Biomedical subjects
Publications and source records attributed to Mary Thompson.
We consider the transition to steady-state flow in the inlet region of a hydrodynamic channel cell and show that a microelectrode positioned within this inlet region allows chronoamperometric results to be recorded, from which information about the extent of the development of the flow profile may be deduced as well as information about the precise dimensions of the microfluidic channel.
A model is developed for the voltammetric response due to surface charge injection at a single point on the surface of a sphere on whose surface the electroactive material is confined. Accordingly, charge diffusion is constrained to the spherical surface and thus mimicks the voltammetric response of immobilised microparticles derivatised with electroactive material. The full cyclic voltammetric response is investigated, and the peak currents, the peak-to-peak separation and the symmetry of the voltammetric wave are shown to be indicative of the heterogeneous kinetics and the geometry of the adsorbed microparticle. The results show strong deviations from the responses expected for planar diffusion.
High intensity microwave radiation is (self-)focused at metal electrodes immersed in aqueous electrolyte solutions to generate highly localized superheating and convection effects. It is shown that, for an electrode pointing downward, low intensity microwave radiation causes density driven convective flow (upward), which at the onset of boiling abruptly switches to a fast jet of liquid moving away from the electrode surface (downward). This "jet-boiling" phenomenon allows extremely high rates of mass transport and mixing to be realized at the electrode surface. Cyclic voltammograms obtained at electrodes placed into a microwave field show very strong mass transport enhancement effects. Cyclic voltammograms recorded at a Pt/Pt ring-disk electrode system (r(1) = 25 microm, r(2) = 32 microm, r(3) = 32.4 microm) in the presence of microwave radiation are employed to further explore mass transport effects under microwave conditions. Mass transport coefficients, collection efficiencies, and temperatures are determined as a function of microwave intensity.
A method is developed whereby spherical and other particles can be derivatised with electroactive species on their surface and then immobilised on the surface of an electrode. The chronoamperometric and voltammetric responses in the limit of reversible electrode kinetics are modelled using a theory of charge movement over the surface of the spheres where this movement is considered as a diffusional process. The model is extended to include different distributions of sphere radii and to model the scenario of truncated spheres resting on the electrode surface. It is found that a good estimation of the truncation angle can be found by fitting the experimental data with theoretical predictions.
The electrochemical oxidation of tris(4-bromophenyl)amine in the presence of 2,6-lutidine is examined in acetonitrile. Voltammetric and spectroscopic investigations suggest that the electrogenerated triaryl aminium radical cation oxidizes 2,6-lutidine in an EC' mechanism, and an equilibrium constant for this homogeneous electron transfer is estimated. The mediated oxidation of a protected phenyl selenoglycoside by this reaction mixture is studied by the use of electrochemical ESR, employing a tubular flow cell, and signal intensity data is found to be consistent with the proposed mechanism, allowing the determination of kinetic parameters by computational simulation. Products of the mediated glycoside oxidation are determined by proton NMR and mass spectrometry.
PURPOSE: The study was designed to determine whether relationships exist among knee muscle spasticity, isometric knee muscle strength, knee muscle balance, gross motor function, and walking efficiency in children with spastic cerebral palsy and to evaluate the relative contributions of impairment measures to functional outcome measures. METHODS: Twenty-seven children with spastic diplegic cerebral palsy participated. Knee muscle strength and spasticity were measured by a hand-held dynamometer and the Ashworth Scale, respectively. Functional abilities were assessed by the Gross Motor Function Measure and by calculating the energy expenditure index from data collected during two three-minute walk tests (comfortable and fast speeds). RESULTS: Significant relationships were found between impairments and functional abilities (r = 0.42-0.85, p < 0.05). Isometric hamstring strength and quadriceps spasticity explained 81.5% of total Gross Motor Function Measure score variance. Quadriceps spasticity explained 56.7% of energy expenditure index variance during comfortable walking. CONCLUSION: Hamstring strength and quadriceps spasticity explain much of the variance in gross motor function and comfortable walking efficiency.
Detecting differentially expressed genes in microarray experiments is a topic that has been well studied in the literature. Many hypothesis testing methods have been proposed that rely on strong distributional assumptions for the gene intensities. However, the shape of microarray data may vary substantially from one experiment to another, and model assumptions may be seriously violated in many cases. The literature on microarray data is mainly based on two distributions: the log-normal and the gamma distributions, that often appear to be effective when used in a Bayesian hierarchical framework. However, if a model that fits the data well in a global manner seems attractive, two points should be regarded with attention: the ability of the model to fit the tail of the observed distribution, and its robustness to a wrong specification of the model, in terms of error rates for the hypothesis tests. In order to focus on these aspects, we propose to use Bayesian models involving the inverse Gaussian distribution to describe gene expression data. We show that these models can be good competitors to the traditional Bayesian or random effect gamma or log-normal models in some situations. A multiple testing procedure is then proposed, based on an asymptotic property of the posterior probability of the one-sided alternative hypothesis. We show that the asymptotic property is well approximated for inverse Gaussian models, even when the number of observations available for each test is very small.
