共查询到20条相似文献,搜索用时 31 毫秒
1.
Qiang Yuan Hao-Yi Wan Tong-Jie Zhang Ji-Ren Liu Long-Long Feng Li-Zhi Fang 《New Astronomy》2009,14(2):152-159
It has been revealed recently that, in the scale free range, i.e. from the scale of the onset of nonlinear evolution to the scale of dissipation, the velocity and mass density fields of cosmic baryon fluid are extremely well described by the self-similar log-Poisson hierarchy. As a consequence of this evolution, the relations among various physical quantities of cosmic baryon fluid should be scale invariant, if the physical quantities are measured in cells on scales larger than the dissipation scale, regardless the baryon fluid is in virialized dark halo, or in pre-virialized state. We examine this property with the relation between the Compton parameter of the thermal Sunyaev–Zel’dovich effect, y(r), and X-ray luminosity, Lx(r), where r being the scale of regions in which y and Lx are measured. According to the self-similar hierarchical scenario of nonlinear evolution, one should expect that (1) in the y(r) ? Lx(r) relation, y(r) = 10A(r)[Lx(r)]α(r), the coefficients A(r) and α(r) are scale-invariant; (2) The relation y(r) = 10A(r)[Lx(r)]α(r) given by cells containing collapsed objects is also available for cells without collapsed objects, only if r is larger than the dissipation scale. These two predictions are well established with a scale decomposition analysis of observed data, and a comparison of observed y(r) ? Lx(r) relation with hydrodynamic simulation samples. The implication of this result on the characteristic scales of non-gravitational heating is also addressed. 相似文献
2.
Boris Garfinkel 《Celestial Mechanics and Dynamical Astronomy》1982,28(1-2):153-154
In previous publications the author has constructed a long-periodic solution of the problem of the motion of the Trojan asteroids, treated as the case of 1:1 resonance in the restricted problem of three bodies. The recent progress reported here is summarized under three headings:
- The nature on the long-periodic family of orbits is re-examined in the light of the results of the numerical integrations carried out by Deprit and Henrard (1970). In the vicinity of the critical divisor $$D_k \equiv \omega _1 - k\omega _2 ,$$ not accessible to our solution, the family is interrupted by bifurcations and shortperiodic bridges. Parametrized by the normalized Jacobi constant α2, our family may, accordingly, be defined as the intersection of admissible intervals, in the form $$L = \mathop \cap \limits_j \left\{ {\left| {\alpha - \alpha _j } \right| > \varepsilon _j } \right\};j = k,k + 1, \ldots \infty .$$ Here, {αj(m)} is the sequence of the critical αj corresponding to the exactj: 1 commensurability between the characteristic frequencies ω1 and ω2 for a given value of the mass parameterm. Inasmuch as the ‘critical’ intervals |α?αj|<εj can be shown to be disjoint, it follows that, despite the clustering of the sequence {αj} at α=1, asj→∞, the family extends into the vicinity of the separatrix α=1, which terminates the ‘tadpole’ branch of the family.
- Our analysis of the epicyclic terms of the solution, carrying the critical divisorD k , supports the Deprit and Henrard refutation of the E. W. Brown conjecture (1911) regarding the termination of the tadpole branch at the Lagrangian pointL 3. However, the conjecture may be revived in a refined form. “The separatrix α=1 of the tadpole branch spirals asymptotically toward a limit cycle centered onL 3.”
- The periodT(α,m) of the libration in the mean synodic longitude λ in the range $$\lambda _1 \leqslant \lambda \leqslant \lambda _2$$ is given by a hyperelliptic integral. This integral is formally expanded in a power series inm and α2 or \(\beta \equiv \sqrt {1 - \alpha ^2 }\) .
3.
