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Primal-dual variable neighborhood search for the simple plant-location problem
Copyright @ 2007 INFORMSThe variable neighborhood search metaheuristic is applied to the primal simple plant-location problem and to a reduced dual obtained by exploiting the complementary slackness conditions. This leads to (i) heuristic resolution of (metric) instances with uniform fixed costs, up to n = 15,000 users, and m = n potential locations for facilities with an error not exceeding 0.04%; (ii) exact solution of such instances with up to m = n = 7,000; and (iii) exact solutions of instances with variable fixed costs and up to m = n = 15, 000.This work is supported by NSERC Grant 105574-02; NSERC Grant OGP205041; and partly by the Serbian Ministry of Science, Project 1583
Radio-continuum study of Large Magellanic Cloud Supernova Remnant J0509-6731
We present a detailed study of Australia Telescope Compact Array (ATCA)
observations ( = 20, 13, 6 & 3~cm) of supernova remnant (SNR)
J0509--6731 in the Large Magellanic Cloud (LMC). The remnant has a ring
morphology with brightened regions towards the south-western limb. We also find
a second brightened inner ring which is only seen in the radio-continuum. The
SNR is almost circular, with a diameter ranging from 7 to 8~pc, and a steep
radio spectral index between 36 and 3~cm of , which is
characteristic of younger SNRs. We also report detection of radially orientated
polarisation across the remnant at 6~cm, with a mean fractional polarisation
level of ~(26~~13)%. We find the magnetic field (168~G)
and ( ~W
m~Hz~sr , 7.35~pc) to be consistent with other young
remnants
The use of seismic methods for the detection of dykes
Seismic methods have become common for the detection of low-throw faults ahead of underground coal mining. Surface seismic methods cannot theoretically be used where dykes occur, because seismic waves transmit from the surface down to the seams, and reflect back to the surface. Consequently, where sub-vertical structure such as dykes occurs, the surface seismic method fails. The ability of seismic methods to image dykes depends on the geometry used, the dyke thickness and the seismic wave propagation mode in relation to dyke composition and internal structure. Surface seismic methods find it difficult to distinguish between faults/fractures and very thin dykes (1-2m in thickness) when the dyke\u27s thickness is less than the seismic wavelength. Consequently, borehole seismic methods have to be used to detect the presence of such thin dykes. This paper presents the first results from an ACARP project, which in part is a breakthrough in seismic technology for the detection of dykes. It explains how surface seismic methods were used to detect a thick dyke and associated faulting. An alternative approach, that of going downhole with seismic sources and receivers (borehole seismic profiling), shows that dyke sides can be imaged at depth, and that in future, it should be possible to produce an image of both sides of a dyke, in its correct orientation, using existing boreholes
The Sigma-D Analysis of Recently Detected Radio Planetary Nebulae in the Magellanic Clouds
Our aim is to investigate and analyze the radio surface brightness to
diameter () relation for recently detected, bright radio-continuum
planetary nebulae (PNe) in the Magellanic Clouds (MC). We apply a Monte Carlo
analysis in order to account for sensitivity selection effects on measured
relation slopes for bright radio PNe in the MCs. In the
plane these radio MCs PNe are positioned among the brightest of the nearby
Galactic PNe, and are close to the sensitivity line of the MCs radio
maps. The fitted Large Magellanic Cloud (LMC) data slope appears to be
influenced with survey sensitivity. This suggests the MCs radio PN sample
represents just the "tip of the iceberg" of the actual luminosity function.
