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  • 1
    Series available for loan
    Series available for loan
    Localisation of induced microseismicity in anisotropic media (2004)
    Hamburg : DGMK
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    Call number: S 97.0506(593-3)
    In: Tight gas reservoirs - natural gas for the future
    Type of Medium: Series available for loan
    Pages: 52 S.
    ISBN: 3936418209
    Series Statement: 593-3
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    Heat capacity data of doped NdBa2Cu3Ox : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6317-6319 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature specific-heat measurements were performed between 0.4 and 4 K on Nd–Ba–Cu–O-samples doped with Ca and additional Nd. In these samples, the specific-heat anomaly due to magnetic ordering of the Nd3+ ions as a function of hole concentration behaves similarly to that of oxygen-deficient NdBa2Cu3Ox. In samples with 0〈Tc〈70 K, a broad anomaly due to short range magnetic interaction was found but no indication for long range magnetic ordering could be observed. In the semiconducting samples, 3D-Ising-like anomalies with TN around 1.6 K were measured. In order to explain the behavior of the magnetic anomaly in the oxygen-deficient undoped samples, one could assume that the magnetic interaction depends on lattice parameters or interatomic distances. Our newest results clearly show, however, that the position and shape of the anomaly is mainly controlled by the density of carriers in the superconducting CuO2 planes, and not by structural properties. Thus, the magnetic rare-earth ions are isolated enough from the CuO2 planes not to influence superconductivity (except for Pr), but are not totally decoupled from the rest of the unit cell and the carrier concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352685
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  • 3
    Electronic Resource
    Electronic Resource
    Traveltime computation for 3D anisotropic media by a finite-difference perturbation method (2003)
    PO Box 1354, 9600 Garsington Road , Oxford OX4 2XG , UK . : Blackwell Publishing Ltd
    Geophysical prospecting 51 (2003), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The first-order perturbation theory is used for fast 3D computation of quasi-compressional (qP)-wave traveltimes in arbitrarily anisotropic media. For efficiency we implement the perturbation approach using a finite-difference (FD) eikonal solver. Traveltimes in the unperturbed reference medium are computed with an FD eikonal solver, while perturbed traveltimes are obtained by adding a traveltime correction to the traveltimes of the reference medium. The traveltime correction must be computed along the raypath in the reference medium. Since the raypath is not determined in FD eikonal solvers, we approximate rays by linear segments corresponding to the direction of the phase normal of plane wavefronts in each cell. An isotropic medium as a reference medium works well for weak anisotropy. Using a medium with ellipsoidal anisotropy as a background medium in the perturbation approach allows us to consider stronger anisotropy without losing computational speed. The traveltime computation in media with ellipsoidal anisotropy using an FD eikonal solver is fast and accurate. The relative error is below 0.5% for the models investigated in this study. Numerical examples show that the reference model with ellipsoidal anisotropy allows us to compute the traveltime for models with strong anisotropy with an improved accuracy compared with the isotropic reference medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.2003.00385.x
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  • 4
    Electronic Resource
    Electronic Resource
    Reference ellipsoids for anisotropic media (2001)
    Oxford, UK : Blackwell Science Ltd
    Geophysical prospecting 49 (2001), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Perturbation methods are common tools for describing wave propagation in weakly anisotropic media. The anisotropic medium is replaced by an average isotropic medium where wave propagation can be treated analytically and the correction for the effect of anisotropy is computed by perturbation techniques. This works well for anisotropies of up to 10%. Some materials (e.g. shales), however, can exhibit a much stronger anisotropy. In this case a background is required which still can be treated analytically but is applicable to stronger P-wave anisotropy. We present an averaging technique to compute a best-fitting ellipsoidal medium to an arbitrary anisotropic medium. Ellipsoidal media are sufficiently simple for analytical expressions to be available for many applications and allow consideration of strong P-wave anisotropy. The averaging of the arbitrary anisotropic medium can be carried out globally (i.e. for the whole sphere) or sectorially (e.g. for seismic waves propagating predominantly in the vertical direction). We derive linear relationships for the coefficients of the ellipsoid which depend on the elastic coefficients of the anisotropic medium. We also provide specifications for best-fitting elliptical and best-fitting isotropic media. Numerical examples for different rocks demonstrate the improved approximation of the anisotropic model obtained using the formulae derived, compared with the conventionally used average isotropic medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.2001.00256.x
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  • 5
    Electronic Resource
    Electronic Resource
    A new constraint on the composition of the topmost continental mantle—anomalously different depth increases of P and S velocity (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 103 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Compared to clear crustal P- and S-waves as well as a strong refracted Pn-wave propagating in the topmost mantle (i.e., 10 to 15 km below the Moho), an anomalously weak appearance of the corresponding refracted shear wave Sn is observed on refraction seismic profiles in SW Germany, France, coastal Maine (NE United States) and Fennoscandia. It is possible that the observation of Pn/PMP ratios close to unity combined with small Sn/SMS ratios (i.e., small Sn amplitudes) is typical for the continental uppermost mantle since this was observed for quite different types of continental crust. It is shown that the observed phenomenon is not a source effect. Several possible causes to explain the observations are studied, also with the aid of synthetic seismograms. The effects of temperature, attentuation and anisotropy have been investigated. Their influence cannot explain the observations. The most likely candidate is a depth-increasing VP/VS ratio (an increase in the order of 0.027 over a depth range of 10 km), forcing P- and S-waves to propagate on different paths in the topmost mantle. The observed phenomenon provides new constraints on the change of composition with depth for the crust mantle transition zone with basalt depletion as the most likely explanation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb01787.x
