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Dissertations / Theses on the topic 'Anisotropic medium'
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Golovnina, Svetlana M. "Modeling and inversion in weakly anisotropic media." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971440751.
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Ellefsen, Karl. "Elastic wave propagation along a borehole in an anisotropic medium." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/52915.
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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.Includes bibliographic references (leaves 262-272).
by Karl John Ellefsen.
Sc.D.
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Tran, Nam Hung. "Hydro-mechanical behavior of deep tunnels in anisotropic poroelastic medium." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2037/document.
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Les tunnels profonds sont souvent construits dans les roches sédimentaires et métamorphiques stratifiées qui présentent habituellement des propriétés anisotropes en raison de leur structure et des propriétés des constituants. Le présent travail vise à étudier les tunnels profonds dans un massif rocheux anisotrope élastique en portant une attention particulière sur les effets des couplages hydromécaniques par des approches analytiques et numériques. Une solution analytique pour un tunnel creusé dans un massif rocheux anisotrope saturé est développée en tenant compte du couplage hydro-mécanique dans le régime permanent. Cette solution analytique est utilisée pour réaliser une série d’études paramétriques afin d'évaluer les effets des différents paramètres du matériau anisotrope sur le comportement du tunnel. Dans un deuxième temps la solution analytique est élargie pour décrire le comportement du tunnel pendant la phase transitoire hydraulique. Afin de compléter ces études analytiques qui prennent en compte seulement un couplage unilatéral (dans le sens que seul le comportement hydraulique influence le comportement mécanique et pas l’inverse) de l’analyse numérique avec un couplage complet, ont été réalisés. Une application de la solution analytique sur la méthode de convergence-confinement est aussi bien abordée qui peut prendre en compte l'influence du front de taille du tunnel sur le travail du soutènement ainsi que sur le massif. La solution obtenue peut servir comme un outil de dimensionnement rapide des tunnels en milieux poreux en le combinant avec des approches de dimensionnement comme celle de convergence confinementDeep tunnels are often built in the sedimentary and metamorphic foliated rocks which exhibits usually the anisotropic properties due to the presence of the discontinuity. The analysis of rock and liner stresses due to tunnel construction with the assumption of homogeneous and isotropic rock would be incorrect. The present thesis aims to deal with the deep tunnel in anisotropic rock with a particular emphasis on the effects of hydraulic phenomenon on the mechanical responses or reciprocal effects of hydraulic and mechanical phenomena by combining analytical and numerical approach. On that point of view, a closed-formed solution for tunnel excavated in saturated anisotropic ground is developed taking into account the hydromechanical coupling in steady-state. Based on the analytical solution obtained, parametric studies are conducted to evaluate the effects of different parameters of the anisotropic material on the tunnel behavior. The thesis considers also to extend the analytical solution with a time-dependent behavior which takes into account the impact of the pore pressure distribution on mechanical response over time, i.e., one way coupling modeling. In addition, some numerical analysis based on fully-coupled modeling, i.e., two ways coupling, are conducted which are considered as the complete solution for the analytical solution. An application of the closed-form solution on convergence-confinement method is as well referred which can take into account the influence of the tunnel face on the work of the support as well as the massif. The obtained solution could be used as a quick tool to calibrate tunnels in porous media by combining with design approaches such as convergence-confinement method
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Wei, Zheng. "Convection of water near 4°C in an anisotropic porous medium." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0013/MQ60920.pdf.
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Alani, Mahdi Ahmed 1954. "Neutral particle Green's function in an infinite medium with anisotropic scattering." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/282874.
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The linear Boltzmann equation for the transport of neutral particles is investigated with the objective of generating benchmark-quality calculations for homogeneous infinite media. In all cases, the problems are stationary, of one energy group, and the scattering is both isotropic and anisotropic. In the transport problems considered, the Green's function is generally the quantity of interest. The solution is obtained through the use of the Fourier transform method. The numerical inversions use standard numerical techniques, such as Gauss-Legendre quadrature, summation of infinite series, and Euler-Knopp acceleration. The most basic source of neutral particles is the point-beam source, or Green's function source. The Green's function in an infinite medium with isotropic scattering is treated as explained in chapter two. The Green's function in an infinite medium with anisotropic scattering is treated using two different mathematical methods as explained in chapters three and four. The results for both cases is shown in chapter 5.
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Pajevic, Sinisa, and George H. Weiss. "Effects of anisotropic optical parameters on the penetration of photons into a turbid medium: Effects of anisotropic optical parameters on the penetration ofphotons into a turbid medium." Diffusion fundamentals 4 (2007) 14, S.- 1-13, 2007. https://ul.qucosa.de/id/qucosa%3A14286.
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There are by now many applications of methods based on near- infrared radiation (NIR) used for optical imaging and
therapeutic purposes in medical settings. Such optical techniques are appealing in not requiring potentially harmful ionizing radiation, being non-invasive, and generally being easily implementable. Since photons are randomly scattered by cell components, successful use of NIR requires knowledge of the photon trajectories expressed in statistical terminology. Until now the necessary analysis has been based on diffusion theory assuming that the scattering coefficient is an isotropic material property. We analyze the properties of the penetration depth when this assumption is violated. By penetration depth will be meant the depth attained in the turbid medium, given its ultimate emission at the planar surface at a time T , as a function of the degree of anisotropy of the scattering coefficient. Our analysis will be based on a continuous-time random walk formalism. Properties of both time-gated and continuous-wave experiments will be derived.
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Choi, Hyung Jip. "On iso- and nonisothermal crack problems of a layered anisotropic elastic medium." Diss., Virginia Polytechnic Institute and State University, 1991. http://hdl.handle.net/10919/53606.
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The iso- and non-isothermal crack problems of layered fiber-reinforced composite materials are investigated within the framework of linear anisotropic thermoelasticity and under the state of generalized plane deformation. The crack is assumed to be parallel to the layer bounding surfaces. By employing the Fourier integral transform technique and the flexibility/stiffness matrix formulation, the current mixed boundary value problems are reduced to solving a set of simultaneous singular integral equations with Cauchy-type kernels. The crack·tip stress intensity factors are then defined in terms of the solution of the integral equations. Numerical results are presented addressing the salient and unique features for a class of crack problems involving highly anisotropic fibrous composite materials. Specifically, the cases of a crack embedded i) within a homogeneous and anisotropic slab, ii) between two bonded dissimilar anisotropic half-spaces and iii) within the matrix-rich interlaminar region of a generally laminated anisotropic slab are considered. The effects of relative crack size, crack location and fiber volume fraction on the stress intensity factors are examined as a function of über angle. For the case of layered composites, the matrix-rich interlaminar region is modeled as a separate interlayer. As the interlayer thickness approaches zero, the interlaminar crack model illustrates no smooth transition to the ideal interface crack model of zero interlayer thickness which exhibits oscillatory stress singularities. The mixed-mode crack tip response is shown to involve the simultaneous presence of three fracture modes. It is demonstrated that the corresponding values of stress intensity factors are strongly influenced by the laminate stacking sequence and layer orientation. In addition, the partially insulated crack surface condition is observed to alleviate the severity of thermally-induced stress fields near the crack tip.Ph. D.
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Pajevic, Sinisa, and George H. Weiss. "Effects of anisotropic optical parameters on the penetration of photons into a turbid medium." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194528.
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There are by now many applications of methods based on near- infrared radiation (NIR) used for optical imaging and
therapeutic purposes in medical settings. Such optical techniques are appealing in not requiring potentially harmful ionizing radiation, being non-invasive, and generally being easily implementable. Since photons are randomly scattered by cell components, successful use of NIR requires knowledge of the photon trajectories expressed in statistical terminology. Until now the necessary analysis has been based on diffusion theory assuming that the scattering coefficient is an isotropic material property. We analyze the properties of the penetration depth when this assumption is violated. By penetration depth will be meant the depth attained in the turbid medium, given its ultimate emission at the planar surface at a time T , as a function of the degree of anisotropy of the scattering coefficient. Our analysis will be based on a continuous-time random walk formalism. Properties of both time-gated and continuous-wave experiments will be derived.
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Fooladi, Samaneh, and Samaneh Fooladi. "Numerical Implementation of Elastodynamic Green's Function for Anisotropic Media." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/623144.
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Displacement Green's function is the building block for some semi-analytical methods like Boundary Element Method (BEM), Distributed Point Source Method (DPCM), etc. In this thesis, the displacement Green`s function in anisotropic media due to a time harmonic point force is studied. Unlike the isotropic media, the Green's function in anisotropic media does not have a closed form solution. The dynamic Green's function for an anisotropic medium can be written as a summation of singular and non-singular or regular parts. The singular part, being similar to the result of static Green's function, is in the form of an integral over an oblique circular path in 3D. This integral can be evaluated either by a numerical integration technique or can be converted to a summation of algebraic terms via the calculus of residue. The other part, which is the regular part, is in the form of an integral over the surface of a unit sphere. This integral needs to be evaluated numerically and its evaluation is considerably more time consuming than the singular part. Obtaining dynamic Green's function and its spatial derivatives involves calculation of these two types of integrals. The spatial derivatives of Green's function are important in calculating quantities like stress and stain tensors. The contribution of this thesis can be divided into two parts. In the first part, different integration techniques including Gauss Quadrature, Simpson's, Chebyshev, and Lebedev integration techniques are tried out and compared for evaluation of dynamic Green’s function. In addition the solution from the residue theorem is included for the singular part. The accuracy and performance of numerical implementation is studied in detail via different numerical examples. Convergence plots are used to analyze the numerical error for both Green's function and its derivatives. The second part of contribution of this thesis relates to the mathematical derivations. As mentioned above, the regular part of dynamic Green's function, being an integral over the surface of a unit sphere, is responsible for the majority of computational time. From symmetry properties, this integration domain can be reduced to a hemisphere, but no more simplification seems to be possible for a general anisotropic medium. In this thesis, the integration domain for regular part is further reduced to a quarter of a sphere for the particular case of transversely isotropic material. This reduction proposed for the first time in this thesis nearly halves the number of integration points for the evaluation of regular part of dynamic Green's function. It significantly reduces the computational time.
