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排序方式: 共有452条查询结果,搜索用时 15 毫秒
1.
To assess the post-earthquake seismic safety of buildings, it is crucial to predict seismic response, and it is necessary to set the appropriate physical parameters of the response analysis model. Numerous methods have been proposed to identify physical parameters. However, most of them are limited to linear systems, and previous researches on nonlinear systems have difficulties in practical applications. In this paper, a nonlinear response analysis model is identified for a full-scale ten-story reinforced concrete building with the degrading tri-linear stiffness model by the modal iterative error correction (MIEC) method, and the accuracy of this technique is discussed by comparing with the shaking table test. 相似文献
2.
Nakamura Hitomi Iwamori Hikaru Morikawa Noritoshi Kharitonova Natalia Chelnokov Georgy Bragin Ivan Chang Qing 《Aquatic Geochemistry》2021,27(4):269-282
Aquatic Geochemistry - Spring waters with high-pCO2 content are widely distributed in the Sikhote-Alin region in Russia. Mukhen spa is one such spring located in the northern Sikhote-Alin region.... 相似文献
3.
Jayanta Kumar Pati Michael H. Poelchau Wolf Uwe Reimold Norihiro Nakamura Yutaro Kuriyama Anuj Kumar Singh 《Meteoritics & planetary science》2019,54(10):2312-2333
The fundamental approach for the confirmation of any terrestrial meteorite impact structure is the identification of diagnostic shock metamorphic features, together with the physical and chemical characterization of impactites and target lithologies. However, for many of the approximately 200 confirmed impact structures known on Earth to date, multiple scale‐independent tell‐tale impact signatures have not been recorded. Especially some of the pre‐Paleozoic impact structures reported so far have yielded limited shock diagnostic evidence. The rocks of the Dhala structure in India, a deeply eroded Paleoproterozoic impact structure, exhibit a range of diagnostic shock features, and there is even evidence for traces of the impactor. This study provides a detailed look at shocked samples from the Dhala structure, and the shock metamorphic evidence recorded within them. It also includes a first report of shatter cones that form in the shock pressure range from ~2 to 30 GPa, data on feather features (FFs), crystallographic indexing of planar deformation features, first‐ever electron backscatter diffraction data for ballen quartz, and further analysis of shocked zircon. The discovery of FFs in quartz from a sample of the MCB‐10 drill core (497.50 m depth) provides a comparatively lower estimate of shock pressure (~7–10 GPa), whereas melting of a basement granitoid infers at least 50–60 GPa shock pressure. Thus, the Dhala impactites register a strongly heterogeneous shock pressure distribution between <2 and >60 GPa. The present comprehensive review of impact effects should lay to rest the nonimpact genesis of the Dhala structure proposed by some earlier workers from India. 相似文献
4.
Tetsu Nakamura Masayuki Hara Miki Oshika Yoshihiro Tachibana 《Climate Dynamics》2015,45(11-12):3547-3562
5.
Mingyu Wu Quanming Lu Martin Volwerk Rumi Nakamura Tielong Zhang 《Astrophysics and Space Science》2018,363(2):22
In this paper, with the in-situ observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes we report a wavy dipolarization front (DF) event, where the DF has different magnetic structures and electron distributions at different \(y\) positions in the Geocentric Solar Magnetospheric (GSM) coordinates. At \(y \sim2.1R_{E}\) (\(R_{E}\) is the radius of Earth), the DF has a relatively simple structure, which is similar to that of a conventional DF. At \(y \sim3.0R_{E}\), the DF is revealed to have a multiple DF structure, where the plasma exhibits a vortex flow. Such a wavy DF could be the results of the interchange instability. The different structure of such a wavy DF at different sites has a great effect on electron acceleration. Fermi acceleration can occur at the site of the DF with a simple or multiple DF structure, while betatron acceleration as a local process has the contribution to energetic electrons only at the site of the DF with a simple structure. 相似文献
6.
Yan-Jie Tang Hong-Fu Zhang Eizo Nakamura Ji-Feng Ying 《Contributions to Mineralogy and Petrology》2011,161(6):845-861
Elemental and Li–Sr–Nd isotopic data of minerals in spinel peridotites hosted by Cenozoic basalts allow us to refine the existing
models for Li isotopic fractionation in mantle peridotites and constrain the melt/fluid-peridotite interaction in the lithospheric
mantle beneath the North China Craton. Highly elevated Li concentrations in cpx (up to 24 ppm) relative to coexisting opx
and olivine (<4 ppm) indicate that the peridotites experienced metasomatism by mafic silicate melts and/or fluids. The mineral
δ7Li vary greatly, with olivine (+0.7 to +5.4‰) being isotopically heavier than coexisting opx (−4.4 to −25.9‰) and cpx (−3.3
to −21.4‰) in most samples. The δ7Li in pyroxenes are considerably lower than the normal mantle values and show negative correlation with their Li abundances,
likely due to recent Li ingress attended by diffusive fractionation of Li isotopes. Two exceptional samples have olivine δ7Li of −3.0 and −7.9‰, indicating the existence of low δ7Li domains in the mantle, which could be transient and generated by meter-scale diffusion of Li during melt/fluid-peridotite
interaction. The 143Nd/144Nd (0.5123–0.5139) and 87Sr/86Sr (0.7018–0.7062) in the pyroxenes also show a large variation, in which the cpx are apparently lower in 87Sr/86Sr and slightly higher in 143Nd/144Nd than coexisting opx, implying an intermineral Sr–Nd isotopic disequilibrium. This is observed more apparently in peridotites
having low 87Sr/86Sr and high 143Nd/144Nd ratios than in those with high 87Sr/86Sr and low 143Nd/144Nd, suggesting that a relatively recent interaction existed between an ancient metasomatized lithospheric mantle and asthenospheric
melt, which transformed the refractory peridotites with highly radiogenic Sr and unradiogenic Nd isotopic compositions to
the fertile lherzolites with unradiogenic Sr and radiogenic Nd isotopic compositions. Therefore, we argue that the lithospheric
mantle represented by the peridotites has been heterogeneously refertilized by multistage melt/fluid-peridotite interactions. 相似文献
7.
