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  • 1
    Monograph available for loan
    Monograph available for loan
    The art of being a scientist : a guide for graduate students and their mentors (2009)
    Cambridge [u.a.] : Cambridge Univ. Press
    Details Availability
    Call number: AWI S6-14-0059 ; 2/N 14.0263
    Description / Table of Contents: "This is a hands-on guide for graduate students and other young researchers wishing to perfect the practical skills that are needed for a successful career in research. By teaching junior scientists to develop effective research habits, the book helps make the experience of graduate study a more efficient, effective and rewarding one. Many graduate students learn these skills "on the job", often by doing them poorly at first, with the result that much valuable time can be lost; this book will help prevent that. The authors have taught a graduate course on the topics covered in this book for many years, and provide a sample curriculum for instructors in graduate schools who wish to teach a similar course. ... The wealth of advice offered in this book is invaluable to students, junior researchers and their mentors in all fields of science, engineering and the humanities."
    Type of Medium: Monograph available for loan
    Pages: X, 286 S. : Ill., graph. Darst.
    Edition: 1. publ. 2009, 5th print. 2013
    ISBN: 9780521743525
    Classification:
    E.7.
    Language: English
    Note: Contents: 1 Introduction. - 2 What is science?. - 3 Choices, choices, choices. - 4 The adviser and thesis committee. - 5 Questions drive research. - 6 Giving direction to our work. - 7 Turning challenges into opportunities. - 8 Ethics of research. - 9 Using the scientific literature. - 10 Communication. - 11 Publishing a paper. - 12 Time management. - 13 Writing proposals. - 14 The scientific career. - 15 Applying for a job. - 16 Concluding remarks. - Appendix A. Futher reading. - Appendix B. A sample curriculum. - Appendix C. The Refer and BibTeX format. - References. - About the authors. - Index.
    Location: AWI Reading room
    Location: Reading room
    Branch Library: AWI Library
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    The contrast in upper mantle shear-wave velocity between the east european platform and tectonic Europe obtained with genetic algorithm inversion of rayleigh-wave group dispersion (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 123 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The stable, Precambrian East European Platform adjoins the younger, tectonically active regions of central and western Europe along a distinct crustal boundary, the Tornquist-Teisseyre Zone (TTZ). Seismic body- and surface-wave studies indicate that there may be a significant change in S-wave velocity at the top of the mantle in the region of the TTZ, with higher velocities under the East European Platform. to confirm these results we use a genetic algorithm (GA) to invert fundamental Rayleigh group-velocity estimates for wave paths across western and central Europe and across the East European Platform to determine ‘average’layered S-velocity models separately for each region. the use of the GA method allows identical model parametrizations and broad parameter search ranges to be used for both regions so that a relatively unbiased estimate of the difference in structure can be obtained.The GA is a guided search technique which requires neither a linearized forward method nor a single starting model and which can be applied to very large model-spaces. Consequently, fewer assumptions and physical approximations are required and a greater range of possible solutions is examined than with many other inversion methods. Here we employ the GA to produce a large set of acceptable solutions and associated misfit values, in contrast to inversion for a single, ‘optimum’solution. the scatter in the set of acceptable solutions gives an estimation of uncertainty, resolution and parameter trade-offs of the non-linear inversion.The scatter of the solutions for the dispersion data shows velocity-depth trade-offs around the Mohorovičić discontinuity, indicates the maximum depth resolution of the inversion, and shows the uncertainty in upper mantle S-velocity estimates. the results indicate a thicker crust and up to 0.3 km s-1 (7 per cent) higher ‘average’S-wave velocities in the upper 100km of the mantle under the East European Platform than under western and central Europe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb06669.x
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  • 3
    Electronic Resource
    Electronic Resource
    Estimation of finite-frequency waveforms through wavelength-dependent averaging of velocity (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The wavelength-smoothing (WS) method was introduced recently (Lomax 1994) as a method for the rapid estimation of the principal features of broad-band wave phenomena in realistic., complicated structures. The WS method is based on the concept that waves at a particular frequency and corresponding wavelength respond to a complicated velocity distribution as if the distribution were smoothed over about a wavelength. This method reproduces several finite-frequency wave phenomena, but has not been given a formal theoretical justification. Here, we use scattering theory and a local, plane-wave approximation to develop a wavelength-averaging (WA) method for modelling finite-frequency wave propagation. The new WA method is similar to the WS method in concept and implementation, but is valid only in a more limited geometry of velocity heterogeneity. In particular, the new formulation performs well for models with complex, but smoothly varying, velocity variations (‘quasi-random’ models), but does less well in models with extensive regions of slowly varying velocity that are separated by strong gradients in velocity (‘deterministic’ models). This limits application of the current formulation of the WA method to predominantly quasi-random structures, although such models may be useful in many problems, particularly for Monte-Carlo-based inversion methods requiring fast forward calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb05297.x
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  • 4
    Electronic Resource
    Electronic Resource
