Dissertations / Theses on the topic 'Scattering'
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Fletcher, John Frederick Alexander. "Scattering and inverse scattering by subfractal random surfaces." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648699.
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Samols, Trevor Mark. "Soliton scattering." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385493.
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Montelongo, Yunuen. "Scattering holography." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709277.
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Smith, Helen. "Scattering ice clouds." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/scattering-ice-clouds(949032cc-fbdd-4fde-a942-163d870a5ddd).html.
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The 2013 meeting of the Intergovernmental Panel on Climate Change concluded that the coupling of clouds to the Earth's climate is one of the biggest uncertainties faced in predicting climate change today. Cirrus clouds are of particular interest because the extensive variability in particle size, shape and complexity poses a number of challenges in the accurate modelling of optical properties. The dependence of the single-scattering properties on particle shape demand accurate representation of the crystal geometries in scattering models, geometries which can vary from simple hexagonal prisms to complex multi-branched aggregates. This work, presented as a series of papers, uses laboratory studies to investigate the single scattering properties of ice crystals. Of particular focus here are columns with internal cavities. The first paper investigates the phase function, P11 and asymmetry parameter, g of varying crystal habits, whilst the second paper focuses on polarised scattering. One of the main findings is the difference in internal structure between hollow columns grown at warmer temperatures (-7 degrees C) and those grown at colder temperatures (-30 degrees C). Measurements were used to create new particle geometries for use in scattering models. The third paper makes use of findings from papers 1 & 2 to create an optical parametrization for cirrus, utilizing the new particle geometry.
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MacDonald, Fred G. R. S. "Positronium - atom scattering." Thesis, Queen's University Belfast, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268233.
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Sandoval, Leonidas. "String scattering amplitudes." Thesis, King's College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261874.
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Satat, Guy. "Imaging through scattering." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98620.
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Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 75-84).
In this thesis we demonstrate novel methods to overcome optical scattering in order to resolve information about hidden scenes, in particular for biomedical applications. Imaging through scattering media has long been a challenge, as scattering corrupts scenes in a non-invertible way. The use of near-visible optical spectrum for biomedical purposes has many advantages, such as optical contrast, optical resolution and nonionizing radiation. Particularly, it has important applications in biomedical imaging, such as sub-dermal imaging for diagnostics, screening and monitoring conditions. We demonstrate methods to overcome and use scattering in order to recover scene parameters. In particular we demonstrate a method for locating and classifying fluorescent markers hidden behind turbid layers using ultrafast time-resolved measurements with a sparse-based optimization framework. This novel method has applications in remote sensing and in-vivo fluorescence lifetime imaging. Another method is demonstrated to resolve blood flow speed within skin tissue. This method is based on a computational photography technique and coherent illumination. This method can be applied in diagnosis and monitoring of burns, wounds, prostheses and cosmetics. A particularly important application of this technology is analysis of diabetic ulcers, which is the main cause for non-traumatic amputations in India. The suggested prototype is suitable for assisting clinicians in assessing the wound healing process. The methods developed in this thesis using ultrafast time-resolved measurements, sparsity-based optimization and computational photography can spur research and applications in biomedical imaging, skin conditions diagnosis and more general modalities of imaging through scattering media.
by Guy Satat.
S.M.
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Ramazanoğlu, Fethï Mübïn. "Scattering and mesons." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36113.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (leaf 22).
We present the P-matrix, an alternative method to parameterize the S-matrix, which is particularly useful for low energy meson-meson scattering. We discuss its basic properties and use it to analyze the isospin 0 and 2 s-wave [pi] [pi] scattering. We construct the S-matrix from our analysis and discuss the physical relevance of its poles. Further details of P for more general cases are provided in the appendices.
by Fethi̇ Mübi̇n Ramazanoğlu.
S.B.
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Kusiak, Steven J. "The scattering support and the inverse scattering problem at fixed frequency /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/6779.
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Schaudt, Kimberly Jean. "Light scattering in dielectric disk arrays and atomic scattering by helium." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185932.
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The exact scalar wave solution for light scattering from a general dielectric disk array is found. The exact solution as well as a numerical solution is also given for an array of three dielectric disks, whose centers are placed on the vertices of an equilateral triangle. The various (differential, total and averaged total) cross sections and the poles of the scattering matrix are given. These results are analyzed in part by considering the effects which arise from the geometry of the system, and in part by comparison with the results (cross sections and poles) for a system with an identical arrangement of three hard (perfectly conducting) disks and with a system of one dielectric disk. This analysis helps rule out structure that arise from the chaos, which is very likely to exist, in the classical (geometric) limit of the three (or more) dielectric disk system. In the future after I study the geometric (classical) and physics (semiclassical) regimes of this system, I plan to reanalyse the exact wave solution in an attempt to discover the traces of the chaos present in the system. Time dependent Hartree-Fock theory (TDHF), with improved formulation and improved computer capabilities, is used to repeat the calculations of charge capture for the He²⁺ on He collision. The results of these calculations allow us to discuss the effects of various numerical truncations and to establish with certainty the viability and the accuracy of TDHF in its application to ion-atom collisions. Initially, we had hoped to find chaos in the TDHF problem, as it is nonlinear. However, due to the complexity and computational difficulties present in the TDHF problem, a simpler scattering system of light scattering from dielectric disk arrays was chosen for study.
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Pandozzi, Fabiano. "Spectroscopic analysis of fractal scattering and hidden layers in complex scattering samples." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106384.
