2,663 research outputs found
High-speed Civil Transport Aircraft Emissions
Estimates are given for the emissions from a proposed high speed civil transport (HSCT). This advanced technology supersonic aircraft would fly in the lower stratosphere at a speed of roughly Mach 1.6 to 3.2 (470 to 950 m/sec or 920 to 1850 knots). Because it would fly in the stratosphere at an altitude in the range of 15 to 23 km commensurate with its design speed, its exhaust effluents could perturb the chemical balance in the upper atmosphere. The first step in determining the nature and magnitude of any chemical changes in the atmosphere resulting from these proposed aircraft is to identify and quantify the chemically important species they emit. Relevant earlier work is summarized, dating back to the Climatic Impact Assessment Program of the early 1970s and current propulsion research efforts. Estimates are provided of the chemical composition of an HSCT's exhaust, and these emission indices are presented. Other aircraft emissions that are not due to combustion processes are also summarized; these emissions are found to be much smaller than the exhaust emissions. Future advances in propulsion technology, in experimental measurement techniques, and in understanding upper atmospheric chemistry may affect these estimates of the amounts of trace exhaust species or their relative importance
The Atmospheric Effects of Stratospheric Aircraft: a First Program Report
Studies have indicated that, with sufficient technology development, high speed civil transport aircraft could be economically competitive with long haul subsonic aircraft. However, uncertainty about atmospheric pollution, along with community noise and sonic boom, continues to be a major concern; and this is addressed in the planned 6 yr HSRP begun in 1990. Building on NASA's research in atmospheric science and emissions reduction, the AESA studies particularly emphasizing stratospheric ozone effects. Because it will not be possible to directly measure the impact of an HSCT aircraft fleet on the atmosphere, the only means of assessment will be prediction. The process of establishing credibility for the predicted effects will likely be complex and involve continued model development and testing against climatological patterns. Lab simulation of heterogeneous chemistry and other effects will continue to be used to improve the current models
Stratospheric aircraft exhaust plume and wake chemistry studies
This report documents progress to date in an ongoing study to analyze and model emissions leaving a proposed High Speed Civil Transport (HSCT) from when the exhaust gases leave the engine until they are deposited at atmospheric scales in the stratosphere. Estimates are given for the emissions, summarizing relevant earlier work (CIAP) and reviewing current propulsion research efforts. The chemical evolution and the mixing and vortical motion of the exhaust are analyzed to track the exhaust and its speciation as the emissions are mixed to atmospheric scales. The species tracked include those that could be heterogeneously reactive on the surfaces of the condensed solid water (ice) particles and on exhaust soot particle surfaces. Dispersion and reaction of chemical constituents in the far wake are studied with a Lagrangian air parcel model, in conjunction with a radiation code to calculate the net heating/cooling. Laboratory measurements of heterogeneous chemistry of aqueous sulfuric acid and nitric acid hydrates are also described. Results include the solubility of HCl in sulfuric acid which is a key parameter for modeling stratospheric processing. We also report initial results for condensation of nitric acid trihydrate from gas phase H2O and HNO3
Anomalous small angle x-ray scattering simulations: proof of concept for distance measurements for nanoparticle-labelled biomacromolecules in solution.
Anomalous small angle X-ray scattering can in principle be used to determine distances between metal label species on biological molecules. Previous experimental studies in the past were unable to distinguish the label-label scattering contribution from that of the molecule, because of the use of atomic labels; these labels contribute only a small proportion of the total scattering signal. However, with the development of nanocrystal labels (of 50-100 atoms) there is the possibility for a renewed attempt at applying anomalous small angle X-ray scattering for distance measurement. This is because the contribution to the scattered signal is necessarily considerably stronger than for atomic labels. Here we demonstrate through simulations, the feasibility of the technique to determine the end-to-end distances of labelled nucleic acid molecules as well as other internal distances mimicking a labelled DNA binding protein if the labels are dissimilar metal nanocrystals. Of crucial importance is the ratio of mass of the nanocrystals to that of the labelled macromolecule, as well as the level of statistical errors in the scattering intensity measurements. The mathematics behind the distance determination process is presented, along with a fitting routine than incorporates maximum entropy regularisation
Reductions in aircraft particulate emissions due to the use of FischerāTropsch fuels
The use of alternative fuels for aviation is likely to increase due to
concerns over fuel security, price stability, and the sustainability of fuel
sources. Concurrent reductions in particulate emissions from these
alternative fuels are expected because of changes in fuel composition
including reduced sulfur and aromatic content. The NASA Alternative Aviation
Fuel Experiment (AAFEX) was conducted in JanuaryāFebruary 2009 to
investigate the effects of synthetic fuels on gas-phase and particulate
emissions. Standard petroleum JP-8 fuel, pure synthetic fuels produced from
natural gas and coal feedstocks using the FischerāTropsch (FT) process, and
50% blends of both fuels were tested in the CFM-56 engines on a DC-8
aircraft. To examine plume chemistry and particle evolution with time,
samples were drawn from inlet probes positioned 1, 30, and 145 m downstream
of the aircraft engines. No significant alteration to engine performance was
measured when burning the alternative fuels. However, leaks in the aircraft
fuel system were detected when operated with the pure FT fuels as a result
of the absence of aromatic compounds in the fuel.
