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  • 1
    ISSN: 1434-6036
    Keywords: 71.70.CH ; 74.70.Vy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutron diffraction, neutron spectroscopy and magnetization measurements have been employed to study the structural, electronic, and magnetic behavior of eleven compounds with the general formula Nd1+y Ca v Ba2−y−v Cu3O x (0≦y≦0.5; 0≦v≦0.25; 6≦x≦7). The structure turned out to react to oxygen reduction similar as other 123-compounds, yielding discontinuities close to the metal-insulator-transition and the well-known relations of bond lengths as a function ofT c. The crystalline electric field (CEF) interaction, splitting the 10-fold degenerate ground-state J-multiplet of the Nd3+-ions into five doublet states, was investigated by neutron spectroscopy. The derived CEF parameters have been used to determine changes in the electronic surroundings of the Nd3+ ions. In addition, with the help of the CEF parameters the thermodynamic magnetic properties of these compounds were calculated which turn out to be in good agreement with the experimental data.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9710
    Keywords: ants ; dominance ; disturbance ; highway ; verge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Species composition and relative abundances of ground-dwelling ants at various distances from a major urban highway in South Africa were sampled using pitfall trapping. Diversity, richness and evenness indices indicated differences between ant assemblages, with samples near to the highway (〈4 m) having the highest species diversity, and farthest ones (32 m) having the lowest. As measured environmental variables did not explain much of the variation in the species spatial pattern, it appears that the ants were influenced mostly by interspecific competition and/or distribution of food resources, especially road kills. Pheidole megacephala was highly dominant at all sites and was negatively associated with several other species. This and other dominant species appeared to be influencing the abundance of the rarer ones. Dominance and high abundances of species in the genera Pheidole, Monomorium, Tetramorium and Paratrechina, along with the occurrence of certain grasses, indicated that the whole sampling area was disturbed. In a suburban setting, a narrow roadside verge (〈4m) is probably adequate. However, for maximum diversity in rural areas, roadsides should be as wide as possible and also rich and heterogenous in native vegetation.
    Type of Medium: Electronic Resource
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