Photometric observations of 107P/Wilson-Harrington     

Seitaro Urakawa  Shin-ichiro Okumura  Tsuyoshi Sakamoto  Shinsuke Abe  Kohei Kitazato  Sunao Hasegawa  Nobuyuki Kawai  Shogo Nagayama  Michitoshi Yoshida 《Icarus》2011,215(1):17-26

We present lightcurve observations and multiband photometry for 107P/Wilson-Harrington using five small- and medium-sized telescopes. The lightcurve has shown a periodicity of 0.2979 day (7.15 h) and 0.0993 day (2.38 h), which has a commensurability of 3:1. The physical properties of the lightcurve indicate two models: (1) 107P/Wilson-Harrington is a tumbling object with a sidereal rotation period of 0.2979 day and a precession period of 0.0993 day. The shape has a long axis mode (LAM) of L₁:L₂:L₃ = 1.0:1.0:1.6. The direction of the total rotational angular momentum is around λ = 310°, β = −10°, or λ = 132°, β = −17°. The nutation angle is approximately constant at 65°. (2) 107P/Wilson-Harrington is not a tumbler. The sidereal rotation period is 0.2979 day. The shape is nearly spherical but slightly hexagonal with a short axis mode (SAM) of L₁:L₂:L₃ = 1.5:1.5:1.0. The pole orientation is around λ = 330°, β = −27°. In addition, the model includes the possibility of binary hosting. For both models, the sense of rotation is retrograde. Furthermore, multiband photometry indicates that the taxonomy class of 107P/Wilson-Harrington is C-type. No clear rotational color variations are confirmed on the surface.  相似文献   

The Weathering of Granodiorite Porphyry in the Thiel Mountains, Inland Antarctica   总被引：2，自引：0，他引：2  

Satoshi Ishimaru  & Kenji Yoshikawa 《Geografiska Annaler: Series A, Physical Geography》2000,82(1):45-57

The weathering of granodiorite porphyry is examined in the extremely cold and dry environment of the inland part of Antarctica. Weathering features include granular disintegration, rock varnish, and sheeting. Sheeting has gradually proceeded since the exposing of the nunatak, but the other types of weathering have not actively advanced in recent times.
Granular disintegration primarily comprises the release of individual crystals. The mechanism of this release is that cracks are created along crystal boundaries and cleavages in phenocrysts mainly due to differential thermal expansion. Plagioclase and hypersthene are released more readily than quartz. Disintegration of plagioclase has produced many prism-shaped holes, 0.5 to 2.0 mm in length, while fine-grained quartz crystals, 0.05 to 0.1 mm in diameter, are incidentally released without cracking.
The reddish brown (10R4/4) rock varnishes result from oxidation and consist of limonite, which fills cracks and penetrates into crystals. Ferrous iron in hypersthene, biotite, ilmenite and magnetite is transformed into limonite by oxidation. Manganese is not found in the varnishes. Sulfur, which is important for oxidation and which may have originated from adhered snow, is concentrated on the surface of the rock.
Sheeting has precipitated rock falls, and has gradually formed a gray mosaic on the varnished wall. The sheeting was caused by gravitational body force, which is internal stress of the rock body due to the mass of the overburden.  相似文献   

GEOLOGY OF MT. PHULCHOKI AREA, CENTRAL NEPAL     

Funakawa Satoshi 《地学前缘》2000,(Z1)

GEOLOGY OF MT. PHULCHOKI AREA, CENTRAL NEPAL  相似文献   

Timescale of magma chamber processes revealed by U–Pb ages,trace element contents and morphology of zircons from the Ishizuchi caldera,Southwest Japan Arc          下载免费PDF全文

Mami Takehara  Kenji Horie  Kenichiro Tani  Takeyoshi Yoshida  Tomokazu Hokada  Shoichi Kiyokawa 《Island Arc》2017,26(2)