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Gnawali, Rudra. "Berreman Approach to Optical Propagation Through Anisotropic Metamaterials." University of Dayton / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1541108034610795.
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AL-Ghezi, Hammid. "Optical Propagation in Anisotropic Metamaterials: Application to Analysis and Design of Metallo-Dielectric Filters." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1628263495632462.
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Chahlafi, Miloud. "Modélisation du rayonnement thermique dans un coeur de réacteur nucléaire dégradé en présence de vapeur et de gouttes d'eau." Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00649477.
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L'objectif de cette thèse est de proposer une modélisation du rayonnement thermique dans un réacteur nucléaire au cours d'un accident grave conduisant à la dégradation des crayons combustibles. Un réacteur étant refroidi par de l'eau, le rayonnement se fait en présence de vapeur et de gouttes d'eau. Le modèle de rayonnement est construit à partir d'expériences de dégradation de crayons fossiles, réalisées sur le réacteur expérimental PHEBUS.Les configurations géométriques accidentelles de grappes de 21 crayons dégradés ont pu être caractérisées en trois dimensions à partir d'images issues de tomographies. Les propriétés radiatives homogénéisées de ces configurations ont été complètement caractérisées à partir de la fonction de distribution cumulée d'extinction Gext et de la fonction de phase de diffusion p. Ces fonctions ont été précisément calculées par une méthode de Monte Carlo. Gext, qui n'est pas de type exponentiel, ne suit pas la loi de Beer. p dépend fortement des angles d'incidence et de diffusion. A partir de l'équation de transfert radiatif généralisée à des milieux non Beeriens, introduite par Taine et al., un tenseur des conductivités radiatives a été déterminé par une méthode de perturbations, en supposant dans une première étape la phase fluide transparente. Les conductivités radiatives axiales et radiales ont été exprimées avec précision en fonction de la porosité, de la surface spécifique et de l'absorptivité locale du milieu poreux. Dans une deuxième étape, une équation de transfert radiatif à trois températures a été établie. Dans ce modèle, les effets de la phase fluide sur le rayonnement ont été couplés aux effets des parois. Les propriétés radiatives de la vapeur et des gouttes d'eau sont calculées en utilisant respectivement le modèle CK et la théorie de Mie, dans les conditions thermohydrauliques typiques des accidents de réacteur. Les flux radiatifs s'expriment en fonction de flux conductifs couplés caractérisés par des conductivités radiatives associées aux champs de températures de chaque phase. Les puissances volumiques échangées par rayonnement entre les phases sont aussi calculées à partir de ce modèle.
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Wang, Xiaojia. "Study of the radiative properties of aligned carbon nanotubes and silver nanorods." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42871.
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Arrays of nanotubes/rods made of appropriate materials can yield unique radiative properties, such as large absorption and optical anisotropy, with broad applications from high-efficiency emitters and absorbers for energy conversion to the polarization conversion via anisotropic responses. The objective of this dissertation is to investigate the radiative properties of arrays formed by aligned carbon nanotubes (CNTs) and silver nanorods (AgNRs).
The CNT arrays used in the present study consist of multi-walled CNTs synthesized vertically on silicon substrates using thermal chemical vapor deposition. Their close-to-unity absorptance is demonstrated by measuring the directional-hemispherical reflectance in the visible and near-infrared spectral ranges using an integrating sphere. The bidirectional reflectance distribution function and angle-resolved reflectance were measured at the 635-nm wavelength. The results demonstrate that high-absorptance CNT arrays may be diffusely or specularly reflecting and have important applications in radiometry. Theoretical modeling based on the effective medium theory (EMT) and reflectivity of an anisotropic medium are developed to explain the high absorption and polarization dependence. The effective optical constants of the CNT array for both ordinary and extraordinary polarizations are quantitatively determined by fitting the angle-resolved reflectance.
The AgNR arrays used in the present study were fabricated using oblique angle deposition, which results in inclined Ag nanorods that can be modeled as an effective homogenous and optically anisotropic thin film. The spectral and directional radiative properties of AgNRs grown on different substrates, including a glass slab with a silver film, and compact disc gratings, were characterized at the 635-nm and 977-nm wavelengths for different polarizations. The results are analyzed based on the EMT, rigorous coupled-wave analysis, and anisotropic thin-film optics. The results of this dissertation help gain a better understanding of radiative properties of anisotropic nanostructures for potential applications in high-efficiency energy conversion, radiometric devices, and optical systems.
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Maupin, Valérie. "Etude des caracteristiques des ondes de surface en milieu anisotrope : application a l'analyse d'anomalies de polarisation a la station de port-aux-francais." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13035.
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Dispersion et polarisation des ondes de surface dans des structures anisotropes lateralement homogenes. L'equation des ondes elastiques dans des structures planes isotropes est perturbee par l'introduction de coefficients elastiques anisotropes. On en deduit l'anomalie de vitesse de phase et l'anomalie de polarisation decomposee sur les modes propres de la structure isotrope de reference. Ces resultats sont illustres par le calcul d'anomalies de vitesse et de polarisation dans des modeles oceaniques ou l'anisotropie est cree par orientation de fissures dans la croute ou de cristaux d'olivine dans le manteau
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Deng, Xiaodong. "Nondestructive evaluation of thermal sprayed coating by acoustic microscopy and Eddy current testing." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0030/document.
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La thèse a mis en œuvre deux méthodes inverses pour l’évaluation non destructive d’un milieu multicouche anisotrope : la microscopie acoustique et les courants de Foucault. Pour la microscopie acoustique, nous avons adapté un modèle de propagation de l'onde acoustique dans un milieu multicouche, en calculant les coefficients de réflexion et de transmission d’un revêtement multicouche sur un substrat et en modélisant la réponse acoustique V(z) propre à la microscopie acoustique. Une méthode inverse utilisant l’algorithme de Levenberg-Marquardt donne accès à l’épaisseur, au module de Young et à la densité du revêtement. Pour les courants de Foucault, une méthode inverse similaire basée sur le formalisme de Tree a été mise au point, qui donne accès à l’épaisseur, à la conductivité électrique et à la perméabilité magnétique du revêtement. Après des vérifications de l’algorithme sur des matériaux massifs de référence, nous avons appliqué ces méthodes à un métal revêtu pour tuyauteries de centrale thermique : de l’acier inoxydable austénitique type 304 revêtu par pulvérisation thermique de superalliage Hastelloy C22 à base de nickel. La corrosion sèche sous l’effet des gaz chauds (air contenant du gaz SO2) amincit graduellement la paroi des tubes, ce qui peut les rendre dangereux. Il a fallu tenir compte de l’effet du grenaillage préalable à la pulvérisation, qui crée une mince couche de martensite à laquelle les courants de Foucault sont très sensibles : un modèle à trois couches substrat / martensite / revêtement a été utilisé. Nous avons caractérisé des échantillons de métal avant et après exposition à l’air avec ou sans SO2 à 650°C. Les deux méthodes d’évaluation non destructive permettent une détermination très satisfaisante de l’épaisseur de revêtement et se complètent bien. L’évaluation des caractéristiques physiques (acoustiques et électromagnétiques) met en évidence des hétérogénités du revêtement liées à son mode d’élaboration et des évolutions au cours du temps. Des pistes d’amélioration des méthodes sont proposéesIn the current work, we investigate the nondestructive evaluation of a thermal sprayed coating (Hastelloy C22 Ni-based alloy) on substrate (type 304 austenitic stainless steel) using acoustic microscopy and ECT method. Two models were built for the evaluation of this kind of material: one is for acoustic V(z) measurement and the other is for swept eddy current measurement. The implementation of these two models is used for the evaluation and properties measurement of the thermal sprayed coatings, such as elastic properties, electromagnetic properties. In particular, the main achievements and results are as follows: 1. Acoustic wave propagation in an anisotropic multilayered medium was investigated. The formula for calculating the reflection and transmission coefficients of the multilayered medium on or without a substrate were derived, which is necessary for the modeling of acoustic V(z) measurement of the thermal sprayed coating on substrate. 2. A model was built for the acoustic V(z) measurement of the thermal sprayed coatings on substrate, which can deal with anisotropic multilayered media. Specifically, we used a model of multilayered coatings with graded properties on substrate to calculate the acoustic reflection coefficient of our sample. Treating the thermal sprayed coating, deposited on a 304 steel substrate, as FGMs, we evaluated the coating thickness and the Young’s modulus evolution along the depth of the coating. 3. A model was built for the swept eddy current measurement of the thermal sprayed coatings. Since before the spraying process, the surface of the substrate is usually shot-peened (SP), the coated material is considered as a three-layer medium. The coating thickness and electromagnetic properties of each of the 3 layers were determined by an effective reverse process. 4. The thermal sprayed coated material after exposure in different conditions, i.e., as-received, heat-treated in air and heat-treated in SO2 environment, and after different exposure time was evaluated by the integrity of acoustic microscopy and ECT method. The coating thickness and the electromagnetic properties of the coated material under different conditions were measured
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Mumcu, Gokhan. "EM Characterization of Magnetic Photonic / Degenerate Band Edge Crystals and Related Antenna Realizations." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1221860344.
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Okhulkova, Tatiana. "Integration of uncertainty and definition of critical thresholds for CO2 storage risk assessment." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLC021/document.
