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1.
From the observed present parameters of the Universe and the model properties of an expansive non-decelerative universe it results that the value of Boltzmann's constant (coefficient)k does not change only before the end of radiation era, but also in the matter era; with the increase of gauge factora, it decreases as (a
–1)1/4. 相似文献
2.
Available data on the distances and radial velocities of galaxies are systematized in order to study the distribution of peculiar
velocities in neighborhoods of the Local cosmic void lying in the direction of the Aquila and Hercules constellations. A sample
of 1056 galaxies is used, with distances measured in terms of the luminosity of the tip of the red giant branch (TRGB), the
luminosity of the cepheids, the luminosity of type 1a supernovae, surface brightness fluctuations (SBF), and the Tully-Fisher
relation. The amplitude of the outflow velocity of the galaxies is found to be ∼300 km/s. The average number density of galaxies
inside the void is roughly a factor of five lower than the average outside it. The Local void population is characterized
by lower luminosities and later morphological types, with medians of M
B
= − 15m.7 and T=8 (Sdm), respectively. 相似文献
3.
In the framework of a previously developed procedure the evolution of small spherically symmetric perturbations in a homogeneous R-W-F universe is analyzed. It turns out that the evolution tendency is mainly predicted by the state of the cosmic background. In the radiation dominated period the universe does not stimulate growing processes, a perturbation will be in a frozen state or it will diffuse. It is found that a dust dominated universe stimulates the perturbation masses to grow. The rate of this cosmic affected growing process is proportional to (R)–1/2 (R being the scale factor). Consequently almost all galaxies were formed at the beginning of the dust dominated era. 相似文献
4.
A. V. Tikhonov 《Astronomy Letters》2007,33(8):499-511
Using the method of searching for arbitrary shaped voids in the distribution of volume-limited samples of galaxies from the DR5 SDSS survey, we have identified voids and investigated their characteristics and the change in these characteristics with decreasing M lim (from ?19.7 to ?21.2, H 0 = 100 km s?1 Mpc?1)—the upper limit on the absolute magnitude of the galaxies involved in the construction of voids. The total volume of the 50 largest voids increases with decreasing M lim with a break near M* = ?20.44—the characteristic value of the luminosity function for SDSS galaxies. The mean overdensity in voids increases with decreasing M lim also with a weak break near M*. The exponent of the dependence of the volume of a void on its rank increases significantly with decreasing M lim starting from M lim ～ ?20.4 in the characteristic range of volumes, which reflects the tendency for greater clustering of brighter galaxies. The averaged profile of the galaxy overdensity in voids has a similar pattern almost at all M lim. The galaxies mostly tend to gravitate toward the void boundaries and to avoid the central void regions; the overdensity profile is flat in the intermediate range of distances from the void boundaries. The axial ratios of the ellipsoids equivalent to the voids are, on average, retained with changing M lim and correspond to elongated and nonoblate void shapes, but some of the voids can change their shape significantly. The directions of the greatest void elongations change chaotically and are distributed randomly at a given M lim. The void centers show correlations reflecting the correlations of the galaxy distribution on scales (35–70)h ?1 Mpc. The galaxy distribution in the identified voids is nonrandom—groups and filaments can be identified. We have compared the properties of the galaxies in voids (in our case, the voids are determined by the galaxies with absolute magnitudes M abs < M lim = ?20.44, except for the isolated galaxies) and galaxies in structures identified using the minimum spanning tree. A bimodal color distribution of the galaxies in voids has been obtained. A noticeable difference is observed in the mean color indices and star formation rates per unit stellar mass of the galaxies in dense regions (structures)—as expected, the galaxies in voids are, on average, bluer and have higher log (SFR/M star). These tendencies become stronger toward the central void regions. 相似文献
5.