R.H. Giese 《Planetary and Space Science》1973,21(3):513-521
To provide material for interpretations of forthcoming zodiacal light measurements the characteristics of 468 single-component, in-ecliptic models are summarized in two survey diagrams. The models are based on Mie theory and on a power law dn ∞ r?γα?kdα for the dependence of the particle number density n on solar distance r and on the size parameter α (circumference/wavelength). The size range involves particles with αmin ≤ α ≤ 120; (αmin = 1,2,4,10,60), flat (k = 2·5) and steep (k = 4) size spectra, and complex refractive indices m = m1 ? m2i with m1 = 1·33; 1·5; 1·7 and m2 = 0; 0·01; 0·05; 0·1.The models suggest that the spatial variation of dust particle number densities should be less than about ∞ r?0·5 in the ecliptic plane. Either dielectric particles of tenth-micron size or absorbing particles of half-micron size or very slightly absorbing particles of some tens of microns in size are able to produce polarization that agrees in sign and location of the maximum with the observations. Ambiguities can only be removed by considering intensity and polarization over a wide range of wavelengths. 相似文献
4.
K.J. Meech J. Pittichová B. Yang P. Candia Y. Fernández D. Polishook G. Sarid 《Icarus》2011,213(1):323-344
We present observational data for Comet 9P/Tempel 1 taken from 1997 through 2010 in an international collaboration in support of the Deep Impact and Stardust-NExT missions. The data were obtained to characterize the nucleus prior to the Deep Impact 2005 encounter, and to enable us to understand the rotation state in order to make a time of arrival adjustment in February 2010 that would allow us to image at least 25% of the nucleus seen by the Deep Impact spacecraft to better than 80 m/pixel, and to image the crater made during the encounter, if possible. In total, ∼500 whole or partial nights were allocated to this project at 14 observatories worldwide, utilizing 25 telescopes. Seventy percent of these nights yielded useful data. The data were used to determine the linear phase coefficient for the comet in the R-band to be 0.045 ± 0.001 mag deg−1 from 1° to 16°. Cometary activity was observed to begin inbound near r ∼ 4.0 AU and the activity ended near r ∼ 4.6 AU as seen from the heliocentric secular light curves, water-sublimation models and from dust dynamical modeling. The light curve exhibits a significant pre- and post-perihelion brightness and activity asymmetry. There was a secular decrease in activity between the 2000 and 2005 perihelion passages of ∼20%. The post-perihelion light curve cannot be easily explained by a simple decrease in solar insolation or observing geometry. CN emission was detected in the comet at 2.43 AU pre-perihelion, and by r = 2.24 AU emission from C2 and C3 were evident. In December 2004 the production rate of CN increased from 1.8 × 1023 mol s−1 to QCN = 2.75 × 1023 mol s−1 in early January 2005 and 9.3 × 1024 mol s−1 on June 6, 2005 at r = 1.53 AU. 相似文献
5.
Europa's surface is chemically altered by radiolysis from energetic charged particle bombardment. It has been suggested that hydrated sulfuric acid (H2SO4·nH2O) is a major surface species and is part of a radiolytic sulfur cycle, where a dynamic equilibrium exists between continuous production and destruction of sulfur polymers Sx, sulfur dioxide SO2, hydrogen sulfide H2S, and H2SO4·nH2O. We measured the rate of sulfate anion production for cyclo-octal sulfur grains in frozen water at temperatures, energies, and dose rates appropriate for Europa using energetic electrons. The measured rate is GMixture(SO42−)=fSulfur (r0/r)βG1 molecules (100 eV)−1, where fSulfur is the sulfur weight fraction, r is the grain radius, r0=50 μm, β≈1.9, and G1=0.4±0.1. Equilibrium column densities N are derived for Europa's surface and follow the ordering N(H2SO4) » N(S)>N(SO2)>N(H2S). The lifetime of a sulfur atom on Europa's surface for radiolysis to H2SO4 is τ(−S)=120(r/r0)β years. Rapid radiolytic processing hides the identity of the original source of the sulfurous material, but Iogenic plasma ion implantation and an acidic or salty ocean are candidate sources. Sulfate salts, if present, would be decomposed in <3800 years and be rapidly assimilated into the sulfur cycle. 相似文献
6.
