187 research outputs found
Randall-Sundrum limit of f(R) brane-world models
By setting some special boundary conditions in the variational principle we
obtain junction conditions for the five-dimensional gravity which in the
Einstein limit transform into the standard Randall-Sundrum
junction conditions. We apply these junction conditions to a particular model
of a Friedmann universe on the brane and show explicitly that the limit gives
the standard Randall-Sundrum model Friedmann equation.Comment: 6 pages, no figures, REVTEX4, minor change
The influence of structural short-range order on the phase diagrams of diluted FCC magnet with arbitrary spin and modified RKKY interaction
A diluted FCC magnet with modified long-range RKKY interaction and arbitrary
Ising spin S is considered within two-sublattice model. In the molecular field
approximation the Gibbs free-energy is derived, from which all magnetic
thermodynamic properties can be self-consistently obtained. In particular, the
phase diagrams are studied for different magnetic ion and free-charge
concentration, the atomic short-range-order (Warren-Cowley) parameter being
taken into account.Comment: 12 pages, 6 figures, revtex4 fil
Non-Keynesian Effects of Fiscal Consolidations in Central Europe in the Years 2000-2013
Last two decades were a period of significant discussion concerning determinants of effectiveness of fiscal policy. After some cases of expansionary episodes of fiscal consolidations in eighties of XX century, an intensive international research on the possibility of non-Keynesian effects of fiscal contractions in highly developed countries has started. The aim of the article is to analyze the possibility of obtaining non-Keynesian effects of fiscal consolidations in post-transformation countries of Central Europe. An important aim of macroeconomic policy in the analyzed economies is to benefit the advantages of convergence process. Thus, the empirical analysis is made within conditional β-convergence framework. The verification of hypothesis of β-convergence enables to identify the long term tendency of output per capita, in the same time it enables to identify non-Keynesian effects of fiscal prudence and to assess their role in the process of reducing GDP gap between the analyzed economies. Then the potential transmission channels for non-Keynesian effects of fiscal policy were analyzed. In the research the data from Eurostat and European Commission for the years 2000-2013 was used. The paper provides arguments in favor of the existence of non-Keynesian effects of fiscal consolidations in Central Europe that support the process of conditional convergence
Scalar dark energy models mimicking CDM with arbitrary future evolution
Dark energy models with various scenarios of evolution are considered from
the viewpoint of the formalism for the equation of state. It is shown that
these models are compatible with current astronomical data. Some of the models
presented here evolve arbitrarily close to CDM up to the present, but
diverge in the future into a number of different possible asymptotic states,
including asymptotic de-Sitter (pseudo-rip) evolution, little rips with
disintegration of bound structures, and various forms of finite-time future
singularities. Therefore it is impossible from observational data to determine
whether the universe will end in a future singularity or not. We demonstrate
that the models under consideration are stable for a long period of time
(billions of years) before entering a Little Rip/Pseudo-Rip induced dissolution
of bound structures or before entering a soft finite-time future singularity.
Finally, the physical consequences of Little Rip, Type II, III and Big Crush
singularities are briefly compared.Comment: 15 pages, 1 figure, version to appear in Physics Letters
Is the future universe singular: Dark Matter versus modified gravity?
The fundamental problem of the occurrence/removal of finite-time future
singularity in the universe evolution for coupled dark energy (DE) is
addressed. It is demonstrated the existence of the (instable or local minimum)
de Sitter space solution which may cure the Type II or Type IV future
singularity for DE coupled with DM as the result of tuning the initial
conditions. In case of phantom DE, the corresponding coupling may help to
resolve the coincidence problem but not the Big Rip (Type I) singularity issue.
We show that modified gravity of special form or inhomogeneous DE fluid may
offer the universal scenario to cure the Type I,II,III or IV future singularity
of coupled (fluid or scalar) DE evolution.Comment: LaTeX 9 page
(Photo)physical properties of new molecular glasses end-capped with thiophene rings composed of diimide and imine units
New symmetrical arylene bisimide derivatives formed by using electron-donating-electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N′-bis(5- aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5- thiophenedicarboxaldehyde or 2,2′-bithiophene-5,5′-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (Eg) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and Eg were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm2 were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of Voc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69-0.90%
Reconstruction of the equation of state for the cyclic universes in homogeneous and isotropic cosmology
We study the cosmological evolutions of the equation of state (EoS) for the
universe in the homogeneous and isotropic
Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) space-time. In particular, we
reconstruct the cyclic universes by using the Weierstrass and Jacobian elliptic
functions. It is explicitly illustrated that in several models the universe
always stays in the non-phantom (quintessence) phase, whereas there also exist
models in which the crossing of the phantom divide can be realized in the
reconstructed cyclic universes.Comment: 29 pages, 8 figures, version accepted for publication in Central
European Journal of Physic
Domain wall brane in squared curvature gravity
We suggest a thick braneworld model in the squared curvature gravity theory.
Despite the appearance of higher order derivatives, the localization of gravity
and various bulk matter fields is shown to be possible. The existence of the
normalizable gravitational zero mode indicates that our four-dimensional
gravity is reproduced. In order to localize the chiral fermions on the brane,
two types of coupling between the fermions and the brane forming scalar is
introduced. The first coupling leads us to a Schr\"odinger equation with a
volcano potential, and the other a P\"oschl-Teller potential. In both cases,
the zero mode exists only for the left-hand fermions. Several massive KK states
of the fermions can be trapped on the brane, either as resonant states or as
bound states.Comment: 18 pages, 5 figures and 1 table, references added, improved version
to be published in JHE
Screening of cosmological constant for De Sitter Universe in non-local gravity, phantom-divide crossing and finite-time future singularities
We investigate de Sitter solutions in non-local gravity as well as in
non-local gravity with Lagrange constraint multiplier. We examine a condition
to avoid a ghost and discuss a screening scenario for a cosmological constant
in de Sitter solutions. Furthermore, we explicitly demonstrate that three types
of the finite-time future singularities can occur in non-local gravity and
explore their properties. In addition, we evaluate the effective equation of
state for the universe and show that the late-time accelerating universe may be
effectively the quintessence, cosmological constant or phantom-like phases. In
particular, it is found that there is a case in which a crossing of the phantom
divide from the non-phantom (quintessence) phase to the phantom one can be
realized when a finite-time future singularity occurs. Moreover, it is
demonstrated that the addition of an term can cure the finite-time future
singularities in non-local gravity. It is also suggested that in the framework
of non-local gravity, adding an term leads to possible unification of the
early-time inflation with the late-time cosmic acceleration.Comment: 42 pages, no figure, version accepted for publication in General
Relativity and Gravitatio
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