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Biomedical subjects

S Dixon

Publications and source records attributed to S Dixon.

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

Lift-off compensation for improved accuracy in ultrasonic lamb wave velocity measurements using electromagnetic acoustic transducers (EMATs).

The crystalline texture of a sheet metal strongly affects its formability, so having knowledge of this texture is of great industrial relevance. The texture of rolled sheet metals, such as aluminium and steel, may be determined by ultrasonic measurement of the velocity of the zero order symmetric (S(0)) Lamb wave as a function of angle to the rolling direction. Electromagnetic acoustic transducers (EMATs) may perform this measurement without contacting the sample, therefore reducing perturbation to the plate wave system, as they are electromagnetically coupled to the sheet. The EMAT system measurements are non-destructive and may be made in real time, therefore offering advantages over the conventional techniques such as X-ray and neutron diffraction. It has been noticed that in the two EMAT pitch-catch system, the apparent arrival times of the ultrasonic waves change with variation in lift-off (distance between sample and transducer) due to impedance and aperture effects. For precise and accurate texture parameters to be obtained, accurate absolute ultrasonic velocity measurement is required and hence lift-off must be compensated for. This is of particular importance to online inspection systems where constant lift-off may be difficult to maintain. The impedance behaviour of various coil geometries has been investigated as a function of lift-off and frequency and compared to the received ultrasonic signal and the drive current pulse profile. Theoretical models have been used to explain the observed behaviour, and hence a scheme has been proposed for the compensation of lift-off effects in real time.

Journal Article↗
PubMed2006

Development of an advanced multimode automatic ultrasonic texture measurement system for laboratory and production line application.

We present work on the development of an ultrasonic texture measurement system for sheet metals using non-contact transducers, suitable for use both in the laboratory and on the production line. Variation of the velocity of the zero-order symmetric (S0) Lamb wave is used to determine the crystallographic texture of polycrystalline metal sheets ranging in thickness from 0.1 to 3 mm. This system features improvements on previous state-of-the-art ultrasonic technology in that it probes velocity over a continuous range of angles using only two electromagnetic acoustic transducers (EMATs). This is demonstrated to offer a significant improvement in accuracy and allows the detection and investigation of asymmetric anisotropies in the sheets. Another advantage of the system is its potential for combining several different measurements using a single pair of transducers. The capability is demonstrated for through-thickness shear wave measurements as well as the zero-order symmetric Lamb wave measurements which are the primary means of determining the texture. The change between generating Lamb and through-thickness bulk waves can be made entirely by changing the electrical circuit connected to the EMATs without modifying the transducer assembly in any way. Measurement of all of the above waves can provide information on the sheet thickness and other physical properties of the sheet in addition to texture. Certain texture parameters can be calculated from both Lamb and shear wave velocities, allowing self-calibration of the system.

Electromagnetic Phenomena↗
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↗
PubMed2006

Quality of life and cost-effectiveness of interferon-alpha in malignant melanoma: results from randomised trial.

A definitive conclusion regarding the value of low-dose extended duration adjuvant interferon-alpha therapy in the treatment of malignant melanoma is only possible once data on health-related quality of life (HRQoL) and costs have been considered. This trial randomised 674 patients to interferon alpha-2a (3 megaunits three times per week for 2 years or until recurrence) or placebo. Health-related quality of life (QoL) was to be assessed up to 60 months using the European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30. Data for the economic analysis, including cost information and the EQ-5D were also collected. Patients in the observation (OBS) group had significantly better mean follow-up quality of on five dimensions of the EORTC QLQ-C30 functional scales: role functioning (P = 0.033), emotional functioning (P = 0.003), cognitive functioning (P = 0.001), social functioning (P = 0.003) and global health status (P = 0.001). Patients in the OBS group had significantly better mean follow-up symptom scores on seven dimensions of the EORTC QLQ-C30 V1 symptom scales. Economic data showed that costs were 3066 pounds higher in the interferon group and produces an incremental cost per quality-adjusted life year of 41,432 pounds at 5 years. The results show that interferon has significant effects on QoL and symptomatology and is unlikely to be cost-effective in this patient group in the UK.

