Search results for "grain"
showing 10 items of 752 documents
Narrative Medicine to integrate patients’, caregivers’ and clinicians’ migraine experiences: the DRONE multicentre project
2021
Abstract Background Although migraine is widespread and disabling, stigmatisation and poor awareness of the condition still represent barriers to effective care; furthermore, research on migraine individual and social impact must be enhanced to unveil neglected issues, such as caregiving burden. The project investigated the migraine illness experience through Narrative Medicine (NM) to understand daily life, needs and personal resources of migraneurs, their caregivers and clinicians, and to provide insights for clinical practice. Methods The project involved 13 Italian headache centres and targeted migraneurs, their caregivers and migraine specialists at these centres. Written narratives, c…
Luminescence properties of Tb3+:Y3Al5O12 nanocrystallites prepared by the sol–gel method
2004
Tb 3+ :YAG nanocrystalline powders have been prepared by the sol-gel route. Structure and morphology of the obtained materials have been studied. The average grain sizes have been determined by X-ray powder diffraction measurements. Photo- and cathodoluminescence spectra of the Tb 3+ :Y 3 Al 5 O 12 powders have been measured. It has been found that the samples at low concentration demonstrate emission ascribable to the 5 D 3 →F J and 5 D 4 → 7 F J transitions. In particular, the concentration dependence of the luminescence spectra and lifetimes have been investigated as a function of the YAG grains sizes. It has been shown that the cross-relaxation responsible for the quenching of the 5 D 3…
Diffusion of Oxygen in Thermally Grown Oxide Scales
2009
High temperature reactivity of materials under oxidizing atmospheres is based on the formation of protective oxide scales. The protectiveness is obtained when the thermally grown oxide scales are dense, continuous and adherent to the metallic substrates (even during thermal shocks); as a matter of fact, the growth of the scale has to be governed by diffusion of species across the growing scale. The diffusing species are coming from the substrate (metallic ions) and/or from the oxidizing atmosphere (oxygen ions). The understanding of growth mechanisms can be reached by making two stage oxidation experiments, using oxygen isotopes. The experiment consists in oxidizing first the metallic subst…
Numerical Determination of Intrinsic Diffusion in Fe-Cr-Al Systems
2010
The intrinsic diffusion coefficients in diffusion aluminide coatings based on Fe-30Cr were determined at 1000oC. The diffusion fluxes were given by the Nernst Planck formulae and the Darken method for multicomponent systems was applied. This paper summarizes some numerical results to determine the composition dependent diffusivities in Fe-Cr-Al systems. The method presented in this study to obtain average intrinsic diffusion coefficients is as an alternative to the Dayananda method. Our method based on empirical parameters allowed us to predict the concentration profile during the interdiffusion process.
Luminescence of cerium doped YAG nanopowders
2007
Abstract Cerium doped YAG nanopowders with grain size ∼ 20 nm have been synthesized by co-precipitation method. Time-resolved luminescence characteristics have been studied. The results obtained have been compared with the luminescence characteristics for well-studied YAG single crystals. In contrast to cerium doped YAG crystals, cerium doped nanocrystal does not reveal luminescence bands due to antisite defects under electron beam pulse and X-ray excitations at 80–300 K temperature range. It was detected that decay kinetic of Ce 3 + related emission in the nanocrystal can be approximated by two exponents with time constants ∼ 9 and ∼ 47 ns at 290 K. It is faster than single exponential dec…
Numerical Determination of Intrinsic Diffusion Coefficient of Aluminide Coatings on Metals
2009
This paper presents a numerical method to determine the composition dependent diffusivities and to predict the concentration profile during the interdiffusion process. The intrinsic diffusion coefficients in diffusion aluminide coatings (Fe-Al) were determined at 1000oC. The obtained diffusion coefficient for iron in Fe3Al or FeAl is in the range 10-10 to 10-9 cm2.s-1. The aluminum diffusion coefficient varies from 10-11 to 10-7 cm2.s-1 in the same phases.The present approach also permits to model the reactive diffusion in the Fe-Al systems.
Effects of Gamma Irradiation on the Kinetics of the Adsorption and Desorption of Hydrogen in Carbon Microfibres
2013
In this study, three types of carbon fibres were used, they were ex-polyacrylonitrile carbon fibres with high bulk modulus, ex-polyacrylonitrile fibres with high strength, and vapour grown carbon fibres. All the samples were subjected to a hydrogen adsorption process at room temperature in an over-pressured atmosphere of 25 bars. The adsorption process was monitored through electrical resistivity measurements. As conditioning of the fibres, a chemical activation by acid etching followed by ¿-ray irradiation with 60Co radioisotopes was performed. The surface energy was deter-mined by means of the sessile drop test. Both conditioning treatments are supplementary; the chemical activation works…
Disequilibrium melt distribution during static recrystallisation
2004
Melt migration and segregation, and the rheology of partially molten rocks in the upper mantle and lower crust, strongly depend on the grain-scale distribution of the melt. Current theory for monomineralic aggregates predicts a perfectly regular melt framework, but high-temperature experiments with rock-forming minerals + melt show considerable deviations from this predicted geometry. Disequilibrium features, such as fully wetted grain boundaries and large melt patches, have been described; these were mainly attributed to surface-energy anisotropy of the minerals. We present static analogue experiments with norcamphor + ethanol that allow continuous in situ observation of the evolving liqui…
Iron bioavailability in iron-fortified cereal foods: The contribution of in vitro studies
2015
Iron deficiency anemia is the most common nutritional deficiency in humans. Not all dietary ingested iron, heme or nonheme, will be available to absorption and negative imbalance between iron requirements and absorption leads to iron deficiency and/or anemia. The recommended iron values usually are based on the genetic and on diet iron-bioavailability, which can be considered as the principal factor that change among the cultures and influences the distinct levels of recommendation among countries. Dietary changes present practical limitations due to be difficult to change food habits. The iron food fortification is considered more cost effective and economically more attractive than iron s…
Scour on alluvial bed downstream of grade-control structures
2004
This paper describes an approach for predicting local scour downstream of grade control structures. The developed analysis applies the incomplete self-similarity (ISS) theory for deducing some physically based dimensionless groups controlling the geometrical pattern of the scour profile. The scour measurements available in the literature in conjunction with numerous unpublished data allow a multiregressive calibration of the ISS relationships. The experimental sample includes different bed grain-size distributions and scales of the erosive phenomenon. The results prove that the ratio between the upstream water head and the weir height is able to explain the measurements of scour depth carri…