Using an adjoint model to improve an optimum interpolation-based data-assimilation system     

X.-Y. HUANG  N. GUSTAFSSON  E. R. KÄLLÉN 《地球，A辑:动力气象学与海洋学》1997,49(2):161-176

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Opposition Effects in Brightness,Color, and Polarization of Comet 1P/Halley: Comparison with Atmosphereless Solar System Bodies     

V. K. Rosenbush 《Solar System Research》2005,39(4):312-321

Systematic and uniform sets of photometric and polarimetric observations of comet 1P/Halley have been analyzed. The phase dependence of brightness for comet Halley was obtained at phase angles α ranging from 1.4° ≤ α ≤ 65°. The following parameters were determined: the amplitude of the opposition effect Δm = 0.75^m ± 0.06^m; the half-width at a half-maximum of intensity HWHM = 6.4° ± 1.6°; the linear phase coefficient β = 0.0045 ± 0.0001 mag/deg for α from 30° ≤ α ≤ 65°; and the phase angle at which a nonlinear increase in brightness starts, α _opp ≈ 31°. For the first time, the phase-angle dependence was obtained for the color of the dust of comet Halley: the color index BC-RC systematically decreases with increasing phase angle. Such a phase behavior of the dust color can be caused by the decrease in the mean size of dust particles that occurs when the comet approaches the Sun. For comet Halley, the negative polarization branch is almost symmetric; the minimal value of polarization is P _min = −1.54% at a phase angle α_min = 10.5°, and the inversion angle is α_inv = 21.7°. A comparative analysis of the phase functions of brightness and polarization has been performed for the cometary dust and atmosphereless bodies. Among the latter are low-albedo asteroids of the P and C types (102 Miriam and 47 Aglaja, respectively), as well as Deimos; high-albedo objects, such as the E-type asteroid 64 Angelina and the icy satellite of Jupiter Europa; and the Moon with its intermediate albedo. The possibility of a weak depression in the negative polarization branch of comets Halley and 47P/Ashbrook-Jackson at phase angles smaller than 2° is discussed.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 4, 2005, pp. 353–363.Original Russian Text Copyright © 2005 by Rosenbush.  相似文献   

信号流图求解部分分式展开     

马洪明  杨玲 《成都信息工程学院学报》1996,(4)

含有多重极点的有理真分式展开为部分分式，不需要计算低阶导数。列出被求函数的各阶导数的关系式，画出各阶导数作为节点的信号流图。该图无环路，既直观表现出各高阶导数的相互关系及影响的单向性，也使求节点增益的梅森公式特别简便。该方法将求高阶导数问题简化为代数运算，特别适合于编制成计算机程序  相似文献   

Gravitational collapse and equilibrium conditions of a toroidal vortex with thermal pressure     

K. Yu. Bliokh  V. M. Kontorovich 《Astronomy Letters》2003,29(11):724-730

We found the equilibrium conditions for a self-gravitating toroidal vortex by taking thermal pressure into account. These conditions are shown to significantly differ from those for a disk or a sphere. The evolution of a thin vortex turns it into a compact vortex that loses mechanical stability for low masses at a polytropic index γ<4/3 but retains stability for sufficiently high masses and densities determined by the velocity circulation in the vortex.  相似文献   

Radiative association in Li+H revisited: the role of quasi-bound states     

O. J. Bennett  A. S. Dickinson  T. Leininger  F. X. Gadéa 《Monthly notices of the Royal Astronomical Society》2003,341(1):361-368

The role in radiative association of narrow resonances arising from quasi-bound levels is examined. For the rate coefficient the contribution from such levels is readily calculated in terms of the Einstein A -coefficient from bound rovibrational levels generated using a suitable alternative boundary condition. By locating systematically all the quasi-bound levels, an enhancement by more than an order of magnitude of the rate coefficient for Li(2s) + H(1s) association above about 600 K is obtained. The effect on the LiH abundance in the early Universe is no more than an increase of a factor of 3 for limited ranges of values of the redshift. For the Li(2p) state the effect of narrow resonances appears to have been taken into account in previous calculations.  相似文献   

A weak outburst of the millisecond X-ray pulsar SAX J1808.4-3658 in October 1996 as detected from RXTE slew data     

M. G. Revnivtsev 《Astronomy Letters》2003,29(6):383-386

Analysis of the RXTE slew data in October 1996 revealed a weak X-ray burst from the millisecond pulsar SAX J 1808.4-3658. The 3–20-keV energy spectrum of the source can be described by a power law with an index of 2.0 and a(3-to 20 keV) luminosity of ～1.4×10³⁵ erg s^?1 (the distance to the source was taken to be 2.5 kpc). Because of the short exposure time, we failed to detect weak pulsations at a frequency of 401 Hz in the source. The (2σ) upper limit of the pulse fraction is ～13%.  相似文献   

CO-Observations of post-starburst galaxies     

Marco Barden  Linda J. Tacconi  Matthew D. Lehnert  Dimitra Rigopoulou 《Astrophysics and Space Science》2001,277(1):95-95

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Multiple bipolar structure of normal magnetic field at the magnetopause     

T Chen  Z.X LiuX.X Zhang 《Planetary and Space Science》2003,51(6):381-386

We describe how a local plasma structure can be changed by a transverse shear flow using numerical simulation to investigate the disturbance process near the magnetopause. The results show that magnetic field lines are bent by transverse shear flow disturbance near the current sheet region. There are multiple bipolar structures of the normal magnetic field in the numerical simulation. We term this new feature as K-point magnetic reconnection, realistic for discussing space observations.  相似文献   

Dissipative-acoustic instability in accretion disks at a nonlinear stage     

A. V. Khoperskov  S. S. Khrapov  E. A. Nedugova 《Astronomy Letters》2003,29(4):246-257

Nonstationary hydrodynamic models of a viscous accretion disk around a central compact object were constructed. Two different numerical methods (TVD and SPH) are used to study the dynamics of dissipatively unstable acoustic perturbations at the nonlinear stage in terms of the standard α-disk model. The standard disk accretion in the Shakura-Sunyaev model is unstable against acoustic waves for various parameters of the system. If the α parameter, which specifies the level of turbulent viscosity, exceeds α?0.03, then a complex nonstationary system of small-scale weak shock waves is formed. The growth rate of the perturbations is higher in the central disk region. For α?0.2, the relative shock amplitude can exceed 50% of the equilibrium disk parameters. The reflection of waves from the disk boundaries and their nonlinear interaction are important factors that can produce unsteady accretion. The luminosity of such a disk undergoes quasi-periodic oscillations at a level of several percent (?5%) of the equilibrium level.  相似文献   

Exchange and correlation interactions in electron-positron plasma     

A. V. Yudin  D. K. Nadyozhin 《Astronomy Letters》2003,29(3):158-162

The effect of particle-particle interaction on the adiabatic index γ for an electron-positron plasma is considered. An improved method for numerically calculating the Hartree-Fock exchange integral is presented and its relativistic asymptotics is determined. An approximation formula is derived for the correlation part of the interaction in the low-density limit. This formula includes degeneracy and the positron component.  相似文献