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Biomedical subjects

W A Hamilton

Publications and source records attributed to W A Hamilton.

At least 19 recordsLinked to original sources
PubMed2005

Shear-induced collapse in a lyotropic lamellar phase.

An entropically stabilized cetylpyridinium chloride, hexanol, and heavy brine lyotropic lamellar phase subjected to shear flow has been observed here by small angle neutron scattering to undergo collapse of smectic order above a threshold shear rate. The results are compared with theories predicting that such a lamellar phase sheared above a critical rate should lose its stability by a loss of resistance to compression due to the suppression of membrane fluctuations.

Cetylpyridinium↗
PubMed2004

Topological relaxation of a shear-induced lamellar phase to sponge equilibrium and the energetics of membrane fusion.

We report time-resolved small angle neutron scattering (t-SANS) measurements of the topological relaxation of Couette shear-induced stacked L(alpha) lamellar states to their multiconnected isotropic L3 sponge equilibrium phases in a surfactant bilayer membrane system. Comparison of this structural relaxation time to the interval between diffusive membrane contacts, as determined from dynamic light scattering or estimated from the shear rates required for L(alpha) saturation, allows us to determine the activation energy barrier to the membrane fusion process reestablishing the solution channel handles that characterize the sponge phase.

Cetylpyridinium↗
PubMed2003

Microbially influenced corrosion as a model system for the study of metal microbe interactions: a unifying electron transfer hypothesis.

The general term biomineralisation refers to biologically induced mineralisation in which an organism modifies its local microenvironment creating conditions such that there is chemical precipitation of mineral phases extracellularly. Most usually this results from an oxidation or reduction carried out by some microbial species, with the formation of a recognised biomineralised product. These reactions play a major role in microbial physiology and ecology, and are of central importance to such engineering consequences as microbial mining and microbially influenced corrosion. This paper will examine metal microbe interactions, both in naturally occurring microbial ecosystems and in two particular cases of biocorrosion, with the objective of putting forward a unifying hypothesis relevant to the understanding of each of these apparently disparate processes.

Anaerobiosis↗
PubMed2002

Scaling of shear-induced transformations in membrane phases.

Surfactant sponges are complex-fluid phases made up of convolutions of bilayer sheets. Although isotropic and free flowing they exhibit transient birefringence when stirred, reminiscent of the birefringence of lamellar phases. Previous attempts to understand this effect have led to confusing and often conflicting results. We have used a novel approach to designing the chemical system that gives us control over the relevant parameters needed to study microstructural and macroscopic responses of these phases to shear. We find a remarkable universal scaling behavior for both sponge and shear-induced lamellar states, which resolves a number of long-standing questions about these systems.

Lipid Bilayers↗
PubMed2001

Adsorbed layer structure of cationic surfactants on quartz.

Recent atomic force microscopy (AFM) surface images of surfactant adsorbed at solid and solution interfaces have shown apparent micellar aggregates familiar from bulk self-assembly. This contradicts the classical picture of laterally unstructured bilayers within which neutron reflectometry (NR) measurements have previously been analyzed. Applying both techniques to surfactant adsorption on quartz, we show that film thickness and coverage parameters derived from NR results are generally consistent with those from AFM and bulk self-assembly. NR by itself allows us to distinguish between actual bilayer and probable aggregate adsorption, which will be of particular importance when a solution's rheology makes AFM imaging impractical.

Journal Article↗
PubMed1999

The same species of sulphate-reducing Desulfomicrobium occur in different oil field environments in the north sea.

Several metabolic types of sulphate-reducing bacteria, including mesophiles and thermophiles, were successfully obtained from four samples from two different North Sea oil fields. The Gram-negative, rod-shaped, sulphate-reducing strains MM6, EF2, FM2, and GF2 were isolated from drain water, and from drilling muds E, F, and G, respectively. All four isolates grew on lactate, pyruvate, glycerol, and ethanol, with optimal growth temperatures between 25 degrees C and 35 degrees C and at salinities between 0 and 5% NaCl. They were capable of using sulphate, thiosulphate or sulphite, but not nitrate, as electron acceptors. These isolates were tentatively identified to be the same species of Desulfomicrobium based on physiological and biochemical characterization, and 16S rRNA gene analysis. Therefore, the same Desulfomicrobium species was present in different samples from distant oil fields. This result suggests that these microorganisms are likely to be widespread throughout oil field systems, and possibly play an important role in the generation of sulphide.

Bacterial Typing Techniques↗
PubMed1999

Fast relaxation of a hexagonal Poiseuille shear-induced near-surface phase in a threadlike micellar solution.

