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Metal-Coated Defect-Core Photonic Crystal Fiber for THz Propagation
Modal solutions for metal-coated defect-core photonic crystal fiber (PCF) with a central air-hole have been obtained by using a full-vectorial finite element method to model the guidance of THz waves. It has been shown that the surface plasmon modes can couple with the defect-core PCF mode to form supermodes, with potential for sensing applications
Gas and liquid-fuelled HVOF spraying of Ni50Cr coating: microstructure and high temperature oxidation
Ni50Cr thermally sprayed coatings are widely used for high temperature oxidation and corrosion in thermal power plants. In this study, a commercially available gas atomised Ni50Cr powder was sprayed onto a power plant alloy (ASME P92) using both gas and liquid fuelled high velocity oxy-fuel (HVOF) thermal spray. Microstructures of the two coatings were examined using SEM-EDX, XRD, oxygen content analysis and mercury intrusion porosimeter. The gas fuelled coating had higher levels of oxygen content and porosity. Shorter term air oxidation tests (4 h) of the free-standing deposits in a thermogravimetric analyser (TGA) and longer term air oxidation tests (100 h) of the coated substrates were performed at 700 °C. The kinetics of oxidation and the oxidation products were characterized in detail in SEM/EDX and XRD. In both samples, oxides of various morphologies developed on top of the Ni50Cr coatings. Cr2O3 was the main oxidation product on the surface of the coatings along with a small amount of NiO and NiCr2O4. Rietveld analysis was performed on the XRD data to quantify the phase composition of the oxides on both Ni50Cr coatings and their evolution with exposure time
Role of oxides and porosity on high temperature oxidation of liquid fuelled HVOF thermal sprayed Ni50Cr coatings
High chromium content in Ni50Cr thermally sprayed coatings can generate a dense and protective scale at the surface of coating. Thus, the Ni50Cr coating is widely used in high temperature oxidation and corrosion applications. A commercially available gas atomized Ni50Cr powder was sprayed onto a power plant steel (ASME P92) using a liquid fuelled high velocity oxy-fuel (HVOF) thermal spray with three processing parameters in this study. Microstructure of as-sprayed coatings was examined using oxygen content analysis, mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDX) and X-ray Diffraction (XRD). Short-term air oxidation tests (4 h) of freestanding coatings (without boiler steel substrate) in a thermogravimetric analyser (TGA) at 700 ℃ were performed to obtain the kinetics of oxidation of the as-sprayed coating. Long-term air oxidation tests (100 h) of the coated substrates were performed at same temperature to obtain the oxidation products for further characterization in detail using SEM / EDX and XRD. In all samples, oxides of various morphologies developed on top of the Ni50Cr coatings. Cr₂O₃ was the main oxidation product on the surface of all three coatings. The coating with medium porosity and medium oxygen content has the best high temperature oxidation performance in this study
The Redshift Distribution of the TOUGH Survey
We present the redshift results from a Very Large Telescope program aimed at
optimizing the legacy value of the Swift mission: to characterize a
homogeneous, X-ray selected, sample of 69 GRB host galaxies. 19 new redshifts
have been secured, resulting in a 83% (57/69) redshift completion, making the
survey the most comprehensive in terms of redshift completeness of any sample
to the full Swift depth, available to date. We present the cumulative redshift
distribution and derive a conservative, yet small, associated uncertainty. We
constrain the fraction of Swift GRBs at high redshift to a maximum of 10% (5%)
for z > 6 (z > 7). The mean redshift of the host sample is assessed to be >
2.2. Using this more complete sample, we confirm previous findings that the GRB
rate at high redshift (z > 3) appears to be in excess of predictions based on
assumptions that it should follow conventional determinations of the star
formation history of the universe, combined with an estimate of its likely
metallicity dependence. This suggests that either star formation at high
redshifts has been significantly underestimated, for example due to a dominant
contribution from faint, undetected galaxies, or that GRB production is
enhanced in the conditions of early star formation, beyond those usually
ascribed to lower metallicity.Comment: 7th Huntsville Gamma-Ray Burst Symposium, GRB 2013: paper 34 in eConf
Proceedings C130414
Swift J1112.2-8238: A Candidate Relativistic Tidal Disruption Flare
We present observations of Swift J1112.2-8238, and identify it as a candidate
relativistic tidal disruption flare (rTDF). The outburst was first detected by
Swift/BAT in June 2011 as an unknown, long-lived (order of days) -ray
transient source. We show that its position is consistent with the nucleus of a
faint galaxy for which we establish a likely redshift of based on a
single emission line that we interpret as the blended [OII]
doublet. At this redshift, the peak X/-ray luminosity exceeded
ergs s, while a spatially coincident optical transient source
had (M at ) during early
observations, days after the Swift trigger. These properties place
Swift J1112.2-8238 in a very similar region of parameter space to the two
previously identified members of this class, Swift J1644+57 and Swift
J2058+0516. As with those events the high-energy emission shows evidence for
variability over the first few days, while late time observations, almost 3
years post-outburst, demonstrate that it has now switched off. Swift
J1112.2-8238 brings the total number of such events observed by Swift to three,
interestingly all detected by Swift over a 3 month period ( of its
total lifetime as of March 2015). While this suggests the possibility that
further examples may be uncovered by detailed searches of the BAT archives, the
lack of any prime candidates in the years since 2011 means these events are
undoubtedly rare.Comment: 11 pages, 5 figures, accepted for publication by MNRA
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