Dispersal rate

Fumes and vapors discharged to the environment via a chimney form a plume, which is approximately cone shaped. Mathematical modeling of dispersal rates is possible. The Gaussian dispersion model is commonly used to calculate the concentration of pollutants at coordinate positions X, Y and Z. (The coordinates are measured from the plume centerline.) The equation used is ... 

If one pound of trifluralin containing 1 ppm NDPA were applied to, and left on, the surface of a one-acre field, 400 pg NDPA could conceivably enter the atmosphere over a several hour period. To calculate how much of that could be inhaled by a single person would require, among other things, a knowledge of dispersion rates, but without them it is apparent that some very small numbers would be encountered. We must resist the temptation, however, to casually equate small numbers with negligible risk without solid justification. 

Diffusion. Hydrogen diffuses through air much more rapidly than other gaseous fuels. With a diffusion coefficient in air of. 61 cm2/s, the rapid dispersion rate of hydrogen is its greatest safety asset. 

CHROMDIFF - Dispersion Rate Model for Chromatography Columns System... 

The first term of Eq. (8.9), identical to that given in Eqs. (8.7), describes turbulent diffusion very close to the source. Particle paths remain straight lines as long as the Lagrangian velocity remains equal to that at the time of departure from the source (Tennekes, 1979). The second term in Eq. (8.9) shows that the dispersion rate slows down relative to the initial stage of turbulent diffusion. This term reflects the fact that Lagrangian velocities gradually lose their correlation as the time interval increases. 

Studies on the kinetics of carbon black dispersion in various rubbers have been reported using a Brabender mixer fitted with cam-type rotors [110]. Dispersion rating, determined by visual inspection of photomicrographs, was found to depend strongly on mixing time. For an SBR emulsion, it was observed that there was an initial delay period where the carbon black agglomerates were thought to be fractured and incorporated into the rubber. Subsequently, the process of dispersion continued for a considerable time thereafter. 

The ( non-dispersed ) rate of fluorescence, Fm(t)> from the entire wavepacket is given [10, 11] as a coherent (double) sum of amplitudes from the excited states comprising the wavepacket, summed over all the possible final states. It can be expressed, in matrix notation, by treating s, s as a single index k, as... 

The movement of biological stressors have been described as diffusion and/or jump-dispersal processes. Diffusion involves a gradual spread from the site of introduction and is a function primarily of reproductive rates and motility. Jump-dispersal involves erratic spreads over periods of time, usually by means of a vector. The gypsy moth and zebra mussel have spread this way the gypsy moth via egg masses on vehicles and the zebra mussel via boat ballast water. Biological stressors can use both diffusion and jump-dispersal strategies, which makes it difficult to predict dispersal rates. An additional complication is that biological stressors are influenced by their own survival and reproduction. 

The addition of a very small amount of styrene-isoprene-styrene (SIS) triblock compatibilizer, introduced as a compounded pellet with PS 685, suppresses the shear flow-induced coalescence appreciably, as seen by comparing Fig. 11.35 with Fig. 11.37. On the other hand, there is no effect of this very small amount of SIS on the dispersion rate. 

Fig. 11.35 Dispersion rate of Blend 2 obtained through carcass analysis TSMEE at 180°C and 120 rpm. [Reprinted with permission from Proceedings of the Tenth Semi-annual Meeting of the Polymer Mixing Study, Polymer Processing Institute, Hoboken, NJ (1995).]...

Figure 4.13 Dispersion rate of carbon black agglomerates in a PE melt depending on the shear stress and stress duration (trials with a single screw extruder) [17]...

Hydrogen-deuterium equilibration took place at around 473 K with Au/Si02, Au/MgO and A11/AI2O3 with particle sizes between 6 and 9nm rate constants and activation energies (75-116 kJ mol-1) were independent of dispersion. Rates were slower with larger particles (>16.5 nm) and the... 

Instantaneous point source and instantaneous sources of various simple geometries Advection, dispersion, rate-limited sorption [58]... 

At the second and third stages, the processes involving plastic deformation of particles are developed. The smaller is particle size, the more efficient are these processes. Dispersion process is overlapped by the formation of secondary particles, while the rate of the latter process is comparable with dispersing rate thus, the surface area remains constant. Chemical reactions take place inside secondary aggregates at the contacts between particles. At the third stage, the crystallization of the products from the solid phase may occur, as well as its repeated amorphization, till some stationary state between these two is achieved. 

The distinction between primary and secondary pollutants is conceptually useful, because primary and secondary species usually show distinctly different patterns of diurnal and seasonal variation in polluted regions of the atmosphere. The ambient concentrations of primary species are controlled largely by proximity to emission sources and rates of dispersion. The highest concentrations of these species tend to occur at nighttime or early morning and in winter in northerly locations, because atmospheric dispersion rates are slowest at these times. By contrast, high concentrations of... 

As previously mentioned, aluminum oxide is used as our primary collector, but other media have been used for special situations. For example, when the Hanford reactors were operating, quantities of hexa-valent Cr were discharged to the Columbia River and subsequently to the ocean, and we were interested in studying the dispersion rate of the Columbia River plume. Alumina did not collect the dichromate ion eflBciently. By using alumina saturated with stannous chloride, the chromium was reduced oa contact to the trivalent state, and this was very eflBciently retained on the bed. We also found that by saturating alumina with barium sulfate, we could collect radium isotopes, presumably by a replacement reaction with the barium on the matrix. For... 

Metapopulation models have been used to examine the dynamics of populations resulting from pesticide application. Sherratt and Jepson (1993) have investigated the impacts of pesticides to invertebrates using single-species and a predator-prey metapopulation models. In the case of the polyphagous predator, persistence of the population in the landscape is enhanced if only a few fields are sprayed, the application rate of the pesticide is low, or the intrinsic toxicity of the pesticide is low. There also appears to be an optimal dispersal rate that maximizes the likelihood of persistence of the predator in a sprayed field. Importantly, there are also patterns of pesticide application that would cause the prey insect population to reach higher densities than would occur otherwise. Dispersal rates of the predator and the prey are important factors determining the prey population densities. The importance of dispersal in the determination of the persistence of a population in a contaminated landscape was discovered in a subsequent study. 

Catalyst Metal dispersion (%) Rate of equilibration (atO.S. m metal)... 

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