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Near-infrared optical spectroscopic measurement of samples is an important analytical tool for the determination of properties such as particle size, chromophore composition, and concentration. This information is invaluable for sample assessment in pharmaceutical, agricultural, and environmental areas. However, samples often exhibit significant light scattering, which complicates measurements. This thesis investigates chemometric approaches including power law and component analysis methods to extract useful sample information from data, while simplified instrumentation is developed to facilitate the acquisition of meaningful data. Photon time-of-flight (TOF) techniques allow sample optical properties to be estimated using temporally resolved measurements of short pulses of light. However, highly scattering samples, such as granular powders, are difficult to model. The shape of photon TOF profiles is largely influenced by the properties of these samples. A power law analysis technique was used to study TOF profiles, and a method was developed that could simultaneously determine analyte concentration and particle size. Compared to traditional steady-state measurements, a 3-fold improvement for absorption coefficient and up to a 5-fold improvement for particle size estimates was achieved. This analysis technique is applicable to a variety of areas including pharmaceutics, cosmetics, and chemical production. While methods exist for studying the optical properties of homogeneous optically scattering samples, those containing multiple layers present an interesting challenge for analysis. Spatially resolved measurements from layered samples contain information about the different layers present. However, complications arise when the layer to be probed is non-scattering. In a diffuse reflectance configuration, this type of layer does not provide information in the same way scattering layers do. An analysis technique was developed that allowed the separation of absorption and scattering components for such a layered sample. Accurate estimates of chromophore concentration were attained, even when an overlaying scattering layer had thicknesses that varied between 1 and 8 mm. This method has practical applications for medical, environmental, and industrial applications. A novel self-calibrating technique was developed for the estimation of absorbing species in a non-scattering layer embedded in a non-uniform scattering matrix. Spatially-resolved, steady-state, multispectral data were acquired from an optical head phantom with realistic topographical and optical properties. Experimental and mathematical techniques were developed that allowed accurate estimates of chromophore concentration. A limit of detection corresponding to 5 µL of blood in a volume of 150 ml of CSF was achieved. This system and technique can be useful for noninvasive medical measurements, especially cerebral bleed detection. The work presented in this thesis details key improvements for the spectroscopic analysis of homogenous and layered scattering samples. Each of these advancements represents a further development of our existing spectroscopic knowledge. Of particular interest within the medical community is the self-calibrating work, which can be used to developed noninvasive diagnostic techniques aimed at improving patient care.La mesure par spectroscopie optique proche infrarouge est un outil d'analyse important pour déterminer les caractéristiques d'un milieu tel la dimension des particules, l'identification de chromophore, et leur concentration. Cette information est de valeur critique pour l'évaluation d'échantillons dans les domaines pharmaceutiques, d'agriculture et environnementaux. Certains échantillons, par contre, diffusent la lumière considérablement, compliquant la mesure. Cette thèse de doctorat examine des méthodes chimiométries comprenant les règles de puissance et les analyses de composante pour extraire de l'information utile d'échantillons à partir des données, alors que l'instrumentation simplifiée est développée pour faciliter l'acquisition des données signicatives. Les techniques utilisant le temps de vol (TDV) des photons permettent de jauger les propriétés visuelles d'échantillons en utilisant la mesure temporale résolue de courtes pulsations de lumière. Il est difficile, par contre, de trouver un modèle pour les milieux à haute diffusion telles les poudres granuleuses. La configuration du profile du TDV photonique est, en grande partie, influencé par les propriétés de l'échantillon. Une analyse des règles de puissance mathématiques fut utilisée afin d'étudier les profiles du TDV, et une méthode fut développée qui pouvait, simultanément, déterminer la concentration des substances sous analyse ainsi que la grandeur des particules. Comparé aux mesures uniformes de fonctionnement traditionnelles, les estimations du coefficient d'absorption futs amélioré par 3 fois et les estimations de grandeurs ont été améliorées par 5 fois. Cette technique d'analyse s'applique à des domaines variés telle la production de produits pharmaceutiques, cosmétiques et chimiques. Quoique des méthodes existent pour étudier les propriétés optiques de substances homogènes à caractères diffusants, les substances ayant de multiples couches présentent un défi d'analyse intéressant. Les mesures faites à des points variés sur l'échantillon à multiples couches donnent de l'information sur les différentes couches présentes. Par contre, la situation se complique lorsque la couche qui doit être sondée n'est pas diffusante. Une couche ayant un facteur de réflexion atténuée, ne révèle pas d'information de la même façon qu'une couche diffusante. Une technique d'analyse fut élaborée qui a permis la séparation des composants d'absorption et diffusants pour ce genre d'échantillon à couche multiple. Des estimations précises de la concentration chromophore ont été obtenues, même lorsque la couche supérieure avait une épaisseur qui variait de 1 à 8 mm. Cette méthode a une utilité pratique dans les domaines médicaux, environnementaux et industriels.Une technique à auto-calibration inusitée fut développée pour estimer les espèces absorbantes dans une couche non diffusante incorporée dans une matrice diffusante dissemblable. Des données multispectrales à point variées, et avec lumière continue ont été obtenues d'une tête optique fantôme ayant des propriétés topographiques et optiques réalistes. Des techniques expérimentales et mathématiques futs développées qui on permit des estimations précises de la concentration chromophore. Une limite de détection correspondant à 5 µL de sang dans un volume de 150 ml de liquide céphalorachidien fut atteinte. Ce système et cette technique peuvent être utiles pour les mesures médicales non invasives, plus précisément pour la détection de saignement cérébrale.Le travail présenté dans cette thèse de doctorat explique les améliorations saillantes pour l'analyse spectroscopique d'échantillons diffusants homogènes et à couches multiples. Chaque amélioration représente une augmentation de nos connaissances de la spectroscopie. La technique à auto-calibration est particulièrement intéressante pour la communauté médicale, car elle peut être utilisée pour développer des techniques non invasives pouvant améliorer le soin de patients.
