Solution to the rotation of the elastic earth by method of rigid dynamics

Hamiltonian mechanics is applied to the problem of the rotation of the elastic Earth. We first show the process for the formulation of the Hamiltonian for rotation of a deformable body and the derivation of the equations of motion from it. Then, based on a simple model of deformation, the solution is given for the period of Euler motion, UT1 and the nutation of the elastic Earth. In particular it is shown that the elasticity of the Earth acts on the nutation so as to decrease the Oppolzer terms of the nutation of the rigid Earth by about 30 per cent. The solution is in good agreement with results which have been obtained by other, different approaches.     

Real-time difference imaging analysis of MOA Galactic bulge observations during 2000

We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg² were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.     

High-sensitive measurement of uranium LIII-edge X-ray absorption near-edge structure (XANES) for the determination of the oxidation states of uranium in crustal materials

The uranium L_III-edge XANES spectra for natural rocks at the concentration range of 0.96–124 mg kg⁻¹ were measured using a log spiral bent crystal Laue analyzer (BCLA) combined with a multi-element Ge detector. It was found that the quality of the XANES spectra using the BCLA was greatly improved due to a reduction of interfering fluorescence from major components such as Rb and Sr. The ratio of signal to background intensities in the U L_III-edge XANES spectra increased by a factor of 2.9–17 with the use of the BCLA, which greatly enhanced the detection limit for the speciation of the oxidation states of U or the U(IV)/U(VI) ratio of natural samples. In addition, it was demonstrated that the fluorescence XANES method coupled with the BCLA enable determination of the speciation of U for various natural samples such as acidic igneous rocks, ferromanganese nodules, sediments, and some sedimentary rocks such as shale and limestone.     

Todorokite formation in seawater by microbial mediation

Microbial manganese oxidation in seawater was carried out in enrichment cultures which were obtained from the seawater supply system at the Marine Science Museum, Tokai University (Shimizu-shi, Japan). The manganese oxide formed was well-crystallized todorokite. The major element composition was within the range of marine manganese concretions and the O/Mn molar ratio was 1.8. The conditions for formation of manganese oxide minerals in marine environments are discussed on the basis of these results.     

The role of tidal vortices in material transport around straits

The strong tidal current (tidal jet) in straits generates tidal vortices with a scale of several kilometers. The role of the vortices in material transport was investigated in the Neko Seto Sea, located in the western part of the Seto Inland Sea of Japan. A clockwise vortex with a diameter of about 0.8 km was observed in Nigata Bay (lying between two straits, the Neko Seto Strait and the Meneko Seto Strait). It was concluded that the clockwise vortex was the tidal vortex which was generated by the tidal jet in the Meneko Seto Strait. The vortex moved into the bay with the tide, but tended to stay on the sand bank in the bay. It was confirmed by current measurement with an ADCP and turbidity measurement that the secondary convergent flow was generated in the bottom layer of the vortex. This secondary flow seemed to contribute to the formation of the sand bank. It was suggested that tidal vortices may play an important role in the sediment transport and formation of topography in and around straits.     

Metal-organic complexes in seawater pumped up from under the ground

Metal-organic complexes of transition elements removed by Amberlite XAD-2 resin from seawater pumped up from under the ground were determined. The proportions of iron, copper and zinc retained on the resin to dissolved forms of these metals were about 70, 40 and 5%, respectively, while manganese, cobalt and nickel were not retained on the resin. These results suggest that although iron may be retained in colloidal form, a significant fraction of copper is present in some organic form(s).     

A preliminary study of carbon system in the East China Sea

In the central part of the East China Sea, the activity of CO₂ in the surface water and total carbonate, pH and alkalinity in the water column were determined in winter and autumn of 1993. The activity of CO₂ in the continental shelf water was about 50 ppm lower than that of surface air. This decrease corresponds to the absorption of about 40 gC/m²/yr of atmospheric CO₂ in the coastal zone or 1 GtC/yr in the global continental shelf, if this rate is applicable to entire coastal seas. The normalized total carbonate contents were higher in the water near the coast and near the bottom. This increase toward the bottom may be due to the organic matter deposited on the bottom. This conclusion is supported by the distribution of pH. The normalized alkalinity distribution also showed higher values in the near-coast water, but in the surface water, indicating the supply of bicarbonate from river water. The residence time of the East China Sea water, including the Yellow Sea water, has been calculated to be about 0.8 yr from the excess alkalinity and the alkalinity input. Using this residence time and the excess carbonate, we can estimate that the amount of dissolved carbonate transported from the coastal zone to the oceanic basin is about 70 gC/m²/yr or 2 GtC/yr/area-of-global-continental-shelf. This also means that the rivers transport carbon to the oceans at a rate of 30 gC/m²/yr of the coastal sea or 0.8 GtC/yr/ area-of-global shelf, the carbon consisting of dissolved inorganic carbonate and terrestrial organic carbon decomposed on the continental shelf.