The role of Fischer-Tropsch catalysis in the origin of methane-rich Titan     

Yasuhito Sekine  Seiji Sugita  Takashi Yamamoto  Toshihiko Kadono 《Icarus》2005,178(1):154-164

Fischer-Tropsch catalysis, which converts CO and H₂ into CH₄ on the surface of iron catalyst, has been proposed to produce the CH₄ on Titan during its formation process in a circum-planetary subnebula. However, Fischer-Tropsch reaction rate under the conditions of subnebula have not been measured quantitatively yet. In this study, we conduct laboratory experiments to determine CH₄ formation rate and also conduct theoretical calculation of clathrate formation to clarify the significance of Fischer-Tropsch catalysis in a subnebula. Our experimental result indicates that the range of conditions where Fischer-Tropsch catalysis proceeds efficiently is narrow (T∼500-600 K) in a subnebula because the catalysts are poisoned at temperatures above 600 K under the condition of subnebula (i.e., H₂/CO = 1000). This suggests that an entire subnebula may not become rich in CH₄ but rather that only limited region of a subnebula may enriched in CH₄ (i.e., CH₄-rich band formation). Our experimental result also suggests that both CO and CO₂ are converted into CH₄ within time significantly shorter than the lifetime of the solar nebula at the optimal temperatures around 550 K. The calculation result of clathration shows that CO₂-rich satellitesimals are formed in the catalytically inactive outer region of subnebula. In the catalytically active inner region, CH₄-rich satellitesimals are formed. The resulting CH₄-rich satellitesimals formed in this region play an important role in the origin of CH₄ on Titan. When our experimental data are applied to a high-pressure model for subnebula evolution, it would predict that there should be CO₂ underneath the Iapetus subsurface and no thick CO₂ ice layer on Titan's icy crust. Such surface and subsurface composition, which may be observed by Cassini-Huygens mission, would provide crucial information on the origin of icy satellites.  相似文献   

Statistical analyses and modeling approaches to hydrodynamic characteristics in alluvial aquifer     

Chie Imagawa  Junichiro Takeuchi  Toshihiko Kawachi  Shunsuke Chono  Kei Ishida 《水文研究》2013,27(26):4017-4027

This study is aimed at quantifying the difference in aquifer's response to recharge between some different locations in a fan aquifer and a delta aquifer for a preliminary study of revealing mechanisms of water transport in alluvial aquifer. The aquifer's response to recharge is statistically quantified with the two viewpoints: (1) timing and volume of recharge and (2) time length of aquifer's holding water. For the first point, a statistical model that links precipitation and groundwater level is introduced, and its parameters are identified using correlation analysis. Our results show that the recharge rate at the toe is higher than that at the apex and at the delta. For the second point, the concept of ‘memory effect’ of aquifer is adopted and quantified using the autocorrelation and spectral analyses. Our results show that the memory effect is longer at the toe of fan than at the apex, and thus, a temporary increase of water level has about five times as long‐term influence on subsequent water levels at the toe of the fan as at the apex. This study demonstrates that the statistical analyses and modeling of hydrological data are useful for characterizing aquifer's hydrodynamics. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Variable stars in the Magellanic Clouds: results from OGLE and SIRIUS     

Yoshifusa Ita  Toshihiko Tanabé  Noriyuki Matsunaga  Yasushi Nakajima  Chie Nagashima  Takahiro Nagayama  Daisuke Kato  Mikio Kurita  Tetsuya Nagata  Shuji Sato  Motohide Tamura  Hidehiko Nakaya  Yoshikazu Nakada 《Monthly notices of the Royal Astronomical Society》2004,347(3):720-728

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In situ observation of penetration process in silica aerogel: Deceleration mechanism of hard spherical projectiles     

Rei Niimi  Toshihiko Kadono 《Icarus》2011,211(2):986-992

A large number of cometary dust particles were captured with low-density silica aerogels by NASA’s Stardust Mission. Knowledge of the details of the capture mechanism of hypervelocity particles in silica aerogel is needed in order to correctly derive the original particle features from impact tracks. However, the mechanism has not been fully understood yet. We shot hard spherical projectiles of several different materials into silica aerogel of density 60 mg cm⁻³ and observed their penetration processes using an image converter or a high-speed video camera. In order to observe the deceleration of projectiles clearly, we carried out impact experiments at two velocity ranges; ∼4 km s⁻¹ and ∼200 m s⁻¹. From the movies we took, it was indicated that the projectiles were decelerated by hydrodynamic force which was proportional to v² (v: projectile velocity) during the faster penetration process (∼4 km s⁻¹) and they were merely overcoming the aerogel crushing strength during the slower penetration process (∼200 m s⁻¹). We applied these deceleration mechanisms for whole capture process to calculate the track length. Our model well explains the track length in the experimental data set by Burchell et al. (Burchell, M.J., Creighton, J.A., Cole, M.J., Mann, J., Kearsley, A.T. [2001]. Meteorit. Planet. Sci. 36, 209-221).  相似文献   

New compact ocean bottom cabled seismometer system deployed in the Japan Sea     

Masanao Shinohara  Toshihiko Kanazawa  Tomoaki Yamada  Yuya Machida  Takashi Shinbo  Shin’ichi Sakai 《Marine Geophysical Researches》2014,35(3):231-242

