Clinoenstatite in volcanic rocks from the Bonin Islands

Multiply-twinned clinoenstatite has been found in andesitic rocks from Chichi-jima and Mukojima in the Bonin Islands.The clinoenstatite occurs as (1) reaction rims around olivine, (2) composite crystals with bronzite, and (3) anhedral phenocrysts rimmed or included by bronzite.The clinoenstatite is chemically characterized by low contents of Ca (less than 0.5 wt.% oxide), Fs (9.2–11.5) and Al (less than 0.6 wt.% oxide) relative to the coexisting bronzite. The partition coefficient, K _{D op} ^cp =(Mg/Fe²⁺)^cp/(Mg/Fe²⁺)^op between coexisting clinoenstatite and bronzite, ranges from 1.02 to 1.32 (average 1.17). The Fe²⁺/Mg+Fe²⁺ ratios of coexisting clinoenstatite and bronzite are different in different rock types, which suggests variable inversion temperatures of protoenstatite to orthopyroxene in boninite.Bronzite phenocrysts in a specimen, ranging from Fs15 to Fs30, coexist with augite phenocrysts, whereas those in the other specimens, ranging from Fs12 to Fs18, do not coexist with augite phenocrysts. These differences in petrographical nature and mineral chemistry among the specimens examined may be due to variations in their quenching stages.The boninite clinoenstatite and bronzite are relatively rich in Ca and Mg, compared with the Papuan and Mariana pyroxenes, which seems to depend upon the rock chemistry.     

Formation of a void and galaxies in a neutrino-dominated universe

The recent discovery of the large honeycomb structure of the Universe has triggered many models of the Universe dominated by dark matter. The neutrino-dominated universe is a favorable model for explaining the size of the large-scale structure and the dark matter of the larger scale than the galactic one. Our calculations on the evolution of density perturbations in a two-component universe composed of neutrinos and dissipative gas on a spherically-symmetric model have shown that the galactic scale does correlate the scale of a void of galaxies: if a neutrino has the mass of some tens eV, galaxies of the typical size form surrounding a typical void.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Shock-wave compression of silica gel as a model material for comets

A shock-wave compression experiment using synthesized silica gel was investigated as a model for a comet impact event on the Earth’s surface. The sample shocked at 20.7 GPa showed considerable structural changes, a release of water molecules, and the dehydration of silanol (Si–OH) that led to the formation of a new Si–O–Si network structure containing larger rings (e.g., six-membered ring of SiO₄ tetrahedra). The high aftershock temperature at 20.7 GPa, which could be close to 800 °C, influenced the sample structure. However, some silanols, which were presumed to be the mutually hydrogen-bonded silanol group, remained at pressures >20.7 GPa. This type of silanol along with a small number of water molecules may remain even after shock compression at 30.9 GPa, although the intermediate structure of the sample recovered was similar to that of silica glass.     

Building Damage and Casualties after an Earthquake

The relationship between building damage patterns and human casualties in Nishinomiya City – one of the most heavily damaged cities in the 1995 Hanshin-Awaji Earthquake Disaster – was investigated using photographs of damaged buildings. First, the photographs of buildings in which casualties occurred were identified, and the building damage patterns were judged based on the photographs considering the existence of survival space. Then the relationship between the building damage pattern and casualty occurrence, and the characteristics of casualty distribution, were investigated. The main findings were as follows: Most casualties occurred in relatively old two-story wooden buildings in which the ground floor completely collapsed without survival space; casualties occurred at all building damage levels including ``no damage', and it can be seen that building damage is the major, but not the sole cause, of casualties in an earthquake; in Nishinomiya City, the regional distributions of casualties due to the collapse of buildings that left no survival space is similar to that of casualties due to other types of building damage.     

Detection of nonlinear waves and their contribution to ocean wave spectra Part I: Theoretical consideration

This is a Part I of a paper of nonlinearities of wind waves in the deep open ocean. First, considerations are given in order to verify the theoretical expression for bound waves from observed data. We compare the contribution of bound waves and double Bragg scattering to the second-order scattering, and we show that the contribution of bound waves is larger, and that bound waves can be detected by measuring the Doppler spectra of HF (high-frequency) radio wave scattering from the sea surface. Moreover, if the theory of the HF radio wave scattering from the sea surface is verified, so is the second-order perturbation theory for bound waves. Then, the contributions of bound waves to ocean wave spectra are investigated on the basis of the nonlinear theory. The bound waves are shown to modify frequency spectra and wave directional distributions at higher frequencies, and it is shown that although the modifications of frequency spectra are smaller for a two-dimensional field case than for a one-dimensional field case, they are not negligible at higher frequencies. On the other hand, the modifications of wave directional distributions are shown to be significant at higher frequencies. These discussions become significant only when bound wave predictions are verified in the open ocean. Consequently, it is shown that nonlinearities of water waves are important in considering both radio wave scattering from the sea surface and the detailed structures of ocean wave spectra at high frequencies.     

