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  • American Institute of Physics (AIP)  (20)
  • American Association for the Advancement of Science  (2)
  • American Association for the Advancement of Science (AAAS)
  • Amsterdam : Elsevier
  • Informa UK Limited
  • Seismological Society of America (SSA)
  • 1985-1989  (24)
Collection
Publisher
Year
  • 11
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1691-1693 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The application of an alternating field (AF) of 60-mT peak to an isotropic sample containing dilutely dispersed particles of γFe2O3 from magnetic tape causes it to become magnetically anisotropic. The anisotropy of initial susceptibility so produced can be described by an oblate ellipsoid of revolution with the unique axis aligned with the AF direction. A consequence of this effect is that an isothermal remanent magnetization (IRM) is then more easily acquired if the direct field is applied perpendicular to the previously applied AF direction than if it is applied parallel to this direction. The anisotropy of IRM acquisition at direct fields between 20 and 40 mT is an order of magnitude greater than the anisotropy of initial susceptibility and is 40% of the maximum possible value.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Time-resolved x-ray scattering studies of phase transition kinetics have been carried out using the wide-bandpass monochromator and fast linear position-sensitive detector system at the IBM/MIT beamline X-20C at the National Synchrotron Light Source (NSLS). We report here on the instrumentation that has been developed for these studies, and in particular on the methods used to measure, change, and control sample temperature with millisecond resolution.
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  • 13
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4226-4228 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A recent study on low-alloy, nonoriented, semiprocessed electrical steels indicated that at 60 Hz and 15 and 17 kG the anomalous loss per cycle Wa increased linearly with t2/ρ, i.e., Wa=Wao+kt2/ρ, where t is sheet thickness, ρ is resistivity, and Wao and k are empirical constants. The present study explores the above relationship over inductions B of 5 to 17 kG and frequencies f of 20 to 200 Hz. A separation of hysteresis loss Wh into synchronous and asynchronous components is also considered. Six laboratory heats with Si+Al〈1.1 wt. % were hot and cold rolled to 0.035, 0.07, and 0.11 cm. The sheets were annealed, critically strained, and decarburized. Longitudinal strips were tested with dc as well as ac current in a 25-cm Epstein frame. The above linear equation was generally valid. At each combination of B and f, the intercepts Wao were always positive, but the slopes k were negative at 5 and 10 kG and positive at 15 and 17 kG. Furthermore, a fifth of the Wa values were negative. The negative Wa and k were associated with lack of flux penetration. Wh, but not Wa, increased with increasing oxygen and decreasing grain size, and these effects resided in the B1.6 component of Wh.
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5004-5018 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond infrared pump–probe experiments determined the vibrational population lifetimes (T1) of the hydroxyl fundamental stretching mode OH(v=1) in 12 alcohols (R3COH) and 8 silanols (R3SiOH) in dilute room temperature CCl4 solutions. T1 for the silanols is in the range 185〈T1〈292 ps, while T1 for the alcohols is much less (T1〈80 ps). The deuterium-exchanged analogs (COD and SiOD) exhibit population relaxation times similar to protonated hydroxyls. An analysis of the vibrational energy levels corresponding to modes involving the four bonds nearest the hydroxyl groups of these molecules is used to qualitatively explain the trends of the observed T1 lifetimes for these systems. Solution T1 lifetimes are also compared to those previously measured for OH(v=1) on the surface of silica and in other condensed-phase, room temperature systems.
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  • 15
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2333-2334 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational, spin-orbit, lambda doublet, and kinetic energy distributions were measured by laser-excited fluorescence techniques for the nitric oxide fragments formed from the vibrational predissociation of nitric oxide dimers in a free jet expansion. The NO fragments, produced following excitation in the dimer ν1 fundamental, were described by a rotational "temperature'' of TR(approximately-equal-to)100 K, with full equilibration of lambda doublet states, and approximately equal populations in the two spin-orbit states. The velocity distributions were isotropic with an average fragment kinetic energy of 400 cm−1. Time-resolved measurements placed a 15 ns upper limit on the predissociation lifetime.
