共查询到20条相似文献，搜索用时 631 毫秒
1.
M. V. Samokhin 《Astrophysics and Space Science》1993,203(1):109-120
The flow of the current along the magnetic field lines in the thin plasma directed opposite to the electric field is considered. The particles moving to the equatorial plane are supposed to have mirror points above the region of absorption (the ionosphere) and the particles moving to the ionosphere are supposed to have mirror points below the region of absorption. The current, therefore, flows. The functions of the distribution of the electrons and ions are considered to be mono-energetic. The energies of the electrons and the ions and their densities on the boundary of absorption are estimated for the potential difference and for the current density which are typical for the auroral field lines. 相似文献
2.
The densities measured by the CACTUS microaccelerometer at altitudes from 270 to 600 km are used to analyze the effect of tidal perturbations in the Earth’s thermosphere caused by the gravitational attraction of the Moon and the Sun. These tidal perturbations are considered a priori small and are not taken into account in modern atmospheric density models. The residuals between the densities measured by the CACTUS microaccelerometer and calculated by models are analyzed, and the density variations correlating with variations of the zenith angles from the Moon to the center of the Earth to the satellite and from the Sun to the center of the Earth to the satellite are found at altitudes from 270 to 600 km. The amplitude of the perturbations revealed in the study grows with height. The phase of the tidal perturbations also varies with height. The amplitude of the density variations is about 30% at 270–320 km and increases to 80% at 520–570 km. The results agree with a priori theoretical estimates obtained for tidal motion of gaseous matter with a variable density. 相似文献
3.
Padma K. Shukla 《Astrophysics and Space Science》1998,264(1-4):235-245
The status of waves and instabilities in magnetized dusty plasmas is summarized. The effects of an external magnetic field
on low-frequency electrostatic and electromagnetic waves in dusty plasmas are discussed. The kinetic and hydrodynamic instabilities
are shown to excite magnetized dusty plasma waves. The presence of the latter can give rise to an oscillatory wake-potential
which can be responsible for the charged dust grain attraction. The relevance of our investigation to laboratory and space
plasmas has been pointed out.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
The occurrence of a large number of high and low amplitude anisotropic wave train events over the years 1981–1994 has been examined along with the different solar features. The results indicate that the time of maximum of diurnal variation significantly remains in the 18-h direction for majority of the high and low amplitude wave trains. The amplitude of diurnal anisotropy remains significantly high and phase shifts towards earlier hours as compared to the quite day annual average values for majority of the HAEs. The diurnal amplitude remains significantly low and phase shifts towards earlier hours as compared to the quiet day annual average values for majority of the LAEs. The occurrence of these enhanced/low amplitude events is found to be dominant during the positive polarity of the Bz component of the interplanetary magnetic field. The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth. The high-speed solar wind streams do not play any significant role in causing these types of events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic ray decreases. 相似文献
5.
Ashraf Owis Francesco Topputo Franco Bernelli-Zazzera 《Celestial Mechanics and Dynamical Astronomy》2009,103(1):1-16
The solution of a feedback optimal control problem arising in orbital mechanics is addressed in this paper. The dynamics is
that of a massless body moving in a central gravitational force field subject also to a drag and a radial modulated force.
The drag is linearly proportional to the velocity and inversely proportional to the square of the distance from the center
of attraction. The problem is tackled by exploiting the properties of a suitably devised linearizing map that transforms the
nonlinear dynamics into an inhomogeneous linear system of differential equations supplemented by a quadratic objective function.
The generating function method is then applied to this new system, and the solution is back transformed in the old variables.
The proposed technique, in contrast to the classical optimal control problem, allows us to derive analytic closed-loop solutions
without solving any two-point boundary value problem. Applications are discussed. 相似文献
6.
讨论运用PCI 9054(美国PLX公司生产的接口芯片)作为接口芯片的PCI(Peripheral Component Interconnect)板卡的软硬件设计,以实现天线跟踪的两个时间同步中断。利用标准秒信号中断作为系统时钟同步信号,并同步产生时间间隔为20ms(或40、50ms,可选)的中断信号,来处理天线跟踪指令输出。中断信号通过PCI中断口INTA#接入计算机,在驱动中识别不同的中断信号,并在应用程序响应中断处理后,命令ACU(Antenna Control Unit)机,实现射电天文望远镜的同步跟踪。其控制过程分3部分阐述:硬件设计、驱动程序设计、安装及应用;着重讨论了前两者的设计方法及思路。 相似文献
7.
