534 research outputs found
Opaque Service Virtualisation: A Practical Tool for Emulating Endpoint Systems
Large enterprise software systems make many complex interactions with other
services in their environment. Developing and testing for production-like
conditions is therefore a very challenging task. Current approaches include
emulation of dependent services using either explicit modelling or
record-and-replay approaches. Models require deep knowledge of the target
services while record-and-replay is limited in accuracy. Both face
developmental and scaling issues. We present a new technique that improves the
accuracy of record-and-replay approaches, without requiring prior knowledge of
the service protocols. The approach uses Multiple Sequence Alignment to derive
message prototypes from recorded system interactions and a scheme to match
incoming request messages against prototypes to generate response messages. We
use a modified Needleman-Wunsch algorithm for distance calculation during
message matching. Our approach has shown greater than 99% accuracy for four
evaluated enterprise system messaging protocols. The approach has been
successfully integrated into the CA Service Virtualization commercial product
to complement its existing techniques.Comment: In Proceedings of the 38th International Conference on Software
Engineering Companion (pp. 202-211). arXiv admin note: text overlap with
arXiv:1510.0142
Observation of light echoes around very young stars
The goal of the paper is to present new results on light echoes from young
stellar objects. Broad band CCD images were obtained over three months at
one-to-two week intervals for the field of NGC 6726, using the large
field-of-view remotely-operated telescope on top of Cerro Burek. We detected
scattered light echoes around two young, low-amplitude, irregular variable
stars. Observations revealed not just one, but multiple light echoes from
brightness pulses of the T Tauri star S CrA and the Herbig Ae/Be star R CrA.
Analysis of S CrA's recurring echoes suggests that the star is located 138 +/-
16 pc from Earth, making these the closest echoes ever detected. The
environment that scatters the stellar light from S CrA is compatible with an
incomplete dust shell or an inclined torus some 10,000 AU in radius and
containing M_{\sun} of dust. The cause of such
concentration at 10,000AU from the star is unknown. It could be the
remnant of the envelope from which the star formed, but the distance of the
cloud is remarkably similar to the nominal distance of the Oort cloud to the
Sun, leading us to also speculate that the dust (or ice) seen around S CrA
might have the same origin as the Solar System Oort cloud.Comment: A&A, in press Received: 16 March 2010 / Accepted: 01 June 201
The destruction and survival of dust in the shell around SN 2008S
SN 2008S erupted in early 2008 in the grand design spiral galaxy NGC 6946.
The progenitor was detected by Prieto et al. in Spitzer Space Telescope images
taken over the four years prior to the explosion, but was not detected in deep
optical images, from which they inferred a self-obscured object with a mass of
about 10 Msun. We obtained Spitzer observations of SN 2008S five days after its
discovery, as well as coordinated Gemini and Spitzer optical and infrared
observations six months after its outburst.
We have constructed radiative transfer dust models for the object before and
after the outburst, using the same r^-2 density distribution of pre-existing
amorphous carbon grains for all epochs and taking light-travel time effects
into account for the early post-outburst epoch. We rule out silicate grains as
a significant component of the dust around SN 2008S. The inner radius of the
dust shell moved outwards from its pre-outburst value of 85 AU to a
post-outburst value of 1250 AU, attributable to grain vaporisation by the light
flash from SN 2008S. Although this caused the circumstellar extinction to
decrease from Av = 15 before the outburst to 0.8 after the outburst, we
estimate that less than 2% of the overall circumstellar dust mass was
destroyed.
The total mass-loss rate from the progenitor star is estimated to have been
(0.5-1.0)x10^-4 Msun yr^-1. The derived dust mass-loss rate of 5x10^-7 Msun
yr^-1 implies a total dust injection into the ISM of up to 0.01 Msun over the
suggested duration of the self-obscured phase. We consider the potential
contribution of objects like SN 2008S to the dust enrichment of galaxies.Comment: 9 pages, 7 figures, 3 tables. rv2. To appear in MNRA
The effects of dust on the optical and infrared evolution of SN 2004et
We present an analysis of multi-epoch observations of the Type II-P supernova
SN 2004et. New and archival optical spectra of SN 2004et are used to study the
evolution of the Halpha and [O I] 6300A line profiles between days 259 and 646.
Mid-infrared imaging was carried out between 2004 to 2010. We include Spitzer
`warm' mission photometry at 3.6 and 4.5um obtained on days 1779, 1931 and
2151, along with ground-based and HST optical and near-infrared observations
obtained between days 79 and 1803. Multi-wavelength light curves are presented,
as well as optical-infrared spectral energy distributions (SEDs) for multiple
epochs. Starting from about day 300, the optical light curves provide evidence
for an increasing amount of circumstellar extinction attributable to newly
formed dust, with the additional extinction reaching 0.8-1.5 magnitudes in the
V-band by day 690. The overall SEDs were fitted with multiple blackbody
components, in order to investigate the luminosity evolution of the supernova,
and then with Monte Carlo radiative transfer models using smooth or clumpy dust
distributions, in order to estimate how much new dust condensed in the ejecta.
