigenvalue is a lower bound for the k-th Dirichlet eigenvalue. This GLB property as well as a priori convergence rates are established in any space dimension. The novel ansatz allows for adaptive mesh-refinement necessary to recover optimal convergence rates for non-smooth eigenfunctions. Striking numerical evidence indicates the superiority of the new adaptive eigensolvers. For the extra-stabilized nonconforming methods (a generalization of) known abstract arguments entitled as the axioms of adaptivity from Carstensen, Feischl, Page, and Praetorius (Comput. Math. Appl., 67.6, 2014) as well as Carstensen and Rabus (SIAM J. Numer. Anal., 55.6, 2017) allow to prove the convergence of the GLB towards a simple eigenvalue with optimal rates.
|
| 309 |
The relative impact of public and private investment on economic growth: the tale of four Southern African economiesMakuyana, Garikai 11 1900 (has links)
The study has empirically examined the relative impact of public and private investment on economic growth and has also tested the crowding in or crowding out effect of public investment on private investment in four Southern African economies – Malawi, South Africa, Zambia and Zimbabwe. The analysis used annual time-series data covering the period from 1970 to 2014. The study provides new evidence to contribute firstly to the current debate regarding the relative importance of public and private investment in economic growth processes and secondly, on whether public investment crowds in or crowds out private investment in the selected countries. For this purpose, the study employed two empirical models using the recently developed Autoregressive Distributed Lag (ARDL)-bounds testing approach to cointegration. Model 1 examines the relative impact of public and private investment on economic growth while Model 2 investigates the crowding in or crowding out effect of gross public investment and its subcomponents (infrastructural and non-infrastructural) on private investment. The results of Model 1 largely supported the private investment-led economic growth strategy. In all the study countries, private investment had a positive impact on economic growth. Also, public investment positively contributed to economic growth in Zimbabwe, but in the remaining study countries, public investment had a negative relationship with economic growth. Results from Model 2 reveal that: (i) the crowding out effect of gross public investment on private investment predominates in the study countries; (ii) infrastructural public investment crowds in private investment in South Africa and Zimbabwe in the long run while it crowds out private investment in Malawi and Zambia in the short run; and (iii) non-infrastructural public investment crowds out private investment in South Africa and Zambia. On balance, the results from Model 2 show that public investment tends to crowd out private investment in the selected countries and this further underscore the importance of the private sector-led economic growth processes in the study countries. / Economics / D. Phil. (Economics)
|
| 310 |
Temporal Variations in the Compliance of Gas Hydrate FormationsRoach, Lisa Aretha Nyala 20 March 2014 (has links)
Seafloor compliance is a non-intrusive geophysical method sensitive to the shear modulus of the sediments below the seafloor. A compliance analysis requires the computation of the frequency dependent transfer function between the vertical stress, produced at the seafloor by the ultra low frequency passive source-infra-gravity waves, and the resulting displacement, related to velocity through the frequency. The displacement of the ocean floor is dependent on the elastic structure of the sediments and the compliance function is tuned to different depths, i.e., a change in the elastic parameters at a given depth is sensed by the compliance function at a particular frequency. In a gas hydrate system, the magnitude of the stiffness is a measure of the quantity of gas hydrates present. Gas hydrates contain immense stores of greenhouse gases making them relevant to climate change science, and represent an important potential alternative source of energy. Bullseye Vent is a gas hydrate system located in an area that has been intensively studied for over 2 decades and research results suggest that this system is evolving over time.
A partnership with NEPTUNE Canada allowed for the investigation of this possible evolution. This thesis describes a compliance experiment configured for NEPTUNE Canada’s seafloor observatory and its failure. It also describes the use of 203 days of simultaneously logged pressure and velocity time-series data, measured by a Scripps differential pressure gauge, and a Güralp CMG-1T broadband seismometer on NEPTUNE Canada’s seismic station, respectively, to evaluate variations in sediment stiffness near Bullseye. The evaluation resulted in a (- 4.49 x10-3± 3.52 x 10-3) % change of the transfer function of 3rd October, 2010 and represents a 2.88% decrease in the stiffness of the sediments over the period. This thesis also outlines a new algorithm for calculating the static compliance of isotropic layered sediments.
|
Page generated in 0.0524 seconds