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101.
Midori Tokutani Naoki Yoshida S. Peng Oh Naoshi Sugiyama 《Monthly notices of the Royal Astronomical Society》2009,395(2):777-780
We calculate the spin temperature and 21-cm brightness of early H ii regions around the first stars. We use outputs from cosmological radiation-hydrodynamics simulations of the formation and evolution of early H ii regions. In the pre-re-ionization era, H ii regions around massive primordial stars have diameters of a few kpc. The gas within the H ii regions is almost fully ionized, but begins recombining after the central stars die off. The relic H ii regions are then seen as bright emission sources in hydrogen 21 cm. We make brightness temperature maps of the H ii regions, accounting for radiative coupling with Lyman α photons in a simplified manner. The spin temperature in the relic H ii region is close to the gas kinetic temperature, generally several hundred to several thousand degrees. We show that the relic H ii region can be as bright as δ T b ∼ 100 mK in differential temperature against the cosmic microwave background for an angular resolution of subarcseconds. While individual early H ii patches will not be identified by currently planned radio telescopes, the collective fluctuations from early H ii regions might imprint signatures in the 21-cm background. 相似文献
102.
A fundamental mechanism on the atomic level for self-diffusion in the proton layer of portlandite, Ca(OH)2, was investigated by conducting hydrogen–deuterium (H–D) exchange diffusion experiments and by deriving potential energy
curves of OH vibrations from optical absorption measurements. Synthetic single crystals of portlandite were used in H–D experiments
between 250 and 450°C at 150 MPa. Arrhenius parameters for proton diffusion perpendicular to the c-axis gave a frequency factor of 1.0 × 10−10 m2/s and activation energy of 0.61 eV (58.5 kJ/mol). The activation energy corresponds to the height of the potential barrier
between two oxygen atoms across an interlayer. The potential barrier height was also theoretically estimated using the OH
potential energy curve (OH-PEC) determined by optical absorption measurements. Experimental and theoretical results suggest
that the potential barrier height cannot be simply determined by overlapping two OH-PECs. The potential barrier derived theoretically
was 3.11 eV. This is too high for the activation energy of the proton diffusion. It implies that the interaction between a
diffusing proton and the vacancy of a proton site, and the shortening of interlayer oxygen distance by thermal vibration reduce
the potential barrier. 相似文献
103.
104.
Naoki Hirose 《Journal of Oceanography》2011,67(3):323-336
Significant impacts of the subgridscale parameterizations have been emphasized in modeling the ocean circulations, but various
different parameter values are applied to similar numerical studies often without any justification. This study objectively
estimates a set of empirical parameters along with their uncertainty for circulation modeling of the East Asian Marginal Seas.
The solutions for 14 major parameters are obtained by using model Green’s functions with constraints of climatological temperature
and salinity data. The largest cost function reduction occurs in the eastern Japan Sea associated with the sharp gradient
of the Polar Front. The calibrated parameters are also validated with realistic transport and path of the Kuroshio in the
final experiment. The inverse estimation shows that freshwater discharges from small rivers can be attributed to the coastal
precipitation over a strip of land 74–81 km wide. The thickness diffusion coefficient may be similar to the isopycnal and
horizontal diffusion coefficients in their magnitude. The accelerated initial condition also contributes to the cost function
reduction resulting in weaker trends of deep temperature. Most importantly, estimated scaling factors suggest a significant
reduction of the reanalyzed wind stress data for more realistic ocean circulations. Possible reasons for the momentum missing
are also discussed. 相似文献
105.
Analysis of summertime atmospheric transport of fine particulate matter in Northeast Asia 总被引:1,自引:0,他引:1
Hikari Shimadera Hiroshi Hayami Yu Morino Toshimasa Ohara Satoru Chatani Shuichi Hasegawa Naoki Kaneyasu 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(3):347-360
In Northeast Asia, the effect of long-range transport of air pollutants is generally pronounced in spring and winter, but can be important even in summer. This study analyzed summer-time atmospheric transport of elemental carbon (EC) and sulfate (SO4 2?) with the Community Multiscale Air Quality (CMAQ) model driven by the Weather Research and Forecasting (WRF) model. The WRF/CMAQ modeling system was applied to regions ranging from Northeast Asia to the Greater Tokyo Area in Japan in summer 2007. In terms of EC, while the model simulated well the effect of long-range transport, the simulation results indicated that domestic emissions in Japan dominantly contributed (85%) to EC concentrations in the Greater Tokyo. In terms of SO4 2?, the simulation results indicated that both domestic emissions (62%) and long-range transport from the other countries (38%) substantially contributed to SO4 2? concentrations in the Greater Tokyo. Distinctive transport processes of SO4 2? were associated with typical summer-time meteorological conditions in the study region. When a Pacific high-pressure system covered the main island of Japan, domestic emissions, including volcanic emission, dominantly contributed to SO4 2? concentrations in the Greater Tokyo. When a high-pressure system prevailed over the East China Sea and low-pressure systems passed north of Japan, synoptic westerly winds associated with this pressure pattern transported a large amount of SO4 2? from the continent to Japan. In addition, although heavy precipitation and strong wind decreased SO4 2? concentrations near the center of a typhoon, peripheral typhoon winds occasionally played an important role in long-range transport of SO4 2?. 相似文献
106.