Anthony Mallama 《Icarus》2009,204(1):11-499
The empirically derived phase curves of terrestrial planets strongly distinguish between airless Mercury, cloud-covered Venus, and the intermediate case of Mars. The function for Mercury is steeply peaked near phase angle zero due to powerful backscattering from its surface, while that for Venus has 100 times less contrast and exhibits a brightness excess near 170° due to Mie scattering from droplets in the atmosphere. The phase curve of Mars falls between those of Mercury and Venus, and there are variations in luminosity due to the planet’s rotation, seasons, and atmospheric states. The phase function and geometric albedo of the Earth are estimated from published albedos values. The curves for Mercury, Venus and Mars are compared to that of the Earth as well as theoretical phase functions for giant planets. The parameters of these different phase functions can be used to characterize exoplanets. 相似文献
8.
Mitsugu Makita 《Solar physics》1986,106(2):269-286
The broad-band circular polarization of sunspots is discussed on the basis of the observations made in the Okayama Astrophysical Observatory. The observation with the spectrograph proves that it is the integrated polarization of spectral lines in the observed spectral range. A velocity gradient in the line-of-sight can produce this integrated polarization due to the differential saturation between Zeeman components of magnetically sensitive lines. The observed degree of polarization and its spatial distribution in sunspots is explained when we introduce a differentially twisted magnetic field in addition to the velocity gradient. The differential twist has the azimuth rotation of the magnetic field along the line-of-sight and generates the circular polarization from the linear polarization due to the magneto-optical effect. The required azimuth rotation is reasonable and amounts at most to 30°. The required velocity gradient is compatible with the line asymmetry and its spatial distribution observed in sunspots. The observed polarity rule leads to the conclusion that the sunspot magnetic field has the differential twist with the right-handed azimuth rotation relative to the direction of the main magnetic field, without regard to the magnetic polarity and to the solar cycle. The twist itself is left-handed under the photosphere, when the sunspot is assumed to be a unwinding emerging magnetic field. 相似文献
9.
M. Yu. Reshetnyak 《Astronomy Letters》2016,42(7):482-487
The inverse problem in a spherical shell to find the two-dimensional spatial distributions of the α-effect and differential rotation in a mean-field dynamo model has been solved. The derived distributions lead to the generation of a magnetic field concentrated inside the convection zone. The magnetic field is shown to have no time to rise from the region of maximum generation located in the lower layers to the surface in the polarity reversal time due to magnetic diffusion. The ratio of the maximum magnetic energy in the convection zone to its value at the outer boundary reaches two orders of magnitude or more. This result is important in interpreting the observed stellar and planetary magnetic fields. The proposed method of solving the inverse nonlinear dynamo problem is easily adapted for a wide class of mathematical-physics problems. 相似文献
10.
Photoelectric observations of the star HD 200925 in the standardUBV system have been secured and analysed. The period is determined to be 0
.
d
267 394. From the period and shape of the light and colour curves, the star HD 200925 appears to be a dwarf cepheid. The physical parameters have been derived. The mass derived for this star is found to agree well with the value inferred from the evolutionary tracks. The star appears to be a post-Main Sequence star in the hydrogen shell burning stage of evolution. The spectral class, for this star, is assigned to be F2 III. 相似文献
11.
Alton P. Mayo 《Celestial Mechanics and Dynamical Astronomy》1979,19(4):317-333
Analytic expressions are derived for the perturbation of planetary orbits due to a thick constant density asteroid belt. The derivations include extensions and adaptations of Plakhov's analytic expressions for the perturbations in five of the orbital elements for closed orbits around Saturn's rings. The equations of Plakhov are modified to include the effect of ring thickness and additional equations are derived for the perturbations in the sixth orbital element, the mean anomaly. The gravitational potential and orbital perturbations are derived for the asteroid belt with and without thickness, and for a hoop approximation to the belt. The procedures are also applicable to Saturn's rings and the newly discovered rings of Uranus.The effects of the asteroid belt thickness on the gravitational potential coefficients and the orbital motions are demonstrated. Comparisons between the Mars orbital perturbations obtained using the analytic expressions and those obtained using numerical integration are discussed. The effects of the asteroid belt on the Earth based ranging to Mars are also demonstrated. 相似文献
12.
P. Devadas Rao N. Ramamani Saleh Mohammed Alladin 《Journal of Astrophysics and Astronomy》1987,8(1):17-31
N-Body simulations have been performed to study the tidal effects of a primary stellar system on a secondary stellar system
of density close to the Roche density. Two hyperbolic, one parabolic and one elliptic encounters have been simulated. The
changes in energy, angular momentum, mass distribution, and shape of the secondary system have been determined in each case.
