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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Environmental geology 39 (2000), S. 1334-1340 
    ISSN: 1432-0495
    Schlagwort(e): Keywords China ; Geochemistry ; River ; Sediment ; Trace metals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  A total of 26 geographically and hydrologically diverse sediment samples were collected from 12 major rivers in eastern China. The 〈63-μm fraction of the sediments was analysed for both total concentrations of Cu, Zn, Pb and Cd, and their associations with various geochemical phases. The geographical variations of sediment-bound trace metals can be related to the bedrock types and weathering processes in the corresponding river basins. The rivers in southern China had notably higher concentrations of trace metals in sediments because of abundant non-ferrous mineral deposits and stronger weathering process in the region. A large proportion of trace metals in these sediments was associated with iron and manganese oxides and organic matter. Relative low levels of trace metals were found in river sediments in northern China, and a significant proportion of the metals was bound to organic matter, carbonates, and the residual fraction. The sediments in the Yellow River, originating from special loess, had the lowest concentrations of trace metals. Most of the trace metals were associated with the carbonates and residual phases.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of environmental contamination and toxicology 65 (2000), S. 343-350 
    ISSN: 1432-0800
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik , Medizin
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 105 (1991), S. 0 
    ISSN: 1365-246X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Splitting functions retrieved from spectra of the free oscillations are sensitive to the lateral variations in P velocity (α), S velocity (β), and density (ρ) simultaneously. In this study they are used to constrain the values of the ratios d ln α/d ln β and d ln ρ/d ln α for the lower mantle. Assuming that the upper mantle structure is obtainable from model M84A (this is not a crucial assumption as experiments indicate), the optimal value of d ln α/d ln β inferred from the modal data is 0.44 and d ln α/d ln β lies in the interval (0.39, 0.60) with 75 per cent confidence, strongly discriminating against the value (0.8) often used. The constraints on density structure of the current data are insufficient to yield new definitive results. The analysis demonstrates, however, that the value of d ln ρ/d ln α could be estimated from a larger set of modal data.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Journal of Chromatography A 667 (1994), S. 219-223 
    ISSN: 0021-9673
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Engineering with computers 12 (1996), S. 120-141 
    ISSN: 1435-5663
    Schlagwort(e): Discontinuous Galerkin ; Error estimation adaptivity ; Postprocessing ; Superconvergence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau , Technik allgemein
    Notizen: Abstract The paper discusses error estimation and h-adaptive finite element procedures for elasticity and plasticity problems. For the spatial discretization error, an enhanced Superconvergent Patch Recovery (SPR) technique which improves the error estimation by including fulfillment of equilibrium and boundary conditions in the smoothing procedure is discussed. It is known that an accurate error estimation on an early stage of analysis results in a more rapid and optimal adaptive process. It is shown that node patches and element patches give similar quality of the postprocessed solution. For dynamic problems, a postprocessed type of error estimate and an adaptive procedure for the semidiscrete finite element method are discussed. It is shown that the procedure is able to update the spatial mesh and the time step size so that both spatial and time discretization errors are controlled within specified tolerances. A time-discontinuous Galerkin method for solving the second-order ordinary differential equations in structural dynamics is also presented. Many advantages of the new approach such as high order accuracy, possibility to filter effects of spurious modes and convenience to apply adaptive analysis are observed. For plasticity problems, some recent work that improved plastic strains and plastic localization is discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Hyperfine interactions 62 (1990), S. 219-224 
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The hyperfine fieldsH f(T), center shifts δ(T) and relative recoilless fractionsf a(T) at different lattice sites of barium ferrite were determined by Mössbauer spectroscopy of57Fe over a temperature range from 12 to 723 K. For ferric iron in the crystalline site (2b), the recoilless fractionf a(T) decreases most with increasing temperature in comparison with that of other sites, corresponding to a characteristic temperature {ie219-1}. These results indicate that the ferric iron in the site (2b) oscillates between two equivalent positions (4e) on either side of the symmetry plane normal to thec-axis.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 12 (1993), S. 179-181 
    ISSN: 1573-4811
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 3585-3603 
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In the paper we present a postprocessed type of a posteriori error estimate and a h-version adaptive procedure for the semidiscrete finite element method in dynamic analysis. In space the super-convergent patch recovery technique is used for determining higher-order accurate stresses and, thus, a spatial error estimate. In time a postprocessing technique is developed for obtaining a local error estimate for one step time integration schemes (the HHT-α method). Coupling the error estimate with a mesh generator, a h-version adaptive finite element procedure is presented for two-dimensional dynamic analysis. It updates the spatial mesh and time step automatically so that the discretization errors are controlled within specified tolerances. Numerical studies on different problems are presented for demonstrating the performances of the proposed adaptive procedure.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 2131-2152 
    ISSN: 0029-5981
    Schlagwort(e): discontinuous Galerkin finite element method ; predictor-multicorrector ; adaptive time integration ; structural dynamics ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: This paper studies a time-discontinuous Galerkin finite element method for structural dynamic problems, by which both displacements and velocities are approximated as piecewise linear functions in the time domain and may be discontinuous at the discrete time levels. A new iterative solution algorithm which involves only one factorization for each fixed time step size and a few iterations at each step is presented for solving the resulted system of coupled equations. By using the jumps of the displacements and the velocities in the total energy norm as error indicators, an adaptive time-stepping procedure for selecting the proper time step size is described. Numerical examples including both single-DOF and multi-DOF problems are used to illustrate the performance of these algorithms. Comparisons with the exact results and/or the results by the Newmark integration scheme are given. It is shown that the time-discontinuous Galerkin finite element method discussed in this study possesses good accuracy (third order) and stability properties, its numerical implementation is not difficult, and the higher computational cost needed in each time step is compensated by use of a larger time step size.
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 9 (1993), S. 273-292 
    ISSN: 1069-8299
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A simple a posteriori local error estimator for time discretization in structural dynamic analysis is presented. It is derived from the difference of the solutions between an ordinary integration method (the Newmark scheme) and another higher-order one which assumes that the derivatives of accelerations vary linearly within each time step. It may be obtained directly without resolving new equations, so the additional computational cost is small and the implementation is convenient. Furthermore, it is shown that this error estimator may also be obtained by Taylor expansion or by a post-processing technique. Accordingly, an adaptive time-stepping procedure, which automatically adjusts the time-step size so that the local error at each time step is within a prescribed accuracy, is described. Numerical examples, including two single-DOF problems, a two-DOF problem and a multi-DOF model, are presented. The results show that the presented local error estimator is simple, reliable and accurate.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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