The Japanese islands are positioned near the subduction zones, and large earthquakes have repeatedly occurred in marine areas around Japan. However, the number of permanent earthquake observatories in the oceans is quite limited. It is important for understanding generation of large earthquakes to observe seismic activities on the seafloor just above these seismogenic zones. An ocean bottom cabled seismometer (OBCS) is the best solution because data can be collected in real-time. We have developed a new compact OBCS system. A developed system is controlled by a microprocessor, and signals from accelerometers are 24-bit digitized. Clock is delivered from the global positioning system receiver on a landing station using a simple dedicated line. Data collected at each cabled seismometer (CS) are transmitted using standard Internet Protocol to landing stations. The network configuration of the system adopts two dual methods. We installed the first practical OBCS system in the Japan Sea, where large earthquakes occurred in past. The first OBCS system has a total length of 25 km and 4 stations with 5 km interval. Installation was carried out in August 2010. The CSs and single armored optical submarine cable were buried 1 m below the seafloor to avoid a conflict with fishing activity. The data are stored on a landing station and sent to Earthquake Research Institute, University of Tokyo by using the Internet. After the installation, data are being collected continuously. According to burial of the CSs, seismic ambient noises are smaller than those observed on seafloor.  相似文献   

Simulating the carbon balance of a temperate larch forest under various meteorological conditions     

Motomu Toda  Masayuki Yokozawa  Akihiro Sumida  Tsutomu Watanabe  Toshihiko Hara 《Carbon balance and management》2007,2(1):1-18

This editorial provides a subject index from published articles, active researchers, and published papers in the field of carbon balance and management.  相似文献   

The comparative study of trihalomethanes in drinking water     

T. S. Imo  T. Oomori  M. Toshihiko  F. Tamaki 《International Journal of Environmental Science and Technology》2007,4(4):421-426

The purpose of this study was to assess exposure of four trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane and bromoform) in drinking water of Okinawa Island and Samoa. Trihalomethanes compounds were determined in the drinking water samples that were collected from the selected consumption sites and treatment plants of both Okinawa and Samoa in 2003–2004. The Chatan and Nishihara Water Treatment Plants (Okinawa) uses both ozonation and chlorination for primary and secondary disinfection. For Samoa Water Treatment Plants only chlorination is used as primary disinfection. Results showed that the mean concentration of trihalomethanes from treatment plants in Okinawa ranged from 0.30 ± 1.81 ?g/L to 11 ± 2.68 ?g/L and from the consumption sites ranged from 2.08 ± 0.32?g/L to 19.39 ± 100 ?g/L. In comparison, the mean concentration of trihalomethanes from the treatment plants in Samoa ranged from 226 ± 81.2 ?g/L to 267 ± 92.3 ?g/L and from the consumption sites were in the ranges 212 ± 101 ?g/L to 387 ± 125 ?g/L. Brominated compounds were commonly seen in all samples collected in Okinawa. Among the trihalomethanes compounds, chloroform was the common detected trihalomethanes in the samples collected from Samoa. The trihalomethanes levels in all samples collected in Okinawa and Samoa were generally below the guideline values in Japan, but some samples displayed levels which exceeded the level of Japan Water Quality and WHO Standards for chlorinated and brominated compounds.  相似文献   

Mechanisms of uranium mineralization by the yeast Saccharomyces cerevisiae     

Toshihiko Ohnuki  Takuo Ozaki  Fuminori Sakamoto  Eiichi Wakai  Haruyuki Iefuji 《Geochimica et cosmochimica acta》2005,69(22):5307-5316

We determined the association of uranium in yeast cells S. cerevisiae grown in medium containing high (1 g · L^-1) or low (0.2 g · L^-1) concentrations of phosphate after exposure for 96 h to a 4 × 10^-4 mol · L^-1 U(VI) solution at pH 3.2 or 4.7. The analysis was made using a field emission scanning electron microscope equipped with energy dispersive spectroscopy (FESEM-EDS), transmission electron microscopy (TEM), and visible diffuse reflectance spectrometry. Cells grown in the high-phosphate medium rapidly accumulated U(VI) from solution at pH 3.2 over the first 24 h, followed by a slow uptake until 96 h, whereas in cells grown in low-phosphate medium, U(VI) accumulation reached a steady state within 24 h. FESEM-EDS analyses revealed the formation of a U(VI)-bearing precipitate on the yeast cells grown in high-phosphate medium after only 48 h exposure; no precipitate was detected on cells grown in low-phosphate medium up to 96 h. These results suggest that sorption onto the cell surfaces was the dominant process initially. Analysis of the U(VI)-bearing precipitates by all three methods demonstrated the presence of H-autunite, HUO₂PO₄ · 4H₂O. Thermodynamic calculations suggest that the chemical compositions of the solutions containing yeast grown in high-phosphate medium were undersaturated with respect to H-autunite, but were supersaturated with ten times more U(VI) and P than were actually observed. Apparently, the sorbed U(VI) on the cell surfaces reacts with P released from the yeast to form H-autunite by local saturation. The U(VI) uptake by yeast cells grown in high phosphate medium at pH 4.7, along with the thermodynamic calculation, indicated that more H-autunite is precipitated in neutral pH solution than in acid solution. Thus, U(VI)-phosphate mineralization on the cells of microorganisms should be taken into account for predicting U(VI) mobility in the environment.  相似文献   

Comparative study of cataclastic rocks from a drill core and outcrops of the Nojima Fault zone on Awaji Island, Japan   总被引：3，自引：0，他引：3  

Aiming Lin  Toshihiko Shimamoto  Tadashi Maruyama  Motoko Sigetomi  Takao Miyata  Keiji Takemura  Hidemi Tanaka  Shinichi Uda  Akihiro Murata 《Island Arc》2001,10(3-4):368-380

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V_pIV_s ratio structure of the Lofoten continental margin, northern Norway, and its geological implications     

Shuichi Kodaira  Martin Bellenberg    Takaya Iwasaki    Toshihiko Kanazawa    Hans B. Hirschleber  Hideki Shimamura 《Geophysical Journal International》1996,124(3):724-740

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