排序方式： 共有46条查询结果，搜索用时 31 毫秒
31.
Hitoshi Tomaru Udo Fehn Zunli Lu Rika Takeuchi Fumio Inagaki Hiroyuki Imachi Ryosuke Kotani Ryo Matsumoto Kan Aoike 《Resource Geology》2009,59(4):359-373
Iodine concentration and radioisotopic composition (129I/I) were measured in the pore waters from the gas hydrate occurrence in the forearc basin offshore Shimokita Peninsula, north-eastern Japan, to determine the source formation of I and accompanying hydrocarbons. Iodine concentrations correlate well with the alkalinity and SO4 patterns, reflecting degradation stages of I-rich buried organic matter, rapidly increasing in the sulfate reduction interval, and becoming constant below 250 meters below the seafloor with an upwelling flux of 1.5 × 10−11 µmol cm−2 year−1. The 129I/I ratios of 300 × 10−15–400 × 10−15 in deep pore waters suggest ages for iodine and hydrocarbon sources as old as 40 Ma. These ages correlate well with the coaly source formations of the Eocene age thought to be responsible for the conventional natural gas deposits underlying the gas hydrate stability zone. Similar profiles are observed in 129I/I ratios of pore waters in the gas hydrate stability zone from the forearc basin in the eastern Nankai Trough, offshore central Japan, where pore waters are enriched in I and reach ages as old as ∼50 Ma through the sediment column. At the outer ridge site along the trough, on the other hand, relatively younger I are more frequently delivered probably through thrusts/faults associated with subduction. The nature of source formations of I and hydrocarbons in the offshore Shimokita Peninsula has a more terrestrial contribution compared with those in the Nankai Trough, but these formations are also considerably older than the host sediments, suggesting long-term transport of I and hydrocarbons for the accumulation of gas hydrates in both locations. 相似文献
32.
基于空间模型的全球粮食安全评价 总被引：3，自引：1，他引：2
This paper presents a scenario-based assessment of global future food security. To do that,the socio-economic and climate change scenarios were defined for the future and were linked to an integrated modeling framework. The crop yields simulated by the GIS-based Environmental Policy Integrated Climate (EPIC) model and crop areas simulated by the crop choice decision model were combined to calculate the total food production and per capita food availability,which was used to represent the status of food availability and stability. The per capita Gross Domestic Product (GDP) simulated by IFPSIM model was used to reflect the situation of food accessibility and affordability. Based on these two indicators,the future food security status was assessed at a global scale over a period of approximately 20 years,starting from the year 2000. The results show that certain regions such as South Asia and most African countries will likely remain hotspots of food insecurity in the future as both the per capita food availability and the capacity of being able to import food will decrease between 2000 and 2020. Low food production associated with poverty is the determining factor to starvation in these regions,and more efforts are needed to combat hunger in terms of future actions. Other regions such as China,most Eastern European countries and most South American countries where there is an increase in per capita food availability or an increase in the capacity to import food between 2000 and 2020 might be able to improve their food security situation. 相似文献
33.
Yusuke Uchiyama Ryosuke Kanki Akiko Takano Hidekatsu Yamazaki Yasumasa Miyazawa 《大气与海洋》2018,56(4):212-229
ABSTRACTFor dynamically consistent, high-resolution, yet cost-effective regional oceanic downscaling modelling, an empirical three-dimensional (3D) density estimate based on publicly available datasets is utilized for the Regional Oceanic Modeling System (ROMS) with simple data assimilation (i.e., TS nudging, where TS stands for temperature and salinity). We rely on a method built upon the two-layer model to reconstruct a mesoscale 3D temperature and salinity field, referred to as Tokyo University of Marine Science and Technology (TUMSAT)-TS, using near real-time altimeter-derived dynamic height along with Argo float profiling data. The TUMSAT-TS is first validated using in situ hydrographic data, then is implemented in the Japan Coastal Ocean Predictability Experiment (JCOPE2)-ROMS downscaling system for the Kuroshio region off Japan. We explore the usability of TUMSAT-TS by carrying out three comparative simulations with temperature and salinity nudging towards the (i) TUMSAT-TS and (ii) JCOPE2-TS fields, and (iii) without the nudging. Whereas the unassimilated case fails to properly account for the Kuroshio, both datasets individually are found to help reproduce the mesoscale variability of the Kuroshio, as well as its transient paths, volume transport, associated kinetic energy (KE) and eddy KE, and seasonally varying stratification. 相似文献
34.
