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  • 1
    Electronic Resource
    Electronic Resource
    The effective microwave surface impedance of high Tc thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6940-6945 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the effective surface impedance Zeff=Reff+iXeff of superconducting thin films on the film thickness d, on the magnetic field penetration depth λ, and on the dielectric properties of the substrate material is investigated theoretically by means of impedance transformations. It was found that the effective surface resistance Reff can be expressed by RSf(d/λ)+Rtrans where RS is the intrinsic surface resistance of the superconductor. The function f(d/λ) describes the altered current density distribution in the film. Rtrans arises from power transmission through the film. It depends on d and λ as well as on the dielectric properties of the substrate material and is significantly altered in the case of a resonant background. The effective surface reactance Xeff of a superconducting thin film can be expressed by XS cosh(d/λ) where XS=ωμ0λ is the intrinsic surface reactance. Measurements of Zeff at 87 GHz have been performed for YBa2Cu3O7−δ thin films grown epitaxially by laser ablation on SrTiO3, MgO, and LaAlO3. With the best films, Reff (77 K) values of 21 mΩ and RS (77 K) values of 8 mΩ were achieved. The temperature dependence of λ was found to be in good agreement to both weak-coupling BCS theory in the clean limit and the empirical two-fluid model relation with λ (0 K) values ranging from 140 to 170 nm and 205 to 250 nm, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345037
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  • 2
    Electronic Resource
    Electronic Resource
    Superconducting multiturn flux transformers for radio frequency superconducting quantum interference devices (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5966-5974 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article describes three planar layouts of superconducting multiturn flux transformers integrated with a coplanar resonator for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. The best magnetic field noise values of 22 and 11.5 fT/Hz1/2 in the white noise regime were obtained for the layout with two input coils and the layout with the labyrinth resonator, respectively. Excess low-frequency noise (about 200 fT/Hz1/2 at 10 Hz) was present. Computer simulation showed that the loss in this trilayer system was dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The rf coupling coefficient krf between the resonator and the flip-chip-coupled SQUID was also estimated. The values krf2(approximate)14×10−3 obtained for the layout with two input coils, and krf2(approximate)45×10−3 for the layout with the labyrinth resonator were considerably higher than the typical value of krf2(approximate)7×10−3 for the single-layer coplanar resonator. These high coupling coefficients have compensated the somewhat degraded unloaded quality factor of the resonator, thus securing the optimum operation of the rf SQUID. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1322382
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  • 3
    Electronic Resource
    Electronic Resource
    Power and magnetic field-induced microwave absorption in Tl-based high Tc superconducting films (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 307-309 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The increase in the microwave surface resistance Rs of high Tc superconductors at elevated microwave power levels is reported for both oriented and unoriented Tl-based films as a function of rf magnetic field at 820 MHz and 18 GHz. The application of dc magnetic fields produces qualitatively similar increases in Rs and in the surface reactance Xs. The increase in Rs with dc field is shown to arise from simple decoupling of grains by intergranular magnetic flux. The increase in Rs with microwave power, on the other hand, is a consequence of hysteretic intergranular processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104670
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  • 4
    Electronic Resource
    Electronic Resource
    Low-resistivity epitaxial YBa2Cu3O7 thin films with improved microstructure and reduced microwave losses (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5572-5578 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of YBa2Cu3O7 have been prepared on SrTiO3 and LaAlO3 substrates by a high-pressure planar dc-sputtering technique. By covering the substrate heater with a frame of polycrystalline YBa2Cu3O7 substantial improvements of the YBa2Cu3O7 film properties were achieved. These are characterized by dc-resistivity values ρ(T) of less than 50 μΩ cm at 100 K and ρ(300 K)/ρ(100 K) values of up to 3.9. Significant deviations from the usual linear ρ(T) behavior were found. Critical temperatures above 90 K, resistive transition widths down to 0.3 K, and critical current densities of about 5 × 106 A/cm2 at 77 K confirm the high quality of the films. As indicated by Rutherford backscattering and high-resolution transmission electron microscopy the films exhibit a microstructure characterized by a reduced density of lattice defects. However, lattice-coherent precipitates with a diameter of about 5–10 nm were observed. As an outstanding feature the films exhibit, besides the initial steep falloff at Tc, a further gradual decrease of the microwave surface resistance at 87 GHz below 50 K by at least one order of magnitude. These results are very promising for millimeter-wave applications of epitaxial YBa2Cu3O7 thin films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350535
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  • 5
    Electronic Resource
    Electronic Resource
