1,285 research outputs found
LOX/hydrocarbon auxiliary propulsion system study
Liquid oxygen (LOX)/hydrocarbon propulsion concepts for a "second generation' orbiter auxiliary propulsion system was evaluated. The most attractive fuel and system design approach identified, and the technology advancements that are needed to provide high confidence for a subsequent system development were determined. The fuel candidates were ethanol, methane, propane, and ammonia. Even though ammonia is not a hydrocarbon, it was included for evaluation because it is clean burning and has a good technology base. The major system design options were pump versus pressure feed, cryogenic versus ambient temperature RCS propellant feed, and the degree of OMS-RCS integration. Ethanol was determined to be the best fuel candidate. It is an earth-storable fuel with a vapor pressure slightly higher than monomethyl hydrazine. A pump-fed OMS was recommended because of its high specific impulse, enabling greater velocity change and greater payload capability than a pressure fed system
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In-work poverty in the East Midlands
Research that explores the nature and scale of in-work poverty in the East Midlands, using several established measures
Observational constraints on the atmospheres of Uranus and Neptune from new measurements near 10 micron
Uranus was detected at 10.3, 11.6 and 12.5 micrometers approximately 1 micrometer spectral bandpasses, with respective brightness temperatures of 74.0 + 0.9 or -1.1, 67.6 + 0.5 or -0.7, and 65.5 + 0.6 or -0.7 K and the first detection of Neptune at 10.3 micrometers with a brightness temperature of 77.5 + 0.7 or -0.9 K. We also detected Neptune at 11.36 micrometers with 2% spectral resolution at 81.0 + 0.8 or -0.9 K. The 10 micrometers continuous of both Uranus and Neptune may in part be due to reflected solar radiation as well as thermal emission. If all of the observed flux is reflected light, then the maximum geometric albedo of Uranus is 0.115 + or - 0.020, and that of Neptune is 0.229 + or - 0.043. In the context of previous observations in this region, the maximum stratospheric C2H6 mixing ratio is found to be 3 x 10 to the -8 power for Uranus and 3 x 10 to the -6 power for Neptune. A value for the maximum mixing ratio in the stratosphere of Neptune on the order of 1 - 0.004 appears to be consistent with the available data
Evaluation of modelling approaches for predicting the spatial distribution of soil organic carbon stocks at the national scale
Soil organic carbon (SOC) plays a major role in the global carbon budget. It
can act as a source or a sink of atmospheric carbon, thereby possibly
influencing the course of climate change. Improving the tools that model the
spatial distributions of SOC stocks at national scales is a priority, both for
monitoring changes in SOC and as an input for global carbon cycles studies. In
this paper, we compare and evaluate two recent and promising modelling
approaches. First, we considered several increasingly complex boosted
regression trees (BRT), a convenient and efficient multiple regression model
from the statistical learning field. Further, we considered a robust
geostatistical approach coupled to the BRT models. Testing the different
approaches was performed on the dataset from the French Soil Monitoring
Network, with a consistent cross-validation procedure. We showed that when a
limited number of predictors were included in the BRT model, the standalone BRT
predictions were significantly improved by robust geostatistical modelling of
the residuals. However, when data for several SOC drivers were included, the
standalone BRT model predictions were not significantly improved by
geostatistical modelling. Therefore, in this latter situation, the BRT
predictions might be considered adequate without the need for geostatistical
modelling, provided that i) care is exercised in model fitting and validating,
and ii) the dataset does not allow for modelling of local spatial
autocorrelations, as is the case for many national systematic sampling schemes
Using remote sensing to forecast forage quality for cattle in the dry savannas of northeast Australia
In the dry savannas of northeast Australia, forage quality is just as important for cattle production as forage quantity. The seasonal trend of forage quality is broadly predictable by land managers, but it is more difficult to predict the point when qualityâwhich depends on local climate, management, and pasture conditionâfalls below the requirement for animal maintenance. In this study we use statistical modelling to forecast how forage quality might change at the crucial time of year, i.e., as the summer wet season transitions to the dry winter. We do this with the aid of historical information associated with a long-term cattle-grazing trial in the dry savannas. We combined multiple years of two measures of forage quality (dietary crude protein and in vivo dry-matter digestibility; respectively DCP and DMD) and ground cover information (specifically the ratio of âgreen grassâ cover to âdead (i.e., non-photosynthetic) grassâ cover, derived from an archive of Landsat satellite imagery) into a linear mixed model that explicitly considered the correlations with time and between variables. DCP and DMD were estimated by near-infrared spectroscopy of fresh faecal samples; values did not have to be temporally coincident with the satellite imagery. With the end of May considered a nominal decision-point, we forecast monthly averages of forage quality for June to August, over a 12-year period at the study site. Over all months and all years, the median absolute error of the forecasts was DCPÂ =Â 0.86%, and DMDÂ =Â 0.95%. The remote sensing information served as a correlated, oft-sampled covariate that helped to guide the forecasts of forage quality. We propose summarising the forecasts (and their uncertainty) as a near-real-time graphical tool for decision-support. Such a product could potentially benefit cattle-grazing enterprises in the northeast of Australia, enabling more timely management of herds through the dry season
