Evaporation metamorphism of primitive dust material in the early solar nebula     

Akihiko Hashimoto  Mineo Kumazawa  Naoki Onuma 《Earth and Planetary Science Letters》1979,43(1):13-21

An evaporation experiment on matrix material of the Murchison (C2) meteorite up to 1900°C in vacuo has revealed the evaporation sequence of primitive dust material and the associated evolution of residual solid phases from hydrous silicates through magnesium silicates and iron-metal to calcium-aluminum oxides. The comparison with primitive meteorites suggests that the evaporation metamorphism coupled with the re-condensation may have played an important role in the generation of diverse primitive meteorites in the early solar nebula.  相似文献   

A classification of meteorites based on oxygen isotopes     

Robert N. Clayton  Naoki Onuma  Toshiko K. Mayeda 《Earth and Planetary Science Letters》1976,30(1):10-18

On the basis of¹⁸O/¹⁶O and¹⁷O/¹⁶O ratios, meteorites and planets can be grouped into at least six categories, as follows: (1) the terrestrial group, consisting of the earth, moon, differentiated meteorites and enstatite chondrites; (2) types L and LL ordinary chondrites; (3) type H ordinary chondrites; (4) anhydrous minerals of C2, C3, C4 carbonaceous chondrites; (5) hydrous matrix minerals of C2 carbonaceous chondrites; (6) the ureilites. Objects of one category cannot be derived by fractionation or differentiation from the source materials of any other category.  相似文献   

Dynamic loading test and simulation analysis of full‐scale semi‐active hydraulic damper for structural control     

Naoki Niwa  Takuji Kobori  Motoichi Takahashi  Hiroshi Midorikawa  Narito Kurata  Takayuki Mizuno 《地震工程与结构动力学》2000,29(6):789-812

A semi‐active hydraulic damper (SHD) for a semi‐active damper system, which is useful for practical structural control especially for large earthquakes, has been developed. Its maximum damping force is set to 1 or 2 MN, and it is controlled by only 70 W of electric power. An SHD with a maximum damping force of 1 MN was applied to an actual building in 1998. This paper first presents the results of a dynamic loading test to confirm the control performance of the SHD. Next, an analytical model of SHDs (SHD model) is constructed with the same concept for two kinds of SHDs based on the test results. Through simulation analyses of the test results using the proposed SHD model, the dynamic characteristics of the SHD can be well represented within practical conditions. Simulation analyses are also carried out using a simple structure model with the SHD model. It is shown that this SHD model can be used to precisely evaluate the control effect of the semi‐active damper system and is useful in practical SHD design under the applied conditions. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Geogrid-based countermeasures against scour behind coastal dikes under tsunami overflow     

Naoki Takegawa  Toshinori Kawabata 《Marine Georesources & Geotechnology》2020,38(1):64-72

Abstract

Following the Great East Japan Earthquake, a massive tsunami caused serious damage to coastal dikes. Local scour at the ground behind these dikes reportedly causes dike failures. It is important to reveal the scour process to establish methods for effective scour countermeasures. Herein, we focus on geogrids. To verify this proposal and examine its design, flume-model experiments were performed for non-liquefied and liquefied grounds behind coastal dikes. The results showed that the scour amount and area were reduced drastically when geogrids were present. Geogrids on the sand-bed surface changed the direction of overflow water. Thus, a scour hole developed away from a coastal dike model. Furthermore, geogrids exerted a scour-reduction effect even during liquefaction.  相似文献   

Probing the evolution of early-type galaxies using multicolour number counts and redshift distributions     

Fumiaki Nakata  Kazuhiro Shimasaku  Mamoru Doi  Nobunari Kashikawa  Wataru Kawasaki  Yutaka Komiyama  Sadanori Okamura  Maki Sekiguchi  Masafumi Yagi  Naoki Yasuda 《Monthly notices of the Royal Astronomical Society》1999,309(4):L25-L29

We investigate pure luminosity evolution models for early-type (elliptical and S0) galaxies (i.e. no number density change or morphological transition), and examine whether these models are consistent with observed number counts in the B , I and K bands, and redshift distributions of two samples of faint galaxies selected in the I and K bands. The models are characterized by the star formation time-scale τ _SF and the time t _gw when the galactic wind starts to blow, in addition to several other conventional parameters. We find that the single-burst model ( τ _SF=0.1 Gyr and t _gw=0.353 Gyr), which is known to reproduce the photometric properties of early-type galaxies in clusters, is inconsistent with the redshift distributions of early-type galaxies in the field environment, owing to overpredictions of the number of galaxies at z ≳1.4 even with strong extinction which is at work until t _gw. In order for dust extinction to be more effective, we treat τ _SF and t _gw as free parameters, and find that models with τ _SF≳0.5 Gyr and t _gw>1.0 Gyr can be made consistent with both the observed redshift distributions and the number counts, if we introduce strong extinction [ E ( B − V )≥1 as a peak value]. These results suggest that early-type galaxies in the field environment do not have the same evolutionary history as described by the single-burst model.  相似文献   

The 21-cm signature of early relic H ii regions     

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   

Proton migration in portlandite inferred from activation energy of self-diffusion and potential energy curve of OH bond     

Naoki Noguchi  Keiji Shinoda 《Physics and Chemistry of Minerals》2010,37(6):361-370

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   

Wind-Tunnel Study of Scalar Transfer Phenomena for Surfaces of Block Arrays and Smooth Walls with Dry Patches   总被引：1，自引：1，他引：0  

Juyeon Chung  Aya Hagishima  Naoki Ikegaya  Jun Tanimoto 《Boundary-Layer Meteorology》2015,157(2):219-236

  相似文献   

Inverse estimation of empirical parameters used in a regional ocean circulation model     

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   

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