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  • American Institute of Physics (AIP)  (10)
  • Institut für Meteorologie und Geophysik  (1)
  • Unikontakt, Ruhr-Universität Bochum
  • 1985-1989  (12)
  • 1
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    Unbekannt
    Geschwindigkeiten seismischer Wellen - Definition und Bedeutung (1987)
    Unikontakt, Ruhr-Universität Bochum
    In:  Princeton, Unikontakt, Ruhr-Universität Bochum, vol. 7, no. 1, pp. 443-487, (ISBN 0-89871-560-1)
    Details
    Publikationsdatum: 1987
    Schlagwort(e): Seismics (controlled source seismology) ; Review article ; Velocity analysis ; Muller
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    BIBLIOGRAFIE SEISMOLOGIE
  • 2
    facet.materialart.
    Unbekannt
    Inversionstheorie geophysikalischer Beobachtungen (1987)
    Institut für Meteorologie und Geophysik
    In:  Vorlesungsskript, 134 S., Universität Frankfurt, Institut für Meteorologie und Geophysik, vol. C 560, 183 pp., no. 70, pp. 253-265, (ISBN 3-933346-037)
    Details
    Publikationsdatum: 1987
    Schlagwort(e): Inversion ; Muller
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    BIBLIOGRAFIE SEISMOLOGIE
  • 3
    Digitale Medien
    Digitale Medien
    Electrophoretic deposition of textured YBa2Cu3O7−x films on silver substrates (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5940-5943 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have deposited 10–20-μm-thick YBa2Cu3O7−x films by an electrophoretic process on silver substrates in a magnetic field of 8 T. X-ray diffraction patterns of these 2.4-cm-diameter samples show a high degree of c-axis texturing perpendicular to the surface. Their microwave surface resistance Rs was measured at 21.5 GHz in the temperature range from 4.2 to 300 K. It was found to drop sharply at 92.4 K to reach 18±3 mΩ at 77 K and less than 3 mΩ at 4.2 K. These first results exceed the values obtained from bulk samples and untextured thick films, and are lower than Rs of pure copper at the same frequency and temperature. The electrophoretic deposition technique is applicable to large substrates of nonplanar geometry and is therefore suitable for applications of high-Tc superconductors in the field of microwave technology.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.343620
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    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    Scaling behavior in the S=1 antiferromagnetic XXZ chain (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3560-3560 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A recent remarkable prediction by Haldane is the 1D integer spin antiferromagnets of XXZ type should show strikingly different T=0 phase behavior from their counterparts with half-integer spin. The consensus of a wide variety of numerical evidence is in support of the Haldane prediction. However, one aspect which has been particularly difficult to confirm has been the behavior in the vicinity of the critical point Δ=Δ2. The point Δ2 is predicted to be a second-order transition in the universality class of the transverse Ising model at its critical field. It has been numerically established that at Δ=Δ2∼1.18–1.20, the Haldane gap disappears and an excited SzT=0 state becomes degenerate with the SzT=0 ground state for Δ≥Δ2. The mapping to the transverse Ising model implies the existence in the limit N→∞ of an infinite continuum of scaling states quasi-degenerate with the ground state(s) at Δ=Δ2. Numerical calculations to determine the presence of these scaling states have been performed up to N=12 spins for the spin-1 XXZ model. The development of this scaling continuum is only apparent for large N, when a class of k=0, SzT=0 high-lying spectral excitations develop a minimum in the vicinity of Δ∼1.18 which intensifies with increasing N. These excitations extrapolate well below the lower edge of the triplet continuum, and we conclude these are the Haldane scaling states. This conclusion is reinforced by a detailed study of the corresponding excitations for the spin-1/2 transverse Ising model. However, we also find a class of k=0, ||SzT||=1 excitations which show similar scaling behavior in the vicinity of Δ2. These states were not included in the Haldane prediction. The implications for the behavior of the correlation functions at Δ2 are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.340716
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  • 5
    Digitale Medien
    Digitale Medien
    Nonintegrability and quantum spin chains (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3950-3952 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This study concerns the concept of nonintegrability in quantum many-body systems, which is related to the important and unresolved problem of quantum chaos. Our findings strongly indicate that nonintegrability affects the reliability of many approximation techniques which have proved to be successful in the study of integrable models. This report is based on finite-size studies of the low-lying spectral excitations of both integrable and nonintegrable 1D quantum spin models. In integrable cases, the characteristic excitation pattern of the infinite system is apparent even in relatively short chains. This is generally not the case in nonintegrable systems where we observe several classes of excitations with qualitatively different character. In some situations, the nature of the lowest-lying excitations actually changes with increasing system size, which makes finite-size studies very vulnerable to misleading conclusions if care is not taken.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.338594
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    Volltext
  • 6
    Digitale Medien
