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排序方式: 共有655条查询结果,搜索用时 15 毫秒
651.
652.
Vladimir A. Krasnopolsky 《Planetary and Space Science》2011,59(10):952-964
This paper deals with two common problems and then considers major aspects of chemistry in the atmospheres of Mars and Venus. (1) The atmospheres of the terrestrial planets have similar origins but different evolutionary pathways because of the different masses and distances to the Sun. Venus lost its water by hydrodynamic escape, Earth lost CO2 that formed carbonates and is strongly affected by life, Mars lost water in the reaction with iron and then most of the atmosphere by the intense meteorite impacts. (2) In spite of the higher solar radiation on Venus, its thermospheric temperatures are similar to those on Mars because of the greater gravity acceleration and the higher production of O by photolysis of CO2. O stimulates cooling by the emission at 15 μm in the collisions with CO2. (3) There is a great progress in the observations of photochemical tracers and minor constituents on Mars in the current decade. This progress is supported by progress in photochemical modeling, especially by photochemical GCMs. Main results in these areas are briefly discussed. The problem of methane presents the controversial aspects of its variations and origin. The reported variations of methane cannot be explained by the existing data on gas-phase and heterogeneous chemistry. The lack of current volcanism, SO2, and warm spots on Mars favor the biological origin of methane. (4) Venus’ chemistry is rich and covers a wide range of temperatures and pressures and many species. Photochemical models for the middle atmosphere (58-112 km), for the nighttime atmosphere and night airglow at 80-130 km, and the kinetic model for the lower atmosphere are briefly discussed. 相似文献
653.
Finding relative satellite orbits that guarantee long-term bounded relative motion is important for cluster flight, wherein
a group of satellites remain within bounded distances while applying very few formationkeeping maneuvers. However, most existing
astrodynamical approaches utilize mean orbital elements for detecting bounded relative orbits, and therefore cannot guarantee
long-term boundedness under realistic gravitational models. The main purpose of the present paper is to develop analytical
methods for designing long-term bounded relative orbits under high-order gravitational perturbations. The key underlying observation
is that in the presence of arbitrarily high-order even zonal harmonics perturbations, the dynamics are superintegrable for
equatorial orbits. When only J
2 is considered, the current paper offers a closed-form solution for the relative motion in the equatorial plane using elliptic
integrals. Moreover, necessary and sufficient periodicity conditions for the relative motion are determined. The proposed
methodology for the J
2-perturbed relative motion is then extended to non-equatorial orbits and to the case of any high-order even zonal harmonics
(J
2n
, n ≥ 1). Numerical simulations show how the suggested methodology can be implemented for designing bounded relative quasiperiodic
orbits in the presence of the complete zonal part of the gravitational potential. 相似文献
654.
<正>Whalfera wiszniewskii sp.nov.is described from the Late Eocene Baltic amber.The genus Whalfera is considered as the only fossil genus confidently assigned to the Rhachlberothinae.Others previously placed in this subfamily belong to Paraberothinae(except perhaps for Oisea).The Late Eocene/present Rhachiberothinae and the Cretaceous Paraberothinae are considered to be the subfamilies of Berothidae. 相似文献
655.
Vladimir Frid Dmitri Doudkinski Gady Liskevich Efim Shafran Arie Averbakh Nikolay Korostishevsky Larisa Prihodko 《Environmental Earth Sciences》2010,60(4):787-798
This paper deals with the integration of electrical resistivity tomography and geochemical methods for studying four different
fire-prone landfills. Landfill gas composition (CH4, H2S, O2, CO, CO2) and subsurface temperature were measured with the constant net 50 × 50 m from the depth 10–60 cm. 28 electrical resistivity
tomography lines were surveyed, while Wenner and Sclumberger electrode arrays were employed for all measurements. At the studied
sites the landfill gas and temperature measurements mapped gas and temperature anomalies over underground fire sources. 2D
electrical resistivity tomography lines, performed over these anomalies, showed these fire sources as high-resistivity zones.
The joint employment of the electrical imaging and geochemical survey seems to be a useful tool in carrying out diagnostic
investigations at fire-prone landfills. 相似文献