7.
The model of a presupernova’s carbon-oxygen (C-O) core with an initial mass of 1.33 M ⊙, an initial carbon abundance X C (0) =0.27, and a mean rate of increase in mass of 5 × 10?7 M ⊙ yr?1 through accretion in a binary system evolved from the central density and temperature ρc=109 g cm?3 and T c=2.05 × 108K, respectively, by forming a convective core and its subsequent expansion to an explosive fuel ignition at the center. The evolution and explosion equations included only the carbon burning reaction 12C+12C with energy release corresponding to the complete conversion of carbon and oxygen (at the same rate as that of carbon) into 56Ni. The ratio of mixing length to convection-zone size αc was chosen as the parameter. Although the model assumptions were crude, we obtained an acceptable (for the theory of supernovae) pattern of explosion with a strong dependence of its duration on αc. In our calculations with sufficiently large values of this parameter, αc=4.0 × 10?3 and 3.0×10?3, fuel burned in the regime of prompt detonation. In the range 2.0×10?3≥αc≥3.0×10?4, there was initially a deflagration with the generation of model pulsations whose amplitude gradually increased. Eventually, the detonation regime of burning arose, which was triggered from the model surface layers (with m ? 1.33 M ⊙) and propagated deep into the model up to the deflagration front. The generation of model pulsations and the formation of a detonation front are described in detail for αc=1.0 × 10?3. 相似文献
8.
We have investigated the characteristics of the distribution of neutron exposures (“DNE” hereafter) in the He-shell nucleosynthesis regions in the model of s-process nucleosynthesis in low-mass AGB (Asymptotic Giant Branch) stars in 13C radiatively burning conditions. The result indicates that although the DNE obtained with this model is still approximately exponential, like those of the previous convective s-process scenarios, the relation between the neutron exposure Δτ of each pulse and the mean neutron exposure τ0 is no longer τ0 = −Δτ/ln r, rather, it is now approximately τ0 = −Δτ/ ln{q[1.0020 + 0.6602(r − q) + 4.6125(r − q)2− 10.8962(r − q)3+ 13.9138(r − q)4]} (r is the overlap factor, q is the mass ratio of the 13C shell to the He shell). This formula unifies the stellar model of radiative s-process with the classical model from the angle of DNE. 相似文献
9.
In the first part of these notes new expressions—simpler than any previously obtained—are presented in integral form for the derivatives of the α n 0 -functions (required for an interpretation of the observed light changes of eclipsing variables) with respect to the fractional radiir 1, 2 and projected separation δ of their centres in terms of the modified Bessel functionsK 0, 1 (x) of the second kind; and utilized for establishing new asymptotic formulae for the computation of ‘boundary integrals’ of the formJ ?1 0 ,n(μ). In the second part of this paper, by a resort to bi-polar coordinates, we shall establish a new type of expansions for the α n 0 -functions valid for any type of eclipses, and converging faster than the expansions of the cross-correlation integral of the form (1) for α n 0 that have so far been established. 相似文献
10.
