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You searched for subject:( mean diffusivity). Showing records 1 – 2 of 2 total matches.

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1. Cai, Wei. Etude expérimentale des cavités latérales en écoulements à surface libre : Experimental study of lateral cavities in open-channel flows.

Degree: Docteur es, Mécanique des fluides, 2015, INSA Lyon

Les cavités latérales sont des zones mortes à surface libre situées sur le côté d’un écoulement fluvial ou côtier. Les vitesses caractéristiques au sein de la cavité étant beaucoup plus faibles que celles de l’écoulement, une couche de mélange se développe à l’interface entre ces deux régions. Cette couche de mélange peut alors transférer de la quantité de mouvement de l’écoulement vers la cavité et ainsi mettre en mouvement la cavité et peut aussi transférer de la masse entre les deux régions, telle une pollution venant de l’écoulement amont. L’étude de cette thèse a alors consisté à étudier les caractéristiques de la couche de mélange, qui est rendue spécifique par le fait qu’elle se développe entre deux coins géométriques formés par l’intersection entre les parois de la cavité et celles de l’écoulement principal. Nous avons alors pu identifier l’origine et l’alternance des mouvements de fluide dans la direction transverse: de la cavité vers l’écoulement et inversement. Concernant la mise en mouvement de la cavité, le choix a été fait de considérer un écoulement principal fixé et de modifier l’extension de la cavité dans la direction perpendiculaire à l’écoulement, passant ainsi d’une cavité rectangulaire alignée avec l’écoulement principal à une cavité allongée dans le sens opposé. La mesure de champ de vitesse par PIV 2D a alors montré une forte évolution de la forme de l’écoulement à mesure que la géométrie de la cavité évolue : un système avec deux cellules alignées dans le sens de l’écoulement à un système à une seule cellule, puis un système à deux cellules et enfin un système complexe 3D ont ainsi été observés pour une cavité de plus en plus allongée. Ensuite, une modification du dispositif expérimental a permis de mesurer de deux façons différentes le transport de scalaire de l’écoulement principal vers la cavité, de comprendre les processus associés à ce transfert et enfin de quantifier cette capacité de transfert pour différents écoulements principaux et différentes géométries de cavités. Nous avons notamment montré que la géométrie de la cavité a peu d’effet alors que le nombre de Reynolds et la profondeur d’eau normalisée ont un effet majeur sur cette capacité de transfert de masse entre les deux régions.

Lateral cavities are free-surface dead-zones located on the side of a fluvial or coastal main flow. As the typical velocities are much larger in the main flow than in the cavity, a mixing layer appears at the interface between both regions. This mixing layer is able to transfer between the main flow and the cavity momentum which then sets the fluid in the cavity in motion and also passive scalar, such as a pollution coming from upstream. The objective of this work was then to investigate the characteristics of the mixing layer, which specificity comes from the fact that it is constrained between the upstream and downstream geometrical corners. It was possible to observe the origin and alternation of the transversal fluid motions: from the cavity towards the main flow and conversely. Regarding the…

Advisors/Committee Members: Mignot, Emmanuel (thesis director), Rivière, Nicolas (thesis director).

Subjects/Keywords: Mécanique analytique; Mécanique des fluides; Cavité; Recirculation; Couche de mélange; Ecoulement; Surface libre; Transfert de masse; Mesures; Débit; Mechanics; Fluid mechanics; Cavity; Recirculation; Mixing layer; Flow; Free surface; Mass transfer; Measurement; Mean diffusivity; 532.050 72

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Cai, W. (2015). Etude expérimentale des cavités latérales en écoulements à surface libre : Experimental study of lateral cavities in open-channel flows. (Doctoral Dissertation). INSA Lyon. Retrieved from http://www.theses.fr/2015ISAL0062

Chicago Manual of Style (16th Edition):

Cai, Wei. “Etude expérimentale des cavités latérales en écoulements à surface libre : Experimental study of lateral cavities in open-channel flows.” 2015. Doctoral Dissertation, INSA Lyon. Accessed October 31, 2020. http://www.theses.fr/2015ISAL0062.

MLA Handbook (7th Edition):

Cai, Wei. “Etude expérimentale des cavités latérales en écoulements à surface libre : Experimental study of lateral cavities in open-channel flows.” 2015. Web. 31 Oct 2020.

Vancouver:

Cai W. Etude expérimentale des cavités latérales en écoulements à surface libre : Experimental study of lateral cavities in open-channel flows. [Internet] [Doctoral dissertation]. INSA Lyon; 2015. [cited 2020 Oct 31]. Available from: http://www.theses.fr/2015ISAL0062.

