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

Una compliance pulmonar disminuida incrementa los test dinámicos de precarga en un modelo pediátrico de lesión pulmonar aguda

Indexación: Web of Science; Scielo.Background Preload dynamic tests, pulse pressure variation (PPV) and stroke volume variation (SVV) have emerged as powerful tools to predict response to fluid administration. The influence of factors other than preload in dynamic preload test is currently poorly understood in pediatrics. The aim of our study was to assess the effect of tidal volume (VT) on PPV and SVV in the context of normal and reduced lung compliance in a piglet model. Material and method Twenty large-white piglets (5.2 ± 0.4 kg) were anesthetized, paralyzed and monitored with pulse contour analysis. PPV and SVV were recorded during mechanical ventilation with a VT of 6 and 12 mL/kg (low and high VT, respectively), both before and after tracheal instillation of polysorbate 20. Results Before acute lung injury (ALI) induction, modifications of VT did not significantly change PPV and SVV readings. After ALI, PPV and SVV were significantly greater during ventilation with a high VT compared to a low VT (PPV increased from 8.9 ± 1.2 to 12.4 ± 1.1%, and SVV from 8.5 ± 1.0 to 12.7 ± 1.2%, both P < 0.01). Conclusions This study found that a high VT and reduced lung compliance due to ALI increase preload dynamic tests, with a greater influence of the latter. In subjects with ALI, lung compliance should be considered when interpreting the preload dynamic tests.Introducción Test dinámicos de precarga, variación de presión de pulso (PPV) y variación de volumen sistólico (SVV) han emergido como herramientas poderosas para predecir respuesta a la administración de fluidos. Actualmente la influencia de factores distintos a la precarga en la determinación de los test dinámicos de precarga es pobremente conocida en pediatría. Nuestro objetivo fue medir el efecto del volumen tidal (VT) sobre PPV y SVV en un contexto de compliance pulmonar normal y disminuida en un modelo porcino. Material y método Veinte cerditos Large-White anestesiados y paralizados (5,2 ± 0,4 kg). PPV y SVV fueron medidos por análisis de contorno de pulso durante ventilación con VT de 6 y 12 mL/kg (VT bajo y alto, respectivamente), ambos previo y posterior a lesión pulmonar aguda (ALI) químicamente inducida con instilación traqueal de polisorbato 20. Resultados Previo a inducción de ALI, PPV y SVV no tuvieron cambios significativos al modificar el VT. Sin embargo, después de ALI, PPV y SVV fueron significativamente mayores durante ventilación con VT alto, respecto a VT bajo (PPV aumentó de 8,9 ± 1,2 a 12,4 ± 1,1%, y SVV de 8,5 ± 1,0 a 12,7 ± 1,2%, ambos P < 0,01). Conclusiones Este estudio encontró que un VT alto y una compliance pulmonar disminuida debido a ALI incrementan los test dinámicos de precarga, con una mayor influencia de esta última. En sujetos con ALI la compliance pulmonar debiera ser considerada al interpretar los test dinámicos de precarga.http://ref.scielo.org/3fhq5

ESTUDIO EXPERIMENTAL DE SENSORES ÓPTICOS TIPO FBG PARA MEDIR DEFORMACIONES Y TEMPERATURAS EN ESTRUCTURAS

La monitorización estructural es un campo que últimamente está recibiendo una gran atención. Ello impulsa al desarrollo de métodos que ayuden a reducir las operaciones de mantenimiento de las estructuras, permitiendo un control remoto y continuo de parámetros que determinen la integridad estructural. Entre éstos, destacan los sistemas ópticos.Torres Górriz, B. (2009). ESTUDIO EXPERIMENTAL DE SENSORES ÓPTICOS TIPO FBG PARA MEDIR DEFORMACIONES Y TEMPERATURAS EN ESTRUCTURAS. http://hdl.handle.net/10251/14022Archivo delegad

Manuel Abreu Adorno: puertorriqueñidad transatlántica

Mediante un análisis a fondo de Llegaron los hippies y No todas la suecas son rubias, el presente artículo busca caracterizar a Manuel Abreu Adorno, primero, como figura de transición en las letras puertorriqueñas entre los escritores de la década del 70 y los de las décadas más recientes, segundo, como precursor del Crack y de McOndo, y finalmente como escritor con una clara visión transatlántica.By means of a close textual analyis of Llegaron los hippies and No todas la suecas son rubias the present article looks to characterize Manuel Abreu Adorno, firstly, as a transitional figure in Puerto Rican letter between the writers of the seventies and those of more recent decades, secondly, as a precursor of the Crack and McOndo, and finally as a writer with a clear transatlantic vision

Study on the influence of different error sources on sky radiance measurements and inversion-derived aerosol products in the frame of aeronet

El objetivo principal de esta tesis es contribuir a la investigación de las causas que hay detrás de las discrepancias entre los productos de inversión obtenidos de plano principal y de almucantar, en concreto, examinar si pueden estar asociados con los errores en la medida de la radiancia. Dentro de las distintas fuentes de error se han considerado la calibración, el apuntamiento de los fotómetros y la existencia de un campo de visión (FOV) finito en los fotómetros. Estos errores se analizan primero en términos de su efecto sobre la medida de radiancia, de manera cualitativa y cuantitativa, para después estudiar su impacto sobre las propiedades de los aerosoles que se obtienen por medio del algoritmo de inversión de AERONET; de entre todas las propiedades este trabajo se centra en la distribución del tamaño, el índice de refracción y el albedo de scattering simple.Departamento de Física Teórica, Atómica y Óptic

