Temporal aggregation

Chemistry may be a unifying force for studies of global environmental phenomena, since chemists have a common paradigm and may be able to facilitate the aggregation or disaggregation of data to the temporal and spatial resolutions needed for global studies more rapidly than other disciplines. The American Chemical Society might provide a forum for... 

In fluorescence correlation spectroscopy (FCS), the temporal fluctuations of the fluorescence intensity are recorded and analyzed in order to determine physical or chemical parameters such as translational diffusion coefficients, flow rates, chemical kinetic rate constants, rotational diffusion coefficients, molecular weights and aggregation. The principles of FCS for the determination of translational and rotational diffusion and chemical reactions were first described in the early 1970s. But it is only in the early 1990s that progress in instrumentation (confocal excitation, photon detection and correlation) generated renewed interest in FCS. 

A quantitative expression for the introduction of primary pollutants into the atmosphere is basic to any air quality model. Emission is most generally described as a geographic, temporal, and chemical distribution that requires a rather massive array of numbers. Some simple models need only the aggregated numbers found in ordinary tabulations... 

Schmitz et al (31) have proposed that the discrepancy between QLS and tracer diffusion measurements can be reconciled by considering the effects of small ions on the dynamics and scattering power of the polyelectrolyte. In this model, the slow mode arises from the formation of "temporal aggregates . These arise as the result of a balance between attractive fluctuating dipole forces coming from the sharing of small ions by several polyions, and repulsive electrostatic and Brownian diffusion forces. This concept is attractive, but needs to be formulated quantitatively before it can be adequately tested. 

Explicitly define the mechanisms and spatial, temporal, and biological dimensions of the system assessed to an appropriate, but not excessive, level of detail. Beware of inappropriate aggregation that may distort or hide important effects. 

The temporal evolution of spatial correlations of both similar and dissimilar particles for d = 1 is shown in Fig. 6.15 (a) and (b) for both the symmetric, Da = Dft, and asymmetric, Da = 0 cases. What is striking, first of all, is rapid growth of the non-Poisson density fluctuations of similar particles e.g., for Dt/r = 104 the probability density to find a pair of close (r ro) A (or B) particles, XA(ro,t), by a factor of 7 exceeds that for a random distribution. This property could be used as a good aggregation criterion in the study of reactions between actual defects in solids, e.g., in ionic crystals, where concentrations of monomer, dimer and tetramer F centres (1 to 3 electrons trapped by anion vacancies which are 1 to 3nn, respectively) could be easily measured by means of the optical absorption [22], Namely in this manner non-Poissonian clustering of F centres was observed in KC1 crystals X-irradiated for a very long time at 4 K [23],... 

The aim of this work is to estimate more accurately fugitive dust emissions due to wind erosion of exposed aggregate storage piles. The model constructed allows to quantify the temporal evolution in the mass flux when a bed of materials is exposed to a turbulent flow. It is based on the interaction between particles take-off and wall turbulence. The model allows as well to take into account materials having a wide size distribution, which is typical of materials such as coal or ore. Some experimental studies have shown a temporal decrease in the mass flux as the bed contains a wide range of particle sizes. This decrease, due to large particles, is predicted by the model. The rate depends on the flow velocity and the characteristics of the particles. 

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