Aviation medicine

Travel by air is a safe means of transport, but puts people at various physiological risks and is a potential means of spreading infectious disease. Physiological risks associated with flying include hypoxia, as atmospheric pressure falls with altitude. The minimum cabin pressure in commercial passenger aircraft (565 mm Hg, 75.1 kPa) brings a healthy individual’s arterial P along the plateau of the oxyhaemoglobin dissociation curve until just at the top of the steep part, but does not cause desaturation. By contrast, people with respiratory disease and a low arterial oxygen pressure may desaturate, which can be overcome by administering 30% oxygen, this being equivalent to breathing air at ground level. There is no evidence that the pressurized aircraft cabin itself encourages transmission of disease, and recirculation of cabin air is not a risk factor for contracting symptoms of upper respiratory tract infection.

Theoretical calculation of the exchange coupling constant in some polymeric nickel(II) complexes using range-separated functionals

The magnetic parameters (J, g) of two nickel(II) 1D polymers (Ni(en)(ox) and Ni(ox) (ampy)2; where en = ethylene diamine, ox = oxalate, ampy = 4-amino-pyridine) were calculated using 6-311+G* basis set and six range-separated DFT functionals (CAM-B3LYP, LC-BLYP, wB97, wB97X, wB97X-D3 and B2T-PLYP) together with the hybrid B3LYP method for sake of comparison. We found that the wB97, CAM-B3LYP and wB97X-D3 methods gave approximate value of J for compound 1 and the B2T-PLYP method was found to be the best method for compound 2. The g values were calculated by the coupled perturbed approach. However, we assume that a higher approximation is needed in order to give satisfactory results for g. A new equation has been proposed to relate the experimental susceptibility to the J and g parameters. The Curie-Weiss law was included in this equation resulting in a good explanation of the steep part of the experimental curve below 20 K.

VLIV LITOLOGIE A MORFOLOGIE VYSOKOGRADIENTOVÝCH KORYT NA DNOVÉ SEDIMENTY: PŘÍKLADOVÁ STUDIE VODNÍHO TOKU KOBYLSKÁ (VSETÍNSKÉ VRCHY, ČESKÁ REPUBLIKA)

High-gradient streams are integral parts of the fluvial systems, which connect the mountainous landscapes with lowland rivers in the sense of water and sediment transport. We analysed downstream grain-size characteristics of bed sediments and sphericity of grains with respect to the local flysch lithology and channel geometry in the 5.4 km long reach of the high-gradient Kobylská Stream (the Vsetín highlands, Outer Western Carpathians, Czech Republic). Results showed a high variability of bed-sediment sizes in the longitudinal course of the Kobylská stream. This condition is given by the occurrence of anthropogenic impact in the studied channel (local bank stabilisations, grade-control structures) and lateral sediment input from the adjacent landslides and bank failures. The lithology of the flysch nappe structure of the basin significantly influenced variations of bed sediment grain-sizes. Different bedrock resistance resulted into inverse correlation between the local river gradient and related bed grain-sizes. Especially the mudstone bedrock layers had significant impact on the fining of bed sediment in the upper steep part of the basin (D50 ≤ 40 mm) and by contrast, sandstone bedrock caused the coarsening of the bed sediment in the middle and lower parts (D50 up to 50 mm) characterised by lower bed gradients.

Sympatholytic and Minimum Anesthetic Concentration-sparing Responses are Preserved in Rats Rendered Tolerant to the Hypnotic and Analgesic Action of Dexmedetomidine, a Selective α2-adrenergic Agonist

Background The development of tolerance to the sympatholytic and anesthetic-reducing effects of alpha(2) agonists after prolonged administration of dexmedetomidine and how the number of available alpha(2) adrenoceptors affects these dexmedetomidine-induced responses was studied. Methods The sympatholytic action of acute and chronic (3 and 10 micrograms.kg-1.h-1 for 7 days) dexmedetomidine, was assessed by the decrease in norepinephrine turnover in the locus coeruleus and hippocampus. The anesthetic-reducing effect of chronic (7 days) dexmedetomidine (5 and 10 micrograms.kg-1.h-1) was studied by determining the minimum alveolar concentration (MAC) for halothane that prevented rats from responding to a supramaximal noxious stimulus of dexmedetomidine (10 or 30 micrograms.kg-1), doses in the steep part of the dose-response curve. The receptor reserve for the norepinephrine turnover and anesthetic-sparing responses to dexmedetomidine was delineated with 0.3-1.0 mg.kg-1 N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline, an irreversible alkylating agent. Results After chronic administration of dexmedetomidine at both doses, acute dexmedetomidine significantly decreased norepinephrine turnover in the hippocampus and locus coeruleus. The baseline minimum anesthetic concentration (MAC) and the MAC-sparing effect to acutely administered dexmedetomidine were preserved after chronic dexmedetomidine treatment. In the N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline experiments, the dexmedetomidine-induced norepinephrine turnover effect required less than 20% and greater than 4% alpha(2) adrenoceptor availability in the locus coeruleus and the dexmedetomidine induced MAC-sparing effect required less than 40% and greater than 20% alpha(2) adrenoceptor availability in the locus coeruleus. Conclusion Tolerance does not develop for either the sympatholytic or MAC-sparing actions of dexmedetomidine, although it is present for the hypnotic response. The durable quality of the sympatholytic and MAC-sparing responses to dexmedetomidine after chronic treatment is explained by a comparatively larger receptor reserve than is needed for the hypnotic and analgesic responses, which are blunted by the same drug treatment regimen.

