Biomedical subjects

J L Elliot

Publications and source records attributed to J L Elliot.

4 recordsLinked to original sources

PubMed2006

Charon's radius and atmospheric constraints from observations of a stellar occultation.

The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies, their radii and densities have remained uncertain. The observation of a stellar occultation by Charon in 1980 established a lower limit on its radius of 600 km (ref. 3) (later refined to 601.5 km; ref. 4) and suggested a possible atmosphere. Subsequent, mutual event modelling yielded a range of 600-650 km (ref. 5), corresponding to a density of 1.56 +/- 0.22 g cm(-3) (refs 2, 5). Here we report multiple-station observations of a stellar occultation by Charon. From these data, we find a mean radius of 606 +/- 8 km, a bulk density of 1.72 +/- 0.15 g cm(-3), and rock-mass fraction 0.63 +/- 0.05. We do not detect a significant atmosphere and place 3sigma upper limits on atmospheric number densities for candidate gases. These results seem to be consistent with collisional formation for the Pluto-Charon system in which the precursor objects may have been differentiated, and they leave open the possibility of atmospheric retention by the largest objects in the outer Solar System.

Journal Article↗

PubMed2003

The recent expansion of Pluto's atmosphere.

Stellar occultations--the passing of a relatively nearby body in front of a background star--can be used to probe the atmosphere of the closer body with a spatial resolution of a few kilometres (ref. 1). Such observations can yield the scale height, temperature profile, and other information about the structure of the occulting atmosphere. Occultation data acquired for Pluto's atmosphere in 1988 revealed a nearly isothermal atmosphere above a radius of approximately 1,215 km. Below this level, the data could be interpreted as indicating either an extinction layer or the onset of a large thermal gradient, calling into question the fundamental structure of this atmosphere. Another question is to what extent Pluto's atmosphere might be collapsing as it recedes from the Sun (passing perihelion in 1989 in its 248-year orbital period), owing to the extreme sensitivity of the equilibrium surface pressure to the surface temperature. Here we report observations at a variety of visible and infrared wavelengths of an occultation of a star by Pluto in August 2002. These data reveal evidence for extinction in Pluto's atmosphere and show that it has indeed changed, having expanded rather than collapsed, since 1988.

Journal Article↗

PubMed1997

Triton's distorted atmosphere.

A stellar-occultation light curve for Triton shows asymmetry that can be understood if Triton's middle atmosphere is distorted from spherical symmetry. Although a globally oblate model can explain the data, the inferred atmospheric flattening is so large that it could be caused only by an unrealistic internal mass distribution or highly supersonic zonal winds. Cyclostrophic winds confined to a jet near Triton's northern or southern limbs (or both) could also be responsible for the details of the light curve, but such winds are required to be slightly supersonic. Hazes and clouds in the atmosphere are unlikely to have caused the asymmetry in the light curve.

Atmosphere↗

PubMed1984

Potential hazards of pediatric rigid bronchoscopy.

Bronchoscopy in infants and children has been facilitated by recent technologic advances. Better optical systems, intense "cold" light sources, and miniaturization of instrumentation have all contributed to the more effective use of the bronchoscope as a diagnostic and therapeutic tool. Despite these advances, two persistent problems remain major concerns for the endoscopist and anesthesiologist. The first concern is selection of an appropriately sized instrument for the pediatric patient. Our measurements demonstrate that the stated size of a rigid bronchoscope's internal diameter may differ significantly from its actual size. In many instances the actual diameter may be significantly greater than the stated size. The second problem concerns difficult ventilation of the patient while the bronchoscope is in place. Our measurements indicate that major increases in resistance to gas flow through the bronchoscope can be encountered particularly when utilizing smaller caliber instruments with accessory sheaths and/or telescopes. Appropriate knowledge and planning preoperatively should minimize the potential hazards associated with these problems.

Adolescent↗