94 research outputs found
Theoretical Limits on Agegraphic Quintessence from Weak Gravity Conjecture
In this paper, we investigate the possible theoretical constraint on the
parameter of the agegraphic quintessence model by considering the
requirement of the weak gravity conjecture that the variation of the
quintessence scalar field should be less than the Planck mass
. We obtain the theoretical upper bound that is
inconsistent with the current observational constraint result
(95.4% CL). The possible implications of the tension between observational and
theoretical constraint results are discussed.Comment: 14 pages, 3 figure
Reconstructing generalized ghost condensate model with dynamical dark energy parametrizations and observational datasets
Observations of high-redshift supernovae indicate that the universe is
accelerating at the present stage, and we refer to the cause for this cosmic
acceleration as ``dark energy''. In particular, the analysis of current data of
type Ia supernovae (SNIa), cosmic large-scale structure (LSS), and the cosmic
microwave background (CMB) anisotropy implies that, with some possibility, the
equation-of-state parameter of dark energy may cross the cosmological-constant
boundary () during the recent evolution stage. The model of ``quintom''
has been proposed to describe this crossing behavior for dark energy. As
a single-real-scalar-field model of dark energy, the generalized ghost
condensate model provides us with a successful mechanism for realizing the
quintom-like behavior. In this paper, we reconstruct the generalized ghost
condensate model in the light of three forms of parametrization for dynamical
dark energy, with the best-fit results of up-to-date observational data.Comment: 8 pages, 3 figures; references added; accepted for publication in
Mod. Phys. Lett.
Statefinder diagnosis in a non-flat universe and the holographic model of dark energy
In this paper, we study the holographic dark energy model in non-flat
universe from the statefinder viewpoint. We plot the evolutionary trajectories
of the holographic dark energy model for different values of the parameter
as well as for different contributions of spatial curvature, in the statefinder
parameter-planes. The statefinder diagrams characterize the properties of the
holographic dark energy and show the discrimination between this scenario and
other dark energy models. As we show, the contributions of the spatial
curvature in the model can be diagnosed out explicitly by the statefinder
diagrams. Furthermore, we also investigate the holographic dark energy model in
the plane, which can provide us with a useful dynamical diagnosis
complement to the statefinder geometrical diagnosis.Comment: 16 pages, 4 figures; final versio
From carbon nanotubes and silicate layers to graphene platelets for polymer nanocomposites
In spite of extensive studies conducted on carbon nanotubes and silicate layers for their polymer-based nanocomposites, the rise of graphene now provides a more promising candidate due to its exceptionally high mechanical performance and electrical and thermal conductivities. The present study developed a facile approach to fabricate epoxy–graphene nanocomposites by thermally expanding a commercial product followed by ultrasonication and solution-compounding with epoxy, and investigated their morphologies, mechanical properties, electrical conductivity and thermal mechanical behaviour. Graphene platelets (GnPs) of 3.5
Sandage-Loeb test for the new agegraphic and Ricci dark energy models
The Sandage-Loeb (SL) test is a unique method to explore dark energy at the
``redshift desert'' (), an era not covered by any other
dark energy probes, by directly measuring the temporal variation of the
redshift of quasar (QSO) Lyman- absorption lines. In this paper, we
study the prospects for constraining the new agegraphic dark energy (NADE)
model and the Ricci dark energy (RDE) model with the SL test. We show that,
assuming only a ten-year survey, the SL test can constrain these two models
with high significance.Comment: 14 pages, 5 figures; version for publication in Phys.Lett.
Holographic tachyon model
We propose in this Letter a holographic model of tachyon dark energy. A
connection between the tachyon scalar-field and the holographic dark energy is
established, and accordingly, the potential of the holographic tachyon field is
constructed. We show that the holographic evolution of the universe with
can be described completely by the resulting tachyon model in a
certain way.Comment: 5 pages, 2 figures; version to appear in Phys. Lett.
A more general interacting model of holographic dark energy
So far, there have been no theories or observational data that deny the
presence of interaction between dark energy and dark matter. We extend
naturally the holographic dark energy (HDE) model, proposed by Granda and
Oliveros, in which the dark energy density includes not only the square of the
Hubble scale, but also the time derivative of the Hubble scale to the case with
interaction and the analytic forms for the cosmic parameters are obtained under
the specific boundary conditions. The various behaviors concerning the cosmic
expansion depend on the introduced numerical parameters which are also
constrained. The more general interacting model inherits the features of the
previous ones of HDE, keeping the consistency of the theory.Comment: 7 pages, 8 figures, references adde
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Dietary antioxidant vitamin C influences the evolutionary path of insecticide resistance in \u3cem\u3eDrosophila melanogaster\u3c/em\u3e
Herbivorous insects encounter a variety of toxic environmental substances ranging from ingested plant defensive compounds to human-introduced insecticidal agents. Dietary antioxidants are known to reduce the negative physiological impacts of toxins in mammalian systems through amelioration of reactive oxygen-related cellular damage. The analogous impacts to insects caused by multigenerational exposure to pesticides and the effects on adaptive responses within insect populations, however, are currently unknown. To address these research gaps, we used Drosophila as a model system to explore adaptive phenotypic responses to acute dichlorodiphenyltrichloroethane (DDT) exposure in the presence of the dietary antioxidant vitamin C and to examine the structural genomic consequences of this exposure. DDT resistance increased significantly among four replicates exposed to a low concentration of DDT for 10 generations. In contrast, dietary intake of vitamin C significantly reduced DDT resistance after mutigenerational exposure to the same concentration of DDT. As to the genomic consequences, no significant differences were predicted in overall nucleotide substitution rates across the genome between any of the treatments. Despite this, replicates exposed to a low concentration of DDT without vitamin C showed the highest number of synonymous and non-synonymous variants (3196 in total), followed by the DDT plus vitamin C (1174 in total), and vitamin C alone (728 in total) treatments. This study demonstrates the potential role of diet (specifically, antioxidant intake) on adaptive genome responses, and thus on the evolution of pesticide resistance within insect populations
Deciphering Heterogeneity in Pig Genome Assembly Sscrofa9 by Isochore and Isochore-Like Region Analyses
Background: The isochore, a large DNA sequence with relatively small GC variance, is one of the most important structures in eukaryotic genomes. Although the isochore has been widely studied in humans and other species, little is known about its distribution in pigs. Principal Findings: In this paper, we construct a map of long homogeneous genome regions (LHGRs), i.e., isochores and isochore-like regions, in pigs to provide an intuitive version of GC heterogeneity in each chromosome. The LHGR pattern study not only quantifies heterogeneities, but also reveals some primary characteristics of the chromatin organization, including the followings: (1) the majority of LHGRs belong to GC-poor families and are in long length; (2) a high gene density tends to occur with the appearance of GC-rich LHGRs; and (3) the density of LINE repeats decreases with an increase in the GC content of LHGRs. Furthermore, a portion of LHGRs with particular GC ranges (50%–51 % and 54%–55%) tend to have abnormally high gene densities, suggesting that biased gene conversion (BGC), as well as time- and energy-saving principles, could be of importance to the formation of genome organization. Conclusion: This study significantly improves our knowledge of chromatin organization in the pig genome. Correlations between the different biological features (e.g., gene density and repeat density) and GC content of LHGRs provide a uniqu
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