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  • 1
    Electronic Resource
    Electronic Resource
    An all-acoustic parametric amplifier in superfluid helium (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4438-4445 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies of nonlinear acoustic interactions in superfluid helium at temperatures below 0.2 K have culminated in the construction of an all-acoustic parametric amplifier at gigahertz frequencies. This device represents the shortest wavelength parametric amplifier ever made, with signal wavelengths shorter than 1000 A(ring) and pump wavelengths shorter than 600 A(ring). In the experiment, plane waves are mixed at a predefined angle in the superfluid helium. Two gain regimes are observed. The first regime is a noncollinear phase-matched process, in which the signal phonon stimulates decay of the pump phonon to create gain at the signal frequency. The second regime is a four-phonon collinear process, in which gain on the signal is created by the second harmonic of the pump. This four-phonon process is unusual and is shown to be a combination of three-phonon processes wherein the lack of conservation of energy and momentum in one process is mostly compensated by the other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346194
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  • 2
    Electronic Resource
    Electronic Resource
    Homogeneous nucleation in supersaturated vapors of polar molecules: Acetonitrile, benzonitrile, nitromethane, and nitrobenzene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3356-3368 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The critical supersaturations (Sc) required for the homogeneous nucleation of acetonitrile, benzonitrile, nitromethane, and nitrobenzene vapors have been measured over wide temperature ranges using a thermal diffusion cloud chamber. At Tr=0.44, the experimental results are higher than the predictions of the classical nucleation theory by 20% (CH3NO2), 50% (CH3CN), 57% (C6H5NO2), and 112% (C6H5CN). This trend correlates well with the dipole moments and to a lesser extent with the polarizabilities of these substances. Corresponding states of simple fluids and scaled nucleation law show that CH3CN and CH3NO2 have similar nucleation behavior which is different from that of C6H5CN and C6H5NO2. Correlations with other less polar substances are examined. The scaled law, with Ω (the excess surface entropy per molecule) determined from the temperature dependence of the bulk surface tension, gives a better description of the experimental results than the classical theory with the exception of nitromethane. The results suggest that the classical theory does not take proper account of the dipole–dipole interaction in calculating the free energy of the embryonic droplets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464108
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  • 3
    Electronic Resource
    Electronic Resource
    High-speed photorefractive polymer composites (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1490-1492 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two photorefractive polymer composites are presented that exhibit the fastest response times reported to date by an order of magnitude (τg(approximate)5 ms at 1 W/cm2), while maintaining large gain coefficients (Γ(approximate)230 and 130 cm−1). These materials show promise for video-rate optical processing applications. The factors limiting the photorefractive speed in these materials are investigated. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122182
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  • 4
    Electronic Resource
    Electronic Resource
    Bulk and surface recombination in InAs/AlAs0.16Sb0.84 3.45 μm light emitting diodes (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 943-945 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of the light generation efficiency of a series of InAs/AlAs0.16Sb0.84 light emitting diodes with p-type InAs active layers is reported. The bulk low-injection radiative efficiency of the p-type material is shown to be as high as 24% at a hole concentration of 1.5×1017 cm−3 but to decrease with increasing hole concentration in a manner consistent with the dominant low-injection nonradiative processes being Auger processes with two holes in their initial states and a total rate constant of 2×10−28 cm6 s−1. The maximum internal low-drive quantum efficiency achieved in the light emitting diodes is shown to be limited by interface recombination at the InAs/AlAs0.16Sb0.84 heterojunction and reabsorption in the active layer in addition to the bulk nonradiative processes in the InAs. A maximum value of ∼9% is achieved. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125911
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  • 5