The inner region containing about 40 per cent of the mass was found to be practically unchanged and the mass exterior to the
tidal radius was found to escape. The intermediate region showed tidal distension. The thickness of this region decreased
as we went from hyperbolic encounters to the elliptic encounter keeping the distance of closest approach constant. The numerical
results for the fractional change in energy have been compared with the predictions of the available analytic formulae and
the usefulness and limitations of the formulae have been discussed. 相似文献
13.
14.
The paper refers to the current status of asteroid hazard in Russia and abroad. The authors emphasize the relevance of a sober
assessment of its real state and specific circumstances working from the principle of reasonable sufficiency. The paper presents
a practical approach to the asteroid hazard problem. It consists of a proposal for a mission to the Apophis asteroid and to
define the main parameters of this hazardous celestial body. The article also considers how the spacecraft would look, as
well as its mission profile for the period of 2012–2014. 相似文献
15.
The algorithm for choosing a trajectory of spacecraft flight to the Moon is discussed. The characteristic velocity values needed for correcting the flight trajectory and a braking maneuver are estimated using the Monte Carlo method. The profile of insertion and flight to a near-circular polar orbit with an altitude of ~100 km of an artificial lunar satellite (ALS) is given. The case of two corrections applied during the flight and braking phases is considered. The flight to an ALS orbit is modeled in the geocentric geoequatorial nonrotating coordinate system with the influence of perturbations from the Earth, the Sun, and the Moon factored in. The characteristic correction costs corresponding to corrections performed at different time points are examined. Insertion phase errors, the errors of performing the needed corrections, and the errors of determining the flight trajectory parameters are taken into account. 相似文献
16.
Gorakh Nath 《中国天文和天体物理学报》2010,10(5)
Non-similarity solutions are obtained for one-dimensional isothermal and adiabatic flow behind strong cylindrical shock wave propagation in a rotational axisymmetric dusty gas,which has a variable azimuthal and axial fluid velocity.The dusty gas is assumed to be a mixture of small solid particles and perfect gas.The equilibrium flow conditions are assumed to be maintained,and the density of the mixture is assumed to be varying and obeying an exponential law.The fluid velocities in the ambient medium are assumed to obey exponential laws.The shock wave moves with variable velocity.The effects of variation of the mass concentration of solid particles in the mixture,and the ratio of the density of solid particles to the initial density of the gas on the flow variables in the region behind the shock are investigated at given times.Also,a comparison between the solutions in the cases of isothermal and adiabatic flows is made. 相似文献
17.
The first aim of the present work is to compute a more accurate and recent model for the Earth’s magnetic field. The second
aim is to determine the effects of the Earth’s magnetic field on the motion of a charged artificial satellite to evaluate
the variations of the orbital elements of the satellite due to these effects. The magnetic field and its variation with time
have been studied at different heights, longitudes and latitudes. The geomagnetic field is considered as a multiple potential
field and the electrical charge of the satellite is assumed to be constant. A new computer code has been constructed to follow
the components of the magnetic field in spherical harmonic models. The Gauss equations are solved numerically. The results
concentrate on the computation of the numerical values of orbital perturbation for the case of a low Earth satellite. RS-1
satellite and space craft gravity probe B (GPB) are chosen as cases of studies for a detailed numerical analysis. 相似文献
18.
The localized ion density depletion region observed at comet Halley can be understood in terms of a thermal instability of the cometary plasma due to the excitation of rotational and vibrational levels of water molecules. The electron energy losses due to these processes peak near 4000 K and at higher temperatures a localized cooling leads to the thermal instability due to the increased radiation loss. The resulting increase in recombination leads to the ion density depletion and the estimates for this depletion at comet Halley agree with the observations. The transport effects at the density depletion region due to the diffusion and thermal conductivity are found have time scales larger than the instability time scale and does not affect the formation of the depletion region. 相似文献
19.
An analytic solution to the two-body problem with a specific drag model is obtained. The model treats drag as a force proportional to the vector velocity and inversely proportional to the square of the distance to the center of attraction. The solution is expressed in terms of known functions and is of a simple and compact form. The time-of-flight is expressed as a quadrature in the ‘true anomaly’. 相似文献
20.
The Newtonian theory of gravitation is modified to include the gravitational energy as a source of gravitational potential,
thus making the theory self-coupled and nonlinear. The modified theory can be derived from a Lorentz-invariant action principle.
The Kepler problem is discussed in this theory and it is shown that the perihelion of the orbit steadily precesses. The rate
of precession is, however, insufficient to account for the observed precession of the perihelion of Mercury. The differences
from the Newtonian theory for the bending of light and the gravitational redshift of spectral lines are shown to be marginal. 相似文献