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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 99-105 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An analytical equation is derived for the error heat flow due to thermal imbalance between the hot plate and the guard in the case of an infinite strip. Finite element calculations show that the same equation can be used for circular plates with negligible error. The equation can also be extended to square plates if corner effects are neglected. By combining the present solution and a previous one by Woodside [Rev. Sci. Instrum. 28, 1033 (1957)], an expression is derived for the effect of the distortion of heat-flow lines near the gap even when thermal balance is obtained. The availability of this expression opens the possibility of using larger gaps than previously, to reduce thermal imbalance errors. The use of two-material specimens (test material over hot plate, insulant over guard and gap) would lessen thermal imbalance errors, material requirements, and edge effects.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9405-9411 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Structures and vibrational frequencies for minima and transition states on the O(1D)+H2S potential energy surface have been characterized at the unrestricted second-order Møller–Plesset (UMP2)=full/6-31G(d) level. The results for the thioperoxide HOSH agree with experimental IR spectra. Gaussian-2 theory was employed to calculate ΔHf,298 for HOSH of −119.3 kJ mol−1, −47.1 kJ mol−1 for the sulfoxide H2SO, and 47.0 kJ mol−1 for the thiooxonium ylide H2OS. We also derived ΔHf,0 for HOS and HSO of −2.7 and −17.0 kJ mol−1, respectively. Comparisons with ΔHf for known asymptotes on the potential energy surface gave good agreement, except in the case of HSO. Rice–Ramsperger–Kassel–Marcus (RRKM) analysis suggests that in most environments, except at low pressures and temperatures, H2OS will be short lived, and rate constants for isomerization of the three bound adducts under thermally equilibrated conditions are derived. The potential energy surface is discussed in the context of single-collision experiments, and pathways leading to SH+OH, 1SO+H2, HSO+H, HOS+H, and 1S+H2O have been analyzed. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 161-169 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Structures and vibrational frequencies for minima and 11 transition states on the O(3P)+H2S potential energy surface have been characterized at the MP2=FULL/6-31G(d) level. GAUSSIAN-2 theory was employed to calculate ΔHf,298 for HSO and HOS of −19.9 and −5.5 kJ mol−1, respectively. The kinetics of HSO=HOS isomerization are analyzed by Rice–Ramsperger–Kassel–Marcus theory. Transition state theory analysis for O+H2S suggests OH+HS is the dominant product channel, with a rate constant given by 1.24×10−16 (T/K)1.746 exp(−1457 K/T) cm3 molecule−1 s−1. Kinetic isotope effects and the branching ratio for H+HSO production are also analyzed. The other possible products H2+SO and H2O+S do not appear to be formed in single elementary steps, but low-barrier pathways to these species via secondary reactions are identified. No bound adducts of O+H2S were found, but results for weakly bound triplet HOSH are presented. The likely kinetics for the reactions OH+SH→S(3P)+H2O, OH+SH→cis and trans 3HOSH, cis 3HOSH→HOS+H, and HSO and HOS+H→H2+3SO are discussed. © 1995 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cyclotron resonance in GaAs/AlGaAs heterostructures, containing a high-mobility two-dimensional electron gas (2DEG), has been investigated with the help of a resonator technique over the frequency range 26–34 GHz. Heterostructures with mobilities from 2×105 to 1.6×106 cm2/V s have been measured. The microwave conductivity of the 2DEG is well described by the Drude model and momentum relaxation time values are found to be close to dc values. The cyclotron mass was found to be 0.068±0.002m0.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1739-1741 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanometer-scale ferromagnetic particles (Fe2O3, Fe3O4) are dispersed within a mutant bacterial chain which is drawn into a macroscopic fiber "rope." Cross-sectional scanning electron microscopy images reveal that the iron oxide particles are intercalated between the walls of the bacterial cells which are bundled into parallel threads. The field-dependent switching is seen to markedly sharpen when the synthesis is conducted within an applied magnetic field. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 847-849 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the application of a technique for performing opacity measurements on hot, dense plasmas. Plasmas were generated by using the x rays emitted from a laser-produced gold plasma to heat an aluminum sample. Observations were made using the technique of point projection spectroscopy. The distribution of ion stages observed is compared with predictions based on Saha distributions, at densities and temperatures deduced from hydrodynamic simulations.