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741.
Georges Meynet 《Astrophysics and Space Science》2002,279(1-2):183-186
Stellar models with axial rotation and very low metallicity Z, typical of the early star generations have been computed. These
models account for the effects of rotation in the same way as previous grids which successfully reproduce the He- and N-enrichments
observed at the surface of massive stars, and also the high numbers of red supergiants observed in low Z galaxies (Meynet and Maeder, 2000; Maeder and Meynet, 2001). At very low metallicity (Z = 0.00001, i.e. one two thousandth of the solar metallicity),these models naturally lead to the production of primary nitrogen.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
742.
743.
Kinwah Wu Roberto Soria Richard W. Hunstead Helen M. Johnston 《Monthly notices of the Royal Astronomical Society》2001,320(2):177-192
We have carried out observations of the X-ray transient GX 339−4 during its high–soft and low–hard X-ray spectral states. Our high-resolution spectroscopic observation in 1999 April suggests that the H α line has a single-peaked profile in the low–hard state as speculated in our previous paper. The He ii λ 4686 line, however, has a double-peaked profile in both the high–soft and low–hard states. This suggests that the line-emission mechanism is different in the two states. Our interpretation is that double-peaked lines are emitted from a temperature-inversion layer on the accretion disc surface when it is irradiatively heated by soft X-rays. Single-peaked lines may be emitted from outflow/wind matter driven by hard X-ray heating. We have constructed a simple plane-parallel model and we use it to illustrate that a temperature-inversion layer can be formed at the disc surface under X-ray illumination. We also discuss the conditions required for the formation of temperature inversion and line emission. Based on the velocity separations measured for the double-peaked lines in the high–soft state, we propose that GX 339−4 is a low-inclination binary system. The orbital inclination is about 15° if the orbital period is 14.8 h. 相似文献
744.
描述了Web服务业务流程执行语言(BPEL4WS)的Petri网模型,并提出了模型的化简规则,用于验证模型中的死锁和乏同步两种结构冲突。最后结合一个业务过程实例,进行建模和化简。 相似文献
745.
Here we report the spectral characteristics of the high and low states of the pulsar 4U 0114 + 65 and examine the change in
the parameters of the spectral model. A power law and a photoelectric absorption by material along the line of sight together
with a high energy cut-off suffice to describe the continuum spectrum in both the states. A fluorescence iron line at ∼6.4
keV is present in the high as well as in the low state, though it is less intense in the latter. The photon index, cut-off
energy and e-folding energy values hardly show any discernible change over the states. We compare these spectral characteristics
as observed with ASCA with those of other satellites. We also compare the spectral characteristics of 4U 0114 + 650 with other
X-ray sources which show intensity variation at different time scales. 相似文献
746.
20世纪 90年代中后期 ,以“3S”技术和“4D”产品的普及推广为标志 ,我国的传统测绘产业开始了向现代地理信息产业的过渡 ,这对测绘行业本身、对其他行业、对整个社会发展都具有重大意义 相似文献
747.
1 Introduction From July 10th to September 26, 2003,“Xuelong”scientific expedition icebreaker executed the 2nd Chinese Arctic Research Expedition (CHINARE2003). The voyage star- ted from Shanghai to Dalian via Yellow Sea and Bo Hai and the cruising rout… 相似文献
748.
U. Mukherjee H. Raichur B. Paul S. Naik N. Bhatt 《Journal of Astrophysics and Astronomy》2006,27(4):411-423
We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several
binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis
with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters
determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray
binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital
phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3–20 keV energy range
were fitted ∼6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at ∼6.4 keV in the restricted
energy range of 0.3–10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The
variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column
density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a
spherically symmetric stellar wind from the companion star. 相似文献
749.
This study discusses the photosynthetic pathway types involved in canopy temperature measurements on a mixed grassland consisting of C3 and C4 plants (dominant species in biomass were Solidago altissima (C3), Miscanthus sinensis (C4), and Imperata cylindrica (C4)). In the wet conditions immediately after the rainy season, the mean canopy temperature for S. altissima was the lowest among the dominant species, mainly due to its leaf conductance being twice as large as the other two species. Despite using the same C4 photosynthetic pathway, M. sinensis had a lower apparent canopy temperature than I. cylindrica due to a smaller proportion of sunlit elements in the field of view. In the dry conditions during late July, the mean canopy temperatures of the three dominant species were within 0·3 °C of one another. These results can be explained by poor water conditions for C3 species (S. altissima). The simultaneous survey of vegetation and thermal imaging can help clarify characteristics of C3 and C4 canopy temperature over complicated grassland. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
750.