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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.
501

On the Variability of Pacific Ocean Tides at Seasonal to Decadal Time Scales: Observed vs Modelled

Devlin, Adam Thomas 17 May 2016 (has links)
Ocean tides worldwide have exhibited secular changes in the past century, simultaneous with a global secular rise in mean sea level (MSL). The combination of these two factors contributes to higher water levels, and may increase threats to coastal regions and populations over the next century. Equally as important as these long-term changes are the short-term fluctuations in sea levels and tidal properties. These fluctuations may interact to yield locally extreme water level events, especially when combined with storm surge. This study, presented in three parts, examines the relationships between tidal anomalies and MSL anomalies on yearly and monthly timescales, with a goal of diagnosing dynamical factors that may influence the long-term evolution of tides in the Pacific Ocean. Correlations between yearly averaged properties are denoted tidal anomaly trends (TATs), and will be used to explore interannual behavior. Correlations of monthly averaged properties are denoted seasonal tidal anomaly trends (STATs), and are used to examine seasonal behavior. Four tidal constituents are analyzed: the two largest semidiurnal (twice daily) constituents, M2 and S2, and the two largest diurnal (once daily) constituents, K1 and O1. Part I surveys TATs and STATs at 153 Pacific Ocean tide gauges, and discusses regional patterns within the entire Pacific Ocean. TATs with statistically significant relations between MSL and amplitudes (A-TATs) are seen at 89% of all gauges; 92 gauges for M2, 66 for S2, 82 for K1, and 59 for O1. TATs with statistically significant relations between tidal phase (the relative timing of high water of the tide) and MSL (P-TATs) are observed at 55 gauges for M2, 47 for S2, 42 for K1, and 61 for O1. Significant seasonal variations (STATs) are observed at about a third of all gauges, with the largest concentration in Southeast Asia. The effect of combined A-TATs was also considered. At selected stations, observed tidal sensitivity with MSL was extrapolated forward in time to the predicted sea level in 2100. Results suggest that stations with large positive combined A-TATs produce total water levels that are greater than those predicted by an increase in MSL alone, increasing the chances of high-water events. Conversely, negative correlation between sea level and tidal properties may mitigate somewhat against sea level rise; changes in total water levels in 2100 at stations with a negative combined A-TAT are less than that predicted by MSL rise alone. Climate change scenarios that take into account greater increases in MSL due to increased Antarctic ice melt show larger changes in total water levels over the same time period. Part II examines the mechanisms behind the yearly (TAT) variability in the Western Tropical Pacific Ocean. Significant amplitude TATs are found at more than half of 26 gauges for each of the two strongest tidal constituents, K1 (diurnal) and M2 (semidiurnal). For the lesser constituents analyzed (O1 and S2), significant trends are observed at ten gauges. Frictional mechanisms related to the El Nino Southern Oscillation (ENSO) are found to be important in influencing tides in the Western Pacific, as well as resonant triad interactions, a nonlinear coupling that exchanges energy between the M2, K1, and O1 tides. Both of these factors contribute to the observed tidal variability in the Solomon Sea region. Part III analyzes the seasonal behavior of tides (STATs) at twenty tide gauges in the Southeast Asian waters, which exhibit variation by 10-30% of mean tidal amplitudes. A barotropic ocean tide model that considers the seasonal effects of MSL, stratification, and geostrophic and Ekman velocity is used to explain the observed seasonal variability in tides due to variations in monsoon-influenced climate forcing, with successful results at about half of all gauges. The observed changes in tides are best explained by the influence of non-tidal velocities (geostrophic and Ekman), though the effect of changing stratification is also an important secondary causative mechanism. From the results of these surveys and investigations, it is concluded that short-term fluctuations in MSL and tidal properties at multiple time scales may be as important in determining the state of future water levels as the long-term trends. Global explanations for the observed tidal behavior have not been found in this study; however, significant regional explanations are found at the yearly time scale in the Solomon Sea, and at the seasonal time scale in Southeast Asia. It is likely that tidal sensitivity to annual and seasonal variations in MSL at other locations also are driven by locally specific processes, rather than factors with basin-wide coherence.
502

Three-dimensional tide and surge modelling and layered particle tracking techniques applied to Southern Australian coastal seas

