共查询到20条相似文献，搜索用时 15 毫秒
1.
Based on a recent communication by the present authors the question of energy dissipation in magnetohydrodynamical waves in an inflating background in general relativity is examined. It is found that the expanding background introduces a sort of dragging force on the propagating wave such that, unlike the Newtonian case, energy gets dissipated as it progresses. This loss in energy having no special-relativistic analogue is, however, not mechanical in nature as in case of an elastic wave. It is also found that the energy loss is model dependent and also depends on the number of dimensions. 相似文献
2.
H. Navasardyan A.R. Petrosian M. Turatto E. Cappellaro J. Boulesteix 《Monthly notices of the Royal Astronomical Society》2001,328(4):1181-1192
In order to investigate the influence of environment on supernova (SN) production, we have performed a statistical investigation of the SNe discovered in isolated galaxies, in pairs and in groups of galaxies. 22 SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and 211 SNe in 170 galaxy members of 116 groups have been selected and studied.
We found that the radial distributions of core-collapse SNe in galaxies located in different environments are similar, and consistent with those reported by Bartunov, Makarova & Tsvetkov . SNe discovered in pairs do not favour a particular direction with respect to the companion galaxy. Also, the azimuthal distributions inside the host members of galaxy groups are consistent with being isotropics. The fact that SNe are more frequent in the brighter components of the pairs and groups is expected from the dependence of the SN rates on the galaxy luminosity.
There is an indication that the SN rate is higher in galaxy pairs compared with that in groups. This can be related to the enhanced star formation rate in strongly interacting systems.
It is concluded that, with the possible exception of strongly interacting systems, the parent galaxy environment has no direct influence on SN production. 相似文献
We found that the radial distributions of core-collapse SNe in galaxies located in different environments are similar, and consistent with those reported by Bartunov, Makarova & Tsvetkov . SNe discovered in pairs do not favour a particular direction with respect to the companion galaxy. Also, the azimuthal distributions inside the host members of galaxy groups are consistent with being isotropics. The fact that SNe are more frequent in the brighter components of the pairs and groups is expected from the dependence of the SN rates on the galaxy luminosity.
There is an indication that the SN rate is higher in galaxy pairs compared with that in groups. This can be related to the enhanced star formation rate in strongly interacting systems.
It is concluded that, with the possible exception of strongly interacting systems, the parent galaxy environment has no direct influence on SN production. 相似文献
3.
Observations of the polarization of stars in the direction of a molecular cloud in Serpens are presented. A dependence of
the degree of linear polarization on total absorption Av is found in their direction, different for stars in the cloud and in its vicinity. On this basis, it is concluded that the
polarizing efficiency of particles in the cloud is reduced.
Translated from Astrofizika, Vol. 43, No. 3, pp. 397-403, July–September, 2000. 相似文献
4.
Nonlinear properties of the quantum magnetoacoustic wave are studied in electron-ion magnetoplasmas. In this regard, cylindrical Korteweg deVries (CKdV) equation is derived for small amplitude perturbations. The solution of the planar KdV equation is obtained using the tanh method and is subsequently used as an initial profile to solve the CKdV equation. It is found that the system under consideration admits compressive solitary structures. Finally, it is found that the amplitude as well as the width of the nonplanar magnetosonic solitary structure increases with the increase in the magnetic field whereas a decrease is observed with the increase in number density of the system. The present study may be beneficial to understand the nonlinear wave propagation in nonplanar geometries in dense plasmas. 相似文献
5.
J. B. Bhowmick 《Astrophysics and Space Science》1979,60(1):183-190
A stellar model in which density in the undisturbed gas is assumed to obey power law is considered. An exact analytic self-similar solution for shock velocity, pressure and density is obtained under the assumption of isothermal conditions in the rear flow field. An expression to study analytically the extent of vacuum in the inner core of the gaseous sphere is deduced for any explosion problem and is applied here to obtain the extent of the inner vacuum analytically. 相似文献
6.
Ding-Qiang Su Xiang-Qun Cui National Astronomical Observatories/NIAOT Chinese Academy of Sciences Nanjing Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2004,4(1):1-9
Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. It is used for correcting telescope errors generated by gravitational and thermal changes. Here, however, we use this technology to realize the configuration of LAMOST, -a task that cannot be done in the traditional way. A comprehensive and intensive research on the active optics used in LAMOST is also reported, including an open-loop control method and an auxiliary closed-loop control method. Another important development is in our pre-calibration method of open-loop control, which is with some new features: simultaneous calculation of the forces and displacements of force actuators and displacement actuators; the profile of mirror can be arbitrary; the mirror surface shape is not expressed by a fitting polynomial, but is derived from the mirror surface shape formula which is highly accurat 相似文献
7.
