994 research outputs found
A low-cost implementation of coroutines for C
We identify a set of primitive operations supporting coroutines, and demonstrate their usefulness. We then address their implementation in C according to a set of criteria aimed at maintaining simplicity, and achieve a satisfactory compromise between it and effectiveness. Our package for the PDP-II under UNIX allows users of coroutines in C programs to gain access to the primitives via an included definitions file and an object library; no penalty is imposed upon non-coroutine users
A semantically-based formatting discipline for Pascal
The abstract (or semantic) syntax of the Pascal language IS identIfied and a linear representation for the trees so formed within tne framework of the concrete syntax for that language is imposed. The indentation seneme 50 formed. augmented with a small number of pragmaticconsiaerations. is compared with several previously proposed formatting schemes for Pascal and an example of rne use of tnls new method is given
A bright millisecond radio burst of extragalactic origin
Pulsar surveys offer one of the few opportunities to monitor even a small
fraction (~0.00001) of the radio sky for impulsive burst-like events with
millisecond durations. In analysis of archival survey data, we have discovered
a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small
Magellanic Cloud. The burst properties argue against a physical association
with our Galaxy or the Small Magellanic Cloud. Current models for the free
electron content in the Universe imply a distance to the burst of <1 Gpc No
further bursts are seen in 90-hr of additional observations, implying that it
was a singular event such as a supernova or coalescence of relativistic
objects. Hundreds of similar events could occur every day and act as insightful
cosmological probes.Comment: 18 pages, 4 figures. Accepted by Science. Published electronically
via Science Express on September 27, 200
Optical Observations of the Binary Millisecond Pulsars J2145-0750 and J0034-0534
We report on optical observations of the low-mass binary millisecond pulsar
systems J0034-0534 and J2145-0750. A faint (I=23.5) object was found to be
coincident with the timing position of PSR J2145-0750. While a galaxy or
distant main-sequence star cannot be ruled out, its magnitude is consistent
with an ancient white dwarf, as expected from evolutionary models. For PSR
J0034-0534 no objects were detected to a limiting magnitude of R=25.0,
suggesting that the white dwarf in this system is cold. Using white dwarf
cooling models, the limit on the magnitude of the PSR J0034-0534 companion
suggests that at birth the pulsar in this system may have rotated with a period
as short as 0.6 ms. These observations provide further evidence that the
magnetic fields of millisecond pulsars do not decay on time scales shorter than
1 Gyr.Comment: 6 pages, uuencoded, gz -9 compressed postscript, accepted by ApJ
Timing models for the long-orbital period binary pulsar PSR B1259-63
The pulsar PSR B1259-63 is in a highly eccentric 3.4-yr orbit with the Be
star SS 2883. Timing observations of this pulsar, made over a 7-yr period using
the Parkes 64-m radio telescope, cover two periastron passages, in 1990 August
and 1994 January. The timing data cannot be fitted by the normal pulsar and
Keplerian binary parameters. A timing solution including a (non-precessing)
Keplerian orbit and timing noise (represented as a polynomial of fifth order in
time) provide a satisfactory fit to the data. However, because the Be star
probably has a significant quadrupole moment, we prefer to interpret the data
by a combination of timing noise, dominated by a cubic phase term, and
and terms. We show that the and are
likely to be a result of a precessing orbit caused by the quadrupole moment of
the tilted companion star. We further rule out a number of possible physical
effects which could contribute to the timing data of PSR B1259-63 on a
measurable level.Comment: LaTeX, 9 pages, 8 figures, accepted for publication in MNRA
Visual acuity as a function of hydrophilic lens topography
Visual acuity as a function of hydrophilic lens topograph
Control in the technical societies: a brief history
By the time control engineering emerged as a coherent body of knowledge and practice (during and just after WW2) professional engineering societies had existed for many decades. Since control engineering is an interdisciplinary branch of the profession, new sections devoted to control were quickly established within the various existing technical societies. In addition, some new bodies devoted specifically or primarily to control were established. This article, a revised version of a paper presented at the IEEE 2009 Conference on the History of Technical Societies, describes how control engineering as a distinct branch of engineering became represented in technical societies in a number of countries
Furnishing the Galaxy with Pulsars
The majority of pulsar population synthesis studies performed to date have
focused on isolated pulsar evolution. Those that have incorporated pulsar
evolution within binary systems have tended to either treat binary evolution
poorly of evolve the pulsar population in an ad-hoc manner. Here we present the
first model of the Galactic field pulsar population that includes a
comprehensive treatment of both binary and pulsar evolution. Synthetic
observational surveys mimicking a variety of radio telescopes are then
performed on this population. As such, a complete and direct comparison of
model data with observations of the pulsar population within the Galactic disk
is now possible. The tool used for completing this work is a code comprised of
three components: stellar/binary evolution, Galactic kinematics and survey
selection effects. Here we give a brief overview of the method and assumptions
involved with each component. Some preliminary results are also presented as
well as plans for future applications of the code.Comment: 3 pages, 3 figures, Conference: "40 years of pulsars: Millisecond
pulsars, magnetars and more", McGill University, Montreal, Canada, ed.
A.Cumming et al., AI
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