371 research outputs found
Continuous Experimentation for Automotive Software on the Example of a Heavy Commercial Vehicle in Daily Operation
As the automotive industry focuses its attention more and more towards the
software functionality of vehicles, techniques to deliver new software value at
a fast pace are needed. Continuous Experimentation, a practice coming from the
web-based systems world, is one of such techniques. It enables researchers and
developers to use real-world data to verify their hypothesis and steer the
software evolution based on performances and user preferences, reducing the
reliance on simulations and guesswork. Several challenges prevent the verbatim
adoption of this practice on automotive cyber-physical systems, e.g., safety
concerns and limitations from computational resources; nonetheless, the
automotive field is starting to take interest in this technique. This work aims
at demonstrating and evaluating a prototypical Continuous Experimentation
infrastructure, implemented on a distributed computational system housed in a
commercial truck tractor that is used in daily operations by a logistic company
on public roads. The system comprises computing units and sensors, and software
deployment and data retrieval are only possible remotely via a mobile data
connection due to the commercial interests of the logistics company. This study
shows that the proposed experimentation process resulted in the development
team being able to base software development choices on the real-world data
collected during the experimental procedure. Additionally, a set of previously
identified design criteria to enable Continuous Experimentation on automotive
systems was discussed and their validity confirmed in the light of the
presented work.Comment: Paper accepted to the 14th European Conference on Software
Architecture (ECSA 2020). 16 pages, 5 figure
Improving model quality through foundational ontologies: Two contrasting approaches to the representation of roles
Several foundational ontologies have been developed recently. We examine two of these from the point of view of their quality in representing temporal changes, focusing on the example of roles. We discuss how these are modelled in two foundational ontologies: the Unified Foundational Ontology and the BORO foundational ontology. These exhibit two different approaches, endurantist and perdurantist respectively. We illustrate the differences using a running example in the university student domain, wherein one individual is not only a registered student but also, for part of this period, was elected the President of the Student Union. The metaphysical choices made by UFO and BORO lead to different representations of roles. Two key differences which affect the way roles are modelled are exemplified in this paper: (1) different criteria of identity and (2) differences in the way individual objects extend over time and possible worlds. These differences impact upon the quality of the models produced in terms of their respective explanatory power. The UFO model concentrates on the notion of validity in “all possible worlds” and is unable to accurately represent the way particulars are extended in time. The perdurantist approach is best able to describe temporal changes wherein roles are spatio-temporal extents of individuals
The bright Gamma-Ray Burst of February 10, 2000: a case study of an optically dark GRB
The gamma-ray burst GRB000210 had the highest gamma-ray peak flux of any
event localized by BeppoSAX as yet but it did not have a detected optical
afterglow. It is therefore one of the events recently classified as dark GRBs
or GHOST (GRB Hiding Optical Source Transient), whose origin is still unclear.
Chandra observations allowed us to localize this GRB within ~1" and a radio
transient was detected with the VLA. We identify the likely (P=0.01) host
galaxy of this burst at z=0.846. The X-ray spectrum of the afterglow shows
intrinsic absorption N_H=5x10**21 cm-2. The amount of dust needed to absorb the
optical flux of this object is consistent with the above HI column density,
given a dust-to-gas ratio similar to that of our Galaxy. We do not find
evidence for a partially ionized absorber expected if the absorption takes
place in a Giant Molecular Cloud. We therefore conclude that either the gas is
local to the GRB, but is condensed in small-scale high-density (n>~10**9 cm-3)
clouds, or that the GRB is located in a dusty, gas-rich region of the galaxy.
Finally, if GRB000210 lies at z>5, its X-ray absorbing medium would have to be
substantially different from that observed in GRBs with optical afterglows.Comment: 29 pages, 7 fig.s, some revisions, ApJ, in pres
Optical and Radio Observations of the Afterglow from GRB990510: Evidence for a Jet
We present multi-color optical and two-frequency radio observations of the
bright SAX event, GRB 990510. The well-sampled optical decay, together with the
radio observations are inconsistent with simple spherical afterglow models. The
achromatic optical steepening and the decay of the radio afterglow both
occuring at day are evidence for hydrodynamical evolution of the
source, and can be most easily interpreted by models where the GRB ejecta are
collimated in a jet. Employing a simple jet model to interpret the
observations, we derive a jet opening angle of , reducing the
isotropic gamma-ray emission of erg by a factor . If the jet interpretation is correct, we conclude that GRB observations
to-date are consistent with an energy for the central source of E \lsim
10^{52} erg.Comment: 12 pages, 2 figures. Version accepted for publication in ApJ Letter
Swings between rotation and accretion power in a millisecond binary pulsar
It is thought that neutron stars in low-mass binary systems can accrete
matter and angular momentum from the companion star and be spun-up to
millisecond rotational periods. During the accretion stage, the system is
called a low-mass X-ray binary, and bright X-ray emission is observed. When the
rate of mass transfer decreases in the later evolutionary stages, these
binaries host a radio millisecond pulsar whose emission is powered by the
neutron star's rotating magnetic field. This evolutionary model is supported by
the detection of millisecond X-ray pulsations from several accreting neutron
stars and also by the evidence for a past accretion disc in a rotation-powered
millisecond pulsar. It has been proposed that a rotation-powered pulsar may
temporarily switch on during periods of low mass inflow in some such systems.
Only indirect evidence for this transition has hitherto been observed. Here we
report observations of accretion-powered, millisecond X-ray pulsations from a
neutron star previously seen as a rotation-powered radio pulsar. Within a few
days after a month-long X-ray outburst, radio pulses were again detected. This
not only shows the evolutionary link between accretion and rotation-powered
millisecond pulsars, but also that some systems can swing between the two
states on very short timescales.Comment: 43 pages, 9 figures, 4 table. Published by Nature on 26 Sep 2013.
