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1.
In this paper, economical and stable recurrence formulae for the Earth's zonal potential and its gradient for Burdet's regularized theory will be established for any number N of the zonal harmonic coefficients. A general recursive computational algorithm based on these formulae is also established for the initial value problem of Burdet oscillator for the prediction of artificial satellites in the Earth's gravitational field with axial symmetry. Applications of the algorithm for the problem of the final state prediction are illustrated by numerical examples of three test orbits each for two geopotential models corresponding to N = 2 and N = 36.A final state of any desired accuracy is obtained for each case study, a result which shows the flexibility of the algorithm.Dept. of Astronomy, KAU 相似文献
2.
Peter M. Millman 《Earth, Moon, and Planets》1973,8(1-2):228-240
The integrated mass indexS for solid particles in the solar system is defined by the equationN = (const)m
–S, whereN is the number of particles counted down to a lower limit of massm. Independent values ofS found from various observational programs are reviewed. These lie generally in the range from 0.4 to 1.4 for the average background of particles, and include data from lunar craters, satellite impacts, meteors, meteorites and asteroids. The trend ofS with mass is reasonably well established for masses less than one gram, but there are many gaps in our knowledge concerning the objects of greater mass.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. 相似文献
3.
Mohamed Adel Sharaf Mervat El-Sayed Awad Mona A. Banaja 《Astrophysics and Space Science》1987,133(2):339-353
In this paper, economical and stable recurrence formulae for the Earth's zonal potential and its gradient for the KS regularized theory will be established for any numberN of the zonal harmonic coefficient. A general recursive computational algorithm based on these formulae is also established for the initial value problem of the KS theory for the prediction of artificial satellites in the Earth's gravitational field with axial symmetry. Applications of the algorithm for the problem of the final state prediction are illustrated by numerical examples of three test orbits each for two geopotential models corresponding toN=2 andN=36. A final state of any desired accuracy is obtained for each case study, a result which shows the flexibility of the algorithm. 相似文献
4.
Many problems in galactic dynamics require computer speeds orders of magnitude larger than what can be achieved on current single-processor machines. In the near future such speeds are likely to become available through computer architectures based on large-scale, fine-grained parallelism. An example of a highly parallel computer is the Connection Machine, with up to 65,636 processors. We have benchmarked gravitationalN-body algorithms on the Connection Machine, and compared those with similar benchmarks which we have obtained on more traditional vector supercomputers. Our conclusions are: (1) The direct summation algorithm, with of orderN
2 interactions forN particles, can be made to run with high efficiency on either type of computer. As a result, the Connection Machine clearly wins in speed over all supercomuters tested, with the exception of an 8-processor ETA, which shows a comparable performance. (2) A more efficient tree algorithm reduces the growth of the number of interactions fromN
2 toN logN. However, the greater complexity of this algorithm causes a considerable degradation of efficiency, by a factor which is larger on the Connection Machine than on vector supercomputers. As a result, out tree code runs at comparable speeds on both types of machines, with the notable exception of the 8-processor ETA, which has an extrapolated speed for running our tree code which is higher than any of the other machines we have tested. 相似文献
5.
We derive general results on the existence of stationary configurations for N co-orbital satellites with small but otherwise arbitrary masses m
i
, revolving on circular and planar orbits around a massive primary. The existence of stationary configurations depends on
the parity of N. If N is odd, then for any arbitrary angular separation between the satellites, there always exists a set of masses (positive or
negative) which achieves stationarity. However, physically acceptable solutions (m
i
> 0 for all i) restrict this existence to sub-domains of angular separations. If N is even, then for given angular separations of the satellites, there is in general no set of masses which achieves stationarity. The case N=3 is treated completely for small arbitrary satellite masses, giving all the possible solutions and their stability, to within
our approximations. 相似文献
6.
Mohamed Adel Sharaf 《Astrophysics and Space Science》1978,57(2):469-478
In this paper, we establish a general variational method for Milne's integral equation. Moreover, a recursive computational algorithm for the method is also constructed. To illustrate the precision of the method as well as the computational algorithm, a numerical example forN=20 is given. 相似文献
7.
