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Cette thèse présente une étude sur les rotations dans les espaces discrets en 2 dimensions et en 3 dimensions. Dans le cadre de l'informatique, l'utilisation des nombres flottants n'est pas recommandée du fait des erreurs de calculs que cela implique. Nous avons donc fait le choix de nous concentrer sur les espaces discrets. Dans le domaine de la vision par ordinateur, la rotation est une transformation requise pour de nombreuses applications. L'utilisation de la rotation continue discrétisée donne des résultats de mauvaise qualité. Pour cette raison, il est nécessaire de développer de nouvelles méthodes de rotation adaptées aux espaces discrets. Nous nous sommes principalement intéressés aux angles charnières qui représentent la discontinuité de la rotation dans les espaces discrets. Dans ces espaces, deux rotations d'une image avec deux angles très proches peuvent donner le même résultat, ce qui est capturé par les angles charnières. L'utilisation de ces angles permet de décrire une rotation qui donne les mêmes résultats que la rotation continue discrétisée tout en n'utilisant que des nombres entiers. Ils permettent aussi de définir une rotation incrémentale qui décrit toutes les rotations possibles d'une image digitale donnée. Les angles charnières peuvent être étendus dans les espaces discrets en trois dimensions. Pour cela, on définit les multi-grilles qui sont des plans de rotations contenant trois ensembles de droites parallèles. Elles représentent les discontinuités de la rotation en 3D. Les multi-grilles permettent d'obtenir les mêmes résultats en 3D que ceux obtenus en 2D / This thesis presents a study on rotation in 2 dimensional and 3 dimensional discrete spaces. In computer science, using floating numbers is problematic due to computation errors. Thus we chose during this thesis to work only in discrete space. In the field of computer vision, the rotation is a transformation required for many applications. Using discretized Euclidean rotation gives bad results. Then, it is necessary to develop new rotation methods adapted to the discrete spaces. We mainly studied the hinge angles that represent the discontinuity of the rotation in the discrete space. Indeed, it is possible to perform two rotations of the same digital image with two angles that are slightly different and obtain the same result. This is captured by hinge angles. Using these angles allow us to describe a discrete rotation that gives the same results than the discretized Euclidean rotation without using floating numbers. They also allow describing an incremental rotation that performs all possible rotations of a given digital image. Using hinge angles can also be extended to the rotations in 3 dimensional discrete spaces. The extension requires the multi-grids that are rotation planes containing three sets of parallel lines. These parallel lines represent the discontinuities of the rotation in 3D discrete space. Thus they are useful to describe the hinge angles in rotation planes. Multi-grids allow obtaining the same results in 3D discrete rotations than the results obtained in 2D discrete rotations. This thesis presents a study on rotation in 2 dimensional and 3 dimensional discrete spaces. In computer science, using floating numbers is problematic due to computation errors. Thus we chose during this thesis to work only in discrete space. In the field of computer vision, the rotation is a transformation required for many applications. Using discretized Euclidean rotation gives bad results. Then, it is necessary to develop new rotation methods adapted to the discrete spaces. We mainly studied the hinge angles that represent the discontinuity of the rotation in the discrete space. Indeed, it is possible to perform two rotations of the same digital image with two angles that are slightly different and obtain the same result. This is captured by hinge angles. Using these angles allow us to describe a discrete rotation that gives the same results than the discretized Euclidean rotation without using floating numbers. They also allow describing an incremental rotation that performs all possible rotations of a given digital image. Using hinge angles can also be extended to the rotations in 3 dimensional discrete spaces. The extension requires the multi-grids that are rotation planes containing three sets of parallel lines. These parallel lines represent the discontinuities of the rotation in 3D discrete space. Thus they are useful to describe the hinge angles in rotation planes. Multi-grids allow obtaining the same results in 3D discrete rotations than the results obtained in 2D discrete rotations

The problem of transfer of radiation in a medium with polarized emission, polarized absorption and Faraday rotation of the plane of polarization is formulated. Solutions are obtained for the case of a homogeneous source. In the range of frequencies for which a medium is optically thick the degree of polarization of synchrotron radiation depends on the type of absorption process and is different for synchrotron absorption and for thermal absorption. It is therefore suggested that the low frequency polarization measurements of radio sources with curved spectra may determine whether synchrotron self -absorption or thermal absorption or another process is responsible for the low frequency curvature in spectra of certain radio sources.

The problem of this study was to investigate the effect of the rotation around two axes of the body upon static balance as measured by the stork stand, the headstand, and the one foot balance.

