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Biomedical subjects

R S Edwards

Publications and source records attributed to R S Edwards.

At least 19 recordsLinked to original sources
PubMed2006

Pulsed Rayleigh wave scattered at a surface crack.

This paper investigates Rayleigh wave interaction with machined slots on flat aluminium blocks to simulate surface breaking cracks. Using a finite element method, Rayleigh wave scattering by narrow slots of varied depth ranging from 0.5 mm to 20 mm is calculated. Pulsed wideband Rayleigh waves with a centre frequency of 590 kHz and -6 dB bandwidth of 520 kHz is considered. Reflection and transmission coefficients are calculated and compare well with the published literature. We and other workers have reported enhancement of the measured amplitude or particle velocity of an apparent Rayleigh wave close to a surface defect. In this paper, it is found that the predicted enhancement of in-plane components of particle velocities close to a crack is significantly higher than that of the out-of-plane components of particle velocities which appears to be mainly due to the mode-converted surface skimming longitudinal wave from the crack that has mainly in-plane components near the sample surface. The enhancement of the in-plane particle velocity will be observed regardless of the type of in-plane sensitive ultrasonic detector used. The explanation of the discrepancy of the reflection and transmission coefficients obtained by pulsed and narrow band or pseudo continuous Rayleigh waves is discussed. The later-arriving Rayleigh waves from reverberation along the inside of the crack surface are observed, as has been previously reported by other workers, and this may also be used to gauge slot depth.

Journal Article↗
PubMed2006

Coupling mechanism of an EMAT.

Electro-magnetic acoustic transducers (EMATs) generate ultrasonic waves in metals through an electromagnetic coupling mechanism. A concept for EMAT generation, using a coil alone without a permanent magnet, but with a pulse generator and a sample, is introduced. A simplified equivalent coil circuit is given, and has been validated by experimental measurements. Such an equivalent circuit is useful for excitation current calculations, which have often been neglected in previous publications in this area but have proved to be of great importance in considering the efficiency and frequency characteristics of ultrasonic generation. Due to the coil sample coupling, the equivalent coil inductance is dependent on the electrical conductivity and magnetic permeability of the metal sample, the lift-off, the coil orientation relative to the metal sample and the coil configuration. The use of a coil alone to generate ultrasound has limited applications as a suitable ultrasonic detector must also be used, but where appropriate this type of generation source provides a robust, non-contact and inexpensive means of ultrasonic generation without worrying the permanent magnet attracting ferromagnetic particles that can prevent from practical on-line application of EMATs.

Journal Article↗
PubMed2005

Depth gauging of defects using low frequency wideband Rayleigh waves.

In non-destructive testing for cracks it is not sufficient to simply detect the presence of a defect, but it is essential to have an accurate measure of the depth. Accurate calibration of the techniques used to gauge defect size is therefore necessary. Recent progress in the field of non-contact ultrasonic testing has led to the development of a practically viable system for generating and detecting wideband Rayleigh waves on electrically conducting or magnetic samples using electro-magnetic acoustic transducers (EMATs). This system has been used to gauge the depth and position of surface breaking defects, and has many applications including metal billet testing and detecting and sizing gauge corner cracking in rails. In this paper we report experiments calibrating the response of EMATs when a defect is present between the generator and receiver, using a calibration sample with slots machined perpendicular to the surface to simulate surface breaking cracks. The depth of the defect can be gauged in the time domain and frequency domain, with an accurate 'fingerprint' of the position given by an enhancement of the signal when the receiver is close to the defect. The best choice of EMAT design for different applications is discussed, as is the best position for the receive EMAT to avoid areas of interference between the Rayleigh wave and bulk waves diffracted from the crack tip.

Journal Article↗
PubMed2003

Quantum coherence in an exchange-coupled dimer of single-molecule magnets.

A multi- high-frequency electron paramagnetic resonance method is used to probe the magnetic excitations of a dimer of single-molecule magnets. The measured spectra display well-resolved quantum transitions involving coherent superposition states of both molecules. The behavior may be understood in terms of an isotropic superexchange coupling between pairs of single-molecule magnets, in analogy with several recently proposed quantum devices based on artificially fabricated quantum dots or clusters. These findings highlight the potential utility of supramolecular chemistry in the design of future quantum devices based on molecular nanomagnets.

Journal Article↗
PubMed2003

Definitive spectroscopic determination of the transverse interactions responsible for the magnetic quantum tunneling in Mn(12)-acetate.

We present detailed angle-dependent single crystal electron paramagnetic resonance (EPR) data for field rotations in the hard plane of the S=10 single molecule magnet Mn(12)-acetate. A clear fourfold variation in the resonance positions may be attributed to an intrinsic fourth-order transverse anisotropy (O(4)/(4)). Meanwhile, a fourfold variation of the EPR line shapes confirms a recently proposed model wherein disorder associated with the acetic acid of crystallization induces a locally varying quadratic (rhombic) transverse anisotropy [O (2)/(2) identical with E(S (2)/(x)-S(2)/(y))]. These findings explain most aspects of the magnetic quantum tunneling observed in Mn(12)-acetate.

