共查询到20条相似文献，搜索用时 578 毫秒
1.
The recent twelve-state R-matrix calculations of electron excitation rates in Ciii by Berrington are used to derive level populations applicable to the solar transition region. Line ratios R = I(2p
2 3
P
e
- 2s2p
3
P
°)/I(2s2p
1
P
° - 2s
2 1
S
e
) and R
2=I(2p
2 1
S
e
- 2s2p
1
P
°)/I(2p
2 3
P
e
- 2s2p
3
P
°) deduced from these data in conjunction with the relevent transition probabilities are found to be in much better agreement with the observed quiet Sun values than those determined from the level population calculations of Keenan et al. 相似文献
2.
The ratios I(K
1)/I(H
1) and I(K
3)/I(H
3) were calculated from four semi-empirical models of sunspot umbra. We determined the dependencies of both ratios of such parameters as temperature gradient and atmospheric opacity. A certain influence on the expected ratios I(K
1)/I(H
1) and I(K
3)/I(H
3) can also come from the FIP effect provided it exists in the chromosphere above sunspot umbra. Theoretical and observed values of I(K
1)/I(H
1) and I(K
3)/I(H
3) are compared. It is shown that for one of the sunspots we observed, the values obtained for the ratio I(K
1)/I(H
1) cannot be explained in terms of existing umbra models. 相似文献
3.
G. V. Abrahamyan 《Astrophysics》2003,46(3):304-318
New methods are applied to samples of classical cepheids in the galaxy, the Large Magellanic Cloud, and the Small Magellanic Cloud to determine the interstellar extinction law for the classical cepheids, R
B:R
V:R
I:R
J:R
H:R
K= 4.190:3.190:1.884:0.851:0.501:0.303, the color excesses for classical cepheids in the galaxy, E(B-V)=-0.382-0.168logP+0.766(V-I), and the color excesses for classical cepheids in the LMC and SMC, E(B-V)=-0.374-0.166logP+0.766(V-I). The dependence of the intrinsic color (B-V)0 on the metallicity of classical cepheids is discussed. The intrinsic color (V-I)0 is found to be absolutely independent of the metallicity of classical cepheids. A high precision formula is obtained for calculating the intrinsic colors of classical cepheids in the galaxy: (<B>-<V>)0=0.365(±0.011)+0.328(±0.012)logP. 相似文献
4.
The electron collision excitation rates recently calculated for transitions in Si xiii by Keenan et al. (1987) are used to derive the electron temperature sensitive ratio G(=(f + i)/r and the density sensitive ratio R(=f/i), where i, f, and r are the intercombination (1s
2
1
S – 1s2p
3
P
1, 2) forbidden (1s
2
1
S – 1s2s
3
S), and resonance (1s
2
1
S – 1s2p
1
P), transitions respectively. Also estimated are the values of R in the low-density limit (R
0) as a function of electron temperature. The theoretical G ratio at the temperature of maximum emissivity for Si xiii, G(T
m) = 0.70, is in much better agreement with the observed G for the 1985, May 5 flare determined by McKenzie et al. (G = 0.60 ± 0.07) than is the earlier calculation of Pradhan, who derived G(T
m) = 0.85. The error in the observed R
0 ratio is so large that both our result and Pradhan's fall within the acceptable limits of uncertainty and hence one cannot estimate which of the two is the more accurate. 相似文献
5.
Constantino Tsallis 《Astrophysics and Space Science》2006,305(3):261-271
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
6.
7.
We present new laboratory data on the multiplets 2s
2
1
S -2s2p
3
P, 2s
22p
2
P - 2s2p
2
4
P, and 2s
22p
2
3
P - 2s2p
3
5
S in nitrogen, oxygen and fluorine, and discuss theZ-dependence of their wave-numbers. These multiplets are very faint in laboratory light sources, but can become prominent in
astrophysical sources of low density. Our results confirm the solar identifications of the nitrogen and oxygen multiplets
made by Burtonet al. Predicted positions of the corresponding multiplets in neon are given. 相似文献
8.