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Dramatic reductions in soot emissions were measured for both the pure FT
fuels (reductions in mass of 86% averaged over all powers) and blended
fuels (66%) relative to the JP-8 baseline with the largest reductions at
idle conditions. At 7% power, this corresponds to a reduction from 7.6 mg kg<sup>ā1</sup>
for JP-8 to 1.2 mg kg<sup>ā1</sup> for the natural gas FT fuel. At full
power, soot emissions were reduced from 103 to 24 mg kg<sup>ā1</sup>
(JP-8 and natural gas FT, respectively). The alternative fuels also produced
smaller soot (e.g., at 85% power, volume mean diameters were reduced from
78 nm for JP-8 to 51 nm for the natural gas FT fuel), which may reduce their
ability to act as cloud condensation nuclei (CCN). The reductions in
particulate emissions are expected for all alternative fuels with similar
reductions in fuel sulfur and aromatic content regardless of the feedstock.
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As the plume cools downwind of the engine, nucleation-mode aerosols form.
For the pure FT fuels, reductions (94% averaged over all powers) in
downwind particle number emissions were similar to those measured at the
exhaust plane (84%). However, the blended fuels had less of a reduction
(reductions of 30ā44%) than initially measured (64%). The likely
explanation is that the reduced soot emissions in the blended fuel exhaust
plume results in promotion of new particle formation microphysics, rather
than coating on pre-existing soot particles, which is dominant in the JP-8
exhaust plume. Downwind particle volume emissions were reduced for both the
pure (79 and 86% reductions) and blended FT fuels (36 and 46%) due to
the large reductions in soot emissions. In addition, the alternative fuels
had reduced particulate sulfate production (near zero for FT fuels) due to
decreased fuel sulfur content.
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To study the formation of volatile aerosols (defined as any aerosol formed as
the plume ages) in more detail, tests were performed at varying ambient
temperatures (ā4 to 20 Ā°C). At idle, particle number and volume
emissions were reduced linearly with increasing ambient temperature, with
best fit slopes corresponding to ā8 Ć 10<sup>14</sup> particles
(kg fuel)<sup>ā1</sup> Ā°C<sup>ā1</sup> for particle number emissions and
ā10 mm<sup>3</sup> (kg fuel)<sup>ā1</sup> Ā°C<sup>ā1</sup> for particle volume
emissions. The temperature dependency of aerosol formation can have large
effects on local air quality surrounding airports in cold regions.
Aircraft-produced aerosols in these regions will be much larger than levels
expected based solely on measurements made directly at the engine exit plane.
The majority (90% at idle) of the volatile aerosol mass formed as
nucleation-mode aerosols, with a smaller fraction as a soot coating.
