ALBERT

Notes: Abstract —We investigate a new nonlinear inversion method for low frequencies to determine the bulk and shear modulus as well as the material density and the location of subsurface inhomogeneities. The solution is a direct exact nonlinear inversion of single scattered waves containing near- and far-field terms for incident P and scattered P and S waves, allowing for inversion of parameters in the vicinity and at distance from the sources and receivers. Because the approach is based on single scattering theory, the range of application includes single strong scattering anomalies of various sizes like magma chambers, gas- or fluid-filled cavities, or buried near-surface obstacles. The replacement of the material properties by a new set of parameters, referred to as scattering factors, allows the inverse problem to be solved analytically. The nonlinear nature of the scattering problem is investigated and implications for the inversion process are discussed. The deviations in the elastic parameters as a function of the scattering factors show a strong asymmetry about zero, and therefore linearized approximations will perform differently, depending on the sign of the perturbation. Based on the low frequency (Rayleigh) approximation, we introduce and evaluate a pair of approximations (Mie) derived by numerical and analytical integration of the Rayleigh approximation. Both approximations are based on the underlying principle of subdividing the inhomogeneities into a number of small noninteracting parts and subsequent integration over the total volume, thus increasing the Rayleigh limit and producing better resolution of the parameter estimates during the inversion. The two Mie approximations, when evaluated as a function of scattering angle and distance, produce similar results in the mid- and far-field of the inhomogeneity and reveal better resolution than the Rayleigh approximation. For three anomalies of ± 50% in bulk modulus, shear modulus, and density, the relative error between the exact solution and the two Mie approximations remains below 10%, 20%, and 30%, respectively, for values of k p R 〈 3.0, where R is the radius of the heterogeneity. However, smaller errors for individual cases are found for values up to k p R≈ 4.5. The performance of the inversion based on the analytically and the numerically integrated Mie approximation is tested for single parameter perturbations, revealing reliable and stable inversion results for the bulk and the shear modulus, reasonable results for the density, and crosstalk between the shear modulus and the density. The results show well-defined locations of the anomalies and slight deviations in the estimates of their magnitudes, which can be explained by amplitude and phase deviations between the analytical solution used for forward modeling and the approximations used for the inversion. The analytical Mie approximation provides a fast means to estimate elastic parameters compared to the more time consuming numerically integrated approximation, while the latter can be applied to more arbitrarily shaped inhomogeneities.

Notes: [Auszug] Fig. 1 Location of cores, C. Cl, BM1973,0,l; C2, BM1973, 0,2; C3, BM1973,0,3; C17, BM1973,0,17. 1963,544 is a British Museum valve lead sample. Fig. 2 Sedimentology of the cores, a, Orange-yellow ooze; b, layer of black manganese-encrusted tubes in light brown ooze; c, layer of brown ...

Notes: [Auszug] Fig. 1 Partial track of the MV Cyclops. Solid line, UK-Japan run; broken line, Japan-UK run. Detritus samples were collected over the intervals indicated by the lines perpendicular to the track; #, central positions of sampling sites. Less is known, however, about the origin of montmorillonite. ...

Notes: [Auszug] Table 1 Trace Element Content of the North Atlantic Aeolian Dusts Collection Dust Potential Trace element contents (p. p. m., except Fe2O3 which is given in wt. %) Total area sample * source area Mn Fe203 Cu Ni Co Cr V Ba Sr carbonate (wt. %) M14 UK ...

Notes: We have observed an anomalous behavior of reverse-bias leakage current in Hg1−xCdxTe n+-on-p photodiodes at 77 K as a function of total 10 MeV electron dose. For ZnS/SiO2 passivated planar configurations of photodiodes with 0.25〈x〈0.5, the leakage current increases superlinearly with increasing total dose greater than 10 krad, saturates at doses between 100 and 200 krad, followed by a dramatic recovery that is sometimes complete to near-preradiation values. For x(approximately-equal-to)0.2, very little or no recovery is observed. The effects of 60CO gamma irradiation are nearly identical.

Notes: We have developed a new approach to the inversion of waveform data for the time-varying moment tensor. the method produces the source model which minimizes the modulus squared of any linear combination of moment tensor components, subject to the constraint that the data are satisfied within specified confidence intervals. This method allows the determination of possible source models other than the least-squares solution, enabling one to determine the significance of certain moment tensor properties; for example, the presence or absence of a volume change (isotropic component) in the source. Synthetic tests were used to examine the effect of microseismic noise and lateral heterogeneity on the extreme models of the isotropic component. Lateral heterogeneity is found to have a strong effect on the estimation of the isotropic component of the moment tensor. the method was tested by using long-period waveforms from the Global Digital Seismic Network to estimate the isotropic part of the moment tensor of a deep Bonin Islands earthquake. Modelling indicates that more than 10 per cent of the mechanism might have to be isotropic for detection of volume change in the presence of 10 per cent random noise and only 2 per cent lateral heterogeneity. the least-squares solution indicates that a relatively large change in volume was involved in the source mechanism. However, the minimum extreme solution shows that this volume change is not actually required by the data and thus may not be significant. the method was also tested on near-source data from the nuclear explosion Harzer. In this case, in spite of fairly large error bounds, it can be concluded that the source has a clear explosive component.

Notes: By means of several low temperature devices the solid hydrous phases of the AgI–NaI–H2O system have been extensively studied by X-ray diffraction, transmission Laue photography, and polarizing microscopy. The density, composition and unit-cell parameters have been determined for three distinct AgI–NaI hydrates for which the stability regions correspond to phases C, E, and F previously reported by Davis [J. Atmos. Sci. (1969), 26, 1042]. The cell assignments are based on determinations of axial ratios from the Laue photographs and interplanar spacing analyses utilizing the Hesse–Lipson technique, Cohen cell-parameter refinement and the de Wolff cell-reliability criteria. All phases are of the composition AgI–NaI–nH2O with phase C at 25 °C having n = 4, ρ = 3.0 g.cm−3 (measured and calculated) and indexing on the basis of a monoclinic cell with parameters a0 = 7.573, b0 = 9.454, c0 = 12.403 Å, and β = 92.43° with Z = 4. Phase F at −10 °C is also monoclinic with a0 = 5.757, b0 = 13.563 and c0 = 12.541 Å and β = 103.05° with Z = 4, and n = 4. Phase E appears to consist of two structures, very similar but differing in cell volume by 2.8%. We believe this to be due to varying water content, the n = 3 phase being metastable. The cell reliability factor is less than 10 for both cells and indexing is considered to be tentative.