362 research outputs found
Real-time Photorealistic Visualisation of Large-scaleMultiresolution Terrain Models
Height field terrain rendering is an important aspect of GIS, outdoor virtual reality applicationssuch as flight simulation, 3-D games, etc. A polygonal model of very large terrain data requiresa large number of triangles. So, even most high-performance graphics workstations have greatdifficulty to display even moderately sized height fields at interactive frame rates. To bringphotorealism in visualisation, it is required to drape corresponding high-resolution satellite oraerial phototexture over 3-D digital terrain and also to place multiple collections of point-location-based static objects such as buildings, trees, etc and to overlay polyline vector objects suchas roads on top of the terrain surface. It further complicates the requirement of interactive framerates while navigation over the terrain. This paper describes a novel approach for objects andterrain visualisation by combination of two algorithms, one for terrain data and the other forobjects. The terrain rendering is accomplished by an efficient dynamic multiresolution view-dependent level-of-detail mesh simplification algorithm. It is augmented with out-of-corevisualisation of large-height geometry and phototexture terrain data populated with 3-D/2-Dstatic objects as well as vector overlays without extensive memory load. The proposedmethodology provides interactive frame rates on a general-purpose desktop PC with OpenGL-enabled graphics hardware. The software TREND has been successfully tested on different real-world height maps and satellite phototextures of sizes up to 16K*16K coupled with thousandsof static objects and polyline vector overlays
Black hole formation in perfect fluid collapse
We construct here a special class of perfect fluid collapse models which
generalizes the homogeneous dust collapse solution in order to include non-zero
pressures and inhomogeneities into evolution. It is shown that a black hole is
necessarily generated as end product of continued gravitational collapse,
rather than a naked singularity. We examine the nature of the central
singularity forming as a result of endless collapse and it is shown that no
non-spacelike trajectories can escape from the central singularity. Our results
provide some insights into how the dynamical collapse works, and into the
possible formulations of the cosmic censorship hypothesis, which is as yet a
major unsolved problem in black hole physics.Comment: Revtex4, To appear in Physical Review
Appearance of the central singularity in spherical collapse
We analyze here the structure of non-radial nonspacelike geodesics
terminating in the past at a naked singularity formed as the end state of
inhomogeneous dust collapse. The spectrum of outgoing nonspacelike null
geodesics is examined analytically. The local and global visibility of the
singularity is also examined by integrating numerically the null geodesics
equations. The possible implications of existence of such families towards the
appearance of the star in late stages of gravitational collapse are considered.
It is seen that the outgoing non-radial geodesics give an appearance to the
naked central singularity as that of an expanding ball whose radius reaches a
maximum before the star goes within its apparent horizon. The radiated energy
(along the null geodesics) is shown to decay very sharply in the neighbourhood
of the singularity. Thus the total energy escaping via non-radial null
geodesics from the naked central singularity vanishes in the scenario
considered here.Comment: 25 pages, 6 figure
Higher dimensional inhomogeneous dust collapse and cosmic censorship
We investigate the occurrence and nature of a naked singularity in the
gravitational collapse of an inhomogeneous dust cloud described by higher
dimensional Tolman-Bondi space-times. The naked singularities are found to be
gravitationally strong in the sense of Tipler. Higher dimensions seem to favour
black holes rather than naked singularities.Comment: 15 pages, LaTeX, 1 figure, 2 table
Higher dimensional dust collapse with a cosmological constant
The general solution of the Einstein equation for higher dimensional (HD)
spherically symmetric collapse of inhomogeneous dust in presence of a
cosmological term, i.e., exact interior solutions of the Einstein field
equations is presented for the HD Tolman-Bondi metrics imbedded in a de Sitter
background. The solution is then matched to exterior HD Scwarschild-de Sitter.
