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Biomedical subjects

R Miller

Publications and source records attributed to R Miller.

At least 73 records · Page 4Linked to original sources
PubMed2003

Description of the adsorption behaviour of proteins at water/fluid interfaces in the framework of a two-dimensional solution model.

In the framework of the two-dimensional non-ideal solution model, surface layer equations of state, adsorption isotherms and functions of the distribution of protein molecules in respect to different molar area were derived. The thermodynamic analysis was based on Butler's equation for the chemical potentials of the components and a first-order model for the non-ideality of surface layer enthalpy and entropy. For concentrated solutions, aggregation of protein molecules in the surface layer was assumed. The resulting equations satisfactorily describe the measured adsorption and surface pressure isotherms of proteins at liquid/fluid interfaces in terms of a set of constant parameters. The model reflects the well-known differences between proteins and ordinary surfactants: a sharp increase in the surface pressure with concentration beyond a certain protein adsorption; an almost constant surface pressure at higher concentrations and a significant increase in the adsorption layer thickness with increasing adsorption for flexible proteins.

Adsorption↗
PubMed2003

Adsorption kinetics of surfactant mixtures from micellar solutions as studied by maximum bubble pressure technique.

The adsorption kinetics of micellar solutions of anionic/cationic SDS/DATB mixtures with mixing ratios of 10/1 and 10/2, respectively, are studied experimentally by means of the maximum bubble pressure method. For long adsorption times the adsorption of the highly surface-active anionic/cationic complex leads to a decrease of dynamic surface tension in comparison to the single SDS system. However, the situation is the reverse for short adsorption times where the dynamic surface tension is increased by addition of the cationic surfactant, although the overall concentration is increased. This unexpected behavior is explained by partial solubilization of free SDS molecules into micelles formed by SDS/DTAB complexes. With increasing overall concentration, when eventually the CMC of SDS is reached, the anionic/cationic complex itself is solubilized by SDS micelles. Finally, no complex micelles, which for their part can solubilize an excess of SDS molecules, are present. Hence, the dynamic properties of the solution are no longer influenced by the depletion of SDS molecules and the mixture tends to behave like a pure SDS solution.

Journal Article↗
PubMed2003

Calibration parameters of the pendant drop tensiometer: assessment of accuracy.

A method is reported for verifying and controlling the accuracy of the calibration parameters, operating in image acquisition, for drop and bubble shape-analysis tensiometry. An error, impartially affecting the calibration parameters of both Cartesian axes, results in a squared error for the determined surface tension. Moreover, in the case where the calibration factors are affected by different errors, the determined value of surface tension is definitely unreliable, depending on the drop (or bubble) size and showing spurious in-phase or out-of-phase alterations. A procedure is illustrated for correcting the calibration parameters, on the basis of the observed results for a reference liquid. Method and procedure are validated by numerical examples.

Journal Article↗
PubMed2003

Atomic qubit manipulations with an electro-optic modulator.

We report new techniques for driving high-fidelity stimulated Raman transitions in trapped-ion qubits. An electro-optic modulator induces sidebands on an optical source, and interference between the sidebands allows coherent Rabi transitions to be efficiently driven between hyperfine ground states separated by 14.53 GHz in a single trapped 111Cd+ ion.

Journal Article↗
PubMed2003

Body mass index, serum sex hormones, and breast cancer risk in postmenopausal women.

BACKGROUND: Obesity is associated with increased breast cancer risk among postmenopausal women. We examined whether this association could be explained by the relationship of body mass index (BMI) with serum sex hormone concentrations. METHODS: We analyzed individual data from eight prospective studies of postmenopausal women. Data on BMI and prediagnostic estradiol levels were available for 624 case subjects and 1669 control subjects; data on the other sex hormones were available for fewer subjects. The relative risks (RRs) with 95% confidence intervals (CIs) of breast cancer associated with increasing BMI were estimated by conditional logistic regression on case-control sets, matched within each study for age and recruitment date, and adjusted for parity. All statistical tests were two-sided. RESULTS: Breast cancer risk increased with increasing BMI (P(trend) =.002), and this increase in RR was substantially reduced by adjustment for serum estrogen concentrations. Adjusting for free estradiol reduced the RR for breast cancer associated with a 5 kg/m2 increase in BMI from 1.19 (95% CI = 1.05 to 1.34) to 1.02 (95% CI = 0.89 to 1.17). The increased risk was also substantially reduced after adjusting for other estrogens (total estradiol, non-sex hormone-binding globulin-bound estradiol, estrone, and estrone sulfate), and moderately reduced after adjusting for sex hormone-binding globulin, whereas adjustment for the androgens (androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and testosterone) had little effect on the excess risk. CONCLUSION: The results are compatible with the hypothesis that the increase in breast cancer risk with increasing BMI among postmenopausal women is largely the result of the associated increase in estrogens, particularly bioavailable estradiol.

