Pressure effect on the divalent cation distribution in nonideal solid solution of forsterite and fayalite

The divalent cation distribution in olivine (Mg, Fe)₂SiO₄ under high pressure and temperature was studied to clarify the detailed state of olivine in the mantle. Single crystal samples were heated for a sufficient period of time for the cations to migrate and quenched fast enough to preserve the equilibrated state under high pressures, and the crystal structure was determined with X-ray method. The pressure effect on the distribution coefficient K _D[= (Fe/Mg) _M1/(Fe/Mg) _M2] was determined for the first time; dK _D/dP?0.02 GPa^?1. A set of five thermodynamic parameters required to describe the regular solution model was determined from data concerning the pressure dependence and the known temperature and compositional effects. As a result we have shown how K _D depends on pressure, temperature, and composition. The notable feature clarified is the very large contribution of nonideality in the olivine solid solution. The K _D of olivine crystals in the mantle is predicted; K _D increases to ～ 2.2 at the depth of 400 km, in contrast to 0.9 ～ 1.2 of natural samples available at the surface of the Earth.     

Nitrous oxide in the sea

A new gas chromatographic method was developed for the measurement of nitrous oxide (N₂O) in seawater. It takes 15 min for the analysis in a sample of 640 ml seawater.By this method, more than 1000 samples taken over various depths and areas in the sea were analyzed. In the western North Atlantic, the N₂O concentration over a range of oceanic depths gave characteristic profiles that were negatively correlated with oxygen profiles, reaching its maximum (c.a. 1 μg/l) in the oxygen-minimum layer at mid-depths. In the Caribbean, the N₂O maximum reached higher concentrations than in the North Atlantic. N₂O was near equilibrium with that in the atmosphere in Atlantic surface waters, but supersaturation of N₂O was observed in surface waters of the Gulf of St. Lawrence in early June and in most surface samples from the Caribbean Sea in March.The estimated rate of N₂O production in the sea may be significant in terms of geochemical cycling of combined nitrogen to the atmosphere.     

North-south asymmetries of solar particle events in upper stratospheric ozone

Stratospheric ozone depressions, following intense solar particle events (SPE) observed by the backscattered ultraviolet (BUV) experiment on the Nimbus-4 satellite, indicate the existence of distinct asymmetries between the Northern and Southern Hemispheres. These asymmetries are observed in the magnitude of the depressions above the 5-mb level, their temporal variations, and the spatial (i.e., latitude and longitude) dependence of these variations. Possible causes of asymmetries, shown by two events on 4 August 1972 and 25 January 1971, can be attributed to: (1) tilt of the interplanetary magnetic field (IMF) with respect to the Earth's dipole magnetic field which influences the precipitation of energetic solar particles into the polar atmospheres; (2) differences in ozone chemistry caused by the large change in atmospheric temperature between summer and winter hemispheres; (3) seasonal differences of the stratosphere's dynamic states which are affected by upward propagating planetary waves in winter in contrast to the relatively undisturbed zonal flow in summer; (4) topographic asymmetry between Northern and Southern Hemispheres.These effects are shown by three-dimensional plots of the events in geographic coordinates and by color contour plots of the stratospheric ozone distributions in geomagnetic and geographic polar coordinates, respectively.     

Ionized helium in prominences and in the chromosphere

Quiescent prominences It is found that Heii 4686 is emitted in the same cold region of 10000 K as hydrogen, metal and neutral helium emission lines. This conclusion is based on the finding that the observed width of 4686 is the same as the calculated width of 4686. The calculated width is derived from the observed widths of hydrogen and metallic lines. The large intensity of Heii 4686 in 10000 K can be explained by the ionization of Heii due to the UV radiation below 228 Å that comes from the corona and the transition region.Loop prominences The very broad width (30 to 50 km s^–1) of 4686 for two post-flare loop prominences shows that the Heii line is emitted in hot regions different from regions of hydrogen and metal emission. From the widths of the Balmer lines and many metallic lines the kinetic temperature for one loop is found to be 16000 K in one part and 7600 K in another part. The electron densities are 10^12.0 cm^–3 and less than 10^11.0 cm^–3 respectively.Chromosphere The intensity of 4686 in the chromosphere can be interpreted in terms of a temperature of 10000 K with the ionization due to UV radiation. But, since observations of the width of 4686 are not available, a definitive conclusion for the chromosphere cannot be reached.     

A Late Cretaceous mammalian dentary from the Ashizawa Formation (Futaba Group), Fukushima,northeastern Japan

A mammalian dentary discovered in the Coniacian Ashizawa Formation (Fukushima, northeastern Japan) is described. The specimen is a fragment of the horizontal ramus of a left edentulous dentary with five alveoli, the distal four of which are plugged with broken roots. Based on the morphologies of the dentary and the roots, it is considered to be of a therian mammal. This constitutes the first discovery of a Mesozoic mammal in northeastern Japan and highlights the potential for future mammal discoveries in the Cretaceous System in northeastern Japan, which will be significant for disclosure of the mammalian faunal evolution in East Asia during the Late Cretaceous.     

