Search results for "Diffusion"

Diffusion, thermodiffusion, and thermal diffusion of polystyrene in solution

1962

The role of melt-fracture degassing in defusing explosive rhyolite eruptions at volcán Chaitén

2012

Explosive volcanic eruptions of silicic magma often evolve towards non-explosive emissions of lava. The mechanisms underlying this transition remain unclear, however, a widely cited idea holds that shear-induced magma fragmentation plays a critical role by fostering volatile loss from fragmentary magma and through ash-filled cracks termed tuffisite. We test this hypothesis by measuring H2O concentrations within glassy tuffisite from the 2008–2011 rhyolitic eruption at volcan Chaiten, Chile. We show that while H2O concentrations decrease next to tuffisite veins and at the margins of obsidian fragments, the depletions cannot account for the disparity in H2O between explosively and effusively …

Functional A Posteriori Error Estimate for a Nonsymmetric Stationary Diffusion Problem

2015

In this paper, a posteriori error estimates of functional type for a stationary diffusion problem with nonsymmetric coefficients are derived. The estimate is guaranteed and does not depend on any particular numerical method. An algorithm for the global minimization of the error estimate with respect to an auxiliary function over some finite dimensional subspace is presented. In numerical tests, global minimization is done over the subspace generated by Raviart-Thomas elements. The improvement of the error bound due to the p-refinement of these spaces is investigated.

Stochastic homogenization: Theory and numerics

2015

In this chapter, we pursue two related goals. First, we derive a theoretical stochastic homogenization result for the stochastic forward problem introduced in the first chapter. The key ingredient to obtain this result is the use of the Feynman-Kac formula for the complete electrode model. The proof is constructive in the sense that it yields a strategy to achieve our second goal, the numerical approximation of the effective conductivity. In contrast to periodic homogenization, which is well understood, numerical homogenization of random media still poses major practical challenges. In order to cope with these challenges, we propose a new numerical method inspired by a highly efficient stoc…

Physics, Techniques and Review of Neuroradiological Applications of Diffusion Kurtosis Imaging (DKI)

2016

In recent years many papers about diagnostic applications of diffusion tensor imaging (DTI) have been published. This is because DTI allows to evaluate in vivo and in a non-invasive way the process of diffusion of water molecules in biological tissues. However, the simplified description of the diffusion process assumed in DTI does not permit to completely map the complex underlying cellular components and structures, which hinder and restrict the diffusion of water molecules. These limitations can be partially overcome by means of diffusion kurtosis imaging (DKI). The aim of this paper is the description of the theory of DKI, a new topic of growing interest in radiology. DKI is a higher or…

Contours of diffusion of electronic data interchange in Finland

1998

Abstract Electronic Data Interchange (EDI)—despite its basic simplicity—forms a complex and inter-organizational innovation. This necessitates multiple points of observation and the use of multiple theoretical frames in accounting EDI diffusion processes. Based on field study data we deliver a multi-level account of EDI diffusion in Finland. The study clarifies how factors located on three levels of analysis can be applied to understand the unfolding of EDI adoption in different organizational constellations, here called diffusion patterns. We examine three families of diffusion patterns: local dyadic patterns; industry-wide networks; and national initiatives. Overall we discern five distin…

Semi-empirical simulations of F-center diffusion in KCl crystals

1997

Abstract The semi-empirical method and 224 atom quantum clusters were used for calculating the activation energy for diffusion of cation and anion vacancies and F-centers in KCl crystals. The relevant activation energies of 1.19 eV, 1.44 eV and 1.64 eV, respectively agree well with the experimental data.

Analysis of the Diffusion-Induced Stress Effect on the Oxidation in Finely Divided Vanadium Ferrites

1999

L'oxydation isotherme des cations fer(II), vanadium(II) et vanadium(III) pour les ferrites spinelles finement divises, lesquels sont oxydes en phases deficitaires en cations, a ete etudiee par thermogravimetrie. La faible temperature de cinetique d'oxydation de chaque cation oxydable a ete expliquee en considerant que l'oxydation genere des contraintes qui en modifie la cinetique ou les cations a la surface sont plus oxydes que dans le volume. Pour cela, il at ete considere que le coefficient de diffusion chimique est donne par la relation D = D 0 exp [-(E' a + pV a )/RT] ou D 0 represente le facteur pre-exponentiel, E' a l'energie d'activation, V a le volume d'activation et p la pression i…

Diffusion of small molecules in edible films: Effect of water and interactions between diffusant and biopolymer

2008

Mass transfers of various molecules in multiphasic food products lead to quality modification and thus require the use of edible films or coatings in-between the foodstuff. Consequently, it is important to assess the barrier properties and efficiencies of edible films as well as to determine the diffusivities of the migrants. Translational diffusion of a reference molecule such as fluorescein, determined by the fluorescence recovery after photobleaching (FRAP) method, displays a threshold of a critical water content inducing an increase of the molecular mobility, and demonstrates that multiple populations of a single molecular specie can be involved in different diffusion kinetics. Further …

Kinetics of dimer F2 type center annealing in MgF2 crystals

2018

Authors are greatly indebted to V. Lisitsyn, A. Ch. Lushchik and R.Vila for stimulating discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The calculations were performed using facilities of the Stuttgart Supercomputer Center (project DEFTD 12939).