3,471 research outputs found
BeppoSAX-WFC monitoring of the Galactic Center region
We review the results obtained with the Galactic center campaigns of the
BeppoSAX Wide Field X-ray Cameras (WFCs). This pertains to the study of
luminous low-mass X-ray binaries (LMXBs). When pointed at the Galactic center,
the WFC field of view contains more than half of the Galactic LMXB population.
The results exemplify the excellent WFC capability to detect brief X-ray
transients. Firstly, the WFCs expanded the known population of Galactic
thermonuclear X-ray bursters by 50%. At least half of all LMXBs are now
established to burst and, thus, to contain a neutron star as compact accretor
rather than a black hole candidate. We provide a complete list of all 76
currently known bursters, including the new case 1RXS J170854.4-321857.
Secondly, the WFCs have uncovered a population of weak transients with peak
luminosities up to ~10^37 erg/s and durations from days to weeks. One is the
first accretion-powered millisecond pulsar SAX J1808.4-3658. Thirdly, the WFCs
contributed considerably towards establishing that nearly all (12 out of 13)
luminous low-mass X-ray binaries in Galactic globular clusters contain neutron
stars rather than black holes. Thus, the neutron star to black hole ratio in
clusters differs from that in the Galactic disk at a marginal confidence level
of 97%.Comment: 10 pages 6 figures, to appear in Proc. "The Restless High-Energy
Universe" (2nd BeppoSAX Symposium), eds. E.P.J. van den Heuvel, J.J.M. in 't
Zand & R.A.M.J. Wijers, Nucl. Instrum. Meth. B Suppl. Se
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Application of Neural Networks for Estimation of Concrete Strength
The uniaxial compressive strength of concrete is the most widely used criterion in producing concrete. Although testing of the uniaxial compressive strength of concrete specimens is done routinely, it is performed on the 28th day after concrete placement. At this point, it is too late to make improvements if the test result does not satisfy the required strength. Therefore, the strength estimation before the placement of concrete is highly desirable. This study presents the first effort in applying neural network-based system identification techniques to predict the compressive strength of concrete based on concrete mix proportions. Back-propagation neural networks were developed, trained, and tested using actual data sets of concrete mix proportions provided by two ready-mixed concrete companies. The compressive strengths estimated by the neural networks were verified by laboratory testing results. This study demonstrated that the neural network techniques are effective in estimating the compressive strength of concrete based on the mix proportions. Application of these techniques will contribute significantly to the concrete quality assurance
Barriers to Implementing the International Integrated Reporting Framework: A Contemporary Academic Perspective
Purpose: This paper is motivated by the International Integrated Reporting Councilâs (IIRC) call for feedback from all stakeholders with knowledge of the International Integrated Reporting Framework , and specifically of the enablers, incentives and barriers to its implementation. The paper synthesises insights from contemporary accounting research into integrated reporting (IR) as a general concept, and integrated reporting as espoused by the IIRC in the (IIRC, 2013). We specifically focus on possible barriers and emphasise the specific issues we feel could be rectified to advance the , along with the areas that may potentially hinder wider adoption and implementation.
Design/methodology/approach: The paper draws upon and synthesises academic analysis and insights provided in the IR and academic literature as well as various directives, policy and framework pronouncements.
Findings: The flexibility and lack of prescription concerning actual disclosures and metrics in the could allow it to be used for compliance, regardless of the other benefits lauded by the IIRC. Thus we see forces, both external and internal, driving adoption, with one prominent example being the European Union Directive on non-financial reporting. Because of the different ways in which IR is understood and enacted, there are numerous theoretical and empirical challenges for academics. Our paper highlights potential areas for further robust academic research, and the need to contribute to policy and practice.
Research limitations/implications: The paper provides the IIRC, academics, regulators and reporting organisations with insights into current practice and the framework. We highlight the need for further development and evidence to help inform improvements both from a policy and a practice perspective. A key limitation of our work is that we draw upon a synthesis of the existing literature which is still in an early stage of development.
Originality/value: The paper provides the IIRC with several insights into the current , and specifically with the enablers, incentives and barriers to its implementation. Also, it provides academic researchers with a number of important observations and an agenda upon which they can build their future research
Masses of Fermions in Supersymmetric Models
We consider the mass generation for the usual quarks and leptons in some
supersymmetric models. The masses of the top, the bottom, the charm, the tau
and the muon are given at the tree level. All the other quarks and the electron
get their masses at the one loop level in the Minimal Supersymmetric Standard
Model (MSSM) and in two Supersymmetric Left-Right Models, one model uses
triplets (SUSYLRT) to break -symmetry and the other use
doublets(SUSYLRD).Comment: 24 pages, 2 figures and 3 table
BeppoSAX observation of the eclipsing dipping X-ray binary X1658-298
Results of a 2000 August 12-13 BeppoSAX observation of the 7.1 hr eclipsing,
dipping, bursting, transient, low-mass X-ray binary (LMXRB) X1658-298 are
presented. The spectrum outside of eclipses, dips and bursts can be modeled by
the combination of a soft disk-blackbody and a harder Comptonized component
with a small amount (1.3 10E21 atom/cm2) of low-energy absorption. In contrast,
an RXTE observation 18 months earlier during the same outburst, measured an
absorption of 5.0 10E22 atom/cm2. Such a change is consistent with a thinning
of the accretion disk as the outburst progresses. Structured residuals from the
best-fit spectral model are present which are tentatively identified with
Ne-K/Fe-L and Fe-K shell emission. The spectral changes during dips are complex
and may be modeled by a strong (~3 10E23 atom/cm2) increase in absorption of
the Comptonized component only, together with reductions in normalizations of
both spectral components. This behavior is in contrast to the ``complex
continuum'' model for X-ray dip sources, where the softer blackbody component
rapidly suffers strong absorption. It is however, similar to that found during
recent XMM-Newton observations of the eclipsing, dipping, LMXRB EXO0748-676.Comment: 11 pages. Accepted for publication in A&A
The first organization meeting will be held on Wednesday afternoon next, the 18th August, at 4 oâclock, at the offices of Smith, Reckitt, Clarke & Co., 62 Wall Street, New York City
Development and Evaluation of an Autonomous Sensor for the Observation of Sediment Motion
Abstract
Measurements within the mobile bed layer have been limited by previous Eulerian-based technologies. A microelectromechanical system device, called a smart sediment grain (SSG), that can measure and record Lagrangian observations of coastal sediments at incipient motion has been developed. These sensors have the potential to resolve fundamental hypotheses regarding the incipient motion of coastal sediments. Angle of repose experiments verified that the sensor enclosure has mobility characteristics similar to coarse gravel. Experiments conducted in a small oscillating flow tunnel verified that the sensors detect incipient motion under various hydrodynamic conditions. Evidence suggests the influence of pressure-gradient-induced sediment motion, contrary to the more commonly assumed bed shear stress criterion. Lagrangian measurements of rotation measured with the newly developed SSG agreed to within 5% of the rotation estimates made simultaneously with high-speed video cameras
Bounds on R-Parity Violating Parameters from Fermion EDM's
We study one-loop contributions to the fermion electric dipole moments in the
Minimal Supersymmetric Standard Model with explicit R-parity violating
interactions. We obtain new individual bounds on R-parity violating Yukawa
couplings and put more stringent limits on certain parameters than those
obtained previously.Comment: 16 pages, LaTe
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