On the modelling of scalar and mass transport in combustor flows

The results of a numerical study of swirling and non-swirling combustor flows with and without density variations are presented. Constant-density arguments are used to justify closure assumptions invoked for the transport equations for turbulent momentum and scalar fluxes, which are written in terms of density-weighted variables. Comparisons are carried out with measurements obtained from three different axisymmetric model combustors. The three experiments cover recirculating flow, swirling flow and variable-density, swirling flow inside model combustors. Together, they offer wide ranging flow conditions to test the validity of the models. Results show that the Reynolds stress/flux models do a credible job of predicting constant-density, swirling and non-swirling combustor flows with passive scalar transport. However, their improvements over algebraic stress/flux models are marginal. The extension of the constant-density models to variable-density flow calculations shows that the models are equally valid for such flows. Therefore, the present results argue well for the adoption of constant-density models for variable-density flows until a successfully validated variable-density model is available.     

Effects of brefeldin-A on Golgi morphology in human cultured fibroblasts observed in three-dimensional stereo scanning electron microscopy

Brefeldin A (BFA) has been reported to cause disassembly of the Golgi. We have used three-dimensional (3-D) high-resolution scanning electron microscopy (HRSEM) to investigate these effects in human skin fibroblast cells. The spontaneous reassembly during prolonged exposure to BFA and some effects of forskolin were observed. A BFA concentration of 5μg/ml caused Golgi complexes to become vesicular, resulting in a progressive decrease in the size of the Golgi. Morphologic changes were visible within 2 min of BFA incubation, and by 30 min no identifiable Golgi could be found. Spontaneous reassembly of the Golgi apparatus upon the removal of the BFA or with continued long-term exposure with BFA could not be confirmed. Preliminary experiments with forskolin were not effective in reversing or inhibiting the effects of BFA in human fibroblast cells grown in culture. This inability for spontaneous reassembly and nonreversal by forskolin may reflect a differential effect of BFA in various cell types. HRSEM has proven to be useful for observing 3-D morphologic effects of BFA in Golgi.     

Photodegradation mechanism and stabilization of polyphenylene oxide and rigid‐rod polymers

Poly(2,4‐dimethyl‐1,4‐phenylene oxide) (PPO), poly(benzo[1,2‐d:5,4‐d′]bisoxazole‐2,6‐diyl‐1,4‐phenylene) (PBO) and poly(benzo[1,2‐d:4,5‐d′]bisthiazole‐2,6‐diyl‐1,4‐phenylene) (PBZT), which are polymers with extended conjugated structures, undergo a self‐sensitized photo‐induced electron‐transfer reaction. A second component is not required. This article presents many similar observations on these polymers when they are exposed to light and evidence to support the proposed photo‐induced electron‐transfer mechanism. Methods to stabilize these polymers against photo‐oxidation are also described. Workers investigating other conjugated polymeric systems may find the experimental methods, observations and polymer stabilization approaches discussed in this review useful. Copyright © 2005 Society of Chemical Industry