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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6231-6231 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The recent determination of the crystal structure of PbFe12O19 by means of single-crystal x-ray diffraction has made it possible to carry out a definitive and comparative analysis of the structure-property relationship of PbFe12O19, SrFe12O19, and BaFe12O19. We have therefore performed 57Fe Mössbauer measurements on oriented, single-crystal, and powder samples of PbFe12O19 at 298 K. For a single-crystal oriented parallel to the c axis, five distinct patterns are observed. The hyperfine fields, isomer shifts, and quadrupole interactions are as follows: 12k: Heff=413 kOe; δ=0.33 mm s−1; Δ=0.35 mm s−1; 4f1: 487 kOe; 0.24 mm s−1; 0.13 mm s−1; 4f2: 514 kOe; 0.39 mm s−1; 0.29 mm s−1; 2a: 496 kOe; 0.30 mm s−1; 0.11 mm s−1; 2b: 399 kOe; 0.30 mm s−1; 2.00 mm s−1. The relative magnitude of each of these parameters is in good agreement with and exhibits the same trend observed for high-purity SrFe12O19. The relative intensity of the 2b pattern for the crystal oriented parallel to the c axis is 8.2%, which approaches its theoretical value; of the total number of iron ions in the structure, 8.33% of them occupy the 2b site. The value for the polycrystalline sample is only 5.4% of the total intensity. However, for a single crystal oriented perpendicular to the c axis, the 2b pattern exhibits a negligible intensity within the experimental error. This result confirms the dynamic disorder in the position of the 2b iron ions and suggests a stronger anisotropy for the case of PbFe12O19 than for SrFe12O19 and BaFe12O19. Even though the trend in hyperfine parameters at 298 K is similar to Sr, Ba, and Pb hexaferrites, PbFe12O19 exhibits hyperfine fields that are consistently lower than those of the Ba and Sr analogues. This result is discussed in terms of the Curie temperatures, magnetic exchange interactions, and structural parameters.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 51 (1991), S. 321-327 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider in detail the consequences of the heavy quark mass limit in the weak decay of 1/2+ heavy baryons to 1/2+ and 3/2+ heavy baryon final states. We also analyze heavy baryon to light baryon transitions as well ase + e −-annihilation into heavy baryon-antibaryonpairs. We discuss possible approximations to the most general approach and some of their implications for future experiments.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4889
    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
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  • 4
    ISSN: 1573-4889
    Keywords: easy diffusion paths ; Al2O3 films ; γ-Al2O3 nucleation sites ; amorphous film
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Thermal oxide films grown on electropolished aluminum specimens have been investigated by transmission electron microscopy of stripped oxide films and ultramicrotomed sections. Particular attention has been focused on the nucleation sites γ-Al 2 O 3 crystals and the relationship of such sites to surface features on the electropolished aluminum surface. It is evident that “easy paths” for the diffusion of oxygen, or the nucleation sites of γ-Al 2 O 3 crystals, are not distributed randomly over the electropolished aluminum surface, but form preferentially in the amorphous oxide layer grown over preexisting metal ridges. Thus, the diffusion of molecular oxygen through cracks in the amorphous oxide layer represents the most realistic and acceptable basis for explaining the local growth of the γ-Al 2 O 3 crystals in thermal oxide films on aluminum, although the cracks have not yet been observed directly.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-4889
    Keywords: aluminium ; amorphous oxide ; γ-Al2O3 ; induction period
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A novel technique has been employed to allow ready detection of fine crystallites, probably of γ-Al2O3, of sizes generally less than 10 nm in thermal oxide films on aluminium. Using this approach, the relationship between the average population density of γ-Al2O3 crystals and oxidation time has been obtained for the first time. Importantly, it has been found that oxidation at temperatures of 515 or 490°C results in fine crystal development almost from the onset of thermal oxidation. Thus, the so-called induction period for the growth of the γ-Al2O3 crystals, determined previously from weight gain data, should now be regarded as the oxidation time required for both the population density and sizes of the crystals to become sufficiently large to cause significant deviation in the weight gain data from the initial inverse logarithmic law describing the growth of the amorphous oxide.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inherited metabolic disease 14 (1991), S. 546-553 
    ISSN: 1573-2665
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Techniques for studying metabolic eventsin vivo in patients with inborn errors are reviewed. Loading or provocation tests that have been used widely are insensitive and frequently non-specific. Compounds labelled with stable isotopes can be used to study enzyme kinetics and substrate turnover, providing more detailed and specific information. Intracellular events may be studied using nuclear magnetic resonance spectroscopy. The results using these techniques to study patients with selected inborn errors are discussed, namely phenylketonuria, glycogen storage disease type I and propionic acidaemia.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 10 (1991), S. 709-711 
    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
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of optimization theory and applications 71 (1991), S. 169-187 
    ISSN: 1573-2878
    Keywords: Rigid prices ; disequilibrium in economic markets ; activity analysis ; complementarity problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper outlines the general principles of constructing mathematical programming models of the market formation for one or several goods in the presence of rigid prices. For the purpose of exposition, it is assumed that each good may be traded internationally and that the domestic price of the good is bounded from above by its import price and from below by its export price. In principle, however, any other institutional factor causing prices to be rigid can be dealt with in a similar manner. The Lagrange multiplier of the market balance of the good can be interpreted as its market price. From a mathematical point of view, one is confronted with a class of mathematical programming problems wherea priori upper and lower bounds have been imposed upon the Lagrange multipliers.
    Type of Medium: Electronic Resource
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