786 research outputs found
The discovery of hard X-ray emission in the persistent flux of the Rapid Burster
We report the first detection with INTEGRAL of persistent hard X-ray emission
(20 to 100 keV) from the Rapid Burster (MXB 1730-335), and describe its full
spectrum from 3 to 100 keV. The source was detected on February/March 2003
during one of its recurrent outbursts. The source was clearly detected with a
high signal to noise ratio during the single pointings and is well
distinguished from the neighboring source GX 354-0. The 3 - 100 keV X-ray
spectrum of the persistent emission is well described by a two-component model
consisting of a blackbody plus a power-law with photon index ~ 2.4. The
estimated luminosity was ~ 8.5x10^{36} erg/s in the 3 - 20 keV energy band and
\~ 1.3x10^{36} erg/s in the 20 - 100 keV energy range, for a distance of 8 kpc.Comment: 5 pages, 6 figures, 1 table. Accepted for publication in A&
Spectral states evolution of 4U 1728-34 observed by INTEGRAL and RXTE: non-thermal component detection
We report results of a one-year monitoring of the low mass X-ray binary
(LMXB) source (atoll type) 4U 1728-34 with INTEGRAL and RXTE. Three time
intervals were covered by INTEGRAL, during which the source showed strong
spectral evolution. We studied the broad-band X-ray spectra in detail by
fitting several models in the different sections of the hardness-intensity
diagram. The soft states are characterised by prominent blackbody emission plus
a contribution from a Comptonized emission. The hard states are characterised
by the presence of an excess flux with respect to the Comptonization model
above 50 keV while the soft component is fainter. To obtain an acceptable fit
to the data this excess is modeled either with a power law with photon index
Gamma ~ 2 or a Comptonization (CompPS) spectrum implying the presence of hybrid
thermal and non-thermal electrons in a corona. This makes 4U 1728-34 one of the
few LMXBs of atoll type showing non-thermal emission at high energy. From our
analysis, it is also apparent that the presence of the hard tail is more
prominent as the overall spectrum becames harder. We discuss also alternative
models which can discribe these hard states.Comment: Accepted for publication in MNRAS (accepted 2011 April 20. Received
2011 April 20; in original form 2010 December 07); 9 pages, 7 figure
INTEGRAL high energy monitoring of the X-ray burster KS 1741-293
KS 1741-293, discovered in 1989 by the X-ray camera TTM in the Kvant module
of the Mir space station and identified as an X-ray burster, has not been
detected in the hard X band until the advent of the INTEGRAL observatory.
Moreover this source has been recently object of scientific discussion, being
also associated to a nearby extended radio source that in principle could be
the supernova remnant produced by the accretion induced collapse in the binary
system. Our long term monitoring with INTEGRAL, covering the period from
February 2003 to May 2005, confirms that KS 1741-293 is transient in soft and
hard X band. When the source is active, from a simultaneous JEM-X and IBIS data
analysis, we provide a wide band spectrum from 5 to 100 keV, that can be fit by
a two component model, a multiple blackbody for the soft emission and a
Comptonized or a cut-off power law model for the hard component. Finally, by
the detection of two X-ray bursters with JEM-X, we confirm the bursting nature
of KS 1741-293, including this source in the class of the hard tailed X-ray
bursters.Comment: 7 pages, accepted for publication on MNRA
Correlated Rounding of Multiple Uniform Matroids and Multi-Label Classification
We introduce correlated randomized dependent rounding where, given multiple points y^1,...,y^n in some polytope Psubseteq [0,1]^k, the goal is to simultaneously round each y^i to some integral z^i in P while preserving both marginal values and expected distances between the points. In addition to being a natural question in its own right, the correlated randomized dependent rounding problem is motivated by multi-label classification applications that arise in machine learning, e.g., classification of web pages, semantic tagging of images, and functional genomics. The results of this work can be summarized as follows: (1) we present an algorithm for solving the correlated randomized dependent rounding problem in uniform matroids while losing only a factor of O(log{k}) in the distances (k is the size of the ground set); (2) we introduce a novel multi-label classification problem, the metric multi-labeling problem, which captures the above applications. We present a (true) O(log{k})-approximation for the general case of metric multi-labeling and a tight 2-approximation for the special case where there is no limit on the number of labels that can be assigned to an object
WIMPs search by scintillators: possible strategy for annual modulation search with large-mass highly-radiopure NaI(Tl)
The DAMA experiments are running deep underground in the Gran Sasso National
Laboratory. Several interesting results have been achieved so far. Here a
maximum likelihood method to search for the WIMP annual modulation signature is
discussed and applied to a set of preliminary test data collected with large
mass highly radiopure NaI(Tl) detectors. Various related technical arguments
are briefly addressed.Comment: 6 pages, 4 figures, LaTex. Contributed paper to TAUP97; to appear in
the Proceeding
Effects of the diabetes manual 1:1 structured education in primary care
Aims
To determine the effects of the Diabetes Manual on glycaemic control, diabetes-related distress and confidence to self-care of patients with Type 2 diabetes. Methods
