共查询到20条相似文献，搜索用时 31 毫秒
1.
V. V. Burdyuzha 《Astronomy Reports》2009,53(5):381-388
We briefly discuss a modern view of the cosmological constant. It is suggested that the cosmological constant was “hardened” at E ～ 150 MeV after the latest (quark-gluon) phase transition. Until this energy was reached, the vacuum component of the Universe evolved (decreased) in a series of discontinuous jumps; i.e., condensates of quantum fields made negative contributions to its positive energy density. This was the quintessence period of the evolution of the Universe, when it underwent an intense loss of symmetry during the first fractions of a microsecond of its existence. However, this point of view is not without criticism, and other approaches are considered. In particular, the small value of the cosmological constant and its ability to accelerate the expansion of the Universe is of great interest. Although all available data on the cosmological constant were recently summarized and classified by S. Nobbenhuis, no satisfactory solution to this problemhas been reached, and this represents a major difficulty for progress in quantum-gravity theory and cosmology. We briefly discuss the possibility for stars to be formed from dark energy (vacuum stars) and the extension of holographic ideas to the entire Universe. We also consider the possibility of solving the problem of the cosmological constant by introducing a universal wave function; i.e., quantum decoherence, which implies the rejection of the Copenhagen interpretation of quantum mechanics and the acceptance of H. Everett’s point of view. 相似文献
2.
A. D. Chernin V.P. Dolgachev L.M. Domozhilova P. Teerikorpi M. Yu. Valtonen 《Astronomy Reports》2010,54(3):185-191
It is shown that the random-motion theorem in cosmology proven in the early 1960s can be generalized to take into account
the presence of a uniform dark-energy background. The role of the dark energy is substantial: its repulsive force exceeds
the gravitational force due to darkmatter and baryons, both on the scale of the Universe as a whole and on local scales of
about 1 Mpc. The generalized random-motion theorem has the form of a differential equation relating the kinetic energy of
the random motion and the potential energy of the particles due to their own gravitational field and the repulsive dark-energy
field. One consequence of the generalized theorem is a virial relation containing the potential energy in the repulsive field. 相似文献
3.
We present a new normalization for the linear density-perturbation spectrum in a multi-parameter model of the Universe. Using the differential mass function for the nearly galaxy clusters obtained from optical data, we have constructed a functional relation between the dispersion of the density contrast σ 8 on the scale 8h ?1 Mpc and the cosmological parameters Ω m , ΩΛ, h, n, f v for each of three theoretical approximations of the mass function: Press-Schechter, Sheth-Tormen and Jenkins. An extended class of models of the Universe with general spatial curvature include four parameters for the matter components: baryons (Ω b ), “cold” dark matter (Ω c ), “hot” dark matter (Ω v ), and the vacuum energy (ΩΛ). It is shown that the most accurate normalization of the power spectrum is achieved with the Sheth-Tormen approximation. 相似文献
4.
The polarization-correction energy-momentum tensor for a semi-classical gravitational theory is derived. This tensor accounts for the creation of particles from a vacuum at a finite temperature. The theory contains an asymptotic cosmological Friedmann solution. The solution obtained turns out to be dynamically stable, so that it can form the observed properties of the Universe. New cosmological solutions describing the early stages of cosmological evolution of a homogeneous isotropic Universe are obtained. One of these corresponds to the simultaneous creation of matter and geometry from the vacuum of a flat, empty space-time without structure. Another solution corresponds to a high-temperature inflation regime. A cosmological scenario for the creation of the observed Universe from “nothing” that includes the properties of all the solutions obtained is put forward. 相似文献
5.
In this study, we discuss the challenges radio astronomers face while observing radio continuum sources. We consider issues related to rms noise, confusion, position accuracy, shot noise and how these issues affect observation results, data analysis and the science goals we are trying to achieve. We mainly focus on the Evolutionary Map of the Universe (EMU-ASKAP) sky survey, EMU Early science survey and Westerbork Observations of the Deep APERTIF Northern sky (WODAN). The study will also be useful for future surveys like with possible continuum surveys through MeerKAT (e.g., MIGHTEE) and SKA-1. The late time Integrated Sachs-Wolfe (ISW) effect detection is one of the major areas of research related to dark energy cosmology. We will particularly discuss how technical, data analysis and mapping issues, affect galaxy over/under density dependent science goals like the detection of the late time Integrated Sachs-Wolfe (ISW) effect through wide-field radio continuum surveys.
相似文献6.
