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  • Cosmology
  • Strong Interactions
  • Springer  (17)
  • 2015-2019
  • 2000-2004  (5)
  • 1995-1999  (12)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    General relativity and gravitation 32 (2000), S. 2339-2343 
    ISSN: 1572-9532
    Keywords: Einstein-Dilaton-Tensor ; Superstring ; Cosmology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that the general solution of the Einstein-Dilaton-antisymmetric-tensors field equations of all superstring theories exhibits a chaotic oscillatory behaviour of the Belinskii-Khalatnikov-Lifshitz type near a cosmological singularity. This result indicates that superstring cosmology is much more complex than is assumed in the scenarios presently discussed in the literature.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    General relativity and gravitation 32 (2000), S. 607-614 
    ISSN: 1572-9532
    Keywords: Cosmology ; causal viscous fluid ; variable G and Λ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Einstein's equations with variable gravitational and cosmological “constants” are considered in the presence of a bulk viscous fluid source described by the truncated causal theory of Israel–Stewart, for the spatially flat homogeneous and isotropic universe. A solution is found in which the cosmological term varies inversely with the square of time. However, the gravitational constant G is found to be increasing with time.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    General relativity and gravitation 32 (2000), S. 615-620 
    ISSN: 1572-9532
    Keywords: Cosmology ; Israel–Stewart–Hiscock theory ; variable G and Λ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A cosmological model with variable G and Λ is considered in the framework of Israel–Stewart–Hiscock (ISH) causal theory. Power law as well as inflationary solutions are obtained. The gravitational constant is found to increase with time.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    General relativity and gravitation 32 (2000), S. 719-733 
    ISSN: 1572-9532
    Keywords: Cosmology ; Newtonian theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a previous paper [9], we derived a post-Newtonian approximation to cosmology which, in contrast to former Newtonian and post-Newtonian cosmological theories, has a well-posed initial value problem. In this paper, this new post-Newtonian theory is compared with the fully general relativistic theory, in the context of the k= 0 Friedmann–Robertson–Walker cosmology. It is found that the post-Newtonian theory reproduces the results of its general relativistic counterpart, whilst the Newtonian theory does not.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    General relativity and gravitation 32 (2000), S. 1125-1134 
    ISSN: 1572-9532
    Keywords: Cosmology ; observations ; science
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is argued that some of the recent claims for cosmology are grossly overblown. Cosmology rests on a very small database: it suffers from many fundamental difficulties as a science (if it is a science at all) whilst observations of distant phenomena are difficult to make and harder to interpret. It is suggested that cosmological inferences should be tentatively made and sceptically received.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 84 (1998), S. 65-75 
    ISSN: 1572-9672
    Keywords: Cosmology ; nucleosynthesis ; abundances ; Quasars: absorption lines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present our measurements of the deuterium to hydrogen ratio (D/H) in QSO absorption systems, which give D/H = 3.40 ± 0.25 × 10-5 based on analysis of four independent systems. We discuss the properties of two systems which provide the strongest constraints on D/H. We outline the systematic effects involved in measurements of D/H and introduce a sophisticated method of analysis which properly accounts for these effects.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 84 (1998), S. 297-308 
    ISSN: 1572-9672
    Keywords: Deuterium ; Interstellar Abundance ; Cosmology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An accurate measurement of the primordial value of D/H would provide one of the best tests of nucleosynthesis models for the early Universe and the baryon density. Such evaluations have been traditionally made using present estimations of the deuterium abundance in the interstellar medium, extrapolated backwards in time with the use of galactic evolution models. Direct estimations of the primordial deuterium abundance have been carried out only recently in QSOs absorbers at high redshift. We will summarize galactic observations of deuterium and suggest that, perhaps, a single D/H value for the interstellar medium is not representative. These evaluations mainly came from observations completed in the far UV with first the Copernicus satellite over the Lyman lines series followed then by H and D Lyman-alpha lines observations with both the IUE and the GHRS on the Hubble Space Telescope. We discuss different known systematics and show that the situation is not yet clear. It is not possible today to claim that we know "the" D/H value in the interstellar medium, if any. Overall and in the context of additional D observations made in the solar system, we conclude that the actual evolution of deuterium from Big-Bang nucleosynthesis to now is not yet understood. More observations, recently made with IMAPS (the Interstellar Medium Absorption Profile Spectrograph) and hopefully to be made with FUSE (the Far Ultraviolet Spectroscopic Explorer to be launched in the fall of 1998), at higher spectral resolution or in many different galactic sites are certainly needed to help us reach a better global view of the evolution of that key element, and thus better constrain any evaluation of its primordial abundance.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 84 (1998), S. 3-14 
