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1.
We investigate the weak stability boundary(WSB) for a new primary, Mars,in the framework of the planar circular restricted 3-body problem, and also in the planar bicircular restricted 4-body problem by including a perturbation due to Jupiter. For the sake of a simple stability/instability criterion, our computations have been done using the equations of motion in polar coordinates. It is found that the relative size of the weakly stable sets around Mars is much larger than that of the Earth-Moon and the Sun-Jupiter systems, as the mass ratio of the Sun-Mars system is significantly smaller.We propose that this difference could be scaled by the Hill radius. In an enlarged view of the domain close to Mars, the geometry of the WSB has been presented for various parameters and compared to previous works. Our results also show that Jupiter’s gravitational force would strongly affect the Martian stable regions and should be taken into account to design a ballistic capture trajectory. 相似文献
2.
Thermal H+ distributions have been measured as the European Space Agency GEOS-1 satellite passed through the late morning equatorial magnetosphere, plasmapause and plasmasphere. The unique capabilities of the on-board Supralhermal Plasma Analysers (SPA) have been used to overcome the retarding floating potential of the satellite and measure the velocity distribution of the cold protons. In the magnetosphere an enhanced source cone of such ions with a temperature of ~ 0.5 eV is a signature of the filling process occurring outside the plasmapause where flux tubes are relatively empty. In the plasmasphere the thermal H+ is essentially isotropic with a temperature less than 0.5 eV but the motion of the satellite introduces apparent drift.These measurements of cold proton velocity distribution now permit a reappraisal of the definition of the “plasmapause”. It becomes inappropriate to use an arbitrary empirical density, e.g. the conventional 10 cm ?3, in order to establish a boundary. It is now possible to identify a plasmapause interaction region where the two cold proton populations co-exist. This region generally lies Earthward of the 10 cm ?3 density level, has a width which is strongly dependent on magnetic activity and the temperature is typically between 0.5 and 1.5 eV. The change from “filled” to “unfilled” flux tubes relates to the physical processes which are occurring and the controlling electric field configuration; in particular, the last closed equipotential. Throughout this region, in going from the plasmasphere to the magnetosphere, the plasma drift motion is expected to change from corotation to a convection which is controlled by E ×B, and is predominantly Sunward due to the dawn-dusk electric field. Crossing the plasmapause on the morning side, little change in drift direction should occur but subtle variations in the ionic velocity distribution do reflect the change in the degree of flux tube density equilibrium.Our first direct measurement of the magnetospheric E × B drift has been reported previously but here measurements from a selected six day period show how the plasma in the plasmapause region responds to changing magnetospheric activity. The drift velocities cannot he derived with high accuracy but the analysis shows that the technique can provide a valid mapping of the magnelospheric electric field. In addition, since the magnetospheric cold plasma distribution is observed after it has come from the ionosphere, a distance of many Earth radii, the scattering and accelerating mechanisms along the flux tube can be studied. For this particular data-set taken in the late morning, the maximum potential drops along the flux tubes were less than a volt. The ionospheric proton source cone is observed to be broad, pitch angle scattering persists up to 40 or even 70°.Although these results throw new light on the plasmaspheric filling process one must recognise that, however the plasmapause is defined, it is not a simple matter to map this boundary from the equatorial plane down to low altitudes and the mid-latitude trough. 相似文献
3.
Studies of the boundary layers in the vicinity of the Earth's dayside magnetopause are important in determining the nature of the processes which couple the magnetosphere to the flowing solar wind, thereby driving magnetospheric convection. In this paper we examine theoretically the magnetic field and plasma properties expected in the boundary regions for various models involving either diffusion or reconnection at the boundary. For diffusion models the transport of magnetosheath momentum across the magnetopause will result in field shears on either side of the boundary, the field rotations being in opposite senses on either side relative to the undisturbed fields. The directions of these rotations depend upon location at the magnetopause relative to the momentum transfer region and to the noon meridian. In reconnection models the effect of the tension of the open boundary layer field lines must be taken into account in addition to the magnetosheath flow, but on the super-Alfvénic flanks of the magnetosphere the latter still dominates, so that qualitatively similar effects will occur in the two models. More detailed, quantitative or statistical studies are then required to distinguish the two models in this regime. In the sub-Alfvénic dayside region, however, open field tension effects will dominate in reconnection models such that boundary layer field and plasma properties will then be determined mainly by the magnetosheath magnetic field configuration. In particular the East-West flow in the magnetospheric boundary layer will be controlled largely by the East-West field in the magnetosheath, leading to flow reversals across the magnetopause in some quadrants of the magnetopause. This behaviour is directly related to the Svalgaard-Mansurov effect and is a signature unique to reconnection models. The boundary layer fields are also expected to tilt towards the field on the opposite side of the boundary in these models on the dayside. “Toward” tilting can also occur in this regime in diffusion models, but “away” tilting, a signature unique to dayside diffusion, should also occur equally frequently. Finally, we briefly discuss previously published high-resolution ISEE 1 and 2 data from the boundary regions in the light of our results. We find that “toward” tilting generally occurs in boundary region crossings previously identified as being reconnection-associated and we present some examples in which the above unique reconnection signature has been observed. During impulsive FTE-like events, however, the field may tilt in either direction, possibly as a result of field line twists, thus complicating our simple picture in this case. We also show that the “reverse draping” observations presented by Hones et al. (1982) approximately satisfy the open magnetopause stress balance conditions. 相似文献
4.
