H_2O Megamasers: Accretion Disks, Jet Interaction, Outflows or Massive Star Formation?     

C. Henkel  J. A. Braatz  A. Tarchi  A. B. Peck  N. M. Nagar  L. J. Greenhill  M. Wang  Y. Hagiwara 《Astrophysics and Space Science》2005,295(1-2):107-116

The 25 years following the serendipitous discovery of megamasers have seen tremendous progress in the study of luminous extragalactic H₂O emission. Single-dish monitoring and high-resolution interferometry have been used to identify sites of massive star formation, to study the interaction of nuclear jets with dense molecular gas and to investigate the circumnuclear environment of active galactic nuclei (AGN). Accretion disks with radii of 0.1–3 pc were mapped and masses of nuclear engines of order 10⁶–10⁸ M were determined. So far, 50 extragalactic H₂O maser sources have been detected, but few have been studied in detail.  相似文献   

Distribution of cyanobacteria and other picophytoplankton in the western North Pacific Ocean,Summer 1989     

Tsuneo Odate  Mitsuru Yanada  Lourdes V. Castillo  Yoshiaki Maita 《Journal of Oceanography》1990,46(4):184-189

Cell densities of phycoerythrin-fluorescing cyanobacteria and other chlorophyll-fluorescing picophytoplankton in the 0.2–2.0 µm size fraction were investigated, using an epifluorescence microscope, in the western North Pacific Ocean (36.5–44.0 °N, 155.0°E) in the summer of 1989. Cyanobacteria were most abundant in the surface of the subtropical water (36.5–38.0°N) and less in the northern sea area (39.5–44.0°N). The cell density of other picophytoplankton was, however, high in the northern part and low in the subtropical water. Results showed that algae other than cyanobacteria may significantly contribute to the picophytoplankton community under the low water temperature conditions of open waters. Chlorophylla concentration represented well the abundance of picophytoplankton other than cyanobacteria, but had no significant correlation with the cyanobacteria cell density. Chlorophylla-based data must be interpreted with caution, since the abundances of cyanobacteria were often considerably different even though the chlorophylla concentrations were the same level.  相似文献   

Duality of turbulence and wave in wind waves     

Yoshiaki Toba 《Journal of Oceanography》1974,30(5):241-242

The three-seconds power law for wind waves of simple spectra, already derived byToba (1972 and 1973), may also be derived by introducing surface-wave properties into the form of the rate of energy dissipation in the theory of turbulence. The universal constantB, which was formerly determined empirically as 0.062 is here obtained asB=(2)^–3/2=0.0635. Thus wind waves have the duality of turbulence and wave.  相似文献   

Seasonal changes in size-fractionated primary production and nutrient concentrations in the temperate neritic water of Funka Bay,Japan     

Yoshiaki Maita  Tsuneo Odate 《Journal of Oceanography》1988,44(6):268-279

Size-fractionated primary productivity and chlorophylla concentration were studied at two stations in the temperate neritic water of Funka Bay, Japan, from April 1984 to May 1985. Size distributions of phytoplankton were discussed in relation to nutrient availability. In the central part of the bay, 66% of the annual primary production occurred during the spring phytoplankton bloom with 95% of the spring production being accounted for by the greater than 10µm size fraction, which was dominated by diatoms. The increase in this large fraction was enhanced at both stations when nutrient concentrations increased in the bay's upper layer. Under low nutrient concentrations during summer, small phytoplankters (<2µm) accounted for 40 to 75% (average 60%) of the total¹⁴C uptake at the central station, and from 25 to 59% (average, 45%) at the coastal station. However, a sudden nutrient enrichment at the coastal station during the summer triggered the growth of the large size fraction. These seasonal and regional changes in total¹⁴C uptake were attributed to the large size fraction, composed mainly of diatoms. From the decreases in various nutrients during diatom blooms, it was further suggested that the predominance of diatoms was determined, not only by nutrient concentrations, but also by their relative availability.Contribution No. 205 from the Research Institute of North Pacific Fisheries, Faculty of Fisheries, Hokkaido University.  相似文献   

Experimental study on strong interaction between regular waves and wind waves—I     

Mitsuhiko Hatori  Masayuki Tokuda  Yoshiaki Toba 《Journal of Oceanography》1981,37(3):111-119

The interaction between mechanically generated regular waves and wind waves is experimentally investigated in a wind-wave tunnel. It is shown that the growth process of regular waves is divided into the four distinct stages as follows: (1) almost independent coexistence of wind waves and regular waves, (2) attenuation of wind waves with simultaneous growth of regular waves, (3) rapid growth of regular waves after disappearance of wind waves, and (4) transition of regular waves to wind waves after the wave breaking. At the second stage there is an apparent relation between the attenuation of wind waves and the growth of regular waves. This fact suggests that there is some strong nonlinear interactions which transfers energy effectively from wind waves to regular waves.  相似文献   

Seasonal changes in the biomass of zooplankton and their food requirement in Funka Bay     

