Some Initial Thoughts

Before we go into some detail for the theoretical background for expert systems, we should take some time to get familiar with some of the concepts of dealing with information in a computer. I decided to use one of the newer developments in chemistry research to focus on a problem that is essential for many aspects in computational chemistry the topic of molecular descriptors. Molecular descriptors describe a molecule in a way that is appropriate for processing in a computer program. Like the term suggests, a molecular descriptor describes certain features of a molecule. 

What good is it to relate an artificial and measured descriptor At this point, we have to think about the application of measured descriptors. Infrared spectra are usually used to confirm the structure of a compound If an infrared spectrum for an unknown compound is measured and we find a similar spectrum in a database, the probability is high that the measured unknown compound is identical to the database compound. Here is an important fact for this approach We do not need to know the details about infrared spectroscopy the simple fact that it is similar assumes the similarity of the unknown compound. This approach is typical for artificial 

Expert systems use this approach for problem solving by separating technical aspects clearly from the domain aspects. Consequently, the domain experts are seldom development experts who create an expert system. However, developers of expert systems are able to create a reusable shell that allows domain experts to enter knowledge in an understandable fashion. 

like descriptors, are seldom directly interpretable. Looking again at an infrared spectrum, it might be possible to assign each peak to a certain movement in a molecule however, these facts do not really help to solve the problem of structure elucidation. Chemists know that a complete structure cannot be derived from an infrared spectrum. This is simply because thermal movement and constitution — even they are related to some extent — are two different things. But there is an interesting detail Nearly all structures produce their unique spectrum. Should an infrared spectrum be specific enough to provide all information to derive a structure  

Structure elucidation with an infrared spectrum cannot be performed simply by interpreting the individual peaks one after another. As a result, we are in need of some mechanism that is able to find patterns in infrared spectra or to use the entire spectrum as pattern, like it is done in the conventional infrared software to identify a compound. If we are not able to obtain a structure from the details, we can either try to use patterns or even the entire data set for comparison. This is how infrared spectra are typically used as pattern for structure elucidation. 

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This document has set down some initial thoughts from a regulatory point of view about the issues involved in allowing the design of a clinical trial to be adapted as the trial progresses. Modification of the sample size based on blinded data and stopping for overwhelming efficacy or futility are forms of adaptation that are already well accepted, but this Reflection Paper considers other possibilities that are more controversial. 

R. J. Pentreath, A System for Radiological Protection of the Environment Some Initial Thoughts and Ideas, J. Radiol. Prot. 19, 117 (1999)... 

Tetrachoroethylene (perchloroethylene, PCE) is the only chlorinated ethene that resists aerobic biodegradation. This compound can be dechlorinated to less- or nonchlorinated ethenes only under anaerobic conditions. This process, known as reductive dehalogenation, was initially thought to be a co-metabolic activity. Recently, however, it was shown that some bacteria species can use PCE as terminal electron acceptor in their basic metabolism i.e., they couple their growth with the reductive dechlorination of PCE.35 Reductive dehalogenation is a promising method for the remediation of PCE-contaminated sites, provided that the process is well controlled to prevent the buildup of even more toxic intermediates, such as the vinyl chloride, a proven carcinogen. 

In addition to the CN-anomalies, similar (anti-)correlations for Na and O, and Mg and A1 have been known for some time to occur in globular cluster giants, though not in field stars (see [21] for a compilation). Initially thought to be... 

Many years ago, after having developed some initial confidence making my very first 70W Flyback in Bombay, I thought to myself, why can t I go all the way Why can t I, say, make a 600 W Flyback It is like if you don t know about the existence of gravity, you can fly. So I did make that 600W Flyback, and also later wondered what the fuss was all about. 

Stable isotope analysis of Earth, Moon, and meteorite samples provides important information concerning the origin of the solar system. 8lsO values of terrestrial and lunar materials support the old idea that earth and moon are closely related. On the other hand three isotope plots for oxygen fractionation in certain meteoric inclusions are anomalous. They show unexpected isotope fractionations which are approximately mass independent. This observation, difficult to understand and initially thought to have important cosmological implications, has been resolved in a series of careful experimental and theoretical studies of isotope fractionation in unimolecular kinetic processes. This important geochemical problem is treated in some detail in Chapter 14. 

Some recent results indicate, however, that the rate of reaction (8.179) may be much greater than initially thought. If so, the depletion of CIO by this route could reduce the effectiveness of this catalytic cycle in reducing the 03 concentration in the stratosphere. 

The mechanism of the electroreductive cyclization reaction has been studied in some detail [22], The initial thought was that it occurred via the cyclization of the radical anion derived, for example, from 25 in the first reduction step. A moment s reflection, however, reveals that there are many more mechanistically viable pathways, especially when one realizes that the transformation involves five steps - two electron transfers (symbolized below by e and d , the latter corresponding to a homogeneous process), two protonations ( p ), and cyclization ( c ). In principle, these could occur in any order, and with any one of the steps being rate-determining. 

At Coventry University [20] we have obtained similar results to Tu under conventional (silent) conditions. Our initial thoughts were that if the effect of the tail off was either a consequence of mass transfer to the electrode, or a consequence of some problem with the diffusion layer, then ultrasound might be expected to have an effect and thus improve the plating rate. Investigations in the presence of ultrasound and at various pH values did not significantly affect the plating characteristics i. e. the plateau effect still remained. However, the overall efficiency in the presence of ultrasound was affected (Fig. 6.10). 

CA 46, 2266(1952 (Initiation of deton in gases. Published theories of deton are reviewed, and some new thoughts on the structure of deton waves and the mechanism of initiation of deton by flames are presented) 14a) F.R. Bowden A.D. Yoffe, "Initiation and Growth of Explosion in Liquids and Solids , Cambridge-UnivPress, England (1952) 14b) J.A. Fay... 

Note, the field of biotechnology continues to evolve and grow at a breath-taking rate, therefore some of tire entries in lids table will liave resulted hi different outcomes Ilian initially thought... 

The structure of the CH2CHC1—CO copolymer has been the subject of some controversy. The CO units were initially thought to be present exclusively in the backbone of the copolymer 20-57). However, Ratti et al. proposed that these polymers contain the —CH2CH(COCl) group, formed by the following rearrangement, Eq. (11), as the repeating unit 21,22). More recent experimental... 

It was initially thought that chain folding in polymers like polyethylene would take place in some sort of regular, ordered fashion, as observed in certain cyclic paraffins (Figure 8-55), with some specific sequence... 

Space does not permit any attempt to be comprehensive in a volume of reasonable size. I have tried, instead, to focus on those elements of polymer science and technology that are somewhat different from the lines of thought in regular chemistry and chemical engineering and in which a student may need some initial help. Few of the ideas dealt with in this text are difficult, but some involve a menial changing of gears to accommodate the differences between macro- and micro-molecules. If this text serves it purpose, it will piepare the reader to learn further from more specialized books and from the research and technological literature. 

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