760 resultados para VARIATIONAL PROLAPSE


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The determination of the displacement and the space-dependent force acting on a vibrating structure from measured final or time-average displacement observation is thoroughly investigated. Several aspects related to the existence and uniqueness of a solution of the linear but ill-posed inverse force problems are highlighted. After that, in order to capture the solution a variational formulation is proposed and the gradient of the least-squares functional that is minimized is rigorously and explicitly derived. Numerical results obtained using the Landweber method and the conjugate gradient method are presented and discussed illustrating the convergence of the iterative procedures for exact input data. Furthermore, for noisy data the semi-convergence phenomenon appears, as expected, and stability is restored by stopping the iterations according to the discrepancy principle criterion once the residual becomes close to the amount of noise. The present investigation will be significant to researchers concerned with wave propagation and control of vibrating structures.

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Ebben a tanulmányban ismertetjük a Nöther-tétel lényegi vonatkozásait, és kitérünk a Lie-szimmetriák értelmezésére abból a célból, hogy közgazdasági folyamatokra is alkalmazzuk a Lagrange-formalizmuson nyugvó elméletet. A Lie-szimmetriák dinamikai rendszerekre történő feltárása és viselkedésük jellemzése a legújabb kutatások eredményei e területen. Például Sen és Tabor (1990), Edward Lorenz (1963), a komplex kaotikus dinamika vizsgálatában jelent®s szerepet betöltő 3D modelljét, Baumann és Freyberger (1992) a két-dimenziós Lotka-Volterra dinamikai rendszert, és végül Almeida és Moreira (1992) a három-hullám interakciós problémáját vizsgálták a megfelelő Lie-szimmetriák segítségével. Mi most empirikus elemzésre egy közgazdasági dinamikai rendszert választottunk, nevezetesen Goodwin (1967) ciklusmodelljét. Ennek vizsgálatát tűztük ki célul a leírandó rendszer Lie-szimmetriáinak meghatározásán keresztül. / === / The dynamic behavior of a physical system can be frequently described very concisely by the least action principle. In the centre of its mathematical presentation is a specic function of coordinates and velocities, i.e., the Lagrangian. If the integral of the Lagrangian is stationary, then the system is moving along an extremal path through the phase space, and vice versa. It can be seen, that each Lie symmetry of a Lagrangian in general corresponds to a conserved quantity, and the conservation principle is explained by a variational symmetry related to a dynamic or geometrical symmetry. Briey, that is the meaning of Noether's theorem. This paper scrutinizes the substantial characteristics of Noether's theorem, interprets the Lie symmetries by PDE system and calculates the generators (symmetry vectors) on R. H. Goodwin's cyclical economic growth model. At first it will be shown that the Goodwin model also has a Lagrangian structure, therefore Noether's theorem can also be applied here. Then it is proved that the cyclical moving in his model derives from its Lie symmetries, i.e., its dynamic symmetry. All these proofs are based on the investigations of the less complicated Lotka Volterra model and those are extended to Goodwin model, since both models are one-to-one maps of each other. The main achievement of this paper is the following: Noether's theorem is also playing a crucial role in the mechanics of Goodwin model. It also means, that its cyclical moving is optimal. Generalizing this result, we can assert, that all dynamic systems' solutions described by first order nonlinear ODE system are optimal by the least action principle, if they have a Lagrangian.

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The phase diagram of the simplest approximation to double-exchange systems, the bosonic double-exchange model with antiferromagnetic (AFM) superexchange coupling, is fully worked out by means of Monte Carlo simulations, large-N expansions, and variational mean-field calculations. We find a rich phase diagram, with no first-order phase transitions. The most surprising finding is the existence of a segmentlike ordered phase at low temperature for intermediate AFM coupling which cannot be detected in neutron-scattering experiments. This is signaled by a maximum (a cusp) in the specific heat. Below the phase transition, only short-range ordering would be found in neutron scattering. Researchers looking for a quantum critical point in manganites should be wary of this possibility. Finite-size scaling estimates of critical exponents are presented, although large scaling corrections are present in the reachable lattice sizes.

