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991.
Pei-Sheng Chen Yi-Fei Gao Hong-Guang Shan 《中国天文和天体物理学报》2007,7(5):657-668
All galaxies with extragalactic H_2O maser sources observed so far are collected. With the 2MASS and the IRAS photometric data an infrared study is performed on those galaxies.By a comparison between the H_2O maser detected sources and non-detected sources in the infrared it is indicated that infrared properties in the IRAS 12-25μm and 60-100μm are important for producing H_2O masers in galaxies.It is also found that the H_2O maser galaxies with different nuclear activity types have rather different infrared properties mainly in the IRAS 12-60μm region. 相似文献
992.
Bryan M. Gaensler Maura McLaughlin Stephen Reynolds Kazik Borkowski Nanda Rea Andrea Possenti Gianluca Israel Marta Burgay Fernando Camilo Shami Chatterjee Michael Kramer Andrew Lyne Ingrid Stairs 《Astrophysics and Space Science》2007,308(1-4):95-99
“Rotating RAdio Transients” (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional brief radio
bursts, with average intervals between bursts ranging from minutes to hours. The burst spacings allow identification of periodicities,
which fall in the range 0.4 to 7 seconds. The RRATs thus seem to be rotating neutron stars, albeit with properties very different
from the rest of the population. We here present the serendipitous detection with the Chandra X-ray Observatory of a bright point-like X-ray source coincident with one of the RRATs. We discuss the temporal and spectral properties of
this X-ray emission, consider counterparts in other wavebands, and interpret these results in the context of possible explanations
for the RRAT population.
B.M.G. acknowledges the support of NASA through LTSA grant NAG5-13023 and of an Alfred P. Sloan Fellowship. 相似文献
993.
Yu Yu Yong-Feng Huang 《中国天文和天体物理学报》2007,7(5):669-674
With the successful launch of Swift satellite,more and more data of early X-ray afterglows from short gamma-ray bursts have been collected.Some interesting features such as unusual afterglow light curves and unexpected X-ray flares are revealed.Especially,in some cases,there is a fiat segment in the X-ray afterglow light curve.Here we present a simplified model in which we believe that the flattening part is due to energy injection from the central engine.We assume that this energy injection arises from the magnetic dipole radiation of a millisecond pulsar formed after the merger of two neutron stars.We check this model with the short GRB 060313.Our numerical results suggest that energy injection from a millisecond magnetar could make part of the X-ray afterglow light curve flat. 相似文献
994.
Li-Feng Xing Shuang-Yi Zhao Wei Su Yan Shen Xiao-Bin Zhang Jian-Yan Wei 《中国天文和天体物理学报》2007,7(4):551-557
We monitored 16 X-ray selected young solar-type stars for light variation and found appreciable periodic light variability with amplitudes of a few hundredths of a magni-tude in nine of the objects. Using the method of Phase Dispersion Minimization (PDM) and Fourier analysis (software PERIOD04), the rotation periods of these stars were determined from the photometric data. The rotation periods of all nine stars are shorter than about 3days. It is suggested that, as with the Pleiades cluster, small amplitude light variations are quite common among young solar-type stars with rotation periods around 3 days or less. This gives further evidence for the spin up of solar-type stars predicted by models of angular momentum evolution of pre-main sequence stars. 相似文献
995.
We report here results from a study of X-ray bursts from 3 magnetar candidates (SGR 1806-20, SGR 1900+14 and AXP 1E 2259+586).
We have searched for a pulse phase dependence of the X-ray burst rate from these sources. X-ray light curves were obtained
with the Proportional Counter Array on-board the Rossi X-ray Timing Explorer during the periods of intense burst activity
in these sources. On detailed analysis of the three sources, we found a very significant burst rate for all pulsar phases.
However, some locations appear to produce bursts slightly more often, rendering the non-isotropic distribution. Only in the
case of SGR 1900+14, there is a clear pulse phase dependence of burst rate. 相似文献
996.
