共查询到20条相似文献，搜索用时 15 毫秒
1.
Fractal property or self-similarity exists abundantly in many aspects in our universe. Fractals are rich in geology and have certain relations to various geological processes. This article presents analyses of fractal properties of 18 impact crater ejecta margins on the surface of Venus. The structured walk method was used to measure the length of perimeter of the ejecta margin and the resulting Richardson plots were investigated. EveryR-plot has a first linear part, a second part and a main scattering part. The variations seen in the second part include information on the formation and geology of the crater ejectas. The fractal dimension of the second part is related to the perimeter of the ejecta and thus to the impact energy. The ratio of the square of the perimeter to the area describes the lobateness of the ejecta and has a positive correlation to the perimeter in a way similar to that between the fractal dimension of the second part and the perimeter. Two linear subparts in the second part indicate different fractal properties due to various processes dominating on different scales. Scattering in the middle of the second part indicates the scale and type of the ejecta lobes. The smooth scattering over the entire second part is related to impact angle and energy. A threshold value beyond which the structured walk method cannot be used was observed at a ruler length of about 1/10 of the perimeter. 相似文献
2.
M. Burša 《Earth, Moon, and Planets》1988,42(1):49-53
A dynamic homogeneous model of Phobos is used: its boundary is an equipotential surface specified by the second zonal and the second sectorial harmonics plus the constant part of the tidal potential due to Mars. The principal moments of inertia, the hydrostatic second zonal harmonic and the secular Love number of Phobos have been estimated. They support the hypothesis that Phobos is formed out of primordial matter by accretion in orbit. 相似文献
3.
Anne Sergysels-Lamy 《Celestial Mechanics and Dynamical Astronomy》1975,11(1):43-51
Hale's method is used to show the existence of symmetric periodic orbits of the second kind for the particular case of the elliptic restricted problem of three bodies. In this treatment we also obtain a new proof of the existence of periodic orbits of the first and second kinds in the circular restricted problem. 相似文献
4.
J. F. Hansen M. J. Edwards D. H. Froula A. D. Edens G. Gregori T. Ditmire 《Astrophysics and Space Science》2007,307(1-3):219-225
We have previously reported the experimental discovery of a second shock forming ahead of a radiative shock propagating in
Xe. The initial shock is spherical, radiative, with a high Mach number, and it sends a supersonic radiative heat wave far
ahead of itself. The heat wave rapidly slows to a transonic regime and when its Mach number drops to two with respect to the
downstream plasma, the heat wave drives a second shock ahead of itself to satisfy mass and momentum conservation in the heat
wave reference frame. We now show experimental data from a range of mixtures of Xe and N2, gradually changing the properties of the initial shock and the environment into which the shock moves and radiates (the
radiative conductivity and the heat capacity). We have successfully observed second shock formation over the entire range
from 100% Xe mass fraction to 100% N2. The formation radius of the second shock as a function of Xe mass fraction is consistent with an analytical estimate. 相似文献
5.
J. F. Hansen M. J. Edwards D. Froula G. Gregori A. Edens T. Ditmire 《Astrophysics and Space Science》2005,298(1-2):61-67
Supernovae launch spherical shocks into the circumstellar medium (CSM). These shocks have high Mach numbers and may be radiative.
We have created similar shocks in the laboratory by focusing laser pulses onto the tip of a solid pin surrounded by ambient
gas; ablated material from the pin rapidly expands and launches a shock through the surrounding gas. Laser pulses were typically
5 ns in duration with ablative energies ranging from 1–150 J. Shocks in ambient gas pressures of ~1 kPa were observed at spatial
scales of up to 5 cm using optical cameras with schlieren. Emission spectroscopy data were obtained to infer electron temperatures
(< 10 eV).
In this experiment we have observed a new phenomena; at the edge of the radiatively heated gas ahead of the shock, a second
shock forms. The two expanding shocks are simultaneously visible for a time, until the original shock stalls from running
into the heated gas. The second shock remains visible and continues to expand. A minimum condition for the formation of the
second shock is that the original shock is super-critical, i.e., the temperature distribution ahead of the original shock
has an inflexion point. In a non-radiative control experiment the second shock does not form. We hypothesize that a second
shock could form in the astrophysical case, possibly in radiative supernova remnants such as SN1993J, or in shock-CSM interaction. 相似文献
6.
