Light diffusion technique

We can answer the first question by direct observation of the inner droplets using confocal microscopy. The dynamics of the inner droplets can be observed by a light diffusion technique suited to turbid media, diffusing wave spectroscopy (DWS). Both observations show that attractive interactions—either depletion or van der Waals interactions—occur between the droplets and the... 

Foam rheology has been a challenging area of research of interest for the yield behavior and stick-slip flow behavior (see the review by Kraynik [229]). Recent studies by Durian and co-workers combine simulations [230] and a dynamic light scattering technique suited to turbid systems [231], diffusing wave spectroscopy (DWS), to characterize coarsening and shear-induced rearrangements in foams. The dynamics follow stick-slip behavior similar to that found in earthquake faults and friction (see Section XU-2D). 

Particles of a size of less than 2 turn are of particular interest in Process Engineering because of their large specific surface and colloidal properties, as discussed in Section 5.2. The diffusive velocities of such particles are significant in comparison with their settling velocities. Provided that the particles scatter light, dynamic light scattering techniques, such as photon correlation spectroscopy (PCS), may be used to provide information about particle diffusion. 

Quasi elastic light scattering techniques allow to measure the diffusion coefficient D of the droplets, the variation of which with the... 

Estimate the volume of bubble-free slurry required to obtain a conversion of 30% for a hydrogen feed rate of 100 ft /min (at 60°F and 1 atm). By a light-transmission technique, Calderbank measured gas-liquid interfacial areas of 0.94 to 2.09 cm /cm for bubble sizes likely to be encountered in this system. Suppose for this illustration Mg = 1.0 cm-/cm of bubble-free slurry. The Henry s law constant for hydrogen in toluene at 50°C is 9.4 (g mole/cm )/(g moles/cm ), and its diffusivity is 1.1 x 10 " cm /sec. The density and viscosity of toluene at 50°C are 0.85 g/cm and 0.45 centi-poises, respectively. Equimolal feed rates of ethylene and hydrogen will be used. 

To measure the droplet size distribution of the primary emulsion (W/O in W/O/W or O/W in O/W/O) that has a micron range (with an average radius of 0.5-1.0 pm), a dynamic light-scattering technique (also referred to as photon correlation spectroscopy PCS) can be apphed. Details of this method are described in Chapter 19. Basically, the intensity fluctuation of scattered light by the droplets as they undergo Brownian diffusion is measured from this, the diffusion coefficient of the droplets can be determined, and in turn the radius can be obtained by using the Stokes-Einstein equation. 

The mechanism and kinetics of photoconductivity have been studied by high-intensity low-duration light pulse techniques (174, 176, 298, 348). The decay of the photocurrent in the bulk is a result of a diffusion-limited bimolecular recombination of electrons and holes with a recombination radius of approximately one molecular diameter (174)-... 

Prior to the development of light scattering techniques, diffusion coefficients were determined from optical studies of concentration gradients. The most widely used... 

These detection schemes are necessarily invasive. Non-invasive methods have been developed based on measuring the spatial distribution of light, diffusely reflected from the tissue surface, as illustrated in Figure 15. This can be analyzed to determine jj, and and thereby to calculate the light distributions e.g. the fluence-depth/radius curve using Equations (3) and (4) or (5) and (4), or computational models for any given source configuration. Specialized diffuse reflectance probes have been developed, both for accessible body surfaces and for endoscopic application. At present these techniques are not in common use for clinical PDT. 

Point-Contact Cell - A high efficiency silicon photovoltaic concentrator cell that employs light trapping techniques and point-diffused contacts on the rear surface for current collection. 

Figure 3.17 Estimates of the temperatures at which the systems become bicontinuous based on results from light-scattering and NMR self-diffusion techniques (a) the...

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