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Romankov, Vladyslav. "Scattering anelastico di neutroni." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10542/.
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Lo scopo della tesi è di illustrare le principali tecniche spettroscopiche per l'indagine della materia mediante l'uso dei neutroni come sonda, con particolare attenzione rivolta alla diffusione anelastica su campioni monocristallini. Nel testo vengono esposti i processi di produzione dei neutroni tramite spallazione, fissione e fusione nucleare, e si descrive il reattore nucleare dell'Institut Laue-Langevin (ILL) di Grenoble. Inoltre, viene presentato uno studio della curva di dispersione dei modi vibrazionali acustici di un campione monocristallino di β-stagno a temperatura ambiente, effettuato presso l'ILL tramite un diffrattometro a triplo-asse. I risultati sono confrontati con i modelli teorici disponibili (S. H. Chen) e con dati sperimentali noti (J. M. Rowe).
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Waddell, John M. "Scattering from rough plates." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA304997.
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Grantier, David Raymond. "Chemically induced raman scattering." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30321.
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Nicholls, G. K. "Coherent multiple parton scattering." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358698.
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Cooper, James Neil. "Positron hydrogen molecule scattering." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/12240/.
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In this thesis, we present Kohn variational calculations of scattering and annihilation parameters for very low energy interactions of positrons with molecular hydrogen. Our analysis includes the first application of the Kohn method for this system in which the interelectronic potential in the molecular target is treated explicitly. All previous Kohn calculations on positron hydrogen molecule scattering have avoided this complication by the use of the method of models. The advantage of the explicit treatment over the method of models is that it allows approximate target wavefunctions of a very high accuracy to be admitted more easily to the Kohn calculations. We find that the accuracy of the approximate target wavefunction is an extremely important factor in obtaining reliable results from the calculations. We carry out an extensive investigation of anomalous, nonphysical behaviour in the results of our Kohn calculations. Our explanations of how these anomalies arise and how they may be avoided significantly improves upon the discussions of these phenomena given in earlier accounts of positron hydrogen molecule scattering calculations by other authors. As with all previous models of positron hydrogen molecule scattering, we find discrepancies between the experimental value of the annihilation parameter, Z effective, and the theoretical value of this quantity as determined from our Kohn calculations. Limitations of the model that could explain these discrepancies are discussed and suggestions for future improvements are proposed.
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Smith, Vaughan Allan. "Scattering and ACTH regulation." Thesis, University of Canterbury. Electrical Engineering, 1992. http://hdl.handle.net/10092/5709.
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The work reported in this thesis is concerned with two completely separate topics - scattering and adrenocorticotropic hormone (ACTH) regulation.
The accuracies of two approximate scattering formulations, the Born approximation and geometrical optics, are investigated and compared. The distortion associated with multiple scattering in Born inversion is shown to be severe in situations where the refractive indices of object components are only slightly (<5%) different from the background. Second and higher order multiple scattering is found to contribute negligible distortion to the reconstruction. Backpropagation is explicitly formulated and implemented for receivers in the far-field, but Fourier interpolation is found to be a preferable method for performing Born inversion in the simulation situation. Shift-and-add, a form of frequency diversity processing which has been previously proposed to reduce distortion in Born inversion, is comprehensively tested. Although the anticipated reduction in distortion is not achieved, some improvement is demonstrated. Furthermore, this work shows the need for iterative solutions to realistic inverse scattering problems.
A new solution to the two-dimensional bent-ray computed tomography problem is developed. It is based on a novel ray description which does not require the ray paths to be known. The refractive index distribution is therefore found by solving linear equations, rather than through the conventional process of ray tracing. Reconstructions of circularly symmetric refractive index distributions demonstrate the feasibility of this approach and encourage further development.
The information available from a recently developed method for sampling pituitary effluent (PES) in the horse is examined. The current sampling interval of 30s is found to be appropriate for measuring ACTH and arginine vasopressin (AVP), but not necessarily corticotropin-releasing hormone (CRH). Blood flow variations are found to have essentially negligible effect on measurement of hormone concentrations at the corticotropes.
A recently proposed model of ACTH regulation, derived from static cell culture results, is tested on PES data and found to be inappropriate for the in vivo situation.
The relationships between AVP, CRH, cortisol and ACTH are examined using cross-correlation, pulse analysis and models of ACTH regulation. The pulse analysis indicates that the delay between AVP or CRH and ACTH is 0-308. Results from all three techniques indicate that AVP is the important physiological ACTH secretagogue in the horse. Results from the modeling analysis suggest that the relative potency of AVP and CRH depends on the cortisol concentration, and that when this is low, CRH is the dominant secretagogue. Modeling results also reveal that the principal effects of cortisol on ACTH secretion occur in the pituitary, and not in the brain as is currently believed. In addition, they show that in some situations AVP, CRR and cortisol are sufficient to explain almost all ACTH secretion, although the pulse analysis indicates that additional secretagogues do have physiological effects. Furthermore, this work demonstrates the need for rapid sampling and makes some suggestions regarding important mechanisms operating in the corticotrope in vivo.
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Grundy, Michael J. "Neutron scattering from interfaces." Thesis, University of Bristol, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357011.
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Huxley, Andrew David. "Neutron scattering from superconductors." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239626.
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Dougherty, Martin Eugene. "Ocean bottom seismic scattering." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/52938.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and Woods Hole Oceanographic Institution, 1990.GRSN 589503
Includes bibliographical references (p. 299-301).
by Martin Eugene Dougherty.
Ph.D.
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Buffler, Andy. "Fast neutron scattering analysis." Doctoral thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/17137.
