共查询到20条相似文献，搜索用时 390 毫秒
1.
This paper deals with five-dimensional black hole solutions in (a) Einstein-Maxwell-Gauss-Bonnet theory with a cosmological
constant and (b) Einstein-Yang-Mills-Gauss-Bonnet theory for spherically symmetric space time. In both the cases the possibility
of phase transition is examined and it is analyzed whether the phase transition is a Hawking-Page type phase transition or
not. 相似文献
2.
Livne E 《The Astrophysical journal》1999,527(2):L97-L100
Delayed detonation in an exploding white dwarf, which propagates from an off-center transition point rather than from a spherical transition shell, is described and simulated. The differences between the results of two-dimensional simulations and the one-dimensional case are presented and discussed. The two-dimensional effects become significant in transition density below 3rho7, where the energetics, the production of Fe group elements, and the symmetry of the explosion are all affected. In the two-dimensional case, the explosion is less energetic and less Ni is produced in the detonation phase of the explosion. For low transition density, the reduction in Ni mass can reach 20%-30%. The asymmetry in abundances between regions close to the transition point and regions far from that point is large and could be a source of polarization patterns in the emitted light. We conclude that the spatial and temporal distribution of transition locations is an important parameter that must be included in delayed detonation models for Type Ia supernovae. 相似文献
3.
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
4.
The properties of adiabatic potential transitions in a current carrying plasma are investigated and classified. It is shown that it is important to include pressure effects since the character of the transition (e.g. whether or not it behaves as a particle accelerator) is determined by whether the speed of a streaming species on entering the transition is less or greater than the “sound speed” of that species. If electrons are the main current carriers in the field aligned current systems associated with the polar ionosphere and magnetosphere we find that, under typical conditions, their drift speed is less than their thermal speed with the implication that if they enter a potential transition their pressure gradient will overcome the electrostatic field so that they are decelerated and heated by the transition. Under disturbed conditions when the field aligned current densities are exceptionally high, potential transitions act as particle accelerators. 相似文献
5.
T. Belloni I. Parolin M. Del Santo J. Homan P. Casella R. P. Fender W. H. G. Lewin M. Méndez J. M. Miller M. van der Klis 《Monthly notices of the Royal Astronomical Society》2006,367(3):1113-1120
On 2004 August 15, we observed a fast (shorter than 10 h) state transition in the bright black hole transient GX 339–4 simultaneously with Rossi X-Ray Timing Explorer ( RXTE ) and INTEGRAL . This transition was evident both in timing and spectral properties. Combining the data from the Proportional Counter Array (PCA), the High-Energy X-ray Timing Experiment (HEXTE) and the Imager on Board the INTEGRAL Satellite (IBIS), we obtained good quality broad-band (3–200 keV) energy spectra before and after the transition. These spectra indicate that the hard component steepened. Also, the high-energy cut-off that was present at ∼70 keV before the transition was not detected after the transition. This is the first time that an accurate determination of the broad-band spectrum across such a transition has been measured on a short time-scale. It shows that, although some spectral parameters do not change abruptly through the transition, the high-energy cut-off increases/disappears rather fast. These results constitute a benchmark on which to test theoretical models for the production of the hard component in these systems. 相似文献
6.
There may exist a transition region from the geometrically thick outer region to the geometrically thin inner region in accretion discs. In this paper we calculate the spectra emitted by the portions of the inner region which are not occulted by the transition region, and deduce the emergent spectra of accretion discs to be observed, taking into account the reflection effect of radiation by the transition region. Our results show that the difference between these emergent spectra of discs and the standard ones of steady accretion disc models is significant when the central portion of discs is occulted by the transition region. It might play a role in the explanation of continuous spectra for some dwarf novae. 相似文献
7.
R. G. Giovanelli 《Solar physics》1975,44(2):315-329
Thermal transfer in closed magnetic tubes in the corona and transition region is described on the basis of a static model in which all heat generated is radiated away, though conduction transfers much of the heat to the transition region prior to emission. The rate of conductive transfer depends on the cross-section of the magnetic tube as it passes through the chromosphere and transition region. This is derived from the pressure in the normal chromosphere. There is then only one main parameter to establish conditions in the corona and transition region, viz. the heating per unit area of the Sun's surface, which must equal the observed radiation from corona and transition region. The density adjusts itself so as to radiate away all heat generated within the tube; conditions in the tube below the transition region have little influence other than to decide where the base of the transition region lies and the width of the region particularly in its lower parts. For the observed rate of heating, the computed densities (or pressures), the ratio of coronal to transition region emissions, and the distribution of radiation in the EUV spectrum agree closely with those observed. The optimum maximum temperatures are found with heating concentrated in the highest regions of the flux tubes. It is only in the lowest 20–40 km of the transition region, where T<105K, that any additional heating is needed to explain EUV line intensities. The equation of heat transfer also has solutions in which the temperature is oscillatory with disance. These do not apply to the normal corona, but may be relevant to prominences. 相似文献
8.
