Dissertations / Theses on the topic 'Anisotropic energy'
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Strümpfer, Johan. "Computing free energy hypersurfaces for anisotropic intermolecular associations." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/6290.
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Adaptive reaction coordinate force biaisng methods have been previously used for calculating the free energy of conformation and chemical reactions amongst others. Here a generalized method is described that is able to produce free energies in multiple dimension, descriptively named the free energies from adaptive reaction coordinate forces (FEARCF) method. To illustrate it a multidemensional intermolecular orientational free energy surface is calculated, and it is demonstrated how to invesrigate complex systems such as protein conformation and liquids.
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Steiner, Pinckney Alston IV. "Anisotropic low-energy electron-enhanced etching of semiconductors in DC plasma." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/27060.
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Cai, Renye. "Original strain energy density functions for modeling of anisotropic soft biological tissue." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCA003/document.
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Cette thèse a porté sur la construction de densités d'énergie de déformation permettant de décrire le comportement non linéaire de matériaux anisotropes tels que les tissus biologiques souples (ligaments, tendons, parois artérielles etc.) ou les caoutchoucs renforcés par des fibres. Les densités que nous avons proposées ont été élaborées en se basant sur la théorie mathématique des polynômes invariants et notamment sur le théorème de Noether et l'opérateur de Reynolds. Notre travail a concerné deux types de matériaux anisotropes, le premier avec une seule famille de fibre et le second avec quatre familles. Le concept de polyconvexité a également été étudié car il est notoire qu'il joue un rôle important pour s'assurer de l'existence de solutions. Dans le cas d'un matériau comportant une seule famille de fibre, nous avons démontré qu'il était impossible qu'une densité polynomiale de degré quelconque puisse prédire des essais de cisaillement avec un chargement parallèle puis perpendiculaire à la direction des fibres. Une densité polynomiale linéaire combinée avec une fonction puissance a permis de contourner cet obstacle. Dans le cas d'un matériau comportant quatre familles de fibre, une densité polynomiale a permis de prédire correctement des résultats d'essai en traction bi-axiale extraits de la littérature. Les deux densités proposées ont été implémentées avec la méthode des éléments finis et en langage C++ dans le code de calcul universitaire FER. Pour se faire, une formulation lagrangienne totale a été adoptée. L'implémentation a été validée par des comparaisons avec des solutions analytiques de référence que nous avons exhibée dans le cas de chargements simples conduisant à des déformations homogènes. Des exemples tridimensionnels plus complexes, impliquant des déformations non-homogènes, ont également été étudiésThis thesis has focused on the construction of strain energy densities for describing the non-linear behavior of anisotropic materials such as biological soft tissues (ligaments, tendons, arterial walls, etc.) or fiber-reinforced rubbers. The densities we have proposed have been developed with the mathematical theory of invariant polynomials, particularly the Noether theorem and the Reynolds operator. Our work involved two types of anisotropic materials, the first with a single fiber family and the second with a four-fiber family. The concept of polyconvexity has also been studied because it is well known that it plays an important role for ensuring the existence of solutions. In the case of a single fiber family, we have demonstrated that it is impossible for a polynomial density of any degree to predict shear tests with a loading parallel and then perpendicular to the direction of the fibers. A linear polynomial density combined with a power-law function allowed to overcome this problem. In the case of a material made of a four-fiber family, a polynomial density allowed to correctly predict bi-axial tensile test data extracted from the literature. The two proposed densities were implemented in C++ language in the university finite element software FER by adopting a total Lagrangian formulation. This implementation has been validated by comparisons with reference analytical solutions exhibited in the case of simple loads leading to homogeneous deformations. More complex three-dimensional examples, involving non-homogeneous deformations, have also been studied
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Fogli, Simone. "Forecasts on the dark energy anisotropic stress for the esa euclid survey." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5614/.
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The cosmological constant Λ seems to be a not satisfactory explanation of the late-time accelerated expansion of the Universe, for which a number of experimental evidences exist; therefore, it has become necessary in the last years to consider alternative models of dark energy, meant as cause of the accelerated expansion. In the study of dark energy models, it is important to understand which quantities can be determined starting from observational data, without assuming any hypothesis on the cosmological model; such quantities have been determined in Amendola, Kunz et al., 2012. In the same paper it has been further shown that it is possible to estabilish a relation between the model-independent parameters and the anisotropic stress η, which can be also expressed as a combination of the functions appearing in the most general Lagrangian for the scalar-tensor theories, the Horndeski Lagrangian. In the present thesis, the Fisher matrix formalism is used to perform a forecast on the constraints that will be possible to make on the anisotropic stress η in the future, starting from the estimated uncertainties for the galaxy clustering and weak lensing measurements which will be performed by the European Space Agency Euclid mission, to be launched in 2020. Further, constraints coming from supernovae-Ia observations are considered. The forecast is performed for two cases in which (a) η is considered as depending from redshift only and (b) η is constant and equal to one, as in the ΛCDM model.
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Xu, Hao. "Theoretical and numerical modeling of anisotropic damage in rock for energy geomechanics." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53035.
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At present, most of the energy power consumed in the world is produced by fossil fuel combustion, which has raised increasing interest in renewable energy technologies, non-conventional oil and gas reservoirs, and nuclear power. Innovative nuclear fuels and reactors depend on the economical and environmental impacts of waste management. Disposals in mined geological formations are viewed as potential consolidated storage facilities before final disposition. Different stress paths during construction result in different kinds of failure mechanisms, which alter rock strength and induce anisotropy of rock elastic properties. Crack propagation in rock can be originated by these engineering activities (excavation, drilling, mining, building overburden), or by changes of the natural environment (tectonic processes, erosion or weathering). Damage is a mathematical variable that can represent a variety of microstructure changes, such as crack density, length, aspect ratio and orientation. The framework of Continuum Damage Mechanics allows modeling the resulting reduction in strength and stiffness, as well as the associated stress-induced anisotropy and irreversible deformation.
This work presents a modeling framework for anisotropic crack propagation in rock, in conditions of stress typical of geological storage and oil and gas extraction. Emphasis is put on the prediction of the damage zone around cavities and ahead of pressurized fracture tips. An original model of anisotropic damage, the Differential Stress Induced Damage (DSID) model, is explained. The Drucker-Prager yield function is adapted to make the damage threshold depend on damage energy release rate and to distinguish between tension and compression strength. Flow rules are derived with the energy release rate conjugate to damage, which is thermodynamically consistent. The positivity of dissipation is ensured by using a non-associate flow rule for damage, while nonelastic deformation due to damage is computed by an associate flow rule. Stress paths simulated at the material point illustrate damaged stiffness and deformation variations in classical rock mechanics tests. The maximum likelihood method was employed to calibrate and verify the DSID model against stress-strain curves obtained during triaxial compression tests and uniaxial compression tests performed on clay rock and shale. Logarithmic transformation, normalization and forward deletion allowed optimizing the formulation of the DSID model, and reduce the number of damage constitutive parameters from seven to two for clay rock. The DSID model was implemented in ABAQUS Finite Element (FE) software. The iterative scheme was adapted in order to account for the non-linearities induce both by damage and damage-induced deformation. FE simulations of laboratory tests capture size an intrinsic anisotropy effects on the propagation of damage in rock. Smeared DSID zones representing shale delamination planes avoid some convergence problems encountered when modeling discontinuities with debonded contact surface elements. FE simulations of tunnel excavation, fracture propagation and borehole pressurization were performed to illustrate the evolution of the damage zone and the impact on energy dissipation, anisotropy of deformation, and loss of stiffness.
Future work will focus on coupling the propagation of fractures with the evolution of the damage process zone, and on the transition from continuum damage to discrete fracture upon crack coalescence.
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Hamad, Wadwood Y. "Energy-balance equations for in-roll stresses for anisotropic materials in wound rolls." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60599.
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This Thesis concerns itself with the thorough investigation of the effects of core material parameters on the structural behaviour of wound rolls in core-roll winding systems. The underlying theme in this work is the derivation, based on the theory of elasticity, of an analytic expression for the core material's elasticity modulus as a function of only material parameters and geometry.The approach undertaken herein is purely theoretical and encompasses the rigorous analysis of principally two models; linear isotropic and anisotropic. As for the former, both planar and axisymmetric geometries are investigated; and in the case of the anisotropic model, an axisymmetric plane stress situation is studied. Moreover, finite-element modelling and analysis for the isotropic condition is carried out to confirm the theoretical findings. The objective is then to apply the results; namely, the inclusion of Poisson's ratio and elasticity modulus of the core material, to modify existing energy-balance roll structure formulae. This undertaking is called for if the aim is to have a valid winding model that simulates the actual winding process; i.e., one which incorporates sensing the presence of the core through layers of wound material. Results are further compared with existing winding models and conclusions are given.
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Pröchtel, Patrick. "Anisotrope Schädigungsmodellierung von Beton mit adaptiver bruchenergetischer Regularisierung Anisotropic damage modeling of concrete regularized by means of the adaptive fracture energy approach /." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1224751435667-29771.
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Gamieldien, Mogamat Riedaa. "Parameterization of the Gay-Berne coarse-grained potential from atomistically detailed anisotropic free energy volumes." Doctoral thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/10567.
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Includes bibliographical references.Simulating a system of 300,000+ atoms, such as an explicitly solvated protein using all atom molecular dynamics on the microsecond time-scale, would require an enormous amount of computing power and specialized software, even with which would still require months of computing time. However, if the atomic degrees of freedom of the system can be reduced (or averaged) in some physically intuitive manner, while still retaining a connection with the underlying atomistic detail, microsecond simulations could be achieved within weeks or days. Coarse-graining, a sub-class of mesoscale modelling, is used to represent molecules in a reduced form as either regular spheroids (ellipsoids) or as continuum models, using specialized interaction potentials. The Gay-Berne is a one such coarse-grain potential, which has been particularly successful in that it has been used in modelling of liquid crystals, protein dynamics and lipid membrane and micelle formation...
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Stevenson, Kip Patrick. "Anisotropic potential energy surfaces for atmospheric gas : unsaturated hydrocarbon molecule interactions from differential scattering experiments /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/11613.
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Li, Bin. "The variational approach to brittle fracture in materials with anisotropic surface energy and in thin sheets." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/393861.
