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

Mars' Atmosphere: Comparison of Entry Profiles with Numerical Models

This presentation was part of the session : Poster SessionsSixth International Planetary Probe WorkshopAs planetary probes enter an atmosphere, they capture measurements which provide thermodynamic information about the atmosphere, but only within a narrow vertical column within that atmosphere over a limited extent of time. In order to place this in situ information into context, it needs to be correlated with other less spatially resolved but more temporally extensive measurements, which can be provided by orbiters as well as numerical models. Before the entry probe is designed and developed, there needs to be some foreknowledge of conditions the probe will experience. Data from previous probes and orbiters can help, and models can aid by permitting investigation of conditions the orbiters may not have observed. Focusing on Mars, there are now six entry profiles available for analysis and interpretation, as well as a decade's worth of remotely sensed atmospheric thermal and aerosol characterization from orbiting platforms. Additionally, there are one-dimensional (vertical) and three-dimensional numerical models of the atmosphere available to provide predictions for entry probes [1,2,3] (and aerobraking spacecraft [4]) and to aid in interpretations of entry probe measurements. This presentation focuses upon the atmospheric variability that can be experienced by a probe, which has a dependency on atmospheric dust load, season, location (latitude and longitude), and "weather" (baroclinic waves, thermal tides, dust storms, etc.) The primary tool is a numerical model of the Martian atmosphere with significant heritage (NASA AMES GCM), with additional comparison to a new model in development with collaboration with the University of Michigan. Haberle, R. M., J.R. Barnes, J.R. Murphy, M. M Joshi, and J. Schaeffer, Meteorological Predictions for the Mars Pathfinder Lander. J. Geophys. Res., 102, 13301-13311, 1997. Tyler Jr., D., J.R. Barnes, E.D. Skyllingstad, Mesoscale and LES Model Studies of the Martian Atmosphere in Support of Phoenix, Submitted, J. Geophys. Res., Spring 2008. Michaels, T. I., and S.C.R. Rafkin, (2008), Meteorological Predictions for Candidate 2007 Phoenix Mars Lander Sites using MRAMS, Submitted, J. Geophys. Res., Spring 2008. Bougher, S.W., J.R. Murphy, J.M. Bell, R.W. Zurek, Prediction of the Structure of the Martian Upper Atmosphere for the Mars Reconnaissance Orbiter (MRO) Mission, Mars, 2, 10-20, 2006.NASA ; New Mexico Space Grant Fellowship ; NSF Atmospheres Program ; International Planetary Probe Worksho

Hydrogen solubility in zirconium intermetallic second phase particles

The enthalpies of solution of H in Zr binary intermetallic compounds formed with Cu, Cr, Fe, Mo, Ni, Nb, Sn and V were calculated by means of density functional theory simulations and compared to that of H in {\alpha}-Zr. It is predicted that all Zr-rich phases (formed with Cu, Fe, Ni and Sn), and those phases formed with Nb and V, offer lower energy, more stable sites for H than {\alpha}-Zr. Conversely, Mo and Cr containing phases do not provide preferential solution sites for H. In all cases the most stable site for H are those that offer the highest coordination fraction of Zr atoms. Often these are four Zr tetrahedra but not always. Implications with respect to H-trapping properties of commonly observed ternary phases such as Zr(Cr,Fe)2, Zr2(Fe,Ni) and Zr(Nb,Fe)2 are also discussed.Comment: manuscript accepted for publication in Journal of Nuclear Materials (2013

The {\gamma} Dor stars as revealed by Kepler : A key to reveal deep-layer rotation in A and F stars

The {\gamma} Dor pulsating stars present high-order gravity modes, which make them important targets in the intermediate-and low-mass main-sequence region of the Hertzsprung-Russell diagram. Whilst we have only access to rotation in the envelope of the Sun, the g modes of {\gamma} Dor stars can in principle deliver us constraints on the inner layers. With the puzzling discovery of unexpectedly low rotation rates in the core of red giants, the {\gamma} Dor stars appear now as unique targets to explore internal angular momentum transport in the progenitors of red giants. Yet, the {\gamma} Dor pulsations remain hard to detect from the ground for their periods are close to 1 day. While the CoRoT space mission first revealed intriguing frequency spectra, the almost uninterrupted 4-year photometry from the Kepler mission eventually shed a new light on them. It revealed regularities in the spectra, expected to bear signature of physical processes, including rotation, in the shear layers close to the convective core. We present here the first results of our effort to derive exploitable seismic diagnosis for mid- to fast rotators among {\gamma} Dor stars. We confirm their potential to explore the rotation history of this early phase of stellar evolution.Comment: 4 pages, 1 figure, proceedings of the 22nd Los Alamos Stellar Pulsation Conference, "Wide-field variability surveys: a 21st-century perspective" held in San Pedro de Atacama, Chile, Nov. 28-Dec. 2, 201

Free healthy breakfasts in primary schools: A cluster randomised controlled trial of a policy intervention in Wales, UK

