Diet,cholesterol metabolism,and atherosclerosis

Effects of diet on acetate incorporation into cholesterol and fatty acids in liver slices, and on the level of plasma cholesterol, were studied in rats and rabbits. Feeding fats and oils in a com-mercial diet stimulated acetate incorporation into rat-liver cholesterol much more than feeding them in a semisynthetic diet. This effect seemed to be specific for cholesterol since incorporation into fatty acids was not similarly affected. High levels of dietary casein inhibited acetate incorporation into both cholesterol and fatty acids. Rat-liver slices generally incorporated more acetate into cholesterol than rabbit-liver slices, but incorpora-tion into fatty acids was often higher in the latter. Rabbit plasma cholesterols were higher on butter diets than on corn oil diets. Further eleva-tion of plasma cholesterol was observed when casein was added to the butter diet but not when it was added to the corn oil diet. Plasma cho-lesterols were elevated, and acetate incorporation into liver cholesterol and fatty acids was inhibited in suckling rats and rabbits whereas recently weaned animals gave results similar to those of adults. The inverse relationship between plasma cholesterol level and acetate incorporation into cholesterol may be attributable to feedback con-trol of liver cholesterol biosynthesis. Other mechanisms which may account for the observed effects of dietary fats and protein on cholesterol metabolism, and the possible relevance of the findings to atherosclerosis, are discussed.     

Some mechanical properties of an epoxy resin system cured with multiple crosslinking agents

Arbitrary cure times and glass transition temperatures are reported for an epoxy resin cocrosslinked by various weight fractions of hexamethylenediamine (HMDA) and m-phenylenediamine (m-PLDA). The glass transition temperatures of the epoxy resin systems studied yielded an excellent fit to an empirical equation developed by Dyvik for copolymers. The cure time parameters were found to be a linear function of the weight fractions of each crosslinking agent present. The mechanical properties of the epoxy resins were measured by an in situ dynamic modulus technique which employed the use of a resin-coated metallic substrate.     

Poly(1,3,4-oxadiazoles). Effect of structure on polymer properties

Poly(1,3,4-oxadiazole-2,5-diylvinylene) and poly(1,4-phenylene-1,3,4-oxadiazole-2,5-diylvinylene) were prepared by polymerizing different quantities of terephthalic acid (T), maleic acid (M), and hydrazine sulfate (HS) in the presence of fuming sulfuric acid. Homopolymers of M and T and various copolymers of M:T were prepared. The polymers were characterized by viscosity, IR, UV, and elemental analysis. Their solubility in different solvents was investigated. The relative thermal stability of the polymers was evaluated by TGA and DTA.     

Hydrolytic degradation of ionically cross-linked polyphosphazene microspheres

The hydrolytic degradation of gel microspheres based on calcium cross-linked phosphazene polyelectrolytes, poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[(carboxylatophenoxy) (glycinato)phosphazene] (PCGPP), was investigated. These microspheres are of importance as carriers in protein and cell encapsulation. Both PCPP and PCGPP ionotropic polyphosphazene hydrogels are degradable in an aqueous environment (pH 7.4, 37°C). The degradation rates can be increased by incorporation of hydrolysis sensitive glycinato groups as the pendant structures in the polymer (PCGPP). Hydrolysis of these polymer hydrogels led to low molecular weight (<1,000 Da) products. The erosion and molecular weight profiles varied also according to the molecular weight of the polyphosphazene constituting the gel beads. Another approach to affect the degradation rates consists of coating microspheres with poly-L -lysine. Ionotropic polyphosphazene hydrogels have potential as biodegradable devices for controlled drug delivery systems. © 1994 John Wiley & Sons, Inc.     

Mechanical Packing of Spherical Particles

An idealized experimental study of particle packing was made. Spherical metal shot of several discrete, narrow size ranges was efficiently packed in glass containers by mechanical vibration. Packing arrangements and the dynamic process of packing were studied visually. One-size spheres packed in an orthorhombic arrangement with a density 62.5% of theoretical density. Forming of high-density multicomponent packings was shown to require at least a sevenfold difference between sphere sizes of the individual components. A quaternary packing with a density 95.1% of theoretical density was formed from spheres with diameter ratios 1:7:38:316 and volume compositions 6.1:10.2:23.0:60.7%, respectively. Such packings could be poured from their glass containers, thus proving that effective mechanical packing is simply an efficient arrangement of spheres of prescribed sizes and proportions. The significance and utility of this work to the ceramic and other industries is discussed.     