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of acetonitrile clusters [CH3CN]N, N=2–256: Melting transitions and even/odd character of small clusters (N=2–9), heat capacities, density profiles, fractal dimension, intracluster dimerization, and dipole orientation (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3791-3802 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermodynamic and structural properties of acetonitrile clusters [CH3CN]N, N=2–15, 20, 30, 60, 128, and 256 have been investigated using Monte Carlo simulation. Interactions in the small clusters (N≤9) are dominated by antiparallel pairing of the molecular dipoles. The simulations reveal rigid ↔ fluid (melting) transitions with a remarkable even–odd alternation in the transition temperatures for the N=2–9 clusters. The higher melting temperatures of the even-N clusters arise as consequences of the antiparallel paired dipoles which provide favorable electrostatic interactions. Even–odd alternation has also been observed in the configurational energies and heat capacities and the percentage of molecules possessing an antiparallel nearest neighbor. These observations are consistent with the fact that Coulomb potential terms dominate the interaction energies in clusters with N〈12. The average density in clusters with N(approximately-greater-than)60 is fairly well represented by the bulk liquid density. Order parameters characterizing dipole orientation indicate that the molecular dipoles tend to lie flat on the cluster surface for N≥30. Significant dimerization within the clusters suggests evaporation of molecules via dimers and an enhancement of evaporative loss over condensation and this may explain the slower nucleation rates observed for acetonitrile compared to the predictions of the classical nucleation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466367
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  • 6
    Electronic Resource
    Electronic Resource
    A Monte Carlo study of methanol clusters (CH3OH)N, N=5–256 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 11199-11208 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermodynamic and structural properties of methanol clusters (CH3OH)N, N=5–15, 20, 30, 60, 128, 256 and the bulk liquid have been investigated using Monte Carlo simulation. Calculated properties as a function of size include electrostatic and dispersive contributions to the configurational energy, configurational heat capacities, fractal dimension, density profiles, order parameters characterizing dipole and bond vector orientation, and the Lindemann index. The cluster heat capacities as a function of N possess an interior maximum near N=128 and converge to the bulk value from above. Monocyclic, semiplanar structures are found to persist at liquidlike temperatures up to about N=12, followed by bi- and polycyclic structures for N=13–20, with the larger clusters gradually becoming more spherical. The average density of the larger clusters is fairly well represented by the bulk value. For clusters with 30 or more molecules, there is a net tendency for the molecular dipoles to lie flat on the cluster surface. The observed trends in heat capacities, density profiles, and dipole alignments parallel to the cluster surface are likely to be general features of clusters of polar molecules. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472919
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  • 7
    Electronic Resource
    Electronic Resource
    Analysis of homogeneous nucleation data of polar molecules: Vapor association, dipole orientation, and elongated clusters (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3369-3379 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present the results of several theoretical models examined in order to explain the observed systematic deviations of the homogeneous nucleation of highly polar substances from the predictions of the classical nucleation theory (CNT). It is found that molecular association in acetronitrile or nitromethane vapor cannot explain the observed higher supersaturations. Similarly, the use of virial coefficient data to obtain a size dependent surface energy correction factor does not reproduce the experimental results. It is shown that orientation of the surface dipoles within the spherical droplets results in higher supersaturations in agreement with the experimental findings. We also generalize the CNT for elongated clusters and show that these clusters can allow for favorable end-to-end and antiparallel alignments of the dipoles. It is found that for reasonable agreement with experiment, acetonitrile, and benzonitrile clusters require a larger degree of elongation compared to nitromethane and nitrobenzene clusters. These results are discussed in relation to molecular simulations of bulk liquids and clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464109
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  • 8
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    Time resolved 3D momentum imaging of ultrafast dynamics by coherent VUV-XUV radiation (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-06-15
    Description: We present a new experimental setup for measuring ultrafast nuclear and electron dynamics of molecules after photo-excitation and ionization. We combine a high flux femtosecond vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) source with an internally cold molecular beam and a 3D momentum imaging particle spectrometer to measure electrons and ions in coincidence. We describe a variety of tools developed to perform pump-probe studies in the VUV-XUV spectrum and to modify and characterize the photon beam. First benchmark experiments are presented to demonstrate the capabilities of the system.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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