¹⁰Be in marine sediments     

Teruo Inoue  Shigeo Tanaka 《Earth and Planetary Science Letters》1976,29(1):155-160

The depth profile of the long-lived radionuclide¹⁰Be in a marine sediment recovered in the vicinity of the Samoan Islands has been precisely assayed with a highly sensitive needle-type gas counter. The obtained irregular pattern of¹⁰Be concentrations with depths ranging from 4.7 to 0.3 dpm/kg dry sediment is interpreted as being due to dilution of¹⁰Be by volcanic eruptions in the past.  相似文献   

Dependence of the build-up of the colour–magnitude relation on cluster richness at z∼ 0.8     

Yusei Koyama  Tadayuki Kodama  Masayuki Tanaka  Kazuhiro Shimasaku  Sadanori Okamura 《Monthly notices of the Royal Astronomical Society》2007,382(4):1719-1728

  相似文献   

Statistical characteristics of medium-latitude VLF emissions (unstructured and structured): Local time dependence and the association with geomagnetic disturbances     

M. Hayakawa  Y. Tanaka 《Planetary and Space Science》1986,34(12):1361-1372

The purpose of the paper is to present the statistical characterictics of mid-latitude VLF emissions (both unstructured hiss and structured emissions) based on the VLF data obtained at Moshiri in Japan (geomag. lat. 35°; L = 1.6) during the period January 1974–March 1984. Local time dependence of occurrence rate and the association with geomagnetic disturbances have been studied for both types of emissions. Both types (unstructured and structured) of mid-latitude VLF emissions are found to have definite correlations with geomagnetic disturbances. Then, the time delay of the emission event behind the associated geomagnetic disturbance has enabled us to estimate the resonant electron energy for VLF hiss to be 5 keV at L = 3–4 and that for structured VLF emissions to be considerably larger, such as 20 keV at L 4. Combined considerations of these estimated resonant energies, theoretical electron drift orbits and the local time dependences, allow us to construct the following model to explain the experimental results in a reasonable way. Electrons in a wide energy range are injected during disturbances around the midnight sector, followed by the eastward drift. Lower energy ( 5 keV) electrons tend to drift closer to the Earth, resulting in the dawnside enhancement of VLF hiss within the plasmasphere. Further, these lower energy electrons are allowed to enter the duskside asymmetric plasmaspheric bulge and to generate VLF hiss there. On the other hand, higher energy (20 keV) electrons tend to drift at L shells farther away from the Earth and those substorm electrons are responsible for the generation of structured VLF emissions around dawn due to an increase of plasma density from the sunlit ionosphere. However, such higher energy electrons are forbidden from entering the duskside of the magnetosphere and so we cannot expect a duskside peak in the occurrence of structured VLF emissions, which is in agreement with the experimental result.  相似文献   

Enhanced chlorophyll associated with island-induced cyclonic eddies in the eastern channel of the Tsushima Straits     

Goh Onitsuka  Akihiko Morimoto  Tetsutaro Takikawa  Atsushi Watanabe  Masatoshi Moku  Yutaka Yoshikawa  Tetsuo Yanagi 《Estuarine, Coastal and Shelf Science》2009,81(3):401-408

The relationship between island-induced cyclonic eddies and chlorophyll a (chl-a) was investigated using field data and satellite images in the eastern channel of the Tsushima Straits. The maximum chl-a concentration around the leeward eddy of the Tsushima Islands was two or three times greater than that of outside the eddy. Two different mechanisms of chl-a enhancement associated with island-induced cyclonic eddies were found in the post-bloom periods. In summer, when nutrients were depleted in the surface layer, eddy pumping increased the nutrient supply in the euphotic zone, resulting in enhanced chl-a around the shallow thermocline near the eddy core. In late autumn, when the mixed layer deepened over the euphotic zone, the mixed layer depth became shallow due to the doming effect of the cyclonic eddy, therefore, the improved irradiance condition led to an increase in the chl-a concentration in the surface mixed layer. Nighttime satellite visible images showed a number of fishing vessels in the lee region of the Tsushima Islands, implying that the enhanced phytoplankton biomass may have resulted in good feeding conditions for fishes and squids in the Tsushima Straits.  相似文献   

