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1.
The influence of the potential well depth US(N)U_{\Sigma}^{(N)} of Σ in nuclear matter on the surface gravitational red-shift of a proto neutron star is examined within the framework of the relativistic mean field theory for the baryon octet system. It is found that as US(N)U_{\Sigma}^{(N)} increases from −35 MeV to +35 MeV, the surface gravitational red-shift increases and the influence of the negative US(N)U_{\Sigma}^{(N)} on the surface gravitational red-shift is larger than that of the positive ones. Furthermore, the M max/R and the surface gravitational red-shift corresponding to the maximum mass all increase as the US(N)U_{\Sigma}^{(N)} increases, M max and R being the maximum mass of the proto neutron star and the corresponding radius respectively.  相似文献   

2.
The effect of the Σ-meson well depth on the gravitational redshift is examined within the framework of relativistic mean field theory for the baryon octet system. It is found that, for a stable neutron star, the gravitational redshift increases with the central energy density increase or with the mass increase but decreases as the radius increases. Considering a change of US(N)U_{\Sigma}^{(N)} from −30 MeV to 30 MeV, for a stable neutron star the gravitational redshift near to the maximum mass increases. In addition, it is also found that the growth of the US(N)U_{\Sigma}^{(N)} makes the gravitational redshift as a function of M max /R increase, the higher the US(N)U_{\Sigma}^{(N)} the less the change in the gravitational redshift.  相似文献   

3.
The isotropic cumulative burst rate of 7030 –6000 +10000 yr–1 at a fluence ofS=8.47×10–9 erg–1 cm–2 determined by Beurleet al. from their observation of two gamma-ray bursts is shown to be statistically improbable. The difficulty arises from their assumption that the power law cumulative distribution function index equals one. Their observations are rediscussed and an upper limit ofN(>8.47×10–9 erg cm–2)<5400 yr–1 is proposed.  相似文献   

4.
We study a model of mergers affecting only the progenitors of present E/SO. We adopt the standard scenarios of star formation as prescribed by Guiderdoni & Rocca-Volmerange. The merging process is parametrized under the assumptions of(1) self-similarity of the Schechter MF and(2) mass conservation. Nine models are discussed. The predictions are compared with counts ofB J ,U +,F +,N + bands. E/SO mergers account for the excess of the faintest blue galaxies without causing excess in redder bands. However, as we no longer have enough mergers at brighter magnitudes, a plain E/SO merging model fits less tightly for the redshift and the colour distributions. Detection effect, a steeper slope of LF may be ways to improve. Our models predict acceptable merger frequencies atz = 0.5 although some models predict more interacting galaxies than observation atz = 0.  相似文献   

5.
A new formula for the distribution of matter in the solar system is derived by assuming that the planets were formed from trapped particles of a cosmic dust disk attached to the Sun. Contrary to Boltzmann's distribution which predicts thermal collapse of this cloud on the Sun, it is found that if the primeval particles move on circular orbits according to Kepler's law, then their velocities obey a 2-D global Maxwellian and their distribution in space is given by p 0 (r)=(α r 2)\exp(-α r) (Km-1); α = 888.73 × 106 Km. The form ofp 0 (r) agrees with the observed mass distribution of the planets and explains their present large angular momentum. PACS numbers: 96.35.Cp, 96.35.Fs This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

6.
We investigate selection effects on the size and frequency relation (logN-logS curve) of cosmic gamma-ray bursts. After analyzing the published data, we find an indication that an effect is caused by the different time profiles of the bursts. The effect is important for small bursts and causes significant changes in the logN-logS curve. in order to avoid this selection effect, we mention that it is essential to use the logN-logP relation of the logN-logS relation, as already suggested by other authors. Here,P is the peak flux of the burst, which is free from bias due to the difference in time profiles. After an analysis of the published data, we find a distribution nearP –3/2 in the range above a peak flux of 40 counts/0.25 s.We also show that the relation between the logN-logP curve and the observed celestial distribution for the bursts can easily be explained by our general arguments on a disk-like spatial distribution of burst sources in the Galaxy.  相似文献   