Grzechnik, Marcus Paul January 2000 (has links)
This thesis reports the development, testing, and application of computer programs for simulating Lagrangian-Stochastic particle dispersion in coastal seas, with particular application to tide and storm induced dispersion in South Australian seas. The three-dimensional tidal equations are briefly discussed for the two types of surge models used, and finite-difference methods for numerically solving these equations are considered. Different methods of simulating flows at open sea boundaries are investigated. The method of particle tracking and the development of the particle tracking model is also described. Various tests are conducted to investigate both the advective and diffusive aspects of dispersion, and a number of scenarios for the simulation of open (ocean) and closed (coastal) boundaries are considered. Various aspects of the particle tracking routine are given specific characteristics according to the nature of the particle being considered. Application of the tide and storm surge model to the Great Australian Bight is described. This uses spherical polar co-ordinates to account for the curvature of the earth, and an oblique boundary element to increase accuracy of the coastline representation. The effect of a low pressure system moving from west to east across the Bight and the resulting significant observed surge at Thevenard during the storm of April 1996 is simulated. This storm resulted in a significant number of deaths in aquaculture farms containing southern bluefin tuna (Thunnas maccoyii) within the Boston Bay region to the extreme east of the Bight due to the agitation of almost neutrally buoyant organic sediments at the sea floor. The effects of this storm are further considered using a Cartesian co-ordinate fine-grid local model of Boston Bay, in Spencer Gulf, South Australia, where both tidal and storm (wind and outside surge) induced flows are simulated. The dispersion of suspended neutrally buoyant sediment throughout the region is considered, and compared with the mortalities of tuna at various farms within the region. Tidal and storm induced currents in the Gulf St. Vincent region, South Australia, have also been modelled using Cartesian co-ordinates. Detailed consideration has been given to the modelling of tides, winds, atmospheric pressures and outside surges from the two open boundaries in Investigator Strait and Backstairs Passage. The information obtained has enabled the modelling of a number of storm surge scenarios. Further to this, various simulations of the dispersion of the larvae of the western king prawn (Penaeus latisulcatus) have been driven using the storm surge model developed. These incorporate currents near the surface and the sea floor, as well as the consideration of changes in behaviour during the life history of the larvae. / Thesis (Ph.D.)--Engineering, Computer and Mathematical Sciences, 2000.
503

Relations architecturales, faciologiques et diagénétiques des carbonates bioclastiques du bassin miocène rhodano-provençal (SE France)

Descote, Pierre-Yves 02 July 2010 (has links) (PDF)
Situé dans le domaine périalpin à moyenne paléolatitude, le Bassin Molassique Rhodano-Provençal enregistre durant le Miocène, une sédimentation bioclastique particulière. Ces séries miocènes sont caractérisées par un réseau de vallées incisées. Cette thèse se fonde sur l'analyse des séries affleurant dans les secteurs de Vénasque (Aquitanien-Langhien) et de Martigues (Aquitanien-Tortonien). L'objectif est d'étudier les corps bioclastiques (pétrographie, architecture sédimentaire, environnements de dépôt et diagenèse) afin de déterminer leur potentiel pétrolier. Après la formation de vallées fluviatiles en bas niveau marin, les sédiments déposés sont dominés par une dynamique tidale strictement sous aquatique. Ils peuvent être séparés en deux groupes : les intervalles bioclastiques et les intervalles marneux, respectivement transgressifs et de haut niveau marin. Les corps bioclastiques présentent le meilleur potentiel réservoir mais sont caractérisés par une forte hétérogénéité interne. Cette hétérogénéité résulte d'une combinaison de facteurs hydrodynamiques, écologiques et diagénétiques associés aux cycles tectono-eustatiques. L'établissement d'un schéma séquentiel précis en relation avec la diagénèse permet de caractériser le potentiel des réservoirs bioclastiques confinés dans des vallées sous-marines. Les dépôts du Miocène rhodanien constituent un analogue terrain exceptionnel pour la compréhension des réservoirs actuellement impliqués dans des systèmes pétroliers.
504

Impact des marées sur la circulation générale océanique dans une perspective climatique