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Bibliography: pages 217-225.The scattering of a beam of fast monoenergetic neutrons is used to determine elemental compositions of small (0.2-1 kg) samples of materials. Particular emphasis is placed on the measurement of concentrations of the elements H, C, N and O, which are the principal constituents of contraband materials, such as explosives and narcotics. Scattered neutrons are detected by liquid scintillators located at forward and at backward angles, and different elements are identified by their characteristic scattering signatures derived either from a combination of time-of-flight and pulse height measurements or from pulse height measurements alone. Atom fractions for H, C, N, O and other elements are derived from unfolding analyses based on these scattering signatures and used to identify materials. Effects of neutron interactions in surrounding materials, either in the neutron beam or between the scatterer and the detectors, can be detected and allowed for in such a way as not to interfere significantly in the identification of the scatterer. The Fast Neutron Scattering Analysis technique provides a non- intrusive method for detecting and identifying sub-kilogram quantities of contraband materials. Methods for locating the positions of small contraband items in packages of volume up to about 0.5m³ are described and a two-stage screening system for detecting contraband hidden in small packages is proposed.
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Maher, Robert Christopher. "Surface enhanced Raman scattering." Thesis, Imperial College London, 2007. http://hdl.handle.net/10044/1/7843.
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Petrak, Benjamin James. "Microcavity Enhanced Raman Scattering." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6354.
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Raman scattering can accurately identify molecules by their intrinsic vibrational frequencies, but its notoriously weak scattering efficiency for gases presents a major obstacle to its practical application in gas sensing and analysis. This work explores the use of high finesse (50 000) Fabry-Pérot microcavities as a means to enhance Raman scattering from gases. A recently demonstrated laser ablation method, which carves out a micromirror template on fused silica--either on a fiber tip or bulk substrates-- was implemented, characterized, and optimized to fabricate concave micromirror templates ~10 µm diameter and radius of curvature. The fabricated templates were coated with a high-reflectivity dielectric coating by ion-beam sputtering and were assembled into microcavities ~10 µm long and with a mode volume ~100 µm3. A novel gas sensing technique that we refer to as Purcell enhanced Raman scattering (PERS) was demonstrated using the assembled microcavities. PERS works by enhancing the pump laser's intensity through resonant recirculation at one longitudinal mode, while simultaneously, at a second mode at the Stokes frequency, the Purcell effect increases the rate of spontaneous Raman scattering by a change to the intra-cavity photon density of states. PERS was shown to enhance the rate of spontaneous Raman scattering by a factor of 107 compared to the same volume of sample gas in free space scattered into the same solid angle subtended by the cavity. PERS was also shown capable of resolving several Raman bands from different isotopes of CO2 gas for application to isotopic analysis. Finally, the use of the microcavity to enhance coherent anti-Stokes Raman scattering (CARS) from CO2 gas was demonstrated.
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Hayes, W. W. "Atom scattering from metals." Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1263396718/.
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Iitaka, Toshiaki. "Inelastic scattering at surfaces /." Electronic version of summary, 1990. http://www.wul.waseda.ac.jp/gakui/gaiyo/1563.pdf.
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Bruna, Joan. "Scattering Representations for Recognition." Palaiseau, Ecole polytechnique, 2013. https://pastel.hal.science/docs/00/90/51/09/PDF/phdmain_final.pdf.
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Ma thèse étudie le problème de la reconnaissance des objets et des textures. Dans ce cadre, il est nécessaire de construire des représentations de signaux avec des propriétés d'invariance et de stabilité qui ne sont pas satisfaites par des approches linéaires. Les opérateurs de Scattering itèrent des décompositions en ondelettes et rectifications avec des modules complexes. Ces opérateurs définissent une transformée non-linéaire avec des propriétés remarquables ; en particulier, elle est localement invariante par translation et Lipschitz continue par rapport à l'action des difféomorphismes. De plus, les opérateurs de Scattering définissent une représentation des processus stationnaires qui capture les moments d'ordre supérieur, et qui peut être estimée avec faible variance à partir d'un petit nombre de réalisations. Dans cette thèse, nous obtenons des nouvelles propriétés mathématiques de la représentation en scattering, et nous montrons leur efficacité pour la reconnaissance des objets et textures. Grâce à sa continuité Lipschitz par rapport à l'action des difféomorphismes, la transformée en scattering est capable de linéariser les petites déformations. Cette propriété peut être exploitée en pratique avec un classificateur génératif affine, qui nous permet d'obtenir l'état de l'art sur la reconnaissance des chiffres manuscrites. Nous étudions ensuite les représentations en Scattering des textures dans le cadre des images et du son. Nous montrons leur capacité à discriminer des phénomènes non-gaussiens avec des estimateurs à faible variance, ce qui nous permet d'obtenir de l'état de l'art pour la reconnaissance des textures. Finalement, nous nous intéressons aux propriétés du Scattering pour l'analyse multifractale. Nous introduisons une renormalisation des coéfficients en Scattering qui permet d'identifier de façon efficace plusieurs paramètres multifractales; en particulier, nous obtenons une nouvelle caractérisation de l'intermittence à partir des coefficients de Scattering ré-normalisés, qui peuvent s'estimer de façon consistanteThis thesis addresses the problem of pattern and texture recognition from a mathematical perspective. These high level tasks require signal representations enjoying specific invariance, stability and consistency properties, which are not satisfied by linear representations. Scattering operators cascade wavelet decompositions and complex modulus, followed by a lowpass filtering. They define a non-linear representation which is locally translation invariant and Lipschitz continuous to the action of diffeomorphisms. They also define a texture representation capturing high order moments and which can be consistently estimated from few realizations. The thesis derives new mathematical properties of scattering representations and demonstrates its efficiency on pattern and texture recognition tasks. Thanks to its Lipschitz continuity to the action of diffeomorphisms, small deformations of the signal are linearized, which can be exploited in applications with a generative affine classifier yielding state-of-the-art results on handwritten digit classification. Expected scattering representations are applied on image and auditory texture datasets, showing their capacity to capture high order moments information with consistent estimators. Scattering representations are particularly efficient for the estimation and characterization of fractal parameters. A renormalization of scattering coefficients is introduced, giving a new insight on fractal description, with the ability in particular to characterize multifractal intermittency using consistent estimators
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Jussila, Adam P. "Simulating Pulsar Signal Scattering in the Interstellar Medium with Two Distinct Scattering Phenomena." Oberlin College Honors Theses / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1528814998720461.
