Global mapping of the degree of space weathering on asteroid 25143 Itokawa by Hayabusa/AMICA observations     

Masateru Ishiguro  Takahiro Hiroi  David J. Tholen  Sho Sasaki  Yuji Ueda  Tokuhiro Nimura  Masanao Abe  Beth E. Clark  Aya Yamamoto  Fumi Yoshida  Ryosuke Nakamura  Naru Hirata  Hideaki Miyamoto  Yasuhiro Yokota  Tatsuaki Hashimoto  Takashi Kubota  Akiko M. Nakamura  Robert W. Gaskell  Jun Saito 《Meteoritics & planetary science》2007,42(10):1791-1800

Abstract— We obtained color images of near‐Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8–3.7 m/pixel. Whole‐disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88‐inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk‐resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite‐like materials have been exposed through weathered layers by excavation. By also examining close‐up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels.  相似文献   

Blending in gravitational microlensing experiments: source confusion and related systematics     

Martin C. Smith  Przemys&#;aw Wo&#;niak  Shude Mao  Takahiro Sumi 《Monthly notices of the Royal Astronomical Society》2007,380(2):805-818

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Numerical model of local scour considering the unsteady sediment inflow and sediment sorting: Application to scour upstream of slit weir     

Kazuyuki Ota  Takahiro Sato  Ryosuke Arai 《国际泥沙研究》2022,37(4):469-483

The current study proposes a novel framework for the numerical model for estimating the temporal scour considering unsteady sediment inflow and the sediment sorting process. The framework was applied to local scour upstream of a slit weir. The scour model is based on an ordinary nonlinear differential equation derived from sediment continuity and scour rate equations. A one-dimensional(1-D)Boussinesq-type model coupled with nonequilibrium sediment transport was incorporated in the scour model to...  相似文献   

Spatial variability and correlation of environmental proxies during the past 18,000 years among multiple cores from Lake Pumoyum Co,Tibet, China   总被引：3，自引：0，他引：3  

Junbo Wang  Liping Zhu  Mitsugu Nishimura  Toshio Nakamura  Jianting Ju  Manping Xie  Watanabe Takahiro  Matsunaka Testsuya 《Journal of Paleolimnology》2009,42(3):303-315

Multiple cores from Lake Pumoyum Co, southern Tibet, provide an improved understanding of the spatial distribution of lake sediments, and how well they represent the paleo-climate. Comparative study of these cores using AMS ¹⁴C dating and environmental proxies clarified their relationships with environmental changes. Our work focused on understanding the spatial similarities among cores covering different time scales, and evaluating variations in sedimentary processes across sites. The four studied cores demonstrate different sedimentation rates, but environmental proxies help synchronize the timing of environmental variations. Sediment variables such as total organic carbon (TOC), inorganic carbon (IC), and grain size in different cores correlate well and corroborate changing trends over the past 10,000 cal years. Differences in sedimentation rates and facies among core sites probably result largely from differences in water depth. The core from the deepest site displays the highest average sedimentation rates and the highest accumulation rates of TOC, but lowest content of IC. Two cores from somewhat shallower sites have plant residues in their lower sections and record similar variations in both the number of layers and their depositional ages. Our results do not indicate any significant variation in sedimentation pattern or its related factors among the three sites. A single core from the deepest site could adequately represent the total lake environment over the time span covered. But cores from somewhat shallower sites might reveal important shifts in the environment over a longer time period.  相似文献   

Isotopic geochemistry of Hualalai shield-stage tholeiitic basalts from submarine North Kona region,Hawaii     

Seiko Yamasaki  Tomomi Kani  Barry B. Hanan  Takahiro Tagami 《Journal of Volcanology and Geothermal Research》2009

