Dissertations / Theses on the topic 'Inhomogeneous'
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Tsai, Wei-Feng. "Inhomogeneous Hubbard models." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1691819901&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Reich, Thorsten Hendrik Bozzo. "Inhomogeneous hard platelet fluids." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983423806.
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Feder, David L. "Inhomogeneous d-wave superconductors." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30085.pdf.
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Feder, David. "Inhomogeneous d-wave superconductors /." *McMaster only, 1997.
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Campbell, Robert Alan. "Inhomogeneous conformal cosmological models /." Title page, contents and summary only, 1985. http://web4.library.adelaide.edu.au/theses/09PH/09phc1888.pdf.
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Lim, Woei Chet. "The Dynamics of Inhomogeneous Cosmologies." Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/1196.
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In this thesis we investigate cosmological models more general than the isotropic and homogeneous Friedmann-Lemaître models. We focus on cosmologies with one spatial degree of freedom, whose matter content consists of a perfect fluid and the cosmological constant. We formulate the Einstein field equations as a system of quasilinear first order partial differential equations, using scale-invariant variables. The primary goal is to study the dynamics in the two asymptotic regimes, i. e. near the initial singularity and at late times. We highlight the role of spatially homogeneous dynamics as the background dynamics, and analyze the inhomogeneous aspect of the dynamics. We perform a variety of numerical simulations to support our analysis and to explore new phenomena.
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Lee, Delman. "Seismic imaging through inhomogeneous media." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305556.
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Arthur, Sarah Jane. "Supernova remnants in inhomogeneous media." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293739.
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Shim, Douglas Fook Kong. "Physics of inhomogeneous polymer systems." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387012.
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Taherzadeh, Shahram. "Sound propagation in inhomogeneous media." Thesis, Open University, 1997. http://oro.open.ac.uk/44452/.
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Hern, Simon David. "Numerical relativity and inhomogeneous cosmologies." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624503.
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Zhang, Yi. "Inhomogeneous deformation in metallic glasses." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613414.
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Borneman, Troy W., David G. Cory, and Martin D. Hürlimann. "Signal optimization in inhomogeneous fields." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192112.
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We demonstrate that pulses derived using Optimal Control Theory (OCT) techniques can be used to significantly enhance the robustness of the Carr-Purcell-Meiboom-Gill sequence (CPMG) [1,2] to inhomogeneities in the static BB0 field. By numerically inverting the Liouville - von Neumann equation, OCT pulses were derived that can be used directly in place of hard pulses in the CPMG sequence to greatly improve the bandwidth of refocusing. To retain the echo stability achieved by the Meiboom-Gill correction to the Carr-Purcell sequence, the refocusing pulses were designed to perform a unitary π-rotation as opposed to just a state inversion transfer. To illustrate this approach we present an example of optimized pulses that show an improved CPMG-like behavior with complete excitation and multiple refocusing over a bandwidth of +/- 2.6 γB1,max B with a pulse duration limited to 10 t180.
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Garg, Himani. "Particle laden inhomogeneous elastic turbulence." Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1I003/document.
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Les expériences de laboratoire montrent que, même dans des solutions très diluées, l’interaction des polymères avec des écoulements fluides peut modifier considérablement les propriétés des écoulements turbulents ou, si l’écoulement est laminaire, peut déclencher un nouveau type de mouvement irrégulier appelé «turbulence élastique». Les écoulements dans un tel régime dynamique sont prometteurs pour améliorer l'efficacité du mélange dans les applications microfluidiques, qui impliquent souvent la présence d'impuretés de taille finie en suspension, telles que des particules solides petites et lourdes. La compréhension de la dispersion des particules dans les écoulements à grand nombre de Reynolds des fluides newtoniens et non newtoniens a déjà été abordée dans des études antérieures, qui ont mis en évidence des effets à la fois à grande et à petite échelle et est un sujet d'intérêt à la fois fondamental et pour des applications environnementales ou industrielles par exemple. Cependant, la dynamique des particules dans les écoulements élastiques et turbulents reste encore peu explorée. L’étude ici vise à étudier les propriétés d’agrégation de particules matérielles ponctuelles (plus lourdes que le fluide porteur) dans les fluides viscoélastiques dans des conditions de turbulence élastique (c’est-à-dire dans le cas de faible inertie du fluide et de grande élasticité). Nous effectuons des simulations numériques directes bi-dimensionelles d’écoulements périodiques avec cisaillement moyen de Kolmogorov avec des solutions de polymères dilués décrites par le modèle Oldroyd-B. Les caractéristiques à petite et grande échelle de la distribution résultante inhomogène de particules sont examinées, en se concentrant sur leur connexion avec la structure sous-jacente de l’écoulement . Notre analyse révèle que les particules sont préférentiellement regroupées dans des régions où les polymères sont instantanément maximalement étirés. L’intensité d’un tel phénomène dépend de l’interaction paramétrée par le nombre de Stokes, entre l’inertie des particules et l’échelle de temps typique associée à l’écoulement de turbulence élastique, et est la plus grande pour des valeurs intermédiaires d’inertie de particules. En particulier, il est montré que la concentration préférentielle de suspensions de particules inertielles dans de tels écoulements ressemblant à la turbulence découle de la nature dissipative de leurs dynamiques. Nous établissons une caractérisation quantitative de ce phénomène (utilisant la corrélation et la dimension de Kaplan-Yorke) qui permet de le relier à l’accumulation de particules dans des régions de l’écoulement filamenteuses fortement déformées produisant des grappes de dimension fractale faiblement supérieure à 1. À plus grande échelle, les particules subissent une ségrégation de type turbophorétique dans la direction non-homogéne de l'écoulement. En effet, nos résultats indiquent que la distribution des particules est fortement liée aux structures moyennes de l’écoulement de type turbulent. En raison de la turbophorèse, les profils de densité moyenne atteignent leur maximum dans les régions où la diffusivité turbulente est la plus faible. L'inhomogénéité à grande échelle de la distribution des particules est interprétée dans le cadre d'un modèle dérivé dans la limite d'inertie des particules, petite mais finie. Les caractéristiques qualitatives de différents observables (telles que L'écart quadratique