101 research outputs found
Are All Static Black Hole Solutions Spherically Symmetric?
The static black hole solutions to the Einstein-Maxwell equations are all
spherically symmetric, as are many of the recently discovered black hole
solutions in theories of gravity coupled to other forms of matter. However,
counterexamples demonstrating that static black holes need not be spherically
symmetric exist in theories, such as the standard electroweak model, with
electrically charged massive vector fields. In such theories, a magnetically
charged Reissner-Nordstrom solution with sufficiently small horizon radius is
unstable against the development of a nonzero vector field outside the horizon.
General arguments show that, for generic values of the magnetic charge, this
field cannot be spherically symmetric. Explicit construction of the solution
shows that it in fact has no rotational symmetry at all.Comment: 6 pages, plain TeX. Submitted to GRF Essay Competitio
Static Black Hole Solutions without Rotational Symmetry
We construct static black hole solutions that have no rotational symmetry.
These arise in theories, including the standard electroweak model, that include
charged vector mesons with mass . In such theories, a magnetically
charged Reissner-Nordstrom black hole with horizon radius less than a critical
value of the order of is classically unstable against the development
of a nonzero vector meson field just outside the horizon, indicating the
existence of static black hole solutions with vector meson hair. For the case
of unit magnetic charge, spherically symmetric solutions of this type have
previously been studied. For other values of the magnetic charge, general
arguments show that any new solution with hair cannot be spherically symmetric.
In this paper we develop and apply a perturbative scheme (which may have
applicability in other contexts) for constructing such solutions in the case
where the Reissner-Nordstrom solution is just barely unstable. For a few low
values of the magnetic charge the black holes retain a rotational symmetry
about a single axis, but this axial symmetry disappears for higher charges.
While the vector meson fields vanish exponentially fast at distances greater
than , the magnetic field and the metric have higher multipole
components that decrease only as powers of the distance from the black hole.Comment: 42 pages, phyzzx. 4 figures (PostScript, 1.7 MB when uncompressed)
available by email from the Authors on reques
wormholes and topological charge
I investigate solutions to the Euclidean Einstein-matter field equations with
topology in a theory with a massless periodic scalar
field and electromagnetism. These solutions carry winding number of the
periodic scalar as well as magnetic flux. They induce violations of a
quasi-topological conservation law which conserves the product of magnetic flux
and winding number on the background spacetime. I extend these solutions to a
model with stable loops of superconducting cosmic string, and interpret them as
contributing to the decay of such loops.Comment: 18 pages (includes 6 figs.), harvmac and epsf, CU-TP-62
Black Hole Masses and Star Formation Rates of z >1 Dust Obscured Galaxies (DOGs): Results from Keck OSIRIS Integral Field Spectroscopy
We have obtained high spatial resolution Keck OSIRIS integral field
spectroscopy of four z~1.5 ultra-luminous infrared galaxies that exhibit broad
H-alpha emission lines indicative of strong AGN activity. The observations were
made with the Keck laser guide star adaptive optics system giving a spatial
resolution of 0.1", or <1 kpc at these redshifts. These high spatial resolution
observations help to spatially separate the extended narrow-line regions ---
possibly powered by star formation --- from the nuclear regions, which may be
powered by both star formation and AGN activity. There is no evidence for
extended, rotating gas disks in these four galaxies. Assuming dust correction
factors as high as A(H-alpha)=4.8 mag, the observations suggest lower limits on
the black hole masses of (1 - 9) x 10^8 solar masses, and star formation rates
<100 solar masses per year. The black hole masses and star formation rates of
the sample galaxies appear low in comparison to other high-z galaxies with
similar host luminosities. We explore possible explanations for these
observations including, host galaxy fading, black hole growth, and the shut
down of star formation.Comment: Accepted for publication in the Astronomical Journal. 12 pages, 6
figures, 5 table
Magnetic resonance imaging evidence for presymptomatic change in thalamus and caudate in familial Alzheimerâs disease
Amyloid imaging studies of presymptomatic familial Alzheimerâs disease have revealed the striatum and thalamus to be the earliest sites of amyloid deposition. This study aimed to investigate whether there are associated volume and diffusivity changes in these subcortical structures during the presymptomatic and symptomatic stages of familial Alzheimerâs disease. As the thalamus and striatum are involved in neural networks subserving complex cognitive and behavioural functions, we also examined the diffusion characteristics in connecting white matter tracts. A cohort of 20 presenilin 1 mutation carriers underwent volumetric and diffusion tensor magnetic resonance imaging, neuropsychological and clinical assessments; 10 were symptomatic, 10 were presymptomatic and on average 5.6 years younger than their expected age at onset; 20 healthy control subjects were also studied. We conducted region of interest analyses of volume and diffusivity changes in the thalamus, caudate, putamen and hippocampus and examined diffusion behaviour in the white matter tracts of interest (fornix, cingulum and corpus callosum). Voxel-based morphometry and tract-based spatial statistics were also used to provide unbiased whole-brain analyses of group differences in volume and diffusion indices, respectively. We found that reduced volumes of the left thalamus and bilateral caudate were evident at a presymptomatic stage, together with increased fractional anisotropy of bilateral thalamus and left caudate. Although no significant hippocampal volume loss was evident presymptomatically, reduced mean diffusivity was observed in the right hippocampus and reduced mean and axial diffusivity in the right cingulum. In contrast, symptomatic mutation carriers showed increased mean, axial and in particular radial diffusivity, with reduced fractional anisotropy, in all of the white matter tracts of interest. The symptomatic group also showed atrophy and increased mean diffusivity in all of the subcortical grey matter regions of interest, with increased fractional anisotropy in bilateral putamen. We propose that axonal injury may be an early event in presymptomatic Alzheimerâs disease, causing an initial fall in axial and mean diffusivity, which then increases with loss of axonal density. The selective degeneration of long-coursing white matter tracts, with relative preservation of short interneurons, may account for the increase in fractional anisotropy that is seen in the thalamus and caudate presymptomatically. It may be owing to their dense connectivity that imaging changes are seen first in the thalamus and striatum, which then progress to involve other regions in a vulnerable neuronal network
Effects of Environmentally Relevant Concentrations of Poultry Litter Associated Contaminates on the Sexual Development of Xenopus laevis
Poultry litter contains high levels of natural sex hormones, nitrogen, phosphorous,
and trace amounts of heavy metals. Poultry litter runoff from poultry and farming
operations in the Delmarva region can have serious impacts on frog development in
the Chesapeake Bay Watershed. In this study, we investigated potential effects of
litter compounds on Xenopus laevis development when exposed to environmental
levels (0.35 and 0.70 g/L) of litter solution. We found that despite rapid hormone
degradation, poultry litter solution still affected X. laevis development. Hormones
were also more persistent in the lower poultry litter concentration, leading to even
greater effects. Slowed growth and increased female gonadal abnormalities were
observed after exposure to 0.35 g/L but not to 0.70 g/L of litter solution, and
increased male gonadal abnormalities were observed after treatment to both litter
concentrations. The developmental impacts examined in this study may have greater
environmental impacts on frog reproduction and survival
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
Changes in lipid composition during sexual development of the malaria parasite Plasmodium falciparum
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