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  • 1995-1999  (12)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7177-7179 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: La1−xLixMnO3 (x=0, 0.1, 0.2, and 0.3) were synthesized by using conventional solid state reaction and partial melting technique. The compounds were determined to be of rhombohedral structure by x-ray powder diffraction. For the x=0.2 and x=0.3 samples, room temperature neutron powder diffraction patterns were collected and analyzed with the Rietveld method. The analysis showed that the Li substitutes onto the La site in the rhombohedral perovskite lattice. Resistivities were measured between 4.2 K and room temperature in the magnetic fields of 0, 1, 2, 4, 8, and 13 T. A wide semiconductor-metal transition at temperatures between 160 and 210 K or between 200–230 K were observed for both samples with x=0.2 and 0.3, respectively. Large magnetoresistances above 20%–80% were achieved at fields from null to 13 T over a wide temperature range from the ferromagnetic transitions down to 4.2 K. However, the x=0 and 0.1 samples show a semiconducting behavior in resistivity measured between 77 and 300 K. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6229-6233 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present photoconductivity data on GaAs quantum wires grown on a V-grooved substrate by flow rate modulation epitaxy. They show that a moderate excitation power density, ∼1 W/cm2, allows the observation of the absorption structure of a single GaAs quantum wire embedded in a p-i-n diode. Furthermore, by increasing the number of active wires inside a diode, the photoconductivity signal is enhanced and additional details of the absorption structure are evidenced. And, finally, a rough quantitative agreement is obtained between the experimental absorption transitions and a simple calculation of the one-dimensional excitonic states using the envelope function approximation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 396-398 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline bulk porous samples with a large number of weak-link grain boundaries and high density polycrystalline bulk samples with strong-link boundaries were synthesized by conventional solid-state reaction and a partial melting technique. The weak-link samples showed large magnetoresistance (MR,Δρ/ρH=[ρ0−ρH]/ρ0), 20–30%, at a low magnetic field of 300 mT and over a wide temperature range from the magnetic transition at 235 to 77 K. The partially melted samples exhibited the same magnetoresistance behavior as that of single crystals with a maximum peak MR of 15% at a narrow temperature range around the ferromagnetic transition. It is suggested that grain boundaries are necessary but not sufficient to account for the MR at low field over a large temperature range. Weak-link grain boundaries rather than strong-link boundaries are responsible for the MR at low field over a large temperature range. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3294-3296 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that the thermal expansion behavior of a material can be substantially modified by the presence of residual stresses. In the case of a composite tube made of two layers of dissimilar steels, in situ neutron diffraction measurements revealed a significant difference in the coefficients of thermal expansion along the radial and tangential directions. It is shown that the observed difference in thermal expansion is due to the change of residual stresses with temperature. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 533-535 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bi2Sr2CaCu2Oy (Bi2212) crystals with CuO inclusions were grown on the surface of KCl flux. The density of CuO incorporations of 109/cm2 was similar to that for Y2BaCuOy in melt-textured YBa2Cu3Oy. The CuO inclusions are needlelike particles with diameter of less than 1 μm. Magnetization measurements show enhanced flux pinning at high magnetic field, compared to crystals without CuO. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 449-455 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Near-surface measurement of residual strain and stress with neutron scattering complements and extends the surface residual stress measurements by X-ray diffraction. However, neutron diffraction measurements near surfaces are sensitive to scattering volume alignment, neutron beam wavelength spread and beam collimation and, unless properly understood, can give large fictitious strains. An analytic calculation and a numerical computation of neutron diffraction peak shifts due to partial burial of the sampling volume have been made and are compared with experimental measurement. Peak shifts in a strain-free nickel sample were determined for conditions where the sample surface is displaced so that the scattering gage volume is partially buried in the sample. The analytic and numerically computed peak shifts take into account the beam collimation, neutron source size, monochromator crystal mosaic spread and the collection of diffracted intensity with a linear position-sensitive counter.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 52-59 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A theory is presented to describe the anomalous peak shift encountered in neutron diffraction residual stress measurements as the specimen is translated into and out of the sampling volume, which is defined by a pair of masking slits inserted before and after the specimen. Analytical formulae for the anomalous peak shift were obtained for both position-sensitive-detector-based diffractometers and conventional scanning diffractometers. The results indicate that the observed peak shift is a complex function of many variables, including the in-pile collimation, slit widths, slit-to-axis distances, mosaic spread of the monochromating crystal, and mismatch in lattice spacing between the sample and the monochromator. Calculations based on the derived analytical formulae are in good agreement with experimental observations. It is shown that by the choice of appropriate experimental conditions, this peak shift anomaly can be suppressed or, in some cases, eliminated altogether.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We detected the loss of a MspI restriction site by a C to T transition at +83 bp and a G to A transition at +84 bp of the 5′-end non-coding region of the human apolipoprotein AI gene. This base change occurred at the “hot spot” (CCGG) for methylation, which may be important in the regulation of gene expression. The population frequency for the loss of the MspI site is 6.1%.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 33 (1998), S. 4333-4339 
    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 Chemical reactions conducted in solution are known to generate solid precursors containing molecular units that help in the formation of high-temperature phases. The structural units are created by controlling the molecular environments in solution, and as a result, phases that normally form and are stable at high temperatures can be synthesized at low or moderately elevated temperatures. However, the application of chemical approaches for synthesizing phases that normally form at high pressure are relatively unknown. In this work, a simple room-temperature aqueous chemical precipitation route has been used to synthesize the high-pressure cubic spinel modification of ZnIn2S4. A solution coordination model (SCM) has been proposed to explain the formation of the high-pressure phase. The crystallinity, phase purity and phase transformation characteristics of the cubic phase have been studied using X-ray diffraction (XRD) including Rietveld refinement, transmission electron microscopy (TEM), and Auger electron microscopy (AEM). Results of these studies are discussed in the light of a proposed solution coordination model (SCM). © 1998 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 16 (1997), S. 858-859 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Abstracts are not published in this journal
    Type of Medium: Electronic Resource
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