9 research outputs found
A Non-Singular Black Hole
We present a completely integrable deformation of the CGHS dilaton gravity
model in two dimensions. The solution is a singularity free black hole that at
large distances asymptoticaly joins to the CGHS solution.Comment: 11 pages, 1 figure, Latex 2
On the quantum origin of the seeds of cosmic structure
The current understanding of the quantum origin of cosmic structure is
discussed critically. We point out that in the existing treatments a transition
from a symmetric quantum state to an (essentially classical) non-symmetric
state is implicitly assumed, but not specified or analyzed in any detail. In
facing the issue we are led to conclude that new physics is required to explain
the apparent predictive power of the usual schemes. Furthermore we show that
the novel way of looking at the relevant issues opens new windows from where
relevant information might be extracted regarding cosmological issues and
perhaps even clues about aspects of quantum gravity.Comment: replacement with final version to appear in Classical and Quantum
Gravit
On Winding Branes and Cosmological Evolution of Extra Dimensions in String Theory
We consider evolution of compact extra dimensions in cosmology and try to see
whether wrapped branes can prevent the expansion of the internal space. Some
difficulties of Brandenberger and Vafa mechanism for decompactification are
pointed out. In both pure Einstein and dilaton gravities, we study cosmology of
winding brane gases in a continuum approximation. The energy momentum tensor is
obtained by coupling the brane action to the gravity action and we present
several exact solutions for various brane configurations. T-duality invariance
of the solutions are established in dilaton gravity. Our results indicate that
phenomenologically the most viable scenario can be realized when there is only
one brane wrapping over all extra dimensions.Comment: 17 pages, RevTex4, 2 figures, a paragraph added, to appear in
Classical and Quantum Gravit
Volume Stabilization and Acceleration in Brane Gas Cosmology
We investigate toy cosmological models in (1+m+p)-dimensions with gas of
p-branes wrapping over p-compact dimensions. In addition to winding modes, we
consider the effects of momentum modes corresponding to small vibrations of
branes and find that the extra dimensions are dynamically stabilized while the
others expand. Adding matter, the compact volume may grow slowly depending on
the equation of state. We also obtain solutions with winding and momentum modes
where the observed space undergoes accelerated expansion.Comment: 20 pages, 3 figures, v2: comments and references added, to appear in
JCA
A review of the renal system and diurnal variations of renal activity in livestock
Kidneys are the main organs regulating water-electrolyte homeostasis in the body. They are responsible for maintaining the total volume of water and its distribution in particular water spaces, for electrolyte composition of systemic fluids and also for maintaining acid-base balance. These functions are performed by the plasma filtration process in renal glomeruli and the processes of active absorption and secretion in renal tubules, all adjusted to an 'activity-rest' rhythm. These diurnal changes are influenced by a 24-hour cycle of activity of hormones engaged in the regulation of renal activity. Studies on spontaneous rhythms of renal activity have been carried out mainly on humans and laboratory animals, but few studies have been carried out on livestock animals. Moreover, those results cover only some aspects of renal physiology. This review gives an overview of current knowledge concerning renal function and diurnal variations of some renal activity parameters in livestock, providing greater understanding of general chronobiological processes in mammals. Detailed knowledge of these rhythms is useful for clinical, practical and pharmacological purposes, as well as studies on their physical performance