3,283 research outputs found

    Heat transfer enhancement using nanofluids in the compression exchanger in a solar Stirling engine

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    In this paper a improvement in the heat exchange of a solar Stirling engine during the compression phase was studied. The viability of using nanoparticles as ceramic oxide (Al2O3 in water) at different concentrations instead of conventional refrigerants (water or air) was evaluated. Since these systems could behave as non- Newtonian fluids the dynamic viscosity was measured, as well as other thermophysical properties. The results showed that the convective heat transfer coefficient could raise one order of magnitude respect to the conventional heat transfer fluids at moderately volume fractions (over 0.15).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

    Characterization and thermophysical properties of rutile and alumina nanofluids

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    The characterization in relation to shape and particle size of alumina and rutile suspensions was performed. The intrinsic viscosity exhibited the presence of nonspherical aggregates in both suspensions although TEM images showed non monodisperse spherical shape of alumina particles. DLS indicated the existence of particle aggregates for both systems. In all cases, the increase in thermal conductivity with respect to the base fluid is verified. The thermal conductivities obtained experimentally were compared with three mathematical models, which yielded lower values than those measured. From rheological measurements and by means of the Peclet number defined in colloidal suspensions, values of thermal conductivity were also proposed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

    Estudio socio Jurídico y tratamiento jurisdiccional a menores infractores de la ley penal en la Provincia de San Román

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    La tesis expone los resultados de una investigación relacionada a las infracciones cometidas por menores y su tratamiento en el órgano Judicial de Juliaca (Provincia de San Román - Puno). En el ámbito de la investigación se ha constatado que los abogados opinan que las infracciones a la ley penal se han incrementado. Esta opinión es coincidente con las fuentes oficiales y otros organismos que consideran que las infracciones a la ley penal se vienen incrementando en los últimos años. Para el incremento a la infracción penal inciden factores de carácter social y cultural principalmente, cuya responsabilidad es tanto del entorno familiar, de la sociedad y del Estado. Los operadores del Derecho, en este caso los abogados, consideran mayoritariamente, en un 45 % que el tratamiento a menores infractores a la ley penal no es la más correcta. Asimismo, los abogados perciben en un 75 % que el Código del Niños y Adolescentes requiere ser actualizada en consideración a las nuevas circunstancias y situación que se vive respecto al incremento de la infracción penal y su tratamiento jurisdiccional. También, de las 15 sentencias analizadas sobre el tratamiento jurisdiccional por infracción a la ley penal 27 % fueron absueltos de la imputación cometida; el 73 % fueron sancionados con diversas formas que permite la norma pertinente. La mayor parte de infractores a la ley penal, fueron sancionados con medida socioeducativa de libertad asistida, esto es el 53 %. En cambio, el 27 % de los investigados fueron absueltos. Un 20 % fueron sancionados con internamiento al haberse comprobado como autores de la infracción penal cometida. Respecto al tipo de infracción penal, se tiene que la mayor parte de menores infractores están relacionados a infracciones contra el matrimonio sean hurtos o robos, esto representa el 60 %. En cambio, las infracciones relacionados a lesiones representa el 20 %, y lo preocupante es las infracciones contra la salud en la modalidad de tráfico ilícito de drogas (TID) que representa el 20 %. En ese sentido, se debe hacer prevaler en el derecho penal juvenil los principios de interés superior del niño u de protección integral, por lo que evita la imposición de una sanción, y cuando ella es inevitable, dispone la menor restricción de derechos posible tratado de no imponer una sanción privativa de libertad. Se debe ser cauteloso, evitando que en la práctica, lejos de suponer una disminución del control social, se llegue más bien a una ampliación de este, que desemboque a unas redes distintas, más amplias y sutiles. A ello se ha referido la criminología crítica al hablar de las sanciones alternativas La tesis culmina con conclusiones respecto a la temática tratada en la investigación y también se hace propuestas de solución a la misma.Tesi

    Clinkering and hydration study of non-active and active Belite-Alite-Ye'elimite (BAY) cements

