Global ETD Search

71	Analyse de doublets sismiques par une méthode de rapport spectral Got, Jean-Luc 09 December 1987 (has links) (PDF) Ce travail est une étude détaillée des rapports spectraux de doublets de séismes.Ses objectifs sont l'étude des sources de petits séismes et la mise au point d'une technique de mesure des variations temporelles du facteur de qualité de la coda des séismes, une mesure clef pour les études de prédiction de séismes. La première partie du mémoire est consacrée à l'estimation des erreurs sur le rapport spectral. Cette analyse méthodologique permet de définir les limites d'application de la méthode du rapport spectral, en particulier pour évaluer les variations de Q dans la coda, dans la mesure où la cohérence à haute fréquence est mauvaise pour de grands temps de parcours. La deuxième partie traite de doublets spatiaux et met en évidence de très faibles changements du processus d'ouverture entre les deux séismes. Plusieurs doublets montrent une organisation azimutale des pentes de rapports spectraux des ondes de volume: celle-ci est expliquée par des décalages du point d'initiation de la rupture par rapport aux limites du plan de faille. Des changements de chute de contrainte et du déplacement moyen sont observés dans un autre cas. Il existe des variations du rapport spectral dans la coda de doublets spatiaux. Elles sont expliquées par la rétrodiffraction des ondes de la coda, et l'organisation azimutale des pentes du rapport spectral. Cette observation incite à la prudence en ce qui concerne l'interprétation de variations du rapport spectral dans la coda en terme de changements temporels de l'atténuation dans la croûte supérieure. La troisième partie est consacrée à ce problème de la mesure précise des changements d'atténuation en fonction du temps. De nombreux auteurs insistent sur l'intérêt de cette mesure pour suivre l'ouverture et la fermeture de microfissures dans la croute et pour prédire des séismes. Les doublets temporeIs sont en théorie un outil privilégié pour détecter de très petites variations de l'atténuation dans le milieu. Cependant, même des doublets localisés à quelques mètres de distance peuvent avoir des sources légèrement différentes, la difficulté étant de bien séparer ce qui est dû à la source de ce qui est dû au milieu. Les résultats de ce travail montrent qu'il n'y a pas eu de variations de l'atténuation supérieure à 1 % à l'échelle régionale, malgré l'occurence d'un séisme de magnitude 6. Par contre, les variations du rapport spectral à basse fréquence, localisée dans la région de Hollister où ont été détectée une variation de la vitesse des ondes 5, sont à relier à un Changement local des conditions de la propagation. Sismologie Doublets de séismes Rapport spectral Atténuation Coda des séismes Sismogenèse Californie centrale Prédiction sismique
72	Diffusion multiple des ondes élastiques dans la lithosphère Margerin, Ludovic 11 December 1998 (has links) (PDF) Nous étudions la dépendance spatio-temporelle de l'énergie de la coda courte-période (> 1Hz) des seismes. Pour celà, nous développons des solutions de l'équation de Transfert Radiatif (TR) pour les ondes élastiques dans des milieux réalistes. Deux approches sont adoptées, l'une numérique basée sur les méthodes de Monte-Carlo, l'autre analytique basée sur l'équation de diffusion. Dans l'approximation acoustique, nous résolvons l'équation de TR pour la croûte terrestre représentée par un guide d'ondes hétérogène. Pour ce modèle, l'énergie de la coda décroît exponentiellement en raison des fuites d'énergie à la base de la croûte. Nous confrontons cette théorie de façon critique à des données du Mexique. Nous concluons que notre modèle avec fuite rend parfaitement compte des observations et nous montrons que l'anélasticité des roches est faible. Enfin nous introduisons le temps de résidence des ondes diffuses pour décrire la décroissance énergétique de la coda. Nous abordons ensuite le problème de diffusion multiple en élasticité complète. Nous tenons compte des conversions entre ondes P et S, ainsi que de leur polarisation, décrite par 5 paramètres de Stokes. Nous montrons que l'énergie de la coda est rapidement dominée par les ondes S. Un équilibre d'énergie universel s'établit rapidement entre les modes P et S, en accord avec le principe d'équipartition . Le phénomène d'équilibrage de l'énergie est également observé pour les ondes de coda du Mexique, démontrant leur caractère diffusif. Enfin, nous calculons le cône de rétro-diffusion cohérente dynamique en champ proche. Nous montrons qu'après un régime transitoire, le cône se stabilise et s'étend sur une longueur d'onde autour de la source. L'ensemble des modèles et observations nous permettent de confirmer la nature diffusive de la coda. Sismologie Transfert radiatif Diffusion multiple Coda Rétrodiffusion cohérente Simulation Monte-Carlo Elasticité Equipartition
