D-Mevalonic acid is the fundamental intermediate in the biosynthesis of the terpenoids and steroids, together classed as poly-isoprenoids. The biogenetic isoprene unit is isopentenyl pyrophosphate which arises by enzymic decarboxylation-dehydration of mevalonic acid pyrophosphate. D-Mevalonic acid is almost quantitatively incorporated into cholesterol synthesized by rat liver homogenates.  [c.262]

CHR) , formed, e g. from the reaction of diazomethane and alcohols or hydroxylamine derivatives in the presence of boron compounds or with metal compounds. Poly-methylene is formally the same as polyethene and the properties of the various polymers depend upon the degree of polymerization and the stereochemistry.  [c.320]

Organic polyesters, obtained either from a diacid and a mono-alcohoi, or from poly-alcohols and a monoacid, or from di-alcohols and a diacid. This class represented 29% of the synthetic base market in France in 1992.  [c.279]

PAO poly alpha-olefins  [c.503]

Abstract All imaging applications for radiography and computerised tomography (CT), which are based on conventional, poly-energetic X-rays uses - with very few exceptions -non-optimal parameter settings for the imaging task at issue. This is due to the complex relationship between imaging parameter settings and final image quality that makes it empirieally tedious to find optimal parameter settings - particularly for industrial applications, because of the wide range of objects, geometry and material, of interest.  [c.208]

Within this work mathematical models of the data collection process for radiography and CT have been developed. The objective has been to develop a functioning simulation environment of the physics in the image/data collection that considers the poly-energetic dependence in the imaging process, including full X-ray energy spectra and detector energy response. The simulation environment is used for fast and cost-effective studies of how parameter variations affect final image quality and indirect - the defect detectability. In this particular case, the simulations have been applied on a high resolution CT application to determine optimal operator parameter settings that maximise the detectability of different defect types in circular objects and to predict the minimum detectable size as a function of object diameter. The simulation environment has also been used to correct for beam hardening artefacts in CT-images.  [c.208]

In this work it has been shown that one of the major difficulties with this BH-correction method is to accurately determine the poly-energetic CT-data function. At least polynomial degrees of eight or higher are required, which implies the sensitivity to data curvature. Here cubic-spline functions were used instead. Figure 12 shows original (left) and BH-corrected Images of a 6.0-mm steel sample. It was imaged with a 130-kV X-ray beam that was filtered with 0.4-rmn tin and 0.6-mm copper. BH, which is clearly discernible in the original image, is  [c.214]

Of particular interest has been the study of the polymer configurations at the solid-liquid interface. Beginning with lattice theories, early models of polymer adsorption captured most of the features of adsorption such as the loop, train, and tail structures and the influence of the surface interaction parameter (see Refs. 57, 58, 62 for reviews of older theories). These lattice models have been expanded on in recent years using modem computational methods [63,64] and have allowed the calculation of equilibrium partitioning between a poly-  [c.399]

Fig. XI-7. Volume fraction profile of 280,000-molecular-weight poly(ethylene oxide) adsorbed onto deuterated polystyrene latex at a surface density of 1.21 mg/m and suspended in D2O, from Ref. 70. Fig. XI-7. Volume fraction profile of 280,000-molecular-weight poly(ethylene oxide) adsorbed onto deuterated polystyrene latex at a surface density of 1.21 mg/m and suspended in D2O, from Ref. 70.
Amphiphilic diblock copolymers in a solvent that is selective for one of the blocks form micelles that have received extensive study [174]. Among the interesting block copolymer systems are block poly electrolytes [175], fluorocarbon-hydrocarbon diblocks [176], and block copolymers compatibilizing immiscible polymer blends [177]. Many technological applications, including enhanced oil recovery, cosmetics, and paints, involve complex mixtures of polymers and surfactants (see Ref. 178 for a review of phase behavior). Numerous interesting properties exist including gelation [179, 180], threadlike structures [181] and rheological changes [182, 183].  [c.482]

Fig. XV-1. Plots of t/CRT vs. C for a fractionated poly(methyl acrylate) polymer at the indicated temperatures in degrees Celsius. [From A. Takahashi, A. Yoshida, and M. Kawaguchi, Macromolecules, 15, 1196 (1982) (Ref. 1). Copyright 1982, American Chemical Society.] Fig. XV-1. Plots of t/CRT vs. C for a fractionated poly(methyl acrylate) polymer at the indicated temperatures in degrees Celsius. [From A. Takahashi, A. Yoshida, and M. Kawaguchi, Macromolecules, 15, 1196 (1982) (Ref. 1). Copyright 1982, American Chemical Society.]
Some polymers, such as functionally terminated poly(dimethyl siloxane) (PDMS), exhibit more complex isotherms such as those due to Koberstein and co-workers [6] shown in Fig. XV-3. Up to six inflection points or transitions, labeled A-F, were observed in these systems. Generally, at large areas the polymer lays flat on the water and between A and B makes a transition to a zigzag stmcture with every other oxygen or silicon at the surface. Between B and C PDMS coils into helices, and from C to D these helices begin to slide past one another and the monolayer collapses. Shorter chains make a transition to upright configurations at E and finally collapse at F. Thus, depending on the functional groups and the subphase, end-functionalized PDMS shows transitions of the macromolecule on the surface as well as transitions involving vertical orientations of whole chains.  [c.539]

They are called didepsides, tridepsides, poly-depsides, etc., depending on the number of phenol residues they contain. Obtained from lichens, present in tea.  [c.129]

