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  • 1
    Electronic Resource
    Electronic Resource
    Ultrasonic measurement of the surface area of porous materials (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4372-4376 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a technique to measure the amount of gas adsorbed on a porous solid using ultrasonic velocity measurements. This allows us to determine both the specific surface area and the porosity of the material. The technique has several advantages over conventional methods of determining absorption isotherms. No calibrated volumes or delicate balances are needed; the only measurements being of gas pressure and sound velocity. There is no need to know the mass of the sample or the dead volume of its container. Continuous and automatic measurements are possible, both during adsorption and desorption. We have demonstrated the usefulness and accuracy of this technique for two samples with very different surface areas (about 100 and 3 m2/g). In both cases, the results agree well with conventional volumetric measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340179
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Granular Nix (SiO2)100−x thin films as low temperature thermometers (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3015-3017 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of granular Nix (SiO2)100−x thin films have been prepared by rf sputtering with nickel concentrations between 60 and 90 at. %. The temperature dependence of the resistance is strongly composition dependent. In films with Ni concentrations below 70%, the resistance increases as the temperature decreases, but shows a crossover to a weaker temperature dependence below about 1 K. The magnetoresistance of these materials is small and negative in applied magnetic fields up to 6 T. The temperature dependence of the resistance and the small magnetoresistance indicate that films with Ni concentrations near 66% may be useful for thermometry over a wide range of temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346410
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Freezing of molecular hydrogen and its isotopes in porous vycor glass (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 113-131 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have made a detailed ultrasonic study of freezing and melting of molecular H2, HD and D2 in the pores of Vycor glass. The behavior was similar to that seen in previous measurements with argon and helium. The hydrogen liquids under cooled about 2.5 K below their bulk triple points before freezing began and there was substantial hysteresis between freezing and melting. The velocity and attenuation began to increase suddenly at the onset of freezing. The velocity continued to increase to the lowest temperatures (2 K) and the attenuation had a broad peak at about two thirds of the freezing temperature. We attribute these effects to stress relaxation via thermally activated vacancy motion in the solid hydrogen, an interpretation confirmed by looking at the frequency dependence of the velocity and attenuation. The magnitude of the velocity and attenuation changes increased in going from H2 to HD to D2, as expected based on their increasing densities and elastic constants. However, there were no qualitative differences between the boson (H2 and D2) and fermion (HD) cases nor, for that matter, between hydrogen and argon. We believe that essentially all the hydrogen was frozen a few tenths of a kelvin belowT F, at the point where the melting/freezing hysteresis began. If even a few per cent of the hydrogen had remained liquid and become superfluid at some lower temperature, it would have been seen as a further increase in the velocity and a critical attenuation peak. The sensitivity of our ultrasonic measurements allowed us to make accurate measurements of the freezing and melting temperatures of the different liquids in Vycor. We found that the fractional undercooling, (T B -T F )/T B , increased as the molecular mass decreased which may indicate the importance of quantum effects on the liquid-solid interfacial energy σ ls .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754630
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Doping dependence of the critical field Hc2 and the transition temperature in Zn doped YBa2(Cu1−xZnx)3O7−δ (1997)
    Springer
    Journal of low temperature physics 107 (1997), S. 491-496 
    Details
    ISSN: 1573-7357
    Keywords: 74.72 Bk ; 74.25 Fy ; 74.25 Ha
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present data on the doping dependence of Tc in Zn doped YBa2(Cu1−xZnx)3O6.94, for x up to 10.6%. We find re-entrant behaviour in the range between 9.0 and 10.6% Zn. Data on the magneto-resistance of a sample with extremely low Tc (9% Zn, zero field resistive onset near 3.5 K) show linear normal resistance in all fields down to 1.8 K in 17.5 T. A resistively defined critical field H*, related to Hc2, shows divergent behaviour. The temperature dependence of H* is well represented by expressions derived for the Bose condensation of pre-formed pairs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02397232
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  • 5
    Electronic Resource
    Electronic Resource
    Excitations Beyond the Roton of Liquid 4He in Aerogel (1999)
    Springer
    Journal of low temperature physics 117 (1999), S. 113-125 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The dynamic structure factor, S(Q, ω), for wavevectors, 2.0≤Q≤3.6 Å −1 of liquid 4 He in 95% porous aerogel has been measured by inelastic neutron scattering methods. The aerogel was grown with deuterated materials and the multiple scattering involving the aerogel was negligible. S(Q, ω) in the superfluid phase consists of a single peak plus broad intensity at higher energy ω, as in bulk superfluid 4 He. The single peak is identified with the phonon-roton excitation at higher Q. The weight in the peak, ZQ , and the excitation energy dispersion curve, ω Q , has the same basic wavevector dependence as in the bulk. The energy ω Q is 2–3% below the bulk value at the end point and the peak is unobservable beyond Q=3 Å −1 within the present statistical precision. No peak is observed at T=2.3 K in normal 4 He suggesting, as in bulk 4 He, that the characteristic excitation at higher Q is associated with the superfluid phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021818123583
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  • 6
    Electronic Resource
    Electronic Resource
    Investigations of Ultrasound Propagation in Porous Impurity-Helium Solids (2000)
    Springer
    Journal of low temperature physics 119 (2000), S. 357-366 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The velocity and attenuation of ultrasound passing through porous impurity-helium solids immersed in liquid 4He have been measured in the temperature range 1.1–2.3 K. These solids were formed by injecting a mixture of impurity (e.g. D2, Ne, N2 or Kr) and helium gases into superfluid 4He. The sound signal seemed to propagate mainly in the helium contained in the pores, rather than through the solid sample itself. We found that the speed of sound at low temperatures is close to and decreases more rapidly with temperature than first sound in bulk helium, similar to behavior observed in aerogel. The attenuation of sound in helium in the “compressed” impurity-helium solids is bigger than in bulk helium and increases rapidly with temperature up to ∼1.65 K, after which a crossover to a much weaker temperature dependence was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004617819633
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