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Symbolic execution and the testing of COBOL programs
The thesis is in two parts. Part one is a review of existing work in the area of software testing and more specifically symbolic execution. Part two is a description of the symbolic execution testing system for COBOL (SYM-BOL). Much of the work presented has been published or accepted for publication.
Part one commences by introducing the aims of software testing and is followed by a review of the tools and techniques of software testing that have been developed over the past 25 years. A simple taxonomy of software testing techniques is given. One potentially powerful technique is symbolic execution. The principles of symbolic execution are described followed by the problems in applying symbolic execution. Part one is completed by a review of existing symbolic execution testing systems. No symbolic execution testing system has previously been built for a commercial data processing language such as COBOL. Part two commences by outlining the features of the SYM-BOL system and describes the user strategies that may be employed when using the system.
The system generates an intermediate form in stages by transforming the source program into one that contains only a limited number of language constructs. Path selection can be automatic or undertaken by the user. In both cases the results of the symbolic execution already undertaken are available to the path selector to help reduce the likelihood of selecting an infeasible path. A description of how the Nag-library linear optimizer E04MBF is used for feasibility checking is given. Feasible solutions are turned into files of test cases. Simple assertions may be included in the source program which do not affect the normal execution of the software but which can be verified by inclusion in the symbolic execution
The detection efficiency of on-axis short gamma ray burst optical afterglows triggered by aLIGO/Virgo
Assuming neutron star (NS) or neutron star/stellar-mass black hole (BH)
mergers as progenitors of the short gamma ray bursts, we derive and demonstrate
a simple analysis tool for modelling the efficiency of recovering on-axis
optical afterglows triggered by a candidate gravitational wave event detected
by the Advanced LIGO and Virgo network. The coincident detection efficiency has
been evaluated for different classes of operating telescopes using observations
of gamma ray bursts. We show how the efficiency depends on the luminosity
distribution of the optical afterglows, the telescope features, and the sky
localisation of gravitational wave triggers. We estimate a plausible optical
afterglow and gravitational wave coincidence rate of 1 yr (0.1
yr) for NS-NS (NS-BH), and how this rate is scaled down in detection
efficiency by the time it takes to image the gravitational wave sky
localization and the limiting magnitude of the telescopes. For NS-NS (NS-BH) we
find maximum detection efficiencies of when the total imaging time is
less than 200 min (80 min) and the limiting magnitude fainter than 20 (21). We
show that relatively small telescopes can achieve similar detection
efficiencies to meter class facilities with similar fields of view,
only if the less sensitive instruments can respond to the trigger and image the
field within 10-15 min. The inclusion of LIGO India into the gravitational wave
observatory network will significantly reduce imaging time for telescopes with
limiting magnitudes but with modest fields of view. An optimal
coincidence search requires a global network of sensitive and fast response
wide field instruments that could effectively image relatively large
gravitational-wave sky localisations and produce transient candidates for
further photometric and spectroscopic follow-up.Comment: 6 pages, 2 figures, version 2, reference added typo correction,
Accepted by MNRA
Detection regimes of the cosmological gravitational wave background from astrophysical sources
Key targets for gravitational wave (GW) observatories, such as LIGO and the
next generation interferometric detector, Advanced LIGO, include core-collapse
of massive stars and the final stage of coalescence of compact stellar
remnants. The combined GW signal from such events occurring throughout the
Universe will produce an astrophysical GW background (AGB), one that is
fundamentally different from the GW background by very early Universe
processes. One can classify contributions to the AGB for different classes of
sources based on the strength of the GW emissions from the individual sources,
their peak emission frequency, emission duration and their event rate density
distribution. This article provides an overview of the detectability regimes of
the AGB in the context of current and planned gravitational wave observatories.
We show that there are two important AGB signal detection regimes, which we
define as `continuous' and `popcorn noise'. We describe how the `popcorn noise'
AGB regime evolves with observation time and we discuss how this feature
distinguishes it from the GW background produced from very early Universe
processes.Comment: accepted for publication in New Astronomy Reviews; 23 pages and 2
figure
Nuclear Equation of State from Observations of Short Gamma-Ray Burst Remnants
The favoured progenitor model for short -ray bursts (SGRBs) is the
merger of two neutron stars that triggers an explosion with a burst of
collimated -rays. Following the initial prompt emission, some SGRBs
exhibit a plateau phase in their -ray light curves that indicates additional
energy injection from a central engine, believed to be a rapidly rotating,
highly magnetised neutron star. The collapse of this `protomagnetar' to a black
hole is likely to be responsible for a steep decay in -ray flux observed at
the end of the plateau. In this letter, we show that these observations can be
used to effectively constrain the equation of state of dense matter. In
particular, we show that the known distribution of masses in binary neutron
star systems, together with fits to the -ray light curves, provide
constraints that exclude the softest and stiffest plausible equations of state.
We further illustrate how a future gravitational wave observation with Advanced
LIGO/Virgo can place tight constraints on the equation of state, by adding into
the picture a measurement of the chirp mass of the SGRB progenitor.Comment: accepted for publication in Phys. Rev.
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