We elaborate the model of accretion disks of young stars with the fossil large-scale magnetic field in the frame of Shakura and Sunyaev approximation. Equations of the MHD model include Shakura and Sunyaev equations, induction equation and equations of ionization balance. Magnetic field is determined taking into account ohmic diffusion, magnetic ambipolar diffusion and buoyancy. Ionization fraction is calculated considering ionization by cosmic rays and X-rays, thermal ionization, radiative recombinations and recombinations on the dust grains. Analytical solution and numerical investigations show that the magnetic field is coupled to the gas in the case of radiative recombinations. Magnetic field is quasi-azimuthal close to accretion disk inner boundary and quasi-radial in the outer regions. Magnetic field is quasi-poloidal in the dusty “dead” zones with low ionization degree, where ohmic diffusion is efficient. Magnetic ambipolar diffusion reduces vertical magnetic field in 10 times comparing to the frozen-in field in this region. Magnetic field is quasi-azimuthal close to the outer boundary of accretion disks for standard ionization rates and dust grain size a d=0.1 μm. In the case of large dust grains (a d>0.1 μm) or enhanced ionization rates, the magnetic field is quasi-radial in the outer regions. It is shown that the inner boundary of dusty “dead” zone is placed at r=(0.1–0.6) AU for accretion disks of stars with M=(0.5–2)?M ⊙. Outer boundary of “dead” zone is placed at r=(3–21) AU and it is determined by magnetic ambipolar diffusion. Mass of solid material in the “dead” zone is more than 3?M ⊕ for stars with M≥1?M ⊙. 相似文献
5.
This study is concerned with the stability of motion of the circumbinary exoplanet Kepler-413b. The analysis is performed within the framework of a flat restricted three-body problem. The stability diagram is plotted in the plane of initial conditions “pericentric distance—eccentricity” using mass calculations of Lyapunov exponents. According to the diagram, the Kepler-413b planet is located in a stable resonance cell, confined by the mean-motion resonances 6: 1 and 7: 1 with a central binary star, which agrees with the conclusions of Kostov et al. (2014) based on calculations of the MEGNO parameter. It is shown that the value of the critical semimajor axis acquired from the empirical formula of Holman and Wiegert (1999) almost coincides with the value obtained directly from the stability diagram; at low and moderate eccentricities of the planetary orbit, the position of the calculated boundary of the chaos zone is in close agreement with the boundary predicted by Shevchenko’s theory (2015). If the planet were in the instability zone, its characteristic Lyapunov time would be only ~1 year. In accordance with the conclusions of Kostov et al. (2014), it has been shown that the planet Kepler-413b is outside the habitability zone of the system. 相似文献
6.
《New Astronomy Reviews》1999,43(8-10):731-735
We present multi-epoch simultaneous 15, 22 and 43 GHz VLBA polarimetric radio observations of the quasar 4C 39.25 which provide further evidence for the ongoing interaction between components `a' and `b' through the monitoring of the total and polarised flux densities of both components, the proper motion of `b' and, more importantly, of the polarisation angle associated with components `a' and `b'. There are strong pieces of evidence indicating that the superluminal component `b' is “colliding” or “crossing” the region associated with the stationary component `a': (i) at millimeter wavelengths, the total flux density of 4C 39.25 has reached a maximum and is already beginning to decline; (ii) at centimeter wavelengths, the total flux density light curve has reached a “plateau” at its maximum value while the polarised flux density is already decreasing; and (iii) the proper motion of 4C 39.25 with respect to the quasi-inertial reference frame defined by the sources observed in the USNO-programme shows a sharp change in the slope during 1997–1998. 相似文献
7.
