907 research outputs found
Survival of the black hole's Cauchy horizon under non-compact perturbations
We study numerically the evolution of spactime, and in particular of a
spacetime singularity, inside a black hole under a class of perturbations of
non-compact support. We use a very simplified toy model of a spherical charged
black hole which is perturbed nonlinearly by a self-gravitating, spherical
scalar field. The latter grows logarithmically with advanced time along an
outgoing characteristic hypersurface. We find that for that class of
perturbations a portion of the Cauchy horizon survives as a non-central, null
singularity.Comment: 5 pages, 4 figure
Universality of massive scalar field late-time tails in black-hole spacetimes
The late-time tails of a massive scalar field in the spacetime of black holes
are studied numerically. Previous analytical results for a Schwarzschild black
hole are confirmed: The late-time behavior of the field as recorded by a static
observer is given by , where
depends weakly on time. This result is carried over to the case of
a Kerr black hole. In particular, it is found that the power-law index of -5/6
depends on neither the multipole mode nor on the spin rate of the black
hole . In all black hole spacetimes, massive scalar fields have the same
late-time behavior irrespective of their initial data (i.e., angular
distribution). Their late-time behavior is universal.Comment: 11 pages, 14 figures, published versio
Effects of testosterone treatment on bone mineral density in hypogonadal men receiving intrathecal opioids
Background
Opioid induced depression of sex hormones is a common finding in chronic pain patients receiving long-term opioids by oral, parenteral and even intrathecal routes of administration. The hypothalamic suppression by opioids leads to a hypogonadal state with low testosterone levels in males and subsequent low bone mineral density (BMD).
Methods
We have studied the effects of intrathecally administered opioids on BMD in a group of male chronic pain patients. In addition, we have studied the effects of supplementary testosterone on bone metabolism to see if the adverse effects of intrathecal opioids can be reversed.
Results
Eleven of the 27 patients were on supplementary testosterone having previously been diagnosed as hypogonadal with low serum testosterone. Duration of testosterone supplementation was greater than 2 years in all 11 patients. Both serum total and free testosterone levels were higher in patients on supplementary testosterone than in patients who did not receive this treatment. Of the 16 patients not on testosterone supplement, 14 (87%) had low serum testosterone levels (<10 nmol/L) and 11 (69%) had low or osteoporotic T scores. Within this group, low free testosterone was associated with low BMD scores, and this persisted after correcting for age. Eight of the patients on testosterone supplement had normal BMDT scores and three (27%) had low or osteoporotic T scores. T and age-corrected BMDZ scores were significantly greater in the 11 patients on testosterone supplements than BMD scores in the other 16 patients.
Conclusion
Testosterone supplementation was found to largely correct the effects of intrathecal opioids on testosterone levels and BMD
Massive fields tend to form highly oscillating self-similarly expanding shells
The time evolution of self-interacting spherically symmetric scalar fields in
Minkowski spacetime is investigated based on the use of Green's theorem. It is
shown that a massive Klein-Gordon field can be characterized by the formation
of certain expanding shell structures where all the shells are built up by very
high frequency oscillations. This oscillation is found to be modulated by the
product of a simple time decaying factor of the form and of an
essentially self-similar expansion. Apart from this self-similar expansion the
developed shell structure is preserved by the evolution. In particular, the
energy transported by each shell appears to be time independent.Comment: 10 pages, to appear in Phys. Rev.
Influence of personality, age, sex, and oestrus state on chimpanzee problem-solving success
Despite the importance of individual problem solvers for group- and individual-level fitness, the correlates of individual problem-solving success are still an open topic of investigation. In addition to demographic factors, such as age or sex, certain personality dimensions have also been revealed as reliable correlates of problem-solving by animals. Such correlates, however, have been little-studied in chimpanzees. To empirically test the influence of age, sex, estrous state, and different personality factors on chimpanzee problem-solving, we individually tested 36 captive chimpanzees with two novel foraging puzzles. We included both female (N = 24) and male (N = 12) adult chimpanzees (aged 14â47 years) in our sample. We also controlled for the femalesâ estrous stateâa potential influence on cognitive reasoningâby testing cycling females both when their sexual swelling was maximally tumescent (associated with the luteinizing hormone surge of a femaleâs estrous cycle) and again when it was detumescent. Although we found no correlation between the chimpanzeesâ success with either puzzle and their age or sex, the chimpanzeesâ personality ratings did correlate with responses to the novel foraging puzzles. Specifically, male chimpanzees that were rated highly on the factors Methodical, Openness (to experience), and Dominance spent longer interacting with the puzzles. There was also a positive relationship between the latency of females to begin interacting with the two tasks and their rating on the factor Reactivity/Undependability. No other significant correlations were found, but we report tentative evidence for increased problem-solving success by the females when they had detumescent estrous swellings
Radiation tails and boundary conditions for black hole evolutions
In numerical computations of Einstein's equations for black hole spacetimes,
it will be necessary to use approximate boundary conditions at a finite
distance from the holes. We point out here that ``tails,'' the inverse
power-law decrease of late-time fields, cannot be expected for such
computations. We present computational demonstrations and discussions of
features of late-time behavior in an evolution with a boundary condition.Comment: submitted to Phys. Rev.
Dipole Perturbations of the Reissner-Nordstrom Solution: The Polar Case
The formalism developed by Chandrasekhar for the linear polar perturbations
of the Reissner-Nordstrom solution is generalized to include the case of dipole
(l=1) perturbations. Then, the perturbed metric coefficients and components of
the Maxwell tensor are computed.Comment: 16 pages, LaTeX, no figures. Submitted for publication in Physical
Review
Radiative falloff in the background of rotating black hole
We study numerically the late-time tails of linearized fields with any spin
in the background of a spinning black hole. Our code is based on the
ingoing Kerr coordinates, which allow us to penetrate through the event
horizon. The late time tails are dominated by the mode with the least multipole
moment which is consistent with the equatorial symmetry of the initial
data and is equal to or greater than the least radiative mode with and the
azimuthal number .Comment: 5 pages, 4 Encapsulated PostScript figures; Accepted to Phys. Rev. D
(Rapid Communication
3D simulations of linearized scalar fields in Kerr spacetime
We investigate the behavior of a dynamical scalar field on a fixed Kerr
background in Kerr-Schild coordinates using a 3+1 dimensional spectral
evolution code, and we measure the power-law tail decay that occurs at late
times. We compare evolutions of initial data proportional to f(r)
Y_lm(theta,phi) where Y_lm is a spherical harmonic and (r,theta,phi) are
Kerr-Schild coordinates, to that of initial data proportional to f(r_BL)
Y_lm(theta_BL,phi), where (r_BL,theta_BL) are Boyer-Lindquist coordinates. We
find that although these two cases are initially almost identical, the
evolution can be quite different at intermediate times; however, at late times
the power-law decay rates are equal.Comment: 12 pages, 9 figures, revtex4. Major revision: added figures, added
subsection on convergence, clarified discussion. To appear in Phys Rev
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