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Considering the disorder caused in manganites by the substitution Mn→Fe or Ga, we accomplish a systematic study of doped manganites begun in previous papers. To this end, a disordered model is formulated and solved using the variational mean-field technique. The subtle interplay between double exchange, superexchange, and disorder causes similar effects on the dependence of T_(C) on the percentage of Mn substitution in the cases considered. Yet, in La_(2/3)Ca_(1/3)Mn_(1-y)Ga_(y)O_(3) our results suggest a quantum critical point (QCP) for y ≈ 0.1–0.2, associated to the localization of the electronic states of the conduction band. In the case of La_(x)Ca_(x)Mn_(1-y)Fe_(y)O_(3) (with x = 1/3,3/8) no such QCP is expected.

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Bayesian methods offer a flexible and convenient probabilistic learning framework to extract interpretable knowledge from complex and structured data. Such methods can characterize dependencies among multiple levels of hidden variables and share statistical strength across heterogeneous sources. In the first part of this dissertation, we develop two dependent variational inference methods for full posterior approximation in non-conjugate Bayesian models through hierarchical mixture- and copula-based variational proposals, respectively. The proposed methods move beyond the widely used factorized approximation to the posterior and provide generic applicability to a broad class of probabilistic models with minimal model-specific derivations. In the second part of this dissertation, we design probabilistic graphical models to accommodate multimodal data, describe dynamical behaviors and account for task heterogeneity. In particular, the sparse latent factor model is able to reveal common low-dimensional structures from high-dimensional data. We demonstrate the effectiveness of the proposed statistical learning methods on both synthetic and real-world data.

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For decades scientists have attempted to use ideas of classical mechanics to choose basis functions for calculating spectra. The hope is that a classically-motivated basis set will be small because it covers only the dynamically important part of phase space. One popular idea is to use phase space localized (PSL) basis functions. This thesis improves on previous efforts to use PSL functions and examines the usefulness of these improvements. Because the overlap matrix, in the matrix eigenvalue problem obtained by using PSL functions with the variational method, is not an identity, it is costly to use iterative methods to solve the matrix eigenvalue problem. We show that it is possible to circumvent the orthogonality (overlap) problem and use iterative eigensolvers. We also present an altered method of calculating the matrix elements that improves the performance of the PSL basis functions, and also a new method which more efficiently chooses which PSL functions to include. These improvements are applied to a variety of single well molecules. We conclude that for single minimum molecules, the PSL functions are inferior to other basis functions. However, the ideas developed here can be applied to other types of basis functions, and PSL functions may be useful for multi-well systems.

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Thesis (Ph.D.)--University of Washington, 2016-08

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We consider a parametric semilinear Dirichlet problem driven by the Laplacian plus an indefinite unbounded potential and with a reaction of superdifissive type. Using variational and truncation techniques, we show that there exists a critical parameter value λ_{∗}>0 such that for all λ> λ_{∗} the problem has least two positive solutions, for λ= λ_{∗} the problem has at least one positive solutions, and no positive solutions exist when λ∈(0,λ_{∗}). Also, we show that for λ≥ λ_{∗} the problem has a smallest positive solution.

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We consider a (p, q)− equation (1 < q < p, p ≥ 2) with a parametric concave term and a (p − 1)− linear perturbation. We show that the problem have five nontrivial smooth solutions: four of constant sign and the fifth nodal. When q = 2 (i.e., (p, 2) equation) we show that the problem has six nontrivial smooth solutions, but we do not specify the sign of the sixth solution. Our approach uses variational methods, together with truncation and comparison techniques and Morse theory.

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Thesis (Ph.D.)--University of Washington, 2016-08

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We present a new discretization for the Hadamard fractional derivative, that simplifies the computations. We then apply the method to solve a fractional differential equation and a fractional variational problem with dependence on the Hadamard fractional derivative.