Kiyoaki?WajimaEmail author Kenta?Fujisawa Masaaki?Hayashida Naoki?Isobe 《Journal of Astrophysics and Astronomy》2014,35(3):215-218
We made simultaneous single-dish and VLBI observations of a gamma-ray narrow-line Seyfert 1 (NLS1) galaxy 1H 0323+342. We found significant flux variation at 8 GHz on a time scale of one month. The total flux density varied by 5.5% in 32 days, corresponding to a variability brightness temperature of 7.0 × 1011 K. We also obtained brightness temperatures of greater than 5.2 × 1010 K from the VLBI images. These high brightness temperatures suggest that the source has nonthermal processes in the central engine. The source structure could be modelled by two elliptical Gaussian components on the parsec scales. The flux of the central component decreases in the same way as the total flux density, showing that the short-term variability is mainly associated with this component. 相似文献
107.
108.
Naoki Kabeya Masanori Katsuyama Masatoshi Kawasaki Nobuhito Ohte Atsuko Sugimoto 《水文研究》2007,21(3):308-322
We measured deuterium excess (d = δD ? 8δ18O) in throughfall, groundwater, soil water, spring water, and stream water for 3 years in a small headwater catchment (Matsuzawa, 0·68 ha) in the Kiryu Experimental Watershed in Japan. The d value represents a kinetic effect produced when water evaporates. The d value of the throughfall showed a sinusoidal change (amplitude: 6·9‰ relative to Vienna standard mean ocean water (V‐SMOW)) derived from seasonal changes in the source of water vapour. The amplitude of this sinusoidal change was attenuated to 1·3–6·9‰ V‐SMOW in soil water, groundwater, spring water, and stream water. It is thought that these attenuations derive from hydrodynamic transport processes in the subsurface and mixing processes at an outflow point (stream or spring) or a well. The mean residence time (MRT) of water was estimated from d value variations using an exponential‐piston flow model and a dispersion model. MRTs for soil water were 0–5 months and were not necessarily proportional to the depth. This may imply the existence of bypass flow in the soil. Groundwater in the hillslope zone had short residence times, similar to those of the soil water. For groundwater in the saturated zone near the spring outflow point, the MRTs differed between shallow and deeper groundwater; shallow groundwater had a shorter residence time (5–8 months) than deeper groundwater (more than 9 months). The MRT of stream water (8–9 months) was between that of shallow groundwater near the spring and deeper groundwater near the spring. The seasonal variation in the d value of precipitation arises from changes in isotopic water vapour composition associated with seasonal activity of the Asian monsoon mechanism. The d value is probably an effective tracer for estimating the MRT of subsurface water not only in Japan, but also in other East Asian countries influenced by the Asian monsoon. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
109.
Kazunari Nawa Naoki Suda Yoshio Fukao Tadahiro Sato Yoshiaki Tamura Kazuo Shibuya Herbert McQueen Heikki Virtanen Jussi Kriinen 《Physics of the Earth and Planetary Interiors》2000,120(4):289-297
Records of superconducting gravimeters (SGs) at Canberra (Australia), Esashi (Japan), Metsähovi (Finland) and Syowa Stations (Antarctica) were analyzed to search for further evidence of background free oscillations of the Earth. Spectrograms for 1-year period and averaged power spectra for seismically quiet periods were obtained for each of the stations. Anomalous features of the oscillations observed at Syowa Station, such as an apparent seasonal variation and a high intensity at frequencies between 3 and 4 mHz, were absent at the other SG stations. Among the SG stations used in this study, the background free oscillations were detected most consistently and distinctly at Canberra, where the noise level was comparable to that at the IDA quietest station, while that at Syowa Station was close to the critical limit for detecting the oscillations. The background free oscillations provide a good reference to evaluate the noise level in the milliHertz band. 相似文献
110.