共查询到20条相似文献，搜索用时 31 毫秒
1.
Russell Dubisch 《Icarus》1974,22(4):474-475
Errors introduced by simple averaging of the ratio of specific heats in a multi-component planetary atmosphere can be ～0.4%, which may be important when integrating through the atmosphere. 相似文献
2.
P. K. Bhatia 《Astrophysics and Space Science》1990,166(2):219-228
The non-radial oscillations of the homogeneous model of a star have been investigated taking into account the variation of the ratio of the specific heats. The stability of the oscillations thus set in is established. 相似文献
3.
We discuss, on the basis of general relativity, the density distribution of stars around a black hole at the centre of a globular cluster. We show that the radial density profile depends on the ratio of specific heats γ and the results by Peebles and by Bahcall and Wolf are particular cases with γ 4/3. We give also the projected density profiles, obtained by numerical integration, for ready comparison with observations. 相似文献
4.
Noboru Kaneko Kazuhiko Morita Tetsuya Satoh Kiyotaka Toyama Masaki Nishimura Makoto Maekawa 《Astrophysics and Space Science》2000,274(3):601-641
We reanalyze the propagation of one-dimensional small-amplitude disturbances of given real frequency ω in a radiating and
scattering grey medium using the Eddington approximation, which has been studied previously by us (Kaneko et al., 1976). Numerical results reveals three frequency regimes to be distinguished, and two wave modes always appear in each frequency
regime. The governing equations and analytic solutions are derived for all wave modes using Whitham's method modified into
quadratic form and approximate methods based on radiation thermodynamics. In the high-frequency regime appear the radiation-wave
and adiabatic sound modes, which are damped by opacity and radiative cooling, respectively. Wave patterns in the intermediate-frequency
and low-frequency regimes depend critically on the importance of radiation, for which the criterion is given in terms of the
ratio of total specific heats at constant pressure and constant volume. When the radition overwhelms the matter (radiation-dominated
case), the radiative mode in the intermediate-frequency regime is the constant-volume diffusion mode. When the matter overwhelms
the radiation (matter-dominated case), damped radiation-wave and damped radiation-diffusion modes newly appear between the
radiation-wave and constant-volume diffusion modes. The acoustic mode in the intermediate-frequency regime is the isothermal
sound mode,which is damped by radiative cooling at higher frequencies and by radiation-thermal drag force at lower frequencies.
Two modes appearing in the low-frequency regime are the isentropic radiation-acoustic and constant-pressure diffusion modes.
The absorption coefficient derived for the former is shown to be a radiation-thermodynamic extension of that of Landau and
Lifshitz (1987). The transition frequencies between all adjacent two modes are also derived to discuss the implications of
them.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
We study the fundamental modes of radiation hydrodynamic waves arising from one-dimensional small-amplitude initial fluctuations
with wave number k in a radiating and scattering grey medium using the Eddington approximation. The dispersion relation analyzed is the same
as that of Paper I (Kaneko et al., 2000), but is solved as a quintic in angular frequency ω while a quadratic in k
2 in Paper I. Numerical results reveal that wave patterns of five solutions are distinguished into three types of the radiation-dominated
and type 1 and type 2 matter-dominated cases. The following wave modes appear in our problem: radiation wave, conservative
radiation wave, entropy wave, Newtonian-cooling wave, opacity-damped and cooling-damped waves, constant-volume and constant-pressure
diffusion modes, adiabatic sound wave, cooling-damped and drag–force-damped isothermal sound waves, isentropic radiation-acoustic
wave, and gap mode. The radiation-dominated case is characterized by the gap between the isothermal sound and isentropic radiation-acoustic
speeds within which there is not any acoustic wave propagating with real phase speed. One of the differences between type
1 and type 2 matter-dominated cases is the connectivity of the constant-volume diffusion mode, which originates from the radiative
mode in the former case, while from the Newtonian-cooling wave in the latter case. Analytic solutions are derived for all
wave modes to discuss their physical significance. The criterion, which distinguishes between radiation-dominated and type
1 matter-dominated cases, is given by Γ0 = 9, where Γ0 = C
p
(tot)/C
V
(tot) is the ratio of total specific heats at constant pressure and constant volume. Waves in a scattering grey medium are also
analyzed, which provides us some hints for the effects of energy and momentum exchange between matter and radiation. 相似文献
6.