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Macconi, Duccio. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11466/.
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L'attenzione è stata posta su tre fenomeni fondamentali di scattering: Thomson, Compton e Compton inverso. Sono state sottolineate alcune ed eventuali applicazioni astrofisiche di questi e valutate le implicazioni o generalizzazioni che da tali fenomeni possono derivare: Synchrotron Self-Compton, Comptonizzazione ed effetto Sunyaev-Zeldovich termico.
Infine è stato preso un caso astrofisico come applicazione di questi fenomeni: Sagittarius A*, una fonte radio proveniente dal centro della nostra galassia, molto studiata negli anni, citando un articolo pubblicato su una rivista scientifica nel 2012.
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Ceccotti, Emilio. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14066/.
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Lo scattering è il processo in cui un’onda elettromagnetica interagisce con la materia, tipicamente un elettrone libero. In tale interazione l’onda cambia direzione e può modificare la propria energia. Se lo scattering produce solo un cambio di direzione, si parla di scattering Thomson, che risulta particolarmente importante per la definizione di sezione d’urto classica. Quando invece la radiazione perde energia e la trasferisce all’elettrone, si ha lo scattering Compton, viceversa, quando la radiazione guadagna energia sottraendola all’elettrone, si ha l’inverse Compton. Questi ultimi due processi producono una modifica nello spettro energetico (SED) di alcune regioni, fenomeno noto come Comptonizzazione. Nel caso in cui la Comptonizzazione agisca sullo spettro della radiazione cosmica di fondo (CMB), si ha l’effetto Sunyaev-Zel’dovich. In particolare, questo si suddivide in un effetto termico, dovuto agli elettroni liberi molto energetici di una regione che fanno inverse Compton sui fotoni della CMB, e in un effetto cinetico, dovuto al moto relativo della regione rispetto alla CMB. Nel presente scritto si focalizzerà l’attenzione su come si può misurare l’evoluzione della temperatura della CMB fino a redshift z = 1, che è un’applicazione del Sunyaev-Zel’dovich termico, e sul calcolo dell’effetto cinetico nell’alone di gas del Gruppo Locale.
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Cerqui, Valeria. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15545/.
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Lo scattering, o diffusione, è un processo di interazione tra radiazione e materia. In particolare a livello astrofisico i processi rilevanti sono interazioni con particelle libere, solitamente elettroni. Essi vengono suddivisi in: scattering Thomson, in
cui lo scattering produce solamente un cambio di direzione, lasciando invariata l'energia del fotone incidente; scattering Compton, dove il fotone incidente perde energia, trasferendola all'elettrone; Compton inverso, dove viceversa allo scattering
Compton, è l'elettrone a trasferire energia al fotone incidente. Lo studio della variazione dello spettro energetico (SED) dei fotoni in caso di scattering multiplo (Compton e Inverse Compton) viene chiamato Comptonizzazione. Nel caso in cui la Comptonizzazione agisca sullo spettro della radiazione cosmica di fondo
(CMB), si presenta l'effetto Sunyaev-Zel'dovich dove si ha uno shift dello spettro di corpo nero della CMB ad energie lievemente maggiori. Nel presente scritto si focalizzerà l'attenzione sulla profondità ottica Thomson, che si presta a varie applicazioni
astrofisiche. Nello specifico verrà trattato il caso di scattering Thomson nell'ambiente delle symbiotic stars (SS) e come la profondità ottica vari a seconda delle fasi del sistema binario.
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Ubertosi, Francesco. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16208/.
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In questo elaborato vengono presentati i principali processi di scattering che hanno importanti riscontri in astrofisica: scattering Thomson, Compton e Inverse Compton. Vengono anche messi in luce fenomeni di particolare rilevanza, quali la Comptonizzazione e il Synchrotron-Self-Compton. Come applicazioni astrofisiche di tali processi si discute dell'effetto Sunyaev-Zeldovich e dei legami di tale fenomeno con la cosmologia e lo studio degli ammassi di galassie. Inoltre viene presentato il risultato di studi che vanno dal 2000 al 2017 su un jet del quasar PKS 0637-752, che presenta una forte emissione di raggi X. Il dibattito sull'origine di tale emissione vede opposti due processi: da una parte si sostiene lo scattering Inverse Compton dei fotoni prodotti per sincrotrone; dall'altra che i fotoni up-scatterati provengano dalla CMB, la radiazione cosmica di fondo.
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Gugole, Matilde. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16378/.