The thermal histories of two geologically active satellites of Saturn—Titan and Enceladus—are discussed. During the Cassini mission, it was found that there are both nitrogen-containing compounds—NH3 and N2-and CO2 and CH4 in the water plumes of Enceladus; at that, ammonia is the prevailing form. This may testify that during evolution, the material
of the satellite was warmed up to T ∼ 500–600 K, when NH3 (the form of nitrogen capable of being accreted) could only be partly converted into N2. Contrary to Enceladus, the temperature inside Titan probably reached values higher than 800 K or even higher than 1000 K,
since the process of the chemical dissociation of ammonia was completely finished on this satellite and its atmosphere contains
only molecular nitrogen. While the internal heating of Titan up to high temperatures can be explained by its large mass, the
heating source for Enceladus’ interior is far from evident. Such traditional heating sources as the energy of gravitational
differentiation and the radiogenic heating due to shortliving 26Al and 60Fe could not be effective. The first one is because of the small size of Enceladus (RE ≈ 250 km), and the inefficiency of the second one is caused by the fact that the satellite was formed not earlier than 8–10
Myr after the formation of calcium and aluminum-enriched inclusions in carbonaceous chondrites (CAI), i.e., after 26Al had completely decayed. In the present paper, we propose other heating mechanisms-the heat of long-living radioactive elements
and tidal heat, which could provide the observed chemical composition of the water plumes of Enceladus rather than only the
differentiation of its protomatter into the ironstone core and the ice mantle. 相似文献
8.
X-ray bursts observed for energies lower than 25 keV are usually interpreted as being produced by a thermal plasma with several million degrees of temperature.A small number of events recorded at Arcetri by real time telemetry of SOLRAD 9 satellite agrees with a thermal interpretation and gives temperatures ranging between 10 × 106 and 30 × 106K and emission measures, N
e
2
dV, between 1047 and 1048 cm–3.An impulsive event recorded on January 7, 1969 shows an anomalous behaviour. In this case the emission has been attributed to bremsstrahlung radiation from electrons with a power law energy distribution dN = KE
-
dE. The values of the spectral index and of the emission measure are given.A tentative interpretation of the event is suggested and the way to produce non-relativistic electrons with a power law energy distribution is investigated. 相似文献
9.
Mohamed Adel Sharaf 《Astrophysics and Space Science》1981,78(2):359-400
In this paper of the series, literal analytical expressions for the coefficients of the Fourier series representation ofG will be established for anyx
i; withn, N positive integers and |i|<1 fori=1, 2, ... n. Moreover, the recurrence formulae satisfied by these coefficients will also be established. Illustrative analytical examples and a full recursive computational algorithm, with its numerical results, are included. The applications of the recurrence formulae are also illustrated by their stencils. As by-products of the analyses are two important periodic integrals developed analytically and computationally. 相似文献
10.
Amr A. Sharaf 《Earth, Moon, and Planets》1993,62(2):93-116
In this paper, a motion prediction algorithm based on the KS regular elements is developed for the motion in the Earth's gravitational field with axial symmetry. The algorithm is of recursive nature and general in the sense that it could be applied for any conic motion whatever the number of zonal harmonic coefficientsN 2 may be. Applications of the algorithm for the problem of the final state prediction are illustrated by numerical examples of eight typical ballistic missiles for geopotential model with zonal harmonic terms up toJ
36. A final state of any desired accuracy is obtained for each case study, a result which shows the efficiency and the flexibility of the algorithm. 相似文献
11.
