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1.
Mihoko Hoshino Mitsuyoshi Kimata Norimasa Nishida Masahiro Shimizu 《Physics and Chemistry of Minerals》2008,35(2):59-70
Dissakisites from Trimouns dolomite mine, France, have two kinds of single crystals: chemical-zoned and homogeneous types.
Back-scattered electron microprobe (BSE) images of these dissakisites reveal both Ca–Al rich dark zones and Fe-ΣREE rich bright
zones. Crystal structures of three dark and two bright zones in a chemical-zoned dissakisite and of a homogeneous zone in
unzoned dissakisite were refined to individual R indices (about 3.0–5.0%) based on 1,400 observed [|F
0| > 4σF
0] reflections measured with MoKα X-radiation using the single crystal diffractometer. The differences in brightness between
their BSE images arise from those in coupled substitutions of the elements occupying A2 and M3 sites. The main reason for
these differences is that ten-coordinated A2 polyhedra and M3 octahedra are directly linked through their shared edge, which
creates a great potential for making this coupled substitution. This zoning indicates that formation of the whole zoned crystal,
where each zone could be grown steadily with its crystallographic axes mutually parallel to each other, may be identified
as autoepitaxy. 相似文献
2.
The model for the 2000 dike intrusion event between Kozushima and Miyakejima volcano, Japan, was reinvestigated. After the sudden earthquake swarm in Miyakejima volcano, a dike intrusion of large volume was detected by the nationwide GPS network (Geonet). The displacements detected with GPS stations over an area with a radius of about 200 km shows a distribution that is consistent with the dike source being located near Miyakejima volcano.The dike was intruded northwestwards between Miyakejima and the neighboring Kozushima volcano. We searched for the parameters in the models that reproduce the regional displacements due to dike intrusion between Miyakejima and Kozushiima islands. We tested three models, (1) the model with a single dike, (2) the model with a dike and a point dislocation source which represents a creep dislocation source and (3) the model with a dike and a deflation source which represents a magma reservoir. Though all three models can match the horizontal displacements near the source area, model 1 fails to reproduce the regional displacements in the central part of Japan. Both models 2 and 3 can reproduce the regional displacement for horizontal components. Model 3 produces slightly better results than model 2 for vertical components. The balance in the volume budget for models 2 and 3 is also consistent with the observations. These results show that we cannot distinguish between the two models using only GPS observation. As there is no direct evidence for such a large creep or ductile source (corresponds to M7 or more) as proposed in model 2 and the active seismic region migrated back and forth within the linear swarm region, the model with a dike and a deep magma source is preferable. For the deflation point source, we obtained a deflation volume of 1.5 km3 at the depth of 20 km below the dike. An additional ~0.95 km3 of volume loss through caldera collapse and edifice deflation took place at Miyakejima. We conclude that the magma that intruded the dike came in part from below Miyakejima and in part from below the sea floor between Miyakejima and Kozushima, perhaps from reservoirs at the Moho.Editorial responsibility: S Nakada, T Druitt 相似文献
3.
Miguel B. Brito Mitsuyoshi Akiyama Yoshitaka Ichikawa Hiroki Yamaguchi Riki Honda Naomitsu Ishigaki 《地震工程与结构动力学》2020,49(8):817-837
A novel low-cost friction sliding system for bidirectional excitation is developed to improve the seismic performance of reinforced concrete (RC) bridge piers. The sliding system is a spherical prototype developed by combining a central flat surface with an inclined spherical segment, characterized by stable oscillation and a large reduction in response accelerations on the flat surface. The inclined part provides a restoring force that limits the residual displacements of the system. Conventional steel and concrete are employed to construct a flat-inclined spherical surface atop an RC pier. The seismic forces are dissipated through the frictions generated during the sliding movements; hence, the seismic resilience of bridges can be ensured with a low-cost design solution. The proposed system is fabricated utilizing a mold created by a three-dimensional printer, which facilitates the use of conventional concrete to construct spherical shapes. The concrete surface is lubricated with a resin material to prevent abrasion from multiple input ground motions. To demonstrate the effectiveness of the system, bidirectional shaking table tests are conducted in the longitudinal and transverse directions of a scaled bridge model. The effect of the inclination angle and the flat surface size is investigated. The results demonstrate a large decrease in response acceleration when the system exhibits circular sliding displacement. Furthermore, the inclination angle that generates the smallest residual displacement is identified experimentally. 相似文献
4.
