High-resolution imaging polarimetry of HL Tau and magnetic field structure     

P. W. Lucas  Misato Fukagawa  Motohide Tamura  A. F. Beckford  Yoichi Itoh  Koji Murakawa  Hiroshi Suto  Saeko S. Hayashi  Yumiko Oasa  Takahiro Naoi  Yoshiyuki Doi  Noboru Ebizuka  Norio Kaifu 《Monthly notices of the Royal Astronomical Society》2004,352(4):1347-1364

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Land subsidence of Jakarta (Indonesia) and its relation with urban development     

Hasanuddin Z. Abidin  Heri Andreas  Irwan Gumilar  Yoichi Fukuda  Yusuf E. Pohan  T. Deguchi 《Natural Hazards》2011,59(3):1753-1771

Jakarta is the capital city of Indonesia with a population of about 9.6 million people, inhabiting an area of about 660 square-km. In the last three decades, urban development of Jakarta has grown very rapidly in the sectors of industry, trade, transportation, real estate, and many others. This exponentially increased urban development introduces several environmental problems. Land subsidence is one of them. The resulted land subsidence will also then affect the urban development plan and process. It has been reported for many years that several places in Jakarta are subsiding at different rates. The leveling surveys, GPS survey methods, and InSAR measurements have been used to study land subsidence in Jakarta, over the period of 1982–2010. In general, it was found that the land subsidence exhibits spatial and temporal variations, with the rates of about 1–15 cm/year. A few locations can have the subsidence rates up to about 20–28 cm/year. There are four different types of land subsidence that can be expected to occur in the Jakarta basin, namely: subsidence due to groundwater extraction, subsidence induced by the load of constructions (i.e., settlement of high compressibility soil), subsidence caused by natural consolidation of alluvial soil, and tectonic subsidence. It was found that the spatial and temporal variations of land subsidence depend on the corresponding variations of groundwater extraction, coupled with the characteristics of sedimentary layers and building loads above it. In general, there is strong relation between land subsidence and urban development activities in Jakarta.  相似文献   

Microbialites and their Responsible Microbes Following the End-Permian Extinction in Sichuan, South China     

Yoichi Ezaki  Jianbo Liu  Natsuko Adachi 《Gondwana Research》2001,4(4):614

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Measurements of the Ca II infrared triplet lines of young stellar objects     

Yoichi Itoh  Keiko Moto＇oka  Yoichi Itoh 《中国天文和天体物理学报》2013,(10):1189-1201

Equivalent widths and line widths of Ca II infrared triplet emission lines were measured in the high-resolution optical spectra of 39 young stellar objects.We found that the equivalent widths of the emission lines decrease with stellar evolution.It has often been claimed that strong chromospheric activity is generated by a dynamo process caused by fast rotation of the photosphere.However,we found no clear correlation between the strength of the Ca II lines and the stellar rotation velocity.Instead,we found that the objects with high mass accretion rates had stronger Ca II emission lines.This correlation supports the turbulent chromosphere model or the magnetic accretion theory for classical T Tauri stars.We also noticed that the equivalent widths of Ca II lines in transitional disk objects are one-tenth of those in classical T Tauri stars,even if the masses of the circumstellar disks are comparable.  相似文献   

Characterization of total suspended solid dynamics in a large shallow lake using long‐term daily satellite images     

Keisuke Hoshikawa  Yoichi Fujihara  Sokly Siev  Seiya Arai  Takashi Nakamura  Hideto Fujii  Ty Sok  Chihiro Yoshimura 《水文研究》2019,33(21):2745-2758