We have detected new HD absorption systems at high redshifts, z
abs = 2.626 and z
abs = 1.777, identified in the spectra of the quasars J0812+3208 and Q1331+170, respectively. Each of these systems consists
of two subsystems. The HD column densities have been determined: log N
HDA = 15.70 ± 0.07 for z
A = 2.626443(2) and log N
HDB = 12.98 ± 0.22 for z
B = 2.626276(2) in the spectrum of J0812+3208 and log N
HDC = 14.83 ± 0.15 for z
C = 1.77637(2) and log N
HDD = 14.61 ± 0.20 for z
D = 1.77670(3) in the spectrum of Q1331+170. The measured HD/H2 ratio for three of these subsystems has been found to be considerably higher than its values typical of clouds in our Galaxy.We
discuss the problem of determining the primordial deuterium abundance, which is most sensitive to the baryon density of the
Universe Ωb. Using a well-known model for the chemistry of a molecular cloud, we have estimated the isotopic ratio D/H=HD/2H2 = (2.97 ± 0.55) × 10−5 and the corresponding baryon density Ωb
h
2 = 0.0205−0.0020+0.0025. This value is in good agreement with Ωb
h
2 = 0.0226−0.00060.0006 obtained by analyzing the cosmic microwave background radiation anisotropy. However, in high-redshift clouds, under conditions
of low metallicity and low dust content, hydrogen may be incompletely molecularized even in the case of self-shielding. In
this situation, the HD/2H2 ratio may not correspond to the actual D/H isotopic ratio. We have estimated the cloud molecularization dynamics and the
influence of cosmological evolutionary effects on it. 相似文献
12.
K. Aksnes 《Celestial Mechanics and Dynamical Astronomy》1976,13(1):89-104
On the basis of expressions derived by Kozai, and new ones developed here, a detailed, semianalytic algorithm is presented for calculating radiation-pressure perturbations in the Keplerian elements. Through some simple modifications, the algorithm is also made to hold whene=0 and/ori=0. The perturbations are obtained by summing over the sunlit segment of the satellite's orbit during each revolution or part thereof. The end points of this segment are evaluated numerically once per revolution. The effect of the inherent uncertainties in the boundaries of the Earth's shadow is discussed. The algorithm is tested by means of numerical integration of the equations of motion and through comparisons with observations of the balloon satellite 1963 30D during a 200-day interval. 相似文献
13.
It has been found that sunspot cycles 10–21, represented by quarterly mean values of Zürich sunspot number, can be suitably described by the F-distribution density function provided it is modified by introducing five characteristic parameters, in order to achieve an optimal fitting of each cycle. The average cycle calculated from cycles 10–21 has been used as a basis to forecast time and magnitude of the maximum of each cycle, as a function of various numbers of the first quarterly mean values in the beginning N = 8 to 16 quarters. The standard deviations at a 99% significance level calculated from the observed values depend on N, and vary from 1.6 to 1.1 quarters and 65 to 16 units of sunspot number. A rather sufficient forecast is obtained from N = 12 quarters (with inaccuracy of ± 1.5 quarters and ± 24 units); the forecast for cycle 22 yielded, for N = 12, the values t
m
= (15.4 ± 1.5) quarters ( 1990.I) and f(t
m
) = (175 ±24 units). 相似文献
14.
We analyze the process of absorption which is produced under conditions of strong magnetic fields in the magnetosphere of a compact stellar source. The magnitude of the magnetic field lies in the range 1012-1013 Gauss, which are common values in modelling pulsars.Analyzing the first absorption lines (N = 0 toN 3) we arrive to the conclusions that the orientation of electron's spin does not change if it absorbs a photon. It means it maintains its orientation opposite to the external magnetic field after the absorption. For the fundamental line (N = 0 toN = 1) the dominant polarization of the photon is. For the next two transition lines (N = 0 toN = 2 andN = 0 toN = 3), the polarization is. In the case that the absorption lines belong to one of the first three transition lines, then the mean photon energy can be approached with the relation
=AN B and thus we get an error of 13.6% with respect to values obtained by the theoretical expression. Also we applied our absorption transition probabilities some known pulsar spectra and we determine which transition feature corresponds in their spectra.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9-13 November, 1992. 相似文献
15.