We have calculated an equilibrium temperature distribution over the column depth of plasma in the transition region between the solar corona and chromosphere by assuming the plasma in the transition region and the chromosphere to be heated by the heat flux from the corona and the energy fluxes from the convective zone, respectively. The corona-chromosphere transition region is shown to be actually a stable, very thin layer in which, however, the standard collision approximation is well applicable for describing the heat flux. The solution we found explains well the currently available results of satellite observations of extreme ultraviolet (EUV) radiation from the transition region. 相似文献
9.
分析ＲＸＴＥ卫星ＰＣＡ探测器对ＣｙｇＸ－１的观测数据,得到了其处于高态及高低态转换时的Ｘ射线短时标爆发（Ｓｈｏｔ）结构．在所观测到的三种态中是不对称的,并且不同的状态中Ｓｈｏｔ的结构有明显差异．Ｓｈｏｔ前后沿可分别由双指数函数近似拟合．Ｓｈｏｔ中的快时变过程是由慢的上升前沿和快的下降后沿构成．在所观测态中Ｓｈｏｔ平均宽度约为０．１１秒（ＦＷＨＭ）,比低态时的宽度窄．同一状态中高能段的Ｓｈｏｔ宽度较低能段窄,且更加不对称．转换态的硬度在Ｓｈｏｔ峰前有明显下降,之后迅速上升,Ｓｈｏｔ期间的平均硬度低于非Ｓｈｏｔ期平均值;而高态时峰前硬度没有明显下降,Ｓｈｏｔ期间的平均硬度高于非Ｓｈｏｔ期间的平均值．本文还就Ｓｈｏｔ的产生机制进行了讨论． 相似文献
10.
A new second-order solution to the two-point boundary value problem for relative motion about orbital rendezvous in one orbit
period is proposed. First, nonlinear differential equations to describe the relative motion between a chaser and a target
are presented considering the second-order terms in the gravity. Then, by regarding the second-order terms as external accelerations,
we establish second-order state transition equations. Moreover, the J2 perturbations effects can also be considered in the
state transition equations. Last, the initial relative velocity to fulfill a rendezvous is determined by solving the state
transition equations. Numerical simulations show that the new second-order state transition equations are accurate. The second-order
solution to the two-point boundary value problem on eccentric orbits is valid even if the relative range is farther than 500 km. 相似文献
11.
K. Maslanka 《Astrophysics and Space Science》1983,97(2):461-463
Dynamical systems methods are used to classify radiation-filled Friedmann world-models into those which admit of a phase transition and those which do not. A simple model of a phase transition is adopted. 相似文献
12.
我们认为存在于太阳高层大气中的一种稳定的物质交换,可以起到冷却日冕和加热色球一日冕过渡区的热机作用。还考虑到来自日冕的热传导和过渡区的辐射损失,计算了太阳过渡区的温度、密度和速度分布。并对物质流通量及速度边值与太阳过渡区厚度之间的关系作了讨论。 相似文献
13.
The structure and energy balance of the chromosphere-corona transition region is investigated by means of a static, planar model which is compared with the results of XUV-resonance-line observations. In this model, the transition region is heated by thermal conduction from the corona and cooled by radiative losses. Comparison of the model with observational results implies that this is the dominant process in the energy balance of the transition region, and that the base of the transition region is inherently non-static and/or non-planar. The model explains the observational finding of Noyes et al. (1970) that the number density and the downward heat flux both increase by the same factor from quiet regions to active regions. The implications of these results are discussed with regard to spicules. 相似文献
14.
Brynildsen N. Maltby P. Brekke P. Haugan S.V.H. Kjeldseth-Moe O. 《Solar physics》1999,186(1-2):141-191
We present results from a study of the spatial distributions of line emission and relative line-of-sight velocity in the atmosphere above 17 sunspot regions, from the chromosphere, through the transition region and into the corona, based on simultaneous observations of ten EUV emission lines with the Coronal Diagnostic Spectrometer – CDS on SOHO. We find that the spatial distributions are nonuniform over the sunspot region and introduce the notation 'sunspot loop' to describe an enhanced transition region emission feature that looks like a magnetic loop, extending from inside the sunspot to the surrounding regions. We find little evidence for the siphon flow. Attention is given to the time variations since we observe both a rapid variation with a characteristic time of a few to several minutes and a slow variation with a time constant of several hours to 1 day. The most prominent features in the transition region intensity maps are the sunspot plumes. We introduce an updated criterion for the presence of plumes and find that 15 out of 17 sunspots contain a plume in the temperature range logT5.2–5.6. The relative line-of-sight velocity in sunspot plumes is high and directed into the Sun in the transition region. Almost all the sunspot regions contain one or a few prominent, strongly redshifted velocity channels, several of the channels extend from the sunspot plume to considerable distances from the sunspot. The flow appears to be maintained by plasmas at transition region temperatures, moving from regions located at a greater height outside the sunspots and towards the sunspot. The spatial correlation is high to moderate between emission lines formed in the transition region lines, but low between the transition region lines and the coronal lines. From detailed comparisons of intensity and velocity maps we find transition region emission features without any sign of coronal emission in the vicinity. A possible explanation is that the emission originates in magnetic flux tubes that are too cold to emit coronal emission. The comparisons suggest that gas at transition region temperature occur in loops different from loops with coronal temperature. However, we cannot exclude the presence of transition region temperatures close to the footpoints of flux tubes emitting at coronal temperatures. Regions with enhanced transition region line emission tend to be redshifted, but the correlation between line emission and relative line-of-sight velocity is weak. We extend our conditional probability studies and confirm that there is a tendency for line profiles with large intensities and red shifts (blue shifts) above the average to constitute an increasing (decreasing) fraction of the profiles as the wavelength shift increases. 相似文献
15.