An in situ electrochemical electron spin resonance (ESR) study on the electro-oxidation of para-chloroaniline, para-bromoaniline, and para-iodoaniline dissolved in acetonitrile at gold electrodes is reported. ESR spectra obtained using a tubular flow cell reveal the presence of a paramagnetic dimer product derived from para-aminodiphenylamine, during oxidative electrolysis, suggesting the coupling of reactive electrogenerated radical cations with neutral parent haloaniline molecules. The ESR signal intensity behaves in a manner expected for a radical species reacting with second-order kinetics, suggesting the paramagnetic dimer is, itself, unstable. The theory describing the ESR signal intensity flow rate behavior for this reaction mechanism is developed for the tubular arrangement and used to extract mechanistic and kinetic data from the experimental results for the cases of para-chloroaniline and para-bromoaniline. Further mechanistic aspects, including proton and halide ion expulsion during dimerization, are explored voltammetrically and with the aid of digital simulations using Digisim. Comparison of the ESR signal and voltammetric measurements suggests that an additional mechanism operates which does not lead to paramagnetic products. Additionally, the in situ electrolysis of N,N-dimethyl-para-bromoaniline is reported to generate the stable radical cation of N,N,N',N'-tetramethylbenzidine, and a mechanism of electro-oxidation is, thus, proposed.
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BACKGROUND: Psychotropic medication prescribing for children and adolescents rose significantly between 2000 and 2002, including antidepressant prescribing. In 2003, the Committee on Safety of Medicines (CSM) advised against using venlafaxine or any selective serotonin receptor inhibitor (SSRI), with the exception of fluoxetine, for childhood and adolescent depression. The aim of this study was to compare the prevalence and incidence of children and adolescents who were prescribed antidepressants in UK primary care, before and after the CSM advice on antidepressant prescribing. We also compared paediatric antidepressant prescribing trends from Mediplus data with national antidepressant prescribing trends in England from the Prescription Pricing Authority (PPA). METHODS: The Disease Analyzer-Mediplus database contains anonymised primary care records for about 3 million patients. Eligible patients were aged or=1 antidepressant prescription between 2000 and 2004. Antidepressants were grouped according to the CSM advice and the British National Formulary. Prevalence and incidence were calculated. The prevalences of 2000, 2002 and 2004 were compared using a Chi-squared test. PPA data on antidepressant prescribing rates were compared with paediatric antidepressant prescribing rates from Mediplus. RESULTS: 5,718 children and adolescents received a total of 25,542 prescriptions between 2000 and 2004. The median number of prescriptions per patient was two (interquartile range 1-5). Common indications included depression and anxiety. Antidepressant prevalence increased from 2000 to 2002 (from 5.4 to 6.6 patients per 1,000 people), with a rise in the number of patients prescribed venlafaxine and SSRIs. However, between 2002 and 2004 there was a decrease in antidepressant prevalence (from 6.6 to 5.7 per 1,000). The prevalence of CSM-contraindicated antidepressants (citalopram, escitalopram, fluvoxamine, paroxetine, sertraline and venlafaxine) declined by a third (from 3.1 to 2.0 per 1,000), but there was no change in fluoxetine prevalence (from 2.1 to 2.3 per 1,000). The number of patients prescribed tricyclic antidepressants dropped marginally (from 2.0 to 1.7 per 1,000). Incidences followed the same trends as the prevalences, but there was a 48% reduction in the incidence of CSM-contraindicated antidepressants between 2002 and 2004. National antidepressant prescribing trends increased; paediatric prescribing trends were similar to national trends between 2000 and 2003; however, there was a 27% reduction in the paediatric prescribing rate of CSM-contraindicated antidepressants between 2002 and 2004. CONCLUSION: Since 2003, fewer children and adolescents have been prescribed antidepressants in primary care. However, fluoxetine and non-SSRI antidepressant prevalences have not risen, implying that they are not prescribed as alternative treatments. This study shows that the CSM advice has had a significant effect in reversing the rising prevalence of antidepressant prescribing to children and adolescents in primary care.
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The extent of passivation of calcite toward dissolution by aqueous acids arising from polymeric coatings based on polyacrylic acid or polyacrylonitrile is evaluated using a channel flow cell technique with microdisc electrode detection. In situ passivation with polyacrylic acid leads to a reduction in the reactivity of calcite toward acid attack with a reduction in the rate constant by up to an order of magnitude compared with untreated calcite. Ex situ passivation with polyacrylic acid for 24 h results in good coverage of the calcite by the polymer but it is shown to erode from the surface when exposed to an aqueous acid solution. In contrast, polyacrylonitrile is demonstrated to form a regular coating after exposure for just 1 h and offers robust potent protection from aqueous acid attack.
The dissolution kinetics of surface-pretreated and weathered calcite was investigated in dilute acid using a channel flow cell with microdisk detection. Two pretreatments were studied, polymaleic acid and phosphoric acid. Treatment with polymaleic acid was shown to significantly passivate calcite but to a lesser extent than the phosphoric acid and the former coating was found to be less effective for protection of calcite from acid attack. However, treatment of calcite with phosphoric acid resulted in the passivation of calcite from acid attack which strongly inhibited dissolution, an effect that was enhanced even further after exposure to the environment.
A novel electrode consisting of crystals of an electroactive organic solid immobilised into a carbon-epoxy electrode has been subjected to insonation, which facilitates the clear characterisation of triple-phase processes occurring at the insulator/solution/electrode interface.