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At least 649 records · Page 36Linked to original sources
PubMed1985

W value measurements for protons in tissue-equivalent gas and its constituent gases.

Values of W (the mean energy required to create an ion pair when a charged particle is stopped in a gas) are needed in radiation dosimetry to convert ionisation chamber current readings to absorbed dose. For neutron dosimetry the most important W values are those for protons, and this paper describes absolute measurements for protons with energies between 1.2 and 3.5 MeV for methane-based tissue-equivalent gas and its constituent gases, i.e. methane, carbon dioxide and nitrogen. An ionisation chamber with a parallel-plate arrangement was used to determine the integrated charge created by a measured number of protons, and W values were determined with an estimated uncertainty of about +/- 0.5%. The results are presented and compared with previous measurements. In general the present data tend to be somewhat lower than previously reported values. Finally the accuracy of a formula for predicting W values for gas mixtures from the values for the individual constituents is investigated.

Animals↗
PubMed1985

W value measurements for 241Am alpha particles in various gases.

Measurements of W, the mean energy expended per ion pair formed, have been performed for 241Am alpha particles stopping in a number of the gases commonly used in ionisation chambers. Both absolute and relative measurements were made with nitrogen used as the reference gas for the relative measurements. The absolute method entailed a simultaneous measurement of a quantity of charge and the number of alpha particles which produced that charge, whilst the relative approach simply required a determination of the ratio of ion currents. Results were obtained for methane-based tissue-equivalent gas, for its constituents, i.e. methane, carbon dioxide and nitrogen, for argon, and also for a gas mixture with a composition approximately equivalent to A-150 plastic.

Americium↗
PubMed1984

Influence of frequent and long-term consumption of legume seeds on excretion of intestinal gases.

The objective of this study was to determine the influence of long-term and frequent consumption of legume seeds on the excretion of fermentation gases. This was done by comparing gas excretion for one group (B) of individuals that habitually consumed legumes to that of another group (NB) of individuals that only infrequently consumed legumes. Gas excretion was measured during one diet period (control) when they consumed their normal diets and during one diet period (bean) when they consumed 100 g (dry weight), daily, of red kidney beans. Twelve men participated in this study on an outpatient basis and received each diet for 23 days. We found that there was neither short-term (no difference throughout the 23 days) nor long-term (NB and B groups were equivalent) adaptation in the quantity of gas that was excreted. However, both groups subjectively expressed greater tolerance and less physical discomfort as the bean-consuming period continued.

Adult↗
PubMed1989

Gases in forage tower silos.

Measurements of hazardous gas concentrations in forage tower silos are described. The problems associated with sampling in silos, the identity and distribution of gases and their rate of evolution, and the effects of forced and natural ventilation are considered. Particular attention is given to conditions at times when entry to the silo by farm personnel is likely and the possibility of farmers carrying out gas measurements is discussed.

Air Pollutants, Occupational↗
PubMed1991

Gases in agricultural slurry stores.

The evolution of gases during the handling of animal slurry was investigated at five sites. Particular attention was paid to the mixing and emptying operations since it is when performing these that personnel are most likely to be at risk of exposure. The main hazard was found to be high transient concentrations of hydrogen sulphide presenting in some cases a serious acute toxicity problem. Time-weighted average exposures did not generally indicate any long-term exposure risk. Other features noted were the evolution of ammonia and methane, although not at high levels, and some increase in the carbon dioxide concentration. Some reduction in oxygen concentration was measured, but generally the risk of poisoning by hydrogen sulphide was more serious than the risk of asphyxiation.

Ammonia↗
PubMed2001

Particles, and not gases, are associated with the risk of death in patients with chronic obstructive pulmonary disease.

OBJECTIVES: We aim to assess the independent association of particles, after controlling for gaseous pollutants, with the risk of death among a cohort of patients with chronic obstructive pulmonary disease (COPD). METHODS: Residents of Barcelona, aged over 35 years, who attended emergency room services for COPD exacerbation from 1985 to 1989 and who died in the period 1990-1995 (n = 2305) were selected. The analysis followed a case-crossover procedure with ambidirectional controls. Air pollution exposure (particulate matter <10 microm (PM(10)), ozone, nitrogen dioxide and carbon monoxide) was measured at the city monitoring stations. RESULTS: Levels of PM(10) (odds ratio for the interquartile difference = 1.11, 95% CI : 1.00- 1.24), but not gaseous pollutants, were associated with mortality for all causes of death after adjusting for meteorological variables and influenza epidemics. In the two-pollutant models, the association of mortality with PM(10) was not confounded by the inclusion of gases, while the association of gaseous pollutants was notably reduced after adjustment for particles. There was no interaction between particles and gaseous pollutants. CONCLUSIONS: Findings reinforce the deleterious role of urban particles as a trigger of death in COPD patients, and suggest that they are the major culprit among the air pollutants. The role of other pollutants, if any, was additive and not multiplicative.