Large, shallow‐water lakes located on floodplains play an important role in creating highly productive ecosystems and are prone to high concentrations of suspended solids due to sediment resuspension. In this study, the aim was to determine the dominant processes governing the total suspended solid (TSS) concentration at the water surface in Tonle Sap Lake, Cambodia, which is a large, shallow‐water lake. Satellite remotely sensed daily reflectance data from 2003 to 2017 were used. Seasonal changes in TSS concentration indicated that bottom sediment resuspension during dry seasons was mostly caused by wind and the TSS concentration was closely correlated with the water depth of the lake. The TSS concentration during flood periods was controlled by both wind and inflow currents from the Tonle Sap River. Additionally, we confirmed that surface/subsurface flow with a low TSS concentration from forests on the floodplain lowered the TSS concentration year round, except during August and September. This fact implied that the floodplain forest area decrease may increase the lake TSS concentration. An analysis of the long‐term changes in TSS indicated that a decrease in the water level during flood periods resulted in the high TSS concentrations observed during the subsequent dry periods. Therefore, climate change and water resource development, which are likely to cause water level reductions in the Mekong River during flood periods, may increase the TSS concentration in Tonle Sap Lake, particularly during the dry season.  相似文献   

Human impacts on large benthic foraminifers near a densely populated area of Majuro Atoll, Marshall Islands     

Yoko Osawa  Yu Umezawa  Yoichi Ide  Toshihiro Miyajima 《Marine pollution bulletin》2010,60(8):1279-1287

Human impacts on sand-producing, large benthic foraminifers were investigated on ocean reef flats at the northeast Majuro Atoll, Marshall Islands, along a human population gradient. The densities of dominant foraminifers Calcarina and Amphistegina declined with distance from densely populated islands. Macrophyte composition on ocean reef flats differed between locations near sparsely or densely populated islands. Nutrient concentrations in reef-flat seawater and groundwater were high near or on densely populated islands. δ¹⁵N values in macroalgal tissues indicated that macroalgae in nearshore lagoons assimilate wastewater-derived nitrogen, whereas those on nearshore ocean reef flats assimilate nitrogen from other sources. These results suggest that increases in the human population result in high nutrient loading in groundwater and possibly into nearshore waters. High nutrient inputs into ambient seawater may have both direct and indirect negative effects on sand-producing foraminifers through habitat changes and/or the collapse of algal symbiosis.  相似文献   

Rifting of Kyushu, Japan, based on the fault-controlled concurrent eruption of oceanic island basalt-type and island arc-type lavas     

Itsuro Kita  Yoshitada Asakawa  Tsutomu Yuri  Mitsuhiro Yasui  Yoichi Shimoike  Masatsugu Yamamoto  Hidenao Hasegawa  Sachihiro Taguchi  Hirochika Sumino 《Bulletin of Volcanology》2012,74(5):1121-1139

The tectonic environment of Kyushu, Japan is affected both by the subduction of the Philippine Sea plate and by the extensional tectonics related to rifting of Okinawa Trough at the eastern margin of the Eurasia Plate. We found that the Sendai fault zone acts as a channel for concurrent eruption of oceanic island basalt (OIB)-type and island arc (IA)-type basaltic rocks, propagating west to east in the Sendai region of southern Kyushu. The location of the Sendai fault zone is likely to correspond to the left-lateral shear zone in southern Kyushu as inferred by GPS Earth Observation Network. A similar magmatic association is present in the Beppu–Shimabara (BS) graben system in central Kyushu. The associate magmas of OIB-type rocks in Kyushu can be classified into typical, EM II-like and their intermediate OIB-type magmas in addition to MORB-like OIB-type magma in ⁸⁷Sr/⁸⁶Sr–Nb/Y systematics. Typical OIB-type and intermediate OIB-type magmas are erupted within the Sendai fault zone and BS graben system, respectively. The former is characterized by highest Nb/Y but low ⁸⁷Sr/⁸⁶Sr similar to MORB-like OIB-type magma erupted in northern Kyushu and the latter has intermediate Nb/Y and ⁸⁷Sr/⁸⁶Sr between typical and EM II-like OIB-type magmas. Almost all the IA-type rocks within the Sendai fault zone are generated from parental IA-type magma in Kyushu and characterized by weak crustal assimilation, having the lowest ⁸⁷Sr/⁸⁶Sr similar to typical OIB-type magma but the highest ¹⁴³Nd/¹⁴⁴Nd of arc magmas in Kyushu. The ages of both types of basaltic rocks within the Sendai fault zone range from 1.6 to <0.01?Ma clearly younger than those of andesitic rocks on northern and southern outsides of the fault zone and become younger from west to east. Initial formation of the fault zone has been induced by the counterclockwise rotation of southern Kyushu during the last 2?Ma as well as the BS graben system. Kyushu has continued to be split into three parts by the Sendai fault zone and BS graben during the Quaternary; northern, central, and southern zones. Their initial formation ages are likely to be linked to the initial rifting age of the middle Okinawa Trough back-arc basin.  相似文献   

