974 resultados para Wiener-Hopf factorization


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La presente disertación tiene el objetivo de analizar por qué el conflicto entre India y Pakistán por Cachemira no ha sido solucionado a la luz del debate entre el realismo ofensivo y el constructivismo social surgido en 1994. La hipótesis de trabajo establece que la estructura anárquica, sumada a las capacidades ofensivas, la desconfianza mutua, la racionalidad, y el deseo de supervivencia entre los Estados, ha propiciado la configuración de un dilema de seguridad que es alimentado por la disparidad de intereses e identidades en contienda. El alcance del objetivo es de carácter analítico y el enfoque primario está basado en la teoría del realismo ofensivo de John Mearsheimer y el constructivismo social de Alexander Wendt.

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La Revolución Naranja de 2004 puede ser considerada un punto de inflexión en el manejo de la política exterior del gobierno de Vladímir Putin. Pues, le demostró que para recuperar el prestigio ruso en el espacio que consideraba propio (postsoviético) se debía abandonar la tendencia de definir la política exterior en términos de hard power e incluir elementos del soft power. De ahí que, el propósito de esta monografía es analizar los factores que afectan la aplicación del soft power como un instrumento de la política exterior rusa enfocada al establecimiento de la hegemonía del Kremlin en Ucrania entre el período 2004 y 2013. Para ello, a partir de la propuesta constructivista de Theodore Hopf se identifican tres elementos interconectados: la figura de Vladímir Putin, la sociedad ucraniana, y, específicamente, la identidad compartida entre Rusia y la población conformada por rusos étnicos y personas afines con la cultura rusa.

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El objetivo de este documento es recopilar algunos resultados clasicos sobre existencia y unicidad ´ de soluciones de ecuaciones diferenciales estocasticas (EDEs) con condici ´ on final (en ingl ´ es´ Backward stochastic differential equations) con particular enfasis en el caso de coeficientes mon ´ otonos, y su cone- ´ xion con soluciones de viscosidad de sistemas de ecuaciones diferenciales parciales (EDPs) parab ´ olicas ´ y el´ıpticas semilineales de segundo orden.

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El canal lumbar estrecho de tipo degenerativo, es una enfermedad que se presenta en pacientes entre la quinta y la sexta década de vida; es la causa más común de cirugía lumbar después de los 65 años. Este trabajo busca determinar cuáles son los factores asociados a la presentación de eventos adversos o re-intervención en cirugía de canal lumbar estrecho en la Fundación Santa Fe de Bogotá en los años comprendidos entre 2003 y 2013. Métodos: se realizó un estudio de prevalencia de tipo analítico, en donde se analizaron 249 pacientes sometidos a intervención quirúrgica por cirugía de canal lumbar estrecho.

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La evolución del concepto de sistema promovió la consolidación de un enfoque que se comenzó a introducir en la revisión de diferentes objetos de estudio especialmente complejos, como los fenómenos sociales, gracias a sus características inter y trans disciplinarias. Este enfoque “sistémico” se promueve desde el campo de la biología y su metodología se incorporó al estudio de asuntos tan diversos como los temas ambientales, la ecología, la investigación en comunicaciones y muchos fenómenos sociales entre los que se encuentra el crecimiento de las ciudades. En el caso de los problemas urbanos, el enfoque sistémico surge como alternativa frente a la propuesta de la escuela funcionalista moderna. A partir de los años 60, las investigaciones urbanas comienzan a utilizar la visión sistémica como forma de aproximarse conceptualmente a lo físico urbano y avanzar en la comprensión de la complejidad de relaciones entre los componentes físicos de la estructura urbana, las racionalidades y acuerdos para el aprovechamiento del territorio natural de soporte, los bienes ambientales, los servicios públicos y los patrones de consumo, entre otros, una forma de metabolismo que permite asumir la ciudad como un ecosistema, soporte conceptual para la puesta en marcha de acciones que contribuyan a la sostenibilidad urbana. El seguimiento a esta visión sistémica y su incorporación como una herramienta de análisis e intervención urbana, sirve en primera instancia para llevar a cabo una reflexión crítica sobre la evolución del pensamiento urbano del siglo XX especialmente a partir de la segunda posguerra.

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For Wiener spaces conditional expectations and $L^{2}$-martingales w.r.t. the natural filtration have a natural representation in terms of chaos expansion. In this note an extension to larger classes of processes is discussed. In particular, it is pointed out that orthogonality of the chaos expansion is not required.

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The purpose of this paper is to show that, for a large class of band-dominated operators on $\ell^\infty(Z,U)$, with $U$ being a complex Banach space, the injectivity of all limit operators of $A$ already implies their invertibility and the uniform boundedness of their inverses. The latter property is known to be equivalent to the invertibility at infinity of $A$, which, on the other hand, is often equivalent to the Fredholmness of $A$. As a consequence, for operators $A$ in the Wiener algebra, we can characterize the essential spectrum of $A$ on $\ell^p(Z,U)$, regardless of $p\in[1,\infty]$, as the union of point spectra of its limit operators considered as acting on $\ell^p(Z,U)$.

