共查询到20条相似文献，搜索用时 31 毫秒
1.
The criterion for the secular stability of nuclear burning is revised for times shorter than the effective time of relaxation into diffusion.Using the Cattaneo equation for the heat flux, we show that before the establishment of steady state resistive flow, conditions for the stability of nuclear burning change of sign quasiperiodically, for any given value of the gravothermal specific heat. Implications of this result in calculations of nuclear fusion in accreting neutron star envelopes are suggested. 相似文献
2.
G.V. Groves 《Planetary and Space Science》1983,31(1):67-71
The global mean vertical energy flux of the (1,1,1) mode of atmospheric oscillation is evaluated at 80 km altitude by classical tidal theory for mean January, April, July and October conditions using revised profiles of water vapour and ozone heating. Fluxes calculated for January and July are lower than those for April and October due to seasonal changes in water vapour, solar declination and Sun-Earth distance. Flux values obtained are compared with a previously stated requirement for maintaining the residual thermosphere and are adequate unless damping, which is ignored in the present calculations, introduces a factor of more than an order of 10 in magnitude. The relative changes of flux between the above four months are noted to be similar in form to the semi-annual variation of thermospheric air densities. 相似文献
3.
E.R. Priest 《Astrophysics and Space Science》1998,264(1-4):77-100
Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it
is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are
outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging
flux motions as the key for x-ray bright points. Furthermore, it has been shown that the large-scale diffuse corona is heated
rather uniformly, so that turbulent reconnection by braiding or ion-cyclotron waves driven by network micro-flares are prime
candidates. Finally, reconnection is the natural explanation for a wide variety of phenomena discovered by SOHO including
explosive events, blinkers, the magnetic carpet and even possibly tornadoes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
The heating of the solar corona by resistive turbulence of coronal magnetic fields is considered. The theory of this process, based on the Taylor-Heyvaerts-Priest hypothesis and a magnetic relaxation equation, is developed. Such an approach allows one to obtain the successive magnetic reconnection configurations and energy balance of the coronal magnetic field in response to prescribed motions of the photospheric footpoints. Two specific models of the coronal magnetic configuration are investigated, namely an array of closely packed flux tubes and a two-dimensional magnetic arcade. 相似文献
5.
Solar flares and magnetospheric substorms are discussed in the context of a general theory of impulsive flux transfer events (IFTE). IFTE theory, derived from laboratory observations in the Double Inverse Pinch Device (DIPD), provides a quantitative extension of neutral sheet theories to include nonsteady field line reconnection. Current flow along the reconnection line increases with magnetic flux storage. When flux build-up exceeds the level corresponding to a critical limit on the current, instabilities induce a sudden transition in the mode of conduction. The resulting IFTE, indifferent to the specific modes and instabilities involved, is the more energetic, the lower the initial resistivity. It is the more violent, the greater the resulting resistivity increase and the faster its growth. Violent events can develop very large voltage transients along the reconnection line. Persistent build-up promoting conditions produce relaxation oscillations in the quantity of flux and energy stored (build-up-IFTE cycles). It is difficult to avoid the conclusion: flares and substorms are examples of IFTE. 相似文献
6.
EUV97 is a solar EUV empirical model that incorporates revised soft X-ray fluxes from the SOLRAD-11 satellite (1976–1979) and uses Lα recently recalibrated to the UARS satellite (1991–present) SOLSTICE Lα. The soft X-ray data have been revised from the original flux values using Mewe's spectral fits to the data. The recalibrated AE-E and SME Lα datasets use UARS Lα for absolute flux values to provide two solar cycles of Lα irradiance extending back to 1977. Lα is used by EUV97 as a proxy for chromospheric EUV irradiances. The EUV97 empirical solar model takes its heritage from the EUV91 model based on a multiple linear regression technique that fits soft X-ray and EUV irradiances to 10.7 cm flux for transition region and coronal emissions or to Lα and Hei 10830 Ú EW for chromospheric emissions. 相似文献
7.