Field measurements of absolute gravity in East Antarctica     

Koichiro Doi  Hideaki Hayakawa  Takahito Kazama  Toshihiro Higashi  Shingo Osono  Yoichi Fukuda  Jun Nishijima  Yuichi Aoyama  Junichi Ueda 《极地研究(英文版)》2013,(4):339-343

Abstract This paper reports the results of field-based absolute gravity measurements aimed at detecting gravity change and crustal displacement caused by glacial isostatic adjustment. The project was initiated within the framework of the 53rd Japanese Antarctic Research Expedition （JARE53）. Absolute gravity measurements, together with GPS measurements, were planned at several outcrops along the Prince Olav Coast and S6ya Coast of East Antarctica, including at Syowa Station. Since the icebreaker Shirase （AGB 5003） was unable to moor alongside Syowa Station, operations were somewhat restricted during JARE53. However, despite this setback, we were able to complete measurements at two sites： Syowa Station and Langhovde. The absolute gravity value at the Syowa Station IAGBN （A） site, observed using an FG-5 absolute gravimeter （serial number 210; FG-5 #210）, was 982 524 322.7＋0.1 ktGal, and the gravity change rate at the beginning of 2012 was -0.26 gGal.a-1. An absolute gravity value of 982 535 584.2~0.7 ktGal was obtained using a portable A-10 absolute gravimeter （serial number 017; A-10 #017） at the newly located site AGS01 in Langhovde.  相似文献   

Four-dimensional variational ocean reanalysis: a 30-year high-resolution dataset in the western North Pacific (FORA-WNP30)     

Norihisa Usui  Tsuyoshi Wakamatsu  Yusuke Tanaka  Nariaki Hirose  Takahiro Toyoda  Shiro Nishikawa  Yosuke Fujii  Yasushi Takatsuki  Hiromichi Igarashi  Haruka Nishikawa  Yoichi Ishikawa  Tsurane Kuragano  Masafumi Kamachi 《Journal of Oceanography》2017,73(2):205-233

We produced a four-dimensional variational ocean re-analysis for the Western North Pacific over 30 years (FORA-WNP30). It is the first-ever dataset covering the western North Pacific over 3 decades at eddy-resolving resolution. The four-dimensional variational analysis scheme version of the Meteorological Research Institute Multivariate Ocean Variational Estimation system (MOVE-4DVAR) is employed to conduct a long-term reanalysis experiment during 1982–2012. After evaluating the basic performance of FORA-WNP30, the interannual to decadal variability is analyzed. Overall, FORA-WNP30 reproduces basic features in the western North Pacific well. One of outstanding features in FORA-WNP30 is that anomalous events such as the Kuroshio large meander and anomalous intrusion of the Oyashio in the 1980s, when there were no altimeter data, are successfully reproduced. FORA-WNP30 is therefore a valuable dataset for a variety of oceanographic research topics and potentially for related fields such as climate study, meteorology and fisheries.  相似文献   

Preliminary results of the Japan-Taiwan joint survey on combining ocean radar data in the Kuroshio upstream region     

Kaoru Ichikawa  Wen Chang Yang  Akihiko Morimoto  Yutaka Yoshikawa  Shigeo Sugitani  Wen-Shan Chiang  Jian-Wu Lai  En Yu Liang  Cho-Teng Liu  Chang-Wei Lee  Kei Yufu  Moeto Kyushima  Satoshi Fujii  Tomoharu Senju  Yoshihiko Ide 《Ocean Science Journal》2013,48(1):141-148

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