Robust Henderson III estimators of variance components in the nested error model

Common methods for estimating variance components in Linear Mixed Models include Maximum Likelihood (ML) and Restricted Maximum Likelihood (REML). These methods are based on the strong assumption of multivariate normal distribution and it is well know that they are very sensitive to outlying observations with respect to any of the random components. Several robust altematives of these methods have been proposed (e.g. Fellner 1986, Richardson and Welsh 1995). In this work we present several robust alternatives based on the Henderson method III which do not rely on the normality assumption and provide explicit solutions for the variance components estimators. These estimators can later be used to derive robust estimators of regression coefficients. Finally, we describe an application of this procedure to small area estimation, in which the main target is the estimation of the means of areas or domains when the within-area sample sizes are small.Henderson method III, Linear mixed model, Robust estimators, Variance component estimators

Dona i Legislació a la Catalunya del segle XVIII. Processos de separació matrimonial

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Sistemas financieros y financiación de las PYMES en España y Europa

Tras la excesiva dependencia del crédito bancario vivida históricamente en Europa los sistemas financieros evolucionan hacia una orientación de mercado y un mayor equilibrio entre la financiación bancaria y no bancaria, todo ello impulsado por la puesta en marcha de mercados alternativos de renta variable y de renta fija de mayor accesibilidad para empresas de menor tamaño. Además, distintas fuentes de financiación tradicionales vuelven a retomar impulso tras la crisis financiera de 2008, al tiempo que otros métodos alternativos de financiación se posicionan como necesarios para la obtención de recursos por parte de pequeños negocios.Following the over-reliance on bank credit historically experienced in Europe, financial systems have evolved towards market orientation and a better balance between bank and non-bank financing, all driven by the launch of alternative equity and fixed income markets of greater accessibility for smaller companies. In addition, a number of traditional sources of funding are regaining momentum following the financial crisis of 2008, while other alternative financing methods are positioned as necessary to obtain resources from small businesses.Universidad de Sevilla. Grado en Administración y Dirección de Empresa

Exploring a multilevel approach with spatial effects to model housing price in San José, Costa Rica

A multilevel model of the housing market for San Jose Metropolitan Region (Costa Rica) was developed, including spatial effects. Hierarchical relations (lower level units nested into higher level) were modeled by specifying multilevel models with random intercepts and a conditional autoregressive (CAR) term to include spatial effects from neighboring units at the higher level (districts). The random intercepts and conditional autoregressive models presented the best fit to the data. Variation at the higher level accounted for 16% of variance in the random intercepts model and 28% in the CAR model. The sign and magnitude of regression coefficients proved remarkably stable across model specifications. Multilevel and CAR models represented an important improvement in modeling housing price, despite most of the variation still occurring at the lower level, by improving the overall model fit and expanding the interpretation of model results. However, the CAR specification only represented a limited advance over the random intercepts formulation.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ingeniería::Programa de Investigación en Desarrollo Urbano Sostenible (ProDUS

Steady-state, self-oscillating and chaotic behavior of a PID controlled nonlinear servomechanism by using Bogdanov-Takens and Andronov-Poincaré-Hopf bifurcations

This paper analyzes a controlled servomechanism with feedback and a cubic nonlinearity by means of the Bogdanov-Takens and Andronov-Poincaré-Hopf bifurcations, from which steady-state, self-oscillating and chaotic behaviors will be investigated using the center manifold theorem. The system controller is formed by a Proportional plus Integral plus Derivative action (PID) that allows to stabilize and drive to a prescribed set point a body connected to the shaft of a DC motor. The Bogdanov-Takens bifurcation is analyzed through the second Lyapunov stability method and the harmonic-balance method, whereas the first Lyapunov value is used for the Andronov-Poincaré-Hopf bifurcation. On the basis of the results deduced from the bifurcation analysis, we show a procedure to select the parameters of the PID controller so that an arbitrary steady-state position of the servomechanism can be reached even in presence of noise. We also show how chaotic behavior can be obtained by applying a harmonical external torque to the device in self-oscillating regime. The advantage of achieving chaotic behavior is that it can be used so that the system reaches a set point inside a strange attractor with a small control effort. The analytical calculations have been verified through detailed numerical simulations

Increasing the reactant conversion through induced oscillations in a continuous stirred tank reactor by using PI control

We report a strategy to increase the reactant conversion in a continuous stirred tank reactor (CSTR) to produce propylene glycol through induced oscillations generated by two controllers PI1 and PI2 that manipulate the reactor outlet flow and the coolant flow rate respectively. It is shown that an adequate parameter choice for the PI controllers allows one to derive sustained oscillations in the concentrations and reactor temperature, which in turn allows increasing the propylene glycol production. For a suitable choice of the PI1 and PI2 controller parameters, we use a complete reactor model that provides with physically feasible parameters. The issues of external disturbance rejection, self-oscillations and stability have also been discussed. The analytical calculations are verified by means of full numerical simulations

Steady-state self-oscillations and chaotic behavior of a controlled electromechanical device by using the first Lyapunov value and the Melnikov theory

In this paper regular and chaotic oscillations in a controlled electromechanical transducer are investigated. The nonlinear control laws are defined by an electric tension excitation and an external force applied to the mobile piece of the transducer. The paper shows that an Andronov–Poincaré–Hopf bifurcation appears as long as adequate parameters are chosen for the nonlinear control laws. The stability of the weak focuses associated to such bifurcation is examined according to the sign of the first Lyapunov value, showing that chaotic behavior can arise when the first Lyapunov value is varied harmonically. The appearance of a homoclinic orbit is investigated assuming an approximated model for the device. On the basis of the parametric equations of the homoclinic orbit and the presence of harmonic disturbances on the platform, it is demonstrated that chaotic oscillations can also appear, and they have been examined by means of the Melnikov theory. Chaotic behavior is corroborated by means of the sensitive dependence, Lyapunov exponents and power spectral density, and it is applied to drive the transducer mobile piece to a predefined set point assuming that noise due to the measurement process can appear in the control signals. The steady-state error associated to such random noise is eliminated by adding a PI linear controller to the control force. Numerical simulations are used to corroborate the analytical results.This work was supported by the “Generalitat Valenciana” (Spain) under Project GV/2012/099 and by “Ministerio de Ciencia e Innovación” (Spain) under Project FIS2011-29803-C02-01

Donar cos a les dones : les Experiències de les dones (segles XVI al XVIII)

La autora desarrolla los rasgos historiográficos más sobresalientes en la evolución de la historia de las mujeres, poniendo especial énfasis en el desarrollo de los estudios dedicados a la Epoca Moderna.The author unfolds the most relevant historiographic features in the evolution of women's history, emphasizing the development of studies devoted to the Modern Age