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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 14 (1998), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Recently, there has been interest in the occurrence of bromide (Br-) in natural waters since it has been demonstrated that Br-, in association with humic substances in raw waters, is readily incorporated into haloacetic acids in the form of organically bound bromine (Br) during water chlorination. We report results of the effects of experimentally rewetting a naturally drained gully mire on the hydrochemistry of Br-, iron (Fe) and dissolved organic carbon (DOC) in the peat water. Results obtained over a three year period showed that rewetting substantially increased the concentrations of these solutes in the pore water, with peak values of 1 mg dm-3 (Br-), 〉 60 mg dm-3 (Fe) and 〉 300 mg dm-3 (DOC) detected in some samples after rewetting, compared with typical values 〈 0.05 mg dm-3 (Br-), 〈 1 mg dm-3 (Fe) and 〈 15 mg dm-3 (DOC) under the drained conditions. Bromide, Fe and DOC release were highly seasonal, with the largest concentrations observed in late-summer to autumn. However, whereas seasonal peak concentrations of Fe and DOC have since remained at these higher levels, seasonal peak concentrations of Br- were progressively attenuated over time, suggesting the latter phenomenon is a flush effect, with no longer-term consequences for water quality.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 90 (1968), S. 648-651 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 37 (1965), S. 1240-1241 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Continuity conditions are derived for a fault modelled as a plane with isolated areas of slip. These slip areas are, for simplicity, taken to be such that their overall effect is that of a distribution of circular cracks; discontinuities in both normal and tangential components of displacement are allowed, depending on the internal conditions. Dry (gas-filled), partial or saturated liquid fill, or a fill of a weak visco-elastic solid are possible within the theory. the results are given in terms of the mean wave, which, at wavelengths long compared with the scale-lengths of the fault structure, is an accurate approximation to the displacement field. the continuity conditions that arise under this scheme are identical to those for a thin layer of visco-elastic material. However, unlike earlier, more empirical models of an ‘averaged’ fault, the parameters involved are directly related to the fault structure and include crack-crack interactions. It is clear from earlier work that a fault of this type is capable of supporting Stoneley waves.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 124 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: This paper studies the effect on the overall properties of a cracked solid of the existence of connections between otherwise isolated cracks and of small-scale porosity within the ‘solid’ material. The intention is to provide effective medium models for the calculation of elastic wave propagation with wavelengths greater than the dimensions of the cracks. The method follows that of earlier papers in which the overall elastic properties are directly related to parameters governing the microstructure, such as crack number density and the mean radius and spacing distance of the cracks. Expressions derived by the method of smoothing are evaluated to second order in the number density of cracks, thereby incorporating crack–crack interactions through both the strain field in the solid and the flow field of fluids in the pores.Flow of interstitial liquids tends to weaken the material; the limit of zero flow is equivalent to isolating the cracks and the limit of free flow is equivalent to dry (gas-filled) cracks. It also introduces additional attenuation. The inclusion of small-scale porosity gives a model of ‘equant porosity’ which is more closely constrained by the details of crack dynamics than earlier models.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 121 (1995), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Elastic scattering from a continuous and laterally unbounded heterogeneous layer has been formulated using the Born approximation. A general solution of the scattered wave equation for the above-stated medium has been given in terms of a Fourier integral over plane waves. Far-field asymptotic expressions for weak elastic scattering by a finite, continuous and inhomogeneous layer have been presented which agree with earlier results. For perturbations of the two elastic parameters and the density having the same form of spatial variation, the spectrum of plane waves scattered from a heterogeneous layer is expressed as a product of an ‘elastic scattering factor’and a ‘distribution factor’. As in earlier results for small-scale heterogeneity, the scattering pattern depends on various combinations of perturbations of elastic parameters and density. In order to show the general characteristics of the elastic wave scattering, some scattering patterns have been given.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: In this paper, we develop an elastodynamic energy transport theory to form expressions for energy transmission through a heterogeneous continuum of large extent. A model of multiple scattering for a random elastic continuum is constructed by an iterative method based on single scattering by a thin heterogeneous layer or screen. This model is available both for strong scattering and for weak scattering, and both for common-type scattering (P-P and S-S) and for converted scattering (P-S and S-P), although here we assume high frequencies so that only forward scattering and common-type scattering are considered. Numerical results have been obtained in terms of the angular spectrum of the energy flux in successive orders of scattering. These results show that coda waves in seismograms mainly come from the scattering of S waves. They also indicate the limits within which first-order scattering can be used, and when, on the other hand, the scattered radiation is dominated by multiple scattering. The results are directly applicable to measurements of seismic energy flux in frequency-surface-wavenumber space.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 102 (1990), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The method of smoothing has lead to the calculation of overall or effective elastic parameters for wave propagation in material containing cracks, valid to second order in the number density of the cracks. Wavespeeds are obtained for wavelengths long compared with crack dimensions by working to the lowest order in frequency. To find the attenuation due to scattering of energy out of the mean wave, calculations to higher order in frequency are necessary and, up to now, attenuation has been obtained by summing over the scattering cross-sections of the cracks, thus neglecting any crack-crack interactions. Here we evaluate scattering attenuation to higher order in the series obtained from the smoothing approximation in order to allow for multiple scattering. It turns out that, for crack radii and crack spacing small compared with a wavelength, the term of lowest order taken from the double scattering component exactly cancels out the sum over scattering cross-sections, leaving only higher order terms to account for attenuation due to scattering. In other words, the effective material parameters contain no attenuation component arising from scattering.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 116 (1994), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The method of smoothing, already applied to isotropic material containing circular cracks, is here applied to the case of circular cracks within an anisotropic matrix. Expressions for the overall elastic parameters are given, as usual, correct to the second order in the number density of cracks. Interior conditions on the cracks may be selected from a range of models as before.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 107 (1991), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Small-scale heterogeneity in crustal structure can be very complex and difficult to describe in detail and yet, at the same time, can be very important for the description of, for instance, tectonic stress and porosity. Statistical properties of such heterogeneity can be derived from the properties of waves of relatively large wavelength as they propagate through the crust. The differences between measured wavelengths and attenuation coefficients and those of compact rock and the variations of these quantities in space and time provide, in principle, a means of determining quantities like the density and orientations of microfractures and the nature of crack infill material. The theoretical basis for inferences of this kind is the concept of the ‘effective’ or ‘equivalent’ material based on an averaging process taken over the microstructure. A number of methods have been used to calculate the properties of the effective medium, several of which are described here.
    Type of Medium: Electronic Resource
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