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Fracture mechanics of brittle materials has focused on bulk materials with isotropic surface energy. In this situation different physical principles for crack path selection are very similar or even equivalent. The situation is radically different when considering crack propagation in brittle materials with anisotropic surface energy. Such materials are important in applications involving single crystals, extruded polymers, or geological and organic materials. When this anisotropy is strong, the phenomenology of crack propagation becomes very rich, with forbidden crack propagation directions or complex sawtooth crack patterns. Thus, this situation interrogates fundamental issues in fracture mechanics, including the principles behind the selection of crack direction. Similarly, tearing of brittle thin elastic sheets, ubiquitous in nature, technology and daily life, challenges our understanding of fracture. Since tearing typically involves large geometric nonlinearity, it is not clear whether the stress intensity factors are meaningful or if and how they determine crack propagation. Geometry, together with the interplay between stretching and bending deformation, leads to complex behaviors, restricting analytical approximate solutions to very simplified settings and specific parameter regimes.
In both situations, a rich and nontrivial experimental record has been successfully understood in terms of simple energetic models. However, general modeling approaches to either fracture in the presence of strong surface energy anisotropy or to tearing, capable of exploring new physics, have been lacking. The success of energetic simple models suggests that variational theories of brittle fracture may provide a unifying and general framework capable of dealing with the more general situations considered here.
To address fracture in materials with strongly anisotropic surface energy, we propose a variational phase-field model resorting to the extended Cahn-Hilliard framework proposed in the context of crystal growth. Previous phase-field models for anisotropic fracture were formulated in a framework only allowing for weak anisotropy. We implement numerically our higher-order phase-field model with smooth local maximum entropy approximants in a direct Galerkin method. The numerical results exhibit all the features of strongly anisotropic fracture, and reproduce strikingly well recent experimental observations. To explore tearing of thin films, we develop a geometrically exact model and a computational framework coupling elasticity (stretching and bending), fracture, and adhesion to a substrate. We numerically implement the model with subdivision surface finite elements. Our simulations qualitatively and quantitatively reproduced the crack patterns observed in tearing experiments.
Finally, we examine how shell geometry affects fracture. As suggested by previous results and our own phase-field simulations, shell shape dramatically affects crack evolution and the effective toughness of the shell structure. To gain insight and eventually develop new concepts for optimizing the design of thin shell structures, we derive the configurational force conjugate to crack extension for Koiter's linear thin shell theory. We identify the conservative contribution to this force through an Eshelby tensor, as well as non-conservative contributions arising from curvature.La mécanica de fractura frágil se ha centrado en materiales tridimensionales con una energía de superficie isotrópica. En esta situación, los diferentes principios para la selección del camino de la fisura son muy similares, o incluso equivalentes. La situación es radicalmente opuesta cuando se considera la propagación de fisuras en medios con energía de superficie anisótropa. Estos materiales son importantes en aplicaciones que involucran materiales cristalinos, polímeros extrudidos, o materiales orgánicos y geológicos. Cuando la anisotropía es fuerte, el fenómeno de la propagación de fisuras es muy rico, con direcciones de propagación prohibidas o complejos patrones de ruptura en dientes de sierra. Por tanto, esta situación plantea cuestiones fundamentales en la mecánica de la fractura, incluyendo los principios de selección de la dirección de propagación de la fractura. Igualmente, el proceso de rasgado de láminas delgadas y frágiles, comunes en la naturaleza, la tecnología y la vida diaria, desafía nuestro entendimiento de la fractura. Dado que el rasgado de estas láminas típicamente involucra grandes no linealidades geométricas, no está claro si los factores de intensidad de esfuerzos son válidos o si, y en tal caso cómo determinan la propagación de fisuras. La interacción entre la geometría, las deformaciones y la curvatura da lugar a comportamientos complejos, lo que restringe las soluciones analíticas aproximadas a ejemplos muy simplificados y a regímenes de parámetros limitados. En ambas situaciones, se han podido interpretar experimentos no triviales con modelos energéticos simples. Sin embargo, no se ha profundizado en modelos generales de fractura en presencia de energía de superficie fuertemente anisótropa o en láminas delgadas, ambas interesantes por su capacidad para explorar nueva física. El mencionado éxito de los modelos energéticos simplificados sugiere que las teorías variacionales de fractura en medios frágiles pueden proveer un marco unificador para considerar situaciones más generales, como las que se consideran en este trabajo. Para caracterizar la fractura en materiales con energía de superficie fuertemente anisótropa, proponemos un modelo variacional de campo de fase basado en el modelo extendido de Cahn-Hilliard. Los modelos de campo de fase existentes para la fractura anisótropa fueron formulados en un contexto que sólo admite anisotropía débil. En este trabajo, implementamos numéricamente nuestro modelo de campo de fase de alto orden con aproximantes locales de máxima entropía en un método directo de Garlerkin. Los resultados numéricos muestran todas las características de fractura con anisotropía fuerte, y reproducen llamativamente bien las últimas observaciones experimentales. Para explorar el rasgado de láminas delgadas, desarrollamos un modelo geométricamente exacto y un esquema computacional que acopla elasticidad (estiramiento y flexión), fractura, y la adhesión a un substrato. Implementamos numéricamente el modelo con elementos finitos basados en superficies de subdivisión. Nuestras simulaciones reproducen los patrones de ruptura, tanto cualitativamente como cuantitativamente, observados en los experimentos de rasgado. Finalmente, examinamos cómo la geometría de la lámina afecta la fractura. Como ha sido sugerido en resultados previos y en nuestras propias simulaciones de campo de fase, la forma de la lámina afecta dramáticamente la evolución de fisuras y la resistencia efectiva del material. Para comprender mejor estos fenómenos y con el objetivo de desarrollar nuevos conceptos para la optimización del diseño de estructuras de láminas delgadas, derivamos la fuerza configuracional conjugada a la extensión de la fractura para la teoría lineal de láminas delgadas de Koiter. Identificamos las contribuciones conservativas a esta fuerza a través del tensor de Eshelby, así como las contriuciones no conservativas que aparecen por el efecto de la curvatura.
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Ross, Ron S. "Planning minimum-energy paths in an off-road environment with anisotropic traversal costs and motion constraints." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/26696.
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Fiz, González Raquel [Verfasser]. "Vapor Phase Growth of Anisotropic Metal Oxide Heterostructures: Growth Models, and Energy & Sensor Applications / Raquel Fiz González." München : Verlag Dr. Hut, 2014. http://d-nb.info/1050331591/34.
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Watanabe, T., H. Yokoyama, Y. Tanaka, and J. Inoue. "Predominant magnetic states in the Hubbard model on anisotropic triangular lattices." American Physical Society, 2008. http://hdl.handle.net/2237/11256.
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Knoke, Till [Verfasser], Heiko von der [Akademischer Betreuer] Mosel, and Alfred [Akademischer Betreuer] Wagner. "On the approximation of anisotropic energy functionals by Riemannian energies via homogenization / Till Knoke ; Heiko von der Mosel, Alfred Wagner." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130326756/34.
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Lindberg, Maria. "Computer simulations of electronic energy transfer and a molecular dynamics study of a decapeptide." Doctoral thesis, Umeå universitet, Kemiska institutionen, 1991. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-118929.
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Electronic energy transfer has been investigated in pure donor systems by means of computer simulations. Calculated properties were the probability that the initially excited donor is excited at a time t after the excitation, Gs(t), the mean square displacement of the excitation and different fluorescence observables. For three dimensional systems the results obtained by Monte Carlo simulations were compared to the so-called GAF-theory {Gouchanour,C. R., Andersen, H. C. and Fayer, M. D., J. Chem. Phys. 81, 4380 (1984)}, and the agreement was found to be good. Anisotropic systems, i.e. mono-, bi- and multilayer systems, were compared to the two-particle model {Baumann,J. and Fayer, M. D., J. Chem. Phys. 85, 4087 (1986)}. The agreement between the Gs(t) calculated from the tp- model and the Monte Carlo simulations were good for all systems investigated. However, the agreement between the fluorescence observables obtained by MC and the tp-model were in general poor. A much better agreement was found when a phenomenological approach was used for calculating the fluorescence depolarization ratios. Three dimensional systems where the donors are rotating on the same time scale as the energy transfer takes place have also been studied and compared to analytical theories. The Molecular Dynamics simulations of decapeptide H142 shows that simulations in a continuum with a relative permeability do not provide a reliable alternative to simulations with explicit solvent molecules.Diss. (sammanfattning) Umeå : Umeå universitet, 1991, härtill 5 uppsatser
digitalisering@umu
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Chen, Kuan-Luen. "Evaluation of weight functions, stress intensity factors, and energy release rates for two-dimensional anisotropic structures by the alternating finite element method, the virtual crack extension tech." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/21226.
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Melo, Marcelo Ferreira de. "Funcionais paramÃtricos elÃpticos em variedades riemannianas." Universidade Federal do CearÃ, 2009. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=4102.
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CoordenaÃÃo de AperfeiÃoamento de NÃvel SuperiorConselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
Neste trabalho, consideramos funcionais paramÃtricos elÃpticos como generalizaÃÃes naturais para o clÃssico funcional Ãrea. Calculamos a primeira variaÃÃo de tais funcionais e, a partir da equaÃÃo de Euler-Lagrange, definimos a curvatura mÃdia anisotrÃpica de uma hipersuperfÃcie imersa em uma variedade Riemanniana como generalizaÃÃo natural da curvatura mÃdia usual. Em seguida, estabelecemos a fÃrmula da segunda variaÃÃo e classificamos as hipersuperfÃcies rotacionalmente simÃtricas que possuem curvatura mÃdia anisotrÃpica constante. A fim de compreender a estabilidade dos exemplo rotacionais,deduzimos a primeira e a segunda fÃrmulas de Minkowski. AlÃm disso, no contexto anisotrÃpico, apresentamos as equaÃÃes fundamentais de Weingarten, Codazzi e Gauss e, por fim, estudamos a harmonicidade da aplicaÃÃo de Gauss.
It is stated that critical points of a parametric elliptic functional in a Riemannian manifold are hypersurfaces with prescrebed anisotropic mean curvature. We prove that the anisotropic Gauss map of surfaces immersed in Euclidean space with constant anisotropic mean curvature is a harmonic map. In the case of rotatioally invariat functionals in some homogeneous three-dimensional ambients, we present a abridged version of a existence result for constant anisotropic mean curvature surfaces as cylinders, spheres, tori and annuli corresponding to the anisotropic analogs of onduloids and nodoids. In the Euclidean case M = R3, examples of stable critical points are provided by the Wulff shapes associated to functional F. Paralleling the case of constant curvature mean spheres, a characterization of Wulff shapes is provided, which answers affirmatively a question posed by M. Koiso and B. Parmer in [13].
