共查询到20条相似文献，搜索用时 203 毫秒
1.
A theoretical model is presented to investigate the existence, formation, and possible realization of nonlinear envelope ion acoustic solitary waves which accompany collisionless electron-positron-ion plasmas with high-energy electrons and positrons (represented by kappa distribution). By employing the reductive perturbation method, the hydrodynamic model and the Poisson equation are reduced to nonlinear Schr?dinger equation. The effects of the superthermal parameters, as well as ion-to-electron temperature ratio on the propagation and stability of the envelope solitary waves are examined. The superthermal parameters (ion-to-electron temperature ratio) give rise to instability (stability) of the solitary excitations, since the instability window is strongly modified. Finally, the present results should elucidate the excitation of the nonlinear ion-acoustic solitary wave packets in superthermal electron-positron-ion plasmas, particularly in interstellar medium. 相似文献
2.
M. Malekjani A. Khodam-Mohammadi N. Nazari-pooya 《Astrophysics and Space Science》2011,332(2):515-524
In this paper, the holographic dark energy model with new infrared cut-off proposed by Granda and Oliveros has been investigated
in spatially non flat universe. The dependency of the evolution of equation of state, deceleration parameter and cosmological
evolution of Hubble parameter on the parameters of new HDE model are calculated. Also, the statefinder parameters r and s in this model are derived and the evolutionary trajectories in s−r plane are plotted. We show that the evolutionary trajectories are dependent on the model parameters of new HDE model. Eventually,
in the light of SNe + BAO + OHD + CMB observational data, we plot the evolutionary trajectories in s−r and q−r planes for best fit values of the parameters of new HDE model. 相似文献
3.
El-Nabulsi Ahmad?Rami 《Astrophysics and Space Science》2011,332(2):491-495
We investigate the late-time dynamics of a four-dimensional universe based on modified scalar field gravity in which the standard
Einstein-Hilbert action R is replaced by f(φ)R+f(R) where f(φ)=φ
2 and f(R)=AR
2+BR
μν
R
μν,(A,B)∈ℝ. We discussed two independent cases: in the first model, the scalar field potential is quartic and for this special form
it was shown that the universe is dominated by dark energy with equation of state parameter w≈−0.2 and is accelerated in time with a scale factor evolving like a(t)∝t
5/3 and B+3A≈0.036. When, B+3A→∞ which corresponds for the purely quadratic theory, the scale factor evolves like a(t)∝t
1/2 whereas when B+3A→0 which corresponds for the purely scalar tensor theory we found when a(t)∝t
1.98. In the second model, we choose an exponential potential and we conjecture that the scalar curvature and the Hubble parameter
vary respectively like
R=hH[(f)\dot]/f,h ? \mathbbRR=\eta H\dot{\phi}/\phi,\eta\in\mathbb{R} and
H=g[(f)\dot]c,(g,c) ? \mathbbRH=\gamma\dot{\phi}^{\chi},(\gamma,\chi)\in\mathbb{R}. It was shown that for some special values of χ, the universe is free from the initial singularity, accelerated in time, dominated by dark or phantom energy whereas the
model is independent of the quadratic gravity corrections. Additional consequences are discussed. 相似文献
4.
Infrared observations of the Orion nebula have been interpreted by Rowan-Robinson (1975) to imply the existence of giant grains, radius 10–2 cm, throughout a volume about a parsec in diameter. Although Rowan-Robinson's model of the nebula has been criticized (e.g., Andriesse, 1976) and the presence of such grains in Orion is disputed, we accept,pro tem, the proposition that they exist, and examine in this paper situations in which giant grains could arise. We find that, while a giant-grain component to the interstellar grain density may exist, it is difficult to understand how giant grains arise to the extent apparently required by the Orion nebula model. 相似文献
5.
6.
