Mechanical structure of JNLT     

N. Itoh  I. Mikami  Y. Yamashita  T. Noguchi 《Astrophysics and Space Science》1989,160(1-2):165-172

The Japanese National Large Telescope (JNLT) requires mechanical performance of high tracking accuracy to achieve good image quality and a mechanical configuration to provide several kinds of focus modes. Under these requirements, a conceptual design for the JNLT mechanical structure has been performed. This paper presents the results of the conceptual design currently under consideration.Paper presented at the symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.  相似文献   

Space weathered rims found on the surfaces of the Itokawa dust particles     

Takaaki Noguchi  Makoto Kimura  Takahito Hashimoto  Mitsuru Konno  Tomoki Nakamura  Michael E. Zolensky  Ryuji Okazaki  Masahiko Tanaka  Akira Tsuchiyama  Aiko Nakato  Toshinori Ogami  Hatsumi Ishida  Ryosuke Sagae  Shinichi Tsujimoto  Toru Matsumoto  Junya Matsuno  Akio Fujimura  Masanao Abe  Toru Yada  Toshifumi Mukai  Munetaka Ueno  Tatsuaki Okada  Kei Shirai  Yukihiro Ishibashi 《Meteoritics & planetary science》2014,49(2):188-214

On the basis of observations using Cs‐corrected STEM, we identified three types of surface modification probably formed by space weathering on the surfaces of Itokawa particles. They are (1) redeposition rims (2–3 nm), (2) composite rims (30–60 nm), and (3) composite vesicular rims (60–80 nm). These rims are characterized by a combination of three zones. Zone I occupies the outermost part of the surface modification, which contains elements that are not included in the unchanged substrate minerals, suggesting that this zone is composed of sputter deposits and/or impact vapor deposits originating from the surrounding minerals. Redeposition rims are composed only of Zone I and directly attaches to the unchanged minerals (Zone III). Zone I of composite and composite vesicular rims often contains nanophase (Fe,Mg)S. The composite rims and the composite vesicular rims have a two‐layered structure: a combination of Zone I and Zone II, below which Zone III exists. Zone II is the partially amorphized zone. Zone II of ferromagnesian silicates contains abundant nanophase Fe. Radiation‐induced segregation and in situ reduction are the most plausible mechanisms to form nanophase Fe in Zone II. Their lattice fringes indicate that they contain metallic iron, which probably causes the reddening of the reflectance spectra of Itokawa. Zone II of the composite vesicular rims contains vesicles. The vesicles in Zone II were probably formed by segregation of solar wind He implanted in this zone. The textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on Itokawa.  相似文献   

Mineral chemistry of MUSES‐C Regio inferred from analysis of dust particles collected from the first‐ and second‐touchdown sites on asteroid Itokawa     

Tomoki Nakamura  Aiko Nakato  Hatsumi Ishida  Shigeru Wakita  Takaaki Noguchi  Michael E. Zolensky  Masahiko Tanaka  Makoto Kimura  Akira Tshuchiyama  Toshihiro Ogami  Takahito Hashimoto  Mitsuru Konno  Masayuki Uesugi  Toru Yada  Kei Shirai  Akio Fujimura  Ryuji Okazaki  Scott. A. Sandford  Yukihiro Ishibashi  Masanao Abe  Tatsuaki Okada  Munetaka Ueno  Junichiro Kawaguchi 《Meteoritics & planetary science》2014,49(2):215-227

The mineralogy and mineral chemistry of Itokawa dust particles captured during the first and second touchdowns on the MUSES‐C Regio were characterized by synchrotron‐radiation X‐ray diffraction and field‐emission electron microprobe analysis. Olivine and low‐ and high‐Ca pyroxene, plagioclase, and merrillite compositions of the first‐touchdown particles are similar to those of the second‐touchdown particles. The two touchdown sites are separated by approximately 100 meters and therefore the similarity suggests that MUSES‐C Regio is covered with dust particles of uniform mineral chemistry of LL chondrites. Quantitative compositional properties of 48 dust particles, including both first‐ and second‐touchdown samples, indicate that dust particles of MUSES‐C Regio have experienced prolonged thermal metamorphism, but they are not fully equilibrated in terms of chemical composition. This suggests that MUSES‐C particles were heated in a single asteroid at different temperatures. During slow cooling from a peak temperature of approximately 800 °C, chemical compositions of plagioclase and K‐feldspar seem to have been modified: Ab and Or contents changed during cooling, but An did not. This compositional modification is reproduced by a numerical simulation that modeled the cooling process of a 50 km sized Itokawa parent asteroid. After cooling, some particles have been heavily impacted and heated, which resulted in heterogeneous distributions of Na and K within plagioclase crystals. Impact‐induced chemical modification of plagioclase was verified by a comparison to a shock vein in the Kilabo LL6 ordinary chondrite where Na‐K distributions of plagioclase have been disturbed.  相似文献   