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L'objectif principal de la thèse est de définir comment l'incertitude peut être prise en compte dans leprocessus d'évaluation des risques pour le stockage de CO2 et de quantifier, à l'aide de modèles numériques,les scénarios de fuite par migration latérale et à travers la couverture. Les scénarios choisis sont quantifiéspar l'approche de modélisation de système pour laquelle des modèles numériques prédictifs ad-hoc sontdéveloppés. Une étude probabiliste de propagation d'incertitude paramétrique par un méta-modèle depolynômes de chaos est réalisée. La problématique de la prise en compte de la variabilité spatiale comme unesource d'incertitude est éclairée et une étude comparative entre représentations homogène et hétérogène de laperméabilité est fournieThe main goal of the thesis is to define how the uncertainty can be accounted for in the process of riskassessment for CO2 storage and to quantify by means of numerical models the scenarii of leakage by lateralmigration and through the caprock. The chosen scenarii are quantified using the system modeling approachfor which ad-hoc predictive numerical models are developed. A probabilistic parametric uncertaintypropagation study using polynomial chaos expansion is performed. Matters of spatial variability are alsodiscussed and a comparison between homogeneous and heterogeneous representations of permeability isprovided
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Puchalla, Jason Lee. "Measuring cosmic microwave background radiation anisotropy on medium angular scales." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36965.
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Tay, Henry. "Wave propagation from isotropic medium into magnetically uniaxial medium." Ohio : Ohio University, 1988. http://www.ohiolink.edu/etd/view.cgi?ohiou1182873135.
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Germaschewski, Kai. "Pulsausbreitung in Medien mit anisotroper Dispersion." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=961816813.
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Bodian, Pape Arago. "Propagation des ultrasons en milieu hétérogène et anisotrope : application à l'évaluation des propriétés d'élasticité et d'atténuation d'aciers moules par centrifugation et de soudures en Inconel." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00679694.
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En sciences et dans l'industrie pour limiter le nombre de maquettes expérimentales dans les projets R&D afin de mieux comprendre et de bien interpréter les phénomènes ultrasonores complexes observés sur site, des simulations de contrôles ultrasonores sont effectuées. Ces simulations sont d'autant plus réalistes que la description des structures à contrôler est précise, en particulier au niveau des constantes d'élasticité et d'atténuation intrinsèque. Les objectifs de cette étude sont d'améliorer d'une part les connaissances sur l'influence des caractéristiques métallurgiques des matériaux anisotropes et hétérogènes sur la propagation ultrasonore et d'autre part les performances des codes de calcul (logiciel ATHENA d'EDF) qui nécessitent de disposer des données d'entrée pertinentes, notamment en ce qui concerne les constantes d'élasticité et l'atténuation ultrasonore. Cette étude est dédiée à la caractérisation des matériaux à gros grains, comme les aciers austéno-ferritiques moulés par centrifugation et les soudures en acier inoxydable austénitique ou en alliages à base nickel. Un système expérimental unique permettant de mesurer les constantes d'élasticité et l'atténuation en incidence oblique à été mis au point. Le point fort de ce dispositif est qu'il permet de travailler au-delà de l'angle critique longitudinal et donc de mesurer les propriétés d'atténuation des ondes transversales. Les constantes d'élasticité sont déduites des vitesses ultrasonores à partir d'un processus d'optimisation basé sur la résolution de problème inverse. Nous avons montré les potentialités d'algorithmes d'optimisation globaux tels que les algorithmes génétiques moins susceptibles de converger vers des minima locaux de la fonction à minimiser. Les résultats obtenus à partir des mesures expérimentales sont en accord avec la littérature. Des résultats de l'atténuation des ondes longitudinales et transversales par décomposition du faisceau en spectre d'ondes planes sont présentés.
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Younes, Tony. "Méthodologie pour la détermination de la dose absorbée dans le cas des petits champs avec et sans hétérogénéités pour des faisceaux de photons de haute énergie." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30312.
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La radiothérapie stéréotaxique nécessite l'utilisation de petits faisceaux de photons issus d'accélérateur linéaire d'électrons avec (WFF) ou sans filtre égalisateur (FFF) définis généralement par un collimateur multi-lames (MLC). La dosimétrie de ces petits faisceaux représente un défi majeur principalement lié au manque d'équilibre électronique latéral et à la perturbation introduite par la présence des détecteurs. Mes travaux de thèse ont consisté à étudier la métrologie de ces faisceaux WFF et FFF dans des milieux homogènes et hétérogènes en combinant des mesures expérimentales, des calculs Monte-Carlo (MC) et des calculs provenant de deux algorithmes utilisés dans le système de planification de traitements : l'Anisotropic Analytical Algorithm (AAA) et Acuros XB (AXB). Pour mener à bien ces travaux, la première partie a consisté à modéliser le MLC haute définition (HDMLC) de l'accélérateur TrueBeam STx avec la plateforme MC GATE. Des fichiers d'espaces de phases, fournis par le constructeur ont été utilisés auxquels ont été rajoutées les géométries des mâchoires et des lames. Cette modélisation a été validée en comparant les calculs MC aux mesures expérimentales dans le cas de champs définis par le HDMLC à géométrie simple et complexe allant de 0.5×0.5 cm² à 16×16 cm². Cette première étape était indispensable pour pouvoir déterminer les facteurs correctifs à appliquer à la mesure de la dose absorbée dans l'eau des petits faisceaux selon le formalisme de l'IAEA TRS-483. Quatre détecteurs ont été étudiés : deux micro-chambres d'ionisation à cavité d'air et deux détecteurs solides (diode et diamant) et les facteurs correctifs ont été obtenus selon trois méthodologies combinant des calculs MC dans un voxel d'eau ou dans le volume sensible des détecteurs (après modélisation complète de ces derniers) ainsi que des mesures expérimentales par films radiochromiques. Un écart moyen inférieur à 1% a été trouvé entre les trois méthodes et les valeurs publiées dans l'IAEA TRS-483, excepté pour le champ de 0.5×0.5 cm². La comparaison avec les algorithmes AAA et AXB a révélé une supériorité de AXB par rapport au AAA avec un accord inférieur à 1% pour le champ 1×1 cm². Pour approfondir l'analyse des facteurs correctifs, les spectres de fluence électronique au sein des détecteurs ont été déterminés afin de séparer les contributions liées à la composition atomique (volume sensible, enrobage) et à la taille du volume sensible. L'impact du potentiel d'ionisation a également été évalué. Pour cela, un code de calcul de fluence différentielle en énergie pour les photons et les électrons a été développé et implémenté dans GATE après l'avoir validé par confrontation avec un autre code MC EGS. L'étape suivante s'est articulée autour de la métrologie des petits faisceaux dans des milieux hétérogènes de type poumon et os. Les calculs MC et AXB permettent d'exprimer la dose absorbée dans le milieu (Dm) et par conversion de la rapporter en dose absorbée dans l'eau (Dw) alors que les algorithmes conventionnels (tel que le AAA) expriment en général directement la Dw. L'impact des compositions atomiques sur le calcul de la dose absorbée, sur la conversion de Dm à Dw ainsi que sur la modification de fluence électronique au sein des hétérogénéités a été analyséStereotactic radiotherapy is based on the use of small photon beams delivered from a linear accelerator with flattening filter (WFF) or flattening filter free (FFF) usually defined by a multi-leaf collimator (MLC). Yet, small field dosimetry is challenging due to the lack of lateral electronic equilibrium and the fluence perturbation introduced by the presence of the detector. The aim of this Ph.D. thesis is to combine experimental measurements, Monte Carlo (MC) calculations and also the calculation of the treatment planning system algorithms: Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB), in order to study the metrology of small fields including WFF and FFF beams in homogeneous and heterogeneous media. For this purpose, the first part consisted on modeling the high definition MLC (HDMLC) of the TrueBeam STx with the MC platform GATE. Phase space files provided by the manufacturer were used in addition to the jaws and MLC geometries for the simulations. In order to validate the model, MC calculations were compared to experimental measurements for MLC fields with standard and complex geometries ranging from 0.5×0.5 cm² à 16×16 cm². This part was essential to be able to determine detector specific correction factors that should be applied to measurement of absorbed dose in water as described in the formalism of the IAEA TRS-483. Four detectors were included in this part: two air-filled micro-ionization chambers and two solid state detectors (diode and diamond). The correction factors were determined using three approaches combining MC calculations in a water voxel or in the detectors' sensitive volume (after they were fully modeled) as well as radiochromic film experimental measurements. An agreement better than 1% was found between the three methods and the IAEA TRS-483 values except for the 0.5×0.5 cm² field. AXB was found to be more accurate than the AAA with a difference less than 1% for the 1×1 cm² field. Aiming to understand the effects related to atomic composition (sensitive volume and extracameral components), the size of sensitive volume and the ionization potential on the detectors response, the electron fluence spectral distributions in the detectors were determined. Therefore, a photon and electron fluence calculation code was developed and implemented in GATE. Its verification was carried out by comparing the fluence spectra to those of EGS MC code. Further, the metrology of small fields in heterogeneous media including bone and lung was studied. MC and AXB allow to report the absorbed dose to medium (Dm) and after a conversion to determine the absorbed dose to water (Dm) while conventional algorithms (such as AAA) usually report Dw directly. The impact of the atomic composition on the absorbed dose calculation, the conversion from Dm to Dw and the electron fluence variation in the heterogeneous media was analyzed. AXB Dm calculations showed good agreement with those of MC in all the heterogeneity types as well as the Dw report in the lung heterogeneity (except for the 0.5×0.5 cm2 field). However, in the bone case significant differences (>5%) were found between AAA, AXB and GATE and also film measurements, leading to the conclusion that the Dw of the three algorithms are not equivalent, including between AXB and GATE. These differences were analyzed by modeling the film and with the electronic fluence variation in different medium. Moreover, the results in the bone case showed that the experimental validation of the Dw as in GATE or AXB cannot be performed without a correction
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Kanzaki, Cabrera Takeichi. "Numerical modeling of anisotropic granular media." Doctoral thesis, Universitat de Girona, 2013. http://hdl.handle.net/10803/133834.