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In questa tesi si andrà a valutare l’utilizzo dei processi di scattering maggiormente utilizzati in astrofisica fornendo alcuni esempi significativi. Scattering significa diffusione, questa parola molto utilizzata in astrofisica sta ad indicare una vasta gamma di processi di interazione tra particelle libere di materia e radiazione elettromagnetica. Nella prima parte dell’elaborato si andranno ad analizzare le varie sottocategorie di questo fenomeno che sono suddivise in base al valore di energia dei fotoni rispetto a quello della particella. Se la particella di materia è sostanzialmente ferma rispetto al fotone andremo a parlare di Scattering Thomson (1.1) o Scattering Compton (1.2); se invece si muove a velocità relativistica bisognerà introdurre alcune modifiche alla trattazione e si parlerà di processo di Compton inverso (1.3); per tutte le altre tipologie di interazioni si avrà il fenomeno di Comptonizzazione (1.4). Nella seconda parte invece ci si soffermerà su esempi di utilizzo di questi processi nello studio di fenomeni relativi all’ambiente astrofisico. Si parte descrivendo l’utilizzo dello scattering Thomson come specchio per rendere visibile la radiazione assorbita dai dischi di accrescimento degli AGN. Il secondo esempio mostra come lo scattering Compton sia stato utilizzato nell’implementazione di un particolare rivelatore astrononomico posto su alcuni telescopi. Il terzo esempio prevede l’utilizzo dell’effetto Sunyaev-Zel’dovich, legato alla Comptonizzazione, nello studio di ammassi di galassie nella missione del satellite PLANCK. Per concludere si analizza la modalità con cui il fenomeno di Compton Inverso sia stato utilizzato per spiegare parte della fonte di raggi γ nella radiazione extragalattica di fondo attraverso al satellite FERMI.
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Siena, Matteo. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19469/.
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Con il termine Scattering si indica un insieme di meccanismi di diffusione della radiazione da parte della materia. Quando interagiscono con una particella carica, i fotoni possono essere assorbiti e quindi riemessi subito dopo in un'altra direzione cambiando la loro energia iniziale oppure no: nel primo caso si parla di Scattering Compton (SC) mentre nel secondo di Scattering Thomson. Inoltre vi è un processo nel quale è la particella carica (l'elettrone nei processi astrofisici) ad avere un'energia maggiore, che la trasferisce così al fotone incidente; si tratta del caso dell'Inverse Compton (IC) ed è un meccanismo molto rilevante in Astrofisica. Tutti questi processi vengono analizzati nel Capitolo 1, mentre nel Capitolo 2 vengono discusse alcune principali applicazioni dell' IC e dello Scattering Thomson, in particolare nel paragrafo 2.1.1 si approfondisce il fenomeno della Catastrofe Compton, che consiste in uno spropositato aumento della luminosità della sorgente che arriverebbe a produrre fotoni via via sempre più energetici diventando una potente sorgente di raggi X e gamma. Queste emissioni, però, non sono state osservate finora e nonostante questo possa essere spiegato per alcune sorgenti tramite una semplice applicazione dell'effetto Doppler, per altre, come le Intra-Day Variable Sources (IDVS), ciò non è possibile, come mostrato nel lavoro pubblicato (e riassunto nella seguente trattazione sempre nel paragrafo 2.1.1) da O. Tsang e J.G. Kirk nel 2007, i quali riesaminano il problema della catastrofe per tali sorgenti mostrando che l'assenza del fenomeno appena descritto può essere spiegato apportando delle modifiche ai processi in gioco. Infine, nell'ultimo paragrafo si analizza il concetto di Luminosità di Eddington, una delle principali applicazioni in ambito astrofisico dello Scattering Thomson.
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Ciccarelli, Cristiano. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/19940/.
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Con il termine scattering si indica una vasta gamma di processi dovuti all’interazione onda-particella, dove la prima viene deflessa (ossia cambia
traiettoria) a causa di un urto con la seconda. Qui saranno analizzati due
fenomeni basati su quest’interazione; a seconda dell’energia dell’onda incidente infatti abbiamo: lo scattering Thomson a basse energie, processo in cui
l’onda viene esclusivamente deviata, e lo scattering Compton ad alte energie,
in cui il fotone, tramite l’urto, trasferisce parte della propria energia alla particella ferma (tipicamente un elettrone). Verr`a studiato anche il caso in cui
sia l’elettrone ad essere pi`u energetico del fotone, questo processo `e chiamato
Inverse Compton (IC) e tramite questo fenomeno l’onda, urtando, acquisisce
energia dalla particella. Nel Capitolo 1 saranno analizzati questi tre scenari e, successivamente, i fenomeni di Synchrothron Self-Compton, Catastrofe
Compton e Comptonizzazione, dovuti alla combinazione del processo di IC
rispettivamente con l’emissione per Sincrotrone e con lo scattering Compton.
Nel secondo capitolo verranno invece illustrate tre applicazioni astrofisiche
di questi fenomeni: prima con lo scattering Thomson e il suo ruolo nello studio degli AGN, qualora questi siano nascosti dai loro tori oscuranti, poi con
l’Inverse Compton e il suo contributo alla Radiazione Extragalattica di Fondo
e infine con una conseguenza fondamentale del fenomeno della Comptonizzazione, l’ effetto Sunyaev Zel’dovich, che permette di identificare ammassi di
galassie studiando la Radiazione Cosmica di Fondo.
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Zangarelli, Riccardo. "Processi di scattering in astrofisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21201/.
Full textAbstract:
L'elaborato contiene una descrizione generale dei principali processi di scattering di importanza astrofisica, a partire dal più semplice fenomeno di scattering Thomson; si prosegue con lo scattering Compton e inverse Compton, del quale si evidenzia la relazione con il sincrotrone (synchrotron self-Compton). Viene analizzata l'evoluzione di uno spettro dominato dai processi Compton e inverse Compton (Comptonizzazione), e si conclude la trattazione dei processi in sè con una breve descrizione dello scattering ad opera della polvere. Infine, vengono esposti degli esempi di applicazioni dei processi in modo da giustificare l'importanza astrofisica di questi ultimi.