Theoretical electron-density-sensitive C III emission line ratios are presented forR
1 =I(2s2p
3
P – 2p
2
3
P)/I(2s2p
1
P – 2p
2
1
S) =I(1176 Å)/I(1247 Å),R
2 =I(2s2p
3
P – 2p
2
3
P)/I(2s
2
1
S – 2s2p
3
P
1) =I(1176 Å)/I(1908 Å), andR
3 =I(2s2p
1
P – 2p
2
1
S)/I(2s
2
1
S – 2s2p
3
P
1) =I(1247 Å)/I(1908 Å). These are significantly different from those deduced previously, principally due to the adoption of improved electron impact excitation rates in the present analysis. Electron densities deduced from the present theoretical line ratios, in conjunction with observed values ofR
1,R
2, andR
3 measured from solar spectra obtained by the Naval Research Laboratory's S082B instrument on boardSkylab, are found to be generally compatible. In contrast, previous diagnostic calculations imply electron densities fromR
1,R
2, andR
3 that differ by up to two orders of magnitude. These results provide observational support for the accuracy of the atomic physics adopted in the present calculations, and the methods employed in the derivation of the theoretical line ratios. 相似文献
9.
A rigorous theoretical investigation of nonlinear electron-acoustic (EA) waves in a plasma system (containing cold electrons, hot electrons obeying a Boltzmann distribution, and hot ions obeying a nonthermal distribution) is studied by the reductive perturbation method. The modified Gardner (MG) equation is derived and numerically solved. It has been found that the basic characteristics of the EA Gardner solitons (GSs), which are shown to exist for α around its critical value α c [where α is the nonthermal parameter, α c is the value of α corresponding to the vanishing of the nonlinear coefficient of the Korteweg-de Vries (K-dV) equation, e.g. α c ≃0.31 for μ=n h0/n i0=0.5, σ=T h /T i =10, n h0, n i0 are, respectively, hot electron and nonthermal ion number densities at equilibrium, T h (T i ) is the hot electron (ion) temperature], are different from those of the K-dV solitons, which do not exist for α around α c , and mixed K-dV solitons, which are valid around α∼α c , but do not have any corresponding double layers (DLs) solution. The parametric regimes for the existence of the DLs, which are found to be associated with positive potential, are obtained. The present investigations can be observed in various space plasma environments (viz. the geomagnetic tail, the auroral regions, the cusp of the terrestrial magnetosphere, etc.). 相似文献
10.
We study the stability of motion in the 3-body Sitnikov problem, with the two equal mass primaries (m
1 = m
2 = 0.5) rotating in the x, y plane and vary the mass of the third particle, 0 ≤ m
3 < 10−3, placed initially on the z-axis. We begin by finding for the restricted problem (with m
3 = 0) an apparently infinite sequence of stability intervals on the z-axis, whose width grows and tends to a fixed non-zero value, as we move away from z = 0. We then estimate the extent of “islands” of bounded motion in x, y, z space about these intervals and show that it also increases as |z| grows. Turning to the so-called extended Sitnikov problem, where the third particle moves only along the z-axis, we find that, as m
3 increases, the domain of allowed motion grows significantly and chaotic regions in phase space appear through a series of
saddle-node bifurcations. Finally, we concentrate on the general 3-body problem and demonstrate that, for very small masses, m
3 ≈ 10−6, the “islands” of bounded motion about the z-axis stability intervals are larger than the ones for m
3 = 0. Furthermore, as m
3 increases, it is the regions of bounded motion closest to z = 0 that disappear first, while the ones further away “disperse” at larger m
3 values, thus providing further evidence of an increasing stability of the motion away from the plane of the two primaries,
as observed in the m
3 = 0 case. 相似文献
11.