moyen de la distribution des particules par rapport à la distribution uniforme) sont, dans une large mesure, indépendantes de l'élasticité du l’écoulement. Quand celle-ci est augmentée, on constate cependant que cette dernière diminue légèrement le degré global moyen de mélange turbophorétiqueLaboratory experiments show that, even in very dilute solutions, the interaction of polymers with fluid flows can dramatically change the properties of turbulent flows or, if the flow is laminar, can trigger a new sort of irregular motion named “elastic turbulence”. Flows in such a dynamical regime are promising for enhancing mixing efficiency in microfluidic applications, which often involve the presence of suspended finite-size impurities, like small and heavy solid particles. The understanding of particle dispersion in high-Reynolds number flows of Newtonian, as well as non-Newtonian, fluids were addressed by previous investigations, and it is a subject of interest both at a fundamental level and for applications, e.g., environmental or industrial ones. However, the dynamics of particles in elastic turbulent flows are still quite unexplored.The present study aims at investigating the aggregation properties of pointlike material particles (heavier than the carrying fluid) in viscoelastic fluids in elastic turbulence conditions (i.e. in the limit of vanishing fluid inertia and large elasticity). We carry out extensive direct numerical simulations of the periodic Kolmogorov mean shear flow of two-dimensional dilute polymer solutions described by the Oldroyd-B model. Both the small- and large-scale features of the resulting inhomogeneous particle distribution are examined, focusing on their connection with the underlying flow structure. Our analysis reveals that particles are preferentially clustered in regions of instantaneously maximally stretched polymers. The intensity of such a phenomenon depends on the interplay, parametrized by the Stokes number, between the particle inertia and the typical time scale associated with the elastic turbulence flow, and is the largest for intermediate values of particle inertia.In particular, it is shown that the preferential concentration of inertial particle suspensions in such turbulent-like flows follow from the dissipative nature of their dynamics. We provide a quantitative characterization of this phenomenon (using correlation and Kaplan-Yorke dimension) that allows to relate it to the accumulation of particles in filamentary highly strained flow regions producing clusters of fractal dimension slightly above 1.At larger scales, particles are found to undergo turbophoretic-like segregation along the non-homogeneity direction of the flow. Indeed, our results indicate that the particle distribution is strongly related to the mean turbulent-like structures of the flow. As an effect of turbophoresis, average density profiles peak in the regions of lowest turbulent eddy diffusivity. The large-scale inhomogeneity of the particle distribution is interpreted in the framework of a model derived in the limit of small, but finite, particle inertia. The qualitative characteristics of different observables (such as root-mean-square deviation of the particle distribution, relative to the uniform one) are, to a good extent, independent of the flow elasticity. When increased, the latter is found, however, to slightly reduce the globally averaged degree of turbophoretic unmixing
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Snigireva, Nina. "Inhomogeneous self-similar sets and measures." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/X682.
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Brockmann, Dirk. "Superdiffusion in scale-free inhomogeneous environments." Doctoral thesis, [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969638884.
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Gupta, Rahul. "Supernova Cosmology in an Inhomogeneous Universe." Thesis, Stockholm University, Stockholm University, Department of Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-42162.
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The propagation of light beams originating from synthetic ‘Type Ia’ supernovae, through an inhomogeneous universe with simplified dynamics, is simulated using a Monte-Carlo Ray-Tracing method. The accumulated statistical (redshift-magnitude) distribution for these synthetic supernovae observations, which is illustrated in the form of a Hubble diagram, produces a luminosity profile similar to the form predicted for a Dark-Energy dominated universe. Further, the amount of mimicked Dark-Energy is found to increase along with the variance in the matter distribution in the universe, converging at a value of ΩX ≈ 0.7.
It can be thus postulated that at least under the assumption of simplified dynamics, it is possible to replicate the observed supernovae data in a universe with inhomogeneous matter distribution. This also implies that it is demonstrably not possible to make a direct correspondence between the observed luminosity and redshift with the distance of a cosmological source and the expansion rate of the universe, respectively, at a particular epoch in an inhomogeneous universe. Such a correspondences feigns an apparent variation in dynamics, which creates the illusion of Dark-Energy.
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Umakanthan, Saravanan. "Mechanics of prestressed and inhomogeneous bodies." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4241.
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In finite elasticity, while developing representation for stress, it is customary to require
the reference configuration to be stress free. This study relaxes this requirement
and develops representations for stress from a stressed reference configuration. Using
the fact that the value of Cauchy stress in the current configuration is independent of
the choice of the reference configuration, even though the formula used to compute
it depends on the choice of the reference configuration, the sought representation is
obtained. It is then assumed that there exists a piecewise smooth mapping between
a configuration with prestresses and a configuration that is stress free, and the representation
obtained above is used to study the mechanical response of prestressed
bodies. The prestress fields are obtained by directly integrating the balance of linear
momentum along with the traction free boundary condition. Then, different classes
of boundary value problems for the type of inhomogeneous and prestressed bodies of
interest are formulated and studied. For the cases studied, it is found that even the
global measures like axial-load required to engender a given stretch ratio for a prestressed
body vary from the homogeneous stress free bodies, though not significantly.
The local measures - stress and deformation - in a prestressed body differ considerably
from their homogeneous stress free counterparts. The above gained knowledge is applied
to understand the mechanics of circumflex arteries obtained from normotensive and hypertensive micro-mini pigs. It is found that the deformation of these arteries
when subjected to inflation and axial extension is not of the form r = r(R), õ =
ã, z = Z. Comparison is also made between the response of an artery at various
levels of smooth muscle activation and stretch ratio as well as normotensive and
hypertensive specimens, using statistical methods.
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Grupp, Michael [Verfasser]. "Scattering in inhomogeneous systems / Michael Grupp." München : Verlag Dr. Hut, 2011. http://d-nb.info/101144142X/34.
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Lim, Kian Min. "DNS of inhomogeneous reactants premixed combustion." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/247342.
