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Biomedical subjects

R F Holub

Publications and source records attributed to R F Holub.

11 recordsLinked to original sources
PubMed1995

Deposition patterns of molecular phase radon progeny (218Po) in lung bifurcations.

Indoor air contamination by radon and its decay products is currently the focus of considerable attention and is considered by many to be the greatest potential cause of lung cancer in the human environment next to smoking. The bifurcations of the human respiratory tract are regions in which enhanced local deposition of particles (hot spots) can occur. These hot spots are important in estimating the risk from radon exposure but existing mathematical models do not characterize them accurately. In this study, radon progeny in the molecular size range were sampled through an aluminium model of a lung bifurcation. The parent and secondary tube diameters used correspond to the third and fourth generations in Weibel's lung model. Steady state, nominally laminar flows were used in the study. Deposition was measured along the inside, outside, top, and bottom walls of the secondary tubes. Experimental results indicate that the deposition along the inside wall is noticeably higher than that along the other walls. The results also show that along the inside, top, and bottom walls the deposition has its overall maximum at the carina. Other maxima are also observed along the secondary tubes downstream from the carina.

Aerosols↗
PubMed1992

The measurement of activity-weighted size distributions of radon progeny: methods and laboratory intercomparison studies.

Over the past 5 y, there have been significant improvements in measurement of activity-weighted size distributions of airborne radon decay products. The modification of screen diffusion batteries to incorporate multiple screens of differing mesh number, called graded screen arrays, have permitted improved size resolution below 10 nm such that the size distributions can now be determined down to molecular sized activities (0.5 nm). In order to ascertain the utility and reliability of such systems, several intercomparison tests have been performed in a 2.4 m3 radon chamber in which particles of varying size have been produced by introducing SO2 and H2O along with the radon to the chamber. In April 1988, intercomparison studies were performed between direct measurements of the activity-weighted size distributions as measured by graded screen arrays and an indirect measurement of the distribution obtained by measuring the number size distribution with a differential mobility analyzer and multiplying by the theoretical attachment rate. Good agreement was obtained in these measurements. A second set of intercomparison studies among a number of groups with graded screen array systems was made in April 1989 with the objective of resolving spectral structure below 10 nm. Again, generally good agreement among the various groups was obtained although some differences were noted. It is thus concluded that such systems can be constructed and can be useful in making routine measurements of activity-weighted size distributions with reasonable confidence in the results obtained.

Air↗
PubMed1989

Evaluation of MDA instant working level meters.

The U.S. Bureau of Mines and the Mine Safety and Health Administration have evaluated, for accuracy and reliability, a commercially available Instant Working Level Meter (IWLM) used by the mining industry to measure short-lived 222Rn-progeny concentrations. Six evaluation parameters were determined experimentally. These included two alpha and two beta detector efficiencies for the short-lived 222Rn progeny and two internal conversion factors. The experimental procedure detailing the evaluation technique is described in the paper. The measuring accuracy of 13 instruments is as follows: average inherent uncertainty (at least 68% confidence interval) is +/- 18%; for counting statistics and rounding at 0.10 WL (2.1 microJ m-3), coefficients of variation range from +/- 15% at low gamma flux backgrounds to +/- 50% at gamma flux backgrounds of 0.39 microC kg-1 h-1 (1.5 mR h-1). All parameters were derived theoretically and measured experimentally. All tests were conducted at a sample flow rate of 2.5 L min-1. A sample air flow rate of 7.5 L min-1 can lower the counting statistics to more acceptable levels at 0.1 WL (2.1 microJ m-3).

Air Pollutants↗
PubMed1987

An experimental evaluation of the efficacy of suloctidil in the treatment of primary degenerative dementia.

A double-blind, placebo-controlled randomized design was employed to test the efficacy and optimal dosage of Suloctidil in the treatment of primary degenerative dementia (PDD i.e., Alzheimer's disease). Initially, 30 geriatric patients with a diagnosis of PDD were matched for age, education, and handedness, and randomly assigned to one of three groups: (a) 600 mg. Suloctidil daily; (b) 450 mg. Suloctidil daily; (c) or placebo, for 12 weeks. All patients were administered individually a brief neuropsychological battery at pretreatment and at 12-week posttreatment. The tests were the Boston Naming Test, the Thurstone Word Fluency Test, the Trail Making Test, and the Grooved Pegboard. While there was differential attrition across the three groups, the results of the Boston Naming Test suggest a medication-dosage effect.

Clinical Trial↗
PubMed1985

Radon-222 and 222Rn progeny concentrations measured in an energy-efficient house equipped with a heat exchanger.

Radon-222 and 222Rn progeny concentrations, barometric pressure and pressure differentials between inside and outside were measured continuously in the basement of a recently constructed energy-efficient house in metropolitan Denver, CO. Although the monitoring equipment was developed primarily for underground mines, it proved to be applicable for house monitoring. Results indicate that for tightly sealed houses, forced-flow transport does not significantly contribute to the 222Rn present even when the pressure within the house is less than the outside pressure by 0.8 Pa (.006 mm Hg). Calculations of 222Rn levels using diffusion as the primary transport mechanism are in agreement with observed data. The diffusion coefficient of 222Rn in the walls and floor surrounding the basement is higher than values previously reported. Ventilation by means of a heat exchanger reduces the 222Rn levels in accordance with measured air exchange rates, regardless of the pressure differential between inside and outside.

Air Pollutants↗
PubMed1984

A comparison of alpha spectroscopy and gross alpha techniques for determining working level in uranium mines and houses.

We have completed an evaluation of two methods that estimate potential alpha energy of radon daughters suspended in air. One method approximates Working Level from a single measurement of gross alpha activity using a generalization of procedures originally described by Kusnetz and Rollé. The second is a linear combination of the count rates from RaA and RaC' determined from a single measurement using alpha spectroscopy as originally suggested by Schiager . These methods were compared in terms of precision and accuracy for a range of radon-daughter concentrations. Even though alpha spectroscopy provides information on two independent variables, it does not always improve the accuracy and precision of the estimate of Working Level in uranium mine atmospheres and houses.

Air Pollutants↗