Apparent difficulty

In the above theory, the interfacial concentrations Coi and Cli are not measurable directly and are therefore of relatively little immediate use. In order to overcome this apparent difficulty, overall mass transfer rate equations are defined by analogy to the film equations. These are based on overall... 

Fig. 1.1. General mechanism of action of steroid hormones. Steroid hormones cross through the plasmatic membrane without apparent difficulty favored by gradient. Some, which can be considered prohormones, are metabolized and transformed into more active products. This is the case with testosterone, which becomes dihydrotestosterone (DHT) in the target tissues of androgens, through the 5-alfa-reductase enzyme. The hormone binds to the receptor, a soluble protein of the cellular cytosol that, in the absence of hormone, is found associated with other proteins (hsp90 and others) that maintain the receptor in an inactive state. The hormone-receptor bond causes the other proteins to separate and a homodimer to be formed. The homodimer is the activated form of the receptor since it is capable of recognizing the genes that depend on that steroid hormone as well as of activating its expression, which leads to the synthesis of specific proteins...

Spectra were examined. The results, however, indicated that the carbon-13 was incorporated only randomly in both compounds. In view of an apparent difficulty for large organic molecules to penetrate into the organism and reach particular biosynthetic sites in intact forms, we have tried the feeding of small basic metabolic units. 

The apparent difficulty of indexing can be overcome if single crystals of the desired phase exist and this brings to mind a characterization step that should never be omitted. Anytime a reaction product is obtained, it should be examined carefully under... 

The synthesis of type II branched-chain sugars should seem a more difficult task because it needs activation of a carbon atom on the sugar template and a control of the stereochemical course of the carbon-carbon bond formation. Probably because of this apparent difficulty several methods have been devised in the last decade, in particular, in the field of organo-metallic and free radical reactions. 

Despite these apparent difficulties, there are now a number of examples for photoinduced electron transfer reactions that are significantly catalyzed. It is the purpose of this chapter to present fundamental concepts and the application of catalysis of photoinduced electron transfer reactions. The photochemical redox reactions, which would otherwise be unlikely to occur, are made possible to proceed efficiently by the catalysis on the photoinduced electron transfer steps. First, the fundamental concepts of catalysis on photoinduced electron transfer are presented. Subsequently, the mechanistic viability is described by showing a number of examples of photochemical reactions that involve catalyzed electron transfer processes as the ratedetermining steps. 

The electronic structure of a solid metal or semiconductor is described by the band theory that considers the possible energy states of delocalized electrons in the crystal lattice. An apparent difficulty for the application of band theory to solid state catalysis is that the theory describes the situation in an infinitely extended lattice whereas the catalytic process is located on an external crystal surface where the lattice ends. In attempting to develop a correlation between catalytic surface processes and the bulk electronic properties of catalysts as described by the band theory, the approach taken in the following pages will be to assume a correlation between bulk and surface electronic properties. For example, it is assumed that lack of electrons in the bulk results in empty orbitals in the surface conversely, excess electrons in the bulk should result in occupied orbitals in the surface (7). This principle gains strong support from the consistency of the description thus achieved. In the following, the principle will be applied to supported catalysts. 

Despite the apparent difficulties, a number of qualitative relationships were developed to categorize Lewis acids. 

Despite the apparent difficulties in quantitatively reproducing a structured spectrum like that of O3 we must emphasize, however, that unstable periodic orbits are probably the only means of interpreting these struc-... 

Kekule valence structures all the combination of Kekule valence structures of interest. The same is also true for finding combinations of Kekule valence structures involved in HH-Clar structures. A better way to obtain the correct combinations of Kekule valence structures instead of construction of various superpositions is to first write down k-Clar structures (or HH-Clar structures) and then decompose them into underlying Kekule valence structures. The apparent difficulty that remains in such an approach, that cannot be avoided, is the case of benzenoids having a large number of Kekuld valence structures which results in large number of decomposition. 

The literature indicates that only rarely has the ultimate objective of a complete structure determination been achieved for working catalysts. The report presented here includes a discussion of the origin of the apparent difficulties and a summary of detailed practical procedures to approach the final target of the characterization. 

This apparent difficulty has led to an alternative hypothesis, that chloroplasts and mitochondria have evolved from episomes containing a limited amount of genes. The episomes were integrated with eukaryotic cells and organized the organelles through adaptation and selection over the course of evolution [6,7]. 

So many people use coffee and tea without apparent difficulty that it is obvious that people do not become physically dependent on caffeine. 

The mass action law for homogeneous reactions in ideal gases and ideal solutions was written in Section 14.2 by straightforward inspection of the balanced equation for the reaction under study. If one or more of the reactants or products was a solid or liquid in its pure state, the procedure was less obvious, because concentration has no meaning for a pure species. This apparent difficulty is resolved by... 

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