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Granular materials are multi-particle systems involved in many industrial process and everyday life. The mechanical behavior of granular media such as sand, coffee beans, planetary rings and powders are current challenging tasks. In the last years, these systems have been widely examined experimentally, analytically and numerically, and they continue producing relevant and unexpected results. Despite the fact that granular media are often composed of grains with anisotropic shapes like rice, lentils or pills, most experimental and theoretical studies have concerned spherical particles. The aim of this thesis has been to examine numerically the behavior of granular media composted by spherical and non-spherical particles. Our numerical implementations have permitted the description of the macroscopic properties of mechanically stable granular assemblies, which have been experimentally examined in a framework of the projects "Estabilidad y dinámica de medios granulares anisótropos" (FIS2008- 06034-C02-02) University of Girona and "Interacciones entre partículas y emergencia de propiedades macroscópicas en medios granulares" (FIS2008-06034-C02-01) University of NavarraEls materials granulars són sistemes de moltes partícules implicats en diversos processos industrials i en la nostra vida quotidiana. El comportament mecànic de conjunts granulars, com la sorra, grans de cafè, anells o pols planetàries, representa actualment un repte per a la ciència. En els últims anys aquests sistemes s’han estudiat àmpliament de forma experimental, analítica i numèrica. De totes maneres, avui dia es continuen obtenint resultats rellevants, i en moltes ocasions, inesperats. Malgrat el fet que els materials granulars sovint estan compostos per grans amb forma anisotròpica, com l’arròs, les llenties o les píndoles, la majoria dels estudis experimentals i teòrics se centren en partícules esfèriques. L’objectiu d’aquesta tesi ha estat analitzar numèricament el comportament dels mitjans granulars compostos per partícules esfèriques i no esfèriques. Els mètodes numèrics implementats han permès la descripció de les propietats macroscòpiques de piles i columnes granulars, que s’han estudiat experimentalment en el marc dels projectes "Estabilidad y dinámica de medios granulares anisótropos" (FIS2008-06034-C02- 02) de la Universitat de Girona i "Interacciones entre partículas y emergencia de propiedades macroscópicas en medios granulares" (FIS2008-06034-C02- 01) de la Universitat de Navarra
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Bird, David John. "Arrival directions of medium energy cosmic rays in the southern hemisphere /." Title page, contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09pb6178.pdf.
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Dauvois, Yann. "Modélisation du transfert thermique couplé conductif et radiatif au sein de milieux fibreux portés à haute température." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC097/document.
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Dans ce travail, les propriétés thermiques effectives du milieu fibreux sont déterminées en tenant compte du couplage conduction et rayonnement. Un échantillon numérique fibreux statistiquement homogène composé de deux phases a été généré en empilant des cylindres finis absorbant dans le vide. Ces cylindres sont dispersés selon des fonctions de distribution de la position de leur centre et de leur orientation. L'interpénétration des cylindres est permis. L'extinction, l'absorption et la diffusion sont caractérisées par des fonctions statistiques radiatives qui permettent de savoir si le milieu est Beerien (ou non). Elles sont déterminées précisément à l'aide d'une méthode de Monte Carlo. On montre que la phase gazeuse a un comportement Beerien et que le phase fibreuse a un comportement fortement non Beerien. Le champ de puissance radiative déposée dans le milieu fibreux est calculé en résolvant un modèle qui couple une Équation du Transfert Radiatif Généralisée (ETRG) et une Équation du Transfert radiatif Classique (ETR). Le modèle de conduction thermique est basé sur une méthode de marche aléatoire ne nécessitant aucun maillage. La simulation du mouvement Brownien de marcheurs dans les fibres permet de résoudre l'équation de l'énergie. L'idée de la méthode est de caractériser la température d'un volume élémentaire par une densité de marcheurs, qui peuvent parcourir le milieu. Le problème est gouverné par les conditions aux limites ; Une concentration constante de marcheurs (ou un flux constant) est associée à une température imposée (ou un flux)In the present work, the effective heat transfer properties of fibrous medium are determined by taking into account a coupling of heat conduction and radiation. A virtual, statistically homogeneous, two-phase fibrous sample has been built by stacking finite absorbing cylinders in vaccum. These cylinders are dispersed according to prescribed distribution functions defining the cylinder positions and orientations. Cylinder overlappings are allowed. Extinction, absorption and scattering are characterised by radiative statistical functions which allow the Beerian behaviour of a medium to be assessed (or not). They are accurately determined with a Monte Carlo method. Whereas the gaseous phase exhibits a Beerian behaviour, the fibre phase is strongly non Beerian. The radiative power field deposited within the fibrous material is calculated by resolving a model which couples a Generalized Radiative Transfer Equation (GRTE) and a classic Radiative Transfer Equation (RTE). The model of conduction transfer is based on a random walk method without meshing. The simulation of Brownian motion of walkers in fibres allows the energy equation to be solved. The idea of the method is to characterize the temperature in an elementary volume by the density of walkers, which roam the medium. The problem is governed by boundary conditions ; A constant concentration of walkers (or a constant flux) is associated with a fixed temperature (or flux)
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Tazi, Hamza. "Propriétés élastiques et anisotropie des roches mères : approche expérimentale multi-échelle et modélisation par milieu effectif." Thesis, Paris Est, 2019. http://www.theses.fr/2019PESC1022.
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La production d’huiles et de gaz issus des réservoirs non conventionnels représente aujourd’hui une très large part de la production d’Amérique du Nord. Une meilleure connaissance des propriétés des roches mères s’avère ainsi un enjeu scientifique et économique. Cette thèse s’oriente autour des propriétés élastiques et de l’anisotropie de ces roches. Elle combine des approches expérimentales à différentes échelles dont les résultats sont intégrés dans des modèles de milieu effectif.Les échantillons caractérisés proviennent des formations Montney et Doig (bassin sédimentaire ouest canadien). Les résultats de nos essais ont été comparés aux données de différentes formations roches mères provenant de la littérature ce qui a permis d’étudier les corrélations entre les propriétés pétroacoustiques et différents paramètres intrinsèques (densité, porosité, composition) et extrinsèques (niveau de confinement appliqué pendant les essais). Les principales observations montrent l’influence de la teneur en argiles et en matière organique et de la porosité sur les vitesses de propagation des ondes, ainsi que l’influence spécifique des argiles sur l’anisotropie du matériau. Les propriétés mécaniques des différents constituants des formations Montney et Doig ont été caractérisées grâce au couplage entre des mesures par nanoindentation et des analyses au MEB-EDS.Les différentes observations et résultats expérimentaux obtenus dans le cadre la thèse ont été intégrés dans une modélisation de type milieu effectif qui se veut représentative de la microstructure des roches mères (peu matures à très matures). Un modèle simplifié constitué de cinq phases isotropes et d’une phase isotrope transverse (argiles) a tout d’abord été défini. Ce modèle permet d’estimer les propriétés élastiques des roches mères mais sous-estime leur anisotropie. Par la suite, ce modèle a été adapté aux spécificités des formations Montney et Doig. Pour ces formations, les observations par microscopie électronique montrent que les argiles et la matière organique sont localisées entre les autres minéraux. Le composite argiles-MO-pores apporte ainsi de la souplesse au milieu en enrobant les autres minéraux. Les propriétés élastiques des différents constituants sont obtenues grâce à la nanoindentation. Les argiles ont été modélisées comme étant isotropes et la muscovite comme étant isotrope transverse. Le modèle propre aux formations Montney et Doig nous a permis d’estimer les propriétés élastiques et l’anisotropie de nos échantillonsThe oil and gas production from unconventional reservoirs represents a large part of North America’s production. Improving the knowledge of source rock characteristics constitutes a major scientific and economic challenge. This thesis focuses on the elastic properties and anisotropy of source rocks and combines a multiscale experimental workflow with modeling using an effective medium approach.The studied samples come from Montney and Doig formations (Western Canada sedimentary basin). Our experimental data have been compared to an experimental database built from literature data of different source rock formations. This comparison illustrates the links between acoustic properties and several source rock internal parameters (density, porosity, composition) and external parameters (confining pressure during acoustic tests). The main observations show the influence of the content of clays and organic matter and of the porosity on the velocities and the specific influence of clays on the anisotropy of source rocks. The different components of Montney and Doig formations have been characterized through the combination of nanoindentation measurements and SEM-EDS analyses.The observations and experimental results of this thesis have been integrated into effective medium models which take into account source rock microstructure. A simple model based on five isotropic phases and one transverse isotropic phase (clays) has first been defined. It allows the estimation of the elastic properties of source rocks, but underestimates their anisotropy. This model has then been adapted to the specificities of Montney and Doig formations. For these formations, SEM observations indicate that clays and organic matter are localized between grains. The clays-OM-pores composite thus adds compliance to Montney and Doig formations by coating the other minerals. The elastic properties measured through nanoindentation are used as input data. The clays are modeled as an isotropic phase and the muscovite as a transverse isotropic phase. The derived model enables us to estimate the elastic properties and the anisotropy of our samples
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Zdravkovic, Lidija. "The stress-strain-strength anisotropy of a granular medium under general stress conditions." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/8919.
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Daher, Naoum. "Principe des puissances virtuelles étendu aux discontinuités et interfaces application à l'acousto-électronique." Besançon, 1987. http://www.theses.fr/1987BESA2022.
