A multivariate generalized independent factor GARCH model with an application to financial stock returns

We propose a new multivariate factor GARCH model, the GICA-GARCH model , where the data are assumed to be generated by a set of independent components (ICs). This model applies independent component analysis (ICA) to search the conditionally heteroskedastic latent factors. We will use two ICA approaches to estimate the ICs. The first one estimates the components maximizing their non-gaussianity, and the second one exploits the temporal structure of the data. After estimating the ICs, we fit an univariate GARCH model to the volatility of each IC. Thus, the GICA-GARCH reduces the complexity to estimate a multivariate GARCH model by transforming it into a small number of univariate volatility models. We report some simulation experiments to show the ability of ICA to discover leading factors in a multivariate vector of financial data. An empirical application to the Madrid stock market will be presented, where we compare the forecasting accuracy of the GICA-GARCH model versus the orthogonal GARCH one

El "Think Different" de las clases magistrales

This article analyzes the most recent literature concerning to the public interventions of the former CEO of Apple, Steve Jobs –in which there come apart the key point for the success of his presentations– and it raises how these might be applies the current teaching. Compartmented in ten practical advices, we will verify how those which seem to be the most outstanding aspects of the keynotes of the company from Cupertino rely on basic postulates of experts in education and Psicology. Reviewing them in a reflexive manner must serve teachers to ponder to what extent it is possible or not to implement them in our master classes and to what extent they serve to improve the teaching and learning process.El presente artículo analiza la bibliografía más reciente en torno a las intervenciones públicas del ex CEO de Apple, Steve Jobs, en la que se desgranan las claves del éxito de sus presentaciones y plantea cómo podrían aplicarse actualmente al ámbito de la docencia. Presentados en forma de diez consejos prácticos, comprobaremos cómo los aspectos más destacables de las keynotes de la compañía de la manzana se apoyan en postulados básicos de expertos en educación y sicología. Repasarlos de forma reflexiva ha de servirnos a los docentes para meditar hasta qué punto es posible aplicarlas en nuestras clases magistrales y en qué medida sirven para mejorar el proceso de enseñanza y aprendizaje

Satisfacción laboral en el sector hotelero de Mallorca

El presente trabajo aborda la satisfacción de los empleados en una muestra de hoteles de Mallorca, dada la importancia que el sector turístico tiene en la economía Mallorquina y en la nacional y las características específicas que presenta el mercado laboral en este sector. En el mismo son frecuentes los contratos temporales, los turnos de trabajo partidos, así como, un deficiente ajuste de los puestos a la capacitación de los empleados, presentándose sobrecualificación o escasez de preparación para el correcto desempeño. Se aborda el estudio desde una perspectiva situacionalista de la satisfacción laboral, aplicando el cuestionario de satisfacción de Chiang y Nuñez (2007) y Chiang et al. (2008) a una muestra de 81 trabajadores en hoteles de Mallorca, que funcionan tanto estacionalmente como permanentemente. Los resultados muestran que no existen diferencias en las dimensiones estudiadas, a excepción de la variable edad: a menor edad, mayor satisfacción laboral y la variable sexo: los hombres están más satisfechos laboralmente y más satisfechos en la dimensión ambiente físico que las mujeres. Se plantea que en futuras lineas de investigación se estudie en base al nicho de mercado de cada hotel y teniendo en cuenta la categoría por estrellas del hotel.The purpose of this work is to study the employees' satisfaction in a sample of hotels in Mallorca, due to the importance that the tourism sector has in the mallorcan and nacional economy and the specific characteristics of the labor market in this sector, such as temporary contracts, split work shifts or a frequent poor adjustment between the worker and the job, indicating overqualification or lack of preparation for the proper performance. The study is approached from a situational perspective of job satisfaction, applying the satisfaction questionnaire of Chiang and Nuñez (2007) and Chiang et al. (2008) to a total of 81 employees of different types of hotels in Mallorca, from hotels open all year round and hotels open seasonally. The results show that there are no differences in the dimensions studied, with the exception of the variable age: the younger, the more satisfied at work and variable sex: men are more satisfied at work and in the physical environment. It is proposed that future research projects study based on the market niche of the hotels and on the star category of hotels.El present treball aborda la satisfacció dels empleats en una mostra d'hotels de Mallorca, donada la importància que el sector turístic té en l'economia Mallorquina i en la nacional i les característiques específiques que presenta el mercat laboral en aquest sector. En el mateix so freqüents els contractes temporals, els torns de treball partits, així com, un deficient ajust dels llocs a la capacitació dels empleats, presentant-se sobrequalificació o escassetat de preparació per al correcte acompliment. S'aborda l'estudi des d'una perspectiva situacionalista de la satisfacció laboral, aplicant el qüestionari de satisfacció de Chiang i Nuñez (2007) i Chiang et al. (2008) a una mostra de 81 treballadors en hotels de Mallorca, que funcionen tant estacionalment com permanentment. Els resultats mostren que no existeixen diferències en les dimensions estudiades, a excepció de la variable edat: a menor edat, major satisfacció laboral i la variable sexe: els homes estan més satisfets laboralment i més satisfets en la dimensió ambienti físic que les dones. Es planteja que en futures línies de recerca s'estudiï sobre la base del nínxol de mercat de cada hotel i tenint en compte la categoria per estrelles de l'hotel

