A dynamical metric and its ground state from the breaking down of the topological invariance of the Euler characteristic

Quantum state wave functionals are constructed in exact form for the graviton-like field theory obtained by breaking down the topological symmetry of the string action related with the Euler characteristic of the world-surface; their continuous and discrete symmetries are discussed. The comparison with the so-called Chern-Simons state, which may be inappropriate as quantum state, allows us to conclude that the found wave functionals will give a plausible approximation to the ground state for the considered field theory

25 anys de formació del professorat al CEP de Menorca

Enguany es compleixen 25 anys de la creació dels centres de formació permanent del professorat vinculats a la política educativa espanyola referent al perfeccionament del professorat dels centres sostinguts amb fons públics. Perfeccionament entès com a base de professionalitat docent i qualitat del sistema educatiu. Malgrat que el seu origen és forà (lifelong learning), formen part del pensament educatiu progressista espanyol (escoles d'estiu, MRP…), ja que coincideixen amb la necessitat de potenciar i activar les pròpies possibilitats i els recursos de cada zona, establir contactes entre els membres, exposar experiències desenvolupades en aquests contextos, etc. Aquest article, per tant, pretén explicar el desenvolupament d’aquests centres, en l’àmbit de les Illes Balears i més concretament de l’illa de Menorca, des dels inicis fins al moment actual

Tecnología, cognición y aprendizaje

En este trabajo se discuten algunos aspectos del uso de tecnologías computacionales en los procesos de adquisición del conocimiento en la escuela, específicamente de los sistemas de simulación, desde una pedagogía crítica y una perspectiva sociocultural. Se subraya la necesaria articulación entre la utilización de los recursos computacionales en el proceso educativo, las estrategias pedagógicas y los contextos socioculturales y se concluye que la participación en la construcción de realidades a través de la simulación computarizada, podría ser la metáfora para la construcción participativa de realidades más acordes con los fines democráticos e igualitarios que la educación debería promover.ITESO, A.C

Efectos de integraciones de firmas en mercados de bienes homogéneos

Este artículo modela los posibles efectos que, ante una integración empresarial, se pueden producir sobre el precio de un mercado de un bien homogéneo. El análisis se realiza a partir de dos escenarios: a) considerando tecnologías similares entre firmas y b) asumiendo algún grado de heterogeneidad por grupos de empresas. Se encuentra que aun en presencia de operaciones en favor de la eficiencia en la oferta del producto, existen riesgos de incremento en precios.Este artigo modela os possíveis efeitos que, diante de uma integração empresarial, podem ser produzidos sobre o preço de um mercado de um bem homogêneo. A análise realiza-se a partir de dois cenários: a) ao considerar tecnologias similares entre empresas e b) ao assumir algum grau de heterogeneidade por grupos de empresas. Encontra-se que, ainda na presença de operações em favor da eficiência na oferta do produto, existem riscos de aumento em preços.This article models the potential effects of firm mergers on the price of a market for homogenous goods. The analysis is carried out according to two scenarios: a) firms have similar levels of technology at their disposal and b) a degree of heterogeneity is assumed between groups of firms. It is found that even when mechanisms are in place to favor efficiency in product supply, there is a risk that prices will increase

Propuesta de un modelo simplificado de detección del riesgo empresarial: estudio empírico aplicado al sector de construcción (PYMES)

Ante la importancia de la actividad constructora en la economía española, tanto por su notable contribución a la formación del Producto Nacional Bruto como al elevado porcentaje de población activa que participa en su proceso productivo, y dada la escasa investigación del sector en España, el objetivo de esta investigación es doble: por una parte, identificar las variables o ratios más significativos de solvencia empresarial en las empresas constructoras, mediante el análisis de una muestra de pequeñas y medianas empresas del sector en España, unas sin problemas de continuidad en su actividad y otras en situación de quiebra o suspensión de pagos. En segundo lugar, una vez detectadas las variables de solvencia construimos, utilizando el análisis gráfico y el análisis multivariante, un sistema de alerta temprana que permita detectar una situación de riesgo empresarial.Before the importance of the construction activity in the Spanish economy, so much for his notable contribution to the training of the National Gross Product as to the high percentage of active population who takes part in his productive process, and given the scanty research of the sector in Spain, the aim of this research is double: on one hand, to identify the variables or the most significant ratios of managerial solvency in the building firms, by means of the analysis of a sample of small and medium companies of the sector in Spain, some without problems of continuity in his activity and others in situation of bankruptcy or suspension of payments. Secondly, once detected the variables of solvency we construct, using the graphical analysis and the analysis multivariant, a system of early alert that allows to detect a situation of managerial risk

