9,517 research outputs found
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. IV. The Parent Luminosity Function of Radio-Loud Blazars
(Abridged) We use a complete sample of active galactic nuclei (AGN) selected
on the basis of relativistically beamed 15 GHz radio flux density to derive the
parent radio luminosity function (RLF) of bright radio-selected blazar cores.
We use a maximum likelihood method to fit a beamed RLF to the observed data and
thereby recover the parameters of the intrinsic (unbeamed) RLF. We analyze two
subsamples of the MOJAVE sample: the first contains only objects of known FR II
class, with a total of 103 sources, and the second subsample adds 24 objects of
uncertain FR class for a total of 127 sources. Both subsamples exclude four
known FR I radio galaxies and two gigahertz-peaked spectrum sources. We obtain
good fits to both subsamples using a single power law intrinsic RLF with pure
density evolution function. We find that a previously reported break in the
observed MOJAVE RLF actually arises from using incomplete bins (because of the
luminosity cutoff) across a steep and strongly evolving RLF, and does not
reflect a break in the intrinsic RLF. The derived space density of the parent
population of the FR II sources from the MOJAVE sample (with L>1.3e25 W/Hz) is
approximately 1600/Gpc^3.Comment: 31 pages, 7 figures and 2 tables. Accepted for publication in ApJ.
Changes: classification of sources based on radio morphology instead of
optical classes; added the parameters of the RLF of the FR II sources; added
more explanations; added a table listing the sample sources; added 2 extra
figures related to the observed break in the RLF; updated reference
A focus group study of student attitudes to lectures
This paper reports on the findings from focus groups, conducted at Macquarie University, on the attitudes of computing students to lectures. Students felt that two things were vital for a good lecture: (1) that the lecturer goes beyond what is written in the lecture notes; (2) that the lecture is interactive, by which students meant that the lecturer asks if students understand concepts and adjusts the delivery accordingly, and also the lecturer answers the students' questions. The students in the focus groups also discussed what makes for a bad lectures: (1) lecturers reading straight from slides; (2) lecturers who 'blame the students', by saying that students don't work hard enough and are too lazy to turn up to lectures; and (3) lecturers who cover the material too slowly or too quickly. The most prominent reason given for not attending lectures was the timetabling of lectures in such a way that students had too few classes in one day to make the sojourn to university worthwhile. Any university seeking to improve attendance at lectures should perhaps look as much to improving its timetabling practices as it does to improving the practices of its individual lecturers. © 2009, Australian Computer Society, Inc
Faraday rotation in the MOJAVE blazars: 3C 273 a case study
Radio polarimetric observations of Active Galactic Nuclei can reveal the
magnetic field structure in the parsec-scale jets of these sources. We have
observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with
the Very Long Baseline Array to study Faraday rotation in a large sample of
jets. Our observations re-confirm the transverse rotation measure gradient in
3C 273. For the first time the gradient is seen to cross zero which is further
indication for a helical magnetic field and spine-sheath structure in the jet.
We believe the difference to previous epochs is due to a different part of the
jet being illuminated in our observations.Comment: 6 pages, 3 figures. To appear in the proceedings of "Beamed and
Unbeamed Gamma-rays from Galaxies", held in Muonio, Finland, April 11-15,
2011. Journal of Physics: Conference Serie
Kinematics of parsec-scale structures in AGN: the 2cm VLBA Survey
We are investigating the kinematics of jets in active galactic nuclei on
parsec scales by studying a representative population of sources. This study is
being carried out using the Very Long Baseline Array at 15 GHz, with more than
800 images taken since 1994. In this contribution we present an overview of the
diversity of kinematics for a complete sample of sources.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E.,
Porcas R.W., Lobanov, A.P., & Zensus, J.A. (eds), MPIfR, Bonn, Germany. 2
pages, 3 figures, needs evn2002.cls style fil
Relativistic Phenomena in Active Galactic Nuclei
The idea that the radio jets in AGN contain material in relativistic motion
is supported by many lines of observational evidence, including morphology,
brightness temperature estimated with interferometers and with intrinsic
variations, interstellar scintillations, X-rays, and superluminal motion. These
are largely independent, and taken together make an irrefutable case for
relativistic motion.Comment: 16 pages, 8 Figures. To appear in "Radio Astronomy at 70: from Karl
Jansky to microjansky", eds. L.I.Gurvits, S.Frey, S.Rawlings, 2004, EDP
Sciences, in pres
Variability and Velocity of Superluminal Sources
We investigate the relation between the Doppler factor determined from
variations in total flux at 22 and 37 GHz, and the apparent transverse velocity
determined from VLBA observations at 2 cm. The data are consistent with the
relativistic beaming theory for compact radio sources, in that the distribution
of beta_{app}/delta_{var}, for 30 quasars, is roughly consistent with a Monte
Carlo simulation. The intrinsic temperature appears to be ~2x10^{10} K, close
to the "equipartition value" calculated by Readhead (1994). We deduce the
distribution of Lorentz factors for a group of 48 sources; the values range up
to about gamma=40.Comment: To be published in "Radio Astronomy at the Fringe", ASP Conf. Ser.
Vol. 300, J. A. Zensus, M. H. Cohen, & E. Ros (eds.), 8 pages, 3 figures,
needs rafringe.st
Relationships between reading, tracing and writing skills in introductory programming
This study analyzed student responses to an examination, after the students had completed one semester of instruction in programming. The performance of students on code tracing tasks correlated with their performance on code writing tasks. A correlation was also found between performance on "explain in plain English" tasks and code writing. A stepwise regression, with performance on code writing as the dependent variable, was used to construct a path diagram. The diagram suggests the possibility of a hierarchy of programming related tasks. Knowledge of programming constructs forms the bottom of the hierarchy, with "explain in English", Parson's puzzles, and the tracing of iterative code forming one or more intermediate levels in the hierarchy. Copyright 2008 ACM
Naive Bayesian prediction of bleeding after heart by-pass surgery
© 2001 ARCME, Univ of WA. Excessive post-operative bleeding occurs in approximately one out of eight patients who undergo heart bypass surgery. Earlier workers have identified laboratory parameters that are correlated with post-operative blood loss but these correlations are not strong enough to be clinically useful. This paper describes a predictor that combines several of these parameters using Naive Bayesian Reasoning, to produce a clinically useful predictor of blood loss
The Two Fluid Drop Snap-off Problem: Experiments and Theory
We address the dynamics of a drop with viscosity breaking up
inside another fluid of viscosity . For , a scaling theory
predicts the time evolution of the drop shape near the point of snap-off which
is in excellent agreement with experiment and previous simulations of Lister
and Stone. We also investigate the dependence of the shape and
breaking rate.Comment: 4 pages, 3 figure
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