22,491 research outputs found
Charge migration mechanisms in the DNA at finite temperature revisited; from quasi-ballistic to subdiffusive transport
Various charge migration mechanisms in the DNA are studied within the
framework of the Peyrard-Bishop-Holstein model which has been widely used to
address charge dynamics in this macromolecule. To analyze these mechanisms we
consider characteristic size and time scales of the fluctuations of the
electronic and vibrational subsystems. It is shown, in particular, that due to
substantial differences in these timescales polaron formation is unlikely
within a broad range of temperatures. We demonstrate that at low temperatures
electronic transport can be quasi-ballistic. For high temperatures, we propose
an alternative to polaronic charge migration mechanism: the
fluctuation-assisted one, in which the electron dynamics is governed by
relatively slow fluctuations of the vibrational subsystem. We argue also that
the discussed methods and mechanisms can be relevant for other organic
macromolecular systems, such as conjugated polymers and molecular aggregates
Influence of Small-Scale Inhomogeneities on the Cosmological Consistency Tests
The current cosmological dark sector (dark matter plus dark energy) is
challenging our comprehension about the physical processes taking place in the
Universe. Recently, some authors tried to falsify the basic underlying
assumptions of such dark matter-dark energy paradigm. In this Letter, we show
that oversimplifications of the measurement process may produce false positives
to any consistency test based on the globally homogeneous and isotropic LCDM
model and its expansion history based on distance measurements. In particular,
when local inhomogeneity effects due to clumped matter or voids are taken into
account, an apparent violation of the basic assumptions ("Copernican
Principle") seems to be present. Conversely, the amplitude of the deviations
also probes the degree of reliability underlying the phenomenological
Dyer-Roeder procedure by confronting its predictions with the accuracy of the
weak lensing approach. Finally, a new method is devised to reconstruct the
effects of the inhomogeneities in a LCDM model, and some suggestions of how to
distinguish between clumpiness (or void) effects from different cosmologies are
discussed.Comment: 18 pages, 2 figures. Improved version accepted for publication as a
Letter in MNRA
Kinematic Constraints to the Transition Redshift from SNe Ia Union Data
The kinematic approach to cosmological tests provides a direct evidence to
the present accelerating stage of the universe which does not depend on the
validity of general relativity, as well as on the matter-energy content of the
Universe. In this context, we consider here a linear two-parameter expansion
for the decelerating parameter, , where and are
arbitrary constants to be constrained by the Union supernovae data. By assuming
a flat Universe we find that the best fit to the pair of free parameters is
() = ( whereas the transition redshift is () (). This
kinematic result is in agreement with some independent analyzes and
accommodates more easily many dynamical flat models (like CDM).Comment: 10 pages, 4 figures, 1 tabl
Deflationary cosmology: constraints from angular size and ages of globular clusters
Observational constraints to a large class of decaying vacuum cosmologies are
derived using the angular size data of compact radio sources and the latest age
estimates of globular clusters. For this class of deflationary
models, the present value of the vacuum energy density is quantified by a
positive parameter smaller than unity. In the case of milliarcsecond
compact radio-sources, we find that the allowed intervals for and the
matter density parameter are heavily dependent on the value of the
mean projected linear size . For pc, the best
fit occurs for , , and , , respectively. This analysis shows that if
one minimizes for the free parameters , and
, the best fit for these angular size data corresponds to a decaying
with and
pc. Constraints from age estimates of globular clusters and old high redshift
galaxies are not so restrictive, thereby suggesting that there is no age crisis
for this kind of cosmologies.Comment: 6 pages, 3 figures, revised version to appear in Phys. Rev.
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