Influence of the Medium

Creep rupture strength of plastic pipes depends on the acting medium influences can be of chemical or physical nature and both types of influence often act simultaneously [810]. 

The ratio of service live in water and in medium is called the chemical resistance factorfcR, see Section 2.5.4. 

Possible causes for changes in service life after exposure to various chemicals include chemical resistance, surface tension in the media, and the surface constitution [810]. 

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Solvent effects on radical polymerization have been reviewed by Coote and Davis,59 Coote et. Barton and Borsig,71 Gromov,72 and Kamachi" 1 A summary of kinetic data is also included in Beuennann and Buback s review.74 Most literature on solvent effects on the propagation step of radical polymerization deals with influences of the medium on rate of polymerization. 

Suppan P. (1990) Solvatochromic Shifts The Influence of the Medium on the Energy of Electronic States, /. Photochem. Photobiol. A50, 293-330. 

For the time being, qualitative or semi-quantitative analysis of the influence of the medium on the electronic factor value rest on the description given by the... 

Equation 6.15 is valid only for rigid, spherical ions. In addition, it originates from Equation 6.14, which is applicable only if the electric field at the ion is due to the applied electric field only, undisturbed by the effects of the other ions in solution. Consequently, Equation 6.15 ignores other forces originating in the counterion atmosphere, leaving the influence of the medium on the mobility... 

The kinetic theory of collisions, which has been so effective in developing the kinetics of vapor-phase reactions, has substantially influenced research on the processes of liquid-phase oxidation and in describing these processes. It has been thought that the lack of laws on which to base liquid-state theory (in contrast to the well-developed kinetic theory of gases) would in principle severely limit the development of a quantitative theory of liquid-phase reactions. At present the characteristics of the liquid state are carefully considered in discussing the mechanism of intermolecular reactions, influence of the medium on reactivity of compounds, etc. 

In interpreting the influence of the medium on chain configuration of the polymers, the medium must be specified as a three-component system polar monomer, polar solvent, nonpolar solvent. 

Owing to the influence of the medium, enzymes should feature different substrate specificities and selectivities than water. This would allow for tuning of these parameters under the control of the operator. 

Let us examine the structure of expression (16). The influence of the dielectric medium constant e0 affects the factor aroused from the long-range Coulomb s field of the donor and acceptor charges, (iexponential factor in g(rDA) is not yet examined. Note, the expression — (l/r )exp —differs from the Green s function of a free electron Go( D,r E) by the numeric factor l/2n only (see formula (6)). Therefore it will be considered that the influence of the medium on Green s function of a free electron does not interact with the donor and the acceptor. 

An impressive illustration of the influence of the medium on the photo-Fries reaction product distribution can be found in Sch. 5 where the products of photolysis of 1-naphthyl 2-methyl 2-phenyl propanoate in hexane solution and within NaY are compared. Remarkably, whereas in solution eight products are formed, within NaY zeolite a single product dominates the product mixture. Cations present within zeolites help to anchor the reactants, intermediates and products to the surfaces of the zeolite and... 

Among more recent investigations the experiments of Hammond, Medic and Hedges [69] deserve special attention. They explain the influence of the medium on orientation when nitrating 2,5-dichloro- and 2,5-dibromo-nitrobenzene. Substitution into all three free positions takes place and derivatives ortho-, meta- and... 

While the internal vibrational modes of molecules can display sharp spectral features, the vibrational spectra of modes of bulk matter are broad and relatively featureless. Nonetheless, Raman and infrared methods can be used to study the bulk, the intermolecular degrees of freedom of condensed matter systems. A great deal of information on bulk degrees of freedom has been extracted from electronic spectroscopy, particularly at low temperatures. Such experiments, however, rely on the influence of the medium on an electronic transition. Using ultrafast Raman techniques, including multidimensional methods, and emerging far-IR methods, it is possible to examine the bulk properties of matter directly. 

Through-space distance dependence 9 The influence of the medium 11 Electron transfer and electron transport 12 The superexchange mechanism 15... 

Figure 12 right illustrates the effect of IPA. The experiments were first performed in air, as a reference, up to a crack length ratio of about 0.45 then the alcohol was added by the sponge without interruption of the experiment. Under the influence of the medium, the crack propagation rates changed instantly. The highest increase of about two decades accompanied... 

Consideration of the dipolarity of the two activated complexes can explain the observed trend. If the reactants are pictured as lying in roughly parallel planes, the dipole moments for the exo orientation are seen to be nearly opposite in direction, whereas for the endo orientation they are parallel. Therefore, the net dipole moment for the endo transition state is greater than that for the exo. Thus, the solvation of the endo activated complex will be more pronounced as the polarity of the solvent increases. This leads to a lowering of the activation enthalpy and preferential formation of the endo adduct. The logarithm of the endojexo product ratio in various solvents has been used to define an empirical solvent polarity scale [124] [cf. Section 7.3). Analogous solvent-dependent endolexo product ratios have been obtained in [4 -1- 2]cycloadditions of cyclopentadiene to other acrylic acid derivatives [560]. Theoretical calculations on exoj endo structures for activated complexes of [4 + 2]cycloadditions have shown that the observed endo preference in polar solvents is due to the influence of the medium, and that secondary orbital interactions are not involved [808]. The solvent has the decisive influence on the exo/endo selectivity. 