This work deals with the structure of the lunar Weak Stability Boundaries (WSB) in the framework of the restricted three and
four body problem. Geometry and properties of the escape trajectories have been studied by changing the spacecraft orbital
parameters around the Moon. Results obtained using the algorithm definition of the WSB have been compared with an analytical
approximation based on the value of the Jacobi constant. Planar and three-dimensional cases have been studied in both three
and four body models and the effects on the WSB structure, due to the presence of the gravitational force of the Sun and the
Moon orbital eccentricity, have been investigated. The study of the dynamical evolution of the spacecraft after lunar capture
allowed us to find regions of the WSB corresponding to stable and safe orbits, that is orbits that will not impact onto lunar
surface after capture. By using a bicircular four body model, then, it has been possible to study low-energy transfer trajectories
and results are given in terms of eccentricity, pericenter altitude and inclination of the capture orbit. Equatorial and polar
capture orbits have been compared and differences in terms of energy between these two kinds of orbits are shown. Finally,
the knowledge of the WSB geometry permitted us to modify the design of the low-energy capture trajectories in order to reach
stable capture, which allows orbit circularization using low-thrust propulsion systems. 相似文献
8.
It is shown that the power ε generated by the solar wind-magnetosphere dynamo is transmitted to the convective motion of magnetospheric plasma. This convective motion generates what we may call the “Pedersen counterpart currents” in the magnetosphere and drives a large part of the “region 1 and 2” field-aligned currents which are closed by the Pedersen currents in the ionosphere. These results are based on a self-consistent set of the ionospheric current and potential distribution patterns obtained from a study of the International Magnetosphere Study Alaska meridian chain data. 相似文献
9.
Possible configurations of the planetary systems of the binary stars α Cen A–BandEZAqr A–C are analyzed. The P-type orbits—circumbinary ones, i.e., the orbits around both stars of the binary, are studied. The choice of these systems is dictated by the fact that α Cen is closest to us in the Galaxy, while EZ Aqr is the closest system whose circumbinary planets, as it turns out, may reside in the “habitability zone.” The analysis has been performed within the framework of the planar restricted three-body problem. The stability diagrams of circumbinary motion have been constructed: on representative sets of initial data (in the pericentric distance–eccentricity plane), we have computed the Lyapunov spectra of planetary motion and identified the domains of regular and chaotic motion through their statistical analysis. Based on present views of the dynamics and architecture of circumbinary planetary systems, we have determined the most probable planetary orbits to be at the centers of the main resonance cells, at the boundary of the dynamical chaos domain around the parent binary star, which allows the semimajor axes of the orbits to be predicted. In the case of EZ Aqr, the orbit of the circumbinary planet is near the habitability zone and, given that the boundary of this zone is uncertain, may belong to it. 相似文献
10.
Plasma and magnetic field data from PROGNOZ-7 have revealed that solar wind (magnetosheath) plasma elements may penetrate the dayside magnetopause surface and form high density regions with enhanced cross-field flow in the boundary layer.The injected magnetosheath plasma is observed to have an excess drift velocity as compared to the local boundary layer plasma, comprising both “cold” plasma of terrestrial origin and a hot ring current component. A differential drift between two plasma components can be understood in terms of a momentum transfer process driven by an injected magnetosheath plasma population. The braking action of the injected plasma may be described as a dynamo process where particle kinetic energy is transferred into electromagnetic energy (electric field). The generated electric field will force the local plasma to , and the dynamo region therefore also constitutes an accelerator region for the local plasma. Whenever energy is dissipated from the energy transfer process (a net current is flowing through a load), there will also be a difference between the induced electric field and the term of the generator plasma. Thus, the local plasma will drift more slowly than the injected generator plasma.We will present observations showing that a relation between the momentum transferred, the injected plasma and the momentum taken up by the local plasma exists. For instance, if the local plasma density is sufficiently high, the differential drift velocity of the injected and local plasma will be small. A large fraction of the excess momentum is then transferred to the local plasma. Conversely, a low local plasma density results in a high velocity difference and a low fraction of local momentum transfer.In our study cases the “cold” plasma component was frequently found to dominate the local magnetospheric plasma density in the boundary layer. Accordingly, this component may have the largest influence on the local momentum transfer process. We will demonstrate that this also seems to be the case. Moreover we show that the accelerated “cold” plasma component may be used as a tracer element reflecting both the momentum and energy transfer and the penetration process in the dayside boundary layer.The high He+ percentage of the accelerated “cold” plasma indicates a plasmaspheric origin. Considering the quite high densities of energetic He+ found in the boundary layer, the overall low abundance of He+ (as compared to e.g. O+) found in the plasma sheet and outer ring current evidently reduces the importance of the dayside boundary layer as a plasma source in the large scale magnetospheric circulation system. 相似文献
11.