Air Pollution↗
PubMed2004

W values of protons in alkane-based TE gases and dimethylether in the energy range 1-100 keV: measurements and additivity models.

W values of tissue-equivalent gases based on propane and butane were measured for protons in the energy range 1-100 keV and compared with those of dimethylether and water vapour. The experimental values of the tissue-equivalent gas mixtures were compared with data calculated from the W values of the mixture components using five existing additivity models and two new models derived within the scope of the present work. Apart from one model--the simplest one--all models show a good agreement with the experimental data.

Algorithms↗
PubMed1985

Errors in measurement of oxygen uptake due to anesthetic gases.

Errors in measurement of exhaled gas volume, mixed expired oxygen and carbon dioxide concentrations, and inspired oxygen concentration and the presence of exhaled anesthetic agents cause errors in on-line calculated oxygen uptake that increase geometrically with increasing inspired oxygen concentration. No one has quantified the decrease in the magnitude of the error that might be realized if directly measured nitrogen concentration were included in the calculation. We used a computer model to evaluate this improvement, assuming an oxygen uptake of 200 ml/min and normal ventilatory parameters. Using a Monte Carlo technique, we generated 100 sets of data points, with random errors averaging 0.5% around the expected gas concentrations, and compared the accuracy of oxygen uptake calculated with and without inclusion of directly measured inspired and expired nitrogen concentrations. When the inspired oxygen fractions were 0.2, 0.5, and 0.8, the calculated oxygen uptakes +/- % standard deviation were 200 +/- 4.3, 200 +/- 12, and 196 +/- 21 when directly measured nitrogen was included versus 200 +/- 3.5, 196 +/- 16, and 205 +/- 71 when it was not. The procedure was repeated, assuming 50 ml/min of anesthetic excretion and the calculated oxygen uptakes were 200 +/- 4.6, 202 +/- 12, and 195 +/- 17 versus 212 +/- 3.8, 251 +/- 17, and 398 +/- 64. Including direct measurement of inhaled and exhaled concentrations of nitrogen or another insoluble inert tracer gas allows accurate measurement of oxygen uptake, even in the presence of exhaled anesthetic gases. It also decreases the error in oxygen uptake determination by a factor of nearly six when the inhaled oxygen fraction is 0.8.

Anesthetics↗
PubMed1982

The liquid barrier filter--a new concept to eliminate particulate contaminants from gases.

We have explored the possibility of using a continuous liquid phase of high gas permeability as a filter to remove particulate contaminants from a gas stream. The liquid, a non-toxic perfluorocarbon, severs upstream and downstream gas phases completely. It can dissolve great quantities of gases and pass them, by diffusion, along even a slight partial pressure gradient. The liquid phase remains intact in the process: there is no convective transfer of gas. Particulate contaminants will, on impact with the continuous liquid phase, lose their momentum and be stopped; our results promise near ideal efficacy of capture. We suggest that filters based on this principle be developed to protect against highly toxic particulate contaminants in an atmosphere.

Air Pollutants↗
PubMed1992

Longevity of expanding gases in vitrectomized eyes.

The effect of lensectomy and vitrectomy on the disappearance of intraocular gas was studied in a rabbit model. Ten rabbits underwent lensectomy and vitrectomy in one eye, and ten others underwent vitrectomy alone in one eye. The second eye of each rabbit served as a control. Equal amounts of perfluorocarbon gas, either perfluoromethane (CF4) or perfluoromethane (C2F6), was injected into both eyes of the 20 animals. After an interval corresponding to one or more half-lives of the gases had elapsed, the residual volumes of gas in the paired eyes were measured directly by an invasive method and compared. The volume of gas in the aphakic vitrectomized eye was 1.3 times greater, on average, than in the paired control eye. There was no significant difference between eyes that had undergone only vitrectomy and the control eyes. It is postulated that vascular congestion and decreased aqueous secretion caused by surgical trauma were responsible for the delay in the disappearance of gas in the eyes that underwent both lensectomy and vitrectomy.

Animals↗
PubMed2005

Nearly smooth granular gases.

Hydrodynamic equations for nearly smooth granular gases are derived from the pertinent Boltzmann equation. The angular velocity distribution field needs to be included in the set of hydrodynamic fields. The angular velocity distribution is strongly non-Maxwellian for the homogeneous cooling state and any homogeneous steady state. In the case of steady wall-bounded shear flows the average spin (created at the boundaries) has a finite penetration length into the bulk.

