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  • 1990-1994  (25)
  • 1992  (25)
  • 1
    Electronic Resource
    Electronic Resource
    Formation of a metastable ferromagnetic τ phase during containerless melt processing and rapid quenching in Mn-Al-C alloys (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 676-680 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Solidification of selected Mn-Al-C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable τ (L10) phase formed directly from the melt. Complete solidification to τ phase was interrupted by the competitive evolution of an equilibrium ε phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic τ phase in a Mn0.55Al0.433C0.017 alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at. % (i.e., Mn0.55Al0.416Co0.034 alloy), a transition in structure development occurred so that the samples exhibited γ2 phase formation as well as τ and ε phases. Both microstructural observations and x-ray diffraction examination were used to guide the interpretation and the analysis of solidification pathways. The attainment of the high liquid undercooling required to nucleate the metastable τ phase from the melt may be facilitated by containerless processing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351326
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  • 2
    Electronic Resource
    Electronic Resource
    Femtosecond coherent transient infrared spectroscopy of CO on Cu(111) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4421-4427 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Femtosecond infrared coherent transients have been measured for the stretch vibration of CO on Cu(111). The free induction decay exhibits a dephasing time (T2) of 2±0.3 ps (and 2±0.1 ps assuming a single exponential decay between 2 and 3 ps). The decay was best fit by exponential relaxation, thereby suggesting that the CO vibrational band is almost entirely homogeneously broadened. The surface sum frequency spectrum was also measured at two coverages (0.10 and 0.45 L) using spectrally narrowed pulses. Interferences were observed leading to a determination of the relative phase and amplitude of the resonant and nonresonant second-order susceptibility in this system. The magnitude of the nonresonant susceptibility was only weakly dependent on coverage, suggesting that the nonresonant polarizability originates in the bulk Cu. Time and frequency domain results were in good agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463884
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  • 3
    Electronic Resource
    Electronic Resource
    E(2)-symmetric two-mode sheared states (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 1237-1246 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is noted that the symmetry of two-mode squeezed states of light is governed by the group Sp(4) that is locally isomorphic to O(3,2). This group has subgroups that are locally isomorphic to the two-dimensional Euclidean group. Two-mode states having the E(2) symmetry are constructed. The translation-like transformations of this symmetry group shear the Wigner distribution function defined over the four-dimensional phase space consisting of two pairs of canonical variables. Sheared states are constructed in the Schrödinger picture of quantum mechanics and in the Fock space for photon numbers. It is shown that the Wigner phase-space picture is a convenient representation of quantum mechanics for calculating measurable quantities of the sheared states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529701
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  • 4
    Electronic Resource
    Electronic Resource
    O(2,1)-like little group for spacelike four-momenta and localized light waves in continuous media (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 3190-3196 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: While a light wave travels in a nonvacuum medium with speed less than the speed of light in vacuum, its energy-momentum four-vector is spacelike. Thus the little group for this light wave is locally isomorphic to O(2,1). It is shown that the transformation of this little group produces observable effects on the light wave, in contrast to the case of the E(2)-like little group for photons in vacuum. It is also shown that the little group can be defined for a localized light wave consisting of a superposition of waves with different frequencies traveling in the same direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529537
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Boron-enhanced low-temperature Si epitaxy by rapid thermal processing chemical vapor deposition (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 474-476 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that epitaxial growth temperatures can be lowered by in situ boron incorporation using rapid thermal processing chemical vapor deposition (RTPCVD). Heavily boron-doped epitaxial layers with very abrupt dopant transition profiles have been grown at 800 °C. Carrier concentrations as high as 5×1019 cm−3 were obtained with defect densities of the order of 102–103 cm−2. The film quality and surface morphology were closely related to dopant concentration. Higher dopant concentrations improved surface morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107861
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  • 6
    Electronic Resource
    Electronic Resource
    Chemical characterization of (In,Ga)As/(Al,Ga)As strained interfaces grown by metalorganic chemical vapor deposition (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 28-30 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used quantitative chemical mapping to determine the chemical abruptness of interfaces in In0.2Ga0.8As/Al0.2Ga0.8As strained multilayers grown by metalorganic chemical vapor deposition. We observe a large difference in the interfacial width, depending on the order in which successive layers are grown; the (Al0.2Ga0.8As on In0.2Ga0.8As) interface is twice as wide as the (In0.2Ga0.8As on Al0.2Ga0.8As).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107651
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  • 7
    Electronic Resource
    Electronic Resource
    Microstructure of the emitter polycrystalline silicon/silicon interface in bipolar transistors after rapid thermal annealing (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 437-438 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use high-resolution transmission electron microscopy to determine the microstructure of the emitter polycrystalline (poly) Si/Si interface of real bipolar transistor devices after rapid thermal annealing. Our results quantify the size and density of interfacial oxide voids (pinholes), the areal fraction of the interface covered with voids, and the amount of epitaxial regrowth after annealing in the range 1000–1150 °C. Correlation of these results with the characteristics of the devices shows that the most dramatic electrical changes occur before 2% of the poly-Si/Si interfacial area is covered with oxide voids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107462
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  • 8
    Electronic Resource
    Electronic Resource
    Poloidal viscosity and radial currents (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 278-279 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Considerable doubt is cast on the L- to H-mode transition mechanism proposed by Shaing [Phys. Rev. Lett. 63, 2369 (1989)]. Contrary to his assertion, a consistent application of the momentum balance equations shows that ion orbit loss current does not drive large poloidal rotation in tokamaks, in steady state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860445
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  • 9
    Electronic Resource
    Electronic Resource
    Alpha-CHERS: A spectroscopic experiment to detect nonthermal alpha particles on TFTR : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5179-5181 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A spectroscopic diagnostic for measurement of slowing-down alpha particles is under development and will be implemented for D–T operation of the Tokamak Fusion Test Reactor. The visible 468.6 nm He+ line (n=3–4) is excited by charge exchange recombination of alphas with a heating neutral beam (55 keV/amu), and the distortion of the line profile caused by alphas with energies up to 0.5–1.0 MeV is observed. Expected intensities are 0.1%–10% of the bremsstrahlung background for D–T discharges with Q=0.2–1.0. Because the signal is small, a high-throughput optical system is needed to achieve the desired signal-to-noise ratio of 10–100. Vertical and horizontal arrays of sightlines with five spatial channels will be used. Initially, two spatial channels will be coupled via fiber optics to an f/3.8 spectrometer equipped with a low-noise charge coupled device detector, with expansion to 5–10 spatial channels planned for D–T operation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143474
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  • 10
    Electronic Resource
    Electronic Resource
    Intense diagnostic neutral beam development for ITER : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4934-4936 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For the next generation, burning tokamak plasmas such as in the International Thermonuclear Experimental Reactor (ITER), diagnostic neutral beams and beam spectroscopy will continue to be used to determine a variety of plasmas parameters such as ion temperature, rotation, fluctuations, impurity content, current density profile, and confined alpha particle density and energy distribution. Present-day low-current, long-pulse beam technology will be unable to provide the required signal intensities because of higher beam attenuation and background bremsstrahlung radiation in these larger, higher-density plasmas. To address this problem, we are developing a short-pulse, intense diagnostic neutral beam. Protons or deuterons are accelerated using magnetic-insulated ion-diode technology, and neutralized in a transient gas cell. A prototype 50-kA, 100-kV, 1-μs accelerator is under construction at Los Alamos. Initial experiments will focus on ITER-related issues of beam energy distribution, current density, pulse length, divergence, propagation, impurity content, reproducibility, and maintenance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143554
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