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The search for clean and efficient combustors is motivated by the increasingly stringent emissions regulations. New gas turbine engines are designed to operate under lean conditions with inhomogeneous reactants to ensure cleanliness and stability of the combustion. This ushers in a new mode of combustion, called the inhomogeneous reactants premixed combustion. The present study investigates the effects of inhomogeneous reactants on premixed combustion, specifically on the interactions of an initially planar flame with field of inhomogeneous reactants. Unsteady and unstrained laminar methane-air flames are studied in one- and two-dimensional simulations to investigate the effects of normally and tangentially (to the flame surface) stratified reactants. A three-dimensional DNS of turbulent inhomogeneous reactants premixed combustion is performed to extend the investigation into turbulent flames. The methaneair combustion is represented by a complex chemical reaction mechanism with 18 species and 68 steps. The flame surface density (FSD) and displacement speed S_d have been used as the framework to analyse the inhomogeneous reactants premixed flame. The flames are characterised by an isosurface of reaction progress variable. The unsteady flames are compared to the steady laminar unstrained reference case. An equivalence ratio dip is observed in all simulations and it can serve as a marker for the premixed flame. The dip is attributed to the preferential diffusion of carbon- and hydrogen- containing species. Hysteresis of S_d is observed in the unsteady and unstrained laminar flames that propagate into normally stratified reactants. Stoichiometric flames propagating into lean mixture have a larger S_d than lean flames propagating into stoichiometric mixtures. The cross-dissipation term contribution to S_d is small (~~10%) but its contribution to the hysteresis of S_d is not (~~50%). Differential propagation of the flame surface is observed in the laminar flame that propagates into tangentially stratified reactants. Stretch on the flame surface is induced by the differential propagation, which in turn increases the flame surface area.
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Hemming, Christopher John. "Resonantly forced inhomogeneous reaction-diffusion systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0022/MQ50344.pdf.
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Shahine, Bilal H. "Photon dose calculations in inhomogeneous media." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ56620.pdf.
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Oliwa, Chris. "Some mathematical problems in inhomogeneous cosmology." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63697.pdf.
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Kettenis, Mark Martinus. "On the inhomogeneous magnetised electron gas." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2001. http://dare.uva.nl/document/60339.
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Clancy, Dominic. "Homogeneous and inhomogeneous superstring cosmological models." Thesis, Queen Mary, University of London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249229.
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Rose, Hamish. "Light propagation in an inhomogeneous universe." Thesis, University of Canterbury. Physics, 2002. http://hdl.handle.net/10092/6183.
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This thesis examines the effect of inhomogeneities on the magnitude-redshift relationship, focusing particularly on the redshift.
We show that a perturbed FRW universe which has the same global behaviour as an exact FRW universe does not have the same light propagation behaviour due to the relationship between redshift and the radial coordinate being influenced by the inhomogeneities introduced. The change in redshift along a light beam depends on the rate of expansion of space so an understanding of the effect of inhomogeneities on the local rate of expansion of space is necessary in order to study the effect of inhomogeneities on redshift.
We create a new description of the evolution of matter fluctuations in the weakly non-linear regime which also describes a relationship between the matter density and the local expansion rate of space. This is subsequently used in the development of a new method of calculating the relationship between the angular diameter distance and the redshift of a distant object.
We use the new magnitude-redshift relationship in conjunction with the supernova data to estimate cosmological parameters and find that
- to a high level of confidence Ω∆ is non-zero
- most likely flat universe is one with cosmological parameters close to {Ωm) Ω∆} = {0.3, 0.7}.
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Heidernätsch, Mario. "On the diffusion in inhomogeneous systems." Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-169979.
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Ziel dieser Arbeit ist die Untersuchung des Einflusses der stochastischen Interpretation der Langevin Gleichung mit zustandsabhängigen Diffusionskoeffizienten auf den Propagator des zugehörigen stochastischen Prozesses bzw. dessen Mittelwerte. Dies dient dem besseren Verständnis und der Interpretation von Messdaten von Diffusion in inhomogenen Systemen und geht einher mit der Frage der Form der Diffusionsgleichung in solchen Systemen. Zur Vereinfachung der Fragestellung werden in dieser Arbeit nur Systeme untersucht die vollständig durch einen ortsabhängigen Diffusionskoeffizienten und Angabe der stochastischen Interpretation beschrieben werden können. Dazu wird zunächst für mehrere experimentell relevante eindimensionale Systeme der jeweilige allgemeine Propagator bestimmt, der für jede denkbare stochastische Interpretation gültig ist. Der analytisch bestimmte Propagator wird dann für zwei exemplarisch ausgewählte stochastische Interpretationen, hier für die Itô und Klimontovich-Hänggi Interpretation, gegenübergestellt und die Unterschiede identifiziert. Für Mittelwert und Varianz der Prozesse werden die drei wesentlichen stochastischen Interpretationen verglichen, also Itô, Stratonovich und Klimontovich-Hänggi Interpretation. Diese systematische Untersuchung von inhomogenen Diffusionsprozessen kann zukünftig helfen diese Art von, in genau einer stochastischen Interpretation, driftfreien Systemen einfacher zu identifizieren. Ein weiterer wesentlicher Teil der Arbeit erweitert die Frage auf mehrdimensionale inhomogene anisotrope Systeme. Dies wird z.B. bei der Untersuchung von Diffusion in Flüssigkristallen mit inhomogenem Direktorfeld relevant. Obwohl hier, im Gegensatz zu eindimensionalen Systemen, der Propagator nicht allgemein berechnet werden kann, wird dennoch der Einfluss der Inhomogenität auf Messgrößen, wie die mittlere quadratische Verschiebung oder die Verteilung der Diffusivitäten, bestimmt. Anhand eines Beispiels wird auch der Einfluss der stochastischen Interpretation auf diese Messgrößen demonstriertThe aim of this thesis is to investigate the influence of the stochastic interpretation of the Langevin equation with state-dependent diffusion coefficient on the propagator of the related stochastic process, or its averages, respectively. This helps to obtain a deeper understanding and to interpret measurement data of diffusion in inhomogeneous systems and is accompanied with the question of the proper form of the diffusion equation in such systems. To simplify the question, in this thesis only systems are considered which can be fully described by a spatially dependent diffusion coefficient and a given stochastic interpretation. Therefore, for several experimentally relevant one-dimensional systems, the respective general propagator is determined, which is valid for any possible stochastic interpretation. Then, the propagator for two exemplary stochastic interpretations, here the Itô and Klimontovich-Hänggi interpretation, are compared and the differences are identified. For mean and variance of the processes three major interpretations are compared, namely the Itô, the Stratonovich and the Klimontovich-Hänggi interpretation. This systematic research on inhomogeneous diffusion process may help in future to identify these kind of, in exactly one stochastic interpretation, drift-free systems more easily. Another important part of this thesis extends this question to multidimensional inhomogeneous anisotropic systems. This is of high relevance, for instance, for the research of diffusion in liquid crystalline systems with an inhomogeneous director field. Although, in contrast to one-dimensional systems, the propagator may not be calculated generally, the influence of the inhomogeneity on measurement data like the mean squared displacement or the distribution of diffusivities is determined. Based on one example, also the influence of the stochastic interpretation on these quantities is demonstrated
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Devany, Daniel L. "Sound propagation in the inhomogeneous ocean." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28551.
