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131.
How supermassive black holes(SMBHs) are spun-up is a key issue in modern astrophysics. As an extension to the study in Wang et al., here we address the issue by comparing the host galaxy properties of nearby(z 0.05) radio-selected Seyfert 2 galaxies. With the two-dimensional bulge+disk decompositions for the SDSS r-band images, we identify a dichotomy in various host galaxy properties for radio-loud SMBHs. By assuming that radio emission from the jet reflects a high SMBH spin, which stems from the well-known Blandford-Znajek mechanism of jet production, high-mass SMBHs(i.e., MBH 107.9 M⊙)have a preference for being spun-up in classical bulges, and low-mass SMBHs(i.e., MBH = 106-107 M⊙)in pseudo-bulges. This dichotomy suggests and confirms that high-mass and low-mass SMBHs are spun-up in different ways, i.e., a major "dry" merger and a secular evolution respectively. 相似文献
132.
Through the study of mutual process between groundwater systems and eco-environmental water demand, the eco-environmental
water demand is brought into groundwater systems model as the important water consumption item and unification of groundwater’s
economic, environmental and ecological functions were taken into account. Based on eco-environmental water demand at Da’an
in Jilin province, a three-dimensional simulation and optimized management model of groundwater systems was established. All
water balance components of groundwater systems in 1998 and 1999 were simulated with this model and the best optimal exploitation
scheme of groundwater systems in 2000 was determined, so that groundwater resource was efficiently utilized and good economic,
ecologic and social benefits were obtained. 相似文献
133.
Water is a necessary element during gas hydrate formations. Therefore, by analyzing water depletion changes in media, the reaction characteristics of methane hydrate in media can be studied. In this study, two water sources supplying some liquid water which may be consumed by the methane hydrate formation reactions were designed and assembled. Using them, the full formation processes of methane hydrate was studied. Experimental results show the following: If heat released from nucleation reaction of methane hydrate is diffused rapidly, the nucleation ratios will be enhanced discernibly. While the hydrate is formed, a force is generated that sucks fresh water from the source into the vicinity of the hydrate, slowing down the cementation process and causing some hydrate grain dissociation. As a result of cementation differences, the hydrate reaction processes with different water sources present linear or quadratic equation characteristics. After a few repeated dissociation and formation processes of some hydrate grains caused by the fresh water, the gas amounts contained in hydrate will be significantly enhanced. 相似文献
134.
Mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradation 总被引:2,自引:0,他引:2
The mass-front velocities of granular flows results from the joint action of particle size gradations and the underlying surfaces.However,because of the complexity of friction during flow movement,details such as the slope-toe impedance effects and momentum-transfer mechanisms have not been completely explained by theoretical analyses,numerical simulations,or field investigations.To study the mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradations we conducted model experiments that recorded the motion of rapid and long-runout rockslides or avalanches.Flume tests were conducted using slope angles of 25°,35°,45°,and 55° and three particle size gradations.The resulting mass-front motions consisted of three stages:acceleration,velocity maintenance,and deceleration.The existing methods of velocity prediction could not explain the slowing effect of the slope toe or the momentum-transfer steady velocity stage.When the slope angle increased from 25° to 55°,the mass-front velocities dropped significantly to between 44.4% and59.6% of the peak velocities and energy lossesincreased from 69.1% to 83.7% of the initial,respectively.The velocity maintenance stages occurred after the slope-toe and mass-front velocity fluctuations.During this stage,travel distances increased as the angles increased,but the average velocity was greatest at 45°.At a slope angle of 45°,as the median particle size increased,energy loss around the slope toe decreased,the efficiency of momentum transfer increased,and the distance of the velocity maintenance stage increased.We presented an improved average velocity formula for granular flow and a geometrical model of the energy along the flow line. 相似文献
135.
通过文本分析和档案分析的方法,立足文学地理学分析框架和研究范式,分析了香港70年代、过渡时期、后殖民时期三部文学界热门且公认具代表性的作品——《我城》《烦恼娃娃的旅程》和《后殖民食物与爱情》,解构了作品中“本土”“国家”和“全球”3个空间维度下再现的地理物象、空间想象、人物活动、地方文化,窥探其内部隐含的文化认同与身份意识问题。结果发现,由于香港社会历史和文化背景不断变迁等原因,香港的文化和身份意识处于不断重塑的状态。通过文本分析,发现香港文学作品中最早萌芽的是“本土”意识。西西的《我城》被认为是本土意识的发轫之作,其在港英政府和回不去的家这一夹缝中在“城”这一空间尺度上勾勒出浓浓的地方意识。其次,在中国恢复行使香港主权这一背景下,《烦恼娃娃的旅程》这一极具回归题材代表性的作品深刻地刻画了香港人在身份认同尺度升级过程中的迷惘。最后,也斯的《后殖民食物与爱情》通过“食物”为线索讲述了回归后的香港故事,为读者认识后殖民时期多元文化混杂下的香港社会提供了细致的观察。通过对三部文学作品的分析,发现港人经历了由殖民统治时期本土身份意识的觉醒以及对中国文化的归属,到回归过渡阶段身份意识的尺度升级及其不适,再到回归后多元文化的交织和协商,不仅在尺度上实现了由地方到国家再到全球化的身份意识塑造,而且在结构上存在中华文化、西方文化和香港本土文化不断协商与冲突的三重性。更为重要的是,通过文学地理视角的讨论,发现这样的文化和身份意识不是属于某个群体的特有特征,而是根植于香港社会的每一寸肌肤,不仅反映了小说作者对香港社会的细致观察,在一定程度上也反映了社会本身所面临的文化和身份困扰。 相似文献
136.