The partitioning of iron between Mg-rich perovskite (Pv) and ferropericlase (Fp) was investigated for a pyrolitic bulk composition over a wide range of simulated lower-mantle pressures and temperatures from 28 to 114 GPa and from 1,900 to 2,300 K, in a laser-heated diamond anvil cell (DAC). The recovered DAC samples are chemically homogeneous, indicating a relatively small temperature gradient during laser heating. The chemical compositions of coexisting Pv, Fp, and Ca-rich perovskite (CaPv) were determined by energy-dispersive X-ray spectroscopy (EDS) using an EDS instrument attached to a transmission electron microscope. Our results demonstrate that at pressures above 90 GPa, Pv becomes more Fe-rich with increasing pressure, which is likely due to the effects of high-spin to low-spin crossover of Fe3+ in Pv. We highlight that such a change in Fe–Mg partitioning between Pv and Fp should have a strong influence on the physical properties of the deep lower mantle. 相似文献
35.
The objectives of this study are to assess land suitability and to predict the spatial and temporal changes in land use types (LUTs) by using GIS-based land use management decision support system. A GIS database with data on climate, topography, soil characteristic, irrigation condition, fertilizer application, and special socioeconomic activities has been developed and used for the evaluation of land productivity for different crops by integrating with a crop growth model—the erosion productivity impact calculator (EPIC). International food policy simulation model (IFPSIM) is also embedded into GIS for the predictions of how crop demands and crop market prices will change under alternative policy scenarios. An inference engine (IE) including land use choice model is developed to illustrate land use choice behavior based on logit models, which allows to analyze how diversified factors ranging from climate changes, crop price changes to land management changes can effect the distribution of agricultural land use. A test for integrated simulation is taken in each 0.1o by 0.1o grid cell to predict the change of agricultural land use types at global level. Global land use changes are simulated from 1992 to 2050. 相似文献
36.
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
37.
38.
Cédric Magen Gwénaëlle Chaillou Sean A. Crowe Alfonso Mucci Bjørn Sundby Aiguo Gao Ryosuke Makabe Hiroshi Sasaki 《Estuarine, Coastal and Shelf Science》2010
To establish the relative importance of terrigenous and marine organic matter in the southern Beaufort Sea, we measured the concentrations and the stable isotopic compositions of organic carbon and total nitrogen in sediments and in settling particles intercepted by sediment traps. The organic carbon content of surface sediment in the Chukchi and southern Beaufort Seas ranged from 0.6 to 1.6% dry wt., without a clear geographical pattern. The CORG:NTOT ratio ranged from 7.0 to 10.4 and did not vary significantly downcore at any one station. Values of δ13CORG and δ15NTOT in the sediment samples were strongly correlated, with the highest values, indicative of a more marine contribution, in the Amundsen Gulf. In contrast, the organic matter content, elemental (CORG:NTOT ratio) and isotopic (δ13CORG and δ15NTOT) composition of the settling particles was different from and much more variable than in the bottom sediments. The isotopic signature of organic matter in the Beaufort Sea is well constrained by three distinct end-members: a labile marine component produced in situ by planktonic organisms, a refractory marine component, the end product of respiration and diagenesis, and a refractory terrigenous component. A three-component mixing model explains the scatter observed in the stable isotope signatures of the sediment trap samples and accommodates an apparent two-component mixing model of the organic matter in sediments. The suspended matter in the water column contains organic matter varying from essentially labile and marine to mostly refractory and terrigenous. As it settles through the water column, the labile marine organic matter is degraded, and its original stable isotope signature changes towards the signature of the marine refractory component. This process continues in the bottom sediment with the result that the sedimentary organic matter becomes dominated by the refractory terrigenous and marine components. 相似文献
39.
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
40.
IntroductionAgriculturallandusepatternsandtheirchangesaretightlyrelatedwithagriculturepolicyandfoodsecurityissuesundergrowingfooddemand,assess mentofglobalclimatechangeimpactsonagricul ture,environmentalissuesduetotheintensificationofagriculturallandusessuchaswaterpollution,soildegradation,andrecentlywaterscarcityissues.Soasustainableandholisticplanningandmanage mentoflandresourcesshouldcombineallthesere latedinformationwithefficienttoolsforassessmentandevaluationinordertopermitbroad ,interact… 相似文献