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The flexure strength of tetragonal ZrO2(Er2O3) single-crystal monofilaments manufactured by the laser-heated floating zone method was measured as a function of the environment (air vs. water) and temperature (from 25 to 800ºC) at loading rates spanning three orders of magnitude to ascertain their susceptibility to the environmental conditions. These mechanical tests were completed with parallel tests on fully-annealed monofilaments (to relieve the thermal residual stresses induced during growth) and by detailed analysis of the fracture surfaces using scanning electron microscopy and micro-Raman spectroscopy. While environmental susceptibility of ZrO2(Y2O3) in previous investigations was always associated with the destabilization of the tetragonal phase, monoclinic phase was not detected on the fracture surfaces of the ZrO2(Er2O3) monofilaments and it was concluded that slow crack growth in this material at high temperature or immersed in water was due to stress-corrosion cracking.Partiendo de fibras monocristalinas de ZrO2(Er2O3) tetragonal fabricadas por un procedimiento de fusión zonal con láser (LHFZ), se efectuaron ensayos de flexión en los que se medía la resistencia mecánica en función de la temperatura (25 a 800 ºC) y el medio (aire o agua). Los ensayos fueron realizados a distintas velocidades con objeto de establecer la susceptibilidad a las condiciones ambientales. La susceptibilidad ambiental de la ZrO2(Y2O3) se había asociado siempre a la desestabilización de la fase tetragonal, pero el análisis de las superficies de fractura mediante microscopía electrónica de barrido y espectroscopia Raman confocal muestran una ausencia completa de fase monoclínica en las superficies de fractura de las fibras. Esta ausencia, junto con los ensayos complementarios sobre fibras sometidas a tratamientos de recocido para eliminar las tensiones residuales provenientes del procesado, indican que el crecimiento subcrítico de grieta se debe a un mecanismo de corrosión bajo tensión.

This investigation was aimed to analyse the mechanical behaviour of an eutectic ceramic Al2O3/YAG processed by directional solidification in a Bridgman furnace. Fracture toughness and young modulus were measured through three point bend tests from room temperature up to 1650 ºC. These tests were performed under stroke control using two different cross-head speeds to analyse the influence of strain rate on the fracture behaviour. The material was brittle up to 1400 ºC and plastic deformation was found at higher temperature. Plastic deformation was reduced, or even disappeared, when the strain rate was increased. Finally, the investigation was completed with the analysis of the deformation and fracture micromechanisms in the crack tip.Esta investigación se ha centrado en el estudio de un eutéctico cerámico Al2O3/YAG fabricado por solidificación direccional mediante el método de Bridgman. Se han realizado ensayos de tenacidad de fractura por flexión en tres puntos y se ha medido el módulo de elasticidad entre temperatura ambiente y 1650 ºC. Así mismo se han utilizado dos velocidades de ensayo para analizar la influencia de la velocidad de deformación en el comportamiento en fractura. El comportamiento ha sido frágil hasta 1400 ºC, temperatura a partir de la cual comienzan a aparecer fenómenos plásticos. Estos se reducen o desaparecen cuando se aumenta la velocidad de deformación del material. Finalmente, el estudio se ha completado con el análisis de los mecanismos de deformación y rotura en el frente de la grieta.

