17 research outputs found
Space-Time Structure of Loop Quantum Black Hole
In this paper we have improved the semiclassical analysis of loop quantum
black hole (LQBH) in the conservative approach of constant polymeric parameter.
In particular we have focused our attention on the space-time structure. We
have introduced a very simple modification of the spherically symmetric
Hamiltonian constraint in its holonomic version. The new quantum constraint
reduces to the classical constraint when the polymeric parameter goes to
zero.Using this modification we have obtained a large class of semiclassical
solutions parametrized by a generic function of the polymeric parameter. We
have found that only a particular choice of this function reproduces the black
hole solution with the correct asymptotic flat limit. In r=0 the semiclassical
metric is regular and the Kretschmann invariant has a maximum peaked in
L-Planck. The radial position of the pick does not depend on the black hole
mass and the polymeric parameter. The semiclassical solution is very similar to
the Reissner-Nordstrom metric. We have constructed the Carter-Penrose diagrams
explicitly, giving a causal description of the space-time and its maximal
extension. The LQBH metric interpolates between two asymptotically flat
regions, the r to infinity region and the r to 0 region. We have studied the
thermodynamics of the semiclassical solution. The temperature, entropy and the
evaporation process are regular and could be defined independently from the
polymeric parameter. We have studied the particular metric when the polymeric
parameter goes towards to zero. This metric is regular in r=0 and has only one
event horizon in r = 2m. The Kretschmann invariant maximum depends only on
L-Planck. The polymeric parameter does not play any role in the black hole
singularity resolution. The thermodynamics is the same.Comment: 17 pages, 19 figure
A century of trends in adult human height
Being taller is associated with enhanced longevity, and higher education and earnings. We reanalysed 1472 population-based studies, with measurement of height on more than 18.6 million participants to estimate mean height for people born between 1896 and 1996 in 200 countries. The largest gain in adult height over the past century has occurred in South Korean women and Iranian men, who became 20.2 cm (95% credible interval 17.5-22.7) and 16.5 cm (13.3-19.7) taller, respectively. In contrast, there was little change in adult height in some sub-Saharan African countries and in South Asia over the century of analysis. The tallest people over these 100 years are men born in the Netherlands in the last quarter of 20th century, whose average heights surpassed 182.5 cm, and the shortest were women born in Guatemala in 1896 (140.3 cm; 135.8-144.8). The height differential between the tallest and shortest populations was 19-20 cm a century ago, and has remained the same for women and increased for men a century later despite substantial changes in the ranking of countries
The Combined Influence of Grazing, Fire, and Herbaceous Productivity on Tree–Grass Interactions
Although Juniperus communities are native to most regions of North America, they have proliferated in many areas of the Great Basin and Great Plains that historically supported grasslands, shrublands, and savannas. Explanations for the observed increases in Juniperus dominance, as well as other woody plant communities, ar