Adult↗
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↗
PubMed2005

Polyurethanes as potential substrates for sub-retinal retinal pigment epithelial cell transplantation.

Transplantation of cultured retinal pigment epithelial (RPE) cells under the failing macular is a potential treatment for age related macular degeneration. An important step in the development of this procedure is the identification of a suitable membrane on which to grow and transplant the cells. This paper evaluates the potential of using polyurethanes in this application since they possess several of the required properties, such as, flexibility, robustness, biostability and good biocompatiblilty although their hydrophobicity can limit cell adhesion. Three commercially available polyether urethanes (Pellethane, Tecoflex and Zytar) were evaluated in terms of their wettability using dynamic contact angle analysis and their ability to support a monolayer of functioning RPE cells (ARPE-19) . Furthermore Pellethane and Tecoflex were treated with a simple air plasma treatment and analysed as above. In the "as received condition" only a few RPE cells attached to the Pellethane and Tecoflex and remained clumped. RPE cells grew to confluence on the Zytar substrate by 7 days without further surface modification. Air gas plasma treatment of both Pellethane and Tecoflex increased the wettability of the surfaces and this resulted in the growth of a monolayer of well-spread RPE cells on both materials. Morphologically these cells grew with a normal 'cobblestone' phenotype. These results demonstrate the potential of these polyurethanes for this application.

Cell Line↗
PubMed2005

Is a chest pain observation unit likely to be cost effective at my hospital? Extrapolation of data from a randomised controlled trial.

OBJECTIVES: The ESCAPE trial showed that chest pain observation unit (CPOU) care appeared to be cost effective compared with routine care. This finding may not be generalizable to hospitals that currently admit fewer patients than the trial hospital or that require higher direct costs to provide CPOU care. This study aimed to explore these issues in sensitivity analyses and develop a nomogram to allow prediction of whether a CPOU will be cost effective in a specific hospital. METHODS: Data from the ESCAPE trial was used to populate a decision analysis model comparing CPOU with routine care. Sensitivity analyses examined the effect of varying the admission rate with routine care and the direct running costs of CPOU care following which the nomogram was created. RESULTS: CPOU care provided improved outcome (0.3936 v 0.3799 QALYs) at lower cost (pound sterling 478 v pound sterling 556 per patient), with fewer patients admitted (37% v 54%). Mean cost of CPOU and routine care was pound sterling 116 and pound sterling 73, respectively, and of inpatient hospital stay was pound sterling 312. The mean post-discharge cost for CPOU and routine care was pound sterling 253 and pound sterling 309, respectively. Sensitivity analyses showed that CPOU care will not reduce costs at a hospital that currently admits fewer than 35% of patients, or a hospital that expects to incur direct CPOU running costs of pound sterling 60 per patient more than the trial hospital. CONCLUSIONS: Findings of the ESCAPE trial are likely to be generalizable to most settings. The nomogram presented here can be used to predict cost effectiveness in a specific hospital.

Cardiac Care Facilities↗
PubMed2004

Wideband low frequency generation and detection of Lamb and Rayleigh waves using electromagnetic acoustic transducers (EMATs).

This paper describes a new type of non-contact electromagnetic transducer (EMAT) that can be used to generate both Lamb and Rayleigh waves on metal samples. The generated waves are wideband and low frequency with a dominant frequency content centred at approximately 200 kHz extending to around 500 kHz. The transducers have been used on both aluminium and steel, but operate more efficiently on aluminium due to its lower electrical resistance and density when compared to steel.

Journal Article↗
PubMed2004

Evaluation of the future supply and demand for blood products in the United Kingdom National Health Service.