A continuum mechanics framework for hyperelastic materials: connecting experiments and modelling

Mención Internacional en el título de doctorLa investigación llevada a cabo en esta Tesis Doctoral proporciona nuevas ideas y metodologías para el desarrollo de modelos constitutivos con base hiperelástica, con fundamentación física y basados en evidencias experimentales. Estos modelos han sido aplicados al estudio del comportamiento termomecánico de polímeros termoplásticos y tejidos blandos en un amplio intervalo de condiciones de trabajo. La simulación de este tipo de sólidos debe considerar grandes desplazamientos, rotaciones y deformaciones, efectos inerciales, cambios de condiciones de contorno durante el proceso de deformación, generación de calor por deformación plástica, y requieren de leyes de comportamiento de material complejas. Con objeto de proporcionar un marco general del continuo para la formulación de modelos constitutivos, se han desarrollado las siguientes actividades: (i) Se ha realizado un análisis experimental y numérico del comportamiento mecánico de materiales hiperelásticos. Este estudio proporciona nuevas observaciones sobre los mecanismos que gobiernan el proceso de deformación de este tipo de sólidos. (ii) Se ha desarrollado un nuevo modelo constitutivo para predecir el comportamiento de polímeros semicristalinos. La formulación de este modelo se basa en evidencias físicas observadas durante el análisis del comportamiento mecánico de polímeros termoplásticos, conectando de esta manera técnicas experimentales con la modelización constitutiva. El modelo ha sido formulado en hipótesis de grandes deformaciones dentro de un marco termodinámicamente consistente que considera: la dependencia del comportamiento mecánico con la presión y la deformación plástica volumétrica; el endurecimiento del material asociado a la sensibilidad con la velocidad de deformación; la generación de calor en el proceso de deformación inducida por disipación plástica y la evolución de la temperatura debida al flujo térmico; el ablandamiento térmico y la expansión térmica del material. Los parámetros del modelo han sido identificados para el polímero poliéter-étercetona (PEEK) y la capacidad predictiva del modelo ha sido verificada para un amplio intervalo de condiciones de carga. (iii) El marco constitutivo del modelo propuesto para polímeros semicristalinos ha sido generalizado para la formulación de modelos transversalmente isótropos con base hiperelástica. Este marco general considera: viscoelasticidad; viscoplasticidad; hiperelasticidad; expansión térmica y anisotropía debida a la orientación de las fibras. El marco general del continuo ha sido particularizado dando lugar a modelos constitutivos para dos materiales específicos: materiales compuestos de matriz termoplástica PEEK reforzados con fibra corta de carbono; y la materia blanca del cerebro. (iv) Finalmente, los modelos constitutivos y las herramientas numéricas desarrolladas en esta tesis doctoral han sido implementados en un código comercial de elementos finitos y se han aplicado al estudio de un problema real: el análisis del comportamiento mecánico de implantes craneales fabricados con polímeros termoplásticos que están expuestos a cargas de impacto. Para este propósito, se ha desarrollado un modelo de cabeza humana en elementos finitos a partir de resonancias magnéticas que incluye tejido dérmico, cráneo, líquido cefalorraquídeo y el tejido cerebral, incluyendo un implante craneal termoplástico que sustituye parte del cráneo.The research carried out in this Doctoral Thesis provides new ideas and methodologies on the development of hyperelastic-based constitutive models and may motivate future contributions within this line