共查询到20条相似文献，搜索用时 234 毫秒
1.
Anthony R. Martin 《Planetary and Space Science》1974,22(1):121-141
The interaction of a conducting body moving through the ionosphere with the surrounding plasma is treated numerically. The Poisson and Vlasov equations are solved using computer techniques to give information about the redistribution of charged particles in the wake behind the body and the perturbation of the electric potential sheaths around the body. Three cases of interest are studied: body size less than, equal to, and greater than the Debye length in the surrounding plasma. A range of body potentials and ion Mach numbers are considered which are typical of conditions found in the ionosphere. Wake features, such as ion-free wake lengths and angles of propagation of disturbances in the wakes, are investigated for these conditions. Physical pictures of the mechanisms of wake formation behind a plate and a disc are built up for the three classes of body size, and differences due to geometry or size are explained. The smaller bodies are comparable in size to instrument booms, diagnostic probes, antennae, etc. and the larger bodies approach the dimensions of ionospheric satellites and space probes. 相似文献
2.
The propagation of waves in a magnetic slab embedded in a magnetic environment is investigated. The possible modes of propagation are examined from the general dispersion relation, both analytically and numerically, for disturbances which are evanescent in the environment. Approximate dispersion relations governing propagation in a slender slab of field are derived both from the general dispersion relation and from an application of the slender flux tube approximation.Several different situations, representative of both photospheric and coronal conditions, are considered. In general, the structures are found to support both fast and slow, body and surface, waves. Under coronal conditions, for two dimensional propagation, disturbances propagate as fast and slow body waves. The fast body waves are analogous to the ducted shear waves of seismology (Love waves). 相似文献
3.
M. Z. Aboelnaga 《Astrophysics and Space Science》1995,225(1):81-91
This paper investigates the regular motions of an axisymmetrical satellite in the field of Newton's attraction of a triaxial body. Both the orbital and the self rotational motions of the two bodies are taken into consideration. The exact solutions are discussed using Poincaré's method of small parameter. In the decomposition of the force function all the harmonic terms up to the third order are taken into account.The results show the existence of eight solutions. The stability of the new group of solutions is discussed using two methods to get the necessary and sufficient conditions required for the stability of these motions. 相似文献
4.
The stability properties of two prominence models are investigated by considering bounds on the marginal stability conditions. It is shown that Low's (1981) model is unstable to localized disturbances and the Hood and Anzer (1990) model is only stable for sufficiently low prominences. The latter result may be modified by including magnetic shear. It is shown that magnetic shear stabilizes coronal loops against Rayleigh-Taylor instabilities and may help to stabilize prominence models as well. 相似文献
5.
This paper presents a generalized problem of the restricted three body studied in Abdul Raheem and Singh with the inclusion that the third body is an oblate spheroidal test particle of infinitesimally mass. The positions and stability of the equilibrium point of this problem is studied for a model in which the primaries is the binary system Struve 2398 (Gliese 725) in the constellation Draco; which consist of a pair of radiating oblate stars. It is seen that additional equilibrium points exist on the line collinear with the primaries, for some combined parameters of the problem. Hence, there can be up to five collinear equilibrium points. Two triangular points exist and depends on the oblateness of the participating bodies, radiation pressure of the primaries and a small perturbation in the centrifugal force. The stability analysis ensures that, the collinear equilibrium points are unstable in the linear sense while the triangular points are stable under certain conditions. Illustrative numerical exploration is given to indicate significant improvement of the problem in Abdul Raheem and Singh. 相似文献
6.
Data received from a network of ionosondes located at distances of 1500–3100 km from the Chelyabinsk meteorite site are used to analyze ionospheric disturbances at a height of approximately 300 km following the flight and explosion of the space body. The fall of the meteoroid is believed to be accompanied by the generation of gravitational waves in the neutral atmosphere and traveling ionospheric disturbances. The velocity and period of the latter are 600–700 m/s and 70–135 min, respectively; the amplitude of relative electron concentration disturbances is 10–20%. There is evidence of the 6–7 h ionospheric presence of wave electron concentration disturbances with relative amplitude of 10–20%, which could have been caused by long-living whirlwinds in the upper atmosphere. 相似文献
7.
The motion of a point mass in the J 2 problem is generalized to that of a rigid body in a J 2 gravity field. The linear and nonlinear stability of the classical type of relative equilibria of the rigid body, which have been obtained in our previous paper, are studied in the framework of geometric mechanics with the second-order gravitational potential. Non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are obtained through a Poisson reduction process by means of the symmetry of the problem. The linear system matrix at the relative equilibria is given through the multiplication of the Poisson tensor and Hessian matrix of the variational Lagrangian. Based on the characteristic equation of the linear system matrix, the conditions of linear stability of the relative equilibria are obtained. The conditions of nonlinear stability of the relative equilibria are derived with the energy-Casimir method through the projected Hessian matrix of the variational Lagrangian. With the stability conditions obtained, both the linear and nonlinear stability of the relative equilibria are investigated in details in a wide range of the parameters of the gravity field and the rigid body. We find that both the zonal harmonic J 2 and the characteristic dimension of the rigid body have significant effects on the linear and nonlinear stability. Similar to the classical attitude stability in a central gravity field, the linear stability region is also consisted of two regions that are analogues of the Lagrange region and the DeBra-Delp region respectively. The nonlinear stability region is the subset of the linear stability region in the first quadrant that is the analogue of the Lagrange region. Our results are very useful for the studies on the motion of natural satellites in our solar system. 相似文献
8.
