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111.
By considering a simple fluid model, we investigate the role of phase transitions in the ISM on the galaxy- scale gas dynamics. Cooling and heating timescales in the ISM are typically shorter than typical galactic rotation timescales, so the individual phases in the ISM can be assumed to be in temperature equilibrium with the radiation field. Using this approximation we can construct an equation of state which depends upon the average density and mass fractions in the individual phases. Previous studies suggest that there is an equilibrium phase fraction as a function of pressure. We incorporate evolution towards this equilibrium state as a relaxation term with a time to obtain equilibrium . We derive a condition in terms of a critical Mach number when one dimensional shocks should be continuous. For small values of the relaxation time we show that the relaxation term acts like a viscosity. We show with one dimensional simulations that increasing causes shocks to become smoother. This work suggests that phase changes can strongly effect the gas dynamics of the ISM across spiral arms and bars. 相似文献
112.
Mantra IB 《The Indonesian journal of geography》1984,14(47):19-34
Internal migration trends in Indonesia are reviewed using 1971 and 1980 census data. The author notes that although migration in 1971 was primarily to Jakarta and Lampung, by 1980 it was more diversified, with significant migration to some of the outer islands. The importance of the national transmigration program is noted. 相似文献
113.
114.
Donald D. Clayton 《Icarus》1977,32(3):255-269
I evaluate several nuclear and chemical problems related both to the recent scenario suggesting that the known isotopic anomalies in the solar system have resulted from a supernova near the protosolar nebula and to the model of extinct presolar carriers. Major features include: (1) Large quantities of extinct 248Cm and 36Cl are predicted from the Cameron-Truran model of a minor injection about 106 yr before condensation; (2) an extinct-carrier model of 26Mg is set forth in detail with a solid chemistry picture of the early solar system; (3) a major thermonuclear supernova responsible for 26Al, 244Pu, and 40K would have to have occurred several million years (3 m.y.) before condensation and contributed a large fraction of the major stable chemical elements; (4) carbon isotope families are to be expected if the oxygen isotope families are due to a late injection of 16O; (5) the Earth and E meteorites may have condensed primarily in a carbon-rich nebula existing before admixtures of a major late 16O-rich mixture; (6) the extinct-presolar-carrier model is the single best explanation of all anomalies. 相似文献
115.
Radiative recombination of N and O provides a significant source for auroral emission in the γ and δ bands of NO with selective population of vibrational levels in the A2Σ+ and C2Π states. This mechanism may account for emissions detected near 2150 Å. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 108 cm?1 near 140 km in an IBC III aurora. The corresponding density for N is about 5 × 107cm?3 and the concentration ratio has a value of about 5.5. 相似文献
116.
W.B. Hubbard 《Icarus》1977,30(2):305-310
A theory which is almost fully analytic is used to investigate Jupiter's cooling rate. We find that a simple model of contraction with adiabatic interior structure gives a total cooling time to the present which is in good agreement with the age of the solar system. The interplay between the surface condition and the cooling rate is exhibited and discussed. The current rate of change of the effective temperature is calculated to be ?1°K/0.145×109 yr. Discrepancies with fully numerical investigations of the Jovian age and cooling rate are noted. 相似文献
117.
Models are developed for the photochemistry of a CO2H2ON2 atmosphere on Mars and estimates are given for the concentrations of N, NO, NO2, NO3, N2O5, HNO2, HNO3, and N2O as a function of altitude. Nitric oxide is the most abundant form of odd nitrogen, present with a mixing ratio relative to CO2 of order 10?8. Deposition rates for nitrite and nitrate minerals could be as large as 3× 105 N equivalent atoms cm?2 sec?1 under present conditions and may have been higher in the past. 相似文献
118.
D.G. King-Hele 《Planetary and Space Science》1977,25(4):343-352
The satellite 1966-51C was launched in June 1966 into a polar orbit with perigee height 180 km, apogee height 3600 km, and orbital period 125 min. The orbit contracted rapidly under the influence of air drag, and the satellite decayed in March 1967. The only available observations are from the NASA Minitrack system, and 825 of these have been used with PROP6 orbit refinement program, to determine orbital parameters at 20 epochs. For most of these orbits the standard deviations in inclination and right ascension of the node are less than 0.002° (corresponding to about 200 m cross-track) and the standard deviations in eccentricity are less than 0.00002 (150 m in height).The variation in inclination is analysed to determine upper-atmosphere zonal wind speeds, with excellent resolution in local time. The results, for heights near 210 km and a representative latitude near 30°, indicate west-to-east winds of 100 ± 40 m/s for local time 18–21 h, and east-to-west winds of 80 ± 25 m/s for 02–04 h and 09–12 h local time. The values of the right ascension of the node are also analysed, and provide independent confirmation of the wind speeds obtained from the inclination. Analysis of the decrease in perigree distance indicates values of density scale height within 5% of those predicted by the COSPAR International Reference Atmosphere 1972, for the conditions experienced by 1966-51C. 相似文献
119.
D.J. Southwood 《Planetary and Space Science》1977,25(6):549-554
It is shown that the field line resonance phenomenon that occurs for quasi-transverse signals in a non-uniform cold plasma generally occurs for disturbances with a compressional magnetic component in a hot plasma like the ring current. The equations describing such localised signals are derived and discussed in various limits. It is pointed out that recent observations of low frequency compressional oscillations on spacecraft may be an example of such localised signals. 相似文献
120.
D. Lorenz 《Astrophysics and Space Science》1982,85(1-2):59-61
An exact cosmological solution to the Einstein-Maxwell equations for the case of Bianchi type III symmetry with stiff matter and an electromagnetic field is constructed. The behaviour of the solution near the singularity and at late stages of the expansion is investigated. 相似文献