J. Perdang 《Astrophysics and Space Science》1975,36(1):111-135
The stellar equilibrium equations for given surface pressureP
* and temperatureT
*, and in the absence of convection, are translated into a nonlinear integral equation, in which the radiusR of the star enters as an eigenvalue. We show that under broad mathematical assumptions on the constitutive equations (equation of state, opacity and energy generation) a global existence and uniqueness property can be formulated. If a valueP
M
is selected, which restricts the allowed pressure and temperature range |P(r)–P
*|+E|T(r)–T
*P
M
(E, arbitrary constant of dimensions of a pressure over temperature), thenat least one solutionP(r),T(r) exists in the pressure-temperature range chosen, for anyR<R
E
. This solution isunique forR<R
c
.R
E
andR
c
are expressed in terms of the constitutive equations, and of the pressure-temperature range adopted. A physical argument in favour of the stability of this solution is presented. 相似文献
12.
Three wavelet functions: the Morlet wavelet, the Paul wavelet, and the DOG wavelet have been respectively performed on both
the monthly Wolf sunspot numbers (Rz) from January 1749 to May 2004 and the monthly group sunspot numbers (Rg) from June 1795 to December 1995 to study the evolution of the Gleissberg and Schwabe periods of solar activity. The main
results obtained are (1) the two most obvious periods in both the Rz and Rg are the Schwabe and Gleissberg periods. The Schwabe period oscillated during the second half of the eighteenth century and
was steady from the 1850s onward. No obvious drifting trend of the Schwabe period exists. (2) The Gleissberg period obviously
drifts to longer periods the whole consideration time, and the drifting speed of the Gleissberg period is larger for Rz than for Rg. (3) Although the Schwabe-period values for Rz and Rg are about 10.7 years, the value for Rz seems slightly larger than that for Rg. The Schwabe period of Rz is highly significant after the 1820s, and the Schwabe period of Rg is highly significant over almost the whole consideration time except for about 20 years around the 1800s. The evolution
of the Schwabe period for both Rz and Rg in time is similar to each other. (4) The Gleissberg period in Rz and Rg is highly significant during the whole consideration time, but this result is unreliable at the two ends of each of the time
series of the data. The evolution of the Gleissberg period in Rz is similar to that in Rg. 相似文献
13.
M. Blaha 《Solar physics》1971,17(1):99-116
Equilibrium population of Fexiv levels in coronal conditions was calculated including configurations 3s
23p, 3s3p
2, 3s
23d, 3p
3, 3s3p3d, 3s
24s, 3s
24p, 3s
24d, 3s
24f. Relative populations of selected levels are given in Table VII. Figure 1 shows the dependence of relative intensities of
the strongest lines on electron density. Certain line ratios can be used for the determination of N
e
.E.g., at T=2 × 106
K and with a dilution factor 0.4, the intensity ratio of λ211.3 and λ219.0 changes by a factor of 65 if N
e
increases from 107 to 1011 (Table VIII). Cascades from the 3s3p3d and 3p
3 configurations are important in the population of some levels of 3s3p
2 (Table VI). A possibility of identification of additional lines in the solar spectrum is indicated.
NAS-NRC Resident Research Associate. 相似文献
14.
When μ is smaller than Routh’s critical value μ
1 = 0.03852 . . . , two planar Lyapunov families around triangular libration points exist, with the names of long and short
period families. There are periodic families which we call bridges connecting these two Lyapunov families. With μ increasing from 0 to 1, how these bridges evolve was studied. The interval (0,1) was divided into six subintervals (0, μ
5), (μ
5, μ
4), (μ
4, μ
3), (μ
3, μ
2), (μ
2, μ
1), (μ
1, 1), and in each subinterval the families B(pL, qS) were studied, along with the families B(qS, qS′). Especially in the interval (μ
2, μ
1), the conclusion that the bridges B(qS, qS′) do not exist was obtained. Connections between the short period family and the bridges B(kS, (k + 1)S) were also studied. With these studies, the structure of the web of periodic families around triangular libration points
was enriched. 相似文献
15.