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Etablissement du principe des puissances virtuelles pour les milieux continus presentant des discontinuites, des surfaces singulieres et des interfaces. Application aux milieux deformables usuels, puis extension a l'electromagnetodynamique et aux semiconducteurs piezoelectriques. Par combinaison de cette formulation avec les principes de la thermodynamique et par construction de lois de comportement, obtention de systemes differentiels et de conditions aux limites necessaires a l'etude des ondes en volume et a l'interface. Application a l'analyse de la propagation des ondes dans les solides anisotropes purement elastiques, electroelastiques et semiconducteurs en vue de la realisation de dispositifs acoustoelectroniques associant les caracteres acoustique et electronique dans le meme milieu
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Vu, Mai Ba. "Contribution à la caractérisation des milieux (visco-)élastiques anisotropes et hétérogènes : application au tissu osseux." Phd thesis, Université Paris-Est, 2011. http://tel.archives-ouvertes.fr/tel-00674157.
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Ce travail est une contribution à la caractérisation mécanique de l'os cortical. Dansce cadre, les méthodes ultrasonores sont des outils puissants pour aider à cette caractérisation.Ainsi, les phénomènes de propagation d'ondes mis en jeu lors des mesurespar les techniques ultrasonores de transmission axiale à la fréquence centrale de 1 MHzsont modélisés. Des méthodes numériques basées sur la méthode des éléments finis sontmises en oeuvre pour résoudre les systèmes d'équations aux dérivées partielles associéesaux conditions aux limites et initiales pour des tissus dont le comportement est supposé(visco-)élastique, anisotrope et/ou hétérogène. L'analyse des résultats de simulation permetde discuter l'influence des divers paramètres, non seulement en termes de propriétésmatérielles mais aussi géométriques, sur la nature des ondes qui se propagent dans lestissus. Nous avons ainsi pu analyse l'impact de ces paramètres sur la vitesse du premiersignal laquelle est considérée comme un indice pertinent pour mesurer la qualité du tissuosseux. Toujours dans le but de caractériser le tissu osseux, et en particulier pour obtenirdes valeurs de propriétés matérielles aussi proches que possible de la réalité, nous avonsdéveloppé une nouvelle méthode basée sur les développements asymptotiques, du typehomogénéisation périodique, pour prédire les modules d'élasticité effective de l'os corticaldu tissu hétérogène.
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Ignace, Richard, M. Al-Malki, J. Simmons, J. Brown, D. Clarke, and J. Carson. "Scattering Polarization due to Light Source Anisotropy II. Envelope of Arbitrary Shape." Digital Commons @ East Tennessee State University, 2009. https://dc.etsu.edu/etsu-works/6256.
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Aims. We consider the polarization arising from scattering in an envelope illuminated by a central anisotropic source. This work extends the theory introduced in a previous paper (Al-Malki et al. 1999) in which scattering polarization from a spherically symmetric envelope illuminated by an anisotropic point source was considered. Here we generalize to account for the more realistic expectation of a non-spherical envelope shape.Methods. Spherical harmonics are used to describe both the light source anisotropy and the envelope density distribution functions of the scattering particles. This framework demonstrates how the net resultant polarization arises from a superposition of three basic “shape” functions: the distribution of source illumination, the distribution of envelope scatterers, and the phase function for dipole scattering.Results. Specific expressions for the Stokes parameters and scattered flux are derived for the case of an ellipsoidal light source inside an ellipsoidal envelope, with principal axes that are generally not aligned. Two illustrative examples are considered: (a) axisymmetric mass loss from a rapidly rotating star, such as may apply to some Luminous Blue Variables, and (b) a Roche-lobe filling star in a binary system with a circumstellar envelope.Conclusions. As a general conclusion, the combination of source anisotropy with distorted scattering envelopes leads to more complex polarimetric behavior such that the source characteristics should be carefully considered when interpreting polarimetric data
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Nadri, Dariush. "Joint non-linear inversion of amplitudes and travel times in a vertical transversely isotropic medium using compressional and converted shear waves." Curtin University of Technology, Department of Exploration Geophysics, 2008. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=17631.
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Massive shales and fractures are the main cause of seismic anisotropy in the upper-most part of the crust, caused either by sedimentary or tectonic processes. Neglecting the effect of seismic anisotropy in seismic processing algorithms may incorrectly image the seismic reflectors. This will also influence the quantitative amplitude analysis such as the acoustic or elastic impedance inversion and amplitude versus offsets analysis. Therefore it is important to obtain anisotropy parameters from seismic data. Conventional layer stripping inversion schemes and reflector based reflectivity inversion methods are solely dependent upon a specific reflector, without considering the effect of the other layers. This, on one hand, does not take the effect of transmission in reflectivity inversion into the account, and on the other hand, ignores the information from the waves travelling toward the lower layers. I provide a framework to integrate the information for each specific layer from all the rays which have travelled across this layer. To estimate anisotropy parameters I have implemented unconstrained minimization algorithms such as nonlinear conjugate gradients and variable metric methods, I also provide a nonlinear least square method, based on the Levenberg-Marquardt algorithm. In a stack of horizontal transversely isotropic layers with vertical axis of symmetry, where the layer properties are laterally invariant, we provide two different inversion schemes; traveltime and waveform inversion.Both inversion schemes utilize compressional and joint compressional and converted shear waves. A new exact traveltime equation has been formulated for a dipping transversely isotropic system of layers. These traveltimes are also parametrized by the ray parameters for each ray element. I use the Newton method of minimization to estimate the ray parameter using a random prior model from a uniform distribution. Numerical results show that with the assumption of weak anisotropy, Thomsen’s anisotropy parameters can be estimated with a high accuracy. The inversion algorithms have been implemented as a software package in a C++ object oriented environment.
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Azam, Md Ali. "Wave reflection from a lossy uniaxial media." Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1179854582.
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Aris, Mohamed. "Investigations expérimentales des effets de la microstructure sur le comportement des milieux granulaires et sur l'instabilité de liquéfaction." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4018.
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Le travail présenté dans ce mémoire a pour objectif d'aboutir à une meilleure caractérisation expérimentale du comportement non drainé du sable d'Hostun à l'échelle locale, en relation avec les différentes méthodes de reconstitution utilisées. On vise en particulier à mettre en évidence la façon dont la microstructure influence les propriétés des sols granulaires, notamment vis-à-vis de l'instabilité de liquéfaction. Le point clé de ce travail consiste en l'utilisation de capteurs piézoélectriques pour mesurer les vitesses d'onde de cisaillement au sein d'éprouvettes triaxiales reconstituées par trois techniques différentes à savoir le damage humide, la pluviation à sec et la pluviation sous eau. Les résultats obtenus mettent en évidence l'influence considérable du mode de fabrication sur le comportement mécanique du sable. Ils montrent que pour une même densité initiale, et à même pression de confinement, le comportement mécanique observé est très différent selon les trois modes de préparation. Les valeurs de vitesses d'onde de cisaillement enregistrées sont différentes d'un mode de déposition à un autre. Concernant l'anisotropie, le matériau préparé par damage humide présente un certain degré d'anisotropie inhérente, qui est toutefois minimal. En revanche, la pluviation à sec et la pluviation sous eau induisent des structures initiales plus isotropesThis work aims to achieve a better experimental characterization of the undrained behavior of the Hostun HN31 sand at the local scale, depending on the different procedures used for sample reconstitution. We particularly highlight the influence of the microstructure on the mechanical behavior of sand especially in relation to liquefaction instability. The key point of this work consists of the use of piezoelectric transducers to measure shear wave velocities within triaxial sand specimens. These specimens have been prepared by different methods, namely: moist tamping, dry pluviation and water pluviation. The obtained results highlight the considerable influence of the deposition mode on the mechanical behavior of sand. They show that for the same initial density, and at the same confining pressure, the mechanical behavior is very different from the three preparation methods. Furthermore, the values of shear wave velocity are different from one deposition mode to another. Concerning the anisotropy, the material prepared by moist tamping presents an inherent degree of anisotropy, which it is however minimal. On the other hand, dry pluviation and water pluviation induce more isotropic initial structures. Moreover, the initial anisotropy is less important than the anisotropy induced by loading. These experimental results indicate that the initial state of a granular medium can not be described by only couple of scalar variables of initial density and confining pressure: a variable that can reflect the initial microstructure and an evolution law of this variable are necessary to model the experimental observations
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Butterworth, Sean. "Shape and chemical anisotropic particles in low dielectric constant media." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/shape-and-chemical-anisotropic-particles-in-low-dielectric-constant-media(d8ace7a1-8993-4a6b-a50d-2a2ea71c10f8).html.
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Electrophoretic displays (EDPs) are an attractive low power technology for small to large area displays. Such display technology has seen a surge of research interest with the launch of successful e-readers in the market place, owing to their lower power consumption and paper-like quality. This work aims to look at the influence of shape on the electrophoretic mobility of particles for such devices. Crosslinked poly(methyl methacrylate) (PMMA) precursor particles with a narrow size distribution were produced by non aqueous dispersion polymerisation utilising a pump-feed method. To produce shape anisotropic particles an adapted version of the dynamic swelling method for polar media was chosen. Suitable monomers were screened by the use of Hansen solubility theory to find monomers which interact with PMMA but not the solvent. It was found that 2- hydroxyethyl methacrylate (HEMA) and N-hydroxyethyl acrylamide (HEAm) were two such suitable monomers, methyl methacrylate (MMA) was also used as a control series.It was found that cluster-like particle morphologies could be produced by the MMA system by the inclusion of small quantities of crosslinking monomer. This was due to precipitation of higher molecular weight polymer segments to the seed particle surface. The cluster-like morphology could be enhanced by use of a polar crosslinking monomer and by sequential reactions. For the polar system, it was found that the reactions with pure monomer were unclean, due to the solubility mismatch of the monomer and the solvent system. This was overcome by a copolymerisation with MMA. The system showed different particle morphologies could be produced by varying the polar monomer content. In one case a sample of pure dumbbell-like particles could be produced. These dumbbell-like particles are thought to be chemical as well as shape anisotropic owing to monomer composition. EPD evaluation for the particles was undertaken and showed that all particles can become highly charged in low dielectric constant media, but that the shape anisotropic particles are prone to adsorption to the cell walls and electrodes.The work outlined in this thesis shows the first reporting of shape anisotropic polymeric particles produced in low dielectric constant solvents system.