Tsuneo Odate  Yoshiaki Maita 《Journal of Oceanography》1988,44(5):228-234

Zooplankton biomass consisting of large and small-size copepods, copepod nauplii and tintinnids were investigated over a period of one year at two stations in Funka Bay, Japan. The food requirement of zooplankton was also estimated using the method of Ikeda and Motoda. Estimated total carbon requirement of zooplankton in the coastal and central parts of the bay was equivalent to 52 and 38% of the annual primary production, respectively. These corresponded to zooplankton production of 12–13 gC·m^–2·yr^–1.The total carbon requirement at each station increased to 63 and 74% of the primary production during summer compared with 26 and 3% in spring or 19 and 17% in winter. The microzooplankton (copepod nauplii and tintinnids) accounted for about half of the carbon requirement from April to November.Food requirements reached 161% at the coastal station and 194% at the central station of the daily organic carbon production during September. Zooplankton may also feed on carbon sources other than living phytoplankton. This could account for the observed decrease in particulate organic carbon in a water column.Contribution No. 202 from the Research Institute of North Pacific Fisheries, Faculty of Fisheries, Hokkaido University.  相似文献   

Anomalous distribution of suspended matter and some chemical compositions in seawater near the seabed: Transport processes     

Masahiro Kajihara  Katsuhiko Matsunaga  Yoshiaki Maita 《Journal of Oceanography》1974,30(5):232-240

Vertical fine distributions of suspended matter and some chemical compositions in seawater were measured in the layer near the seabed. Distributions of organic suspended matter were almost uniform throughout the layer, but others were anomalous. However, with respect to their peak heights and distribution patterns, the tendency of profiles was the same on the whole. We suggested that these anomalous distributions were primarily caused by the destruction of the large flocculent particle on the seabed and by upward diffusion of disintegrated particles. The similarity of profiles between chemical compositions of dissolved substances and suspended matter of non-dissolved substances, was explained by assuming that pore water in the large particle was simultaneously transported with disintegrated particles after the destruction. An equation for the vertical distribution of suspended matter near the seabed was derived, provided that the rate of destruction of large flocculent particle was in proportion to the current velocity on the seabed. The equation represented the existence of the anomalous distribution, which was continuously changing its pattern. Measurements of vertical profiles of suspended matter showed almost the same tendency with the theory. From the characteristics of the theoretical equation, it was expected that the eddy diffusivity near the seabed was 1050 cm²/sec.  相似文献   

Prediction of ocean waves based on the single-parameter growth equation of wind waves (II) introduction of grid method     

Paimpillil S. Joseph  Sanshiro Kawai  Yoshiaki Toba 《Journal of Oceanography》1981,37(1):9-19

The present study is a modification of the wave prediction model presented in the first paper of this title (Kawai et al., 1979) based on the Toba's (1978) single parameter equation of the wind wave growth. The introduction of a grid method reduces the two defects pointed out inKawai et al., i.e., the absence of the prediction of certain instants at fixed points, and the concentration of wave energy at certain points in the wind direction, arising from the lack of treatment of the lateral spreading of wave energy around the wind direction. The new model is applied to the same set of data. The results shows overall improvements, such as the elimination of certain overestimate in the first study and the coincidence of the predicted maximum with the measured one. The swells are separately hindcasted and a very good agreement with measurement is obtained.  相似文献   

A new expression for the production rate of sea water droplets on the sea surface     

Noriko Iida  Yoshiaki Toba  Masaaki Chaen 《Journal of Oceanography》1992,48(4):439-460

A new set of empirical formulas for the production rate and the number concentration of sea-water droplets on the sea surface are proposed, synthesizing past observation data of sea-salt particles in the sea and water droplets in wind-wave tanks. A new levelz _c is introduced as the effective wind-sea surface where seawater droplets are produced. The new formulas are expressed in linear functions in logarithmic scales ofu*²/v _p , a parameter to describe overall conditions of airsea boundary processes, whereu _* is the friction velocity of air,v the kinematic viscosity of air and _p the peak angular frequency of wind-wave part of wave spectra. A model of coexistence of spray droplets and suspended particles near the sea surface is proposed. As for the independent parameter, a comparison between the uses ofu*²/v _p and ofu _* ³ which was the traditional way of parameterization excluding wave measure, shows that the advantage of usingu*²/v _p is statistically significant with a confidence limit 89% in F-test.  相似文献   

A numerical study on the generation of the small meander of the Kuroshio off southern Kyûshû     

Yoshihiko Sekine  Yoshiaki Toba 《Journal of Oceanography》1981,37(5):234-242

The generation of small meanders of the Kuroshio off southern Kyûshû is investigated. Basing on the fact that the small meanders tend to follow an increase in velocity of the Kuroshio in the Satsunan region (Sekine andToba, 1981), the influence of this velocity increase on the quasi-stationary path of the Kuroshio is studied numerically. Simplified bottom and coastal topographies are employed in a two layer model ocean. A quasi-stationary numerical solution with a constant inflow is used for the initial condition, and a temporal increase in the inflow with corresponding leakage is employed as the boundary condition to investigate nonlinear effects due to the increase in current velocity. Experiments for four different physical models are carried out to determine the specific roles of the continental slope, the planetary-effect, and density stratification. Temporal increase in the inflow tends to cause offshore shift of the current path. But the topographic effect of the continental slope is strong enough that no significant shift of the current path occurs in the case of the barotropic ocean. However, in the case of a baroclinic ocean, temporal increase in the inflow does cause generation of small meanders, because density stratification diminishes the topographic effect. A larger density stratification provides more favorable condition for the appearance of the small meander, and a cyclonic eddy is formed on the continental side of the small meander path.  相似文献