共查询到20条相似文献，搜索用时 31 毫秒
1.
This paper discusses the propagation of waves in the early Universe simulated by rarefied, homogeneous ambiplasma (a mixed matter-antimatter ionized gas) placed in a uniform magnetic field. A rich variety of oscillations appear due to enhanced degrees of freedom in the ambiplasma. These oscillations have been analyzed for the propagation vector along and across the direction of magnetic field both in a symmetric and asymmetric ambiplasma. It is found that the oscillations do not grow in different situations which have been discussed. Dispersion curves have been drawn and various cut-offs and resonances have been found out. The study is concluded by highlighting some characteristic features of the waves in the ambiplasma. 相似文献
2.
Sylvie Jancart Anne Lemaitre Vincent Letocart 《Celestial Mechanics and Dynamical Astronomy》2003,86(4):363-383
Interested in the role of the inclination in our results (Jancart and Lemaitre, 2001), we analyze the process of resonance trapping due to general dissipation forces in the frame of the spatial restricted three body problem and in the case of external mean motion resonances. We compute our simulations by using the three-dimensional Extended Schubart Averaging integrator developed by Moons (1994) for all mean motion resonances. We complete it by adding the averaged contributions of general dissipative forces like Murray has proposed in the article (1994). The behavior of the inclination is especially pointed out. 相似文献
3.
In this paper we examine the recently introduced Dvali-Gabadadze-Porrati (DGP) gravity model. We use a space-time metric in which the local gravitation source dominates the metric over the contributions from the cosmological flow. Anticipating ideal possible solar system effects, we derive expressions for the signal time delays in the vicinity of the Sun. and for various ranges of the angle θ of the signal approach, The time contribution due to DGP correction to the metric is found to be proportional to b 3/2/c 2 r 0. For r 0 equal to 5 Mpc and θ in the range [−π/3,π/3], Δt is equal to 0.0001233 ps. This delay is extremely small to be measured by today’s technology but it could be probably measurable by future experiments. 相似文献
4.
本文叙述了电水准的采用能适应低纬子午环的高精度要求 ,分析了水平差的个别测量值产生跳变的原因 :既有其本身的结构问题 ,也有仪器其它部件的不良影响。文中还介绍了对电水准作局部改善的情况。 相似文献
5.
The Tunguska event on 30 June 1908 has been subjected to much speculation within different fields of research. Publication of the results of the 1961 expedition to the Tunguska area (Florensky, 1963) supports that a cometary impact caused the event. Based on this interpretation, calculations of the impactor energy release and explosion height have been reported by Ben-Menahem (1975), and velocity, mass, and density of the impactor by Petrov and Stulov (1975). Park (1978) and Turco et al., 1981, Turco et al., 1982, used these numbers to calculate a production of ca. 30 × 106 tons of NO during atmospheric transit. This paper presents a high-resolution study of nitrate concentration in the Greenland ice sheet in ca. 10 years covering the Tunguska event. No signs of excess nitrate are found in three ice cores from two different sites in Greenland in the years following the Tunguska event. By comparing these results with results for other aerosols generally found in the ice, the lack of excess NO3? following the Tunguska event can be interpreted as indicating that the impactor nitrate production calculated by Park (1978) and Turco et al., 1981, Turco et al., 1982 are 1–2 orders of magnitude too high. To explain this it is suggested, from other lines of reasoning, that the impactor density determined by Petrov and Stulov (1975) probably is too low. 相似文献
6.
M.S. Kovner V.V. Lebedev T.A. Plyasova-Bakounina V.A. Troitskaya 《Planetary and Space Science》1976,24(3):261-267
The generation of low-frequency waves in the solar wind by the flux of protons accelerated in the magnetosheath is considered. It is shown that pulsations are produced in two partly overlapping frequency ranges. The growth rate of waves is maximal when the angle θ between the direction of the interplanetary magnetic field and the front of the bow shock is not equal . The dependence of the increment of perturbation on the solar wind velocity is analysed. A satisfactory agreement between theory and experimental results on the connection of Pc3–4 properties and parameters of the solar wind is obtained. 相似文献
7.
One of the goals of comet research is the determination of the chemical composition of the nucleus because it provides us
with the clues about the composition of the nebula in which comet nuclei formed.
It is well accepted that photo-chemical reactions must be considered to establish the abundances of mother molecules in the
coma as they are released from the comet nucleus or from distributed dust sources in the coma. However, the mixing ratios
of mother molecules in the coma changes with heliocentric distance. To obtain the abundances in the nucleus relative to those
in the coma, we must turn our attention to the release rates of mother molecules from the nucleus as a function of heliocentric
distance. For this purpose, we assume three sources for the coma gas: the surface of the nucleus (releasing mostly water vapor),
the dust in the coma (the distributed source of several species released from dust particles), and the interior of the porous
nucleus (the source of many species more volatile than water). The species diffusing from the interior of the nucleus are
released by heat transported into the interior. Thus, the ratio of volatiles relative to water in the coma is a function of
the heliocentric distance and provides important information about the chemical composition and structure of the nucleus.
