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  • American Institute of Physics (AIP)  (11)
  • 1985-1989  (11)
  • 1980-1984
  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3323-3325 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Uniform, cubic 0.05-μm iron oxide particles were formed by forced hydrolysis of ferric perchlorate. These particles were reduced to α-Fe by heating in hydrogen at temperatures between 300 and 500 °C. The effect of reduction temperature and various prereduction treatments on the microstructure of the iron particles will be discussed. Complete reduction to α-Fe was established by 57Fe Mössbauer spectroscopy and x-ray diffraction. Magnetic measurements on epoxy and polyurethane films containing these particles with various mass fractions gave coercivities as high as 1000 Oe. The relationship between the magnetic measurements and the microstructure will be discussed. Na2SiO3 is found to be the best coating material for the process of reducing iron oxide particles to iron.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3233-3235 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Isolated ultrafine ferromagnetic particles exhibit large coercivities which scale approximately as 1/d, until the diameter d becomes sufficiently small for the particles to become single domains. Many applications, e.g., magnetic recording, require high densities of particles in a film. Thus, it is of interest to study the effect of packing fraction, and ultimately particle contact, on the coercivities of the small particles. Uniform cubic iron particles having sides ∼500 A(ring) and coercivities as high as 1000 Oe have been prepared. The effect of packing fraction on the coercivities of these particles is presented herein. The coercivities of pressed pellets of these particles is reported and correlated with the microstructures (or nanostructures), and the behavior of uncoated metal particles is compared to that of silicate-coated metal particles.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 1003-1009 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Ab initio SCF calculations are presented which deal with the structure of polyenes, as model systems for polyacetylene (PA). We used a double zeta quality basis set, and determined the structure of clusters up to C22H24 as well as the vibrational spectra of clusters up to C12H14, including infrared intensities. All of these data are analyzed by comparing with experimental information available on polyacetylene and previous theoretical studies. Specifically, we identified the vibrational modes corresponding to the observed absorption bands of PA. We comment on controversial points such as the relative contributions of internal coordinates to these modes, on the magnitude of interaction force constants, and also on the effect of light polarization on the absorption of some vibrational modes. We establish that the inclusion of polarization function in the basis set does not lead to significant changes in structural or energetic properties. Convergence of the cluster properties toward the 1D polymer properties was also tested with ab initio crystal orbital calculations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1471-1477 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Infrared spectra have been obtained for dimers formed from acetylene, methyl acetylene, and ethylene using a wide variety of free jet source conditions. An F-center laser was used to excite various C–H stretch fundamentals in the range 3000–3300 cm−1. Rotational structure was resolved in the spectra of both acetylene and methyl acetylene dimers when dilute mixtures of either gas in helium were expanded from high pressures. The spectrum of the ethylene dimer showed no such structure even when formed in very dilute mixtures. These results contradict previous suggestions that the vibrational relaxation lifetime is uniformly short for all polyatomic dimers.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5703-5707 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Diffusion Monte Carlo calculations are reported for liquid 4He using a Lennard-Jones potential and for solid molecular hydrogen using a reliable spherical pair potential and Axilrod–Teller three body interactions. Calculated thermodynamic and structural properties are in good agreement with experiment over a range of densities. Discrepancies between calculated and experimental values for hydrogen at the highest densities are attributed to the neglect of anisotropy in the calculations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 873-879 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Infrared predissociation spectra have been measured for ethylene clusters near the ν7 (950 cm−1) monomer band using CO2 lasers. One of the CO2 lasers was piezoelectrically scanned over a 240 MHz range around each rotational lasing transition, to obtain high resolution spectra of the ν7 band. The resulting spectra showed fine structure with widths of the order of 20 MHz, representing a lower limit on the predissociation lifetime of around 10 ns. The fine structure is shown to be due to ethylene dimers, and the broad background is attributed to a superposition of inhomogeneous contributions from larger clusters.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3891-3895 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: In-plane total differential scattering cross sections for H2 scattered from N2 and HF are reported. The data are analyzed in terms of spherical and anisotropic potentials using single channel and IOS methods for calculating the differential cross sections. In the case of H2/HF the diffraction oscillations are highly damped at small angles, suggesting that the anisotropy is large.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 3554-3562 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Infrared predissociation spectra of water clusters have been measured in the frequency range 3000–3800 cm−1 using a molecular beam–color center laser apparatus. The transition from a spectrum resembling that of liquid water to that of the dimer is clearly seen. Detailed theoretical analyses using normal mode theory, local mode theory, and a quantum simulation method are used to interpret the spectrum in terms of a potential surface that includes both intramolecular and intermolecular degrees of freedom.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7563-7589 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Close-coupled scattering calculations have been carried out for rotationally inelastic collisions between HF molecules. Integral cross sections were determined for vibrationally elastic transitions j1 j2→j '1 j 2(v1v2), which refer to collisions HFa (v1, j1)+HFb (v2, j2)+ΔE→HFa (v1, j '1 )+HFb (v2, j 2), where ΔE is the energy gap. Total energies between 241.1 and 3900 cm−1 (0.03 and 0.48 eV) were considered. When v1=v2, the rotational exchange transitions j1 j2→j2 j1(v1v2) are energetically resonant (i.e., ΔE=0), and the corresponding cross sections increase as the collision energy decreases. Particularly large cross sections are obtained for the j j+1→j+1 j(vv) transitions, which are both resonant and coupled to first order by the dipole–dipole interaction. When v1≠v2, the j j+1→j+1 j(v1v2) transitions are no longer resonant, and the corresponding cross sections are greatly reduced at small to moderate collision energies. The dependence of the j1 j2→j '1 j 2(v1v2) cross sections upon the vibrational states of the molecules, the collision energy, and the interaction potential used is discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2182-2191 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The total differential cross section for Ar–HF was measured at a collision energy of 1637 K (141 meV). Although diffraction oscillations were not resolved, a broad primary rainbow peak was observed. Scattering calculations were carried out for the Ar–HF interaction potentials developed by Douketis et al. and Hutson and Howard. The spherical potential and infinite order sudden approximations do not give a good description of the total differential scattering. The final-l labeled coupled states approximation, on the other hand, is in good agreement with the more accurate close coupled approximation. Neither potential predicts cross sections which are in good agreement with the measured scattering intensities. Contributions to the total scattering from elastic and inelastic processes were investigated using the coupled states approximation. The contributions to the total scattering from different initial HF rotational states were also studied. The total scattering for j initial=0 differs significantly from that for other values of j initial. It is therefore important to know the distribution of rotational states in the HF beam if one is to compare calculated total differential cross sections with measured ones. The largest inelastic cross section is for the j=0 to j'=1 transition. Collisions in which the Ar atom interacts strongly with the anisotropic potential well, rather than near head-on collisions off the repulsive wall of the potential, are responsible for the large j=0 to j'=1 cross section. The results of accurate SCF calculations for Ar–HF are also reported in this paper.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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