Los números reales y procesos infinitos en el bachillerato

El presente trabajo expone ciertos aspectos de los números racionales e irracionales que generalmente son poco trabajados en las clases sobre los números reales en el bachillerato. La célebre paradoja de Aquiles y la tortuga sirve de pretexto para analizar a los números racionales y su periodicidad vía la noción de serie. Por lo que respecta a los números irracionales, la comparación del lado de un cuadrado y su diagonal nos sirven para introducir el concepto de inconmensurabilidad. Se presenta también un pequeño software, a manera de demo para apoyo de los temas tratados

Failure analysis of the collapse of a raised steel wine tank

As structural damage or even catastrophic collapses are sometimes due to improper design, underestimated design loads or unexpectedly extreme loads, progressive collapse and structural robustness has recently received a great deal of attention, while the number of scientific papers published on the topic has grown considerably. This paper describes an analysis of the failure of a 106 m3 steel raised wine tank belonging to a local wine producer that suddenly collapsed, fortunately without personal injury, but causing significant damage to the company's facilities. The collapse generated the progressive failure of other tanks next to the first one that failed. After several visits to inspect the accident on site, a diagnosis was made to determine the causes. Possible reasons were examined by visual inspections and experimental tests on steel specimens recovered from the collapsed structures, which allowed to determine the mechanical properties and study the fracture surfaces by scanning electron microscopy and micrographs. On the other hand, the load-carrying capacities of the structure were studied by a linear-static finite-element and a nonlinear-static push-over analysis. The collapse mechanism of the system was found to be due to cyclic horizontal loads generated by a pressurized air injection system. The results allowed to conclude that this type of structure is highly vulnerable to horizontal loads and has very little capacity to activate alternative loas paths. The paper also describes a possible solution that could be used to improve the mechanical performance of this structural typology against horizontal loading, based on the lessons learned from the experience

Improvement in PWV estimation from GPS due to the absolute calibration of antenna phase center variations

Climatology of column-integrated atmospheric water vapor over Spain has been carried out by means of three techniques: soundings, sun photometers and GPS receivers. Comparing data from stations equipped with more than one of these instruments, we found that a large discontinuity occurred on November 6, 2006, in the differences between the data series from GPS receivers and those from the other two techniques. Prior to that date, the GPS data indicate a wet bias of 2–3 mm for all stations when compared with sounding or photometer data, whereas after that date this bias practically reduces to zero. The root mean square error also decreases about half of its value. On November 6, 2006, the International GNSS Service adopted an absolute calibration model for the antennas of the GPS satellites and receivers instead of the relative one. This change is expected to be an improvement, increasing the accuracy of station position determination and consequently benefiting post-processing products such as zenith total delay from which the atmospheric water vapor content is calculated

Jovens e eleições democráticas. Uma investigação-acção cogenerativa com um grupo de estudantes de ensino médi