The development of cellular ceramics with a biological structure, like bones and wood, has been a matter of interest in recent years. A low density highly interconnected structure, perfected by evolution, rises as the principal advantage of these materials. In the case of biomimetic SiC (biomorphic SiC, or bioSiC), the fabrication process technique is quite simple: a piece of wood is pyrolysed and is infiltrated with molten silicon after, the final product is a composite Si/SiC, which replicates the wood anisotropic microstructure This work focus on the mechanical properties of bioSiC fabricated using eucalyptus wood as precursor (hard wood with a bimodal channel distribution). It has been studied the mechanical behavior of this bioSiC (compression strength, flexure strength, fracture toughness and elastic modulus) between 25 and 1350 oC. It is also discussed the relationship between mechanical behavior of the material and its microstructure.El desarrollo de materiales cerámicos con una estructura de tipo celular, similar a la del hueso o la madera, ha sido una cuestión que ha suscitado un gran interés en los últimos años. Su atractivo se debe al hecho de poseer una estructura porosa altamente interconectada de baja densidad, perfeccionada por la evolución. En el caso del SiC biomórfico (bio-SiC) el proceso de fabricación es sencillo: se piroliza una pieza de madera y a continuación se inyecta con silicio líquido, el material así obtenido es un compuesto Si/SiC en el que el SiC mimetiza la estructura de la madera original. En este trabajo se estudian las propiedades mecánicas del SiC biomórfico fabricado a partir de eucalipto (madera dura con una distribución bimodal de poros). Se ha estudiado el comportamiento mecánico del mismo (resistencia a compresión, resistencia a flexión, tenacidad de fractura y módulo de elasticidad) entre 25 y 1350 oC. Asimismo, se discute la relación entre el comportamiento mecánico del material y su microestructura.

The mechanical properties and the critical current were studied in three commercial multi-filamentary BSCCO 2223 tapes (formed by Bi2Sr2Ca2Cu3O10+x high-temperature ceramic superconductors embedded in a Ag-Mg alloy) subjected to monotonic and fatigue tension at 77 K in the longitudinal direction. It was found that transport properties were not comprised under monotonic tensions if the maximum tensile stress remained below the conventional 0.2% yield strength. This magnitude was reduced by 10% to 20% in the case of fatigue loading, and the service life of the tape was dictated by the mechanical fatigue life.Las propiedades mecánicas y la evolución de la corriente crítica durante una solicitación mecánica han sido evaluadas en tres cintas comerciales multifilamento formadas por una aleación Ag-Mg reforzada con fibras superconductoras cerámicas de alta temperatura crítica Bi2Sr2Ca2Cu3O10+x (denominadas cintas BSCCO 2223). Estas cintas fueron sometidas a una solicitación monótona creciente y a fatiga mecánica a 77 K a lo largo de la dirección longitudinal. Los resultados obtenidos revelan que las propiedades de transporte eléctrico no se ven afectadas bajo tensiones monótonas crecientes si la tensión máxima a tracción es inferior al límite elástico de la cinta definido a partir del 0.2% de deformación ingenieril. Sin embargo, la corriente crítica se reduce entre un 10% y 20% bajo una solicitación cíclica, lo que indica que la vida en servicio de estas cintas está condicionada por su comportamiento bajo fatiga mecánica.

The flexure strength of directionally-solidified Al2O3-ZrO2(Y2O3) and Al2O3-Y3Al5O12 eutectic ceramic composites processed by the laser-heating floating zone method was studied from 25ºC to 1427ºC. The effect of microstructure, residual stresses and temperature on the flexure strength and the associated fracture mechanisms was assessed for each material.Se ha medido la resistencia a flexión de los compuestos cerámicos eutécticos Al2O3-ZrO2 (Y2O3) y Al2O3-Y3Al5O12 procesados por la técnica de fusión zonal asistida por láser en el intervalo de temperaturas de 25ºC a 1427ºC. Se ha investigado el efecto de la microestructura, de las tensiones residuales y de la temperatura sobre la resistencia a flexión y los mecanismos de fractura asociados para cada material.

The mechanical properties at 77 K and at 300 K were determined in two polycristalline graphites with different microstructures and in a C/C composite. The flexure strength and the fracture toughness were evaluated and the micromechanic failure was studied in situ with a long distance microscope. The results obtained showed that the mechanical properties of these carbon materials are not affected by the cryogenic temperatures. The porosity is the main responsible of the mechanical failure in the graphites while in the composite, the matrix/yarn interface deflect the crack nucleated in the mattrix, presenting the best mechanical behavior.En este trabajo se han evaluado las propiedades mecánicas a 77 y a 300 K de dos grafitos policristalinos con microestructuras muy diferentes y de un compuesto C/C. Se realizaron ensayos de flexión en tres puntos y de tenacidad, y en éstos últimos se midió in situ la iniciación y la evolución del daño en el fondo de la entalla con un microscopio de larga distancia focal. Los resultados obtenidos muestran que las temperaturas criogénicas no afectan el comportamiento mecánico de los compuestos de carbono estudiados. Además, la porosidad presente en los grafitos es el mecanismo de rotura dominante mientras que en el material compuesto, la intercara débil entre matriz y haz de fibras detiene y desvía las grietas nucleadas en la matriz, presentando el mejor comportamiento mecánico.