C. D. Andriesse 《Astrophysics and Space Science》1979,61(1):205-215
The mass flux from a star is adopted to result from a fluctuation of the photosphere, which is not in complete thermal equilibrium. Because of the large difference between the dynamical and thermal relaxation times, its state can be approximated by a partial equilibrium. Using a theory of thermodynamic fluctuations, the mass flux is expressed in a correlation function of gravitational perturbations of the photosphere. A hypothesis is proposed that the susceptibility to these perturbations, if normalized to the available thermal energy, is the same for all stars. Its value is obtained by considering the upper limit to the mass flux. This results in a mean mass loss ofL
3/2 (R/M)9/4/G
7/4, where the symbols have their common meaning. The result is compared to empirical data on the mass flux from some 50 stars of various luminosities and luminosity classes. With a possible exception for late-type (super) giants the agreement is good, in many cases within a factor 2. 相似文献
8.
J. H. Hough 《Astrophysics and Space Science》1997,248(1-2):269-276
Polarimetry at near-infrared wavelengths is shown to be an important tool in understanding the properties of the obscuring
torus in NGC1068. We present evidence for the existence of aligned grains in the torus, which produce polarized flux through
dichroism, and show how the torus itself can be observed in silhouette in polarized flux images.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
K. A. Hämeen-Anttila 《Astrophysics and Space Science》1978,56(2):421-430
In statistical Keplerian systems the disordered component of collisionally induced motion of matter introduces new terms into the flux vector. This contribution, which is calculated from a transport equation, tends to reduce the density gradient and causes the expansion which is observed in computer simulations of collisional systems. A quantitative comparison with Trulsen's (1972) simulations confirms the revised expression of the flux vector. 相似文献
10.
Using the sunspot numbers reported during the Maunder minimum and the empirical relations between the mode frequencies and
solar activity indices, the variations in the total solar irradiance and 10.7 cm radio flux for the period 1645 to 1715 is
estimated. We find that the total solar irradiance and radio flux during the Maunder minimum decreased by 0.19% and 52% respectively,
as compared to the values for solar cycle 22.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
The theory of the relaxation of pulsar angular velocity is compared with observational data for the first eight glitches of the Vela pulsar. Solutions of the inverse problem in relaxation theory are obtained in the regions of exponential and linear relaxation in the core of the neutron star. From these solutions, a distribution of vortices is found that results in the observed relaxation of the pulsar's angular velocity. It is shown that the pinning of neutron vortices plays the primary role in the region of exponential relaxation, while in the region of linear relaxation one must allow for the variation of the angular velocity of the superfluid component. 相似文献
12.
V. G. Ledenev 《Solar physics》1994,149(2):279-288
The problem of energetic electron flux propagation in the solar coronal plasma is solved with due regard for the influence of the oppositely directed neutralizing cold electron flux and the kinematic escape effect of the electrons with different velocities. It is shown that the flux electrons are accelerated in the process of propagation, thus forming a beam, whose velocity is constant on rather long time scales. Three regimes can be realized in this case. In the first regime, plasma waves do not have time to be excited because they escape rapidly from resonance with the beam. In the second regime, waves are excited, but the beam does not have time to relax. The third regime is quasi-linear relaxation.The generation of solar type III radio bursts in the second regime of electron flux propagation is considered. 相似文献
13.