    A unified approach to ray bending, ray perturbation and paraxial ray theories (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 115 (1993), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: In the past, perturbation theory has been formulated for the case that either a slowness model was perturbed and the effect of this perturbation on rays was determined, or for the case where the slowness was fixed and where estimates of the ray position were deformed towards the true ray. In this paper both problems are combined in a single perturbation theory. The theory also accommodates arbitrary perturbations to the endpoints of rays and leads to a simple linear differential equation for the ray perturbation. Expressions are derived for the second-order perturbation of the traveltime. This quantity describes the effect of the ray perturbation on the traveltime and of the bias in the traveltime due to the fact that the reference curve need not be a true ray. The second-order traveltime perturbation can be evaluated efficiently by a single integration along the reference curve. In contrast to formalisms using ray-centred coordinates, endpoints perturbations in an arbitrary direction are allowed. This is of importance in tomographic inversions which incorporate earthquake relocations. The cross-term between the slowness perturbations and the source relocations is derived explicitly. The fact that the reference curve does not need to be a true ray in the reference medium allows for an iterative application of ray perturbation theory. The use of the second-order traveltime perturbation allows one to correct for the bias in the traveltime due to the fact that the reference curve is not a ray. A proof is given that the equation for the ray perturbation is consistent with earlier results derived in ray-centred coordinates and the relation with the ray bending theory of Julian & Gubbins (1977) is established. For a fixed-slowness model and for fixed-ray endpoints the two theories are equivalent except at isolated points, this is illustrated with an analogy from classical mechanics. This difference, which results in superior numerical properties for the new algorithm, is illustrated by several numerical examples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb01199.x
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  • 5
    Electronic Resource
    Electronic Resource
    Are long-period body wave coda caused by lateral heterogeneity? (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 107 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: bData from two broad-band arrays in western Europe (NARS and GRF) are used to study the character of long-period body wave coda. The events studied are at epicentral distances of 40d̀ to 60d̀, in the Hindu Kush region and on the Mid-Atlantic Ridge, sampling the upper mantle to a depth of about 1000 km. The periods studied are 5-50 s. The long-period coda of P at GRF (interstation distance about 10 km) are strongly coherent, whereas the long-period coda of PP-, PPP- and S-waves are incoherent. This indicates that the latter coda consists of scattered waves. To investigate the nature of the scattering process, the data of GRF are analysed for slowness and azimuth variations in the coda intervals. A new beamforming algorithm is presented to deal with the low frequences and relatively short time intervals. The method is based on Backus-Gilbert inverse theory. The results show that the incoherent long-period coda intervals almost entirely consist of surface waves; these waves are scattered from the preceding body waves. Some calculations with linearized theory for body wave to Rayleigh wave conversion at topography at the surface or at the Moho show that realistic scatterers can account for the observed (constant) coda level. The beamforming results show that the phases in the P coda all arrive along the great circle. As scattering calculations point out that body wave to body wave scattering is inefficient, it is concluded that the long-period P coda does not contain a significant amount of scattered energy. Synthetic seismo-grams obtained with the reflectivity method show that spherically symmetric upper mantle models can explain these coda waves. For events in the Hindu Kush region, an upper mantle with a thick lid overlying a pronounced low-velocity zone (LVZ) is necessary to explain the character of the P coda at GRF. Such an upper mantle agrees with previous studies of similar great circle paths. The strong coherence of the P coda at GRF is lost on the scale of NARS (station separation about 200 km). This suggests lateral variations in the upper mantle at a scale of about 200 km. It appears from previous studies of the upper mantle under Europe that these variations must be sought in the LVZ. It is shown that the long-period P coda is sensitive to variations in the P velocity structure of the LVZ. This suggests the P coda (i.e. PdP phases) as a tool for monitoring lateral variations in the LVZ and possibly to prove the existence or absence of a LVZ in the P velocity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb01162.x
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  • 6
    Electronic Resource
    Electronic Resource
    The attenuation of surface waves due to scattering (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 98 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Surface wave attenuation is usually attributed to inelastic properties of the Earth, but a considerable part of the surface wave attenuation may be due to scattering by lateral heterogeneities. For body waves, the theory describing attenuation due to scattering is well known. In this paper, a similar theory is presented, which describes the attenuation of surface waves due to scattering. The Born approximation is used to derive the scattered wavefield, therefore only weak heterogeneities can be described. Some numerical experiments are performed for periods between 25 and 100 s. For realistic scatterers the conversions from the fundamental mode to the higher modes cannot be neglected. The Q−1 values computed for scattering media are of the same order of magnitude as measured Q−1 data. A whole range of attenuation curves as a function of frequency can be obtained by varying the parameters of the scattering experiment. This leads to believe that Q−1 data inversions to Q−1 depth models should be regarded with some suspicion, because the contribution of scattering to the attenuation cannot be neglected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb05523.x
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  • 7
    Electronic Resource
    Electronic Resource
