6,911 research outputs found
ECONOMIC MODELING OF FARM PRODUCTION AND CONSERVATION DECISIONS IN RESPONSE TO ALTERNATIVE RESOURCE AND ENVIRONMENTAL POLICIES
Environmental Economics and Policy, Farm Management,
Data handling methods and target detection results for multibeam and sidescan data collected as part of the search for SwissAir Flight 111
The crash of SwissAir Flight 111, off Nova Scotia in September 1998, triggered one of the largest seabed search surveys in Canadian history. The primary search tools used were sidescan sonars (both conventional and focussed types) and multibeam sonars. The processed search data needed to be distributed on a daily basis to other elements of the fleet for precise location of divers and other optical seabed search instruments (including laser linescan and ROV video). As a result of the glacial history of the region, many natural targets, similar in gross nature to aircraft debris were present. These included widespread linear bedrock outcrop patterns together with near ubiquitous glacial erratic boulders. Because of the severely broken-up nature of the remaining aircraft debris, sidescan imaging alone was often insufficient to unambiguously identify targets. The complementary attributes of higher resolution, but poorly located, sidescan imagery together with slightly lower resolution, but excellently navigated multibeam sonar proved to be one of critical factors in the success of the search. It proved necessary to rely heavily on the regional context of the seabed (provided by the multibeam sonar bathymetry and backscatter imagery) to separate natural geomorphic targets from anomalous anthropogenic debris. In order to confidently prove or disprove a potential target, the interpreter required simultaneous access to the full resolution sidescan data in the geographic context of the multibeam framework. Specific software tools had to be adapted or developed shipboard to provide this capability. Whilst developed specifically for this application, these survey tools can provide improved processing speed and confidence as part of more general mine hunting, hydrographic, engineering or scientific surveys
The X-ray Line Emission from the Supernova Remnant W49B
The Galactic supernova remnant W49B has one of the most impressive X-ray
emission line spectra obtained with the Advanced Satellite for Cosmology and
Astronomy (ASCA). We use both plasma line diagnostics and broadband model fits
to show that the Si and S emission lines require multiple spectral components.
The spectral data do not necessarily require individual elements to be
spatially stratified, as suggested by earlier work, although when ASCA line
images are considered, it is possible that Fe is stratified with respect to Si
and S. Most of the X-ray emitting gas is from ejecta, based on the element
abundances required, but is surprisingly close to being in collisional
ionization equilibrium. A high ionization age implies a high internal density
in a young remnant. The fitted emission measure for W49B indicates a minimum
density of 2 cm^-3, with the true density likely to be significantly higher.
W49B probably had a Type Ia progenitor, based on the relative element
abundances, although a low-mass Type II progenitor is still possible. We find
persuasive evidence for Cr and possibly Mn emission in the ASCA spectrum--the
first detection of these elements in X-rays from a cosmic source.Comment: 22 pages incl 8 postscript figures, to appear in Ap
Introduction: Increasing and maintaining physical activity in special populations
Exercise Physiology in Special Populations covers the prevalent health conditions that are either linked to an inactive lifestyle or whose effects can be ameliorated by increasing physical activity and physical fitness. The book explores physiological aspects of obesity and diabetes before moving on to cardiac disease, lung disease, arthritis and back pain, ageing and older people, bone health, the female participant, neurological and neuromuscular disorders, and spinal chord injury. The author team includes many of the UK?s leading researchers and exercise science and rehabilitation practitioners that specialise in each of the topic areas
The Extraordinarily Rapid Expansion of the X-ray Remnant of Kepler's Supernova (SN1604)
Four individual high resolution X-ray images from ROSAT and the Einstein
Observatory have been used to measure the expansion rate of the remnant of
Kepler's supernova (SN 1604). Highly significant measurements of the expansion
have been made for time baselines varying from 5.5 yrs to 17.5 yrs. All
measurements are consistent with a current expansion rate averaged over the
entire remnant of 0.239 (+/-0.015) (+0.017,-0.010) % per yr, which, when
combined with the known age of the remnant, determines the expansion parameter
m, defined as , to be 0.93 (+/-0.06) (+0.07,-0.04). The error
bars on these results include both statistical (first set of errors) and