Ratan K. Majumder M. A. Halim B. B. Saha Reo Ikawa Toshio Nakamura Makoto Kagabu Jun Shimada 《Environmental Earth Sciences》2011,64(5):1343-1352
A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers,
Bangladesh using environmental isotope (2H, 18O, 13C, 3H, and 14C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ2H = 7.7 δ18O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ18O and δ2H). The δ18O and δ2H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling
evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the
shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU,
which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of 14C activity is associated with the heavier δ13C values, which indicates the presence of geochemical reactions affecting the 14C concentration along the groundwater flow system. Both vertical and lateral decrease of 14C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which
discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the
Bengal Delta aquifers, Bangladesh. 相似文献
8.
Tomohiro Nakamura Takahiro Toyoda Yoichi Ishikawa Toshiyuki Awaji 《Journal of Oceanography》2010,66(1):41-60
A steady quasi-geostrophic 2.5-layer model, forced by both Ekman pumping and a mass source/sink situated at the western boundary
has been constructed to investigate the effect of diapycnal transport due to convection in the Okhotsk Sea and tidal mixing
at the Kuril Straits on the intermediate layer in the North Pacific. The model illustrates a combined effect of the wind-driven
and mass-driven circulations. First, net mass input induces a “barotropic” mode inter-gyre flow along the western boundary
through the dynamical influence of Kelvin waves. This flow creates characteristic curves (geostrophic contours) that facilitate
inter-gyre communication through the western boundary layer from the location of the mass source to the subtropical gyre.
Due to the effect of wind-driven circulation, the offshore part turns eastward into the interior, encircles the outer rim
of the region (which would otherwise be the pool region in the absence of mass input), and then encounters the western boundary.
Eventually, the water fed into the lower layer flows mostly along this path and later flows away to the equatorial region.
Conversely, in the upper layer, water is fed from the equator to the subtropics, and to the subpolar interior region through
the western boundary current. The water then circulates along the outer rim and is absorbed into the mass sink. The model
is controlled mainly by three nondimensional parameters: (1) the ratio of net mass input rate to the maximum Sverdrup transport
(Q/T
Sv
max
), which affects the inter-gyre communication by altering the paths of geostrophic contours, (2) the ratio of a mass input
rate into the lower layer to that in total (Q
2/Q), which controls the vertical structure of the inter-gyre flow, and (3) the measure of the wind forcing effect relative to
the β effect, which determines the horizontal extent of the area influenced by the mass input. The other parameter regimes with
respect to Q/T
Sv
max
and Q
2/Q are also presented. 相似文献
9.
Nobuo Ishiyama Takumi Akasaka Futoshi Nakamura 《Aquatic Sciences - Research Across Boundaries》2014,76(3):437-449
Management of wetland connectivity is important for biodiversity conservation. In the modern agricultural landscape, the natural connections between floodplain wetlands have been greatly altered. Agricultural ditches and channelized streams are widely distributed in floodplains, which may contribute to the maintenance of wetland connectivity and biodiversity. To determine how these watercourse networks affect wetland biodiversity, we examined the relationship between the species richness of aquatic animals and wetland connectivity, with a special focus on species mobility. From July to August 2011, fish and aquatic insects were collected from 24 wetlands in northern Japan. To determine the degree of wetland connectivity, we assessed the relative importance of individual wetlands in maintaining the entire wetland network using two connectivity indices: hydrologic connectivity via watercourses and spatial connectivity defined as Euclidian distances between wetlands using graph theory. We found that only high mobility groups of both taxa could enhance species richness in either a hydrologic (fish) or spatial (insect) wetland network. The species richness of insects with high-flying ability was found to increase as spatial connectivity increased. Furthermore, the species richness of fish with high-swimming ability was positively influenced by hydrologic connectivity, most likely because highly mobile species were able to reach suitable habitats and migrate from source populations in a wetland network owing to their good mobility. Our findings indicate that hydrologic network is important for maintaining biodiversity as well as spatial connectivity. It is important to focus conservation efforts on key wetlands with high hydrologic and spatial connectivity in future wetland management. 相似文献
10.
Genki I. Matsumoto Yukinori Tani Koji Seto Tomoko Tazawa Masumi Yamamuro Takahiro Watanabe Toshio Nakamura Tetsuo Takemura Satoshi Imura Hiroshi Kanda 《Journal of Paleolimnology》2010,44(2):677-693
Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological
changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica
inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen,
and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm)
overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca.
7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year.
Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine
environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought
about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced
changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine
period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms.
During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the
lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom
of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared
to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface,
ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher
than during the coastal marine period. 相似文献