Summary of taxa and distribution of Sirenia in the North Pacific Ocean

Abstract North Pacific fossil sirenians comprise representatives of three subfamilies of the Dugongidae: Halitheriinae ( Metaxytherium arctodites , Middle Miocene, North America), Hy-drodamalinae ( Dusisiren spp., Early-Late Miocene, and Hydrodamalis spp., Late Miocene-Pleistocene, North America and Japan), and Dugonginae ( Dioplotherium allisoni , Early-Middle Miocene, North America). Indeterminate dugongid remains are also known from the Late Oligocene of Japan, and the discovery of additional taxa in the western Pacific, especially in Paleogene rocks, can be anticipated. The known North Pacific Neogene taxa apparently dispersed into the Pacific from the Caribbean. Metaxytherium gave rise in the Pacific to Dusisiren ; a series of chronospecies of the latter genus eventually culminated in Hydrodamalis , which was exterminated by humans circa AD 1768. Dioplotherium left no known descendants in the Pacific. The Recent Dugong probably entered the Pacific from the Indian Ocean. The presence in the North Pacific Miocene of at least three sympatric dugongid lineages, together with desmostylians, is evidence for a diversity of marine plants that was reduced by subsequent climatic cooling.     

Fugacity-concentration relationship of dilute hydrogen in water at elevated temperature and pressure

The fugacity vs. concentration ratio(Y) of dilute hydrogen dissolved in water was determined at temperatures below 500°C and pressures below 1000 bar by measuring H₂ concentrations in magnetite-hematite-water and palladium hydride-water systems. Combining these results with reported solubility data of H₂ in water and with the Shaw's expression for the activity-composition relationship of H₂H₂O mixture at higher temperatures, theP-T-Y diagram was constructed over theP-T range below 900°C and 1000 bar.     

Effect of occurrence rate of acoustic emissions on their statistical behavior

The parameterm in Ishimoto-Iida's relation was investigated for acoustic emissions (AEs) occurring in rock samples under uniaxial compression. In the experiment, we found: 1) The large AEs are counted without serious error but the number of small AEs is systematically underestimated at high AE rates, 2) the frequency distribution of maximum AE amplitudes becomes nonlinear in logarithmic scale with increasing AE rate, and 3) there exists a strong negative correlation betweenm-value and AE rate. The miscount of small AEs was interpreted as due to overlap of the large and small AEs. We call the miscount masking effect. A statistical analysis based on the masking effect showed that them-value decreases more effectively as the AE rate increases, and thus the masking effect is a possible origin both for the nonlinear frequency distribution of maximum AE amplitudes and for the negative correlation ofm-value with AE rate. We emphasize that one should be careful of the masking effect to examine correctly the change, ofm-value. In order to eliminate the masking effect, AEs should be measured by a measurement system with low sensitivity. Even if the masking effect is eliminated, them-value decreases before the main fracture of a rock sample. Them-value is a key parameter to predict the main fracture.     

Laboratory Study of O(1S) Formation Process in the Photolysis of O3 and its Atmospheric Implications

A high-sensitive technique to detect O(¹S) atoms using vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy has been applied to study the O(¹S) production process from the UV photodissociation of O₃, N₂O, and H₂O₂. The quantum yields for O(¹S) formation from O₃ photolysis at 215 and 220 nm are determined to be (1.4 ± 0.4) × 10⁻⁴ and (5 ± 3) × 10⁻⁵, respectively. Based on thermochemical considerations, the O(¹S) formation from O₃ photolysis at 215 and 220 nm is attributed to a spin-forbidden process of O(¹S)+O₂(X³Σ_g ⁻). Analysis of the Doppler profile of O(¹S) produced from O₃ photolysis at 193 nm also indicates that the O(¹S) atoms are produced from the spin-forbidden process. In the photolysis of N₂O and H₂O₂ at 193 nm, no discernible signal of O(¹S) atoms has been detected. The upper limit values of the quantum yields for O(¹S) production from N₂O and H₂O₂ photolysis at 193 nm are estimated to be 8 × 10⁻⁵ and 3 × 10⁻⁵, respectively. Using the experimental results, the impact of the O(¹S) formation from O₃ photolysis on the atmospheric OH radical formation through the reaction of O(¹S)+H₂O has been estimated. The calculated results show that the contribution of the O(¹S)+H₂O reaction to the OH production rate is ∼2% of that of the O(¹D)+H₂O reaction at 30 km altitude in mid-latitude. Implications of the present laboratory experimental results for the terrestrial airglow of O(¹S) at 557.7 nm have also been discussed.     

