25,542 research outputs found
Geometric model of black hole quantum -portrait, extradimensions and thermodynamics
Recently a short scale modified black hole metric, known as holographic
metric, has been proposed in order to capture the self-complete character of
gravity. In this paper we show that such a metric can reproduce some geometric
features expected from the quantum -portrait beyond the semi-classical
limit. We show that for a generic this corresponds to having an effective
energy momentum tensor in Einstein equations or, equivalently, non-local terms
in the gravity action. We also consider the higher dimensional extension of the
metric and the case of an AdS cosmological term. We provide a detailed
thermodynamic analysis of both cases, with particular reference to the
repercussions on the Hawking-Page phase transition.Comment: 36 pages, 8 figures, invited paper to the special issue "Entropy in
Quantum Gravity and Quantum Cosmology" edited by R. Garattini for the journal
"Entropy", accepted for publication; v2 version matching that published on
the journa
Rotating Spiral Waves with Phase-Randomized Core in Non-locally Coupled Oscillators
Rotating spiral waves with a central core composed of phase-randomized
oscillators can arise in reaction-diffusion systems if some of the chemical
components involved are diffusion-free. This peculiar phenomenon is
demonstrated for a paradigmatic three-component reaction-diffusion model. The
origin of this anomalous spiral dynamics is the effective non-locality in
coupling, whose effect is stronger for weaker coupling. There exists a critical
coupling strength which is estimated from a simple argument. Detailed
mathematical and numerical analyses are carried out in the extreme case of weak
coupling for which the phase reduction method is applicable. Under the
assumption that the mean field pattern keeps to rotate steadily as a result of
a statistical cancellation of the incoherence, we derive a functional
self-consistency equation to be satisfied by this space-time dependent
quantity. Its solution and the resulting effective frequencies of the
individual oscillators are found to agree excellently with the numerical
simulation.Comment: 10 pages, 6 figure
Energy oscillations and a possible route to chaos in a modified Riga dynamo
Starting from the present version of the Riga dynamo experiment with its
rotating magnetic eigenfield dominated by a single frequency we ask for those
modifications of this set-up that would allow for a non-trivial magnetic field
behaviour in the saturation regime. Assuming an increased ratio of azimuthal to
axial flow velocity, we obtain energy oscillations with a frequency below the
eigenfrequency of the magnetic field. These new oscillations are identified as
magneto-inertial waves that result from a slight imbalance of Lorentz and
inertial forces. Increasing the azimuthal velocity further, or increasing the
total magnetic Reynolds number, we find transitions to a chaotic behaviour of
the dynamo.Comment: 8 pages, 8 figures, submitted to Astronomische Nachrichte
A Study Of A New Class Of Discrete Nonlinear Schroedinger Equations
A new class of 1D discrete nonlinear Schrdinger Hamiltonians
with tunable nonlinerities is introduced, which includes the integrable
Ablowitz-Ladik system as a limit. A new subset of equations, which are derived
from these Hamiltonians using a generalized definition of Poisson brackets, and
collectively refered to as the N-AL equation, is studied. The symmetry
properties of the equation are discussed. These equations are shown to possess
propagating localized solutions, having the continuous translational symmetry
of the one-soliton solution of the Ablowitz-Ladik nonlinear
Schrdinger equation. The N-AL systems are shown to be suitable
to study the combined effect of the dynamical imbalance of nonlinearity and
dispersion and the Peierls-Nabarro potential, arising from the lattice
discreteness, on the propagating solitary wave like profiles. A perturbative
analysis shows that the N-AL systems can have discrete breather solutions, due
to the presence of saddle center bifurcations in phase portraits. The
unstaggered localized states are shown to have positive effective mass. On the
other hand, large width but small amplitude staggered localized states have
negative effective mass. The collison dynamics of two colliding solitary wave
profiles are studied numerically. Notwithstanding colliding solitary wave
profiles are seen to exhibit nontrivial nonsolitonic interactions, certain
universal features are observed in the collison dynamics. Future scopes of this
work and possible applications of the N-AL systems are discussed.Comment: 17 pages, 15 figures, revtex4, xmgr, gn
Incorporating characteristics of human creativity into an evolutionary art algorithm
A perceived limitation of evolutionary art and design algorithms is that they rely on human intervention; the artist selects the most aesthetically pleasing variants of one generation to produce the next. This paper discusses how computer generated art and design can become more creatively human-like with respect to both process and outcome. As an example of a step in this direction, we present an algorithm that overcomes the above limitation by employing an automatic fitness function. The goal is to evolve abstract portraits of Darwin, using our 2nd generation fitness function which rewards genomes that not just produce a likeness of Darwin but exhibit certain strategies characteristic of human artists. We note that in human creativity, change is less choosing amongst randomly generated variants and more capitalizing on the associative structure of a conceptual network to hone in on a vision. We discuss how to achieve this fluidity algorithmically
On Spin Dependence of Relativistic Acoustic Geometry
This work makes the first ever attempt to understand the influence of the
black hole background space-time in determining the fundamental properties of
the embedded relativistic acoustic geometry. To accomplish such task, the role
of the spin angular momentum of the astrophysical black hole (the Kerr
parameter -- a representative feature of the background black hole metric)
in estimating the value of the acoustic surface gravity (the representative
feature of the corresponding analogue space time) has been investigated for
axially symmetric inflow of hydrodynamic fluid onto a rotating black hole.
Since almost all astrophysical black holes are supposed to posses some degree
of intrinsic rotation, the influence of the Kerr parameter on classical
analogue models is very important to understand.
For certain values of the initial boundary conditions describing the
aforementioned flow, more than one acoustic horizons, namely two black hole
type and one white hole type, may form, where the surface gravity may become
formally infinite at the acoustic white hole. The connection between the
corresponding analogue Hawking temperature with astrophysically relevant
observables associated with the spectral signature has been discussed.Comment: 22 pages, 11 figures, Comments welcom
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