73	Natural hydrate-bearing sediments: Physical properties and characterization techniques Dai, Sheng 27 August 2014 (has links) An extensive amount of natural gas trapped in the subsurface is found as methane hydrate. A fundamental understanding of natural hydrate-bearing sediments is required to engineer production strategies and to assess the risks hydrates pose to global climate change and large-scale seafloor destabilization. This thesis reports fundamental studies on hydrate nucleation, morphology and the evolution of unsaturation during dissociation, followed by additional studies on sampling and pressure core testing. Hydrate nucleation is favored on mineral surfaces and it is often triggered by mechanical vibration. Continued hydrate crystal growth within sediments is governed by capillary and skeletal forces; hence, the characteristic particle size d10 and the sediment burial depth determine hydrate morphologies in natural sediments. In aged hydrate-bearing sand, Ostwald ripening leads to patchy hydrate formation; the stiffness approaches to the lower bound at low hydrate saturation and the upper bound at high hydrate saturation. Hydrate saturation and pore habit alter the pore size variability and interconnectivity, and change the water retention curve in hydrate-bearing sediments. The physical properties of hydrate-bearing sediments are determined by the state of stress, porosity, and hydrate saturation. Furthermore, hydrate stability requires sampling, handling, and testing under in situ pressure, temperature, and stress conditions. Therefore, the laboratory characterization of natural hydrate-bearing sediments faces inherent sampling disturbances caused by changes in stress and strain as well as transient pressure and temperature changes that affect hydrate stability. While pressure core technology offers unprecedented opportunities for the study of hydrate-bearing sediments, careful data interpretation must recognize its inherent limitations. Methane hydrate Hydrate-bearing sediments Nucleation Hydrate morphology Water retention curve Network model simulation Clay Frozen sand Creep Coda wave interferometry Sampling disturbance Pressure core technology P-wave Hydraulic conductivity Pore water sampling
74	Sistemas de arquivos paralelos: alternativas para a redução do gargalo no acesso ao sistema de arquivos / Parallel File Systems: alternatives to reduce the bottleneck in accessing the file system Carvalho, Roberto Pires de 23 September 2005 (has links) Nos últimos anos, a evolução dos processadores e redes para computadores de baixo custo foi muito maior se comparada com o aumento do desempenho dos discos de armazenamento de dados. Com isso, muitas aplicações estão encontrando dificuldades em atingir o pleno uso dos processadores, pois estes têm de esperar até que os dados cheguem para serem utilizados. Uma forma popular para resolver esse tipo de empecílio é a adoção de sistemas de arquivos paralelos, que utilizam a velocidade da rede local, além dos recursos de cada máquina, para suprir a deficiência de desempenho no uso isolado de cada disco. Neste estudo, analisamos alguns sistemas de arquivos paralelos e distribuídos, detalhando aqueles mais interessantes e importantes. Por fim, mostramos que o uso de um sistema de arquivos paralelo pode ser mais eficiente e vantajoso que o uso de um sistema de arquivos usual, para apenas um cliente. / In the last years, the evolution of the data processing power and network transmission for low cost computers was much bigger if compared to the increase of the speed of getting the data stored in disks. Therefore, many applications are finding difficulties in reaching the full use of the processors, because they have to wait until the data arrive before using. A popular way to solve this problem is to use a parallel file system, which uses the local network speed to avoid the performance bottleneck found in an isolated disk. In this study, we analyze some parallel and distributed file systems, detailing the most interesting and important ones. Finally, we show the use of a parallel file system can be more efficient than the use of a usual local file system, for just one client. acesso concorrente afs afs availability bridge bridge ceft-pvfs ceft-pvfs coda coda computação distribuída computação paralela concurrent access disco magnético disco rígido disponibilidade distributed computing distributed file system escalabilidade fail over file replication file service file system file system bottleneck gargalo no sistema de arquivos gfs gfs hard disk ide ide latência latency magnetic disk nfs nfs nfsp nfsp parallel computing parallel file system pio pio pvfs pvfs pvfs2 pvfs2 replicação de arquivos sad scalability scsi scsi security segurança serviço de arquivos sistema de arquivos sistema de arquivos distribuídos sistema de arquivos paralelos sprite sprite sva sva tolerância a falhas
75	Sistemas de arquivos paralelos: alternativas para a redução do gargalo no acesso ao sistema de arquivos / Parallel File Systems: alternatives to reduce the bottleneck in accessing the file system Roberto Pires de Carvalho 23 September 2005 (has links) Nos últimos anos, a evolução dos processadores e redes para computadores de baixo custo foi muito maior se comparada com o aumento do desempenho dos discos de armazenamento de dados. Com isso, muitas aplicações estão encontrando dificuldades em atingir o pleno uso dos processadores, pois estes têm de esperar até que os dados cheguem para serem utilizados. Uma forma popular para resolver esse tipo de empecílio é a adoção de sistemas de arquivos paralelos, que utilizam a velocidade da rede local, além dos recursos de cada máquina, para suprir a deficiência de desempenho no uso isolado de cada disco. Neste estudo, analisamos alguns sistemas de arquivos paralelos e distribuídos, detalhando aqueles mais interessantes e importantes. Por