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  • 1990-1994  (21)
  • 1955-1959
  • 1920-1924
  • 1910-1914
  • Chemistry  (16)
  • 36.10.Dr  (5)
  • 1
    ISSN: 1434-601X
    Keywords: 13.10. + q ; 23.20.-g ; 36.10.-k ; 36.10.Dr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The probabilities for non-radiative (n.r.) excitationsP n.r. in the muonic nuclides208Pb,232Th, and238U have been determined from (μ−,γγ)-measurements by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The value ofP n.r. (3p→1s), measured for the first time, is about 90% for the actinides232Th and238U, but only about 8% for208Pb. The value ofP n.r. (3d→1s) is found to be 10 % for233Th, 13% for238U, and about 4% for208Pb. For208Pb a vanishing strength of the n.r. decay of the 2p-level is found, while for232Th and for238U n.r. strengths of about 20% and 26%, respectively, are observed. By regarding two subcomplexes of the 2p→1s transitions leading to different mean excitation energies the n.r. transition probabilities were found to be different for238U only, 21.6% and 31.1.%, respectively.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-601X
    Keywords: 13.10.+q ; 23.20.−g ; 36.10.−k ; 36.10.Dr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The probability for non-radiative (n.r.) excitations in muonic209Bi was determined from a (μ −,γγ)-measurement by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The values of Pn.r(3p→1s)=(17.9±2.0)% and Pn.r.(3d→1s)=(3.0±2.2)% were measured for the first time. The strength of the n.r. decay of the 2p-level was found to be (4.2±2.2)%. The n.r. transition probabilities of two subcomplexes of the (2p→1s)-transition leading to different mean excitation energies are (3.2±1.8)% and (5.0±2.0)%, respectively.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-601X
    Keywords: 13.10.+q ; 14.60.Ef ; 25.85.Ge ; 27.90.+b ; 36.10.Dr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ratios of prompt to delayed fission yields for the isotopes233U,234U,235U,236U,238U,237Np,242Pu, and244Pu and the fission probabilities relative to each other have been investigated experimentally. Using the value of the total fission probability for237Np the absolute probabilities for prompt and delayed fission have been determined. The fission probabilities per muon captureP fc have been derived for all the isotopes and compared with an evaluation based on excitation functions from theory.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-601X
    Keywords: 23.20.−g ; 25.85.−W ; 36.10.−k ; 36.10.Dr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In the spectrum of muonic X-rays of238U measured in coincidence with prompt fission events a structure has been found which is attributed to 2p→1s transitions of the muon attached to heavy fragments. The intensityI s of this structure relative to the strengthI pf observed for prompt fission has been determined to beI s/I pf=(6.0± 2.1) %. Although the experimental significance for the appeareance of this phenomenon is weak, this is the first experimental indication for its occuxence.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-601X
    Keywords: 13.10. + q ; 13.35. + s ; 14.60.Ef ; 25.85.-w ; 27.90. + b ; 36.10.Dr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The time spectra for muon induced fission of233U,234U,235U,236U,238U, and237Np were measured simultaneously, detecting both fragments in coincidence in a fast multi parallel plate avalanche detector. The observed mean lifetimes τ are 68.9 ± 0.3 ns, 70.6 ± 0.2 ns, 72.2 ±0.2 ns, 74.3 ± 0.3 ns, 77.0 ±0.4 ns, and 69.8 ±0.2 ns for the above isotopes, respectively. No second time component, tentatively ascribed to a possible fission isomer, was observed. The deduced total capture rates are compared with theoretical predictions.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 7 (1990), S. 16-31 
    ISSN: 0887-3585
    Keywords: BPTI ; dithiothreitol ; DTT-sensitive mutants ; protein folding ; random mutagenesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A genetic screening procedure has been developed to identify mutant forms of bovine pancreatic trypsin inhibitor (BPTI) that can fold to an active conformation but are inactivated more rapidly than the wild type protein. Small cultures of Escherichia coli containing plasmids with mutagenized BPTI genes were grown in microtiter plates, lysed, and treated with dithiothreitol (DTT). Under these conditions, unfolding and inactivation of wild-type protein has a half-time of about 10 hours. Variants of BPTI that are inactivated within 1 hour were identified by adding trypsin and a chromogenic substrate. Approximately 11,000 mutagenized clones were screened in this way and 75 clones that produce proteins that can fold but are inactivated by DTT were isolated. The genes coding for 68 “DTT-sensitive” mutant proteins were sequenced, and 25 different single amino acid substitutions at 15 of the 58 residues of the protein were identified. Most of the altered residues are largely buried in the core of the naive wild-type structure and are highly conserved among proteins homologous to BPTI. These results indicate that a large fraction of the sequence of the protein contributes to the kinetic stability of the active conformation, but it also appears that substitutions can be tolerated a most sites without completely preventing folding Because this genetics, further studies of the isolated mutants are expected to provide information about the roles of the altered residues in folding and unfolding.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 15 (1993), S. 322-329 