    Topography of the 400 km discontinuity from observations of long-period P400P phases (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 109 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: New evidence is presented for lateral variation of the depth of upper mantle discontinuities. This evidence is derived from an analysis of amplitude of P400P phases (underside reflections from the 400 km discontinuity) for great circle paths with bounce points in the upper mantle near the Hawaii-Emperor hotspot chain. The data are long-period, from WWSSN, SRO and RSTN stations. The epicentral distance ranges from 95° to 115°, which ensures that no other major phases arrive in the time window of interest. Observed P400P amplitudes are compared with synthetic amplitudes for both a laterally homogeneous model and models including 3-D topography on the discontinuities. The observations permit models of topography that can be characterized by undulations of the 400 km discontinuity with wavelengths in the range 600–2000 km, and peak-to-peak amplitude of the order of 30–40 km. Such long-wavelength structure causes quite strong (de)focusing of PdP phases; synthetic PdP waveforms reveal that topography not only affects its amplitude, but also smears out the PdP wave, causing overlap between different PdP phases. This mechanism is proposed as the reason for the lack of well-developed PdP phases reported in the literature. The fact that the waveforms can be seriously distorted prohibits the use of PdP phases in a waveform inversion. The curvature of the discontinuity can be explained as the signature of convection currents crossing the discontinuity. Although the data cover the Hawaii hotspot, no signature of a plume structure can be detected in the data, probably because the resolving power of the data is too low.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00124.x
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  • 8
    Electronic Resource
    Electronic Resource
    Ray perturbation theory for traveltimes and ray paths in 3-D heterogeneous media (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 109 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Both paraxial ray tracing and two-point ray tracing are powerful tools for solving wave propagation problems. When a slowness model is mildly perturbed from a reference model, one can use perturbation theory for the determination of the ray positions and the traveltimes. An extension of Fermat's theorem is presented, which states that the traveltime is stationary with respect to the perturbations in the ray position provided that the endpoints of the ray are perturbed along the wavefront of the unperturbed ray. It is shown that when the ray perturbation satisfies this condition the second-order traveltime perturbation can be computed from the first-order ray perturbation. A perturbation analysis of the equation of kinematic ray tracing leads to a simple second-order differential equation for the ray deflection expressed in ray coordinates. This constitutes a perturbation method based on a Lagrangian formulation, and leads to a first-order expression for the ray deflection and a second-order expression for the traveltime perturbation. This is of relevance to non-linear traveltime tomography because it leads to an efficient method for evaluating the lowest order ray deflection and the non-linear effect this has on the traveltimes. The theory is applicable both to two-point ray tracing and to the determination of paraxial rays. The derivations in this paper are completely self-contained. All expressions, including the transformation to ray coordinates, are derived from first principles. In this way one obtains insight in the approximations that are actually made. A scale analysis leads to dimensionless numbers that give an indication whether the theory is applicable to a specific problem. For the special case of a layered reference medium the final equations are particularly simple. Plane discontinuities in the reference model and the slowness perturbation are incorporated in the theory. The final expressions for the ray deflection and the traveltime perturbation can be implemented numerically in a simple way. It is indicated how applications to very large-scale problems can be achieved. Several examples, including the propagation of waves through a quasi-random model of the earth's mantle illustrate the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00099.x
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  • 9
    Electronic Resource
    Electronic Resource
    Solving large linear inverse problems by projection (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: As originally formulated by Backus & Gilbert (1970), ill-posed linear inverse problems possess a unique minimum norm solution, and a locally averaged property of the model may be estimated with a resolution that is a monotonic function of its variance. Application of Backus–Gilbert theory requires the inversion of an N x N matrix, where N is the number of data, and therefore becomes cumbersome for large N. In this paper we show how Lanczos iteration may be used to project the original linear problem on a problem of much smaller size in order to obtain an approximation to the Backus–Gilbert solution without the need of matrix inversion. To calculate the resolution in the projected system one only needs to invert a symmetric tridiagonal matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb01792.x
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  • 10
    Electronic Resource
    Electronic Resource
    The reflection and transmission of plane P- and S-waves by a continuously stratified band: a new approach using invariant imbedding (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 96 (1989), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The reflection and transmission of plane P- and S-waves by a laterally homogeneous band is discussed. A dyadic representation of a ‘plane wave Green's tensor’ is derived, which is used to describe the reflection and transmission of plane waves by a thin homogeneous layer in the first Born approximation. From this, the reflection and transmission by an arbitrarily thick continuously stratified band is derived using invariant imbedding. We derive an exact set of matrix Ricatti equations which describe the reflection and transmission of plane waves by the laterally homogeneous band. These equations remain regular at turning points, and incorporate both homogeneous and inhomogeneous waves within the heterogeneity. It is not necessary for the band to be stratified; the density and the elasticity tensor of the band may have an arbitrary depth dependence. It is shown that in case the band is a smooth heterogeneity without turning points, its only effect is a phase shift of the transmitted wave. In a numerical example for the analogue case of 1-D scattering in quantum mechanics the behaviour of homogeneous and inhomogeneous (tunneling) waves is illustrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1989.tb06006.x
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