F. Zagury 《Astronomische Nachrichten》2012,333(2):160-165
This article discusses the interstellar extinction curve in the visible and the value of the ratio of absolute to selective extinction RV = AV/E (B – V). It is concluded that the visible extinction curve is likely to be linear in the visible and that indirect estimates of RV from tentative determinations of AV or from infrared and UV observations are questionable. There is currently no evidence of any variation of RV with direction. If RV is close to 3, as it has been inferred from mid‐infrared data, starlight in the visible is extinguished by a factor F /F0 = (2.5 e–2μm/λ)E (B –V). But if the visible wavelength range alone is considered, 4 appears as its most natural and probable value and F /F0 = e–2E (B –V)/λ (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
Recent R-matrix calculations of electron excitation rates for Mg vii and Si ix are used to determine the theoretical density sensitive emission line ratios R
1= I(2s2p
3
1
D
0 - 2s
2
2p
2
1
D
e
)/I(2s2p
3
3
S
0 - 2s
2
2p
2
3
P
2
e
) and R
2= I(2s2p
3
1
P
0 - 2s
2
2p
2
1
D
e
)/I(2s2p
3
3
S
0 - 2s
2
2p
2
3
P
2
e
). These are found to be quite similar to the earlier results of Mason and Bhatia. Electron densities derived using observed R
1 and R
2
ratios from Skylab NRL XUV spectra of solar flares and active regions are in good agreement, and compare favourably with those deduced from ions formed at similar electron temperatures to Mg vii and Si ix. 相似文献
17.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2012,337(1):367-372
Combining the kinematical definitions of the two dimensionless parameters, the deceleration q(x) and the Hubble t
0
H(x), we get a differential equation (where x=t/t
0 is the age of the universe relative to its present value t
0). First integration gives the function H(x). The present values of the Hubble parameter H(1) [approximately t
0
H(1)≈1], and the deceleration parameter [approximately q(1)≈−0.5], determine the function H(x). A second integration gives the cosmological scale factor a(x). Differentiation of a(x) gives the speed of expansion of the universe. The evolution of the universe that results from our approach is: an initial
extremely fast exponential expansion (inflation), followed by an almost linear expansion (first decelerated, and later accelerated).
For the future, at approximately t≈3t
0 there is a final exponential expansion, a second inflation that produces a disaggregation of the universe to infinity. We
find the necessary and sufficient conditions for this disaggregation to occur. The precise value of the final age is given
only with one parameter: the present value of the deceleration parameter [q(1)≈−0.5]. This emerging picture of the history of the universe represents an important challenge, an opportunity for the
immediate research on the Universe. These conclusions have been elaborated without the use of any particular cosmological
model of the universe. 相似文献
18.
In this paper, we have investigated that tilted Bianchi Type I cosmological models for stiff perfect fluid under a supplementary
condition A = B
n
between metric potentials, is not possible. The tilted solution is also not possible when we assume A = t
ℓ, B = t
m
, C = t
n
; ℓ, m and n are constants for ε = p. Thus to preserve tilted nature of model, we assume p = γε, 0 ≤ γ ≤ 1 (barotropic equation of state) for the case A = t
ℓ
B = t
m
and C = t
n
. The physical and geometrical aspects of the models are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
K. S. Adhav 《Astrophysics and Space Science》2011,335(2):611-617
The Bianchi type-V cosmological model with variable modified Chaplygin gas having the equation of state p=Aρ−B/ρ
α
, where 0≤α≤1, A is a positive constant and B is a positive function of the average scale factor a(t) of the universe [i.e. B=B(a)] has been studied. While studying its role in accelerated phase of the universe, it is observed that the equation of state
of the variable modified Chaplygin gas interpolates from radiation dominated era to quintessence dominated era. The statefinder
diagnostic pair {r,s} is adopted to characterize different phases of the universe. 相似文献
20.
The transport of thermal radiation has been considered within a finite slab which absorb and scatter anisotropically. The problem involves the space-dependent single-scattering albedow(x). Two approximations are taken forw(x). In the first it is represented in exponential form asw(x)=w
0 exp(–x/s), wherew
0 ands are given constants andx is the optical variable. The second approximation assumes the formw(x) =
r=0
R
d
r
*
p
r
(x/a), whered
r
*
are known expansion coefficients anda is the half optical thickness of the slab. Analytic expressions for the forward, backward radiation intensities and fluxes are given in each approximation. The solution of the linear transport equation is performed on the basis of integral Fourier transforms. 相似文献