Objective: The present study evaluated the impact of a national school programme of universal free healthy breakfast provision in Wales, UK. Design: A cluster randomised controlled trial with repeated cross-sectional design and a 12-month follow-up. Primary outcomes were breakfast skipping, breakfast diet and episodic memory. Secondary outcomes were frequency of eating breakfast at home and at school, breakfast attitudes, rest-of-day diet and class behaviour. Setting: Primary schools in nine local education authority areas. Subjects: A total of 4350 students (aged 9–11 years) at baseline and 4472 at follow-up in 111 schools. Results: Students in intervention schools reported significantly higher numbers of healthy food items consumed at breakfast and more positive attitudes towards breakfast eating at 12 months. Parents in intervention schools reported significantly higher rates of consumption of breakfast at school and correspondingly lower rates of breakfast consumption at home. No other significant differences were found. Conclusions: The intervention did not reduce breakfast skipping; rather, pupils substituted breakfast at home for breakfast at school. However, there were improvements in children’s nutritional intake at breakfast time, if not the rest of the day, and more positive attitudes to breakfast, which may have implications for life-course dietary behaviours. There was no impact on episodic memory or classroom behaviour, which may require targeting breakfast skippers

Aerosol hygroscopicity in the marine atmosphere: a closure study using high-time-resolution, multiple-RH DASH-SP and size-resolved C-ToF-AMS data

We have conducted the first airborne hygroscopic growth closure study to utilize data from an Aerodyne compact Time-of-Flight Aerosol Mass Spectrometer (C-ToF-AMS) coupled with size-resolved, multiple-RH, high-time-resolution hygroscopic growth factor (GF) measurements from the differential aerosol sizing and hygroscopicity spectrometer probe (DASH-SP). These data were collected off the coast of Central California during seven of the 16 flights carried out during the MASE-II field campaign in July 2007. Two of the seven flights were conducted in airmasses characterized by continental origin. These flights exhibited elevated organic volume fractions (VF_(organic)=0.56±0.19, as opposed to 0.39±0.20 for all other flights), corresponding to significantly suppressed GFs at high RH (1.61±0.14 at 92% RH, as compared with 1.91±0.07 for all other flights), more moderate GF suppression at intermediate RH (1.53±0.10 at 85%, compared with 1.58±0.08 for all other flights), and no measurable GF suppression at low RH (1.31±0.06 at 74%, compared with 1.31±0.07 for all other flights). Organic loadings were slightly elevated in above-cloud aerosols, as compared with below-cloud aerosols, and corresponded to a similar trend of significantly suppressed GF at high RH, but more moderate impacts at lower values of RH. A hygroscopic closure based on a volume-weighted mixing rule provided good agreement with DASH-SP measurements (R^2=0.78). Minimization of root mean square error between observations and predictions indicated mission-averaged organic GFs of 1.22, 1.45, and 1.48 at 74, 85, and 92% RH, respectively. These values agree with previously reported values for water-soluble organics such as dicarboxylic and multifunctional acids, and correspond to a highly oxidized, presumably water-soluble, organic fraction (mission-averaged O:C=0.92±0.33). Finally, a backward stepwise linear regression revealed that, other than RH, the most important predictor for GF is VF_(organic), indicating that a simple emperical model relating GF, RH, and the relative abundance of organic material can provide accurate predictions (R^2=0.77) of hygroscopic growth for the California coast

Selected reliability studies for the NERVA program

An investigation was made into certain methods of reliability analysis that are particularly suitable for complex mechanisms or systems in which there are many interactions. The methods developed were intended to assist in the design of such mechanisms, especially for analysis of failure sensitivity to parameter variations and for estimating reliability where extensive and meaningful life testing is not feasible. The system is modeled by a network of interconnected nodes. Each node is a state or mode of operation, or is an input or output node, and the branches are interactions. The network, with its probabilistic and time-dependent paths is also analyzed for reliability and failure modes by a Monte Carlo, computerized simulation of system performance

Quantum Chessboards in the Deuterium Molecular Ion

We present a new algorithm for vibrational control in deuterium molecules that is feasible with current experimental technology. A pump mechanism is used to create a coherent superposition of the D2+ vibrations. A short, intense infrared control pulse is applied after a chosen delay time to create selective interferences. A `chessboard' pattern of states can be realized in which a set of even- or odd-numbered vibrational states can be selectively annihilated or enhanced. A technique is proposed for experimental realization and observation of this effect using 5 fs pulses of 790 nm radiation, with intermediate intensity (5e13 W/cm2)Comment: 12 pages, 5 figure

Positioning adolescents in literacy teaching and learning

Secondary literacy instruction often happens to adolescents rather than with them. To disrupt this trend, we collaborated with 12th-grade “literacy mentors” to reimagine literacy teaching and learning with 10th-grade mentees in a public high school classroom. We used positioning theory as an analytic tool to (a) understand how mentors positioned themselves and how we positioned them and (b) examine the literacy practices that enabled and constrained the mentor position. We found that our positioning of mentors as collaborators was taken up in different and sometimes unexpected ways as a result of the multiple positions available to them and institutional-level factors that shaped what literacy practices were and were not negotiable. We argue that future collaborations with youth must account for the rights and duties of all members of a classroom community, including how those rights and duties intersect, merge, or come into conflict within and across practices.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by a Faculty Research Award from the School of Education at Boston University. (Faculty Research Award from the School of Education at Boston University)Accepted manuscrip