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1.
In this paper, we investigate the dynamics of Born–Infeld (B–I) phantom model in the ω–ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in ω–ω′ plane, and show mathematically the property of attractor solutions which correspond to ω
φ
∼−1, Ω
φ
=1, which avoid the “Big rip” problem and meets the current observations well.
相似文献
2.
We study numerically the asymmetric periodic orbits which emanate from the triangular equilibrium points of the restricted
three-body problem under the assumption that the angular velocity ω varies and for the Sun–Jupiter mass distribution. The
symmetric periodic orbits emanating from the collinear Lagrangian point L
3, which are related to them, are also examined. The analytic determination of the initial conditions of the long- and short-period
Trojan families around the equilibrium points, is given. The corresponding families were examined, for a combination of the
mass ratio and the angular velocity (case of equal eigenfrequencies), and also for the critical value ω = 2
, at which the triangular equilibria disappear by coalescing with the inner collinear equilibrium point L
1. We also compute the horizontal and the vertical stability of these families for the angular velocity parameter ω under consideration.
Series of horizontal–critical periodic orbits of the short-Trojan families with the angular velocity ω and the mass ratio
μ as parameters, are given. 相似文献
3.
Anirudh Pradhan Rekha Jaiswal Kanti Jotania Rajeev Kumar Khare 《Astrophysics and Space Science》2012,337(1):401-413
We present two dark energy (DE) models with an anisotropic fluid in Bianchi type-VI
0 space-time by considering time dependent deceleration parameter (DP). The equation of state (EoS) for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations.
Under the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution
of the universe, the EoS parameter for DE changes from ω>−1 to ω=−1 in first model whereas from ω>−1 to ω<−1 in second model which is consistent with recent observations. The cosmological constant Λ is found to be a positive decreasing
function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results
from recent type Ia supernovae observations. The cosmic jerk parameter in our derived models is also found to be in good agreement
with the recent data of astrophysical observations. The physical and geometric aspects of both the models are also discussed
in detail. 相似文献
4.
In the present investigation we measure the differential rotation of strong magnetic flux during solar cycles 21 – 23 with
the method of wavelet transforms. We find that the cycle-averaged synodic rotation rate of strong magnetic flux can be written
as ω=13.47−2.58sin 2
θ or ω=13.45−2.06sin 2
θ−1.37sin 4
θ, where θ is the latitude. They agree well with the results derived from sunspots. A north–south asymmetry of the rotation rate is
found at high latitudes (28°<θ<40°). The strong flux in the southern hemisphere rotates faster than that in the northern hemisphere by 0.2 deg day−1. The asymmetry continued for cycles 21 – 23 and may be a secular property. 相似文献
5.
V. T. Doroshenko S. G. Sergeev E. Yu. Vovk Yu. S. Efimov S. A. Klimanov S. V. Nazarov 《Astronomy Letters》2010,36(9):611-633
Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy NGC 7469 over the
period 1995–2009. In 1995–2000, the optical brightness of the galactic nucleus changed almost by 1
m
in the U band. In 2000–2009, the amplitude of the optical variations was considerably lower. Regular X-ray observations began only
in 2003. The X-ray fractional variability amplitude is higher than the optical one. The optical variability amplitude decreases
with increasing wavelength. The full width at half maximum of the X-ray and B-band autocorrelation functions is about 8 and 62 days, respectively. The structure functions (SF) in the X-ray range on time scales up to 7 days and in the optical range on time scales up to 100 days have the form of a
power law SF(τ) ∼ τ
b
, where τ is the time shift. On time scales of more than a day, where both structure functions have been determined rather reliably,
their slopes differ markedly: b = 1.34 ± 0.06 and b = 0.25 ± 0.05 for the optical and X-ray ranges, respectively. The X-ray and B-band structure functions begin to flatten, respectively, near 6–8 days and on time scales of about 90 days. The observed
structure functions can be described by the model of a superposition of independent Gaussian flares whose number changes with
duration ω as n(ω) ∼ ω
α and whose amplitudes depend on duration as A(ω) ∼ ω
β. The flux distribution and the flux-amplitude relation are consistent with the model of a light curve in the form of a superposition
of random flares. Once the fast intensity variations have been filtered out on long time scales, the X-ray light curve correlates
well with the optical one. No lag of the X-ray variations relative to those in the B band is detected. The light variations in the R and I bands lag behind those in the B band calculated from the centroid of the cross-correlation function by 2.6 and 3.5 days, respectively, at a 3σ confidence level. 相似文献
6.