Includes Supplementary information. Minor differences with published version
may exis
BeppoSAX Observations of GRB980425: Detection of the Prompt Event and Monitoring of the Error Box
We present BeppoSAX follow-up observations of GRB980425 obtained with the
Narrow Field Instruments (NFI) in April, May, and November 1998. The first NFI
observation has detected within the 8' radius error box of the GRB an X-ray
source positionally consistent with the supernova 1998bw, which exploded within
a day of GRB980425, and a fainter X-ray source, not consistent with the
position of the supernova. The former source is detected in the following NFI
pointings and exhibits a decline of a factor of two in six months. If it is
associated with SN 1998bw, this is the first detection of X-ray emission from a
Type I supernova above 2 keV. The latter source exhibits only marginally
significant variability. The X-ray spectra and variability of the supernova are
compared with thermal and non-thermal models of supernova high energy emission.
Based on the BeppoSAX data, it is not possible to firmly establish which of the
two detected sources is the GRB X-ray counterpart, although probability
considerations favor the supernova.Comment: 16 pages, Latex, 6 PostScript figures and 1 GIF figure, 2 tables,
submitted to The Astrophysical Journa
Long-term spectral and timing properties of the soft gamma-ray repeater SGR 1833-0832 and detection of extended X-ray emission around the radio pulsar PSR B1830-08
SGR 1833-0832 was discovered on 2010 March 19 thanks to the Swift detection
of a short hard X-ray burst and follow-up X-ray observations. Since then, it
was repeatedly observed with Swift, Rossi X-ray Timing Explorer, and
XMM-Newton. Using these data, which span about 225 days, we studied the
long-term spectral and timing characteristics of SGR 1833-0832. We found
evidence for diffuse emission surrounding SGR 1833-0832, which is most likely a
halo produced by the scattering of the point source X-ray radiation by dust
along the line of sight, and we show that the source X-ray spectrum is well
described by an absorbed blackbody, with temperature kT=1.2 keV and absorbing
column nH=(10.4+/-0.2)E22 cm^-2, while different or more complex models are
disfavoured. The source persistent X-ray emission remained fairly constant at
about 3.7E-12 erg/cm^2/s for the first 20 days after the onset of the bursting
episode, then it faded by a factor 40 in the subsequent 140 days, following a
power-law trend with index alpha=-0.5. We obtained a phase-coherent timing
solution with the longest baseline (225 days) to date for this source which,
besides period P=7.5654084(4) s and period derivative dP/dt=3.5(3)E-12 s/s,
includes higher order period derivatives. We also report on our search of the
counterpart to the SGR at radio frequencies using the Australia Telescope
Compact Array and the Parkes radio telescope. No evidence for radio emission
was found, down to flux densities of 0.9 mJy (at 1.5 GHz) and 0.09 mJy (at 1.4
GHz) for the continuum and pulsed emissions, respectively, consistently with
other observations at different epochs.Comment: 12 pages, 7 colour figures and 3 tables, accepted for publication in
MNRAS. Figure 6 in reduced quality and abstract abridged for astro-ph
submissio
Milestones in the Observations of Cosmic Magnetic Fields
Magnetic fields are observed everywhere in the universe. In this review, we
concentrate on the observational aspects of the magnetic fields of Galactic and
extragalactic objects. Readers can follow the milestones in the observations of
cosmic magnetic fields obtained from the most important tracers of magnetic
fields, namely, the star-light polarization, the Zeeman effect, the rotation
measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio
polarization observations, as well as the newly implemented sub-mm and mm
polarization capabilities.
(Another long paragraph is omitted due to the limited space here)Comment: Invited Review (ChJA&A); 32 pages. Sorry if your significant
contributions in this area were not mentioned. Published pdf & ps files (with
high quality figures) now availble at http://www.chjaa.org/2002_2_4.ht
A Relativistic Type Ibc Supernova Without a Detected Gamma-ray Burst
Long duration gamma-ray bursts (GRBs) mark the explosive death of some
massive stars and are a rare sub-class of Type Ibc supernovae (SNe Ibc). They
are distinguished by the production of an energetic and collimated relativistic
outflow powered by a central engine (an accreting black hole or neutron star).
Observationally, this outflow is manifested in the pulse of gamma-rays and a
long-lived radio afterglow. To date, central engine-driven SNe have been
discovered exclusively through their gamma-ray emission, yet it is expected
that a larger population goes undetected due to limited satellite sensitivity
or beaming of the collimated emission away from our line-of-sight. In this
framework, the recovery of undetected GRBs may be possible through radio
searches for SNe Ibc with relativistic outflows. Here we report the discovery
of luminous radio emission from the seemingly ordinary Type Ibc SN 2009bb,
which requires a substantial relativistic outflow powered by a central engine.
The lack of a coincident GRB makes SN 2009bb the first engine-driven SN
discovered without a detected gamma-ray signal. A comparison with our extensive
radio survey of SNe Ibc reveals that the fraction harboring central engines is
low, ~1 percent, measured independently from, but consistent with, the inferred
rate of nearby GRBs. Our study demonstrates that upcoming optical and radio
surveys will soon rival gamma-ray satellites in pinpointing the nearest
engine-driven SNe. A similar result for a different supernova is reported
independently.Comment: To appear in Nature on Jan 28 2010. Embargoed for discussion in the
press until 13:00 US Eastern Time on Jan 27 (Accepted version, 27 pages,
Manuscript and Suppl. Info.
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