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  • 1
    Electronic Resource
    Electronic Resource
    Orientation and relaxation of nonlinear elastic dumbbells in electric fields: Modeling transient electric birefringence (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5943-5949 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The orientation and extension of a finitely extensible nonlinearly elastic (FENE) dumbbell in an electric field is analyzed to model the nonlinear phenomena observed during orientation and relaxation of flexible polymer molecules in transient electric birefringence measurements. In the model the dumbbell interacts with the electric field via an induced dipole with a dipole moment proportional to the end-to-end separation of the dumbbell. The electric field produces a strong "elongational'' deformation of the molecule which has analogies with the deformations produced by elongational flow. The steady state birefringence, as a function of field strength, is calculated in two ways: first using matched expansions around low and high field conditions, and then using Peterlin's approximation of preaveraging the connector force law. Both techniques yield similar results: Kerr law behavior is observed at low field strengths and saturation of birefringence at high field strengths. Birefringence relaxation after the field is removed shows a strong field dependence on the initial rate of relaxation. Previously proposed means of analyzing birefringence relaxation data for flexible molecules are discussed in light of this observation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455545
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  • 2
    Electronic Resource
    Electronic Resource
    The structures and dipole moments of Ar–PF3 and Kr–PF3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6949-6955 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complexes of PF3 with Ar and Kr, were studied by Fourier transform microwave spectroscopy. The force constants and amplitudes of vibration for the van der Waals modes of the complexes and the average moments of inertia and structural parameters were estimated from the centrifugal distortion constants. The distance (Rc.m. )ave between the rare-gas atom and the center of mass of PF3 is 3.959 A(ring) for the Ar complex and 4.077 A(ring) for Kr while the angle (θc.m. )ave between the Rc.m. vector and the C3 axis of the PF3 is 69.30° and 67.25°, respectively. The dipole moments of both complexes and of free PF3 were determined. The induced dipole components estimated for the rare gas using electric fields from ab initio calculations of PF3 agree with the experimental values for a conformation with the rare gas over a PF2 face. The PF2 face conformation is also consistent with the observed and ab initio estimates of the 83 Kr nuclear quadrupole coupling constant for the 83 Kr–PF3 species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456270
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  • 3
    Electronic Resource
    Electronic Resource
    Undulator heat loading studies on x-ray monochromators cooled with liquid gallium : International conference on synchrotron radiation instrumentation (SRI−88) (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 1973-1976 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Heat loading tests were conducted with up to 360 W of undulator radiation incident on liquid-gallium-cooled silicon monochromators. Rocking curve measurements and temperature profiles (infrared camera) were obtained as a function of beam current. With large heat loads, the width of the rocking curves were observed to broaden and the gain in output flux per mA of beam current was significantly less at high beam currents than during low-current operation. The best performance was obtained using a slotted crystal with cooling channels located 0.76 mm below the surface. This crystal showed strong heating effects only above 40 mA and continued to produce an increase in output flux with beam current at the highest current tested of 76 mA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140851
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  • 4
    Electronic Resource
    Electronic Resource
    New method for measuring ion temperatures in hot D–T plasma (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1078-1080 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new method has been found to measure the ion temperature of a hot D–T plasma. The new method makes use of two new neutron dosimetry reactions, 54Fe(n,2n)53Fe and 27Al(n,2n)26Al. What makes these reactions special is that their threshold energies are quite close to the centroid of the energy distribution of the neutrons emitted from a D–T plasma. This makes their reaction yields sensitive to only the upper half of the neutron energy distribution and therefore sensitive to both changes in the centroid and the width of the neutron energy distribution. The sensitivity to the width of the neutron energy distribution allows one to measure the ion temperature. If the plasma is in thermal equilibrium the ion temperature can be calculated from the ratio of the yields of the 54Fe(n,2n)53Fe reaction to the 27Al(n, p)27Mg reaction or a similar nonsensitive reaction. No absolute measurements are needed. Using both of the new dosimetry reactions the asymmetry of the neutron energy distribution for nonequilibrium conditions (neutral beams) can be measured. The 54Fe(n,2n)53Fe reaction is sensitive enough to monitor a single shot in TFTR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138228
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  • 5
    Electronic Resource
    Electronic Resource
    Automated system for the characterization of liquid foam (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 746-751 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A device is described which measures, on line, the bubble size distribution and volume fraction of gas in a liquid foam. There are four elements in the device: a flow channel, meniscus detection, velocity detection, and microcomputer data acquisition. The foam flows into a gently converging capillary to reorder the foam bubbles into alternating slugs of gas and liquid. The passage of the meniscus between a gas and liquid slug is detected by a matched light emitting diode/phototransistor pair. When gas is in the detection path, the detector signal is "low,'' and when liquid is in the path, the signal is "high.'' The volume fraction of gas is determined from the ratio of time the detector signal is low to the total elapsed time. A second detector pair is located a fixed distance further down the capillary. From the time shift between signals at the first detector and those at the second, the velocity of the foam in the capillary can be calculated. From the velocity, time that the detector signal is "low,'' and known capillary geometry, the volume of a gas bubble can be determined. An IBM PC is used for rapid data acquisition and calculation. The device has been tested under a range of foam conditions to validate its performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138162
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  • 6
    Electronic Resource
    Electronic Resource
    Dependence of the nonlinear transmission properties of fused silica fibers on excimer laser wavelength (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4035-4040 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear transmission properties of commercially available fused silica fibers have been determined as a function of excimer laser wavelength. Accurate two-photon absorption coefficients have been measured and the influence of color center formation is discussed. Two-photon absorption and color center formation dominate the ArF and KrF transmission at high intensities while both of these effects are negligible at the XeCl and XeF laser wavelengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343987
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  • 7
    Electronic Resource
    Electronic Resource
    Absolute total cross sections for the scattering of low energy electrons by CCl4, CCl3F, CCl2F2, CClF3, and CF4 (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 813-819 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute total electron scattering cross sections were measured with a time-of-flight electron transmission spectrometer for incident electron energies ranging from 0.6 to 50 eV. The halomethanes studied exhibit low energy structure which can be associated with electron capture processes. Comparisons are made with recent experiments and calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450580
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  • 8
    Electronic Resource
    Electronic Resource
    Absolute total cross section for the scattering of low energy electrons by methanea) (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5424-5427 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The absolute total electron scattering cross section for methane (inelastic+elastic, integrated over all angles) was measured with a time-of-flight electron transmission spectrometer for incident energies from 1.3 to 50 eV. The major discrepancies that exist between recent absolute measurements of the total cross section are discussed with careful consideration of probable error limits. Comparisons are also made with recent calculations of the elastic cross section.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448575
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