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Showing 1 to 20 of 25 for “"Diffusion Coefficient (D)"”.
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Studies of Surface Diffusion
… different topics, all concerned with surface diffusion are considered. First, the relationship between the diffusion coefficient D and the jump rate (GAMMA) is examined. It is shown that in analogy to alloy diffusion, the diffusivity is given by
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Transient and steady state electrochemical studies of transport dynamics and equilibria in thin polymer films containing redox centers
… The goal was to intercompare the electron diffusion coefficient (D$\sb{\rm E}$) of the system obtained by transient and steady state electrochemical methods and to evaluate the effect of equilibrium changes in the film on the magnitude of these values. Chronocoulometry (CC), ac impedance …
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Channeling studies of the location of zinc in gallium-arsenide
The diffusion of zinc in GaAs is highly anomalous in that the diffusion coefficient (D) is proportional to the zinc concentration squared in marked contrast to Fick's law which predicts that D is concentration independent. D is also very sensitive to the ambient conditions during diffusion, …
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Dynamics and structures of linear and supercoiled DNAs
… various amounts of ethidium. The translational diffusion coefficient $(D\sb{0})$ and the plateau diffusion coefficient $(D\sb{plat})$ characterizing internal motions over short distances (225 A) are determined by dynamic light scattering. The torsion constant ($\alpha$) between base-pairs is …
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Oblique-incidence fiber-optic reflectometry for measuring absorption and scattering in turbid media
… measuring the absorption and reduced scattering coefficients, $\mu\sb{a}$ and $\mu\sb{s}\sp\prime ,$ of semi-infinite turbid media. Obliquely incident light produces a spatial distribution of diffuse reflectance that is not centered about the point of light entry. The shift in the center of …
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Profiling of Relaxation Time and Diffusivity Distributions with Low Field NMR
… for the determination of relaxation time or diffusion-relaxation time distributions as a function of sample height. One-dimensional T 2 and D-T 2 profiles can be determined with a low-field Maran Ultra spectrometer by implementing nuclear magnetic resonance imaging techniques. Frequency …
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Channeling studies of the location of zinc in GaAs
The diffusion of zinc in GaAs is highly anomalous in that the diffusion coefficient (D) is proportional to the zinc concentration squared in marked contrast to Fick's law which predicts that D is concentration independent. D is also very sensitive to the ambient conditions during diffusion, …
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Effect of pH on adsorption and desorption equilibria and kinetics of 2-nitrophenol and phenol onto two activated carbons.
… were described by the homogeneous surface diffusion model and it was not necessary to utilize separate terms for slow and rapid adsorption mechanisms. Also, it was found that the surface diffusion coefficient, D$\rm\sb{s},$ within the HSSD model was essentially the same at all pHs. …
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The influence of power ultrasound on leather processing
… has been attributed mainly to an increased diffusion coefficient (D) of dyestuff in the presence of ultrasound. It was found that sonication is more effective in the initial phases than in the late phases of the dyeing process. Application of ultrasound during the fatliquoring process or …
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Investigation of NMR properties of gel volume change with magnetic resonance imaging
… the relaxation behavior is categorized into five diffusion regimes. Two empirical models are proposed, one for the spin echo and the other the gradient echo sequence, to account for the relaxation dependence of such variables as sphere radius R, δω , and diffusion coefficient D in these regimes. …
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Modeling Diffusion-Controlled Emissions of Volatile Organic Compounds From Layered Building Materials
… the emission of VOCs from building materials. Diffusion has been shown to control the rate of mass transfer within certain types of building materials. The primary objective of this research is to develop a fundamental diffusion-based model for single and double layer building materials. The …
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Finite Element Analysis to Investigate Lipid Absorption in UHMWPE Under Mechanical Loading
… degradation pathways. One involves the diffusion of lipid species from synovial fluid into the UHMWPE matrix. Lipids diffuse particularly into amorphous regions and, by inter- acting with them, alter the chemical and mechanical structure over time. The combination of cyclic mechanical …
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Investigation into reliability and performance of an implantable closed-loop insulin delivery device
… fluorescein sodium was determined as a Fickian diffusion controlled release mechanism. The diffusion coefficient (D) for FITC-insulin in the non-polymerised dex2M-conA gel (NP gel) determined using mathematical models, QSS and TL slope methods was 1.05 ± 0.02 x 10-11 m2/s and in the cross-linked …
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Investigating the Electron Transport and Light Scattering Enhancement in Radial Core-Shell Metal-Metal Oxide Novel 3D Nanoarchitectures for Dye Sensitized Solar Cells
… a practical limit because of the low electron diffusion coefficient (D<sub>n</sub>) in this mesoporous film photoanode. This work focuses on the influence of the advanced core-shell nanoarchitecture geometry on electron transport and also on the influence of electron-ion interactions. In order …
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Application of MRI and low-field NMR in biopharmaceutical development
… of a protein sample was developed, called Diffusion-Relaxation water NMR (DRwNMR). This utilises the water proton signal, exploiting the change in transverse relaxation rate [R₂(¹H₂O)] and diffusion coefficient [D(¹H₂O)] to give this information. Importantly, the DRwNMR method overcomes the …
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Dynamics of nanoparticles in complex fluids.
… polymer solutions and binary mixture.</p> <p>The diffusion of gold nanoparticles in semidilute and entangled solutions of polystyrene (PS) in toluene were studied using fluctuation correlation spectroscopy (FCS). In our experiments, the particle radius (R ≈ 2.5 nm) was much smaller compared to the …
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Rapid assessment of the potential chloride resistance of structural concrete
… artificial sea water and evolution of chloride diffusion over the test period. The ageing factor of concrete mixes, which describes the development of diffusion coefficient (D) from the unsteady to steady-state determined from this research was compared with those reported in The Concrete …
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Ion and polymer transport in polymerized ionic liquids
… once normalized by Tg. To probe the polymer self-diffusion, fluorescent labels was copolymerized into these linear PILs and polymer diffusion coefficient (D) was measured by fluorescence recovery after photobleaching (FRAP). The experimental diffusion-MW scaling closely followed the expected D~N-1 …
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Development of the gel plating process for selective gold metallization
… be reaction rate controlled at short times and diffusion controlled at longer times. A reaction rate model and a diffusion model with a heterogeneous reaction were fit to plating rate data at 50 °C and 60 °C. The reaction rate model was used to determine the rate constant, k, for the cathodic …
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Modeling Diffusion-Controlled Emissions of Volatile Organic Compounds from Building Materials
… mechanisms governing emissions behaviors, diffusion appears to be one of the most significant. The primary objective of this research was to demonstrate that the VOC emissions source behavior of a diffusion-controlled homogenous building material could be predicted using a mechanistic …
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