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Finlayson, Neil. "Inhomogeneous lens stuctures for integrated optics." Thesis, University of Glasgow, 1985. http://theses.gla.ac.uk/4929/.
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The thesis is concerned with the design, analysis, fabrication am evaluation of integrated optic lenses which are inhomogeneous either in physical shape or in refractive index profile. The thesis has nine chapters. Chapter one, the introduction, illustrates the importance of these lenses within the domain of integrated optiCS, where the complicated mathematical functions required to describe the lens profiles are most easily realised. Connections are made between the study of these lenses and the exciting new field of optical computing. A special class of non-uniform lenses which are conceptually perfect optical instruments forms the main area of interest in the present study. Historically, the development of these lenses has followed two distinct lines, related to two possible methods of physically obtaining the required variation in path of light rays passing through the lens. In one method the optical path is made to vary directly, whilst the other method involves controlling the fi'lysical path, and thus the optical path, through the principle of equivalence. The dual development has been continued in the field of integrated optiCS, where lenses based on direct control of the optical path are termed variable-index lenses and those based on physical path control are termed geodesic lenses. The perfect variable-index lens studied in this work was the well-known Luneburg lens. Perfect geodesic lens designs have also been published. The design formulae for both types of lens are presented in chapter two. A simpler lens, of spherical geometry, is also presented which is easily analyzed and characterised and which serves as an archetypal model against which the performance of the more sophisticated lenses can be assessed. Chapter three investigates the problems involved in modelling fabrication conditions in a thermal-evaporation-invacuum environment so that lens profiles can actually be constructed. Chapter four goes into methods of tracing rays through these lenses in some detail. Ray-tracing has long been the classical tool of optical designers, providing a useful guide to optical performance. Ray methods, which effectively provide image error evaluations, are not entirely-appropriate for those lenses which are conceptually perfect within the geometrical optics approximation. Diffraction effects prevent the lenses from attaining true perfection. In such cases the wave-field produced by the lenses in the image space is the important quantity. In chapter five, the beam-propagation method (BPM) is used to study diffraction arrl associated effects in inhomogeneous lenses. '!he method allows the propagation of complicated waveshapes in lnhomogeneous media, normally a difficult task. Furthermore, anlsotropic effects and the interaction between acoustic waves aoo optical waves can be studied with the method. Negative focal shifts are reported which are not predicted by geometrical optics or the usual approximate diffraction theories. The fabrication of lenses is considered in chapter six. Planar waveguide measurements car r ied out on the var ious materials used in the study are presented. A major problem in the fabrication of geodesic lenses, that of obtaining a uniform wavegulde layer over the complete lens area, is dealt with in some detail in chapter seven. In chapter eight, extensive tests on the experimental performance of several lenses are reported. Near diffraction-limited performance is reported for geodesic lenses. More limited performance figures are obtained for Luneburg lenses though the possibility of high performance is lndicated if profile resolution can be improved. The themes of the thesls are pulled together for discussion in chapter nine and conclusions are drawn as to the relative merits of the various lenses. Possible means of improving fabrication procedures, thus driving lenses closer to ultimate resolution limits, are presented. The greatest problem faced is that of scatter ing in the waveguide, which appears to be accentuated as the waveguide traverses the lens surface. If the scattering problem can be successfully dealt with it is concluded that integrated optical lenses could be important and viable components in addresslng the problem of fast, high-throughput data processing.
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Humphreys, Neil Paul. "Obervational analysis of the inhomogeneous universe." Thesis, University of Portsmouth, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310380.
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Hancorn, Simon Douglas John. "Nuclear magnetic resonance in inhomogeneous fields." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389838.
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Gupta, Ajay. "Turbulent inhomogeneous autoignition of liquid fuels." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/51547.
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Autoignition is a multi-physics phenomenon that occurs in wide-ranging engineering applications, such as diesel engines, gas turbines and jet-engine afterburners. In these applications, autoignition occurs in the presence of flow inhomogeneities and turbulence. Further, liquid fuel autoignition presents a case of chemically reacting flow where processes such as jet break-up, atomisation, droplet evaporation (interfacial heat and mass transfer), turbulent mixing and chemical reaction occur simultaneously in the presence of important flow, mixture and phase inhomogeneities. The multi-scale nature and direct coupling between these various contributing processes, present a challenging fundamental problem which cannot be understood by extrapolation from homogeneous, inhomogeneous (gaseous) and even single droplet combustion studies. This thesis presents an experimental study on autoignition of polydispersed droplets generated by single liquid jets of pure liquid n-heptane and n-pentane injected axisymmetrically from a circular nozzle into a confined turbulent hot coflow of air at atmospheric pressure. Distinct phenomena are identified concerning the emergence of various autoignition regimes --- no autoignition, random spots and continuous flame; the occurrence of these regimes depends on the reaction conditions of air temperature, air velocity, and liquid fuel injection velocity. In the random spots regime, autoignition appears in the form of well-defined localised spots occurring randomly along the length of the reactor. Optical measurements of these random spots are made from which the autoignition lengths/locations are measured and are used to infer average delay (or residence) times from injection. At higher air temperatures and lower liquid fuel injection velocities, autoignition is observed to move closer to the injector; the corresponding delay times also decrease. With increasing air velocity and hence turbulent fluctuations, autoignition moves downstream but the delay times decrease. The shorter delay times are also associated with faster evaporation of the liquid fuel. The results from this work suggest that turbulent inhomogeneous autoignition of liquid fuels cannot be directly predicted from chemical delay times from homogeneous studies and that the effects of evaporation, and turbulent mixing, as quantified by the mixture fraction and conditional scalar dissipation rate must be accounted for. The results also provide insights into the flow conditions leading up to the various observed autoignition phenomena for liquid fuels, and constitute a valuable data-set that can contribute towards developing and validating models of advanced multiphase turbulent combustion and chemically reacting flows.