We report Arecibo (2380-MHz, 13-cm) observations of Asteroid 1580 Betulia in May-June 2002. We combine these continuous-wave Doppler spectra and delay-Doppler images with optical lightcurves from the 1976 and 1989 apparitions in order to estimate Betulia's shape and spin vector. We confirm the spin vector solution of Kaasalainen et al. [Kaasalainen, M., and 21 colleagues, 2004. Icarus 167, 178-196], with sidereal period P=6.13836 h and ecliptic pole direction (λ,β)=(136°,+22°), and obtain a model that resembles the Kaasalainen et al. convex-definite shape reconstruction but is dominated by a prominent concavity in the southern hemisphere. We find that Betulia has a maximum breadth of 6.59±0.66 km and an effective diameter of 5.39±0.54 km. These dimensions are in accord with reanalyzed polarimetric and radar data from the 1970s. Our effective diameter is 15% larger than the best radiometric estimate of Harris et al. [Harris, A.W., Mueller, M., Delbó, M., Bus, S.J., 2005. Icarus 179, 95-108], but this difference is much smaller than the size differences between past models. Considering orbits of test particles around Betulia, we find that this asteroid's unusual shape results in six equilibrium points close to its equatorial plane rather than the usual four points; two of these six points represent stable synchronous orbits while four are unstable. Betulia's close planetary encounters can be predicted for over four thousand years into the future. 相似文献
997.
998.
杨丽娟. 2022. 地质学在中国的传播与发展——以地质学教科书为中心(1853~1937). 杭州:浙江古籍出版社:1~312. 相似文献
999.
借助色谱- 质谱(GC- MS)和色谱- 质谱- 质谱(GC- MS- MS)分析,对黔南坳陷凯里残余油藏凯棠和洛棉剖面上储层沥青中的烃类组成进行了系统分析,以判断其所遭受生物降解作用的程度,探寻在极端降解原油中是否还存在原生生物标志物,为这类原油的油源研究开拓新的途径和方法。结果表明:凯棠剖面上的储层沥青中尽管仍可检测到较为完整的C19- 30三环萜烷和C27- 35藿烷系列,但C19- 29脱甲基三环萜烷系列和C26- 34 25- 降藿烷系列丰富而完整,甾烷系列中C21- 22低分子量甾烷和重排甾烷优势明显,这一系列特征表明这些沥青遭受了剧烈生物降解作用的改造。但三芳甾类仍保存完好,依据原油生物降解程度的评判标准,判断其生物降解级别介于8~9级之间。洛棉剖面上的储层沥青中藿烷系列基本消失殆尽,三环萜烷系列及其脱甲基产物和25- 降藿烷系列的分布因极端生物降解作用而发生显著变异,某些化合物如C23T、C24T、C23NTE和C28- 29NH成为优势成员;甾烷系列中C21- 22低分子量甾烷占绝对优势,三芳甾类完全消失,据此判断该剖面上沥青的生物降解级别已达到10级或更严重。由于这两个剖面上的沥青遭受了极端生物降解作用的改造,常用的甾、萜类生物标志物完全失去了实用价值。但是,在所分析的这些沥青中都检测到三个系列的C27- 35 8,14- 开环藿烷系列,它们与塔里木盆地塔中地区海相端元油中存在的同类标志物的分布特征相似。正常海相端元油和极端生物降解沥青中同时检测到这三个系列的8,14- 开环藿烷,这一事实表明这类生物标志物在成因上具有原生性,而与生物降解作用无关。此外,在极端生物降解作用沥青中的完好保存,表明它们具有极强的抗生物降解能力,因而它们在此类原油的油源研究中可能具有潜在的实用价值。 相似文献
1000.
关于渤海湾盆地渤中19- 6凝析气田凝析油成熟度存在成熟与高成熟两种截然不同观点,尚未达到统一定论。本文综合利用轻烃、饱和烃和芳烃成熟度参数对凝析油成熟度进行了综合判定,并深入分析了凝析油和天然气的成因关系及凝析气藏形成机制。结果表明:异庚烷值与庚烷值、Ts/(Ts+Tm)与C29Ts/(C29Ts+C29H)、甲基单金刚烷指数与甲基双金刚烷指数、甲基菲指数、二苯并噻吩类成熟度参数和TNR2显示渤中19- 6凝析气田凝析油处于成熟阶段。结合天然气成熟度和储层流体包裹体特征,可知渤中19- 6凝析气田的原油成藏期早于天然气,随着晚期大量天然气的充注,油气会发生相控混溶作用形成含液态烃的气流体,当温度和压力达到混溶后烃类体系的露点以上,则形成凝析气藏。 相似文献