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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 37 (1985), S. 165-170 
    ISSN: 1432-0649
    Keywords: 42.55.Hq ; 33.80Be ; 42.60.By
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experimental measurements of small-signal gain in an optically-pumped NH3 amplifier are carried out at pressures ranging from 40 Torr to 760 Torr, and the results are used to validate a rate-equation model describing the amplifier dynamics. The gain measurements show that dilute mixtures of 〈0.5% NH3 in N2 are reqired to minimize the problems of gas heating due to pump absorption. The model is used to extrapolate the results to gas pressures of several atmospheres, and to demonstrate the potential for highpressure operation of optically-pumped NH3 lasers. For a pump intensity of 100 MW/cm2, calculations indicate that operation of an NH3−N2 laser is feasible up to a pressure of 10 atm, which would provide a maximum continuous tuning range of 4 cm−1. High-resolution spectroscopy reveals that gain on a few NH3 transitions is eliminated at high pressures due to the presence of overlapping absorptions in other NH3 bands.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 36 (1985), S. 115-124 
    ISSN: 1432-0649
    Keywords: 42.55.Dk ; 42.60.By
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A detailed study of the gain dynamics of the pulsed, optically pumped 4.3 μm CO2 laser is described. Small-signal gain coefficients as high as 14%/cm are measured in a 4.3 μm amplifier using low-power pulses from a 4.3 μm probe laser. The measurements are compared with a rate-equation model and good quantitative agreement is obtained. The model, which uses no adjustable parameters, is described in detail. Gain is studied as a function of optical pumping power, gas mixture, gas pressure and discharge excitation of the 4.3 μm amplifier. Optimization of the gain is discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 51 (1990), S. 371-373 
    ISSN: 1432-0649
    Keywords: 33.80.Be ; 42.55.Hq ; 42.60.By
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A simple and efficient NH3 laser was tuned over more than 70 vibrational band transitions between 10.08 and 14.14 μm. The active medium was a dilute mixture of ammonia in argon and was optically pumped by the 9R(30) transition of a pulsed TEA-CO2 laser. Output energies greater than 1 J per pulse were observed on several of the strongest lines. In a non-selective cavity an energy conversion efficiency of greater than 35% was obtained with a maximum output energy of 4.6J. Optically pumped NH3 is shown to be a flexible and efficient system for the downconversion of CO2 radiation.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 50 (1990), S. 345-354 
    ISSN: 1432-0649
    Keywords: 33.80.Be ; 42.55.Hq ; 42.60.By
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A pulsed transversely excited CO2 laser operating on the 9R(30) transition is used to optically pump mixtures of NH3 in buffer gas. A simple oscillator/amplifier system characterizes the performance of the NH3 amplifier in the 11 μm region. Small-signal gain coefficients of 〉10%/cm measured on the aQ(3,3) transition at 10.7 μm, while pump conversion efficiencies of ∼50% are shown to occur under saturation conditions. The NH3 laser system is described by a rate-equation model, which is validated by comparison with experiment over a wide range of operating conditions. Measurements are made for NH3 concentrations ranging from 0.05 to 0.2%, with Ar, N2, and He buffer gas pressures from 170 to 700 Torr, and for gas temperatures from 200 to 300 K. Optically pumped NH3 is shown to be a versatile and efficient system for the amplification of mid-infrared radiation.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1041
    Keywords: Essential hypertension ; clonidine ; plasma levels ; concentration-effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of oral doses of 300 µg of clonidine hydrochloride on blood pressure, sedation and saliva production in 5 essential hypertensives were qualitatively similar to the effects in normotensive subjects. Peak plasma clonidine concentration (1.34±0.28 ng/ml) and plasma half-life (10.0 ±0.8 h) were similar to normotensives. During chronic oral dosing there was no evidence of drug accumulation. Some tolerance to the sedative and salivary flow effects occurred but no tolerance to the hypotensive effect was observed. There was a linear relationship between reduction in saliva flow and plasma levels of clonidine. The hypotensive effect was also related to plasma level at low concentrations. At plasma levels 〉1.5 ng/ml the hypotensive effect was diminished. This loss of effect at high plasma concentration may be related to the peripheral, post-synaptic alpha-adrenoceptor agonist action of the drug.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    European journal of clinical pharmacology 24 (1983), S. 15-19 
    ISSN: 1432-1041
    Keywords: hypertension ; mianserin ; clonidine ; methyldopa ; depression ; α2 receptors ; interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The concurrent administration of tricyclic antidepressants has been shown in man to result in a clinically significant impairment of the antihypertensive effect of clonidine. This interaction is thought to be related to competition for central α2 receptors where clonidine acts as an agonist and the tricyclics act as antagonists. Although it seems to cause less cardiovascular effects than tricyclic antidepressants, the tetracyclic antidepressant, mianserin also has been reported to be an α receptor antagonist and may, therefore, also interfere with the antihypertensive activity of centrally-acting drugs. This study investigates the effects of acute and chronic mianserin administration in patients with essential hypertension established on long term treatment with either clonidine or methyldopa. The first dose of mianserin was not associated with an increase in blood pressure and during a further two weeks of mianserin therapy there were no significant alterations in blood pressure, supine or erect. Similarly, mianserin did not alter heart rate either after acute or after chronic administration. Mianserin itself had a sedative effect but there was no interference with the sedation attributable to clonidine or methyldopa. Mianserin caused no reduction in salivary flow and did not influence the reduced saliva production caused by clonidine. Both clonidine and methyldopa are associated with a reduction in sympathetic outflow but there was no evidence in this study of any further change in plasma noradrenaline or 24 h urinary catecholamine excretion. This study demonstrates that if mianserin is given acutely or chronically, it does not interfere with the effects of the centrally acting antihypertensive drugs, clonidine and methyldopa. Mianserin may therefore be a suitable antidepressant for patients receiving these antihypertensive agents if drug treatment for depression is indicated.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    European journal of clinical pharmacology 21 (1981), S. 97-102 
    ISSN: 1432-1041
    Keywords: mianserin ; clonidine ; pharmacodynamics ; interaction ; alpha2-receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary There is evidence that clonidine's hypotensive effect is reduced by the concurrent administration of tricyclic antidepressants. It has been proposed that this results from an interaction at α2-receptors in the brain stem where clonidine acts as a relatively selective agonist and the tricyclic antidepressants as antagonists. Mianserin is an antidepressant with a tetracyclic structure and, although it has been reported to cause less cardiovascular disturbance, there is evidence that it also has α-adrenoceptor blocking effects. This study in 6 normotensive healthy male volunteers was designed to investigate a possible interaction between clonidine and the antidepressant mianserin. Administration of the first dose of 20 mg mianserin was associated with acute cardiovascular effects, notably transient postural hypotension, but no significant disturbance of heart rate or blood pressure was detected after 3 days continuous treatment with mianserin 20 mg tid. Following pre-treatment with mianserin or placebo the responses to a single oral dose of 300 µg clonidine were then assessed. The combination of mianserin and clonidine was not associated with any attenuation of clonidine's hypotensive effect, erect or supine, but there was significant attenuation of clonidine's supine bradycardic effect. There was no evidence that mianserin interfered with the ability of clonidine to diminish salivary flow, cause sedation, and reduce catecholamine output, but it was noted that mianserin itself had a very pronounced sedative effect. Mianserin alone had no significant effect on salivary flow. This short term study demonstrates that mianserin does not significantly interfere with the responses to a single oral dose of clonidine.
    Type of Medium: Electronic Resource
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