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  • 11
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Microstructural characterization of boron-containing SiC-reinforced SiC composites exposed at high temperature in high-water-vapor-pressure environments was used to determine surface recession rates and to understand the controlling degradation processes under these conditions. Results showed that composite degradation was controlled by a series of reactions involving the formation of silica, boria, borosilicate glass, and gaseous products. Comparison of results (from characterization of composites exposed at 1200°C and 1.5 atm of H2O in a laboratory furnace and in the combustion zone of a gas turbine) showed that these reactions were common to both exposure conditions and, consequently, there was little effect of gas velocity on degradation rates of boron-containing SiC/SiC composite materials.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 0006-3592
    Keywords: endocellulase ; exocellulase ; Thermomonospora fusca ; Trichoderma reesei ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The activities of six purified Thermomonospora fusca cellulases and Trichoderma reesei CBHI and CBHII were determined on filter paper, swollen cellulose, and CMC. A simple method to measure the soluble and insoluble reducing sugar products from the hydrolysis of filter paper was found to effectively distinguish between exocellulases and endocellulases. Endocellulases produced 34% to 50% insoluble reducing sugar and exocellulases produced less than 8% insoluble reducing sugar. The ability of a wide variety of mixtures of these cellulases to digest 5.2% of a filter paper disc in 16 h was measured quantitatively. The specific activities of the mixtures varied from 0.41 to 16.31 μmol cellobiose per minute per micromole enzyme. The degree of synergism ranged from 0.4 to 7.8. T. reesei CBHII and T. fusca E3 were found to be functionally equivalent in mixtures. The catalytic domains (cd) of T. fusca endocellulases E2 and E5 were purified and found to retain 93% and 100% of their CMC activity, respectively, but neither cd protein could digest filter paper to 5.2%. When E2cd and E5cd were substituted in synergistic mixtures for the native proteins, the mixtures containing E2cd retained 60%, and those containing E5cd retained 94% of the original activity. Addition of a β-glucosidase was found to double the activity of the best synergistic mixture. Addition of CBHI to T. fusca crude cellulase increased its activity on filter paper 1.7-fold. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4992-5001 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transient absorption measurements between 400 nm and 570 nm are used to extract information on the vibrational relaxation of iodine in the complexing solvent mesitylene. The well characterized nature of the I2-arene complex makes it an excellent prototype for the study of relaxation processes in the presence of weak interactions. The data and analysis presented here demonstrate the rapid nonexponential vibrational relaxation of I2 in the interacting solvent mesitylene. The peak of the population distribution has dropped below n=10 by 11 ps and n=7 by 15.5 ps. The energy relaxation is characterized by a biexponential decay with time constants of 4.41±0.08 ps and 20.3±0.7 ps. Quantitative comparisons of relaxation in a variety solvents are made by using a simple time-delay to peak absorption characterization of the relaxation. The initial 4.4 ps decay in mesitylene is significantly faster than the time scales for relaxation in noninteracting hydrocarbon solvents. The difference in the relaxation rate cannot be attributed to a change in vibrational frequency as the vibrational frequency of I2 has only a small dependence on the solvent. It is suggested that the vibrational relaxation of I2 in mesitylene through the high-lying levels is better characterized as an "intramolecular" vibrational energy redistribution process than relaxation to a solvent bath. The ultrafast vibrational relaxation occurs via the anharmonic coupling of the I–I stretching coordinate and the I-MST stretching coordinate of an I2-MST complex. © 1998 American Institute of Physics.
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 4985-4993 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One- and two-color kinetics have been combined with broadband ultraviolet transient absorption spectroscopy in the 265–300 nm region to elucidate the photophysics of cis-hexatriene in cyclohexane solvent. The lowest singlet excited state, the 2 1A1 state, is observed to have a lifetime of 200±50 fs. The ground-state hexatriene is produced vibrationally hot. The excess vibrational energy permits ultrafast isomerization around the C–C single bonds in hexatriene. This results in a dynamic equilibrium of the three cis-hexatriene rotamers, which then relaxes multiexponentially to the room-temperature distribution in which the di-s-trans-Z-hexatriene form predominates. The peak of the mono-s-trans (cZt-HT) population is estimated to be ∼50%. Vibrational cooling results in trapping of a small amount, ∼8%, of cZt-HT that relaxes on a much longer time scale as the barrier to isomerization becomes important. An estimate of the absorption spectrum of cZt-HT is deduced from analysis of the spectral data at 50 ps. © 1997 American Institute of Physics.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 58 (1998), S. 494-501 
    ISSN: 0006-3592
    Keywords: mixture optimization ; cellulase ; experimental design ; synergism ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A factorial experimental design approach was used to optimize mixtures of six cellulases (five Thermomonospora fusca cellulases and plus/minus Trichoderma reesei CBHI along with β-glucosidase) so as to maximize the glucose produced from filter paper. Optimized mixture A and mixture B produced glucose at 25 and 8.3 μmol glucose/μmol enzyme/min, respectively, which are 8 and 1.5 times higher than the sum of the activity of the individual cellulases. In both mixtures, the glucose yield depended on the ratio and the cellulases used. Most enzymes showed synergistic interactions that increased the glucose yield. The yield of glucose with the optimum mixtures depended on the total enzyme concentration. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58: 494-501, 1998.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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