Astrobiology, like many (but not all) sciences, must take into account questions of the “Why?”, “Where?”, “How?” and “When?” type. In this introductory chapter, we explain why, in this book, we will only consider two of these questions that are, moreover, deeply interrelated. Chronology is by definition related to the “when?” question but as soon as we are interested in the history of Earth or the history of life, it is impossible to treat these questions and their answers without explicit references to the “how?” questions. We also present in this chapter the genesis and the aim of the book. 相似文献
12.
Dieter Stöffler Natalia A. Artemieva Kai Wünnemann W. Uwe Reimold Juliane Jacob Birgit K. Hansen Iona A. T. Summerson 《Meteoritics & planetary science》2013,48(4):515-589
We report results of an interdisciplinary project devoted to the 26 km‐diameter Ries crater and to the genesis of suevite. Recent laboratory analyses of “crater suevite” occurring within the central crater basin and of “outer suevite” on top of the continuous ejecta blanket, as well as data accumulated during the past 50 years, are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations (Artemieva et al. 2013). The properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting. In a new approach, we reconstruct the minimum/maximum volumes of all allochthonous impact formations (108/116 km3), of suevite (14/22 km3), and the total volume of impact melt (4.9/8.0 km3) produced by the Ries impact event prior to erosion. These volumes are reasonably compatible with corresponding values obtained by numerical modeling. Taking all data on modal composition, texture, chemistry, and shock metamorphism of suevite, and the results of modeling into account, we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement. Numerical modeling indicates that only a very small fraction of suevite can be derived from the “primary ejecta plume,” which is possibly represented by the fine‐grained basal layer of outer suevite. The main mass of suevite was deposited from a “secondary plume” induced by an explosive reaction (“fuel‐coolant interaction”) of impact melt with water and volatile‐rich sedimentary rocks within a clast‐laden temporary melt pool. Both melt pool and plume appear to be heterogeneous in space and time. Outer suevite appears to be derived from an early formed, melt‐rich and clast‐poor plume region rich in strongly shocked components (melt ? clasts) and originating from an upper, more marginal zone of the melt pool. Crater suevite is obviously deposited from later formed, clast‐rich and melt‐poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper, central zone of the melt pool. Genetically, we distinguish between “primary suevite” which includes dike suevite, the lower sublayer of crater suevite, and possibly a basal layer of outer suevite, and “secondary suevite” represented by the massive upper sublayer of crater suevite and the main mass of outer suevite. 相似文献
13.
PROGNOZ-7 observations of intense “magnetosheath-like” plasma deep inside the high latitude boundary layer, the plasma mantle, indicates that solar wind plasma elements may occasionally penetrate the magnetopause and form high density regions in the plasma mantle. These “magnetosheath-like” regions are usually associated with strong flow of solar wind ions (e.g. H+ and He2+) and the presence of terrestrial ions (e.g. O+). The magnetosheath-like structures may roughly be classified as “newly injected” or “stagnant”. The newly injected structures have characteristics very similar to those found in the magnetosheath, i.e. strong antisunward flow and magnetosheath ion composition and density. The magnetic field characteristics may, however, differ considerably from those found further out in the magnetosheath. The “stagnant” structures are characterized by a reduced plasma flow, a lower density and a different ion composition as compared to that in the magnetosheath. In a few cases newly injected structures were even found in the innermost part of the mantle (i.e. forming a “boundary region” adjacent to the lobe). These cases were also associated with fairly strong fluxes of O+ ions in the outer mantle. Whilst the newly injected type of magnetosheath-like structure contained almost no O+ ions, the stagnant regions were intermixed by an appreciable amount of ionospheric ions. The newly injected and stagnant penetration regions had both in common a diamagnetic decrease of the ambient magnetic field. The newly injected structures, however, were also associated with a considerable reorientation of the magnetic field vector. A common feature for penetration regions well separated from the magnetopause is that they are mainly observed for a southward IMF. A third category of plasma mantle penetrated events, denoted “open magnetopause” events, usually occurred when the IMF was away and northward. Characteristics for these events were a smooth transition/rotation of the magnetic field vector near the magnetopause, and fairly high ion densities in the mantle and the transition region. 相似文献
14.
