The photochemical products of benzene in Titan’s upper atmosphere     

M.L. Delitsky  C.P. McKay 《Icarus》2010,207(1):477-484

The Cassini spacecraft detected benzene high in Titan’s atmosphere as well as the presence of large mass positive and negative ions. Previous work has suggested that these large mass ions could be composed of fused-ring polycyclic aromatic hydrocarbon compounds. These fused-ring PAHs, such as naphthalene and anthracene, are usually the result of high temperature processes that may not occur in Titan’s thin, cold, upper thermosphere. Here we suggest that a different class of aromatic compounds, polyphenyls, may be a better explanation of the data. Polyphenyls can grow to be large polymeric structures and could condense to form the aerosols seen in Titan’s cloud and hazes. They have similar properties to fused-ring PAHs (for example, electron affinity, ionization potential) and could be the negative ion species seen in the CAPS instrument data from the Cassini spacecraft.  相似文献   

Multi-wavelength simulations of atmospheric radiation from Io with a 3-D spherical-shell backward Monte Carlo radiative transfer model     

Sergey L. Gratiy  Andrew C. Walker  David B. Goldstein  Laurence M. Trafton 《Icarus》2010,207(1):394-408

Conflicting observations regarding the dominance of either sublimation or volcanism as the source of the atmosphere on Io and disparate reports on the extent of its spatial distribution and the absolute column abundance invite the development of detailed computational models capable of improving our understanding of Io’s unique atmospheric structure and origin. Improving upon previous models, Walker et al. (Walker, A.C., Gratiy, S.L., Levin, D.A., Goldstein, D.B., Varghese, P.L., Trafton, L.M., Moore, C.H., Stewart, B. [2009]. Icarus) developed a fully 3-D global rarefied gas dynamics model of Io’s atmosphere including both sublimation and volcanic sources of SO₂ gas. The fidelity of the model is tested by simulating remote observations at selected wavelength bands and comparing them to the corresponding astronomical observations of Io’s atmosphere. The simulations are performed with a new 3-D spherical-shell radiative transfer code utilizing a backward Monte Carlo method. We present: (1) simulations of the mid-infrared disk-integrated spectra of Io’s sunlit hemisphere at 19 μm, obtained with TEXES during 2001-2004; (2) simulations of disk-resolved images at Lyman-α obtained with the Hubble Space Telescope (HST), Space Telescope Imaging Spectrograph (STIS) during 1997-2001; and (3) disk-integrated simulations of emission line profiles in the millimeter wavelength range obtained with the IRAM-30 m telescope in October-November 1999. We found that the atmospheric model generally reproduces the longitudinal variation in band depth from the mid-infrared data; however, the best match is obtained when our simulation results are shifted ∼30° toward lower orbital longitudes. The simulations of Lyman-α images do not reproduce the mid-to-high latitude bright patches seen in the observations, suggesting that the model atmosphere sustains columns that are too high at those latitudes. The simulations of emission line profiles in the millimeter spectral region support the hypothesis that the atmospheric dynamics favorably explains the observed line widths, which are too wide to be formed by thermal Doppler broadening alone.  相似文献   

Theory of the rotation of Janus and Epimetheus     

Benoît Noyelles 《Icarus》2010,207(2):887-902

The saturnian coorbital satellites Janus and Epimetheus present a unique dynamical configuration in the Solar System, because of high-amplitude horseshoe orbits, due to a mass ratio of order unity. As a consequence, they swap their orbits every 4 years, while their orbital periods is about 0.695 days. Recently, Tiscareno et al. (Tiscareno, M.S., Thomas, P.C., Burns, J.A. [2009]. Icarus 204, 254-261) got observational informations on the shapes and the rotational states of these satellites. In particular, they detected an offset in the expected equilibrium position of Janus, and a large libration of Epimetheus.We here propose to give a three-dimensional theory of the rotation of these satellites in using these observed data, and to compare it to the observed rotations. We consider the two satellites as triaxial rigid bodies, and we perform numerical integrations of the system in assuming the free librations as damped.The periods of the three free librations we get, associated with the three dimensions, are respectively 1.267, 2.179 and 2.098 days for Janus, and 0.747, 1.804 and 5.542 days for Epimetheus. The proximity of 0.747 days to the orbital period causes a high sensitivity of the librations of Epimetheus to the moments of inertia. Our theory explains the amplitude of the librations of Janus and the error bars of the librations of Epimetheus, but not an observed offset in the orientation of Janus.  相似文献   

Viscous liquid film flow on dune slopes of Mars     

Diedrich Möhlmann  Akos Kereszturi 《Icarus》2010,207(2):654-658

It is shown that viscous liquid film flow (VLF-flow) on the surfaces of slopes of martian dunes can be a low-temperature rheological phenomenon active today on high latitudes. A quantitative model indicates that the VLF-flows are consistent with the flow of liquid brines similar to that observed by imaging at the Phoenix landing site. VLF-flows depend on the viscosity, dynamics, and energetics of temporary darkened liquid brines. The darkening of the flowing brine is possibly, at least partially, attributed to non-volatile ingredients of the liquid brines. Evidence of previous VLF-flows can also be seen on the dunes, suggesting that it is an ongoing process that also occurred in the recent past.  相似文献   

Precession and nutation in the η Carinae binary system: evidence from the X-ray light curve     