Boris Garfinkel 《Celestial Mechanics and Dynamical Astronomy》1973,8(2):207-212
If a dynamical problem ofN degress of freedom is reduced to the Ideal Resonance Problem, the Hamiltonian takes the form 1 $$\begin{array}{*{20}c} {F = B(y) + 2\mu ^2 A(y)\sin ^2 x_1 ,} & {\mu \ll 1.} \\ \end{array} $$ Herey is the momentum-vectory k withk=1,2?N, x 1 is thecritical argument, andx k fork>1 are theignorable co-ordinates, which have been eliminated from the Hamiltonian. The purpose of this Note is to summarize the first-order solution of the problem defined by (1) as described in a sequence of five recent papers by the author. A basic is the resonance parameter α, defined by 1 $$\alpha \equiv - B'/\left| {4AB''} \right|^{1/2} \mu .$$ The solution isglobal in the sense that it is valid for all values of α2 in the range 1 $$0 \leqslant \alpha ^2 \leqslant \infty ,$$ which embrances thelibration and thecirculation regimes of the co-ordinatex 1, associated with α2 < 1 and α2 > 1, respectively. The solution includes asymptotically the limit α2 → ∞, which corresponds to theclassical solution of the problem, expanded in powers of ε ≡ μ2, and carrying α as a divisor. The classical singularity at α=0, corresponding to an exact commensurability of two frequencies of the motion, has been removed from the global solution by means of the Bohlin expansion in powers of μ = ε1/2. The singularities that commonly arise within the libration region α2 < 1 and on the separatrix α2 = 1 of the phase-plane have been suppressed by means of aregularizing function 1 $$\begin{array}{*{20}c} {\phi \equiv \tfrac{1}{2}(1 + \operatorname{sgn} z)\exp ( - z^{ - 3} ),} & {z \equiv \alpha ^2 } \\ \end{array} - 1,$$ introduced into the new Hamiltonian. The global solution is subject to thenormality condition, which boundsAB″ away from zero indeep resonance, α2 < 1/μ, where the classical solution fails, and which boundsB′ away from zero inshallow resonance, α2 > 1/μ, where the classical solution is valid. Thedemarcation point 1 $$\alpha _ * ^2 \equiv {1 \mathord{\left/ {\vphantom {1 \mu }} \right. \kern-\nulldelimiterspace} \mu }$$ conventionally separates the deep and the shallow resonance regions. The solution appears in parametric form 1 $$\begin{array}{*{20}c} {x_\kappa = x_\kappa (u)} \\ {y_1 = y_1 (u)} \\ {\begin{array}{*{20}c} {y_\kappa = conts,} & {k > 1,} \\ \end{array} } \\ {u = u(t).} \\ \end{array} $$ It involves the standard elliptic integralsu andE((u) of the first and the second kinds, respectively, the Jacobian elliptic functionssn, cn, dn, am, and the Zeta functionZ (u). 相似文献
11.
《Chinese Astronomy and Astrophysics》1982,6(1):76-78
Using the rigorous solution for the perturbing potential obtained in Ref. /1/, which contains a non-wavy term, we found a relation between the thickness of the galaxy and the radius r0 at which the arms start, αr0 = 7. From Ref. /2/, we selected 50 spiral galaxies, found their r0 values, hence their average thickness. 相似文献
12.
Zeng-yuan Yue 《Chinese Astronomy and Astrophysics》1983,7(3):186-194
It is shown that the asymptotic σ1(r) and ψ1(r) relations can be derived very simply by using the method of double series expansion, where σ1, ψ1(r,0) and ψ1 are the surface density perturbation, the gravitational potential perturbation at the symmetric plane Z=0 and the average potential perturbation respectively. The results are accurate to the order of both m2(kr)?2 and k〈∣z∣〉, where m is the number of spiral arms, k is the radial wave number, r is the distance from the centre of the galaxy, and 〈∣z∣〉 is the average vertical distance of a star from the Symmetrie plane Z=0. Such an accuracy is usually sufficient for the discussion of spiral modes in a spiral galaxy of small but finite disk thickness. It is pointed out that ψ1(r,0)~(σ1(r) relation can be expressed in a unified form for different vertical density profiles if 〈∣z∣〉 is adopted as the thickness scale, and that ψ1(r,0)~(σ1(r) can be expressed in a unified form for different vertical density profiles if 〈∣z?z∣〉 the average vertical separation between two stars, is adopted as the thickness scale. Only the value of the ratio is a functional of the vertical density profile. However, for the usual physically meaningful profiles, these values are very close to each other: It is for the Gaussian profile, for the profile, and 1.5 for the profile. 相似文献
13.
We have investigated how the gradients of temperature and expansion velocities will change the emergent profiles from an extended medium in spherical symmetry. Variation of the source function and expansion velocities are assumed. The following variations of temperature are employed:
- T(r) ; T0 (isothermal case)
- T(r) ; T0(r/r0)1/2
- T(r) ; T0(r/r0)-1
- T(r) ; T0(r/r0)-2
- T(r) ; T0(r/r0)-3
14.
