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871.
872.
The single-degenerate (SD) channel for the progenitors of type Ia supernovae (SNe Ia) is one of the most popular channels, in which a carbon–oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit, and then explodes as a SN Ia. We show the initial and final parameter space for SNe Ia in a ( $\log P^{\mathrm{i}},M_{2}^{\mathrm{i}}$ ) plane and find that the positions of some famous recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951, are well explained by our model. The model can also explain the space velocity and mass of Tycho G, which is now suggested to be the companion star of Tycho’s supernova. Our study indicates that the SSS, V Sge, might be the potential progenitor of supernovae like SN 2002ic if the delayed dynamical-instability model due to Han and Podsiadlowski (Mon. Not. R. Astron. Soc. 368:1095, 2006) is appropriate. Following the work of Meng et al. (Mon. Not. R. Astron. Soc. 395:2103, 2009a), we found that the SD model (WD+MS) with an optically thick wind can explain the birth rate of supernovae like SN 2006X and reproduce the distribution of the color excess of SNe Ia. The model also predicts that at least 75% of all SNe Ia may show a polarization signal in their spectra. 相似文献
873.
广西钦州湾海岸带孢粉组合和沉积环境演变 总被引:2,自引:1,他引:1
对广西钦州湾海岸滩涂的4个钻孔的沉积物进行孢粉分析,结合 210Pb法测得沉积速率,讨论了该地区大约150年来的沉积环境演变规律.钦州湾地区具有19世纪中-末叶较现在偏凉的区域性气候; 20世纪初期西海岸沉积物中红树林花粉Rhizophora和Aegiceras锐减,反映出红树林滩衰退的特征; 60年代和70年代,钦州湾西海岸线明显向内陆迁移,高潮滩环境向低潮滩演化; 而80年代始,东海岸线由于钦江流域来沙的迅速堆积,沉积速率较高,岸线向海推移明显,沉积物中木本植物花粉和禾本科均有所增加,这和围垦修堤的人类活动加速了低潮滩向高潮滩演化有关.钦州湾总体表现出西向扩张,东向缩减的趋势. 相似文献
874.
华北地块北缘中元古代沉积层序中出现多个沉积间断和不整合面。此次研究对其中5个不整合面进行了野外考察,分析了它们的地质特征和空间分布,认为它们与不同的地质过程有关。大红峪组底部不整合面是早期裂谷盆地演化为被动大陆边缘的记录,属于裂解不整合面性质;高于庄组底部和杨庄组底部的不整合面是海平面变化造成被动大陆边缘内部高地沉积间断和海岸超覆沉积的结果;铁岭组顶部不整合面可能与弧后环境发生挤压抬升有关;下马岭组沉积后的抬升可能是相邻大陆地块碰撞作用的产物。华北地块北缘中元古代层序中不整合面的形成与Columbia和Rodinia超大陆的形成和裂解过程密切相关。 相似文献
875.
876.
877.
Toru Tamura Yoshiki Saito Sotham Sieng Bunnarin Ben Meng Kong Im Sim Sokuntheara Choup Fumio Akiba 《Quaternary Science Reviews》2009,28(3-4):327-344
Modern deltas are understood to have initiated around 7.5–9 ka in response to the deceleration of sea-level rise. This episode of delta initiation is closely related to the last deglacial meltwater events and eustatic sea-level rises. The initial stage of the Mekong River delta, one of the world's largest deltas, is well recorded in Cambodian lowland sediments. This paper integrates analyses of sedimentary facies, diatom assemblages, and radiocarbon dates for three drill cores from the lowland to demonstrate Holocene sedimentary evolution in relation to sea-level changes. The cores are characterized by a tripartite succession: (1) aggrading flood plain to natural levee and tidal–fluvial channel during the postglacial sea-level rise (10–8.4 ka); (2) aggrading to prograding tidal flats and mangrove forests around and after the maximum flooding of the sea (8.4–6.3 ka); and (3) a prograding fluvial system on the delta plain (6.3 ka to the present). The maximum flooding of the sea occurred at 8.0 ± 0.1 ka, 2000 years before the mid-Holocene sea-level highstand, and tidal flats penetrated up to 20–50 km southeast of Phnom Penh after a period of abrupt ~5 m sea-level rise at 8.5–8.4 ka. The delta progradation then initiated as a result of the sea-level stillstand at around 8–7.5 ka. Another rapid sea-level rise at 7.5–7 ka allowed thick mangrove peat to be widely deposited in the Cambodian lowland, and the peat accumulation endured until 6.3 ka. Since 6.3 ka, a fluvial system has characterized the delta plain, and the fluvial sediment discharge has contributed to rapid delta progradation. The uppermost part of the sedimentary succession, composed of flood plain to natural-levee sediments, reveals a sudden increase in sediment accumulation over the past 600–1000 years. This increase might reflect an increase in the sediment yield due to human activities in the upper to middle reaches of the Mekong, as with other Asian rivers. 相似文献
878.
This study reports results from an analysis of the relationship between atmospheric forcing and model‐simulated water and energy fluxes for the North American Land Data Assimilation System Project Phase 2 (NLDAS‐2). The relationships between mean monthly precipitation and total runoff are stronger in the Sacramento (SAC) and variable infiltration capacity (VIC) models, which grew out of the hydrological community, than in the Noah and Mosaic models, which grew out of the soil‐vegetation‐atmosphere transfer (SVAT) community. The reverse is true for the relationship between mean monthly precipitation and evapotranspiration. In addition, surface energy fluxes in VIC are less sensitive to model forcing (except for air temperature) than those in the Noah and Mosaic model. Notwithstanding these general conclusions, the relationships between forcings and model‐simulated water and energy fluxes for all models vary for different seasons, variables, and regions. These findings will ultimately inspire a combination of SVAT‐type model energy components with hydrological model water components to develop a SVAT‐hydrology model to improve both evapotranspiration and total runoff simulations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
879.
由金刚石共晶体与硬质合金基座制成的复合体是一种新型超硬研磨材料,用它和特制的钻头胎体制成的复合片取心钻头适用于可钻性小于Ⅶ级岩石的钻进,它的应用可大大提高煤系地层(特别是煤心)的采取率。 相似文献
880.
引言我国地震系统数字化台网改造工作正在全面展开 ,不仅需要高质量的数字化地震观测仪器 ,提高观测质量 ;同样也需要一种适合遥测台工作特点的供电系统 ,提高遥测台地震观测仪器的连续运行率。在遥测台网的监测工作中 ,由于原有的电源不尽完善 ,不能完全适应遥测台的工作环境 ,造成地震信号断记的现象时有发生。一直是困扰遥测台网监测工作质量的一个难题。为此 ,我们研制了 LN-GDXT-1型多功能电源。LN-GDXT-1型多功能电源具有性能稳定 ,输入交流电压范围宽 ,停电时持续供电时间长 ,免维护等特点 ,是一种较为理想的遥测台供电系统。1… 相似文献