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排序方式: 共有137条查询结果,搜索用时 15 毫秒
21.
Kotaro Kohno Koichiro Nakanishi Tomoka Tosaki Kazuyuki Muraoka Rie Miura Hajime Ezawa Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):279-285
Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0)
and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component
is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions
of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby
spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging
of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between
the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on
the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed
in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in
the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation
rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these
ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these
molecular lines are free from dust extinction. 相似文献
22.
Masanobu Shimada Hiromi Oaku Yasushi Mitomi Hiroshi Murakami Akira Mukaida Yasuhisa Nakamura Joji Ishizaka Hiroshi Kawamura Tasuku Tanaka Motoaki Kishino Hajime Fukushima 《Journal of Oceanography》1998,54(5):401-416
We present calibration and validation results of the OCTS’s ocean color version-3 product, which mainly consists of the chlorophyll-a concentration (Chl-a) and the normalized water-leaving radiance (nLw). First, OCTS was calibrated for the inter-detector sensitivity difference, offset, and absolute sensitivity using external
calibration source. It was also vicariously calibrated using in-situ measurements for water (Chl-a andnLw) and atmosphere (optical thickness), which were acquired synchronously with OCTS under cloud-free conditions. Second, the
product was validated using selected 17 in-situ Chl-a and 11 in-situnLw measurements. We confirmed that Chl-a was estimated with an accuracy of 68% for Chl-a less than 2 mg/m3, andnLw from 94% (band 2) to 128% (band 4). Geometric accuracy was improved to 1.3 km. Stripes were significantly reduced by modifying
the detector normalization factor as a function of input radiance. 相似文献
23.
Hajime Fukushima Akiko Higurashi Yasushi Mitomi Teruyuki Nakajima Toshimitsu Noguchi Toshio Tanaka Mitsuhiro Toratani 《Journal of Oceanography》1998,54(5):417-430
This paper first describes the atmospheric correction algorithm for OCTS visible band data used at NASDA/EOC. Sharing a basic
structure with Gordon and Wang’s Sea WiFS algorithm, it uses 10 candidate aerosol models including the “Asian dust model”
introduced in consideration of the unique feature of aerosols over the east Asian waters. Based on the observations at 670
and 865 nm bands, the algorithm selects a pair of aerosol models that account best for the observed spectral reflectances,
and synthesizes the aerosol reflectance used for the atmospheric correction. Two different schemes for determining the value
of the parameter for the aerosol model selection are presented and their anticipated estimation error is analyzed in terms
of retrieved water reflectance at 443 nm. The results of our numerical simulation show that the standard deviation of the
estimation error of the “weighted average” scheme is mostly within the permissible level of ±0.002, reducing the error by
18% on average compared to the “simple average” scheme. The paper further discusses the expected error under the old CZCS-type
atmospheric correction, which assumes constant aerosol optical properties throughout the given image. Although our algorithm
has a better performance than the CZCS algorithm, further analysis shows that the error induced by the assumption taken in
the algorithm that the water-leaving radiance at 670 nm band is negligibly small may be large in high pigment concentration
waters, indicating the necessity for future improvements. 相似文献
24.
Naohisa Nishida Taku Ajioka Ken Ikehara Rei Nakashima Hajime Katayama Tomoyuki Sato Seishiro Furuyama Toru Tamura 《Sedimentology》2020,67(1):559-575
Sandy shelf sediments are important elements of clastic sedimentary systems because of their wide distribution in the geological record and their significance as hydrocarbon reservoirs. Although many studies have investigated shelf sediments influenced by waves or tidal currents, little is known about shelf sediments influenced by oceanic currents, particularly their lithofacies characteristics and stratigraphic evolution. This study investigated the stratigraphic evolution of shelf sediments off the Kujukuri strandplain facing the Pacific Ocean, which is influenced by the strong Kuroshio Current. Sediment cores were obtained from six locations on the Kujukuri shelf (34 to 124 m water depth) using a vibrocorer. The dominant lithofacies is mud-free sand with low-angle cross-lamination associated with alternating beds of finer and coarser sand with cross-lamination. These display depositional processes influenced by storm waves and the Kuroshio Current, respectively. This finding is consistent with the previously presented modern and historical observations of the Kuroshio Current and estimates of the storm-wave base. Radiocarbon dates show that the sediment succession formed during the last transgressive and highstand stages after 13·1 ka. The depositional processes during the stages represent a transition from storm waves with abundant sediment supply to both storm waves and the Kuroshio Current with sediment starvation mainly due to its trapping in the strandplain. Comparison to other Holocene–Modern shelf systems suggests that the sandy shelf successions are strongly influenced by oceanic currents under conditions of limited riverine input and open coastal geometry. The resultant sand-dominated succession is characterized by reversal of the proximal to distal grain-size trend compared to the fining for most other recognized wave/storm-dominated shelf successions. This is because of seaward increase in the influence of the Kuroshio Current. Thus, shelf deposits are naturally complex, and these may be further complicated by the additional influence of oceanic currents above the usual wave-dominated and tide-dominated end members. 相似文献
25.