Statistical characteristics of individual waves in laboratory wind waves

On the basis of data on the statistical characteristics of individual waves in laboratory wind waves reported in part I of this series, a self-consistent similarity regime is found to exist among properties of the individual waves, such as the nondimensional frequency, the wave number, the phase speed, and the steepness. Also, it is shown that forms of past empirical formulas for the development of the peak wave can be derived starting from the 3/2-power law, as an extension of the persent laboratory experimental data. In the derivation, only values of the coefficient of the 3/2-power law, and the fraction of momentum transferred from the wind retained by the wind waves, remain on an empirical basis.     

Detailed observation of the wind-exerted surface flow by use of flow visualization methods

Detailed observations were performed of the wind-exerted surface flow, before and after the generation of wind waves. As flow visualization techniques, 6 classes of polystyrene beads of from 0.33 mm to 1.93 mm in diameter, with a specific gravity of 0.99, and also, hydrogen bubble lines, were used. Experiments were carried out at three ranges of the wind speed: 4.0, 6.2 and 8.6ms^–1 in the mean in the wind-wave tunnel section, and the observations were made at 2.85 m in fetch. In the case of 6.2 m s^–1, when the initial surface skin flow attains 0.22 cm in the scale thickness and 16 cm s^–1 in the surface velocity in about 3 second from the onset of the wind, regular waves of about 1.7 cm in wave length appear on the water surface. In one second after that, the downward thrust of the surface flow and the consequent forced convection commences, and the transition of the surface layer to a turbulent state occurs. Ordinary wind waves begin to develop from this state. In developed wind waves the viscous skin flow grows on the windward side of the crests, frequently producing macroscopic skin flows, and these skin flows converge to make a downward thrust at the lee side, and the viscous skin layer disappears there. The velocity of the downward flow has a maximum at the phase of about 30, and the value is of the order of 10 cm s^–1 at 4-mm depth after the orbital velocity of the sinusoidal wave is subtracted. As the process through which the wind stress acts on the water surface, it is considered that the following particular one may be real: the skin friction concentrated at the windward side of the crest produces skin flows, which thrust into the inner region to make the forced convection, carrying the acquired momentum. The viscous shearing stress just before the generation of the surface undurations was about 1/4 of the total shearing stress under the existence of wind waves. It is considered that the increase of the wind stress by wind waves is caused by this mechanism.     

Meridional distribution and carbon biomass of autotrophic picoplankton in the Central North Pacific Ocean during late northern summer 1990

The meridional distribution of autotrophic picoplankton groups in the central north Pacific was studied during the late northern summer of 1990. Sampling was along a section at 175°N which extended from 45°N to 8°S. The section is far from coastal regions and included subarctic, central gyre, and equatorial areas. Five autotrophic picoplankton groups, autotrophic microflagellate, red-fluorescing picoplankton,Synechococcus, prochlorophyte, and orange-fluorescing picoplankton, were identified from samples taken at stations distributed along this section. These five groups showed distinctive differences in their meridional and vertical distributions. The autotrophic microflagellates and red-fluorescing picoplankton showed distributions that were similar to that of chlorophyll a, which was dominated by the <3 μm size fraction. However, the vertical distribution of these groups was different.Synechococcus was found mostly in surface waters (PAR<10%) and was particularly abundant in the Kuroshio Extension and south of the equatorial region where the nitracline was shallow (50–75 m). Prochlorophytes were abundant in the deep euphotic layer (PAR 1-0.1%) from the south of the Kuroshio Extension to the south of the equatorial area. Orange-fluorescing picoplankton, which may be one kind of cyanobacteria but is larger than typical Synechococcus, were mostly distributed in the oligotrophic surface waters of the central gyre. The carbon biomass estimates for these organisms showed that these five groups dominated in different areas. The vertical distribution of carbon biomass did not correspond to that of chlorophyll a in the central gyre and south of the equator because of the larger carbon/ chlorophyll a ratio of Synechococcus and orange-fluorescing picoplankton relative to that of the other picoplankton.     

Three-year investigations into sperm whale-fall ecosystems in Japan

We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls.     

Statistical characteristics of individual waves in laboratory wind waves I. Individual wave spectra and similarity structure

Statistical characteristics of individual waves in laboratory wind waves have been studied by use of a wind-wave tunnel. The individual waves are defined by actual undulations of the water surface at any instant, and are characterized by concentrated shearing stress and strong vorticity at their crests. A conspicuous self-similarity structure is found in the individual wave field. The similarity manifests itself as a simple spectral form, and as the statistical 3/2-power law between nondimensional wave height and wave period, and further as the -1/2-power relationship between nondimensional phase speed and frequency, for waves of the high frequency side. The normalized energy spectrum, specially defined for individual waves, has a form practically equivalent to the traditional spectrum for component waves in the main frequency range from 0.7 to 1.5 in the frequency normalized by the peak frequency, but does not have secondary peaks at harmonics. The phase speed of individual waves also coincides with that of component waves in the main frequency range.