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  • 16
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 2361-2364 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond infrared spectroscopy was used to measure the vibrational energy relaxation time T1 of OH(v=1) and OD(v=1) groups chemisorbed on silica surfaces over the temperature range 100≤T≤800 K. The observed T1 times and their temperature dependencies are discussed in terms of a multiphonon relaxation mechanism. Limiting low temperature lifetimes are T1=220±20 ps (1σ) for OH(v=1) and T1=149±10 ps for OD(v=1).
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  • 17
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5286-5288 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational level distribution of the NO fragments formed as a result of the predissociation of the vibrationally excited NO–C2H4 (ν7) van der Waals molecule was measured by laser excited fluorescence techniques. The distribution was found to be Boltzmann in character, described by the rotational temperature 75±15 K. An average kinetic energy release of ≈105 cm−1 per fragment, in an isotropic flux distribution, was determined from Doppler profiles of the NO fragments in selected rotational levels.
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  • 18
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6235-6237 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Direct picosecond measurements of the vibrational predissociation rates of the nitric oxide dimer excited to v=1 levels of the symmetric (ν1=1870 cm−1) and antisymmetric (ν4=1789 cm−1) N–O stretching fundamentals are reported. Lifetimes obtained are 880±260 ps for ν1 and 39±8 ps for ν4 excitations.
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  • 19
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2236-2239 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational-, spin-, and lambda doublet-state distributions for nitric oxide (NO) formed in the CO2 laser multiphoton dissociation of methyl nitrite, CH3ONO, in a pulsed molecular beam are reported. Upon methyl nitrite photolysis by temporal square wave infrared laser pulses at 983 cm−1 of 50 ns duration and 800 MW/cm2 intensity, the low-lying rotational levels of the nitric oxide fragments formed in the 2Π1/2 (F1) and 2Π3/2 (F2) spin-orbit states exhibited Boltzmann-like population distributions, characterizable by the rotational temperatures TR (F1)=400±10 K and TR (F2)=530±100 K; the integrated populations for J〈30.5 of the two spin components were in the ratio F1/F2=2.7 : 1. For those highly rotationally excited levels with J(approximately-greater-than)24.5 there is no measurable spin preference, the level population depending solely on total internal energy Eint. There is no apparent preference for formation of either lambda doublet component and there is no observable fragment alignment, the nascent NO species exhibiting an isotropic distribution of angular momentum vectors.
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  • 20
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5216-5231 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond infrared transmission spectroscopy was used to directly measure the vibrational energy relaxation time T1 of hydroxyl groups chemisorbed on the surface of colloidal silica (SiO2). T1 was obtained for OH(νstretch=1) in the strongly bound "isolated sites'' of fumed silica particles in vacuum and dispersed in several liquids at T=293 K. At the SiO2/vacuum interface, T1=204±20 ps. When the SiO2 particles are surrounded by solvents, the relaxation time of the surface OH(v=1) groups decreases: for the liquids CCl4, CF2Br2, CH2Cl2, and C6H6, T1(ps)=159±16, 140±30, 102±20, and 87±30, respectively. T1 does not depend on the size of the SiO2 particles for the range 70 A(ring)≤ diameter ≤150 A(ring), or on the surface OH coverage up to an average density of 4 OH/100 A(ring)2. Significant amounts of physisorbed water (5 H2O/100 A(ring)2) decreased T1 for the isolated OH(v=1) to T1=56±10 ps. For comparison to the surface hydroxyls, the vibrational deactivation time for OH(v=1) groups in the bulk of fused silica (OH/SiO2≈130 ppm by weight) was determined to be T1=109±11 ps. These observations are discussed in terms of the possible mechanisms of vibrational energy flow in these systems. The observed T1 values demonstrate that the spectral linewidths (e.g., IR and Raman) observed for these surface vibrations are too large (by factors of 200–2000) to be caused solely by T1 uncertainty broadening. The slow transfer of vibrational energy between surface and lattice vibrations may have important implications for surface chemistry.
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