Aged↗
PubMed2003

Local magnetic susceptibility of the positive muon in the quasi-one-dimensional S=1/2 antiferromagnet dichlorobis (pyridine) copper (II).

We report muon spin rotation measurements of the local magnetic susceptibility around a positive muon in the paramagnetic state of the quasi-one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II). Signals from three distinct sites are resolved and have a temperature dependent frequency shift which is significantly different than the magnetic susceptibility. This difference is attributed to a muon induced perturbation of the spin 1/2 chain. The obtained frequency shifts are compared with transfer matrix density-matrix renormalization-group numerical simulations.

Journal Article↗
PubMed2003

Dilational surface viscoelasticity of polymer solutions.

A review of recent results on the dilational surface viscoelastic properties of aqueous solutions of non-ionic polymers is given. In the frequency range from 0.001 up to 1000 Hz the methods of transverse and longitudinal surface waves and the oscillating barrier method were applied. Viscoelastic behavior of adsorbed polymer films significantly differs from the behavior of films formed by only conventional surfactants of low molecular weight. For example, the dynamic surface elasticity of the former systems is low and almost constant in a broad concentration range. One can observe the increase of the surface elasticity only at extremely low concentrations and/or in the range of semi-dilute solutions. If the surface stress relaxation in conventional surfactant solutions is usually determined by the diffusional exchange between the surface layer and the bulk phase, the relaxation processes in the polymer systems proceed mainly inside the surface layer. Possible mechanism of the latter relaxation is discussed.

Biophysical Phenomena↗
PubMed2003

Relation between rheological properties and structural changes in monolayers of model lung surfactant under compression.

rSP-C surfactant monolayers spread on a native physiological model substrate show two plateau regions in the pi/A-isotherm. The first corresponds to the main phase transition in the monolayer from a LE to a LC phase. Its course is non-horizontal because of the complex composition of the lung surfactant. The second plateau, which is much more pronounced, cannot be attributed to a change of the phase state. Brewster angle microscopy images taken in this region show a sharp apparent decrease of the aggregation degree from the LE to the LC state. This process can be considered as a change in the monolayer orientation relative to the direction of the propagated light. Such a change can be the result of monolayer folding and formation of a thicker layer, which is supported by results of rheological measurements. The dilatation elasticity obtained from oscillating barrier and longitudinal wave measurements reveals a pure elastic behaviour with a steep increase in the second plateau region. Because of the insolubility of the pure lipid components, a possible explanation is squeezing protein components of rSP-C or its complexes with lipids out of the monolayer into the bulk.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2003

Comparison of various models describing the adsorption of surfactant molecules capable of interfacial reorientation.

The thermodynamic model for describing the adsorption of surfactant molecules in different adsorption states, the reorientation model, is reconsidered on a more rigorous level. The resulting model equations are used to describe experimental surface pressure data published in the literature. The new model proposed contains three physical parameters and describes the experimental dependencies Pi(c) for oxethylated alcohols very accurately.

Journal Article↗
PubMed2003

Sitting time and work patterns as indicators of overweight and obesity in Australian adults.

