共查询到20条相似文献，搜索用时 31 毫秒
1.
Jiong Liu Ye-Fei Yuan Xiao-Long Deng Center for Astrophysics University of Science Technology of China Hefei 《中国天文和天体物理学报》2007,7(2):304-316
Synchro-curvature radiation describes the emission from a relativistic charged par- ticle which is moving and spiralling in a curved magnetic field. We investigate the maser emission for synchro-curvature radiation including drift of the guiding center of the radiating electron. It is shown that under some conditions the absorption coefficient can be negative, so maser can happen. These conditions are different from those needed for maser emission of curvature radiation including drift of the charged particles. We point out that our results, in- cluding the emissivity, can reduce to these of curvature radiation. Previously it was found that synchro-curvature radiation can not generate maser in vacuum, but we argue that synchro- curvature radiation including drift can generate maser even in vacuum. We discuss the possi- bilities of the potential applications of the synchro-curvature maser in modeling gamma ray bursts and pulsars. 相似文献
2.
The coherent plasma process such as parametric decay instability (PDI) has been applied to a homogeneous and unmagnetized
plasma. These instabilities cause anomalous absorption of strong electromagnetic radiation under specific conditions of energy
and momentum conservation and thus cause anomalous heating of the plasma. The maximum plasma temperatures reached are functions
of luminosity of the radio radiation and plasma parameters. We believe that these processes may be taking place in many astrophysical
objects. Here, the conditions in the sources 3C 273, 3C 48 and Crab Nebula are shown to be conducive to the excitation of
PDI. These processes also contribute towards the absorption of 21cm radiation 相似文献
3.
The article discusses the progress made in studying space radiation in the heliosphere using SINP MSU instruments on board a spacecraft built by the Lavochkin Association, in predicting flight radiation conditions, and in studying the radiation resistance of spacecraft components. 相似文献
4.
Current surface conditions (strong oxidative atmosphere, UV radiation, low temperatures and xeric conditions) on Mars are considered extremely challenging for life. The question is whether there are any features on Mars that could exert a protective effect against the sterilizing conditions detected on its surface. Potential habitability in the subsurface would increase if the overlaying material played a protective role. With the aim of evaluating this possibility we studied the viability of two microorganisms under different conditions in a Mars simulation chamber. An acidophilic chemolithotroph isolated from Río Tinto belonging to the Acidithiobacillus genus and Deinococcus radiodurans, a radiation resistant microorganism, were exposed to simulated Mars conditions under the protection of a layer of ferric oxides and hydroxides, a Mars regolith analogue. Samples of these microorganisms were exposed to UV radiation in Mars atmospheric conditions at different time intervals under the protection of 2 and 5 mm layers of oxidized iron minerals. Viability was evaluated by inoculation on fresh media and characterization of their growth cultures. Here we report the survival capability of both bacteria to simulated Mars environmental conditions. 相似文献
5.
Exact relations for radiation heat flux at the boundaries of a slab with diffusely reflecting boundary conditions and internal source are obtained in terms of the reflection and transmission coefficients of a source free slab with isotropic boundary conditions. The integral equation defining the radiation heat flux contains explicitly the internal source. So, the particular solution for radiative transfer equation is not required. Available exact values for albedos give exact values of radiation heat flux. Padé approximant technique is used to obtain numerical values for homogenous media. 相似文献
6.
It has been argued that the loss-cone-driven electron cyclotron maser instability can account for the properties of millisecond microwave spike bursts observed during some solar flares. However, as it propagates outward from the corona, maser radiation undergoes gyroresonance absorption when its frequency is a harmonic of the local electron-cyclotron frequency. Existing analytical models using slab geometries predict that this absorption should be sufficiently strong to prevent the radiation from being seen at the observed levels, except under highly restrictive conditions or for unrealistic plasma parameters. A more comprehensive analysis is presented here to determine if and when maser radiation can escape to produce microwave spike bursts. This analysis employs numerical raytracing and incorporates propagation and absorption of fundamental maser emission in a realistic model of a coronal flux loop. It is found that ranges of physical conditions do exist under which maser radiation can escape to an observer and that these conditions are much more limiting for fundamental emission in the extraordinary ()-mode than in the ordinary (o)-mode. Detailed investigation implies that escaping radiation in the -mode is highly directional and chiefly observable toward the center of the solar disk, while escapingo-mode radiation is found to emerge from the corona over a much wider range of directions, with some cases corresponding to radiation observable near the solar limb. 相似文献
7.