Conversion efficiencies of up to 2.8% were measured for the partitioning
of gas-phase precursors (unburned hydrocarbons and SO<sub>2</sub>) to form volatile
aerosols. Highest conversion efficiencies were measured at 45% power
Demonstration of a Regulatory Method for Aircraft Engine Nonvolatile PM Emissions Measurements with Conventional and Isoparaffinic Kerosene fuels
The aviation industry is exploring the economic viability and environmental sustainability of the use of alternative fuels to power aircraft main engines and auxiliary power units. The International Civil Aviation Organization is also developing a regulatory standard for aircraft engine nonvolatile particulate matter (nvPM) emissions to meet the growing public demand for improvement in air quality. This study compared the nvPM emissions in the exhaust stream of a small (<26.7 kN thrust) mixed turbofan aircraft engine burning a conventional Jet A fuel as well as a Sasol isoparaffinic kerosene (IPK) fuel derived from coal, using a standardized sampling and measurement system. The goal of the study was to demonstrate the regulatory system on a small mixed turbofan engine and to assess the suitability and limitations of using such systems for turbofan engines burning fuels with different fuel properties. Significant reductions in both nvPM number- and mass-based emission indices were observed with the IPK fuel across the full spectrum of engine thrust settings. The percent reduction in nvPM mass-based emissions was higher than the reduction in nvPM number-based emissions for the corresponding engine thrust settings because smaller and fewer particles were generated with IPK fuel combustion. PM size distribution mean diameters for the IPK fuel were found to be smaller than that for Jet A. The composition of the organic PM emissions for the two fuels was almost identical, and the organic PM was also found to be proportional to the soot concentration. The nvPM mass-based emissions for the mixed turbofan engine measured with the standardized system exhibited a high degree of measurement uncertainty at low engine thrust settings. This limitation was not encountered for nvPM number-based emissions
Laser-Spectroscopic Investigation of OH-Radical Concentrations in the Exhaust Plane of Jet Engines
Hydroxyl radical (OH) emissions are relevant for oxidation reactions in the post flame chemistry of exhaust gases emitted from jet engines. No direct measurements of OH concentrations are available to date due to the low abundance and the short lifetime of this radical species. The first application of a combined technique based on Raman scattering and laser_induced fluorescence (LIF) spectrometry is presented here for measurements in the exhaust gases of a commercial jet engine operated in a test rig. From the measurements, upper limits for OH concentrations in the exit plane were determined in the range of 90 ppbv for take off and 80 ppbv for ap_idle. The values are significantly below the predictions of model calculations based on HONO and HNO3 in_flight concentration measurements presented recently. Possibilities for further increase of the detection sensitivity for OH are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86750/1/Sick34.pd
Interventions for behaviour change and self-management in stroke secondary prevention: protocol for an overview of reviews
Abstract Background Stroke secondary prevention guidelines recommend medication prescription and adherence, active education and behavioural counselling regarding lifestyle risk factors. To impact on recurrent vascular events, positive behaviour/s must be adopted and sustained as a lifestyle choice, requiring theoretically informed behaviour change and self-management interventions. A growing number of systematic reviews have addressed complex interventions in stroke secondary prevention. Differing terminology, inclusion criteria and overlap of studies between reviews makes the mechanism/s that affect positive change difficult to identify or replicate clinically. Adopting a two-phase approach, this overview will firstly comprehensively summarise systematic reviews in this area and secondly identify and synthesise primary studies in these reviews which provide person-centred, theoretically informed interventions for stroke secondary prevention. Methods An overview of reviews will be conducted using a systematic search strategy across the Cochrane Database of Systematic Reviews, PubMed and Epistomonikas. Inclusion criteria: systematic reviews where the population comprises individuals post-stroke or TIA and where data relating to person-centred risk reduction are synthesised for evidence of efficacy when compared to standard care or no intervention. Primary outcomes of interest include mortality, recurrent stroke and other cardiovascular events. In phase 1, two reviewers will independently (1) assess the eligibility of identified reviews for inclusion; (2) rate the quality of included reviews using the ROBIS tool; (3) identify unique primary studies and overlap between reviews; (4) summarise the published evidence supporting person-centred behavioural change and self-management interventions in stroke secondary prevention and (5) identify evidence gaps in this field. In phase 2, two independent reviewers will (1) examine person-centred, primary studies in each review using the Template for Intervention Description and Replication (TIDieR checklist), itemising, where present, theoretical frameworks underpinning interventions; (2) group studies employing theoretically informed interventions by the intervention delivered and by the outcomes reported (3) apply GRADE quality of evidence for each intervention by outcome/s identified from theoretically informed primary studies. Disagreement between reviewers at each process stage will be discussed and a third reviewer consulted. Discussion This overview will comprehensively bring together the best available evidence supporting person-centred, stroke secondary prevention strategies in an accessible format, identifying current knowledge gaps
Strangeness Enhancement in and Interactions at SPS Energies
The systematics of strangeness enhancement is calculated using the HIJING and
VENUS models and compared to recent data on , and
collisions at CERN/SPS energies (). The HIJING model is used to
perform a {\em linear} extrapolation from to . VENUS is used to
estimate the effects of final state cascading and possible non-conventional
production mechanisms. This comparison shows that the large enhancement of
strangeness observed in collisions, interpreted previously as possible
evidence for quark-gluon plasma formation, has its origins in non-equilibrium
dynamics of few nucleon systems. % Strangeness enhancement %is therefore traced
back to the change in the production dynamics %from to minimum bias
and central collisions. A factor of two enhancement of at
mid-rapidity is indicated by recent data, where on the average {\em one}
projectile nucleon interacts with only {\em two} target nucleons. There appears
to be another factor of two enhancement in the light ion reaction relative
to , when on the average only two projectile nucleons interact with two
target ones.Comment: 29 pages, 8 figures in uuencoded postscript fil
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