Advanced Micro-XRF Method to Separate Sedimentary Rhythms and Event Layers in Sediments: Its Application to Lacustrine Sediment from Lake Suigetsu,Japan

Event-related sedimentary layers, which are deposited occasionally due to volcanic eruptions, earthquakes or heavy rains, are often contained in the rhythmical sequences of lacustrine and marine sediments. We have developed an analytical method for separating the sedimentary rhythms and the event layers identified using the scanning X-ray analytical microscope (SXAM) and obtained sequential profiles of seven elements Al, Si, K, Ca, Ti, Mn, and Fe in the lacustrine sediment from Lake Suigetsu, Japan. Two types of event layers could be detected from the elemental composition of 33 layers of sediment: three known volcanic ash layers and 30 clay layers containing 12 turbidites. The recurrence interval of the latter, which may potentially be initiated and archived by locally important earthquakes, is estimated to be an average of 640 ± 160 years by using Sompi event analysis (SEA) based on an autoregressive (AR) model. After removing those portions that represented event layers from the elemental profiles, we obtained event-removed (ER) temporal profiles based on the tephrochronology of the three volcanic ash layers. The ER temporal profiles of manganese and iron, probably representing the siderite content, showed a millennial-scale variation in the Holocene that corresponded well with ice-rafting events in the North Atlantic.     

Formation of bipolar flow by the stellar wind embeded in molecular disk

The interaction of the isotropic stellar wind with the rotating isothermal cloud surrounding the young star is investigated. The density distribution of the cloud is taken as that for the equilibrium state of the rotating isothermal cloud modified by adding the rarefied interstellar gas in the polar region. The development of the shock envelope and the structure of the shell induced by the stellar wind are obtained. It is shown that the envelope of the shock front elongates and opens to the polar direction with half opening angle of about 20 degrees resulting the bipolar flow which is able to reproduce well the observed properties for the outflow in the bipolar sources.     

Process of the Tsushima Current formation revealed by ADCP measurements in summer

In order to clarify detailed current structures over the continental shelf margin in the East China Sea, ADCP measurements were carried out in summers in 1991 and 1994 by the quadrireciprocal method (Katoh, 1988) for removing diurnal and semidiurnal tidal flows from observed flows, together with CTD measurements. We discussed the process of the Tsushima Current formation in the East China Sea. The Tsushima Current with a volume transport of 2 Sv (1 Sv=10⁶ m³s^–1) was found north of 31°N. A current with a volume transport of 0.4 Sv was clearly found along the 100 m isobath. Between the Kuroshio and the current along the 100 m isobath, southeastward component of velocity was dominant compared to northwestward one. Four eastward to southeastward currents were found over the sea bed shallower than 90 m depth. Total volume transport of these four currents was 1 Sv, and they seemed to be originated from the Taiwan Strait. Intrusion of offshore water into the inner shelf northwest of Amami Oshima was estimated to have a volume transport of 0.6 Sv. It is concluded that the Tsushima Current is the confluence of these currents over the continental shelf margin with the offshore water intruding northwest of Amami Oshima.     

Sulfur bacteria originating from the water and organisms in a hydrothermally active area of the mid-okinawa trough

Hydrothermal venting and associated fauna were observed in the mid-Okinawa Trough during deep-sea diving byShinkai 2000. Water and organisms were collected there for on-board cultivation of sulfur bacteria. Sulfur bacteria capable of growing on an inorganic medium containing thiosulfate were subcultured and isolated. The isolated chemoautotrophic sulfur bacteria were all rod- to beanshaped, nonsporing, and gram-negative. They could also grow on an organic medium and thus were shown to be facultative chemoautotrophs. Their facultative chemoautotrophy would result in synergetic metabolism of both inorganic and organic substrates; thus the sulfur bacteria could be highly adaptive to nutritional diversity of hydrothermal vent areas.     

Modification of the damping function in the k–ε model to analyse oscillatory boundary layers

A simple relationship has been developed between the wall coordinate y⁺ and Kolmogorov's length scale using direct numerical simulation (DNS) data for a steady boundary layer. This relationship is then utilized to modify two popular versions of low Reynolds number k–ε model. The modified models are used to analyse a transitional oscillatory boundary layer. A detailed comparison has been made by virtue of velocity profile, turbulent kinetic energy, Reynolds stress and wall shear stress with the available DNS data. It is observed that the low Reynolds number models used in the present study can predict the boundary layer properties in an excellent manner.