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  • 1
    ISSN: 1432-0630
    Keywords: 78.30
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The incorporation of impurities in films of Bi-substituted iron garnets grown by liquid phase epitaxy has been studied by successively adding small amounts of SiO2 and CaCO3 to the melt before film growth. It is found that very small additions of CaCO3 to the melt profoundly influences the optical absorption coefficient and the electrical properties. The impurity absorption ofn-type YIG doped with Si4+ and Pb2+ ions is investigated and its wavelength dependence compared to that ofp-type YIG. The optical transitions involved in the impurity absorption of iron garnets are discussed in terms of transition reaction, photon energy and dependence on the impurity concentration. Depending on the photon energy, one or several transitions may give rise to impurity absorption.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Betrachtet wird die Herleitung von Gleichgewichtsbedingungen des Zuwachses aus virtuellen Arbeiten. Der mathematische Aufbau dieser Gleichungen in den gebräuchlichsten Darstellungsarten und ihre Brauchbarkeit für numerische Anwendungen wird diskutiert. Der Einfluß der Vernachlässigung der durch nichtkonservative Belastung verursachten nichtsymmetrischen Steifigkeitselemente wird angegeben, und die nicht im Gleichgewicht befindlichen Belastungsanteile werden berücksichtigt. Anschließend wird die Verwendung von Näherungen von Werkstoffgesetzen bei unelastischer Deformation im Hinblick auf die Verwendung in der methode der finiten Elemente diskutiert. Besondere Beachtung gilt den verschiedenen Näherungen und Annahmen in diesen Beziehungen und der Bedeutung der Wahl der Darstellungsart für Probleme mit geometrischen und werkstoffbedingten Nichtlinearitäten.
    Notes: Summary The derivation of incremental equilibrium equations from virtual work considerations is reviewed. The mathematical structure of these equations in the most common modes of description is discussed, and their feasibility for numerical applications is evaluated. The out-of-balance loading terms are included, and the effect of neglecting nonsymmetric stiffness terms originating from nonconservative loading is given. Then the use of exact and approximate constitutive laws for large inelastic deformation is discussed in the context of finite element applications. Emphasis is given to the various levels of approximations and assumptions in the latter type of relations and to their importance in the choice of mode of descriptions for problems with material and geometrical nonlinearities.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2940-2944 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A RHEED system, consisting of a high-resolution (75-μm FWHM) and high-brightness (10-μA) electron gun, and a phosphor screen with high resolution and good linearity, was developed. The system is based on concepts from projection television. The results show that this setup is particularly useful for obtaining quantitative RHEED patterns.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1392-1394 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of disturbing pulses on the switchable polarization in ferroelectric films of PbZrxTi1−xO3 with x=0.36 and 0.71 has been investigated. The two compositions were selected because of their different hysteresis shapes. Pulse measurements were carried out with a varying number of disturbing pulses at different amplitudes, interrupted by single shot read/write pulses. It was found that the composition with the squarer loop (x=0.36) showed less sensitivity to disturbing pulses, i.e., the switchable polarization did not significantly degrade with 109 disturbing pulses of amplitude 1.2 V. In addition, these results demonstrate that degradation of the stored polarization due to parasitic disturbing voltages in high density ferroelectric random access memories can be kept at an acceptable level.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 611-613 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The switching time (ts) for polarization reversal in ferroelectric films of PbZr0.53Ti0.47O3 and La-substituted PbTiO3 has been investigated. The films were prepared by spin-on and metalorganic decomposition followed by processing into ferroelectric capacitors having electrode areas ranging from 9 to 50 000 μm2. Pulse measurements show that under all our experimental conditions ts is instrumentally limited and that therefore the true switching time is smaller than the experimental resolution of 1.8 ns. This very fast polarization reversal can be explained by a nucleation-rate-controlled switching mechanism.
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  • 6
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In a randomized trial, three alternative schemes of treatment of preterm labour with ritodrine (long infusion, short infusion, and intramuscular injection) were compared with standard treatment by bed rest and sedatives. None of the ritodrine treatments were found to be better in postponing delivery than the standard treatment. However, the Bishop scores of the patients in the standard treatment group tended to be lower than of the patients treated with ritodrine. Moreover, all cases of congenital malformation and polyhydramnios occurred in the patients treated with ritodrine. The incidence of respiratory insufficiency was significantly higher in infants of mothers treated with ritodrine. The mean birth weight was highest in the standard treatment group.
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of low-temperature photoluminescence (PL) spectra with the thickness of the layer (3–400 μm) is investigated on high-quality GaN grown by hydride vapor-phase epitaxy. With increasing layer thickness, three acceptor bound exciton peaks are found to reduce in intensity, although the impurity concentrations, measured by secondary ion mass spectrometry, do not depend on the sample thickness. The observed acceptor transitions are attributed to intrinsic defects, originating from the substrate/layer interface and decreasing in density with the thickness of the layer. The optical properties, studied by reflectance, temperature and excitation power dependent PL, are compared to those of homoepitaxial GaN films grown by metalorganic chemical vapor deposition. © 2001 American Institute of Physics.
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  • 8
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A photoluminescence (PL) study of GaN homoepitaxial layers grown by metal–organic chemical-vapor deposition demonstrates the high optical quality of N-face layers deposited on vicinal (0001¯) GaN substrates. In contrast to broad PL emission in exact (0001¯) layers, narrow-bound (0.9 meV) and free- (A and B) excitonic transitions are observed. By following the PL spectra as a function of temperature and excitation power, the main optical transitions in the Ga- and the misoriented N-face layers are found to be the same. Observed differences are related to the distinct creation of donor and acceptor states in the samples of different polarities. © 2000 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 3326-3328 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pulse switching investigations of ferroelectric PbZr0.44Ti0.56O3 capacitors prepared by organometallic chemical vapor deposition were done to simulate a ferroelectric memory. The released charge from the ferroelectric capacitor was measured with a reference capacitor, representing the bitline capacitances in a memory. A large reference capacitor will result in complete switching at low voltages, but gives a small detection signal. For a small reference capacitor partial switching and substantial backswitching of the ferroelectric material occurs. Here, a higher detection signal and improved endurance ((approximately-greater-than)1012 cycles) are found. Scaling the results indicates the feasibility of 0.2 μm2 capacitors operating at 3 V. © 1994 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1363-1367 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two different signal-processing systems are described for the conversion of reflection high-energy electron diffraction (RHEED) patterns, displayed on a phosphor screen, into quantitative data. Both systems are based on the use of a sensitive video camera. One system using a multichannel boxcar integrator is particularly suited to simultaneous temporal measurements of different RHEED beams and integrated line intensities, while the other can be applied to fast data acquisition of line profiles. The system performance is illustrated and discussed.
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