Michael Nauenberg 《Celestial Mechanics and Dynamical Astronomy》2007,97(1):1-15
Numerical solutions are presented for a family of three dimensional periodic orbits with three equal masses which connects
the classical circular orbit of Lagrange with the figure eight orbit discovered by C. Moore [Moore, C.: Phys. Rev. Lett. 70, 3675–3679 (1993); Chenciner, A., Montgomery, R.: Ann. Math. 152, 881–901 (2000)]. Each member of this family is an orbit with finite angular momentum that is periodic in a frame which rotates
with frequency Ω around the horizontal symmetry axis of the figure eight orbit. Numerical solutions for figure eight shaped
orbits with finite angular momentum were first reported in [Nauenberg, M.: Phys. Lett. 292, 93–99 (2001)], and mathematical proofs for the existence of such orbits were given in [Marchal, C.: Celest. Mech. Dyn. Astron.
78, 279–298 (2001)], and more recently in [Chenciner, A. et al.: Nonlinearity 18, 1407–1424 (2005)] where also some numerical solutions have been presented. Numerical evidence is given here that the family
of such orbits is a continuous function of the rotation frequency Ω which varies between Ω = 0, for the planar figure eight
orbit with intrinsic frequency ω, and Ω = ω for the circular Lagrange orbit. Similar numerical solutions are also found for
n > 3 equal masses, where n is an odd integer, and an illustration is given for n = 21. Finite angular momentum orbits were also obtained numerically for rotations along the two other symmetry axis of the
figure eight orbit [Nauenberg, M.: Phys. Lett. 292, 93–99 (2001)], and some new results are given here. A preliminary non-linear stability analysis of these orbits is given
numerically, and some examples are given of nearby stable orbits which bifurcate from these families. 相似文献
7.
K. Karami M. Jamil M. Roos S. Ghaffari A. Abdolmaleki 《Astrophysics and Space Science》2012,340(1):175-184
We study the entropy-corrected version of the new agegraphic dark energy (NADE) model and dark matter in a spatially non-flat Universe and in the framework of Hořava-Lifshitz cosmology. For the two cases containing noninteracting and interacting entropy-corrected NADE (ECNADE) models, we derive the exact differential equation that determines the evolution of the ECNADE density parameter. Also the deceleration parameter is obtained. Furthermore, using a parametrization of the equation of state parameter of the ECNADE model as ω Λ(z)=ω 0+ω 1 z, we obtain both ω 0 and ω 1. We find that in the presence of interaction, the equation of state parameter ω 0 of this model can cross the phantom divide line which is compatible with the observation. 相似文献
8.
Naveen Bijalwan 《Astrophysics and Space Science》2011,334(1):139-143
A most general exact solution to the Einstein-Maxwell equations for static charged perfect fluid is sought in terms of pressure.
Subsequently, metrics (e
λ
and e
υ
), matter density and electric intensity are expressible in terms of pressure. Consequently, Pressure is found to be an invertible
arbitrary function of ω(=c
1+c
2
r
2), where c
1 and c
2(≠0) are arbitrary constants, and r is the radius of star, i.e. p=p(ω). We present a general solution for charged pressure fluid in terms for ω. We list and discuss some old and new solutions which fall in this category. 相似文献
9.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,327(1):111-115
We investigate five-dimensional Brans–Dicke cosmology with spacetime described by the homogeneous, anisotropic and flat spacetime
with the topology M
1×R
3×S
1 where S
1 is taken in the form of a circle. We conjecture throughout this letter that the extra-dimension compactifies as the visible
dimensions expand like b(t)≈a
−1(t) and that the non-minimal coupling between the scalar field and the matter is of the form f(φ)∝
φ
2. The model gives rise to a transition from a decelerated epoch to an accelerated epoch for large values of the Brans–Dicke
parameter ω. The model predicts crossing of the phantom divided barrier unless the universe is governed by a growing matter field. 相似文献
10.