Hasanuddin Z. Abidin H. Andreas M. Gamal Ony K. Suganda Irwan Meilano M. Hendrasto M. A. Kusuma D. Darmawan M. A. Purbawinata A. D. Wirakusumah F. Kimata 《GPS Solutions》2006,10(2):75-84
Papandayan is an A-type active volcano located in the southern part of Garut Regency, about 70 km southeast of Bandung, Indonesia. Its earliest recorded eruption, and the most violent and devastating outburst, occurred in 1772. The latest eruptions occurred in the period from 11 November–8 December 2002, and consisted of phreatic, freatomagmatic, and magmatic types of eruption. During the latest eruption period, GPS surveys were conducted at several points inside and around the crater in a radial mode, using the reference point located at the Papandayan observatory, about 10 km from the crater. At the points closest to the erupting craters, GPS displacements up to a few decimeters were detected, whereas at the points outside the crater, the displacements were at the centimeter level. The magnitude of displacements observed at each point also showed a temporal variation according to the eruption characteristics. The results show that deformation during eruption tends to be local, e.g. just around the crater. The pressure source is difficult to be properly modeled from GPS results, due to the limited GPS data available and differences in topography, geological structure, and/or rheology related to each GPS station. 相似文献
5.
A. Kyono M. Kimata M. Matsuhisa Y. Miyashita K. Okamoto 《Physics and Chemistry of Minerals》2002,29(4):254-260
The crystal structure of stibnite [Sb2S3, Pnma, a=11.314(2), b=3.837(2), c=11.234(3) Å, V= 487.7(3) Å3 at 293 K] was refined in situ at 230, 173, and 128 K. It is a major characteristic of the structure that the Sb–S secondary bonds enclosing Sb 5s2 inert lone-pair electrons at 293 K are significantly shorter than the corresponding sum of the Sb and S van der Waals radii. Concerning the temperature dependence, although both the polyhedral volume and the cation eccentricity of the two SbS7 polyhedra exhibit continuous contractions with decreasing temperature, the sphericity values remain constant, indicating isotropic shrinkage. Consequently, the geometries of Sb 5s2 inert lone-pair electrons and ligand atoms remain unchanged at low temperatures. This is because the crystal structure of stibnite at low temperature induces contraction with attractive interactions, which is called the orbital overlap between Sb 5s2 inert lone-pair electrons and ligand orbitals to maintain the coordination environment. In this case, Sb 5s2 lone-pair electrons are not inert, but active. Such orbital overlaps of inert lone-electron pairs can provide a reasonable explanation for shorter secondary bonds and lower band gap energy of the binary compounds containing heavy elements such as Sb, Te, Pb, and Bi, which are key factors in tracing the origins of color, luster, and semiconductivity of their minerals or compounds. 相似文献
6.
The distribution of inorganic nitrogen compounds and the metabolic rates of these compounds by microorganisms as a whole were investigated in the Seas of Hiuchi and Bingo. The results obtained are as follows:
- Of inorganic nitrogen compounds, the contents in sea water, those in bottom muds, the uptake or liberation rates of microorganisms as a whole in sea water, and the liberation rates from bottom muds to sea water are 0.2～4.0 μg at. N/l, 3～60 μg at.N/100 g, 0.01～0.5 μg at.N//lhr, and 0.3～1.9 μg at.N/100 cm2/hr, respectively, and these contents or rates of ammonia usually are the largest of these inorganic nitrogen compounds.
- From the above-mentioned results and the others, it is suggested that the nitrogen in the seas circulates mainly in sea water itself and the course of nitrogen cycle, which passes through bottom muds, is not so important, and further that, of the cycle of inorganic nitrogen compounds, the main course is the course which ammonia is liberated from organic nitrogen compounds and it is immediately uptaked by microorganisms, and the course which it is oxidized to nitrate and the others are not so important.
7.
Over the last two decades, the probabilistic assessment of reinforced concrete (RC) structures under seismic hazard has been developed rapidly. However, little attention has been devoted to the assessment of the seismic reliability of corroded structures. For the life‐cycle assessment of RC structures in a marine environment and earthquake‐prone regions, the effect of corrosion due to airborne chlorides on the seismic capacity needs to be taken into consideration. Also, the effect of the type of corrosive environment on the seismic capacity of RC structures has to be quantified. In this paper, the evaluation of the displacement ductility capacity based on the buckling model of longitudinal rebars in corroded RC bridge piers is established, and a novel computational procedure to integrate the probabilistic hazard associated with airborne chlorides into life‐cycle seismic reliability assessment of these piers is proposed. The seismic demand depends on the results of seismic hazard assessment, whereas the deterioration of seismic capacity depends on the hazard associated with airborne chlorides. In an illustrative example, an RC bridge pier was modeled as single degree of freedom (SDOF). The longitudinal rebars buckling of this pier was considered as the sole limit state when estimating its failure probability. The findings show that the life‐cycle reliability of RC bridge piers depends on both the seismic and airborne chloride hazards, and that the cumulative‐time failure probabilities of RC bridge piers located in seismic zones can be dramatically affected by the effect of airborne chlorides. