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

Comparação de modelos digitais de elevação para a ilha de São Sebastião - SP.

Os produtos gerados a partir de modelos digitais de elevação (MDEs) podem contribuir para pesquisas ambientais, planejamento e gestão do território. No entanto há diferenças nos resultados dos produtos finais. Essas diferenças dependem do MDE a ser utilizado. Este trabalho gerou uma carta de declividade e uma carta hipsométrica da Ilha de São Sebastião - SP a partir de três modelos digitais de elevação. O objetivo deste artigo foi comparar por meio da análise de histograma os produtos gerados pelos MDEs SRTM, ASTER e TOPODATA

Ejercicio de negociación: una decisión de rutina

It shows an exercise whose objective is to get the students or participants to design the strategy they will follow during a negotiation process, taking into account the basic principles of a price negotiation. It simulates a typical negotiation between a buyer and a seller, each of whom has information that the other does not know. Each party must negotiate the price at which it will be willing to enter into the transaction. A second objective is to record the evolution of the negotiation process in order to measure the strength and sequence of the arguments, as well as the style of the negotiation. To this end, the instructor's guide suggests that the participant should define his strategy, prepare the arguments with which he will support it and define his negotiation style.Muestra un ejercicio cuyo objetivo es lograr que los estudiantes o participantes diseñen la estrategia que seguirán durante un proceso de negociación, teniendo en cuenta los principios básicos de una negociación de precios. Simula una negociación típica entre un comprador y un vendedor, cada uno de los cuales tiene información que el otro desconoce. Cada parte debe negociar el precio al que estará dispuesta a realizar la transacción. Un segundo objetivo es registrar la evolución del proceso de negociación para medir la fuerza y ​​secuencia de los argumentos, así como el estilo de la negociación. Para ello, la guía del instructor sugiere que el participante defina su estrategia, prepare los argumentos con los que la sustentará y defina su estilo de negociación

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

Mapeamento de áreas de preservação permanentes em topos de morros para a Amazônia Legal usando metodologia apropriada a grande volume de dados.

bitstream/item/65444/1/COT-57-Mapeamento-de-Areas-de.pd

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

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

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 $\Delta = \sqrt{2}\pi = 4.44$, reproducing the symmetries of the critical Choptuik solution.Comment: RevTeX 3.1, 28 pages, 5 figures; discussion rewritten to clarify several issue