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Batycky, Richard Panko. "Inhomogeneous Stokes flow through porous media." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36640.
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Bull, Philip J. "Dark energy and the inhomogeneous universe." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:8032ef45-5be2-451d-9cab-ebeccdf389f2.
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In this thesis, I study the relativistic effects of matter inhomogeneities on the accelerating expansion of the Universe. The acceleration is often taken to be caused by the presence of an exotic fluid called Dark Energy, or else a non-zero 'cosmological constant' term in the field equations of General Relativity. I consider whether this result could instead be an artefact caused by using an incorrect model to interpret observations. The standard 'concordance' cosmological model assumes the Cosmological Principle, which states that the matter distribution on large scales is homogeneous. One possibility is that correction terms appear in the field equations when small-scale inhomogeneities are smoothed over to produce this homogeneous model. These 'backreaction' effects could affect the dynamics of the spacetime, causing an apparent acceleration. I clarify the relationship between acceleration of the averaged spacetime and acceleration inferred from observable quantities, and show that they are closely related in statistically-homogeneous spacetimes. Another possibility is that the Universe could be inhomogeneous on large scales. If there was a large ‘void’, with us at the centre, the lensing of light by the void could reproduce the observations that imply cosmic acceleration. I show that a popular class of void models, based on spherically-symmetric Lemaitre-Tolman-Bondi spacetimes, are unable to simultaneously fit a selection of observational data, thus effectively ruling-out this possibility. These data include the Kinematic Sunyaev-Zel'dovich (KSZ) effect, which is a distortion/shift of the Cosmic Microwave Background (CMB) frequency spectrum caused by the Compton scattering of photons by hot gas in galaxy clusters. This, and other distortions of the CMB frequency spectrum, are sensitive to the degree of anisotropy in the CMB about a scattering cluster. I suggest tests involving these observables that exploit the strong link between isotropy and homogeneity to (a) distinguish between different causes of a deviation from spatial flatness on the horizon scale, and (b) potentially confirm the Cosmological Principle using observations. Finally, I describe a novel Bayesian CMB component separation method for extracting the Sunyaev-Zel'dovich signal of clusters from CMB sky maps.
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Adach, J. "Focussed ultrasonic fields in inhomogeneous media." Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/847127/.
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The simplest source of focussed ultrasound used in medicine is the spherical cap transducer. It appeared that the theory of O'Neil, invariably used for predictions had not been previously tested comprehensively under narrowband low amplitude conditions. Extensive measurements on four weakly focussed transducers in water have shown that this theory is a poor predictor of the field actually radiated under these conditions. If the nominal geometrical parameters of a transducer are replaced in the theory by effective values derived from pressure amplitude extrema, a greatly improved fit between theory and experiment can be realised. A reliable protocol for the determination of effective parameters has been proposed. It has been shown that the effective parameters defined from measurements in water can be used with comparable success to predict the fields in castor oil. A novel method, using a spherical cap transducer and a miniature hydrophone, has been developed for the measurement of ultrasonic attenuation in penetrable media. Use of the technique for measuring the frequency dependence of the coherent scattering component of the attenuation in a suspension of polystyrene beads in a castor oil matrix, presenting refractive index variations of 35%, gave results in good agreement with the theory of Waterman and Truell. Amplitude measurements in the suspension have shown that the coherent part of the field is not defocussed. The defocussing observed in soft human tissue such as breast, by Poster and Hunt, appears to be largely due to the incoherent scattering contribution and its quantification is identified as the subject of future investigation.
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Grassi, Matías Pablo. "Spin waves in inhomogeneous magnetization distributions." Thesis, Strasbourg, 2021. http://www.theses.fr/2021STRAE014.
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Des distributions inhomogènes de l’aimantation existent lorsque le matériau n’est pas uniforme, ou lorsqu’une texture magnétique se forme dans un matériau homogène. Dans les deux cas, les symétries brisées modifient l’excitation et la propagation des ondes de spin et donnent lieu à des phénomènes surprenants. Dans ce contexte, nous avons étudié la propagation des ondes de spin dans une bicouche avec un contraste de l’aimantation de saturation dans la configuration Damon-Eshbach. Nous avons trouvé, à l’aide de simulations et expériences (spectroscopie d'ondes de spin propagatives et diffusion de Brouillon), que le système montre une très forte non-réciprocité en fréquence qui peut être utilisée pour réaliser une diode magnonique. Par ailleurs, nous avons étudié la dynamique des ondes de spin dans des couches minces qui présentent des domaines magnétiques en rubans faibles. Nous avons montré que ces ondes de spin peuvent être interprétées comme une extension des modes de Damon-Eshbach dans l’état saturé, qui s’adaptent à la brisure de symétrie. Nous avons également montré que les deux modes d’ondes de spin de plus basse fréquence correspondent aux modes de Goldstone et Higgs de la texture en rubans. Ces résultats ont été confirmés par des mesures de diffusion Brillouin et de résonance ferromagnétiqueInhomogeneous magnetization distributions may exist because the magnetic parameters are distributed, or because magnetic textures nucleate in homogenous materials. In both cases, the broken symmetries affect the spin-wave excitation and propagation, leading to a number of intriguing phenomena. In this context, we have studied the propagation of spin waves in a bilayer with a saturation magnetization contrast for the Damon-Eshbach configuration. We have found, by means of simulations and experiments (Propagating Spin Wave Spectroscopy and Brillouin Light Scattering), that this system shows a strong frequency non-reciprocity which can be used for the realization of a spin-wave diode. We have also studied the spin-wave dynamics in thin films which exhibit weak magnetic stripe domains. We have shown how these modes can be interpreted as an extension of the Damon-Eshbach spectrum of the saturated state, which adapts to the symmetry breaking. Furthermore, we have identified the two lowest frequency modes to the Goldstone- and Higgs- modes of the stripe texture. These results were confirmed by Brillouin Light Scattering and Ferromagnetic Resonance experiments
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Niemi, Daniel, and Joel Hambraeus. "Heat Transport in Inhomogeneous Harmonic Chains." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-275699.