    ISSN: 0887-3585
    Keywords: unfolded proteins ; mutations ; BPTI ; gel electrophoresis ; disulfide-formation kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effects of amino acid replacements on the hydrodynamic volume of reduced and unfolded bovine pancreatic trypsin inhibitor (BPTI) have been examined by gel electrophoresis. The electrophoretic mobilities of the reduced forms of 46 BPTI variants were compared at room temperature in the absence of denaturants. The single substitutions examined include many different types of replacements at sites throughout the polypeptide, and, collectively, alter 22 of the 58 residues of the wild-type protein. The only substitutions found to alter the electrophoretic mobility of the reduced protein by more than ∼3% are those that change the net charge of the protein. For nine mutants, the rates of disulfide formation in the reduced protein were also examined and found to be very similar to that of the wild-type protein. These results suggest that any structure that may be present in the reduced protein is either relatively insensitive to amino acid replacements or does not greatly influence the averaged properties of the polypeptide chain. © 1993 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 39 (1992), S. 1151-1160 
    ISSN: 0006-3592
    Keywords: fluorescence ; monitoring ; methane ; fermentation ; NAD(P)H ; F420 ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: On-line in situ fluorescence measurements of the methanogenic fermentation were conducted with reactors receiving either glucose or a mixture of volatile fatty acids as the substrate. The reactors were perturbed from steady-state conditions in order to assess the response of fluorescencemonitoring probes. Two fluorescence-monitoring probes were evaluated over a period of 8 months; they performed in a consistent manner, and their response was not significantly affected by the changes in pH and redox potential encountered during routine reactor operation. A commercially available probe, designed to measure NAD(P)H, demonstrated particular promise for detecting imbalance caused by the entry of air, inhibitor addition and was capable of distinguishing between different substrates. This fluorescence-monitoring probe detected imbalance more rapidly than other on-line measurements such as pH, Eh, or gas production, or off-line measurements such as volatile fatty acid concentration or gas composition. An experimental fluorescence-monitoring probe, designed to measure coenzyme F420, also showed some promise in this regard. The response of the fluorescence-monitoring probes also revealed details of the metabolic routes in the reactors and the probes represent a useful research tool. For example, a failure to observe the characteristic response of the NAD(P)H-monitoring probe to formate addition during the metabolism of acetate, propionate, or glucose strongly suggests that any formate liberated during their catabolism is degraded via a different route to exogenously added formate.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 251-257 
    ISSN: 0887-6266
    Keywords: poly(aryl-ether-ether-ketone) (PEEK), solvent-induced crystallinity in ; crystallization of PEEK, solvent-induced ; sorption of solvents in PEEK, crystallinity induced by ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The amount and structure of the crystals formed by the solvent-induced crystallization (SIC) following a sorption-desorption cycle of five fluids (benzene, toluene, chloroform, methylene chloride, and carbon disulfide) in amorphous PEEK was determined by wideangle x-ray scattering (WAXS). The SIC crystal structure was compared with that produced by thermal methods, both those formed at low temperature by heating the amorphous material 10-20°C above Tg or by cooling from the melt. Although smaller in size, the SIC crystals are tighter and more organized than those produced thermally. The WAXS data indicates that all five fluids produce approximately 35% crystallinity in PEEK. Gravimetric data suggest that a low-density region, consisting of either microvoids or highly disordered amorphous region, surrounds the crystals.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 441-449 
    ISSN: 1040-7685
    Keywords: open-tubular columns ; supercritical fluid chromatography ; retention ; selectivity ; pressure ; temperature ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied solute retention for n-hydrocarbons, (low-molecular-weight) polystyrenes, an ethoxylated surfactant, and a selectivity test mix on open-tubular columns with methyl-, biphenyl-, and cyanopropyl-substituted stationary phases for pressures up to 680 atm and temperatures up to 240°C. The solute elution range varied tremendously with column choice, with the least retentive stationary phases providing the highest elution range. However, the best resolution and largest analysis range were obtained with the most retentive stationary phase and the highest pressures. Increasing the temperatures above 160°C did not cause a large increase in elution pressure for the solutes used in this study. Exceptionally large shifts in selectivity with temperatures up to about 160°C occurred for the biphenyl and cyanopropyl stationary phases. The availability of pressures higher than 680 atm, coupled with adequately retentive stationary phases used at optimal temperatures, would further increase the analysis scope of opentubular supercritical fluid chromatography.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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