Auto-stratification in drying colloidal dispersions: a diffusive model.

The mechanism by which the particles in a drying film come into close packing during solvent evaporation has an important role to play in the final film morphology. During drying the particles can develop non-uniform concentrations across the vertical height of the film, depending on their diffusion rate. By applying the principles of classical diffusion mechanics to a hard sphere system, a theory for this novel method of stratification during drying of a two component film has been derived. The model is dependent on the particle Peclet numbers and when one is above unity and the other below, maximum stratification is observed.

Autostratification in drying colloidal dispersions: experimental investigations.

In films cast from a colloidal dispersion comprising two particle sizes, we experimentally examine the distribution of particles normal to the substrate. The particle concentrations at various positions in the film are determined through atomic force microscopy and NMR profiling. The results are compared to a previously derived diffusional model. Evidence for diffusional driven stratification is found, but the importance of other flows is also highlighted. The conditions that enhance particle stratification are found to be a colloidally stable dispersion, low initial volume fractions, a low concentration of the stratifying particle, and for the Peclet numbers of the two components to straddle unity.

Dental hard tissue modification and removal using sealed transverse excited atmospheric-pressure lasers operating at lambda=9.6 and 10.6 microm.

Pulsed CO(2) lasers have been shown to be effective for both removal and modification of dental hard tissue for the treatment of dental caries. In this study, sealed transverse excited atmospheric pressure (TEA) laser systems optimally tuned to the highly absorbed 9.6 microm wavelength were investigated for application on dental hard tissue. Conventional TEA lasers produce an initial high energy spike at the beginning of the laser pulse of submicrosecond duration followed by a long tail of about 1-4 micros. The pulse duration is well matched to the 1-2 micros thermal relaxation time of the deposited laser energy at 9.6 microm and effectively heats the enamel to the temperatures required for surface modification at absorbed fluences of less than 0.5 J/cm(2). Thus, the heat deposition in the tooth and the corresponding risk of pulpal necrosis from excessive heat accumulation is minimized. At higher fluences, the high peak power of the laser pulse rapidly initiates a plasma that markedly reduces the ablation rate and efficiency, severely limiting applicability for hard tissue ablation. By lengthening the laser pulse to reduce the energy distributed in the initial high energy spike, the plasma threshold can be raised sufficiently to increase the ablation rate by an order of magnitude. This results in a practical and efficient CO(2) laser system for caries ablation and surface modification.

Personality factors affecting pilot combat performance: a preliminary investigation.

Reviews of the research literature have generally concluded that personality factors contribute little to pilot performance. One possible explanation for the failure to find stronger relationships may be due to the lack of appropriate taxonomies for both personality constructs and for performance constructs. The present research was designed to examine the relationship between personality and combat performance using the "Big Five" model of personality and a multi-component model of pilot combat performance. A sample of 100 USAF pilots rated the importance of 60 traits for effective performance on performance dimensions such as flying skills and crew management. The results indicated that pilots from different aircraft agreed that the personality trait of Conscientiousness was the most important determinant of performance on all performance dimensions. Implications for pilot selection are discussed.

The influence of dietary fat levels and environmental temperature on digestible energy and absorbability of animal fat in catfish diets.

A study was conducted on the effects of three dietary levels of animal fat (5%, 10%, and 15%) and two environmental temperatures (23 and 28 degrees) on the digestible energy (DE) and apparent absorbability (AA) of animal fat in diets of 150 g catfish. Results obtained by the use of the chromic oxide indicator technique demonstrated that at 28 degrees and substitution levels up to 10% of diet, animal fat had a DE value of 7,000 kcal/kg and an AA of 94%. At the 15% level of substitution, both DE and AA were substantially reduced. At each level of substitution, DE and AA values were considerably lower in fish reared at 23 degrees. At supplemental levels up to 10% of diet, the DE and AA values for catfish at 23 degrees were 6,130 kcal/kg and 70%, respectively. Results from this study reconfirmed previous growth data which indicated that animal fat is an excellent dietary energy source for catfish which are reared at optimum temperatures.

Supplementation of a semipurified casein diet for catfish with free amino acids and gelatin.

Semipurified diets with casein as the sole protein source were supplemented with gelatin, arginine, cystine, methionine or tryptophan, and fed to channel catfish (Ictalurus punctatus) fingerlings. Increasing the arginine level from 1.1% to 1.7% of diet by the isonitrogenous substitution of gelatin for casein resulted in a significant enhancement of growth. However, the addition of free arginine, cystine, tryptophan or methionine to casein had little effect on growth or food conversion. These data substantiate a previous report that suggested catfish were similar to carp in their inability to utilize free amino acids.

Effects of dietary lipids, dietary protein and environmental temperatures on growth, feed conversion and body composition of channel catfish.

Studies were conducted to determine the effects of several lipid supplements in practical-type diets for channel catfish (Ictalurus punctatus) fingerlings reared at 23 degrees and 28 degrees. Maximum growth and feed efficiency were obtained when diets were supplemented with 9% animal tallow, 9% menhaden oil or a combination of the two (4.5% of each). A growth suppression was observed when fish were fed a diet containing a combination of 3% corn oil, 3% animal tallow and 3% menhaden oil. In studies on interactions of dietary protein and lipid at 23 degrees and 28 degrees, increasing dietary protein from 25% to 35% resulted in higher gains. At 28 degrees, increasing dietary lipid from 5% to 12% resulted in increased gains with diets containing 35% protein but not withdiets containing 25% protein. At 23 degrees, 5% lipid was sufficient in all cases. Carcass lipid levels increased with increasing temperature and were positively correlated with weight gains and negatively correlated with carcass moisture content. Improved protein conversion (protein fed: protein gained) was noted when dietary protein levels were increased from 25% to 35%; when dietary lipid levels were increased from 5% to 12%; and when environmental temperature was increased from 23 degrees to 28 degrees.