7.
The cornerstones of Boltzmann-Gibbs and nonextensive statistical mechanics respectively are the entropies S BG ≡ −k ∑ i = 1 W p i ln p i and S q ≡ k (1−∑ i = 1 W p i q )/(q−1) (q∊ℜ S 1 = S BG ). Through them we revisit the concept of additivity, and illustrate the (not always clearly perceived) fact that (thermodynamical) extensivity has a well defined sense only if we specify the composition law that is being assumed for the subsystems (say A and B). If the composition law is not explicitly indicated, it is tacitly assumed that A and B are statistically independent. In this case, it immediately follows that S BG (A+B) = S BG (A)+S BG (B), hence extensive, whereas S q (A+B)/k = [S q (A)/k]+[S q (B)/k]+(1−q)[S q (A)/k][S q (B)/k], hence nonextensive for q ≠ 1. In the present paper we illustrate the remarkable changes that occur when A and B are specially correlated. Indeed, we show that, in such case, S q (A+B) = S q (A)+S q (B) for the appropriate value of q (hence extensive), whereas S BG (A+B) ≠ S BG (A)+S BG (B) (hence nonextensive). We believe that these facts substantially improve the understanding of the mathematical need and physical origin of nonextensive statistical mechanics, and its interpretation in terms of effective occupation of the W a priori available microstates of the full phase space. In particular, we can appreciate the origin of the following important fact. In order to have entropic extensivity (i.e., lim N→∞ S(N)/N < ∞, where N≡ numberof elements of the system), we must use (i) S BG , if the number W eff of effectively occupied microstates increases with N like W {{eff}}∼ W ∼ μ N (μ ≥ 1); (ii) S q with q = 1−1/ρ, if W {{eff}}∼ N^ρ < W (ρ ≥ 0). We had previously conjectured the existence of these two markedly different classes. The contribution of the present paper is to illustrate, for the first time as far as we can tell, the derivation of these facts directly from the set of probabilities of the W microstates.  相似文献   

8.
The physical characteristics radius, mass, mean density, gravitational potential and acceleration, gravitational and internal energy are presented with the aid of the gamma function forN-dimensional, radially-symmetric polytropes. The virial theorem with external pressure is derived in the relativistic limit, with Newtonian gravitation still valid. The gravitational energy of polytropes obeying the generalized Schuster—Emden integral is shown to be finite. Finiteness of mass and radius is discussed for the cases of practical interestN=1 (slab),N=2 (cylinder), andN=3 (sphere). Uniform contraction or expansion ofN-dimensional polytropes is considered in the last section.  相似文献   

9.
The statistical mechanics of an isolated self-gravitating system consisting ofN uniform mass sheets is considered using both canonical and microcanonical ensembles. The one-particle distribution function is found in closed form. The limit for large numbers of sheets with fixed total mass and energy is taken and is shown to yield the isothermal solution of the Vlasov equation. The order of magnitude of the approach to Vlasov theory is found to be 0(1/N). Numerical results for spatial density and velocity distributions are given.  相似文献   

10.
The [SI] lines are due to transitions within the 3s23p4 ground configuration of neutral sulphur. The results are presented from a search for the [Si] lines in the Fraunhofer spectrum. Two identifications are proposed with faint features in the Fraunhofer spectrum: 1D2-1S0 at = 7725.02 Å and 3P2-1D2 at = 10821.23 Å. Their measured equivalent widths are shown to confirm the value for the solar abundance of sulphur, logN S = 7.21 (in the scale logN H = 12.00), which is derived from the permitted high-excitation lines. These lines give the first convincing identification of [Si] lines in an astrophysical source.  相似文献   

11.
Ostryakov  V.M.  Stovpyuk  M.F. 《Solar physics》1999,189(2):357-372
The energy and charge spectra of Fe ions accelerated in gradual events are calculated numerically. Our results are compared with the available observations. Stripping of Fe ions by thermal electrons and protons during ion acceleration in the solar corona results in the dependence of mean charge barq Feon energy. We consider the influence of varying plasma parameters (temperature T, number density N, and spectral index of turbulence S) on the charge distribution of iron. Our calculations indicate T106 K and N(0.5–1)×1010 cm–3at the accelerating site, provided the characteristic acceleration time is about 1 s. The calculated charge spectra for S>2 and S<2 turn out to be different, but some theoretical and experimental uncertainties do not yet allow this parameter to be extracted from observational data. The theoretically obtained charge distributions of Fe could be important in the light of ACE spacecraft data which are currently available for analysis.  相似文献   

12.
We discuss a new N-body simulation method for studying black hole binary dynamics. This method avoids previous numerical problems due to large mass ratios and trapped orbits with short periods. A treatment of relativistic effects is included when the associated time-scale becomes small. Preliminary results with up to N = 2.4 × 10 5 particles are obtained showing systematic eccentricity growth until the relativistic regime is reached, with subsequent coalescence in some cases. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

