排序方式： 共有24条查询结果，搜索用时 15 毫秒
1.
2.
Comet 73P-B/Schwassmann-Wachmann 3 was observed with IRCS/Subaru at geocentric distance of 0.074 AU on UT 10 May 2006. Multiple H2O emission lines were detected in non-resonant fluorescence near 2.9 μm. No significant variation in total H2O production rate was found during the (3 h) duration of our observations. H2O rotational temperatures and ortho-to-para abundance ratios were measured for several positions in the coma. The temperatures extracted from two different time intervals show very similar spatial distributions. For both, the rotational temperature decreased from ∼110 to ∼90 K as the projected distance from the nucleus increased from ∼5 to ∼30 km. We see no evidence for OPR change in the coma. The H2O ortho-para ratio is consistent with the statistical equilibrium value (3.0) for all spatially resolved measurements. This implies a nuclear spin temperature higher than ∼45 K. 相似文献
3.
4.
W. A. Mulder 《Computational Geosciences》1997,1(1):85-108
Simulation of wave propagation for seismic purposes is usually restricted to a small portion of the earth. Artificial boundary
conditions are required where the subsurface model is truncated. Absorbing boundaries should ensure that waves hitting the
artificial boundaries are not reflected. The vast amount of literature on the subject suggests that “good” conditions have
not been found, and only “reasonable” solutions exist. A cursory overview of existing and a few new ideas is presented that
may guide the construction of suitable boundary conditions. Because the intended application of the boundary conditions was
a high-order finite-difference code that runs on a parallel computer, we have restricted our attention to local boundary conditions.
A fundamental problem in the design of accurate local boundary conditions is pointed out: accuracy is required to keep the
amount of reflected energy small, but at the same time allows for growing low-frequency modes. We have settled for Higdon’s
boundary conditions. Higdon proposes to include some damping to suppress the growing low-frequency modes. We show that third-order
conditions provide acceptable results for the simple scalar wave equation and the acoustic equation. In the elastic case,
an additional low-frequency growing mode may occur. This mode can be suppressed by using a dissipative boundary scheme and
by increasing the amount of damping. The increase in damping results in an increase in the amount of reflected energy, which
is larger than in the scalar case. Numerical experiments exhibit a reasonable performance, although some improvement would
be useful, particularly in the anisotropic elastic case.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
针对自然伽马等常规测井系列长期仅能将鄂尔多斯盆地延长组长73砂层组大规模发育的与烃源岩相关的高伽马砂岩解释为“油页岩等优质烃源岩”的问题,根据岩心观察及测录井资料、电子探针薄片和大量页岩油实际生产资料的分析,对长73砂层组内与烃源岩相关的高伽马砂岩的定义、成因以及其发育特征与长7油层组页岩油试油效果的关系进行了探索性的研究。研究表明,鄂尔多斯盆地长73砂层组内与烃源岩相关的高伽马砂岩可划分为狭义和广义两种类型,高放射性的成因可能与深部热水作用有关,首次发现其发育特征与长7油层组页岩油试油效果关系密切。该项研究对鄂尔多斯盆地延长组长7油层组页岩油的大规模高效勘探与开发具有重要的理论和现实意义。 相似文献
6.
The aim of this paper is to evaluate the results of a survey of the availability and uptake of port reception facilities within the North Sea area. The evaluation is based primarily on original survey data from the autumn of 2002 which followed on from a similar survey conducted in the summer of 2000. The EU Directive on port reception facilities for ship-generated waste etc. (Directive 2000/59/EC) was due to enter into force in December 2002, and required all EU ports to provide reception facilities to meet the needs of the vessels normally calling in at them. This paper examines the readiness of North Sea ports to meet that requirement and also considers the actual uptake levels of facilities, where ports were able to provide such information. 相似文献
7.
Tsunami deposit associated with the 2011 Tohoku‐oki tsunami in the Hasunuma site of the Kujukuri coastal plain,Japan 
下载免费PDF全文
下载免费PDF全文 Dan Matsumoto Yuki Sawai Koichiro Tanigawa Osamu Fujiwara Yuichi Namegaya Masanobu Shishikura Kyoko Kagohara Haruo Kimura 《Island Arc》2016,25(5):369-385
We describe the detailed sedimentary characteristics of a tsunami deposit associated with the 2011 Tohoku‐oki tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick tsunami deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The tsunami deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging and grain‐size analysis. The deposit covers the pre‐existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well‐sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the tsunami deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the tsunami‐related sedimentation. 相似文献
8.
The nucleus of the Comet 73P/Schwassmann–Wachmann had been split into many fragments at least past two returns. Since the
related dense dust trail has been detected in the space infrared observation, the strong activity of the meteor shower is
highly expected in the future. We applied the so-called dust-trail theory to this interesting object, and obtained several
results on the future encounter with the dust trail. In this paper we introduce our results on the forecasts. 相似文献
9.
The postperovskite phase transition of Fe and Al-bearing MgSiO3 bridgmanite, the most aboundant mineral in the Earth's lower mantle, is believed to be a key to understanding seismological observations in the D″ layer, e.g., the discontinuous changes in seismic wave velocities. Experimentally reported phase transition boundaries of Fe and Al-bearing bridgmanite are currently largely controversial and generally suggest wide two-phase coexistence domains. Theoretical simulations ignoring temperature effects cannot evaluate correctly two-phase coexistence domains under high-temperature. We show high-pressure and high-temperature phase transition boundaries for various compositions with geophysically relevant impurities of Fe2+SiO3, Fe3+Fe3+O3, Fe3+Al3+O3, and Al3+Al3+O3 derived from the ab initio finite-temperature free energies calculated combining the internally consistent LSDA + U method and a lattice dynamics approach. We found that at ～ 2500 K, incorporations accompanied by Fe3+ expand the two-phase coexistence domains distinctly, implying that D″ seismic discontinuities likely arise from the phase transition of Fe2+-bearing bridgmanite. 相似文献
10.
针对1″SRTM数据和基于1∶50000地形图生成的DEM在黄土侵蚀区对地表形态表达能力的差异性问题,提出了一套完整的评价分析指标体系。选取陕西黄土高原6大典型黄土地貌样区,从地形属性(高程、坡度、坡向、坡长)和地形特征(山顶点、流水线、流域边界)两大方面评估了两种数据对表达黄土侵蚀区的地形表达能力。结果表明:1″SRTM对地表形态的表达能力接近1∶50000地形图所生成的DEM,但总体上还是1∶50000地形图所生成的DEM对地表形态的表达比较好,尤其是在地形比较破碎的地区。本文为1″SRTM数据在部分区域替代地形图生成的Hc-DEM,并用于与地学相关领域的研究提供了重要依据。 相似文献