An experimental and computational study of tip clearance effects on a transonic turbine stage

This paper describes an experimental and computational investigation into the influence of tip clearance on the blade tip heat load of a high-pressure (HP) turbine stage. Experiments were performed in the Oxford Rotor facility which is a 1½ stage, shroudless, transonic, high pressure turbine. The experiments were conducted at an engine representative Mach number and Reynolds number. Rotating frame instrumentation was used to capture both aerodynamic and heat flux data within the rotor blade row. Two rotor blade tip clearances were tested (1.5% and 1.0% of blade span). The experiments were compared with computational fluid dynamics (CFD) predictions made using a steady Reynolds-averaged Navier–Stokes (RANS) solver. The experiments and computational predictions were in good agreement. The blade tip heat transfer was observed to increase with reduced tip gap in both the CFD and the experiment. The augmentation of tip heat load at smaller clearances was found to be due to the ingestion of high relative total temperature fluid near the casing, generated through casing shear.This work was sponsored by Rolls-Royce plc and the Isle of Man Government.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.ijheatfluidflow.2015.09.00

Korg: fitting, model atmosphere interpolation, and Brackett lines

We describe several updates to Korg, a package for 1D LTE spectral synthesis of FGKM stars. Built-in functions to fit observed spectra via synthesis or equivalent widths make it easy to take advantage of Korg's automatic differentiation. Comparison to a past analysis of 18 Sco shows that we obtain significantly reduced line-to-line abundance scatter with Korg. Fitting and synthesis are facilitated by a rigorously-tested model atmosphere interpolation method, which introduces negligible error to synthesized spectra for stars with $T_\mathrm{eff} \gtrsim 4000\,\mathrm{K}$. For cooler stars, atmosphere interpolation is complicated by the presence of molecules, though we demonstrate an adequate method for cool dwarfs. The chemical equilibrium solver has been extended to include polyatomic and charged molecules, extending Korg's regime of applicability to M stars. We also discuss a common oversight regarding the synthesis of hydrogen lines in the infrared, and show that Korg's Brackett line profiles are a much closer match to observations than others available. Documentation, installation instructions, and tutorials are available at https://github.com/ajwheeler/Korg.jl.Comment: Submitted to AJ, comments welcom

Seabed image acquisition and survey design for cold water coral mound characterisation

Cold-water coral (CWC) habitats are commonly regarded as hotspots of biodiversity in the deep-sea. However, a standardised approach to monitoring the effects of climate change, anthropogenic impact and natural variability through video-surveying on these habitats is poorly-established. This study is the first attempt at standardising a cost-effective video-survey design specific to small CWC mounds in order to accurately determine the proportion of facies across their surface. The Piddington Mound of the Moira Mounds, Porcupine Seabight, offshore Ireland has been entirely imaged by downward-facing video in 2011 and 2015. The 2011 video data is navigated into a full-mound, georeferenced video mosaic. A quadrat-based manual classification of this video mosaic at 0.25 m2 resolution shows the exact proportion of facies abundance across the mound surface. The minimum number of random downward-facing images from the mound are determined to accurately characterise mound surface facies proportions. This minimum sample size is used to test the effectiveness of various common survey designs for ROV-video-based habitat investigations. Single-pass video lines are not representative of the mound surface whilst gridded survey designs yield best results, similar to 100% mound coverage. The minimum sample size and manual classification are applied to the 2015 video data to show a 19% mound surface facies change over 4 years at 0.25 m2 resolution. The proportion of live coral facies show little change while coral rubble facies show most change. This highlights an inconsistency between temporally-separated data sets and implies that in 20 years, the mound surface may almost entirely change

Analytic Inversion of Emission Lines of Arbitrary Optical Depth for the Structure of Supernova Ejecta

We derive a method for inverting emission line profiles formed in supernova ejecta. The derivation assumes spherical symmetry and homologous expansion (i.e., $v(r) \propto r$), is analytic, and even takes account of occultation by a pseudo-photosphere. Previous inversion methods have been developed which are restricted to optically thin lines, but the particular case of homologous expansion permits an analytic result for lines of {\it arbitrary} optical depth. In fact, we show that the quantity that is generically retrieved is the run of line intensity $I_\lambda$ with radius in the ejecta. This result is quite general, and so could be applied to resonance lines, recombination lines, etc. As a specific example, we show how to derive the run of (Sobolev) optical depth $\tau_\lambda$ with radius in the case of a pure resonance scattering emission line.Comment: 6 pages, no figures, to appear in Astrophysical Journal Letters, requires aaspp4.sty to late

Thermochromic Metal Halide Perovskite Windows with Ideal Transition Temperatures

Urban centers across the globe are responsible for a significant fraction of energy consumption and CO2 emission. As urban centers continue to grow, the popularity of glass as cladding material in urban buildings is an alarming trend. Dynamic windows reduce heating and cooling loads in buildings by passive heating in cold seasons and mitigating solar heat gain in hot seasons. In this work, we develop a mesoscopic building energy model that demonstrates reduced building energy consumption when thermochromic windows are employed. Savings are realized across eight disparate climate zones of the United States. We use the model to determine the ideal critical transition temperature of 20 to 27.5 {\deg}C for thermochromic windows based on metal halide perovskite materials. Ideal transition temperatures are realized experimentally in composite metal halide perovskite film composed of perovskite crystals and an adjacent reservoir phase. The transition temperature is controlled by co-intercalating methanol, instead of water, with methylammonium iodide and tailoring the hydrogen-bonding chemistry of the reservoir phase. Thermochromic windows based on metal halide perovskites represent a clear opportunity to mitigate the effects of energy-hungry buildings