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Zhang, Yuwen. "Excitation des ondes élastiques au sein d'un demi-espace anisotrope à l'aide des transducteurs interdigites : Application au quartz et au niobate de lithium." Besançon, 1988. http://www.theses.fr/1988BESA2034.
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Par synthese de fourier, expression des ondes acoustiques sous forme d'integrale, evaluee dans le champ lointain par la methode de la plus grande pente dans le domaine complexe du nombre d'onde. Determination des ondes de surface et des ondes de volume rampantes d'apres les singularites de l'integrant et des ondes de volume rayonnees qui se propagent dans une direction commandable par la frequence d'excitation, a l'approximation geometrique du rayon. Calcul de leur diagramme de rayonnement pour un grand nombre de configurations du quartz et de linbo::(3). Proposition de nouveaux dispositifs electroacoustiques utilisant ces ondes de volume
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Dolaptchiev, Stamen. "An asymptotic, nonlinear model for anisotropic, large scale flows in the tropics /." Potsdam : Potsdam Institute für Climate Impact Research, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014749296&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Dal, Pai Alexandre [UNESP]. "Anisotropia da irradiância solar difusa medida pelo método de sombreamento Melo-Escobedo: fatores de correção anisotrópicos e modelos de estimativa." Universidade Estadual Paulista (UNESP), 2005. http://hdl.handle.net/11449/101722.
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Universidade Estadual Paulista (UNESP)
No presente trabalho é apresentado um modelo de correção anisotrópico para radiação difusa medida com anel de sombreamento Melo-Escobedo (ME) em função do índice de claridade (razão da radiação global pela extraterrestre). São propostos ainda dois modelos estatísticos da fração difusa isotrópica ( ) e anisotrópica ( ) em função do índice de claridade na estimativa das irradiações horária, diária e mensal. A base de dados das radiações global, direta na incidência e difusa medida pelo anel de sombreamento ME utilizada compreende o período de 1996 a 2002 monitorada pelo Laboratório de Radiometria Solar da UNESP/Botucatu/SP. O modelo de correção anisotrópico, obtido a partir das irradiâncias difusa medida pelo anel de sombreamento Melo-Escobedo (raio 40cm e largura 10cm) e medida pelo método da diferença (referência), considerou três intervalos discretos de por meio de três equações: (0 < < 0,30 - nublado); (0,30 < < 0,65 - parcialmente nublado); e (0,65 < < 1 - aberto). O modelo anisotrópico foi validado comparando-se a irradiância difusa anisotrópica estimada com a irradiância difusa de referência numa base de dados independente, mostrando bons resultados conforme os indicativos estatísticos MBE(%) = 0,25%, 0,51% e -0,38% e RMSE(%)= 5,78%, 9,83% e 12,93% para as coberturas de céu nublado, parcialmente nublado e aberto, respectivamente....
The present work presents an anisotropic correction model as a function of the clearness index (global/extraterrestrian radiation) for the diffuse radiation measurements with the Melo-Escobedo (ME) shadowring. Two statistical estimate models for the isotropic ( ) and anisotropic ( ) diffuse fraction as a function of clearness index are also proposed to estimate the hourly, daily and monthly diffuse irradiations. The global, diffuse measured by the shadowring ME and the direct radiations measurements were provided by the Laboratory of Solar Radiometry of UNESP/Botucatu/SP in the period from 1996 to 2002. The anisotropic correction model, obtained from the comparison between the diffuse irradiance measured by the Melo-Escobedo shadowring (radius of 40cm and width of 10cm) and the diffuse irradiance measured by the difference method (reference), considered three discreet intervals, with three equations: (0 < <0,30 - cloudy); (0,30 < <0,65 - partially cloudy); and (0,65 < <1 - clear). The anisotropic correction model was validated through the comparison of the anisotropic diffuse irradiance and the reference diffuse irradiance with an independent database, showing good results according to the statistical indicators MBE (%) = 0,25%, 0,51% and -0,38% and RMSE (%) = 5,78%, 9,83% and 12,93% for cloudy, partially cloudy and clear skies, respectively. The anisotropic correction model showed to be dependent of the shadowring dimensions, and for a same radius-width relationship, the smaller radius (20cm) and width (5cm) shadowring needed smaller numeric correction than the larger ray (40cm) and width (10cm) one. The anisotropic correction model was applied in the diffuse irradiance measurements obtained with a 5 minutes frequency automated operating system. The algorithm calculated hourly, daily and monthly anisotropic diffuse irradiations and compared to the ones from the reference diffuse ...(Complete abstract, access undermentioned eletronic address).
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Dal, Pai Alexandre 1974. "Anisotropia da irradiância solar difusa medida pelo método de sombreamento Melo-Escobedo : fatores de correção anisotrópicos e modelos de estimativa /." Botucatu : [s.n.], 2005. http://hdl.handle.net/11449/101722.
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Orientador: João Franscisco EscobedoBanca: Luiz Roberto Angelocci
Banca: Paulo Ademar Martins Leal
Banca: Roberto Vicente Calheiros
Banca: Augusto José Pereira Filho
Resumo: No presente trabalho é apresentado um modelo de correção anisotrópico para radiação difusa medida com anel de sombreamento Melo-Escobedo (ME) em função do índice de claridade (razão da radiação global pela extraterrestre). São propostos ainda dois modelos estatísticos da fração difusa isotrópica ( ) e anisotrópica ( ) em função do índice de claridade na estimativa das irradiações horária, diária e mensal. A base de dados das radiações global, direta na incidência e difusa medida pelo anel de sombreamento ME utilizada compreende o período de 1996 a 2002 monitorada pelo Laboratório de Radiometria Solar da UNESP/Botucatu/SP. O modelo de correção anisotrópico, obtido a partir das irradiâncias difusa medida pelo anel de sombreamento Melo-Escobedo (raio 40cm e largura 10cm) e medida pelo método da diferença (referência), considerou três intervalos discretos de por meio de três equações: (0 < < 0,30 - nublado); (0,30 < < 0,65 - parcialmente nublado); e (0,65 < < 1 - aberto). O modelo anisotrópico foi validado comparando-se a irradiância difusa anisotrópica estimada com a irradiância difusa de referência numa base de dados independente, mostrando bons resultados conforme os indicativos estatísticos MBE(%) = 0,25%, 0,51% e -0,38% e RMSE(%)= 5,78%, 9,83% e 12,93% para as coberturas de céu nublado, parcialmente nublado e aberto, respectivamente...(Resumo completo, clicar acesso eletrônico abaixo).
Abstract: The present work presents an anisotropic correction model as a function of the clearness index (global/extraterrestrian radiation) for the diffuse radiation measurements with the Melo-Escobedo (ME) shadowring. Two statistical estimate models for the isotropic ( ) and anisotropic ( ) diffuse fraction as a function of clearness index are also proposed to estimate the hourly, daily and monthly diffuse irradiations. The global, diffuse measured by the shadowring ME and the direct radiations measurements were provided by the Laboratory of Solar Radiometry of UNESP/Botucatu/SP in the period from 1996 to 2002. The anisotropic correction model, obtained from the comparison between the diffuse irradiance measured by the Melo-Escobedo shadowring (radius of 40cm and width of 10cm) and the diffuse irradiance measured by the difference method (reference), considered three discreet intervals, with three equations: (0 < <0,30 - cloudy); (0,30 < <0,65 - partially cloudy); and (0,65 < <1 - clear). The anisotropic correction model was validated through the comparison of the anisotropic diffuse irradiance and the reference diffuse irradiance with an independent database, showing good results according to the statistical indicators MBE (%) = 0,25%, 0,51% and -0,38% and RMSE (%) = 5,78%, 9,83% and 12,93% for cloudy, partially cloudy and clear skies, respectively. The anisotropic correction model showed to be dependent of the shadowring dimensions, and for a same radius-width relationship, the smaller radius (20cm) and width (5cm) shadowring needed smaller numeric correction than the larger ray (40cm) and width (10cm) one. The anisotropic correction model was applied in the diffuse irradiance measurements obtained with a 5 minutes frequency automated operating system. The algorithm calculated hourly, daily and monthly anisotropic diffuse irradiations and compared to the ones from the reference diffuse ...(Complete abstract, access undermentioned eletronic address).
Doutor
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Günther, Anke. "Magnetische Anisotropie gebänderter Eisenerze und deren Beziehung zu kristallographischen Vorzugsorientierungen /." Geesthacht : GKSS-Forschungszentrum, 2003. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=012829479&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Neher, Heiko Peter. "Zeitabhängiges Materialverhalten und Anisotropie von weichen Böden : Theorie und Anwendung /." Stuttgart : Inst. für Geotechnik, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=017316980&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Jean, Philippe. "Propagation d'ondes en milieux anisotropes : application à la sismique entre puits." Phd thesis, Grenoble 1, 1989. http://tel.archives-ouvertes.fr/tel-00781643.