E. Tavabi 《Astrophysics and Space Science》2014,350(2):489-493
A large percent of spicules shows a surge-like behavior on the solar limb, supporting a multi-component model with twisted threads. The counterpart of limb spicules foot-points is investigated on the disk, and this re-examination indicates that the interpretation of transverse motion of off-limb spicules could directly be related to rotational motion at the feet of disk spicules. Related bright elements move and vary in brightness on the timescales of chromospheric oscillations. The motions are similar to random displacements of the bright elements along the network boundaries with amplitudes of about 200 to 400 km, with evidence of “spinning” or vortex motion. We find a clear evidence and in several cases for splitting process and suggesting a formation mechanism for doublet (or multi-component) spicules. A general inter chromospheric network velocity pattern with twists existing before the emergence and eruption of spicules seems to be required. In this paper a helical- kink mode propagation consistent with the new evidence of spicule multiple structure is presented and provides an explanation for the origin of the Alfvenic wave propagation along the spicules. The evidence of spinning spicules remains unclear from disk Dopplergram observations, we use a 3D time slice “column” diagrams (2D in x and y and time in z being the 3d dimension) by consecutive partly transparent slices put in perspective to show the rotational behavior at the chromospheric rosettes, and provide a wealth of information on spinning motion, helical wave propagation and splitting. 相似文献
15.
Meteorite and meteoroid: New comprehensive definitions 总被引：1，自引：0，他引：1
Abstract– Meteorites have traditionally been defined as solid objects that have fallen to Earth from space. This definition, however, is no longer adequate. In recent decades, man‐made objects have fallen to Earth from space, meteorites have been identified on the Moon and Mars, and small interplanetary objects have impacted orbiting spacecraft. Taking these facts and other potential complications into consideration, we offer new comprehensive definitions of the terms “meteorite,”“meteoroid,” and their smaller counterparts: A meteoroid is a 10‐μm to 1‐m‐size natural solid object moving in interplanetary space. A micrometeoroid is a meteoroid 10 μm to 2 mm in size. A meteorite is a natural, solid object larger than 10 μm in size, derived from a celestial body, that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and that later collided with a natural or artificial body larger than itself (even if it is the same body from which it was launched). Weathering and other secondary processes do not affect an object’s status as a meteorite as long as something recognizable remains of its original minerals or structure. An object loses its status as a meteorite if it is incorporated into a larger rock that becomes a meteorite itself. A micrometeorite is a meteorite between 10 μm and 2 mm in size. Meteorite– “a solid substance or body falling from the high regions of the atmosphere” ( Craig 1849 ); “[a] mass of stone and iron that ha[s] been directly observed to have fallen down to the Earth’s surface” (translated from Cohen 1894 ); “[a] solid bod[y] which came to the earth from space” ( Farrington 1915 ); “A mass of solid matter, too small to be considered an asteroid; either traveling through space as an unattached unit, or having landed on the earth and still retaining its identity” ( Nininger 1933 ); “[a meteoroid] which has reached the surface of the Earth without being vaporized” (1958 International Astronomical Union (IAU) definition, quoted by Millman 1961 ); “a solid body which has arrived on the Earth from outer space” ( Mason 1962 ); “[a] solid bod[y] which reach[es] the Earth (or the Moon, Mars, etc.) from interplanetary space and [is] large enough to survive passage through the Earth’s (or Mars’, etc.) atmosphere” ( Gomes and Keil 1980 ); “[a meteoroid] that survive[s] passage through the atmosphere and fall[s] to earth” ( Burke 1986 ); “a recovered fragment of a meteoroid that has survived transit through the earth’s atmosphere” ( McSween 1987 ); “[a] solid bod[y] of extraterrestrial material that penetrate[s] the atmosphere and reach[es] the Earth’s surface” ( Krot et al. 2003 ). 相似文献
16.
This paper is devoted to clarify the algorithmic definition of the weak stability boundary in the framework of the planar
Restricted Three Body Problem. The role of the invariant hyperbolic manifolds associated to the central manifolds of the libration
points L
1 and L
2, as boundary of the weak stability region, is shown. 相似文献
17.
