Differentiation of sugar assimilation characteristics and colony phenotypes in pathogenic and commensal oral candidal isolates

A comparison of sugar assimilation patterns has been made using 72 oral candidal isolates recovered from diseased and non-diseased patients. Significant differences were demonstrated between isolates recovered from diseased versus healthy mouths. In addition, significant changes in colony phenotype (switch frequency and morphologic predominance) were found to relate to predictive data generated from carbon source utilization data. These results suggest that biochemical properties and colony phenotypic characteristics may hold promise in predicting the behavior of oral candidal isolates in disease.

Transport of L-proline and its regulation in Leishmania tropica promastigotes

Leishmania tropica promastigotes transport L-proline through an active uptake system that has saturation kinetics, temperature dependence, a requirement for metabolic energy and transport against a concentration gradient. In experiments lasting 10 min, less than 10% of the proline transported is incorporated into macromolecules. The remainder is largely unaltered proline with an intracellular concentration nearly 60 times that in the reaction mixture. The uptake system has a relatively broad specificty; it is competitively inhibited by D-proline as well as by alanine, methionine, valine, azetidine-2-carboxylate, thioproline, 3,4-dehydropoline, hydroxyproline and alpha-aminoisobutyric acid. Pre-established intracellular proline pools exchange with external proline as well as compounds that compete with it for uptake. Evidence is presented that feedback inhibition and transinhibition may regulate proline uptake in this organism.

On Building Models for the Grinding Process

A new technique of building models for the grinding process is introduced. The grinding model is postulated in terms of grain distributions on the abrasive wheel and kinematic grinding conditions. Transverse workpiece profiles are conjectured as sample realizations of the stochastic grinding process. The sample spectrum of experimentally ground workpiece profiles is proposed as a means to estimate parameters in the postulated model through a nonlinear regression method. A model for a specified grinding process was developed based upon ten workpieces ground within a preselected practical region. The model is limited to single-pass surface grinding without crossfeed. The model was evaluated in regard to its validity, versatility, and sensitivity.

Simulation Study of the Grinding Process

A model in terms of grain distributions and kinematic conditions has been recently developed [8] for a specified grinding process. Using this model, an exploratory attempt was made to study the grinding process with respect to the surface topography and nature of surface interactions by simulation on a digital computer. Fundamental grinding parameters, such as the effective grain density, grain spacings, chip depths, and chip areas, are employed to describe the grain-workpiece interactions. The grinding process is studied under a systematic variation of table speed, wheel depth of cut, and grain apex angle. The physical significance of the Z-distribution and stochastic nature of the grinding process is also discussed.