Bessières, Laurent 30 March 2007 (has links) (PDF)
La marée océanique a longtemps été considérée comme un phénomène haute fréquence dont la zone d'influence se limitait aux plateaux continentaux. Ainsi, la marée n'apparaissait pas susceptible d'interagir sur la circulation océanique grande échelle et in fine sur la dynamique basse fréquence du climat. Ce n'est qu'à la fin des années 1990, lorsque la mesure altimétrique et les solutions hydrodynamiques globales de marées ont atteint une précision centimétrique, qu'une connexion entre les marées et le climat est devenue envisageable. Dans cette perspective, l'objectif de cette étude est d'explorer quels sont les effets de la marée sur la circulation océanique grande échelle. Ces effets ont lieu à travers deux processus physiques essentiels liés à la marée : (i) sa dynamique fortement non-linéaire et (ii) la dissipation de son énergie en plein océan, sous la forme de mélange vertical ou de chaleur.<br />Pour examiner chacun de ces aspects, la méthode retenue consiste à paramétriser les effets de la marée dans un modèle tridimensionnel de circulation générale océanique (OGCM) dédié au climat : NEMO. Pour ce faire nous utilisons les sorties 'off line' d'un modèle hydrodynamique bidimensionnel dédié à la marée : MOG2D-G. Dans un premier temps nous déterminons et nous décrivons pour la première fois une carte de la circulation résiduelle de marée (CRM) mondiale générée par la dynamique non-linéaire de la marée. Cette CRM obtenue par l'intermédiaire de MOG2D-G est alors introduite sous la forme d'un forçage extérieur dans l'OGCM NEMO. Dans un second temps, nous examinons la dissipation de l'énergie des marées. Tout d'abord nous quantifions la fraction de l'énergie de marée qui est dissipée en chaleur, ceci afin de déterminer si, à l'instar du flux géothermal, elle est susceptible de jouer un rôle important sur la circulation abyssale. Après avoir écarté cette possibilité, nous considérons la fraction d'énergie de marée qui se dissipe localement en mélange vertical via les ondes internes : le "tidal mixing" (TM). Le TM résulte d'un transfert d'énergie du mode barotope vers les modes baroclines. Ce transfert est diagnostiqué grâce au modèle MOG2D-G et intégré dans NEMO par l'intermédiaire d'une paramétrisation du mélange turbulent vertical.<br />Nous concluons : (i) que l'effet des marées sur la circulation océanique grande échelle et in fine sur le climat ne peut être significatif qu'à travers le TM, (ii) que l'introduction du TM local dans les OGCM est essentielle pour représenter correctement le transport des masses d'eaux abyssales et (iii) qu'il est désormais crucial de considérer le TM engendré loin du site de génération des ondes internes
505

Patterns in the larval vertical distribution of marine benthic invertebrates in a shallow coastal embayment

Lloyd, Michelle 20 September 2011 (has links)
Processes during the meroplanktonic phase regulate population dynamics for many marine benthic invertebrates. I examined changes in vertical distribution of different meroplanktonic larvae in a coastal embayment during a stable period, at high temporal frequencies and spatial resolutions. Plankton samples were collected at 6 depths (3, 6, 9, 12, 18, 24 m) using a pump, every 2-h over a 36- and a 25-h period, during a spring and neap tide, respectively, concurrently with measures of temperature, salinity, fluorescence and current velocity. For 10 gastropod taxa, larval vertical distribution was mostly related to the thermal structure of the water column. Each of 7 taxonomic groups was found either exclusively near the surface, associated with the fluorescence maximum, or showed diel changes in distribution. These larvae that occupy different depths in the water column exhibit different dispersal potentials. / Biogeographical data contained in this thesis will be submitted to the Oceanographic Biogeographic Information System (OBIS) and may be accessed on-line at http://www.iobis.org
506

Effects of tidal bores on turbulent mixing : a numerical and physical study in positive surges

Simon, Bruno 24 October 2013 (has links) (PDF)
Tidal bores are surge waves propagating upstream rivers as the tide rushes into estuaries. They induce large turbulences and mixing of the river and estuary flow of which effects remain scarcely studied. Herein, tidal bores are investigated experimentally and numerically with an idealised model of positive surges propagating upstream an initially steady flow. The experimental work estimated flow changes and typical turbulent length scale evolution induced by undular bores with and without breaking roller. The bore passage was associated with large free surface and flow velocity fluctuations, together with some variations of the integral turbulent scales. Coherent turbulent structures appeared in the wake of leading wave near the bed and moved upward into the water column during the bore propagation. The numerical simulations were based on previous experimental work on undular bores. Some test cases were realised to verify the accuracy of the numerical methods. The results gave access to the detailed flow evolution during the bore propagation. Large velocity reversals were observed close to the no-slip boundaries. In some configurations, coherent turbulent structures appeared against the walls in the wake of the bore front.
507

Elemental abundance investigation of two candidate extragalactic globular clusters (NGC 5024, NGC 5466)

