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141.
U6+-phases are common alteration products, under oxidizing conditions, of uraninite and the UO2 in spent nuclear fuel. These U6+-phases are subjected to a radiation field caused by the α-decay of U, or in the case of spent nuclear fuel, incorporated actinides, such as 239Pu and 237Np. In order to evaluate the effects of α-decay events on the stability of the U6+-phases, we report, for the first time, the results of ion beam irradiations (1.0 MeV Kr2+) of U6+-phases. The heavy-particle irradiations are used to simulate the ballistic interactions of the recoil-nucleus of an α-decay event with the surrounding structure. The Kr2+-irradiation decomposed the U6+-phases to UO2 nanocrystals at doses as low as 0.006 displacements per atom (dpa). U6+-phases accumulate substantial radiation doses (∼1.0 displacement per atom) within 100,000 yr if the concentration of incorporated 239Pu is as high as 1 wt.%. Similar nanocrystals of UO2 were observed in samples from the natural fission reactors at Oklo, Gabon. Multiple cycles of radiation-induced decomposition to UO2 followed by alteration to U6+-phases provide a mechanism for the remobilization of incorporated radionuclides. 相似文献
142.
Masayoshi Nakashima Satoshi Iwai Mamoru Iwata Toru Takeuchi Shinzo Konomi Takashi Akazawa Kazuhiro Saburi 《地震工程与结构动力学》1994,23(12):1299-1313
This paper presents the results of a pilot test conducted for evaluating the energy dissipation behaviour of shear panels made of low yield steel whose 0.2 per cent offset yield stress is 120 MPa. A total of six full-scale shear panels were tested with the loading condition, stiffener spacing, and magnitude of axial force as test variables. The shear panels tested yielded at a shear force that is approximately 1/3 of the yield shear force of equivalent shear panels made of common mild steel. Shear panels with proper stiffener arrangement exhibited stable hysteresis, thus ensuring large energy dissipation capacity. Sufficient strain hardening was observed in the shear panels tested, with their energy dissipation capacity about 1.5 times larger than that of an equivalent linear-elastic and perfect-plastic system. Plate buckling did not lead the shear panels to immediate degradation in their energy dissipation capacity. Post-buckling resistance was found to be a subject that requires further studies for quantifying the performance of shear panels made of low yield stress steel as hysteretic dampers. 相似文献
143.
Permafrost covers a significant area of the Qinghai-Tibet Plateau. Slope instability problem in the region was often neglected, though it plays important roles in engineering construction and landform processes. In this paper, the slope instability phenomena in the permafrost regions on the plateau are discussed. The slope failures often occur in the forms of thaw-induced landslides and gelifluction. Thaw-induced landslides are closely related to active layer detachment and changes of permafrost conditions. Such landslides include retrogressive flow and thaw slump and are hazardous to engineering constructions. Gelifluction includes deep-seated movement and surface movement. It is an important factor in landform planation because it may spread over a large area and remain active for a long period of time. 相似文献
144.
Masanori Kurosawa Kunihiro Shima Satoshi Ishii Kimikazu Sasa 《Geostandards and Geoanalytical Research》2006,30(1):17-30
The concentrations of fifty trace elements, including relatively volatile elements and transition metal elements, in fused glasses of Geological Survey of Japan rock reference materials GSJ JR-2, JA-1, JA-2, JB-1a, JB-3, JGb-1 and JF-1 were determined by particle (proton) induced X-ray emission (PIXE) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The fused glasses were prepared by rapid fusion and subsequent quenching in welded platinum capsules and were found to be homogeneous for major elements and for trace elements with concentrations of more than 1 μg g-1 within the observed precision (± 10% mean) on a 70 μm sampling scale. The values obtained by PIXE and LA-ICP-MS for the transition elements (Cr, Mn, Fe, Ni and Cu), the relatively volatile elements (Zn, Ga, Rb and Pb) and the refractory elements (Y, Zr, Nb and Th) with concentrations greater than a few μg g-1 showed good agreement (within 10 % relative difference). The values for almost all the elements detected at concentrations higher than 1 μg g-1 as determined by LA-ICP-MS also agreed well with the reference values (mean relative difference < ± 10%), except for B and Cu. The good agreement confirmed the appropriateness of the NIST SRM 600 series glass calibration reference material for LA-ICP-MS analysis of glasses with variable major-element compositions for almost all elements. The concentrations of Cu in all the samples were lower than the reference values, which was attributed to adsorption of the transition metals onto the platinum capsule during preparation. 相似文献
145.