This article presents the results of a co-generative action-research, whose objective was to evaluate a didactic module designed from the Chilean presidential election of 2017, which was aimed at the development of civic competencies and the encouragement of expectations of future electoral participation of high school students. The research was conducted by establishing a collaborative partnership between the professional research team and a high school teacher, according to Greenwood and Levin’s ideas. Specifically, twenty-nine students inquired and debated for four weeks about the proposals of the candidates, as well as the socially live issues associated with them. Subsequently, the students’ ideas about the experience were explored through questionnaires, semi-structured interviews, and a discussion group. Complementarily, classroom observations were conducted, and the participating teacher was interviewed. After that, the information obtained was processed using the qualitative content analysis method. The results point to the effectiveness of the module implemented in the development of citizenship competencies and to the importance students give to the discussion of the social reality in the classroom, in an atmosphere of respect for diverse opinions. In turn, the conclusions identify several strengths and weaknesses to be considered in future applications. Likewise, they highlight the students’ active role and the debate on controversial issues in citizenship education and suggest that these elements should be considered in the new Chilean citizenship subject.Este artículo presenta los resultados de una investigación-acción cogenerativa, cuyo objetivo de indagación fue valorar un módulo didáctico diseñado a partir de la elección presidencial chilena de 2017, el cual estuvo destinado al desarrollo de competencias ciudadanas y al incentivo de las expectativas de participación electoral futura en jóvenes de secundaria. Para llevarla adelante, se estableció una asociación colaborativa entre el equipo investigador profesional y un docente del sistema escolar, según los planteamientos de Greenwood y Levin. En concreto, veintinueve estudiantes indagaron y debatieron durante cuatro semanas en torno a las propuestas de los diversos candidatos y candidatas, así como respecto a las cuestiones socialmente vivas asociadas a ellas. Posteriormente, se exploró en sus ideas sobre las actividades realizadas, mediante cuestionarios, entrevistas semiestructuradas y un grupo de discusión. Complementariamente, se realizaron observaciones de clases y se entrevistó al docente. Tras ello, la información obtenida fue tratada a partir del método de análisis cualitativo de contenido. Los resultados apuntan a la eficacia del módulo implementado en el desarrollo de competencias ciudadanas y a una alta valoración del estudiantado respecto a la discusión de la realidad social en clases en un ambiente de respeto por las diversas opiniones. Por su parte, las conclusiones establecen una serie de fortalezas y debilidades a tener en cuenta en sus futuras aplicaciones. Asimismo, destacan el rol activo del alumnado y la importancia de debatir cuestiones socialmente vivas en la formación ciudadana, por lo que se sugiere considerar tales elementos en la nueva asignatura chilena de ciudadanía.Este artigo apresenta os resultados de uma investigação-acção cogenerativa cujo objetivo foi avaliar um módulo didáctico concebido a partir da eleição presidencial chilena de 2017, destinado ao desenvolvimento de competências de cidadania e incentivar as expectativas de participação eleitoral futura em estudantes do ensino médio. Para conseguir isso, uma parceria colaborativa foi estabelecida entre pesquisadores profissionais e um professor do sistema escolar, de acordo com as idéias de Greenwood e Levin. Especificamente, vinte e nove estudantes investigaram e debateram durante quatro semanas as propostas dos vários candidatos e as questões socialmente vivas associadas a eles. Posteriormente, as idéias de estudantes sobre as atividades realizadas foram exploradas por meio de questionários, entrevistas semiestruturadas e um grupo de discussão. Além disso, foram realizadas observações de aula e o professor foi entrevistado. Em seguida, as informações obtidas foram tratadas com base no método de análise qualitativa de conteúdo. Os resultados apontam para a efetividade do módulo utilizado no desenvolvimento de competências de cidadania e para uma alta avaliação dos estudantes quanto à discussão da realidade social nas aulas, em um ambiente de respeito pelas diversas opiniões. Por outro lado, as conclusões estabelecem uma série de pontos fortes e fracos a serem levados em consideração em aplicações futuras. Da mesma forma, destacam o papel ativo dos estudantes e a importância de discutir questões socialmente vivas na educação cidadã, por isso sugere-se considerar tais elementos na nova matéria chilena de cidadania

Diurnal cycle of precipitable water vapor over Spain

Knowledge of the diurnal cycle of precipitable water vapor (PWV) is very limited owing to the lack of data with sufficient temporal resolution. Currently, GPS receivers have proven to be a suitable technique to determine PWV diurnal variations. In this study, the annual and seasonal diurnal cycles of PWV have been obtained from GPS data for 10 locations over Spain. The minimum value of PWV is reached approximately at the same time at all the stations, ∼0430–0530 UTC, whereas the maximum is reached in the second half of the day, but with a larger dispersion of its occurrence between stations. The annual sub-daily variability ranges from 0.41 to 1.35 mm (3–7%). The highest values are recorded at the stations on the Mediterranean coast, with a doubling of the values of the stations on the Atlantic coast or inland. The winter cycle is quite similar at all locations, whereas in summer local effects are felt strongly, making the diurnal cycle quite different between stations. The PWV mean diurnal cycle is strongest in summer and weakest in spring, with a sub-daily variability of 1.34 and 0.66 mm respectively. Harmonic analysis shows that the first two harmonics can explain 97% of the variance. The diurnal (24 h) harmonic explains 85% of the variance, has mean amplitude of 0.40 mm, and the peak time is from early afternoon to evening. The semi-diurnal (12 h) harmonic is weaker, with an amplitude of 0.13 mm, and peak time between 0400 and 1000 UTC. The diurnal cycle of temperature alone would be a proxy for PWV cycle during the night, but not during the daytime. The breeze regime is the main factor responsible for the phase lag between PWV and temperature cycles during daytime. No clear correlation between the daily cycle of precipitation and PWV has been found

Nanopartículas de óxido de silicio y aluminio para la producción de 5-hidroximetilfurfural desde galactosa

