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  • 71.30.+h  (1)
  • nitrogen dioxide  (1)
  • 1995-1999  (2)
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  • 1995-1999  (2)
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  • 1
    ISSN: 1090-6487
    Schlagwort(e): 75.30.Kz ; 75.50.−y ; 71.30.+h
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A giant isotope effect, wherein the low-temperature metallic state is replaced by an insulator state, was recently observed when 18O was substituted for 16O in (La0.25Pr0.75)0.7Ca0.3MnO3 [N. A. Babushkina, L. M. Belova, O. Yu. Gorbenko et al., Nature (London) 391, 159 (1998)]. In the present work, the temperature evolution of the magnetic structure of two samples of this compound is studied by neutron diffraction. One sample contained a natural mixture of oxygen isotopes, 99.7% 16O, while the other was enriched to 75% with the isotope 18O. It is established that the samples are crystallographically identical at room temperature. As the temperature decreases, the sample with 16O undergoes successive antiferromagnetic (T AFM=5150 K) and ferromagnetic (T FM=110 K) transitions, which lead to the establishment of a noncollinear ferromagnetic structure, while a purely antiferromagnetic (T AFM=150 K) order arises in the sample with 18O. The temperature dependences of the intensities of the diffraction peaks associated with the charge ordering differ substantially in samples with 16O and 18O, and they correlate with the behavior of their electric resistance and magnetic structure.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Environmental monitoring and assessment 50 (1998), S. 37-51 
    ISSN: 1573-2959
    Schlagwort(e): nitrogen dioxide ; passive sampler ; small area variation ; urban air
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Two-week average NO2 concentrations were measured in Amsterdam (NL), Huddersfield (UK) and Prague (CZ) at 80 sites in each study area, to assess small area spatial variation, using a tube type and a badge type passive sampler. The badges appeared to be less robust than the tubes. The lower detection limit for tubes and badges was 3.7 and 0.91 µg/m3, respectively for fortnightly measurements. Accuracy of the samplers was determined with reference methods (chemiluminescence). The mean ratio of the concentration measured by diffusion tube over that by the reference method was 1.16, 1.03 and 0.77 in Amsterdam, Huddersfield and Prague, respectively. Standardizing the badges for the results obtained in Amsterdam, the relative mean ratio of the concentration measured by the badges over that by the reference method was 0.95 and 0.58 in Huddersfield and Prague, respectively. NO2 concentrations measured by the two designs did not differ significantly. Mean NO2 concentrations were 36, 26 and 22 µg/m3 in Amsterdam, Huddersfield and Prague, respectively. The precision of duplicate tubes and badges was 8% and 11%, respectively. Both samplers are suitable for determining real variation in small area NO2 concentrations in the ranges which occurred. It is concluded that low-cost, simple NO2 passive samplers can provide reliable information about variation in NO2 concentrations within urban or rural areas on a small spatial scale. Based on its robustness and its precision, tubes were preferred over badges.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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