19,263 research outputs found
Servitization and operations management : a service-dominant logic approach
Managing organisational performance in sectors such as equipment provision has become increasingly complex as competition has heightened and firms have felt pressure to add value through the provision of services (Baines et al, 2007; Howard and Caldwell, 2011;
Neely et al., 2011). This provision is commonly referred to as the servitization of manufacturing (Vandermerwe & Rada, 1988). By extending the traditional offering of equipment to include service activities however, underlying operational delivery systems and processes have become more complex to manage and co-ordinate. No longer are firms simply making and shipping products; they are now engaged in a more complex world of design and delivery (Neely et al., 2011). This study aims to explore servitization from a value perspective through the lens of Service-Dominant (S-D) logic, and to propose its implications for operations management
Improved Limits on Sterile Neutrino Dark Matter using Full-Sky Fermi Gamma-Ray Burst Monitor Data
A sterile neutrino of ~keV mass is a well motivated dark matter candidate.
Its decay generates an X-ray line that offers a unique target for X-ray
telescopes. For the first time, we use the Gamma-ray Burst Monitor (GBM)
onboard the Fermi Gamma-Ray Space Telescope to search for sterile neutrino
decay lines; our analysis covers the energy range 10-25 keV (sterile neutrino
mass 20-50 keV), which is inaccessible to X-ray and gamma-ray satellites such
as Chandra, Suzaku, XMM-Newton, and INTEGRAL. The extremely wide field of view
of the GBM enables a large fraction of the Milky Way dark matter halo to be
probed. After implementing careful data cuts, we obtain ~53 days of full sky
observational data. We observe an excess of photons towards the Galactic
Center, as expected from astrophysical emission. We search for sterile neutrino
decay lines in the energy spectrum, and find no significant signal. From this,
we obtain upper limits on the sterile neutrino mixing angle as a function of
mass. In the sterile neutrino mass range 25-40 keV, we improve upon previous
upper limits by approximately an order of magnitude. Better understanding of
detector and astrophysical backgrounds, as well as detector response, will
further improve the sensitivity of a search with the GBM.Comment: 16 pages, 11 figures, references added, discussion expanded, some
typos fixed, matches the published versio
The Re-Acceleration of the Shock Wave in the Radio Remnant of SN 1987A
We report on updated radio imaging observations of the radio remnant of
Supernova 1987A (SN 1987A) at 9 GHz, taken with the Australia Telescope Compact
Array (ATCA), covering a 25-year period (1992-2017). We use Fourier modeling of
the supernova remnant to model its morphology, using both a torus model and a
ring model, and find both models show an increasing flux density, and have
shown a continuing expansion of the remnant. As found in previous studies, we
find the torus model most accurately fits our data, and has shown a change in
the remnant expansion at Day 9,300 210 from 2,300 200 km/s to 3,610
240 km/s. We have also seen an increase in brightness in the western lobe
of the remnant, although the eastern lobe is still the dominant source of
emission, unlike what has been observed at contemporary optical and X-ray
wavelengths. We expect to observe a reversal in this asymmetry by the year
2020, and note the south-eastern side of the remnant is now beginning to
fade, as has also been seen in optical and X-ray data. Our data indicate that
high-latitude emission has been present in the remnant from the earliest stages
of the shockwave interacting with the equatorial ring around Day 5,000.
However, we find the emission has become increasingly dominated by the
low-lying regions by Day 9,300, overlapping with the regions of X-ray emission.
We conclude that the shockwave is now leaving the equatorial ring, exiting
first from the south-east region of the remnant, and is re-accelerating as it
begins to interact with the circumstellar medium beyond the dense inner ring.Comment: 22 pages, 14 figures. Accepted to Ap
Algorithms for FFT Beamforming Radio Interferometers
Radio interferometers consisting of identical antennas arranged on a regular
lattice permit fast Fourier transform beamforming, which reduces the
correlation cost from in the number of antennas to
. We develop a formalism for describing this process and
apply this formalism to derive a number of algorithms with a range of
observational applications. These include algorithms for forming arbitrarily
pointed tied-array beams from the regularly spaced Fourier-transform formed
beams, sculpting the beams to suppress sidelobes while only losing
percent-level sensitivity, and optimally estimating the position of a detected
source from its observed brightness in the set of beams. We also discuss the
effect that correlations in the visibility-space noise, due to cross-talk and
sky contributions, have on the optimality of Fourier transform beamforming,
showing that it does not strictly preserve the sky information of the
correlation, even for an idealized array. Our results have applications to a
number of upcoming interferometers, in particular the Canadian Hydrogen
Intensity Mapping Experiment--Fast Radio Burst (CHIME/FRB) project.Comment: 17 pages, 4 figures, accepted to Ap
The elasticity of demand for gasoline: A semi-parametric analysis: Working paper series--02-33
We use a semi-parametric conditional median as a robust alternative to the parametric conditional mean to estimate the gasoline demand function. Our approach protects against data and specification errors and may yield a more reliable basis for public policy decisions that depend on accurate estimates of gasoline demand. As a comparison, we also estimated the parametric translog conditional mean model. Our semi-parametric estimates imply that gasoline demand becomes more price elastic, but also less income elastic, as incomes rise. In addition, we find that demand appears to become more price elastic as prices increase in real terms
Evolution of the Radio Remnant of Supernova 1987A: Morphological Changes from Day 7000
We present radio imaging observations of supernova remnant 1987A at 9 GHz,
taken with the Australia Telescope Compact Array over 21 years from 1992 to
2013. By employing a Fourier modeling technique to fit the visibility data, we
show that the remnant structure has evolved significantly since day 7000
(mid-2006): the emission latitude has gradually decreased, such that the
overall geometry has become more similar to a ring structure. Around the same
time, we find a decreasing trend in the east-west asymmetry of the surface
emissivity. These results could reflect the increasing interaction of the
forward shock with material around the circumstellar ring, and the relative
weakening of the interaction with the lower-density material at higher
latitudes. The morphological evolution caused an apparent break in the remnant
expansion measured with a torus model, from a velocity of 4600+150-200 km/s
between day 4000 and 7000 to 2400+100-200 km/s after day 7000. However, we
emphasize that there is no conclusive evidence for a physical slowing of the
shock at any given latitude in the expanding remnant, and that a change of
radio morphology alone appears to dominate the evolution. This is supported by
our ring-only fits which show a constant expansion of 3890+/-50 km/s without
deceleration between days 4000 and 9000. We suggest that once the emission
latitude no longer decreases, the expansion velocity obtained from the torus
model should return to the same value as that measured with the ring model.Comment: 11 pages, 5 figures, accepted for publication in ApJ, Figure 1 has
been scaled dow
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