In addition to the clinical management of blood supplies, the UK National Blood Service (NBS) examines short-term supply and demand to predict any potential shortages in blood supplies. However, very little data are available on the medium- and long-term trends. This paper describes blood product use in a United Kingdom Hospital Trust in 1999 and combines it with donor information to project the effect of demographic changes on demand and supply over the next 25 years. Overall, 2801 (4%) inpatients received transfusions of blood products. The proportion of inpatients receiving blood products increased with age. Patients aged >70 years used 46% of the total blood product supply, whereas patients aged <30 years used 10%. The estimated total cost associated with blood product use was pound 2 million during 1999 (2001-2002 prices). The results show that within 20 years, demand for blood products is expected to increase by 20% relative to the supply. The estimates in this study are a valuable aid to better long-term planning of supplies. As there is a paucity of data concerning blood product use in UK hospitals and blood use varies greatly between hospitals, further studies are required to guide blood product use policy.

Adult↗
PubMed2004

Psychological treatment for insomnia in the regulation of long-term hypnotic drug use.

OBJECTIVES: To evaluate the clinical and cost impact of providing, in routine general practice settings, a cognitive-behaviour therapy (CBT) package for insomnia to long-term hypnotic drug users with chronic sleep difficulties; and to identify factors associated with variations in clinical outcomes. DESIGN: A pragmatic cluster randomised controlled trial with two treatment arms (a CBT-treated 'sleep clinic' group, and a 'no additional treatment' control group), with post-treatment assessments starting at 3, 6 and 12 months. SETTING: Twenty-three general practices in Sheffield, UK. PARTICIPANTS: In total, 209 patients (aged 31-92 years) with chronic sleep problems who had been receiving repeat hypnotic drug prescriptions for at least 1 month (mean = 13.4 years) were recruited into the trial. INTERVENTIONS: The intervention consisted of six 50-minute sessions as follows: introduction and sleep assessment, basic sleep hygiene, stimulus control and sleep restriction procedures, progressive relaxation, cognitive treatments, and review and discharge. MAIN OUTCOME MEASURES: These included: global sleep quality [as measured by the Pittsburgh Sleep Quality Index (PSQI)], frequency of hypnotic drug use, mean dose of hypnotics consumed, health-related quality of life [as measured by the Short-Form 36 (SF-36)], NHS service costs and overall cost utility. RESULTS: At 3- and 6-month follow-ups, patients treated with CBT showed improved global PSQI scores as well as improvements in the SF-36 dimensions of vitality at 3 months and physical functioning and mental health at 6 months. CBT-treated patients also reported reductions in the frequency of hypnotic drug use compared with the control group, with many CBT-treated patients reporting zero drug use at the follow-up assessments. Clinical improvements were maintained within the CBT group at the 12-month follow-up, with PSQI scores and the frequency of hypnotic drug use continuing to show significant reductions relative to the control group. Multiple regression analyses of PSQI scores within the sleep clinic group alone indicated that the magnitude of pre- to post-treatment change in overall sleep quality was closely related to Hospital Anxiety and Depression Scale depression scores at 3-, 6-and 12-month follow-ups. In each model higher depression scores at baseline were associated with poorer treatment outcomes. No significant relationship was found between the patient's age and PSQI outcomes in any of these analyses. Within the sleep clinic group, reductions in drug use showed no significant association with the hypnotic product consumed. At the 3-month follow-up low-frequency drug use was reported by 22.9% (8/35) of temazepam users, 33.3% (5/15) of nitrazepam users and 38.9% (7/18) of zopiclone users. The total cost of service provision was GBP154.40 per patient (1999/2000 prices). The mean incremental cost per quality-adjusted life-year (QALY) at 6 months was GBP3418; this figure was insensitive to changes in costs. A simple model also showed that extending the evaluation period beyond 6 months may improve the cost-effectiveness of CBT. The incorporation of hidden costs associated with hypnotic drug treatment (e.g. accidents) also reduces the cost per QALY ratio, although to a much lesser degree. CONCLUSIONS: In routine general practice settings, psychological treatment for insomnia can improve sleep quality, reduce hypnotic drug use, and improve health-related quality of life at a favourable cost among long-term hypnotic users with chronic sleep difficulties. These positive outcomes appear robust over time, persisting for at least 1 year among the more treatment-adherent patients. While these benefits may be reduced among those patients presenting with higher levels of psychological distress, the present study clearly indicates that older age per se presents no barrier to successful treatment outcomes. Further research should assess the long-term clinical and cost-effectiveness of psychological treatments for insomnia among non-hypnotic-using patients, and establish the minimum psychological treatment input required.

