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Biomedical subjects

P D Fletcher

Publications and source records attributed to P D Fletcher.

10 recordsLinked to original sources
PubMed2001

Electrical currents and liquid flow rates in micro-reactors.

For micro-reactor devices in which liquids are pumped by electro-osmotic flow (EOF), in situ monitoring of the electrical currents in the channel networks provides a valuable diagnostic tool. We demonstrate here that the voltage-current characteristics of a micro-reactor channel network can be accurately modelled using measurements of the full 3-D geometry of the channel network, the liquid conductivity and the channel wall-liquid surface conductivity. It is shown that surface conductivity provides a significant contribution to the overall measured electrical currents in channel networks for which the ratio of surface area to volume is high. Following correction for surface conductivity, the electrical currents are proportional to the liquid volumetric flow rates measured in the different branches of the channel network. The constant of proportionality is related to the zeta potential of the channel wall-liquid surface. Measurements of the variation of electrical currents and volumetric flow rates as a function of the applied voltages allows the determination of the surface conductivity and zeta potential within the micro-reactor which enables the prediction of the voltages required to produce the desired flow rates in any channel section. In situ logging of the electrical currents, incorporated within the control system, allows continuous monitoring of the liquid flow rates during micro-reactor operation.

Journal Article↗
PubMed2001

Quantitative 3-dimensional profiling of channel networks within transparent lab-on-a-chip microreactors using a digital imaging method.

We have developed a method for the quantitative 3-dimensional profiling of micron sized channel networks within optically transparent "lab-on-a-chip" microreactor devices. The method involves capturing digitised microscope images of the channel network filled with an optically absorbing dye. The microscope is operated in transmission mode using light filtered through a narrow bandpass filter with a maximum transmission wavelength matching the wavelength of the absorbance maximum of the dye solution. Digitised images of a chip filled with solvent and dye solution are analysed pixel by pixel to yield a spatially resolved array of absorbance values. This array is then converted to optical path length values using the Beer-Lambert law, thereby providing the 3D profile of the channel network. The method is capable of measuring channel depths from 10 to 500 microm (and probably even smaller depths) with an accuracy of a few percent. Lateral spatial resolution of less than 1 microm is achievable. It has been established that distortion of the measured profiles resulting from a mismatch in refractive index between the dye solution and the glass of the microreactors is insignificant. The method has been successfully used here to investigate the effects of thermal bonding and etch time on channel profiles. The technique provides a convenient, accurate and non-destructive method required to determine channel profiles; information which is essential to enable optimisation of the operating characteristics of microreactor devices for particular applications.

Journal Article↗
PubMed1995

Relationships between physical growth, mental development and nutritional supplementation in stunted children: the Jamaican study.

The relationship between physical growth and change in mental development on the Griffiths mental development scales was investigated in 127 stunted Jamaican children over a 2-year period. The role of nutritional supplementation in this relationship was examined. There were no consistent associations between changes in weight-for-height or head circumference and developmental change. Height gain over 2 years was significantly associated with change in mental age, and locomotor and hearing and speech subscale scores. Height gain in the first year predicted change in mental age, and hearing and speech in the second year. Some of the effect of supplementation on development was shared with linear growth. Therefore, nutrition probably explains part of the relationship between growth and development. However, supplementation also had effects on development independent of growth. The benefits of supplementation on development and the extent to which they were shared with growth varied among the subscales.

Body Height↗
PubMed1988

A quasi-elastic neutron-scattering study of the molecular mobility of water associated with a protein both in aqueous solution and adjacent to a charged surfactant interface.

The quasi-elastic incoherent neutron-scattering method has been used to investigate the mobility of water molecules associated with the protein, alpha-chymotrypsin, both in aqueous solution and adjacent to a charged surfactant interface. The latter was studied by solubilizing the protein as monomer in the aqueous cores of small water-in-oil microemulsion droplets (radius 3.5 nm). The droplets were stabilised by an interfacial shell of a double-chain surfactant (Aerosol-OT). The spectra of the water in both these protein-containing system contained a component corresponding to a 7-fold reduction in mobility as compared with bulk water. The integrated intensity of this 'immobilised' spectra component shows that a maximum of approx. 450 water molecules, corresponding to half complete monolayer coverage, are associated with a single protein molecule. This value of 450 may contain a contribution from exchangeable hydrogens within the protein, but this contribution is estimated to be small. The mobility of the remainder of the water is unaffected. The solvation behaviour of the protein is similar in bulk water and in the microemulsion water droplets.

Chemical Phenomena↗
PubMed1977

Oral manifestations of secondary hyperparathyroidism related to long-term hemodialysis therapy.

Patients on long-term hemodialysis therapy may develop secondary hyperparathyroidism with oral symptoms. As the life expectancy of the dialysis patient increases, the dentist is seeing these manifestations with increasing frequency. A review of the subject is presented along with a case illustrating dramatic roentgenographic changes in a patient who was placed on hemodialysis when the technique was in its infancy.

Adult↗
PubMed1977

Tetracyclines: double blind clinical study to evaluate the effectiveness in periodontal surgery.

Twenty consecutive hospital patients who were to have periodontal surgery were assigned to one of two groups in a double blind clinical study. Ten were placed on tetracycline 250 mg, 6 times per day for 5 days. The other ten were given an identical appearing placebo 6 times per day for 5 days. The capsules were placed in a brown envelope so that neither the patient nor the periodontist knew which medication was being administered. The patients were randomly assigned to one of the two groups and were evaluated subjectively and objectively on the 3rd day and the 7th day. Statistically there were no differences between the two groups. In both groups there was some inflammation on the 3rd day but on the 7th day, it had subsided. Tetracycline is not recommended for routine prophylactic use in periodontal surgery.

Clinical Trials as Topic↗
PubMedDate not supplied

Risk indicators of childhood undernutrition in Kingston, Jamaica.

In Jamaica, early childhood undernutrition remains a problem; however, the health of all children cannot be monitored due to limited resources. Therefore, there is a need for the early identification of children at risk of undernutrition. A simple screening instrument for use by paraprofessionals in the primary health care system was developed. We conducted a case-control study using 649 children, aged 6 to 48 months. The cases were undernourished (weight-for-age less than 80% of the reference) and identified from a survey. The children's guardians were given a questionnaire comprising 31 variables thought to be associated with undernutrition and which were present from 6 weeks of age. Nine variables were significantly associated with undernutrition. Multiple logistic regression analysis indicated that low birth weight, short birth spacing, being born at home, poor ante-natal and post-natal clinic attendance, overcrowding and a lack of house-hold possessions were independent predictors of undernutrition. Using these variables, a simple scoring system was developed to identify high risk children. It had a sensitivity and specificity of 56% and 76% respectively and a positive predictive values of 31%. This simple screening instrument should be easy to use in the primary health care system. However, its low sensitivity indicates that it is difficult to identify children who are at risk of undernutrition from 6 weeks of age. Subsequent high morbidity and poor child care which were not measured may account for some of the missed cases.

Birth Intervals↗