Asociación entre variables cualitativas: ejemplo práctico de análisis de correspondencias

Traballo Fin de Grao en Matemáticas. Curso 2018-2019[ES] El análisis de correspondencias es una técnica de la estadística descriptiva aplicada a tablas de contingencia cuyo objetivo es la visualización de una nube de puntos multidimensional asociada a unas ciertas variables en un espacio de menor dimensión. Se generan mapas que plasman los puntos intentando respetar al máximo sus posiciones en el espacio original perdiendo el mínimo de información, lo que nos permite elaborar un análisis exploratorio de ellos rápido y eficaz además de poder establecer asociaciones entre las variables. Las proyecciones habitualmente son sobre espacios de dimensión 2 por nuestra familiaridad con ellos. Se tratará el contraste de la homogeneidad de la tabla, se introducirá una medida más adecuada para esta técnica (la distancia ji-cuadrado) y se expresará la varianza de la tabla en función de estos conceptos. Esta nueva medida de la varianza es lo que queremos conservar al realizar la proyección de la tabla. Se introducirán diversos tipos de análisis de correspondencias y técnicas para su implementación, así como realizar inferencia y contrastes sobre los datos. Todo el trabajo se acompaña de varios ejemplos para facilitar la comprensión de qué se está haciendo. Por último, llevaremos a la práctica todo lo introducido a lo largo del trabajo en un estudio médico real con las pretensiones de resumir los datos, establecer un análisis descriptivo y establecer relaciones entre varias enfermedades comunes y la calidad y forma de vida de 820 pacientes.[EN] Correspondence analysis is a technique of descriptive statistics applied to contingency tables whose objective is the visualization of a multidimensional point cloud associated to certain variables in a space of smaller dimension. Maps are generated trying to respect as much as possible their positions in the original space, losing the minimum of information, which allows us to elaborate an exploratory analysis of them quickly and eficiently as well as being able to establish associations between the variables. The projections are usually on spaces of dimension 2 because of our familiarity with them. The contrast of the homogeneity of the table will be treated, a more appropriate measure will be introduced for this technique (the chi-square distance) and the variance of the table will be expressed in terms of these concepts. This new measure of variance is what we want to keep when projecting the table. Various types of correspondence analysis and techniques for its implementation will be introduced, as well as inference and contrasts on the data. All the work is accompanied by several examples to facilitate the understanding of what is being done. Finally, we will put into practice everything introduced during the work in a real medical study with the aim of summarizing the data, establishing a descriptive analysis and establishing relationships between several common diseases and the quality and way of life of 820 patients

Learning Einstein’s Theory of Special Relativity: State Of the Art

En este artículo se analizan las dificultades de aprendizaje de la Teoría de la Relatividad Restringida de Einstein. La información se ha obtenido y seleccionado de las bases de datos Web of Science, Scopus, Educational Resources Information Center y Google Scholar, teniendo en cuenta los índices de valoración Journal Citation Reports (JCR), Scimago Journal Rank (SJR) e Índice Compuesto de Difusión Secundaria (ICDS). Para el análisis y las conclusiones se establecieron las dificultades de aprendizaje del alumnado relacionadas con la Relatividad Restringida de Einstein, respecto a los siguientes conceptos: Espacio y tiempo. Causalidad y simultaneidad. Sistemas de referencia. Energía. Masa. Luz. El presente estudio ha constituido el fundamento del diseño de una propuesta de enseñanza basada en la formulación geométrica de Minkowski, dirigida a estudiantes de bachillerato.In this article we analyze the learning difficulties of Einstein's Theory of Restricted Relativity. The information has been obtained and selected from the Web of Science, Scopus, Educational Resources Information Center and Google Scholar databases, taking into account the Journal Citation Reports (JCR), Scimago Journal Rank (SJR) and Composite Index of Secondary Dissemination (ICDS). For the analysis and the conclusions the learning difficulties of the students related to the Restricted Relativity of Einstein were established, with respect to the following concepts: Space and time. Causality and simultaneity. Reference frames. Energy. Mass. Light. This study has been the basis for the design of a teaching proposal based on the geometric formulation of Minkowski, aimed at high school students

Effects of Shoot Size and Genotype on Energy Properties of Poplar Biomass in Short Rotation Crops