Womack M. Homich A. Festou M. C. Mangum J. Uhl W. T. Stern S. A. 《Earth, Moon, and Planets》1997,77(3):259-264
On-the-Fly maps of emission from the HCO+ J = 3-2 transition at 267.6 GHz were obtained of C/1995 O1 (Hale-Bopp) on 1997 Mar 15.6 UT using the NRAO 12-m telescope
with high spatial resolution. Unlike the relatively symmetric and centralized maps of the neutral species CO, HCN and H2CO, the spatial extent of HCO+ emission is very diffuse with a complex structure characterized by at least two physically different regions. The bulk of
the HCO+ emission peaks in intensity ∼175,000 km anti-sunward from the nuclear position. This peak emission does not fall directly
along the anti-sunward direction, but is rotated by ∼10 degrees toward the east from the anti-sunward direction. A substantial
void, or decrease, of HCO+ emission is observed within ∼ 55,000 km of the nucleus. The HCO+ emission in this void is roughly half the intensity of the emission observed 100,000 km away. This decrease of HCO+ emission near the nucleus may indicate that production or excitation of HCO+ is inhibited, or perhaps that HCO+ is easily destroyed in the inner coma, especially within ∼50,000 km of the nucleus. This void roughly coincides with the
approximate location and size of the so-called “diamagnetic cavity” in the coma and may mark a significant transition region
in the inner coma of Hale-Bopp
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Ekkehard Nowotny 《Astrophysics and Space Science》1984,103(2):249-270
On the basis of the hydrodynamical equations of a two-component gas (photons and hydrogen with coupling via Thomson scattering) in the recombination era of the Universe (standard model), the evolution of the density perturbations up to second order are calculated. It is shown, that the generated second-order amplitudes of the density fluctuations of the matter reach values of the same order as the first-order amplitudes within only one tenth of the expansion time for fluctuations with wavelengths corresponding to 107
M
. Upper limits in the density fluctuations (for the gravitationally instable modes) up to which first-order calculations are valid, are given. This calculation indicates that the linear perturbation analysis is very restricted, especially at wavelengths near the lower limit of the Jeans length.The linear analysis would be a good approximation only for density fluctuations of the matter with the density contrast less than 10–5–10–4 at the recombination era. Therefore, a nonlinear analysis which is not based on a perturbation series is required for studying the evolution of the density perturbations, because for this we need a density contrast of 10–2–10–3 at the end of the recombination era. 相似文献
7.
K. P. Dere G. E. Brueckner R. A. Howard M. J. Koomen C. M. Korendyke R. W. Kreplin D. J. Michels J. D. Moses N. E. Moulton D. G. Socker O. C. St. Cyr J. P. Delaboudinière G. E. Artzner J. Brunaud A. H. Gabriel J. F. Hochedez F. Millier X. Y. Song J. P. Chauvineau J. P. Marioge J. M. Defise C. Jamar P. Rochus R. C. Catura J. R. Lemen J. B. Gurman W. Neupert F. Clette P. Cugnon E. L. Van Dessel P. L. Lamy A. Llebaria R. Schwenn G. M. Simnett 《Solar physics》1997,175(2):601-612
We present the first observations of the initiation of a coronal mass ejection (CME) seen on the disk of the Sun. Observations
with the EIT experiment on SOHO show that the CME began in a small volume and was initially associated with slow motions of
prominence material and a small brightening at one end of the prominence. Shortly afterward, the prominence was accelerated
to about 100 km s-1 and was preceded by a bright loop-like structure, which surrounded an emission void, that traveled out into the corona at
a velocity of 200–400 km s-1. These three components, the prominence, the dark void, and the bright loops are typical of CMEs when seen at distance in
the corona and here are shown to be present at the earliest stages of the CME. The event was later observed to traverse the
LASCO coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest is the fact that this large-scale event, spanning
as much as 70 deg in latitude, originated in a volume with dimensions of roughly 35" (2.5 x 104 km). Further, a disturbance that propagated across the disk and a chain of activity near the limb may also be associated
with this event as well as a considerable degree of activity near the west limb. 相似文献
8.
H. Feng K. W. Jones S. Tomov B. Stewart G. F. Herzog C. Schnabel D. E. Brownlee 《Meteoritics & planetary science》2005,40(2):195-206
Abstract— The internal structures of type I spherules (melted micrometeorites rich in iron) have been investigated using synchrotron‐based computed microtomography. Variations from sphericity are small—the average ratio of the largest to the smallest semimajor axis is 1.07 ± 0.06. The X‐ray tomographs reveal interior cavities, four spherules with metal cores with diameters ranging from 57 to 143 μm and, in two spherules, high attenuation features thought to be nuggets rich in platinumgroup elements. Bulk densities range from 4.2 to 5.9 g/cm3 and average grain densities from 4.5 to 6.5 (g/cm3) with uncertainties of 10–15%. The average grain densities are those expected for materials containing mostly oxides of iron and nickel. The tomographic density measurements indicate an average void space of 5+8‐5%. The void spaces may be contraction features or the skeletons of bubbles that formed in the molten precursors during atmospheric passage. 相似文献
9.
Y. C. Whang 《Solar physics》1970,14(2):489-502
This paper presents a continued study of the two-dimensional guiding-center model of the solar wind interaction with the Moon. The characteristics theory and the computational method are discussed. The magnetic permeability of plasma is (1 + /2)–1 in the solar wind flow upstream of the Moon, and it changes to 1 in the void region of the lunar wake. The gradual change of the magnetic permeability in the penumbral region from the interplanetary condition to the void condition is explained as the source of field perturbations in the lunar wake. Perturbations of the magnetic field propagate as magnetoacoustic waves in a frame of reference moving with the plasma flow. Computer solutions were obtained to show that (i) the two principal perturbations of the magnetic field in the lunar wake (the umbral increase and the penumbral decrease) are confined to a region bounded by a Mach cone tangent to the lunar body, and (ii) the penumbral increases occur outside the lunar Mach cone. Computer solutions are also used to identify the source of field perturbations and to simulate the solar wind-moon interaction under varying interplanetary conditions. 相似文献
10.