Adriane Steinacker † Yuri A. Shchekinov 《Monthly notices of the Royal Astronomical Society》2001,325(1):208-220
Within a framework of 2D magnetohydrodynamic (MHD) simulations, we explore the dynamical regimes initiated by a supernova explosion in a magnetized stratified interstellar medium (ISM). We concentrate on the formation of large-scale magnetic structures and outflows connected with the Parker instability. For the sake of simplicity we only show models with a fixed explosion energy corresponding to a single supernova (SN) occurring in host galaxies with different fixed values of the gravitational acceleration g and different ratios of specific heats. We show that in general, depending on these two parameters, three different regimes are possible: a slowly growing Parker instability on time-scales much longer than the galactic rotation period for small g; the Parker instability growing at roughly the rotation period, which for ratios of specific heats larger than one is accompanied by an outflow resulting from the explosion for intermediate g; and a rapidly growing instability and a strong blow-out flow for large g . By means of numerical simulations and analytical estimates we show that the explosion energy and gravitational acceleration which separate the three regimes scale as Eg 2 ∼constant in the 2D case. We expect that in the 3D case this scaling law is Eg 3 ∼constant . Our simulations demonstrate furthermore that a single SN explosion can lead to the growth of multiple Parker loops in the disc and large-scale magnetic field loops in the halo, extending over 2–3 kpc horizontally and up to 3 kpc vertically above the mid-plane of the disc. 相似文献
7.
Etienne Van Hemelrijck 《Earth, Moon, and Planets》1988,40(2):149-164
The latitudinal and seasonal variation of the direct solar radiation incident at the top of the atmosphere of Uranus and Neptune has been recalculated by use of updated values for the period of axial rotation and the oblateness. Values for the solar radiation are given in Watt per square meter instead of the unit used in earlier papers (calories per square centimeter per planetary day). The solar radiation averaged over a season and a year as a function of planetocentric latitude has also been reviewed. In addition, attention is made to the ratio of the solar radiation incident on an oblate planet to that incident on a spherical planet. 相似文献
8.
The shape and intensity distribution of tails for several large comets are estimated on the basis of grain properties in the solar radiation field. The following results are obtained: (1) The ratio of the maximum radiation pressure force to the gravitaional force acting on dust grains in cometary tails is found to be less than 2.5. This means that grains such as graphite particles in the size range 0.02–0.2 μm do not exist in them, because such particles would allow forces greater than 2.5 (2) Tail substances supplied near the time of perihelion passage for the Sun-grazing comet Ikeya-Seki (1965 VIII) and Comet Seki-Lines (1962 III) were composed of particular grains which had values of radiation pressure ratio less than 1.0. Therefore, it is concluded that the material was composed of silicate grains only, since iron grains had sublimated and there were no graphite particles. 相似文献
9.
In this paper, we suggest that a solar flare may be triggered by a lack of thermal equilibrium rather than by a magnetic instability. The possibility of such a thermal nonequilibrium (or catastrophe) is demonstrated by solving approximately the energy equation for a loop under a balance between thermal conduction, optically thin radiation and a heating source. It is found that, if one starts with a cool equilibrium at a few times 104 K and gradually increases the heating or decreases the loop pressure (or decreases the loop length), then, ultimately, critical metastable conditions are reached beyond which no cool equilibrium exists. The plasma heats up explosively to a new quasi-equilibrium at typically 107 K. During such a thermal flaring, any magnetic disruption or particle acceleration are secondary in nature. For a simple-loop (or compact) flare, the cool core of an active-region loop heats up and the magnetic tube of plasma maintains its position. For a two-ribbon flare, the material of an active-region (or plage) filament heats up and expands along the filament; it slowly rises until, at a critical height, the magnetic configuration becomes magnetohydrodynamically unstable and erupts violently outwards. In this case thermal nonequilibrium acts as a trigger for the magnetic eruption and subsequent magnetic energy release as the field closes back down. 相似文献
10.
