14,213 research outputs found
J0316+4328: a Probable "Asymmetric Double" Lens
We report a probable gravitational lens J0316+4328, one of 19 candidate
asymmetric double lenses (2 images at a high flux density ratio) from CLASS.
Observations with the Very Large Array (VLA), MERLIN and the Very Long Baseline
Array (VLBA) imply that J0316+4328 is a lens with high confidence. It has 2
images separated by 0.40", with 6 GHz flux densities of 62 mJy and 3.2 mJy. The
flux density ratio of ~19 (constant over the frequency range 6-22 GHz) is the
largest for any 2 image gravitational lens. High resolution optical imaging and
deeper VLBI maps should confirm the lensing interpretation and provide inputs
to detailed lens models. The unique configuration will give strong constraints
on the lens galaxy's mass profile.Comment: Accepted to MNRAS Letters. 5 pages, 6 figures, 3 table
A Determination of H_0 with the CLASS Gravitational Lens B1608+656: I. Time Delay Measurements with the VLA
We present the results of a program to monitor the four-image gravitational
lens B1608+656 with the VLA. The system was observed over a seven month period
from 1996 October to 1997 May. The 64 epochs of observation have an average
spacing of 3.6~d. The light curves of the four images of the background source
show that the flux density of the background source has varied at the ~5%
level. We measure time delays in the system based on common features that are
seen in all four light curves. The three independent time delays in the system
are found to be Delta t_{BA} = 31 +/- 7~d, Delta t_{BC} = 36 +/- 7~d, and Delta
t_{BD} = 76^{+9}_{-10}~d at 95% confidence. This is the first gravitational
lens system for which three independent time delays have been measured. A
companion paper presents a mass model for the lensing galaxy which correctly
reproduces the observed image positions, flux density ratios, and time delay
ratios. The last condition is crucial for determining H_0 with a four-image
lens. We combine the time delays with the model to obtain a value for the
Hubble constant of H_0 = 59^{+8}_{-7} km/s/Mpc at 95% confidence (statistical)
for (Omega_M, Omega_{Lambda}) = (1,0). In addition, there is an estimated
systematic uncertainty of +/- 15 km/s/Mpc from uncertainties in modeling the
radial mass profiles of the lensing galaxies. The value of H_0 presented in
this paper is comparable to recent measurements of H_0 from the gravitational
lenses 0957+561, PG1115+080, B0218+357, and PKS1830-211.Comment: Accepted for publication in ApJ. 20 pages, 13 figure
Massive Gravity Theories and limits of Ghost-free Bigravity models
We construct a class of theories which extend New Massive Gravity to higher
orders in curvature in any dimension. The lagrangians arise as limits of a new
class of bimetric theories of Lovelock gravity, which are unitary theories free
from the Boulware-Deser ghost. These Lovelock bigravity models represent the
most general non-chiral ghost-free theories of an interacting massless and
massive spin-two field in any dimension. The scaling limit is taken in such a
way that unitarity is explicitly broken, but the Boulware-Deser ghost remains
absent. This automatically implies the existence of a holographic -theorem
for these theories. We also show that the Born-Infeld extension of New Massive
Gravity falls into our class of models demonstrating that this theory is also
free of the Boulware-Deser ghost. These results extend existing connections
between New Massive Gravity, bigravity theories, Galileon theories and
holographic -theorems.Comment: 11+5 page
Positive practices : solution-focused and narrative therapeutic techniques with children with sexually harmful behaviours
This article explores the use of solution-focused and Narrative Therapeutic approaches with a boy who had sexually harmful behaviours. The paper will highlight the practical challenges of working with someone who is 'problem-saturated' through institutionalisation and who is also subjected to powerful discourses claiming the 'truth' about him. The use of solution-focused and Narrative Therapeutic principles and approaches will be demonstrated in the work described, in a way that allows the reader to reflect on how these may differ from modernist understandings and responses to this behaviour
Modification of surface energy in nuclear multifragmentation
Within the statistical multifragmentation model we study modifications of the
surface and symmetry energy of primary fragments in the freeze-out volume. The
ALADIN experimental data on multifragmentation obtained in reactions induced by
high-energy projectiles with different neutron richness are analyzed. We have
extracted the isospin dependence of the surface energy coefficient at different
degrees of fragmentation. We conclude that the surface energy of hot fragments
produced in multifragmentation reactions differs from the values extracted for
isolated nuclei at low excitation. At high fragment multiplicity, it becomes
nearly independent of the neutron content of the fragments.Comment: 11 pages with 13 figure
Large-Scale CO Maps of the Lupus Molecular Cloud Complex
Fully sampled degree-scale maps of the 13CO 2-1 and CO 4-3 transitions toward