fim, mostramos que o uso de um sistema de arquivos paralelo pode ser mais eficiente e vantajoso que o uso de um sistema de arquivos usual, para apenas um cliente. / In the last years, the evolution of the data processing power and network transmission for low cost computers was much bigger if compared to the increase of the speed of getting the data stored in disks. Therefore, many applications are finding difficulties in reaching the full use of the processors, because they have to wait until the data arrive before using. A popular way to solve this problem is to use a parallel file system, which uses the local network speed to avoid the performance bottleneck found in an isolated disk. In this study, we analyze some parallel and distributed file systems, detailing the most interesting and important ones. Finally, we show the use of a parallel file system can be more efficient than the use of a usual local file system, for just one client. acesso concorrente afs bridge ceft-pvfs coda computação distribuída computação paralela disco magnético disco rígido disponibilidade escalabilidade gargalo no sistema de arquivos gfs ide latência nfs nfsp pio pvfs pvfs2 replicação de arquivos sad scsi segurança serviço de arquivos sistema de arquivos sistema de arquivos distribuídos sistema de arquivos paralelos sprite sva tolerância a falhas afs availability bridge ceft-pvfs coda concurrent access distributed computing distributed file system fail over file replication file service file system file system bottleneck gfs hard disk ide latency magnetic disk nfs nfsp parallel computing parallel file system pio pvfs pvfs2 scalability scsi security sprite sva
76	Development and application of LC-MS-based differential metabolic profiling in plant systems / Entwicklung und Anwendung von LC-MS-basierendem Metabolitenprofiling an pflanzlichen Systemen Ratzinger, Astrid 17 July 2008 (has links) No description available. 000 Allgemeines Wissenschaft Agricultural Sciences - unbiased data processing LC-MS comparative analysis XCMS CODA normalization xylem sap <i>Brassica napus</i> plant-pathogen interaction sesame phosphorus mobilization 30 Naturwissenschaften RA Naturwissenschaften
77	Pre-Existing Film Music Re:sourced : Technical Aspects and Narratological Implications of Audible Diegetic Transitions in Joker and Other Films / Förflyttning av tidigare existerande filmmusik : Tekniska aspekter och narratologiska implikationer av hörbara diegetiska övergångar i Joker och andra filmer Danstål Skiöld, Martin January 2023 (has links) This thesis concerns itself with a phenomenon found in film music that can be described as audible diegetic transitions. In short, an audible diegetic transition occurs when film music shifts from one implied musical placement to another by changing its presented sound quality. This occurs predominantly through the employment of music that is pre-existing in relation to the release of the film where the music is utilised. These audible diegetic transitions are categorised as aural displacements and transaural displacements which are both anchored in previous research concerning stable musical placements. In order to answer the research questions regarding technical aspects and narratological implications, the thesis is centred around a film music analysis. The demarcation of said analysis uses pre-existing songs from the film Joker (Philips, 2019) as its main focus. In order to provide a colourful and meaningful discussion the selected material also contains a variety of examples from other films. The analysis shows that the selected audible diegetic transitions can provide narratological implications both for a film as a whole and for a specific scene or sequence in any film. In Joker specifically, the audible diegetic transitions arguably contain the narratological implication of adding to the retrospective and unreliable narration, which is important for the story of the film. The thesis also argues that the technical aspects of the analysed audible diegetic transitions can be condensed into being either diegetic to commentary, or vice versa. Diegetic music is, in this context, defined as music that is implied as being heard in the acoustic space of the story-world, whereas commentary music is an umbrella term defined as music that is not implied being heard in the acoustic space of the story-world. The analysis shows that these transitions can transpire either instantly or gradually with the change of sound quality from being either narrow or wide. These technical aspects contribute in understanding the narratological implications of said audible diegetic transition by categorising them as either emotive or grounding. Both of these narratological implications can be concluded and described as swift enforcers of the relationship between the one consuming the film and the characters, or locations, of the film they are consuming. Audible diegetic transitions figuratively breach the fourth wall that is the screen. film music technical aspects narratological implications audible diegetic transitions transaural displacements diegetic non-diegetic intra-diegetic meta-diegetic supra-diegetic trans-diegetic sound advance bridge lag story discourse instant gradual emotive grounding narrow wide Joker Baby Driver Coda Guardians of the Galaxy Star Wars Musicology Musikvetenskap

Page generated in 0.0669 seconds