共查询到20条相似文献，搜索用时 46 毫秒
1.
F. Darabi 《Astrophysics and Space Science》2012,338(1):171-177
We study a gravitational model in which scale transformations play the key role in obtaining dynamical G and Λ. We take a non-scale invariant gravitational action with a cosmological constant and a gravitational coupling constant.
Then, by a scale transformation, through a dilaton field, we obtain a new action containing cosmological and gravitational
coupling terms which are dynamically dependent on the dilaton field with Higgs type potential. The vacuum expectation value
of this dilaton field, through spontaneous symmetry breaking on the basis of anthropic principle, determines the time variations of G and Λ. The relevance of these time variations to the current acceleration of the universe, coincidence problem, Mach’s cosmological
coincidence and those problems of standard cosmology addressed by inflationary models, are discussed. The current acceleration
of the universe is shown to be a result of phase transition from radiation toward matter dominated eras. No real coincidence
problem between matter and vacuum energy densities exists in this model and this apparent coincidence together with Mach’s
cosmological coincidence are shown to be simple consequences of a new kind of scale factor dependence of the energy momentum
density as ρ∼a
−4. This model also provides the possibility for a super fast expansion of the scale factor at very early universe by introducing
exotic type matter like cosmic strings. 相似文献
2.
《Experimental Astronomy》2009,23(1):435-461
As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe
different characteristics of the instrument.
相似文献
| Charles S. CockellEmail: |
3.
K. S. Dwarakanath Siddharth Malu Ruta Kale 《Journal of Astrophysics and Astronomy》2011,32(4):529-532
We have discovered a giant radio halo in the massive merging cluster MACSJ0417.5-1154. This cluster, at a redshift of 0.443,
is one of the most X-ray luminous galaxy cluster in the MAssive Cluster Survey (MACS) with an X-ray luminosity in the 0.1–2.4
keV band of 2.9×1045 erg s − 1. Recent observations from GMRT at 230 and 610 MHz have revealed a radio halo of ∼ 1.2 × 0.3 Mpc2 in extent. This halo is elongated along the North-West, similar to the morphology of the X-ray emission from Chandra. The
1400 MHz radio luminosity (L
r) of the halo is ∼2 × 1025 W Hz − 1, in good agreement with the value expected from the L
x − L
r correlation for cluster halos. 相似文献
4.
Using a kappa velocity distribution function for the electrons of the background plasma, the dynamics of a beam of hot electrons
streaming through the plasma and the generation of Langmuir waves are investigated in the frame work of quasilinear theory.
It is shown that the Langmuir waves are strongly damped by high energy tail of the Kappa distribution function. The spatial
expansion of the beam is reduced and the spectral density of Langmuir waves becomes narrower. The height of the plateau in
the beam distribution function increases at small velocities and the average velocity of beam is larger than that of a Maxwellian
distribution. The influence of Kappa velocity distribution function on the gasdynamical parameters is investigated. It is
found that, the height of plateau in the beam distribution function, and its lower velocity boundary are enhanced while, the
local beam width in velocity space decreases. 相似文献
5.
VZ Cnc is a population I double mode high amplitude δ Scuti variable. We observed the star and collected the data from January 2007 to January 2009 to determine 14 times of maximum
light. We also searched its times of maximum light from other papers and from IBVS and got 57 values. We collected a total
of 194 times of maximum light and used them to perform an (O-C) analysis and concluded that there may be no tendency of binary
orbital light time effect. But by parabola tendency, it shows a continuous period increasing at the rate of 1.4×10−8 per year; this is compatible with the stellar evolution model calculation both in direction and size. 相似文献
6.
We investigate the interacting NADE model in non-flat universe. The effects of spatial curvature Ω
k
, interaction coefficient α and the main parameter of NADE, n, on EoS parameter w
d
and deceleration parameter q are studied. We obtain a minimum value for n in both early and present time, in order to that our DE model crosses the phantom divide. Also in a closed universe, changing
the sign of q is strongly dependent on α. It has been shown that the quantities w
d
and q have a different treatment for various spatial curvature. At last, we calculate the statefinder diagnostic and w−w
′ analysis in non flat universe. In non flat universe, the statefinder trajectories are discriminated by both n and α. 相似文献
7.
