Effect of surface lipopolysaccharide on the nature of membrane vesicles liberated from the Gram-negative bacterium Pseudomonas aeruginosa

Membrane vesicles (MVs) were isolated from three isogenic lipopolysaccharide (LPS) mutants derived from the Gram-negative bacterium Pseudomonas aeruginosa PAO1 and compared with the parent strain. Parent cells possessed serotype 05 (A+B+) LPS whereas the three mutants contained A+B-, A-B+ and A-B-. The MVs from the mutants contained their expected phenotypic LPS and varied in size, especially A-B- MVs. Mass and total protein differences were also noted. When the parent and mutant cells were treated with the outer membrane-perturbing antibiotic gentamicin, all cells produced 3-5 times more MVs and these had great variation in size, mass and total protein. It is concluded that the type of cellular LPS affects both the natural and gentamicin-induced development of MVs.     

Regulation of the cystic fibrosis transmembrane conductance regulator Cl- channel by negative charge in the R domain

Phosphorylation by cAMP-dependent protein kinase (PKA) regulates the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. We previously showed that in vivo PKA phosphorylated 4 serines (Ser-660, Ser-737, Ser-795, and Ser-813) within the R domain. Here we show that a mutant CFTR lacking all 4 serines can still be phosphorylated by PKA to yield an activated Cl- channel, but channel open-state probability was substantially reduced. We also observed phosphorylation and Cl- channel activity in another mutant lacking all 8 consensus PKA serines in the R domain. We were unable to identify the residual phosphorylation sites by tryptic phosphopeptide mapping. These data suggest two possible interpretations: (a) additional, as yet unidentified, phosphorylation sites within CFTR may also open the channel, or (b) the 4 serines, previously identified as in vivo PKA phosphorylation sites, are the primary regulatory sites within CFTR, but in their absence, other sites can be phosphorylated to open the channel. The additional sites are likely located within the R domain: CFTR delta R-S660A, which lacks much of the R domain (residues 708-835) and replaces Ser-660 with an alanine, was no longer regulated by PKA. Substitution of aspartate for consensus PKA phosphorylation sites in the R domain mimicked the effect of phosphorylation. Mutants containing six or more serine-to-aspartate substitutions generated Cl- channels that opened without PKA phosphorylation. These results suggest that the R domain keeps the channel closed and that phosphorylation of the R domain or insertion of the negatively charged aspartate opens the channel, perhaps by electrostatic interactions.     

Parallel fem algorithms based on recursive spatial decomposition—I. Automatic mesh generation

This paper discusses an automatic meshing scheme that is suitable for parallel processing. Meshes derived from solid models through recursive spatial decompositions inherit the hierarchical organization and the spatial addressability of the underlying grid. These two properties are exploited to design a meshing algorithm capable of operating in parallel (concurrent) processing environments. The concept of a meshing operator for parallel processing is defined and algorithms for various stages of the automatic meshing scheme are presented. A systematic simulation of fine- and coarse-grain parallel configurations is used to evaluate the performance of the meshing scheme. A companion paper focuses on parallel processing for the analysis of these automatically derived meshes via hierarchical substructuring.     

Heat transfer and gas holdup studies in a bubble column: Air-water-sand system

Air-holdup and heat transfer coefficient data are reported for the air-water and air-water-sand system as a function of air velocity in the temperature range 297-343 K as measured in a 0.305 m diameter bubble column operating in semi-batch mode and equipped with either a five- or seven-tube bundle. A 65 μm average size sand powder is used at concentrations of 5 and 10 mass percent in the slurry. Available correlations of gas holdup and heat transfer coefficients are examined on the basis of these data. These are found inappropriate and inadequate for representing these experimental data. Gas holdup data are well represented by an approach based on Nicklin's (1962) work, and heat transfer data are adequately represented by a simple semi-empirical expression. Accurate experimental data on additional systems are needed to develop a reliable heat transfer theory particularly for process representation at temperatures higher than ambient.     

Predicting the life of high-temperature structural components in power plants

The concept of time-dependent fracture mechanics has been used to develop the quantitative life-prediction methodology and inspection criteria for high-temperature structural components. As an example, the methodology was applied to steam pipes. Leak-before-break analyses were utilized to determine the flaw inspection criteria of steam pipes. Both static and cyclic loading conditions were included in the life-prediction analyses. Increasing the frequency of shutdowns was found to decrease the remaining life. The effects of operating pressures and temperatures and material properties on the life of steam pipes were quantified.     

Dependence of Heat-Transfer coefficient for immersed surfaces in a gas-fluidized bed on pressure

The correlations and theories developed for the prediction of heat-transfer coefficients for immersed surfaces in fluidized beds are examined for their applicability and appropriateness at different pressures. It is found that the pressure dependence of minimum fluidization velocity and heat-transfer coefficient for ‘small’ and ‘large’ particle systems can be reconciled with an adequate interpretation of available correlations and model expressions on the basis of a recently proposed particle classification scheme. The latter utilizes the concept of Archimedes number to provide a particle classification scheme which interprets particles into different categories, keeping both hydrodynamic and thermal behaviors of the bed consistent with each other at the same time. Good agreement of the available experimental data with appropriate theories is demonstrated.