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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 156 (1945), S. 234-234 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN our search for the presence of antibiotic substances in the higher plants used in China for food or for drugs, we have examined the tubers of the waterchestnut, Eleocharis tuberosa. The waterchestnuts, bought in the local market, were washed and crushed in a Carver laboratory hydraulic ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 31 (1996), S. 4141-4147 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The mechanical loss (Q −1) and shear modulus (G) were measured as a function of temperature in the range 130 K 〈 T 〈 430 K for BaTiO3 ceramics by an inverted pendulum at low frequencies ranging between 1-0.01 Hz. The Q −1 (T) and G(T) curves exhibit the three phase transitions observed in BaTiO3. Each phase transition induces a loss peak and an anomaly in the elastic modulus. Moreover, three other loss peaks (R) are located below the phase transition temperature. These peaks can be described by an Arrhenius relationship, and the activation energies are determined as 0.92, 0.68, and 0.45 eV for the peak located in the tetragonal-, orthorhombic-, and rhombohedral-phase, respectively. These peaks are due to the interaction between the domain walls and the diffusion of oxygen vacancies in the domains.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 31 (1996), S. 4951-4955 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The mechanical loss (Q −1) and Young's modulus (E) were measured as a function of temperature in the range 100 K〈T〈450 K on rectangular plate specimens of BaTiO3 driven electrostatically in flexural vibration mode at resonance frequencies between 2–4 kHz. Q −1(T) and E(T) curves show the following three phase transitions in BaTiO3: rhombohedral to orthorhombic (T R-O), orthorhombic to tetragonal (T O-T), and tetragonal to cubic (T Curie). Each phase transition induces a very narrow mechanical loss peak of Q −1 and a very sharp anomaly in the elastic modulus. Moreover, three other mechanical loss peaks are located below the phase transition temperatures in coarse grained specimens and these peaks seem to be associated with the motion of domain walls. These secondary peaks are not observed in fine grained undoped ceramics. The use of dopants such as Co or Nb produces an attenuation of the mechanical loss, a smoothing of elastic modulus anomalies, and a shifting of the phase transition temperatures.
    Type of Medium: Electronic Resource
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