We present the equivalent width measurements of the hydrogen H
α
line, the oxygen near-IR triplet OI 7772–5 Å\AA and of a number of FeII lines in several B, Be, and shell stars in optical and near-infrared regions. A study of the correlations
between all these measured quantities has been made. The correlations of strength of lines with collected data of the near-IR
color excess, the rotational velocity and the intrinsic polarization are also obtained and presented. 相似文献
8.
Simultaneous measurements of the nightglow profiles of the O2(b1Σg+?X3Σg?) A-band, the atomic oxygen green line and the OH (8?3) Meinel band are presented. The altitude profiles are used to determine both the excitation mechanisms for the oxygen emissions and the atomic oxygen altitude distribution. It is shown that the measurements are consistent with a green line excitation through the Barth mechanism and that the molecular oxygen emission is excited through oxygen recombination and the reaction between OH1 and atomic oxygen. The derived atomic oxygen concentrations,6.2 × 1011cm?3at 98km, are consistent with the Jacchia (1971) model. 相似文献
9.
10.
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
11.
12.
J.W. BeemanF. Bellini L. Cardani N. Casali I. DafineiS. Di Domizio F. Ferroni F. OrioG. Pessina S. PirroC. Tomei M. Vignati 《Astroparticle Physics》2012,35(9):558-562
TeO2 crystals have proven to be superb bolometers for the search of neutrinoless double beta decay in many respects. However, if used alone, they do not exhibit any feature that allows to discriminate an α energy deposit from a β/γ one. This fact limits their ability to reject the background due to natural radioactivity and eventually affects the sensitivity of the search. In this paper we show the results of a TeO2 crystal where, in coincidence with its bolometric heat signal, also the luminescence light escaping the crystal is recorded. The results show that we are able to measure the light produced by β/γ particles, which can be explained as due to Cerenkov emission. No light is detected from α particles, allowing the rejection of this background source. 相似文献
13.
The zirconium oxide (ZrO) is well known for its astrophysical importance. The radiative transition parameters that include
Franck-Condon (FC) factor, r-centroid, electronic transition moments, Einstein coefficient, band oscillator strengths, radiative
life time and effective vibrational temperature have been estimated for e
1Π–X
1Σ+ and 1Σ+–X
1Σ+ band systems of 90ZrO molecule for the experimentally known vibrational levels using RKR potential energy curves. A reliable numerical integration
method has been used to solve the radial Schr?dinger equation for the vibrational wave functions of upper and lower electronic
states based on the latest available spectroscopic data and known wavelengths. The estimated radiative transition parameters
are tabulated. The effective vibrational temperatures of these band systems of 90ZrO molecule are found to be below 4200 K. Hence, the radiative transition parameters help us to ascertain the presence of
90ZrO molecule in the interstellar medium, S stars and sunspots. 相似文献
14.
N2 2P fluorescent intensity was monitored as a function of incident photon energy from 40 to 70 eV. A structure was seen near 52.2 eV. This feature is attributed to the scattering of photoelectrons originating from the N2 2σg molecular orbital with a binding energy of about 37.7 eV. The kinetic energy of these photoelectrons corresponds to the peak of the 2P excitation cross section at 14.5 eV. 相似文献
15.
Two monochromatic pictures of the Comet Kohoutek (1973f) were taken on January 15, 1974 in the resonance light (A2Σ ? X2 ∏) of the radical OH with a photographic telescope placed on board the NASA 990 Convair airplane. From an intensity profile we derive the production rate of OH radicals QOH = 4 xsx 1028 moleculesec ?1sr?1 at 0.6 AU and the lifetime of the OH radical which is τOH = 4.5 × 104 sec at 0.6 AU. This short lifetime (very similar to the lifetime of H2O) combined with the high total production rate of gas in comets can explain the observed velocity of 8km sec?1 for the H-atoms: The H-atoms produced by photodissociation of H2O are thermalized at short distancesfrom the nucleus; the H-atoms produced by photodissociation of OH have a velocity of ?8km sec?1 and can reach the outer part of the hydrogen envelope. 相似文献
16.