Biomechanical Phenomena↗
PubMed2003

Selling candles in a post-Edison world: phasing with noble gases bound within engineered sites.

The utility of noble gases for phase determination has been limited by the lack of naturally occurring binding sites in proteins. Wild-type T4 lysozyme contains one such binding site. By mutating large hydrophobic residues to alanine, additional noble-gas binding sites have been successfully introduced into this protein. Using data from xenon derivatives of the wild type, two single mutants and the corresponding double mutant, experimental phases for T4 lysozyme have been determined using standard multiple isomorphous replacement (MIR) techniques. These phases, which were obtained from room-temperature data collected on a rotating-anode source, are comparable in quality with phases calculated using selenomethionine-based multiwavelength anomalous dispersion (MAD) methods on frozen crystals at a synchrotron. In addition, this method of introducing noble-gas binding sites near specific residues should provide useful information for determining the register of amino acids within electron-density maps and the positions of molecules within the unit cell.

Binding Sites↗
PubMed1979

The effects of some hydrophobic gases on the pulmonary surfactant system.

1. Decompression from exposures to raised ambient pressure of sulphur hexafluoride, carbon tetrafluoride, hexafluoro-ethane and nitrous oxide results in the formation of dense foam and pulmonary oedema. 2. The degree of pulmonary oedema produced is dependent on the exposure pressure, although the exposure time required is short in comparison to tissue saturation times. 3. The effect is not prevented by atropine, ephedrine or hydrocortisone. 4. The effect is also produced in vitro by saturated solutions of halothane, chloroform and ether. 5. It is suggested that the mechanism of action is physical with physico-chemical factor involved being a differential partition of these gases within the surfactant: membrane complex.

Animals↗
PubMedDate not supplied

Performance characteristics of A 150 plastic-equivalent gases in A 150 plastic proportional counters for 14.8-MeV neutrons.

Two recently developed A 150 plastic-equivalent gas mixtures have been tested for suitability in proportional counter applications. Methane- and propane-based "tissue-equivalent" gases were also included for comparison purposes. Event-size weighted dose distributions were measured in a 14.8-MeV neutron beam. Resolution was found to be independent of gas mixture. Moreover the gains of the two A 150 mixtures were the same, and comparable to that of the methane-based gas mixture. The ionization yield per event size was also independent of the hydrogenous gas mixture employed. Neutron doses determined with the proportional counter were in reasonable agreement with those obtained from an ionization chamber.

Fast Neutrons↗
PubMed1963

Diffusion of gases from alveolus to precapillary arteries.

A cardiac catheter with a platinum electrode just proximal to its tip, "wedged" in a branch of the pulmonary artery, was used to demonstrate the appearance of hydrogen or oxygen at the tip of the catheter after inhalation of these gases.

Arteries↗
PubMed1978

Toxic gases from fires.

The major lethal factors in uncontrolled fires are toxic gases, heat, and oxygen deficiency. The predominant toxic gas is carbon monoxide, which is readily generated from the combusion of wood and other cellulosic materials. Increasing use of a variety of synthetic polymers has stimulated interest in screening tests to evaluated the toxicity of polymeric materials when thermally decomposed. As yet, this country lacks a standardized fire toxicity test protocol.

Carbon Monoxide Poisoning↗
PubMed1972

Control of Penicillium martensii development and penicillic acid production by atmospheric gases and temperatures.

The effects of various gaseous environments and temperatures on development of Penicillium martensii NRRL 3612 and production of penicillic acid (PA) were determined. Accumulation of PA in mold-inoculated corn was measured following incubation under air; 20% CO(2), 20% O(2), 60% N(2); 40% CO(2), 20% O(2), 40% N(2); and 60% CO(2), 20% O(2), 20% N(2). Although reduced temperature initially inhibited PA production, at the end of the trial the largest quantity of PA (120 mug/g of corn) was found in air-incubated corn at the lowest test temperature (5 C). Atmospheres enriched with 60% CO(2) reduced PA accumulation below a detectable level at 5 and 10 C after a 4-week incubation period. Spore germination tests were carried out in a liquid growth medium incubated for 16 hr under several test conditions. Germ tube outgrowth at 30 C ranged from 36% in air to 2% in 60% CO(2), whereas no germination was observed in CO(2)-enriched gases at 10 C. When spore respiration rates were measured in air and O(2) in a liquid growth medium, complete removal of CO(2) from the reaction atmosphere did not reduce O(2) uptake.

Air↗