Growth of quartz crystals twinned after Japan Law

The flattened or elongated morphology often observed in contact twinned crystals has been referred to the so-called re-entrant corner effect at twin junctions. To re-investigate the validity of this mechanism, natural quartz crystals twinned after Japan Law have been subjected to re-growth in a commercial synthetic quartz autoclave, and the change in their morphology and surface microtopography by re-growth studied. It is found that although twin re-entrant corners may play a role of preferential growth sites, this role can be weakened considerably and in fact can become almost negligible when crystals grow under high supersaturation condition. Preferential growth at the re-entrant corner of a twin junction is probably due to clusters of dislocations concentrated in the composition plane, and not due to the so-called re-entrant corner effect in its original sense.     

Boron isotopic composition of fumarolic condensates and sassolites from Satsuma Iwo-jima,Japan

¹¹B/¹⁰B ratios of the high temperature fumarolic gases (>465°C) of this island were found to be constant within the limits of experimental error (¹¹B/¹⁰B = 4.066). This value may represent the ¹¹B/¹⁰B ratio of boron in the andesite magma. ¹¹B/¹⁰B ratios of the low temperature fumarolic gases (<235°C) were found to vary from 4.053 to 4.077. ¹¹B/¹⁰B ratios of some sassolites were approximately equal to that of the fumarolic condensates and the other ones were slightly enriched in ¹⁰B compared to the fumarolic condensates.     

226Ra chronology of a coastal marine sediment

Unsupported²²⁶Ra (t₁₂ = 1620years) in marine sediments can provide a basis for measuring rates of accumulation of the order of centimeters per thousand years. The excess radium apparently enters the sediments incorporated in phytoplankton. The sensitivity of the method depends upon the initial value of the unsupported²²⁶Ra and of the value of²³⁰Th, a parent of²²⁶Ra, in the sedimentary components.²²⁶Ra dating was applied to a sediment taken from the slope of the San Clemente Basin in the Southern California coastal region. Rates of sedimentation over two half-lives of the nuclide were found to be either 5.2 or 5.3 cm/1000 years depending upon which of two models for the geochronology is used. One model assumes that the²³⁰Th brings to the deposit an amount of²²⁶Ra in equilibrium with it. The other is based upon the growth of the²²⁶Ra from the²³⁰Th in the sedimentary components.^238+239Pu and²¹⁰Pb levels in the upper strata indicated sedimentation rates of the order of 100–500 cm/1000 years, i.e. much faster accumulations. We suggest these derived rates are spurious and reflect bioturbative activities of surface-living organisms.     

Activation energy for thermal release of Ar from some DSDP submarine rocks

From the experimental data on stepwise thermal release of neutron induced ³⁹Ar (³⁹K (n, p) ³⁹Ar) from rocks and minerals, Arrhenius plots were constructed, which gave activation energies for the thermal release process. The activation energies for DSDP Leg 58 and Leg 60 submarine volcanic rocks range from 12 to 20 kcal/mol, whereas those for granodiorites and the K-feldspar separates have activation energies ranging from 37 to 48 kcal/mol. The smaller activation energies for the submarine volcanic rocks reflect the grain boundary diffusion process, while the thermal diffusion of ³⁹Ar from granodiorites and K-feldspar is essentially controlled by a volume diffusion. The grain boundary diffusion for the submarine volcanic rocks suggests that K resides essentially in the grain boundaries.     

Dissipation of the rare gases contained in the primordial Earth's atmosphere

If the Earth was formed by accumulation of rocky bodies in the presence of the gases of the primordial solar nebula, the Earth at this formation stage was surrounded by a massive primordial atmosphere (of about 1 × 10²⁶ g) composed mainly of H₂ and He. We suppose that the H₂ and He escaped from the Earth, owing to the effects of strong solar wind and EUV radiation, in stages after the solar nebula itself dissipated into the outer space.The primordial atmosphere also contained the rare gases Ne, Ar, Kr and Xe whose amounts were much greater than those contained in the present Earth's atmosphere. Thus, we have studied in this paper the dissipation of these rare gases due to the drag effect of outflowing hydrogen molecules. By means of the two-component gas kinetic theory and under the assumption of spherically symmetric flow, we have found that the outflow velocity of each rare gas relative to that of hydrogen is expressed in terms of only two parameters — the rate of hydrogen mass flow across the spherical surface under consideration and the temperature at this surface. According to this result, the rare gases were dissipated below the levels of their contents in the present atmosphere, when the mass loss rate of hydrogen was much greater than 1 × 10¹⁷ g/yr throughout the stages where the atmospheric mass decreased from 1 × 10²⁶ g to 4 × 10¹⁹ g.     