Solar rotation rate has been measured using the sunspot positions recorded by W.C. Bond during the period 1847 – 1849 at the
Harvard College Observatory. From the drawings carried out by Bond we have selected the sunspots and groups of sunspots with
more reliable positions presented in three or more drawings on successive days. We have calculated from the positions of the
selected sunspots (41 in total) a synodic rotation rate of ω=[(12.92±0.08)−(1.5±1.0)sin 2
φ] degrees/day, where φ is the heliographic latitude. This rate, although slightly lower, is similar to the actual solar rotation rate, confirming
no important changes in the solar rotation during the last 160 years. 相似文献
7.
Apparent horizon and event horizon thermodynamics of?a?Vaidya?black hole using Damour-Ruffini method
Using Damour-Ruffini method, Hawking radiation from the apparent horizon of a Vaidya black hole is calculated. The thermodynamics
can be built successfully on the apparent horizon. In the meantime, when a time-dependent perturbation is given to the apparent
horizon, the first law of thermodynamics can also be constructed successfully at a new supersurface near the apparent horizon.
The expressions of the characteristic position and temperature are consistent with the previous results. It is concluded that
the thermodynamics should be constructed on the apparent horizon exactly while the event horizon thermodynamics is just one
of the perturbations near the apparent horizon. These conclusions can be regarded as providing some new evidences for our
previous viewpoint. 相似文献
8.
Here we consider our universe as homogeneous spherically symmetric FRW model and analyze the thermodynamics of this model
of the universe in scalar-tensor theory. Assuming the first law of thermodynamics validity of the generalized second law of
thermodynamics (GSLT) at the event horizon is examined in both the cases when the universe is filled with perfect fluid and
the holographic dark energy. 相似文献
9.
A review of visual and photographic data on the appearance of Uranus indicates that markings frequently occur on the planet. The featureless images obtained by the Stratoscope II balloon telescope are possibly the result of the broad spectral band that was used. Difference, or ratio, picture techniques which enhance color or polarization contrasts are proposed as the basis for Uranus imagery on the '79 MJU Mission. An attempt is made to predict the aspect of Uranus at high resolution on the basis of what is currently known about the Uranus atmosphere. The planet should have no visible surface, the tops of a thick NH3 cloud layer should exist near the 3–4 bar level and there is a very uncertain possibility of a thin, broken CH4 cloud layer near 300 mbar. It is proposed that if the choice of an MJU imaging system rests on Uranus objectives alone (i.e., excluding the satellites) then the system should emphasize photo-polarimetric observations between 5500 and 10 000 Å. If, however, the total mission objectives are the basis of choice then a high resolution imaging system, based on the Mariner Jupiter-Saturn system, but including a solid state silicon array would be a more suitable choice. The performance of such a system at Uranus is analyzed. 相似文献
10.
11.
Berger T.E. De Pontieu B. Fletcher L. Schrijver C.J. Tarbell T.D. Title A.M. 《Solar physics》1999,190(1-2):409-418
TRACE observations of active regions show a peculiar extreme ultraviolet (EUV) emission over certain plage areas. Termed `moss'
for its spongy, low-lying, appearance, observations and modeling imply that the phenomenon is caused by thermal conduction
from 3–5 MKcoronal loops overlying the plage: moss is the upper transition region emission of hot coronal loops. The spongy
appearance is due to the presence of chromospheric jets or `spicules' interspersed with the EUV emission elements. High cadence
TRACE observations show that the moss EUV elements interact with the chromospheric jets on 10 s time scales. The location
of EUV emission in the moss does not correlate well to the locations of underlying magnetic elements in the chromosphere and
photosphere, implying a complex magnetic topology for coronal loop footpoint regions. We summarize here the key observations
leading to these conclusions and discuss new implications for understanding the structuring of the outer solar atmosphere.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005286503963 相似文献
12.
