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  • 1
    Electronic Resource
    Electronic Resource
    Expression in Escherichia coli, purification and kinetic analysis of the aspartokinase and aspartate semialdehyde dehydrogenase from the rifamycin SV-producing Amycolatopsis mediterranei U32 (2000)
    Springer
    Applied microbiology and biotechnology 54 (2000), S. 52-58 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The operon encoding aspartokinase and aspartate semialdehyde dehydrogenase was cloned and sequenced from rifamycin-SV-producing Amycolatopsis mediterranei U32 previously. In the present work, these two genes were introduced into the auxotrophic Escherichia coli strain CGSC5074 (ask −) and E. coli X6118 (asd −), respectively. The A. mediterranei U32 aspartokinase and aspartate semialdehyde dehydrogenase genes can be functionally expressed in E. coli and the gene products are able to substitute for the E. coli enzymes. Histidine-tagged aspartokinase and aspartate semialdehyde dehydrogenase were partially purified from E. coli cellular extracts and their kinetic characteristics were studied. Both aspartokinase and aspartate semialdehyde dehydrogenase showed typical Michaelis-Menten type substrate saturation patterns. Aspartokinase has K m values of 3.4 mM for aspartate and 2.3 mM for ATP, while aspartate semialdehyde dehydrogenase has K m values of 1.25 mM for dl-aspartate semialdehyde and 0.73 mM for NADP, respectively. Aspartokinase was inhibited by l-threonine, l-lysine, and l-methionine, but not by l-isoleucine and diaminopimelate. Aspartate semialdehyde dehydrogenase was not inhibited by any of the end-product amino acids at a concentration of less than 5 mM. Hill plot analysis suggested that aspartokinase was subject to allosteric control by l-threonine. Repression of both aspartokinase and aspartate semialdehyde dehydrogenase gene transcription in A. mediterranei U32 by l-lysine, l-methionine, l-threonine, and l-isoleucine were found. The network of regulation of aspartokinase and aspartate semialdehyde dehydrogenase in rifamycin SV-producing A. mediterranei U32 is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002530000345
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  • 2
    Electronic Resource
    Electronic Resource
    Anomalous temperature dependence of photoluminescence from InAs quantum dots (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2529-2532 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-assembled InAs quantum dots are fabricated on a GaAs substrate by molecular beam epitaxy. The dots are covered by several monolayers of In0.2Ga0.8As before a GaAs cap layer and an in situ postgrowth annealing is performed to tune the emission to higher energy. The temperature dependence of photoluminescence from this structure demonstrates a slower redshift rate of the peak position, a gradual broadening of the linewidth and an abnormal enhancement of integrated intensity as the temperature is increased from 15 to 300 K. These phenomena are closely related to the introduction of an InGaAs layer and to the intermixing of In and Ga atoms during annealing. We propose a model to explain the unusual increase in PL intensity, which fits the experimental data well. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288231
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  • 3
    Electronic Resource
    Electronic Resource
    Self-organized type-II In0.55Al0.45As/Al0.50Ga0.50As quantum dots realized on GaAs(311)A (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3741-3743 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-organized In0.55Al0.45As/Al0.50Ga0.50As quantum dots are grown by the Stranski–Krastanow growth mode using molecular beam epitaxy on the GaAs(311)A substrate. The optical properties of type-II InAlAs/AlGaAs quantum dots have been demonstrated by the excitation power and temperature dependence of photoluminescence spectra. A simple model accounting for the size-dependent band gap of quantum dots is given to qualitatively understand the formation of type-II In0.55Al0.45As/Al0.50Ga0.50As quantum dots driven by the quantum-confinement-induced Γ→X transition. The results provide new insights into the band structure of InAlAs/AlGaAs quantum dots. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126768
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  • 4
    Electronic Resource
    Electronic Resource
    In-situ Formation of TiC/Hadfield Steel Composites (1998)
    Springer
    Journal of materials science 17 (1998), S. 1527-1529 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006529307807
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  • 5
    Electronic Resource
    Electronic Resource
    Secondary M6C Precipitation in a Cobalt–base Superalloy (1999)
    Springer
    Journal of materials science 18 (1999), S. 303-305 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006627122234
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  • 6
    Electronic Resource
    Electronic Resource