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It is still to this day a challenge for theoretical physicists to derive Fourier’s law from microscopic models. Motivated by this, we study in this thesis the thermal conduction properties of harmonic chains. A semi-analytical method and simulation are used to find that on average the conduction through harmonic chains resembles Fourier like conduction when impurities of the form k_i=kw_i and 1/m_i=1/m*w_i are introduced, where k_i and m_i are the spring constants and masses of the chain and w_i are weights drawn from a random distribution. A few of these distributions are studied in detail, with similar results.Also the classical field theory limit of this model is studied. It is shown by analytical means that heat is transported diffusively in this model when impurities are introduced, whereas the transport is completely ballistic in the absence of impurities.
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De, Klerk David. "Investigating multi-directional inhomogeneous granular suspensions." Doctoral thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31229.
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Granular flows in rotating drums find many applications in industry, even though the dynamics of their granular media is not fully understood. Several models of granular flow and granular suspensions (where a viscous fluid is present in the voids between the granular particles) have been proposed in the last decade and a half. These models are unified in the way that dimensional analysis is employed to describe bulk properties of the flow in terms of a number of dimensionless parameters. However, applicability to rotating drums has not been demonstrated for many of these models. Furthermore, most studies rely on numerical simulations or experiments of slowly rotating drums that are not easily identified with industrial applications that operate in higher Froude regimes. This thesis presents a series of Positron Emission Particle Tracking (PEPT) experiments and Discrete Element Method (DEM) simulations of rotating drums with a viscous fluid. The three aims of the thesis are, to investigate the use of the Ergodic hypothesis when analysing PEPT data, to test the use of the lubrication approximation in the DEM simulations and to compare results from rotating drums to the latest models of granular rheology and granular suspensions. Two sets of PEPT experiments were carried out with a drum (radius R = 230 mm and length L = 200 mm) which was forced to rotate around its axis. The first series of experiments, used to investigate the use of the ergodic hypothesis, used a fixed rotation rate (ω = 0.6ωc = 0.6 p g/R) and three different particle sizes (5 mm, 8 mm and 10 mm). A radio labelled tracer particle’s location was recorded for 10 h for each of the three particle sizes. The second series of experiments, intended to test rheology models of dense suspensions and the use of the lubrication approximation in DEM, used 10 mm diameter glass spheres and glycerol/water mixtures in a drum. The second configuration was simulated with DEM using the Hertz-Mindlen contact model for particle-particle interactions. The effect of a viscous force between particles in close proximity to each other was captured by a lubrication approximation. Particle level data from experiments and simulations are transformed to smooth fields by a coarsegraining method which is described in detail. The ergodic assumption (which states that time averages of the PEPT tracer is equivalent to the ensemble average and central to analysing PEPT data) is evaluated using the first series of experiments. It was found that the average velocity can be established after 15 min tracking time, however the solids fraction still shows under sampled regions after tracking for 3 h. Several techniques were used to investigate this, including as Poincaré maps and the global mixing index. A variation on the averaging technique is shown to account for under sampled regions in the solids fraction.
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Kötter, Mirko. "Optimal investment in time inhomogeneous Poisson models." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979754747.
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Akram, Farhan. "Active contours for intensity inhomogeneous image segmentation." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/442961.
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La “inhomogeneidad” (falta d'homogeneïtat) d'intensitat és un problema ben conegut en la segmentació d'imatges, la qual cosa afecta la precisió dels mètodes de segmentació basats en la intensitat. En aquesta tesi, es proposen mètodes de contorn actiu basat en fronteres i regions per segmentar imatges inhomogènies. En primer lloc, s'ha proposat un mètode de contorn actiu basat en fronteres mitjançant Diferència de Gaussianes (DoG), que ajuda a segmentar l'estructura global de la imatge. En segon lloc, hem proposat un mètode de contorn actiu basat en regions per corregir i segmentar imatges inhomogènies. S'ha utilitzat un nucli de transformació de fase (phase stretch transform - PST) per calcular noves intensitats mitjanes i camps de polarització, que s'empren per definir una imatge ajustada de polarització. En tercer lloc, s'ha proposat un altre mètode de contorn actiu basat en regions utilitzant un funcional d'energia basat en imatges ajustades locals i globals. El camp de polarització s'aproxima amb una distribució Gaussiana i el biaix de les regions no homogènies es corregeix dividint la imatge original pel camp aproximat de polarització. Finalment, s'ha proposat un mètode híbrid de contorns actius multifàsic (quatre fases) per dividir una imatge de RM cerebral en tres regions diferents: matèria blanca (WM), matèria grisa (GM) i líquid cefaloraquidi (CSF). En aquest treball, també s'ha dissenyat un mètode de post-processat (correcció de píxels) per millorar la precisió de les regions WM, GM i CSF segmentades. S'han utilitzat resultats experimentals tant amb imatges sintètiques com amb imatges reals de RM del cervell per a una comparació quantitativa i qualitativa amb mètodes de contorns actius de l'estat de l'art per mostrar els avantatges de les tècniques de segmentació proposades.La “inhomogeneidad” (falta de homogeneidad) de intensidad es un problema bien conocido en la segmentación de imágenes, lo que afecta la precisión de los métodos de segmentación basados en la intensidad. En esta tesis, se proponen métodos de contorno activo basado en bordes y regiones para segmentar imágenes inhomogéneas. En primer lugar, se ha propuesto un método de contorno activo basado en fronteras mediante Diferencia de Gaussianas (DoG), que ayuda a segmentar la estructura global de la imagen. En segundo lugar, hemos propuesto un método de contorno activo basado en regiones para corregir y segmentar imágenes inhomogéneas. Se ha utilizado un núcleo de transformación de fase (phase stretch transform - PST) para calcular nuevas intensidades medias y campos de polarización, que se emplean para definir una imagen ajustada de polarización. En tercer lugar, se ha propuesto otro método de contorno activo basado en regiones utilizando un funcional de energía basado en imágenes ajustadas locales y globales. El campo de polarización se aproxima con una distribución Gaussiana y el sesgo de las regiones no homogéneas se corrige dividiendo la imagen original por el campo aproximado de polarización. Finalmente, se ha propuesto un método híbrido de contornos activos multifásico (cuatro fases) para dividir una imagen de RM cerebral en tres regiones distintas: materia blanca (WM), materia gris (GM) y líquido cefalorraquídeo (CSF). En este trabajo, también se ha diseñado un método de post-procesado (corrección de píxeles) para mejorar la precisión de las regiones WM, GM y CSF segmentadas. Se han utilizado resultados experimentales tanto con imágenes sintéticas como con imágenes reales de RM del cerebro para una comparación cuantitativa y cualitativa con métodos de contornos activos del estado del arte para mostrar las ventajas de las técnicas de segmentación propuestas.