of investigation. To achieve the main objective of providing a general continuum mechanics framework, the methodology has been divided into the following specific activities: (i) With the aim of supporting the modelling assumptions of the framework, an experimental and numerical analysis of the mechanical behaviour of hyperelastic materials has been conducted. This study provides new insights into the mechanisms that govern the deformation process. (ii) A new constitutive model for semi-crystalline thermoplastic polymers has been developed. The formulation of this model is based on physical evidence from the analysis of the mechanical behaviour of thermoplastic polymers, thereby connecting experiments with modelling. In this sense, the model accounts for strain rate and temperature dependencies, and pressure sensitivity within a thermodynamically consistent framework formulated in finite deformations. The model parameters have been identified for polyether-ether-ketone (PEEK) and the model has been validated for a wide range of loading conditions. (iii) The constitutive framework of the model proposed for semi-crystalline polymers has been generalized for transversely isotropic hyperelastic-based models. This general framework allows for the formulation of constitutive models taking into account: viscoelasticity, viscoplasticity, hyperelasticity, thermal expansion and anisotropy induced by fibre orientation. The general continuum framework has been particularized, providing constitutive models for two materials: short carbon fibre reinforced PEEK composites; and white matter of brain. (iv) Finally, the constitutive and numerical tools developed in this thesis have been implemented in finite element commercial codes and applied to study a real problem, the analysis of the mechanical behaviour of thermoplastic cranial implants subjected to impact loading. For this purpose, a finite element head model comprising scalp, skull, cerebral falx, cerebrospinal fluid and brain tissue, with a cranial implant replacing part of the skull, has been developed from magnetic resonance imaging data.The author of the Doctoral Thesis is indebted to the Ministerio de Ciencia e Innovación de España (ProjectDPI/2011-24068) and to the Ministerio de Economía y Competitividad de España (ProjectDPI/2014-57989-P) for financial support towards part of this work.Programa Oficial de Doctorado en Ingeniería Mecánica y de Organización IndustrialPresidente: José Fernández Sáez.- Secretario: Miguel Ángel Martínez Barca.- Vocal: Isaías Sidney Chocron Benloulo

A multivariate generalized independent factor GARCH model with an application to financial stock returns

We propose a new multivariate factor GARCH model, the GICA-GARCH model , where the data are assumed to be generated by a set of independent components (ICs). This model applies independent component analysis (ICA) to search the conditionally heteroskedastic latent factors. We will use two ICA approaches to estimate the ICs. The first one estimates the components maximizing their non-gaussianity, and the second one exploits the temporal structure of the data. After estimating the ICs, we fit an univariate GARCH model to the volatility of each IC. Thus, the GICA-GARCH reduces the complexity to estimate a multivariate GARCH model by transforming it into a small number of univariate volatility models. We report some simulation experiments to show the ability of ICA to discover leading factors in a multivariate vector of financial data. An empirical application to the Madrid stock market will be presented, where we compare the forecasting accuracy of the GICA-GARCH model versus the orthogonal GARCH one.ICA, Multivariate GARCH, Factor models, Forecasting volatility