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Retinskaya, Ekaterina. "Reverse engineering of heavy-ion collisions : unraveling initial conditions from anisotropic flow data." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01068777.
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Ultra-Relativistic heavy-ion physics is a promising field of high energy physics connecting two fields: nuclear physics and elementary particle physics. Experimental achievements of the last years have provided an opportunity to study the properties of a new state of matter created in heavy-ion collisions called quark-gluon plasma. The initial state of two colliding nuclei is affected by fluctuations coming from wave- functions of nucleons. These fluctuations lead to the momentum anisotropy of the hadronic matter which is observed by the detectors. The system created in the collision behaves like a fluid, so the initial state is connected to the final state via hydrodynamic evolution. In this thesis we model the evolution with relativistic viscous hydrodynamics. Our results, combined with experimental data, give non trivial constraints on the initial state, thus achieving "reverse engineering" of the heavy-ion collisions. The observable which characterizes the momentum anisotropy is the anisotropic flow vn. We present the first measurements of the first harmonic of the anisotropic flow called directed flow v1 in Pb-Pb collisions at the LHC. We then perform the first viscous hydrodynamic modeling of directed flow and show that it is less sensitive to viscosity than higher harmonics. Comparison of these experimental data with the modeling allows to extract the values of the dipole asymmetry of the initial state, which provides constraints on the models of initial states. A prediction for directed flow v1 in Au-Au collisions is also made for RHIC. We then perform a similar modeling of the second and third harmonics of the anisotropic flow, called respectively elliptic v2 and triangular v3 flow. A combined analysis of the elliptic and triangular flow data compared with viscous hydrodynamic calculations allows us to put constraints on initial ellipticity and triangularity of the system. These constraints are then used as a filter for different models of initial state. At the end of this thesis, we show perspectives in the studies of the initial state which are opened by recent measurements of event-plane correlations which could shed light on the initial state fluctuations.
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Simas, Emanuelle Reis. "Fotoquímica de polímeros conjugados contendo centros de transferência de carga e migração de energia." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-24032011-093724/.
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Neste trabalho foram estudados os processos de migração e transferência de energia em derivados de polifluoreno, de estrutura totalmente conjugada e de conjugação confinada. A dinâmica de estado excitado dos derivados PF-BNI, PFOPPV e PFPPV foi estudada em solução diluída de diferentes solventes através de espectroscopia eletrônica de alta resolução temporal. O derivado PF-BNI, contendo N-(2-benzotiazol)-1,8-naftalimida (BNI) como terminador da cadeia de poli(9,9\'dioctilfluoreno), foi sintetizado pela rota de Yamamoto. O material apresenta alto rendimento quântico de fluorescência e suas propriedades de emissão são moduladas pela polaridade do solvente. As medidas de fluorescência resolvida no tempo mostraram a migração do exciton singlete ao longo da cadeia polimérica e a formação de um estado excitado de transferência de carga intracadeia (ICCT). Os derivados PFOPPV e PFPPV são copolímeros de fluoreno contendo unidades fluoreno-vinileno-fenileno no segmento cromofórico. No PFOPPV o segmento cromofórico é confinado entre segmentos alifáticos (-(CH2)8-) flexíveis, no PFPPV a cadeia principal é totalmente conjugada. A dinâmica de estado excitado dos derivados, PFOPPV e PFPPV, é caracterizada pela presença de segmentos cromofóricos contendo isômeros cis e trans. No PFOPPV, a sua estrutura segmentada permite a transferência de energia entre os segmentos cromofóricos, via interações dipolo-dipolo. A transferência acarreta a depolarização da emissão de fluorescência. No caso do PFPPV a migração de energia ocorre em menos de 20 ps e o decaimento de fluorescência decorre da emissão de segmentos contendo isômeros cis e trans, já na condição estacionária.This work reports the study of energy transfer and migration processes in fully conjugated and segmented polyfluorene derivatives. The excited-state dynamics of the derivatives, PF-BNI, PFOPPV and PFPPV was studied in diluted solution of different solvents by means of ultrafast time-resolved spectroscopy. Poly(9,9\'-dioctylfluorene) end-capped with N-(2-benzothiazole)-1,8-naphthalimide, named PF-BNI, was prepared via Yamamoto-coupling reaction. This derivative is a highly fluorescence material with emission modulated by solvent polarity. Time-resolved fluorescence measurements showed the singlet exciton migration through the polymer backbone and the formation of an intrachain charge transfer excited-state (ICCT). PFOPPV and PFPPV are both fluorene copolymers containing fluorene-vinylene-phenylene moieties in the backbone. Whereas the PFPPV backbone is fully conjugated, the chromophore segment in PFOPPV backbone is confined between aliphatic (-(CH2)8-) flexible segments. The excited-state dynamics of both copolymers is characterized by the presence of conjugated moieties containing cis and trans isomers. The segmented structure of PFOPPV allows the resonant energy transfer between the chromophores, which is provided by dipole-dipole interactions. The energy transfer process leads to the depolarization of PFOPPV fluorescence emission. For PFPPV the energy migration occurs in less than 20 ps and the fluorescence decay is ascribed to the emission of chromophore segments containing cis and trans, already in a photostationary condition.
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Wu, Yang. "Azimuthal anisotropy in gold-gold collisions at 4.5 GeV center-of-mass energy per nucleon pair using fixed-target mode at the Relativistic Heavy-Ion Collider." Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1562355001935965.
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Lam, Yukyam 1982. "Dark energy and CMB anisotropy." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32743.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.Includes bibliographical references (p. 59-60).
According to the WMAP and earlier COBE observations, the Cosmic Microwave Background (CMB) anisotropy power on large angular scales appears to be significantly lower than predicted by the standard model of cosmology. We propose a scalar field model of the dark energy as a mechanism for suppressing low l multipoles through late-Universe evolution of metric fluctuations and the integrated Sachs-Wolfe (ISW) effect. We find that for a constant dark energy equation of state, theoretical predictions actually give a larger (instead of a desired smaller) value of the quadrupole and other low l multipoles.
by Yukyan Lam.
S.B.
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Yang, Lixiang. "Modeling Waves in Linear and Nonlinear Solids by First-Order Hyperbolic Differential Equations." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1303846979.
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Kumar, Deepak. "Thin film growth by combinatorial epitaxy for electronic and energy applications." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMC255.
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Les oxydes de métaux de transition à structure pérovskite ABO3 présentent des degrés de liberté structurels et électroniques fortement enchevêtrés. On s'attend donc à découvrir des phases et des propriétés exotiques en agissant sur le réseau par le biais de divers stimuli externes. L'ingénierie des contraintes épitaxiales dans les couches minces d'oxydes est un moyen important d'adapter la distorsion du réseau cristallin par l'effet coopératif de Jahn Teller. En utilisant les couches minces actives PrVO3 de Jahn Teller comme système modèle, la corrélation structurelle avec le magnétisme est établie. Nous imposons différentes contraintes de contrainte épitaxiale dans les films minces PrVO3 via différents moyens, tels que, en utilisant divers substrats monocristallins disponibles dans le commerce, l'épaisseur du film, des substrats avec des orientations de surface cristallines différentes, etc. En conséquence, des phases nouvelles et cachées, absentes du composé en vrac, commencent à apparaître. Notamment, la contrainte de compression dans les films de PrVO3 améliore l'interaction de super échanges menant à une augmentation de la température de Neel antiferromagnétique, une forte anisotropie magnétique dans les films minces de PrVO3 cultivés sur des substrats SrTiO3 orientés (001), 110 et 111, sont quelques exemplesTransition-metal oxides with an ABO3 perovskite structure exhibit strongly entangled structural and electronic degrees of freedom and thus, one expects to unveil exotic phases and properties by acting on the lattice through various external stimuli. The epitaxial strain engineering in oxide thin films is an important mean to tailor the crystal lattice distortion through cooperative Jahn Teller effect. Using the Jahn Teller active PrVO3 thin films as a model system, the structural correlation with the magnetism is established. We impose different strength of epitaxial strain in PrVO3 thin films via different means, such as, using various commercially available single crystal substrates, film thickness, substrates with different crystal surface orientations, etcetera. As a result, new and hidden phases that are absent in the bulk compound, begin to appear. Namely, the compressive strain in PrVO3 films enhances the super-exchange interaction leading to an increased antiferromagnetic Neel temperature, a strong magnetic anisotropy in PrVO3 thin films grown on (001)-, (110)- and (111)-oriented SrTiO3 substrates, are few examples
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Pascon, Aline Maria 1987. "Anisotropia de larga escala em raios cósmicos de altíssima energia no Observatório Pierre Auger." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277557.
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Orientador: Carola Dobrigkeit ChinellatoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-12T14:28:59Z (GMT). No. of bitstreams: 1 Pascon_AlineMaria_M.pdf: 7108044 bytes, checksum: c42a3aa2a12d613b0ce9e4e8da6014dc (MD5) Previous issue date: 2008
Resumo: Foi aplicado o método de reconstrução de uma anisotropia de raios cósmicos para certo número de direções simuladas, a partir de uma distribuição consistindo de modulação dipolar sobreposta a um fluxo isotrópico. Usou-se o método proposto por J. Aublin e E. Parizot, que permite reconstruir a amplitude e orientção do dipolo no espaço 3D para um observatório que possui apenas uma visão parcial do céu, como é o caso do Observatório Pierre Auger Sul. Admitiu-se que a exposição do observatório para uma dada direção depende apenas da declinação, sendo independente da ascensão reta. A modulação dipolar foi considerada apontando na direção do centro galáctico e levou-se em conta o efeito do erro experimental na determinação da direção fazendo-a utuar segundo uma distribuição gaussiana de meia largura igual ao erro experimental do detector (1,5o). Estudou-se a capacidade de reconstrução deste dipolo, em direção e amplitude, para as condições do Observatório Pierre Auger, para vários valores de amplitude do dipolo e vários números de eventos, e foram obtidos os limites de tempo observacional necessários para detecção em cada caso, para um fluxo de eventos com energias acima de 10 18,5 eV . Por fim, calculou-se o número de eventos e o tempo necessário de observação para detectar uma anisotropia dipolar de 1%, para as condições do Observatório Pierre Auger, para atingir um valor de significância considerável, de 3, valor mínimo necessário para dar atenção à possível existência de anisotropia dipolar
Abstract: A method to study the anisotropy of a cosmic-ray distribution was applied to a number of directions simulated from an angular distribution of arrival directions consisting of a dipolar modulation of an otherwise isotropic ux. The method was suggested by J. Aublin and E. Parizot and allows reconstructing the amplitude and the dipole orientation in 3D space for a partial-sky coverage observatory like the Southern site of the Pierre Auger Observatory. The exposure of the observatory was assumed to be dependent only on the declination of the arrival directions and not on its right ascension. The dipolar modulation was taken to be pointing towards the galactic center. The experimental uncertainty in the direction measurements was also considered, represented by a smearing of all directions with a Gaussian uctuation with a half width corresponding to the experimental uncertainty (1,5 o). The capability of the Southern Pierre Auger Observatory of reconstructing the dipole modulation was studied for various dipole amplitudes and number of events. The observational time which is necessary for the detection was evaluated assuming that the observatory is fully efficient for energies above 10 18,5 eV . The number of events and corresponding observational time for detecting a 1% dipolar anisotropy with the Pierre Auger Observatory with a 3 s significance was also estimated
Mestrado
Teorias Especificas e Modelos de Interação ; Sistematica de Particulas : Raios Cosmicos
Mestre em Física
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MORADI, KAMRAN. "Acoustic Manipulation and Alignment of Particles for Applications in Separation, Micro-Templating, and Device Fabrication." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/1753.
