Fallback disks, magnetars and other neutron stars

The presence of matter with angular momentum, in the form of a fallback disk around a young isolated neutron star will determine its evolution. This leads to an understanding of many properties of different classes of young neutron stars, in particular a natural explanation for the period clustering of AXPs, SGRs and XDINs. The spindown or spinup properties of a neutron star are determined by the dipole component of the magnetic field. The natural possibility that magnetars and other neutron stars may have different strengths of the dipole and higher multipole components of the magnetic field is now actually required by observations on the spindown rates of some magnetars. This talk gives a broad overview and some applications of the fallback disk model to particular neutron stars. Salient points are: (i) A fallback disk has already been observed around the AXP 4U 0142+61 some years ago. (ii) The low observed spindown rate of the SGR 0418+5729 provides direct evidence that the dipole component of the field is in the 1012G range. All properties of the SGR 0418+5729 at its present age can be explained by spindown under torques from a fallback disk. (iii) The anomalous braking index of PSR J1734-3333 can also be explained by the fallback disk model which gives the luminosity, period, period derivative and the period second derivative at the present age. (iv) These and all applications to a variety of other sources employ the same disk physics and evolution, differing only in the initial conditions of the disk

Evaluation of Noise Performance of Multi-Lane Highways in the State of Qatar

In recent years, a growing number of people are complaining to transportation authorities for the traffic noise as a result of increased traffic volume on the highways. Therefore, transportation authorities are actively pursuing ways to reduce the traffic noise. In recent years, quieter pavement has become one of the cost-effective ways of sustainable highway noise reduction. However, for design and construction of quieter pavements, proper and accurate noise measurement is of paramount importance for evaluating the noise level of existing pavement as well as evaluating noise level of newly constructed pavements. In this study, the variation of noise level among different lanes of existing multi-lane highways in the State of Qatar was examined. Tire-pavement noise was measured by using onboard sound intensity (OBSI) technique. OBSI test results showed that highest noise level was observed at outer lane of multilane highways. This is probably due to the pavement distress caused by the heavy vehicle travelling at the outer lane of multi-lane highways.This paper was made possible by the NPRP grant (NPRP 7-110-2-056) from the Qatar National Research Fund (a member of Qatar Foundation)Scopu

On fallback disks and magnetars

The discovery of a disk around the anomalous X-ray pulsar 4U 0142+61, has rekindled the interest in fallback disks around magnetars. We briefly review the assumptions of fallback disk models and magnetar models. Earlier data in optical and near IR bands combined with new Spitzer data in the mid-IR range are compatible with a gas disk. Higher multipole fields with magnetar strengths together with a dipole field of 1012-1013 G on the neutron star surface are compatible with the presence of a disk around the neutron star. The possible presence and properties of a fallback disk after the supernova explosion is a likely initial condition to complement the initial rotation period and initial dipole field in determining the evolutionary paths and different types of isolated neutron stars

A natural limit on the observable periods of anomalous x-ray pulsars and soft gamma-ray repeaters

We investigate the dependence of the evolution of neutron stars with fallback disks on the strength of the magnetic dipole field of the star. Using the same model as employed by Ertan et al. (2009), we obtain model curves for different dipole fields showing that the neutron stars with magnetic dipole fields greater than ∼ 1013 G on the surface of the star are not likely to become anomalous X‐ray pulsars (AXPs) and soft gamma‐ray repeaters (SGRs). Other sources with conventional dipole fields evolve into the AXP phase if their disk can penetrate the light cylinder. The upper limits to the observed periods of AXP and SGRs could be understood if the disk becomes inactive below a low temperature around 100 K. We summarize our present and earlier results indicated by the evolutionary model curves of these sources with an emphasis on the importance of the minimum disk temperature and the X‐ray irradiation in the long‐term evolution of AXPs and SGRs with fallback disks

Using ontological contexts to assess the relevance of statements in ontology evolution

Ontology evolution tools often propose new ontological changes in the form of statements. While different methods exist to check the quality of such statements to be added to the ontology (e.g., in terms of consistency and impact), their relevance is usually left to the user to assess. Relevance in this context is a notion of how well the statement fits in the target ontology. We present an approach to automatically assess such relevance. It is acknowledged in cognitive science and other research areas that a piece of information flowing between two entities is relevant if there is an agreement on the context used between the entities. In our approach, we derive the context of a statement from online ontologies in which it is used, and study how this context matches with the target ontology. We identify relevance patterns that give an indication of rele- vance when the statement context and the target ontology fulfill specific conditions. We validate our approach through an experiment in three dif- ferent domains, and show how our pattern-based technique outperforms a naive overlap-based approach

OntoMathPROOntoMath^{PRO} Ontology: A Linked Data Hub for Mathematics

In this paper, we present an ontology of mathematical knowledge concepts that covers a wide range of the fields of mathematics and introduces a balanced representation between comprehensive and sensible models. We demonstrate the applications of this representation in information extraction, semantic search, and education. We argue that the ontology can be a core of future integration of math-aware data sets in the Web of Data and, therefore, provide mappings onto relevant datasets, such as DBpedia and ScienceWISE.Comment: 15 pages, 6 images, 1 table, Knowledge Engineering and the Semantic Web - 5th International Conferenc

Long-term evolution of dim isolated neutron stars

The X-ray dim isolated neutron stars (XDINs) have periods in the same range as the anomalous X-ray pulsars (AXPs) and the soft gamma-ray repeaters (SGRs). We apply the fallback disc model, which explains the period clustering and other properties of AXP/SGRs, to the six XDINs with measured periods and period derivatives. Present properties of XDINs are obtained in evolutionary scenarios with surface dipole magnetic fields B-0 similar to 10(12) G. The XDINs have gone through an accretion epoch with rapid spin-down earlier, and have emerged in their current state, with the X-ray luminosity provided by neutron star cooling and no longer by accretion. Our results indicate that the known XDINs are not likely to be active radio pulsars, as the low B-0, together with their long periods place these sources clearly below the 'death valley'