Control phenomena

It is possible to conclude from the preceding that the study of the laws governing thermal explosions will increase understanding of the phenomena controlling the spontaneous ignition of combustible mixtures and forced ignition in general. 

The important impact of these experimental insights for molecular modeling is that the development of structure versus property relations of PEMs does not require multiscale approaches going all the way to the macroscopic scale. Rather, the main job is done if one arrives at the scale of several 10s of nanometers. Notably, operation at low hydration emphasizes even more the importance of (sub)nanoscale phenomena controlled by explicit interactions in the polymer-water-proton system. 

A high Damkohler number means that the global rate is controlled by mass transfer phenomena. So, the process rate can be rewritten in terms of the Damkohler number and the external effectiveness factor for each reaction order can be deduced, as shown in Table 5.5. In Figure 5.3, the external effectiveness factor versus the Damkohler number is depicted for various reaction orders. It is clear that the higher the reaction order, the more obvious the external mass transfer limitation. For Damkohler numbers higher than 0.10, external mass transfer phenomena control the global rate. In the case of n = 1, the external effec-... 

Is this experimental data set a good test of the chemical reaction mechanism What phenomena control the shape of the silane density profile (and the absolute number densities) Comment on the agreement between measured and calculated temperature profiles (keep in mind that the agreement at zero height is exact as a boundary condition of the calculation. How might such temperature (and flow) discrepancies affect chemistry studies (in cases where chemistry is important) ... 

This assumption is based on three relevant indications. First, this wave results in a limiting-current. This means that steady-state transport phenomena control the rate of this reaction, which is not compatible with a possible oxidation of metallic copper to Cu(I) or Cu(II). If the latter were to be valid, a peak-shaped response should have been obtained because of the limited available amount of metallic copper (initially deposited by reduction of Cu(II) or Cu(I) in the reduction wave). In addition, the second voltammetric oxidation wave in the backward scan direction is actually compatible with such a dissolution reaction. 

As noted above, as the size difference between the solvent and solute become progressively smaller, viscous flow rapidly becomes less important, and molecular interactions become dominant factors. In this limit, molecular solution (or sorption) and diffusion phenomena control the relative transport rates of the solute and solvent. This transition region is an area of ongoing discussion regarding what is a pore and what is not a pore ... 

The advent of fs pulse lasers recently opened new perspectives for asymmetric photochemistry. The elaboration of this field still is in the theoretical realm. Pulse sequence [125,126] and coherence [127] scenarios are set up for chiral molecular products from achiral precursors. If, for example, phosphinothiotic acid H2PO(SH) molecules are preoriented, which can be effected by laser action, and a special sequence of cpl pulses is used, then the theoretical prediction is that the l enantiomer is transformed to the r enantiomer, but the reverse process is suppressed and vice versa for a different pulse sequence [125]. Chapter 2 of this book is dedicated to these coherent phenomena controlling asymmetric photoreactions. 

In view of the great importance of chemical reactions in solution, it is not surprising that basic aspects (structure, energetics, and dynamics) of elementary solvation processes continue to motivate both experimental and theoretical investigations. Thus, there is growing interest in the dynamical participation of the solvent in the events following a sudden redistribution of the charges of a solute molecule. These phenomena control photoionization in both pure liquids and solutions, the solvation of electrons in polar liquids, the time-dependent fluorescence Stokes shift, and the contribution of the solvent polarization fluctuations to the rates of electron transfer in oxidation-reduction reactions in solution. 

The range of possible applications of multiscale simulations methods to electrochemical systems is extensive. Electrochemical phenomena control the existence and movement of charged species in the bulk, and across interfaces between ionic, electronic, semiconductor, photonic and dielectric materials. The existing technology base of the electrochemical field is massive and of long-standing [15, 16]. The pervasive occurrence of these phenomena in technological devices and processes, and in natural systems, includes ... 

The complexity of phenomena controlling the chemical composition of waters. In the soil layers, this composition would depend principally on biological and biochemical processes, in relation to the activity of organisms but at the level of phreatic waters the chemical composition would rather be controlled by physicochemical conditions (solution-mineral equilibria). 

We have introduced the factor a to account for the degree of dissociation, but as pointed out quite eloquently by Pitzer and Brewer (1961) in their revision of the text by Lewis and Randall, the value of a varies with the method used to measure it a situation not uncommon in studies of complex phenomena controlled by molecular interactions. Therefore it is to a large extent up to the investigator whether to use stoichiometric or ionic properties. Stoichiometric properties may be used whether or not ionic association is important, and have the advantage of not requiring estimates of a. 

The long-term mechanical behaviour of argillites impacts the reversibility and the performance of the repository through the following phenomena controlled by i) the evolution of the damaged zone, ii) the evolution of cracks (opening/closure) and of permeability, iii) interaction with the engineered barrier. 

Current theories to explain hysteresis of contact angles are primarily based on the concepts of surface roughness, surface heterogeneity, friction, and adsorption phenomena. Unintentional adsorption, or contamination—the result of inadequate experimental technique—is, however, the most frequent explanation. As all systems involving solids are subject to the reasons indicated above for hysteresis, we chose the system mercury-benzene-water, which should be affected only by adsorption phenomena, controllable under proper experimentation. An additional advantage is the fact that all interfacial tensions involved can be measured. 

Aside from the above interactions between air pollutants and solid surfaces, the RFGC was recently applied to describe and quantify the physical and chemical phenomena controlling the exchange of gas pollutants between the atmospheric and water environments and vice versa. 

The phenomena controlling gradient elution have often been misunderstood by many practicing chromatogra-phers, who often consider it as subject to more experimental problems, less reproducible, slower, and more difficult to transfer from one instrument (laboratory) to another than isocratic elution, the reason being more complex equipment, more tedious method development, and more difficult interpretation of results. That is why some workers try to avoid gradient elution however, by doing so they can miss undeniable benefits of this technique. 

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