    Digitale Medien
    Classical spin clusters: Integrability and dynamical properties (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4438-4440 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A pair of exchange-coupled classical spins with biaxial exchange and single-site anisotropy represents a Hamiltonian system with two degrees of freedom for which the integrability question is nontrivial. We have found that such a system is completely integrable if the model parameters satisfy a certain condition. For the integrable cases, the second integral of the motion (in addition to the Hamiltonian), which guarantees integrability, is determined explicitly. It can be reconstructed numerically by means of time averages of dynamical variables over all trajectories. In the nonintegrable cases, the existence of the time averages is still guaranteed, but they no longer define an analytic invariant, and their determination is subject to long-time anomalies. Our numerical calculation of time averages for two lines of initial conditions reveals a number of interesting features of such nonanalytic invariants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.338402
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  • 7
    Digitale Medien
    Digitale Medien
    A laser-induced fluorescence and information-theory investigation of energy transfer processes in benzene–argon collisions (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 810-821 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: This paper reports the results of an extensive study of the internal energy-transfer processes that occur in benzene–argon collisions. We used laser-induced fluorescence and information theory for determining the energy-transfer rates between internal states of benzene in the ground electronic state (1A1g). The method provides an estimate for the rate of rotational relaxation. It gives a measure of the fraction of molecules that absorb the laser radiation at a frequency near the center of the ν18 absorption band of benzene. The use of information theory gives estimates for all of the vibrational energy transfer rates. These fit the experimental data reasonably well. However, some of the data do deviate from the information theory model. This suggests that the statistical assumptions of the model are not sufficiently restrictive. One such restriction may be in the number of vibration quanta changing per collision..
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.448507
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  • 8
    Digitale Medien
    Digitale Medien
    Two-laser resonance-enhanced photoionization spectrum of benzene (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3490-3497 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: This paper reports results of an experiment involving two-laser resonance-enhanced photoionization of benzene. The excitation sources were two frequency-doubled dye lasers. The first laser pumped the molecule to a selected vibronic level of its first excited singlet state (1B2u), from where it was ionized by a time-delayed pulse of the second laser. The ion yield depends on the intermediate vibronic state as well as on the wavelength of the ionizing laser. From the structures and intensities of the measured ion spectra we derived vibrational frequencies and molecular parameters of the ground electronic state of the ion to a remarkable accuracy. The contributions of autoionizing Rydberg levels to the ionization cross section can clearly be distinguished from direct ionization. Several resonance peaks were assigned to transitions to vibrational modes within these Rydberg states.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455859
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  • 9
    Digitale Medien
    Digitale Medien
    Heisenberg spin chains: Quantum-classical crossover and the Haldane conjecture (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3319-3321 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A comprehensive investigation has been made of the spectral excitations and static properties of Heisenberg antiferromagnetic chains of spin 1/2, 1, 3/2, and 2, using Lanczös, Bethe Ansatz, and Monte Carlo techniques. An unusual and unanticipated crossover mechanism for spin chains with 1/2≤S≤∞ has been discovered. The validity of the Haldane conjecture concerning the presence of a spectral excitation gap for integer-spin chains has been investigated by exact finite chains calculations of (a) the primary singlet-triplet excitation gap, (b) higher excitation gaps, and (c) the Fourier transform of the ground state correlation functions. A new Monte Carlo method has extended the spin-1 gap calculations to N=32.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.335134
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  • 10
    Digitale Medien
    Digitale Medien
    The iodine donor in ZnSxSe1−x alloys (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6322-6327 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The energy position of an iodine-related donor has been tracked through the alloyed system ZnSx Se1−x, where 0.60〈x〈1.00. Both optical and thermal energies have been measured with junction space-charge techniques. The results suggest that the optical threshold energies and lattice-relaxation effects are almost independent of x, although the activation energy of the thermal emission rate increases considerably with increasing x. Detailed measurements of the temperature dependence of the capture cross section for electrons show that the enthalpy of the iodine-related center is fairly constant for higher values of x.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.342093
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