Chutter, Ashley 27 March 2009 (has links)
High resolution spectra have been analyzed for two and three stars respectively in the candidate extragalactic globular clusters, NGC 5024 and NGC 5466, with the High-Resolution Spectrograph on the 9.2 m Hobby-Eberly Telescope. The goal of this investigation is to evaluate the proposed extragalactic origins of these two globular clusters. Evidence of a tidal tail in NGC 5466 (Belokurov et al., 2006) and the association of NGC 5024 with the Sagittarius stream (Martinez-Delgado et al., 2004) targeted the clusters as likely remnants of recent accretion events and thus potentially of extragalactic origin. Determination of their chemical abundance patterns could provide unique evidence to either support or dispute these claims. NGC 5024 has been associated with a proposed wrap in the Sagittarius stream which could be supported if the chemistry of NGC 5024 is similar to other clusters associated with the stream. NGC 5466 has the longest tidal tail known, which hints at an origin in a now dispersed dwarf spheroidal galaxy. Additional evidence for these clusters' capture origins has been compiled by Yoon & Lee (2002), demonstrating that these two low metallicity clusters, along with five others, are aligned in a single highly inclined plane in the outer halo. Confirmation that these clusters are remnants of dwarf galaxies would support a Galactic history which includes recent accretion events. Such evidence may bolster the cold dark matter hierarchical clustering scenario, which postulates the presence of a significant amount of substructure in the Milky Way. Unfortunately, at the metallicity of the target clusters ([Fe/H] = -1.9), the chemical distinction between Galactic stars and known dSph stars is not significant. The low [alpha/Fe] of dSph stars seen at higher metallicity is not apparent at [Fe/H] = -1.9 in either Galactic or dSph stars. Aside from a few mild discrepancies, NGC 5024 and NGC 5466 appear chemically similar to the Galactic field stars and globular clusters compiled by Pritzl et al. (2005). A moderate enhancement in the [Ba/Y] ratios relative to the halo field stars is the only positively detected chemical signature that is typically observed in dSph stars. Comparisons with Galactic GCs of similar age, metallicity and horizontal branch morphology (NGC 2298, NGC 6397 and NGC 5897) reveal a few other differences, but these could be attributed to systematic effects in the different analysis techniques. Although NGC 5024 has a similar metallicity to the GC Arp 2 that was stripped from the merging Sagittarius dwarf, neither Arp 2 (Mottini et al., 2008) nor the clusters in this study show any particularly unusual chemical abundance patterns. Thus, no conclusive evidence in support of or in opposition to the target clusters' proposed extragalactic origins has been discovered.
508

Three-dimensional tide and surge modelling and layered particle tracking techniques applied to Southern Australian coastal seas

Grzechnik, Marcus Paul January 2000 (has links)
This thesis reports the development, testing, and application of computer programs for simulating Lagrangian-Stochastic particle dispersion in coastal seas, with particular application to tide and storm induced dispersion in South Australian seas. The three-dimensional tidal equations are briefly discussed for the two types of surge models used, and finite-difference methods for numerically solving these equations are considered. Different methods of simulating flows at open sea boundaries are investigated. The method of particle tracking and the development of the particle tracking model is also described. Various tests are conducted to investigate both the advective and diffusive aspects of dispersion, and a number of scenarios for the simulation of open (ocean) and closed (coastal) boundaries are considered. Various aspects of the particle tracking routine are given specific characteristics according to the nature of the particle being considered. Application of the tide and storm surge model to the Great Australian Bight is described. This uses spherical polar co-ordinates to account for the curvature of the earth, and an oblique boundary element to increase accuracy of the coastline representation. The effect of a low pressure system moving from west to east across the Bight and the resulting significant observed surge at Thevenard during the storm of April 1996 is simulated. This storm resulted in a significant number of deaths in aquaculture farms containing southern bluefin tuna (Thunnas maccoyii) within the Boston Bay region to the extreme east of the Bight due to the agitation of almost neutrally buoyant organic sediments at the sea floor. The effects of this storm are further considered using a Cartesian co-ordinate fine-grid local model of Boston Bay, in Spencer Gulf, South Australia, where both tidal and storm (wind and outside surge) induced flows are simulated. The dispersion of suspended neutrally buoyant sediment throughout the region is considered, and compared with the mortalities of tuna at various farms within the region. Tidal and storm induced currents in the Gulf St. Vincent region, South Australia, have also been modelled using Cartesian co-ordinates. Detailed consideration has been given to the modelling of tides, winds, atmospheric pressures and outside surges from the two open boundaries in Investigator Strait and Backstairs Passage. The information obtained has enabled the modelling of a number of storm surge scenarios. Further to this, various simulations of the dispersion of the larvae of the western king prawn (Penaeus latisulcatus) have been driven using the storm surge model developed. These incorporate currents near the surface and the sea floor, as well as the consideration of changes in behaviour during the life history of the larvae. / Thesis (Ph.D.)--Engineering, Computer and Mathematical Sciences, 2000.
509

