521 research outputs found
Interacting Three Fluid System and Thermodynamics of the Universe Bounded by the Event Horizon
The work deals with the thermodynamics of the universe bounded by the event
horizon. The matter in the universe has three constituents namely dark energy,
dark matter and radiation in nature and interaction between then is assumed.
The variation of entropy of the surface of the horizon is obtained from unified
first law while matter entropy variation is calculated from the Gibbss' law.
Finally, validity of the generalized second law of thermodynamics is examined
and conclusions are written point wise.Comment: 7 page
Phosphinecarboxamide based InZnP QDs – an air tolerant route to luminescent III–V semiconductors
We describe a new synthetic methodology for the preparation of high quality, emission tuneable InP-based quantum dots (QDs) using a solid, air- and moisture-tolerant primary phosphine as a group-V precursor. This presents a significantly simpler synthetic pathway compared to the state-of-the-art precursors currently employed in phosphide quantum dot synthesis which are volatile, dangerous and air-sensitive, e.g. P(Si(CH3)3)3
Large-scale magnetic fields from inflation in dilaton electromagnetism
The generation of large-scale magnetic fields is studied in dilaton
electromagnetism in inflationary cosmology, taking into account the dilaton's
evolution throughout inflation and reheating until it is stabilized with
possible entropy production. It is shown that large-scale magnetic fields with
observationally interesting strength at the present time could be generated if
the conformal invariance of the Maxwell theory is broken through the coupling
between the dilaton and electromagnetic fields in such a way that the resultant
quantum fluctuations in the magnetic field has a nearly scale-invariant
spectrum. If this condition is met, the amplitude of the generated magnetic
field could be sufficiently large even in the case huge amount of entropy is
produced with the dilution factor as the dilaton decays.Comment: 28 pages, 5 figures, the version accepted for publication in Phys.
Rev. D; some references are adde
Cosmological Evolution Across Phantom Crossing and the Nature of the Horizon
In standard cosmology, with the evolution of the universe, the matter density
and thermodynamic pressure gradually decreases. Also in course of evolution,
the matter in the universe obeys (or violates) some restrictions or energy
conditions. If the matter distribution obeys strong energy condition (SEC), the
universe is in a decelerating phase while violation of SEC indicates an
accelerated expansion of the universe. In the period of accelerated expansion
the matter may be either of quintessence nature or of phantom nature depending
on the fulfilment of the weak energy condition (WEC) or violation of it. As
recent observational evidences demand that the universe is going through an
accelerated expansion so mater should be either quintessence or phantom in
nature. In the present work we study the evolution of the universe through the
phantom barrier (i.e. the dividing line between the quintessence and phantom
era) and examine how apparent and event horizon change across the barrier.
Finally, we investigate the possibility of occurrence of any singularity in
phantom era.Comment: 7 pages and 4 figure
Validity of Generalized Second Law of Thermodynamics in the Logamediate and Intermediate scenarios of the Universe
In this work, we have investigated the validity of the generalized second law
of thermodynamics in logamediate and intermediate scenarios of the universe
bounded by the Hubble, apparent, particle and event horizons using and without
using first law of thermodynamics. We have observed that the GSL is valid for
Hubble, apparent, particle and event horizons of the universe in the
logamediate scenario of the universe using first law and without using first
law. Similarly the GSL is valid for all horizons in the intermediate scenario
of the universe using first law. Also in the intermediate scenario of the
universe, the GSL is valid for Hubble, apparent and particle horizons but it
breaks down whenever we consider the universe enveloped by the event horizon
Holographic Dark Energy in Braneworld Models with a Gauss-Bonnet Term in the Bulk. Interacting Behavior and the w =-1 Crossing
We apply bulk holographic dark energy in general braneworld models with a
Gauss-Bonnet term in the bulk and an induced gravity term and a perfect fluid
on the brane. Without making any additional assumptions we extract the
Friedmann equation on the physical brane and we show that a
- coupling arises naturally by the full 5D dynamics. The
low-energy (late-time) evolution reveals that the effective 4D holographic dark
energy behaves as ``quintom'', that is it crosses the phantom divide
during the evolution. In particular, the Gauss-Bonnet contribution decreases
the present value of , while it increases the growing rate of
with , in comparison with the case where such a term is
absent.Comment: 16 pages, version published in Phys. Lett.
Large-scale magnetic fields from inflation due to a -even Chern-Simons-like term with Kalb-Ramond and scalar fields
We investigate the generation of large-scale magnetic fields due to the
breaking of the conformal invariance in the electromagnetic field through the
-even dimension-six Chern-Simons-like effective interaction with a fermion
current by taking account of the dynamical Kalb-Ramond and scalar fields in
inflationary cosmology. It is explicitly demonstrated that the magnetic fields
on 1Mpc scale with the field strength of G at the present time
can be induced.Comment: 18 pages, 6 figures, version accepted for publication in Eur. Phys.
J.
The impacts of environmental warming on Odonata: a review
Climate change brings with it unprecedented rates of increase in environmental temperature, which will have major consequences for the earth's flora and fauna. The Odonata represent a taxon that has many strong links to this abiotic factor due to its tropical evolutionary history and adaptations to temperate climates. Temperature is known to affect odonate physiology including life-history traits such as developmental rate, phenology and seasonal regulation as well as immune function and the production of pigment for thermoregulation. A range of behaviours are likely to be affected which will, in turn, influence other parts of the aquatic ecosystem, primarily through trophic interactions. Temperature may influence changes in geographical distributions, through a shifting of species' fundamental niches, changes in the distribution of suitable habitat and variation in the dispersal ability of species. Finally, such a rapid change in the environment results in a strong selective pressure towards adaptation to cope and the inevitable loss of some populations and, potentially, species. Where data are lacking for odonates, studies on other invertebrate groups will be considered. Finally, directions for research are suggested, particularly laboratory studies that investigate underlying causes of climate-driven macroecological patterns
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
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