Chandreyee Sengupta Ramesh Balasubramanyam † 《Monthly notices of the Royal Astronomical Society》2006,369(1):360-368
Gas deficiency in cluster spirals is well known and ram-pressure stripping is considered the main gas removal mechanism. In some compact groups too gas deficiency is reported. However, gas deficiency in loose groups is not yet well established. Lower dispersion of the member velocities and the lower density of the intragroup medium in small loose groups favour tidal stripping as the main gas removal process in them. Recent releases of data from the H i Parkes All-Sky Survey (HIPASS) and catalogues of nearby loose groups with associated diffuse X-ray emission have allowed us to test this notion. In this paper, we address the following questions: (i) do galaxies in groups with diffuse X-ray emission statistically have lower gas content compared to the ones in groups without diffuse X-ray emission? (ii) does H i deficiency vary with the X-ray luminosity, L X , of the loose group in a systematic way? We find that (i) galaxies in groups with diffuse X-ray emission, on average, are H i deficient, and have lost more gas compared to those in groups without X-ray emission; the latter are found not to have significant H i deficiency; (ii) no systematic dependence of the H i deficiency with L X is found. Ram-pressure-assisted tidal stripping and evaporation by thermal conduction are the two possible mechanisms to account for this excess gas loss. 相似文献
8.
Prominences and filaments are thought to arise as a consequence of a magnetized plasma undergoing thermal instability. Therefore, the thermal stability of a magnetized plasma is investigated under coronal conditions. The equilibrium structure of the plasma is approximated by a 1-D slab configuration. This is investigated in thermal instability taking into account optically thin plasma radiation and anisotropic thermal conduction. The thermal conduction perpendicular to the magnetic field is taken to be small but non-zero.The classic rigid wall boundary conditions which are often applied in the literature, either directly on the plasma or indirectly through some other medium, are replaced by a more physical situation in which the plasma column is placed in a low-density background stretching towards infinity. Results for a uniform equilibrium structure indicate the major effect of this change is on the eigenfunctions rather than on the growth rate. Essentially, perpendicular thermal conduction introduces field-aligned fine structure. It is also shown that in the presence of perpendicular thermal conduction, thermal instability in a slab model is only possible if the inner plasma has the shortest thermal instability time scale.Research Assistant of the National Fund for Scientific Research (Belgium). 相似文献
9.
We investigate the electron-positron pair concentration in an optically thin mildly relativistic plasma which is supposed to exist in active galactic nuclei. Firstly the equilibrium concentration is calculated when copious soft photons are supplied through the cyclotron higher harmonics. It is shown that the attainable states of the plasma are strongly restricted. Secondly we examine the pair production in a hot accretion plasma around a massive black hole, comparing relevant time scales. We find that significant pair production occurs when the accretion rate is moderately high and the infall velocity is slow compared to the free fall.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984 相似文献
10.
The fluid approach is employed to investigate theoretically the effect of strong electrostatic interaction on the dust acoustic (DA) shock waves near to the liquid-crystal phase transition in strongly coupled dusty plasma. The strong electrostatic interaction is modeled by effective electrostatic temperature which is considered as a dynamical variable. It is shown that the nonlinear evolution of dust acoustic shock waves in the present model is governed by a Burger equation, the coefficients in which are modified by strong coupling effect. Then, it is shown that how the perturbation of the effective electrostatic temperature modifies the basic properties of the DA shock waves. 相似文献
11.
Utpal Kumar Samanta Prasanta Chatterjee Manimala Mej 《Astrophysics and Space Science》2013,345(2):291-296
Solitons and shocks are addressed in a pair ion plasma in the presence of a kappa distribution. The dissipation is taken care of through the kinematic viscosity of both positive and negative ions in the plasma. The Kadomtsev–Petviashvili–Burger (KPB) equation is derived using the small amplitude expansion method. The Abel equation is obtained from the KPB equation and a solution is obtained by using the factorization method. The effect of the parameters κ and β (temperature ratio of ion species) is observed. Analytically we can find both solitons and shocks. The change of profile from soliton to shocks is shown in the figures. This study may be of wide relevance for the study of the formation of shocks and solitons in laboratory-produced pair ion plasmas. 相似文献
12.
De Sitter背景时空中NUT-Kerr-Newman黑洞的玻色子熵 总被引：1，自引：0，他引：1
众所周知，一般黑洞的欧拉示性数都为2(或者为0)，而NUT—Kerr—Newman黑洞是个例外，其欧拉示性数大于2.因此计算NUT—Kerr—Newman黑洞的玻色子熵有特殊的意义．运用在brick-wall方法的基础上发展起来的膜模型计算了NUT-Kerr—Newman黑洞在de Sitter时空背景下的玻色子熵．结果表明，在选取适当的截断因子的情况下，该黑洞的熵仍满足Bekenstein—Hawking面积定律． 相似文献
13.
The nonstationary dynamics of vortices in conventional type II superconductors and in neutron stars is examined in the Newtonian
approximation. A relaxation equation is obtained for vortices approaching an equilibrium distribution after a change in an
external magnetic field. The relaxation times are estimated for vortices in low-temperature superconductors and for proton
vortices in the superconducting core of a neutron star. It is shown that the proton vortex system created by entrainment currents
is rigidly coupled to the neutron vortices.
Translated from Astrofizika, Vol. 52, No. 2, pp. 291–300 (May 2009). 相似文献
14.
