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  • 1
    Electronic Resource
    Electronic Resource
    Gravitational collapse of a dust ball — The external observer's point of view (1985)
    Springer
    Astrophysics and space science 116 (1985), S. 349-354 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The problem of collapse of a dust ball has been studied in detail from the point of view of an external observer (O). It is seen that although there is no material pressure from the point of view of the comoving observer, there is a non-vanishing material pressure in the ball from the point of view of O. In the early stages of collapse (w.r.t. O), this pressure is positive everywhere inside the ball, while during the later stages, if one goes outwards from the centre towards the surface of the ball, this pressure is negative up to a certain value of the radial coordinate, and then changes its sign thereafter. On the basis of this pressure, one can understand the physics of the whole scenario of collapse w.r.t. O; in particular, the important feature is that in the ultimate stages an event horizon is formed asymptotically and there is no collapse to a point (as takes place from the point of view of the comoving observer).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00653789
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  • 2
    Electronic Resource
    Electronic Resource
    Stellar structures with constant local adiabatic index under extreme relativistic conditions (1983)
    Springer
    Astrophysics and space science 93 (1983), S. 247-254 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Stellar structures with a constant local adiabatic index Γ have been discussed under the extreme relativistic condition (dP/dρ=1, at the center of the configuration). The equation of state,PαρΓ, where ρ r is the rest-mass density leads to the relations, (i)ρ=AP 1/Γ−P/(Γ−1) between energy density and pressure, and (ii)e=NP between internal energy density and pressure, where the constantN may be called local polytropic index. The local adiabatic index, Γ, is found to be related to the adiabatic index, γ, through a simple relation, Γ=γ(1+P/ρ). The maximum value of surface redshift comes out to be 0.614 when σ=(P/ρ)0=0.6. The structure are bound for σ≤0.83 and the maximum value of the binding coefficient is 0.181 at σ=0.4. For bound structures the central redshift z0≤8.24. The maximum mass of neutron star based upon such a model comes out to be 2.39M ⊙ (for σ=0.4) and the maximum size comes out to be 13.7 km (for σ=0.2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648731
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  • 3
    Electronic Resource
    Electronic Resource
    Physically realizable relativistic stellar structures (1984)
    Springer
    Astrophysics and space science 102 (1984), S. 49-66 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Relativistic stellar structures can be obtained both analytically and by computation, but all these models do not stand the tests of physical reality. It is shown that for a physically reasonable solution dρ/dr ∝-r and d(e v /dr ∝r near the centre, d(P/ρ)/dr〈-0 and (dP/dρ)〉-(P/ρ). If we change the variabler tox=Cr 2, whereC is a constant, the field equations are reduced to a form which is easier to solve. A new set of exact solutions is obtained by consideringe v ∝(1-x) n . Also, a method has been given to obtain generalized solution. It is shown that the solution discussed by Durgapal and Rawat (1980) is the only exact solution which in its most generalized form for a given density distribution stands all the tests of physical reality and for which both (P/ρ) and (dP/dρ) decrase with increasing value ofr. Neutron star model is proposed by assuming ρ〉-2×1014g cm−3. Two specific cases are considered, viz.,P〈-1/3ρ and dP/dρ〈-1, respectively. The structures are found to be bound and stable under radial perturbations. The models have been studied for slow rotation and the mass of the Crab pulsar has been estimated for different mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00651061
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  • 4
    Electronic Resource
    Electronic Resource
    Massive configurations with constant densities (1982)
    Springer
    Astrophysics and space science 88 (1982), S. 469-475 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two new classes of solutions with constant observed proper and rest mass densities are described. Unlike the well-known solution of constant coordinate mass density, these solutions pertain to realistic physical situations. For these solutions, the various relevant parameters, viz. the redshifts (dP/dρ)0 and binding coefficients have been calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01092712
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  • 5
    Electronic Resource
    Electronic Resource
    Polytropic spheres with isothermal cores (1983)
    Springer