    ISSN: 1572-9672
    Keywords: Cosmology ; Nucleosynthesis ; Light Elements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Now that extragalactic deuterium observations are being made, Big Bang Nucleosynthesis (BBN) is on the verge of undergoing a transformation. Previously, the emphasis was on demonstrating the concordance of the Big Bang Nucleosynthesis model with the abundances of the light isotopes extrapolated back to their primordial values using stellar and Galactic evolution theories. Once the primordial deuterium abundance is converged upon, the nature of the field will shift to using the much more precise primordial D/H to constrain the more flexible stellar and Galactic evolution models (although the question of potential systematic error in 4He abundance determinations remains open). The remarkable success of the theory to date in establishing the concordance has led to the very robust conclusion of BBN regarding the baryon density. The BBN constraints on the cosmological baryon density are reviewed and demonstrate that the bulk of the baryons are dark and also that the bulk of the matter in the universe is non-baryonic. Comparison of baryonic density arguments from Lyman-α clouds, x-ray gas in clusters, and the microwave anisotropy are made and shown to be consistent with the BBN value.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Foundations of science 2 (1997), S. 61-64 
    ISSN: 1572-8471
    Keywords: General Relativity ; Cosmology ; Black holes ; Nonlinearity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General
    Notes: Abstract The author proposes to add another dichotomy to the list of essential tensions proposed by Professor Duda, namely beauty and ugliness. Physicists believe that only beautiful theories describe the world correctly, and that General Relativity is one of the most beautiful physical theories. The author explains why physicists regard this theory as beautiful.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 230 (1995), S. 237-262 
    ISSN: 1572-946X
    Keywords: Cosmology ; South Africa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper reviews research in theoretical cosmology in South Africa, providing an overview of the work that has been done and the groups involved in that work.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 225 (1995), S. 221-226 
    ISSN: 1572-946X
    Keywords: Black holes ; General relativity ; Cosmology ; Mathematical physics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The bounds for the energy change rate of a Maxwell field in the outer space of a rotating black hole, calculated by de Vries (1994) and de Vries (1995), enable us to deduce limits for the rotation and the mass of black holes. For this purpose we assume that a certain part of the anisotropies of the cosmic background radiation is due to absorption or superradiance of black holes (Teukolsky, 1973, Starobinskii and Churilov, 1973). The knowledge of these anisotropies yields bounds for rotation and mass of the black holes in the observable universe.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 227 (1995), S. 13-24 
    ISSN: 1572-946X
    Keywords: Cosmology ; Cosmological Redshift ; History of Cosmology ; Cosmic Background Radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We analyse the history of modern cosmology based on the redshift phenomenon and on the cosmic background radiation (CBR). We show the models of different authors for the interpretation of the redshift and how the tired light models predicted the correct value of 2.7 K temperature previous to Gamow and collaborators.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 74 (1995), S. 471-474 
    ISSN: 1572-9672
    Keywords: Cosmology ; Gravitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider the influence of the nonlinear stage of gravitational instability on the two-point correlation functions of gravitationally bound objects. Based on the theory of nonlinear gravitational contraction of a single density peak of dissipationless matter (Gurevich and Zybin, 1988a,b; 1990) we develop a method for calculating the two-point correlation functions of different objects of any mass. The method works good in the region of strong correlations and can be easily extended to calculate higher correlation functions. We show that the main contribution to the correlation function ξi in the region of strong correlations ξi ≫ 1 is made by pair systems located outside large clusters of objects. In this region the shape of ξi is determined only by the nonlinear dynamics of gravitational contraction of dissipationless matter and has the form ξi ≈C τ −α, where α≈1.8 is a universal parameter.