El problema del calentamiento global, fuentes de recursos fósiles limitadas y amenazas de desabastecimiento empujan al desarrollo de nuevos métodos de obtención de recursos procedentes de fuentes renovables, tales como la biomasa. La biomasa procedente de las algas presenta diferentes carbohidratos en su composición que pueden transformarse, mediante deshidratación en presencia de catalizadores, en 5-hidroximetilfurfural (HMF), una molécula plataforma muy estudiada por su potencial en el campo de los materiales poliméricos y biocombustibles. En este trabajo, se exponen los resultados obtenidos con nanopartículas de sílice y aluminio mesoporosas, que muestran prometedores rendimientos de HMF desde galactosa, un monosacárido abundante en muchas algas. Las nanopartículas con diferente relación Si/Al poseen un diámetro entre 300 y 100 nm. Su estructura porosa facilita la difusión de los reactivos y productos en el proceso de deshidratación, con un núcleo de silicio y una corteza de aluminio, tal y como puede apreciarse en las imágenes de EDX. Los datos texturales revelan que la mayor parte del área superficial de las nanoesferas corresponde a mesoporos, lo que minimiza las limitaciones difusionales en el proceso catalítico. La menor área superficial se obtiene con el catalizador con menor relación Si/Al. Los análisis muestran que estos materiales son activos en el proceso de deshidratación de galactosa y se puede alcanzar un 40% de rendimiento en HMF. Más elevadas concentraciones de aluminio en el material proporcionaron una mayor actividad en la conversión de galactosa y rendimiento en HMF a tiempos cortos, pero los resultados para los diferentes catalizadores tienden a igualarse a tiempos más largos. Tras 7 horas de reacción, se consume casi la totalidad de la galactosa inicialmente presente y el balance de carbono se reduce a valores entre 60 y 40% del inicial debido a la formación de polímeros solubles e insolubles en el medio de reacción.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Evaluación de daños de un acero A572 grado 60 en condiciones de siniestro

La investigación determinó las propiedades mecánicas de un acero A572 grado 60 que fue sometido a un incendio. La muestra obtenida después del siniestro sirvió para tomar las probetas cortadas por la técnica “WaterJet”. Se llevaron a cabo ensayos mecánicos de tensión y dureza rockwell, arrojando resultados semejantes a los típicos observados en este material. Se realizó un análisis metalográfico obteniendo imágenes por medio de microscopia óptica, a estas imágenes se les determinó un cálculo de porcentaje de fases por medio del software Image J. El acero fue analizado también por Microscopia electrónica de barrido para observar la microestructura después del incendio.This research determined the mechanical properties of steel A572 grade 60 that was subjected to a sinister fire. Mechanical stress tests and Rockwell hardness were carried out, giving similar results than the typical ones observed in this material. A metallographic analysis was carried out obtaining images using optical microscopy; these images were used to determine a percentage of phases employing the Image J software. The steel was also analyzed by Scanning Electron Microscopy to see microstructure after the fire

Variación de la precipitación y temperatura en el municipio de Teziutlán, Puebla

El municipio de Teziutlán se ubica en la zona nororiente del estado de Puebla, se caracteriza por tener un clima templado húmedo con lluvias distribuidas generalmente todo el año, sin embargo en los últimos años se ha observado que hay un cambio en cuánto a la precipitación y temperatura, teniendo como referencia las inundaciones y deslaves en el municipio de Teziutlán, causando pérdidas económicas en el sector agropecuario e incluso pérdidas humanas. En este trabajo se analizó los datos estadísticos en bloques de 10 años para observar la variación de la precipitación y temperatura. Los resultado indican que el periodo de lluvia se ha desfasado un mes y la temperatura se ha incrementado entre 0.5 a 1.5 °C., tomando en cuenta las estadísticas marcan que entre 9 y 11 años hay un periodo de retorno de precipitación y esquiaje donde la precipitación anual varía de1500 mm a 3600 mm

Prevalence of Trypanosoma cruzi and organ alterations in Virginia opossums (Didelphis virginiana) from western Mexico – short communication

Small populations of Virginia opossum (Didelphis virginiana) in western Mexico are endangered by hunting and natural predators as well as by different kinds of diseases. After two serological analyses using Serodia® latex particle agglutination and indirect haemagglutination (IHA) tests, 35 (53.03%) of 66 collected opossums in two small towns in western Mexico were positive for the presence of Trypanosoma cruzi. Twenty-eight of the 35 seropositive opossums had pathological lesions: 11 had changes in only one organ, 13 in two organs, and four had pathological changes in three organs. Splenomegaly was the most common finding in the examined opossums, followed by hepatomegaly. These potentially fatal pathological changes could contribute to the scarcity of the opossum population, even leading to the extinction of this species in western Mexico