Tropical Cyclone Prediction on Subseasonal Time-Scales

Here we discuss recent progress in understanding tropical cyclone (TC) subseasonal variability and its prediction. There has been a concerted effort to understand the sources of predictability at subseasonal time-scales, and this effort has continued to make progress in recent years. Besides the Madden-Julian Oscillation (MJO), other modes of variability affect TCs at these time-scales, in particular various equatorial waves. Additionally, TC activity is also modulated by extratropical processes via Rossby wave breaking. There has also been progress in the ability of models to simulate the MJO and its modulation of TC activity. Community efforts have created multi-model ensemble datasets, which have made it possible to evaluate the forecast skill of the MJO and TCs on subseasonal time-scales in multiple forecasting systems. While there is positive skill in some cases, there is strong dependence on the ensemble system considered, the basin examined, and whether the storms have extratropical influences or not. Furthermore, the definition of skill differs among studies. Forecasting centers are currently issuing subseasonal TC forecasts using various techniques (statistical, statistical-dynamical and dynamical). There is also a strong interest in the private sector for forecasts with 3-4 weeks lead time

Hubble Space Telescope and Ground-Based Observations of the Type Iax Supernovae SN 2005hk and SN 2008A

We present Hubble Space Telescope (HST) and ground-based optical and near-infrared observations of SN 2005hk and SN 2008A, typical members of the Type Iax class of supernovae (SNe). Here we focus on late-time observations, where these objects deviate most dramatically from all other SN types. Instead of the dominant nebular emission lines that are observed in other SNe at late phases, spectra of SNe 2005hk and 2008A show lines of Fe II, Ca II, and Fe I more than a year past maximum light, along with narrow [Fe II] and [Ca II] emission. We use spectral features to constrain the temperature and density of the ejecta, and find high densities at late times, with n_e >~ 10^9 cm^-3. Such high densities should yield enhanced cooling of the ejecta, making these objects good candidates to observe the expected "infrared catastrophe," a generic feature of SN Ia models. However, our HST photometry of SN 2008A does not match the predictions of an infrared catastrophe. Moreover, our HST observations rule out a "complete deflagration" that fully disrupts the white dwarf for these peculiar SNe, showing no evidence for unburned material at late times. Deflagration explosion models that leave behind a bound remnant can match some of the observed properties of SNe Iax, but no published model is consistent with all of our observations of SNe 2005hk and 2008A.Comment: 20 pages, 15 figure

Temperature and nitrogen supply interact to determine protein distribution gradients in the wheat grain endosperm

Gradients exist in the distribution of storage proteins in the wheat (Triticum aestivum L.) endosperm and determine the milling properties and protein recovery rate of the grain. A novel image analysis technique was developed to quantify both the gradients in protein concentration, and the size distribution of protein bodies within the endosperm of wheat plants grown under two different (20 °C or 28 °C) post-anthesis temperatures, and supplied with a nutrient solution with either high or low nitrogen content. Under all treatment combinations protein concentration was greater in the endosperm cells closest to the aleurone layer, and decreased towards the centre of the two lobes of the grain, i.e. a negative gradient. This was accompanied by a decrease in size of protein bodies from the outer to the inner endosperm layers in all but one of the treatments. Elevated post-anthesis temperature had the effect of increasing the magnitude of the negative gradients in both protein concentration and protein body size, whilst limiting nitrogen supply decreased the gradients

Type II-P Supernovae from the SDSS-II Supernova Survey and the Standardized Candle Method

We apply the Standardized Candle Method (SCM) for Type II Plateau supernovae (SNe II-P), which relates the velocity of the ejecta of a SN to its luminosity during the plateau, to 15 SNe II-P discovered over the three season run of the Sloan Digital Sky Survey - II Supernova Survey. The redshifts of these SNe - 0.027 < z < 0.144 - cover a range hitherto sparsely sampled in the literature; in particular, our SNe II-P sample contains nearly as many SNe in the Hubble flow (z > 0.01) as all of the current literature on the SCM combined. We find that the SDSS SNe have a very small intrinsic I-band dispersion (0.22 mag), which can be attributed to selection effects. When the SCM is applied to the combined SDSS-plus-literature set of SNe II-P, the dispersion increases to 0.29 mag, larger than the scatter for either set of SNe separately. We show that the standardization cannot be further improved by eliminating SNe with positive plateau decline rates, as proposed in Poznanski et al. (2009). We thoroughly examine all potential systematic effects and conclude that for the SCM to be useful for cosmology, the methods currently used to determine the Fe II velocity at day 50 must be improved, and spectral templates able to encompass the intrinsic variations of Type II-P SNe will be needed.Comment: Accepted for publication by ApJ; data used in this paper can be downloaded from http://sdssdp47.fnal.gov/sdsssn/photometry/SNIIp.tgz; citation errors correcte