Journal Article↗
PubMed1997

A comparative study of Ocusert Pilo 40, intensive pilocarpine and low-dose pilocarpine in the initial treatment of primary acute angle-closure glaucoma.

Acetazolamide and pilocarpine have a central role in the initial management of primary acute angle closure glaucoma (PACG), but there is no consensus concerning their mode of delivery, as borne out by a recent survey of senior UK ophthalmologists reported below. Ocusert Pilo 40 was developed to remain in situ releasing pilocarpine for up to one week. In view of its potential advantages, a trial of Ocusert Pilo 40's efficacy in PACG was conducted. In two separate controlled studies, eyes diagnosed with PACG were randomised to receive Ocusert Pilo 40, and either an intensive pilocarpine regimen or a low-dose pilocarpine treatment. All patients also received Diamox 500 mg i.v. Two hours after starting topical treatment, the study was terminated and ocular and systemic response to treatment and the eventual outcome were assessed. In both studies, intravenous Diamox caused a fall of intraocular pressure (IOP) within 30 min. Over the treatment period, a comparable reduction in IOP was seen in the Ocusert-treated, the intensive-pilocarpine-treated, and the low-dose-pilocarpine-treated groups. No damage to the corneas were observed.

Acetazolamide↗
PubMed1987

Ophthalmic emergencies in a district general hospital casualty department.

A survey of ophthalmic emergencies attending the casualty department of a district general hospital over a 12-month period is presented. The total number of new casualty attendances was 30,649 of which 1870 (6.1%) presented with an ophthalmic problem. There was a 3 to 1 male to female preponderance and a peak age of presentation between 20 and 30 years. The main aetiological factors were trauma 65.6% and inflammation 21.7%. Of the trauma patients 80% had sustained minor trauma (abrasions or foreign material to the cornea or conjunctiva) and of the patients with inflammation 71% had either conjunctivitis or blepharitis. There was a trend towards increased numbers in the summer months. The percentage of patients with inflammatory disease was higher in the early summer and the winter months. Nine of the 11 patients with acute angle closure glaucoma presented between November and February. All patients were initially seen by the accident and emergency medical staff, who were able to treat 69% without further consultation. No serious pathology was overlooked. It is suggested that, in the district general hospital setting, co-operation between the eye and the accident and emergency departments can be to their mutual benefit.

Adolescent↗
PubMed1985

Retinal detachment in retinitis pigmentosa.

Three cases of retinal detachment occurring in patients with retinitis pigmentosa are presented and three previously reported cases reviewed. All the detachments were rhegmatogenous. One patient had a horseshoe tear, one had oral bay tears, two had dialyses, one a giant tear and in one case the break was not specified. Three patients were high myopes. All the patients were young males. The five operable cases all responded satisfactorily to conventional surgery. Histologically apparent adhesions between retinal pigment epithelium and neuroretina have been described in advanced cases of retinitis pigmentosa in older patients and may not be present in younger patients with less advanced disease. Until these adhesions occur patients with retinitis pigmentosa may have no additional protection against retinal detachment.

Adolescent↗
PubMed1982

Behaviour of the fellow eye in acute angle-closure glaucoma.

A retrospective study of 245 fellow eyes of patients admitted in primary acute angle-closure glaucoma (ACG) is presented. Twenty-five (10.2%) had acute ACG in the fellow eye on presentation. Of the remaining 220, 33 (15%) subsequently developed acute ACG before prophylactic surgery was performed. Possible predisposing factors were analysed. The main findings were that acute ACG in the fellow eye occurred most frequently in hospital, or during the first month after discharge if prophylactic surgery was not performed. The instillation of mydriatics in the operated eye increased the risk to the fellow eye. Pilocarpine and carbonic anhydrase inhibitors confer the best protection on the fellow eye, but no medical regimen entirely prevented an attack of acute ACG in the fellow eye.

Acute Disease↗
PubMed1980

Trabeculectomy combined with cataract extraction: a follow-up study.

Fifty-nine eyes undergoing combined cataract extraction and trabeculectomy were studied. The follow-up period ranged from 6 months to 2 years. The visual outcome and postoperative control of intraocular pressure have been compared in chronic open-angle, chronic closed-angle, and secondary glaucoma. Good results were obtained in both primary open- and closed-angle glaucoma, but not in secondary glaucoma.

Adult↗
PubMed1977

Perceptual load in searching for sloping colored lines camouflaged by colored backgrounds: a separate-groups investigation.

Altogether 168 men searched briefly for colored sloping lines embedded in a background of random color. Using a separate-groups experimental design, search for six kinds of target was found to be less effective after practice than search for a single kind of target. Reducing the number of colors of targets from three to one was considerably more beneficial than reducing the number of main directions of slope from two to one. Reducing the number of kinds of target without reducing the number of relevant stimulus values was also found to improve the effectiveness of search, but search was even more effective when the number of relevant stimulus colors was reduced. The results can be predicted from the total number of selection operations required. However, a more precise fit needs to reflect the considerably greater difficulty of searching for a number of directions of slope. When targets were poorly camouflaged, search was equally effective whether there were four colors or only a single color of target to search for.

Adolescent↗