    In-situ synthesis of a TiC-Fe composite in liquid iron (1997)
    Springer
    Journal of materials science 16 (1997), S. 1830-1832 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018576904132
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  • 7
    Electronic Resource
    Electronic Resource
    Carbide behaviour during high temperature low cycle fatigue in a cobalt-base superalloy (1999)
    Springer
    Journal of materials science 34 (1999), S. 2859-2864 
    Details
    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 The carbide behaviour of a directionally solidified cobalt-base superalloy has been investigated after low cycle fatigue at 900°C. During fatigue, primary carbides, M7C3 and MC, decomposed sluggishly and a great amount of secondary carbide, chromium-rich M23C6 precipitated. The inhomogeneous distribution of M23C6 brought about a different dislocation substructure. In the vicinity of the primary carbides, densely-distributed fine M23C6 pinned up dislocations effectively, resulting in a uniform distribution of dislocations, while in the interior of grains, since precipitates were coarse and scarce, dislocations were arranged in a planar array and piled up in the front of the precipitates. M23C6 also acted as an obstacle deflecting fatigue crack. Primary carbides on the surface of specimens were oxidizied preferentially, causing a precipitate depletion around them. The oxidized primary carbides were crack initiation sites. The primary carbides hindered fatigue crack propagation, causing the formation of shear steps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004683301816
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  • 8
    Electronic Resource
    Electronic Resource
    Isolation and characterization of a temperate bacteriophage from a ruminal acetogen (1995)
    Springer
    Current microbiology 31 (1995), S. 336-339 
    Details
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Nine acetogenic bacterial cultures recently isolated from the bovine rumen were tested for phage susceptibility by plaque formation. Both clear plaques and plaques with turbid centers were occasionally seen, but could not be used repeatedly to lyse pure cultures of acetogens, suggesting the possibility of a temperate phage. Five of the nine acetogenic isolates showed a response to mitomycin C induction. Acetogenic isolate H3HH was chosen for further study because it produced the greatest lysogenic response to mitomycin C. The bacteriophage was induced with mitomycin C, examined by transmission electron microscopy, and shown to have a hexagonal head (diameter, 59 ηm), a long flexible tail (192 ηm), and a flat collar (diameter, 31 ηm). The bacteriophage was classified within Bradley's group B. Bacteriophage DNA was determined to contain 36.2 kilobases of linear double-stranded DNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00294695
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  • 9
    Electronic Resource
    Electronic Resource
    Study of interaction between polyethylene glycol and chitosan by viscosity method (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1275-1281 
    Details
    ISSN: 0887-6266
    Keywords: chitosan ; polyethylene glycol polyblend ; intermolecular interaction ; viscometry ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular structures of polyethylene glycol (PEG) and chitosan (CS) are illustrated as follows: 1CS2PEG\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm HO} \hbox{--} {\rm CH}_2 {\rm CH}_2 \rlap{--} ({\rm O} \hbox{--} {\rm CH}_2 {\rm CH}_2 \rlap{--} {\rm O} \hbox{--} {\rm CH}_2 {\rm CH}_2 \hbox{--} {\rm OH} $$\end{document} The intermolecular interactions between these two polymers were studied by viscometry with a thermodynamic parameter α, which was first proposed by Sun et al. The weight additive rule of the intrinsic viscosity of polyblend relating to the values of each polymeric constituent was attested to with PEG/CS polyblend. The calculation formula of Huggins coefficient for polyblend, km, was theoretically deduced, and a very simple expression of α was obtained. First, the values of α for PEG/CS blends with different PEG molecular weight were estimated from the experimental viscosity data of the polyblends with different mixed ratio. According to these values of α, it can be predicted that an attractive interaction exists between the molecule of PEG and that of CS. Second, the viscosity of CS was measured in pseudo-solvents (PEG dissolved in 0.01N sodium chloride aqueous solution) with different PEG concentrations. From these viscosity data, the values of cross Huggins coefficient are calculated to be all larger than the values of the Huggins coefficient both for CS and for PEG. On the revised α criterion, the dissimilar molecular interaction in PEG/CS polyblend is demonstrated to be attractive too. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1275-1281, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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