A family of charge analogues of a neutral solution with g
44=(1+Cr
2)6 has been obtained by using a specific electric intensity, which involves a parameter K. Both neutral and charged solutions are analysed physically subject to the surface density 2×1014 gm/cm3 (neutron star). The neutral solution is well behaved for 0.0<Ca
2≤0.10477 while its charge analogues are well behaved for a wide range of a parameter K (0≤K≤72) i.e. pressure, density, pressure-density ratio, velocity of sound is monotonically decreasing and the electric intensity
is monotonically increasing in nature for the given range of the parameter K. The maximum mass and radius occupied by the neutral solution are 3.4126M
Θ and 18.9227 km for Ca
2=0.10447 respectively. While the red shift at centre Z
0=0.9686 and red shift at the surface Z
a
=0.4612. For the charged solution, the maximum mass and radius are 5.6111M
Θ and 17.2992 km respectively for K=3.0130 and Ca
2=0.2500, with the red shift Z
0=3.0113 and Z
a
=1.0538. 相似文献
13.
Between 24 March 2008 and 2 April 2008, the three active regions (ARs) NOAA 10987, 10988 and 10989 were observed daily by the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) while they traversed the solar disk. We use these measurements and the nonlinear force-free magnetic field code XTRAPOL to reconstruct the coronal magnetic field for each active region and compare model field lines with images from the Solar Terrestrial RElations Observatory (STEREO) and Hinode X-ray Telescope (XRT) telescopes. Synoptic maps made from continuous, round-the-clock Global Oscillations Network Group (GONG) magnetograms provide information on the global photospheric field and potential-field source-surface models based on these maps describe the global coronal field during the Whole Heliosphere Interval (WHI) and its neighboring rotations. Features of the modeled global field, such as the coronal holes and streamer-belt locations, are discussed in comparison with extreme ultra-violet and coronagraph observations from STEREO. The global field is found to be far from a minimum, dipolar state. From the nonlinear models we compute physical quantities for the active regions such as the photospheric magnetic and electric current fluxes, the free magnetic energy and the relative helicity for each region each day where observations permit. The interconnectivity of the three regions is addressed in the context of the potential-field source-surface model. Using local and global quantities derived from the models, we briefly discuss the different observed activity levels of the regions. 相似文献
14.
mille E.O. Ishida Ribamar R.R. Reis Alan V. Toribio Ioav Waga 《Astroparticle Physics》2008,28(6):547-552
Cosmic acceleration is investigated through a kink-like expression for the deceleration parameter (q). The new parametrization depends on the initial (qi) and final (qf) values of q, on the redshift of the transition from deceleration to acceleration (zt) and the width of such transition (τ). We show that although supernovae (SN) observations (Gold182 and SNLS data samples) indicate, at high confidence, that a transition occurred in the past (zt > 0) they do not, by themselves, impose strong constraints on the maximum value of zt. However, when we combine SN with the measurements of the ratio between the comoving distance to the last scattering surface and the SDSS + 2dfGRS BAO distance scale (Sk/Dv) we obtain, at 95.4% confidence level, and for (Sk/Dv+Gold182), and and for (Sk/Dv+SNLS), assuming qi = 0.5 and qf = −1. We also analyze the general case, qf (−∞, 0) finding the constraints that the combined tests (Sk/Dv+SNLS) impose on the present value of the deceleration parameter (q0). 相似文献
15.