The dynamics of near-surface conformations in complex fluids under flow should dramatically affect their rheological properties. We have made the first measurements resolving the decay kinetics of a hexagonal phase induced in a threadlike polyionic micellar system under Poiseuille shear near a quartz surface. Upon cessation of shearing flow, this minimum interference crystalline phase formed within approximately 20 microm of the surface "melts" to a metastable two-dimensional liquid of aligned micelles in approximately 0.7 s. This is some three orders of magnitude shorter than the time required for bulk (Couette) shear-aligned micelles in this system to reach a fully entangled state.

Journal Article↗
PubMed1998

Identification and Phylogenetic analysis of thermophilic sulfate-reducing bacteria in oil field samples by 16S rDNA gene cloning and sequencing.

Thermophilic sulfate-reducing bacteria (SRB) have been recognized as an important source of hydrogen sulfide (H2S) in hydrocarbon reservoirs and in production systems. Four thermophilic SRB enrichment cultures from three different oil field samples (sandstone core, drilling mud, and production water) were investigated using 16S rDNA sequence comparative analysis. In total, 15 different clones were identified. We found spore-forming, low G+C content, thermophilic, sulfate-reducing Desulfotomaculum-related sequences present in all oil field samples, and additionally a clone originating from sandstone core which was assigned to the mesophilic Desulfomicrobium group. Furthermore, three clones related to Gram-positive, non-sulfate-reducing Thermoanaerobacter species and four clones close to Clostridium thermocopriae were found in enrichment cultures from sandstone core and from production water, respectively. In addition, the deeply rooted lineage of two of the clones suggested previously undescribed, Gram-positive, low G+C content, thermophilic, obligately anaerobic bacteria present in production water. Such thermophilic, non-sulfate-reducing microorganisms may play an important ecological role alongside SRB in oil field environments.

Journal Article↗
PubMed1998

Bioenergetics of sulphate-reducing bacteria in relation to their environmental impact.

The cellular physiology of the sulphate-reducing bacteria, and of other sulphidogenic species, is determined by the energetic requirements consequent upon their respiratory mode of metabolism with sulphate and other oxyanions of sulphur as terminal electron acceptors. As a further consequence of their, relatively, restricted catabolic activities and their requirement for conditions of anaerobiosis, sulphidogenic bacteria are almost invariably found in nature as component organisms within microbial consortia. The capacity to generate significant quantities of sulphide influences the overall metabolic activity and species diversity of these consortia, and is the root cause of the environmental impact of the sulphidogenic species: corrosion, pollution and the souring of hydrocarbon reservoirs.

Energy Metabolism↗
PubMed1983

Axillofemoral and femorofemoral grafts: a 6-year experience with emphasis on the relationship of peroperative flow measurement to graft survival.

Over a 6-year period 64 axillofemoral bypass and femorofemoral crossover grafts have been performed in 58 patients, most of whom were considered unfit for intra-abdominal surgery. Indications were peripheral ischaemia in 78 per cent and disabling claudication in 22 per cent. The limb salvage rate at 3 years was 75 per cent. No claudicants lost limbs, but only one-third of patients presenting with forefoot gangrene or ulceration avoided amputation. Most patients presenting with ischaemic symptoms at rest had associated femoropopliteal and distal disease, confirmed by the ankle pressure index measurements, and this influenced graft patency. Although the cumulative patency at 3 years for all grafts combined was 57 per cent with similar patencies for both the axillofemoral and femorofemoral grafts, early occlusion was more common in axillofemoral grafts and this may be reduced in bifemoral grafts by the increased flow rate in the vertical limbs. Peroperative electromagnetic flowmeter measurements were made after reconstruction on 55 femoral arteries in 46 of the patients and graft flow velocities were derived from these measurements. Comparison between velocities from those grafts remaining patent and those subsequently occluding showed a high incidence of occlusion in grafts with a maximal velocity after distal vasodilatation of less than 8 cm/s. Graft occlusion after the first postoperative month was more commonly associated with other factors such as continued smoking, severity of distal disease and perigraft infection.

Aged↗
PubMed1983

On-line analysis of the femoral artery flow velocity waveform and its application in the diagnosis of arterial disease.

Analysis of the instantaneous peak velocity waveform obtained from the common femoral artery can be used to provide an objective assessment of arterial disease in the leg. The calculation of waveform indices pulsatility index and rise time together with principal component analysis has been found to be the ideal method by which to assess the flow data on-line.

Blood Flow Velocity↗
PubMed1983

Simple Assay for Accurate Determination of [S]sulfate Reduction Activity.

A method is described for the assay of [S]sulfate reduction in which filter paper wicks are used to trap [S]sulfide. The simplicity of the technique enables large numbers of samples to be conveniently processed. Enhanced sensitivity is achieved since all acid-volatile [S]sulfides produced during the incubation period are counted. Recovery of radioactivity from added Na(2)S is excellent (mean, 100.1%; standard deviation, 1.81; n = 9) and is unaffected by sulfide concentrations of up to 400 mug per sample. Field trial results with anoxic sediment samples are presented.

Journal Article↗