Internal diffusivity

Diffuse-reflectance MIRS has found a number of applications for dealing with hard-to-handle solid samples, such as polymer films, fibers, or solid dosage forms. Reflectance MIR spectra are not identical to the corresponding absorption spectra, but sufficiently close in general appearance to provide the same level of information. Reflectance spectra can be used for both qualitative and quantitative analysis. Basically, reflection of radiation may be of four types specular, diffuse, internal, and attenuated total. 

B = 0.67. This reaction order corresponds to the shrink core reaction model. The reaction is under diffusion control, and the oxidizing agent reacts only on the surface because it has no time to diffuse internally, so the particle size becomes smaller as the conversion degree increases. In this case, the apparent kinetic constant will depend on the particle size and parameters derived fiem internal diffusion, in addition to the parameters mentioned before. 

Diffusion Data, Diffusion International Centre, Cleveland, OH. 

Sotelo, J.L., Benitez, RJ., Beltran-Heredia, J., and Rodriguez, C. (1994), Gas holdup and mass transfer coefficients in bubble columns. 1. Porous glass-plate diffusers, International Chemical Engineering, 34(1) 82-90. 

Vesala, T. 1993. On Droplet Evaporation in the Presence of a Condensing Substance The Effect of Internal Diffusion, International Journal of Heat Mass Transfer, vol. 36, no. 3, pp. 695-703. 

Bronze process External diffusion Internal diffusion... 

Freund, L. B. (1995a), Evolution of waviness on the surface of a strained elastic solid due to stress-driven diffusion. International Journal of Solids and Structures 32, 911-923. 

By changing the outer boundary condition, external resistance can be included in the diffusion model, though this makes the mathematical resolution of the model more difficult. In this case, two parameters must be identified (i) the effective diffusivity (internal resistance) and (ii) the mass transfer coefficient (external resistance). In order to reduce the number of possible solutions, the effective diffusivity identified by neglecting the external resistance can be used as the start value of diffusivity. 

Diffuse internal reflectance (DRIFT). DRIFT uses potassium bromide pellets for sample preparation and, therefore, has certain limitations in use with hygroscopic materials. 

At US examination, ankle ligaments with partial tears may appear swollen with focal or diffuse internal hypoechoic areas (Figs. 16.39,16.40) (Krappel et al. 1997 Peetrons et al. 2004). In complete ruptures. 

Physico-chemical processes within the cocoa beans encompass diffusion, internal destruction (due to acetic acid ingress), and enzymatic processes (Figure 16.5), which are influenced by several environmental factors, such as timing of initial entry of molecules and heat, pH (determined by duration, speed and intensity of acidification), temperature (speed of fermentation), and moisture (speed of fermentation and drying) (Schwan et al. 1995 Thompson et al. 2007,2013). Biochemical and physical changes within the bean cotyledons can be divided into two broad phases. The first... 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

Rotational diffusion coefficient, Dg, internal motion rate parameter, angle between the internal rotation axis and the internuclear axis... 

Isotropic rotational diffusion with one internal degree of freedom... 

Physical properties affecting catalyst perfoniiance include tlie surface area, pore volume and pore size distribution (section B1.26). These properties regulate tlie tradeoff between tlie rate of tlie catalytic reaction on tlie internal surface and tlie rate of transport (e.g., by diffusion) of tlie reactant molecules into tlie pores and tlie product molecules out of tlie pores tlie higher tlie internal area of tlie catalytic material per unit volume, tlie higher the rate of tlie reaction... 

The transport of particles in the plasma is diffusive or convective for the neutrals, whereas the charge carriers move under the influence of the external and internal electric and magnetic fields. The drift velocityv of the charged particles is proportional to the electric field E ... 

There are two types of stmctures one provides an internal pore system comprising interconnected cage-like voids the second provides a system of uniform channels which, in some instances, are one-dimensional and in others intersect with similar channels to produce two- or three-dimensional channel systems. The preferred type has two- or three-dimensional channel systems to provide rapid intracrystalline diffusion in adsorption and catalytic apphcations. 

Fig. 8. Combined flow reactor models (a) parallel flow reactors with longitudinal diffusion (diffusivities can differ), (b) internal recycle—cross-flow reactor (the recycle can be in either direction), comprising two countercurrent plug-flow reactors with intercormecting distributed flows, (c) plug-flow and weU-mixed reactors in series, and (d) 2ero-interniixing model, in which plug-flow reactors are parallel and a distribution of residence times dupHcates that...

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