A quantitative approach to the problem of the influence of the medium on the dissociation constants of acids, which eliminates the proton accepting tendency of the solvent, involves a comparison of the dissociation constants of a series of acids with the value for a reference acid. Consider the acid HA in the solvent S the dissociation constant is given by... 

In the absence of spectral information in the gas phase, it is common to compare calculated features of the vibrational spectrum to data measured in rare gas matrix, the premise being that the latter medium perturbs the H-bonded system as little as possible. The influence of the medium was considered via a self-consistent reaction-field formalism wherein inductive interactions between the polar system and the polarizable medium are incorporated into a model Hamiltonian ". The calculations made use of the 6-31G basis set at the SCF level. 

A comparison of the ff, values (Table XII) obtained by using CCI4 and acetone or DMSO as solvents illustrates the strong influence of the medium on the value of the inductive effect of substituted pyrimidinyl groups. The best agreement between the (t, values has been noted for solvents of the same type, such as acetone and DMSO (82MI1). 

Diffusion is the most fundamental mechanism of gas migration in that it requires only a partial pressure (concentration) gradient. The rate of diffusion of a gas is then determined by the medium in which diffusion takes place, its temperature and absolute pressure, and the diffusion coefficient of the gas. The diffusion coeffiecient is a function of molecular weight, the shape of molecules, and their intermolecular attraction. Every gas thus has a different diffusion coefficient. The influence of the medium in which gas diffusion occurs is related to the density of the medium gases diffuse less quickly through a solid than through another gas. The rate at which a gas diffuses in a specified medium is sometimes termed its diffusivity. 

The nature of media effects relates to the fact that, since the microscopic displacement field is the net field to which molecules of the medium are exposed, it corresponds to a fundamental electric field dynamically dressed by interaction with the surroundings. The quantized radiation is in consequence described in terms of dressed photons or polaritons. A full and rigorous theory of dressed optical interactions using noncovariant molecular quantum electrodynamics is now available [25-27], and its application to energy transfer processes has been delineated in detail [10]. In the present context its deployment leads to a modification of the quantum operators for the auxiliary fields d and h, which fully account for the influence of the medium—the fundamental fields of course remain unchanged. Expressions for the local displacement electric and the auxiliary magnetic field operators [27], correct for all microscopic interactions, are then as follows... 

Product concentration, yield, and productivity are among the most important process variables in determining conversion costs.The concentration of the product influences its recovery and refining costs. Raw material costs are affected by the yield. Productivity, or the rate of product formation per unit of process capacity, helps determine the amount of capital, labor, and indirect costs assignable to the product. The influence of the medium on the interplay of these three variables cannot be ignored. 

Monolayers of distearoyl lecithin at hydrocarbon/water interfaces undergo temperature and fatty acid chain length dependent phase separation. In addition to these variables, it is shown here that the area and surface pressure at which phase separation begins also depend upon the structure of the hydrocarbon solvent of the hydrocarbon oil/aqueous solution interfacial system. Although the two-dimensional heats of transition for these phase separations depend little on the structure of the hydrocarbon solvent, the work of compression required to bring the monomolecular film to the state at which phase separation begins depends markedly upon the hydrocarbon solvent. Clearly any model for the behavior of phospholipid monolayers at hydrocarbon/water interfaces must account not only for the structure of the phospholipid but also for the influence of the medium in which the phospholipid hydrocarbon chains are immersed. 

According to the accepted photo-physical concepts on the influence of the medium on emission spectra, the effects observed may be divided into general (non-specific) and specific ones.7 General effects result in changes in orientation polarizability of the emitter microenvironment whose value depends on dielectric constant and refractive index of the medium. Maximum spectral shift is observed for the emitters with maximum changes in dipole moments upon excitation and in the medium with... 

Fig. IX-31. Influence of the medium on the strength of potassium chloride polycrystals...

For the mechanism of halogenation of heterocycles and the influence of the medium (solvent, addition of acid to convert A-heterocycles into their conjugated acids, and addition of base for production of the anions from acidic heterocycles such as imidazole and pyrrole), as well as the influence of temperature a review by Eisch717 should be consulted. 

Thus, the influence of the medium DO concentration in the fermentation was investigated. Fermentations were carried out with DO concentration set points at 1.0, 4.0, and 6.0 mg/1. Those values correspond, respectively, to 14, 57, and 86% of the saturation concentration of oxygen that was equal to 7.0 mg/1 in the defined fermentation conditions. This value was calculated using an expression stated by Blanch and Clark [20] for the temperature and medium composition used in the experiments. The control system (with the PLC) actuated in the oxygenation device to raise the oxygenation rate (for example, raising the oxygen gas pressure) any time that the DO concentration in the medium got below the set point. 

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