Field studies were conducted to evaluate the effect of crop rotation on annual bluegrass plant population dynamics, seed rain, and seed bank in 1996 and 1997 at two sites. Growth-chamber studies were conducted to determine the influence of the mother plant environment on annual bluegrass germination. The change in population, seed rain, seed in seed bank and germination behavior of annual bluegrass at Site 1 was different from those at Site 2. The highest population of annual bluegrass was observed in the meadowfoam-perennial ryegrass rotation and the lowest population was observed in the continuous perennial ryegrass and meadowfoam-spring wheat rotations at Site 1 in 1997, whereas continuous perennial ryegrass and winter wheat-perennial ryegrass rotations had the highest populations at Site 2 in 1997. Differences in the number of annual bluegrass seed in the seed bank occurred at both sites. The greatest reduction of annual bluegrass seed in the seed bank was observed over time in the meadowfoam-spring wheat rotation at both sites. At both sites, most of the seed was deposited on the surface to 0 to 2.5 cm soil depth and the number of seed decreased with soil depth. The mother plant environment and the date of seed maturity had an effect on annual bluegrass germination. At the seed collection date of 5/8/97, the annual bluegrass seed collected from the canopy of continuous perennial ryegrass and from the seedling perennial ryegrass following meadowfoam had the highest germination at 15/25 C at Site 1. Seed collected from continuous perennial ryegrass on 5/6/97 and 5/22/97 had the highest germination among all test temperatures regimes at Site 2. Seed collected from seedling perennial ryegrass following meadowfoam at the second collection date of 5/28/97 at Site 1 and 5/22/97 at Site 2 had the lowest germination at all temperature regimes except 5 C constant temperature. The 15/25 C was the best temperature regime for germination of annual bluegrass collected from any mother plant environment on any seed collection date at Site 1 and Site 2. / Graduation date: 1999

This thesis is a collection of four papers that explore the economics of forest carbon sequestration and optimal harvest decision, considering carbon storage in three major carbon pools: biomass, dead organic matter and wood product. The first three papers use a dynamic programming approach to determine the optimal harvest decision for a forest stand in the boreal forest of western Canada that provides both timber harvest volume and carbon sequestration services. The last paper uses an analytical model to confirm the findings in the first three papers that show that the optimal rotation age is dependent on the carbon stocks in the dead organic matter and wood product pools. In the first paper, the state of the forest at any point in time is described by stand age and the amount of carbon in the dead organic matter pool. The results of the study indicate that while optimal harvest age is relatively insensitive to carbon stocks in dead organic matter, initial carbon stock levels significantly affect economic returns to carbon management. In the second paper, the system is described by three state variables: stand age and the amount of carbon in the dead organic matter and wood product pools. The results of the study suggest that optimal behaviour of a landowner does not change much between cases where the market considers and ignores carbon storage in the wood product pool or between cases where the market considers and ignores fossil fuel carbon emissions. The third paper demonstrates that alternative baselines have little or no effect on the optimal decision, but can have a large effect on financial return to landowner. In the third paper, the forest stand is described by four state variables: the age of the stand, the initial stand age, carbon stocks in the DOM pool and the initial carbon stocks in the DOM pool. In the last paper, an analytical model is used to demonstrate that the optimal harvest decision is dependent on the initial DOM and wood product stocks. This finding is consistent with the results in the previous papers. / Forest Biology and Management

The accounting profession, particularly the public company auditing profession, has experienced a drastic transformation over the last decade. Following a series of costly accounting scandals that tarnished the profession’s credibility, Congress passed the Sarbanes-Oxley Act of 2002 (SOX) for more rigorous regulation of public companies and public accounting firms. The new policy changed audit interactions with clients and included a mandate for the periodic rotation of audit partners on audit engagements to increase auditor independence. Currently being debated are further changes that may lead to additional restrictions and more work for auditors and their clients. This thesis explores the issue of auditor independence in the audit process and examines whether the periodic rotation of audit firms should be mandated in the U.S.

The leakage flow through straight through labyrinth seals with tooth on stator was investigated by performing CFD simulations .ANSYS Fluent is used to simulate the fluid flow through straight through Labyrinth seals. The effect of seal geometry on discharge coefficient, carry over coefficient and expansion factor is studied by varying clearance, pitch, tooth height, tooth width ,Reynolds number and rotor speed. Derived quantities Such as carry over coefficient, coefficient of discharge and expansion factor are analyzed as a function of the tooth with preceding cavity to predict the effectiveness of the seal. To understand the effect of varying seal geometries and swirl, 2D CFD simulations were performed. It was found that the clearance to pitch ratio is a strong geometry factor which affect the performance of the seal. The carryover coefficient which describes the portion of kinetic energy carried over from one cavity to the next is also examined. It was found to be a function of Reynolds number and shaft speed. Discharge coefficient describes the losses which occur when fluid flows through the cavity and under the tooth. Just like the carryover coefficient, it is also discovered that it is a strong function of Reynolds number and shaft speed.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

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