Crank-Nicholson solutions are obtained to the time-dependent Fokker-Planck equation for propagation in the interplanetary medium following a point in time injection of energetic solar particles and including the acceleration terms $$\frac{\partial }{{\partial T}}\left( {D_{TT} \frac{{\partial U}}{{\partial T}}} \right) - \frac{\partial }{{\partial T}}\left( {\frac{{D_{TT} U}}{{2T}}} \right)$$ . The diffusion coefficient in kinetic energyD TT is allowed to be either independent of radial distance,R(AU), or follow the lawD TT=D0T2R 0 2 /(A2+R2) in either case with the 1 AU value ofD TT at 10 MeV ranging between 10?4 (MeV)2 s?1 and zero. The spatial diffusion mean free path at the Earth's orbit is fixed at λ‖ AU at 10 MeV according to numerical estimates made by Moussas and Quenby. However, a variety ofR dependences are allowed. Reasonable agreement with experimental data out to 4 AU is obtained with the above values ofD TT and the spatial diffusion coefficientK r=K0R?2 forR«1 andK r=K0R0.4 forR»1 AU. It is only in the decay phases of prompt events as seen at 2–4 AU that significant differences in the temporal behaviour of the events can be distinguished, depending on the value ofD TT chosen within the above range. Experimental determination of the decay constant is difficult. 相似文献
15.
By a gravitational potential Φ′(r) = − G0M/r (I + α + α In r) with |α|≪ 1 a motion δφ of the perihelion of a planet is resulting which is neither depending on the central-mass M nor on the semi-axis of the KEPLER -ellipse δφ ≈︁ - απ. Therefore, |α| must be smaller than 10−8. 相似文献
16.
A four-parameter model which assumes a Gaussian dependence of both temperature and pressure on distance from center is used to fit the compact part of coronal active regions as observed in X-ray photographs from a rocket experiment. The four parameters are the maximum temperature T M, the maximum pressure P M= 2NMkTM, the width of the pressure distribution σ P, and the width of the temperature distribution σ T = α1/2σP. The maximum temperature T M ranges from 2.2 to 2.8 × 106K, and the maximum density N M from 2 to 9 × 109cm?3. The range of σ P is from 2 to 4 × 109 cm and that of α from 2 to 7. 相似文献
17.
We present a well behaved class of charged analogue of M.C. Durgapal (J. Phys. A, Math. Gen. 15:2637, 1982) solution. This solution describes charged fluid balls with positively finite central pressure, positively finite central density; their ratio is less than one and causality condition is obeyed at the centre. The outmarch of pressure, density, pressure-density ratio and the adiabatic speed of sound is monotonically decreasing, however, the electric intensity is monotonically increasing in nature. This solution gives us wide range of parameter for every positive value of n for which the solution is well behaved hence, suitable for modeling of super dense stars. Keeping in view of well behaved nature of this solution, one new class of solution is being studied extensively. Moreover, this class of solution gives us wide range of constant K (0≤K≤2.2) for which the solution is well behaved hence, suitable for modeling of super dense stars like strange quark stars, neutron stars and pulsars. For this class of solution the mass of a star is maximized with all degree of suitability, compatible with quark stars, neutron stars and pulsars. By assuming the surface density ρ b =2×1014 g/cm3 (like, Brecher and Capocaso, Nature 259:377, 1976), corresponding to K=0 with X=0..235, the resulting well behaved model has the mass M=4.03M Θ , radius r b =19.53 km and moment of inertia I=1.213×1046 g?cm2; for K=1.5 with X=0.235, the resulting well behaved model has the mass M=4.43M Θ , radius r b =18.04 km and moment of inertia I=1.136×1046 g?cm2; for K=2.2 with X=0.235, the resulting well behaved model has the mass M=4.56M Θ , radius r b =17.30 km and moment of inertia I=1.076×1046 g?cm2. These values of masses and moment of inertia are found to be consistent with the crab pulsars. 相似文献
18.
