Search results for "Diffusion"
showing 10 items of 1615 documents
Controlling diffusion of 3He by buffer gases: a structural contrast agent in lung MRI.
2006
Purpose: To study the influence of admixing inert buffer gases to laser-polarized 3 He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. Materials and Methods: The diffusion coefficient of 3 He was altered by admixing buffer gases of various molecular weights ( 4 He, N2, and SF6). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laserpolarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. Results: Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted …
Diffusive Modeling of Aggradation and Degradation in Artificial Channels
2008
The unsteady flow and solid transport simulation problem in artificial channels is solved using a three-equation model, coupled with a local erosion law. The three equations are the water mass and momentum balance equations, as well as the total solid load balance equation. It is shown that even during severe hydrological events inertial terms can be neglected in the momentum equation without any substantial change in the solution sought. Empirical equilibrium formulas were used to estimate the solid load as a function of the flow variables. Local erosion, due to the scour generated at the jump between two channels connected at different bottom elevations, was estimated adapting a literatur…
The role of DWI sequences in preclinical investigations of the sacroiliac joints anomalies in patients with Crohn's disease. Our experience
2016
Learning objectives Background Findings and procedure details Conclusion Personal information References
The Diffusion of Crisis-Related Communication on Social Media: An Empirical Analysis of Facebook Reactions
2018
During a crisis, authorities need to effectively disseminate information. We address the problem of deciding how crisis-related information should be published on Facebook to reach as many people as possible. We examine three recent terrorist attacks in Berlin, London and Stockholm. Our specific focus lies with official Facebook pages by municipalities and emergency service agencies. We collected posts about the events, along with the number of shares, likes and emotional reactions to them. In a regression analysis, several variables were examined that capture decisions on which information to publish and how. Posts containing condolences were found to result in three times as many emotiona…
Do Foreign Direct Investment (FDI) and Trade Openness Explain the Disparity in ICT Diffusion between Asia-Pacific and the Islamic Middle Eastern Coun…
2010
This study investigates the impact of FDI and trade openness on ICT diffusion in the Asia-Pacific and Middle East regions from 1996-2005. The results indicate that while dissimilarities exist between the economies included in this study in terms of their level of socio-economic and political development, education and the growth of GDP have had a positive impact on ICT diffusion in both regions. However, while FDI has generally had a positive and significant impact on ICT diffusion in Asia-Pacific economies, its impact on Middle Eastern economies has been detrimental. The results of this study also show that trade-openness has had, in general, a positive and significant impact on ICT diffus…
Diffusion of theories and theoretical models in the Ibero‐American research on information behavior
2021
Ibero-American research on information behavior (IB) lacks the visibility typical of other parts of the world, and little is known about it in countries outside the area. The objective of this paper has therefore been to analyze the way in which Ibero-American research incorporates various theoretical references to empirical research on IB. The results point to the existence of different focuses of research in the past 10 years, in the sense of a reduced empirical approach and a moderate to minimal use of theories in the design of such research. Furthermore, the most cited theories and models of IB at an international level are those most widely applied in this geographical area, and the us…
Crystal structure, magnetic properties and esr studies of (4-apyH)4[CuIIBr4] [CuIBr2]2: a novel Cu(II)⧹Cu(I) system containing bromocuprate(I) chains…
1998
Abstract The synthesis, crystal structure, ESR spectra and magnetic properties are reported for the Cu(II)⧹Cu(I) compound (4-apyH)4[Cu3Br8] (4-apyH = C5H7N2 = 4-aminopyridinium). Single-crystals of the compound were grown by slow diffusion of n-hexane on an ethanolic solution of (4-apyH)2[CuBr4] · H2O. The crystal structure is made up of organic cations, isolated [CuIIBr4]2− anions and infinite [CuIBr2]nn− chains composed of edge-sharing CuIBr4 tetrahedra. N–H · · · Br hydrogen bond interactions between organic counter cations and inorganic anionic units are present and contribute to the cohesiveness of the crystal packing. Magnetic susceptibility measurements showed a good isolation of Cu(…
Diffusion of labeled macromolecules in molten polystyrenes studied by a holographic grating technique
1984
Diffusion de polystyrene, de differentes masses moleculaires marque a la fluoresceine. Influence de la temperature
High-speed solid state fluorination of Nb2O5 yields NbO2F and Nb3O7F with photocatalytic activity for oxygen evolution from water
2021
Solid state reactions are slow because the diffusion of atoms or ions through the reactant, intermediate and crystalline product phases is the rate-limiting step. This requires days or even weeks of high temperature treatment, and consumption of large amounts of energy. We employed spark-plasma sintering, an engineering technique that is used for high-speed consolidation of powders with a pulsed electric current passing through the sample to carry out the fluorination of niobium oxide in minute intervals. The approach saves time and large amounts of waste energy. Moreover, it allows the preparation of fluorinated niobium oxides on a gram scale using poly(tetrafluoroethylene) (®Teflon) scrap…
Electrochemical and Electronic Structure Investigations of the [S3N3]• Radical and Kinetic Modeling of the [S4N4]n/[S3N3]n (n = 0, −1) Interconversion
2009
Voltammetric studies of S4N4 employing both cyclic (CV) and rotating disk (RDE) methods in CH2Cl2 at a glassy carbon electrode reveal a one-electron reduction at −1.00 V (versus ferrocene/ferrocenium), which produces a second redox couple at −0.33 V, confirmed to be the electrochemically generated [S3N3]− by CV studies on its salts. Diffusion coefficients (CH2Cl2/0.4 M [nBu4N][PF6]) estimated by RDE methods: S4N4, 1.17 × 10−5 cm2 s−1; [S3N3]−, 4.00 × 10−6 cm2 s−1. Digital simulations of the CVs detected slow rates of electron transfer for both couples and allowed for a determination of rate constants for homogeneous chemical reaction steps subsequent to electron transfer. The common paramet…