281 research outputs found
Accelerating dark energy models in bianchi Type-V space-time
Some new exact solutions of Einstein's field equations in a spatially
homogeneous and anisotropic Bianchi type-V space-time with minimally
interaction of perfect fluid and dark energy components have been obtained. To
prevail the deterministic solution we choose the scale factor , which yields a time dependent deceleration parameter (DP),
representing a model which generates a transition of the universe from the
early decelerating phase to the recent accelerating phase. We find that for , the quintessence model is reproducible with present and expected
future evolution of the universe. The other models (for ), we observe
the phantom scenario. The quintessence as well as phantom models approach to
isotropy at late time. For different values of , we can generate a class of
physically viable DE models. The cosmic jerk parameter in our descended model
is also found to be in good concordance with the recent data of astrophysical
observations under appropriate condition. The physical and geometric properties
of spatially homogeneous and anisotropic cosmological models are discussed.Comment: 12 pages, 6 figure
A bibliometric investigation of service failure literature and a research agenda
Purpose - This research studies the citations made in service failure literature, and assesses the knowledge construction of this region of exploration to date.
Design/methodology/approach - The bibliometric investigation assesses 416 service failure articles in business associated research. Multidimensional scaling (MDS) is employed to uncover the scope of the scholarly impacts that have helped understand the nature of the service failure literature. The establishment of knowledge in the service failure literature is revealed by analysing co-citation data to identify significant topical impacts.
Findings - The theoretical model combines five areas with significant propositions for the future improvement of service failure as an area of investigation. The most important research themes in-service failure literature are service failure, service failure communication, the recovery process, recovery offer and intention.
Research limitations/implications - Potential research concentrating on the service failure literature could use search terms improved from the literature review, or use a comparable approach whereby a board of well-informed scholars approved the keywords used.
Practical implications - This paper is beneficial for any reader who is interested in understanding the components of the perception of justice and recovery and how it improves repurchase intention.
Originality/value - The study seeks to influence resource and recovery-based concepts and utilises the five supporting knowledge groups to suggest a plan for future research that fills existing gaps and offers the possibility of expanding and enhancing the service failure literature
Bianchi type II models in the presence of perfect fluid and anisotropic dark energy
Spatially homogeneous but totally anisotropic and non-flat Bianchi type II
cosmological model has been studied in general relativity in the presence of
two minimally interacting fluids; a perfect fluid as the matter fluid and a
hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field
equations have been solved by applying two kinematical ans\"{a}tze: we have
assumed the variation law for the mean Hubble parameter that yields a constant
value of deceleration parameter, and one of the components of the shear tensor
has been considered proportional to the mean Hubble parameter. We have
particularly dwelled on the accelerating models with non-divergent expansion
anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we
consider in the context of dark energy, can produce results that can be
produced in the presence of isotropic fluid in accordance with the \Lambda CDM
cosmology. However, the derived model gives additional opportunities by being
able to allow kinematics that cannot be produced in the presence of fluids that
yield only isotropic pressure. We have obtained well behaving cases where the
anisotropy of the expansion and the anisotropy of the fluid converge to finite
values (include zero) in the late Universe. We have also showed that although
the metric we consider is totally anisotropic, the anisotropy of the dark
energy is constrained to be axially symmetric, as long as the overall energy
momentum tensor possesses zero shear stress.Comment: 15 pages; 5 figures; matches the version published in The European
Physical Journal Plu
Minimalistic mycoplasmas harbor different functional toxin-antitoxin systems
Mycoplasmas are minute bacteria controlled by very small genomes ranging from 0.6 to 1.4 Mbp. They encompass several important medical and veterinary pathogens that are often associated with a wide range of chronic diseases. The long persistence of mycoplasma cells in their hosts can exacerbate the spread of antimicrobial resistance observed for many species. However, the nature of the virulence factors driving this phenomenon in mycoplasmas is still unclear. Toxin-antitoxin systems (TA systems) are genetic elements widespread in many bacteria that were historically associated with bacterial persistence. Their presence on mycoplasma genomes has never been carefully assessed, especially for pathogenic species. Here we investigated three candidate TA systems in M. mycoides subsp. capri encoding a (i) novel AAA-ATPase/subtilisin-like serine protease module, (ii) a putative AbiEii/AbiEi pair and (iii) a putative Fic/RelB pair. We sequence analyzed fourteen genomes of M. mycoides subsp. capri and confirmed the presence of at least one TA module in each of them. Interestingly, horizontal gene transfer signatures were also found in several genomic loci containing TA systems for several mycoplasma species. Transcriptomic and proteomic data confirmed differential expression profiles of these TA systems during mycoplasma growth in vitro. While the use of heterologous expression systems based on E. coli and B. subtilis showed clear limitations, the functionality and neutralization capacities of all three candidate TA systems were successfully confirmed using M. capricolum subsp. capricolum as a host. Additionally, M. capricolum subsp. capricolum was used to confirm the presence of functional TA system homologs in mycoplasmas of the Hominis and Pneumoniae phylogenetic groups. Finally, we showed that several of these M. mycoides subsp. capri toxins tested in this study, and particularly the subtilisin-like serine protease, could be used to establish a kill switch in mycoplasmas for industrial applications
Non-vacuum Solutions of Bianchi Type VI_0 Universe in f(R) Gravity
In this paper, we solve the field equations in metric f(R) gravity for
Bianchi type VI_0 spacetime and discuss evolution of the expanding universe. We
find two types of non-vacuum solutions by taking isotropic and anisotropic
fluids as the source of matter and dark energy. The physical behavior of these
solutions is analyzed and compared in the future evolution with the help of
some physical and geometrical parameters. It is concluded that in the presence
of isotropic fluid, the model has singularity at and represents
continuously expanding shearing universe currently entering into phantom phase.