Intensity inhomogeneity is a well-known problem in image segmentation, which affects the accuracy of intensity-based segmentation methods. In this thesis, edge-based and region-based active contour methods are proposed to segment intensity inhomogeneous images. Firstly, we have proposed an edge-based active contour method based on the Difference of Gaussians (DoG), which helps to segment the global structure of the image. Secondly, we have proposed a region-based active contour method to both correct and segment intensity inhomogeneous images. A phase stretch transform (PST) kernel has been used to compute new intensity means and bias field, which are employed to define a bias fitted image. Thirdly, another region-based active contour method has been proposed using an energy functional based on local and global fitted images. Bias field is approximated with a Gaussian distribution and the bias of intensity inhomogeneous regions is corrected by dividing the original image by the approximated bias field. Finally, a hybrid region-based multiphase (four-phase) active contours method has been proposed to partition a brain MR image into three distinct regions: white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF). In this work, a post-processing (pixel correction) method has also been devised to improve the accuracy of the segmented WM, GM and CSF regions. Experimental results with both synthetic and real brain MR images have been used for a quantitative and qualitative comparison with state-of-the-art active contour methods to show the advantages of the proposed segmentation techniques.
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Piwnicki, Paul. "Electromagnetic Fields in Moving and Inhomogeneous Media." Doctoral thesis, KTH, Alfvén Laboratory, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3270.
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The present thesis deals with electromagnetic effectscreated by the motion or inhomogeneity of a dielectricmedium.In the first paper the quantum R\"ontgen effect isdiscussed. Here a rotating Bose-Einstein condensate -- oranother kind of quantum fluid -- is placed in a chargedcapacitor. The medium's rotation creates a magnetic field.Quantum media can only rotate in form of vortices, which leadsto a magnetic field corresponding to the field of a magneticmonopole. In the remaining part of the thesis the geometricalrepresentation of electromagnetic fields in moving andinhomogeneous media is discussed. It is shown that aninhomogeneously moving dielectric, e.g., a vortex, defines aspace-time metric and light rays follow null-geodesics definedby this metric. This means that light propagation in a movingmedium is analogous to light propagation in a gravitationalfield. The possibility of creating laboratory models ofastronomical objects, e.g., black holes is discussed. Theapplicability of the newly developed media with extremely lowgroup velocity for the actual creation of such an experiment isconsidered. Furthermore, a model for the case of the slowlymoving medium is discussed. Here the light propagation isanalogous to the motion of a charged particle propagatingthrough a magnetic field. The velocity of the flow correspondsto the vector potential. Consequently, light propagation in avortex corresponds to the Aharonov-Bohm effect. Finally, acomplete geometrical description of light in an inhomogeneousdielectric at rest is presented. It is shown that lighttrajectories are geodesics of a three-dimensional metricdefined by the medium. Here even the propagation of the fieldsis discussed in the language of differential geometry and it isshown that the field vectors are parallel transported along therays. These considerations can be generalized to thefour-dimensional case where the field-strength tensor isparallel transported along the ray. This emphasizes thefar-reaching analogy between light in moving media and light ingravitational fields.
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Norwood, Timothy John. "Nuclear magnetic resonance in inhomogeneous magnetic fields." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24875.
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The work described in this thesis was initiated in an attempt to overcome the limitations imposed upon NMR spectroscopy by magnetic field inhomogeneity in two specific areas: high resolution spectroscopy in isotropic liquids, and chemical shift resolved NMR imaging in isotropic liquids.
In both cases magnetic field inhomogeneity may degrade the resolution of spectra to such an extent that no useful information can be obtained from them. In high resolution NMR spectroscopy it is necessary to be able to extract accurately the parameters present within the spectrum such as chemical shifts, coupling constants and peak areas. In chemical shift resolved imaging experiments the requirements are less stringent; and it is only necessary that the resonances of different chemical species be resolved. However, even the less stringent requirements of NMR imaging are often difficult to meet as the sample volumes required are often several orders of magnitude larger than those required in conventional high resolution NMR spectroscopy.
The use of zero-quantum coherence has been investigated as a potential solution to the magnetic field inhomogeneity problem in both of these areas. Zero-quantum coherences are independent of magnetic field inhomogeneity and contain the parameters desired in both cases, though they are displayed in a way which differs from conventional NMR spectra.
In this thesis, existing zero-quantum coherence experiments have been evaluated for use with inhomogeneous magnetic fields, and, where necessary, adapted for this purpose. Several completely new experiments have been developed for producing broad-band decoupled zero-quantum coherence spectra and also for presenting coupling constants and chemical shifts in a manner which is as close to conventional NMR spectra as possible, hence facilitating ease of use. Zero-quantum coherence has been evaluated as a tool for identifying unknown compounds and also for identifying the components of complex mixtures by "signature" recognition.
Both decoupled and non-decoupled zero-quantum coherence experiments are adapted to provide imaging experiments which allow the separation of the images of different chemical species in inhomogeneous magnetic fields. The two-dimensional J-resolved experiment is also adapted for this purpose.Science, Faculty of
Chemistry, Department of
Graduate
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Zhang, Junfang, and junfang zhang@csiro au. "Computer simulation of nanorheology for inhomogeneous fluids." Swinburne University of Technology. Centre for Molecular Simulation, 2005. http://adt.lib.swin.edu.au./public/adt-VSWT20050620.095154.