Groundwater and surface water interactions in an alluvial plain, Tuul River Basin, Ulaanbaatar, Mongolia

Drinking water supplies in Ulaanbaatar, the capital of Mongolia, are completely dependent on groundwater sourced from pumping wells located in an alluvial plain of the Tuul River which flows through Ulaanbaatar. The interaction between groundwater in the alluvial plain and river surface water was investigated using a hydrological and multi-tracers approach. The observed groundwater contour map clearly shows that the Tuul River recharges the floodplain groundwater and groundwater flows from east to west. The similarity of chemical and stable isotopic compositions suggests that groundwater is mainly recharged by Tuul River water in the vicinity of the river. In addition, considering groundwater contours and chemical composition, groundwater in the northern and southern mountain sides contribute to floodplain groundwater. Stable isotopic information suggests that winter season precipitation also contributes to the groundwater, because groundwater in a specific region has a considerably lower isotopic ratio. Using the End Member Mixing Analysis applying oxygen-18, SiO₂ and HCO₃ ^- as tracers, the contribution ratios of the Tuul River, groundwater in the northern and southern mountain regions, and winter season precipitation to floodplain groundwater are estimated to be 58% to 85%, 1% to 54%, 0% to 16%, and 0% to 12%, respectively.     

Analytical direct planetary perturbations on the orbital motion of satellites

An analytical expansion of the disturbing function arising from direct planetary perturbations on the motion of satellites is derived. As a Fourier series, it allows the investigation of the secular effects of these direct perturbations, as well as of every argument present in the perturbation. In particular, we construct an analytical model describing the evection resonance between the longitude of pericenter of the satellite orbit and the longitude of a planet, and study briefly its dynamic. The expansion developed in this paper is valid in the case of planar and circular planetary orbits, but not limited in eccentricity or inclination of the satellite orbit.     

Color measurements of volcanic ash deposits from three different styles of summit activity at Sakurajima volcano,Japan: Conduit processes recorded in color of volcanic ash

We measured quantitatively colors of volcanic ash deposits erupted from three different styles of summit activity (Strombolian activity, Vulcanian explosions and continuous ash venting activity) at Sakurajima volcano from 1974 to 1985. Colors of Strombolian ash samples have larger yellow components of their visible spectra (b^? values) than those of explosion and continuous venting ash samples. Colors of explosion ash samples show larger variation in both red and yellow components of their visible spectra (a^? and b^? values, respectively), while colors of continuous venting ash samples are in the narrow ranges within colors of explosion ash samples. Colors of components with lower densities than 3.1 g/cm³ (groundmass and phenocrystic plagioclase) obtained by magnetic and heavy liquid separation methods are similar to the unseparated bulk ash samples. This result suggests that the color variations of ash deposits are mainly originated from the particles composed of groundmass. The particles can be classified into three different types of particles with different vesicularity and crystallinity (vesicular particle [VP], dense particle with vesicles [DPV] and dense particle without vesicles [DP]). Analytical results of component proportions, chemical compositions of groundmass glasses, ferrous iron contents and surface ferric materials show that (1) VP has larger yellow components of the visible spectrum (b^? values) and high ferrous iron content, and is less crystallized than the DP and DPV, (2) DP has larger red and yellow components of its visible spectrum (a^? and b^? values, respectively) and involves ferric materials on the surfaces produced by oxidation process, and (3) DPV has smaller red and yellow components of its visible spectrum (a^? and b^? values, respectively) and involves less ferric materials on the ash surfaces. Color differences of ash deposits from three different activity styles can be explained by the different mixing ratios of VP, DPV and DP. During the Strombolian activity, the VP is a main component in the ash, which is formed from relatively less degassed and crystallized magma. In the Vulcanian explosion and continuous ash venting activity, the proportions of DPV and DP in ash are larger than that in the Strombolian activity. The highly crystallized DP may correspond to a vent cap, and DPV to a magma below the cap. The color measurements of ash deposits provide information on the pre-eruptive processes at the shallower levels of a conduit.     

Expansion of the disturbing function for high eccentricity and large amplitude of libration

Following some ideas, developed by Woltjer (1928), Message (1989), Yokoyama (1988, 1989) and Duriez (1990) an expansion of the disturbing function is given for high values of the eccentricity and large amplitude of libration. The classical expansion can be obtained as a particular case of the present model. Several asteroids with high eccentricity and large amplitude of libration are tested and the results are much better than those obtained from the classical theory.