A modified perturbation technique, developed earlier by the authors, has been used to study the effect of rapid uniform and differential rotation on the equilibrium structure of early type stars. The models are in convective equilibrium with significant radiation pressure. The effect of both uniform and differential rotation on various structural parameters like mass, radius, central condensation etc., are calculated for different values ofy
c (the ratio of central radiation pressure to central gas pressure). 相似文献
11.
Ni Xiang-bin 《Chinese Astronomy and Astrophysics》1988,12(4):320-323
We think that a steady material exchange in the upper solar atmosphere can act as a heat engine that cools the corona and heats the corona-chromosphere transition region. We have considered heat conduction from the corona and radiation loss in the transition region and have calculated the temperature, density and velocity distributions in the transition region. Also discussed is the relation between the material flux, the velocity boundary value and the thickness of the transition region. 相似文献
12.
Carolin Früh Thomas M. Kelecy Moriba K. Jah 《Celestial Mechanics and Dynamical Astronomy》2013,117(4):385-404
The orbital and attitude dynamics of uncontrolled Earth orbiting objects are perturbed by a variety of sources. In research, emphasis has been put on operational space vehicles. Operational satellites typically have a relatively compact shape, and hence, a low area-to-mass ratio (AMR), and are in most cases actively or passively attitude stabilized. This enables one to treat the orbit and attitude propagation as decoupled problems, and in many cases the attitude dynamics can be neglected completely. The situation is different for space debris objects, which are in an uncontrolled attitude state. Furthermore, the assumption that a steady-state attitude motion can be averaged over data reduction intervals may no longer be valid. Additionally, a subset of the debris objects have significantly high area-to-mass ratio (HAMR) values, resulting in highly perturbed orbits, e.g. by solar radiation pressure, even if a stable AMR value is assumed. Note, this assumption implies a steady-state attitude such that the average cross-sectional area exposed to the sun is close to constant. Time-varying solar radiation pressure accelerations due to attitude variations will result in un-modeled errors in the state propagation. This work investigates the evolution of the coupled attitude and orbit motion of HAMR objects. Standardized pieces of multilayer insulation (MLI) are simulated in a near geosynchronous orbits. It is assumed that the objects are rigid bodies and are in uncontrolled attitude states. The integrated effects of the Earth gravitational field and solar radiation pressure on the attitude motion are investigated. The light curves that represent the observed brightness variations over time in a specific viewing direction are extracted. A sensor model is utilized to generate light curves with visibility constraints and magnitude uncertainties as observed by a standard ground based telescope. The photometric models will be needed when combining photometric and astrometric observations for estimation of orbit and attitude dynamics of non-resolved space objects. 相似文献
13.
Kosarev I. B. Loseva T. V. Nemtchinov I. V. Shuvalov V. V. Greely R. 《Solar System Research》2002,36(4):278-292
This paper presents the results of the calculation of spectral and angular characteristics of radiation emitted by the disturbed region after the vertical impacts on the Martian surface of stony meteoroids with radii R
0 from 1 to 100 m at speeds of 11–20 km/s. The time dependences are given for the density of the radiation flux incident on horizontal surface areas located at different distances from the impact point. For small impactors (R
0= 1 m), the heating of the surface and surrounding gas by the radiation impulse from the hot region formed after the impact is insignificant even at the crater edge. However, the radiation impulse that heats up the surface is also emitted during the meteoroid flight through the atmosphere. Although this heating is insufficient to initiate evaporation, heat transfer by turbulent diffusion leads to the formation of a layer with temperatures that substantially exceed the initial temperature of the atmosphere. For large impactors (R
0 = 100 m), the total specific impulse of the plume radiation gives rise to the emergence of the heated layer with a thickness on the order of several meters within several kilometers of the impact point. The formation of this warm layer may lead to the formation of a high-speed jet moving along the Martian surface as well as eddies at the front of the precursor with a subsequent intense rise of dust. 相似文献
14.
