2,355 research outputs found
An Analytic Model with Critical Behavior in Black Hole Formation
A simple analytic model is presented which exhibits a critical behavior in
black hole formation, namely, collapse of a thin shell coupled with outgoing
null fluid. It is seen that the critical behavior is caused by the
gravitational nonlinearity near the event horizon. We calculate the value of
the critical exponent analytically and find that it is very dependent on the
coupling constants of the system.Comment: 21pp., ReVTeX, 7 figures (postscript, compressed and uuencoded),
TIT/HEP-266/COSMO-4
An extreme critical space-time: echoing and black-hole perturbations
A homothetic, static, spherically symmetric solution to the massless
Einstein- Klein-Gordon equations is described. There is a curvature singularity
which is central, null, bifurcate and marginally trapped. The space-time is
therefore extreme in the sense of lying at the threshold between black holes
and naked singularities, just avoiding both. A linear perturbation analysis
reveals two types of dominant mode. One breaks the continuous self-similarity
by periodic terms reminiscent of discrete self-similarity, with echoing period
within a few percent of the value observed numerically in near-critical
gravitational collapse. The other dominant mode explicitly produces a black
hole, white hole, eternally naked singularity or regular dispersal, the latter
indicating that the background is critical. The black hole is not static but
has constant area, the corresponding mass being linear in the perturbation
amplitudes, explicitly determining a unit critical exponent. It is argued that
a central null singularity may be a feature of critical gravitational collapse.Comment: 6 revtex pages, 6 eps figure
Surface gravity in dynamical spherically symmetric spacetimes
A definition of surface gravity at the apparent horizon of dynamical
spherically symmetric spacetimes is proposed. It is based on a unique foliation
by ingoing null hypersurfaces. The function parametrizing the hypersurfaces can
be interpreted as the phase of a light wave uniformly emitted by some far-away
static observer. The definition gives back the accepted value of surface
gravity in the static case by virtue of its nonlocal character. Although the
definition is motivated by the behavior of outgoing null rays, it turns out
that there is a simple connection between the generalized surface gravity, the
acceleration of any radially moving observer, and the observed frequency change
of the infalling light signal. In particular, this gives a practical and simple
method of how any geodesic observer can determine surface gravity by measuring
only the redshift of the infalling light wave. The surface gravity can be
expressed as an integral of matter field quantities along an ingoing null line,
which shows that it is a continuous function along the apparent horizon. A
formula for the area change of the apparent horizon is presented, and the
possibility of thermodynamical interpretation is discussed. Finally, concrete
expressions of surface gravity are given for a number of four-dimensional and
two-dimensional dynamical black hole solutions.Comment: 35 pages, revtex, 3 figures included using eps
Perturbations and Critical Behavior in the Self-Similar Gravitational Collapse of a Massless Scalar Field
This paper studies the perturbations of the continuously self-similar
critical solution of the gravitational collapse of a massless scalar field
(Roberts solution). The perturbation equations are derived and solved exactly.
The perturbation spectrum is found to be not discrete, but occupying continuous
region of the complex plane. The renormalization group calculation gives the
value of the mass-scaling exponent equal to 1.Comment: 12 pages, RevTeX 3.1, 1 figur
Continuous Self-Similarity Breaking in Critical Collapse
This paper studies near-critical evolution of the spherically symmetric
scalar field configurations close to the continuously self-similar solution.
Using analytic perturbative methods, it is shown that a generic growing
perturbation departs from the critical Roberts solution in a universal way. We
argue that in the course of its evolution, initial continuous self-similarity
of the background is broken into discrete self-similarity with echoing period
, reproducing the symmetries of the critical
Choptuik solution.Comment: RevTeX 3.1, 28 pages, 5 figures; discussion rewritten to clarify
several issue
Análise da savana e queimadas no Parque Indígena de Tumucumaque (PA) através de imagens de satélite Landsat.
The Tiriyós Savanna, inserted in the Indian Park of Tumucumaque (PA), and the occurrence of fires were analyzed using satellite images. The savanna common and permanent area in the years of 1986 and 2005 was 4.109,72 km2. The total retraction and expansion areas in the same years were 287,3 km2 and 151,8 km2, respectively. From the burnt area, 38,5% presented only one focus of fire in 9 years (from 1998 August to 2006 October); in 23,6% of the area there was fire each 4 and a half years; 25,3% each 31 months; 10,8% each 18 months and 1,8% each year. The total estimated burnt area was 4.086 km2, at maximum. The fires are considered one of the pressure factors for the advance of the amazon savannas and in the change of the coverage and usage of the earth in the Tiriyós savanna area, but the analysis of the satellite images in the years of 1986 and 2005 showed that there was a retraction of 135,5 km2 in 20 years
Educação ambiental e agroecossistemas sustentáveis em WebGIS.
Este trabalho mostra o uso tecnologias de sensoriamento remoto para disponibilizar informações georreferenciadas pela Internet pelo instrumental WebGIS. Dessa forma, objetiva-se contribuir na disseminação dos dados oriundos de sistemas agrícolas sustentáveis e na educação ambiental agrícola
Analytical treatment of critical collapse in 2+1 dimensional AdS spacetime: a toy model
We present an exact collapsing solution to 2+1 gravity with a negative
cosmological constant minimally coupled to a massless scalar field, which
exhibits physical properties making it a candidate critical solution. We
discuss its global causal structure and its symmetries in relation with those
of the corresponding continously self-similar solution derived in the
case. Linear perturbations on this background lead to approximate
black hole solutions. The critical exponent is found to be .Comment: 22 pages, 6 figures. Major changes in the discussions of Sects. 2 and
5. The value of the critical exponent has been revised to \gamma = 2/
Critical phenomena of collapsing massless scalar wave packets
An analytical model that represents the collapse of a massless scalar wave
packet with continuous self-similarity is constructed, and critical phenomena
are found. In the supercritical case, the mass of black holes is finite and has
the form , with .Comment: Latex file, including 2 figures, avalaible upon reques
Recommended from our members
Recombinant methioninase combined with doxorubicin (DOX) regresses a DOX-resistant synovial sarcoma in a patient-derived orthotopic xenograft (PDOX) mouse model.
Synovial sarcoma (SS) is a recalcitrant subgroup of soft tissue sarcoma (STS). A tumor from a patient with high grade SS from a lower extremity was grown orthotopically in the right biceps femoris muscle of nude mice to establish a patient-derived orthotopic xenograft (PDOX) mouse model. The PDOX mice were randomized into the following groups when tumor volume reached approximately 100 mm3: G1, control without treatment; G2, doxorubicin (DOX) (3 mg/kg, intraperitoneal [i.p.] injection, weekly, for 2 weeks; G3, rMETase (100 unit/mouse, i.p., daily, for 2 weeks); G4 DOX (3mg/kg), i.p. weekly, for 2 weeks) combined with rMETase (100 unit/mouse, i.p., daily, for 2 weeks). On day 14 after treatment initiation, all therapies significantly inhibited tumor growth compared to untreated control, except DOX: (DOX: p = 0.48; rMETase: p < 0.005; DOX combined with rMETase < 0.0001). DOX combined with rMETase was significantly more effective than both DOX alone (p < 0.001) and rMETase alone (p < 0.05). The relative body weight on day 14 compared with day 0 did not significantly differ between any treatment group or untreated control. The results indicate that r-METase can overcome DOX-resistance in this recalcitrant disease
- …