13.
The resonance of GEOS-II (1968-002A) with 13th-order terms of the geopotential is analyzed. The odd-degree geopotential coefficients (13, 13), (15, 13), and (17, 13) given by Yionoulis most accurately model the resonance effects on GEOS-II of any of the published sets of 13th-order coefficients. However, this set is not adequate for precision orbit determination; additional even-degree coefficients are required.Values ofC 14,13(=0.57×10–21) andS 14,13(=6.5×10–21) to be used with the odd-degree set of Yionoulis were obtained from an analysis of the observed along-track position variation of GEOS-II. These coefficients, when used with those of Yionoulis, yield greatly improved fits to the data and orbital prediction capability. However, further refinement is possible because the small effects of the remaining even-degree resonant terms were not modeled.The composite coefficientsC 13,13(=1.7×10–20) andS 13,13(=+2.7×10–20) were obtained under the assumption that the (13, 13) spherical harmonic of the geopotential is responsible for all of the observed along-track variation of GEOS-II due to resonance. The good agreement of these deliberately composite values with some published values ofC 13,13 andS 13,13 suggests that some of the published values may also be composite to some extent.These coefficients are hereinafter referred to as the APL coefficients.  相似文献   

14.
The distribution functions for the total linear and angular momentum ofN particles selected from an equilibrium gas are derived. The most probable momentum increases withN. If the particles of an astronomical system are assumed to come from an original cosmic gas, universal mass-versus-momentum relations can be derived. The derived mass-versus-angular momentum relation is similar but not identical to that which has been reported. The derived relationship applies to the initial conditions and evolutionary effects may account for the difference between this prediction and the observed relationship.  相似文献   

15.
An electron temperature estimate based on the absoluteB H/B[Nii] ratio is established over this part of the IC 1318 b, c, complex for which the absorption of light by dust is demonstrably low. This estimate gives an electron temperature of 6900 K±1200 K. Contour maps showing the overall distribution of the electron temperatureT e for constantf(=N(N+)/N(N)) and the overall distribution off for constantT e are also produced. The limitations of the method and the validity of the results are also discussed.  相似文献   

16.
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   

17.
The population densities of all levels with principal quantum numbern=2 in a number of helium-like ions with nuclear charge numberZ, in the range 6 to 28 have been evaluated as a function of various parameters, i.e., electron temperature,T e, electron density,N e, radiation temperature,T r, dilution factor,W, and of the state of ionization. The spectral line fluxes from all possible radiative transitions from these levels have been calculated for an optically thin plasma. The effects of cascades following collisional excitation of higher levels or radiative and dielectronic recombination have been computed in detail. Innershell ionization of the lithium-like ion to form the helium-like ion in a 23 S or 21 S state has been considered. It can have a strong influence on the forbidden line intensity in a non-equilibrium plasma. Collisional and radiative coupling of levels of the same multiplicity (e.g. 23 S 1 and 23 P 2,1,0) have been considered as a function ofT e, Ne orT r, W, respectively. The computations were performed both for stationary and time-varying plasmas. In the latter case strong departures from a stationary ionization equilibrium can significantly alter the line fluxes. A few examples of the results are shown and discussed.  相似文献   

18.
An analysis of the Perseid meteoroid mass distribution is given. It is shown that particle mass distributions are qualitatively the same along the entire orbit of the stream. The extra minima in the cross sections of the stream at the ascending and descending branches of the curve of the parameter S indicate a jetlike nature of the stream. The variations of the nodal longitudes of maximum stream activity versus the minimum observed mass of meteoroids are found along the entire orbit of the stream. The positions of maximum activity for particles with minimum detectable masses larger than 1 and 10?3 g are shifted by 1.4 degrees in solar longitude, with larger longitudes for smaller particles.  相似文献   

19.
Effects of Hall current on free convection and mass transfer flow through a porous medium bounded by a vertical surface has been analysed. The problem is solved analytically. The velocity profiles are shown on graphs. Effects ofm (Hall parameter).K * (permeability parameter), and Sc (Schmidt number) on velocity are discussed.  相似文献   

20.
Umbral spectra are shown to contain an absorption feature attributable to the Tl i transition 6p 2 P°3/2–7s 2 S 1/2 at 5350 Å. Analysis of the umbral spectrum suggests a solar abundance in the 0.72< log N(Tl)T<1.10 on the standard scale log N(H) = 12.00. Unidentified blends limit the accuracy of the abundance determination.  相似文献   

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