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This dissertation studies the manipulation of particles using acoustic stimulation for applications in microfluidics and templating of devices. The term particle is used here to denote any solid, liquid or gaseous material that has properties, which are distinct from the fluid in which it is suspended. Manipulation means to take over the movements of the particles and to position them in specified locations.
Using devices, microfabricated out of silicon, the behavior of particles under the acoustic stimulation was studied with the main purpose of aligning the particles at either low-pressure zones, known as the nodes or high-pressure zones, known as anti-nodes. By aligning particles at the nodes in a flow system, these particles can be focused at the center or walls of a microchannel in order to ultimately separate them. These separations are of high scientific importance, especially in the biomedical domain, since acoustopheresis provides a unique approach to separate based on density and compressibility, unparalleled by other techniques. The study of controlling and aligning the particles in various geometries and configurations was successfully achieved by controlling the acoustic waves.
Apart from their use in flow systems, a stationary suspended-particle device was developed to provide controllable light transmittance based on acoustic stimuli. Using a glass compartment and a carbon-particle suspension in an organic solvent, the device responded to acoustic stimulation by aligning the particles. The alignment of light-absorbing carbon particles afforded an increase in visible light transmittance as high as 84.5%, and it was controlled by adjusting the frequency and amplitude of the acoustic wave. The device also demonstrated alignment memory rendering it energy-efficient. A similar device for suspended-particles in a monomer enabled the development of electrically conductive films. These films were based on networks of conductive particles. Elastomers doped with conductive metal particles were rendered surface conductive at particle loadings as low as 1% by weight using acoustic focusing. The resulting films were flexible and had transparencies exceeding 80% in the visible spectrum (400-800 nm) These films had electrical bulk conductivities exceeding 50 S/cm.
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Saoudi, Rania. "Comportement des matériaux magnétiques nanocristallins FeCuNbSiB lors du vieillissement sous contraintes thermique et électrique." Electronic Thesis or Diss., Lyon 1, 2023. http://www.theses.fr/2023LYO10132.
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Dans le contexte de l'augmentation de l'efficacité énergétique, les systèmes électriques passent par une conception très compactée afin de réduire leurs volumes et poids, spécifiquement dans les systèmes intervenant dans les transports (automobile, ferroviaire et aérien). Cette compacité amène les matériaux magnétiques des nouveaux convertisseurs électriques à fonctionner dans environnements sévères (hautes températures et hautes fréquences). Cette thèse est consacrée pour étudier le comportement dans le temps (vieillissement) des matériaux nanocristallins FeCuNbSiB dédié à la conception des transformateurs, des inductances et des capteurs de courants. Différentes nuances de ces matériaux sont étudiées sachant que les échantillons sont fournis par APERAM Imphy sous forme des tores. En premier temps, les nanocristallins sont étudiées lors du vieillissement continu sous différentes températures. Plusieurs grandeurs macroscopiques magnétiques sont mesurées à chaque période de vieillissement. Afin d'expliquer le mécanisme du vieillissement, une analyse des énergies d'anisotropies est menée, compléter par des mesures à différentes échelles (locale, mésoscopique et microscopique). En deuxième temps, les propriétés magnétiques des nanocristallins sont suivis durant leur vieillissement thermique sous excitation alternée. Cette dernière est appliquée en utilisant des circuits électroniques conçus pour des capteurs de courant fluxgate fournis par LEM. Au final, l'impact du vieillissement magnétique des nanocristallins sur l'évolution des paramètres des capteurs est étudiéIn the context of increasing energy efficiency, electrical systems need to be designed in a very compact way in order to reduce their volume and weight, specifically in systems used in transportation (automotive, rail and airplanes). This compactness leads the magnetic materials of the new electrical converters to operate in severe environments (high temperatures and high frequencies). This thesis focuses on the behavior over time (aging) of FeCuNbSiB nanocrystalline materials dedicated to the design of transformers, inductors and current sensors. Different grades of nanocrystalline materials were provided by our collaborator APERAM Imphy in the form of wound cores. At first, nanocrystalline materials are studied during continuous aging under different temperatures. In aim to monitor aging evolution, several macroscopic magnetic properties are measured at each aging period. In order to explain the aging mechanism, an analysis of the anisotropy energies is conducted, completed by measurements at different scales (local, mesoscopic and microscopic). Thereafter, the magnetic properties of nanocrystalline materials are monitored during their thermal aging under alternating excitation. The latter is applied using electronic circuits designed for fluxgate current sensors provided by LEM. Finally, the impact of magnetic aging of nanocrystals on the evolution of sensor parameters is studied
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Mohammad, Nopoush. "NON-EQUILIBRIUM HYDRODYNAMICS OF THE QUARK-GLUON PLASMA." Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1554403936171225.
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Lauback, Stephanie Diane. "Magnetic Actuation of Biological Systems." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1494262695434601.
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Münchmeyer, Moritz. "Large-scale anisotropies in the high energy cosmic ray sky." Paris 6, 2012. http://www.theses.fr/2012PA066651.
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Boghrat, Pedram. "Search for ultra high energy cosmic ray anisotropy with Auger." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1750728181&sid=5&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Graham, Lilian Joan. "Ultra high energy gamma ray point sources and cosmic ray anisotropy." Thesis, Durham University, 1994. http://etheses.dur.ac.uk/5594/.
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The experimental set-up at the Baksan Air Shower Array, used to detect air showers above ~0.2xl0(^14)eV, is described. An estimation of the angular resolution using the cosmic ray shadow of the Sun and the Moon gives a value of ~2.5˚ which is consistent with previous estimates from Monte-Carlo simulations. Using data from this array covering 1985-1992, a search is made for 7-ray emission from 18 candidate sources. Upper limits to the flux from these sources are stated in all cases. A periodicity search is made on data for which the excess for a single transit of a particular source is above 3(7. The results of this periodicity analysis on such days points to 4 possible observations of pulsed emission at the 95% confidence level. These are 4U0115+63 on 19.03.89, PSR19534-29 on 12.02.85, 1E2259+586 on 01.08.91 and PSR0655+64 on 12.08.89. Without confirmation from other groups however the findings are not significant enough to stand alone. A harmonic analysis has been performed on the 8 years of data and after pressure corrections and a Farley & Storey analysis to eradicate any spurious sidereal variations we find negligible evidence of 2nd or 3rd harmonic but a 1st harmonic amplitude and phase of (12.7 ±1.2) x 10(^-4) at 23.1 ± 0.3hr right ascension. When one takes into account the cosϐ effect on the sidereal anisotropy this value becomes 17.4±1.6xl0(^-4).Future developments and improvements to be undertaken at BASA, including the building of a muon detector, are outlined.
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Marquezin, Cássia Alessandra. "Técnicas de fluorescência no monitoramento de membranas modelo." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-26032009-154339/.
