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  • 2000-2004  (2)
  • 1975-1979  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' journal of analytical chemistry 368 (2000), S. 384-388 
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Δ4-3-Ketosteroids exhibit an intensive negative Cotton effect on the circular dichroism (CD) spectra in the wavelength range for the n-π* electronic transition (270–¶350 nm). With hydroxylamine hydrochloride, Δ4-3-ketosteroid compounds can be transformed into oxime derivatives. Following oxime formation, positive ellipticity with low intensity can be registered in this wavelength range. The quantitative determination of Δ4-3-ketosteroids is based on the considerable difference between the ellipticities before and after oxime formation. The difference ellipticity for the six ketosteroids examined (norethisterone, levonorgestrel, levonorgestrel acetate, methyltestosterone, testosterone phenylpropionate, nortestosterone phenylpropionate) varies linearly with the concentration in the interval 6 × 10–6–3 × 10–3 mol/L. The method can be well applied to determination of Δ4-3-ketosteroid contamination of norgestimate [(+)-13-ethyl-17-hydroxy-18,19-dinor-17α-pregn-4-en-20-yn-3-one oxime acetate]; 0.02–10% impurity can be measured.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 9 (1976), S. 241-250 
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé On a étudié à l'aide d'un Derivatograph, sous diverses conditions, la réaction de mélanges binaires et ternaires des carbonates alcalins avec l'oxyde d'aluminium. L'identification des produits formés a été effectuée par diffraction des rayons X. Si les mélanges binaires et ternaires de carbonates contiennent du carbonate de lithium, il se forme toujours 1'α-métaaluminate de lithium, qui, à température plus élevée, se transforme en la formeγ. Si la carbonate de lithium est utilisé seul, on peut obtenir aussi l'ortho-dialuminate.
    Abstract: Zusammenfassung Die Reaktionen binärer und ternärer Alkalikarbonatmischungen mit Aluminiumoxid wurden mittels eines Derivatographen unter verschiedenen Bedingungen untersucht. Die Reaktionsprodukte wurden durch Röntgendiffraktion identifiziert. In Gegenwart Li2CO3-haltiger binärer und ternärer Karbonatmischungen war das Produkt stets α-Lithium-meta-aluminat, das bei höheren Temperaturen in dieγ-Form überging, während bei Einsatz von Li2CO3 auch Orthodialuminat erhalten werden konnte.
    Notes: Abstract Reactions of binary and ternary alkali metal carbonate mixtures with aluminium oxide were studied by means of a derivatograph under different conditions. Reaction products were identified by X-ray diffraction. In the presence of binary and ternary carbonate, mixtures containing Li2CO3 the product was alwaysα-lithium metaaluminate, transforming to theγ-form at higher temperatures, while using only Li2CO3 the orthodialuminate could be obtained too.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4854
    Keywords: wide gap amorphous silicon ; photoluminescence ; electroluminescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A series of samples of hydrogenated amorphous silicon (a-Si:H) was prepared from silane diluted highly with He by the microwave electron-cyclotron-resonance PE CVD. Such a wide gap (E≥2.0 eV) a-Si:H emits room temperature photoluminescence (PL) in the visible region. We attempt to reveal the microscopic origin of this PL by monitoring variations of PL intensity vs frequency of infrared vibrations in the vicinity of 2100 cm−1. We find that oligosilanes -(SiH2)n- act as one type of possible luminescence centres. We report also on room temperature electroluminescence (EL) from p-i-n junctions. Surprisingly, and unlike p-i-n structures from standard a-Si:H, weak EL radiation with external quantum efficiency of the order of 10−5% is emitted under reverse bias only. EL and PL emission spectra resemble strongly each other, except high energy wing of the EL spectrum. This high energy widening indicates the participation of hot electrons in the EL excitation mechanism.
    Type of Medium: Electronic Resource
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