12,119 research outputs found
Implications of Spontaneous Glitches in the Mass and Angular Momentum in Kerr Space-Time
The outward-pointing principal null direction of the Schwarzschild Riemann
tensor is null hypersurface-forming. If the Schwarzschild mass spontaneously
jumps across one such hypersurface then the hypersurface is the history of an
outgoing light-like shell. The outward-- pointing principal null direction of
the Kerr Riemann tensor is asymptotically (in the neighbourhood of future null
infinity) null hypersurface-forming. If the Kerr parameters of mass and angular
momentum spontaneously jump across one such asymptotic hypersurface then the
asymptotic hypersurface is shown to be the history of an outgoing light-like
shell and a wire singularity-free spherical impulsive gravitational wave.Comment: 16 pages, TeX, no figures, accepted for publication in Phys. Rev.
The Goldberg-Sachs theorem in linearized gravity
The Goldberg-Sachs theorem has been very useful in constructing algebraically
special exact solutions of Einstein vacuum equation. Most of the physical
meaningful vacuum exact solutions are algebraically special. We show that the
Goldberg-Sachs theorem is not true in linearized gravity. This is a remarkable
result, which gives light on the understanding of the physical meaning of the
linearized solutions.Comment: 6 pages, no figures, LaTeX 2
The Distance to the Soft Gamma Repeater SGR 1627-41
We report millimeter observations of the line of sight to the recently
discovered Soft Gamma Repeater, SGR 1627-41, which has been tentatively
associated with the supernova remnant SNR G337.0-0.1 Among the eight molecular
clouds along the line of sight to SGR 1627-41, we show that SNR G337.0-0.1 is
probably interacting with one of the most massive giant molecular clouds (GMC)
in the Galaxy, at a distance of 11 kpc from the sun. Based on the high
extinction to the persistent X-ray counterpart of SGR 1627-41, we present
evidence for an association of this new SGR with the SNR G337.0-0.1; they both
appear to be located on the near side of the GMC. This is the second SGR
located near an extraordinarily massive GMC. We suggest that SGR 1627-41 is a
neutron star with a high transverse velocity (~ 1,000 \kms) escaping the young
(~ 5,000 years) supernova remnant G337.0-0.1Comment: 17 pages, including 2 figures. Accepted for publication in the
Astrophysical Journal Letter
Kerr-Schild Symmetries
We study continuous groups of generalized Kerr-Schild transformations and the
vector fields that generate them in any n-dimensional manifold with a
Lorentzian metric. We prove that all these vector fields can be intrinsically
characterized and that they constitute a Lie algebra if the null deformation
direction is fixed. The properties of these Lie algebras are briefly analyzed
and we show that they are generically finite-dimensional but that they may have
infinite dimension in some relevant situations. The most general vector fields
of the above type are explicitly constructed for the following cases: any
two-dimensional metric, the general spherically symmetric metric and
deformation direction, and the flat metric with parallel or cylindrical
deformation directions.Comment: 15 pages, no figures, LaTe
What Kind of âBig Governmentâ is the Big Society? A Reply to Bulley and Sokhi-Bulley
This article is a reply to Bulley and Sokhi-Bulley's recent article on the Big Society. We put forward two main criticisms of Bulley and Sokhi-Bulley's governmentality-focused approach in our alternative reading of the Big Society. Firstly, we argue that, given the ethopolitical strategies Bulley and Sokhi-Bulley focus their attention on are unlikely to produce the kind of transformation in the ethical outlook of citizens they suppose, the real historical significance of the Big Society must lie elsewhere. Secondly, we argue that Bulley and Sokhi-Bulley overlook the lines of continuity and discontinuity linking the Big Society to the forms of neo-liberal governmentality that have preceded it in British politics. In the final section of the article, we argue that the Cameron project amounts to both a partial continuation of the type of neo-liberal governmental rationality characteristic of the New Labour project and a partial reversion to a more rudimentary Thatcherite form of neo-liberal governmentality
An experimental evaluation of a loop versus a reference design for two-channel microarrays