U–Pb geochronology and trace element chemistry of zircons in a microscale analysis were applied to the Ishizuchi caldera in the Outer Zone of Southwest Japan in order to estimate the timescale of the magma process, in particular, the magma differentiation. This caldera is composed mainly of ring fault complexes, major pyroclastic flow deposits, and felsic intrusion including central plutons. Using SHRIMP‐IIe, our new U–Pb zircon ages obtained from the major pyroclastic flow deposits (Tengudake pyroclastic flow deposits), granitic rocks from central plutons (Soushikei granodiorite and Teppoishigawa quartz monzonite), and rhyolite from the outer ring dike (Tenchuseki rhyolite) and the inner ring dike (Bansyodani rhyolite) are 14.80 ±0.11 Ma, 14.56 ±0.10 Ma, 14.53 ±0.12 Ma, 14.55 ±0.11 Ma and 14.21 ±0.19 Ma, respectively. Based on the U–Pb ages, the Hf contents and the REE patterns of the zircons, three stages are recognized in the evolutionary history of the magma chamber beneath the Ishizuchi caldera: (i) climactic Tengudake pyroclastic flow eruption; (ii) Tenchuseki rhyolite intrusion into the outer ring dike and central pluton intrusion; and (iii) Bansyodani rhyolite intrusion in the inner ring dike. These results indicate a magma evolution history of the Ishizuchi caldera system which took at least ca 600 kyr from the climatic caldera‐forming eruption to the post‐caldera intrusions. Our new geochronological data suggest that the Ishizuchi caldera formed as part of the voluminous and episodic magmatism that occurred in the wide zone along the Miocene forearc basin of Southwest Japan during the inception of the young Philippine Sea Plate subduction.  相似文献   

Reliability of U‐shaped steel dampers used in base‐isolated structures subjected to biaxial excitation          下载免费PDF全文

Diana Ene  Satoshi Yamada  Yu Jiao  Shoichi Kishiki  Yoshinao Konishi 《地震工程与结构动力学》2017,46(4):621-639

A reliable performance of anti‐seismic devices when the upper‐structure is subjected to strong biaxial seismic excitation is of vital importance to ensure the latter doesn't reach critical behavior. U‐shaped steel dampers are hysteretic devices used to dissipate the earthquake‐induced energy of base‐isolated structures. In the framework of performance‐based design, which is gaining more and more recognition, it is of particular importance to assess the performance of base‐isolated structures with such dampers under different intensity levels of bidirectional ground motion. To achieve this goal, an analytical model able to simulate the bidirectional displacement response of an isolation system is adopted. Incremental dynamic analysis (IDA) is used to obtain the relation between the earthquake‐induced bidirectional damage of U‐shaped steel dampers and different intensity levels of the considered records. The performance of the dampers is categorized into 5 levels delimited by 4 limit states for which fragility curves are derived. The results obtained using the bidirectional approach are quantitatively compared to those given by employing an in‐plane model (widely used in current design practices in Japan) with the purpose of assessing whether the latter provides unconservative estimates of the performance of the dampers. The main conclusion is that, for large seismic intensities, the safety margin against fracture of the dampers is significantly overestimated when an in‐plane model is adopted. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Low cyclic fatigue and hysteretic behavior of U‐shaped steel dampers for seismically isolated buildings under dynamic cyclic loadings          下载免费PDF全文

Yu Jiao  Shoichi Kishiki  Satoshi Yamada  Diana Ene  Yoshinao Konishi  Yuuma Hoashi  Masao Terashima 《地震工程与结构动力学》2015,44(10):1523-1538

Energy dissipation devices are necessary for base‐isolated buildings to control the deformation in the isolation system and to dissipate the earthquake‐induced energy. U‐shaped steel dampers (also known as U‐dampers) dissipate energy through plastic deformation of specially designed U‐shaped steel elements. This type of device can be installed at several locations in the isolation system. U‐dampers have been widely used in Japan for different types of isolated structures, such as hospitals, plants and residential buildings, since the 1995 Kobe Earthquake. Previous research has used static tests to estimate the performance of U‐dampers. However, the ultimate plastic deformation capacities and hysteretic behaviors of full‐scale U‐dampers under dynamic excitations still remain unclear. In addition, it is unclear whether the initial temperature has an effect on the hysteretic behavior and plastic deformation capacity of U‐dampers. In this paper, two series of dynamic loading tests of U‐dampers were conducted to evaluate the issues described earlier. The major findings of the study are (i) the loading speed has little effect on the plastic deformation capacity of U‐dampers; (ii) method to evaluate the ultimate plastic deformation capacities of U‐shaped steel dampers of different sizes is established using a Manson–Coffin relation‐based equation that is based on the peak‐to‐peak horizontal shear angle γ_t, which is defined as the lateral deformation amplitude (peak‐to‐peak amplitude) divided by the height of the dampers; (iii) the loading rate and the initial temperature have a minimal effect on the hysteretic behavior of the U‐dampers; and (iv) a bilinear model is proposed to simulate the force‐deformation relationships of the U‐dampers. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献