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Apresentamos os resultados de estudos sobre a utilização de técnicas baseadas no fenômeno de fluorescência para a investigação de processos relacionados a membranas modelo. Nessa investigação, estão envolvidas medidas de propriedades espectrais de absorção e emissão de luz por cromóforos adequados, determinação xperimental de perfis de decaimento temporal da fluorescência e correlação temporal de emissão fluorescente, bem como a utilização apropriada de metodologias para análise e interpretação dos dados experimentais. Foram utilizados diversos compostos que apresentam absorção e emissão na região ultravioleta/visível, como as sondas lipofílicas 2-Amino-N-hexadecil-benzamida (Ahba), 6-lauryl-2-dimethylaminonaphthalene (Laurdan), N-(7-nitrobenz-2-oxa-1,3- diazol-4-yl) (NBD), em diferentes condições: meio aquoso homogêneo, suspensões de micelas de Sodium Dodecyl Sulfate (SDS), Cetyl-trimethyl-ammonium-bromide (CTAB) e 3-(Dodecyl-Dimethyl-Ammonio)-propane-sulfonate (DPS) e vesículas de fosfolipídios, como o 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC), o 1,2-Dimyristoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)](Sodium Salt) (DMPG) e o 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine (POPC). Supressores alquilpiridínios de diferentes comprimentos da cadeia alquila e, portanto, diferentes afinidades por agregados anfifílicos, foram utilizados em experimentos de supressão da fluorescência da sonda Ahba. Usando o formalismo que descreve fenômenos de supressão dependente de colisões entre fluoróforo e supressor, observamos que as taxas de supressão são maiores em presença de agregados anfifílicos carregados negativamente: micelas de SDS e vesículas de DMPG; em micelas zwiteriônicas o processo é mais eficiente quando a hidrofobicidade do supressor é grande, o que ocorre quando a cadeia alquila é mais longa. Realizamos experimentos de transferência de energia por ressonância de Förster (FRET) onde o grupo fluorescente da sonda lipofílica Ahba atuou como doador. Como aceitadores utilizamos os compostos Acridina Laranja, -(2,4,dinitrofenil)-etilenodiamina (Eddnp) e o NBD ligado a fosfolipídios. Fizemos uso do programa CONTIN para análise de dados experimentais de perfis de decaimento da fluorescência em sistemas em que ocorre transferência de energia e obtivemos distribuições de distâncias para os pares Ahba/Eddnp e Ahba/NBD-fosfolipídios na presença de vesículas de fosfolipídios. Para este último par, verificou-se que a distribuição de distâncias depende da temperatura do sistema, ou seja, da fase da bicamada, da concentração de aceitador e da posição onde o NBD está ligado ao fosfolipídio. Analisamos a utilização da sonda Laurdan em presença de vesículas de DMPC e POPC, em experimentos de espectroscopia de correlação de fluorescência. Embora tenha apresentado sinal elevado de fluorescência, a sonda é fotodegradável. Os mesmos experimentos de correlação de fluorescência foram realizados com o Ahba que, apesar de ter se mostrado bastante fotoestável, revelou não ser uma sonda adequada para uso em tal técnica. O espectro de excitação a dois fótons foi obtido para esta sonda, com máximo de absorção em 695 nm. Em experimentos de microscopia de fluorescência, o Ahba mostrou ser um bom marcador fluorescente para membranas lipídicas, ao possibilitar a aquisição de imagens de fluorescência de vesículas gigantes marcadas.In this work we showed results from studies about the use of fluorescence spectroscopy techniques as a tool to investigate amphiphilic aggregates, used as a model of the cell membrane. We performed measurements on the spectral properties of light absorption and emission of adequate chromophors, registered the experimental timeresolved decay of fluorescence and time correlated fluorescence emission of the probes and used also adequate methodologies for the analysis and interpretation of experimental data. Several compounds presenting absorption and emission in the UV/visible spectral range were employed: the lipophilic probes 2-Amino-N-hexadecil-benzamida (Ahba), 6-lauryl-2-dimethylaminonaphthalene (Laurdan), N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) (NBD), in different environment:homogeneous aqueous medium, micelles of surfactants like Sodium Dodecyl Sulfate (SDS), Cetyl-trimethyl-ammonium-bromide (CTAB) and 3- (Dodecyl-Dimethyl-Ammonio)-propane-sulfonate (DPS) and phospholipid vesicles of 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC), 1,2-Dimyristoyl-sn-Glycero-3- [Phospho-rac-(1-glycerol)](Sodium Salt) (DMPG) and 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine (POPC). Alkyilpyridinium halides with different alkyl chain length were employed fluorescence quenchers of the Ahba probe. Using the Stern-Volmer model to describe the quenching phenomena dependent on fluorophor/quencher collision, we observed that higher quenching rates were obtained in the presence of negatively charged amphiphilic agreggates: SDS micelles and DMPG vesicles; in the presence of zwitterionic vesicles the quenching efficiency was more efficient when the quencher hydrophobicity was high (long alkyl chain). We performed Förster resonance energy transfer (FRET) experiments where the fluorescent moiety of the probe Ahba was the energy donor. As acceptors molecules we used Acridine Orange, Ethylene-diamine-dinitrophenyl (Eddnp) and NBD-labeled phospholipids. The computational package CONTIN was adapted to analyze the experimentally obtained fluorescence decay profiles of the donor in the presence of the acceptor, in order to determine the distance distribution between the Ahba/Eddnp and Ahba/NBD-phospholipids pairs in the presence of lipid vesicles. For the Ahba/NBD pair, the distances were dependent on the emperature of the system (or the phase bilayer behavior), the acceptor concentration and the NBD position in the phospholipid. We observed that the Laurdan probe can be used in studies about DMPC vesicles diffusion using fluorescence correlation spectroscopy techniques. Investigation about the use of the probe Ahba with this technique had shown that its maximum absorption for two photon excitation occurs near to 695 nm, but it is not an appropriated probe to FCS experiments due to its very low brightness. On the other hand, Ahba can be used as a membrane fluorescent label in membrane fluorescence microscopy, as we can see in the fluorescence imaging experiments with giant vesicles labeled with Ahba.
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Hamilton, Nicholas Michael. "Anisotropy of the Reynolds Stress Tensor in the Wakes of Counter-Rotating Wind Turbine Arrays." PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/1848.
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A wind turbine array was constructed in the wind tunnel at Portland State University in a standard Cartesian arrangement. Configurations of the turbine array were tested with rotor blades set to rotate in either a clockwise or counter-clockwise sense. Measurements of velocity were made with stereo particle-image velocimetry. Mean statistics of velocities and Reynolds stresses clearly show the effect of direction of rotation of rotor blades for both entrance and exit row turbines. Rotational sense of the turbine blades is visible in the mean spanwise velocity W and the Reynolds shear stress -[macron over vw]. The normalized anisotropy tensor was decomposed yielding invariants [lowercase eta] and [lowercase xi], which are plotted onto the Lumley triangle. Invariants of the normalized Reynolds stress anisotropy tensor indicate that distinct characters of turbulence exist in regions of the wake following the nacelle and the rotor blade tips. Eigendecomposition of the tensor yields principle components and corresponding coordinate system transformations. Characteristic spheroids are composed with the eigenvalues from the decomposition yielding shapes predicted by the Lumley triangle. Rotation of the coordinate system defined by the eigenvectors demonstrates streamwise trends, especially trailing the top rotor tip and below the hub of the rotors. Direction of rotation of rotor blades is evidenced in the orientation of characteristic spheroids according to principle axes. The characteristic spheroids of the anisotropy tensor and their relate alignments varies between cases clearly seen in the inflows to exit row turbines. There the normalized Reynolds stress anisotropy tensor shows cumulative effects of the rotational sense of upstream turbines. Comparison between the invariants of the Reynolds stress anisotropy tensor and terms from the mean mechanical energy equation indicate a correlation between the degree of anisotropy and the regions of the wind turbine wakes where turbulence kinetic energy is produced. The flux of kinetic energy into the momentum-deficit area of the wake from above the canopy is associated with prolate characteristic spheroids. Flux upward into the wake from below the rotor area is associate with oblate characteristic spheroids. Turbulence in the region of the flow directly following the nacelle of the wind turbines demonstrates more isotropy compared to the regions following the rotor blades. The power and power coefficients for wind turbines indicate that flow structures on the order of magnitude of the spanwise turbine spacing that increase turbine efficiency depending on particular array configuration.
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Bird, David John. "Arrival directions of medium energy cosmic rays in the southern hemisphere /." Title page, contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09pb6178.pdf.
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Dundovic, Andrej [Verfasser], and Günter [Akademischer Betreuer] Sigl. "On Anisotropies of Ultra-high Energy Cosmic Rays / Andrej Dundovic ; Betreuer: Günter Sigl." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/1162275243/34.
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Menon, Nanda. "A study of electronic structure anisotropy by spatially resolved electron energy loss spectroscopy." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624123.
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French, Jarin C. "Molecular Dynamics Studies of Anisotropy in Grain Boundary Energy and Mobility in UO₂." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/89643.
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Nuclear energy is a proven large-scale, emission-free, around-the-clock energy source. As part of improving the nuclear energy efficiency and safety, a significant amount of effort is being expended to understand how the microstructural evolution of nuclear fuels affects the overall fuel performance. Grain growth is an important aspect of microstructural evolution in nuclear fuels because grain size can affect many fuel performance properties. In this work, the anisotropy of grain boundary energy and mobility, which are two important properties for grain growth, is examined for the light water reactor fuel uranium dioxide (UO₂) by molecular dynamics simulations. The dependence of these properties on both misorientation angle and rotation axis is studied. The anisotropy in grain boundary energy is found to be insignificant in UO₂. However, grain boundary mobility shows significant anisotropy. For both 20º and 45º misorientation angles, the anisotropy in grain boundary mobility follows a trend of M₁₁₁>M₁₀₀>M₁₁₀, consistent with previous experimental results of face-centered-cubic metals. Evidences of grain rotation during grain growth are presented. The rotation behavior is found to be very complex: counterclockwise, clockwise, and no rotation are all observed.M.S.
Energy needs in the world increase year after year. As part of the effort to address these increasing needs, an increasing effort is needed to study each aspect of energy generation. For energy generated via nuclear fission, i.e., nuclear energy, many things need to be understood to gain maximum efficiency with maximum safety. At the core of a nuclear reactor, transport of energy generated by nuclear fission is heavily dependent on the microscopic structure (microstructure) of the materials being used as fuel. Thus, this work examines the microstructure of the most common nuclear fuel, uranium dioxide (UO₂). The microstructure changes based on at least two properties: grain boundary energy, and grain boundary mobility. This work examines how these properties change based on the orientation of individual crystallites within the polycrystalline material. An additional aspect of microstructural evolution, namely grain rotation, is briefly discussed.
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De, Domenico Manlio. "Propagation of Ultra-High Energy Cosmic Rays and anisotropy studies with the Pierre Auger Observatory: the multiscale approach." Doctoral thesis, Università di Catania, 2012. http://hdl.handle.net/10761/992.
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The main goal of this thesis is the investigation of the arrival directions of ultra-high energy cosmic rays (UHECRs). The clustering of such events, collected by the Pierre Auger Observatory, is used to infer the nature of sources and their density, as well as other physical unknowns. Results are based on the comparison between real and simulated data. Hence, an ad hoc Monte Carlo code (HERMES) for the realistic simulation of UHECR propagation in the Universe and a novel method (MAF) to quantify the amount of clustering in a data set of few UHECR events have been developed.
In the first chapter, a general overview of UHECR physics is given, with particular attention to the Auger Observatory and the most recent results regarding its measurements.
In the second and third chapters, we present the general structure of HERMES and we discuss the procedures adopted to simulate the propagation of UHECRs in a magnetized Universe. In the second chapter, magnetic fields are treated, and their impact on the propagation of UHECRs is discussed. In particular, we simulate the diffusion of charged particles in both turbulent and structured magnetic fields for energy values ranging from 10^17 to 10^21 eV. In the third chapter, the propagation of protons and heavier nuclei is treated. We define the cosmological framework of HERMES and we parameterize the cosmic background radiation (CBR). The parameterizations for the cross section of the interactions between nuclei and CBR photons are discussed, as well as the relevant energy-loss processes. The impact of propagation on the GZK horizon of UHE protons is investigated, and comparisons between our results and the literature those obtained with other simulators are presented.
In the fourth chapter, a novel method is introduced to estimate the statistical significance of clustering in the arrival direction distribution of few events, a necessary requirement because of the current small number of events observed above 5x10^19 eV. The method involves a multiscale procedure, based on information theory and extreme value statistics, providing high discrimination power, even in presence of strong background isotropic contamination. It is extended to allow correlation analysis with catalogues of sources. Here, the term "multiscale" explicitly indicates the dependence on the angular scale adopted to investigate the arrival directions of UHECRs. It is shown that MAF has some valuable features, it is: i) semi-analytical, ii) very sensitive to small, medium and large scale clustering, iii) not biased against the null hypothesis.
