23 research outputs found
Connection between horizons and algebraic type
We study connections between both event and quasilocal horizons and the
algebraic type of the Weyl tensor. The relation regarding spacelike future
outer trapping horizon is analysed in four dimensions using double-null
foliation.Comment: 4 pages, to appear in Proceedings of Spanish relativity meeting 201
Effectiveness of CFD simulation for the performance prediction of phase change building boards in the thermal environment control of indoor spaces
This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2013 ElsevierThis paper reports on a validation study of CFD models used to predict the effect of PCM clay boards on the control of indoor environments, in ventilated and non-ventilated situations. Unlike multi-zonal models, CFD is important in situations where localised properties are essential such as in buildings with complex and large geometries. The employed phase change model considers temperature/enthalpy hysteresis and varying enthalpy-temperature characteristics to more accurately simulate the phase change behaviour of the PCM boards compared to the standard default modelling approach in the commercial CFD codes. Successful validation was obtained with a mean error of 1.0 K relative to experimental data, and the results show that in addition to providing satisfactory quantitative results, CFD also provides qualitative results which are useful in the effective design of indoor thermal environment control systems utilising PCM. These results include: i) temperature and air flow distribution within the space resulting from the use of PCM boards and different night ventilation rates; ii) the fraction of PCM experiencing phase change and is effective in the control of the indoor thermal environment, enabling optimisation of the location of the boards; and iii) the energy impact of PCM boards and adequate ventilation configurations for effective night charging.This work was funded through sponsorship from the UK Engineering and Physical Sciences Research Council (EPSRC), Grant No: EP/H004181/1
Hawking Radiation as Tunneling for Extremal and Rotating Black Holes
The issue concerning semi-classical methods recently developed in deriving
the conditions for Hawking radiation as tunneling, is revisited and applied
also to rotating black hole solutions as well as to the extremal cases. It is
noticed how the tunneling method fixes the temperature of extremal black hole
to be zero, unlike the Euclidean regularity method that allows an arbitrary
compactification period. A comparison with other approaches is presented.Comment: 17 pages, Latex document, typos corrected, four more references,
improved discussion in section
Interacting entropy-corrected holographic dark energy with apparent horizon as an infrared cutoff
In this work we consider the entropy-corrected version of interacting
holographic dark energy (HDE), in the non-flat universe enclosed by apparent
horizon. Two corrections of entropy so-called logarithmic 'LEC' and power-law
'PLEC' in HDE model with apparent horizon as an IR-cutoff are studied. The
ratio of dark matter to dark energy densities , equation of state parameter
and deceleration parameter are obtained. We show that the cosmic
coincidence is satisfied for both interacting models. By studying the effect of
interaction in EoS parameter, we see that the phantom divide may be crossed and
also find that the interacting models can drive an acceleration expansion at
the present and future, while in non-interacting case, this expansion can
happen only at the early time. The graphs of deceleration parameter for
interacting models, show that the present acceleration expansion is preceded by
a sufficiently long period deceleration at past. Moreover, the thermodynamical
interpretation of interaction between LECHDE and dark matter is described. We
obtain a relation between the interaction term of dark components and thermal
fluctuation in a non-flat universe, bounded by the apparent horizon. In
limiting case, for ordinary HDE, the relation of interaction term versus
thermal fluctuation is also calculated.Comment: 20 pages, 8 figures, figures changed, some Ref. is added, changed
some sentences, accepted by General relativity and gravitation (GERG
Corrections to Hawking-like Radiation for a Friedmann-Robertson-Walker Universe
Recently, a Hamilton-Jacobi method beyond semiclassical approximation in
black hole physics was developed by \emph{Banerjee} and
\emph{Majhi}\cite{beyond0}. In this paper, we generalize their analysis of
black holes to the case of Friedmann-Robertson-Walker (FRW) universe. It is
shown that all the higher order quantum corrections in the single particle
action are proportional to the usual semiclassical contribution. The
corrections to the Hawking-like temperature and entropy of apparent horizon for
FRW universe are also obtained. In the corrected entropy, the area law involves
logarithmic area correction together with the standard inverse power of area
term.Comment: 10 pages, no figures, comments are welcome; v2: references added and
some typoes corrected, to appear in Euro.Phys.J.C; v3:a defect corrected. We
thank Dr.Elias Vagenas for pointing out a defect of our pape
Highly Damped Quasinormal Modes of Kerr Black Holes: A Complete Numerical Investigation
We compute for the first time very highly damped quasinormal modes of the
(rotating) Kerr black hole. Our numerical technique is based on a decoupling of
the radial and angular equations, performed using a large-frequency expansion
for the angular separation constant_{s}A_{l m}. This allows us to go much
further in overtone number than ever before. We find that the real part of the
quasinormal frequencies approaches a non-zero constant value which does not
depend on the spin s of the perturbing field and on the angular index l:
\omega_R=m\varpi(a). We numerically compute \varpi(a). Leading-order
corrections to the asymptotic frequency are likely to be of order 1/\omega_I.