The topic of this work is the theoretical study of a disc-shaped acoustic transducer made with a 1-3 piezoelectric composite material. This material consists of PZT ceramic rods embedded in a polymer matrix. A modeling of this ideal transversally periodic structure is proposed. It is based on a finite element approach derived from homogenization techniques mainly used for composite material studies. The analysis focuses on a representative unit cell with specific boundary conditions on the lateral surfaces taking accurately into account the periodicity of the structure. The first step proposed is the development of a three-dimensional Fortran code with complex variables, especially adapted for this problem. Using the principle of correspondence of Lee-Mandel, this technique allows the prediction of the damping properties of the transducer from the complex modulus of the constituents. Both the versatility of the method and the rigorous character of the model are pointed out through various boundary conditions and mixed loadings. An interesting result is that, despite the lossy polymer matrix, a 1-3 composite can advantageously replace a much heavier massive transducer, in terms of efficiency and loss factor.El objetivo de este trabajo es el estudio teórico de un transductor acústico con forma de disco construido con un composite piezoeléctrico 1-3. Este material consiste en barras cerámicas de PZT embebidas en una matriz polimérica. Se propone un modelo de su estructura periódica transversal ideal basándose en una aproximación mediante elementos finitos derivada de técnicas de homogeneización usadas principalmente para estudios de materiales compuestos. El análisis se enfoca a una celdilla unidad representativa con unas condiciones de contorno específicas sobre las superficies laterales, teniendo en cuenta adecuadamente la periodicidad de la estructura. El primer paso propuesto es el desarrollo de un código Fortran tridimensional con variables complejas, adaptado especialmente a este problema. Usando el principio de correspondencia de Lee- Mandel, esta técnica permite la predicción de las propiedades amortiguadas del transductor a partir de los módulos complejos de los constituyentes. Tanto la versatilidad del método como el carácter riguroso del modelo se ponen de manifiesto a través de varias condiciones de contorno y mezcla de cargas. Un resultado interesante es que, a pesar de la matriz polimérica, un composite 1-3 puede reemplazar ventajosamente a un transductor masivo mucho más pesado en términos de eficacia y factor de pérdidas.

The mechanical properties of Bi2Sr2CaCu2O8+δ superconductor fibres processed by laser-induced directional solidification at different growth rates were studied. Tensile and diametral compression (Brazilian test) tests were performed to analyse the longitudinal and transversal strength. The elastic modulus was determined using the flexural vibration resonance method. Flexure tests were also carried out to compare with the literature data. In addition, polished sections of the as-received fibres and the fracture surfaces of the broken samples were analysed in the scanning electron microscope. The fibres were highly anisotropic and the transverse fibre strength was very low due to the early failure by cleavage of the grains perpendicularly to the c axis. The degree of anisotropy and the longitudinal strength increased as the fibre growth rate decreased while the transverse strength followed the opposite trend. This behaviour was due to changes in the porosity and the alignment of the crystals along the fibre axis.En este trabajo se han estudiado las propiedades mecánicas de fibras superconductoras Bi2Sr2CaCu2O8+δ fabricadas por solidificación direccional inducida por láser y crecidas a distintas velocidades. Se realizaron ensayos de tracción directa e indirecta (ensayo brasileño para evaluar la resistencia a tracción en las direcciones longitudinal y transversal respecto a la de crecimiento. El módulo elástico de las fibras en la dirección longitudinal se obtuvo midiendo la frecuencia fundamental de resonancia en flexión y se realizaron ensayos de flexión para comparar con los resultados disponibles en la literatura. El trabajo se completa con el estudio de las secciones longitudinales y transversales del material sin ensayar y el análisis fractográfico de las probetas rotas. Las fibras resultaron altamente anisótropas siendo su resistencia en la dirección transversal muy baja, debido a la fractura por clivaje de los planos perpendiculares al eje c. El grado de anisotropía y la resistencia a tracción en la dirección longitudinal aumentaron al disminuir la velocidad de crecimiento mientras que la resistencia mecánica en la dirección transversal disminuyó. Este comportamiento se debió a diferencias en la distribución de la porosidad y a la alineación de los granos.