Finally, in the fifth, sixth and seventh chapters, Monte Carlo simulations are extensively adopted to investigate real data. In the fifth chapter we use multiscale methods to explore the effects of experimental uncertainties on clustering and correlation of UHECRs with catalogues. In the sixth chapter, energy losses due to secondary particle production or photo-disintegration, as well as deflections due to galactic (GMF) and extragalactic magnetic fields (EMF), are taken into account. All of such interactions, together with the distribution of sources, produce different arrival directions of events at Earth. Hence, clustering in events detected with the Auger Observatory and in simulated sky maps of UHECRs, mimicking realistic astrophysical scenarios, is used to put bounds on some relevant unknowns, as the fraction of protons in the data, the density of sources and the strength of the turbulent component of the EMF. Moreover, the possibility that nearby active galactic nuclei and black holes could be responsible for the observed flux of UHECRs is explored in detail. In the seventh chapter, we perform a more extended study which takes into account additional observables, as the elongation rate and the energy spectrum. By varying the underlying assumptions, we have outlined an astrophysical scenario able to explain Auger data from a phenomenological point of view.
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Keller, A. "Evolution of Ion-Induced Ripple Patterns - Anisotropy, nonlinearity, and scaling." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-61101.
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This thesis addresses the evolution of nanoscale ripple patterns on solid surfaces during low-energy ion sputtering. Particular attention is paid to the long-time regime in which the surface evolution is dominated by nonlinear processes. This is explored in simulation and experiment.
In numerical simulations, the influence of anisotropy on the evolution of the surface patterns in the anisotropic stochastic Kuramoto-Sivashinsky (KS) equation with and without damping is studied. For a strong nonlinear anisotropy, a 90 rotation of the initial ripple pattern is observed and explained by anisotropic renormalization properties of the anisotropic KS equation. This explanation is supported by comparison with analytical predictions. In contrast to the isotropic stochastic KS equation, interrupted ripple coarsening is found in the presence of low damping. This coarsening seems to be a nonlinear anisotropy effect that occurs only in a narrow range of the nonlinear anisotropy parameter.
Ex-situ atomic force microscopy (AFM) investigations of Si(100) surfaces sputtered with sub-keV Ar ions under oblique ion incidence show the formation of a periodic ripple pattern. This pattern is oriented normal to the direction of the ion beam and has a periodicity well below 100 nm. With increasing ion fluence, the ripple pattern is superposed by larger corrugations that form another quasi-periodic pattern at high fluences.
This ripple-like pattern is oriented parallel to the direction of the ion beam and has a periodicity of around one micrometer. Interrupted wavelength coarsening is observed for both patterns. A dynamic scaling analysis of the AFM images shows the appearance of anisotropic scaling at large lateral scales and high fluences. Based on comparison with the predictions of different nonlinear continuum models, the recent hydrodynamic model of ion erosion, a generalization of the anisotropic KS equation, is considered as a potentially powerful continuum description of this experiment.
In further in-situ experiments, the dependence of the dynamic scaling behavior of the sputtered Si surface on small variations of the angle of incidence is investigated by grazing incidence small angle X-ray scattering (GISAXS). A transition from strongly anisotropic to isotropic scaling is observed. This indicates the presence of at least two fixed points in the system, an anisotropic and an isotropic one. The dynamic scaling exponents of the isotropic fixed point are in reasonable agreement with those of the Kardar-Parisi-Zhang (KPZ) equation. It remains to be seen whether the hydrodynamic model is able to show such a transition from anisotropic to isotropic KPZ-like scaling.
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Benoit, Jean-Pierre. "Étude expérimentale et théorique d'une turbulence homogène soumise à des effets couplés de rotation et de déformation plane." Ecully, Ecole centrale de Lyon, 1992. http://www.theses.fr/1992ECDL0026.
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L'étude théorique des caractéristiques anisotropes d'une turbulence homogène soumise à des gradients moyens plans est abordée dans l'espace spectral. Différents couplages du taux de rotation/déformation sont examinés de part et d'autre du cas central de cisaillement pur. La résolution du problème linéaire est réalisée sur l'équation du spectre de la fluctuation de vitesse. La solution numérique est détaillée dans le cas des écoulements elliptiques afin de faire le lien avec les études de stabilité de ces écoulements périodiques. L'approche non linéaire porte sur l'équation du tenseur spectral d'ordre 2. Une fermeture du type EDQNM est utilisée pour décrire l'évolution des corrélations triples. Le calcul du terme non linéaire de l'équation de Craya est simplifié en utilisant une décomposition en harmoniques sphériques pour le tenseur d'ordre 2. L'étude expérimentale, menée parallèlement, fournit les évolutions anisotropes des tensions de Reynolds pour les cas de couplage suivants: déformation pure plane, déformation dominante, cisaillement pur et rotation dominante. Les résultats linéaires donnent les tendances de l'anisotropie. Par contre, le calcul non linéaire se heurte à un problème de réalisabilité du tenseur spectral. Cet écueil tend à prouver que le degré de troncature des séries d'harmoniques sphériques, choisi égal à 2, pour une simplification de la modélisation, est trop bas
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Short, Geoffrey. "Study of magnetic anisotropy by Magnetic Circular X-ray Dichroism." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310961.
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Peixoto, Carlos Jose Todero. "Reconstrução de chuveiros atmosféricos extensos detectados pelo Observatório Pierre Auger utilizando métodos robustos." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277465.
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Orientador: Carlos Ourivio EscobarTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Desde os primeiros Raios Cósmicos de alta energia detectados por Pierre Auger na década de 30, toda a comunidade de Física de Radiação Cósmica procura técnicas matemáticas e métodos estatísticos mais adequados para analisar estes eventos. Estes processos de análise são imprescindíveis na estimativa da energia da partícula primária, bem como no cálculo do ângulo de chegada q . A estimativa desta energia e do ângulo q é o final de toda uma rede de trabalho e o começo de uma nova linha de pesquisa na busca pelas possíveis fontes que produziram tais eventos. Ao longo deste trabalho refizemos o princípio de reconstrução dos "chuveiros de Auger", os chamados "Chuveiros Atmosféricos Extensos" ( C.A.E.), utilizando um conceito relativamente novo de estatística, hoje denominada Estatística Robusta. O Método dos Mínimos Quadrados ou Least Square -LS, apresentado por Gauss e Legendre, possuía limitações que eles próprios já reconheciam e tentaram resolver, sem sucesso. Desde fins do século XVIII e come¸ co do século XIX, os métodos estritamente paramétricos, em especial o Método dos Mínimos Quadrados e a média aritmética, foram questionados quando utilizados para descrever distribuições pouco comportadas ou com grandes utuações. Algumas das principais questões estavam relacionadas a como tratar pontos muito distantes da distribuição principal (os chamados outliers) e como estes influenciavam a própria distribuição. A saída convencional mais utilizada foi a rejeição dos outliers e de pontos que apresentassem grandes desvios em relação a média. Porém, a perda de informações sobre a própria distribuição tornava-se inevitável. O modelo paramétrico mostrou-se apenas uma aproximação da realidade, uma vez que as flutuações, apesar de serem consideradas, não são "bem-vindas"; são vistas apenas como um erro inerente à observação. Então, no fim do século XIX apareceram as primeiras tentativas de extrair informação das flutuações, classificando-as e as considerando parte integral da descrição da distribuição. Se um método estatístico for capaz de descrever os dados observados, incluindo e classificando as flutuações inerentes, este passa a ser conhecido como "Método Robusto" ou "Estatística Robusta", onde a nomenclatura "Robusta" está relacionada à capacidade do método ou modelo de "resistir" às flutuações fornecendo uma descrição da realidade com razoável independência destas mesmas flutuações. Com base em dois métodos robustos, Mínima Mediana Quadrada (Least Median Square - LMS) e Mínimos Quadrados "Aparados" (Least Trimmed Square - LTS), aplicamos estes nos ajustes da Função Distribuição Lateral de Chuveiros (Lateral Distribution Function - LDF) extraindo o valor de S 1000, parâmetro necessário para estimar a energia da partícula primária. Os valores para S1000 calculados a partir de estatística convencional (Mínimos Quadrados) e estatística robusta (LMS e LTS) são comparados. O valor de S1000, para chuveiros de mesma energia, depende do ângulo q dos primários, já que o CAE sofre atenuação na atmosfera, atenuação esta tanto maior quanto maior, for q . Para levar em conta a atenuação no cálculo do espectro de energia, em que todos os ângulos de chegada são considerados (até 60 graus), é introduzido o parâmetro S38, onde 38 graus é a mediana dos dados do Auger. A atenuação é calculada usando-se o método do Constant Intensity Cut (CIC) o qual depende da validade de várias hipóteses. As três hipóteses supostas pela Colaboração Auger são apresentadas neste trabalho. Correlacionamos, assim, todos os novos valores de S38 com os valores da chamada "Energia Híbrida", obtida diretamente do programa de análise da Colaboração Auger. Esta correlação nos permite recorrigir a energia com base em detecção híbrida, que é a grande vantagem do Observatório Pierre Auger. Esta correlação nos permite estabelecer a escala de energia ou calibração do detector de superfície com base na determinação calorimétrica da energia feita pelo detector de flurescência, que é o grande avançoo trazido para o campo pelo Obvservatório Pierre Auger. Com os novos resultados de energia, refizemos os cálculos de minimização para a correlação de radiação cósmica com fontes extra-galácticas obtendo correlações que não estão em correspondência biunívoca com aquelas obtidas pelo método convencional de análise. Por fim fazemos uma análise das próprias estações outliers tentando extrair alguma informação relacionada à performance do detector de superfície. Os apêndices incluídos após as conclusões foram colocados neste trabalho apenas por motivos didáticos como consulta rápida para o leitor leigo em métodos de detecção de radiação cósmica
Abstract: Since the first ultra high-energy cosmic rays detected by Pierre Auger (the 30s) the entire community of Physics of Cosmic Rays search for mathematical techniques and more appropriate statistical methods to analyze these events. These analysis processes are essential for the estimate of the energy of the primary particle as well as in the calculation of the angle of arrival q . The estimate of the energy and the angle q is the end of a long chain of analysis and the beginning of a new line of research in the search for the possible sources that produced such events. Throughout this work we re-analysed the reconstruction chain of the "Auger showers", the socalled "Extensive Air Showers - EAS", using a relatively new concept of statistics, known as Robust Statistics. The Least Square Method - LS, presented by Gauss and Legendre had limitations already recognized by themselves who tried to overcome them without success. Since the end of the eighteenth century and beginning of the nineteenth century, strictly parametric methods, especially the Least Squares and the arithmetic average, were questioned when used to describe distributions with bad behavior or with large uctuations. Some of the main issues were related to how to deal with points far way from the main distribution (the so-called outliers) and how it in uenced the main distribution. The more conventional way out used was the rejection of the outliers and points that produced large deviations from average. But the loss of information about the distribution was inevitable. The parametric model proved to be only an approximation of reality, since uctuations, despite being considered, are not "welcome"; are seen only as an error inherent in observation. Then, at the end of the nineteenth century there appeared the first attempts to extract information from uctuations sorting them out and considering them as an integral part of the description of the distribution. Whether a statistical method is able to describe observed data, including and sorting the uctuations inherent, then becomes known as "Robust Method" or "Robust Statistic", where the nomenclature "Robust" is related the ability of the method or model to "Resist" the uctuations by providing a description of reality with reasonable independence these same uctuations. Based on two robust methods: Least Median Square - LMS and Least Trimmed Square - LTS; we apply these to adjust the Lateral Distribution Function - LDF extracting the value of S1000, parameter needed to estimate the energy of the primary particle. The values for S1000 calculated from conventional statistic (Least Square) and robust statistic (LMS and LTS) are compared. The parameter S1000 is dependent on the angle of arrival of the shower, then we apply a correction factor called S38. This correlates S1000 and and, currently, there are several ways to calculate this factor. The three hypotheses most used by Auger Collaboration are presented in this work. We then correlate all new values of S38 with the values of the so-called "Hybrid Energy", obtained directly from analysis software of the Auger Collaboration. This relationship allows us to correct the energy based on hybrid detection that is great advantage of the Pierre Auger Observatory. This relationship allows us to establish the energy scale or calibration of the surface detector on the basis of the calorimetric determination of the energy done by the uorescence detector which is the great advancement brought to the field by the Pierre Auger Observatory. With the new results for the energy we reanalysed the the correlation with extra-galactic sources of cosmic ray getting new correlations, which are absent in the conventional methods of analysis. Finally we make an analysis of the surface stations outliers by themselves trying to extract some information relevant for their performance. Appendices included after the conclusions were placed in this work only for a rapid consultation by lay readers in methods of detection of cosmic rays