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  • 14
    ISSN: 1572-9672
    Keywords: Cosmology ; Microwave Background Anisotropies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Here follows a preliminary report on the construction of fake millimeter and sub-millimeter skies, as observed by virtual instruments,e.g. the COBRA/SAMBA mission, using theoretical modeling and data extrapolations. Our goal is to create maps as realistic as possible of the relavant physical contributions which may contribute to the detected signals. This astrophysical modeling is followed by simulations of the measurement process itself by a given instrumental configuration. This will enable a precise determination of what can and cannot be achieved with a particular experimental configuration, and provide a feedback on how to improve the overall design. It is a key step on the way to define procedures for the separation of the different physical processes in the future observed maps. Note that this tool will also prove useful in preparing and analyzing current (e.g. balloon borne) Microwave Background experiments.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 231 (1995), S. 169-176 
    ISSN: 1572-946X
    Keywords: Gamma-ray bursts ; Neutron stars ; Cosmology ; Gamma-rays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The modelling of gamma-ray burst (GRB) spectra has considerable potential for increasing the understanding of these enigmatic sources. A diversity of ideas and analyses has been generated over the last two decades to explain line features and continuum shapes, encompassing both older galactic neutron star and “new age” cosmological source models. This paper reviews some of the highlights of these studies, discussing the merits and limitations of various ideas, and in particular their compatibility with the observational data. The first focus will be on continuum models for GRBs, which include optically thin synchrotron emission and resonant Compton upscattering near galactic neutron stars, while the synchrotron and non-magnetic inverse Compton scattering mechanisms are prominent in the less well-developed cosmological scenarios. Line formation scenarios will then be discussed, in particular the scattering model for producing cyclotron features, which remains the only viable explanation for the Ginga observations of double lines. Absorption-like line production in cosmological burst models is generally difficult, though interesting notions such as femtolensing interference patterns have been proffered.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 231 (1995), S. 377-388 
    ISSN: 1572-946X
    Keywords: Gamma-ray bursts ; Neutron stars ; Cosmology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We review models of cosmological gamma-ray bursts (GRBs). The statistical and γ-ray transparency issues are summarized. Neutron-star and black-hole merger scenarios are described and estimates of merger rates are summarized. We review the simple fireball models for GRBs and the recent work on non-simple fireballs. Alternative cosmological models, including models where GRBs are analogs of active galactic nuclei and where they are produced by high-field, short period pulsars, are also mentioned. The value of neutrino astronomy to solve the GRB puzzle is briefly reviewed.
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 74 (1995), S. 259-268 
    ISSN: 1572-9672
    Keywords: Cosmology ; Quasar Spectra ; Physical Constants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Gamow was one of the pioneers who studied the possible variability of fundamental physical constants. Some versions of modern Grand Unification theories do predict such variability. The paper is concerned with three of the constants: the fine-structure constant α, the ratio of the proton massm p to the electron massm e, and the ratio of the neutron massm n tom e. It is shown on the basis of the quasar spectra analysis, that all the three constants revealed no statistically significant variation over the last 90% of the life time of the Universe. At the 2δ significance level, the following upper bounds are obtained for the epoch corresponding to the cosmological redshiftsz∼2–3: Δα/α〈1.5×10−3, Δm p/m p〈2×10−3, and Δm/m〈3×10−4, where Δx is a possible deviation of a quantityx from its present value,m=m p+m n, and the nucleon masses are in units ofm e. (According to new observational data which became known most recently, Δm p/m p〈2×10−4) In addition a possible anisotropy of the high-redshift fine splitting over the celestial sphere is checked. Within the relative statistical error 3δ 〈 1% the values of α turned out to be the same in various quadrants of the celestial sphere, which corresponds to their equality in causally disconnected areas. However, at the 2δ level a tentative anisotropy of estimated Δα/α values is found in directions that approximately coincide with the direction of the relic microwave background anisotropy. The revealed constraints serve as criteria for selection of those theoretical models which predict variation of α,m p orm n with the cosmological time.
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