东亚地区春季二氧化硫的输送与转化过程研究I.模式及其验证 总被引:5,自引:0,他引:5
结合新近评估的东亚地区污染源资料,作者利用一个耦合的区域化学输送模式系统以探讨东亚地区春季期间气象过程、气相与液相化学过程、非均相化学过程、气溶胶过程和干湿沉降过程对二氧化硫输送及转化过程的影响,并研究二氧化硫和硫酸盐气溶胶的空间分布及变化特征.模拟的二氧化硫和硫酸盐气溶胶的浓度值与2001年春季飞机和地面获取的观测值进行了比较.比较结果显示,模拟值与观测值具有很好的一致性,模式系统很好地反映了二氧化硫和硫酸盐气溶胶的分布特征和变化规律,再现了许多观测到的重要特征,为进一步分析模拟结果奠定了基础. 相似文献
26.
This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke.A series of experiments are conducted with different types of sedime... 相似文献
27.
Shigehiro Fujino Hajime Naruse Dan Matsumoto Norihiko Sakakura Apichart Suphawajruksakul Thanawat Jarupongsakul 《Island Arc》2010,19(3):389-398
Measurements of thickness and grain size along flow‐parallel transects across onshore deposits of the 2004 Indian Ocean tsunami revealed macroscopic horizontal variations and provided new insights into tsunami sedimentation. The tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to deposit a kilometer‐wide blanket of sand on the land surface. The tsunami deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and deposited 1 km or more inland. Although the thickness of the tsunami deposits is strongly influenced by local topography, they generally thin landward. In areas of low‐relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland. 相似文献
28.
Badri Bhakta Shrestha Hajime Nakagawa Kenji Kawaike Yasuyuki Baba Hao Zhang 《Natural Hazards》2012,61(2):577-602
Experience shows that debris flows containing large woody debris (driftwood) can be more damaging than debris flows without
driftwood. In this study, the deposition process of debris flows carrying driftwood was investigated using numerical simulations
and flume experiments. Debris-flow trapping due to driftwood jamming in a slit-check dam was also investigated. A numerical
model was developed with an interacting combination of Eulerian expression of the debris flow and Lagrangian expression of
the driftwood, in which the fluctuating coordinates and rotation of the driftwood were treated stochastically. The calculated
shapes and thicknesses of a debris-flow fan and the positions and orientations of the deposited driftwood on a debris-flow
fan were consistent with experimental flume results. The jamming of driftwood in a slit-check dam was evaluated based on geometry
and probability. The simulated results of outflow discharge and the proportion of driftwood passed through the slit-check
dam also agreed with the experimental results. 相似文献
29.
To determine the existence of p-nitrophenol (PNP)-lowering bacteria in intestine of Japanese coastal fish, the gastro-intestinal contents were incubated in Brain Heart Infusion (BHI) broth and minimal medium (MM) broths containing 1 mmol/L PNP at 30 °C for 7 days. Among 26 samples of 19 fish species, 17 samples showed a decrease in PNP of 0.5-0.8 mmol/L in BHI broth, but no decrease was shown in MM broth. Eighteen PNP-lowering bacterial strains were isolated from four fishes. All of the strains were identified as Lactococcus lactis subsp. lactis. Three L. lactis strains JS1-3 isolated from Japanese seabass Lateolabrax japonicus showed the highest PNP-lowering activity (0.44 mmol/L). Optimum temperature and pH for the growth and PNP decreasing corresponded with the marine environment. These results suggested that marine fishes have PNP decreasing bacteria in their intestine. These bacteria might protect host fish from toxicities of PNP and PNP related compounds. 相似文献
30.
A numerical study of tropospheric ozone in the springtime in East Asia 总被引:11,自引:0,他引:11
The Models-3 Community Multi-scale Air Quality modeling system (CMAQ)coupled with the Regional Atmospheric Modeling System (RAMS)is applied to East Asia to study the transport and photochemical transformation of tropospheric ozone in March 1998.The calculated mixing ratios of ozone and carbon monoxide are compared with ground 1evel observations at three remote sites in Japan and it is found that the model reproduces the observed features very well.Examination of several high episodes of ozone and carbon monoxide indicates that these elevated levels are found in association with continental outflow,demonstrating the critical role of the rapid transport of carbon monoxide and other ozone precursors from the continental boundary layer.In comparison with available ozonesonde data,it is found that the model-calculated ozone concentrations are generally in good agreement with the measurements,and the stratospheric contribution to surface ozone mixing ratios is quite limited. 相似文献