    Neutron-induced microwave loss in ceramic YBa2Cu3O7−δ (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2462-2464 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An increase by over three orders of magnitude from 0.58 mΩ to 1.17 Ω was observed at 4.0 K in the 3 GHz microwave surface resistance of ceramic YBa2Cu3O7−δ following exposure to neutrons. The transport resistivity of an unirradiated pellet was linear in temperature down to Tc with a room-temperature value of 2.13 mΩ cm and a resistivity extrapolated to 4.0 K of 0.53 mΩ cm. Following irradiation, the resistivity rose with decreasing temperature from a room-temperature value of 1.5 Ω cm to a maximum at around 45 K with little change evident at Tc . These results, in conjunction with eddy current, susceptibility, iodometric titration, and thermally stimulated luminescence measurements on irradiated and unirradiated samples, collectively suggest that the effect of neutron irradiation has been to decrease intergranular coupling without the development of an insulating phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103256
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  • 6
    Electronic Resource
    Electronic Resource
    Simulation of the superconducting multiturn flux transformer integrated with a coplanar resonator (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3606-3608 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The analysis of the structure of a superconducting multiturn flux transformer integrated with a coplanar resonator for radio-frequency superconducting quantum interference devices is described. Electromagnetic simulations indicate that the loss is dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The simulated current distribution at its resonant frequency shows that the highest current density is distributed on the multiturn input coil. This current distribution leads to a very high loss when the loss tangent of the dielectric film is high. However, for the same loss tangent of the dielectric film, it is possible to get a reasonably high unloaded quality factor by providing a normal shunt for the multiturn input coil. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126721
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  • 7
    Electronic Resource
    Electronic Resource
    Excess low-frequency noise in AlGaN/GaN-based high-electron-mobility transistors (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2126-2128 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-frequency 1/f noise characteristics of AlGaN/GaN high-electron-mobility transistors with gate length scaled down to 150 nm grown on sapphire by metalorganic chemical vapor deposition have been studied. Certain features of the 1/f noise have been revealed in these short-gate transistors. The low-frequency noise spectra show drastically different behavior depending on the gate voltage VG in the range of low (VGt≤VG≤0) and high (VG〈VGt) biases. The noise spectra-gate bias dependences allow one to distinguish a spatial redistribution of effective noise sources in the transistor channel. The Hooge parameter has been deduced separately for the ungated region, αHp(similar, equals)10−3, and for the gated region, αHa(similar, equals)2×10−4, of the transistor channel. These values are as low as those previously observed in nitride heterostructures grown on silicon carbide substrates. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1463202
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  • 8
    Electronic Resource
    Electronic Resource
    High quality epitaxy of YBa2Cu3O7−x on silicon-on-sapphire with the multiple buffer layer YSZ/CeO2 (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1429-1431 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality YBa2Cu3O7−x films on silicon-on-sapphire were grown using a multiple buffer layer, consisting of YSZ and CeO2. Ion channeling reveals the high crystalline perfection of the YBa2Cu3O7−x films. A channeling minimum yield for the Ba signal as low as 3% was measured. The normal state resistivity of 200 μΩ cm at 300 K, critical temperatures above 90 K, with transition widths down to 0.5 K, critical current densities above 2×106 A/cm2 at 77 K and surface resistance values of 1.4 mΩ at 18.9 GHz and 77 K confirm the high quality of the YBa2Cu3O7−x films. These results are very promising for integrated superconductor and semiconductor applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109647
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  • 9
    Electronic Resource
    Electronic Resource
    OLIGOSACCHARIDES IN HUMAN MILK: Structural, Functional, and Metabolic Aspects (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Nutrition 20 (2000), S. 699-722 
    Details
    ISSN: 0199-9885
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Research on human milk oligosaccharides (HMOs) has received much attention in recent years. However, it started about a century ago with the observation that oligosaccharides might be growth factors for a so-called bifidus flora in breast-fed infants and extends to the recent finding of cell adhesion molecules in human milk. The latter are involved in inflammatory events recognizing carbohydrate sequences that also can be found in human milk. The similarities between epithelial cell surface carbohydrates and oligosaccharides in human milk strengthen the idea that specific interactions of those oligosaccharides with pathogenic microorganisms do occur preventing the attachment of microbes to epithelial cells. HMOs may act as soluble receptors for different pathogens, thus increasing the resistance of breast-fed infants. However, we need to know more about the metabolism of oligosaccharides in the gastrointestinal tract. How far are oligosaccharides degraded by intestinal enzymes and does oligosaccharide processing (e.g. degradation, synthesis, and elongation of core structures) occur in intestinal epithelial cells? Further research on HMOs is certainly needed to increase our knowledge of infant nutrition as it is affected by complex oligosaccharides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.nutr.20.1.699
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  • 10
    Electronic Resource
    Electronic Resource
    Electrodynamic Properties of High Temperature Superconductor Films (1993)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 130-132 (Jan. 1993), p. 373-404 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/00/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.130-132.373.pdf
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