Exploring ICA for time series decomposition

In this paper, we apply independent component analysis (ICA) for prediction and signal extraction in multivariate time series data. We compare the performance of three different ICA procedures, JADE, SOBI, and FOTBI that estimate the components exploiting either the non-Gaussianity, or the temporal structure of the data, or combining both, non-Gaussianity as well as temporal dependence. Some Monte Carlo simulation experiments are carried out to investigate the performance of these algorithms in order to extract components such as trend, cycle, and seasonal components. Moreover, we empirically test the performance of those three ICA procedures on capturing the dynamic relationships among the industrial production index (IPI) time series of four European countries. We also compare the accuracy of the IPI time series forecasts using a few JADE, SOBI, and FOTBI components, at different time horizons. According to the results, FOTBI seems to be a good starting point for automatic time series signal extraction procedures, and it also provides quite accurate forecasts for the IPIs.ICA, Signal extraction, Multivariate time series, Forecasting

Multiple Order Dual-Band Active Ring Filters with Composite Right/Left Handed Cells

In this paper, a novel dual-band active filter topology is presented. The non-linear phase response of a composite right/left-handed cell is used to achieve the desired dual-band performance. Additionally, the proposed structure based on coupled ring resonators yields a very compact solution in which high-order implementations can be easily obtained by cascading multiple rings. The theoretical principles of this type of filters are analyzed in detail. Finally, three prototypes based on first-, second- and third-order structures validate the feasibility of this type of filters. Good agreement between simulations and measurements has been achieved

Noise Figure Measurement of Differential Amplifiers Using non-Ideal Baluns

This paper analyzes the noise and gain measurement of microwave differential amplifiers using two passive baluns. A general model of the baluns is considered, including potential losses and phase/amplitude unbalances. This analysis allows de-embedding the actual gain and noise performance of the isolated amplifier by using single-ended measurements of the cascaded system and baluns. Finally, measured results from two amplifier prototypes are used to validate the theoretical principles

Levaduras vínicas recombinantes

Levaduras vínicas recombinantes. Método de obtención de cepas que secretan una mayor concentración de manoproteínas al medio, cepa de la levadura Saccharomyces cerevisiae depositada en la Colección Española de Cultivos Tipo (CECT), con el número CECT 13012, y usos de dichas cepas.Peer reviewedConsejo Superior de Investigaciones Científicas (España)B1 Patente con informe sobre el estado de la ténic

Microstructural modelling of hard-magnetic soft materials: Dipole-dipole interactions versus Zeeman effect

Hard-magnetic soft materials are a class of magneto-active polymers (MAPs) where the fillers are composed of hard-magnetic (magnetised) particles. These materials present complex magneto-mechanical couplings, which require the development of modelling frameworks in understanding their responses at the very beginning of conceptualisation and design. Most of the current constitutive approaches available in the literature for hard-magnetic MAPs do not consider dipole–dipole interactions of the embedded particles. However, such interactions among the magnetised particles generate internal forces within the composite that need to be balanced by mechanical stress from the polymeric matrix networks. This fact may imply an initial stretch of the polymeric network and suggests that such dipole–dipole interactions may be important during the MAP deformation process. To address these crucial points, in this contribution, we propose a novel constitutive model relating microstructural characteristics of hard-magnetic MAPs. The model accounts for polymeric network pre-stretch, dipole–dipole interactions, Zeeman effect as well as viscous mechanisms which are formulated on the finite deformation theory. The results obtained herein highlight the importance of accounting for the dipole–dipole interactions and the polymeric network pre-stretch to understand the complex magneto-mechanically coupled behaviour of hard-magnetic MAPs.The authors acknowledge support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 947723, project 4D-BIOMAP). D.G.G. acknowledges support from the Talent Attraction, Spain grant (CM 2018-2018-T2/IND-9992) from the Comunidad de Madrid, Spain. M. H. acknowledges the funding through an EPSRC, United Kingdom Impact Acceleration Award (EP/R511614/1)