648 research outputs found
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
Understanding the interface between the Mental Capacity Act’s Deprivation of Liberty Safeguards (MCA-DoLS) and the Mental Health Act (MHA)
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
. 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., ), 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 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 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
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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
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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
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