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  • 1
    Electronic Resource
    Electronic Resource
    Mechanism of O-acetylserine sulfhydrylase fromSalmonella typhimurium LT-2 (1992)
    Springer
    Amino acids 2 (1992), S. 119-125 
    Details
    ISSN: 1438-2199
    Keywords: Amino acids ; O-Acetylserine sulfhydrylase ; Pyridoxal 5′-phosphate ; 5-thio(2-nitrobenzoate) ; Acid-base chemistry pH dependence ; Stereochemistry ; Borohydride reduction ; Active site sequence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary O-Acetylserine sulfhydrylase is a pyridoxal 5′-phosphate (PLP) dependent enzyme that catalyzes the final step of L-cysteine biosynthesis inSalmonella, viz. the conversion of O-acetyl-L-serine (OAS) and sulfide to L-cysteine and acetate. A spectrophotometric assay is available using 5-thio(2-nitrobenzoate) (TNB) as an analog of sulfide and monitoring the disappearance of absorbance at 412 nm. The enzyme catalyzes a ping pong mechanism withα-aminoacrylate in Schiff base with the active site PLP as a covalent intermediate. Using data obtained from the pH dependence of kinetic parameters, the acid-base chemical mechanism and the optimum protonation state of enzyme and substrate functional groups necessary for binding has been determined. The Schiff base and theα-amine of the substrate OAS are unprotonated for binding. There also appears to be a requirement for one active site general base to accept a proton from theα-amine and to donate a proton to form cysteine. The enzyme also catalyzes an OAS hydrolase activity, and the pH dependence of this reaction suggests that the active site lysine that participated in the Schiff base linkage is protonated to start the second half reaction, and has a pK of about 8.2. The stereochemistry of3H-borohydride reduction of the Schiff base in free enzyme has been determined by degradation of the resulting pyridoxyllysine to pyridoxamine and measuring3H-release with apo-aspartate aminotransferase. The sequence around the active site lysine is AsnProSerPheSerValLysCysArg.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806082
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic field enhancement of high-T c superconducting pancake coils by Mu metal sheets (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 73-76 
    Details
    ISSN: 1572-9605
    Keywords: High-T c superconductor ; pancake coil ; mu metal ; magnetic field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract High permeability ring-shaped mu metal sheets have been used to enhance magnetic fields in the bore of Bi-based high-T c superconducting coils. The central magnetic fieldB 0, generated by pancake coils placed between mu metal sheets, was measured at liquid nitrogen temperature 77 K. The increasing rate (IR) of the central magnetic fieldB 0 for single pancake coils was from 15 to 63% by using a 0.1 mm thick mu metal sheet. IR was decreased when the originalB 0 value increased. The thickness of mu metal sheets also affected IR. It was found that IR increased as the number of mu metal sheets was increased. In a test double-pancake coil IR reached 101%,B 0 was enhanced from 902 to 1815 G, when the total thickness of mu metal sheets on the top and bottom surface of the coil was 2.0 mm. These results indicate that the well-designed high-permeability materials can significantly enhance the magnetic fields generated by high-T c superconducting coils and magnets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728428
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  • 3
    Electronic Resource
    Electronic Resource
    Development of high-T c superconducting Bi-2223 tape joints (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 281-285 
    Details
    ISSN: 1572-9605
    Keywords: Bi 2223 ; tape joints
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract High-T c superconducting joints between Ag-clad Bi-2223 tapes have been developed for persistent current applications. Two presintered tapes with one side of the silver stripped were lapped and then wrapped by a silver foil. The complex was uniaxially pressed followed by appropriate sintering to form a high-T c superconducting tape joint. It was found that the ratio of critical currents through the joint to that of the tape,I cj/Ic, depended on the uniaxial pressure and the sintering conduction. At liquid-nitrogen temperature 77 K,I cj/Ic=99% has been achieved. Persistent current loops formed by Bi-2223 tapes have also been fabricated and tested. Joint resistance of a loop was determined to be ∼4×10−13 Ω between the decay time of 120 and 3600 sec.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727549
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  • 4
    Electronic Resource
    Electronic Resource
    Variational approximations in energy space for the regulator problem with time delay (1980)
    Springer
    Journal of optimization theory and applications 30 (1980), S. 293-307 
    Details
    ISSN: 1573-2878
    Keywords: Spline approximation ; energy space ; time-delay systems ; Ritz-Trefftz method ; a priori error bounds ; a posteriori error bounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We consider a variational procedure for approximating the solution of the state regulator problem with time delay. Motivated by a dual formulation of the problem, we introduce a positive-definite functionalF over a certain energy space of Mikhlin and obtain approximating solutions by the Ritz-Trefftz idea of minimizing it over finite-dimensional subspaces. The resulting approximating solutions, in turn, furnish suboptimal solutions which converge to the optimal solution of the regulator problem with time delay. A priori error bounds in terms of splines are given. A posteriori error bounds are also obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00934500
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  • 5
    Electronic Resource
    Electronic Resource
    Dual variational principles with deviating argument and discontinuous extremals (1977)
    Springer
    Journal of optimization theory and applications 23 (1977), S. 593-605 
    Details
    ISSN: 1573-2878
    Keywords: Dual variational principles ; corner conditions ; second variation ; regulator problem ; linear neutral functional differential equations ; lower and upper bounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We study dual or complementary variational principles for functionals with deviating argument and discontinuous extremals. Local conditions for the existence of a pair of dual extremum principles are given. Results are then applied to the control problem involving linear neutral differential-difference equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00933299
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    Paper (German National Licenses)
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