4,019 research outputs found
Interpretations of the Accelerating Universe
It is generally argued that the present cosmological observations support the
accelerating models of the universe, as driven by the cosmological constant or
`dark energy'. We argue here that an alternative model of the universe is
possible which explains the current observations of the universe. We
demonstrate this with a reinterpretation of the magnitude-redshift relation for
Type Ia supernovae, since this was the test that gave a spurt to the current
trend in favour of the cosmological constant.Comment: 12 pages including 2 figures, minor revision, references added, a
paragraph on the interpretation of the CMB anisotropy in the QSSC added in
conclusion, general results unchanged. To appear in the October 2002 issue of
the "Publications of the Astronmical Society of the Pacific
On the nature of the quasi-stellar objects
Quasi-stellar objects at cosmological distances or local objects - optical properties of quasi- stellar objects and radio emission from star
Is the present expansion of the universe really accelerating?
The current observations are usually explained by an accelerating expansion
of the present universe. However, with the present quality of the supernovae Ia
data, the allowed parameter space is wide enough to accommodate the
decelerating models as well. This is shown by considering a particular example
of the dark energy equation-of-state ,
which is equivalent to modifying the \emph{geometrical curvature} index of
the standard cosmology by shifting it to where is a
constant. The resulting decelerating model is consistent with the recent CMB
observations made by WMAP, as well as, with the high redshift supernovae Ia
data including SN 1997ff at . It is also consistent with the newly
discovered supernovae SN 2002dc at and SN 2002dd at which
have a general tendency to improve the fit.Comment: Replaced with the accepted version to appear in MNRA
Modeling Repulsive Gravity with Creation
There is a growing interest in the cosmologists for theories with negative
energy scalar fields and creation, in order to model a repulsive gravity. The
classical steady state cosmology proposed by Bondi, Gold and Hoyle in 1948, was
the first such theory which used a negative kinetic energy creation field to
invoke creation of matter. We emphasize that creation plays very crucial role
in cosmology and provides a natural explanation to the various explosive
phenomena occurring in local (z<0.1) and extra galactic universe. We exemplify
this point of view by considering the resurrected version of this theory - the
quasi-steady state theory, which tries to relate creation events directly to
the large scale dynamics of the universe and supplies more natural explanations
of the observed phenomena. Although the theory predicts a decelerating universe
at the present era, it explains successfully the recent SNe Ia observations
(which require an accelerating universe in the standard cosmology), as we show
in this paper by performing a Bayesian analysis of the data.Comment: The paper uses an old SNeIa dataset. With the new improved data, for
example the updated gold sample (Riess et al, astro-ph/0611572), the fit
improves considerably (\chi^2/DoF=197/180 and a probability of
goodness-of-fit=18%
Inhomogeneities in the Microwave Background Radiation interpreted within the framework of the Quasi-Steady State Cosmology
We calculate the expected angular power spectrum of the temperature
fluctuations in the microwave background radiation (MBR) generated in the
quasi-steady state cosmology (QSSC). The paper begins with a brief description
of how the background is produced and thermalized in the QSSC. We then discuss
within the framework of a simple model, the likely sources of fluctuations in
the background due to astrophysical and cosmological causes. Power spectrum
peaks at , 180-220 and 600-900 are shown to be related in this
cosmology respectively to curvature effects at the last minimum of the scale
factor, clusters and groups of galaxies. The effect of clusters is shown to be
related to their distribution in space as indicated by a toy model of structure
formation in the QSSC. We derive and parameterize the angular power spectrum
using six parameters related to the sources of temperature fluctuations at
three characteristic scales. We are able to obtain a satisfactory fit to the
observational band power estimates of MBR temperature fluctuation spectrum.
Moreover, the values of `best fit' parameters are consistent with the range of
expected values.Comment: 27 pages, including 5 figures; to appear in Astrophys.
The Cast Structure of High-Speed Steel
The cause and effects of the formation of coarse cellular carbides in high-speed steels are reviewed and attention is drawn to possible methods of investigating the problem and perhaps eliminating it
Cross-Newell equations for hexagons and triangles
The Cross-Newell equations for hexagons and triangles are derived for general
real gradient systems, and are found to be in flux-divergence form. Specific
examples of complex governing equations that give rise to hexagons and
triangles and which have Lyapunov functionals are also considered, and explicit
forms of the Cross-Newell equations are found in these cases. The general
nongradient case is also discussed; in contrast with the gradient case, the
equations are not flux-divergent. In all cases, the phase stability boundaries
and modes of instability for general distorted hexagons and triangles can be
recovered from the Cross-Newell equations.Comment: 24 pages, 1 figur
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