Biomedical subjects

A L Hutchinson

Publications and source records attributed to A L Hutchinson.

7 recordsLinked to original sources

PubMed2001

Spectroscopic detection of biological NO with a quantum cascade laser.

Two configurations of a continuous wave quantum cascade distributed feedback laser-based gas sensor for the detection of NO at a parts per billion (ppb) concentration level, typical of biomedical applications, have been investigated. The laser was operated at liquid nitrogen temperature near lambda = 5.2 microns. In the first configuration, a 100 m optical path length multi-pass cell was employed to enhance the NO absorption. In the second configuration, a technique based on cavity-enhanced spectroscopy (CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous analysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb when using CES. The two techniques are compared, and potential future developments are discussed.

Breath Tests↗

PubMed2001

Absorption spectroscopy with quantum cascade lasers.

Novel pulsed and cw quantum cascade distributed feedback (QC-DFB) lasers operating near lambda=8 micrometers were used for detection and quantification of trace gases in ambient air by means of sensitive absorption spectroscopy. N2O, 12CH4, 13CH4, and different isotopic species of H2O were detected. Also, a highly selective detection of ethanol vapor in air with a sensitivity of 125 parts per billion by volume (ppb) was demonstrated.

Air Pollution, Indoor↗

PubMed2000

Self-mode-locking of quantum cascade lasers with giant ultrafast optical nonlinearities.

We report on the generation of picosecond self-mode-locked pulses from midinfrared quantum cascade lasers, at wavelengths within the important molecular fingerprint region. These devices are based on intersubband electron transitions in semiconductor nanostructures, which are characterized by some of the largest optical nonlinearities observed in nature and by picosecond relaxation lifetimes. Our results are interpreted with a model in which one of these nonlinearities, the intensity-dependent refractive index of the lasing transition, creates a nonlinear waveguide where the optical losses decrease with increasing intensity. This favors the generation of ultrashort pulses, because of their larger instantaneous intensity relative to continuous-wave emission.

Journal Article↗

PubMed2000

Effective utilization of quantum-cascade distributed-feedback lasers in absorption spectroscopy.

A variable duty cycle quasi-cw frequency scanning technique was applied to reduce thermal effects resulting from the high heat dissipation of type I quantum-cascade lasers. This technique was combined with a 100-m path-length multipass cell and a zero-air background-subtraction technique to enhance detection sensitivity to a parts-in-10(9) (ppb) concentration level for spectroscopic trace-gas detection of CH4, N2O, H2O, and C2H5OH in ambient air at 7.9 micrometers. A new technique for analysis of dense high resolution absorption spectra was applied to detection of ethanol in ambient air, yielding a 125-ppb detection limit.

Air Pollution, Indoor↗

PubMed1999

Methane concentration and isotopic composition measurements with a mid-infrared quantum-cascade laser.

A quantum-cascade laser operating at a wavelength of 8.1 micrometers was used for high-sensitivity absorption spectroscopy of methane (CH4). The laser frequency was continuously scanned with current over more than 3 cm-1, and absorption spectra of the CH4 nu 4 P branch were recorded. The measured laser linewidth was 50 MHz. A CH4 concentration of 15.6 parts in 10(6) ( ppm) in 50 Torr of air was measured in a 43-cm path length with +/- 0.5-ppm accuracy when the signal was averaged over 400 scans. The minimum detectable absorption in such direct absorption measurements is estimated to be 1.1 x 10(-4). The content of 13CH4 and CH3D species in a CH4 sample was determined.

Atmosphere↗

PubMed1988

X-ray diffraction studies of lipid phase transitions in cholesterol-rich membranes at sub-zero temperatures.

In X-ray diffraction studies of hydrated (greater than 60%) cholesterol/dioleoylphosphatidylcholine mixtures the lipid packing band showed an abrupt transition from liquid crystal-type to gel-type position and definition at a temperature which decreased progressively to almost -50 degrees C as the proportion of cholesterol was increased to a saturation level of about 50 mol%. Plots of transition temperature against composition (mol% cholesterol) and of peak position against composition provided evidence of a significant change in phospholipid configuration at about 20 mol% cholesterol. However, the data overall suggested a uniform dispersion of the cholesterol molecules in the phospholipid bilayer at all concentrations up to the saturation point. Parallel studies of hydrated lipid extract of erythrocyte membranes and of several cholesterol-rich membrane preparations showed a similar overall change from liquid crystal-type packing at +20 degrees C to a gel-type packing at -30 degrees C to -40 degrees C but without displaying a defined transition temperature.

Animals↗

PubMed1976

Chondrodysplasia punctata-23 cases of a mild and relatively common variety.

A common form of chondrodysplasia punctata has been defined by characteristic clinical and radiologic features in 23 patients seen in Melbourne. The patients presented during infancy because of failure to thrive, apparent mental retardation, and/or unusual appearance. The typical facies is almost diagnostic, and the diagnosis is completed by finding punctate calcification in the calcaneum in lateral radiographs of the feet, and sometimes in other sites. Growth and developmental progress improved during childhood and the final outcome seems likely to comprise low normal height and intelligence with persistence of typical facies. Mild cases probably pass unrecognized at present. Seventeen patients were male. Paternal age was significantly increased; however, family data did not support a genetic cause. Illnesses during pregnancy were unusually frequent, and anticonvulsants taken during pregnancy may have had an etiologic role in some patients.

Adult↗