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In this thesis, we use nonequilibrium molecular dynamics (NEMD) methods to investigate the structural and dynamic properties of highly confined atomic and polymeric fluids undergoing planar Poiseuille flow. We derive 'method of planes' expressions for pressure tensor and heat flux vector for confined inhomogeneous atomic fluids under the influence of three-body forces. Our derivation is validated against NEMD simulations of a confined atomic fluid acted upon
by a two-body Barker-Fisher-Watts force coupled with the Axilrod-Teller three-body force. Our method of planes calculations are in excellent agreement with the equivalent mesoscopic route of integrating the momentum and energy continuity equations directly from the simulation data. Our calculations reveal that three-body forces have an important consequence for the isotropic pressure, but have negligible in�uence on the shear stress and heat flux vector for a confined simple fluid. We use the non-local linear hydrodynamic constitutive model, proposed by Evans and Morriss [1] for computing a viscosity kernel, a function of compact support, for inhomogeneous nonequilibrium fluids. Our results show that the viscosity kernel, �(y),
has a peak at y = 0, and gets smaller and decays to zero as y increases. Physically, it
means that the strain rate at the location where we want to know the stress contributes
most to the stress, and the contribution of the strain rate becomes less significant as the
relative distance y increases. We demonstrate that there is a limitation in the model
when it is applied to our confined fluids due to the effect of domain restriction on inverse
convolution. We study the nanorheology of simple polymeric fluids. Our NEMD simulation results show that sufficiently far from the walls, the radius of gyration for molecules under shear in the middle of the channel follows the power law, Rg / N�, where N is the number of
bonds and the exponent has a value � = 0:60�0:04, which is larger than the melt value
of 0:5 for a homogeneous equilibrium �uid. Under the conditions simulated, we find that
viscous forces dominate the flow, resulting in the onset of plug-like flow velocity pro�les
with some wall slippage. An examination of the streaming angular velocity displays a strong correlation with the radius of gyration, being maximum in those regions where Rg is minimum and vice-versa. The angular velocity is shown to be proportional to half the strain rate su�ciently far from the walls, consistent with the behaviour for homogeneous fluids in the linear regime. Finally, we make some concluding remarks and suggestions for future work in the
final chapter.
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Darian, Bahman K. "Gauge fields in homogeneous and inhomogeneous cosmologies." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22973.pdf.
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Razoumov, Alexei O. "Calculating the inhomogeneous reionization of the universe." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ48698.pdf.
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Moncet, Jean-Luc. "Narrowband models of radiation in inhomogeneous atmospheres." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61924.
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Várnai, Tamás. "Reflection of solar radiation by inhomogeneous clouds." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40459.
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The goal of this study is to improve knowledge about how cloud inhomogeneities affect the reflection of solar radiation. In particular, it addresses two main questions: what the processes through which inhomogeneities influence solar reflection are, and how this influence can be taken into account in albedo retrievals based on future satellite measurements.The first question is important, since present methods give numerical results only about the overall radiative effect of cloud inhomogeneities, but cannot determine the degree to which various mechanisms are responsible for this overall effect. This study establishes a theoretical framework which defines and evaluates the various processes through which cloud inhomogeneities influence solar radiation. This framework is then used to examine quantitatively the inhomogeneity effects that occur in irregular cloud fields. Among other insights, it is shown and explained that identical variations in cloud optical thickness can cause much stronger inhomogeneity effects if they are due to variations in geometrical cloud thickness, and not in volume extinction coefficient (as assumed in previous studies of irregular cloud fields). The differences in albedo can exceed 0.05, and the relative differences in reflectance toward the zenith can be greater than 25% for overhead sun, and 50% for oblique sun. Also, a possible explanation is given for a phenomenon observed in previous studies: that cloud reflectivity toward the zenith increases with decreasing solar elevation.
This study also develops an albedo retrieval algorithm that considers radiative inhomogeneity effects. The algorithm takes advantage of the unique multi-view capability of the Multi-angle Imaging SpectroRadiometer (MISR) placed on the Earth Observing System-AM satellite (to be launched in 1998). This instrument will offer new possibilities for albedo retrievals since, unlike present instruments, it will measure the radiation reflected in not only one, but nine directions. The potential accuracy of the algorithm is analyzed for a dataset obtained by using a Monte Carlo model to simulate radiative transfer through a large number of irregular cloud fields. The results indicate that using multi-view measurements can improve the accuracy of satellite-based albedo retrievals by a factor of three or more.
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Drijkoningen, Guy Gerard. "On generalized ray theory in inhomogeneous media." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291754.
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Hui, Victor Chak-lam. "Quasi-particles in inhomogeneous superconductors and superfluids." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304831.
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Nadathur, Seshadri. "Inflation, large-scale structure and inhomogeneous cosmologies." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:b8c5c6ff-53be-4c1e-97bc-4442c5bfba30.
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Determining cosmological parameters from current observational data requires knowledge of the primordial density perturbations generated during inflation. We begin by examining a model of inflation along a flat direction of the minimal supersymmetric Standard Model (MSSM) and the power spectrum of perturbations it can produce. We consider the fine-tuning issues associated with this model and discuss a modification of the potential to include a hybrid transition that reduces the fine-tuning, without affecting the viability of the model. However, supersymmetric flat directions might play a role in other models of inflation as well. In particular, they may cause a feature in the primordial power spectrum of perturbations, unlike the scale-free spectrum assumed in the standard Lambda Cold Dark Matter (LCDM) cosmological model. We then show that in the presence of such a feature, an alternative cosmological model with a large local void and no dark energy provides a good fit to both Type Ia supernovae and the cosmic microwave background (CMB) data from the WMAP satellite. Constraints from the locally measured Hubble parameter, baryon acoustic oscillations and primordial nucleosynthesis are also satisfied. This degeneracy motivates a search for other independent observational tests of LCDM. The integrated Sachs-Wolfe (ISW) imprint of large-scale structure on the CMB is one such test. The ISW imprint of superstructures of size ~100 Mpc/h at redshift z~0.5 has been detected with >4 sigma significance, however it has been noted that the signal is much larger than expected. We revisit the calculation using linear theory predictions in a LCDM cosmology and find the theoretical prediction is inconsistent by >3 sigma with the observation. If the observed signal is indeed due to the ISW effect then huge, extremely underdense voids are far more common in the observed universe than predicted by LCDM.