Eight poplar genotypes grown in a short rotation forest plantation established in an acid soil in South Europe were sampled at the age of 7 years to determine the energy properties regarding thermochemical conversion. The goal was to address the effect of selection of genotypes or shoot size at harvest on the energy quality of biomass. Between 34 and 50 biomass samples were obtained for each genotype: three disks were systematically sampled along the stem and were pooled together with a subsample of leafless branches representative of the biomass share of this component. Several energy properties were determined: higher calorific value, net calorific value, fresh moisture content, basic density, ash, volatile matter, fixed carbon content and elemental composition. Genotype had a significant effect on most of these properties, and the balsam genotypes displayed superior quality parameters and also higher biomass yield than the Euramerican genotypes. As a covariate, shoot basal diameter had a significant effect on the moisture content, basic density, ash content and on the concentrations of the elements N, K, Ca, Mg, S, Na and C. It was concluded that genotypes with low nutrient requirements planted at low density (<8000 cuttings ha−1 ) and harvested at a long enough rotation (7 years) produce good yields and high chip quality. Poplar short rotation crops can be grown to produce chips of A2 quality for non-industrial heating use (according to UNE-EN ISO 17225-4), able to be combusted in domestic thermal facilities of <1 MWth power.This work was financially supported by project RTA2014-00007-00007-C03-02, Spanish Ministry of Economy and CompetitivityS

Arte de la Edad del Bronce: Los grabados rupestres de Cova da Bruxa y Laxe das Rodas (Muros, A Coruña): Actuación aqueológica y revisión intrepretativa

This article provides the results achieved in the fieldwork and subsequents study of the petroglyphs of Laxe das Rodas and Cova da Bruxa (Muros, A Coruña), after the developement of the research projects “Domumentación e rexistro da estación rupestre da Laxe das Rodas”, and “Proxecto de domumentación, de rexistro e de acondicionamento do entorno da estación rupestre de Laxe das Rodas (Muros, A Coruña)”, of the History Departament at the University of Santiago de Compostela, the municipality of Muros, and the Comunidad Autónoma of Galicia (Xunta de Galicia), with the collaboration the Area of Prehistory of the University of Murcia.Este artículo ofrece los resultados obtenidos en los trabajos de campo y posterior estudio de los conjuntos grabados de Laxe das Rodas y Cova da Bruxa (Muros, A Coruña), tras el desarrollo de los proyectos de investigación: “Domumentación e rexistro da estación rupestre da Laxe das Rodas” y “Proxecto de domumentación, de rexistro e de acondicionamento do entorno da estación rupestre de Cova da Bruxa (Serres, A Coruña)”, en los que participaron el Grupo de Estudos para a Prehistoria do Noroeste Ibérico (GEPN), del Departamento de Historia I de la Facultad de Geografía e Historia de la Universidad de Santiago de Compostela, el Concello de Muros y la Xunta de Galicia, con la colaboración en la dirección científica del Área de Prehistoria de la Universidad de Murcia

Elemental composition of raw and torrefied pellets made from pine and pine-eucalyptus blends

Debarked Pinus radiata wood was blended with debarked Eucalyptus nitens wood in three different proportions: 100% pine (100P), 90% pine-10% eucalyptus (90P/10E) and 60% pine-40% eucalyptus (60P/40E). The pellets were torrefied in dry and non-oxidative conditions at different temperatures (210, 240, 270 and 300 °C) and residence times (40 and 60 min) to enhance the energy properties and determine the elemental composition (18 elements). For raw pellets, the concentrations of Na, K, Zn, B and Cl increased significantly with the proportion of eucalyptus wood, with Cl levels being 60% higher in the 60P/40E than in the 100P pellets. The concentrations of most elements (C, Mg, Al, P, Ca, Fe, Cu) tended to increase (+35% for C, +200–250% for the others) with torrefaction severity, independently of the mixture. Decreases in H and O concentrations were also independent of the mixture. Torrefaction decreased the Cl content by 63–77%, which compensated for the high levels in mixtures with eucalyptus. Increases in the high heating value (by as much as 37%) with torrefaction occurred in parallel with an increase in carbon content and a decrease in the atomic H:C and O:C ratios, particularly in the 260 to 300 °C transition. Torrefaction compensated for the negative effect of the inclusion of eucalyptus, with the alkali index remaining at a relatively safe maximum value of 0.10 kg GJ−1This research was partly funded by a Grant from the Competitive Reference Research Unit Program of the Galician Autonomous Government, cofunded by ERDF (ref. EDC431C 2022/28). The laboratory pelletizer was also funded by the Consellería de Cultura, Educación e Universidade (contract 2021-1716)S

Arqueología y arquitectura de San Martiño de Mondoñedo (Foz, Lugo). Revisión crítica y nuevas aportaciones