T. N. Woods F. G. Eparvier R. Hock A. R. Jones D. Woodraska D. Judge L. Didkovsky J. Lean J. Mariska H. Warren D. McMullin P. Chamberlin G. Berthiaume S. Bailey T. Fuller-Rowell J. Sojka W. K. Tobiska R. Viereck 《Solar physics》2012,275(1-2):115-143
The highly variable solar extreme ultraviolet (EUV) radiation is the major energy input to the Earth’s upper atmosphere, strongly impacting the geospace environment, affecting satellite operations, communications, and navigation. The Extreme ultraviolet Variability Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will measure the solar EUV irradiance from 0.1 to 105?nm with unprecedented spectral resolution (0.1?nm), temporal cadence (ten seconds), and accuracy (20%). EVE includes several irradiance instruments: The Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence spectrograph that measures the solar EUV irradiance in the 5 to 37?nm range with 0.1-nm resolution, and the MEGS-B is a normal-incidence, dual-pass spectrograph that measures the solar EUV irradiance in the 35 to 105?nm range with 0.1-nm resolution. To provide MEGS in-flight calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV irradiance in broadbands between 0.1 and 39?nm, and a MEGS-Photometer measures the Sun’s bright hydrogen emission at 121.6?nm. The EVE data products include a near real-time space-weather product (Level?0C), which provides the solar EUV irradiance in specific bands and also spectra in 0.1-nm intervals with a cadence of one minute and with a time delay of less than 15?minutes. The EVE higher-level products are Level?2 with the solar EUV irradiance at higher time cadence (0.25?seconds for photometers and ten seconds for spectrographs) and Level?3 with averages of the solar irradiance over a day and over each one-hour period. The EVE team also plans to advance existing models of solar EUV irradiance and to operationally use the EVE measurements in models of Earth’s ionosphere and thermosphere. Improved understanding of the evolution of solar flares and extending the various models to incorporate solar flare events are high priorities for the EVE team. 相似文献
16.
暗物质既是宇宙必需的组成部分,更是一个依然扑朔迷离的难题。根据对宇宙大爆炸余辉——微波背景辐射——的研究,你、我、每一件日常用品、行星、恒星、星云和星系等,我们周围可见的所有物质仅占据宇宙质量能量的4.9%。与之形成对比的是,暗物质占据了宇宙的26.8%,是普通物质的5倍多,但它们的本质至今不明。 相似文献
17.
We have reanalysed and compared the dipoles of the 1.2-Jy and 0.6-Jy (QDOT) IRAS galaxy samples. We find strong indications from both samples for (a) significant contributions to the gravitational field that shapes the Local Group motion from depths up to ∼ 170 h −1 Mpc and (b) a large-scale coherence of the dipole anisotropy, indications provided mainly by the fact that the differential dipoles of large equal-volume shells are aligned with the CMB dipole and exhibit significant dipole signals. The two IRAS dipoles are indistinguishable within 50 h −1 Mpc and beyond ∼ 130 h −1 Mpc while the QDOT dipole, having a lower flux limit, continues growing with respect to the 1.2-Jy sample up to ∼ 100 h −1 Mpc in agreement with Rowan-Robinson et al. 相似文献
18.
19.
M. Schüssler 《Astronomische Nachrichten》2007,328(10):1087-1091
Various methods (or recipes) have been proposed to predict future solar activity levels – with mixed success. Among these, some precursor methods based upon quantities determined around or a few years before solar minimum have provided rather high correlations with the strength of the following cycles. Recently, data assimilation with an advection-dominated (flux-transport) dynamo model has been proposed as a predictive tool, yielding remarkably high correlation coefficients. After discussing the potential implications of these results and the criticism that has been raised, we study the possible physical origin(s) of the predictive skill provided by precursor and other methods. It is found that the combination of the overlap of solar cycles and their amplitude-dependent rise time (Waldmeier's rule) introduces correlations in the sunspot number (or area) record, which account for the predictive skill of many precursor methods. This explanation requires no direct physical relation between the precursor quantity and the dynamo mechanism (in the sense of the Babcock-Leighton scheme or otherwise). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
S. Ferraz-Mello 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):243-248
The word "average" and its variations became popular in the sixties and implicitly carried the idea that "averaging" methods
lead to "average" Hamiltonians. However, given the Hamiltonian H = H0(J) + ∈R(θ, J), (∈ < < 1), the problem of transforming it into a new Hamiltonian H* (J*) (dependent only on the new actions J*), through a canonical transformation given by zero-average trigonometrical series has no general solution at orders higher
than the first.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献