If the large scale structure of the Universe was created, even partially, via Zeldovich pancakes, than the fluctuations of the CMB radiation should be formed due to bulk comptonization of black body spectrum on the contracting pancake. Approximate formulae for the CMB energy spectrum after bulk comptonization are obtained. The difference between comptonized energy spectra of the CMB due to thermal and bulk comptonozation may be estimated by comparison of the plots for the spectra in these two cases.
相似文献7.
A. F. Zakharov 《Astronomy Reports》2006,50(2):79-90
Gravitational lensing is a powerful tool for studies of the distribution of matter (including dark matter) in the Universe. The characteristic angular separation of images and characteristic variability time scale depend on the characteristic masses of the gravitational lenses. The construction of the RADIOASTRON space interferometer in the coming years will provide qualitatively new conditions for investigations of microlensing of distant quasars in the radio, since it will become possible not only to resolve individual microimages of these quasars, but also to observe astrometric microlensing (i.e., the shift of an image of a distant quasar, sometimes called weak microlensing). Astrometric microlensing by compact objects in the Galactic halo is not a very significant effect for the RADIOASTRON interferometer, since the probability of such events is low and the characteristic time scales involved appreciably exceed the proposed operational lifetime of the interferometer. 相似文献
8.
This paper presents an exact analytical solution to fully coupled axisymmetric consolidation of a semi‐infinite, transversely isotropic saturated soil subjected to a uniform circular loading at the ground surface. The analysis is under the framework of Biot's general theory of consolidation. First, the governing equations of consolidation are transformed into a set of equivalent partial differential equations with the introduction of two auxiliary variables. These partial differential equations are then solved using Hankel–Laplace integral transforms. Once solutions in the transformed domain have been obtained, the actual solutions in the physical domain for displacements and stress components of the solid matrix, pore‐water pressure and fluid discharge can be finally obtained by direct numerical inversion. The accuracy of the numerical solutions developed is confirmed by comparison with an existing exact solution for an isotropic and saturated soil that is a special case of the more general problem addressed. Numerical analyses are also presented to investigate the influence of the degree of material anisotropy on the consolidation settlement. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
9.
The properties of gravitationally bound clouds (halos) of dark matter derived via numerical simulations of the distribution
of dark matter in the Universe are investigated. The analysis makes use of a catalog of halos obtained in the European “MareNostrum
Universe” project, which has achieved a better balance between resolution and representativeness than catalogs used earlier
for similar studies. This has made it possible to refine the main tendencies displayed by the evolution of the halo masses
and the angular velocities and density profiles of the halos. The results are compared with the newest available observational
data and with known results obtained earlier in numerical simulations with lower resolution and using smaller samples of halos,
making it possible to trace the influence of these factors on the results obtained. Disagreements between observations and
numerical models obtained in earlier studies are confirmed, and possible ways to explain them discussed. 相似文献
10.
A number of models have been established to simulate the behaviour of solute transport due to chemical pollution, both in croplands and groundwater systems. An approximate polynomial solution to convection–dispersion equation (CDE) based on boundary layer theory has been verified for the use to describe solute transport in semi-infinite systems such as soil column. However, previous studies have only proposed low order polynomial solutions such as parabolic and cubic polynomials. This paper presents a general polynomial boundary layer solution to CDE. Comparison with exact solution suggests the prediction accuracy of the boundary layer solution varies with the order of polynomial expression and soil transport parameters. The results show that prediction accuracy increases with increasing order up to parabolic or cubic polynomial function and with no distinct relationship between accuracy and order for higher order polynomials (\(n\geqslant 3\)). Comparison of two critical solute transport parameters (i.e., dispersion coefficient and retardation factor), estimated by the boundary layer solution and obtained by CXTFIT curve-fitting, shows a good agreement. The study shows that the general solution can determine the appropriate orders of polynomials for approximate CDE solutions that best describe solute concentration profiles and optimal solute transport parameters. Furthermore, the general polynomial solution to CDE provides a simple approach to solute transport problems, a criterion for choosing the right orders of polynomials for soils with different transport parameters. It is also a potential approach for estimating solute transport parameters of soils in the field. 相似文献
11.