Methods for investigating the stability of line-tied, cylindrically-symmetric magnetic fields are presented. The energy method is used and the perturbed potential energy integral is manipulated to produce simple tests that predict either stability to general coronal disturbances or instability to localized modes, both satisfying photospheric line-tying. Using these tests the maximum amount of magnetic energy, that can be stored in the coronal magnetic field prior to an instability, can be estimated. The tests are applied to four different classes of equilibria and results are obtained for both arcade and loop geometries. 相似文献
9.
Phase-speed diagrams, showing the allowable spectrum of surface and body waves in a magnetically structured atmosphere, are constructed for the interface and the slab. The diagrams (illustrated for photospheric flux tubes, photosphere-chromosphere magnetic canopy, and coronal conditions) classify disturbances for both the normal modes of a structure and incident wave propagation on a structure, allowing a simple application once sufficiently detailed observations of waves become available. 相似文献
10.
F.Z. Feygin A.L. Kalisher V.A. Pilipenko O.A. Pokhotelov K. Dobeś 《Planetary and Space Science》1979,27(7):913-923
The stability of the hot plasma located at the curvilinear geomagnetic field in relation to the generation of Alfvén oscillations is investigated. A general expression for the increment is obtained. The increments for the short wavelength disturbances and special energy distribution function in a parabolic magnetic field are presented. The obtained theoretical results are used in interpreting the oscillations of the “auroral radiation” type. The polarization relations in Alfvén waves are investigated. 相似文献
11.
The stability of the Lundquist field is analysed in the light of the energy principle. The results show: (1) form = 0 disturbances, the Lundquist field is stable; (2) form = 1 disturbances, the Lundquist field will turn unstable in certain conditions. Whether the field will remain stable or not depends on parameters such as the helical pinch angle and radius and length of the prominence. Comparison between theory and observations reveals that a kink instability in the Lundquist field may be a critical physical reason for eruptive prominences with helical patterns. 相似文献
12.
Badam Singh Kushvah 《Astrophysics and Space Science》2011,333(1):49-59
This paper describes design of the trajectory and analysis of the stability of collinear point L
2 in the Sun-Earth system. The modified restricted three body problem with additional gravitational potential from the belt
is used as the model for the Sun-Earth system. The effect of radiation pressure of the Sun and oblate shape of the Earth are
considered. The point L
2 is asymptotically stable up to a specific value of time t correspond to each set of values of parameters and initial conditions. The results obtained from this study would be applicable
to locate a satellite, a telescope or a space station around the point L
2. 相似文献
13.
S. A. Wagner 《Monthly notices of the Royal Astronomical Society》2006,370(4):1915-1920
The linear analysis of hydrodynamic stability of the local thermal balance in a homogeneous moving gas is revisited to get information about the development of a spatially limited perturbation as seen at a fixed location. The consideration concerns both the evolution of the perturbed quantities inside a domain where the perturbation initially localizes and spreading the perturbation outside this domain. Inside the initial perturbation domain, the conditions for the exponential growth/decay are found to coincide with the well-known Field's criteria, ensuing the analysis of the normal modes. However, as soon as the modal isentropic stability criterion is satisfied the perturbation outside its initial domain asymptotically spreads out with a subsonic velocity not depending on the initial perturbation field. It enables the gas flow to carry the disturbances away and leads to an improved stability criterion for inhomogeneous thermally balanced flows where the modally unstable region appears to be spatially bounded. The spreading velocity, playing a key role in the new stability criterion, is calculated as a function of the same derivatives of the heating/cooling function as the modal instability criteria exploit. 相似文献
14.
A. W. Hood 《Solar physics》1986,105(2):307-312
Using the localised, ballooning ordering, the effect of a density stratification on the ideal MHD stability of magnetic fields is investigated. It is found that, when the photospheric density is very much greater than the coronal value, the line tying conditons are best simulated by assuming that all coronal disturbances vanish at the photospheric boundary. This is commonly known as the rigid wall conditions. 相似文献
15.
Ahmed E. Radwan 《Astrophysics and Space Science》1992,187(1):9-25
The dynamical oscillation and instability of a gas cylinder of zero inertia immersed in a resistive liquid has been developed for symmetric perturbations. In the absence of the magnetic field we have used the conservation of energy to study such problem for all symmetric and asymmetric perturbations. In the latter it is found that the temporal amplification is much lower than that of the full fluid jet. The model is capillary stable for all short and long wavelengths in the asymmetric perturbation while in the symmetric disturbances it is stabilizing or not according the perturbed wavelength is shorter than the gas cylinder circumference or not. The resistivity is stabilizing or destabilizing according to restrictions. The electromagnetic body force is stabilizing for all wavelengths in the rotationally-symmetric disturbances. The Lorentz body force, for high magnetic field intensity, could be suppressing the destabilizing character of the present model. This may be due to the fact that the acting magnetic field is uniform and that the fluid is considered to be incompressible. 相似文献
16.