H. Oberhummer A.N. Ivanov N.I. Troitskaya M. Faber 《Astrophysics and Space Science》1997,258(1-2):133-144
The present status of the nuclear reaction rates determining the solar neutrino flux is discussed. This includes the reaction
rates for the two branching ratios of the three pp-chains involving the reactions 3He(3He,2p)4He and 3He(4He,γ)7Be for the
first branching, and 7Be(e−, νe)7Li and 7Be(p, γ)8B for the second branching. Mainly we will concentrate on the basic nuclear
reaction p + p → D + e+ + νe of the pp-chains. This reaction rate can only be determined using the theoretical methods. The
present status of the application of the relativistic field theory model of the deuteron for this reaction will be discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
The heating of a spinning artificial satellite by natural radiation sources such as the Sun and the Earth results in temperature gradients arising across the satellite's surface. The corresponding anisotropic emission of thermal radiation leads to a recoil force, commonly referred to as “thermal force”. A quantitative theory of this effect is developed, based on more general assumptions than used so far, to model such radiation forces on spherically symmetric LAGEOS-like satellites. In particular, the theory holds for any ratio of the three basic timescales of the problem: the rotation period of the satellite, the orbital period around the Earth, and the relaxation time for the thermal processes. Thus, the simplifying assumption of a comparatively fast rotational motion is avoided, which will fail for LAGEOS within the next decade, owing to magnetic dissipation effects. A number of predictions about the future behaviour of non-gravitational long-term orbital perturbations of LAGEOS become possible with the new theory. In particular the Yarkovsky-Schach thermal force effects are studied arising as a consequence of the solar radiation flux onto the satellite, periodically interrupted by eclipses. Starting on about year 2005, the orbital perturbation effects predicted by the new theory are substantially different from those inferred in the fast-rotation case. This holds not only for the long-term semimajor axis effects, but also for eccentricity and inclination perturbations. 相似文献
15.
Minoru Umezu 《Astrophysics and Space Science》1998,259(4):343-354
We find that the hydrogen flux near the boundary of the semiconvection zone with Ledoux's neutral condition is unreasonably
positive while it is reasonably negative throughout the semiconvection zone with Schwarzschild's neutral condition.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
A theory of the relaxation of pulsar angular velocity is compared with observational data for the first eight glitches of the Vela pulsar. The inverse problem of the theory of relaxation is considered and solutions of this problem in the regions of exponential and linear relaxation are found. General features in the distribution of neutron vortices in these regions immediately after a glitch are determined. It is shown that these properties may be related to the size of the glitch in pulsar angular velocity. 相似文献
17.
R. Chan 《Astrophysics and Space Science》1997,257(2):299-309
An analytical solution of the Einstein's equations is found for a collapsing radiating body, consisting of an isotropic fluid
with shear undergoing radial heat flow with outgoing radiation. The behavior of the density, pressure, heat flux, mass and
luminosity are analyzed for a body of 6 M⊙.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
It is analytically indicated that self-generated magnetic fields are modulationally unstable with respect to the uniform state
of a plasma; such an instability would cause the formation of the field localization. It is able to expect that this localized
magnetic flux is responsible for small-scale inhomogeneous magnetic fields, which are required for explanation of the fine
structure of auroral kilometric radiaton (AKR).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
We extend the flux limited diffusion theory in a moving fluid to be able to treat any combination of absoption and scattering.The extended flux limited diffusion theory is fully flux limited and displays the correct behavior in the free streaming limit and in the near thermodynamic equilibrium limit. 相似文献
20.
In the mean, bipolar active regions are oriented nearly toroidally, according to Hale's polarity law, with a latitude-dependent tilt known as Joy's Law. The tilt angles of individual active regions deviate from this mean behavior and change over time. It has been found that on average the change is toward the mean angle at a rate characteristic of 4.37 days (Howard, 1996). We show that this orientational relaxation is consistent with the standard model of flux tube emergence from a deep dynamo layer. Under this scenario Joy's law results from the Coriolis effect on the rising flux tube (D'Silva and Choudhuri, 1993), and departures from it result from turbulent buffeting of the tubes (Longcope and Fisher, 1996). We show that relaxation toward Joy's angle occurs because the turbulent perturbations relax on shorter time scales than the perturbations from the Coriolis force. The turbulent perturbations relax more rapidly because they are localized to the topmost portion of the convection zone while the Coriolis perturbations are more widely distributed. If a fully-developed active region remains connected to the strong toroidal magnetic field at the base of the convection zone, its tilt will eventually disappear, leaving it aligned perfectly toroidally. On the other hand, if the flux becomes disconnected from the toroidal field the bipole will assume a tilt indicative of the location of disconnection. We compare models which are connected and disconnected from the toroidal field. Only those disconnected at points very deep in the convection zone are consistent with observed time scale of orientational relaxation. 相似文献