Náhlá srdeční zástava a význam kapnometrie v kardiopulmonální resuscitaci / A sudden cardiac arrest and use of capnometry in cardiopulmonary resuscitation

Pokorná, Milana January 2011 (has links)
The study is focused on advanced life support (ALS) performed by rescue team physicians in an out-of-hospital setting. The first part of the study analyzes diagnostic possibilities and correctness of assumed aetiology of the sudden cardiac arrest during cardiopulmonary resuscitation (CPR) in the field. It introduces an original method of "Crosscheck Tables" and applies this method to 211 cases of CPR provided by physicians of the Emergency Care Service. The study demonstrates that significantly misleading conclusions can result from a global analysis of a set of cases. It stresses importance of diagnostic analyses applied to individual cases. The second part of the study concentrates on changes in PETCO2 level as related to the return of spontaneous circulation (ROSC - Return of Spontaneous Circulation) as opposed to the circulation fully dependent on chest compressions. The study demonstrates that in constantly ventilated patients undergoing CPR in an out-of-hospital setting, PETCO2 is significantly higher (about 10 mmHg) after ROSC than before ROSC. It demonstrates that a sudden increase in PETCO2 exceeding 10 mmHg is likely to indicate the moment of ROSC. The study also support a view that steadily low levels of PETCO2 values (<10 mmHg) indicate a low chance for a successful resuscitation outcome. Key...
510

PROBLEMA DE ALOCAÇÃO DE BERÇOS EM PORTOS GRANELEIROS COM RESTRIÇÕES DE ESTOQUE E CONDIÇÕES FAVORÁVEIS DE MARÉ / PROBLEM OF ALLOCATION OF CRADLES IN PORTS GRANARY SHIPS WITH SUPPLY RESTRICTIONS AND CONDITIONS FAVORABLE OF TIDE

Barros, Victor Hugo 22 March 2010 (has links)
Made available in DSpace on 2016-08-17T14:53:08Z (GMT). No. of bitstreams: 1 Victor Hugo Barros Silva.pdf: 4177386 bytes, checksum: 324ffa71e5b64047e7a54ab199bb9241 (MD5) Previous issue date: 2010-03-22 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The problem of allocating berth positions for vessels in tidal grain port terminals is discussed in this work. A berth defines a specific location alongside a quay where a ship loader is available for loading or unloading vessels, accommodating only one vessel at time. In tidal ports, draft conditions depend on high tide conditions, since available depth under the low tide is not adequate to the movement of ships. Some port terminals at the port complex of São Luís, Maranhão, are associated to important transnational enterprises which maintain a strong control over the stock level of their goods. Since the stock level sometimes depends on a continuous process of consumption or production of grains, the decision making of loading or unloading vessels must contemplate the amount of the grain stored in the port yards. Therefore, a basic criterion for decision making is to give priority to the vessels related to the most critical grain stock level. This paper presents two integer linear programming models based on the transportation problem to represent the discussed problem. Some problem instances could be solved by a commercial solver. As an alternative to larger instances, which require large running time, an implementation of Simulated Annealing (SA) and the algorithm known as Population Training Algorithm for Linear Programming (PTA/LP) are used to solve the problem. / O Problema de Alocação de Berços em Portos Graneleiros com Restrições de Estoque e Condições Favoráveis de Maré é abordado neste trabalho. Um berço define um local especifico ao longo do cais onde um carregador de navio está disponível para carregar ou descarregar navios, acomodando apenas um navio por vez. Em portos que sofrem a influência da variação das marés, as condições de navegação dependem de condições favoráveis de maré, uma vez que a profundidade na maré baixa restringe a movimentação de navios. Alguns terminais no complexo portuário de São Luís, Maranhão, estão associados a importantes empresas multinacionais que mantêm um forte controle sobre os níveis de estoque de seus produtos. Uma vez que o nível de estoque, por vezes, depende de um processo contínuo de consumo ou produção de granéis, a tomada de decisão de carregar ou descarregar navios deve levar em conta as cargas armazenadas nos pátios do porto. Desta forma, um critério básico para tomadas de decisão é dar prioridade aos navios relacionada aos níveis mais críticos de estoque. Este trabalho apresenta dois modelos de programação linear baseado no problema de transporte para representar o problema abordado. Algumas instâncias do problema puderam ser resolvidas por um solver comercial. Como alternativa suas instâncias maiores, que exigem grande tempo de execução, uma implementação do Simulated Annealing (SA) e do algoritmo conhecido como Algoritmo de Treinamento Populacional para Programação Linear (ATP/PL) são empregadas para resolução do problema.

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