José Antonio Belinchón 《Astrophysics and Space Science》2009,323(3):307-315
We study a massive cosmic strings with BII symmetries cosmological models in two contexts. The first of them is the standard
one with a barotropic equation of state. In the second one we explore the possibility of taking into account variable “constants”
(G and Λ). Both models are studied under the self-similar hypothesis. We put special emphasis in calculating the numerical values
for the equations of state. We find that for ω∈(0,1], G, is a growing time function while Λ, behaves as positive decreasing time function. If ω=0, both “constants”, G and Λ, behave as true constants. 相似文献
11.
Given the complexity involved in a flux-transport-type dynamo driven by both Babcock – Leighton and tachocline α effects, we present here a step-by-step procedure for building a flux-transport dynamo model calibrated to the Sun as a guide
for anyone who wishes to build this kind of model. We show that a plausible sequence of steps to reach a converged solution
in such a dynamo consists of (i) numerical integration of a classical α – ω dynamo driven by a tachocline α effect, (ii) continued integration with inclusion of meridional circulation to convert the model into a flux-transport dynamo
driven by only a tachocline α effect, (iii) final integration with inclusion of a Babcock – Leighton surface α effect, resulting in a flux-transport dynamo that can be calibrated to obtain a close fit of model output with solar observations. 相似文献
12.
The exact nonlinear cylindrical solution for incompressible Hall – magnetohydrodynamic (HMHD) waves, including dissipation,
essentially from electron – neutral collisions, is obtained in a uniformly rotating, weakly ionized plasma such as exists
in photospheric flux tubes. The ω – k relation of the waves, called here Hall – MHD waves, demonstrates the dispersive nature of the waves, introduced by the Hall
effect, at large axial and radial wavenumbers. The Hall – MHD waves are in general elliptically polarized. The partially ionized
plasma supports lower frequency modes, lowered by the factor δ≡ratio of the ion mass density to the neutral particle mass density, as compared to the fully ionized plasma (δ=1). The relation between the velocity and the magnetic field fluctuations departs significantly from the equipartition found
in Alfvén waves. These short-wavelength and arbitrarily large amplitude waves could contribute toward the heating of the solar
atmosphere. 相似文献
13.
In this paper we study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic
FRW universe filled with barotropic fluid and dark energy. The scale factor is considered as a power law function of time
which yields a constant deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect
fluid as well as direct interaction with it. The cosmic jerk parameter in our derived models is consistent with the recent
data of astrophysical observations. It is concluded that in non-interacting case, all the three open, close and flat universes
cross the phantom region whereas in interacting case only open and flat universes cross the phantom region. We find that during
the evolution of the universe, the equation of state (EoS) for dark energy ω
D
changes from ω
D
>−1 to ω
D
<−1, which is consistent with recent observations. 相似文献
14.
José Antonio Belinchón 《Astrophysics and Space Science》2009,323(2):185-195
We study a perfect fluid Bianchi II models with time varying constants under the self-similarity approach. In the first of
the studied model, we consider that only vary G and Λ. The obtained solution is more general that the obtained one for the classical solution since it is valid for an equation
of state ω∈(−1,∞) while in the classical solution ω∈(−1/3,1). Taking into account the current observations, we conclude that G must be a growing time function while Λ is a positive decreasing function. In the second of the studied models we consider
a variable speed of light (VSL). We obtain a similar solution as in the first model arriving to the conclusions that c must be a growing time function if Λ is a positive decreasing function. 相似文献
15.