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The aim of this double blind randomized clinical trial was to compare the short-term and long-term outcomes of stapled haemorrhoidopexy (SH group) performed using a circular stapler with that of the Milligan-Morgan haemorrhoidectomy (MMH group). A total of 79 consecutive patients with grade III haemorrhoids were randomized into two groups treated with SH (n. 39) and MMH (n. 40). The outcomes of the procedures were evaluated postoperatively and over a follow-up period of minimum 2 years. Patients undergoing the SH procedure showed greater short term advantages than MMH group with reduced pain, shorter length of hospital stay, earlier return to work and high patient satisfaction. Long-term follow-up has indicated more favourable results in MMH group in terms of resumption of symptoms with absence of residual prolapse and risk of recurrence of prolapse. At two years follow-up recurrent prolapse was confirmed in six patients of SH group (13%) whereas in none of the MMH group. At six months follow-up there weren’t significant difference in the mean satisfaction score for the two groups. At two years the mean satisfaction score was higher in the MMH group vs SH group. Seven patients in the SH group needed a reoperation whereas none in MMH group. From January 2009, in our Surgery Unit the patients are always informed about a higher recurrence rate of SH and we perform this technique only when the patient choices to accept this risk to take advantage of the short-term benefits of this procedure.

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Colonic lipomas larger than 2 cm in diameter are likely to be symptomatic. In some cases a complication is the first clinical sign. Massive lower intestinal bleeding or obstruction, acute bleeding, prolapse or perforation or, rarely, acute intussusception with intestinal obstruction require urgent surgery. Diagnosis is often made following colonoscopy, which can also have a therapeutic role. Imaging procedures such as CT has a secondary role. Patients with small asymptomatic colonic lipomas need regular follow up. For larger (diameter > 2 cm) and/or symptomatic lipomas, resection should be considered, although the choice between endoscopic or surgical resection remains controversial. We believe that even lipomas > 2 cm can safely be removed by endoscopic resection. If surgery is indicated, we consider laparoscopy to be the ideal approach in all patients for whom minimally invasive surgery is not contraindicated.

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Al analizar los resultados deficientes de las Pruebas Saber, del PTA ( Programa Todos a Aprender del MEN), y la participación en las Olimpiadas del Conocimiento, de los estudiantes de la Institución Educativa Rural Benigno Mena González del municipio de San Jerónimo, se consideró implementar un proyecto pedagógico, como plan de mejoramiento para la enseñanza y aprendizaje de las matemáticas, que sirviera como una iniciativa para fortalecer los pensamientos numérico y variacional en los estudiantes de secundaria de la Institución; se buscaba, con la implementación de esta propuesta, desarrollar habilidades en dominio, comprensión y solución de situaciones problemas cotidianas dentro del contexto escolar y desde la innovación de nuevas prácticas metodológicas en los procesos educativos. Desde esta perspectiva, nace el interrogante: ¿Cómo modelar una situación problema, teniendo como motivo la unidad facilitadora solidaria denominada Belisol, para fortalecer el pensamiento numérico y variacional, en los estudiantes de la Institución Educativa Rural Benigno Mena González del municipio de San Jerónimo?, para dar tránsito a una propuesta de investigación innovadora. Ahora bien, para intervenir y reflexionar sobre este interrogante, se propuso el método de Investigación Acción Participación (IAP), el cual se aplica a estudios que se interesan sobre realidades humanas y problemáticas cotidianas o sociales, que además, sean reales, de la acción, y de constante participación de los sujetos, entidades o comunidades involucradas; aquí cabe la posibilidad de un aprendizaje cooperativo, colectivo, y por supuesto, colaborativo donde se ha planteado como motivo de la situación problema planteada la unidad financiera llamada Belisol con el fin de exteriorizar los fundamentos de una acción formativa, orientada a la incursión en el ámbito de la educación matemática económica financiera, a través del ejercicio del ahorro escolar y el trueque, promoviendo de esta manera el espíritu solidario en la comunidad Benigniana.