The S pole distribution on magnetic grains in pyroxenite determined by magnetotactic bacteria

North-seeking bacteria (NSB) with 1 μm diameters migrate to the S pole only. They were applied to identify the S pole determination on a polished surface of magnetite-rich pyroxenite whose natural remanent magnetization (NRM) intensity was 5.64 × 10⁻³ Am² kg⁻¹. The microscopic observations were performed under dark-field illumination in a controlled magnetic field to 10 μT. The NSB formed clusters on limited areas of magnetite grains and scattered over the whole magnetite grains.

The NRM decreased to 1.02 × 10⁻⁵ Am² kg⁻¹ by alternating field (AF) demagnetization to 60 mT but no clusters appeared, while small populations of the NSB scattered on each grain. These scattered bacteria may gather toward the S pole resulting from magnetic domain walls.

When the sample acquired saturation isothermal remanent magnetization (SIRM) to 1 T, the NSB formed dense clusters at the opposite side to the applied field direction on the many grains as expected. This evidence indicated that the NSB can be useful micro-organisms for the determination of fine magnetic structures. Some grains also had NSB clusters at the edge of the grains toward the field direction or did not exhibit any clusters. The complicated distribution of the clusters (the S poles) may be explained by shape anisotropy of the magnetic grains.     

Tides and tidal currents in the Tusima Strait

Tides and tidal currents in the Tusima Strait are described, and cotidal charts are re-edited on the basis of intensive analysis of observed data. Some remarkable features are revealed as follows;

Predictive modelling of rainfall-induced landslide hazard in the Lesser Himalaya of Nepal based on weights-of-evidence

Landslide hazard mapping is a fundamental tool for disaster management activities in mountainous terrains. The main purpose of this study is to evaluate the predictive power of weights-of-evidence modelling in landslide hazard assessment in the Lesser Himalaya of Nepal. The modelling was performed within a geographical information system (GIS), to derive a landslide hazard map of the south-western marginal hills of the Kathmandu Valley. Thematic maps representing various factors (e.g., slope, aspect, relief, flow accumulation, distance to drainage, soil depth, engineering soil type, landuse, geology, distance to road and extreme one-day rainfall) that are related to landslide activity were generated, using field data and GIS techniques, at a scale of 1:10,000. Landslide events of the 1970s, 1980s, and 1990s were used to assess the Bayesian probability of landslides in each cell unit with respect to the causative factors. To assess the accuracy of the resulting landslide hazard map, it was correlated with a map of landslides triggered by the 2002 extreme rainfall events. The accuracy of the map was evaluated by various techniques, including the area under the curve, success rate and prediction rate. The resulting landslide hazard value calculated from the old landslide data showed a prediction accuracy of > 80%. The analysis suggests that geomorphological and human-related factors play significant roles in determining the probability value, while geological factors play only minor roles. Finally, after the rectification of the landslide hazard values of the new landslides using those of the old landslides, a landslide hazard map with > 88% prediction accuracy was prepared. The methodology appears to have extensive applicability to the Lesser Himalaya of Nepal, with the limitation that the model's performance is contingent on the availability of data from past landslides.     

Lithium depletion in G and K dwarfs

We present deep wide-field (16.4×16.4 arcmin²) Washington CT ₁ CCD surface photometry of the giant elliptical galaxy NGC 4472, the brightest member of the Virgo cluster. Our data cover a wider and deeper field than any previous CCD photometry. A single King model does not give a good fit to the surface brightness profiles of NGC 4472, but they can be fitted approximately using two King models: with the separate models representing the inner and outer regions . Surface brightness profiles for the outer region can also be fitted approximately by a de Vaucouleurs law. There is clearly a negative colour gradient within 3 arcmin of NGC 4472, in the sense that the colour gets bluer with increasing radius. The slope of the colour gradient for this region is derived to be Δ μ ( C − T ₁)=−0.08 mag arcsec⁻² for Δ log  r =1, which corresponds to a metallicity gradient of Δ[Fe/H]=−0.2 dex. However, the surface colour becomes gradually redder with increasing radius beyond 3 arcmin. A comparison of the structural parameters of NGC 4472 in C and T ₁ images has shown that there is little difference in the shapes of ellipses observed using isochromes or isophotes. In addition, photometric and structural parameters of NGC 4472 have been determined.