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  • 1
    Electronic Resource
    Electronic Resource
    Spectrum of γ-Fluids: A statistical derivation (1996)
    Springer
    International journal of theoretical physics 35 (1996), S. 2013-2018 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spectrum of massless bosonic and fermionic fluids satisfying the equation of statep=(γ−1)ρ is derived using elementary statistical methods. As a limiting case, the Lorentz-invariant spectrum of the vacuum (γ=0,p=−ρ) is deduced. These results are in agreement with our earlier derivation for bosons using thermodynamics and semiclassical considerations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02302425
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  • 2
    Electronic Resource
    Electronic Resource
    Ages of the universe for FRW-type models in wesson's 5D variable mass theory of gravity (1994)
    Springer
    Astrophysics and space science 219 (1994), S. 29-34 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The age of the universe is computed for spatially homogeneous and isotropic cosmological models of the relativistic Wesson's 5D variable mass theory of gravity. It is shown that if the pressure in the mass dimension is negligible, ages old enough to agree with the observations can only be obtained if the cosmological constant is different from zero. In addition, unlike the standard FRW models in Einstein's 4D theory, the age value itself is not affected by the nature of the matter content (matter and radiation dominated models give the same age).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00657857
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  • 3
    Electronic Resource
    Electronic Resource
    Non-vacuum cosmological solutions of 5D variable mass theory of gravity (1994)
    Springer
    Astrophysics and space science 215 (1994), S. 53-58 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A class of non-vacuum expanding cosmological solutions of Wesson's 5D theory of gravity with variable rest mass is derived. The models are spatially homogeneous and isotropic and the source of gravitation is a pressureless fluid (dust) plus a cosmological constant term. The general and unified solution is found for the equations and some properties of different limiting cases are studied. Particularly, it is shown that for null cosmological constant the predicted age of the universe is smaller than the ones of the 4D FRW models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00627459
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  • 4
    Electronic Resource
    Electronic Resource
    Generalized Stefan-Boltzmann law (1995)
    Springer
    International journal of theoretical physics 34 (1995), S. 127-134 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Thermodynamics arguments have been employed to derive how the energy densityρ depends on the temperatureT for a fluid whose pressurep obeys the equation of statep = (γ −1)ρ, whereγ is a constant. Three different methods, among them the one considered by Boltzmann (Carnot cycle), lead to the expressionρ = ηTγ/(γ −1), whereη is a constant. This result also appears naturally in the framework of general relativity for spacetimes with constant spatial curvature. Some particular cases are vacuum (p = −ρ), cosmic strings (p= −1/3ρ), radiation (p = 1/3ρ), and stiff matter (p = ρ). It is also shown that such results can be adapted for blackbody radiation inN spatial dimensions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00670992
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  • 5
    Electronic Resource
    Electronic Resource
    On the thermodynamic properties of the quantum vacuum (1995)
    Springer
    International journal of theoretical physics 34 (1995), S. 1835-1842 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Several thermodynamic relations for the vacuum state have been derived by assuming that it behaves like a relativistic perfect simple fluid. Unlike the usual fluids, the vacuum becomes hotter when it undergoes an adiabatic expansion (TV −1=const). A new Lorentz-invariant spectrum for the vacuum is also suggested which is compatible with the usual equation of statep=−ρ and the other thermodynamic constraints. Some cosmological consequences of these results have also been discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00674064
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  • 6
    Electronic Resource
    Electronic Resource
    Cosmologies with Photon Creation and the 3K Relic Radiation Spectrum (1997)
    Springer
    General relativity and gravitation 29 (1997), S. 805-813 
    Details
    ISSN: 1572-9532
    Keywords: DEVIATION OF CMBR FROM BLACKBODY SHAPE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new Planckian type distribution for cosmologies with photon creation is derived using thermodynamics and semiclassical considerations. This spectrum is preserved during the evolution of the universe and compatible with the present spectral shape of the cosmic microwave background radiation (CMBR). Accordingly, the widely spread feeling that cosmologies with continuous photon creation are definitely ruled out by the COBE limits on deviation of the CMBR spectrum from blackbody shape should be reconsidered. It is argued that a crucial test for this kind of cosmologies is provided by measurements of the CMBR temperature at high redshifts. For a given redshift z greater than zero, the temperature is smaller than the one predicted by the standard FRW model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018850330860
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  • 7
    Electronic Resource
    Electronic Resource
    LETTER: On the Minimal Angular Size in Open, ΛCDM, and Scalar Field Cosmologies (2000)
    Springer
    General relativity and gravitation 32 (2000), S. 1851-1857 
    Details
    ISSN: 1572-9532
    Keywords: Angular diameter ; dark matter ; open and flat universes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We propose a simple method for determining the redshift z m at which the angular size of an extragalactic source with fixed proper diameter takes its minimal value. A closed analytical expression, which is often convenient for numerical evaluation is derived. The method is exemplified with the following FRW type expanding universes: the open matter dominated models (ΩΛ = 0), a critical density model with cosmological constant (ΩΛ ≠ 0), and the class of scalar field cosmologies proposed by Ratra and Peebles. The influence of systematic evolutionary effects is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001988831930
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  • 8
    Electronic Resource
    Electronic Resource
    Inhomogeneous two-fluid cosmologies (1988)
    Springer
    General relativity and gravitation 20 (1988), S. 1019-1035 
    Details
    ISSN: 1572-9532
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new class of expanding cosmological solutions is derived. The matter content of these models is a mixture of two interacting simple fluids: the first one, homogeneous and isotropic with equation of statep = (γ-1)ρ, the dynamics of which is given by the FRW equation and the second one an inhomogenous dust. The limiting case of two dusts corresponds to the Szekeres' universes of class II. A large subclass of the models evolve to a FRW phase for all physically meaningful values of the polytropic indexγ and the curvature parameterk. A gauge condition, under which the metric is invariant, is shown to exist for k≠0. In particular, it explains why the parabolic model is a peculiar solution in the class found by Szekeres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00759023
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  • 9
    Electronic Resource
    Electronic Resource
    Uniform Newtonian models with variable mass (1991)
    Springer
    General relativity and gravitation 23 (1991), S. 455-463 
    Details
    ISSN: 1572-9532
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A Newtonian version of the spatially homogeneous and isotropic cosmological models with variable mass is presented. Under the assumption that the mass variation is a strict cosmological effect, its influence on the evolution of the scale function is established for the case of a dust-filled universe. Unlike the usual Newtonian models the present value of the deceleration parameter (q ≏ 1) obtained from the luminosity distance versus redshift relation can be fitted for a time-decreasing mass. It is also shown that the hyperbolic, parabolic or elliptic character of the fluid motion can be modified along the expansion. Likewise, a Friedmann-type equation with a variable “curvature term” indicates that in the frame-work of a full geometric variable mass theory, the same may occur with the open, flat or closed character of the universe spatial section.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00756608
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  • 10
    Electronic Resource
    Electronic Resource
    The relation between the relativistic 5D Wesson theory and the Newtonian variable mass theory (1992)
    Springer
    General relativity and gravitation 24 (1992), S. 171-177 
    Details
    ISSN: 1572-9532
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The existence of Newtonian analogs to spatially homogeneous and isotropic cosmological models of the relativistic 5D Wesson variable mass theory is investigated. By treating the continuous universe “matter creation process” by the methods of standard hydrodynamics, it is shown that classical analogs are obtained only if the cosmological constant is null and the spatial curvature is positive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00756784
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