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Ce travail a pour but d'étudier l'influence de la position de la source, du type de la source sur la propagation du champ d'onde dans un milieu stratifié plan, et d'observer l'importance que prendront certaines phases complexes quand la distance entre puits augmentera. Les effets du tubage ne seront pas pris en compte. Le calcul complet des sismogrammes synthétiques a été effectué par la méthode des nombres d'onde discrets, couplée à la méthode de propagation de Kennett. Les résultats montrent, dans le cas où la source est située dans une couche dont les vitesses de propagation des ondes sont plus grandes que celles des couches voisines, que l'énergie du front d'onde diminue rapidement à partir de la profondeur de la source au plus l'offset entre les puits augmente. Des ondes guidées apparaissent dans des couches où les vitesses sont faibles. Comme celles-ci proviennent de l'interférence d'onde n'ayant pas une incidence postcritique sur les interfaces limitant ces couches, des rayonnement d'énergie dans les couches avoisinantes sont observables à partir des différents modes de ces ondes guidées. Quand la source se situe dans une couche où les vitesses de propagation des ondes sont faibles par rapport à celles des couches voisines, les effets vont être très différents. A partir d'offsets relativement faibles, le front direct va avoir une incidence critique sur les interfaces limitant la couche source. Ce qui va engendrer une onde guidée de très forte amplitude. L'essentiel de l'énergie sortira de la couche source, sous là forme d'onde de cisaillement. Mais quel que soit leur mode de création, les diagrammes de polarisation de ces ondes guidées montrent un mouvement elliptique prograde suivant la direction de propagation.
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Tigges, Ulrike. "Untersuchungen zum mehrdimensionalen Wassertransport unter besonderer Berücksichtigung der Anisotropie der hydraulischen Leitfähigkeit /." Kiel : Institut für Pflanzenernährung und Bodenkunde, Universität Kiel, 2000. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=009650111&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Godoy, Denise Aparecida Moreira de. "Anisotropia azimutal elíptica de elétrons de decaimentos de quarks pesados em colisões de Pb-Pb a SNN = 2.76 TeV medida no experimento ALICE." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-07102014-151944/.
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Nessa tese serão apresentadas medidas de anisotropia azimutal elíptica de elétrons de decaimentos de quarks pesados feitas no perimento de colisão de íons pesados ALICE (A Large Ion Collider Experiment, em inglês). As medidas foram obtidas em colisões de Pb-Pb com energia de centro de massa por par de nucleons (psNN) igual a 2.76 TeV com o colisor de hadrons LHC (Large Hadron Collider, em inglês). Colisões ultrarelativísticas de íons pesados podem alcançar temperaturas e/ou densidades de energia suficientemente altas para formar o Plasma de Quarks e Gluons (QGP, na sigla em inglês), o estado da matéria onde os partons estão desconfinados dos hadrons. O parâmetro de anisotropia azimutal elíptica é um dos observáveis mais importantes utilizados no estudo da formação do QGP. Esse parâmetro é quantificado pelo segundo harmônico, denominado v2, da distribuição do ângulo azimutal das partículas em relação ao ângulo do plano de reação, o qual é definido pela direção do parâmetro de impacto e pela direção do feixe de partículas. Medidas de anisotropia azimutal elíptica de quarks pesados (charm e beauty) são interessantes, pois os quarks pesados são sondas sensíveis às propriedades do QGP, visto que eles são predominantemente produzidos em processos iniciais de espalhamento duro e interagem com o meio desconfinado. Medidas de v2 de elétrons de decaimentos de quarks pesados em baixos valores de momento transversal indicam movimento coletivo de quarks pesados e possível termalização no QGP. Por outro lado, medidas de v2 de elétrons de decaimentos de quarks pesados em altos valores de momento transversal são interpretadas como uma dependência da geometria do meio por onde os quarks pesados atravessam e perdem energia. Serão mostrados resultados de v2 de elétrons de decaimentos de quarks pesados em função do momento transversal em colisões de Pb-Pb a psNN = 2.76 TeV em eventos com centralidades 20-40% e 30-50%. O resultado é comparado com previsões teóricas e medida obtida em colisões de Au-Au a psNN = 0.2 TeV no experimento RHIC. Resultados preliminares de v2 de elétrons de decaimentos de charm e beauty, separadamente, também serão mostrados em colisões de Pb-Pb a psNN = 2.76 TeV em eventos com centralidade 30-50%.This thesis presents measurements of the elliptic azimuthal anisotropy of electrons from heavy-flavour decays with the A Large Ion Collider Experiment (ALICE). The measurement is performed for the first time in Pb-Pb collisions at center-of-mass energy per colliding nucleon pair psNN = 2.76 TeV at the Large Hadron Collider (LHC). In heavy-ion collisions at ultrarelativistic energies sufficiently high temperature and/or energy density can be achieved to form the Quark-Gluon Plasma (QGP), the state of matter predicted by Quantum Chromodynamics (QCD) in which quarks and gluons are deconfined from hadrons. One of the most important probes of the QGP formation is the elliptic azimuthal anisotropy, which is quantified by the second harmonic v2 of the particle azimuthal angle distribution with respect to the angle of the reaction plane, which is defined by the impact parameter direction and the beam direction. In addition, heavy quarks (charm and beauty) serve as a sensitive probe of the QGP properties since they are predominantly produced in initial hard scattering processes and interact with the deconfined medium. The transverse momentum dependence of the heavy-flavour decay electron v2 can be used to investigate the QGP properties. The measurement of v2 of electrons from heavy-flavour decays at low transverse momentum provides a way to test whether heavy quarks take part in the collective motion in the medium. Whereas, v2 of electrons from heavy-flavour decays at high transverse momentum is interpreted as a path length dependence of heavy-quark energy loss within the created dense medium. Results of the elliptic azimuthal anisotropy of electrons from heavy-flavour decays as a function of tranverse momentum obtained in 20-40% and 30-50% central Pb-Pb collisions at psNN = 2.76 TeV will be shown. The measurement is compared with theoretical predictions and previous measurement at the RHIC experiment. Preliminary measurements of the elliptic azimuthal anisotropy of electrons from charm and beauty as a function of tranverse momentum in 30-50% central Pb-Pb collisions at psNN = 2.76 TeV will be shown as well.
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Walde, Tom. "Modellierung der Textur- und Anisotropieentwicklung beim Walzen : Kopplung der Finite Elemente Methode mit mikrostrukturbasierten Modellen /." Freiburg, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014638016&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Mälzer, Gotthard. "Mechanische und mikrostrukturelle Untersuchungen zum Kriechverhalten der einkristallinen Superlegierung LEK 94 bei Temperaturen um 1000 °C unter Verwendung einer Minikriechprobe /." Düsseldorf : VDI-Verl, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=015624033&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Barros, Suelen Fernandes de. "Medida do alinhamento atômico de Ta, W e Au por impacto de elétrons pela distribuição angular dos raios x L." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-14062018-103044/.
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Foram realizadas medidas do alinhamento atômico do Ta, W e Au depois da ionização da subcamada L3 desses elementos por impacto de elétrons, via distribuição angular das linhas de raios x L, empregando alvos finos. As medições foram realizadas na linha de feixe de 10100 keV do Microtron de São Paulo. Os alvos foram confeccionados no Laboratório de Filmes Finos, pela técnica de deposição física de vapor (alvo de Au), e no Laboratório de Materiais Magnéticos, pela técnica de sputtering (alvos de Ta e W), enquanto que a caracterização deles foi realizada no Laboratório de Materiais e Feixes Iônicos, pela técnica de espectrometria de retroespalhamento Rutherford. O Microtron de São Paulo, bem como os laboratórios onde os alvos foram confeccionados e caracterizados, estão no Instituto de Física da Universidade de São Paulo. Os raios x decorrentes da ionização dos alvos foram detetados simultaneamente por três Silicon Drift Detectors localizados a 31°, 90° e 125° com relação à direção do feixe incidente. A determinação da eficiência de pico dos detetores foi realizada com um modelo analítico testado separadamente. As intensidades das linhas do multipleto de raios x L foram ajustadas em um único procedimento empregando funções Voigt para descrevê-las. O parâmetro de alinhamento A20 foi estimado a partir do conjunto de intensidades das linhas Ll, L1 e L2. A fim de comparar os resultados experimentais com as previsões teóricas foi calculado o parâmetro de alinhamento com a aproximação de Born de ondas planas não relativística, empregando as aproximações de HartreeSlater e DiracHartreeSlater para descrever os potenciais atômicos. Os resultados experimentais confirmaram a emissão não isotrópica dos raios x decorrentes de vacâncias preenchidas na subcamada L3, sendo que a magnitude desta anisotropia varia com a energia do feixe de elétrons incidente. Além disso, foram observadas anisotropias de sinais opostos para as linhas L1 e L2. A dependência em energia do parâmetro de alinhamento A20 mostra uma queda rápida de A20, com duas inversões de sinal, uma em torno de 2 E/E(L3) e outra em torno de 8 E/E(L3), e um valor não nulo de alinhamento em torno de 10 E/E(L3), para os três elementos estudados. A comparação dos resultados experimentais com os cálculos realizados mostra um bom acordo ate cerca de 5 E/E(L3) para o feixe de elétrons incidente, a partir deste ponto o experimento evidencia uma segunda inversão no sinal de A20, que não é prevista por essa teoria. Este é, a nosso saber, o primeiro trabalho a quantificar o alinhamento atômico na ionização de átomos pesados por impacto de elétrons, via distribuição angular de raios x na faixa de 1 a 10 E/E(L3).Measurements of the atomic alignment of Ta, W and Au after the ionization of the L3 subshell of these elements were performed by electron impact via the angular distribution of x-ray lines employing thin targets. The targets were made in the Laboratório de Filmes Finos, by the technique of physical vapor deposition (Au target), and in the Laboratório de Materiais Magnéticos, by the sputtering technique (Ta and W targets), while their characterization was performed in the Laboratório de Materiais e Feixes Iônicos, by Rutherford Backscattering Spectrometry. The Microtron of São Paulo, as well as the laboratories where the targets were made and characterized, are placed at Instituto de Física of the Universidade de São Paulo. The x-rays from the ionization of the targets were detected simultaneously by three Silicon Drift Detectors placed at 31°, 90° and 125° with respect to the direction of the incident beam. The determination of the full energy peak efficiency of the detectors was performed with an analytical model previously tested. In the data analysis the L x-ray multiplet lines were fitted in a single procedure employing Voigt functions to describe them, and the Ll, L1 and L2 lines were employed simultaneously in the estimation of the alignment parameter A20. In order to compare the experimental results with the theoretical predictions, the alignment parameter was calculated with the non-relativistic plane-wave Born approximation using HartreeSlater and DiracHartreeSlater atomic potentials. The experimental results confirmed the nonisotropic emission of x-rays from filled vacancies in the L3 subshell, with the magnitude of this anisotropy varying with the energy of the incident electron beam. In addition, anisotropies of opposite signs were observed for the L1 and L2 lines. The energy dependence of the alignment parameter A20 shows a sharp fall of A20, with two sign inversions, one around 2 E/E(L3) and another around 8 E/E(L3), and a non-zero alignment value around 10 E/E(L3), for the three studied elements. Comparison of the experimental results with the performed calculations shows a good agreement up to about 5 E/E(L3) for the incident electron beam, from which the experiment evidences a second inversion in the sign of A20, which is not predicted by this theory. This is, to our knowledge, the first work to quantify the atomic alignment in the ionization of heavy atoms by electron impact, via an angular distribution of x-rays in the interval from 1 to 10 E/E(L3).