Sergei M. Poleshchikov 《Celestial Mechanics and Dynamical Astronomy》2003,85(4):341-393
The sets of L-matrices of the second, fourth and eighth orders are constructed axiomatically. The defining relations are taken from the regularization of motion equations for Keplerian problem. In particular, the Levi-Civita matrix and KS-matrix are L-matrices of second and fourth order, respectively. A theorem on the ranks of L-transformations of different orders is proved. The notion of L-similarity transformation is introduced, certain sets of L-matrices are constructed, and their classification is given. An application of fourth order L-matrices for N-body problem regularization is given. A method of correction for regular coordinates in the Runge–Kutta–Fehlberg integration method for regular motion equations of a perturbed two-body problem is suggested. Comparison is given for the results of numerical integration in the problem of defining the orbit of a satellite, with and without the above correction method. The comparison is carried out with respect to the number of calls to the subroutine evaluating the perturbational accelerations vector. The results of integration using the correction turn out to be in a favorable position. 相似文献
16.
The EUV observations from the SMM satellite of two sunspots are presented here. These observations show the sunspots (a) to be regions of lower intensity than the surrounding plage, contrary to that found by previous authors, and (b) to have line intensities which vary little over a period of several hours. An upper limit to mass flows of 2km s-1 is derived, indicating a relatively simple energy balance for the chromosphere-corona transition zone with thermal conduction being balanced by radiative losses. Electron densities derived from Niv to Civ line ratios imply electron pressures (log N
eTe) of 15.0 to 15.3. 相似文献
17.
In the solar system satellite systems of Jupiter, Saturn and Uranus are typical ones. The distribution of the semi-major axis of satellite orbits in each system may be expressed by an empirical formula corresponding to the Titius-Bode law. We found that it can be written as an = B′ · Bn, where B′ and B are constants. Values of B′ and B depend on formation conditions of each system. Satellites should be formed in the gas-satellitesimal disk around a planet and by aggregation of satellitesimals. The gas is the major component in the disk and its damping effect must play an important role in the process of aggregation of satellitesimals. It may be proved that radial small perturbation in the disk can cause the gravitational instability and the formation of gaseous rings with increased density, where satellitesimals can easy aggregat into satellites. 相似文献
18.
Patrick Petitjean 《Astrophysics and Space Science》2002,281(1-2):467-470
I describe briefly the status of an ongoing mini-survey for molecular hydrogen in high-redshift Damped Lyman-α systems using
UVES at the VLT. H2 is detected in about 30% of the cases. When H2 is not detected the molecular fraction f = 2N(H2)/(2N(H2)+N(HI) is smaller than 10-5. Therefore, most of the DLA systems arise in warm (T > 3000 K) and diffuse neutral gas embedded in a strong UV flux. The very recent detection of HD molecules in a Damped Lyman-α
system at z
abs = 2.337 demonstrates the possibility to discuss the high redshift chemistry.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
19.
Electron impact excitation rates for Fexxi, calculated with theR-matrix code, are used to determine theoretical electron density sensitive emission line ratios involving transitions in the 121–146 wavelength range. The observed ratios for a solar flare, obtained with a grazing spectrometer on board the OSO-5 satellite, imply electron densities which are consistent, with discrepancies that do not exceed 0.3 dex. In addition, the derived values ofN
e
are similar to those estimated for the high temperature regions of other solar flares. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations. 相似文献
20.
Andrej G. Sokolsky Akmal A. Vakhidov Nickolay N. Vasiliev 《Celestial Mechanics and Dynamical Astronomy》1995,63(3-4):357-374
The problem of computation of elliptic Hansen coefficients and their derivatives is considered for constructing a motion theory of an artificial Earth satellite with large eccentricity. An algorithm for analytical and numerical computation of these coefficients and their derivatives is described. The recurrence relations for derivatives of the first and second order and initial values for recurrences are obtained. As an example, numerical values of some elliptic Hansen coefficients are given for the orbit with eccentricityk=0.74. 相似文献