Regression-based imputation of explanatory discrete missing data

Imputation of missing values is a strategy for handling non-responses in surveys or data loss in measurement processes, which may be more effective than ignoring the losses and omitting them. The characteristics of variables presenting missing values must be considered when choosing the imputation method to be used; in particular when the variable is a count the literature dealing with this issue is scarce. If the variable has an excess of zeros it is necessary to consider models including parameters for handling zero-inflation. Likewise, if problems of over- or under-dispersion are observed, generalizations of the Poisson, such as the Hermite or Conway Maxwell Poisson distributions are recommended for carrying out imputation. The aim of this study was to assess the performance of various regression models in the imputation of a discrete variable based on Poisson generalizations, in comparison with classical counting models, through a comprehensive simulation study considering a variety of scenarios and a real data example. To do so we compared the results of estimations using only complete data, and using imputations based on the most common count models. The COMPoisson distribution provides in general better results in any dispersion scenario, especially when the amount of missing information is large

Software design to calculate and simulate the mechanical response of electromechanical lifts

Los ingenieros de levantamiento y las empresas de elevación que están involucradas en el proceso de diseño de nuevos productos o en la investigación y desarrollo de componentes mejorados exigen una herramienta predictiva de la respuesta del sistema delgado de elevación antes de probar prototipos costosos. Se presenta un método para resolver el movimiento de cualquier sistema de elevación especificado por medio de un programa de computadora. Se deriva la respuesta mecánica del ascensor que funciona en una instalación y configuración definidas por el usuario, para una excitación dada y otros parámetros de configuración de motores eléctricos reales y su sistema de control. Se usa un modelo mecánico con 6 grados de libertad. Las ecuaciones gobernantes se integran paso a paso a través del algoritmo Meden-Kutta en la plataforma MATLAB. Los datos de entrada consisten en la velocidad del punto de ajuste para un viaje estándar y los parámetros de control de varios controladores y máquinas de accionamiento de elevación. El programa informático calcula y traza con mucha precisión el desplazamiento vertical, la velocidad, la aceleración instantánea y el historial de tirones del automóvil, el contrapeso, el bastidor, los pasajeros / cargas y la unidad de elevación en un viaje estándar entre dos pisos de la instalación deseada. Se muestran el par resultante, la tensión del cable y la desviación del gráfico de velocidad con respecto a la velocidad del punto de referencia. El diseño del software se implementa en una versión demo del programa informático llamado ElevaCAD. Más adelante, el programa ofrece la posibilidad de seleccionar la configuración del sistema de elevación y los parámetros de rendimiento de cada componente. Además de la respuesta general del sistema, se grafica información detallada de transitorios, vibraciones de los componentes del ascensor, niveles de calidad de viaje, análisis modal y espectro de frecuencia (FFT).Lift engineers and lift companies which are involved in the design process of new products or in the research and development of improved components demand a predictive tool of the lift slender system response before testing expensive prototypes. A method for solving the movement of any specified lift system by means of a computer program is presented. The mechanical response of the lift operating in a user defined installation and configuration, for a given excitation and other configuration parameters of real electric motors and its control system, is derived. A mechanical model with 6 degrees of freedom is used. The governing equations are integrated step by step through the Meden-Kutta algorithm in the MATLAB platform. Input data consists on the set point speed for a standard trip and the control parameters of a number of controllers and lift drive machines. The computer program computes and plots very accurately the vertical displacement, velocity, instantaneous acceleration and jerk time histories of the car, counterweight, frame, passengers/loads and lift drive in a standard trip between any two floors of the desired installation. The resulting torque, rope tension and deviation of the velocity plot with respect to the setpoint speed are shown. The software design is implemented in a demo release of the computer program called ElevaCAD. Further on, the program offers the possibility to select the configuration of the lift system and the performance parameters of each component. In addition to the overall system response, detailed information of transients, vibrations of the lift components, ride quality levels, modal analysis and frequency spectrum (FFT) are plotted.peerReviewe

Left-censored recurrent event analysis in epidemiological studies: a proposal when the number of previous episodes is unknown

Left censoring can occur with relative frequency when analysing recurrent events in epidemiological studies, especially observational ones. Concretely, the inclusion of individuals that were already at risk before the effective initiation in a cohort study, may cause the unawareness of prior episodes that have already been experienced, and this will easily lead to biased and inefficient estimates. The objective of this paper is to propose a statistical method that performs successfully in these circumstances. Our proposal is based on the use of models with specific baseline hazard, imputing the number of prior episodes when unknown, with a stratified model depending on whether the individual had or had not previously been at risk, and the use of a frailty term. The performance is examined in different scenarios through a comprehensive simulation study.The proposed method achieves notable performance even when the percentage of subjects at risk before the beginning of the follow-up is very elevated, with biases that are often under 10\% and coverages of around 95\%, sometimes somewhat conservative. If the baseline hazard is constant, it seems to be that the ``Gap Time'' approach is better; if it is not constant, the ``Counting Process'' seems to be a better choice. Because of the lack of knowledge of the prior episodes that have been experienced by a part (or all) of subjects, the use of common baseline methods is not advised. Our proposal seems to perform acceptably in the majority of the scenarios proposed, becoming an interesting alternative in this context.Comment: 1 table, 2 supplementary tables, 4 figure