Adult↗
PubMed2003

The detectability of kissing bonds in adhesive joints using ultrasonic techniques.

This paper concerns a study of the detectability of dry contact kissing bonds in adhesive joints using three ultrasonic inspection techniques. Conventional normal incidence longitudinal and shear wave inspection were conducted on dry contact kissing bonds using a standard damped ultrasonic transducer and an electro-magnetic acoustic transducer (EMAT) respectively. The detectability of the dry contact kissing bonds was assessed by calculating the reflection coefficient of the imperfect interface at varying loads for a number of surface roughnesses. A high power ultrasonic method was also employed to determine the non-linear behavior of the adhesive interface. The non-linearity of the interface was determined by the ratio of the amplitudes of the first harmonic and fundamental frequencies of the transmitted waveform. It was found that the high power technique showed the greatest sensitivity to these kissing bonds at low contact pressures, however at high loads conventional longitudinal wave testing was more sensitive. It was also noted that a combination of two or more techniques could provide enhanced information about the kissing bond compared to a single technique alone.

Adhesives↗
PubMed2001

Identification of a new form of death-associated protein kinase that promotes cell survival.

In this study, two alternatively spliced forms of the mouse death-associated protein kinase (DAPK) have been identified and their roles in apoptosis examined. The mouse DAPK-alpha sequence is 95% identical to the previously described human DAPK, and it has a kinase domain and calmodulin-binding region closely related to the 130-150 kDa myosin light chain kinases. A 12-residue extension of the carboxyl terminus of DAPK-beta distinguishes it from the human and mouse DAPK-alpha. DAPK phosphorylates at least one substrate in vitro and in vivo, the myosin II regulatory light chain. This phosphorylation occurs preferentially at Ser-19 and is stimulated by calcium and calmodulin. The mRNA encoding DAPK is widely distributed and detected in mouse embryos and most adult tissues, although the expression of the encoded 160-kDa DAPK protein is more restricted. Overexpression of DAPK-alpha, the mouse homolog of human DAPK has a negligible effect on tumor necrosis factor (TNF)-induced apoptosis. Overexpression of DAPK-beta has a strong cytoprotective effect on TNF-treated cells. Biochemical analysis of TNF-treated cell lines expressing mouse DAPK-beta suggests that the cytoprotective effect of DAPK is mediated through both intrinsic and extrinsic apoptotic signaling pathways and results in the inhibition of cytochrome c release from the mitochondria as well as inhibition of caspase-3 and caspase-9 activity. These results suggest that the mouse DAPK-beta is a negative regulator of TNF-induced apoptosis.

Alternative Splicing↗
PubMed2001

Evaluation of the HUD lead hazard control grant program: early overall findings.

This study evaluates the effectiveness of lead hazard control methods used in the Lead Hazard Control (LHC) grant program of U.S. Department of Housing and Urban Development. The LHC Program awards funds to local jurisdictions to address lead hazards in privately owned, low-income dwellings. Grantees in 14 cities, states, or counties collected environmental data in over 2600-treated dwellings making this the largest study of residential lead hazard control ever undertaken. Grantees employed a range of treatments, the most common being replacement of windows and repair of deteriorated lead-based paint. In this paper, dust lead loading levels and blood lead levels of children (6 months-6 years, if present) were observed at four periods of time (preintervention, immediate, and 6- and 12-months postintervention) in 1212 dwellings. Dust lead loading levels were also observed in a subset of these dwellings at 24- and 36-months postintervention. The geometric mean floor and window dust lead loadings declined at least 50 and 88% (P<0.0001), respectively, immediately postintervention. Three years later, floor dust lead loadings remained at or below the immediate postintervention levels. Window dust lead loadings had moderate increases, but remained substantially reduced from preintervention levels and below clearance standards. At 1 year after intervention, geometric mean age-adjusted blood lead levels had declined from 11.0 to 8.2 microg/dL, a 26% decline (P<0.0001). The LHC Program interventions produced blood lead declines similar to or greater than the percentage changes reported in earlier 1-year lead intervention studies.