Council of Science Editors:

Cai W. Etude expérimentale des cavités latérales en écoulements à surface libre : Experimental study of lateral cavities in open-channel flows. [Doctoral Dissertation]. INSA Lyon; 2015. Available from: http://www.theses.fr/2015ISAL0062

2. Gupta, Aman. Ultra-High Field MR Diffusion Tensor Imaging Characterization of Rabbit Tendons and Ligaments.

Degree: 2012, University of Illinois – Chicago

Tendons and ligaments are dense, fibrous connective tissues that facilitate transmission of loads from muscle to bone (tendon) or from bone to bone (ligament). These tissues are subjected to wear and tear from day-to-day mechanical usage leading to sprains, tendinopathies, or ruptures, each of which is a major source of musculoskeletal disability. Clinically, the diagnosis of tendon and ligament injury is based on a clinical examination as well as magnetic resonance imaging (MRI) of the relevant tissues. MRI is a reliable, non-invasive tool for detecting large and complete tears; however, conventional T1 and T2-weighted grayscale images exhibit poor contrast and a low signal-to-noise ratio which makes identification of low-grade injuries more challenging to delineate. Therefore, there exists a need for reliable, quantitative and more robust imaging approaches to assess tendon and ligament microstructure and integrity. One of these MR approaches is diffusion tensor imaging (DTI), an advanced MRI technique primarily used in neuroimaging applications. DTI assesses tissue microstructural organization by quantifying the 3D diffusion of water molecules within tissues. It relies on the basic diffusion principle that water molecules diffuse more readily along (i.e., parallel to), rather than across physical barriers (e.g., collagen fibers). Diffusion of water molecules can be quantified by the diffusion tensor in each voxel, whereby the magnitude and orientation of water diffusion can be computed throughout the tissue, thus revealing the fiber microstructure. The primary aims of the proposed studies are to demonstrate applicability and reliability of the DTI technique for tendons and ligaments, and determine the sensitivity of b-values to DTI derived parameters of tissue integrity. This is the first study to show feasibility and applicability of DTI on Tendons and Ligaments at ultra-high magnetic fields with high resolutions and measure DTI metrics from both tissue types. High Fractional Anisotropy values of 0.67 for semitendinosus tendons and 0.66 for medial collateral ligaments shows the highly anisotropic nature of these soft connective tissues.Axial diffusivity is about 3 times the radial diffusivity which shows diffusion directional anisotropy indicating diffusion preference along the fibers then across them. The present study showed fiber tractography of these tissues at ultra-high magnetic fields with a histological correlation confirming the highly-organized parallel collagen fiber microstructure. Diffusion tensor imaging is sensitive to the diffusional anisotropy differences and can show microstructural differences between tendons and ligaments through DTI metrics at 11. 7 T field strength. The current work also found the most feasible range of b-values of 300-600 s/mm2 which will be best suited for these tissue types at the given magnetic field strength of 11.7T and get more reliable DTI measurements. DTI metrics can provide insight into 3D tissue integrity and … Advisors/Committee Members: Magin, Richard L. (advisor), Wang, Vincent M. (committee member), Stebbins, Glenn T. (committee member), Royston, Thomas J. (committee member), Akpa, Belinda S. (committee member), Zelazny, Anthony M. (committee member).

Subjects/Keywords: Diffusion Tensor Imaging; Tendon; Ligament; Magnetic Resonance Imaging; ultra-high field; Fractional Anisotropy; Mean Diffusivity; Tractography; b-value optimization

…56 Figure 4.9(c): Frequency distribution of Mean Diffusivity of six… …57 Figure 4.9(d): Frequency distribution of Mean diffusivity of six Medial… …66 Figure 4.10 (b): Variation of Mean Diffusivity for the central nine slices for… …71 Figure 4.11 (b): Variation of Mean Diffusivity for the six samples for both… …87 Figure 5.2: Average Mean Diffusivity values for six rabbit semitendinosus tendons at… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Gupta, A. (2012). Ultra-High Field MR Diffusion Tensor Imaging Characterization of Rabbit Tendons and Ligaments. (Thesis). University of Illinois – Chicago. Retrieved from http://hdl.handle.net/10027/9137

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Gupta, Aman. “Ultra-High Field MR Diffusion Tensor Imaging Characterization of Rabbit Tendons and Ligaments.” 2012. Thesis, University of Illinois – Chicago. Accessed October 31, 2020. http://hdl.handle.net/10027/9137.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Gupta, Aman. “Ultra-High Field MR Diffusion Tensor Imaging Characterization of Rabbit Tendons and Ligaments.” 2012. Web. 31 Oct 2020.

Vancouver:

Gupta A. Ultra-High Field MR Diffusion Tensor Imaging Characterization of Rabbit Tendons and Ligaments. [Internet] [Thesis]. University of Illinois – Chicago; 2012. [cited 2020 Oct 31]. Available from: http://hdl.handle.net/10027/9137.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Gupta A. Ultra-High Field MR Diffusion Tensor Imaging Characterization of Rabbit Tendons and Ligaments. [Thesis]. University of Illinois – Chicago; 2012. Available from: http://hdl.handle.net/10027/9137

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.