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Maudet, Florian. "Couches nanostructurées par dépôt en incidence oblique : corrélations microstructure et propriétés optiques pour application aux traitements antireflets hautes performances dans le visible étendu et l'infrarouge." Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2295/document.
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Les traitements antireflets (AR) sont très largement utilisés pour améliorer la transmission de systèmes optiques composés de hublots, lentilles, de lames séparatrices,… Dans cette thèse les gammes spectrales visées sont le visible étendu [400-1800nm] et le moyen infrarouge [3,7-4,8µm]. La méthode de nanostructuration par dépôts de films minces utilisant des techniques PVD en incidence oblique (Oblique Angle Deposition) a été choisie car elle permet d’envisager des AR hautes performances sur une large gamme de longueur d’onde, via un procédé industrialisable. L’introduction de porosité via le contrôle des angles de dépôt est utilisée pour nanostructurer l’architecture de chaque couche et de l’empilement ; méthode permettant de modifier et d’optimiser les propriétés optiques des couches constituantes en vue d’un design complet optimal. Une cartographie des indices effectifs accessibles par OAD a été dégagée concernant les trois matériaux déposés (TiO2, SiO2 et Ge). Mais les propriétés optiques de ces couches nanostructurées diffèrent largement de celles des couches denses du fait de la présence d’anisotropie, de gradient d’indice, de diffusion et d’absorption. A partir de caractérisations microstructurales, chimiques et optiques poussées (AFM, MEB, MET, tomographie FIB, tomographie MET, EDX, EELS, spectrophotométrie et ellipsométrie généralisée) un modèle optique analytique plus complexe et couplé à des analyses par éléments finis (FDTD) est présenté. L’ensemble du travail a permis d’élaborer par OAD de simples antireflet bicouches démontrant déjà de hauts niveaux de transmission, supérieurs aux traitements AR existants (interférentiel) ou en développement (Moth-eyes)Anti-reflective (AR) coatings are widely used to improve the transmission of optical systems composed of window, lenses, separating filters,... In this thesis, the spectral ranges targeted are the extended visible [400-1800nm] and the mid infrared [3.7-4.8µm]. Thin film deposition nanostructuring method using oblique angle deposition (oblique angle deposition) PVD technique was chosen because it allows high performance AR to be considered over a wide wavelength range, by an industrial process. The introduction of porosity with the control of deposition angle is used to nanostructure the architecture of each layer and stack; a method for modifying and optimizing the optical properties of the constituent layers for optimal complete design. A mapping of the effective indices accessible by OAD has been identified for the three materials deposited (TiO2, SiO2 and Ge). However optical properties of these nanostructured layers differ greatly from those of dense layers due to the presence of anisotropy, index gradient, diffusion and absorption. Based on advanced microstructural, chemical and optical characterizations (AFM, SEM, TEM, FIB tomography, TEM tomography, EDX, EELS, spectrophotometry and generalized ellipsometry) a more complex analytical optical model coupled with finite element analyses (FDTD) is presented. All the work has enabled OAD to develop simple two-layer anti-reflective coatings that already demonstrate high levels of transmission, superior to existing (interferential) or work in progress (Moth-eyes) AR treatments
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Melo, Marco Antonio Assis de. "Filtro difusão-mediana com determinação automática dos parâmetros com aplicações em sinais de ECG e sensor piezoelétrico." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-20072009-154001/.
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O objetivo deste trabalho é filtrar sinais corrompidos por ruído Gaussiano ou impulsivo, preservando a amplitude e a morfologia do sinal original. Normalmente, um filtro linear é utilizado nesta tarefa, porém este filtro altera significativamente as amplitudes e as bordas dos sinais, bem como insere atrasos no sinal. Mostra-se neste trabalho que a difusão anisotrópica em conjunto com filtro mediana é muito mais eficaz do que os filtros lineares para esta aplicação. A difusão anisotrópica é uma filtragem iterativa, onde o sinal é filtrado repetidamente. A difusão anisotrópica é controlada por uma função denominada parada-na-aresta, por um parâmetro de escala e pelo número de iterações. Neste trabalho, testamos três bem conhecidas funções parada-na-aresta, concluindo que a função de parada na aresta de Malik e Perona consegue o maior fator de redução de ruído. Infelizmente, esta função é extremamente sensível ao número de iterações, onde o fator de redução de ruído deteriora-se rapidamente antes e depois do ponto ótimo. Como não se conhece o sinal sem ruído, não é possível determinar precisamente qual é o melhor momento de encerrar as iterações do filtro anisotrópico. Desenvolve-se neste trabalho um novo método de parada de difusão baseado na análise da resposta de freqüência do sinal filtrado. Também mostramos como determinar automaticamente um valor de escala adequado. Aplicamos a técnica proposta em eletrocardiograma (ECG). complexo QRS e as Contrações Ventriculares Prematuras (Premature Ventricular Contractions - PVCs) são informações importantes contidas no sinal de ECG. Quando esses sinais são adquiridos no mundo real, eles são freqüentemente corrompidos por eletromiogramas (EMG), artefatos ruidosos provenientes da atividade elétrica associada às contrações musculares. EMG é considerado o ruído de ECG mais difícil de ser eliminado. Ao filtrar o sinal de ECG para remover EMG, não se pode alterar a informação do complexo QRS e anomalia PVC, para não comprometer o diagnóstico clínico. O sinal EMG é modelado como sendo ruído Gaussiano ou, de uma forma mais realística, como ruído com distribuição alfa-estável com características impulsivas. Aplicamos a técnica proposta para filtrar sinais de eletrocardiograma reais do banco de dados de Massachusetts Institute of Technology - Beth Israel Hospital (MIT-BIH). Também é analisada nesta tese a filtragem de sinais provenientes de sensor piezoelétrico. Estes sinais são usados em sistemas reais de corte de aço duro. Em geral uma ferramenta de corte tem sensores piezoelétricos, usados para medição do esforço do corte. Quando a ferramenta de corte se encosta à peça a ser cortada, o sinal do sensor produz uma informação que decai erroneamente ao longo do tempo. Aplicamos a difusão anisotrópica em conjunto com o filtro mediana para determinar o decaimento do sinal do sensor piezoelétrico ao longo do tempo, e assim compensar esta distorção e melhorar o corte de aço duro.This thesis aims to filter signals corrupted by Gaussian or impulsive noise, preserving the amplitude and the morphology of the original signal. Typically, a linear filter is used for this task, but this filter significantly alters the amplitudes and the edges of the signals and inserts delays in the signal. This work shows that the anisotropic diffusion in conjunction with median filter is much more effective than linear filters for this application. The anisotropic diffusion is an iterative filter, where the signal is filtered repeatedly. An edge-stopping function, a scale parameter and the number of iterations control the anisotropic diffusion. In this study, we tested three well-known edge-stopping functions, concluding that the Perona and Maliks function yields the largest noise reduction factor. Unfortunately, this function is extremely sensitive to the number of iterations, where the noise reduction factor deteriorates quickly before and after the optimal point. As we do not have access to the original noiseless signal, it is not possible to determine precisely the best moment to stop the iterations of the anisotropic filtering. We develop in this paper a new method to determine the best stopping time based on the analysis of the frequency response of the filtered signal. We also show how to determine automatically an adequate scale parameter. We apply the proposed technique to filter electrocardiogram (ECG). The QRS complex and Premature Ventricular Contractions (PVCs) are important information in the ECG signal. When these signals are acquired in the real world, they are often corrupted with noise artifacts from the electrical activity associated with muscle contractions called Electromyography (EMG). EMC is considered the most difficult noise to be eliminated from ECG. When the ECG signal is filtered to remove EMG, the information of the QRS complex and the PVC abnormality must not be altered, to not compromise the clinical diagnosis. We model the EMG signal as Gaussian noise or, more realistically, as alpha stable distribution noise with impulsive characteristics. We apply this technique to filter the real ECG signals from the Massachusetts Institute of Technology - Beth Israel Hospital database (MIT-BIH). This thesis also analyzes the filtering of signals from piezoelectric sensor. These signals are used in real systems for cutting hard steel. In general, a cutting tool has piezoelectric sensors, used to measure the cutting force. When the cutting tool touches the part to be cut, the signal from the sensor produces information that falsely decays over the time. We apply the anisotropic diffusion in conjunction with the median filter to determine the decay of the signal, and therefore offset this distortion and improve the hard steel cutting.
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Nair, Nikhil. "A Computationally Efficient Model for the Simulation of Catalytic Monolith Reactors with Detailed Chemistry." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374005338.
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Hauschild, Bernd. "Zur Formulierung eines einfachen Elastizitätsgesetzes für inhomogene Balken aus anisotropen Werkstoffen /." Aachen : Shaker, 1992. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=003672536&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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