Observations and Comments on the Displacement of Pre-Adsorbed Water from BPL Activated Carbon by Chloropicrin Vapour

The breakthrough curves of chloropicrin vapour through beds of BPL activated carbon pre-equilibrated at different relative humidities (RH) have been measured. The associated water displacement curves and effluent temperature profiles are also presented. At first, as the experimental RH increases, the slope of the breakthrough curves gradually decreases. However, at high RH (i.e. 80%) the curve becomes distinctly biphasic. It is proposed that the initial steep part of the curve is the result of a build-up of water in the macro (transport) pore structure of the carbon which restricts access of chloropicrin to the micropores. The accumulation of water in the transport pores is a consequence of both the high carbon water content at RH 80% and the limitation on the amount of water that can be carried away in the air- stream (which rapidly reaches saturation). The shape of the water displacement curves is also influenced by re-adsorption of displaced water further along the filter bed. In most experiments there is a significant depression in the temperature of the effluent airstream. At RH 80% the overall process is notably endothermic.

The Compression Set Behavior of Nitrile Rubber

The compression set (C.S.) of a vulcanizate depends on the formulation, processing, and conditions of cure. The following factors are the most important: (a) the type of elastomer, (b) the curing system, (c) the type and amount of filler, (d) the type and amount of plasticizer, (e) the type and amount of antioxidant, (f) the type of cure (press, steam, or hot air), and (g) the cure time and temperature. The present paper is intended, as far as possible, to describe these relationships quantitatively. Most tests will refer to nitrile rubber. We have modified the C.S. method described in ASTM D-395. The deviations are as follows : (1) When C.S. is plotted as a function of the duration of compression, the resulting curves rise steeply for roughly the first seven days, afterwards becoming flatter. The higher the test temperature, the steeper the curve. The ordinary compression times of 22 and 70 h still correspond to the steep part of the C.S. curve; here relatively small inaccuracies in the compression time and test temperature bring large errors in the C.S. readings. Therefore, to improve the correlation between C.S. readings and field behavior the test was extended to seven days in most cases. Longer test times would have been experimentally impractical. (2) As a rule, only C.S. figures relating to 20°, 70°, and 100° C are found in the literature, so test temperatures were extended to include practical conditions. Generally, therefore, C.S. readings were taken at twelve different temperatures ranging from −60° C to +160° C. (3) According to the standards the test pieces should be cooled to room temperature after removal of the load and before the recovery measurement is carried out. Only ASTM D-1229-62 requires the remeasurement to be taken at the load temperature. This ensures accurate measurements of the C.S. at low temperatures. In our tests this was done in every case because at high temperature the C.S. readings are lower since (1) many elastomers recover better at elevated temperatures than at room temperature and (2) the thermal expansion of the test piece can be measured in addition to the recovery. Nevertheless, the differences between remeasurements taken at room temperature and the test temperature are small if the test temperature is fairly high. Where lower test temperatures are used, the remeasurement should always be taken at test temperature if useful results are to be obtained. In all the tests the time allowed for recovery between removal of the load and the remeasurement was thirty min.

Electron spin resonance spectroscopy of irradiated DNA

Much work has been done in the last few years to study the effect of ionizing radiation on DNA . In a typical experiment a DNA sample is sealed off under vacuum in a quartz tube and irradiated at one end. The sample is then moved to the other (unirradiated) end and placed in the e. s. r. spectrometer. Results take the form, first, of spectra, which can obviously be obtained under a variety of irradiation and measurement conditions (variation of temperature has been a common procedure) and, secondly, of yield curves, where the area under the absorption curve is taken as a measure of the total free radicals and the radical concentration is plotted against dose. The curves usually show an exponential increase—the free radical concentration levelling off between 10 17 and 10 18 spins/g at a dose of about 1 Mrad. From the initial steep part of the curve the yield or G -value may be estimated as the number of free radicals produced by 100 eV of absorbed energy. Typical values for DNA lie between ½ and 2.

The fit of the continents around the Atlantic

The geometrical fit of the continents now separated by oceans has long been discussed in relation to continental drift. This paper describes fits made by numerical methods, with a ‘least squares’ criterion of fit, for the continents around the Atlantic ocean. The best fit is found to be at the 500 fm. contour which lies on the steep part of the continental edge. The root-mean-square errors for fitting Africa to South America, Greenland to Europe and North America to Greenland and Europe are 30 to 90 km. These fits are thought not to be due to chance, though no reliable statistical criteria are available. The fit of the block assembled from South America and Africa to that formed from Europe, North America and Greenland is much poorer. The root-mean-square misfit is about 130 km. These geometrical fits are regarded as a preliminary to a comparison of the stratigraphy, structures, ages and palaeomagnetic results across the joins.