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Chen, Xiaojun. "Multiple Scattering from Bubble Clouds." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_theses/36.
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Multiple scattering effects from bubble clouds are investigated in this study. A high performance, general purpose numerical tool for multiple scattering calculations is developed. This numerical tool is applied in three computational scenarios in this study. The total scattering cross section of a bubble cloud is investigated. Numerical results indicate that the resonant frequency of the bubble cloud is much lower than that of a single bubble. The variation of resonant frequency of multiple scattering is also studied. It is found that the resonant frequency decreases as the number of bubbles increases, or as the void fraction of the bubble cloud decreases. Phase distributions of bubble oscillations in various multiple scattering scenarios are presented. It is found that, at resonance, the bubbles synchronize to the same phase, which is indicative of the lowest mode of collective oscillation. At wave localization, half of the bubbles oscillate at phase 0 while the other half oscillate at phase Pi. An intuitive interpretation of this behavior is given.
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Ott, Frédéric. "Neutron scattering on magnetic nanostructures." Habilitation à diriger des recherches, Université Paris Sud - Paris XI, 2009. http://tel.archives-ouvertes.fr/tel-00429509.
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Öhrn, Angelica. "Neutron Scattering at 96 MeV." Doctoral thesis, Uppsala universitet, Tillämpad kärnfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8425.
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Data on elastic scattering of 96 MeV neutrons from 56Fe, 89Y and 208Pb in the angular interval 10-70° are presented. The previously published data on 208Pb have been extended, as a new method has been developed to obtain additional information at the most forward angles. The results are compared with phenomenological and microscopic optical potentials. The theory predictions are in general in good agreement with the experimental data. A study of the deviation of the zero-degree cross section from Wick's limit has been performed. The data on 208Pb are in agreement with Wick's limit, while those on lighter nuclei overshoot the limit significantly. A novel analysis method has been developed to obtain the inelastic neutron emission cross sections from the existing 56Fe data. The method is based on folding a trial spectrum with the response of the detector setup. The data cover the angular interval 26-65° and an excitation energy range of 0-45 MeV, ranges hitherto not studied. The results are compared with nuclear model predictions and found to be in good agreement with the experimental data.
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Mohammed, Abdelsalam. "Theoretical Studies of Raman Scattering." Doctoral thesis, KTH, Teoretisk kemi (stängd 20110512), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-28332.
Full textAbstract:
Different theoretical approaches have been presented in this thesis to study the Raman scattering effect. The first one is response theory applied up to third order of polarization, where the determination of α, β and γ is used to calculate linear Raman scattering (resonance Raman scattering (RRS) and normal Raman scattering (NRS)), hyper Raman scattering (HRS) and coherent anti-Stokes Raman scattering (CARS), respectively. The response theory refers to adiabatic time-dependent density functional theory in the complex domain with applications on RRS and NRS, and to a recently developed methodology (Thorvaldsen et al. [105, 106]) for the analytic calculation of frequency-dependentpolarizability gradients of arbitrary order, here with applications on CARSand HRS. Various systems have been studied with the response theory, such as explosive substances (DNT, TNT, RDX and H2O2), optical power limiting materials (platinum(II) acetylide molecules), DNA bases (methylguanine-methylcytosine) and other systems (Trans-1,3,5-hexatriene and Pyridine). We have explored the dependency of the calculated spectra on parametrization in terms of exchange-correlation functionals and basis sets, and on geometrica loptimization. The second approach refers to time-dependent wave packet methodology for RRS and its time-independent counterpart in the Kramers-Heisenberg equation for the scattering cross section, which reduces the calculation of the RRS amplitude to computation of matrix elements of transition dipole moments between vibrational wave functions. The time-dependent theory has been used to examine RRS as a dynamical process where particular attention is paid to the notion of fast scattering in which the choice of photon frequency controls the scattering time and the nuclear dynamics. It is shown that a detuning from resonance causes a depletion of the RRS spectrum from overtones and combination bands, a situation which is verified in experimental spectra. The cross section of NRS has been predicted for the studied molecules to be in the order of 10−30 cm2/sr. A further increase in sensitivity with a signal enhancement up to 104 to 105 is predicted for the RRS technique, while CARS conditions imply an overall increase of the intensity by several orders of magnitude over NRS. In contrast to RRS and CARS, the HRS intensity is predicted to be considerably weaker than NRS, by about four orders of magnitude. However, silent modes in NRS can be detected by HRS which in turncan provide essential spectroscopic information and become complementary to NRS scattering. With the above mention methodological development for NRS, RRS, CARS and HRS, we have at our disposal a powerful set of modelling tools for the four different Raman techniques. They have complementary merits and limitations which facilitate the use of these spectroscopes in applications of Raman scattering for practical applications, for instance stand-off detection of foreign substances.QC 20110112
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Leaman, Nye Abigail. "Scattering of internal gravity waves." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/238679.
