26,403 research outputs found
Store capacity optimisation
The problem is one of increasing the efficiency of distributing paper rolls from the manufacturing plants to the customers. A related problem is one of utilising the available capacity at the customer stores in an effective manner. During the MISG, several approaches to the above problems were proposed. In this report we describe the problem and several methods for solving it. Preliminary results are provided for some of these
A deep search for pulsar wind nebulae using pulsar gating
Using the Australia Telescope Compact Array (ATCA) we have imaged the fields
around five promising pulsar candidates to search for radio pulsar wind nebulae
(PWNe). We have used the ATCA in its pulsar gating mode; this enables an image
to be formed containing only off-pulse visibilities, thereby dramatically
improving the sensitivity to any underlying PWN. Data from the Molonglo
Observatory Synthesis Telescope were also used to provide sensitivity on larger
spatial scales. This survey found a faint new PWN around PSR B0906-49; here we
report on non-detections of PWNe towards PSRs B1046-58, B1055-52, B1610-50 and
J1105-6107. Our radio observations of the field around PSR B1055-52 argue
against previous claims of an extended X-ray and radio PWNe associated with the
pulsar. If these pulsars power unseen, compact radio PWN, upper limits on the
radio flux indicate that less than 1e-6 of their spin-down energy is used to
power this emission. Alternatively PSR B1046-58 and PSR B1610-50 may have
relativistic winds similar to other young pulsars and the unseen PWN is
resolved and fainter than our surface brightness sensitivity threshold. We can
then determine upper limits on the local ISM density of 2.2e-3 cm^-3 and 1e-2
cm^-3, respectively. Furthermore we constrain the spatial velocities of these
pulsars to be less than ~450 km/s and thus rule out the association of PSR
B1610-50 with SNR G332.4+00.1 (Kes 32). Strong limits on the ratio of unpulsed
to pulsed emission are also determined for three pulsars.Comment: 10 pages, 5 figures, MNRAS in pres
Origin of the transient unpulsed radio emission from the PSR B1259-63 binary system
We discuss the interpretation of transient, unpulsed radio emission detected
from the unique pulsar/Be-star binary system PSR B1259-63. Extensive monitoring
of the 1994 and 1997 periastron passages has shown that the source flares over
a 100-day interval around periastron, varying on time-scales as short as a day
and peaking at 60 mJy (~100 times the apastron flux density) at 1.4 GHz.
Interpreting the emission as synchrotron radiation, we show that (i) the
observed variations in flux density are too large to be caused by the shock
interaction between the pulsar wind and an isotropic, radiatively driven,
Be-star wind, and (ii) the radio emitting electrons do not originate from the
pulsar wind. We argue instead that the radio electrons originate from the
circumstellar disk of the Be star and are accelerated at two epochs, one before
and one after periastron, when the pulsar passes through the disk. A simple
model incorporating two epochs of impulsive acceleration followed by
synchrotron cooling reproduces the essential features of the radio light curve
and spectrum and is consistent with the system geometry inferred from pulsed
radio data.Comment: To be published in Astrophysical Journal Letters 7 pages, 1
postscript figur
First-principles study of symmetry lowering in relaxed BaTiO3/SrTiO3 superlattices
The crystal structure and local spontaneous polarization of
(BaTiO3)m/(SrTiO3)n superlattices is calculated using a first-principles
density functional theory method. The in-plane lattice constant is 1% larger
than the SrTiO3 substrate to imitate the relaxed superlattice structure and the
symmetry is lowered to monoclinic space group Cm which allows polarization to
develop along the [110] and [001] directions. The polarization component in the
[110] direction is found to develop only in the SrTiO3 layers and falls to zero
in the BaTiO3 layers, whereas the polarization in the [001] direction is
approximately uniform throughout the superlattice. These findings are
consistent with recent experimental data and first-principles results for
epitaxially strained BT and ST.Comment: 4 pages, 2 figure
Systematic Variation in Willingness to Pay for Agricultural Land Preservation and Implications for Benefit Transfer: A Meta-Analysis
Despite prior studies examining willingness to pay for farmland preservation there has been no quantitative, systematic analysis of findings across the literature. This paper presents the first statistical meta-analysis of farmland preservation values. Results confirm systematic variations in willingness to pay, with value surfaces corresponding to theoretical expectations. Findings also provide significant insight into the potential for valid meta-analytic, function based benefit transfer. Results suggest, for example, that transfer validity is critically dependent on jurisdictional scale. Transfer errors are modest for community scale farmland preservation, but large for state scale preservation policies in which per acre welfare estimates are small.Land Economics/Use,
Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission
We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both
experimentally and using a three-dimensional carrier dynamics simulation. A
uniform density of vacancies was formed over the optical absorption depth of
bulk GaAs samples by performing multi-energy implantations of arsenic ions (1
and 2.4MeV) and subsequent thermal annealing. In a series of THz emission
experiments the frequency of peak THz power was found to increase significantly
from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to
10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast
carrier dynamics to reproduce and explain these results. The effect of the
ion-induced damage was included in the simulation by considering carrier
scattering at neutral and charged impurities, as well as carrier trapping at
defect sites. Higher vacancy concentrations and shorter carrier trapping times
both contributed to shorter simulated THz pulses, the latter being more
important over experimentally realistic parameter ranges.Comment: 6 pages, 7 figure
Limits on radio emission from pulsar wind nebulae
We report on a sensitive survey for radio pulsar wind nebulae (PWN) towards
27 energetic and/or high velocity pulsars. Observations were carried out at 1.4
GHz using the Very Large Array and the Australia Telescope Compact Array, and
utilised pulsar-gating to search for off-pulse emission. These observing
parameters resulted in a considerably more sensitive search than previous
surveys, and could detect PWN over a much wider range of spatial scales (and
hence ambient densities and pulsar velocities). However, no emission clearly
corresponding to a PWN was discovered. Based on these non-detections we argue
that the young and energetic pulsars in our sample have winds typical of young
pulsars, but produce unobservable PWN because they reside in low density (n
approx 0.003 cm^-3) regions of the ISM. However, non-detections of PWN around
older and less energetic pulsars can only be explained if the radio luminosity
of their winds is less than 1e-5 of their spin-down luminosity, implying an
efficiency at least an order of magnitude smaller than that seen for young
pulsars.Comment: 9 pages, 3 embedded EPS files. Accepted to MNRA
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