V. V. Burdyuzha 《Astronomy Reports》2012,56(6):403-409
The evolution of the vacuum component of the Universe is studied in both the quantum and classical regimes. Our Universe has emerged as a result of a tunneling process, beginning with an oscillating mode and passing on to a Friedmann mode, and it very probably had a high symmetry for the Planck parameters. In the first fractions of a second (the quantum regime), as it cooled, the vacuum component of the Universe lost its high degree of symmetry due to phase transitions; i.e., its positive energy density was subject to negative contributions from quantum field condensates (by 78 orders of magnitude). After the last (quark-hadron) phase transition, the vacuum energy ??froze.?? At this time (10?6 s), the vacuum energy density can be calculated using the formula of Zel??dovich and substituting the mean values of the pseudo-Goldstone boson (??-mesons) masses characterizing the chromodynamic vacuum. Chiral symmetrywas lost at that time. The dynamics of the equilibrium vacuum after its ??hardening?? is considered using the holographic principle. During the next 4 × 1017 s (the classical regime), the vacuum component of the Universe was reduced by 45 orders of magnitude due to the creation of new quantum states during its expansion. It is possible to solve the cosmological-constant problem using the holographic principle, since the 123 problematic orders of magnitude disappear in usual physical processes. The vacuum energy density is also calculated in the classical regime to a redshift of 1011 using a ??cosmological calculator.?? 相似文献
12.
O. V. Verkhodanov A. I. Kopylov Yu. N. Pariiskii N. S. Soboleva A. V. Temirova O. P. Zhelenkova 《Astronomy Reports》2002,46(7):531-542
BV RI data are presented for the majority of steep-spectrum objects in the RC catalog with m R <23.5m. Previously developed programs are applied to these data to estimate the redshifts and ages of the stellar systems of the host galaxies. Applying this program to the color data (BV RI JHK) for distant radio galaxies with spectroscopic redshifts indicates that this approach provides accurate estimates of the redshifts of such radio galaxies, close to those obtained using field galaxies (～20%). The age estimates are much less trustworthy, but a lower limit to the ages of objects that are not very distant (z<1.5) can be determined with certainty. We have identi fied several galaxies whose formal ages exceed the age of the Universe at the corresponding z in simple Cold Dark Matter models for the Universe. The possibility of using such objects to elucidate the role of “dark energy” is discussed. This paradox disappears in models with cosmological constants (Λ terms) equal to 0.6–0.8. 相似文献
13.
It is known that ΛCDM cosmological models predict too many dark halos compared to the observed numbers. This excess is derived from the virialized mass in the Local Supercluster and its vicinity. Taking into account cosmological velocity fluctuations during the formation of the dark halo population makes it possible to eliminate this remaining contradiction in the ΛCDM model. Based on Press-Schechter formalism, a model describing the formation of the dark halo population is developed, taking into account kinematic effects in the dark matter. A quantitative explanation of the virialized-mass deficit in the local Universe is obtained in this model. 相似文献
14.
A model for the formation of supermassive black holes at the center of a cluster of primordial black holes is developed. It is assumed that ～10?3 of the mass of the Universe consists of compact clusters of primordial black holes that arose as a result of phase transitions in the early Universe. These clusters also serve as centers for the condensation of dark matter. The formation of protogalaxies with masses of the order of 2 × 108 M ⊙ at redshift z = 15 containing clusters of black holes is investigated. The nuclei of these protogalaxies contain central black holes with masses ～105 M ⊙, and the protogalaxies themselves resemble dwarf spherical galaxies with their maximum density at their centers. Subsequent merging of these induced protogalaxies with ordinary halos of dark matter leads to the standard picture for the formation of the large-scale structure of the Universe. The merging of the primordial black holes leads to the formation of supermassive black holes in galactic nuclei and produces the observed correlation between the mass of the central black hole and the bulge velocity dispersion. 相似文献
15.
This paper presents a three‐dimensional energy‐based solution for the time‐dependent response of a deeply embedded and unsupported semi‐infinite tunnel of circular cross‐section. The tunnel is taken to be excavated quasi‐instantaneously from an infinite rock body that initially exhibits an isotropic stress state and that is made up of a homogeneous, isotropic and viscoelastic material. The viscoelastic behaviour is modelled by means of Burger's model, and the rock is taken to behave volumetrically linear elastic and to exhibit exclusively deviatoric creep. This viscoelastic problem is transformed into the Laplace domain, where it represents a quasi‐elastic problem. The displacement fields in the new solution are taken to be the products of independent functions that vary in the radial and longitudinal directions. The differential equations governing the displacements of the system and appropriate boundary conditions are obtained using the principle of minimum potential energy. The solutions for these governing equations in the Laplace domain are then obtained analytically and numerically using a one‐dimensional finite difference technique. The results are then transformed back into the time domain using an efficient numerical scheme. The accuracy of the new solution is comparable with that of a finite element analysis but requires much less computation effort. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
16.
During the process of one‐dimensional consolidation with a threshold gradient, the seepage front moves downward gradually, and the problem is indicated as a Stefan problem. The novel feature in this Stefan problem is a latent heat that varies inversely with the rate of the moving boundary. An exact solution for the external load that increases in proportion to the square root of time is constructed using the similarity transformation technique. Computational examples concerning the effect of different parameters on the motion of the seepage front are presented. The exact solution provides a worthwhile benchmark for verifying the accuracy of numerical and approximate methods. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
17.