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Crop irrigation has long been recognized as having been important for the evolution of social complexity in several parts of the world. Structural evidence for water management, as in the form of wells, ditches and dams, is often difficult to interpret and may be a poor indicator of past irrigation that may have had no need for such constructions. It would be of considerable value, therefore, to be able to infer past irrigation directly from archaeo-botanical remains, and especially the type of archaeo-botanical remains that are relatively abundant in the archaeological record, such as phytoliths. Building on the pioneering work of Rosen and Wiener (1994), this paper describes a crop-growing experiment designed to explore the impact of irrigation on the formation of phytoliths within cereals. If it can be shown that a systemic and consistent relationship exists between phytolith size, structure and the intensity of irrigation, and if various taphonomic and palaeoenvironmental processes can be controlled for, then the presence of past irrigation can feasibly be inferred from the phytoliths recovered from the archaeological record.

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The goal of the review is to provide a state-of-the-art survey on sampling and probe methods for the solution of inverse problems. Further, a configuration approach to some of the problems will be presented. We study the concepts and analytical results for several recent sampling and probe methods. We will give an introduction to the basic idea behind each method using a simple model problem and then provide some general formulation in terms of particular configurations to study the range of the arguments which are used to set up the method. This provides a novel way to present the algorithms and the analytic arguments for their investigation in a variety of different settings. In detail we investigate the probe method (Ikehata), linear sampling method (Colton-Kirsch) and the factorization method (Kirsch), singular sources Method (Potthast), no response test (Luke-Potthast), range test (Kusiak, Potthast and Sylvester) and the enclosure method (Ikehata) for the solution of inverse acoustic and electromagnetic scattering problems. The main ideas, approaches and convergence results of the methods are presented. For each method, we provide a historical survey about applications to different situations.

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The mobile component of a community inhabiting a submarine boulder scree/cliff was investigated at Lough Hyne, Ireland at dawn, midday, dusk and night over a 1-week period. Line transects (50 m) were placed in the infralittoral (6 m) and circumlittoral (18 m) zones and also the interface between these two zones (12 m). The dominant mobile fauna of this cliff consisted of echinoderms (6 species), crustaceans (10 species) and fish (23 species). A different component community was identified at each time/depth interval using Multi-Dimensional Scaling (MDS) even though both species diversity (Shannon-Wiener indices) and richness (number of species) remained constant. These changes in community composition provided indirect evidence for migration by these mobile organisms. However, little evidence was found for migration between different zones with the exception of the several wrasse species. These species were observed to spend the daytime foraging in the deeper zone, but returned to the upper zone at night presumably for protection from predators. For the majority of species, migration was considered to occur to cryptic habitats such as holes and crevices. The number of organisms declined during the night, although crustacean numbers peaked, while fish and echinoderms were most abundant during day, possibly due to predator-prey interactions. This submarine community is in a state of flux, whereby, community characteristics, including trophic and energetic relationships, varied over small temporal (daily) and spatial (m) scales.

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We model the large scale fading of wireless THz communications links deployed in a metropolitan area taking into account reception through direct line of sight, ground or wall reflection and diffraction. The movement of the receiver in the three dimensions is modelled by an autonomous dynamic linear system in state-space whereas the geometric relations involved in the attenuation and multi-path propagation of the electric field are described by a static non-linear mapping. A subspace algorithm in conjunction with polynomial regression is used to identify a Wiener model from time-domain measurements of the field intensity.

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This article has been written in memory of Norbert Wiener and is dedicated to him. Takes a look at how cybernetics provides an extremely useful framework for the control and operation of real-world systems. With the true advent of computers and simple communications, many more processes can and will be viewed from a systems standpoint. Examples are given of how cybernetics can be applied to industrial processes and how it is seen as an important, integral part of future systems science.

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In this paper a new nonlinear digital baseband predistorter design is introduced based on direct learning, together with a new Wiener system modeling approach for the high power amplifiers (HPA) based on the B-spline neural network. The contribution is twofold. Firstly, by assuming that the nonlinearity in the HPA is mainly dependent on the input signal amplitude the complex valued nonlinear static function is represented by two real valued B-spline neural networks, one for the amplitude distortion and another for the phase shift. The Gauss-Newton algorithm is applied for the parameter estimation, in which the De Boor recursion is employed to calculate both the B-spline curve and the first order derivatives. Secondly, we derive the predistorter algorithm calculating the inverse of the complex valued nonlinear static function according to B-spline neural network based Wiener models. The inverse of the amplitude and phase shift distortion are then computed and compensated using the identified phase shift model. Numerical examples have been employed to demonstrate the efficacy of the proposed approaches.