A complete relativistic ionized accretion disc in Cygnus X-1     

A.J. Young †  A.C. Fabian  R.R. Ross  Y. Tanaka 《Monthly notices of the Royal Astronomical Society》2001,325(3):1045-1052

The galactic black hole candidate Cygnus X-1 is observed to be in one of two X-ray spectral states: either the low/hard (low soft X-ray flux and a flat power-law tail) or high/soft (high blackbody-like soft X-ray flux and a steep power-law tail) state. The physical origin of these two states is unclear. We present here a model of an ionized accretion disc, the spectrum of which is blurred by relativistic effects, and fit it to the ASCA , Ginga and EXOSAT data of Cygnus X-1 in both spectral states. We confirm that relativistic blurring provides a much better fit to the low/hard state data and, contrary to some previous results, find the data of both states to be consistent with an ionized thin accretion disc with a reflected fraction of unity extending to the innermost stable circular orbit around the black hole. Our model is an alternative to those that, in the low/hard state, require the accretion disc to be truncated at a few tens of Schwarzschild radii, within which there is a Thomson-thin, hot accretion flow. We suggest a mechanism that may cause the changes in spectral state.  相似文献   

Non-equilibrium Condensation ina Primordial Solar Nebula: Formation of Refractory Metal Nuggets     

Kyoko K. TanakaHidekazu Tanaka  Kiyoshi Nakazawa 《Icarus》2002,160(1):197-207

We present a theoretical investigation of non-equilibrium condensation of refractory metalsinthe primordial solar nebula, in relation to the origin of “Fremdlinges” included inCAIs. Todescribe the nucleation process of grains from vapor, weadopted asemi-phenomenological modelmodified fromthe classical nucleation theoryby the introductionof the second virial coefficient of vapor. This modelachieves excellent agreement with nucleation rate experiment. However,the second virial coefficients are unknown for a vapor of refractory metals. To overcome this, weexpress the nucleation rate by theuse of the chemical potential of dimersinsteadof the second virial coefficient.On the basis of this new nucleation theory,we have performed numerical simulations ofnon-equilibrium condensation of refractory metals andfind thattheircondensation temperatures, T_c, decrease considerably in comparison withequilibrium condensation. Even if the characteristiccooling time scale is aslarge as 1×10⁵ years, the decrease in T_c isfrom 200 to 400 Kfor rare elements such as W, Re,and Os. This remarkablenon-equilibrium behaviormainly stemsfromthelow totalpressure in the primordial solar nebula. From our new modelwealso obtainthe typical size ofgrainsformed in condensation. We findthatthe cooling time should be ?1×10⁵ years for sub-micron-sized or largerrefractory metal nuggetsto form.  相似文献   

Evolution of disk galaxies regulated by supernova remnants     

Yutaka D. Tanaka  Satoru Ikeuchi  Asao Habe 《Astrophysics and Space Science》1986,119(1):207-210

Assuming that a disk galaxy is composed of an ambient pervasive gas, small clouds, molecular clouds and stars, its evolution is studied through examining the interchange processes among them. Main results obtained are: (1) The star formation rate is directed by the formation process of molecular clouds. (2) Depending upon the parameters there may be three or four types of evolution of disk galaxies: the no star formation case, the active in the past and inactive at present star formation case, the burst-like star formation case and the very active in star formation case.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan between 30 September–6 October, 1984.  相似文献   

Seasonal variation in Tsushima Warm Current paths over the shelf off the San’in coast,Japan     

Akihiko Morimoto  Yutaka Isoda  Tatsuji Tameishi  Shimpei Moriwaki 《Continental Shelf Research》2009,29(11-12):1437-1447