The geochemical data of Hualalai tholeiitic basalts allow extension of the temporal variations established at Mauna Loa back in time, and provide important information for the long-term temporal variation of the Hawaiian lavas. We report new Hf, Pb, Nd, and Sr isotope compositions for 32 Hualalai tholeiitic basalts collected from deep submarine portions of the North Kona region. The samples were collected from the lower section of the North Kona bench (dives K218 and K219), a submarine stratigraphic section at Hualalai volcano's northwest rift zone (dive S690), and an elongate ridge outboard of the central section of the bench (dive S692), during two JAMSTEC Hawaii cruises in 2001 and 2002. The Hualalai shield-stage tholeiitic basalts have magma source isotopic signatures similar to Mauna Loa. The new data shows temporal Pb and Sr isotope trends that correspond to the long-term temporal variations in Loa-trend lavas, and the Hualalai–Mauna Loa lavas seem to show inter-shield geochemical excursions. Variation in Pb and Sr isotopes at Hualalai appears to take place over a longer time scale than at Mauna Loa. The merged Hualalai–Mauna Loa isotopic trends support models where heterogeneous material in the plume conduit is distributed chaotically, with variable cross-sectional density and length scale.  相似文献   

关于地铁地震响应的模型振动试验及数值分析   总被引：10，自引：0，他引：10  

车爱兰  岩楯敞广  葛修润 《岩土力学》2006,27(8):1293-1298

为明确大地震时地铁的破坏过程及原因,以1995 年日本阪神－淡路大地震中遭受严重破坏的神户大开地铁车站为对象,进行了一系列的模型振动试验和动力有限元分析。对于作用于地下结构的地震动土压的发生原理、地震波输入方向、结构的埋设深度、地基与结构间的刚性比对地震动土压的影响及在地基-结构系统的非线性响应下结构周围地基终局状态时的地震动土压进行了研究。明确了地震动土压的极限值及在大地震时周围地基的残余应变引起的静止土圧力的存在。为今后改进地震土压力计算方法、提高地下结构抗震设计水平提供了依据。  相似文献   

Near-infrared spectrophotometry of Asteroid 25143 Itokawa from NIRS on the Hayabusa spacecraft     

Kohei Kitazato  Beth E. Clark  Shinsuke Abe  Takahiro Hiroi  Paul A. Abell  Faith Vilas 《Icarus》2008,194(1):137-145

A photometric analysis of the S-type Asteroid 25143 Itokawa is performed over multiple wavelengths ranging from 0.85 to 2.10 μm based on disk-resolved reflectance spectra obtained with the Hayabusa near-infrared spectrometer (NIRS). We derive the global photometric properties of Itokawa in terms of Hapke's photometric model. We find that Itokawa has a single-scatter albedo that is 35-40% less than that of Asteroid 433 Eros. Itokawa also has a single-particle phase function that is more strongly back-scattering than that of Eros. Despite its hummocky surface strewn with large boulders, Itokawa exhibits an opposition effect. However, the total amplitude of the opposition surge for Itokawa was estimated to be less than unity while Eros and other S-type asteroids have been found to have model values exceeding unity. The wavelength dependence of the opposition surge width reveals that coherent backscatter contributes to the opposition effect on Itokawa's surface. The photometric roughness of Itokawa is well constrained to a value of 26° ± 1° which is similar to Eros, suggesting that photometric roughness models the smallest surface roughness scale for which shadows exist.  相似文献   

Economic valuation of the Seto Inland Sea by using an Internet CV survey     

Tsuge T  Washida T 《Marine pollution bulletin》2003,47(1-6):230-236

We estimate the economic value of the natural environment damaged in the Seto Inland Sea after the introduction of the Law on Temporary Measures for the Environmental Conservation of the Seto Inland Sea (Setouchi Law) and the value of the natural environment that survived, using a Contingent Valuation (CV) survey on an Internet web site. The CV survey contains three plans. Plan 1 is to restore 4 ha of reclaimed land. By estimating the Willingness To Pay (WTP) for plan 1, we can appraise the value of the natural environment that was damaged as a result of the original reclamation. Plan 2 is to transplant Zostera (eel-grass) into an area of 10 ha offshore. Plan 3 is to preserve the shore area, a natural habitat for rare animal species, under the National Trust Program. From the WTP for plans 2 and 3, we can estimate the value of the shore area and the areas a little farther offshore. The value of the natural environment damaged in the Seto Inland Sea as a result of reclaiming projects after the introduction of the Setouchi Law and the value of the existing natural environment of the Seto Inland Sea from the WTP for the plans were estimated to about 172 trillion yen (1.46 trillion dollars) and about 424 trillion yen (3.60 trillion dollars), respectively. The results indicate that in the 25 years since the introduction of the Setouchi Law, we have degraded every year about 6.88 trillion yen (58.5 billion dollars) worth of the natural environment by reclaiming. Some seaweed farms and natural shore areas, natural habitats to rare marine life-forms like the horseshoe crab and the fiddler crab have survived, but their value amounts to about 80% of Japan's GDP.  相似文献   