Doutorado
Teorias Especificas e Modelos de Interação ; Sistematica de Particulas ; Raios Cosmicos
Doutor em Ciências
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Salvador, Marcelo. "Distribuição de barreiras de energia de nanopartículas magnéticas em campo externo." reponame:Repositório Institucional da UFSC, 2014. https://repositorio.ufsc.br/xmlui/handle/123456789/128600.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2014.Made available in DSpace on 2015-02-05T20:09:47Z (GMT). No. of bitstreams: 1 327324.pdf: 3541315 bytes, checksum: 6521363a229cc4e9ee23484c98698dde (MD5) Previous issue date: 2014
Neste trabalho estudamos o comportamento da magnetização de um sistema de nanopartículas magnéticas não interagentes, monodomínio, com anisotropia uniaxial. Foram realizadas simulações de Monte Carlo através do algoritmo de Metropolis para analisar a relaxação magnética das nanopartículas inicialmente magnetizadas à saturação, na ausência e na presença de um campo magnético externo. A lei de escala Tln(t) foi utilizada para computar os dados da relaxação em diferentes temperaturas, gerando uma única curva mestra para cada valor de campo aplicado. Através dessas curvas podemos obter as distribuições das barreiras de energia do sistema e verificar a influência do campo externo na inversão da magnetização.
Abstract : In this work the behavior of the magnetization of a system composed by noninteracting magnetic nanoparticles, monodomains, with uniaxial anisotropy is studied. Monte Carlo simulations were performed through the Metropolis algorithm to analyse the magnetic relaxation when, at the beginning of the experiment, all the nanoparticles are magnetized to saturation, in the presence or absence of an external magnetic field. The scaling law Tln(t) was used to compute the relaxation data for different temperatures providing one master curve for each value of the applied field. From these curves we find the energy barriers distribution of the system and we verify the effect of the magnetic field on magnetization reversal.
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Vachhani, Shraddha J. "Stored energy maps in deformed metals using spherical nanoindentation." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51813.
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Microstructure changes that occur during the deformation and heat treatments involved in wrought processing of metals are of central importance in achieving the desired properties or performance characteristics in the finished products. However, thorough understanding of the evolution of microstructure during thermo-mechanical processing of metallic materials is largely hampered by lack of methods for characterizing reliably their local (anisotropic) properties at the sub-micron length scales. Recently, remarkable advances in nanoindentation data analysis techniques have been made which now make it possible to obtain quantitative information about the local mechanical properties of constituent individual grains in polycrystalline metallic samples. In this work, a novel approach that combines mechanical property information obtained from spherical nanoindentation with the complementary structure information measured locally at the indentation site, using Electron Backscattered Diffraction (EBSD), is used to systematically investigate the local structure-property relationships in fcc metals. This work is focused on obtaining insights into the changes in local stored energies of polycrystalline metallic samples as a function of their crystal orientation at increasing deformation levels. Furthermore, using the same approach, the evolution of mechanical properties in the grain boundary regions in these samples is studied in order to better understand the role of such interfaces during deformation and recrystallization processes. The findings provide valuable information regarding development of stored energy gradients in polycrystalline materials during macroscopic deformation.
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Ballardini, Mario <1986>. "Cosmological Constraints on Cosmic Inflation and Scalar-Tensor Dark Energy Models from CMB Anisotropies and Galaxy Clustering." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7764/1/Thesis.pdf.
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This thesis investigates the most recent cosmological bservations in order to constrain cosmic inflation and what is probably the simplest model of modified gravity.
We provide a detailed calculation for the scalar spectral index and for the tensor-to-scalar ratio, in slow-roll approximation, for a selection of single field inflationary models and we compare them with Planck 2015 data, taking into account reheating uncertainties.
We studied selected theoretically motivated parametrizations of the primordial power spectrum with departure from the near scale invariance, providing a better
fit to the CMB temperature power spectrum with respect to the simplest slow-roll inflationary models. For a selection of models, we forecast the capability of future spectroscopic, photometric, and radio surveys, in combination with CMB measurements, to constrain parametrized features in the primordial power spectrum.
We studied a simple class of modified gravity models alternative to ΛCDM, based on Induced Gravity, or a Brans-Dicke like, with a monomial potential with positive
values of the exponent. Cosmological constraints for this class of dark energy models are derived from CMB alone and in combination with external dataset, such as BAO
and H0 local measurements.
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Zhang, Hongbin. "Relativistic Density Functional Treatment of Magnetic Anisotropy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-25132.
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Spin-orbit coupling (SOC) reduces the spatial symmetry of ferromagnetic solids. That is, the physical properties of ferromagnetic materials are anisotropic, depending on the magnetization direction. In this thesis, by means of numerical calculations with full-relativistic density functional theory, we studied two kinds of physical properties: surface magnetic anisotropy energy (MAE) and anisotropic thermoelectric power due to Lifshitz transitions. After a short introduction to the full-relativistic density functional theory in Chapter 2, the MAE of ferromagnetic thin films is studied in Chapter 3. For such systems, separation of different contributions, such as bulk magnetocrystalline anisotropy (MCA) energy, shape anisotropy energy, and surface/interface anisotropy energy, is crucial to gain better understanding of experiments. By fitting our calculating results for thick slabs to a phenomenological model, reliable surface MAE could be obtained. Following this idea, we have studied the MAE of Co slabs with different geometries, focusing on the effects of orbital polarization correction (OPC). We found that the surface anisotropy is mainly determined by the geometry. While OPC gives better results of orbital moments, it overestimates the MAE. In the second part of Chapter3, the effects of electric fields on the MAE of L10 ferromagnetic thin films are studied. Using a simple model to simulate the electric field, our calculations are in good agreement with previous experimental results. We predicted that for CoPt, even larger effects exist. Moreover, we found that it is the amount of screening charge that determines the magnetoelectric coupling effects. This gives us some clue about how to achieve electric field control of magnetization direction. In Chapter 4, Lifshitz transitions in L10 FePt caused by a canted magnetic field are studied. We found several Lifshitz transitions in ordered FePt with tiny features in DOS. Using a two-band model, it is demonstrated that at such transitions, the singular behaviour of kinetic properties is due to the interband scattering, and the singularity itself is proportional to the derivative of the singular DOS. For FePt, such singularity will be smeared into anomaly by chemical disorder. Using CPA, we studied the effects of energy level broadening for the critical bands in FePt. We found that for experimentally available FePt thin films, Lifshitz transitions would induce up to a 3% increase of thermopower as the magnetization is rotated from the easy axis to the hard axisSpin-Bahn-Kopplung reduziert die Symmetrie ferromagnetischer Festkörper. Das bedeutet, dass die physikalischen Eigenschaften ferromagnetischer Stoffe anisotrop bezüglich der Magnetisierungsrichtung sind. In dieser Dissertation werden mittels numerischer voll-relativistischer Dichtefunktional-Rechnungen zwei Arten physikalischer Eigenschaften untersucht: magnetische Oberflächen-Anisotropieenergie (MAE) und anisotrope Thermokraft durch Lifshitz-Übergänge. Nach einer kurzen Einführung in die relativistische Dichtefunktional-Theorie in Kapitel 2 wird in Kapitel 3 die MAE ferromagnetischer dünner Filme untersucht. In diesen Systemen ist es für ein Verständnis experimenteller Ergebnisse wichtig, verschiedene Beiträge zu separieren: Volumenanteil der magnetokristallinen Anisotropie (MCA), Formanistropie und Oberflächen bzw. Grenzflächenanisotropie. Durch Anpassen berechneter Daten für dicke Schichten an ein phänomenologisches Modell konnten verlässliche Oberflächen Anisotropien erhalten werden. In dieser Weise wurde die MAE von Co- Schichten mit unterschiedlichen Geometrien untersucht, wobei der Einfluss von Orbitalpolarisations-Korrekturen (OPC) im Vordergrund stand. Es wurde gefunden, dass die Oberflächenanisotropie hauptsächlich von der Geometrie bestimmt wird. Während OPC bessere Ergebnisse für die Orbitalmomente liefert, wird die MAE überschätzt. Im zweiten Teil von Kapitel 3 wird der Einfluss elektrischer Felder auf die MAE von dünnen ferromagnetischen Filmen mit L10-Struktur untersucht. Unter Verwendung eines einfachen Modells zur Simulation des elektrischen Feldes liefern die Rechnungen gute Übereinstimmung mit vorliegenden experimentellen Ergebnissen. Es wird vorhergesagt, dass für CoPt ein noch größerer Effekt existiert. Weiterhin wurde gefunden, dass die magnetoelektrische Kopplung von der Größe der Abschirmladung bestimmt wird. Dies ist eine wichtige Einsicht, um die Magnetisierungsrichtung durch ein elektrisches Feld kontrollieren zu können. In Kapitel 4 werden Lifshitz-Übergänge untersucht, die ein gekantetes Magnetfeld hervorruft. Es wurden mehrere Lifshitz-Übergänge in geordnetem FePt gefunden, welche kleine Anomalien in der Zustandsdichte hervorrufen. Mit Hilfe eines Zweiband-Modells wird gezeigt, dass an solchen Übergängen das singuläre Verhalten kinetischer Eigenschaften durch Interband- Streuung verursacht wird und dass die Singularität proportional zur Ableitung der singulären Zustandsdichte ist. In FePt wird durch chemische Unordnung diese Singularität zu einer Anomalie verschmiert. Der Einfluss einer Verbreiterung der Energieniveaus der kritischen Bänder in FePt wurde mittels CPA untersucht. Es wurde gefunden, dass in experimentell verfügbaren dünnen FePt-Filmen Lifshitz-Übergänge bis zu 3% Erhöhung der Thermokraft erzeugen, wenn die Magnetisierung von der leichten in die harte Richtung gedreht wird
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Tristram, Matthieu. "De Archeops à Planck : analyse des anisotropies du fond diffus cosmologique." Phd thesis, Université Joseph Fourier (Grenoble), 2005. http://tel.archives-ouvertes.fr/tel-00011003.