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Internal gravity waves play a fundamental role in the dynamics of stably stratified regions of the atmosphere and ocean. In addition to the radiation of momentum and energy remote from generation sites, internal waves drive vertical transport of heat and mass through the ocean by wave breaking and the mixing subsequently produced. Identifying regions where internal gravity waves contribute to ocean mixing and quantifying this mixing are therefore important for accurate climate and weather predictions. Field studies report significantly enhanced measurements of turbulence near 'rough' ocean topography compared with those recorded in the ocean interior or near more gradually varying topography (e.g. Toole et al. 1997, J. Geophys. Res. 102). Such observations suggest that interaction of waves with rough topography may act to skew wave energy spectra to high wavenumbers and hence promote wave breaking and fluid mixing. This thesis examines the high wavenumber scatter and spatial partitioning of wave energy at 'rough' topography containing features that are of similar scales to those characterising incident waves. The research presented here includes laboratory experiments using synthetic schlieren and PIV to visualise two-dimensional wavefields produced by small amplitude oscillations of cylinders within linear salt-water stratifications. Interactions of wavefields with planar slopes and smoothly varying sinusoidal topography are compared with those with square-wave, sawtooth and pseudo knife-edge profiles, which have discontinuous slopes. Far-field structures of scattered wavefields are compared with linear analytical models. Scatter to high wavenumbers is found to be controlled predominantly by the relative slopes and characterising length scales of the incident wavefield and topography, as well as the shape and aspect ratio of the topographic profile. Wave energy becomes highly focused and the spectra skewed to higher wavenumbers by 'critical' regions, where the topographic slope is comparable with the slope of the incident wave energy vector, and at sharp corners, where topographic slope is not defined. Contrary to linear geometric ray tracing predictions (Longuet-Higgins 1969, J. Fluid Mech. 37), a significant back-scattered field can be achieved in near-critical conditions as well as a forward scattered wavefield in supercritical conditions, where the slope of the boundary is steeper than that of the incident wave. Results suggest that interaction with rough benthic topography could efficiently convert wave energy to higher wavenumbers and promote fluid mixing in such ocean regions.
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Antonsen, Carolina. "Surface scattering using KeV ions." Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/5393.
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Klos, Richard A. "Scattering from X-ray mirrors." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/35710.
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Scattering from X-ray Mirrors deals with the the phenomena observed when x-rays are reflected from high quality mirror surfaces at grazing incidence. The presence of micro- irregularities in the reflecting surface causes power to be deviated away from the specular direction and into the wings of the angular distribution of radiation. Both theoretical and experimental investigations are presented. The two principal theories of the scattering of electromagnetic radiation are reviewed and are shown to produce identical results in the smooth surface limit. The scalar theory is further developed so as to be applicable to a scattering surface which can be described by an arbitrary surface height distribution function for any surface autocovariance function. The theoretical advances reported suggest a means by which the surface height distribution statistics of mirror surfaces might be derived from experimental scattering measurements. The experimental work in the thesis deals with a scattering experiment designed to test these theoretical developments. The development work involved in the construction of the Variable Angle Scattering Experiment (VASE) is presented and the anomalous results obtained from scattering measurements from two test flat x-ray mirrors are discussed. A shadowing model is devised to account for the anomalous results from the VASE. The shadowing model is then shown to be in good agreement with the VASE data and with data from other scattering experiments. The shadowing model, which provides a means of measuring the properties of pure mirror surfaces, is further developed to enable measurements of surface structure on mirrors which have become specked with small sparse contaminant features, thus allowing highly sensitive estimates of contaminant density and height to be made.
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Gaspard, Pierre. "Chaos, scattering and statistical mechanics." Doctoral thesis, Universite Libre de Bruxelles, 1996. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212440.
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Slaughter, Daniel Stephen, and d. slaughter@aip org au. "Superelastic Electron Scattering from Caesium." Flinders University. Chemistry Physics and Earth Sciences, 2007. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20071009.100421.
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This thesis describes an experimental study of superelastic electron scattering from
the 6^2P_3/2
state of caesium. The present status of electron-atom collision studies is
initially reviewed and the motivation behind the current work is then presented. A
description of the theoretical framework is subsequently provided in the context of
the present experimental study, followed by an overview of the several theoretical
approaches for describing electron-atom interactions which are currently available.
The apparatus and experimental setup used throughout the project are also described
in detail. Technical specifications and data are provided, including diagrams (where
appropriate) for a laser frequency locking system, electron gun and spectrometer,
atomic beam source and data acquisition system. The experimental procedures are
explained and discussed, including a detailed analysis of the optical pumping
process required to excite the atomic target. A substantial component of this project
was to address several potential sources of systematic error and to reduce these
wherever possible. All of the errors and uncertainties relevant to the experiment are
discussed in chapter 5.
In chapter 6 the results of the present superelastic electron scattering experiments are
reported for incident electron energies of 5.5eV, 8.5eV and 13.5eV, corresponding
to superelastic electron energies of 7eV, 10eV and 15eV. These results are presented
as three reduced Stokes parameters, P1, P2, P3 and a coherence parameter, P+ . For
comparison, predictions from a number of currently available theories are presented alongside the experimental results. Finally, conclusions are drawn on this work in the context of the current status of electron-atom scattering from alkali-metals.
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Hornidge, David Lee. "Elastic photon scattering from deuterium." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0024/NQ43514.pdf.
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Ryan, Patricia Ann. "TE Scattering from Short Bumps." Connect to resource, 1987. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1223494770.
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Schreiber, A. W. "Spin dependent deep inelastic scattering /." Title page, contents and abstract only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phs378.pdf.
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Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1991.Copies of author's previously published articles inserted. Includes bibliographical references (leaves 171-190).
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Garousi, Mohammad R. (Mohammad Reza). "Superstring scattering from Dirichlet branes." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40351.
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We derive fully covariant expressions for all two-point scattering amplitudes of two massless closed strings from a Dirichlet p-brane. This construction relies on the observation that there is a simple relation between these D-brane amplitudes in type II superstring theory and four-point scattering amplitudes for type I open superstrings. From the two-point amplitudes, we derive the long range background fields for the D-branes, and verify that as expected they correspond to those of extremally charged p-brane solutions of the low energy effective action.
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Nield, V. M. "Neutron scattering studies of disorder." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316918.
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An, Shuwang. "Neutron scattering from adsorbed species." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297936.
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