Doran J. Baker William R. Pendleton Gerald J. Romick Vincent B. Wickwar Murray I. Baron 《Planetary and Space Science》1978,26(7):619-634
The ground-level zenith radiance of the atmospheric emission at λ1.27 μm was radiometrically observed to increase by a factor of approximately two with the onset of an IBC III+ auroral breakup above Chatanika, Alaska, on 10 March 1975. Time-resolved optical spectra clearly show that the slow component of the enhancement is associated with the (0,0) band of the infrared atmospheric system of O2. Photometric and incoherent scatter radar data are used to define the energy-deposition profile and the absolute energy flux for the event. The magnitude of the O2λ1.27-μm enhancement compares favourably with the predictions of an auroral excitation model which includes only secondary-electron excitation of molecular oxygen in the O2(a1Δg) source term. 相似文献
17.
Based on a set of 11 CME events we study the impact of projection effects by tracking CME leading edge features in the plane of sky (traditional CME tracking) from combined STEREO-SECCHI and SOHO-LASCO observations up to 20R ⊙. By using CME observations from two vantage points and applying triangulation techniques, the source region location of the CME on the solar surface was determined (heliospheric longitude and latitude) to correct for projection effects. With this information, the directivity and “true” speed of a CME can be estimated in a simple way. The comparison of the results obtained from the spacecraft pairs SOHO-LASCO/STEREO-A and SOHO-LASCO/STEREO-B allows us to study the reliability of the method. The determined CME source region is generally coincident within ?10°. 相似文献
19.
KAr and/or 40Ar39Ar plateau ages of Allende samples—whole rock, matrix, chondrules, white inclusions–range from 3.8 AE for matrix of ?5 AE for some white inclusions, but cluster strongly near 4.53 AE. This age marks the dominant KAr resetting of Allende materials. Age spectra show disturbances due to 39Ar recoil or some other argon redistribution processes. Possible explanations for the apparent presolar ages (>4.6 AE) include: ?20% loss of 39Ar; ?40% loss of 40K ～3.8 AE ago with no loss of 40Arl trapped argon of unique 40Ar/36Ar isotopic composition; admixture of “very old” presolar grains. 相似文献
20.
With the sample of 105 emission line galaxies selected from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4), we have investigated the relations of the [OII]λ3727/Hα flux ratio with the dust extinction, the ionization state of interstellar gas and the metal abundance of galaxies. It is found that the dust extinction correction has a significant effect on the [OII]λ3727/Hα flux ratio. Before and after the dust distinction correction is made, the mean [OII]λ3727/Hα flux ratios are 0.48 and 0.89, respectively. After the dust extinction is corrected, the dispersion of the distribution of F([OII]λ3727) as a function of F(Hα) is obviously reduced. The [OII]λ3727/Hα flux ratio of metal-poor galaxies decreases with the increasing ionization degree of interstellar gas, but this relation does not exist in metal-rich galaxies. Besides, it is found that the [OII]λ3727/Hα flux ratio is correlated with the metal abundance. When 12 + lg(O/H) > 8.5, the [OII]λ3727/Hα flux ratio decreases with the increasing metal abundance; for the galaxies of 12 + lg(O/H) > 8.5, the spectral flux ratio correlates positively with the metal abundance. Finally, by using the parameters of gas ionization degree and metal abundances of galaxies, the formulae for calculating the [OII]λ3727/Hα flux ratios of different types of galaxies are given. With the [OII]λ3727/Hα flux ratio given by these formulae, the star formation rate can be derived by using the [OII]λ3727-line flux, for the galaxies of the redshift z > 0.4, such as the large number of galaxies to be observed by the LAMOST telescope. 相似文献