Paul S. Wesson 《Astrophysics and Space Science》1975,37(1):235-256
Attention is given to four reasons for believing that the upper limit on the rotation of the Universe ω set by isotropy of the 3K background may not be appropriate to the local system because of its hierarchical structure. In particular, recent work of Rubinet al. (1973) on the anisotropy of Hubble's parameter (H) as determined by certain galaxies is examined. The anisotropy inH is a 1st order harmonic effect, inconsistent with an origin in an acceleration of the expansion of the Universe (U α;4≠0), but explicable as being due to a large peculiar velocity of the Local Group. This compromises limits set on ω by isotropy of the 3K field, as does the realization that only weak limits can be set if the last-scattering surface (z *) is notz *→∞ but is at smallz * (as expected in a hierarchy). In a rotating Universe, the 3-spaces of constant density cannot be orthogonal on the world lines of matter: a number test of Gödell based on this is generalized and applied (after consideration of Galactic obscuration) to the local Universe, by taking data on clusters of galaxies from the Abell and Zwicky catalogues. Data from the former give only a marginally significant result for the component ω1 of ω in one direction, but a bootstrap argument is applied which takes significance over from Abell's data (considered as a class of galaxies) to Zwicky's data (taken as a class of clusters), giving a statistically significant result on the hypothesis that clusters are the fundamental units of the Universe: it seems likely that ω1r?(const)r-n with 0?n?1 over the interval 500–1000 Mpc (H=60 km s?1 Mpc?1) with a total rotation of ω<2ω1, and ω1 = 1.2 (+0.25) x 10-18 s-1 evaluated on data out to 103 Mpc. Strictly, the quoted value of the rotation only applies to a region of space that in some sense has an isotropic limit: if the actual hierarchy has a large density-dependence away from a local origin (i.e., large thinning factor), then the numerical value of the rotation is smaller than the quoted value but still finite and significant. 相似文献
19.
Resonances in a geo-centric synchronous satellite under the gravitational forces of the Sun, the Moon and the Earth including it’s equatorial ellipticity have been investigated. The resonance at two points resulting from the commensurability between the mean motion of the satellite and Γ (angle measured from the minor axis of the Earth’s equatorial ellipse to the projection of the satellite on the plane of the equator) is analyzed. The amplitude and the time period of the oscillation have been determined by using the procedure of Brown and Shook. We have observed that the amplitude and the time period of the oscillation decrease as Γ increases in the first quadrant. The radial deviation (Δr) and the tangential deviation (r c Δθ) have been determined. Here r c represents the synchronous altitude. The effects of the arithmetic sum of amplitudes λ i involved in the perturbation equations on orbital inclination 0°≤α 0≤90° are shown. It is observed that $\sum_{i = 1}^{46} \lambda_{i}$ increases as α 0 increases. We have also determined the displacement ΔD (called drift) due to the oscillatory terms under the summation sign involved in the equations of motion of the satellite. We have observed that the value of ΔD is less than 0.5°. 相似文献
20.
Green's Theorem is developed for the spherically-symmetric steady-state cosmic-ray equation of transport in interplanetary space. By means of it the momentum distribution functionF
o(r,p), (r=heliocentric distance,p=momentum) can be determined in a regionr
arrbwhen a source is specified throughout the region and the momentum spectrum is specified on the boundaries atr
a
andr
b
. Evaluation requires a knowledge of the Green's function which corresponds to the solution for monoenergetic particles released at heliocentric radiusr
o
, Examples of Green's functions are given for the caser
a
=0,r
b
= and derived for the cases of finiter
a
andr
b
. The diffusion coefficient is assumed of the form = o(p)r
b
. The treatment systematizes the development of all analytic solutions for steady-state solar and galactic cosmic-ray propagation and previous solutions form a subset of the present solutions. 相似文献