Risk assessment of maize drought disaster in southwest China using the Environmental Policy Integrated Climate model 总被引:2,自引:0,他引:2
The East Asian monsoon has a tremendous impact on agricultural production in China. An assessment of the risk of drought disaster in maize-producing regions is therefore important in ensuring a reduction in such disasters and an increase in food security. A risk assessment model, EPIC(Environmental Policy Integrated Climate) model, for maize drought disasters based on the Erosion Productivity Impact Calculator crop model is proposed for areas with the topographic characteristics of the mountainous karst region in southwest China. This region has one of the highest levels of environmental degradation in China. The results showed that the hazard risk level for the maize zone of southwest China is generally high. Most hazard index values were between 0.4 and 0.5,accounting for 47.32% of total study area. However,the risk level for drought loss was low. Most of the loss rate was 0.1, accounting for 96.24% of the total study area. The three high-risk areas were mainlydistributed in the parallel ridge–valley areas in the east of Sichuan Province, the West Mountain area of Guizhou Province, and the south of Yunnan Province.These results provide a scientific basis and support for the reduction of agricultural drought disasters and an increase in food security in the southwest China maize zone. 相似文献
137.
We constrain the distance of the gamma-ray burst (GRB) prompt emission site from the explosion centre R , by determining the location of the electron's self-absorption frequency in the GRB prompt optical-to-X/γ-ray spectral energy distribution, assuming that the optical and the γ-ray emissions are among the same synchrotron radiation continuum of a group of hot electrons. All possible spectral regimes are considered in our analysis. The method has only two assumed parameters, namely the bulk Lorentz factor of the emitting source Γ and the magnetic field strength B in the emission region (with a weak dependence). We identify a small sample of four bursts that satisfy the following three criteria: (1) they all have simultaneous optical and γ-ray detections in multiple observational time intervals, (2) they all show temporal correlations between the optical and γ-ray light curves and (3) the optical emission is consistent with belonging to the same spectral component as the γ-ray emission. For all the time intervals of these four bursts, it is inferred that R ≥ 1014 (Γ/300)3/4 ( B /105 G)1/4 cm. For a small fraction of the sample, the constraint can be pinned down to R ≈ 1014 –1015 cm for Γ∼ 300 . For a second sample of bursts with prompt optical non-detections, only upper limits on R can be obtained. We find no inconsistency between the R -constraints for this non-detection sample and those for the detection sample. 相似文献
138.
Li Fang Rong Xiang Meixun Zhao Liping Zhou Jianguo Liu Lanlan Zhang 《中国海洋大学学报(英文版)》2013,12(4):629-638
Assemblages of benthic foraminifera in a sediment core (C02) near the western margin of the southern Yellow Sea Mud were studied to decipher the phase evolution of Holocene paleoenvironmental changes associated with the Holocene marine transgression. It appears that during the early Holocene (11.2–10.1 kyr BP), the faunal was dominated by low salinity and shallow water species Cribrononion subincertum, Buccella frigida and Ammonia beccarii, reflecting a near coast depositional environment. A rapid increase of the relative abundance of Ammonia compressiuscula between 10.1–9.3 kyr BP indicates that the sea level rose rapidly during that time period. From 9.3–7.7 kyr BP, the benthic foraminiferal assemblage was dominated by high percentage of A. compressiscula, suggesting that the sea level was relatively stable. An obvious transition of benthic foraminifera, from the A. compressiuscula-dominated assemblage to an Ammonia ketienziensis-dominated assemblage, occurred between 7.7–6.2 kyr BP, possibly corresponding to a second sea level rapid rise period in the Yellow Sea during the Holocene. This transition may correspond to the gradually strengthened Yellow Sea warm current (YSWC) and finally is established the modern-type circulation in the Yellow Sea. It may also mark the formation of the Yellow Sea cold bottom water (YSCBW) during that period. Since then, the benthic foraminiferal assemblage based on core C02 was dominated by typical YSCBW species, A. ketienziensis, Astrononion italicum and Hanzawaia nipponica, at 6.2–4 kyr BP. A non-deposition period occurred since ~4 kyr BP, which possibly related to the hydrology changes caused by the East Asia monsoon. The two obvious benthic foraminiferal transitions recorded in core C02 during the early and middle Holocene provide evidence that the Yellow Sea has undergone a two-phase rapid sea level rise during the Holocene marine transgression. 相似文献
139.
140.
回顾了日冕磁的研究历史,介绍了我们首镒提出的日冕磁场的微波诊断方法及其应用的带来的启迪,提出进一步开展日冕磁场及其相关研究的建议。 相似文献