797 research outputs found
Improving rail wear and RCF performance using laser cladding
Laser cladding has been considered as a method for improving the wear and RCF performance of standard grade rail. This paper presents results of small scale tests carried out to assess the wear and RCF performance of rail which had been laser clad. Using the laser cladding process premium metals can be deposited on to the working surface of standard rail with the aim of enhancing the wear and RCF life of the rail. Various laser clad samples were tested using a twin-disc method. The candidate metals were clad on to standard R260 grade rail discs and were tested against a disc of standard wheel material. During the tests, wear rates and RCF initiation were monitored and compared to those of a standard rail disc. Six candidate cladding materials were chosen for this test: A multi-phase Manganese Steel Variant (MMV), Martensitic Stainless Steel (MSS), TWIP Steel, NiCrBSi, Stellite 12 and Stellite 6. The MSS, Stellite 6, and Stellite 12 samples showed reduced wear rates relative to the standard R260 Grade rail discs, and also produced a reduction in wheel steel wear. The RCF initiation resistance of all of the candidate materials was superior compared to the R260 Grade material
Automated lithological mapping using airborne hyperspectral thermal infrared data: A case study from Anchorage Island, Antarctica
The thermal infrared portion of the electromagnetic spectrum has considerable potential for mineral and lithological mapping of the most abundant rock-forming silicates that do not display diagnostic features at visible and shortwave infrared wavelengths. Lithological mapping using visible and shortwave infrared hyperspectral data is well developed and established processing chains are available, however there is a paucity of such methodologies for hyperspectral thermal infrared data. Here we present a new fully automated processing chain for deriving lithological maps from hyperspectral thermal infrared data and test its applicability using the first ever airborne hyperspectral thermal data collected in the Antarctic. A combined airborne hyperspectral survey, targeted geological field mapping campaign and detailed mineralogical and geochemical datasets are applied to small test site in West Antarctica where the geological relationships are representative of continental margin arcs. The challenging environmental conditions and cold temperatures in the Antarctic meant that the data have a significantly lower signal to noise ratio than is usually attained from airborne hyperspectral sensors. We applied preprocessing techniques to improve the signal to noise ratio and convert the radiance images to ground leaving emissivity. Following preprocessing we developed and applied a fully automated processing chain to the hyperspectral imagery, which consists of the following six steps: (1) superpixel segmentation, (2) determine the number of endmembers, (3) extract endmembers from superpixels, (4) apply fully constrained linear unmixing, (5) generate a predictive classification map, and (6) automatically label the predictive classes to generate a lithological map. The results show that the image processing chain was successful, despite the low signal to noise ratio of the imagery; reconstruction of the hyperspectral image from the endmembers and their fractional abundances yielded a root mean square error of 0.58%. The results are encouraging with the thermal imagery allowing clear distinction between granitoid types. However, the distinction of fine grained, intermediate composition dykes is not possible due to the close geochemical similarity with the country rock
The change of Fermi surface topology in Bi2Sr2CaCu2O8 with doping
We report the observation of a change in Fermi surface topology of
Bi2Sr2CaCu2O8 with doping. By collecting high statistics ARPES data from
moderately and highly overdoped samples and dividing the data by the Fermi
function, we answer a long standing question about the Fermi surface shape of
Bi2Sr2CaCu2O8 close to the (pi,0) point. For moderately overdoped samples
(Tc=80K) we find that both the bonding and antibonding sheets of the Fermi
surface are hole-like. However for a doping level corresponding to Tc=55K we
find that the antibonding sheet becomes electron-like. This change does not
directly affect the critical temperature and therefore the superconductivity.
However, since similar observations of the change of the topology of the Fermi
surface were observed in LSCO and Bi2Sr2Cu2O6, it appears to be a generic
feature of hole-doped superconductors. Because of bilayer splitting, though,
this doping value is considerably lower than that for the single layer
materials, which again argues that it is unrelated to Tc
Dual character of the electronic structure in YBa2Cu4O8: conduction bands of CuO2 planes and CuO chains
We use microprobe Angle-Resolved Photoemission Spectroscopy (muARPES) to
separately investigate the electronic properties of CuO2 planes and CuO chains
in the high temperature superconductor, YBa2Cu4O8. In the CuO2 planes, a two
dimensional (2D) electronic structure with nearly momentum independent bilayer
splitting is observed. The splitting energy is 150 meV at (pi,0), almost 50%
larger than in Bi2Sr2CaCu2O(8+d) and the electron scattering at the Fermi level
in the bonding band is about 1.5 times stronger than in the antibonding band.
The CuO chains have a quasi one dimensional (1D) electronic structure. We
observe two 1D bands separated by ~ 550meV: a conducting band and an insulating
band with an energy gap of ~ 240meV. We find that the conduction electrons are
well confined within the planes and chains with a non-trivial hybridization.Comment: 4 pages, 4 figure
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The Tabby cat locus maps to feline chromosome B1.
The Tabby markings of the domestic cat are unique coat patterns for which no causative candidate gene has been inferred from other mammals. In this study, a genome scan was performed on a large pedigree of cats that segregated for Tabby coat markings, specifically for the Abyssinian (Ta-) and blotched (tbtb) phenotypes. There was linkage between the Tabby locus and eight markers on cat chromosome B1. The most significant linkage was between marker FCA700 and Tabby (Z = 7.56, theta = 0.03). Two additional markers in the region supported linkage, although not with significant LOD scores. Pairwise analysis of the markers supported the published genetic map of the cat, although additional meioses are required to refine the region. The linked markers cover a 17-cM region and flank an evolutionary breakpoint, suggesting that the Tabby gene has a homologue on either human chromosome 4 or 8. Alternatively, Tabby could be a unique locus in cats
Identifying the Background Signal in ARPES of High Temperature Superconductors
One of the interesting features of the photoemission spectra of the high
temperature cuprate superconductors is the presence of a large signal (referred
to as the "background'') in the unoccupied region of the Brillouin zone. Here
we present data indicating that the origin of this signal is extrinsic and is
most likely due to strong scattering of the photoelectrons. We also present an
analytical method that can be used to subtract the background signal
Momentum anisotropy of the scattering rate in cuprate superconductors
We examine the momentum and energy dependence of the scattering rate of the
high temperature cuprate superconductors using angle resolved photoemission
spectroscopy. The scattering rate is of the form a + b*w. The inelastic
coefficient b is found to be isotropic. The elastic term, a, however, is found
to be highly anisotropic in the pseudogap phase of optimal doped samples, with
an anisotropy which correlates with that of the pseudogap. This can be
contrasted with heavily overdoped samples, which show an isotropic scattering
rate in the normal state
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