    Astrophysics and space science 90 (1983), S. 139-145 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The paper deals with massive fluid spheres with an isothermal core (having finite central density) and a polytropic envelope in terms of the General Relativity. The matching of the solutions in the core and envelope has been done using Bondi's condition,H=0 and also without it. The study reveals that since this condition does not correspond to any particular physical situation the maximum values of fractional core size, fractional core mass and the redshift do not occur atH=0, but that they occur at some other point. Within the permissible physical conditions (dP/dρ≤1) the maximum values ofM core/M,R core/R and the surface redshift, for an isothermal coreP=ρ/3, are respectively 0.473, 0.554, and 0.565. Using the conditionH=0, it has been shown that for isothermal cores corresponding to the equation of the stateP≥0.6ρ, the configurations are pulsationally unstable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00651554
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  • 6
    Electronic Resource
    Electronic Resource
    Studies into Glomerella phyllanthh pai affecting phyllanthus acidus II genetical behaviour (1974)
    Springer
    Mycopathologia 52 (1974), S. 319-324 
    Details
    ISSN: 1573-0832
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Sex compatibility of the three sector isolates ofGlomerella phyllanthii was studied. The two isolates (P1 and P2) are distinct from the parent isolate (P) in their sex reactions. Perithecial line developed in crosses P×P1 and P×P2 (H1 and H2 respectively). These lines represent the hybrid lines. All the three sector isolates are homothallic and self fertile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02198761
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  • 7
    Electronic Resource
    Electronic Resource
    Possible detection of a ring system in Saturn's magnetosphere (1984)
    [s.l.] : Nature Publishing Group
    Nature 312 (1984), S. 621-622 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Figure 1 shows the path of the star relative to the planet. The outermost ellipse is the projection on the sky plane of a circular ring at 14 radii. The next ellipse inwards represents the projection of the observed ring. The visible inner rings are also shown for comparison. Fig. 1 Path of the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/312621a0
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  • 8
    Electronic Resource
    Electronic Resource
    Gravitational collapse of a massive sphere of constant energy density (1988)
    Springer
    Astrophysics and space science 143 (1988), S. 187-191 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Gravitational collapse of a massive sphere of constant density has been studied from the point of view of a Keplerian observer. The asymptotic nature of collapse is attributed to the development of negative gravitational pressure acting radially outwards within the structure. The region of negative pressure asymptotically covers the entire interior asu=mass/radius tends to half.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00636766
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  • 9
    Electronic Resource
    Electronic Resource
    A study of massive classical polytropes in general relativity (1989)
    Springer
    Astrophysics and space science 159 (1989), S. 203-218 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A detailed study of classical polytropes in general relativity has been presented for χO (≡(dP/dE)O)≤ 1.0 and σO(≡(P/E O)≤χO. The behaviour of various structural parameters with ≡σO/χO, σO and χO are the values ofP/E and dP/dE at the centre) has been studied. The most important result of this study is the fact the qualitative behaviour of all the structural parameters depends only on the value of µO for the various assigned χO values. The maximum value of surface red shift occurs when µO=0.6 and for χO=1.0 it equals 0.618. These structures are gravitationally bound for µO≤0.8 and most so for µO=0.4. The maximum value of binding coefficient comes out to be 0.181 when χO=1.0. These structures have been used to model neutron stars. The maximum mass of neutron star based upon such a model comes out to be 2.55M ⊙ (for µO=0.4 and χO=1.0) and maximum size comes out to be 15.0 km (for µO=0.2 and χO=1.0). It is also seen that the structures are pulsationally stable for µ≤0.6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00650083
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  • 10
    Electronic Resource
    Electronic Resource
    A two-density neutron star model with continuity of density (1990)
    Springer
    Astrophysics and space science 167 (1990), S. 41-53 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Tolman's V solution has found wide application to the redshift problems in astrophysics but it has a drawback that there is singularity at the centre. We have developed a two-density model with a parabolic density distribution in the core ande ν ∝r 2n in the envelope. The most distinctive feature of the model is that there is a continuity of all four variables (E, P, λ, and ν) at the boundary. In other analytic core-envelope models the continuity of only three varaibles is possible. This two-density structure has been used to model neutron stars and their mass, size, and red shifts have been obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642061
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