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  • 1990-1994  (8)
  • 1
    Electronic Resource
    Electronic Resource
    Linear theory of a field-emitter-array distributed amplifier (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7098-7110 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A small-signal theory of a field-emission-array distributed amplifier consisting of two microstriplike transmission lines is developed to calculate the premodulation in the input channel and the gain in the output channel. A first-order perturbation analysis is used to treat the beam-wave coupling in this device within the framework of a cold fluid model. The dependence of the linear gain on frequency, beam voltage, beam current, and the circuit parameters is derived to determine the parameter range for operation of the device. It is found that the height of the circuit is restricted to lie between 80 and 120 μm to maintain high electronic gain and low loss arising from the finite conductivity of the metal surfaces. In an output line having a substrate with a relative dielectric constant, εr=4, a net gain of 7 dB/cm is calculated with a beam voltage of 60 V and a beam current of 2.14 A/cm in each wedge of a seven-wedge emitter array. As the beam voltage is increased in the range 60–100 V, the net gain decreases from 7.0 to 3.0 dB/cm, while the frequency for maximum gain increases from 50 to 80 GHz with a corresponding increase in the bandwidth. The small-signal instantaneous bandwidth is in excess of 60%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345060
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Numerical simulation of field emission and tunneling: A comparison of the Wigner function and transmission coefficient approaches (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4409-4427 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantum transport through one-dimensional potential barriers is usually analyzed using either the transmission coefficient (TC) or the Wigner distribution function (WDF) approach. Fast, accurate, and efficient numerical algorithms are developed for each and are compared for (a) calculating current-field relationships for field-emission potentials with silicon parameters (and current-voltage relationships for resonant tunneling diodes), (b) their ability to accommodate scattering, self-consistency, and time dependence, and for (c) the behavior of their "particle trajectory'' interpretations. In making the comparisons, the concern will be on the ability of each method to be incorporated into a larger ensemble-particle Monte Carlo simulation; it is argued that, in this regard, the WDF approach has significant advantages. Since the TC calculations rely on the Airy function approach, a detailed comparison of this method is made with the widely used Wentzel–Kramers–Brillouin and Fowler–Nordheim approaches for the general problem of field emission from a material into the vacuum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352779
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Frequency multiplied harmonic gyrotron-traveling-wave-tube amplifier (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2058-2062 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical simulations of a W-band two-stage tapered, frequency multiplied gyrotron- traveling-wave-tube amplifier are reported. Unlike conventional harmonic gyrodevices, a drive signal at the fundamental harmonic frequency is injected in the first stage for beam modulation, and amplified output radiation is extracted from the third harmonic cyclotron resonance interaction. Numerical results show that broadband millimeter wave radiation is obtained with an efficiency of 10%–15%, a gain of ∼30 dB, and an instantaneous bandwidth of ∼10% at a center frequency of 95 GHz for Δvz/vz=2%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870600
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  • 4
    Electronic Resource
    Electronic Resource
    Absolute instabilities in gyropeniotron amplifiers (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3800-3805 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical current, oscillation frequency, and characteristic wave number for the excitation of absolute instability in gyropeniotron amplifiers are calculated from the linear dispersion relation by following the Briggs–Bers criterion. Numerical results are presented for some cases of interest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860334
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Linear analysis of backward wave oscillations in azimuthally varying transverse electric (TE) modes (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1639-1646 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linear analysis for a gyrotron backward wave oscillator operating at a general transverse electric (TEln) mode of a cylindrical waveguide (slotted or uniform cross section) has been developed using a Maxwell–Vlasov equation under the tenuous beam approximation. The equation is solved by Laplace transformation to allow easy insertion of the boundary values. The start-oscillations conditions are determined from an interference of the waveguide and beam modes with appropriate amplitudes and phases. The theory is used to determine the design parameters for stable operation of a second cyclotron harmonic gyropeniotron amplifier at 35 GHz in the π mode of a six vane magnetron-type circuit with a 70 kV, 3 A beam.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860960
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear analysis of the Cerenkov maser (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2506-2515 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear evolution of the Cerenkov maser amplifier is investigated numerically for a configuration that consists of an energetic electron beam propagating through a dielectric-lined cylindrical waveguide. An axial guide magnetic field is included in the formulation in order to improve beam confinement. A set of coupled nonlinear differential equations is derived in three dimensions that governs the evolution of both the electromagnetic field and the trajectories of an ensemble of electrons. The system is assumed to be azimuthally symmetric, and the electromagnetic field is represented as a superposition of the TM0n modes of the vacuum waveguide. The initial conditions are chosen to model the simultaneous injection of either a solid or annular electron beam, and an electromagnetic wave of arbitrary input power. Thermal effects are treated under the assumption that the beam is initially monoenergetic but exhibits a pitch angle spread; however, the subsequent evolution of the beam is treated in a self-consistent manner. This class of distribution is appropriate to the treatment of diode-produced beams and describes a beam with an initial axial energy spread. This is the crucial determinant in the efficiency, since saturation occurs by means of an axial bunching mechanism that results in the phase trapping of the beam. The specific parameters used in the numerical analysis correspond to experiments conducted at Dartmouth College [J. Appl. Phys. 58, 627 (1985)], and good agreement is found between theory and experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859515
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Alkylation of 2-oxy-substituted 1-sulfonylallyl and 1-sulfonylvinyl anions. New routes to functionalized carbocycles and dihydrofurans (1991)
    s.l. : American Chemical Society
    The @journal of organic chemistry 56 (1991), S. 3556-3564 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00011a021
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Isomer differentiation and structural characterization of penem β-lactam antibiotics by mass-analyzed ion kinetic energy spectrometry (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 26 (1991), S. 703-708 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of clinically significant penem β-lactams, both free acids and sodium salts, were investigated by mass-analyzed ion kinetic energy spectrometry (MIKES) following fast atom bombardment (FAB) ionization. The collisionally activated dissociation (CAD) products of [M + H] + and [M + Na]+ ions are described. Carbon dioxide loss was observed for some of the free acids, whereas a daughter ion generated by β-lactam ring cleavage was characteristic of the sodiated species. Other fragments included successive cleavages and rearrangements of the substituent side-chain, permitting complete characterization of these chains. The fragmentation pattern for both protonated and sodiated species were more clearly established by CAD MIKES than by normal FAB mass spectral analyses. A notable feature of this technique was its ability to differentiate between pairs of regioisomeric penems on the basis of their fragmentation patterns. These compounds could not be differentiated in the usual mass spectra.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210260807
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