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 132-136 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper discusses the use of a photoconductively switched radial transmission line transformer as a high-gradient particle accelerator power system. In particular, a 1.8-m-radius radial line with a one-way transit time of 10 ns was fabricated and the voltage attenuation/amplification of a radially traveling wave measured. These results are compared with numerical solutions to the radial-wave equations using the method of characteristics. The line was operated as a step-down transformer by driving the inner radius with a pulse generator and measuring open circuit voltage at its outer radius. The voltage attenuation of the transformer agrees fairly well with an approximate theory for short-pulse propagation along the line (where pulse lengths are roughly one-tenth the one-way transit time of the line), and a more accurate computer solution using the method of characteristics has correctly predicted the voltage response of the line. These results imply that moderate voltage, short duration pulses (approximately 1 ns) can be amplified to very high voltages by uniformly driving the outside radius of this type of transmission line. The use of photoconductive switches to generate a radially converging, high-power wave transient required for high-gradient particle accelerators is suggested as an alternative to other methods because the switches can be synchronized to within several tens of picoseconds, and control of subsequent sections can be accomplished for relativistic systems.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6682-6685 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the magnetization reversal and magnetoresistance (MR) behavior of a lateral spin-injection device. The device consists of a two-dimensional electron gas (2DEG) system in an InAs quantum well and two ferromagnetic (Ni80Fe20) contacts: an injector (source) and a detector (drain). Spin-polarized electrons are injected from the first contact and propagating through InAs are collected by the second contact. By engineering the shape of the permalloy film distinct switching fields (Hc) from the injector and the collector have been observed by scanning Kerr microscopy and MR measurements. Magneto-optic Kerr effect (MOKE) hysteresis loops demonstrate that there is a range of magnetic field (20–60 Oe), at room temperature, over which magnetization in one contact is aligned antiparallel to that in the other. The MOKE results are consistent with the variation of the magnetoresistance in the spin-injection device. © 1999 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2100-2105 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A noninvasive voltage probe, consisting of a one-dimensional channel, has been fabricated within a modulation doped GaAs/AlGaAs heterostructure. With precision piezoelectric scanning equipment this probe has been brought to within 14 nm of a semiconductor device which includes surface gates and a 300 nm deep two-dimensional electron gas. Measurements of voltages applied to these conducting layers have been made at room temperature and at 4.2 K using the sensitive conductance of the one-dimensional channel. A voltage resolution of 0.48 mV has been observed at 4.2 K. Probe conductance measurements have also been made as a function of probe–sample separation. The conductance–separation data were fitted using a simple parallel plate capacitor model and a height resolution of 4 nm was calculated. Images of the sample layers have been obtained and a lateral resolution of 760 nm observed. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2839-2847 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The silicon photoconductive power switch has the potential to replace gaseous discharge switches like thyratrons, krytrons, ignitrons, and spark gaps, that are commonly found in high-voltage and high-current pulse circuits. This offers the possibility of developing advanced laser and radar drive circuits that are all-solid state, and which enjoy the advantages of improved efficiency, compactness, and life expectancy. Silicon operating at liquid-nitrogen temperature is especially attractive as a power switch because at 77 K it displays an extremely low coefficient of thermal expansion, a large optical absorption depth for 1.06-μm light, and a large thermal conductivity. These factors allow low-temperature silicon to switch power levels an order of magnitude greater than at 300 K, and an experimental cryogenic silicon photoconductive power switch (PCPS) has been made to switch pulses of 15-kV, 1.2-kA, 0.5-μS duration at 100-Hz recurrent frequency. Temperature and thermal stress profiles generated in the switch during operation have been calculated and experimentally verified, and the upper power limits for this switch technology are established. It is shown that the silicon switch compares favorably with thyratrons in terms of electrical ratings and energy transfer efficiency, and should be considered in advanced pulser designs.
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