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  • 1
    Electronic Resource
    Electronic Resource
    Two-point quasifractional approximant in physics. Truncation error (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 1470-1477 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The quasifractional approximation method is developed in a systematic manner. This method uses simultaneously the power series, and at a second point, the asymptotic expansion. The usual form of the approximants is two or more rational fractions, in terms of a suitable variable, combined with auxiliary nonfractional functions. Coincidence in the singularities in the region of interest is pursued. Equal denominators in the rational fractions is required so that the solution of only linear algebraic equations is needed to determine the parameters of the approximant. An upper bound is obtained for the truncation error for a certain class of functions, which contains most of the functions for which this method has been applied so far. It is shown that quasifractional approximants can be derived as a mixed German and Latin polynomial problem in the context of Hermite–Padé approximation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529304
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic measurements with a SQUID magnetometer: Possible artifacts induced by sample-holder off-centering : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5088-5090 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Asymmetries in sample holders used for magnetic measurements on magnetometers based on induction methods, such as those equipped with SQUID sensors, can lead to substantial errors and/or important artifacts which resemble phase transitions. They occur under the conditions for which sample and/holder have signals of opposite sign, but are nearly equal in magnitude. The most serious errors can occur often, but not exclusively, for compounds having intermediate magnetic dilution. We present here a general discussion of the problem illustrated by measurements of a polyoxometallate with the known Keggin structure K6[Fe(III)W12O40]⋅nH2O, done on a SHE VTS model 905. While one of the obvious solutions to this problem is the use of holders with a signal much smaller than that of the sample, it would be preferable if, in addition, the holder had a response of the same sign as that of the sample, for all temperatures and fields measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348132
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  • 3
    Electronic Resource
    Electronic Resource
    Generation of high-energy x-radiation using a plasma flow switch (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1999-2007 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments with coaxial plasma guns at currents in excess of ten megamperes have resulted in the production of high-voltage pulses (0.5 MV) and hard x radiation (10–200 keV). The x-radiation pulse occurs substantially after the high-voltage pulse suggesting that high-energy electrons are generated by dynamic processes in a very high speed ((approximately-greater-than)106 m/s), magnetized plasma flow. Such flows, which result from acceleration of relatively low-density plasma (10−4 vs 1.0 kg/m3) by magnetic fields of 20–30 T, support high voltages by the back electromotive force-u×B during the opening switch phase of the plasma flow switch. A simple model of classical ion slowing down and subsequent heating of background electrons can explain spectral evidence of 30-keV electron temperatures in fully stripped aluminum plasma formed from plasma flows of 1–2 × 106 m/s. Similar modeling and spectral evidence indicates tungsten ion kinetic energies of 4.5 MeV and 46 keV electron temperatures of a highly stripped tungsten plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348773
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  • 4
    Electronic Resource
    Electronic Resource
    High voltage pulse generation using current mode second breakdown in a bipolar junction transistor (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1031-1036 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The characteristics of a bipolar junction transistor operating in the avalanche region and then triggered into current mode second breakdown are formulated. If the time the BJT is subjected to secondary breakdown is limited the BJT may be used as a nanosecond, high voltage switch without sustaining damage. Several methods of fast pulse generation, electrical and optical, using this mode of operation are discussed. A 2000 V pulse generator, into 50 Ω, with a risetime of approximately 1 ns, jitter 〈100 ps, is then designed using these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142054
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  • 5
    Electronic Resource
    Electronic Resource
    Material dependence of positron implantation depths (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2962-2964 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New experiments and Monte Carlo simulations of positron implantation in gold are presented which, when compared with earlier work on aluminum, clearly demonstrate that the material dependence of positron implantation profiles is not adequately described by the simple mass density scaling factor in the widely used expression for median implantation depths. There is excellent agreement between the experimental results and the simulations which use the Penn dielectric formalism to describe inelastic scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105812
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  • 6
    Electronic Resource
    Electronic Resource
    Iso-electronic impurity-induced disordering: AlxGa1−xAs-GaAs/In (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2880-2882 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented on the disordering of an AlxGa1−xAs-GaAs laser structure using indium solid sources. Using separate and co-diffusion of silicon and indium from thin-film sources, indium was inferred to have a higher diffusion coefficient than silicon, and to result in a similar degree of impurity-induced disordering. The degree of index guiding was tested by excess-loss measurements in single-mode raised-cosine s-bends. In particular, structures patterned by SiO2/In disordering had excess losses similar to those patterned with SiO2. A 260 μm transition length for 3 dB loss was measured for 1-μm-wide guides with 100 μm guide offsets, which corresponds to a lateral index of refraction difference of ≈0.8–1.0%. There was no evidence for increased linear loss due to the presence of a dilute InGaAs alloy at the measurement wavelength of 870 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105840
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  • 7
    Electronic Resource
    Electronic Resource
    Area scaling in slab rf-excited carbon monoxide lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1281-1283 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A large area (slab) waveguide carbon monoxide laser, excited by a transverse radio frequency discharge and cooled by diffusion, has been demonstrated at electrode temperatures down to −30 °C. A maximum laser power of 120 W has been achieved from a sealed 386×2 mm discharge at an extraction efficiency of 17%. Discharge area scaling factors of 15.5 kW m−2 have been observed and cw power extraction exceeding 50 W using tap water cooling has been achieved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105475
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  • 8
    Electronic Resource
    Electronic Resource
    Native oxide stabilization of AlAs-GaAs heterostructures (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1199-1201 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data are presented on the stabilization of AlAs-GaAs heterostructures against atmospheric (destructive) hydrolysis using the native oxide that can be formed (N2+H2O, 400 °C, 3 h) on the AlAs layer. The ∼0.1-μm-thick native oxide formed from the AlAs layer is shown to be stable with aging (∼100 days), while unoxidized samples degrade through the AlAs (0.1 μm) down into the GaAs as deep as ∼1 μm. Relative to oxides formed (∼25 °C) on AlAs (or AlxGa1−xAs, x (approximately-greater-than) 0.7) under atmospheric conditions (hydrolysis), oxides formed (via N2 +H2O) at higher temperatures ((approximately-greater-than)400 °C) are much more stable and seal the underlying crystal (e.g., GaAs).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105213
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  • 9
    Electronic Resource
    Electronic Resource
    Stopping of 10–50 keV positrons in aluminum (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 164-166 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on new observations of positron stopping in a series of Al foils mounted on glass backplates for incident energies E in the range 10–50 keV. The measured median penetration depths for E(approximately-greater-than)30 keV are found to differ significantly from values derived from the empirical power law model of A. P. Mills, Jr. and R. J. Wilson [Phys. Rev. A 26, 490 (1982)]. The associated disparity between the measured implantation profiles and their analytic representations, and the consequent implications for defect profiling analysis, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106007
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