Motivation: Despite theoretical arguments that socalled "loop designs" of two-channel DNA microarray experiments are more efficient, biologists keep on using "reference designs". We describe two sets of microarray experiments with RNA from two different biological systems (TPA-stimulated mammalian cells and Streptomyces coelicor). In each case, both a loop and a reference design were performed using the same RNA preparations with the aim to study their relative efficiency. Results: The results of these experiments show that (1) the loop design attains a much higher precision than the reference design, (2) multiplicative spot effects are a large source of variability, and if they are not accounted for in the mathematical model, for example by taking log-ratios or including spot-effects, then the model will perform poorly. The first result is reinforced by a simulation study. Practical recommendations are given on how simple loop designs can be extended to more realistic experimental designs and how standard statistical methods allow the experimentalist to use and interpret the results from loop designs in practice
Emergence of the Shackleton Range from beneath the Antarctic Ice Sheet due to glacial erosion
This paper explores the long-term evolution of a subglacial fjord landscape in the Shackleton Range, Antarctica. We propose that prolonged ice-sheet erosion across a passive continental margin caused troughs to deepen and lower the surrounding ice-sheet surface, leaving adjacent mountains exposed. Geomorphological evidence suggests a change in the direction of regional ice flow accompanied emergence. Simple calculations suggest that isostatic compensation caused by the deepening of bounding ice-stream troughs lowered the ice-sheet surface relative to the mountains by ~800m. Use of multiple cosmogenic isotopes on bedrock and erratics (26Al, 10Be, 21Ne) provides evidence that overriding of the massif and the deepening of the adjacent troughs occurred earlier than the Quaternary. Perhaps this occurred in the mid-Miocene, as elsewhere in East Antarctica in the McMurdo Dry Valleys and the Lambert basin. The implication is that glacial erosion instigates feedback that can change ice-sheet thickness, extent, and direction of flow. Indeed, as the subglacial troughs evolve over millions of years, they increase topographic relief; and this changes the dynamics of the ice sheet. © 2013 Elsevier B.V
Large-Scale Structures Behind the Southern Milky Way from Observations of Partially Obscured Galaxies
We report here on extragalactic large-scale structures uncovered by a deep
optical survey for galaxies behind the southern Milky Way. Systematic visual
inspection of the ESO/SRC-survey revealed over 10000 previously unknown
galaxies in the region 265 < l < 340, |b| < 10. With subsequently obtained
redshifts of more than 10% of these galaxies, new structures across the Milky
Way are unveiled, such as a filament at ~ 2500 km/s connecting to the Hydra
and Antlia clusters, a shallow extended supercluster in Vela (~ 6000km/s), and
a nearby (4882 km/s), very massive (M ~ 2-5 10^15 Msun), rich Coma-like cluster
which seems to constitute the previously unidentified center of the Great
Attractor. The innermost part of the Milky Way where the foreground obscuration
in the blue is 5mag, respectively HI-column densities greater than 6 10^21 /
cm^2 remains fully opaque. In this approximately 8 degrees wide strip, the
forthcoming blind HI-survey with the multi-beam system at Parkes will provide
the only tool to unveil this part of the extragalactic sky.Comment: Presented at the Multibeam Workshop on ``HI in the Local Universe'',
Sydney, May 13-15 1996. Accepted 2.11.1996 for publication by PASA.
Latex-file with 4 encapsulated postscript files. Version with original
figures available at
http://www.atnf.csiro.au/~lstavele/13beam/proceedings/korteweg/korteweg.htm
Errors in kinematic distances and our image of the Milky Way Galaxy
Errors in the kinematic distances, under the assumption of circular gas
orbits, were estimated by performing synthetic observations of a model disk
galaxy. It was found that the error is < 0.5 kpc for most of the disk when the
measured rotation curve was used, but larger if the real rotation curve is
applied. In both cases, the error is significantly larger at the positions of
the spiral arms. The error structure is such that, when kinematic distances are
used to develope a picture of the large scale density distribution, the most
significant features of the numerical model are significantly distorted or
absent, while spurious structure appears. By considering the full velocity
field in the calculation of the kinematic distances, most of the original
density structures can be recovered.Comment: Accepted for publication in A
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