3,672 research outputs found
The return of the bursts: Thermonuclear flashes from Circinus X-1
We report the detection of 15 X-ray bursts with RXTE and Swift observations
of the peculiar X-ray binary Circinus X-1 during its May 2010 X-ray
re-brightening. These are the first X-ray bursts observed from the source after
the initial discovery by Tennant and collaborators, twenty-five years ago. By
studying their spectral evolution, we firmly identify nine of the bursts as
type I (thermonuclear) X-ray bursts. We obtain an arcsecond location of the
bursts that confirms once and for all the identification of Cir X-1 as a type I
X-ray burst source, and therefore as a low magnetic field accreting neutron
star. The first five bursts observed by RXTE are weak and show approximately
symmetric light curves, without detectable signs of cooling along the burst
decay. We discuss their possible nature. Finally, we explore a scenario to
explain why Cir X-1 shows thermonuclear bursts now but not in the past, when it
was extensively observed and accreting at a similar rate.Comment: Accepted for publication in The Astrophysical Journal Letters. Tables
1 & 2 merged. Minor changes after referee's comments. 5 pages, 4 Figure
On the addition of degrees of freedom to force-balanced linkages
The design of shaking-force balanced linkages can be approached by deriving these linkages from balanced linkage architectures. When desired, a possible step is to add degrees-of-freedom (dof), for instance by substituting a link with a n-dof equivalent linkage for which the balanced design of the other links is not affected. This paper shows how the coupler link of a shaking-force balanced 4R four-bar linkage, applied as a 5R five-bar linkage, can be substituted with an equivalent 2-dof pantograph
Characterization by Mossbauer spectroscopy of Fe phases in highly weathered serpentinitic soil from southern Cameroon
Volume: 53Start Page: 73End Page: 8
On the Use of Quantum Algebras in Rotation-Vibration Spectroscopy
A two-parameter deformation of the Lie algebra u is used, in conjunction
with the rotor system and the oscillator system, to generate a model for
rotation-vibration spectroscopy of molecules and nuclei.Comment: 10 pages, Latex File, published in Modern Group Theoretical Methods
in Physics, J. Bertrand et al. (eds.), Kluwer Academic Publishers (1995),
27-3
Investigating human audio-visual object perception with a combination of hypothesis-generating and hypothesis-testing fMRI analysis tools
Primate multisensory object perception involves distributed brain regions. To investigate the network character of these regions of the human brain, we applied data-driven group spatial independent component analysis (ICA) to a functional magnetic resonance imaging (fMRI) data set acquired during a passive audio-visual (AV) experiment with common object stimuli. We labeled three group-level independent component (IC) maps as auditory (A), visual (V), and AV, based on their spatial layouts and activation time courses. The overlap between these IC maps served as definition of a distributed network of multisensory candidate regions including superior temporal, ventral occipito-temporal, posterior parietal and prefrontal regions. During an independent second fMRI experiment, we explicitly tested their involvement in AV integration. Activations in nine out of these twelve regions met the max-criterion (A < AV > V) for multisensory integration. Comparison of this approach with a general linear model-based region-of-interest definition revealed its complementary value for multisensory neuroimaging. In conclusion, we estimated functional networks of uni- and multisensory functional connectivity from one dataset and validated their functional roles in an independent dataset. These findings demonstrate the particular value of ICA for multisensory neuroimaging research and using independent datasets to test hypotheses generated from a data-driven analysis
Status of center dominance in various center gauges
We review arguments for center dominance in center gauges where vortex
locations are correctly identified. We introduce an appealing interpretation of
the maximal center gauge, discuss problems with Gribov copies, and a cure to
the problems through the direct Laplacian center gauge. We study correlations
between direct and indirect Laplacian center gauges.Comment: Presented by S. Olejnik at the NATO Advanced Research Workshop
"Confinement, Topology, and other Non-Perturbative Aspects of QCD", Jan.
21-27, 2002, Stara Lesna, Slovakia. 10 pages, 3 figures (8 EPS files), uses
crckapb.st
Continuous heating of a giant X-ray flare on Algol
Giant flares can release large amounts of energy within a few days: X-ray
emission alone can be up to ten percent of the star's bolometric luminosity.
These flares exceed the luminosities of the largest solar flares by many orders
of magnitude, which suggests that the underlying physical mechanisms supplying
the energy are different from those on the Sun. Magnetic coupling between the
components in a binary system or between a young star and an accretion disk has
been proposed as a prerequisite for giant flares. Here we report X-ray
observations of a giant flare on Algol B, a giant star in an eclipsing binary
system. We observed a total X-ray eclipse of the flare, which demonstrates that
the plasma was confined to Algol B, and reached a maximum height of 0.6 stellar
radii above its surface. The flare occurred around the south pole of Algol B,
and energy must have been released continously throughout its life. We conclude
that a specific extrastellar environment is not required for the presence of a
flare, and that the processes at work are therefore similar to those on the
Sun.Comment: Nature, Sept. 2 199
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