Effect of microstructure and temperature on the erosion rates and mechanisms of modified EB PVD TBCs

Thermal barrier coatings (TBCs) have now been used in gas turbine engines for a number of decades and are now considered to be an accepted technology. As there is a constant drive to increase the turbine entry temperature, in order to increase engine efficiency, the coatings operate in increasingly hostile environments. Thus there is a constant drive to both increase the temperature capabilities of TBCs while at the same time reducing their thermal conductivities. The thermal conductivity of standard 7 wt% yttria stabilized zirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can be reduced in two ways: the first by modification of the microstructure of the TBC and the second by addition of ternary oxides. By modifying the microstructure of the TBC such that there are more fine pores, more photon scattering centres are introduced into the coatings, which reduce the heat transfer by radiation. While ternary oxides will introduce lattice defects into the coating, which increases the phonon scattering, thus reducing the thermal conductivity via lattice vibrations. Unfortunately, both of these methods can have a negative effect on the erosion resistance of EB PVD TBCs. This paper compares the relative erosion rates of ten different EB PVD TBCs tested at 90à ° impact at room temperature and at high temperature and discusses the results in term of microstructural and temperature effects. It was found that by modifying the coating deposition, such that a low density coating with a highly â  featheredâ  microstructure formed, generally resulted in an increase in the erosion rate at room temperature. When there was a significant change between the room temperature and the high temperature erosion mechanism it was accompanied by a significant decrease in the erosion rate, while additions of dopents was found to significantly increase the erosion rate at room and high temperature. However, all the modified coatings still had a lower erosion rate than a plasma sprayed coatings. So, although, relative to a standard 7YSZ coating, the modified coatings have a lower erosion resistance, they still perform better than PS TBCs and their lower thermal conductivities could make them viable alternatives to 7YSZ for use in gas turbine en

Elite coaches’ use and engagement with performance analysis within Olympic and Paralympic sport

The use and implementation of performance analysis and feedback by 18 elite Olympic/Paralympic coaches (coaching experience 16.1 ± 7.4; experience using performance analysis 8.3 ± 4.8 years) was explored via an online questionnaire (mean time to complete = 29 minutes). Likert scales were used to facilitate cross-sport comparison. Comment boxes were included to enable additional information to be provided if deemed necessary. Training goals, athlete discussion and coaching philosophy were the most prominent features influencing analysis direction. Time available had the greatest impact upon feedback provision. The main analysis techniques used were video, performance reports, and trend analysis. Coaches with greater experience delivered significantly more feedback sessions within 1-hour of performance. Feedback sessions were < 20-minutes in duration and delivered in a balanced (experienced) or mostly positive (inexperienced) approach. Feedback was delivered consistently according to a preferred schedule, face-to-face, and within an individual format. Sessions were usually coach led, however considerable value in a combined or analyst led approach was demonstrated. The findings have begun to illustrate practice within elite sport from the perspective of a key user of performance analysis, i.e. the coach, and have clear implications for practitioners by identifying the key areas coaches’ value from performance analysis

The implementation of performance analysis and feedback within Olympic sport: the performance analyst’s perspective

The study considered performance analysis and feedback from the perspective of the performance analyst through the investigation of the ‘what’, ‘how’, and ‘when’ of practice within a selection of Olympic sports. Twenty-three performance analysts (experience 6.4 ± 4.1 years) engaged in a structured interview (85 ± 15 minutes) regarding their processes within applied practice. Likert scales (All the time, Often, Sometimes, Rarely, Never) were used to facilitate cross sport and environment comparison. The performance analysts highlighted the experience of their coaches as the most prominent feature influencing analysis direction and time had the greatest impact upon feedback provision. The main analysis techniques used were video, profiling and performance reports. Feedback was delivered primarily either, 1) < 1-hour post-performance within sessions lasting < 10-minutes or 2) the following day within sessions lasting 25+ minutes. Video feedback was usually coach led, however data delivery was more evenly distributed between coach and analyst. Very similar processes across the participants were identified, despite a wide variety of sports and participant experience levels. The findings have begun to illustrate practice within elite sport whilst highlighting the importance and need for further practitioner-based investigation regarding the use of performance analysis and feedback within applied context

Performance analysis practice within Olympic and Paralympic sports: a comparison of coach and analyst experiences

Concordance between 18 coaches (mean performance analysis experience: 8.3 ± 4.8 years) and 23 performance analysts (mean: 6.4 ± 4.1 years) regarding their performance analysis delivery within applied Olympic and Paralympic environments was investigated using survey-based methods. There was clear agreement on the provision, importance and need for full video. The majority of analysts (73.9%) provided profiling often or all of the time, whereas only one third of coaches felt that this was the required amount. Coaches not only agreed that coaching philosophy was the main factor directing analysis but also emphasised that training goals, level or age of athlete and discussions with athletes were influencers, far more than the analysts realised. A potential barrier for better communication was time, highlighted by all analysts as a major factor impacting their role. The majority of analysts (87%) attempted to provide feedback to athletes within one hour of performance, often or all the time. Coaches expressed a similar philosophy but were far more likely to want to provide feedback at later times. These findings should be utilised by analysts and coaches to review practice, identify gaps within practice and highlight areas for development

Metal-poor dwarf galaxies in the SIGRID galaxy sample. I. HII region observations and chemical abundances

In this paper we present the results of observations of seventeen HII regions in thirteen galaxies from the SIGRID sample of isolated gas rich irregular dwarf galaxies. The spectra of all but one of the galaxies exhibit the auroral [OIII] 4363A line, from which we calculate the electron temperature, Te, and gas-phase oxygen abundance. Five of the objects are blue compact dwarf (BCD) galaxies, of which four have not previously been analysed spectroscopically. We include one unusual galaxy which exhibits no evidence of the [NII] {\lambda}{\lambda} 6548,6584A lines, suggesting a particularly low metallicity (< Zsolar/30). We compare the electron temperature based abundances with those derived using eight of the new strong line diagnostics presented by Dopita et al. (2013). Using a method derived from first principles for calculating total oxygen abundance, we show that the discrepancy between the Te-based and strong line gas-phase abundances have now been reduced to within ~0.07 dex. The chemical abundances are consistent with what is expected from the luminosity-metallicity relation. We derive estimates of the electron densities and find them to be between ~5 and ~100 cm-3. We find no evidence for a nitrogen plateau for objects in this sample with metallicities 0.5 > Zsolar > 0.15.Comment: 46 pages, 15 figures, 6 tables, 1 appendix. Accepted for publication in the Astrophysical Journa