PubMed Health⌕ Search

Biomedical subjects

S D Evans

Publications and source records attributed to S D Evans.

11 recordsLinked to original sources
PubMed2003

Surface energy of ethylene-co-1-butene copolymers determined by contact angle methods.

Wilhelmy plate measurements of contact angles with a series of test liquids are used to calculate the surface energies of two poly(ethylene-co-1-butene) random copolymers. Results from five methods of calculation are reported: one-liquid (Good-Girifalco and Neumann), two-liquid (harmonic mean and geometric mean), and three-liquid (Lifshitz-van der Waals acid-base) methods. We find that all five methods are sensitive to the choice of test liquids used for contact angle measurements, as previously reported, but consistent results are obtained if recommended combinations of liquids are used. The mean results of the three-liquid acid-base method are judged to be the most reliable and informative, leading to surface energies of 30.8 mJ/m2 for poly(ethylene-co-1-butene) copolymer composed of 92 mol% ethylene and 30.2 mJ/m2 for copolymer composed of 88 mol% ethylene.

Journal Article↗
PubMed2000

Discrete membrane arrays.

This review describes various methods for the attachment of phospholipid bilayers to solid supports. The simplest approach involves vesicle unrolling onto a surface that has been previously modified with a continuous self-assembled monolayer (SAM). The choice of a suitable SAM can lead to the formation of attached bilayers that have the desired biomimetic properties and are suitable for studying transmembrane proteins. However, there are intrinsic problems associated with this approach if one is interested in studying ion transport phenomena. In particular, the relatively low resistance values found for such bilayers do not permit studies of single ion channels. For such studies to be carried out the background leakage through the lipid film must be greatly reduced. In an attempt to reduce the problems of leakage we have formed patterned SAMs in which a blocking, hydrophobic, layer covers 90% of the electrode surface. The remaining portion of the surface, which is hydrophilic, supports the formation of a bilayer. This approach has led to an improvement in the quality of the bilayers formed but has still not provided bilayers with sufficiently high specific resistances to study single ion channels. Finally, we describe new approaches based on the formation of bilayers suspended over small apertures. These 'suspended' bilayers are similar in structure to those used in black lipid membrane experiments and give rise to highly blocking bilayer membranes. Unfortunately, this approach requires the use of solvents to create the suspended bilayer and they are relatively fragile.

Lipid Bilayers↗
PubMed1999

Quantitative magnetic resonance imaging of fresh and frozen-thawed trout.

Magnetic resonance imaging (MRI) has been used to visualise the major organs and muscular-skeletal frame-work of fresh rainbow trout (Salmo gairdneri) in two dimensions, and to identify the spatial distribution of lipid- and collagen-rich tissues. Quantitative MRI provides the MR parameters (T1, T2, M0, T1sat, Msat/M0, and the Magnetisation Transfer (MT) rate) for the tissue water; variations in those parameters enable distinction to be made between a freshly killed trout and one which has been frozen-thawed. The effects of freezing method, repeat freeze-thawing, and storage time on the MR parameters are discussed.

Animals↗
PubMed1997

Drug-induced hyperthermia.

Drug-related causes of hyperthermia can often be overlooked in the setting of elevated body temperature. This article reviews the pathophysiology, presentation, and treatment of several drug-induced hyperthermia syndromes: malignant hyperthermia, neuroleptic malignant syndrome, sympathomimetic poisoning, and anticholinergic toxicity. Although the general approach is similar, specific management strategies may be required for each syndrome.

Cholinergic Antagonists↗
PubMed1992

Spectrophotometric measurements of haemoglobin saturation and concentration in skin during the tuberculin reaction in normal human subjects.

A non-invasive technique employing light-guide spectrophotometry is described for the measurement of haemoglobin concentration and oxygenation in human skin. Measurements were carried out in the visible wavelength range (500-620 nm) and a series of experiments were carried out in vitro and in vivo in order to calibrate the system. Indices were derived for the measurement of relative haemoglobin concentration and absolute oxygen saturation. The technique was applied to measure the changes in these parameters occurring during the course of the tuberculin reaction in human skin. The results are compared with those from laser Doppler flowmetry and transcutaneous oxygen measurements which were carried out concurrently. Divergence between the intracapillary and tissue oxygenation during the course of the reaction provides evidence for the existence of increased diffusion resistance for oxygen; a model is proposed. The study demonstrates the potential clinical usefulness of light-guide spectrophotometry for the non-invasive investigation of tissue oxygen supply.

Adult↗
PubMedDate not supplied

Measurement of textural changes of food by MRI relaxometry.

This article summarises the current status of, and future prospects for, the use of magnetic resonance imaging (MRI) to evaluate the texture of a range of foods, and changes therein which accompany pathogen infection, natural ageing, damage, ripening and processing. The basic concept is that the magnetic resonance parameters of water are sufficiently sensitive to the texture of the food matrix, that magnetic resonance images of the spatial distribution of those parameters are effectively maps of the structural status of the foodstuff. This is illustrated in the context of the effects of pathogen infection in cucumbers, internal necrosis of melons, bruising in peaches, ripening of pineapples, and the effect of freeze-thawing on meat and fish.

Animals↗