BACKGROUND: Increasing levels of physical inactivity and sedentariness are contributing to the current overweight and obesity epidemic. In this paper, the findings of two recent studies are used to explore the relationships between sitting time (in transport, work and leisure), physical activity and body mass index (BMI) in two contrasting samples of adult Australians. METHODS: Data on sitting time, physical activity, BMI and a number of demographic characteristics were compared for participants in two studies-529 women who were participants in a preschool health promotion project ('mothers'), and 185 men and women who were involved in a workplace pedometer study ('workers'). Relationships between age, number of children, physical activity, sitting time, BMI, gender and work patterns were explored. Logistic regression was used to predict the likelihood of being overweight or obese, among participants with different physical activity, sitting time and work patterns. RESULTS: The total reported time spent sitting per day (across all domains) was almost 6 h less among the mothers than the workers (P<0.001), and compared with the mothers, a significantly greater proportion of the workers was classified as overweight or obese (BMI > or =25 kg/m(2)). Univariate analysis found that, compared with men in full-time work, women who worked full-time (OR=0.42, CI: 0.24-0.74), part-time (OR=0.35, CI: 0.20-0.59) or in full-time home duties (OR=0.51, CI: 0.29-0.88) were about half as likely to be overweight or obese. Participants who reported high daily levels of sitting (> or =7.4 h) were also significantly more likely than those who reported 'low' levels (<4.7 h/day) to be overweight or obese (OR=1.68, CI: 1.16-2.42). Multivariate analysis (including physical activity, work patterns and sitting time) confirmed that full-time and part-time working women (but not 'home duties' women) were less likely to report BMI > or =25 kg/m(2) than full-time working men (full-time: OR=0.44, CI: 0.25-0.78; part-time: OR=0.45, CI: 0.24-0.86), but the OR for BMI > or =25 among those in the high sitting category was attenuated (OR=1.61, CI 0.96-2.71). CONCLUSIONS: The findings suggest a need for inclusion of measures of both activity and inactivity in future studies, so that the complex relationships between these behavioural determinants of BMI can be clarified.

Adolescent↗
PubMed2003

Social adjustment in three cultures: data from families affected by chronic blood disorders. A sibling study.

This study explores the rate of psychosocial dysfunction in affected and unaffected children from families with haemophilia or beta-thalassaemia, as part of a cross-sectional, multicentre study into the resilience of 115 families with blood disorders. Sociodemographic and developmental data were collected from the parents using a standardized and semi-structured interview format, and medical data were obtained from the clinician. The children's social functioning over the year prior to the assessment was assessed with The Social Adjustment Scale adapted for school-aged children. Children with beta-thalassaemia showed significantly higher rates of social dysfunction than their unaffected siblings or children with haemophilia and their siblings. Older children showed significantly higher social dysfunction at school. The high rate of social dysfunction in children with beta-thalassaemia compared with unaffected siblings is likely to have a basis in the negative experiences associated with their medical problems. In contrast, the therapeutic advances in haemophilia allows boys to lead an almost normal life. Overall, the rates of social dysfunction in families with both these disorders proved commoner than reported in population surveys, but with the unavailability of local population controls, caution needs to be exercised in the interpretation of this finding.

Adolescent↗
PubMed2003

An integrated genetic data environment (GDE)-based LINUX interface for analysis of HIV-1 and other microbial sequences.

MOTIVATION: Sequence databases encode a wealth of information needed to develop improved vaccination and treatment strategies for the control of HIV and other important pathogens. To facilitate effective utilization of these datasets, we developed a user-friendly GDE-based LINUX interface that reduces input/output file formatting. DESIGN AND RESULTS: GDE was adapted to the Linux operating system, bioinformatics tools were integrated with microbe-specific databases, and up-to-date GDE menus were developed for several clinically important viral, bacterial and parasitic genomes. Each microbial interface was designed for local access and contains Genbank, BLAST-formatted and phylogenetic databases. AVAILABILITY: GDE-Linux is available for research purposes by direct application to the corresponding author. Application-specific menus and support files can be downloaded from (http://www.bioafrica.net).

Database Management Systems↗
PubMed2003

Performance evaluation of the Sysmex XT-2000i automated hematology analyzer.

The Sysmex XT-2000i automated hematology analyzer was evaluated at Saint Louis Children's Hospital (SLCH), St. Louis, MO, USA. Complete blood count results from the Sysmex XT-2000i were compared to results from the Sysmex XE-2100 for 114 pediatric and adult patient samples. Manual differentials were performed on each specimen by 2 experienced medical technologists using guidelines established in the National Committee for Clinical Laboratory Standards (NCCLS) document H20-A. Carryover, precision, linearity, correlation, stability, and mixing-test studies were also performed. The XT-2000i results showed excellent correlation with the results from the XE-2100 for the following parameters: white blood cells; red blood cells; hemoglobin; hematocrit; mean corpuscular volume; mean corpuscular hemoglobin; mean corpuscular hemoglobin concentration; red blood cell distribution width by standard deviation; red blood cell distribution width by coefficient of variation; mean platelet volume; platelets; percent neutrophils, lymphocytes, monocytes, eosinophils, and basophils; and reticulocyte percent and number. In our evaluation of the XT-2000i the correlation coefficients for all complete blood counts and differential parameters compared well with those of the XE-2100. We concluded that the XT-2000i demonstrated comparable analytical performance to its predecessor, the XE-2100.

Adult↗