91,933 research outputs found
Toward an understanding of thermal X-ray emission of pulsars
We present a theoretical model for the thermal X-ray emission and cooling of
isolated pulsars, assuming that pulsars are solid quark stars. We calculate the
heat capacity for such a quark star, and the results show that the residual
thermal energy cannot sustain the observed thermal X-ray luminosities seen in
typical isolated X-ray pulsars. We conclude that other heating mechanisms must
be in operation if the pulsars are in fact solid quark stars. Two possible
heating mechanisms are explored. Firstly, for pulsars with little
magnetospheric activities, accretion from the interstellar medium or from the
material in the associated supernova remnants may power the observed thermal
emission. In the propeller regime, a disk-accretion rate 1% of
the Eddington rate with an accretion onto the stellar surface at a rate of
could explain the observed emission luminosities of the
dim isolated neutron stars and the central compact objects. Secondly, for
pulsars with significant magnetospheric activities, the pulsar spindown
luminosities may have been as the sources of the thermal energy via reversing
plasma current flows. A phenomenological study between pulsar bolometric X-ray
luminosities and the spin energy loss rates presents the probable existence of
a 1/2-law or a linear law, i.e. or
. This result together with the thermal
properties of solid quark stars allow us to calculate the thermal evolution of
such stars. Thermal evolution curves, or cooling curves, are calculated and
compared with the `temperature-age' data obtained from 17 active X-ray pulsars.
It is shown that the bolometric X-ray observations of these sources are
consistent with the solid quark star pulsar model.Comment: Astroparticle Physics Accepte
A Phone Learning Model for Enhancing Productivity of Visually Impaired Civil Servants
Phone-based learning in civil service is the use of voice technologies to deliver learning and capacity building training services to
government employees. The Internet revolution and advancement in Information and Communications Technology (ICT) have given rise
to online and remote staff training for the purpose of enhancing workers productivity. The need for civil servants in Nigeria to develop
capacity that will enhance knowledge is a key requirement to having competitive advantage in the work place. Existing online learning
platforms (such as web-based learning, mobile learning, etc) did not consider the plight of the visually impaired. These platforms provide
graphical interfaces that require sight to access. The visually impaired civil servants require auditory access to functionalities that exist in
learning management system on the Internet. Thus a gap exist between the able-bodied and visually impaired civil servants on
accessibility to e-learning platform. The objective of this paper is to provide a personalized telephone learning model and a prototype
application that will enhance the productivity of the visually impaired workers in Government establishments in Nigeria. The model was
designed using Unified Modeling Language (UML) diagram. The prototype application was implemented and evaluated. With the
proposed model and application, the visually and mobility impaired worker are able to participate in routine staff training and
consequently enhances their productivity just like their able-bodied counterparts. The prototype application also serves as an alternative
training platform for the able-bodied workers. Future research direction for this study will include biometric authentication of learners
accessing the applicatio
Interactions between a massless tensor field with the mixed symmetry of the Riemann tensor and a massless vector field
Consistent couplings between a massless tensor field with the mixed symmetry
of the Riemann tensor and a massless vector field are analyzed in the framework
of Lagrangian BRST cohomology. Under the assumptions on smoothness, locality,
Lorentz covariance, and Poincare invariance of the deformations, combined with
the requirement that the interacting Lagrangian is at most second-order
derivative, it is proved that there are no consistent cross-interactions
between a single massless tensor field with the mixed symmetry of the Riemann
tensor and one massless vector field.Comment: LaTeX, 24 page
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