The formation of solar-wind stream structure is investigated. Characteristic features of the solar and coronal magnetic-field structure, morphological features of the white-light corona, and radio maps of the solar-wind transition (transonic) region are compared. The solar-wind stream structure is detected and studied by using radio maps of the transition region, the raggedness of its boundaries, and their deviation from spherical symmetry. The radio maps have been constructed from radioastronomical observations in 1995–1997. It is shown that the structural changes in the transition region largely follow the changes occurring in regions closer to the Sun, in the circumsolar magnetic-field structure, and in the solar-corona structure. The correlations between the magnetic-field strength in the solar corona and the location of the inner (nearest the Sun) boundary of the transition region are analyzed. The distinct anticorrelation between the coronal magnetic-field strength and the distance of the transition region from the Sun is a crucial argument for the penetration of solar magnetic fields into plasma streams far from the Sun. 相似文献
16.
B. Kmpfer 《Astronomische Nachrichten》1988,309(1):19-24
Phenomenological models of cosmic phase transitions are presented. We consider phase transitions (i) with fixed initial and final states or (ii) in the relaxation time approximation. The Friedmann equations are solved and the entropy production due to the non-equilibnum transition is calculated for a bag model equation of state. Numerical examples are given for the confinement transition, but the formulae presented apply directly to the GUT transition, too. 相似文献
17.
Hasi Ray 《Astrophysics and Space Science》2003,283(3):415-436
Accurate theoretical data for the transition probabilities are highly demanding in astrophysics and in the study of plasma
in astrophysical objects and fusion devices. Na-like highly stripped ions of iron group, specially NiXVIII is very important
in this respect. A highly improved basis in a relativistic many-body coupled-cluster method (CCM) to include correlation properly
is employed to calculate excitation energies, the electric quadrupole (E2) transition line strengths and transition probabilities
for NiXVIII. The effect of correlation is studied thoroughly. The present improved data for different atomic/ionic properties
are compared with the available theoretical and/or experimental data and they are in agreement. Some E2 transition data are
reported for the first time.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
在模拟超新星演化时,考虑非奇异一奇异夸克相变因素,与没有考虑奇异相变的情况相比,得到了更强的激波．这可能是奇异相变增加了星核区对流不稳定性所致在本文的计算环境里,一阶奇异夸克相变的结果使具有128MO铁星核的WW（88）模型爆发,打破了瞬发机制只能使约1．1MO铁星核模型爆发的上限,并支持了戴子高等人所作出的奇异夸克相变能提高超新星爆发机会的论断． 相似文献
19.
20.
Previous studies using observations made at low spatial and spectral resolution showed that the resonance lines of He i and He ii are anomalously strong in the quiet Sun when compared with other transition region lines formed at similar temperatures. Here, the higher spatial and spectral resolution provided by the Coronal Diagnostic Spectrometer ( cds ) instrument on board the Solar and Heliospheric Observatory ( SOHO ) is used to re-examine the behaviour of the He i and He ii lines and other transition region lines, in quiet regions near Sun centre. Supergranulation cell boundaries and cell interiors are examined separately. Near-simultaneous observations with the sumer instrument provide information on the lower transition region and the electron pressure. While the lines of He i and He ii have a common behaviour, as do the other transition region lines, the behaviour of the helium lines relative to the other transition region lines is significantly different. The emission measure distributions that account for all transition region lines, except those of helium, fail to produce sufficient emission in the He i and He ii resonance lines by around an order of magnitude, in both supergranulation cell boundary and cell interior regions. The electron pressure appears to be higher in the cell interiors than in the average cell boundaries, although the uncertainties are large. While the VAL-D model gives a closer match to the He i 584.3-Å line, it does not successfully reproduce other transition region lines. 相似文献