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Earthquakes in Kenya are common along the Kenya Rift Valley because of the slow divergent movement of the rift and hydrothermal processes in the geothermal fields. This implies slow but continuous radiation of seismic energy, which relieves stress in the subsurface rocks. On the contrary, the NW-SE trending rift/fault zones such as the Aswa-Nyangia fault zone and the Muglad-Anza-Lamu rift zone are the likely sites of major earthquakes in Kenya and the East African region. These rift/fault zones have been the sites of a number of strong earthquakes in the past such as the M w = 7.2 southern Sudan earthquake of 20 May 1990 and aftershocks of M w = 6.5 and 7.1 on 24 May 1990, the 1937 M s = 6.1 earthquake north of Lake Turkana close to the Kenya-Ethiopian border, and the 1913 M s = 6.0 Turkana earthquake, among others. Source parameters of the 20 May 1990 southern Sudan earthquake show that this earthquake consists of only one event on a fault having strike, dip, and rake of 315°, 84°, and ?3°. The fault plane is characterized by a left-lateral strike slip fault mechanism. The focal depth for this earthquake is 12.1 km, seismic moment M o = 7.65 × 1019 Nm, and moment magnitude, M w = 7.19 (?7.2). The fault rupture started 15 s earlier and lasted for 17 s along a fault plane having dimensions of ?60 km × 40 km. The average fault dislocation is 1.1 m, and the stress drop, ?σ, is 1.63 MPa. The distribution of historical earthquakes (M w ≥ 5) from southern Sudan through central Kenya generally shows a NW-SE alignment of epicenters. On a local scale in Kenya, the NW–SE alignment of epicenters is characterized by earthquakes of local magnitude M l ≤ 4.0, except the 1928 Subukia earthquake (M s = 6.9) in central Kenya. This NW–SE alignment of epicenters is consistent with the trend of the Aswa-Nyangia Fault Zone, from southern Sudan through central Kenya and further southwards into the Indian Ocean. We therefore conclude that the NW–SE trending rift/fault zones are sites of strong earthquakes likely to pose the greatest earthquake hazard in Kenya and the East African region in general. 相似文献
9.
After the occurrence of various destructive earthquakes in Japan, extensive efforts have been made to improve the seismic performance of bridges. Although improvements to the ductile capacities of reinforced concrete (RC) bridge piers have been developed over the past few decades, seismic resilience has not been adequately ensured. Simple ductile structures are not robust and exhibit a certain level of damage under extremely strong earthquakes, leading to large residual displacements and higher repair costs, which incur in societies with less-effective disaster response and recovery measures. To ensure the seismic resilience of bridges, it is necessary to continue developing the seismic design methodology of RC bridges by exploring new concepts while avoiding the use of expensive materials. Therefore, to maximize the postevent operability, a novel RC bridge pier with a low-cost sliding pendulum system is proposed. The seismic force is reduced as the upper component moves along a concave sliding surface atop the lower component of the RC bridge pier. No replaceable seismic devices are included to lengthen the natural period; only conventional concrete and steel are used to achieve low-cost design solutions. The seismic performance was evaluated through unidirectional shaking table tests. The experimental results demonstrated a reduction in the shear force transmitted to the substructure, and the residual displacement decreased by establishing an adequate radius of the sliding surface. Finally, a nonlinear dynamic analysis was performed to estimate the seismic response of the proposed RC bridge pier. 相似文献
10.
Mihoko Hoshino Mitsuyoshi Kimata Norimasa Nishida Masahiro Shimizu 《Physics and Chemistry of Minerals》2010,37(5):255-263
Euhedral dissakisites from Trimouns dolomite mine, France, is compositionally zoned. Back-scattered electron (BSE) images
reveal that each of the described dissakisite crystals has three distinct compositional zones: normal zoned core (Mg-rich),
oscillatory zoned middle (Ca–Al-rich) and homogeneous rim (Fe–ΣREE-rich). The latter zone with Fe2+ > Mg corresponds to allanite-(Ce). Dissakisite-(Ce) also displays pronounced zoning in Fe/Mg which may suggest that the temperature
of crystallization continuously decreased from core to rim. Despite a systematic increase in Fe/Mg of the dissakisite with
an allanite rim, there is no monotonic decrease in the REE zoning: the normal zoned core and homogeneous rim are rich in La,
Ce and Pr, but the relatively REE-poor oscillatory zoned middle is relatively abundant in Y, Sm and Gd. Discontinuous variation
in REE content of the dissakisite, with the allanite rim may indicate a localized change in either the relative concentration
of various ligands or pH of the crystallizing fluid. Observations under the polarizing microscope confirm that the different
zones have simultaneous extinction. These chemical and optical observations suggest that epitaxial crystallization of dissakisite,
from Trimouns, passes through three formation stages. The ternary Fe2+–Mg2+–(Al + Fe)3+ diagram illustrates that in general dissakisite can be classified into two groups, (Al + Fe)3+-rich and an Mg-rich; dissakisite from Trimouns belongs to the former group. Chondrite-normalized REE patterns of dissakisites
from Trimouns are similar to those of allanites formed by hydrothermal fluids. In conclusion, it is clear from the above two
geochemical characteristics that dissakisites from Trimouns are of (Al + Fe)3+-type, and were derived from hydrothermal fluids. 相似文献