G. Lessner 《Astrophysics and Space Science》1984,100(1-2):359-367
It is shown that in the radiation era of the Universe spatial temperature fluctuations (T/T)<10–5 in the cosmic plasma lead to huge changes of the density up to (/)104. This effect results from the fact that the cosmic plasma in the radiation era can be considered as a general relativistic Boltzmann gas which is found in the very vincinity of equilibrium. 相似文献
11.
Abstract Partly shock-melted Yanzhuang H-chondrite, now classified as petrological type H6 but before the shock event of type H4, was subjected to the shock-heating 2.6 Ma ago at the time it was spalled off its parent body and came into being as a meteoroid of ca. 30 cm radius. At that time the unmelted portion of the meteoroid suffered an almost complete loss of its radiogenic 4He and 40Ar while the contents of the most volatile non-noble gas elements Zn and Se were not measurably affected. The melted portion of Yanzhuang is also essentially void of radiogenic 4He (10 ± 4 × 10?8 cm3 STP/g) but it has retained some 80% of its radiogenic 40Ar, presumably because in the melt the increase of the diffusion length more than compensated the increase of the diffusion constant. 相似文献
12.
Matteo Viel Jörg M. Colberg T.-S. Kim 《Monthly notices of the Royal Astronomical Society》2008,386(3):1285-1293
We investigate the properties of 1D flux 'voids' (connected regions in the flux distribution above the mean-flux level) by comparing hydrodynamical simulations of large cosmological volumes with a set of observed high-resolution spectra at z ∼ 2. After addressing the effects of box size and resolution, we study how the void distribution changes when the most significant cosmological and astrophysical parameters are varied. We find that the void distribution in the flux is in excellent agreement with predictions of the standard Λcold dark matter (ΛCDM) cosmology, which also fits other flux statistics remarkably well. We then model the relation between flux voids and the corresponding 1D gas-density field along the line of sight and make a preliminary attempt to connect the 1D properties of the gas-density field to the 3D dark matter distribution at the same redshift. This provides a framework that allows statistical interpretations of the void population at high redshift using observed quasar spectra, and eventually it will enable linking the void properties of the high-redshift universe with those at lower redshifts, which are better known. 相似文献
13.
H. Alfvén 《Astrophysics and Space Science》1983,89(2):313-324
Progress in laboratory studies of plasmas and in the methods of transferring the results to cosmic conditions, together within situ measurements in the magnetospheres, are now causing a ‘paradigm transition’ in cosmic plasma physics. This involves an introduction ofinhomogeneous models with double layers, filaments, ‘cell walls’, etc. Independently, it has been discovered that the mass distribution in the universe is highly inhomogeneous; indeed,hierarchical. According to de Vaucouleurs, the escape velocity of cosmic structures is 102–103 times below the Laplace-Schwarzschild limit, leaving avoid region which is identified as a key problem in cosmology. It is shown that a plasma instability in the dispersed medium of the structures may produce this void and, hence, explain the hierarchical structure. The energy which is necessary may derive either from gravitation or from annihilation caused by a breakdown of cell walls. The latter alternative is discussed in detail. It leads to a ‘Fireworks Model’ of the evolution of the metagalaxy. It is questioned whether the homogeneous four-dimensional big bang model can survive in an universe which is inhomogeneous and three-dimensional. 相似文献
14.
Persistent electrostatic charge is a characteristic feature in lunar soil and results in cohesion forces between the grains ranging in the order of 102 dyn. We suggest that this phenomenon is responsible for the initial aggregation of grains in the formative era of the solar system. The effect would become important when the relative velocity between particles at grazing incidence or collision has been reduced to order of 102 m s–1. The electrostatic adhesion mechanism would also explain the suggestion from optical polarization measurements that small asteroids accumulate silicate dust.Electrostatic accretion and bonding would consequently appear to be a process of basic importance in the solar system, both in the formative era and today.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. 相似文献
15.
To reconstruct dark energy models the redshift z eq , marking the end of radiation era and the beginning of matter-dominated era, can play a role as important as z t , the redshift at which deceleration parameter experiences a signature flip. To implement the idea we propose a variable equation of state for matter that can bring a smooth transition from radiation to matter-dominated era in a single model. A popular Λ∝ ρ dark energy model is chosen for demonstration but found to be unacceptable. An alternative Λ∝ ρ a 3 model is proposed and found to be more close to observation. 相似文献
16.