Landslide risk evaluation and hazard zoning for rapid and long-travel landslides in urban development areas   总被引：8，自引：6，他引：2  

Kyoji?SassaEmail author  Gonghui?Wang  Hiroshi?Fukuoka  Fawu?Wang  Takahiro?Ochiai  Masanori?Sugiyama  Tatsuo?Sekiguchi 《Landslides》2004,1(3):221-235

Risk evaluation for earthquake-induced rapid and long-travel landslides in densely populated urban areas is currently the most important disaster mitigation task in landslide-threatened areas throughout the world. The research achievements of the IPL M-101 APERITIF project were applied to two urban areas in megacities of Japan. One site is in the upper slope of the Nikawa landslide site where previous movements were triggered by the 1995 Hyogoken-Nambu earthquake. During detailed investigation, the slope was found to be at risk from a rapid and long-travel landslide induced by sliding surface liquefaction by earthquakes similar in scale to the 1995 event. A new plan to prevent the occurrence of this phenomenon was proposed and the plan was implemented. Another area is the Tama residential area near Tokyo. A set of field and laboratory investigations including laser scanner, geological drilling and ring-shear tests showed that there was a risk of sliding surface liquefaction for both sites. A geotechnical computer simulation (Rapid/LS) using the quantitative data obtained in the study allowed urban landslide hazard zoning to be made at individual street level.  相似文献   

The rate of fluvial incision during the Late Quaternary period in the Abukuma Mountains, northeast Japan, deduced from tephrochronology     

Takahiro  Yamamoto 《Island Arc》2005,14(2):199-212

Abstract River incision into bedrock results in the decrease of burial depths, which can be of critical importance, for example, in the safe long‐term storage of high‐level radioactive waste. For the long‐term prediction of river erosion, it is essential to know the rate of incision during the Late Quaternary period. In the Abukuma Mountains on the forearc side of northeast Japan, a low‐relief peneplain that was uplifted in the Pliocene period is widely developed. Degradational fluvial terraces that are discontinuously distributed along draining rivers are scattered in the study area. The fluvial sediments were mainly transported from the summit regions as debris flows or hyperconcentrated flows. The terrace deposits are capped by a series of eolian veneers containing key tephra beds. From the oldest to the youngest, these tephra beds are the 150–125 ka Iizuna–Kamitaru tephra, the 135–125 ka Hiuchigatake–Tagashira tephra, the 120 ka Adatara–Dake tephra, the 70–80 ka Bandai–Hayama‐2 tephra, the 45 ka Numazawa–Mizunuma tephra and the 42 ka Bandai–Hayama‐1 tephra. Using tephrochronological data, the terraces are divided into three groups: higher, middle and lower. The ages of formation of the higher, middle and lower terraces are estimated to be within marine isotope stage (MIS) 6, MIS 5.4–5.2 and MIS 3 to MIS 2, respectively. The incision rate, calculated from the relative height between the terrace surface and present‐day valley floor fill, is 1.5–0.8 m/10 000 years in the elevations from 350 to 700 m. The calculated rate does not show significant differences between the higher, middle and lower terraces. All the relative heights decrease with increasing elevation, because the erosional rates of streams in the upper reaches are lower than those in downstream reaches where the discharge rates are higher. This value can be regarded as an estimate of the rate of incision in granitic mountains where there is no volcanic or distinct tectonic activity.  相似文献