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401.
Daisuke Takahashi Kazuo Kido Yoshinori Nishida Naoto Kobayashi Naoyuki Higaki Hideo Miyake 《Continental Shelf Research》2007
We conducted hydrographic observations in 2002 to investigate the anticyclonic eddy that emerges every summer in Funka Bay, Hokkaido, Japan, and elucidate dynamical structure and wind-driven upwelling within the eddy. The anticyclonic eddy has a vertical scale of 32 m and is characterized by a strong baroclinic flow and a sharp pycnocline with a concave isopycnal structure. The sharp pycnocline occurs below a warm and relatively low-salinity water termed summer Funka Bay water (FS), which is formed by heating from solar radiation and dilution from river discharge in summertime Funka Bay. Flow of the anticyclonic eddy rotates as a rigid body at each layer, and the horizontal scale and rotation period of the eddy in the surface layer are about 15 km and 2.2 days, respectively. The dynamical balance of the anticyclonic eddy is well explained by the gradient flow balance. The contribution of centrifugal force to the gradient flow balance is about 27%. Therefore, the effect of the nonlinear term associated with centrifugal force cannot be neglected in considering the dynamics of the anticyclonic eddy in summertime Funka Bay. In addition, upwelling of subsurface water was observed in the surface layer of the central part of the eddy. The formation mechanism of this upwelling is consistent with interaction between horizontal uniform wind and the eddy. This upwelling is driven by upward Ekman pumping velocity related to the horizontal divergence of Ekman transport. In summertime Funka Bay, there are two wind effects that affect the anticyclonic eddy: a decay effect of the upwelling of subsurface water resulting from horizontal uniform wind (mainly northwesterly wind), and a maintenance or spin-up effect of horizontal non-uniform wind (mainly southerly–southeasterly seasonal wind) with negative wind stress curl. 相似文献
402.
403.
Naoko Kato Hiroshi Sato Masayuki Orito Kazuomi Hirakawa Yasutaka Ikeda Tanio Ito 《Tectonophysics》2004,388(1-4):75
A NS trending Cenozoic fold-and-thrust belt has developed in the western part of the Hidaka Collision Zone (HCZ), central Hokkaido, Japan. A quantitative estimation of the late Cenozoic convergence rate at the front of the Hidaka thrust system is important in revealing the plate tectonic framework around northern Japan. High-resolution seismic reflection profiling across the active fault-related folds was carried out to ascertain the temporal change in the crustal shortening rate. Overlapping ramp anticlines and growth folds within thrust sheets were examined using balanced cross-sections combined with industry seismic and drilling data. The rate of shortening was examined using a 3.5 Ma horizon and late Quaternary horizons at 115 and 41 ka. These horizons show that the convergence rate of the Hidaka thrust system has not decreased during the last 3.5 Ma. This suggests that the plate boundary between the Eurasian (Amurian) and North American (Okhotsk) plates has not jumped from the central part of Hokkaido to the eastern part of the Sea of Japan since 3.5 Ma and that a significant amount of plate convergence is still being absorbed in the Hidaka Collision Zone. 相似文献
404.
The ground-based direction finding carried out at Ceduna, Australia (L=1.93) has yielded the structure for mid-latitude whistlers and their duct ionospheric transmission mechanism. It is found that the ducts tend to take place (or be formed) at the same latitudes and that such sheet-shaped duct includes some inhomogeneities within it which act as field-aligned ducts. 相似文献
405.
Yusuke Miyajima Ayaka Saito Hiroyuki Kagi Tatsunori Yokoyama Yoshio Takahashi Takafumi Hirata 《Geostandards and Geoanalytical Research》2021,45(1):189-205
Uncertainty for elemental and isotopic measurements in calcite by LA‐ICP‐MS is largely controlled by the homogeneity of the reference materials (RMs) used for calibration and validation. In order to produce calcite RMs with homogeneous elemental and isotopic compositions, we incorporated elements including U, Pb and rare earth elements into calcite through heat‐ and pressure‐induced crystallisation from amorphous calcium carbonate that was precipitated from element‐doped reagent solution. X‐ray absorption spectra showed that U was present as U(VI) in the synthesised calcite, probably with a different local structure from that of aqueous uranyl ions. The uptake rate of U by our calcite was higher in comparison with synthetic calcite of previous studies. Variations of element mass fractions in the calcite were better than 12% 2RSD, mostly within 7%. The 207Pb/206Pb ratio in the calcite showed < 1% variations, while the 238U/206Pb ratio showed 3–24% variations depending on element mass fractions. Using the synthetic calcite as primary RMs, we could date a natural calcite RM, WC‐1, with analytical uncertainty as low as < 3%. The method presented can be useful to produce calcite with controlled and homogeneous element mass fractions and is a promising alternative to natural calcite RMs for U‐Pb geochronology. 相似文献
406.
The positive europium (Eu) anomaly, enrichment of Eu abundance relative to the neighboring elements, is often observed for water interacted with the rocks. Not only high temperature (~400°C) water-rock interaction such as seafloor hydrothermal fluids, but also relatively lower temperature interaction, less than 100°C, cause positive Eu anomaly. However, relationship between the degree of Eu anomaly and interaction temperature has not been investigated. Water-rock interaction experiments at three different reaction temperatures were performed in this study to reveal the cause of positive Eu anomaly. Comparison of the results under different solution chemistry and temperature conditions showed that the basalt containing plagioclase released larger abundances of REEs than the basaltic glass. The degree of Eu anomaly assessed by Eu/Eu* value was smaller when 0.7 M NaCl solution was used for liquid phase for both solid phases. On the other hand, the Eu/Eu* became larger with increasing reaction temperature for basalts interacted with ultra-pure water. Therefore, it is suggested that the Eu anomaly is potentially used as a fluid-rock interaction thermometer under low salinity condition. 相似文献
407.
