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  • 1
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Coulometric detection ; Mandelic acids ; Phenylglycols ; Urine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method has been developed for the quantification of urinary 3,4-dihydroxymandelic acid (DOMA), 4-hydroxy-3-methoxymandelic acid (VMA), 3,4-dihydroxyphenylglycol (DHPG), and 4-hydroxy-3-methoxyphenyglycol (MHPG). Separation and determination of these compounds in biological samples was previously thought to be very difficult. In this work the separation has been achieved by reversed-phase high-performance liquid chromatography with step-wise gradient elution with three mobile phases. The conditions for coulometric detection have been optimized for effective determination of these compounds. In analysis of a sample of human urine, after a simple deproteinization proceudre, DOMA, VMA, DHPG, and MHPG were separated from interferences and quantified successfully; the average levels of these compounds in six different samples were 33.87±1.03, 1202±41.3, 31.3±1.92, and 80.6±2.15 μg (24 h)−1, respectively. Their precursors E, MN, DOPA, DA, NE, DOPAC, HVA, 3MT, and NMN, and the indolamine 5HT and its metabolite 5HIAA (a list of abbreviations is given at the end of the paper) can also be determined simultaneously in the same chromatographic run. The overlapping peak of DHPG was resolved by deconvolution.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper reports an electrochemical study on terbia and yttria stabilized zirconia. (Tb, Y)-ZrO2 solid solutions with a fluorite type structure were prepared by using citrate synthesis and sintered at 1500°C. They are mixed electronic and oxygen ionic conductive, as well as oxygen semipermeable materials at elevated temperatures. The total electrical conductivity reaches 3.8 S m−1 at 900°C and the oxygen permeation is about 6.5 × 10−6 mol m−2 s−1 at 1100°C. The electrical conductivity of zirconia doped with a total of 30 mol % of terbia and yttria increases with oxygen partial pressure when P O 2 is below 10−2 atm, and decreases as the oxygen partial pressure rises above 10−2 atm. This is ascribed to the defect association and the predomination of oxygen ionic conductivity. The oxygen semipermeation is proportional to the square root of the oxygen partial pressure, and is not influenced by the variation of oxygen ionic or electronic conduction. The results indicate that the surface exchange reaction is most probably the rate limiting step for the oxygen semipermeation.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9605
    Keywords: Doping ; Thermal Conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The thermal conductivity K(T) vs temperature has been measured for (Y,Pr)Ba2Cu3O7, (Y,Tb)Ba2Cu3O7 and YBa2(Cu,Zn)3O7 single crystals from 10≤T≤280K. For YBa2Cu3O7(YBCO), a strong enhancement in K(T) is observed for T≤Tcwith a peak in K(T) at approximately T≈Tc/2 with a sharp change in slope of K(T) at Tc. These results are similar to those reported previously. For the selectively doped YBCO, the peak in K(T) is shifted to lower temperatures and occurs at T≈ 20K independent of Tc and the impurity concentration. In addition, the sharp change in slope of K(T) at Tc is not apparent for the doped crystals. These results are discussed along with a theoretical model for electronic conduction including both impurity and inelastic scattering from spin fluctuations.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9605
    Keywords: Magnetic Ordering ; Dielectric Constants ; Polarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Measurements of the low frequency (1 KHz-1 MHz) c axis dielectric constant of La2Cu1−xZnxO4+δ (x=0, 0.07) single crystals exhibit ferroelectric-like values with a large enhancement in the vicinity of the magnetic ordering temperature. The possibility of a simultaneous (anti)ferroelectric-antiferromagnetic transition is suggested in these systems.
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  • 5
    ISSN: 1572-9605
    Keywords: Doping ; Specific Heat ; Hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The electrical resistivity ρ(T,x) and magnetic susceptibility χ(T,H), and specific heat C(T,x) have been measured on single crystals of Y1−x TbxBa2Cu3O7. The results strongly suggest the appearance of strong 4f electron hybridization. It becomes apparent that the Tb doped system possesses properties that largely deviate from the well-known behavior of the other high Tc and doped high Tc systems.
    Type of Medium: Electronic Resource
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