Bubble and crystal textures provide information with regard to the kinetics of the vesiculation and crystallization processes. They also provide insights into the fluid mechanical behavior of magma in a conduit. We performed textural (bubble and crystal) and compositional analyses of pyroclasts that were obtained from the Tenjo pyroclastic flow, which resulted on account of the eruption in 838 A.D. on Kozu Island, about 200 km south of Tokyo, Japan. Pyroclasts in one flow unit (300∼2,060 kg/m3; average density 1330 kg/m3) can be classified into three types on the basis of vesicle textures. Type I pyroclasts have small isolated spherical bubbles with higher vesicularities (67–77 vol.%) and number density (10.8–11.7 log m−3). Type II pyroclasts have vesicularities similar to type I (61–69 vol.%), but most bubbles exhibit evidences of bubble coalescence, and lower number densities than type I (8.9–9.5 log m−3). Type III pyroclasts contain highly deformed bubbles with lower vesicularities (16–34 vol.%) and number densities (8.2–9.0 log m−3). The microlite volume fraction (DRE converted) also changes consistently across type I, type II, and type III as 0.06, 0.08, and 0.10–0.15, respectively. However, the number density of the microlites remains nearly invariant in all the pyroclast types. These facts indicate that the variation in the microlite volume fraction is controlled not by the number density (i.e., nucleation process), but by the size (i.e., growth process); the growth history of each type of microlite was different. Water content determinations show that the three types of pumices have similar H2O contents (2.6±0.2 wt%). This fact implies that all three types were quenched at nearly the same depth (35±5 MPa, assuming that the magma was water-saturated) in the conduit. If the crystal sizes are limited only by growth time, a variation in this parameter can be related to the residence time, which is attributed to the flow heterogeneity in the conduit. By assuming a laminar Poiseuille-type flow, these textural observations can be explained by the difference in ascent velocity and shearing motion across the conduit, which in turn results in the differences in growth times of crystals, degrees of deformation, and bubble coalescence. Consequently, for crystals in the inner part of the conduit, the crystal growth time from nucleation to quenching is shorter than that near the conduit wall. The vesicle texture variation of bubbles in types I, II, and III results from the difference in the deformation history, implying that the effect of degassing occurred primarily towards the conduit wall. 相似文献
146.
147.
Operational Data Assimilation System for the Kuroshio South of Japan: Reanalysis and Validation 总被引:3,自引:5,他引:3
Masafumi Kamachi Tsurane Kuragano Hiroshi Ichikawa Hirohiko Nakamura Ayako Nishina Atsuhiko Isobe Daisuke Ambe Masazumi Arai Noriaki Gohda Satoshi Sugimoto Kumi Yoshita Toshiyuki Sakurai Francesco Uboldi 《Journal of Oceanography》2004,60(2):303-312
We describe an operational ocean data assimilation system for the Kuroshio and its validation using a nine-year reanalysis
(historical run from 1993 to 2001) dataset of upper-ocean state estimation in the North Pacific. The horizontal structure
of volume transport of the Ryukyu Current System (RCS) is shown from the reanalysis: The RCS is connected to the flow of the
subtropical gyre, and its volume transport gradually increases from south-east of Okinawa (5–10 Sv) to the east of Amami-Ohshima
Island (20 Sv). Comparing the reanalysis with independent observations on the southeast slope of the Amami-Ohshima Island
indicates that the root mean square differences (RMSDs) are 0.076 (0.037) m/s in the period of December 1998 to November 1999
(November 1999 to November 2000) respectively. The reanalysis field has a bias (3.1 Sv) of the volume transport of the RCS
and the RMSD (3.5 Sv) which is larger than the observed variability (2.81 Sv). Surface velocity and the Kuroshio axis south
of Japan are also examined. Comparison of the reanalysis and ADCP data gave maximum RMSD of 0.749 (0.271) m/s in the strong
(weak) current regions, respectively. The annual mean value of the axis error is 19 km in 1998. The RMSD of the error is at
most 50 km, in 294 cases in the observation period, which is smaller than the observed root mean square variability of the
axis (64 km).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
148.