[Resumen] En este trabajo se pretende, en primer lugar, revisar y analizar de forma crítica y comparada toda la información histórico-artística y arqueológica existente sobre San Martiño de Mondoñedo, para posteriormente ofrecer algunos nuevos datos sobre los orígenes y evolución de este emblemático edificio entre la Alta y Plena Edad Media. Para ello nos basaremos en una aproximación arqueológica a los paramentos del edificio así como en la datación mediante Luminiscencia y Radiocarbono de diversos elementos de la cúpula de este edificio. Frente a las ideas tradicionalmente sostenidas, los resultados preliminares, a falta de nuevos y necesarios estudios, sugieren que no hay indicios para hablar de una ocupación del siglo VI en el lugar, y que el edificio románico actual, pese a emplear piezas reutilizadas, no parece presentar restos de muros prerrománicos en pie. Por su parte, la datación de morteros de la cúpula confirma su construcción en el siglo XII.[Abstract] This paper aims to offer a critical and comparative review and analysis of the historical-artistic and archaeological information pertaining to San Martiño de Mondoñedo and to then provide some new information on the origins and evolution of this iconic building, which dates to the period between the early and central Middle Ages. In doing so, we have adopted an archaeological approach to the walls of the building and conducted luminescence and radiocarbon dating of samples from the dome. Contradicting traditionally held ideas, the preliminary results (which require confirmation in future studies), suggest that there is no evidence of the site having been settled in the 6th century and that the existing Romanesque building does not comprise standing sections of pre-Romanesque walls, though it does contain some reused pieces. Mortar from the dome has been dated, providing confirmation that it was built in the 12th century

Arqueología y arquitectura de San Martiño de Mondoñedo (Foz, Lugo). Revisión crítica y nuevas aportaciones

[ES] En este trabajo se pretende, en primer lugar, revisar y analizar de forma crítica y comparada toda la información histórico-artística y arqueológica existente sobre San Martiño de Mondoñedo, para posteriormente ofrecer algunos nuevos datos sobre los orígenes y evolución de este emblemático edificio entre la Alta y Plena Edad Media. Para ello nos basaremos en una aproximación arqueológica a los paramentos del edificio así como en la datación mediante Luminiscencia y Radiocarbono de diversos elementos de la cúpula de este edificio. Frente a las ideas tradicionalmente sostenidas, los resultados preliminares, a falta de nuevos y necesarios estudios, sugieren que no hay indicios para hablar de una ocupación del siglo VI en el lugar, y que el edificio románico actual, pese a emplear piezas reutilizadas, no parece presentar restos de muros prerrománicos en pie. Por su parte, la datación de morteros de la cúpula confirma su construcción en el siglo XII.[EN] This paper aims to offer a critical and comparative review and analysis of the historical-artistic and archaeological information pertaining to San Martiño de Mondoñedo and to then provide some new information on the origins and evolution of this iconic building, which dates to the period between the early and central Middle Ages. In doing so, we have adopted an archaeological approach to the walls of the building and conducted luminescence and radiocarbon dating of samples from the dome. Contradicting traditionally held ideas, the preliminary results (which require confirmation in future studies), suggest that there is no evidence of the site having been settled in the 6th century and that the existing Romanesque building does not comprise standing sections of pre-Romanesque walls, though it does contain some reused pieces. Mortar from the dome has been dated, providing confirmation that it was built in the 12th century.S

Semiclassical approach to black hole absorption of electromagnetic radiation emitted by a rotating charge

We consider an electric charge, minimally coupled to the Maxwell field, rotating around a Schwarzschild black hole. We investigate how much of the radiation emitted from the swirling charge is absorbed by the black hole and show that most of the photons escape to infinity. For this purpose we use the Gupta-Bleuler quantization of the electromagnetic field in the modified Feynman gauge developed in the context of quantum field theory in Schwarzschild spacetime. We obtain that the two photon polarizations contribute quite differently to the emitted power. In addition, we discuss the accurateness of the results obtained in a full general relativistic approach in comparison with the ones obtained when the electric charge is assumed to be orbiting a massive object due to a Newtonian force.Comment: 8 pages (revtex), 8 figure

Quantization of the Proca field in the Rindler wedge and the interaction of uniformly accelerated currents with massive vector bosons from the Unruh thermal bath

We canonically quantize the Proca field in the Rindler wedge and compute the total response rate of a uniformly accelerated current interacting with massive vector Rindler particles from the Unruh thermal bath. We explicitly verify that the result obtained is exactly the same as the emission rate of massive vector particles in the Minkowski vacuum as analyzed by inertial observers. Eventually our results are interpreted in terms of the interaction of static electrons coupled to $Z^0$ bosons present in Hawking radiation close to the event horizon of a black hole.Comment: 5 pages, no figure