A brief discussion on the causal structure singularities and horizons is
provided. It turns out that the collapse proceed in the same way as in the
Minkowski background, i.e., the strong curvature naked singularities form and
that the higher dimensions seem to favor black holes rather than naked
singularities.Comment: 7 Pages, no figure
The phase relation between sunspot numbers and soft X-ray flares
To better understand long-term flare activity, we present a statistical study
on soft X-ray flares from May 1976 to May 2008. It is found that the smoothed
monthly peak fluxes of C-class, M-class, and X-class flares have a very
noticeable time lag of 13, 8, and 8 months in cycle 21 respectively with
respect to the smoothed monthly sunspot numbers. There is no time lag between
the sunspot numbers and M-class flares in cycle 22. However, there is a
one-month time lag for C-class flares and a one-month time lead for X-class
flares with regard to sunspot numbers in cycle 22. For cycle 23, the smoothed
monthly peak fluxes of C-class, M-class, and X-class flares have a very
noticeable time lag of one month, 5 months, and 21 months respectively with
respect to sunspot numbers. If we take the three types of flares together, the
smoothed monthly peak fluxes of soft X-ray flares have a time lag of 9 months
in cycle 21, no time lag in cycle 22 and a characteristic time lag of 5 months
in cycle 23 with respect to the smoothed monthly sunspot numbers. Furthermore,
the correlation coefficients of the smoothed monthly peak fluxes of M-class and
X-class flares and the smoothed monthly sunspot numbers are higher in cycle 22
than those in cycles 21 and 23. The correlation coefficients between the three
kinds of soft X-ray flares in cycle 22 are higher than those in cycles 21 and
23. These findings may be instructive in predicting C-class, M-class, and
X-class flares regarding sunspot numbers in the next cycle and the physical
processes of energy storage and dissipation in the corona.Comment: 8 pages, 3 figures, Accepted for publication in Astrophysics & Space
Scienc
Semiclassical Instability of the Cauchy Horizon in Self-Similar Collapse
Generic spherically symmetric self-similar collapse results in strong
naked-singularity formation. In this paper we are concerned with particle
creation during a naked-singularity formation in spherically symmetric
self-similar collapse without specifying the collapsing matter. In the generic
case, the power of particle emission is found to be proportional to the inverse
square of the remaining time to the Cauchy horizon (CH). The constant of
proportion can be arbitrarily large in the limit to marginally naked
singularity. Therefore, the unbounded power is especially striking in the case
that an event horizon is very close to the CH because the emitted energy can be
arbitrarily large in spite of a cutoff expected from quantum gravity. Above
results suggest the instability of the CH in spherically symmetric self-similar
spacetime from quantum field theory and seem to support the existence of a
semiclassical cosmic censor. The divergence of redshifts and blueshifts of
emitted particles is found to cause the divergence of power to positive or
negative infinity, depending on the coupling manner of scalar fields to
gravity. On the other hand, it is found that there is a special class of
self-similar spacetimes in which the semiclassical instability of the CH is not
efficient. The analyses in this paper are based on the geometric optics
approximation, which is justified in two dimensions but needs justification in
four dimensions.Comment: 14 pages, 4 figures, minor errors corrected and some sentences added
in the introduction, accepted for publication in Physical Review
Naked Singularity Explosion
It is known that the gravitational collapse of a dust ball results in naked
singularity formation from an initial density profile which is physically
reasonable. In this paper, we show that explosive radiation is emitted during
the formation process of the naked singularity.Comment: 6 pages, 3 figures, Accepted for Publication in Phys. Rev. D as a
Rapid Communicatio
Formation of a galaxy with a central black hole in the Lemaitre-Tolman model
We construct two models of the formation a galaxy with a central black hole,
starting from a small initial fluctuation at recombination. This is an
application of previously developed methods to find a Lemaitre-Tolman model
that evolves from a given initial density or velocity profile to a given final
density profile. We show that the black hole itself could be either a collapsed
object, or a non-vacuum generalisation of a full Schwarzschild-Kruskal-Szekeres
wormhole. Particular attention is paid to the black hole's apparent and event
horizons.Comment: REVTeX, 22 pages including 11 figures (25 figure files). Replacement
has minor changes in response to the referee, and editorial corrections. To
appear in PR
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