A cluster randomized, controlled trial of an intervention group vs. a 6-month delayed-intervention control group with a nested qualitative study. Participants were 48 urban general practices in the West Midlands, UK, with high population deprivation levels and 245 adults with Type 2 diabetes with a mean age of 62 years recruited pre-randomization. The Diabetes Manual is 1:1 structured education designed for delivery by practice nurses. Measured outcomes were HbA1c, cardiovascular risk factors, diabetes-related distress measured by the Problem Areas in Diabetes Scale and confidence to self-care measured by the Diabetes Management Self-Efficacy Scale. Outcomes were assessed at baseline and 26 weeks. Results
There was no significant difference in HbA1c between the intervention group and the control group [difference −0.08%, 95% confidence interval (CI) −0.28, 0.11]. Diabetes-related distress scores were lower in the intervention group compared with the control group (difference −4.5, 95% CI −8.1, −1.0). Confidence to self-care Scores were 11.2 points higher (95% CI 4.4, 18.0) in the intervention group compared with the control group. The patient response rate was 18.5%. Conclusions
In this population, the Diabetes Manual achieved a small improvement in patient diabetes-related distress and confidence to self-care over 26 weeks, without a change in glycaemic control. Further study is needed to optimize the intervention and characterize those for whom it is more clinically and psychologically effective to support its use in primary care
Discovery of type-I X-ray bursts from the low-mass X-ray binary 4U 1708-40
We report the discovery of type-I X-ray bursts from the low-mass X-ray binary
4U 1708-40 during the 100 ks observation performed by BeppoSAX on 1999 August
15-16. Six X-ray bursts have been observed. The unabsorbed 2-10 keV fluxes of
the bursts range from ~ (3-9)x10^(-10) erg cm^(-2)s^(-1). A correlation between
peak flux and fluence of the bursts is found, in agreement with the behaviour
observed in other similar sources. There is a trend of the burst flux to
increase with the time interval from the previous burst. From the value of the
persistent flux we infer a mass accretion rate Mdot~7x10^(-11) Msun/yr, that
may correspond to the mixed hydrogen/helium burning regime triggered by
thermally unstable hydrogen. We have also analysed a BeppoSAX observation
performed on 2001 August 22 and previous RXTE observations of 4U 1708-40, where
no bursts have been observed; we found persistent fluxes of more than a factor
of 7 higher than the persistent flux observed during the BeppoSAX observation
showing X-ray bursts.Comment: accepted for publication in MNRA
Derivative corrections to D-brane actions with constant background fields
We study derivative corrections to the effective action for a single D-brane
in type II superstring theory coupled to constant background fields. In
particular, within this setting we determine the complete expression for the
(disk level) four-derivative corrections to the Born-Infeld part of the action.
We also determine 2n-form 2n-derivative corrections to the Wess-Zumino term.
Both types of corrections involve all orders of the gauge field strength, F.
The results are obtained via string sigma-model loop calculations using the
boundary state operator language. The corrections can be succinctly written in
terms of the Riemann tensor for a non-symmetric metric.Comment: 28 pages, LaTeX (uses pstricks); v2: minor typos corrected,
references adde
Peripheral sensitisation of nociceptors via G-proteindependent potentiation of mechanotransduction currents
Mechanical stimuli impinging on the skin are converted into electrical signals by mechanically gated ion channels located at the peripheral nerve endings of dorsal root ganglion (DRG) neurons. Under inflammatory conditions sensory neurons are commonly sensitised to mechanical stimuli; a putative mechanism that may contribute to such sensitisation of sensory neurons is enhanced responsiveness of mechanotransduction ion channels. Here we show that the algogens UTP and ATP potentiate mechanosensitive RA currents in peptidergic nociceptive DRG neurons and reduce thresholds for mechanically induced action potential firing in these neurones. Pharmacological characterisation suggests that this effect is mediated by the Gq-coupled P2Y2 nucleotide receptor. Moreover, using the in vitro skin nerve technique, we show that UTP also increases action potential firing rates in response to mechanical stimuli in a subpopulation of skin C-fibre nociceptors. Together our findings suggest that UTP sensitises a subpopulation of cutaneous C-fibre nociceptors via a previously undescribed G-protein-dependent potentiation of mechanically activated RA-type currents
A Hard X-ray View on Scorpius X-1 with INTEGRAL: non-Thermal Emission ?
We present here simultaneous INTEGRAL/RXTE observations of Sco X-1, and in
particular a study of the hard X-ray emission of the source and its correlation
with the position in the Z-track of the X-ray color-color diagram. We find that
the hard X-ray (above about 30 keV) emission of Sco X-1 is dominated by a
power-law component with a photon index of ~3. The flux in the power-law
component slightly decreases when the source moves in the color-color diagram
in the sense of increasing inferred mass accretion rate from the horizontal
branch to the normal branch/flaring branch vertex. It becomes not significantly
detectable in the flaring branch, where its flux has decreased by about an
order of magnitude. These results present close analogies to the behavior of GX
17+2, one of so-called Sco-like Z sources. Finally, the hard power law in the
spectrum of Sco X-1 does not show any evidence of a high energy cutoff up to
100 - 200 keV, strongly suggesting a non-thermal origin of this component.Comment: 5 pages including 3 figures. Accepted for publication by ApJ Letter
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