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    The aim of AIM is to promote industry-driven, interdisciplinary research in material science and engineering in order to provide leading-edge, sustainable solutions to the challenges facing engineers in today’s changing society and environment. http://www.ucl.ac.uk/aim/conference-info/37ccsThe manufacturing process of ye'elimite rich cements emit about 15-37% less CO2 to the atmosphere than OPC. Cements that contain belite, ye’elimite and ferrite, known as BYF cements, are promising eco-friendly binders. However, belite, their main phase, shows a slow hydrating behaviour; therefore the corresponding mortars present lower mechanical strengths than OPC at early ages. To solve this problem, BYF clinkers can be activated by: i) forming alite jointly with belite and ye’elimite during clinkering, known as BAY clinkers. The alite and ye’elimite reaction with water should develop high mechanical strengths at early ages, besides, belite contributes to later curing times. ii) A second activation is based on the stabilisation of alpha forms of belite by dopants. The objective of this work is to obtain two types of BAY clinkers (standard and active BAY) using CaF2 as mineraliser and borax as dopant agent to stabilize alpha forms of belite phase. After that, anhydrite was added as sulphate source to obtain the corresponding cements. The hydration behaviour of these cements has been studied through rheological and x-ray diffraction measurements, the latter combined with Rietveld quantitative phase analysis. In addition, mechanical and dimensional properties of BAY mortars are also presented and discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

    Genotoxicidad en leucocitos por la quimioprofilaxis de sangre con Violeta de Genciana y su prevención con antioxidantes

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    El violeta de genciana (GV) se usa como aditivo en la sangre para eliminar el Trypanosoma cruzi en la quimioprofilaxis de la infección por enfermedad de Chagas vía transfusión sanguínea, cuando no es posible un control previo de laboratorio o bajo situaciones de emergencia. En estos estudios se encontraron efectos genotóxicos del GV empleando el ensayo Cometa, cuando el se lo agrega a la sangre bajo las condiciones empleadas para esterilizarla para transfusión. El efecto genotóxico fue aún más intenso si la sangre se mantiene con GV por 48 horas. Los resultados obtenidos con el ensayo Cometa sugieren la formación de bases hidroxiladas de ADN como resultado de un ataque de especies reactivas de oxígeno y apoyan la genotoxicidad del GV y su potencial carcinogénico ya informado previamente. Los efectos genotóxicos observados en el ensayo Cometa fueron parcialmente prevenidos por administración previa a la rata donante de la sangre de antioxidantes que ya tienen uso clínico seguro, como α-tocoferol; ácido lipoico o N-acetilcisteína. El ácido lipoico fue capaz también de reaccionar in vitro con GV. Los resultados sugieren un uso potencial de estos antioxidantes para prevenir los efectos secundarios no deseados del GV para el individuo recipiente de la sangre.Fil: Diaz Gomez, Maria Isabel. Universidad Nacional de San Martin. Instituto de Investigación e Ingeniería Ambiental; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigacion y Desarrollo Estrategicos para la Defensa; Argentina;Fil: Castro, Jose Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigacion y Desarrollo Estrategicos para la Defensa; Argentina; Universidad Nacional de San Martin. Instituto de Investigación e Ingeniería Ambiental; Argentina

    Advanced synchrotron studies of ye'elimite-based cement pastes

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    Synchrotron characterization techniques [1] are being used to study Portland-based cements and recently also CSA and related cements. A key property of these techniques is that they do not require sample preparation, so the microstructures of the pastes can be preserved. The classical application of synchrotron tools is powder diffraction used to determine the crystalline phase content evolution with hydration including the overall amorphous fraction. Furthermore, other most advanced techniques are being applied to ye'elimite-containing pastes such as i) Total Scattering Synchrotron Powder Diffraction (TS-SXPD), and ii) Ptychographic Synchrotron X-ray Computed Tomography (PSXCT). All these applications will be reviewed here. TS-SXPD data coupled with the Pair Distribution Function (PDF) analysis methodology [2] allows having a better insight about the nanocrystalline/amorphous atomic arrangements in the gels. It has been very recently shown that nanogibbsite with very small particles, 3nm, is the main constituent of ye'elimite-gypsum hydration paste [2]. Nanogibbsite particles being smaller than those originated from the hydration of monocalcium aluminate. In addition, PSXCT is a tomographic technique that profits from the partly coherent nature of the synchrotron beam to provide better (smaller) resolution, which can be lower than 100 nm. It also provides the mass densities if the chemical stoichiometries are known. This technique has been applied to ye'elimite hydration to determine the microstructure and chiefly the bulk densities of nanogibbsite [3]. The microstructure evolution at early age was also followed [4]. Figure 1 shows an example of a slide of the electron density tomogram for a ye'elimite paste at 8 days of hydration and the corresponding histogram for the full volume with all phases identified.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.This work has been supported by Spanish MINECO through BIA2014-57658-C2 and BIA2017-82391-R, which are co-funded by FEDER

