61 research outputs found
Newtonian versus relativistic nonlinear cosmology
Both for the background world model and its linear perturbations Newtonian
cosmology coincides with the zero-pressure limits of relativistic cosmology.
However, such successes in Newtonian cosmology are not purely based on Newton's
gravity, but are rather guided ones by previously known results in Einstein's
theory. The action-at-a-distance nature of Newton's gravity requires further
verification from Einstein's theory for its use in the large-scale nonlinear
regimes. We study the domain of validity of the Newtonian cosmology by
investigating weakly nonlinear regimes in relativistic cosmology assuming a
zero-pressure and irrotational fluid. We show that, first, if we ignore the
coupling with gravitational waves the Newtonian cosmology is exactly valid even
to the second order in perturbation. Second, the pure relativistic correction
terms start appearing from the third order. Third, the correction terms are
independent of the horizon scale and are quite small in the large-scale near
the horizon. These conclusions are based on our special (and proper) choice of
variables and gauge conditions. In a complementary situation where the system
is weakly relativistic but fully nonlinear (thus, far inside the horizon) we
can employ the post-Newtonian approximation. We also show that in the
large-scale structures the post-Newtonian effects are quite small. As a
consequence, now we can rely on the Newtonian gravity in analyzing the
evolution of nonlinear large-scale structures even near the horizon volume.Comment: 8 pages, no figur
Transformation of in-plane in at fixed oxygen content
This paper reveals the origin of variation in the magnitude and temperature
dependence of the normal state resistivity frequently observed in different
YBCO single crystal or thin film samples with the same . We investigated
temperature dependence of resistivity in thin films
with 7- and 6.90, which were subjected to annealing in argon at
400-420 K (). Before annealing these films exhibited a non-linear
, with a flattening below 230 K, similar to and
observed in untwinned and twinned YBCO crystals, respectively.
For all films the annealing causes an increase of resistivity and a
transformation of from a non-linear dependence towards a more
linear one (less flattening). In films with 7- the increase of
resistivity is also associated with an increase in . We proposed the
model that provides an explanation of these phenomena in terms of thermally
activated redistribution of residual O(5) oxygens in the chain-layer of YBCO.
Good agreement between the experimental data for , where t is
the annealing time, and numerical calculations was obtained.Comment: 8 pages, 9 figures, submitted to PR
Dark Energy from structure: a status report
The effective evolution of an inhomogeneous universe model in any theory of
gravitation may be described in terms of spatially averaged variables. In
Einstein's theory, restricting attention to scalar variables, this evolution
can be modeled by solutions of a set of Friedmann equations for an effective
volume scale factor, with matter and backreaction source terms. The latter can
be represented by an effective scalar field (`morphon field') modeling Dark
Energy.
The present work provides an overview over the Dark Energy debate in
connection with the impact of inhomogeneities, and formulates strategies for a
comprehensive quantitative evaluation of backreaction effects both in
theoretical and observational cosmology. We recall the basic steps of a
description of backreaction effects in relativistic cosmology that lead to
refurnishing the standard cosmological equations, but also lay down a number of
challenges and unresolved issues in connection with their observational
interpretation.
The present status of this subject is intermediate: we have a good
qualitative understanding of backreaction effects pointing to a global
instability of the standard model of cosmology; exact solutions and
perturbative results modeling this instability lie in the right sector to
explain Dark Energy from inhomogeneities. It is fair to say that, even if
backreaction effects turn out to be less important than anticipated by some
researchers, the concordance high-precision cosmology, the architecture of
current N-body simulations, as well as standard perturbative approaches may all
fall short in correctly describing the Late Universe.Comment: Invited Review for a special Gen. Rel. Grav. issue on Dark Energy, 59
pages, 2 figures; matches published versio
Spinor model of a perfect fluid and their applications in Bianchi type-I and FRW models
Different characteristic of matter influencing the evolution of the Universe
has been simulated by means of a nonlinear spinor field. Exploiting the spinor
description of perfect fluid and dark energy evolution of the Universe given by
an anisotropic Bianchi type-I (BI) or isotropic Friedmann-Robertson-Walker
(FRW) one has been studied.Comment: 10 pages, 8 Figure
Conformal and Affine Hamiltonian Dynamics of General Relativity
The Hamiltonian approach to the General Relativity is formulated as a joint
nonlinear realization of conformal and affine symmetries by means of the Dirac
scalar dilaton and the Maurer-Cartan forms. The dominance of the Casimir vacuum
energy of physical fields provides a good description of the type Ia supernova
luminosity distance--redshift relation. Introducing the uncertainty principle
at the Planck's epoch within our model, we obtain the hierarchy of the Universe
energy scales, which is supported by the observational data. We found that the
invariance of the Maurer-Cartan forms with respect to the general coordinate
transformation yields a single-component strong gravitational waves. The
Hamiltonian dynamics of the model describes the effect of an intensive vacuum
creation of gravitons and the minimal coupling scalar (Higgs) bosons in the
Early Universe.Comment: 37 pages, version submitted to Gen. Rel. Gra
Phylogeny of rock-inhabiting fungi related to Dothideomycetes
The class Dothideomycetes (along with Eurotiomycetes)
includes numerous rock-inhabiting fungi (RIF), a group of ascomycetes that
tolerates surprisingly well harsh conditions prevailing on rock surfaces.
Despite their convergent morphology and physiology, RIF are phylogenetically
highly diverse in Dothideomycetes. However, the positions of main
groups of RIF in this class remain unclear due to the lack of a strong
phylogenetic framework. Moreover, connections between rock-dwelling habit and
other lifestyles found in Dothideomycetes such as plant pathogens,
saprobes and lichen-forming fungi are still unexplored. Based on multigene
phylogenetic analyses, we report that RIF belong to Capnodiales
(particularly to the family Teratosphaeriaceae s.l.),
Dothideales, Pleosporales, and Myriangiales, as
well as some uncharacterised groups with affinities to
Dothideomycetes. Moreover, one lineage consisting exclusively of RIF
proved to be closely related to Arthoniomycetes, the sister class of
Dothideomycetes. The broad phylogenetic amplitude of RIF in
Dothideomycetes suggests that total species richness in this class
remains underestimated. Composition of some RIF-rich lineages suggests that
rock surfaces are reservoirs for plant-associated fungi or saprobes, although
other data also agree with rocks as a primary substrate for ancient fungal
lineages. According to the current sampling, long distance dispersal seems to
be common for RIF. Dothideomycetes lineages comprising lichens also
include RIF, suggesting a possible link between rock-dwelling habit and
lichenisation
The model of a flat (Euclidean) expansive homogeneous and isotropic relativistic universe in the light of the general relativity, quantum mechanics, and observations
Physics of the Cosmic Microwave Background Radiation
The cosmic microwave background (CMB) radiation provides a remarkable window onto the early universe, revealing its composition and structure. In these lectures we review and discuss the physics underlying the main features of the CMB
Approaches to Identifying the Periphery and Peripheralization in the Space of Modern Russia
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