《Chinese Astronomy and Astrophysics》1985,9(3):241-245
I suggest that the pulsation in solar microwave bursts is a modulation of gyro-synchrotron radiation. Whistler waves at the foot of a coronal loop (radio source) interact with nonthermal electrons with loss-cone distribution at the top. As a consequence, electrons outside the loss-cone diffuse into the loss-cone, pass through the loop foot, sink in the atmosphere, and emit gyro-synchrotron radiation as additional pulses. Electrons remaining outside the loss-cone give the background radiation of the burst.Assuming the configuration of a magnetic dipole lying below the photosphere, I calculated the period of pulsation to be 1 s- 1 min. The ratio of the pulse peak to background intensity is calculated to be 0 – 100%; the calculated pulse width is about 0.3 – 50 s. These values are consistent with the observed values. A brief discussion of the probable interpretation of fast, millisecond structures is also given. 相似文献
15.
The effect of a uniform magnetic field on the envelope convection zone of an 8.8M
star has been studied. The adiabatic exponents
i
(i=1, 2, 3), adiabatic temperature gradient and specific heat of stellar matter has been computed. It is shown that the magnetic field tends to increase the values of adiabatic temperature gradient and specific heats of stellar matter in the envelope convection zone. 相似文献
16.
A.L. Poplavsky 《New Astronomy》2012,17(3):362-367
The interaction of fragmented plasma of active galactic nuclei jets with galactic haloes via gravitational scattering and lensing by dark matter subhaloes is studied using analytical calculations and numerical Monte-Carlo method. The lensing of jet radiation by halo masses is found to be negligible and unobservable. Moving through a galactic halo jet plasma fragments are sequentially deflected on hyperbolic orbits by gravitational field of subhaloes and deviates at some angles when leaving halo, causing widening of the jet. Based on this model jet opening angles are calculated numerically for various values of jet and halo characteristics. Though these angles are very small, gravitational scattering by halo masses results in specific radial profile of jet radiation intensity, that does not depend on halo mass distribution and jet properties. The intensity of jet radiation, obeying the derived profile, decreases by reasonable observable factors giving possibility to probe the presence of dark matter subhaloes. 相似文献
17.
We investigate linear acoustic-gravity waves in three different semi-empirical model atmospheres of large sunspot umbrae. The sunspot filter theory is applied, that is, the resonant transmission of vertically propagating waves is modelled. The results are compared with observed linear sunspot oscillations. For three umbral models we present the transmission coefficients and the energy density of the oscillations with the maxima of transmission. The height dependence of the adiabatic coefficient (the ratio of specific heats) strongly influences the calculated resonance frequencies. The variable can explain the observed closely spaced resonance period peaks. The first resonance in the 3 min range is interpreted as a resonance of the upper chromosphere only, while the higher order peaks are resonances of the whole chromosphere. 相似文献
18.
The total ionizing component of cosmic radiation was measured up to an altitude of 1550 km. An upper bound to the ratio of average-to-minimum specific ionization was determined by comparing the ionization with the count-rate observations from the Explorer IV satellite. This result implied that protons are the predominant species which gave rise to the observed ionization. 相似文献
19.
M. J. Miketinac 《Astrophysics and Space Science》1974,28(1):193-203
Frequencies of non-radial oscillation of polytropic models of stars, belonging to spherical harmonics of ordersl=1, 2 and 3, are evaluated, in a second approximation, by a variational method. Equilibrium configurations in the presence of toroidal magnetic fields are obtained numerically without any restriction on the field strength. The value of the ratio of the specific heats, , is assumed to be equal to 5/3 and only two polytropic indeces,n=1.5 and 3.0, are considered. It is found that a polytropic star stays stable for magnetic fields considerably stronger than expected from the results obtained by the weak field perturbation methods. 相似文献
20.
Leonard C. Rosen 《Astrophysics and Space Science》1969,5(1):92-102
A perturbation treatment is used to find the distribution functions from the Boltzmann transport equation for a two-component ionized, degenerate gas. General expressions are found for the diffusion coefficient and relative diffusion velocity. Tables are given for specific values of spin and mass ratio. 相似文献