Z. Abraham  D. Falceta-Gonçalves 《Monthly notices of the Royal Astronomical Society》2010,401(1):687-694

It is believed that η Carinae is actually a massive binary system, with the wind–wind interaction responsible for the strong X-ray emission. Although the overall shape of the X-ray light curve can be explained by the high eccentricity of the binary orbit, other features like the asymmetry near periastron passage and the short quasi-periodic oscillations seen at those epochs have not yet been accounted for. In this paper we explain these features assuming that the rotation axis of η Carinae is not perpendicular to the orbital plane of the binary system. As a consequence, the companion star will face η Carinae on the orbital plane at different latitudes for different orbital phases and, since both the mass-loss rate and the wind velocity are latitude dependent, they would produce the observed asymmetries in the X-ray flux. We were able to reproduce the main features of the X-ray light curve assuming that the rotation axis of η Carinae forms an angle of  29°± 4°  with the axis of the binary orbit. We also explained the short quasi-periodic oscillations by assuming nutation of the rotation axis, with an amplitude of about  5°  and a period of about 22 days. The nutation parameters, as well as the precession of the apsis, with a period of about 274 years, are consistent with what is expected from the torques induced by the companion star.  相似文献   

Wind-driving protostellar accretion discs – I. Formulation and parameter constraints     

Arieh Königl  Raquel Salmeron  Mark Wardle 《Monthly notices of the Royal Astronomical Society》2010,401(1):479-499

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Swift observations of the X-ray and UV evolution of V2491 Cyg (Nova Cyg 2008 No. 2)     

K. L. Page  J. P. Osborne  P. A. Evans  G. A. Wynn  A. P. Beardmore  R. L. C. Starling  M. F. Bode  A. Ibarra  E. Kuulkers  J.-U. Ness  G.J. Schwarz 《Monthly notices of the Royal Astronomical Society》2010,401(1):121-130

We present extensive, high-density Swift observations of V2491 Cyg (Nova Cyg 2008 No. 2). Observing the X-ray emission from only one day after the nova discovery, the source is followed through the initial brightening, the super-soft source phase and back to the pre-outburst flux level. The evolution of the spectrum throughout the outburst is demonstrated. The UV and X-ray light curves follow very different paths, although changes occur in them around the same times, indicating a link between the bands. Flickering in the late-time X-ray data indicates the resumption of accretion. We show that if the white dwarf (WD) is magnetic, it would be among the most magnetic known; the lack of a periodic signal in our later data argues against a magnetic WD, however. We also discuss the possibility that V2491 Cyg is a recurrent nova, providing recurrence time-scale estimates.  相似文献   

Chlorophyll production,in response to nutrient additions,by the algae in Lake Taupo water     

E. White  G. W. Payne 《新西兰海洋与淡水研究杂志》2013,47(3):501-507

In batch cultures of Lake Taupo water, phosphorus was the nutrient limiting plant growth from January to June, and nitrogen took over this role from July to December. Chlorophyll production by algae was often stimulated by trace element additions, but it was uncertain whether total cytoplasmic production was also involved.  相似文献   

厦门国家级珍稀海洋物种自然保护区文昌鱼(Branchiostoma belcheri)种群健康评价     

黄良敏  黎中宝  吝涛  李元跃  陈融斌  王家樵  陈强  李军 《海洋与湖沼》2013,44(1):103-110

利用2009-2010年四个季度月用底栖生物抓斗式采样器捕获的文昌鱼样品,从其资源分布、年龄结构、生物学和生态学特征等方面对厦门国家级珍稀海洋物种自然保护区文昌鱼的种群健康状况进行评价研究.结果表明:(1)文昌鱼种群资源分布衰减趋势明显,只在黄厝—前埔海区、小嶝岛—角屿海区和南线—十八线海区3个核心区还有分布,但资源密度低,分布范围狭小,而在鳄鱼屿实验区未能发现.(2)文昌鱼体重与体长之间关系:W=6.6895×10-4L3.1818;体长与体质量生长方程分别为:厶=65.63[1-e-0.68(t+032)],Wt=404.62[1-e-0.68(t+032)]3.1818;夏季、冬季航次的优势体长组分别为25-35mm和35-45mm,优势体重组分别为25-50mg和50-100mg;秋季低龄鱼较多,而冬季高龄鱼比例较高.(3)采用ELEFAN Ⅰ技术分析了厦门文昌鱼的Von Bertalanffy生长参数K、L∞、总死亡系数Z、自然死亡系数M和开发率E,发现其生长参数K值较大,自然死亡系数较高,开发率较大(0.69).综之,厦门自然保护区内的文昌鱼种群健康状况整体不佳,应注意资源保护,加强保护文昌鱼栖息地的底质和水质以及防止过度捕捞以实现其资源可持续利用.  相似文献   

青蛤(Cyclina sinensis)cDNA文库构建及免疫相关因子基因的筛选     

高玮玮  潘宝平 《海洋与湖沼》2013,44(1):90-94

在鳗弧菌侵染下,利用SMART方法构建了青蛤的cDNA文库,并采用高通量测序方法和BLASTX比对筛选出ESTs及免疫相关因子的基因.结果表明,所构建的cDNA文库的库容量为1.12×106,插入片段均在500bp以上;大于100bp的有效ESTs序列1113条,平均长度725bp,拼接后获得一致性序列420条,其中包括126个叠联群和294个单拷贝EST,BLASTX比对后获得注释序列271条,进一步筛选获得青蛤免疫相关因子基因序列45条,为克隆其免疫防御相关因子的基因提供了重要的基础.  相似文献