The possibility of investigation of the cosmic plasma dynamics by the radio interference technique based on a finite time of radio wave propagation between the sounding and responding stations is shown. By locating the sounding station on a spacecraft the greatest contribution to the phase difference ΔΦ(t)or the phase difference growth rate between the sounding and response signals are caused by disturbances in close proximity to the spacecraft. This method permits interplanetary shock waves and tangential discontinuities to be registered and the velocities and plasma density changes on their fronts to be determined. By using experimental data of ΔΦ(t) or one can also obtain information about plasma concentration jump, location and motion of bow shock wave and magnetopause and plasmapause. Available experimental data about different disturbances of cosmic plasma were analysed and the requirements on frequency stability of spacecraft-borne and groundbased radio equipment were estimated to register those disturbances. In most cases relative stability 10?11–10?13 provided by present atomic frequency standards is sufficient. 相似文献
17.
The planetary dynamics of 4/3, 3/2, 5/2, 3/1 and 4/1 mean motion resonances is studied by using the model of the general three body problem in a rotating frame and by determining families of periodic orbits for each resonance. Both planar and spatial cases are examined. In the spatial problem, families of periodic orbits are obtained after analytical continuation of vertical critical orbits. The linear stability of orbits is also examined. Concerning initial conditions nearby stable periodic orbits, we obtain long-term planetary stability, while unstable orbits are associated with chaotic evolution that destabilizes the planetary system. Stable periodic orbits are of particular importance in planetary dynamics, since they can host real planetary systems. We found stable orbits up to 60° of mutual planetary inclination, but in most families, the stability does not exceed 20°–30°, depending on the planetary mass ratio. Most of these orbits are very eccentric. Stable inclined circular orbits or orbits of low eccentricity were found in the 4/3 and 5/2 resonance, respectively. 相似文献
18.
Numerical determination of stability regions for orbital motion in uniformly rotating second degree and order gravity fields 总被引：3，自引：0，他引：3
W. Hu 《Planetary and Space Science》2004,52(8):685-692
The stability of orbital motion about a uniformly rotating arbitrary second degree and order gravity field is investigated. A normalized form of the equations of motion are derived and analyzed. A numerical stability criteria is proposed and used to evaluate the stability of initially near-circular orbits in the equatorial plane of the body. Regions of stable and unstable motion are clearly delineated, and are seen to be strongly related to resonances between the mean motion and the body rotation rate. 相似文献
19.
We present some refinements of the previously reported magnetic polarity conditions in solar-terrestrial relations. Appropriately selected subsets were used from the longest available data sets, the geomagnetic aa-index and the surface air temperature. The solar corpuscular impacts have conspicuous effects in the tropospheric behaviour. We reported previously a new kind of semi-annual fluctuation and opposite tropospheric responses to the effects coming from different regions of the Sun as well as their dependence on the orientation of the solar main magnetic dipole. It is shown in the present paper that the semi-annual fluctuation governed by shock and fluctuating disturbances (which originate from the lower-latitude solar regions) exhibits sign reversals in consecutive cycles. The effect can be detected only in the absence of recurrent disturbances (coming mainly from the polar regions). This complex phenomenon implies that the corpuscular events may preserve some of their polarity conditions of their specific solar origin even at the Earth's distance, and on the other hand the small-scale structure of the IMF plays an important role in the link between the solar particles and the tropospheric response. 相似文献
20.
This article provides a method for finding initial conditions for perturbed frozen orbits around inhomogeneous fast rotating asteroids. These orbits can be used as reference trajectories in missions that require close inspection of any rigid body. The generalized perturbative procedure followed exploits the analytical methods of relegation of the argument of node and Delaunay normalisation to arbitrary order. These analytical methods are extremely powerful but highly computational. The gravitational potential of the heterogeneous body is firstly stated, in polar-nodal coordinates, which takes into account the coefficients of the spherical harmonics up to an arbitrary order. Through the relegation of the argument of node and the Delaunay normalization, a series of canonical transformations of coordinates is found, which reduces the Hamiltonian describing the system to a integrable, two degrees of freedom Hamiltonian plus a truncated reminder of higher order. Setting eccentricity, argument of pericenter and inclination of the orbit of the truncated system to be constant, initial conditions are found, which evolve into frozen orbits for the truncated system. Using the same initial conditions yields perturbed frozen orbits for the full system, whose perturbation decreases with the consideration of arbitrary homologic equations in the relegation and normalization procedures. Such procedure can be automated for the first homologic equation up to the consideration of any arbitrary number of spherical harmonics coefficients. The project has been developed in collaboration with the European Space Agency (ESA). 相似文献