We show that aperiodic and quasiperiodic variability of bright LMXBs – atoll and Z‐sources – on ∼ sec‐msec time scales is caused primarily by variations of the luminosity of the boundary layer. The emission of the accretion disk is less variable on these time scales and its power density spectrum follows P disk(f ) ∝ f –1 law, contributing to observed flux variation at low frequencies and low energies only. The kHz QPOs have the same origin as variability at lower frequencies, i.e. independent of the nature of the “clock”, the actual luminosity modulation takes place on the neutron star surface. The boundary layer spectrum remains nearly constant in the course of the luminosity variations and is represented to certain accuracy by the Fourier frequency resolved spectrum. In the investigated range of ∼ (0.1 – 1) Edd it depends weakly on the global mass accretion rate and in the limit ∼ Edd is close toWien spectrum with kT ∼ 2.4 keV. Its independence on the global value of lends support to the theoretical suggestion by Inogamov & Sunyaev (1999) that the boundary layer is radiation pressure supported. Based on the knowledge of the boundary layer spectrum we attempt to relate the motion along the Z‐track to changes of physically meaningful parameters. Our results suggest that the contribution of the boundary layer to the observed emission decreases along the Z‐track from conventional ∼50% on the horizontal branch to a rather small number on the normal branch. This decrease can be caused, for example, by obscuration of the boundary layer by the geometrically thickened accretion disk at ∼ Edd. Alternatively, this can indicate significant change of the structure of the accretion flow at ∼ Edd and disappearance of the boundary layer as a distinct region of the significant energy release associated with the neutron star surface. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
R. Caimmi 《Astronomische Nachrichten》1996,317(6):401-412
Starting from the equations of hydrodynamics, which include both collisional and collisionless ideal fluids, the special case of pseudo-arotropes with anisotropic pressure distribution along tangential or vertical direction (in respect to a “vertical” rotation axis) is considered. We find that vertical motions are equivalent to an imaginary rotation, and call “pseudo-otation” the combination of rotation and real or imaginary peculiar circular motions. By use of a necessary condition for equilibrium, i.e. the coincidence of the boundary with an isopotential (gravitational + rotational centrifugal + real peculiar or imaginary peculiar centrifugal) surface, a new method of finding bifurcation points from axisymmetric to triaxial pseudo-arotropic sequences – discussed in an earlier paper – is dealt with for the systems under discussion. A simple application to the special case where the isopycnic surfaces are spheroidal discloses that, on one hand, steadily pseudo-otating, heterogeneous spheroids, cannot be equilibrium configurations and, on the other hand, the same results obtained by use of the virial technique hold when the current method can work. Then the coincidence of the boundary with an isopotential surface and the validity of the virial equations of the second order make two independent (necessary) conditions for equilibrium and both must be satisfied. Under the further assumptions of steady rotation and homeoidally or focaloidally striated distribution of matter, the configurations for which a bifurcation point must necessarily occurr, are determined. In the former alternative a connection is also established, between local (on the boundary) and global anisotropy of pressure distribution; in particular, it is found that local isotropy (on the boundary) involves global isotropy and vice versa. In both cases, the right amount of of anisotropy turns out to yield violation of a treshold for stability, ϵrot = −Erot/Epot ⩽ 0.14, conjectured by Ostriker and Peebles (1973). This result gives additional support to a conclusion established in an earlier paper: it seems more germane to speak about Ostriker-eebles conjecture for stability in connection with visible bodies of galaxies, instead of Ostriker-eebles criterion for stability in connection with self-ravitating fluids. 相似文献
19.
We present a hybrid combination of forward and inverse reconstruction methods using multiple observations of a coronal mass ejection (CME) to derive the three-dimensional (3D) “true” height?–?time plots for individual CME components. We apply this hybrid method to the components of the 31 December 2007 CME. This CME, observed clearly in both the STEREO A and STEREO B COR2 white-light coronagraphs, evolves asymmetrically across the 15-solar-radius field of view within a span of three hours. The method has two reconstruction steps. We fit a boundary envelope for the potential 3D CME shape using a flux-rope-type model oriented to best match the observations. Using this forward model as a constraining envelope, we then run an inverse reconstruction, solving for the simplest underlying 3D electron density distribution that can, when rendered, reproduce the observed coronagraph data frames. We produce plots for each segment to establish the 3D or “true” height?–?time plots for each center of mass as well as for the bulk CME motion, and we use these plots along with our derived density profiles to estimate the CME’s asymmetric expansion rate. 相似文献
20.
Review of concepts of stability 总被引：1，自引：0，他引：1
Victor Szebehely 《Celestial Mechanics and Dynamical Astronomy》1984,34(1-4):49-64