High-intensity diffusion

HID high-intensity diffusion HTS high-temperature superconductor... 

It has been demonstrated that samples of the same concentration but different particle sizes give different diffuse reflectance spectra [44]. For polystyrene spheres, the absorbance increases as the particle diameter decreases from 90 to 2 p,m. Particles with diameters 2-10 p-m give undistorted high-intensity diffuse reflectance spectra that may be used for quantitative analysis. 

The sizes and concentration of the free-volume cells in a polyimide film can be measured by PALS. The positrons injected into polymeric material combine with electrons to form positroniums. The lifetime (nanoseconds) of the trapped positronium in the film is related to the free-volume radius (few angstroms) and the free-volume fraction in the polyimide can be calculated.136 This technique allows a calculation of the dielectric constant in good agreement with the experimental value.137 An interesting correlation was found between the lifetime of the positronium and the diffusion coefficient of gas in polyimide.138,139 High permeabilities are associated with high intensities and long lifetime for positron annihilation. 

Convection mixers use a different principle for blending. These mixers have an impeller. This class includes ribbon blenders, orbiting screw blenders, vertical and horizontal high-intensity mixers, as well as diffusion blenders with an intensifier bar. Scale-up considerations are similar to those for the tumble blenders. 

In reality, of course, mixing cannot be perfectly instantaneous. In practice, CSTR reactors are designed to create high-intensity turbulence that enhances mixing. Also very low-pressure systems can often be considered as stirred reactors. At low pressure (e.g., below 1 Torr), the molecular-diffusion rate is very high owing to long mean-free paths. 

Figure 5.14 shows the toluene distribution of the solvent-diffused sample (5 min cured). The image contrast is based on the difference in swelling capability throughout the sample. More toluene is imbibed into the PBD-rich matrix and less solvent is imbibed into the ZDA-rich domains. Therefore, the ZDA-rich domain is shown as low intensity (blue) and PBD-rich region is shown as high intensity (red, yellow or green). The difference in toluene distribution results from the differences in solubility and crosslink density. 

Because of the potentially high intensities occuring in femtosecond pulses, free electrons are generated by MPI and avalanche mechanisms. Then it is necessary to account for the response of the optical field to the presence of a dilute plasma. Since the relevant times scales are so short, plasma diffusion and ion motion are neglected, and the free-electron density p is usually obtained as a solution to an equation of the following form [7,12,13]... 

Many factors are involved in this complex reaction. Secondary thermal reactions follow the primary photo process and these are subject to temperature effects. At high intensities the reaction may be so rapid that diffusion of materials through the cell wall becomes a limiting factor and the quantum efficiency of the proc-... 

Since the velocities of the dissolved macromolecules are far less than the velocity of light, the Doppler shift will be extremely small and thus the frequency shifts are very small. The high intensity of the laser source makes it possible, however, to measure weakly scattered light and to observe very small frequency shifts. Like conventional light scattering, DLS can be used successfully to determine the molecular weight, size and shape of macromolecules. Moreover, DLS is such a powerful tool that also the diffusion coefficient can be measured, and that in a more elegant manner than many other classical tools (Sun, 1994,2004). 

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