Narito Kurata Takuji Kobori Motoichi Takahashi Toshihisa Ishibashi Naoki Niwa Jun Tagami Hiroshi Midorikawa 《地震工程与结构动力学》2000,29(5):629-645
The authors developed a semi‐active hydraulic damper (SHD) and installed it in an actual building in 1998. This was the first application of a semi‐active structural control system that can control a building's response in a large earthquake by continuously changing the device's damping coefficient. A forced vibration test was carried out by an exciter with a maximum force of 100 kN to investigate the building's vibration characteristics and to determine the system's performance. As a result, the primary resonance frequency and the damping ratio of a building that the SHDs were not jointed to, decreased as the exciting force increased due to the influence of non‐linear members such as PC curtain walls. The equivalent damping ratio was estimated by approximating the resonance curves using the steady‐state response of the SDOF bilinear hysteretic system. After the eight SHDs were jointed to the building, the system's performance was identified by a response control test for steady‐state vibration. The elements that composed the semi‐active damper system demonstrated the specified performance and the whole system operated well. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
408.
P. R. Fagundes Y. Sahai I. S. Batista M. A. Abdu J. A. Bittencourt H. Takahashi 《Annales Geophysicae》1999,17(8):1053-1063
In December 1995, a campaign was carried out to study the day-to-day variability in precursor signatures to large-scale ionospheric F-region plasma irregularities, using optical diagnostic techniques, near the magnetic equator in the Brazilian sector. Three instruments were operated simultaneously: (a) an all-sky (180° field of view) imaging system for observing the OI 630 nm nightglow emission at Alcântara (2.5°S, 44.4°W); (b) a digisonde (256-Lowell) at São Luis (2.6°S, 44.2°W); and (c) a multi-channel tilting filter-type zenith photometer for observing the OI 630 nm and mesospheric nightglow emissions at Fortaleza (3.9°S, 38.4°W). During the period December 14–18, 1995 (summer in the southern hemisphere), a good sequence of the OI 630 nm imaging observations on five consecutive nights were obtained, which are presented and discussed in this study. The observing period was geomagnetically quiet to moderate (Kp = 0+ to 5+ Dst = 18 nT to −37 nT). On four nights, out of the five observation nights, the OI 630 nm imaging pictures showed formations of transequatorial north-south aligned intensity depletions, which are the optical signatures of large-scale ionospheric F-region plasma bubbles. However, considerable day-to-day variability in the onset and development of the plasma depleted bands was observed. On one of the nights it appears that the rapid uplifting of the F-layer in the post-sunset period, in conjunction with gravity wave activity at mesospheric heights, resulted in generation of very strong plasma bubble irregularities. One of the nights showed an unusual formation of north-south depleted band in the western sector of the imaging system field of view, but the structure did not show any eastward movement, which is a normal characteristic of plasma bubbles. This type of irregularity structure, which probably can be observed only by wide-angle imaging system, needs more investigations for a better understanding of its behaviour. 相似文献
409.
Junko Takahashi David A. Williams 《Monthly notices of the Royal Astronomical Society》2000,314(2):273-278
The chemical desorption of an adsorbed CO molecule in the vicinity of H2 -forming sites on cosmic dust grains in cold dense clouds is investigated theoretically, mainly using a model based on a classical molecular dynamics computational simulation. As a model surface for icy mantles of dust grains, an amorphous water ice slab is generated at 10 K, and the first and the second H atoms are thrown on to the model surface to reproduce the recombination process of the two H atoms, H+H→H2 . Then, the time and space dependence of the local temperature increase of icy mantles caused by the release of H2 formation energy in the vicinity of H2 -forming sites is examined. It is found that icy mantles are heated locally up to about 30 K in the surface region at R 4 Å and about 20 K at 4 R 6 Å, where R is the distance from the H2 -forming site. The critical temperature of CO desorption is estimated to be about 20–30 K under conditions in typical dense clouds, which might be seen to be comparable to the above result. However, the lifetime of local heating of icy mantles is found to be too short, compared with the time-scale of CO desorption (1013 s) and that for H2 forming in the vicinity of an adsorbed CO molecule (more than 2×1013 s). Thus, it is found that the efficiency of chemical desorption of CO on a large dust grain is negligible. On the other hand, chemical desorption can occur on a small dust grain with size less than 20 Å. 相似文献
410.
We investigated dam behaviours during high-flow events and their robustness against perturbations in meteorological conditions using the H08 global hydrological model. Differences in these behaviours were examined by comparing simulation runs, with and without dams and using multiple meteorological datasets, at a case-study site, Fort Peck Dam on the Missouri River, USA. The results demonstrated that dam-regulated river flow reduced temporal variability over large time periods and also dampened inter-forcing discrepancies in river discharge (smoothing effects). However, during wet years, differences in peak flow were accentuated downstream of the dam, resulting in divergence in simulated peak flow across the meteorological forcing (pulsing effect). The pulsing effect was detected at other major dams in global simulations. Depending upon the meteorological forcing, the dams act as a selective filter against high-flow events. Synergy between a generic dam scheme and differences in meteorological forcing data might introduce additional uncertainties in global hydrological simulations. 相似文献