In anisotropic fluid, the model has no initial singularity and exhibits the
uniform accelerating expansion. However, the spacetime does not achieve
isotropy as in both of these solutions.Comment: 20 pages, 5 figures, accepted for publication in Astrophys. Space Sc
Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter
The Bianchi type III dark energy models with constant deceleration parameter
are investigated. The equation of state parameter is found to be time
dependent and its existing range for this model is consistent with the recent
observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy
clustering statistics. The physical aspect of the dark energy models are
discussed.Comment: 12 pages, 2 figures, Accepted version of IJT
Reconstruction of , and models inspired by variable deceleration parameter
We study an special law for the deceleration parameter, recently proposed by
Akarsu and Dereli, in the context of , and
theories of modified gravity. This law covers the law of Berman for obtaining
exact cosmological models to account for the current acceleration of the
universe, and also gives the opportunity to generalize many of the dark energy
models having better consistency with the cosmological observations. Our aim is
to reconstruct the , and models inspired by this
law of variable deceleration parameter. Such models may then exhibit better
consistency with the cosmological observations.Comment: 18 pages, Published online in Astrophys. Space. Sc
Cosmology of a Scalar Field Coupled to Matter and an Isotropy-Violating Maxwell Field
Motivated by the couplings of the dilaton in four-dimensional effective
actions, we investigate the cosmological consequences of a scalar field coupled
both to matter and a Maxwell-type vector field. The vector field has a
background isotropy-violating component. New anisotropic scaling solutions
which can be responsible for the matter and dark energy dominated epochs are
identified and explored. For a large parameter region the universe expands
almost isotropically. Using that the CMB quadrupole is extremely sensitive to
shear, we constrain the ratio of the matter coupling to the vector coupling to
be less than 10^(-5). Moreover, we identify a large parameter region,
corresponding to a strong vector coupling regime, yielding exciting and viable
cosmologies close to the LCDM limit.Comment: Refs. added, some clarifications. Published in JHEP10(2012)06
Observational constraints on conformal time symmetry, missing matter and double dark energy
The current concordance model of cosmology is dominated by two mysterious
ingredients: dark matter and dark energy. In this paper, we explore the
possibility that, in fact, there exist two dark-energy components: the
cosmological constant , with equation-of-state parameter
, and a `missing matter' component with , which we
introduce here to allow the evolution of the universal scale factor as a
function of conformal time to exhibit a symmetry that relates the big bang to
the future conformal singularity, such as in Penrose's conformal cyclic
cosmology. Using recent cosmological observations, we constrain the present-day
energy density of missing matter to be . This is
consistent with the standard CDM model, but constraints on the energy
densities of all the components are considerably broadened by the introduction
of missing matter; significant relative probability exists even for
, and so the presence of a missing matter component
cannot be ruled out. As a result, a Bayesian model selection analysis only
slightly disfavours its introduction by 1.1 log-units of evidence. Foregoing
our symmetry requirement on the conformal time evolution of the universe, we
extend our analysis by allowing to be a free parameter. For this more
generic `double dark energy' model, we find and
, which is again consistent with the standard
CDM model, although once more the posterior distributions are
sufficiently broad that the existence of a second dark-energy component cannot
be ruled out. The model including the second dark energy component also has an
equivalent Bayesian evidence to CDM, within the estimation error, and
is indistinguishable according to the Jeffreys guideline.Comment: Revised version emphasising a different version of the underlying
symmetry, as published in JCA
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