V.N. Zharkov 《Planetary and Space Science》2010,58(10):1381-1390
The effects of the equilibrium figure theory to within terms of the second order in a small parameter α on figure parameters and gravitational moments of the Galilean satellite Io have been considered. Integro-differential equations of the theory of figure to second order have been first solved numerically. Relations between the low-order coefficients of the gravitational field for satellites in hydrostatic equilibrium are generalized according to the second order theory. To show the effects of the second approximation, two three-layer trial models of Io are used. The considered models of the Io’s interiors differ by the size and density of the core, while having the same thickness and density of the crust, and the mantle density difference is only 20 kg/m3. The corrections of second order in smallness to the gravitational moments J2 and C22 decrease the third decimal digit of model gravitational moments by two units. As the effects of third and forth harmonics are determined mostly by outer layers of Io, to distinguish between model mantle density, the gravitational moments J4, C42 and C44 should be determined to accuracy with three or four decimal digits. The second order corrections mostly effect the semi-axis a, and less the semi-axes b and c. 相似文献
7.
The first and second order generating functions and the first second and third order new J-S-U-N Hamiltonians are calculated by the Hori-Lie procedure. 相似文献
8.
Zuzanna Niedzielska 《Celestial Mechanics and Dynamical Astronomy》1994,58(3):203-213
The stability of the triangular libration points in the case when the first and the second order resonances appear was investigated. It was proved that the first order resonances do not cause instability. The second order resonances may lead to instability. Domains of the instability in the two-dimensional parameter space were determined. 相似文献
9.
Hans Rosenberg 《Solar physics》1975,42(1):247-257
The observational evidence is reviewed for the occurrence of type III solar radio bursts in pairs with frequency ratio two to one. We show that the observations can be explained under the hypothesis that there is a tendency for a type III burst to be followed by a second burst within approximately one second. This explanation leads to fewer difficulties than the hypothesis that type III bursts occur in pairs, one member being emitted at the fundamental of the local coronal plasma frequency, the other at its second harmonic. We conclude that in general, type III bursts are emitted at the second harmonic of the plasma frequency and that type III theories should account for this and only under very special circumstances (which are rare) for the emission at the fundamental and the second harmonic. 相似文献
10.
N. Sekiguchi 《Earth, Moon, and Planets》1970,2(2):136-139
The probable semi-amplitudes of the second and third modes of the Moon's free librations are inferred from the observed semi-amplitude of its first mode, using the statistical relations between the exciting actions and the amplitudes of the free librations, derived in the author's previous paper (Sekiguchi, 1970). It is likely that the semi-amplitudes of these librations exceed some second of arc. 相似文献
11.
A continuous transition from early Friedmann-like radiation era through to late time cosmic acceleration passing through a long Friedmann-like matter dominated era followed by a second phase of radiation era has been realized in modified theory of gravity containing a combination of curvature squared term, a linear term, a three-half term and an ideal fluid. Thus the history of cosmic evolution is explained by modified theory of gravity singlehandedly. The second phase of radiation-like era might provide an explanation to the hydrogen and helium reionization at low redshift. 相似文献
12.
Huang Guangs LI 《Solar physics》1987,114(2):363-373
A theoretical analysis of electron-cyclotron maser instabilities indicates that the distribution function of non-thermal electrons influences millisecond radio spikes in solar flares, and that a hollow beam distribution is more likely than a loss-cone distribution. The restrictions of classical theories of cyclotron resonant absorption are discussed and a formula is derived for the absorption coefficient near the resonant frequency. Finally, the computations show that for typical coronal parameters, the growth rates of the fundamental of fast extraordinary modes are much faster than those of their second harmonics; and because the directional angle of the fundamental is smaller, its resonant absorption may be neglected. Moreover, the band-width of the fundamental is consistent with observation of radio spikes; therefore, we claim that the millisecond radio spikes in the decimetric range are composed mainly of fundamentals of the fast extraordinary modes. The second harmonics of fast extraordinary modes may be generated for directions near to the vertical to the magnetic field, but it is impossible to observe both fundamental and second harmonics in the same direction. 相似文献
13.
Plots of 12-month moving averages of the radio emission values for 1947–2002 indicated that the ratios (maximum/minimum) of
the solar cycles 19–23 were low (∼ 1.2) in the upper chromosphere and lower corona (frequencies near 15 000 MHz), rose to
maximum levels of ∼ 3.5 in the middle corona (frequencies ∼ 2000±500 MHz), and dropped thereafter to ∼ 2.5. In some cycles,
there were two maxima separated by about 2 years. In cycles 20 and 23, mostly the second maximum was larger than the first
maximum, but in cycles 21 and 22, some parameters showed the first maximum larger while others showed the second maximum larger.
There was no systematic shift from first maximum to second maximum, with frequency or temperature (or altitude). 相似文献
14.