Representing addition and subtraction : learning the formal conventions
The study was designed to test the effects of a structured intervention in teaching children to represent addition and subtraction. In a post-test only control group design, 90 five-year-olds experienced the intervention entitled Bi-directional Translation whilst 90 control subjects experienced typical teaching. Post-intervention testing showed some significant differences between the two groups both in terms of being able to effect the addition and subtraction operations and in being able to determine which operation was appropriate. The results suggest that, contrary to historical practices, children's exploration of real world situations should precede practice in arithmetical symbol manipulation
Calibration of the Herschel SPIRE Fourier Transform Spectrometer
The Herschel SPIRE instrument consists of an imaging photometric camera and
an imaging Fourier Transform Spectrometer (FTS), both operating over a
frequency range of 450-1550 GHz. In this paper, we briefly review the FTS
design, operation, and data reduction, and describe in detail the approach
taken to relative calibration (removal of instrument signatures) and absolute
calibration against standard astronomical sources. The calibration scheme
assumes a spatially extended source and uses the Herschel telescope as primary
calibrator. Conversion from extended to point-source calibration is carried out
using observations of the planet Uranus. The model of the telescope emission is
shown to be accurate to within 6% and repeatable to better than 0.06% and, by
comparison with models of Mars and Neptune, the Uranus model is shown to be
accurate to within 3%. Multiple observations of a number of point-like sources
show that the repeatability of the calibration is better than 1%, if the
effects of the satellite absolute pointing error (APE) are corrected. The
satellite APE leads to a decrement in the derived flux, which can be up to ~10%
(1 sigma) at the high-frequency end of the SPIRE range in the first part of the
mission, and ~4% after Herschel operational day 1011. The lower frequency range
of the SPIRE band is unaffected by this pointing error due to the larger beam
size. Overall, for well-pointed, point-like sources, the absolute flux
calibration is better than 6%, and for extended sources where mapping is
required it is better than 7%.Comment: 20 pages, 18 figures, accepted for publication in MNRA
The effect of the impact of comet Shoemaker Levyâ9 on Jupiter's aurorae
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95050/1/grl8225.pd
Coordination Chemistry and Sensing Properties Towards Anions and Metal Ions of a Simple Fluorescent Urea
The coordination and sensing properties towards anions and transition metal ions of the simple novel fluorescent urea 1-(2-aminophenyl)-3-(naphthalen-1)-yl)urea (L) were investigated in solution, and in the solid state. An electron donating amine group in the molecular skeleton of L decreased the acidity of the urea NHs that are usually deprotonated by basic anions and allowed for a good degree of affinity towards fluoride in DMSO-d6-0.5 %H2O. Moreover, the amine moiety acted as a further binding group for metal ions. Indeed, L was able to bind Zn2+ both in solution and in the solid state, and to respond to the presence of this metal ion in MeCN with an enhancement of the fluorescence emission. Although solution studies evidenced the formation of a 1 : 1 complex of L with Zn2+, complexes with a 2 : 1 ligand-to-metal stoichiometry were isolated in the solid state. DFT calculations helped to clarify the stability reasons behind these results
Surface Structure of Liquid Metals and the Effect of Capillary Waves: X-ray Studies on Liquid Indium
We report x-ray reflectivity (XR) and small angle off-specular diffuse
scattering (DS) measurements from the surface of liquid Indium close to its
melting point of C. From the XR measurements we extract the surface
structure factor convolved with fluctuations in the height of the liquid
surface. We present a model to describe DS that takes into account the surface
structure factor, thermally excited capillary waves and the experimental
resolution. The experimentally determined DS follows this model with no
adjustable parameters, allowing the surface structure factor to be deconvolved
from the thermally excited height fluctuations. The resulting local electron
density profile displays exponentially decaying surface induced layering
similar to that previously reported for Ga and Hg. We compare the details of
the local electron density profiles of liquid In, which is a nearly free
electron metal, and liquid Ga, which is considerably more covalent and shows
directional bonding in the melt. The oscillatory density profiles have
comparable amplitudes in both metals, but surface layering decays over a length
scale of \AA for In and \AA for Ga. Upon controlled
exposure to oxygen, no oxide monolayer is formed on the liquid In surface,
unlike the passivating film formed on liquid Gallium.Comment: 9 pages, 5 figures; submitted to Phys. Rev.
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