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  • 6
    Electronic Resource
    Electronic Resource
    Localized vibrational modes in metallic solids (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 395 (1998), S. 876-878 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Filled skutterudite antimonides, are cubic compounds with the formula RM4Sb12, where R is a rare-earth element (such as La or Ce), and M is a transition metal (for example, Fe or Co). The rare-earth ion is weakly bound in an oversized atomic cage formed by the other atoms. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/27625
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  • 7
    Electronic Resource
    Electronic Resource
    Ray synthetic seismograms for a 3-D anisotropic lithospheric structure
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 51 (1988), S. 1-23 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(88)90017-9
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  • 8
    Electronic Resource
    Electronic Resource
    An Attempt to Integrate Reflection Seismics and Balanced Profiles (1999)
    Springer
    Pure and applied geophysics 156 (1999), S. 207-232 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Balancing, reflection seismic, modelling, prestack depth migration, velocity determination.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Different techniques in Geophysics and Geology are used to derive the structure of the subsurface. They are based on different data sets, i.e., seismic and geological data, and a combination of these techniques should produce better earth models. The case study presented in this paper is based on data of the German Continental Reflection program (DEKORP) collected in the Münsterland basin and the Rhenish Massif located at the northern border of the Rhenohercynian fold and thrust belt of the Mid-European Variscides. In this study we present an attempt to integrate balanced profiles, i.e., structural geology, and reflection seismics. The integration is performed by synthetically modelling seismic waves according to the acquisition of the field data, where the velocity model is based on the balanced profile. The synthetic data are compared with the field observations. Differences between observed data and field data are either caused by velocity errors in the model or by errors in the balanced profile. Criteria are developed to interpret these differences in order to improve the joint model of geologists and geophysicists. The case study presented in this paper shows that the combination of balanced profiles and reflection seismics may lead to shortcuts in the determination of seismic velocities of the subsurface. These shortcuts can reduce processing times and processing costs of reflection seismic data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050297
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  • 9
    Electronic Resource
    Electronic Resource
    Wave front construction in smooth media for prestack depth migration (1996)
    Springer
    Pure and applied geophysics 148 (1996), S. 481-502 
    Details
    ISSN: 1420-9136
    Keywords: Kirchhoff migration ; ray tracing ; wave front construction ; perturbation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We implemented a wave front construction algorithm specifically designed for smooth media for application to prestack depth migration. The highest priority was given to maximum computational speed to allow an extension of the techniques to 3D media. A simple grid-based model representation in combination with fast bilinear interpolation is used. It is shown that this procedure has no distorting effects on the ray tracing results for smooth media. In our implementation, wave front construction (WFC) has proven to be as fast as some of the recently developed methods for travel time computations. WFC has advantages over these methods, since amplitudes and other ray theoretical quantities are available, and it is not restricted to the calculation of only first arrivals. Thus, it meets the requirements for migration in complex media. Furthermore, WFC allows for introduction of a perturbation scheme for computing travel times for slightly varying models simultaneously. This has applications for, e.g., prestack velocity estimation techniques. The importance of later arrivals for migration in complex media is demonstrated by prestack images of the Marmousi data set.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874576
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  • 10
    Electronic Resource
    Electronic Resource
    Non fermi liquid ground states in strongly correlated f-electron materials (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 223-249 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experimental efforts to characterize and develop an understanding of non Fermi liquid (NFL) behavior at low temperature in f-electron materials are reviewed for three f-electron systems: M1−xUxPd3 (M = Sc, Y), U1−xThxPd2Al3, and UCu5−xPdx. The emerging systematics of NFL behavior in f-electron systems, based on the present sample of nearly ten f-electron systems, is updated. Many of the f-electron systems exhibit the following temperature dependences of the electrical resistivity p, specific heat C, and magnetic susceptibility χ for T ≪ T0, where To is a characteristic temperature: P(T) ∼ 1 –aT/T 0, where a 〈 0 or 〉 0, C(T)/T ∼ (-1/T o) In (T/bT 0), and χ(T) ∼ 1 −c(T/To)1/2. In several of the f-electron systems, the characteristic temperature To can be identified with the Kondo temperature Tk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752290
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