The luminosity evolution was consistent with the decay of 56Co in the ejecta up
until about day 690, after which an additional emission source is required, in
agreement with the findings of Kotak et al. (2009). Clumped dust density
distributions consisting of 20% amorphous carbons and 80% silicates by mass
were able to match the observed optical and infrared SEDs, with dust masses
that increased from 8x10^{-5} Msun on day 300 to 1.5x10^{-3} Msun on day 690,
still significantly lower than the values needed for core collapse supernovae
to make a significant contribution to the dust enrichment of galaxies.Comment: 24 pages, 12 figures, 9 tables, published in MNRA
The Three-Dimensional Circumstellar Environment of SN 1987A
We present the detailed construction and analysis of the most complete map to
date of the circumstellar environment around SN 1987A, using ground and
space-based imaging from the past 16 years. PSF-matched difference-imaging
analyses of data from 1988 through 1997 reveal material between 1 and 28 ly
from the SN. Careful analyses allows the reconstruction of the probable
circumstellar environment, revealing a richly-structured bipolar nebula. An
outer, double-lobed ``Peanut,'' which is believed to be the contact
discontinuity between red supergiant and main sequence winds, is a prolate
shell extending 28 ly along the poles and 11 ly near the equator. Napoleon's
Hat, previously believed to be an independent structure, is the waist of this
Peanut, which is pinched to a radius of 6 ly. Interior to this is a cylindrical
hourglass, 1 ly in radius and 4 ly long, which connects to the Peanut by a
thick equatorial disk. The nebulae are inclined 41\degr south and 8\degr east
of the line of sight, slightly elliptical in cross section, and marginally
offset west of the SN. From the hourglass to the large, bipolar lobes, echo
fluxes suggest that the gas density drops from 1--3 cm^{-3} to >0.03 cm^{-3},
while the maximum dust-grain size increases from ~0.2 micron to 2 micron, and
the Si:C dust ratio decreases. The nebulae have a total mass of ~1.7 Msun. The
geometry of the three rings is studied, suggesting the northern and southern
rings are located 1.3 and 1.0 ly from the SN, while the equatorial ring is
elliptical (b/a < 0.98), and spatially offset in the same direction as the
hourglass.Comment: Accepted for publication in the ApJ Supplements. 38 pages in
apjemulate format, with 52 figure
Run-in periods and clinical outcomes of antipsychotics in dementia:A meta-epidemiological study of placebo-controlled trials
PURPOSE: Run-in periods are used to identify placebo-responders and washout. Our aim was to assess the association of run-in periods with clinical outcomes of antipsychotics in dementia. METHODS: We searched randomized placebo-controlled trials of conventional and atypical antipsychotics for neuropsychiatric symptoms (NPS) in dementia in electronic sources and references of selected articles. We extracted (a) the presence of a run-in period, use of placebo/investigated drug during run-in (versus washout only), and run-in duration (1 week or more) and (b) the reduction in NPS, number of participants with somnolence, extrapyramidal symptoms (EPS), and deaths per treatment group. We pooled clinical outcomes comparing antipsychotic and placebo groups in trials with and without run-in. RESULTS: We identified 35 trials. Twenty-nine trials used run-in. The pooled standardized mean difference in the reduction of NPS was -0.170 (95% CI, -0.227 to -0.112) in trials with run-in and -0.142 (95% CI, -0.331 to 0.047) in trials without run-in. The pooled odds ratio for somnolence was 2.8 (95% CI, 2.3-3.5) in trials with run-in and 3.5 (95% CI, 1.2-10.7) in trials without run-in; for EPS, these ORs were 1.8 (95% CI, 1.4-2.2) and 2.0 (95% CI, 1.3-3.1) respectively, and for mortality 1.4 (95% CI, 1.0-2.0) and 1.6 (95% CI, 0.7-3.4). The use of placebo/investigated drug during run-in and run-in duration did not affect the estimates in a consistent way. CONCLUSIONS: The use of run-in in trials might have led to overestimated efficacy and especially underestimated risks of side effects of antipsychotics compared with placebo for NPS in dementia
The Young, Massive, Star Cluster Sandage-96 After the Explosion of SN 2004dj in NGC 2403
The bright Type II-plateau supernova (SN) 2004dj occurred within the young,
massive stellar cluster Sandage-96 in a spiral arm of NGC 2403. New
multi-wavelength observations obtained with several ground-based and
space-based telescopes are combined to study the radiation from Sandage-96
after SN 2004dj faded away. Sandage-96 started to dominate the flux in the
optical bands starting September 2006 (~800 d after explosion). The optical
fluxes are equal to the pre-explosion ones within the observational
uncertainties. An optical Keck spectrum obtained ~900 d after explosion shows
the dominant blue continuum from the cluster stars shortward of 6000 \AA as
well as strong SN nebular emission lines redward. The integrated spectral
energy distribution (SED) of the cluster has been extended into the ultraviolet
region by archival XMM-Newton and new Swift observations, and compared with
theoretical models. The outer parts of the cluster have been resolved by the
Hubble Space Telescope, allowing the construction of a color-magnitude diagram.