Our goal is to determine the abundance ratios of various mother molecules relative to water from many remote-sensing observations
of the coma as a function of heliocentric distance. Comet Hale-Bopp is ideal for this purpose since it has been observed using
instruments in many different wavelength regions over large ranges of heliocentric distances. The ratios of release rates
of species into the coma are than modeled assuming various chemical compositions of the spinning nucleus as it moves from
large heliocentric distance through perihelion. Since the heat flow into the nucleus will be different after perihelion from
that before perihelion, we can also expect different gas release rates after perihelion compared to those observed before
perihelion. Since not all the data are available yet, we report on progress of these calculations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
9.
M. R. Sanad 《Astrophysics and Space Science》2013,344(2):389-404
We present low and high resolution ultraviolet spectra of the Capella spectroscopic binary system from the observations taken by the International Ultraviolet Explorer (IUE) during the period between 1978–1990 and 1978–1995. Thirteen profile of Capella showing variations of line fluxes at different orbital phases are presented. This paper focuses on the C IV emission line at 1550 Å produced in the transition region of the secondary star and Mg II emission lines at 2800 Å produced in the stellar chromosphere of the secondary star by calculating spectral line fluxes. Our results show that there are significant variations of line fluxes with time. These spectral variations are similar to that found in the EUV by Dupree and Brickhouse (in Int. Astron. Union Symp. 176P:184D, 1995) in the UV for H 1 Ly?α by Ayres et al. (in Astrophys. J. 402:710A, 1993), and in the near IR by Katsova (in Astrophys. Space Sci. 252:427K, 1997). We attribute these variations in line fluxes to the variations of both density and temperature in the line emitting regions as a result of the intermediate-scale magnetic fields responsible for stellar activity leading to these spectral variations. 相似文献
10.
The depth variations of the fossil cosmic ray tracks and agglutinates have been examined in the (0.6–0.7)m deep Apollo 12 and 16 drive cores, in the 2.4 m Apollo 15 deep drill core and in a 0.6 m long section of the Apollo 17 deep drill core. These data indicate Moon-wide short duration episodes of impacts of meteorites of size 10 cm–1m on the lunar surface. Based on the longest continuous Apollo 15 deep drill core record, these impact episodes occurred about 150, 400 and 700 m.y. ago. The enhancements in the meteorite flux may be due to solar dynamical processes or they may be related to excursions of the solar system, once in each orbit, through a certain dusty region of the galaxy.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May 1978. 相似文献
11.
We propose an interpretation of the enrichments in volatiles observed in the four giant planets with respect to the solar abundance. It is based on the assumption that volatiles were trapped in the form of solid clathrate hydrates and incorporated in planetesimals embedded in the feeding zones of each of the four giant planets. The mass of trapped volatiles is then held constant with time. The mass of hydrogen and of not trapped gaseous species continuously decreased with time until the formation of the planet was completed, resulting in an increase in the ratio of the mass of trapped volatiles to the mass of hydrogen (Gautier et al., Astrophys. J. 550 (2001) L227). The efficiency of the clathration depends upon the amount of ice available in the early feeding zone. The quasi-uniform enrichment in Ar, Kr, Xe, C, N, and S observed in Jupiter is reproduced because all volatiles were trapped. The non-uniform enrichment observed in C, N and S in Saturn is due to the fact that CH4, NH3, and H2S were trapped but not CO and N2. The non-uniform enrichment in C, N and S in Uranus and Neptune results from the trapping of CH4, CO, NH3 and H2S, while N2 was not trapped. Our scenario permits us to interpret the strongly oversolar sulfur abundance inferred by various modelers to be present in Saturn, Uranus and Neptune for reproducing the microwave spectra of the three planets. Abundances of Ar, Kr and Xe in these three are also predicted. Only Xe is expected to be substantially oversolar. The large enrichment in oxygen in Neptune with respect to the solar abundance, calculated by Lodders and Fegley (Icarus 112 (1994) 368) from the detection of CO in the upper troposphere of the planet, is consistent with the trapping of volatiles by clathration. The upper limit of CO in Uranus does not exclude that this process also occurred in Uranus. 相似文献
12.
Using simultaneous observations of the same solar regions in the lines H and Civ 1548 Å, we have derived schematic models of closed magnetic lines from dynamical constraints. We conclude that the magnetic loops are closed at higher levels above facular than above non-facular regions. This result remains valid whatever are the assumed density models and even if we take into account the 3 min oscillations. The center-to-limb behaviour is well predicted by taking into account the relative opacity in chromosphere and transition region. 相似文献
13.
B. N. G. Guthrie 《Astrophysics and Space Science》1976,43(2):425-431
The sky distribution of deviations from the mean Hubble relation for the brightest galaxies in clusters is non-random for the velocity range 4000<V
r<25 000 km s–1. Deviations in visual magnitude are mainly positive in one large region of the sky and mainly negative in another region; the difference between the regions is 0.37±0.08
m
and is independent of colour. Various explanations are discussed briefly, and galactic or intergalactic absorption may be excluded. 相似文献
14.
