Related physical structures

At the present time there exist no flux relations wich a completely sound cheoretical basis, capable of describing transport in porous media over the whole range of pressures or pore sizes. All involve empiricism to a greater or less degree, or are based on a physically unrealistic representation of the structure of the porous medium. Existing models fall into two main classes in the first the medium is modeled as a network of interconnected capillaries, while in the second it is represented by an assembly of stationary obstacles dispersed in the gas on a molecular scale. The first type of model is closely related to the physical structure of the medium, but its development is hampered by the lack of a solution to the problem of transport in a capillary whose diameter is comparable to mean free path lengths in the gas mixture. The second type of model is more tenuously related to the real medium but more tractable theoretically. 

The relation between the dusty gas model and the physical structure of a real porous medium is rather obscure. Since the dusty gas model does not even contain any explicit representation of the void fraction, it certainly cannot be adjusted to reflect features of the pore size distributions of different porous media. For example, porous catalysts often show a strongly bimodal pore size distribution, and their flux relations might be expected to reflect this, but the dusty gas model can respond only to changes in the... 

This section briefly reviews prediction of the native structure of a protein from its sequence of amino acid residues alone. These methods can be contrasted to the threading methods for fold assignment [Section II.A] [39-47,147], which detect remote relationships between sequences and folds of known structure, and to comparative modeling methods discussed in this review, which build a complete all-atom 3D model based on a related known structure. The methods for ab initio prediction include those that focus on the broad physical principles of the folding process [148-152] and the methods that focus on predicting the actual native structures of specific proteins [44,153,154,240]. The former frequently rely on extremely simplified generic models of proteins, generally do not aim to predict native structures of specific proteins, and are not reviewed here. 

Organic Relating to or derived from living matter that has organs or an organized physical structure. Organic chemistry is the study of carbon compounds. 

This book focuses on the relationships between the chemical structure and the related physical characteristics of plastics, which determine appropriate material selection, design, and processing of plastic parts. The book also contains an in-depth presentation of the structure-property relationships of a wide range of plastics, including thermoplastics, thermosets, elastomers, and blends. 

One of the oldest and most familiar quantitative relationships for relating the structure of substituted benzene derivatives to both equilibrium constants and rate constants is the "Hammett Equation." See Louis Hammett, Physical Organic Chemistry, 184199. 

The primary and secondary structures greatly influence possible processing scenarios. Here, the secondary structure is generally the same as the physical structure and the primary structure is generally the same as the chemical structure. The end properties and uses are governed by intrinsic properties that in turn are related to the primary and secondary structures—the chemical and physical structures. 

Recently two different disciplines, chemical structural elucidation and transmission electron microscopy, were utilized in the study of pectin, with particular emphasis on tobacco pectin. The goal was to help bridge the gap between knowledge of their chemical structures to understanding the complex physical structures revealed by microscopy. To provide background on chemical structure, a study established that tobacco pectin was present as a series of related rhamnogalacturonans. 

Solid-state systems are frequently classified according to their physical, structural or chemical properties. Such schemes are extremely helpful since properties related to any such classification are typically known and facilitate identifying solids with special material classes. The best-known examples of these schemes are conductivity or resistivity measurements by means of which metals are easily distinguishable from insulators. However, frequently clear-cut decisions between material classes are not possible, since anisotropy, chemical composition, binding forces and local effects wash out distinct properties and lead to competition or coexistence. 

In this article we have considered some structural and energetic features of proteins that have been observed through physical techniques, particularly X-ray crystallography and nuclear magnetic resonance spectroscopy. We have not considered the details of the energetics of enzymic reactions, which are discussed in recent reviews,3-6 37 but have mentioned certain features related to structural observations. 

Five zeolite minerals have been considered identical with mordenite with space group Cmcm. The possibility of a family of structures is considered four related ordered structures including Cmcm are proposed. Two of these (Cmcm and Imcm) have a one-dimensional system of large pores. The remaining pair (Cmmm and Immm) have a two-dimensional pore system with a second set of smaller channels. X-ray diffraction results show that synthetic and most mineral specimens have the Cmcm structure but also reveal mixtures of Cmmm, Immm, and Imcm with the Cmcm structure in three mineral specimens. Electron diffraction examination of a ptilolite sample reveals the Cmcm structure with an inter growth of the idealized structure Cmmm. Further tentative evidence for the existence of more than one ((mordenitef) framework structure, based on physical property characteristics, is discussed. 

We have already discussed the possibility of changes in fractional free-volume being related to the physical structure of polymers. To show this in greater detail, a special study was made102. Hie viscoelastic properties and relaxation time spectra were studied in a filled system where a powder of hardened epoxy resin was used as the filler and the same epoxy resin as the matrix. Thus the system was identical from the chemical point of view, the only difference being in die method of preparation. 

The development is reviewed of liquid-crystalline polymers whose mesophase formation derives from the nature of the chemical units in the main chain. The emphasis lies primarily on highly aromatic condensation polymers and their applications. The general properties of nematic phases formed by such polymers are surveyed and some chemical structures capable of producing nematic phases are classified in relation to their ability to form lyotropic and thermotropic systems. The synthesis, properties, physical structure and applications of two of the most important lyotropic systems and of a range of potentially important thermotropic polymers are discussed with particular reference to the production and use of fibres, films and anisotropic mouldings. 

Much less information is available with regard to the action of hydrolyzing reagents in the gaseous state in relation to the physical structure of cellulose. With respect to enzymatic cleavage, the possibility of enhancing the reaction rate by increasing the accessibility is well known (6), but there are still open questions as to the relevance of the different ways to do this. 

The purpose of the present review is to summarize how cobalt-linked absorption spectra and other physical properties have been utilized in attempts to elucidate relations between structure and function in these enzymes. The emphasis will be on carbonic anhydrase not only because it reflects the author s own interests, but mainly because it is the most extensively studied cobalt enzyme. Its environmentally-sensitive absorption spectrum has furnished essential information as to the role of the metal ion in the catalytic reaction. For other enzymes, the probe properties of cobalt are just beginning to be explored, but significant advances have recently been reported (7). 

The knowledge of fundamental relations between the properties of rare earths and the electronic and physical structure of the host compound is essential for the development of improved or new materials. However, up to now only a rather small amount of high-pressure studies compared to ambient pressure studies has been performed. It is hoped that this chapter has demonstrated the ability of high-pressure physics in exploring fundamental relationships especially for rare-earth ions and will stimulate further experimental and theoretical work in this area. 

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