The imaginary part grows without bound, the spacing between consecutive modes
being a monotonic function of a.Comment: 5 pages, 3 figure
Unruh--DeWitt detectors in spherically symmetric dynamical space-times
In the present paper, Unruh--DeWitt detectors are used in order to
investigate the issue of temperature associated with a spherically symmetric
dynamical space-times. Firstly, we review the semi-classical tunneling method,
then we introduce the Unruh--DeWitt detector approach. We show that for the
generic static black hole case and the FRW de Sitter case, making use of
peculiar Kodama trajectories, semiclassical and quantum field theoretic
techniques give the same standard and well known thermal interpretation, with
an associated temperature, corrected by appropriate Tolman factors. For a FRW
space-time interpolating de Sitter space with the Einstein--de Sitter universe
(that is a more realistic situation in the frame of CDM cosmologies),
we show that the detector response splits into a de Sitter contribution plus a
fluctuating term containing no trace of Boltzmann-like factors, but rather
describing the way thermal equilibrium is reached in the late time limit. As a
consequence, and unlike the case of black holes, the identification of the
dynamical surface gravity of a cosmological trapping horizon as an effective
temperature parameter seems lost, at least for our co-moving simplified
detectors. The possibility remains that a detector performing a proper motion
along a Kodama trajectory may register something more, in which case the
horizon surface gravity would be associated more likely to vacuum correlations
than to particle creation.Comment: 19 pages, to appear on IJTP. arXiv admin note: substantial text
overlap with arXiv:1101.525
A Comment or two on Holographic Dark Energy
It has, quite recently, become fashionable to study a certain class of
holographic-inspired models for the dark energy. These investigations have,
indeed, managed to make some significant advances towards explaining the
empirical data. Nonetheless, surprisingly little thought has been given to
conceptual issues such as the composition and the very nature of the implicated
energy source. In the current discourse, we attempt to fill this gap by the way
of some speculative yet logically self-consistent arguments. Our construction
takes us along a path that begins with an entanglement entropy and ends up at a
Hubble-sized gas of exotic particles. Moreover, our interpretation of the dark
energy turns out to be suggestive of a natural resolution to the
cosmic-coincidence problem.Comment: 18 pages; (v2) an oversight in Section 2.1 is rectified and a few
citations adde
Generalized Second Law of Thermodynamics in Gravity with Entropy Corrections
We study the generalized second law (GSL) of thermodynamics in
cosmology. We consider the universe as a closed bounded system filled with
component fluids in the thermal equilibrium with the cosmological boundary. We
use two different cosmic horizons: the future event horizon and the apparent
horizon. We show the conditions under which the GSL will be valid in specific
scenarios of the quintessence and the phantom energy dominated eras. Further we
associate two different entropies with the cosmological horizons: with a
logarithmic correction term and a power-law correction term. We also find the
conditions for the GSL to be satisfied or violated by imposing constraints on
model parameters.Comment: 17 pages, no figure, title changed, version accepted for publication
in Astrophysics and Space Scienc
Plasminogen-binding site of the thermostable region of fibrinogen fragment D
AbstractAffinity chromatography of plasminogen and its proteolytic fragments on immobilized fibrinogen TSD fragment has shown that the latter contains a plasminogen-binding site which is complementary to the lysine-binding site(s) of plasminogen molecule 1–3 kringle structures