systematic (second set) uncertainty. According to this result the X-ray remnant
is expanding at a rate that is remarkably close to free expansion and nearly
twice as fast as the mean expansion rate of the radio remnant. The expansion
rates as a function of radius and azimuthal angle are also presented based on
two ROSAT images that were registered to an accuracy better than 0.5
arcseconds. Significant radial and azimuthal variations that appear to arise
from the motion of individual X-ray knots are seen. The high expansion rate of
the X-ray remnant appears to be inconsistent with currently accepted dynamical
models for the evolution of Kepler's SNR.Comment: 14 pages, including 7 postscript figs, LaTeX, emulateapj. Accepted by
Ap
E-Business Enabled Networks and Fourth Party Logistics (4PL) Providers: An Overview
The Internet has been a key to optimizing the supply chain, enabling real-time data to be shared between supply chain partners, which usually connect together as an e-business network. Nowadays the focus is on building-in value added products/services, thereby enabling the network to differentiate itself from its competitors in a more sustainable manner. In this context, outsourcing has provided significant cost reductions for businesses, with the use of third party logistics providers (3PLs). This is today only a ‘qualifying criterion’ for most businesses, and no longer a competitive advantage. The creation of a fourth party logistics provider (4PL) aims at moving the client to a more competitive position, by analysing relevant business risk, and monitoring relevant KPI’s, and applying these within a 4PL providers efficient alliance network
Revealing New Physical Structures in the Supernova Remnant N63A through Chandra Imaging Spectroscopy
We present Chandra X-ray observations of the supernova remnant (SNR) N63A in
the Large Magellanic Cloud (LMC). N63A, one of the brightest LMC remnants, is
embedded in an H II region and probably associated with an OB association. The
optical remnant consists of three lobes of emission contained within the
approximately three times larger X-ray remnant. Our Chandra data reveal a
number of new physical structures in N63A. The most striking of these are the
several ``crescent''-shaped structures located beyond the main shell that
resemble similar features seen in the Vela SNR. In Vela, these have been
interpreted as arising from high speed clumps of supernova ejecta interacting
with the ambient medium. Another distinct feature of the remnant is a roughly
triangular ``hole'' in the X-ray emission near the location of the optical
lobes and the brightest radio emission. X-ray spectral analysis shows that this
deficit of emission is a result of absorption by an intervening dense cloud
with a mass of ~450 M_sun that is currently being engulfed by the remnant's
blast wave. We also find that the rim of the remnant, as well as the
crescent-shaped features, have considerably softer X-ray spectra than the
interior. Limits on hard X-ray emission rule out a young, energetic pulsar in
N63A, but the presence of an older or less active one, powering a wind nebula
with a luminosity less than ~4e10^34 erg/s, is allowed.Comment: 18 pages, 5 figures (2 color), accepted for publication in Ap
The X-ray Iron Emission from Tycho's Supernova Remnant
We present the results of broadband fits to the X-ray spectrum of Tycho's
supernova remnant obtained by the Solid-State Imaging Spectrometers on the ASCA
Observatory. We use single-temperature, single-ionization-age, nonequilibrium
ionization models to characterize the ejecta and the blast-shocked interstellar
medium. Based on the Fe K emission at 6.5 keV, previous spectral studies have
suggested that the Fe ejecta in this Type Ia remnant are stratified interior to
the other ejecta. The ASCA data provide important constraints from the Fe L
emission near 1 keV as well as the Fe K emission. We find that the simplest
models, with emission from the ejecta and blast wave each at a single
temperature and ionization age, severely underestimate the Fe K flux. We show
that there is little Fe emission associated with the Si and S ejecta shell. The
blast-shocked interstellar medium has abundances roughly 0.3 times the solar
value, while the ejecta, with the exception of Fe, have relative abundances
that are typical of Type Ia supernovae. The addition of another component of Fe
emission, which we associate with ejecta, at a temperature at least two times
higher and an ionization age 100 times lower than the Si ejecta, does
provide a good fit to the spectrum. This model is consistent with X-ray imaging
results. Although fluorescent emission from dust in the remnant may contribute
to the Fe K flux, we conclude that it is unlikely to dominate.Comment: 23 pages, LaTex; 4 postscript figures, 2 postscript tables. To appear
in ApJ, vol 49
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