K. Grainge B. Alachkar Shaun Amy D. Barbosa M. Bommineni P. Boven R. Braddock J. Davis P. Diwakar V. Francis R. Gabrielczyk R. Gamatham S. Garrington T. Gibbon D. Gozzard S. Gregory Y. Guo Y. Gupta J. Hammond D. Hindley U. Horn R. Hughes-Jones M. Hussey S. Lloyd S. Mammen S. Miteff V. Mohile J. Muller S. Natarajan J. Nicholls R. Oberland M. Pearson T. Rayner S. Schediwy R. Schilizzi S. Sharma S. Stobie M. Tearle B. Wang B. Wallace L. Wang R. Warange R. Whitaker A. Wilkinson N. Wingfield 《Astronomy Reports》2017,61(4):288-296
The Square Kilometre Array (SKA) will be the world’s largest and most sensitive radio telescope. It will address fundamental unanswered questions about our Universe including how the first stars and galaxies formed after the Big Bang, how dark energy is accelerating the expansion of theUniverse, the role of magnetism in the cosmos, the nature of gravity, and the search for life beyond Earth. This project envisages the construction of 133 15-m antennas in South Africa and 131072 log-periodic antennas in Australia, together with the associated infrastructure in the two desert sites. In addition, the SKA is an exemplar Big Data project, with data rates of over 10 Tbps being transported from the telescope to HPC/HTC facilities. 相似文献
18.
The measurement of surface energy balance over a land surface in an open area in Bangalore is reported. Measurements of all
variables needed to calculate the surface energy balance on time scales longer than a week are made. Components of radiative
fluxes are measured while sensible and latent heat fluxes are based on the bulk method using measurements made at two levels
on a micrometeorological tower of 10m height. The bulk flux formulation is verified by comparing its fluxes with direct fluxes
using sonic anemometer data sampled at 10Hz. Soil temperature is measured at 4 depths. Data have been continuously collected
for over 6 months covering pre-monsoon and monsoon periods during the year 2006. The study first addresses the issue of getting
the fluxes accurately. It is shown that water vapour measurements are the most crucial. A bias of 0.25% in relative humidity,
which is well above the normal accuracy assumed by the manufacturers but achievable in the field using a combination of laboratory
calibration and field intercomparisons, results in about 20W m−2 change in the latent heat flux on the seasonal time scale. When seen on the seasonal time scale, the net longwave radiation
is the largest energy loss term at the experimental site. The seasonal variation in the energy sink term is small compared
to that in the energy source term. 相似文献
19.
采用Green函数、保角映射等方法分析SH波上方垂直入射时弹性半空间中椭圆形弹性夹杂与任意方位裂纹的相互作用。首先,求解含椭圆形弹性夹杂的弹性半空间内任意一点承受时间谐和出平面线源荷载作用时的位移基本解,即Green函数,再结合裂纹切割法构造裂纹,得到SH波上方垂直入射时椭圆夹杂和裂纹同时存在条件下的位移场与应力场。作为算例,给出大量的数值结果,探讨不同参数情况下弹性夹杂周边动应力集中系数（DSCF）、地表位移及裂纹尖端动应力强度因子（DSIF）的分布规律,结果表明不同参数的变化会对三者的分布带来一定的影响。 相似文献
20.
三类边坡失稳判据的统一性 总被引：2，自引：0，他引：2
将热力学理论中材料破坏的能量机制引入边坡工程中,推导了强度折减过程中边坡的能量方程,利用FLAC3D二次开发了能量的计算程序,并应用于某经典边坡算例中。通过与Spencer法的计算结果对比发现：强度折减法中边坡的稳定性与能量变化关系紧密,由此提出了4种新的失稳判据--能量突变失稳判据,且4种能量突变失稳判据理论上是统一的。通过对比发现：动能突变判据与数值计算收敛性判据、重力势能降突变判据与特征点垂直位移突变判据、耗散能增量突变判据与塑性区贯通判据分别存在对应关系,证明了常见的3类失稳判据也是统一的。通过算例试算发现,3类判据判定结果不相等主要是由收敛标准和网格精度等人为因素造成的,本质上是因为数值计算是一种近似解。工程应用中,可通过3类失稳判据判定结果的一致性来自评安全系数的计算精度,一致性越好,精度越高。提高计算精度的根本办法是严格收敛标准和精细网格划分,但应同时兼顾数值计算的时长,从而实现计算效率最大化。 相似文献