The fitting of the cluster SED with theoretical isochrones results in cluster
ages between 10--40 Myr, depending on metallicity and the model family. The
isochrone fitting indicates that the resolved part of the cluster has a bimodal
age distribution: a younger population at ~10--16 Myr, and an older one at
~32--100 Myr which is similar to the age distribution of the nearby field
stars. These stars may have been captured from the field during the cluster
formation. The young age of Sandage-96 suggest 12 < M_prog < 20 M_\odot as the
most probable mass range for the progenitor of SN 2004dj. This is consistent
with, but perhaps slightly higher than, most of the other Type II-plateau SN
progenitor masses determined so far.Comment: accepted in Ap
SN 2007od: A Type IIP SN with Circumstellar Interaction
SN 2007od exhibits characteristics that have rarely been seen in a Type IIP
supernova (SN). Optical V band photometry reveals a very steep brightness
decline between the plateau and nebular phases of ~4.5 mag, likely due to SN
2007od containing a low mass of 56Ni. The optical spectra show an evolution
from normal Type IIP with broad Halpha emission, to a complex, four component
Halpha emission profile exhibiting asymmetries caused by dust extinction after
day 232. This is similar to the spectral evolution of the Type IIn SN 1998S,
although no early-time narrow (~200 km s-1) Halpha component was present in SN
2007od. In both SNe, the intermediate-width Halpha emission components are
thought to arise in the interaction between the ejecta and its circumstellar
medium (CSM). SN 2007od also shows a mid-IR excess due to new dust. The
evolution of the Halpha profile and the presence of the mid-IR excess provide
strong evidence that SN 2007od formed new dust before day 232. Late-time
observations reveal a flattening of the visible lightcurve. This flattening is
a strong indication of the presence of a light echo, which likely accounts for
much of the broad, underlying Halpha component seen at late-times. We believe
the multi-peaked Halpha emission is consistent with the interaction of the
ejecta with a circumstellar ring or torus (for the inner components at \pm1500
km s-1), and a single blob or cloud of circumstellar material out of the plane
of the CSM ring (for the outer component at -5000 km s-1). The most probable
location for the formation of new dust is in the cool dense shell created by
the interaction between the expanding ejecta and its CSM. Monte Carlo radiative
transfer modeling of the dust emission from SN 2007od implies that up to 4x
10-4Msun of new dust has formed. This is similar to the amounts of dust formed
in other CCSNe such as SNe 1999em, 2004et, and 2006jc.Comment: 35 pages, 6 figures. Accepted for publication in Ap
An Extremely Bright Echo Associated With SN 2002hh
We present new, very late-time optical photometry and spectroscopy of the
interesting Type II-P supernova, SN 2002hh, in NGC 6946. Gemini/GMOS-N has been
used to acquire visible spectra at six epochs between 2004 August and 2006
July, following the evolution of the SN from age 661 to 1358 days. Few optical
spectra of Type II supernovae with ages greater than one year exist. In
addition, g'r'i' images were acquired at all six epochs. The spectral and
photometric evolution of SN 2002hh has been very unusual. Measures of the
brightness of this SN, both in the R and I bands as well as in the H-alpha
emission flux, show no significant fading over an interval of nearly two years.
The most straightforward explanation for this behavior is that the light being
measured comes not only from the SN itself but also from an echo off of nearby
dust. Echoes have been detected previously around several SNe but these echoes,
at their brightest, were ~8 mag below the maximum brightness of the SN. At V~21
mag, the putative echo dominates the light of SN 2002hh and is only ~4 mag
below the outburst's peak brightness. There is an estimated 6 magnitudes of
total extinction in V towards SN 2002hh. The proposed explanation of a
differential echo/SN absorption is inconsistent with the observed BVRI colors.Comment: 24 pages, 6 figures. Accepted for publication in the Ap
X-ray Evolution of SNR 1987A: The Radial Expansion
We present the evolution of the radial expansion of SNR 1987A as measured
using Chandra X-ray observations taken over the last 10 years. To characterize
the complex structure of the remnant and isolate the expansion measurement, we
fit the images to several empirical models including: a simple circular torus,
a torus with bilateral lobes, and a torus with four tangentially extended
lobes. We discuss the results of this measure in the context of the overall
evolution of the supernova remnant, for which we believe we have measured the
end of the free expansion phase and its transition to the adiabatic phase (at
least along the equatorial ring). The timing of this event is in agreement with
early predictions of the remnant evolution.Comment: Accepted for publication in ApJ, 21 pages, 4 figures, 3 table
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