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L'analyse des anisotropies du fond diffus cosmologique (CMB) en température et en polarisation permet de contraindre une grande partie des paramètres cosmologiques décrivant le modèle du Big-Bang et l'Univers primordial. Cette thèse s'articule autour des mesures de l'expérience embarquée en ballon Archeops et de la future mission satellite Planck dont Archeops est le prototype. Après une description générale du modèle standard en cosmologie et de la physique du CMB, cette thèse aborde plus particulièrement le mécanisme de "reheating" qui, à la fin de l'inflation, permet le réchauffement de l'Univers et la formation de la matière.
La suite de ce travail présente les expériences Archeops et Planck et l'analyse de leurs données. Dans ce cadre, j'ai développé plusieurs méthodes permettant l'étude des signaux des rayons cosmiques, la mesure des temps de réponse des bolomètres ainsi que la prise en compte de l'asymétrie des lobes optiques.
L'étude des anisotropies passe par l'estimation des spectres de puissance en température et polarisation. Je présente une méthode rapide et non-biaisée donnant également une estimation analytique précise des barres d'erreur sans avoir recours aux simulations Monte-Carlo. Cette méthode a fourni la dernière estimation du spectre de puissance d'Archeops.
Enfin, la dernière partie traite de l'implication des résultats d'Archeops pour WMAP et Planck. Une analyse jointe Archeops-WMAP montre la cohérence des mesures CMB sur une large gamme de fréquences et la détection de l'effet Sunyaev-Zel'dovich. Par ailleurs, l'extrapolation des spectres polarisés des avant-plans galactiques mesurés par Archeops sert de référence pour Planck.
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Ohlson, Alice Elisabeth. "Investigating Parton Energy Loss in the Quark-Gluon Plasma with Jet-hadron Correlations and Jet Azimuthal Anisotrophy at STAR." Thesis, Yale University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3578426.
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In high-energy collisions of gold nuclei at the Relativistic Heavy Ion Collider (RHIC) and of lead nuclei at the Large Hadron Collider (LHC), a new state of matter known as the Quark-Gluon Plasma (QGP) is formed. This strongly-coupled, deconfined state of quarks and gluons represents the high energy-density limit of quantum chromodynamics. The QGP can be probed by high-momentum quarks and gluons (collectively known as partons) that are produced in hard scatterings early in the collision. The partons traverse the QGP and fragment into collimated "jets" of hadrons. Studies of parton energy loss within the QGP, or medium-induced jet quenching, can lead to insights into the interactions between a colored probe (a parton) and the colored medium (the QGP).
Two analyses of jet quenching in relativistic heavy ion collisions are presented here. In the jet-hadron analysis, the distributions of charged hadrons with respect to the axis of a reconstructed jet are investigated as a function of azimuthal angle and transverse momentum (pT). It is shown that jets that traverse the QGP are softer (consisting of fewer high-pT fragments and more low-p T constituents) than jets in p+p collisions. There are also indications that the shapes of the distributions of charged hadrons about the jet axis are modified by interactions with the QGP. The results are quantitatively consistent with two models of medium-induced radiative parton energy loss.
A measurement of jet v2, defined as the correlation between reconstructed jets and the reaction plane or 2nd-harmonic participant plane (approximated by the 2nd-harmonic event plane), provides information about the medium-induced pathlength-dependence of parton energy loss. The event plane is reconstructed with detectors at forward pseudorapidity in order to reduce the artificial jet – event plane bias, which results from jet fragments being included in the event plane calculation. A non-zero jet v2 is measured, indicating that more jets are reconstructed with a higher energy in-plane compared to out-of-plane, which demonstrates that the parton energy loss depends on the length of the parton's path through the QGP.
The data analyzed here were collected in [special characters omitted] = 200 GeV Au+Au and p+p collisions at the STAR detector at RHIC. A novel method for measuring jet v2 is also proposed and tested in simulation.
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El, Amraoui Rachid. "Etude de modèles de turbulence pour application aux écoulements à masse volumique variable avec et sans combustion." Rouen, 1993. http://www.theses.fr/1993ROUES029.
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Dans ce mémoire, nous avons testé les performances et évalué la capacité des modèles classiques de turbulence pour prédire les écoulements turbulents à masse volumique constante et variable soit par mélange de gaz de masses molaires différentes soit par dégagement de chaleur (combustion). Ainsi, les modèles k-epsilon et ASM formulés en moyenne de Favre (moyenne pondérée par la masse) sont mis en oeuvre et implantés dans un code de combustion turbulente. 3 types d'écoulement ont été choisis pour la validation de ces 2 modèles. Les résultats du calcul de l'écoulement d'air isotherme derrière la marche descendante de Kim (1978) montrent d'une part que le modèle ASM améliore le calcul des niveaux d'énergie cinétique de turbulence et d'autre part que seule une modification de l'équation de l'énergie cinétique serait susceptible d'améliorer la position du point de récollement prédite par les 2 modèles k-epsilon et ASM. Concernant les effets de variation de masse volumique en situation isotherme les calculs ont été menés par le modèle k-epsilon pour 2 jets. Le premier est léger et le second est lourd par rapport à l'écoulement d'air extérieur. Les résultats du champ dynamique (moyenne et fluctuations) sont satisfaisants. Les fluctuations du scalaire inerte sont correctement prédites dans le cas du jet léger et moins bien prédites pour le jet lourd. Dans la 3ème partie nous avons calculé la flamme de diffusion de Takagi et al (1981). Les tensions de Reynolds sont surestimées par le modèle k-epsilon. L'amélioration apportée par le modèle ASM est significative. Nous avons établi que: 1) le modèle ASM prédit l'effet d'anisotropie du à la combustion et; 2) aucun des deux modèles ne permet de reproduire l'effet de relaminarisation ni celui de l'expansion des échelles intégrales de turbulence due au dégagement de chaleur
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Sophys, Gabriel. "Formation of a Quark-Gluon-Plasma : understanding the energy and system size dependence." Thesis, Nantes, 2018. http://www.theses.fr/2018NANT4057/document.
Full textAbstract:
La ChromoDynamique Quantique (CDQ) décrit les interactions entre les partons. Ces partons sont confinés dans les hadrons, cependant la CDQ prédit un nouvel état de la matière où les partons sont dé-confinés des hadrons : Le Plasma de Quarks et de Gluons (PQG). L'étude du PQG est un axe de recherche challengeant puisque l'on observe expérimentalement les hadrons et non les partons. Dans cette thèse, j'étudie les anisotropies des angles azimutaux de la production de particule qui est directement liée à l'anisotropie du fluide. Cette anisotropie, due à une anisotropie spatiale initiale, donne des informations sur les propriétés du PQG et son expansion. qui est directement liée à l'anisotropie du fluide. On observe des effets « d'écoulement » lors des collisions d'ions lourds (AA) aux hautes énergies du RHIC et du LHC mais également aux basses énergies du Beam Energy Scan (BES). Récemment, des effets d'écoulement ont été également observés lors des collisions de petits systèmes (pp). La problématique de cette thèse est : Est-ce qu'un « plasma en expansion collectif » est créé dans tous les systèmes : grand (AA) ou petit (pp) des basses énergies du BES aux hautes énergies du LHC ? EPOS est un générateur d'évènements dédie à l'étude des collisions d'ions lourds et proton-proton. J'analyse l'écoulement anisotropique avec EPOS pour tous types de systèmes (pp, AA), énergies (LHC, RHIS, BES), pour tous types de « sondes » d'écoulement. Pour effectuer mon analyse, j'ai développé un framework facilement utilisable indépendamment des futurs développements d'EPOS. C'est très important car les résultats de mon analyse vont impacter sur les prochaines mises à jour du modèle à petite taille de système et à basse énergieQuantum ChromoDynamics (QCD) describes the interaction between partons (nuclear matter's degrees of freedom). These partons are usually confined into hadrons, however QCD predicts that a new state of matter exists where partons are deconfined from hadrons: the Quark Gluon Plasma (QGP). The QGP is formed in high energy heavy ion collisions. QGP study is exiting and theoretically challenging research field mainly because instead of partons, hadrons are observed. In this thesis, I study anisotropies in the azimuthal angle of particle production, which is directly related to the fluid's anisotropy. The fluid anisotropy is the response of the system to some initial space anisotropy and provides information on the properties of the QGP and its expansion. As in heavy ion (AA) collisions at high energies of RHIC and LHC, “flow-like” effects are hinted at Beam Energy Scan (BES) low energies. Very recently, unexpected “flow-like features” have also been observed in small systems like proton-proton (pp). In this thesis, I try to answer the following question: Is there a “collectively expanding plasma” in all systems : big (PbPb) or small (pp), from BES low energies to LHC higher energies? EPOS is an event generator dedicated to the study of proton-proton and heavy ion collisions. I analyze anisotropic flow with EPOS for all kind of systems (pp, AA), energies (LHC, RHIC, BES), and all kinds of flow “probes”. To perform my analysis, I developped a framework that can already be easily used, independently of further EPOS's developments. This fact is very important, because results of this analysis will impact incoming updates of the model at little system sizes and low energies