The technique of probability imaging is applied to the bright, well resolved, infrared binary star Aqr. It is shown how the second probability density function (pdf) contains all pertinent information to reconstruct the binary system with no ambiguity. Relations between the second pdf and other techniques (speckle masking technique and fork algorithm) are briefly indicated. An analysis of the behaviour of the second pdf under additive signal-independent nose is undertaken. As expected from the general theory of signal processing, the second pdf of the noise is found to blur the second pdf of the signal by means of a convolution relation.Based on observations obtained at ESO, La Silla, Chile. 相似文献
15.
16.
Theory of the motion of an artificial Earth satellite 总被引：1，自引：0，他引：1
Felix R. Hoots 《Celestial Mechanics and Dynamical Astronomy》1981,23(4):307-363
An improved analytical solution is obtained for the motion of an artificial Earth satellite under the combined influences of gravity and atmospheric drag. The gravitational model includes zonal harmonics throughJ
4, and the atmospheric model assumes a nonrotating spherical power density function. The differential equations are developed through second order under the assumption that the second zonal harmonic and the drag coefficient are both first-order terms, while the remaining zonal harmonics are of second order.Canonical transformations and the method of averaging are used to obtain transformations of variables which significantly simplify the transformed differential equations. A solution for these transformed equations is found; and this solution, in conjunction with the transformations cited above, gives equations for computing the six osculating orbital elements which describe the orbital motion of the satellite. The solution is valid for all eccentricities greater than 0 and less than 0.1 and all inclinations not near 0o or the critical inclination. Approximately ninety percent of the satellites currently in orbit satisfy all these restrictions. 相似文献
17.
C. Íbanoğlu E.R. Pekünlü V. KESKÍn Z. Tunca S. Evren M.C. Akan 《Astrophysics and Space Science》1997,257(1):11-21
The peculiar chromospherically active binary system RT Lac was observed in B and V bands between 1989 and 1992. The four-year photoelectric B and V light curves are presented. The light and colour variations in the four special regions of the light curve between 1978 and 1992 are discussed. The available photometry obtained by the present authors defines at least three consecutive maxima in the variation of the brightness of the system at second maximum and in mid-primary eclipse. The behaviour of the light and colour changes in mid-primary and at second maximum harmonizes with the common property of the RS CVn-type binaries. However, the light changes at first maximum do not resemble either at second maximum or in mid-primary minimum. Therefore, we conclude that the observed features cannot be attributed to the spottedness of the more massive component alone. The signs of the starspots are masked by the matter in front of the more massive component at the first maximum. The present data indicate that the magnetic cycle in RT Lac is about 12 years, which is analogous to the Sun's 11-year sunspot cycle. 相似文献
18.
N. N. Samus’ V. P. Goranskii O. V. Durlevich A. V. Zharova E. V. Kazarovets N. N. Kireeva E. N. Pastukhova D. B. Williams M. L. Hazen 《Astronomy Letters》2003,29(7):468-479
We present a new electronic version of the second volume of the fourth edition of the General Catalogue of Variable Stars (GCVS), which contains data on 13480 variable stars in the constellations Cygnus-Orion (the order of constellations in the Catalogue follows the Latin alphabet). The new version takes into account the Name Lists of Variable Stars from no. 67 to 76 for the same constellations. The main distinctive feature of the new version is that it contains improved equatorial J2000.0 coordinates for 13446 stars (including those for 5052 stars with an allowance made for proper motions), based on the identifications with positional catalogs using finding charts, as well as on our new measurements. We searched for a number of stars on original plates from the collections of several observatories and using digital sky survey images. The new version also includes a file of remarks to the second and third GCVS volumes. Apart from a complete update of the positional information, we took into account several corrections that were found to be necessary after the publication of the second GCVS volume (1985). We present a list of references to new Internet resources. 相似文献
19.
Peter J. Brown Alice A. Breeveld Stephen Holland Paul Kuin Tyler Pritchard 《Astrophysics and Space Science》2014,353(1):89-96
This paper studies the motion of an infinitesimal mass in the framework of Robe’s circular restricted three-body problem in two cases; the first case is when the hydrostatic equilibrium figure of the first primary is an oblate spheroid, the shape of the second primary is considered as an oblate spheroid with oblateness coefficients up to the second zonal harmonic, while the first primary is a Roche ellipsoid in the second case and the full buoyancy of the fluid is taken into account. In case one; it is observed that there are two axial libration points on the line joining the centres of the primaries, points on the circle within the first primary are also libration points under certain conditions. It is further found that the first axial point is stable, while the second one is conditionally stable, and the circular points are unstable. It is found in case two that there is exist only one libration point (0,0,0) this point is stable. 相似文献