Shock layer in two solute chromatography: effect of axial dispersion and mass transfer

A theoretical study for two solute chromatography when axial dispersion or interphase mass transfer is significant is presented. With a Langmuir isotherm the mathematical theory of the shock layer plays a key role in generating asymptotic solutions, from which one can deduce the effect of axial dispersion or mass transfer resistance. A full discussion is given for the existence and uniqueness of the asymptotic solution. If a shock layer exists, the end states satisfy the compatibility condition and it propagates at the same speed as the corresponding shock. Analytic expressions are developed for the case of equal Peclet numbers (or equal Stanton numbers) whereas for other cases the shock layer profiles are determined numerically. Comparison between transient solutions and shock layers demonstrates the validity and usefulness of the present study.     

Heat inactivation of staphylococcus epidermidis at various water activities

Members of the family Micrococcaceae play an important role in food spoilage and even in food poisoning. In contrast to members of the family Enterobacteriaceae, these bacteria can grow in media with low water activities. Therefore, the heat resistance of Staphylococcus epidermidis, a rather resistant member of the family Micrococcaceae, was studied at water activities between 0.87 and 1.00. The heat inactivation curves were clearly biphasic at all temperatures and water activities tested. Especially at low water activities, the D-values of the tail phase were extremely high (at 0.87 water activity, a D-value at 70 degrees C of 500 s was recorded).     

Friction properties of a phenolic resin filled with iron and graphite—Sensitivity to load,speed and temperature

A phenolic resin filled with iron and graphite was investigated for its frictional properties sliding against gray cast iron. The frictional force was found to be a power function of the normal load (P) and the sliding speed (V) at a fixed temperature; F = μP^aV^b at T_i where μ is the coefficient of friction which is constant and independent of the load and speed, and a and b are one set of parameters at the temperature T_i. The parameter a is found to range from 0.77 to 0.97 depending upon the temperature. Brake fade is found to be governed by the three mechanisms—load fade, speed fade, and temperature fade.     

Abrasion resistance of silica-reinforced decorative laminates Part 1 — examination of the standard testing method

The existing standard test of the National Electrical Manufacturers Association, U.S.A., (NEMA) for determining the abrasion resistance of decorative laminates was critically examined. Special attention was given to the rapid deterioration of the abrasive paper during testing of silica-reinforced decorative laminates and to its effect on the abrasion resistance of the laminates. It was shown that the abrasion resistance of decorative laminates determined by the present testing method is a combined measure of the properties of the material and the abrasive paper, and that the present testing method is probably not suitable for testing some varieties of decorative laminates, especially those laminates which are reinforced with silica particles.It was also shown that under abrasive wear conditions reinforced overlays may or may not be more abrasion-resistant than unreinforced overlays. It was suggested that the abrasive paper should be replaced before major damage occurred, the degree of damage depending on the properties of the material under test.The frictional force, under abrasive or cutting-type wear conditions, was found to depend strongly on the number of cutting grains and possibly on the size of each scratch. The frictional force thus decreases rapidly with deterioration of the abrasive paper.     

Selective interference with the maintenance of location information in working memory.

In 3 experiments, the nature of the events that interfere with spatial working memory was examined in order to clarify the roles of imagery, attention. and other processes in the short-term maintenance of location information. Looking and pointing at secondary task stimuli selectively interfered with memory for the locations of primary task stimuli. Secondary tasks that involved either mentally rotating primary task stimuli or making color or shape discriminations about primary or secondary task stimuli interfered with spatial working memory only if the required response was visually guided, but not if the response was verbal. Taken together, these findings support P. S. Goldman-Rakic's (1987) hypothesis regarding multiple representational domains and are consistent with known properties and connections of neurons believed to subserve the perception and maintenance of spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermal plasma synthesis of SiC- Si3N4 composite powders from SiCH3CI3- NH3- H2

SiC-Si₃N₄ composite powders were synthesized by introducing trichloromethylsilane, ammonia, and hydrogen into a high-temperature radiofrequency (RF) thermal plasma argon gas. Powders were characterized by XRD, TEM, and FT-IR. Silicon carbide and silicon nitride were formed independently into separate powders. Silicon carbide was formed as β-SiC crystalline powder and silicon nitride was in an amorphous state. The crystalline SiC powders were in the size range of 75 to 200 nm and amorphous Si₃N₄ powders were 5 to 60 nm. When the mole ratio of ammonia to trichloromethylsilane was between 1 and 2, SiC-Si₃N₄ composite powders were formed, and when it was higher than 4, Si₃N₄ powders were formed.     

Diffusion of radioactively tagged penetrants through random and block styrene–butadiene copolymers and filled cis-polybutadiene

The diffusion of radioactively tagged n-hexadecane in trace amounts has been studied in 22 random styrene–butadiene (SBR) copolymers with different styrene contents and butadiene microstructures; in several SBR block copolymers with different average block lengths (also diffusion of tagged 1,1-diphenyl ethane); in a triblock SBR copolymer cast from different solvents and also molded at elevated temperature; and in cis-polybutadiene filled to different extents with carbon black, calcium carbonate, and microglass spheres. The diffusion coefficient in random SBR copolymers decreased with increasing content of styrene and/or vinyl configuration and could be correlated with fractional free volume on the basis of linear additivity of the cis, trans, vinyl, and styrene moieties. In SBR block copolymers, the diffusion coefficient increased with increasing average block sequence length. For the triblock copolymer, the diffusion coefficient was approximately the same for samples molded or cast from solvents which are good for polybutadiene, but was far smaller for a sample cast from ethyl acetate, in which the polystyrene domains are probably lamellar. The effect of fillers on diffusion in cis-polybutadiene was compared with calculations on the basis of several theoretical models.     

Diffusion of radioactively tagged penetrants through rubbery polymers. I. Penetrants with very low solubility

The diffusion of radioactively tagged n-hexadecane, 1,7-heptanediol, and ethylene glycol has been studied in one polar and six nonpolar rubbery polymers. The penetrant–polymer pairs included some in which the two components were miscible in all proportions and some in which they were nearly incompatible (solubility of penetrant in polymer of the order of 1%). The theory for the thin smear method for measuring the diffusion coefficient was evaluated for incompatible pairs with two cases: case 2, when the rate-limiting step is diffusion through the polymer; and case 3, when the rate-limiting step is entry into the polymer across the penetrant–polymer interface. They are easily distinguished experimentally from each other and from case 1, which refers to completely miscible pairs. In examples of case 3, e.g., ethylene glycol with butadiene or styrene–butadiene rubbers, the half-time for saturating the polymer surface in contact with the penetrant was found to be several days at 25°C. The diffusion coefficients, when compared in four hydrocarbon rubbers, of n-hexadecane and 1,7-heptanediol were similar in magnitude even though in each rubber the hexadecane was soluble in all proportions and the diol only very slightly. The diffusion coefficient of ethylene glycol, despite its extreme thermodynamic incompatibility, appeared to be somewhat larger than those of the other penetrants.