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  • 1990-1994  (2)
  • 1991  (2)
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  • 1990-1994  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 52 (1991), S. 223-233 
    ISSN: 1432-0630
    Keywords: 44.25 ; 44.60+f ; 47.25.Q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The temperature oscillation accompanying the photoacoustic effect generates a periodic variation of the vapor pressure of a liquid. The propagation of the oscillating concentration of the vapor in the inert cell gas (air) is described by a mass diffusion wave on which a convective motion of the gas is superposed. The diffusion wave characterized by the diffusion coefficient of the cell gas alone can be measured by the Mirage effect, whereas a microphone detects the total mass flux including the convective flux, which increases with temperature. On approaching the boiling temperature, the convective flow will govern the oscillating transport of mass. The photoacoustic signal is determined directly from the flux of heat and mass at the boundary between liquid and gas using the Gauss' divergence theorem. We have found that the temperature behaviour of the amplitude and phase angle of the photoacoustic signal depends on the length of the gas column in the cell. The contribution of thermal expansion to the photoacoustic signal is considered using the composite piston model. The results of the calculations agree fairly well with the experimental data.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1440
    Keywords: Calcium carbonate ; Phosphate ; Chronic renal failure ; Aluminium ; Hyperparathyroidism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Calcium carbonate has been successfully used as a phosphate binder in patients with chronic renal failure; however, a high frequency of hypercalcaemia has been reported. To study the effects of calcium carbonate preparations with different dissolution characteristics on the incidence of this side effect, we conducted a double-blind, crossover trial in 21 patients undergoing chronic haemodialysis. Aluminium hydroxide therapy was replaced with calcium carbonate. The subjects then randomly received either an enteric-coated or a gastric-coated preparation. Calcium carbonate (3.1–3.6 g/d) controlled serum phosphate concentrations as effectively as aluminium hydroxide (2.9 g/d). Concurrently, there was a significant rise in mean serum calcium and a fall in serum concentrations of both parathyroid hormone and osteocalcin, the latter suggesting a decrease in bone turnover. Overall, hypercalcaemic episodes developed in 9 patients (43%) and occurred at a considerable frequency (33 episodes per 100 patient-months) during treatment with the gastric-coated formulation. Following conversion to enteric-coated calcium carbonate (3.6 g/d) patients had fewer occurrences of hypercalcaemia (12 episodes per 100 patient-months,P〈0.05) and, as compared to the gastric-coated preparation, increases in serum calcium 〉3.00 mmol/l were not observed at all. Hyperaluminaemia was regressive during therapy with calcium carbonate, but addition of small doses of aluminium hydroxide caused a large rise in serum aluminium concentrations after infusion of desferrioxamine, indicating an enhanced rate of absorption or aberrant compartmentalization of aluminium. We conclude that calcium carbonate can control hyperphosphataemia in dialysis patients. However, undesirable hypercalcaemic episodes may occur, the frequency and severity of which can be lowered by the use of an enteric-coated preparation. Concomitant use of aluminium hydroxide and calcium carbonate should be restricted to patients in whom the degree of aluminium accumulation is monitored by serial desferrioxamine tests.
    Type of Medium: Electronic Resource
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