Evapotranspiration and water source of a tropical rainforest in peninsular Malaysia          下载免费PDF全文

Marryanna Lion  Yoshiko Kosugi  Satoru Takanashi  Shoji Noguchi  Masayuki Itoh  Masanori Katsuyama  Naoko Matsuo  Siti‐Aisah Shamsuddin 《水文研究》2017,31(24):4338-4353

To evaluate water use and the supporting water source of a tropical rainforest, a 4‐year assessment of evapotranspiration (ET) was conducted in Pasoh Forest Reserve, a lowland dipterocarp forest in Peninsular Malaysia. The eddy covariance method and isotope signals of rain, plant, soil, and stream waters were used to determine forest water sources under different moisture conditions. Four sampling events were conducted to collect soil and plant twig samples in wet, moderate, dry, and very dry conditions for the identification of isotopic signals. Annual ET from 2012 to 2015 was quite stable with an average of 1,182 ± 26 mm, and a substantial daily ET was observed even during drought periods, although some decline was observed, corresponding with volumetric soil water content. During the wet period, water for ET was supplied from the surface soil layer between 0 and 0.5 m, whereas in the dry period, approximately 50% to 90% was supplied from the deeper soil layer below 0.5‐m depth, originating from water precipitated several months previously at this forest. Isotope signatures demonstrated that the water sources of the plants, soil, and stream were all different. Water in plants was often different from soil water, probably because plant water came from a different source than water that was strongly bound to the soil particles. Plants showed no preference for soil depth with their size, whereas the existence of storage water in the xylem was suggested. The evapotranspiration at this forest is balanced and maintained using most of the available water sources except for a proportion of rapid response run‐off.  相似文献   

Intermineral oxygen three‐isotope systematics of silicate minerals in equilibrated ordinary chondrites          下载免费PDF全文

David McDougal  Daisuke Nakashima  Travis J. Tenner  Noriko T. Kita  John W. Valley  Takaaki Noguchi 《Meteoritics & planetary science》2017,52(11):2322-2342

High‐precision oxygen three‐isotope ratios were measured for four mineral phases (olivine, low‐Ca and high‐Ca pyroxene, and plagioclase) in equilibrated ordinary chondrites (EOCs) using a secondary ion mass spectrometer. Eleven EOCs were studied that cover all groups (H, L, LL) and petrologic types (4, 5, 6), including S1–S4 shock stages, as well as unbrecciated and brecciated meteorites. SIMS analyses of multiple minerals were made in close proximity (mostly <100 μm) from several areas in each meteorite thin section, to evaluate isotope exchange among minerals. Oxygen isotope ratios in each mineral become more homogenized as petrologic type increases with the notable exception of brecciated samples. In type 4 chondrites, oxygen isotope ratios of olivine and low‐Ca pyroxene are heterogeneous in both δ¹⁸O and Δ¹⁷O, showing similar systematics to those in type 3 chondrites. In type 5 and 6 chondrites, oxygen isotope ratios of the four mineral phases plot along mass‐dependent fractionation lines that are consistent with the bulk average Δ¹⁷O of each chondrite group. The δ¹⁸O of three minerals, low‐Ca and high‐Ca pyroxene and plagioclase, are consistent with equilibrium fractionation at temperatures of 700–1000 °C. In most cases the δ¹⁸O values of olivine are higher than those expected from pyroxene and plagioclase, suggesting partial retention of premetamorphic values due to slower oxygen isotope diffusion in olivine than pyroxene during thermal metamorphism in ordinary chondrite parent bodies.  相似文献