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661.
In this paper, from a Hamiltonian point of view, the nonlinear optimal control problems are transformed into nonlinear two-point boundary value problems, and a symplectic adaptive algorithm based on the dual variational principle is proposed for solving the nonlinear two-point boundary value problem. The state and the costate variables within a time interval are approximated by using the Lagrange polynomial and the costate variables at two ends of the time interval are taken as independent variables. Then, based on the dual variational principle, the nonlinear two-point boundary value problems are replaced by a system of nonlinear equations which can preserve the symplectic structure of the nonlinear optimal control problem. Furthermore, the computational efficiency of the proposed symplectic algorithm is improved by using the adaptive multi-level iteration idea. The performance of the proposed algorithm is tested by the problems of Astrodynamics, such as the optimal orbital rendezvous problem and the optimal orbit transfer between halo orbits.  相似文献   
662.
As soon as the energies of electrons near the Fermi surface exceed Q, the threshold energy of inverse β-decay, electron capture (EC) dominates inside a neutron star. The high-energy neutrons released by EC will destroy anisotropic 3 P 2 neutron Cooper pairs in the degenerate superfluid. By colliding with the neutrons produced in the process n+(nn↓)→n+n+n, the kinetic energies of the neutrons released by EC will be transformed into thermal energy. A portion of this thermal energy will be transported from the star interior to the star surface by conduction, then converted to a thermal spectrum of soft X-rays and γ-rays. By introducing two important parameters: the Landau level-superfluid modified factor and the overal soft X/γ-ray efficiency coefficient, we compute the theoretical luminosity L X of a magnetar under our model and plot a diagram of L X as a function of magnetic field strength B. Numerical calculations based on our model agree well with the observed properties of magnetar candidates.  相似文献   
663.
Abstract– The Grimsby meteorite (H4–6) fell on September 25, 2009. As of mid‐2010, 13 fragments totaling 215 g have been recovered. Records of the accompanying fireball from the Southern Ontario Meteor Network, including six all‐sky video cameras, a large format CCD, infrasound and radar records, have been used to characterize the trajectory, speed, orbit, and initial mass of the meteoroid. From the four highest quality all‐sky video records, the initial entry velocity was 20.91 ± 0.19 km s?1 while the derived radiant has a local azimuth of 309.40° ± 0.19° and entry angle of 55.20° ± 0.13°. Three major fragmentation episodes are identified at 39, 33, and 30 km height, with corresponding uncertainties of approximately 2 km. Evidence for early fragmentation at heights of approximately 70 km is found in radar data; dynamic pressure of this earliest fragmentation is near 0.1 MPa while the main flare at 39 km occurred under ram pressures of 1.5 MPa. The fireball was luminous to at least 19.7 km altitude and the dynamic mass estimate of the largest remaining fragment at this height is approximately several kilograms. The initial mass is constrained to be <100 kg from infrasound data and ablation modeling, with a most probable mass of 20–50 kg. The preatmospheric orbit is typical of an Apollo asteroid with a likely immediate origin in either the 3:1 or ν6 resonances.  相似文献   
664.
Torsional waves supported by magnetic flux tubes have long been thought to bear a high potential for supplying energy and momentum to the upper solar atmosphere, thereby contributing to its heating and to the driving of dynamic events like spicules. This hope rested on the belief that their propagation is not impeded by cutoff restrictions, unlike longitudinal and kink waves. We point out that this applies only to thin, isothermal tubes. When they widen in the chromosphere, and as a result of temperature gradients, cutoff restrictions arise. We compare them to recent observational reports of such waves and of vortex motions and find that their long period components are already affected by cutoff restrictions. An observational strategy is proposed that should permit the derivation of better information on vortex flows from off‐center observations with next generation telescopes (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
665.