Child↗
PubMed2001

High accuracy non-contact ultrasonic thickness gauging of aluminium sheet using electromagnetic acoustic transducers.

Aluminium sheet thickness has been calculated from ultrasonic data obtained using a send-receive, radially polarised electromagnetic acoustic transducer (EMAT). Sheets in the thickness range between 0.1 and 0.5 mm have been measured using this non-contact approach at a stand-off of up to 1.5 mm. Normal incidence shear waves generated and detected in the sheet and the resultant waveforms have been processed using transit time measurements and Fourier analysis. Two broad band EMAT systems have been used to perform the measurements with centre frequencies of approximately 5 MHz and frequency content up to 10 and 20 MHz respectively. The most accurate measurements of thickness on thin sheets have been made using Fourier analysis and have yielded measurements accurate to within 0.2% (or 0.4 microm) for 280 microm thick aluminium sheets. Discrete shear wave echoes can be observed for sheets down to a thickness of 250 microm using the higher frequency EMAT system. However temporal measurements of these signals yield lower accuracy results when compared to the Fourier analysis method which is capable of sub-micron accuracy.

Aluminum↗
PubMed2001

Evaluation of a hospital diabetes specialist nursing service: a randomized controlled trial.

AIMS: To evaluate the effectiveness and cost implications of a hospital diabetes specialist nursing service. METHODS: We conducted a prospective, open, randomized, controlled trial of standard in-patient care for adults with diabetes, with and without the intervention of a diabetes specialist nursing (DSN) service. The setting was a single UK university hospital. SUBJECTS: were unselected patients referred to the hospital DSN service. Primary outcome measures were length of hospital stay and patterns of readmission (frequency and time to first readmission). Secondary outcome measures were subjects' diabetes-related quality of life, diabetes knowledge score, satisfaction with treatment, and GP and community care contacts following discharge. Costs were estimated from the hospital and published sources. RESULTS: Median length of stay was lower in the intervention group (11.0 vs. 8.0 days, P < 0.01). Readmission rates were the same in the two groups (25%), and mean time to readmission was similar in the two groups, although slightly less in the control group (278 vs. 283 days, P = 0.80). The cost per patient for nursing input was 38.94 pounds sterling. However, when the reduced length of stay was accounted for, the intervention produced a mean cost per admission of 436 ponds sterling lower than that of the control group (P = 0.19). Patients in the intervention group were more knowledgeable regarding their diabetes and more satisfied with their care. CONCLUSIONS: Diabetes specialist nurses are potentially cost saving by reducing hospital length of stay (LOS). There was no evidence of an adverse effect of reduced LOS on re-admissions, use of community resources, or patient perception of quality of care.

Adult↗
PubMed2001

Surface immunolocalisation of HPr in the equine pathogen Streptococcus equi.

We have investigated the surface localisation of the phosphotransferase system protein HPr in the equine pathogen Streptococcus equi subsp. equi using immunogold localisation and transmission electron microscopy. Like the LppC acid phosphatase lipoprotein, a reference surface antigen, the S. equi HPR could be clearly detected on the surfaces of intact cells. This study is consistent with previous reports that some streptococcal HPr is cell surface associated and suggests that the extracytoplasmic mobilisation and transfer of phosphate groups by streptococci warrant further investigation.

Bacterial Proteins↗