Specifically, our results imply that sensitivity selection tends to flatten the
slope of the relation. Although MCs PNe appear to share the similar
evolution properties as Galactic PNe, small number of data points prevented us
to further constrain their evolution properties.Comment: 5 pages, 2 figures, updated references, Astronomy and Astrophysics,
in pres
Enhancing coherency analysis for fault detection and mapping using 3D diffraction imaging
Automatic detection of geological discontinuities such as small throw faults, and pinch-outs is an important problem in the interpretation of 3D seismic data. This is commonly done using coherency analysis. However coherency may be affected by noise, which may create false anomalies. We propose a new interpretation workflow for the detection and mapping of faults, which enhances the coherency-type analysis with identification and detection of diffractions produced by the discontinuities. The algorithm utilizes migrated and unmigrated stacked seismic volumes and the cube of stacking (NMO) velocities. Tests on a simple 2.5 D model show that the method is capable in detecting and mapping of faults below seismic resolution
Seismic exploration of mineral resources - An Australian perspective
The only geophysical method that can image deep structures with the precision required for targeting and discovering new resources is reflection seismic. However, mineral prospecting with seismic methods is not straightforward. Lack of understanding of the seismic response, necessity to adapt the method to the specifics of each target and underestimating the complexity of mineral environments introduced complexities that have resulted in its sporadic rather than systematic application. Here we present and briefly discuss the results and the lessons learnt after more than a decade of dedicated investigations in different mineralised environments. We expect that seismic will become a standard geophysical method for exploration of most brown and then green fields
Radio Continuum Study of the Large Magellanic Cloud Supernova Remnant Honeycomb Nebula
We present the first and deepest Australia Telescope Compact Array radio
continuum images of the Honeycomb Nebula at 2000 and 5500 MHz solely from
archival data. The resolutions of these images are 3.6 x 2.8 arcsec2 and 1.3 x
1.2 arcsec2 at 2000 and 5500 MHz. We find an average radio spectral index for
the remnant of -0.76 +- 0.07. Polarisation maps at 5500 MHz reveal an average
fractional polarisation of 25 +- 5% with a maximum value of 95 x 16. We
estimate the equipartition field for Honeycomb Nebula of 48 +- 5 {\mu}G, with
an estimated minimum energy of Emin = 3 x 1049 erg. The estimated surface
brightness, {\Sigma}1 GHz , is 30 x 10-20 W m-2 Hz-1 sr-1; applying the
{\Sigma}-D relation suggests this supernova remnant is expanding into a
low-density environment. Finally, using Hi data, we can support the idea that
the Honeycomb Nebula exploded inside a low-density wind cavity. We suggest that
this remnant is likely to be between late free expansion stage and early Sedov
phase of evolution and expanding into a low-density medium
Faraday Rotation as a diagnostic of Galactic foreground contamination of CMB maps
The contribution from the residuals of the foreground can have a significant
impact on the temperature maps of the Cosmic Microwave Background (CMB).
Mostly, the focus has been on the galactic plane, when foreground cleaning has
taken place. However, in this paper, we will investigate the possible
foreground contamination, from sources outside the galactic plane in the CMB
maps. We will analyze the correlation between the Faraday rotation map and the
CMB temperature map. The Faraday rotation map is dependent on the galactic
magnetic field, as well as the thermal electron density, and both may
contribute to the CMB temperature. We find that the standard deviation for the
mean cross correlation deviate from that of simulations at the 99.9% level.
Additionally, a comparison between the CMB temperature extrema and the extremum
points of the Faraday rotation is also performed, showing a general overlap
between the two. Also we find that the CMB Cold Spot is located at an area of
strong negative cross correlation, meaning that it may be explained by a
galactic origin. Further, we investigate nearby supernova remnants in the
galaxy, traced by the galactic radio loops. These super nova remnants are
located at high and low galactic latitude, and thus well outside the galactic
plane. We find some correlation between the Faraday Rotation and the CMB
temperature, at select radio loops. This indicate, that the galactic
foregrounds may affect the CMB, at high galactic latitudesComment: 13 pages, 22 figures, 6 table
The yield of air fluorescence induced by electrons
The fluorescence yield for dry air and pure nitrogen excited by electrons is
calculated using a combination of well-established molecular properties and
experimental data of the involved cross sections. Particular attention has been
paid to the role of secondary electrons from ionization processes. At high
pressure and high energy, observed fluorescence turns out to be proportional to
the ionization cross section which follows the Born-Bethe law. Predictions on
fluorescence yields in a very wide interval of electron energies (eV - GeV) and
pressures (1 and 1013 hPa) as expected from laboratory measurements are
presented. Experimental results at energies over 1 MeV are in very good
agreement with our calculations for pure nitrogen while discrepancies of about
20% are found for dry air, very likely associated to uncertainties in the
available data on quenching cross sections. The relationship between
fluorescence emission, stopping power and deposited energy is discussed.Comment: 27 pages, 12 figures, 64 references. Accepted in Astroparticle
Physic
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