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101.
M. Kato 《Astronomische Nachrichten》2010,331(2):140-145
I review various phenomena associated with mass‐accreting white dwarfs (WDs) in the view of supersoft X‐ray sources. When the mass‐accretion rate is low (Ṁacc < a few × 10–7 M⊙yr–1), hydrogen nuclear burning is unstable and nova outbursts occur. A nova is a transient supersoft X‐ray source (SSS) in its later phase which timescale depends strongly on the WD mass. The X‐ray turn on/off time is a good indicator of the WD mass. At an intermediate mass‐accretion rate an accreting WD becomes a persistent SSS with steady hydrogen burning. For a higher mass‐accretion rate, the WD undergoes “accretion wind evolution” in which the WD accretes matter from the equatorial plane and loses mass by optically thick winds from the other directions. Two SSS, namely RX J0513‐6951 and V Sge, are corresponding objects to this accretion wind evolution. We can specify mass increasing WDs from light‐curve analysis based on the optically thick wind theory using multiwavelength observational data including optical, IR, and supersoft X‐rays. Mass estimates of individual objects give important information for the binary evolution scenario of type Ia supernovae (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
102.
The velocity profiles and properties of proto-magnetar winds are investigated.It is found that the corotation of wind matter with magnetic field lines significantly affects r-process nucleosynthesis and could lead to long duration γ-ray bursts and hyper-energetic supernovae. 相似文献
103.
运用相对运动的地球动力学理论,把软流圈以上的岩石圈和软流圈以下的地球内圈,作为两个独立的运动单元来考察它们随地球自转时所发生的变化和各自的运动状态。完整的岩石圈碎裂成岩石块之后,它们各自作为独立的单元,在纬向西漂力、经向离极力和洋底扩张力联合作用下,产生相对运动。 相似文献
104.
105.
Jonathan D. Phillips Linda L. Martin Viva G. Nordberg William A. Andrews 《地球表面变化过程与地形》2004,29(7):799-819
Central Kentucky is characterized by a mixture of karst and ?uvial features, typically manifested as mosaic of karst‐rich/channel‐poor (KRCP) and channel‐rich/karst‐poor (CRKP) environments. At the regional scale the location and distribution of KRCP and CRKP areas are not always systematically related to structural, lithological, topographic, or other controls. This study examines the relationship of KRCP and CRKP zones along the Kentucky River gorge area, where rapid incision in the last 1·5 million years has lowered local base levels and modi?ed slopes on the edge of the inner bluegrass plateau. At the scale of detailed ?eld mapping on foot within a 4 km2 area, the development of karst and ?uvial features is controlled by highly localized structural and topographic constraints, and can be related to slope changes associated with retreat of the Kentucky River gorge escarpment. A conceptual model of karst/?uvial transitions is presented, which suggests that minor, localized variations are suf?cient to trigger a karst–?uvial or ?uvial–karst switch when critical slope thresholds are crossed. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
106.
Using a mesoscale model,a numerical study on a heavy rainfall case occurring in the Changjiang-Huaihe River Basin is made in this paper.The influence of the intensity of northeasterly wind in front of the Qinghai-Xizang high at upper level on the low level wind field and development of mesoscale systems as well as heavy rainfall is investigated.The model well reproduced the heavy rainfall process and the weather systems associated.And it indicates that the strong northeasterly flow around the high at upper troposphere will bring about not only the strengthening of low level southeasterly wind,but also the appearance of shear-line and mesoscale vortex at low level.The coupling of northerly wind at upper level and southerly wind at lower level constructs a vertical indirect circulation which is most favourable for the development of convective motions.Its ascending branch in the shear-line area is very strong and shows a pronounced mesoscale characteristic. 相似文献
107.
The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the
Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric
Research (NCEP/NCAR) reanalyses for the period 1987–1996. Two dominant ISOs are found in all years, with a period between
30–60 days and 10–20 days respectively. Although the ISOs themselves explain only about 10–25% of the daily variance, the
spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances),
indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics
of the two modes and their interannual variability are studied in detail.
The synoptic structure of the 30–60 day mode is similar in all years and is shown to be intimately related to the strong (‘active’)
or weak (‘break’) phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of
Bengal corresponds to the ‘active’ (‘break’) phase of monsoon strengthening (weakening) the entire large scale monsoon circulation.
The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough).
The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The
vorticity pattern associated with the 30–60 day mode has a bi-modal meridional structure similar to the one associated with
the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30–60 day mode is consistent with
fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10–20
day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30–60 day mode. Elsewhere
in the Indian Ocean, this mode is almost always weaker than the 30–60 day mode. In the Bay of Bengal region, the wind curl
anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs
in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay.
On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly
mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree
well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite
structure of the 30–60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean
winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual
variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence
of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual
scales. 相似文献
108.
109.
半空间非水平层状介质瑞雷面波的频散方程 总被引:2,自引:0,他引:2
由于工程勘察中的一些特殊情况,使面波以往的一些理论和结论受到了不同程度的限制。本文从弹性动力学虚功变分原理出发,在重点分析自由表面外力提供的能量来源时,引入了等效面波(能量)震源概念。然后用有限元法建立了半空间多个非水平层状介质瑞雷西波的频散方程。这项工作有助于面波理论和应用技术的发展完善。 相似文献
110.