Long-term static and dynamic monitoring to failure scenarios assessment in steel truss railway bridges: A case study

The latest studies on failures in steel truss-type bridge found that they are highly vulnerable to damage and thus prone to potential local or total collapse. Many authors recommend monitoring the critical elements in the existing steel truss-type bridges in real time to anticipate any failures in local members. Although mechanical strain is the most frequently used variable for this purpose, this method also happens to be the most expensive monitoring strategy. This paper describes a case study of failure scenarios assessment in a steel truss-type railway bridge after extensive long-term monitoring conducted by the authors, based on measuring vertical deflections and modal frequencies. The structure has both an isostatic and a hyperstatic configuration, and was assessed by means of a combination of: (i) long-term monitoring results, and (ii) a finite element analysis to simulate several failure scenarios. A sensitivity study of the different failure scenarios has been carried out, identifying those that can be detected. The results are used to define practical recommendations for failure detection by measuring vertical deflections and modal frequencies

In-plane shear cyclic behavior of windowed masonry walls reinforced with textile reinforced mortars

The current experimental study is focused on the mechanical performance of masonry walls under in-plane cyclic shear forces. All specimens were fabricated with a central window, in which the geometry considered the recommendations of the Spanish structural seismic design code. Windows represent a weak area in the masonry structure, in which there are stress concentrations responsible for crack initiation. In order to improve the mechanical strength and ductility, a reinforcement with a Textile Reinforced Mortar (TRM) was used on both sides of the wall. The performance of the unreinforced and reinforced masonry has been discussed in terms of strength and ductility gain, stiffness degradation and energy dissipation capacity. The experimental tests comprised an initial vertical preload, and shear cycles with increasing amplitude. All tests were monitored by means of traditional displacement transducers, and digital image correlation. The analysis of the images showed the time evolution of the overall crack distribution. The TRM effect could be observed as an increase of the mechanical strength (maximum shear from 120 kN to more than 300 kN), higher displacements (drift from 9 to 35 mm), and more energy dissipation (the cumulative energy loss from 2.7 to 12.7 kN·m). In addition, the TRM reinforcements were capable of controlling the crack initiation and growth. The widespread crack along mortar joints observed in the unreinforced masonry became localized cracks (from the window’s corners mainly), in which crack growth direction was not determined by masonry joints.The authors would like to acknowledge Mapei Spain S.A. for the materials supplied in this research. This research was funded by Spanish Ministry of Economy and Competitiveness, grant number BIA2015-69952-R and Spanish Ministry of Science, Innovation and Universities, grant number RTI2018-101148-B-I00

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

Comprobación de la actividad inhibitoria del extracto hidro-alcohólico de Piper peltatum sobre hialuronidasa.

El objetivo de la investigación fue comprobar la actividad inhibitoria del extracto hidroalcohólico de Piper Peltatum sobre la hialuronidasa. Se efectuó la recolección de la materia vegetal y se analizaron los parámetros de calidad de la droga cruda y del extracto hidroalcohólico. Mediante el tamizaje fitoquímico se determinó la presencia de alcaloides, terpenos, fenoles y flavonoides. De igual forma con los métodos colorimétricos se cuantifico los compuestos fenólicos y flavonoides. Se empleó diferentes concentraciones del extracto vegetal (1000; 250; 100; 50; 25; 12,5 y 6,25 µg/mL) para las pruebas de inhibición de la hialuronidasa; se utilizó un grupo control de máxima actividad enzimática y un blanco negativo. Se determinó que el mejor resultado en la inhibición de la hialuronidasa bovina fue a la concentración de 250 µg/mL con un 81,13% de inhibición; los resultados más relevantes se obtuvieron frente a los venenos de serpiente cobra (Naja naja) a concentraciones más diluidas 6,25 µg/mL con un 40,17% de inhibición mientras que en la especie Bothrops atrox la actividad fue menos significativa a concentración de 12,5 con un 24,7% de inhibición. La diferencia en el porcentaje de inhibición puede darse por la variabilidad genética de las dos especies, y la cantidad de hialuronidasa presente en el veneno. Es recomendable realizar esta investigación con venenos de otras de serpientes debido a su uso tradicional en las mordeduras.The objective of the research was to verify the inhibitory activity of the hydroalcoholic extract of Piper peltatum on hyaluronidase. The vegetal matter was collected and the crude drug and the hydroalcoholic extract quality parameters were analyzed. Through the photochemical screening, the presence of alkaloids, terpenes, phenols and flavonoids were determined. In the same way with the colorimetric methods, the phenolic and flavonoid compounds were quantified. Different contractions of the plant extract (1000; 250; 100; 50; 25; 12,5 y 6,25 µg/mL) were used for hyaluronidase inhibition test; a control group of maximum enzymatic activity and a negative target was used. It was determined that the best result in the inhibition of bovine hyaluronidase was at the concentration of 250 µg/mL with 81.13% inhibition; the most relevant results were obtained against snake venom cobra (Naja naja) at concentrations and more diluted 6,25 µg/mL with a 40,17% inhibition while in the Bothrops atrox species the activity was less significant at the concentration of 12,5 with 24,7% inhibition. The difference between the percentages of inhibition can be given by the genetic variability of the two species, and amount of hyaluronidase present in the venom. It is advisable to perform this investigation with venom from other snakes due to its traditional use in bites