Shotaro Nakayama Gerrit Blacquière Tomohide Ishiyama Satoshi Ishikawa 《Geophysical Prospecting》2019,67(6):1498-1521
The application of blended acquisition has drawn considerable attention owing to its ability to improve the operational efficiency as well as the data quality and health, safety and environment performance. Furthermore, the acquisition of less data contributes to the business aspect, while the desired data density is still realizable via subsequent data reconstruction. The use of fewer detectors and sources also minimizes operational risks in the field. Therefore, a combined implementation of these technologies potentially enhances the value of a seismic survey further. One way to encourage this is to minimize any imperfection in deblending and data reconstruction during processing. In addition, one may derive survey parameters that enable a further improvement in these processes as introduced in this study. The proposed survey design workflow iteratively performs the following steps to derive the survey parameters responsible for source blending as well as the spatial sampling of detectors and sources. The first step is the application of blending and sampling operators to unblended and well-sampled data. We then apply closed-loop deblending and data reconstruction. The residue for a given design from this step is evaluated and subsequently used by genetic algorithms to simultaneously update the survey parameters related to both blending and spatial sampling. The updated parameters are fed into the next iteration until they satisfy the given termination criteria. We also propose a repeated encoding sequence to form a parameter sequence in genetic algorithms, making the size of problem space manageable. The results of the proposed workflow are outlined using blended dispersed source array data incorporating different scenarios that represent acquisition in marine, transition zone and land environments. Clear differences attributed solely to the parameter design are easily recognizable. Additionally, a comparison among different optimization schemes illustrates the ability of genetic algorithms along with a repeated encoding sequence to find better solutions within a computationally affordable time. The optimized parameters yield a notable enhancement in the deblending and data reconstruction quality and consequently provide optimal acquisition scenarios. 相似文献
149.
Minoru Wada Yukiko Takano Saki Nagae Yuka Ohtake Yu Umezawa Shinichi Nakamura Makoto Yoshida Yukihiko Matsuyama Mitsunori Iwataki Satoshi Takeshita Tatsuya Oda 《Journal of Oceanography》2018,74(6):587-593
Acute and severe hypoxia associated with harmful algal bloom has become one of the major causes for the environmental deterioration of coastal areas. Although it is generally thought that a large part of the dissolved oxygen consumption at a bloom site is initiated by heterotrophic bacteria that attack organic matter derived from dead or dying algal cells, precise microbial processes leading to the hypoxia are yet to be examined. Here we show temporal dynamics of extracellular dissolved organic carbon (DOC) of the red tide forming raphidophyte Chattonella marina and bacterial populations associating with the algae under laboratory conditions. During the growth of non-axenic strains of C. marina, we monitored abundance of algae, associated bacteria, and DOC in the culture media. Bacterial cell abundance increased in response to the increase in DOC both at the beginning and the late log phase of the algal growth. Flow cytometric analysis revealed that transient increase in the percentage of respiratory-active bacterial cells also coincided with the timing of the increase in bacterial abundance and DOC. These results strongly suggest that DOC released from growing C. marina fuels respiration and growth of planktonic bacteria surrounding the algae. This has implications for the role of DOC released from C. marina bloom before the collapse in mediating interactions between neighboring algae and bacterial assemblage which may eventually lead to algal bloom-associated hypoxia. 相似文献
150.
Napakhwan Whanpetch Masahiro Nakaoka Hiroshi Mukai Takao Suzuki Satoshi Nojima Takashi Kawai Chittima Aryuthaka 《Estuarine, Coastal and Shelf Science》2010
Seagrass beds are susceptible to various natural and human-induced disturbances. Disturbances affect not only seagrasses, but also the abundance and diversity of associated macrofaunal communities. The Andaman Sea coast of Thailand was heavily affected by the tsunami of December 26, 2004. To examine its impact on seagrass macrofaunal communities, we compared the abundance, diversity and taxa composition by quantitative samplings in 2001 (before the tsunami) and in 2005 and 2006 (after the tsunami). Macrobenthic animals and sediments were collected from vegetated and nonvegetated areas of two sites that had received different levels of tsunami disturbances. A large decline in abundance and diversity was observed in the nonvegetated areas after the tsunami, whereas an increase was observed in the vegetated areas. The magnitude of decline and subsequent recovery of abundance and diversity of macrobenthic animals in nonvegetated areas were similar between the two sites, suggesting that their temporal changes were not solely related to the magnitude of the tsunami disturbance. Similarity of the benthic animals differed greatly between 2001 and 2005–2006 at the nonvegetated areas, whereas it varied less among the 3 years at the seagrass-vegetated areas. This study demonstrated that the presence of seagrass vegetation alters the patterns of temporal variation in macrofaunal assemblages and subsequent recovery processes following a tsunami. 相似文献