Hamid M. K. Al-Naimiy 《Astrophysics and Space Science》1978,53(1):3-11
The radiation of a charge rotating in a circle with the constant velocity (in the external magnetic field) in the isotropic plasma with random inhomogeneities of the electron density has been considered. A general expression is obtained for the radiation intensity at thenth harmonic, which is a generalization of the known Shott formula. In the ultra-relativistic case the conditions are clarified under which the inhomogeneity effect on the form of the spectrum of radiation from a particle is essential. An asymptotic formula is derived for the spectral intensity in the region of sufficiently low frequencies. The mechanism of transient radiation in this case is shown to prevail over the synchrotron one. 相似文献
8.
Assuming spherical symmetry we analyse the dynamics of an inhomogeneous dark radiation vaccum on a Randall and Sundrum 3-braneworld.
Under certain natural conditions we show that the effective Einstein equations on the brane form a closed system. On a de
Sitter brane and for negative dark energy density we determine exact dynamical and inhomogeneous solutions which depend on
the brane cosmological constant, on the dark radiation tidal charge and on its initial configuration. We also identify the
conditions leading to the formation of a singularity or of regular bounces inside the dark radiation vaccum.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
We give the radiation of anN-charged particles system associated with the succeeding terms in the expansion in the inverse powers of the velocity of light of the four vector force on the material system in a slow motion. We investigate the conditions under which theN-charged particles system may recoil while emitting electromagnetic radiation. Furthermore, the lowest-order secular effects in the radiation arise from dipole and quadrupole radiations exactly as it is expected from the classical theory. 相似文献
10.
E. R. Seaquist 《Astrophysics and Space Science》1972,15(2):284-292
It is shown that relativistic electrons in the presence of circularly polarized hydromagnetic waves emit synchrotron radiation which is partially circularly polarized. The relation between the degree of polarization of the radiation and the energy density and wavelength of the waves is derived, and the factors determining the sense of polarization are discussed. Waves of the type required are generated by pitch angle anisotropies in a relativistic electron gas. An application of the result to conditions expected in quasistellar objects shows that the degree of circular polarization of synchrotron radiation in these objects may be of order 1% or greater. 相似文献
11.
We have deduced the intensity spectral function for the spin-flip synchrotron radiation in the presence of a plasma. Using parameters appropriate to astrophysical conditions, we have attempted to compare the characteristics of the spin-flip synchrotron radiation and the normal synchrotron radiation in a magnetized plasma arising from an electron or positron rotating around the magnetic field. A rotating charge gives the maximum possible synchrotron radiative power as compared to a charge of the same energy but moving in a helical path. Since the spin-flip radiational does not depend on the form of the orbital path, whether circular or helical or along a straight line, the analysis presented here gives the lower limit of the relative importance of the spin-flip radiation to the normal synchrotron radiation emitted by the same radiator. 相似文献
12.
Spectropolarimetric features of thermal cyclotron radiation of solar coronal loops and the possibility of interpretation of the observed reversal of the sense of polarization of centimeter and decimeter waves are discussed. To this end, thermal cyclotron radiation is computed in terms of the simplest model of a three-dimensional hot loop (a half-torus). Such a loop is shown to be capable of changing appreciably the properties of the radiation of a solar active region at centimeter and decimeter wavelengths. A detailed analysis is performed to determine the conditions under which the radiation spectrum of an active region containing a coronal loop may have a complex pattern with several maxima or relatively narrow-band cyclotron lines, and the sense of polarization may change several times in the wavelength interval considered. These conditions are modelled by such parameters as the structure of the magnetic field, electron density, and size of the loop. The results of the computations of two-dimensional brightness temperature distributions at different wavelengths for ordinary and extraordinary waves at fixed points of the loop and the integrated parameters of the flux and polarization of radiation in terms of the model discussed are reported. Cases are considered where the line of sight is crossed by one or two loops. The expected distribution of polarization across the source in the model considered is compared to the results of RATAN-600 observations of the solar active region AR 7962 made on May 12–14, 1996. 相似文献
13.