    Plagas de la yuca, reconocimiento, vigilancia y manejo

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    Applications of synchrotron x-ray powder diffraction in hydrated cements: high-resolution and high-pressure studies

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    The main aim of this study is to apply synchrotron radiation techniques for the study of hydrated cement pastes. In particular, the tetracalcium aluminoferrite phase, C4AF in cement nomenclature, is the major iron-containing phase in Ordinary Portland Cement (OPC) and in iron rich belite calcium sulfoaluminate cements. In a first study, the hydration mechanism of pure tetracalcium aluminoferrite phase with water-to-solid ratio of 1.0 has been investigated by HR-SXRPD (high resolution synchrotron X-ray powder diffraction). C4AF in the presence of water hydrates to form mainly an iron-containing hydrogarnet-type (katoite) phase, C3A0.84F0.16H6, as single crystalline phase. Its crystal structure and stoichiometry were determined by the Rietveld method and the final disagreement factors were RWP=8.1% and RF=4.8% [1]. As the iron content in the product is lower than that in C4AF, it is assumed that part of the iron also goes to an amorphous iron rich gel, like the hydrated alumina-type gel, as hydration proceeds. Further results from the high-resolution study will be discussed. In a second study, the behavior of pure and iron-containing katoites (C3AH6 and C3A0.84F0.16H6) under pressure have been analyzed by SXRPD using a diamond anvil cell (DAC) and then their bulk moduli were determined. The role of the pressure transmitting medium (PTM) has also been studied. In this case, silicone oil as well as methanol/ethanol mixtures have been used as PTM. Some “new peaks” were detected in the pattern for C3A0.84F0.16H6 as pressure increases, when using ethanol/methanol as PTM. These new peaks were still present at ambient pressure after releasing the applied pressure. They may correspond to crystalline nordstrandite or doyleite from the crystallization of amorphous aluminium hydroxide. The results from the high-pressure study will also be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Acknowledgments: We thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beam time. We also thank the financial support by BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R (FEDER)

    Rheological study of the aggregation state of alumina nanofluids

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    Se adjunta una comunicación, aunque se han publicado tres comunicaciones más.The presence of alumina solid particles in aqueous phase induces a change in the viscosity of the suspension from Newtonian to non- Newtonian flow. Besides, the presence of solid particles is adequate for the use as a heat exchanger fluid. The effect of nanoparticle size on thermal properties of nanofluids is still today a question, which is far from being answered. In this respect, the results reported in the literature are contradictory [1], probably due to the formation of aggregates when particles are dispersed in the liquid phase. Regarding to the nanoparticle shape influence in thermal conductivity, cylinders and spheres have been considered as the more effective in heat transfer. Spherical nanoparticles of alumina, which is one of the most investigated nanofluid, dispersed in water were used in this study. TEM images showed a mean average diameter of 50 nm. However, DLS measurements showed monodispersed particles of 260 nm. Very recently [2], the relationship between shear rheology and aggregation state of suspensions has been reviewed. Mechanical and physical properties of the resultant materials depend on shape, size and size distribution, which are considered determining parameters in the formation of particle aggregates. The steady shear flow (figure 1) has shown that these clusters, when they are at rest, are formed by highly branched aggregates that erode when shear rate increases, until a suspension of individual particles is achieved. These results are in good agreement with the intrinsic viscosity obtained by Money and Krieger-Dougherty models. In both cases, these values are far from the 2.5 corresponding to spherical particles. The temperature effects were also taken into account.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
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