Tadashi Hirayama 《Solar physics》1971,19(2):384-400
The abundance of helium relative to hydrogen is spectroscopically determined in prominences and in the chromosphere by using 1952, 1958, 1962 and 1966 eclipse data. Care is taken in the intensity calibration of emission lines, the self-absorption, and the departure from local thermodynamic equilibrium. We find from the line profiles and intensities of prominences and the chromosphere that the neutral helium lines are emitted in the metal-hydrogen emitting region where the kinetic temperature is low enough, 6000 8000 K, so that only the ionization due to UV radiation from the corona can explain the intensity of neutral helium emission. Also we find that the intensity ratio of Hei 3888.65 to H8 3889.05 increases towards the upper boundaries of prominences and of the chromosphere and that it approaches to a universal limiting value, both in various prominences or in the chromosphere, where it is considered that the ionization of neutral helium and hydrogen is nearly complete. From these facts the helium to hydrogen number ratio is found to be 6.5 ± 1.5%.A new schematic model of the chromosphere is presented where spicules have no hot region of emitting neutral helium lines. Here it is suggested that the kinetic temperature of spicules, 6000 8000 K, would be primarily determined by the radiation temperature of the corona and the transition region beyond the Lyman continuum of hydrogen which happens to be around those temperatures. 相似文献
15.
A. V. Nesterenok 《Astrophysics and Space Science》2018,363(7):151
A magnetohydrodynamic model of a steady, transverse C-type shock in a dense molecular cloud is presented. A complete gas–grain chemical network is taken into account: the gas-phase chemistry, the adsorption of gas species on dust grains, various desorption mechanisms, the grain surface chemistry, the ion neutralization on dust grains, the sputtering of grain mantles. The population densities of energy levels of ions CI, CII and OI and molecules H2, CO, H2O are computed in parallel with the dynamical and chemical rate equations. The large velocity gradient approximation is used in the line radiative transfer calculations. The simulations consist of two steps: (i) modelling of the chemical and thermal evolution of a static molecular cloud and (ii) shock simulations. A comparison is made with the results of publicly available models of similar physical systems.The focus of the paper is on the chemical processing of gas material and ice mantles of dust grains by the shock. Sputtering of ice mantles takes place in the shock region close to the temperature peak of the neutral gas. At high shock speeds, molecules ejected from ice mantles are effectively destroyed in hot gas, and their survival time is low—of the order of dozens of years. After a passage of high-speed C-type shock, a zone of high abundance of atomic hydrogen appears in the cooling postshock gas that triggers formation of complex organic species such as methanol. It is shown that abundances of some complex organic molecules (COMs) in the postshock region can be much higher than in the preshock gas. These results are important for interpretation of observations of COMs in protostellar outflows. 相似文献
16.
Ana I. Gómez de Castro Willem Wamsteker Martin Barstow Noah Brosch Norbert Kappelmann Wollfram Kollatchny Domitilla de Martino Isabella Pagano Alain Lecavelier des Étangs David Ehenreich Dieter Reimers Rosa González Delgado Francisco Najarro Jeff Linsky 《Astrophysics and Space Science》2006,303(1-4):133-145
Progress of modern astrophysics requires the access to the electromagnetic spectrum in the broadest energy range. The Ultraviolet is a fundamental energy domain since it is one of the most powerful tool to study plasmas at temperatures in the 3,000–300,000 K range as well as electronic transitions of the most abundant molecules in the Universe. Moreover, the UV radiation field is a powerful astrochemical and photoionizing agent.The objective of this review is to describe the crucial issues that require access to the UV range. A summary has been added to the end with a more classic view of UV needs by astronomical object type; this approach is followed at length in the rest of the contributions of this issue. 相似文献
17.
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
18.
Pavel Koubský 《Astrophysics and Space Science》2005,296(1-4):165-168
A brief review of Be stars in binaries is presented. Attention is paid to systems, where the Be phenomenon is clearly connected
to the duplicity, but is not a simple consequence of mass transfer. 相似文献
19.
Subject to the condition that atoms be conserved – i.e. without nuclear transmutations – we conjecture that it is impossible
to synthesise organic materials in appreciable quantity from inorganic materials without the intervention of biological systems.
The restriction is not a consequence of a mystic quality in the laws of physics and chemistry but of the practical disposition
of materials on the Earth and in the cosmos generally. It is a corollary that biology is the means by which an approximation
to thermodynamic equilibrium is maintained in materials at temperatures ∼ 300 K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
John A. Russell 《Meteoritics & planetary science》1990,25(3):177-180
Abstract— A shutter-chopped, direct photograph of a 1980 Perseid meteor is discussed in which no shutter breaks are apparent. Evidence is considered that it is indeed a Perseid and that the phenomenon is the result of an extraordinary fragmentation of the meteoroid. Tentative evidence is presented for the existence in 1980 of a second radiant from which the apparently unchopped meteor and a second meteor, also showing marked fragmentation, emanated. The fragmentation of these two meteors and the concentration of their radiant are consonant with the concept of their origin from recently released material from the nearby parent comet. 相似文献