158 research outputs found
Effect of the cosmological constant on the bending of light and the cosmological lens equation
We revisit the effect of cosmological constant on the light
deflection and its role in the cosmological lens equation. First, we re-examine
the motion of photon in the Schwarzschild spacetime, and explicitly describe
the trajectory of photon and deflection angle up to the second-order
in . Then the discussion is extended to the contribution of the cosmological
constant in the Schwarzschild-de Sitter or Kottler spacetime.
Contrary to the previous arguments, we emphasize the following points: (a) the
cosmological constant does appear in the orbital equation of light,
(b) nevertheless the bending angle of light does not change its form
even if since the contribution of is thoroughly
absorbed into the definition of the impact parameter, and (c) the effect of
is completely involved in the angular diameter distance .Comment: Revised version accepted for publication in Physical Review D. 5
pages including 3 figures and 4 references are adde
Effect of Gravity on the Macro-Segregation of Larger Steel Ingots
Upon the problem involved in the study of solidification and segregation of larger steel ingots numerous papers have hitherto been published. Nevertheless their nature
is still vague from both the scientific and practical
points of view.
Previous studies have been devoted to the measurement of specific physical values of molten steel, the detailed observation of the sections of solidified ingots, simulat-ion experiments using different materials, experiments on the formation and change of non-metallic inclusions, etc. Isn't there any room for re-examination in these methods of study? Even if these items could be clarified in details, it would not give rise to a satisfactory solut-ion for the phenomenon of ''differential freezing" and to the reduction of segregation and other accompanied defects.
We feel much necessity of thorough studies on the solidi-fication and segregation of large steel ingots, before we rush into the epoch of large scale vacuum casting of steel ingots
Secular increase of the Astronomical Unit: a possible explanation in terms of the total angular momentum conservation law
We give an idea and the order-of-magnitude estimations to explain the
recently reported secular increase of the Astronomical Unit (AU) by Krasinsky
and Brumberg (2004). The idea proposed is analogous to the tidal acceleration
in the Earth-Moon system, which is based on the conservation of the total
angular momentum and we apply this scenario to the Sun-planets system. Assuming
the existence of some tidal interactions that transfer the rotational angular
momentum of the Sun and using reported value of the positive secular trend in
the astronomical unit, , the suggested
change in the period of rotation of the Sun is about in the case
that the orbits of the eight planets have the same "expansion rate." This value
is sufficiently small, and at present it seems there are no observational data
which exclude this possibility. Effects of the change in the Sun's moment of
inertia is also investigated. It is pointed out that the change in the moment
of inertia due to the radiative mass loss by the Sun may be responsible for the
secular increase of AU, if the orbital "expansion" is happening only in the
inner planets system. Although the existence of some tidal interactions is
assumed between the Sun and planets, concrete mechanisms of the angular
momentum transfer are not discussed in this paper, which remain to be done as
future investigations.Comment: 4 pages, accepted for publication in PAS
Application of Time Transfer Function to McVittie Spacetime: Gravitational Time Delay and Secular Increase in Astronomical Unit
We attempt to calculate the gravitational time delay in a time-dependent
gravitational field, especially in McVittie spacetime, which can be considered
as the spacetime around a gravitating body such as the Sun, embedded in the
FLRW (Friedmann-Lema\^itre-Robertson-Walker) cosmological background metric. To
this end, we adopt the time transfer function method proposed by Le
Poncin-Lafitte {\it et al.} (Class. Quant. Grav. 21:4463, 2004) and Teyssandier
and Le Poncin-Lafitte (Class. Quant. Grav. 25:145020, 2008), which is
originally related to Synge's world function and enables to
circumvent the integration of the null geodesic equation. We re-examine the
global cosmological effect on light propagation in the solar system. The
round-trip time of a light ray/signal is given by the functions of not only the
spacial coordinates but also the emission time or reception time of light
ray/signal, which characterize the time-dependency of solutions. We also apply
the obtained results to the secular increase in the astronomical unit, reported
by Krasinsky and Brumberg (Celest. Mech. Dyn. Astron. 90:267, 2004), and we
show that the leading order terms of the time-dependent component due to
cosmological expansion is 9 orders of magnitude smaller than the observed value
of , i.e., ~[m/century]. Therefore, it is not possible
to explain the secular increase in the astronomical unit in terms of
cosmological expansion.Comment: 13 pages, 2 figures, accepted for publication in General Relativity
and Gravitatio
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