3,688 research outputs found
Physical aspects of naked singularity explosion - How does a naked singularity explode? --
The behaviors of quantum stress tensor for the scalar field on the classical
background of spherical dust collapse is studied. In the previous works
diverging flux of quantum radiation was predicted. We use the exact expressions
in a 2D model formulated by Barve et al. Our present results show that the back
reaction does not become important during the semiclassical phase. The
appearance of the naked singularity would not be affected by this quantum field
radiation. To predict whether the naked singularity explosion occurs or not we
need the theory of quantum gravity. We depict the generation of the diverging
flux inside the collapsing star. The quantum energy is gathered around the
center positively. This would be converted to the diverging flux along the
Cauchy horizon. The ingoing negative flux crosses the Cauchy horizon. The
intensity of it is divergent only at the central naked singularity. This
diverging negative ingoing flux is balanced with the outgoing positive
diverging flux which propagates along the Cauchy horizon. After the replacement
of the naked singularity to the practical high density region the instantaneous
diverging radiation would change to more milder one with finite duration.Comment: 18 pages, 16 figure
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
MNE R&D internationalization in developing Asia
In line with the recent shift of R&D internationalization towards developing Asia, this Perspective paper reviews, contextualises, and evaluates the evolving patterns of creation, transfer, and assimilation of knowledge in multinational enterprises (MNEs). A typology is proposed consisting of four stylized nodes: West (industrialized mature economies), East One (emerging industrializing economies of developing Asia), East Two (Asian economies at an earlier stage of industrialization), and East Three (Asian economies with limited visible signs of industrialization). Within these nodes, this paper applies an institution-based view to discuss their diverse national innovation environment (with particular attention paid to governments, indigenous firms, and institutional conditions), and the network perspective to propose an intra-regional knowledge hierarchy, reflecting dynamic knowledge links
The structure of non-spacelike geodesics in dust collapse
We study here the behaviour of non-spacelike geodesics in dust collapse
models in order to understand the casual structure of the spacetime. The
geodesic families coming out, when the singularity is naked, corresponding to
different initial data are worked out and analyzed. We also bring out the
similarity of the limiting behaviour for different types of geodesics in the
limit of approach to the singularity.Comment: 23 pages, 6 figures, to appear in PR
Physical interpretation of gauge invariant perturbations of spherically symmetric space-times
By calculating the Newman-Penrose Weyl tensor components of a perturbed
spherically symmetric space-time with respect to invariantly defined classes of
null tetrads, we give a physical interpretation, in terms of gravitational
radiation, of odd parity gauge invariant metric perturbations. We point out how
these gauge invariants may be used in setting boundary and/or initial
conditions in perturbation theory.Comment: 6 pages. To appear in PR
Power, energy, and spectrum of a naked singularity explosion
Naked singularity occurs in the gravitational collapse of an inhomogeneous
dust ball from an initial density profile which is physically reasonable. We
show that explosive radiation is emitted during the formation process of the
naked singularity. The energy flux is proportional to
for a minimally coupled massless scalar field, while is proportional to
for a conformally coupled massless scalar field, where
is the `remained time' until the distant observer could observe
the singularity if the naked singularity was formed. As a consequence, the
radiated energy grows unboundedly for both scalar fields. The amount of the
power and the energy depends on parameters which characterize the initial
density profile but do not depend on the gravitational mass of the cloud. In
particular, there is characteristic frequency of singularity above
which the divergent energy is radiated. The energy flux is dominated by
particles of which the wave length is about at each moment. The
observed total spectrum is nonthermal, i.e., for . If the naked singularity formation could
continue until a considerable fraction of the total energy of the dust cloud is
radiated, the radiated energy would reach about erg. The
calculations are based on the geometrical optics approximation which turns out
to be consistent as a rough order estimate. The analysis does not depend on
whether or not the naked singularity occurs in its exact meaning. This
phenomenon may provide a new candidate for a source of ultra high energy cosmic
rays or a central engine of gamma ray bursts.Comment: 34 pages, 13 postscript figures included, to appear in Phys. Rev. D,
grammatical errors correcte
Boundary Scattering in Ballistic Graphene
We report magnetotransport measurements in ballistic graphene/hexagonal boron
nitride mesoscopic wires where the charge carrier mean free path is comparable
to wire width . Magnetoresistance curves show characteristic peak structures
where the peak field scales with the ratio of cyclotron radius
and wire width as , due to diffusive boundary
scattering. The obtained proportionality constant between and
differs from that of a classical semiconductor 2D electron system where
.Comment: 14 pages, 4 figure
Nakedness and curvature strength of shell-focusing singularity in the spherically symmetric space-time with vanishing radial pressure
It was recently shown that the metric functions which describe a spherically
symmetric space-time with vanishing radial pressure can be explicitly
integrated. We investigate the nakedness and curvature strength of the
shell-focusing singularity in that space-time. If the singularity is naked, the
relation between the circumferential radius and the Misner-Sharp mass is given
by with along the first radial
null geodesic from the singularity. The is closely related to the
curvature strength of the naked singularity. For example, for the outgoing or
ingoing null geodesic, if the strong curvature condition (SCC) by Tipler holds,
then must be equal to 1. We define the ``gravity dominance condition''
(GDC) for a geodesic. If GDC is satisfied for the null geodesic, both SCC and
the limiting focusing condition (LFC) by Kr\'olak hold for and
, not SCC but only LFC holds for , and neither
holds for , for the null geodesic. On the other hand, if GDC is
satisfied for the timelike geodesic , both SCC and LFC are satisfied for
the timelike geodesic, irrespective of the value of . Several examples
are also discussed.Comment: 11 pages, Accepted for Publication in Classical and Quantum Gravity,
References Updated, Grammatical Errors Correcte
Thermodynamics of ideal quantum gas with fractional statistics in D dimensions
We present exact and explicit results for the thermodynamic properties
(isochores, isotherms, isobars, response functions, velocity of sound) of a
quantum gas in dimensions D>=1 and with fractional exclusion statistics 0<=g<=1
connecting bosons (g=0) and fermions (g=1). In D=1 the results are equivalent
to those of the Calogero-Sutherland model. Emphasis is given to the crossover
between boson-like and fermion-like features, caused by aspects of the
statistical interaction that mimic long-range attraction and short-range
repulsion. The full isochoric heat capacity and the leading low-T term of the
isobaric expansivity in D=2 are independent of g. The onset of Bose-Einstein
condensation along the isobar occurs at a nonzero transition temperature in all
dimensions. The T-dependence of the velocity of sound is in simple relation to
isochores and isobars. The effects of soft container walls are accounted for
rigorously for the case of a pure power-law potential.Comment: 15 pages, 31 figure
- …