three members of the Lupus Molecular Cloud Complex - Lupus I, III, and IV -
trace the column density and temperature of the molecular gas. Comparison with
IR extinction maps from the c2d project requires most of the gas to have a
temperature of 8-10 K. Estimates of the cloud mass from 13CO emission are
roughly consistent with most previous estimates, while the line widths are
higher, around 2 km/s. CO 4-3 emission is found throughout Lupus I, indicating
widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the
NW end and along the edge of the B228 ridge in Lupus I, and a coherent velocity
gradient across the ridge, are consistent with interaction between the
molecular cloud and an expanding HI shell from the Upper-Scorpius subgroup of
the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be
stars, and shows no sign of external influence. Slightly warmer gas around the
core of Lupus IV and a low line width suggest heating by the
Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an HI shell.Comment: 54 pages, 27 figures, 5 tables. To appear in ApJS. Preprint also
available (with full-size figures) from
http://www.astro.ex.ac.uk/people/nfht/publications.html Datacubes available
from http://www.astro.ex.ac.uk/people/nfht/resources.htm
Massive Quantum Liquids from Holographic Angel's Trumpets
We explore the small-temperature regime in the deconfined phase of massive
fundamental matter at finite baryon number density coupled to the 3+1
dimensional N=4 SYM theory. In this setting, we can demonstrate a new type of
non-trivial temperature-independent scaling solutions for the probe brane
embeddings. Focusing mostly on matter supported in 2+1 dimensions, the
thermodynamics indicate that there is a quantum liquid with interesting
density-dependent low-temperature physics. We also comment about 3+1 and 1+1
dimensional systems, where we further find for example a new thermodynamic
instability.Comment: 18+1 pages, 6 figures; replaced fig. 6 and comments in sec. 5.2;
minor explanations added and typos fixed, final version published in JHEP
(modulo fig. 3); factor of \sqrt{\lambda} and corresponding comments fixe
Quasinormal modes of massive charged flavor branes
We present an analysis and classification of vector and scalar fluctuations
in a D3/D7 brane setup at finite termperature and baryon density. The system is
dual to an N=2 supersymmetric Yang-Mills theory with SU(N_c) gauge group and
N_f hypermultiplets in the fundamental representation in the quenched
approximation. We improve significantly over previous results on the
quasinormal mode spectrum of D7 branes and stress their novel physical
interpretation. Amongst our findings is a new purely imaginary scalar mode that
becomes tachyonic at sufficiently low temperature and baryon density. We
establish the existence of a critical density above which the scalar mode stays
in the stable regime for all temperatures. In the vector sector we study the
crossover from the hydrodynamic to the quasiparticle regime and find that it
moves to shorter wavelengths for lower temperatures. At zero baryon density the
quasinormal modes move toward distinct discrete attractor frequencies that
depend on the momentum as we increase the temperature. At finite baryon
density, however, the trajectories show a turning behavior such that for low
temperature the quasinormal mode spectrum approaches the spectrum of the
supersymmetric zero temperature normal modes. We interpret this as resolution
of the singular quasinormal mode spectrum that appears at the limiting D7 brane
embedding at vanishing baryon density.Comment: 56 pages, 40 figure
Dirty black holes: Entropy versus area
Considerable interest has recently been expressed in the entropy versus area
relationship for ``dirty'' black holes --- black holes in interaction with
various classical matter fields, distorted by higher derivative gravity, or
infested with various forms of quantum hair. In many cases it is found that the
entropy is simply related to the area of the event horizon: S = k
A_H/(4\ell_P^2). For example, the ``entropy = (1/4) area'' law *holds* for:
Schwarzschild, Reissner--Nordstrom, Kerr--Newman, and dilatonic black holes. On
the other hand, the ``entropy = (1/4) area'' law *fails* for: various types of
(Riemann)^n gravity, Lovelock gravity, and various versions of quantum hair.
The pattern underlying these results is less than clear. This paper
systematizes these results by deriving a general formula for the entropy: S =
{k A_H/(4\ell_P^2)}
+ {1/T_H} \int_\Sigma [rho - {L}_E ] K^\mu d\Sigma_\mu
+ \int_\Sigma s V^\mu d\Sigma_\mu. (K^\mu is the timelike Killing vector,
V^\mu the four velocity of a co--rotating observer.) If no hair is present the
validity of the ``entropy = (1/4) area'' law reduces to the question of whether
or not the Lorentzian energy density for the system under consideration is
formally equal to the Euclideanized Lagrangian. ****** To appear in Physical
Review D 15 July 1993 ****** [Stylistic changes, minor typos fixed, references
updated, discussion of the Born-Infeld system excised]Comment: plain LaTeX, 17 pages, minor revision
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