Under the two initial 1‐D one parameter velocity distribution forms (one is normal, the other is exponential), the z direction scale height evolution of normal neutron stars in the Galaxy is studied by numerical simulation. We do statistics for the cases at different time segments, also do statistics for the cumulative cases made of each time segment. The results show in the cumulative cases the evolution curves of the scale heights are smoother than in the each time segment, i.e., the cumulation improve the signal‐to‐noise ratio. Certainly the evolution cases are different at different Galactic disk locations, which also have very large difference from the average cases in the whole disk. In the initial stages of z evolution of normal neutron stars, after the beginning transient states, the cumulative scale heights increase linearly with time, and the cumulative scale height increasing rates have linear relationship with the initial velocity distribution parameters, which have larger fluctuation in the vicinity of the Sun than in the whole disk. We utilize the linear relationship of the cumulative scale height increasing rates vs. the initial velocity distribution parameters in the vicinity of the Sun to make comparison with the observation near the Sun. The results show if there is no magnetic decay, then the deserved initial velocity parameters are obvious lower than the present well known results from some authors; whereas if introducing magnetic decay, for the 1‐D normal case we can make consistence among concerning results using magnetic decay time values which are supported by some authors, while for the 1‐D exponential case the results show the lackness of young pulsar samples in the larger z in the vicinity of the Sun (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
666.
In this paper we present a comprehensive analysis of the dynamics in the region of the (3556) Lixiaohua asteroid family. The family lies in a particularly interesting region of the phase space, crossed by several two-body and three-body mean motion resonances. Also, members of this family can have close encounters with large asteroids, such as Ceres. We have identified the mean motion resonances which contribute to the long-term dynamical evolution of the family and our results confirm that the members of this family can be classified into a number of groups, exhibiting different dynamical behavior. We show for the first time that in the Lixiaohua region, apart from the chaotic diffusion in proper eccentricity and inclination (e p and I p ), there is at least one extended chaotic zone where several resonances overlap, thus giving rise to chaotic diffusion in proper semi-major axis (a p ) as well. Using a code of Monte Carlo type, we simulate the evolution of the family, according to the model which combines the chaotic diffusion (in a p , e p and I p ), Yarkovsky/YORP thermal effect and random walk in a p due to the close encounters with massive asteroids. These simulations show that all these effects should be taken into account in order to accurately explain the observed distribution of family members in the space of proper elements, although a “minimal” model that accounts for chaotic diffusion in (e p , I p ), Yarkovsky-induced drift in a p and random walk in a p due to the close encounters with the most massive asteroids is enough to grossly characterize the shape of the family.  相似文献   
667.
668.
We present the results of the monitoring of a sample of 5 HBLs in the B, V and R bands during 2003–2008. All sources in our monitoring project show significant rapid optical variations, except 1ES 1959+650, however; for 1ES 1959+650, the gamma-ray variability on a timescale of ~7 hours has been observed by Holder et al. (Astrophys. J. 583:L9, 2003). Using these variability timescales, we estimate the black hole masses for each source with the Kerr black hole theory.  相似文献   
669.
The region surrounding the Mawrth Vallis outflow channel on Mars hosts thick layered deposits containing diverse phyllosilicate minerals. Here we report detection of the Ca-sulfate bassanite on the outflow channel floor, requiring a more complex aqueous chemistry than previously inferred for this region. The sulfate-bearing materials underlie phyllosilicate-bearing strata, and provide an opportunity for testing proposed models of martian geochemical evolution with a future landed mission.  相似文献   
670.
Z. Peeters  R.L. Hudson  M.H. Moore 《Icarus》2010,210(1):480-487
The radiation chemistry, thermal stability, and vapor pressure of solid-phase carbonic acid (H2CO3) have been studied with mid-infrared spectroscopy. A new procedure for measuring this molecule’s radiation stability has been used to obtain intrinsic IR band strengths and half-lives for radiolytic destruction. We report, for the first time, measurements of carbonic acid’s vapor pressure (0.290-2.33 × 10−11 bar for 240-255 K) and its enthalpy of sublimation (71 ± 9 kJ mol−1). We also report the first observation of a chemical reaction involving solid-phase carbonic acid. Possible applications of these findings are discussed, with an emphasis on the outer Solar System icy surfaces.  相似文献   
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