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  • 1985-1989  (7)
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  • 1
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Acidogenesis and solventogenesis byClostridium beijerinckii NRRL B-593 has been studied in batch growth, and in sucrose-limited chemostat and recycling fermentor growth. Cells grown in batch culture without pH control primarily produced either butyric and acetic acids, or these acids plus butanol, ethanol and isopropanol in ratios depending on the medium's content of reducing agent, calcium and iron. Cells in chemostat-culture at a mass doubling time (td) of 5.8 h produced primarily butyric and acetic acids at pH 6.8 and these acids plus butanol, ethanol and isopropanol at pH 4.8. Cells grown in a recycling fermentor (in which the td continuously increases) at pH 6.8 entered solventogenesis at a td of 43 h, producing primarily propanol, ethanol and butanol, along with butyric acid, but with greatly decreased production of acetic acid. Although “clostridial form” morphology, succeeded by sporulation, usually accompanied solventogenesis, the association was not invariant so that solventogenesis and sporogenesis can occur separately in this species.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2021-2023 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optically and thermally stimulated luminescence in CaS:Ce,Sm have been studied. Subsequent to exposure to ionizing radiation, this material can be optically stimulated by infrared laser sources such as an InGaAsP (1.20 μm) laser and a Nd:YAG (1.06 μm) laser. The resulting optically stimulated luminescence is the characteristic Ce3+ doublet emission. This material has a deep trap with a ∼330 °C thermoluminescence peak. However, the thermal stimulation results in both Sm3+ and Ce3+ characteristic emissions. It appears that charge compensation in the form of additional sulfur ions in the interstitials is possible in CaS:Ce,Sm and the charge motion between the Ce3+ ions at different symmetry sites results in Ce3+ emissions from the 330 °C peak.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1363-1366 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optically stimulated luminescence and thermally stimulated luminescence in MgS:Ce,Sm and MgS:Eu,Sm have been investigated. It appears that samarium in the form of Sm3+ ion acts as a thermally stable electron trap in MgS:Ce,Sm and MgS:Eu,Sm. A Sm3+ ion becomes a Sm2+ ion capturing an electron when these materials are exposed to UV radiation at room temperature, while the free hole is captured by a Ce3+ (or Eu2+). On optically stimulating an UV treated sample, the trapped electrons are released from Sm2+ ions and are recaptured by Ce4+ (or Eu3+) ions leading to the luminescence which is characteristic of Ce3+ (or Eu2+) emission. However, thermal stimulation of these UV treated samples results in luminescence which is characteristic of Sm3+ emissions, indicating that the thermoluminescence results from the release of holes from Ce4+ (or Eu3+) and Sm3+ acts as a luminescence center.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work we study CaF2:Ce,Mn and use optical absorption, photoluminescence (excitation and emission), and x-ray-induced luminescence to characterize the role played by Ce in various lattice sites during these processes. The data indicate that energy transfer takes place from Ce to Mn, predominantly from Ce3+ in tetragonal sites (i.e., Ce3+-F−int centers with C4v symmetry). There is also some evidence of transfer from higher-order clusters of these defects. In contrast, however, we note that there is no evidence of energy transfer in x-ray-excited luminescence; an increase in the Ce concentration causes a decrease in the Mn2+ emission. It appears from the present investigations that, during x-ray excitation, nonlocally compensated Ce3+ ions of cubic symmetry compete with Mn2+ ions for free electrons released during irradiation. Thus, the data indicate that tetragonal Ce3+ sites are dominant during UV excitation and give rise to energy transfer to Mn2+, whereas cubic Ce3+ sites are dominant during irradiation with high-energy ionizing radiations and no energy transfer takes place.
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  • 5
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Mixtures of CaCO3∶SiO2 in 2∶1 molar ratio were subjected separated to thermal analysis with varying concentration of Cr2O3 (0.1 to 5%) as dopant. The activation energy (E a) and enthalpy (ΔH) shows a decreasing trend with 0.1 to 1% Cr2O3 and attains a minimum value with 1% dopant. 0.1 to 0.5% Cr2O3 helps in the formation of β and γ C2S, (Cement Chemistry notations, C = CaO, S = SiO2) phases at 1400° C and above but 1% Cr2O3 stabilizes β-C2S phase along with a little free lime and CaCrO4. A small quantity of CaCrO4, Cr2SiO2 and α-C2S are also formed along with the major phases with 5% Cr2O3 indicating that Cr3+ can substitute both Ca2+ and Si4+ ions in the C2S lattice.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 155-157 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 137-139 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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