3,333 research outputs found
Modeling the Pulse Profiles of Millisecond Pulsars in the Second LAT Catalog of gamma-ray Pulsars
Significant gamma-ray pulsations have been detected from ~40 millisecond
pulsars (MSPs) using 3 years of sky-survey data from the Fermi LAT and radio
timing solutions from across the globe. We have fit the radio and gamma-ray
pulse profiles of these MSPs using geometric versions of slot gap and outer gap
gamma-ray emission models and radio cone and core models. For MSPs with radio
and gamma-ray peaks aligned in phase we also explore low-altitude slot gap
gamma-ray models and caustic radio models. The best-fit parameters provide
constraints on the viewing geometries and emission sites. While the exact
pulsar magnetospheric geometry is unknown, we can use the increased number of
known gamma-ray MSPs to look for significant trends in the population which
average over these uncertainties.Comment: 4 pages, 2 figures, to appear in the proceedings of the 5th
International Symposium on High-Energy Astronom
The Effect of Different Magnetospheric Structures on Predictions of Gamma-ray Pulsar Light Curves
The second pulsar catalogue of the Fermi Large Area Telescope (LAT) will
contain in excess of 100 gamma-ray pulsars. The light curves (LCs) of these
pulsars exhibit a variety of shapes, and also different relative phase lags
with respect to their radio pulses, hinting at distinct underlying emission
properties (e.g., inclination and observer angles) for the individual pulsars.
Detailed geometric modelling of the radio and gamma-ray LCs may provide
constraints on the B-field structure and emission geometry. We used different
B-field solutions, including the static vacuum dipole and the retarded vacuum
dipole, in conjunction with an existing geometric modelling code, and
constructed radiation sky maps and LCs for several different pulsar parameters.
Standard emission geometries were assumed, namely the two-pole caustic (TPC)
and outer gap (OG) models. The sky maps and LCs of the various B-field and
radiation model combinations were compared to study their effect on the
resulting LCs. As an application, we compared our model LCs with Fermi LAT data
for the Vela pulsar, and inferred the most probable configuration in this case,
thereby constraining Vela's high-altitude magnetic structure and system
geometry.Comment: 6 pages, 4 figures, conference article, appears in Proceedings of
SAIP2012, the 57th Annual Conference of the South African Institute of
Physics, edited by Johan Janse van Rensburg, ISBN: 978-1-77592-070-
Constraining viewing geometries of pulsars with single-peaked gamma-ray profiles using a multiwavelength approach
Since the launch of the Large Area Telescope (LAT) on board the Fermi
spacecraft in June 2008, the number of observed gamma-ray pulsars has increased
dramatically. A large number of these are also observed at radio frequencies.
Constraints on the viewing geometries of 5 of 6 gamma-ray pulsars exhibiting
single-peaked gamma-ray profiles were derived using high-quality radio
polarization data (Weltevrede et al., 2010). We obtain independent constraints
on the viewing geometries of 6 by using a geometric emission code to model the
Fermi LAT and radio light curves (LCs). We find fits for the magnetic
inclination and observer angles by searching the solution space by eye. Our
results are generally consistent with those previously obtained (Weltevrede et
al., 2010), although we do find small differences in some cases. We will
indicate how the gamma-ray and radio pulse shapes as well as their relative
phase lags lead to constraints in the solution space. Values for the flux
correction factor corresponding to the fits are also derived (with errors).Comment: 6 pages, 2 figures, 1 table, Proceedings of SAIP2011, the 56th Annual
Conference of the South African Institute of Physics (ISBN:
978-1-86888-688-3), ed. I. Basson and A. E. Botha, http://www.saip.org.za,
pp. 531-53
Enhanced Accessibility for People with Disabilities Living in Urban Areas
[Excerpt] People with disabilities constitute a significant proportion of the poor in developing countries. If internationally agreed targets on reducing poverty are to be reached, it is critical that specific measures be taken to reduce the societal discrimination and isolation that people with disabilities continue to face. Transport is an important enabler of strategies to fight poverty through enhancing access to education, employment, and social services.
This project aims to further the understanding of the mobility and access issues experienced by people with disabilities in developing countries, and to identify specific steps that can be taken to start addressing problems. A major objective of the project is to compile a compendium of guidelines that can be used by government authorities, advocacy groups, and donor/loan agencies to improve the access of people with disabilities to transport and other services in urban areas
The safety and efficacy of the propofol/ Alfentanil/ Ketamine-bolus technique in midazolam pre-medicated patients undergoing office based plastic or reconstructive surgery
Magister Scientiae - MScThe purpose of this research project was to assess the safety and efficacy of a combination of drugs for conscious sedation in patients undergoing office-based plastic and reconstructive surgery. A pilot study was done to determine the safety of the co-administration of the drugs used in the sedation technique.South Afric
Prediking oor politieke sake - riglyne vanuit Romeine 12-15
Preaching on political issues is a very topical matter, especially in the current situation in South Africa. This matter is extensively dealt with in literature in the field of the Old and New Testament, Homiletics and Ethics. The aim with this article is to explore the Pauline paranesis in Romans 12-15 to discern concrete guidelines on handling political issues in preaching. As point of departure the expression God’s mercy (Romans 12:1) is investigated closely, as the concept of God’s mercy is the foundation stone of the total paranesis in Romans 12-15. Regarding preaching on political issues, the fact that the new aeon has already come and will finally come, leads to certain conclusions. The responsibility of the congregation to test and approve what God's will is - also in political matters - is stressed. The kingdom of God as the predominant kingdom, relativises earthly (political) kingdoms. The responsibility to equip the congregation to discern political issues in the light of Scripture is dealt with in this regard. Finally, perspectives are given on the relation between state and believer. In conclusion the command to Christians to love each other as believers, to live in peace with everyone and to love enemies is also highlighted
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