We analyse the dark energy problem using observational H(z) data plus the curvature constraint given by WMAP. After a non-parametric
statistical study covering the most probable range of Ω
m0 and H
0 from different combination of data, we investigate the possibility of having the dark energy EoS parameter ω
x
≠−1. In order to keep strict flatness (1% of deviation from Ω=1), our results point out this is the case for 0.20≲Ω
m0≲0.23 and H
0≈67 km/s/Mpc, with ω
x
≈−0.55. However, if we admit a 10% deviation from the flatness condition, ω
x
may have any value in the range [−1.2,−0.5] for 0.20≲Ω
m0≲0.35 and 67≲H
0≲74 km/s/Mpc. 相似文献
16.
The focussing of gravitational radiation by the interior and exterior gravitational field of a Newtonian gravitational lens
is considered. A graphical method for determining the caustic structure of a Newtonian gravitational lens is presented and
the caustic structure of a solar type gravitational lens is discussed. Estimates of the amplitude magnification in the caustic
region indicate that waves with frequencies less than a critical cutoff frequency ω
c
are not amplified significantly. For a lens of massM this cutoff frequency is ω
c
≈(10-1πM)-1; for the Sun ω
c
≈104s-1.
Work supported in part by National Science Foundation Grant PHY78-05368. 相似文献
17.
Using specialized codes for the search of periodic and linear components we show that direct solar radiation leads to short-period
variations of all the orbital elements of geosynchronous satellites. The variation period of the semimajor axis a, orbit inclination i and the longitude of the ascending node Ω is 1 day. Eccentricity e, the argument of perigee ω and the mean anomaly M vary with a period of 0.5 days. Direct solar radiation also leads to long-period variations in e, ω and M with a period of 1 year. The elements a, i and Ω undergo variations only in the amplitude of diurnal variations with a period of 1 or 0.5 years. Secular variability
(linear components) are not detected. To obtain the initial value array of the orbital elements we used the Lagrange equations
of perturbed motion in the form of a Gaussian with their subsequent integration via a special method of harmonics: the values
of the derived orbital elements, obtained from the Lagrange equations, were presented through the periodic functions that
are easy to integrate. 相似文献
18.
We have discussed non-linear stability in photogravitational non-planar restricted three body problem with oblate smaller
primary. By photogravitational we mean that both primaries are radiating. We normalized the Hamiltonian using Lie transform
as in Coppola and Rand (Celest. Mech. 45:103, 1989). We transformed the system into Birkhoff’s normal form. Lie transforms reduce the system to an equivalent simpler system
which is immediately solvable. Applying Arnold’s theorem, we have found non-linear stability criteria. We conclude that L
6 is stable. We plotted graphs for (ω
1,D
2). They are rectangular hyperbola. 相似文献
19.
In this paper we have investigated the beat wave excitation of an ion-acoustic wave at the difference frequency of two kinetic
(or shear) Alfvén waves propagating in a magnetized plasma with β<1 (β=8π
n
e0
T
e/B
0
2
, where n
e0 is the unperturbed electron number density, T
e is the electron temperature, and B
0 is the external magnetic field). On account of the interaction between two kinetic Alfvén waves of frequencies ω
1 and ω
2, the ponderomotive force at the difference frequency ω
1−ω
2 leads to the generation of an ion-acoustic wave. Also because of the filamentation of the Alfvén waves, magnetic-field-aligned
density dips are observed. In this paper we propose that the ion-acoustic wave generated by this mechanism may be one of the
possible mechanisms for the heating and acceleration of solar wind particles. 相似文献
20.
D. M. Sedrakian 《Astrophysics》1997,40(3):260-266
Equations are obtained for the dynamics of the rotation of a two-component model neutron star within the framework of the
generai theory of relativity. It is shown that for steady rotation of the star’s normal component, Ωc = const, the angular velocity Ωs of the superfluid component depends on the coordinates and is Ωc + ω, where ω is the nondiagonal component of the metric tensor.
Translated from Astrofizika, Vol. 40, No. 3, pp. 403–412, August, 1997. 相似文献