Zhang Gong-liang 《Chinese Astronomy and Astrophysics》1982,6(4):350-355
Taking as basis my dimensional solution of the propagation equation of solar cosmic rays in interplanetary space and using the equivalent diffusion coefficient found from observed data on solar protons, I discuss the effects of propagation on the hydrogen-to-hellum ratio Including its variation with the speed of the solar wind and with location in space. After eliminating the variations with solar distance and energy from the HEOS and PIONEER data collected by Perron et al., this ratio will be seen to increase with the magnetic longitude of the parent flare. The Initial value of the hydrogen-to-helium ratio at the Sun's surface, obtained after applying the corrections for propagation, is close to the value in the solar wind. 相似文献
15.
Nevena St. Markova 《Astrophysics and Space Science》1986,123(1):5-19
In the Coudé focus of the 2 m RCC telescope at the National Astronomical Observatory of the Bulgarian Academy of Science 47 spectrograms covering the range from 3500 to 4900 Å (about 1400 Å) with a reciprocal dispersion of 9 Å mm–1 and a spectral resolution of 0.18 Å were obtained. The photometric and position behaviour of Balmer lines were investigated over a long time-scale, i.e. March 1981 to August 1982.The hydrogen line profiles were rectified in the way discribed by de Groot (1969). It is found that the absorption consists of three and sometimes four components. Their position behaviour may be expalined by the existence of two kinds of shells: pulsating and steadily expanding, and it is quite possible that shells of the first type may become shells of the second type in the outer parts of the P Cyg envelope.The total emission and absorption equivalent widths of the H11, H9, and H lines change with conspicuous minima and maxima. The amplitude of these variations increases with decrease in the upper quantum number. For example,W
tot
abs
change by about 38% for H and 22% for H9.Our data suggest a periodic change in the radial velocities, intensity of each separate absorption component, total equivalent widths and profiles. 相似文献
16.
The velocity of microturbulent motions in the solar photosphere at the level of formation of weak Fraunhofer lines (h 150 km) is found to be 0.1 ± 0.2 km s–1. The observations have been performed with the double-pass spectrometer in Kiev. Apart from thermal motions and damping effects we have taken into account convective and wave motions when calculating the broadening of absorption lines. 相似文献
17.
Rudolf A. Treumann 《Astrophysics and Space Science》1993,201(1):135-147
Information in the universe evolves according to a nonlinear law, which results from a combination of nonlinear dynamics and quantum theory. The Kolmogoroff-Sinai entropy rate of the Universe evolves in inverse proportion to the temperature. Since the evolution of temperature is known from standard cosmology, the time dependence of the universal entropy rate can be determined and the temporal evolution of the universal information content can be calculated. Information starts growing at the enormous rate of 1044 bits per second from an initial value of at least 2 (seven) bits at Planck time. However, it reaches its contemporary value only if one or more inflationary phases have been passed by the Universe in the course of its evolution. 相似文献
18.
本文叙述了度盘偏斜现象及其对读数显微镜Reticon比例尺测定值的影响 ,分析了产生度盘偏斜的原因和修正方法 ,文章讨论了是否需要对比例尺加上与天顶距有关的修正项问题 ,结论是只要把度盘偏心控制在 5μm以内 ,就不必加改正。 相似文献
19.
Rodolfo Batista Negri Antonio Fernando Bertachini de Almeida Prado Alexander Sukhanov 《Celestial Mechanics and Dynamical Astronomy》2017,129(3):269-284
The swing-by maneuver is a technique used to change the energy of a spacecraft by using a close approach in a celestial body. This procedure was used many times in real missions. Usually, the first approach to design this type of mission is based on the “patched-conics” model, which splits the maneuver into three “two-body dynamics.” This approach causes an error in the estimation of the energy variations, which depends on the geometry of the maneuver and the system of primaries considered. Therefore, the goal of the present paper is to study the errors caused by this approximation. The comparison of the results are made with the trajectories obtained using the more realistic restricted three-body problem, assumed here to be the “real values” for the maneuver. The results shown here describe the effects of each parameter involved in the swing-by. Some examples using bodies in the solar system are used in this part of the paper. The study is then generalized to cover different mass parameters, and its influence is analyzed to give an idea of the amount of the error expected for a given system of primaries. The results presented here may help in estimating errors in the preliminary mission analysis using the “patched-conics” approach. 相似文献
20.
X-ray photographs obtained with a zone plate camera on October 3, 1967 in the wavelength band 49.5–52.5 Å have been investigated photometrically.The most intense X-ray emission corresponds with active regions in H and Ca ii. About one quarter of the total solar flux is emitted by the three brightest X-ray sources (A, E and J). X-ray emission from quiet regions is also observed. Limb brightening is found, also at the poles, which indicates a higher electron density at the poles than during solar minimum.The brightest X-ray regions have a very small core of the order of 20. No relation to magnetic field strengths of sunspots has been found. However, a correlation with active prominences cannot be ruled out. X-ray source A is related either to prominence activity or to flare activity. One X-ray region (J) is probably related to flare activity.Assuming an electron temperature of 3 × 106K to 5 × 106K for coronal active regions an emission measure of a few times 1049 cm–3 is derived, which yields an electron density of a few times 1010 cm–3. 相似文献