The mechanism of brightness outbursts of comets based on selective absorption of solar ultraviolet radiation by hydrogen atoms
in the cometary head is considered. Due to this process, influence of the radiation on parent and daughter molecules in the
near-nucleus region of the cometary head is different. As a result, under certain physical conditions in the cometary coma,
the electronic-temperature increase may cause an outburst in the brightness of the comet. 相似文献
14.
Mark G. Wolfire 《Astrophysics and Space Science》2011,336(1):229-233
Photodissociation Regions (PDRs) are gas phases in which ultraviolet radiation plays a role in the heating or chemistry. The
physics of PDRs determines the emitted radiation and physical conditions in both the diffuse atomic interstellar medium and
the dense molecular phases. High energy laboratory experiments can provide constraints on the survival of small grains which
dominate gas heating and in the interaction of X-rays with gas and grains. 相似文献
15.
A. Katsambas Ch. Andoniou J. Stratigos I. Arvanitis F. Zolota C. Varotsos C. Cartalis D. N. Asimakopoulos 《Earth, Moon, and Planets》1991,53(3):191-204
The purpose of this study is to present a new simple model algorithm for simulating the solar ultaviolet radiation reaching the surface of the Earth. The algorithm is capable of providing both the direct and diffuse solar ultraviolet radiation, for different atmospheric conditions, time, and geographic locations. An application of the model relates to the calculation of the minimum energy input of ultraviolet radiation to be received by a human to allow an erythema development. 相似文献
16.
H. A. Zachariades 《Astrophysics and Space Science》1991,176(1):105-121
An oblique, rotating magnetized sphere emits electromagnetic waves which, for large magnetization, can quickly accelerate charged particles to very high energies. A central, attractive Coulomb force can trap particles in the region beyond the light cylinder by balancing the accelerating influence of the radiation on the particles. We sample some of the particle orbits possible under these dynamical conditions. A general feature of these orbits is that non-interacting particles started with random initial conditions in the domain of attraction of these orbits will arrange themselves on a curve corotating with the axis of magnetization. Such particle configurations can be a source of pulsed radiation. In the idealized case of no interparticle interactions the spectral index for the radiation emitted by one frequently occurring configuration is found to be –2/3, for emission from radio to -ray frequencies. The dynamical conditions in this simple model closely match those prevalent in outer pulsar magnetospheres, making it possible that part of the radiation from pulsars is emitted by trapped plasma in the region beyond the light cylinder. 相似文献
17.
Tilemahos J. Kalvouridis 《Astrophysics and Space Science》2008,317(1-2):107-117
We deal with some new aspects of the photo-gravitational Copenhagen case of the restricted three-body problem; more particularly, the distribution and the attracting domains of the stationary solutions of small particles that move in the neighborhood of two major bodies with equal masses when one or both primaries are radiation sources with constant luminosity. Under these conditions, each particle is subjected not only to gravitational forces but to the radiation emitted from the primaries as well. 相似文献
18.
The purpose of this study is to analyze the dynamical role of a radiation field on the growth rate of the unstable Kelvin-Helmholtz (KH) perturbations. As a first step toward this purpose, the analyze is done in a general way, irrespective of applying the model to a specific astronomical system. The transition zone between the two layers of the fluid is ignored. Then, we perform a linear analysis and by imposing suitable boundary conditions and considering a radiation field, we obtain appropriate dispersion relation. Unstable modes are studied by solving the dispersion equation numerically, and then growth rates of them are obtained. By analyzing our dispersion relation, we show that for a wide range of the input parameters, the radiation field has a destabilizing effect on KH instability. In eruptions of the galaxies or supermassive stars, the radiation field is dynamically important and because of the enhanced KH growth rates in the presence of the radiation; these eruptions can inject more momentum and energy into their environment and excite more turbulent motions. 相似文献
19.
The problem of the gravitational instability of an inviscid plasma cloud is investigated by taking into account radiative effects. It is shown that, on given conditions, the radiation stabilizes the system. 相似文献
20.
Based on the standard cosmological model, we calculate the correction to the rate of two-photon 2s ? 1s transitions in the hydrogen atom under primordial hydrogen plasma recombination conditions that arises when the induced transitions under equilibrium background radiation with a blackbody spectrum and plasma recombination radiation are taken into account. 相似文献