Prospects for Detecting the 326.5 MHz Redshifted 21-cm HI Signal with the Ooty Radio Telescope (ORT)
Observations of the redshifted 21-cm HI fluctuations promise to be an important probe of the post-reionization era (z≤ 6). In this paper we calculate the expected signal and foregrounds for the upgraded Ooty Radio Telescope (ORT) which operates at frequency ν o = 326.5 MHz which corresponds to redshift z = 3.35. Assuming that the visibilities contain only the HI signal and system noise, we show that a 3 σ detection of the HI signal (～1 mK) is possible at angular scales 11′ to 3° with ≈1000 h of observation. Foreground removal is one of the major challenges for a statistical detection of the redshifted 21 cm HI signal. We assess the contribution of different foregrounds and find that the 326.5 MHz sky is dominated by the extragalactic point sources at the angular scales of our interest. The expected total foregrounds are 104?105 times higher than the HI signal. 相似文献
17.
Dimension of the Earth's General Ellipsoid 总被引：1，自引：0，他引：1
Burša Milan Kenyon Steve Kouba Jan Raděj Karel Šíma Zdislav Vatrt Viliam Vojtíšková Marie 《Earth, Moon, and Planets》2002,91(1):31-41
The problem of specifying the Earth's mean (general)ellipsoid is discussed. This problem has been greatly simplified in the era of satellite altimetry, especially thanks to the adopted geoidal geopotential value, W0 = (62 636 856.0 ± 0.5) m2 s-2.Consequently, the semimajor axis a of the Earth's mean ellipsoid can be easily derived. However, an a priori condition must be posed first. Two such a priori conditions have been examined, namely an ellipsoid with the corresponding geopotential that fits best W0 in the least squares sense and an ellipsoid that has the global geopotential average equal to W0. It has been demonstrated that both a priori conditions yield ellipsoids of the same dimension, with a–values that are practically identical to the value corresponding to the Pizzetti theory of the level ellipsoid: a = (6 378 136.68 ± 0.06) m. 相似文献
18.
We assume the Universe during the recombination era as a three-component fluid constituted by neutral hydrogen, plasma, and radiation; such fluids are coupled via the effects of photorecombination, photoionization, and Thomson scattering. The hydrodynamical modes are calculated and the relation with the gravitational instabilities is established. In addition to the well-known Jeans's instability modes two additional ones in the neighbourhood of 1013
M
are obtained in the case of an open Universe. 相似文献
19.
A. V. Tikhonov 《Astronomy Letters》2006,32(11):727-733
A method for detecting voids in the galaxy distribution is presented. Using this method, we have identified 732 voids with a radius of the seed sphere R seed > 4.0h ?1 Mpc in a volume-limited sample of galaxies from the southern part of the 2dFGRS survey. 110 voids with R seed > 9.0h ?1 Mpc have a positive significance. The mean volume of such voids is ～19 × 103 h ?3 Mpc3. Voids with R seed > 9.0h ?1 Mpc occupy 55% of the sample volume. We construct a dependence of the volumes of all the identified voids on their ranks and determine parameters of the galaxy distribution. The dependence of the volume of voids on their rank is consistent with a fractal model (Zipf’s power law) of the galaxy distribution with a fractal dimension D ≈ 2.1 (given the uncertainty in determining the dimension using our method and the results of a correlation analysis) up to scales of ～25h ?1 Mpc with the subsequent transition to homogeneity. The directions of the greatest elongations of voids and their ellipticities (oblateness) are determined from the parameters of equivalent ellipsoids. The directions of the greatest void elongations have an enhanced concentration to the directions perpendicular to the line of sight. 相似文献
20.
Under the assumption of a power law (k·R
n=C,C=const.) between the gravitational constantk and the radius of curvatureR of the Universe and forP=1/3 the exact solution is sought for the cosmological equations of Brans and Dicke. The solution turns out to be valid for closed space and the parameter of the scalar-tensor theory is necessarily negative. The radius of curvature increases linearly with respect to the age of the Universe while the gravitational constant grows with the square of the radius of curvature. It has been shown (Lessner, 1974) that in this case (KR
2) the spatial component of the field equations is independent of the remaining equations. However, our solution satisfies this independent equation. This solution for the radiation-dominated era corresponds to the solution for the matter-dominated era found by Dehnen and one of the authors (Dehnen and Obregón, 1971). Our solution, as is the solution previously obtained for the matter-dominated era, is in contradiction to Dirac's hypothesis in which the gravitational constant should decrease with time in an expanding Universe. 相似文献