Symmetrically normalized instrumental-variable estimation using panel data

In this paper we discuss the estimation of panel data models with sequential moment restrictions using symmetrically normalized GMM estimators. These estimators are asymptotically equivalent to standard GMM but are invariant to normalization and tend to have a smaller finite sample bias. They also have a very different behaviour compared to standard GMM when the instruments are poor. We study the properties of SN-GMM estimators in relation to GMM, minimum distance and pseudo maximum likelihood estimators for various versions of the AR(1) model with individual effects by mean of simulations. The emphasis is not in assessing the value of enforcing particular restrictions in the model; rather, we wish to evaluate the effects in small samples of using alternative estimating criteria that produce asymptotically equivalent estimators for fixed T and large N. Finally, as an empírical illustration, we estimate by SN-GMM employment and wage equations using panels of UK and Spanish firms

Los efectos del consumo de alcohol, tabaco y cannabis en las patologías ocualres

El consumo de alcohol, tabaco y cannabis está ampliamente extendido en la sociedad hoy en día , y son múltiples las consecuencias que esto supone en la salud de los ciudadanos. Son muchos los estudios que evidencian el efecto negativo que producen estas drogas en el cerebro, sistema nervioso, sistema circulatorio y sistema digestivo; pero la relación de su consumo con las principales enfermedades ocula res no está del todo clara y faltan evidencias científicas contundentes. En este trabajo se revisa la bibliografía más actual para analizar de qué manera afecta el consumo de estas sustancias en la aparición y desarrollo de las cataratas, la degeneración macular asociada a la edad, la retinopatía diabética y el glaucoma. Por otro lado, se expone el papel actual de los antioxidantes en la prevención y protección de estas patologías, ya qu e contribuyen a compensar el efecto que las drogas producen mediante el estrés oxidativo (principal mecanismo que produce daño celular en estas enfermedades)Universidad de Sevilla. Grado en Óptica y Optometrí

Symmetrically normalized instrumental-variable estimation using panel data.

In this paper we discuss the estimation of panel data models with sequential moment restrictions using symmetrically normalized GMM estimators. These estimators are asymptotically equivalent to standard GMM but are invariant to normalization and tend to have a smaller finite sample bias. They also have a very different behaviour compared to standard GMM when the instruments are poor. We study the properties of SN-GMM estimators in relation to GMM, minimum distance and pseudo maximum likelihood estimators for various versions of the AR(1) model with individual effects by mean of simulations. The emphasis is not in assessing the value of enforcing particular restrictions in the model; rather, we wish to evaluate the effects in small samples of using alternative estimating criteria that produce asymptotically equivalent estimators for fixed T and large N. Finally, as an empírical illustration, we estimate by SN-GMM employment and wage equations using panels of UK and Spanish firms.Panel data; Instrumental variables; Symmetric normalization; Autoregressive models; Employment equations;

On the Whitham Hierarchies: Reductions and Hodograph Solutions

A general scheme for analyzing reductions of Whitham hierarchies is presented. It is based on a method for determining the $S$-function by means of a system of first order partial differential equations. Compatibility systems of differential equations characterizing both reductions and hodograph solutions of Whitham hierarchies are obtained. The method is illustrated by exhibiting solutions of integrable models such as the dispersionless Toda equation (heavenly equation) and the generalized Benney system.Comment: 24 page

Generating Quadrilateral and Circular Lattices in KP Theory

The bilinear equations of the $N$-component KP and BKP hierarchies and a corresponding extended Miwa transformation allow us to generate quadrilateral and circular lattices from conjugate and orthogonal nets, respectively. The main geometrical objects are expressed in terms of Baker functions.Comment: 20 pages, 1 figure, LaTeX2e with AMSLaTeX, Babel, graphicx and psfrag package

Implementation of Special Singular Finite Elements for Cracks along Adhesive Interfaces in Mode III

El MEF puede aplicarse a la Mecánica de la Fractura para simular tensiones en el entorno del borde de grieta; así se puede calcular el Factor de Intensificación de Tensiones. Los elementos lineales aportan tensiones constantes en su interior, por lo cual no son apropiados para captar la tendencia al infinito, requiriéndose mallas densas. Para reducir el coste computacional, se diseñan Elementos Singulares, cuyas funciones de forma y/o disposición de los nodos permite captar mejor las tensiones en torno al borde de grieta con menor número de elementos. Aun así, un comportamiento correcto de cualquier elemento singular es muy dependiente del mallado de la pieza: forma, disposición y tamaño de los elementos alrededor de la región mallada con elementos singulares, y el tamaño relativo entre elementos y grieta entre otros. El objetivo de este trabajo es desarrollar un breve manual de uso de un nuevo Elemento Singular con singularidad logarítmica adaptado para interfases adhesivas en modo III. Como objetivo secundario, el proceso de pruebas se generaliza para extrapolarse fácilmente. Finalmente, los códigos y macros generados se adjuntan para que el proceso se aplique fácilmente a nuevos Elementos Singulares.FEM can be applied to Fracture Mechanics to simulate stresses in the neighborhood of a crack tip; thus, the Stress Intensity Factor can be estimated. Linear Elements bear constant tensions inside, so they are not suitable for capturing the tendency to infinity, hence requiring dense meshes. To reduce computation time, Singular Elements are designed, whose basis functions and/or nodal placing allow to better fit stresses around the crack tip with a lesser number of elements. However, the correct behavior of any Singular Element is heavily dependent on the part meshing: shape, placing and size of the elements surrounding the singular-element-meshed region near the crack and the relative size between elements and crack among others. The purpose of this work is to develop a series of guidelines on the use of a newly programmed Singular Element with a logarithmic singularity adapted to adhesive interfaces in mode III. As a secondary purpose, the testing process is generalized so that it can be easily extrapolated. Finally, generated codes and macros are appended so that the process can be easily applied to another element.Universidad de Sevilla. Grado Ingeniería Aerospacia

Crony capitalism and neoliberal paradigm (Part II)

This is the second and final part of Crony Capitalism and Neoliberal Paradigm, the first part was posted earlier on this very blog

European Union’s key figures

With the objective to draw some conclusions about macroeconomic stability and economic structure, this article examines for the 28 Member States of the European Union, the following aspects: GDP and AIC per capita, General Government Gross Debt, Labour Productivity (monetary units and percentages), Average Annual Wages, Annual Hours Worked, Jobless and Average Hourly labour Costs. To develop this analysis, Member States have been divided into three blocks by the number of inhabitants: less than 6 million, between 6 and 17 million and more than 17 million