Using long-term sea surface temperature (SST) and acoustic Doppler current profiler (ADCP) data, we examined variations in the current axis of the Tsushima Warm Current (TWC) off the San’in coast of Japan, near the entrance to the Japan Sea. There were large horizontal temperature gradients along the shelf edge in the southwestern Japan Sea from October to May, suggesting that the second branch of the TWC appears not only in spring and autumn but also in winter. From the ADCP data analysis, we found that currents with speeds of approximately 20 cm s^?1 and greater appeared around the shelf edge off San’in coast in all seasons. The SST and ADCP data analyses suggested that the second branch of the TWC exists around the shelf edge off the San’in coast throughout the year. This finding differed from those of previous studies. A relatively strong current (speed greater than 15 cm s^?1) appeared on the shore side in all seasons, except at line W in winter. This current might be the first branch of the TWC. The first branch seemed to occur around in 100 m isobaths, but shifted northward and southward because the bottom topography around lines W and M was relatively flat and the shelf was broad. The first branch was very obscure, and it was difficult to define the two branches of the TWC off the San’in coast from the seasonally averaged vectors. However, snapshots of current distribution derived from the ADCP data clearly showed these branches. Hence, both the first and second branches might occur throughout the year off the San’in coast.  相似文献   

Hydraulic properties of and pressure-head dynamics in thick pyroclastic-fall deposits in Atsuma,Northern Japan: implications for the role of water in shallow landslides induced by the 2018 Hokkaido Eastern Iburi Earthquake     

Aoki  Toshiya  Katsura  Shin&#;ya  Koi  Takashi  Tanaka  Yasutaka  Yamada  Takashi 《Landslides》2022,19(8):1813-1824

Landslides - The 2018 Hokkaido Eastern Iburi Earthquake triggered numerous shallow landslides on slopes covered with thick pyroclastic-fall deposits. The landslides occurred more frequently on...  相似文献   

Stream temperature sensitivity to climate warming in California’s Sierra Nevada: impacts to coldwater habitat   总被引：2，自引：0，他引：2  

Sarah E. Null  Joshua H. Viers  Michael L. Deas  Stacy K. Tanaka  Jeffrey F. Mount 《Climatic change》2013,116(1):149-170

Water temperature influences the distribution, abundance, and health of aquatic organisms in stream ecosystems, so understanding the impacts of climate warming on stream temperature will help guide management and restoration. This study assesses climate warming impacts on stream temperatures in California’s west-slope Sierra Nevada watersheds, and explores stream temperature modeling at the mesoscale. We used natural flow hydrology to isolate climate induced changes from those of water operations and land use changes. A 21 year time series of weekly streamflow estimates from WEAP21, a spatially explicit rainfall-runoff model were passed to RTEMP, an equilibrium temperature model, to estimate stream temperatures. Air temperature was uniformly increased by 2°C, 4°C, and 6°C as a sensitivity analysis to bracket the range of likely outcomes for stream temperatures. Other meteorological conditions, including precipitation, were unchanged from historical values. Raising air temperature affects precipitation partitioning into snowpack, runoff, and snowmelt in WEAP21, which change runoff volume and timing as well as stream temperatures. Overall, stream temperatures increased by an average of 1.6°C for each 2°C rise in air temperature, and increased most during spring and at middle elevations. Viable coldwater habitat shifted to higher elevations and will likely be reduced in California. Thermal heterogeneity existed within and between basins, with the high elevations of the southern Sierra Nevada and the Feather River watershed most resilient to climate warming. The regional equilibrium temperature modeling approach used here is well suited for climate change analysis because it incorporates mechanistic heat exchange, is not overly data or computationally intensive, and can highlight which watersheds are less vulnerable to climate warming. Understanding potential changes to stream temperatures from climate warming will affect how fish and wildlife are managed, and should be incorporated into modeling studies, restoration assessments, and licensing operations of hydropower facilities to best estimate future conditions and achieve desired outcomes.  相似文献