Chlorination of polystyrene

Chlorination of a low molecular weight polystyrene in the α position was studied by following changes in the infrared spectrum, glass transition temperature, and molecular weights of the polymer. The logarithm of the absorbance ratio at 2920 and 1500 cm^?1 as a function of mole per cent chlorination was linear. The glass transition temperatures, determined by use of a differential scanning calorimeter (DSC), were found to obey an equation developed by Dyvik for copolymers. The molecular weight of the chlorinated polystyrene decreased as a function of chlorination.     

Dynamic gas disengagement: A new technique for assessing the behaviour of bubble columns

A precise measure of the liquid motion and distribution of bubble sizes is essential for designing gas-liquid reactors for complex reactions in which product distribution may be a function of bubble size. A theoretical approach is presented which shows how the interaction of bubble size distribution and bubble rise velocity functions leads to predictions of the overall steady state hold-up in a bubble column within which the liquid flow is understood. Since this approach is based on a physical understanding of how bubble flow at a given superficial velocity must relate to the static hold-up, the theory can be immediately extended to describe the disengagement of gas bubbles if the gas feed is cut off. Thus the dynamic gas hold-up during gas disengagement can be used to provide new insights into the fundamentals of bubble column behaviour. In this way it becomes possible in principle to inter-relate macroscopic properties such as surface area, gas phase residence time distribution and intensity of mixing in the liquid phase.A new experimental technique is described which measures the dynamic gas hold-up during gas disengagement Experimental results at a nominal 20 mm/s gas superficial velocity are compared with various approaches based upon the theory. The effects of the accompanying induced liquid movements are represented by a simplified core-annulus circulation model. Bubble size distributions and liquid circulation can then be related to both the static and dynamic hold-up behaviour. It is shown that ambiguity due to uncertainty about the relative differences in bubble size distribution in upflow and downflow regions can be resolved from a knowledge of the surface area.     

Determination of particle size distribution in a modified hop extract emulsion by electrical resistivity

A procedure has been developed which is suitable for the evaluation of particle size distribution in emulsions of modified hop extracts. A Coulter Counter Model A and a Coulter Counter Model B equipped with a Model M Data Converter were used to assess the weight percent distribution of particles smaller than 10 μm in diameter. The influences of electrolyte concentration, length of analysis, and concentration of the hop extract particles were factors affecting the reproducibility of the study. It was found that identical distribution curves could be obtained with either instrument. The Model B Coulter Counter with the Model M Data Converter is preferred since weight fractions are provided directly and lengthy calculation procedures are eliminated. Coincidence correction on particle counts was unnecessary under the controlled conditions of the analysis.     

The effect of fine grinding of quartz sand and felspar on the properties of semiporcelain

Glass and Ceramics -     

Effect of thermal hysteresis on the gas permeation properties of 6FDA‐based polyimides

The effect of thermal hysteresis on the polymer chain packing and permeation properties of two 6FDA‐based polyimide isomers was investigated. Thermal quenching resulted in a small increase in the fractional free volume of the polyimides with respect to the samples that had been annealed. Quenching from above the glass‐transition temperature also resulted in larger increases in the permeabilities for both 6FDA–6FmDA and 6FDA–6FpDA with respect to annealed samples. Meta‐connected 6FDA–6FmDA exhibited a larger increase in the permeability after quenching than the para‐connected isomer, 6FDA–6FpDA. This larger increase in the permeability for 6FDA–6FmDA may have been due to differences in the effects of the increases in the free volume on the intersegmental resistance to chain motions. Although physical aging over a 3‐month period resulted in a reduction in the permeability of quenched samples of 6FDA–6FpDA, the quenched samples maintained higher permeabilities than the annealed samples. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1174–1182, 2004