Introduction: The Internet is a dynamic environment which is continuously being updated. Search engines have been, currently are and in all probability will continue to be the most popular systems in this information cosmos. Method: In this work, special attention has been paid to the series of changes made to search engines up to this point, which are currently in common usage; we also consider the objectives set for an immediate future in which, undoubtedly, searches will be increasingly attuned to user needs. Analysis and Results: Since they originated, these information recovery systems have seen developments in their search algorithms and interfaces for presentation of results whilst their users' information seeking behaviour has changed substantially, making it possible to distinguish up to three generations (the latest of these is still being developed). Changes in users' habits and routines when interacting with these systems show a road map which is increasingly concerned with improving the searching experience. Conclusions: Therefore, we are dealing not only with technological development, but also with an evolving process with regard to the use of information, in turn leading to a new Internet search paradigm. (Contains 1 table and 9 figures.)

Purpose: To propose a minimum specification dataset to characterize liquid ocular endotamponades (OEs), namely silicone oil (SO), heavy SO (HSO), perfluorodecalin (PFD), and perfluoro-octane (PFO), in terms of physicochemical properties, purity and available evidence of safety, in line with ISO16672:2020. Methods: An evidence-based consensus using the expert panel technique was conducted. Two facilitators led a committee of 11 European experts. Facilitators prepared a dataset for each compound including the list of specifications relevant for the safety, identified by the group members on the basis of expertise and a comprehensive literature review. Each item was ranked by each member using a 9-point scale from 1 "absolutely to not include" to 9 "absolutely to include" in two rounds followed by discussion. Only items reaching consensus (score ≥ 7 from ≥ 75% of members) were included in the final datasets. Results: For all OEs, consensus was reached to include manufacturer, density, refractive index, chemical composition, dynamic viscosity, interfacial and surface tension, endotoxins, in vitro cytotoxicity assessment, and any evidence from ex vivo and/or in vivo tests for safety assessment. Additional specifications were added for SO (molecular weight distribution, content of oligosiloxanes with MW ≤ 1000 g/mol, spectral transmittance) and PFD/PFO (% of pure PFD/PFO in the final product, vapor pressure, chemical analyses performed for safety assessment). Conclusion: The proposed evidence-based minimum specification datasets for SO, HSO, PFD, and PFO have the potential to provide surgeons and health service purchasers with an easily available overview of the most relevant information for the safety assessment of OEs. [ABSTRACT FROM AUTHOR]

State-of-the-art eye trackers provide valuable information for diagnosing reading problems by measuring and interpreting people's gaze paths as they read through text. Abnormal conditions such as visual field defects, however, can seriously confound most of today's existing methods for interpreting reading gaze patterns. Our objective was to research how visual field defects impact reading gaze path patterns, so the effects of such neurological pathologies can be explicitly incorporated into more comprehensive reading diagnosis methodologies. A cross-sectional, non-randomized, pilot clinical study including 45 patients with various neurologic disorders and 30 normal controls was designed. Participants underwent ophthalmologic/neuropsychologic and eye-tracker examinations using two reading tests of words and numbers. The results showed that the use of the eye tracker showed that patients with brain damage and an altered visual field require more time to complete a reading-text test by fixating a greater number of times (p < 0.001); with longer fixations (p = 0.03); and a greater number of saccades in these patients (p = 0.04). Our study showed objective differences in eye movement characteristics in patients with neurological diseases and an altered visual field who complained of reading difficulties. These findings should be considered as a bias factor and deserve further investigation. [ABSTRACT FROM AUTHOR]