Biomedical subjects

Stephen J Allen

Publications and source records attributed to Stephen J Allen.

5 recordsLinked to original sources

PubMed2005

Kinetic modeling of the adsorption of basic dyes by kudzu.

The use of kudzu, a rapidly growing, high-climbing perennial leguminous vine, for the adsorption of basic dyes from aqueous solution has been investigated at various initial dye concentrations, masses of kudzu, and agitation rates. The extent and rate of adsorption of the three basic dyes (Basic Red 22, Basic Yellow 21, and Basic Blue 3) were analyzed using a pseudo-first-order and a pseudo-second-order kinetic model. While both rate mechanisms provided an acceptable degree of correlation with the experimental sorption rate data, the pseudo-second-order model gave a much higher degree of correlation, suggesting that this model could be used in design and simulation applications.

Adsorption↗

PubMed2004

Effect of shear on concentrated hydrous ferric floc rheology.

The primary interest of this work is to determine the effect of continuous shear, variable shear rate, and shear history on concentrated hydrous ferric floc rheology. The floc suspensions are strongly shear degrading with the behaviour being adequately described by a power law model. This is supported by images of the floc particles, which indicate a breakdown in floc structure, with the release of water and formation of smaller particles, after the application of shear. A shear rate sweep of the sample produces a hysteresis loop due to the time dependency of the samples. Higher shear rates are shown to destroy more structure, resulting in an overall decrease in floc viscosity. This is irreversible, and occurs due to a breakdown in floc structure to release trapped water and produce smaller floc particles. Shear also causes an instantaneous reduction in viscosity. This effect is instantaneously recoverable, and is due to a decrease in floc particle aggregation. Floc behaviour within the shear rate range 20-250 s(-1) is also adequately modelled by the Sisko model.

Flocculation↗

PubMed2003

A human complement receptor 1 polymorphism that reduces Plasmodium falciparum rosetting confers protection against severe malaria.

Parasitized red blood cells (RBCs) from children suffering from severe malaria often adhere to complement receptor 1 (CR1) on uninfected RBCs to form clumps of cells known as "rosettes." Despite a well documented association between rosetting and severe malaria, it is controversial whether rosetting is a cause or a correlate of parasite virulence. CR1-deficient RBC show greatly reduced rosetting; therefore, we hypothesized that, if rosetting is a direct cause of malaria pathology, CR1-deficient individuals should be protected against severe disease. In this study, we show that RBC CR1 deficiency occurs in up to 80% of healthy individuals from the malaria-endemic regions of Papua New Guinea. This RBC CR1 deficiency is associated with polymorphisms in the CR1 gene and, unexpectedly, with alpha-thalassemia, a common genetic disorder in Melanesian populations. Analysis of a case-control study demonstrated that the CR1 polymorphisms and alpha-thalassemia independently confer protection against severe malaria. We have therefore identified CR1 as a new malaria resistance gene and provided compelling evidence that rosetting is an important parasite virulence phenotype that should be a target for drug and vaccine development.

Adult↗

PubMed2003

Effect of freeze-thaw process on partitioning of contaminants in ferric precipitate.

The primary interest of this work was to determine the processing conditions which will provide the most water removal from the precipitate after freezing and thawing. The work examined the effect of variables such as freezing time, freezing temperature, and pre-treatment steps, e.g. agitation or concentration, on the freeze thaw process of ferric precipitates. The extent of dewatering of freeze thawed samples was not significantly affected by freezing rate or curing time, provided the floc was completely frozen. However, a pre-concentration step was found to produce a more concentrated residual. The relatively low degree of structure within the ferric flocs makes them particularly suitable for freeze-thaw conditioning. Only a slight increase in leach out of contaminant from the floc was observed. Thus, the experiments indicate that this is a very simple and effective method of dewatering precipitates, which does not require the use of additional additives.

Chemical Precipitation↗

PubMed2003

Comparison of optimised isotherm models for basic dye adsorption by kudzu.

This study assesses the use of dried (5% w/w moisture) kudzu (Peuraria lobata ohwi) as an adsorbent medium for the removal of two basic dyes, Basic Yellow 21 and Basic Red 22, from aqueous solutions. The extent of adsorption was measured through equilibrium sorption isotherms for the single component systems. Equilibrium was achieved after 21 days. The experimental isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson, Temkin and Toth isotherm equations. A detailed error analysis was undertaken to investigate the effect of using different error criteria for the determination of the single component isotherm parameters. The performance of the kudzu was compared with an activated carbon (Chemviron F-400). Kudzu was found to be an effective adsorbent for basic dye colour removal; though its capacity for colour removal was not as high as an activated carbon, the potential appeared to exist to use it as an alternative to activated carbon where carbon cost was prohibitive.

Adsorption↗