ALBERT

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.

Notes: A combination of X-ray powder diffraction and single-crystal Laue photography was used to determine the unit-cell parameters for letovicite. μr = 247.25. The unit cell is triclinic, P1 or P{\bar 1}, and has dimensions a0 = 5.87(1), b0 = 10.17(3), c0 = 8.27(1) Å, α = 101.1(4), β = 111.1(1), γ = 89.9(2)°, V = 450.7 Å3, Z = 2, Dx = 1.82 Mg m−3. The M(20) cell reliability is 23.8. Many weak powder spectra were observed, which preclude the possibility of monoclinic cell symmetry previously reported. Projection of the letovicite Laue data along [001] reveals the striking pseudo-hexagonal symmetry observed optically. The JCPDS Diffraction File No. for ammonium hydrogen sulfate is 35-1500.

Notes: Recently discovered errors in sample preparation for the original study by Davis & Johnson [J. Appl. Cryst. (1984). 17, 331–333] have revealed that the reference intensity ratio data of Table 1 are incorrect. The reference intensity ratios for the three sets of reflections given in Table 1 have been remeasured and are as follows: 020 + 1{\bar 1}0 = 1.92; 021 + 002 = 1.16; and 1{\bar 3}0 = 0.88. The resulting average reference intensity ratio for the letovicite 111 reflection (the strongest of the pattern) is 1.15(5). Fortunately, the reference constant study was completed independently of the powder diffraction and Laue study and hence the cell constants, diffraction intensities and spacings presented in this paper are not affected by these errors.

Notes: The density, composition, X-ray powder data, unit-cell parameters, and stability fields are reported for five phases of the AgI–NH4I–H2O chemical system. The determinations were made by X-ray powder diffraction but with some aid from polarizing optical microscopy. Provisional cell assignments are: phase An (4AgI.NH4I) is cubic, phase Bn (3AgI.NH4I.6H2O) monoclinic, phase Cn (AgI.2NH4I) orthorhombic, phase E〈inf/〉n (AgI.2NH4I.H2O) orthorhombic, and phase Fn (2AgI.NH4I.2H2O) monoclinic. Upon combustion of an acetone solution of silver iodide and ammonium iodide, phase An forms and, when injected into the atmosphere, transforms to phases Fn or Bn as determined by the available moisture and temperature.

Notes: An X-ray diffraction study of the AgI–KI–H2O chemical system was conducted by injecting an acetonic solution of a 2:1 mole ratio of AgI:KI directly upon an inert substrate thermally strapped to a thermoelectric cold stage. The atmosphere over the stage was controlled from 0.6 mb water vapor pressure to saturation while the temperature was varied from −22 to 25°C. Under these conditions four distinct crystalline phases are formed. Crystals of phase AK (KAg4I5) appear as the acetone evaporates. Moisture available from the ambient atmosphere functions as a catalyst as the newly formed AK transforms to phase BK (K2AgI3). At higher vapor pressures a second transformation results in phase CK. All phases break down and form an aqueous solution of KI plus equant AgI crystals (complex DK) at saturation vapor pressures. Another hydrous phase EK occurs below 0°C. The most probable composition of phases CK and EK is KAg2I3.H2O and KAg3I4.8H2O respectively. Nucleation studies show that the KI system is a poorer artificial nucleant of ice than the NH4I–AgI system above −10°C. Kinetics of the system suggest an absence of any free AgI for aerosols released from airborne platforms or from ground seeding stations.

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: Abstract Inorganic arsenic and its methylated metabolites were determined in urine from adults and children in Cornwall and from corresponding control groups in Glasgow. In the mineralised south-west of England, where it has been suggested that the highly enriched soil arsenic concentrations may at least be a cofactor in the increased incidence of skin cancer, urinary arsenic levels were, in general, only slightly elevated. The potential for increased intake of inorganic arsenic in Cornwall was, however, reflected in the more frequent occurrence of trivalent inorganic arsenic and monomethylarsonic acid in urine and, of especial significance, in two comparatively highly elevated sum of arsenic species concentrations of 48.7 and 20.8 μg g−1 creatinine recorded for two pre-school children. These findings are discussed with reference to recommended limits and pathways of exposure to inorganic arsenic.