Resins formed from the reaction of poly(vinyl alcohol) with aldehydes. The formal derivative (from methanal) is used in wire coatings and adhesives and the bulyral (from butanal) is used in metal paints, wood-sealers, adhesives and in safety glass interlayers.  [c.323]

Prepared generally by ester interchange from polyvinylacelate (ethanoate) using methanol and base also formed by hydrolysis of the acetate by NaOH and water. The properties of the poly(vinyl alcohol) depend upon the structure of the original polyvinyl acetate. Forms copolymers. Used as a size in the textile industry, in aqueous adhesives, in the production of polyvinyl acetates (e.g. butynal) for safety glasses. U.S. production 1980  [c.323]

CT produces maps of the linear attenuation coefficients (p) that depends on the object material composition and density. However, when poly-energetic X-ray sources are used accurate p measurements is prevented because of the CT-artefact called beam-hardening (BH). It results in false p-gradients towards the centre of the object, indicating a non-existing density or composition gradient, see figure 12. One method to correct for, or limit the effect of, BH is to linearise CT-data, in which poly-energetic CT-data for a certain object thickness is transformed to its corresponding mono-energetic CT-data. This requires knowledge of the poly-energetic CT-data as a function of object thickness. This is usually measured with object material of different thickness. However, the material preparation makes this method tedious to use. With accurate simulations the poly-energetic CT data for any arbitrary object material and thickness can be obtained without extra sample preparation. A priori information of material density and composition is required, though.  [c.214]

The surface tension of polymer melts can be strongly influenced by the potential surface activity of the chain ends [100]. While the density of a polymer depends on its molecular weight, the primary effect on surface tension is not through density variation but rather due to preferential adsorption or depletion of the ends at the surface. Koberstein and co-workers [101] have demonstrated this effect with end-functionalized poly(dimethylsiloxane). Their pendant drop studies (see Section II-7) of low-molecular-weight polymers having amine-, hydroxyl- or mcf yZ-terminal groups show surface tensions decreasing, independent of, or increasing with molecular weight due to the higher, intermediate, or lower surface energies, respectively, of the end groups. The end groups also alter the interfacial tension between immiscible polymer blends [102] in a similar way. The addition of block copolymers to immiscible polymer blends is analogous to adding a surface active agent to immiscible liquids. The intetfacial tension is reduced by the adsorption of the block copolymer at the interface until it is saturated [103].  [c.70]

An example of an alkaline hydrolysis is that of the saponification of mono-layers of a-monostearin [304] the resulting glycerine dissolved while the stearic acid anion remained a mixed film with the reactant. Equation IV-64 was obeyed, with k = ik (OH ) and showing an apparent activation energy of 10.8 kcal/mol. O Brien and Lando [305] found strong pH effects on the hydrolysis rate of vinyl stearate and poly(vinyl stearate) monolayers. Davies [306] studied the reverse type of process, the lactonization of y-hydroxystearic acid (on acid substrates). Separate tests showed that AV for mixed films of lactone and acid was a linear function of composition at constant rr, which allowed a modification of Eq. IV-66 to be used. The pseudo-first-order rate constant was proportional to the hydrogen ion concentration and varied with film pressure, as shown in Fig. IV-27. This variation of k with jr could be accounted for by supposing that the y-hydroxystearic acid could assume various configurations.  [c.152]

The reports were that water condensed from the vapor phase into 10-100-/im quartz or pyrex capillaries had physical properties distinctly different from those of bulk liquid water. Confirmations came from a variety of laboratories around the world (see the August 1971 issue of Journal of Colloid Interface Science), and it was proposed that a new phase of water had been found many called this water polywater rather than the original Deijaguin term, anomalous water. There were confirming theoretical calculations (see Refs. 121, 122) Eventually, however, it was determined that the micro-amoimts of water that could be isolated from small capillaries was always contaminated by salts and other impurities leached from the walls. The nonexistence of anomalous or poly water as a new, pure phase of water was acknowledged in 1974 by Deijaguin and co-workers [123]. There is a mass of fascinating anecdotal history omitted here for lack of space but told very well by Frank [124].  [c.248]

See pages that mention the term Poly : [c.18]    [c.18]    [c.35]    [c.60]    [c.80]    [c.149]    [c.175]    [c.259]    [c.276]    [c.278]    [c.299]    [c.319]    [c.319]    [c.320]    [c.320]    [c.320]    [c.320]    [c.321]    [c.322]    [c.322]    [c.322]    [c.322]    [c.322]    [c.322]    [c.323]    [c.323]    [c.323]    [c.335]    [c.359]    [c.389]    [c.390]    [c.421]   
Carey organic chemistry (0) -- [ c.190 , c.269 , c.270 , c.883 ]

Langes handbook of chemistry (1999) -- [ c.0 , c.9 , c.10 ]

Plastics materials (1999) -- [ c.0 , c.53 , c.62 , c.73 , c.107 , c.376 , c.415 , c.423 , c.695 , c.834 , c.897 ]

Chemistry of Organic Fluorine compounds II (1995) -- [ c.54 , c.1110 , c.1111 ]

Organic chemistry (0) -- [ c.190 , c.269 , c.270 , c.883 ]

A guide to chalcogen-nitrogen chemistry (1926) -- [ c.285 , c.286 , c.287 , c.288 ]

Corrosion, Volume 2 (2000) -- [ c.18 , c.72 ]