4,563 research outputs found
Chemical-looping combustion - a thermodynamic study
Published versio
Space Velocities of L- and T-type Dwarfs
(Abridged) We have obtained radial velocities of a sample of 18 ultracool
dwarfs (M6.5-T8) using high-resolution, near-infrared spectra obtained with
NIRSPEC and the Keck II telescope. We have confirmed that the radial velocity
of Gl 570 D is coincident with that of the K-type primary star Gl 570 A, thus
providing additional support for their true companionship. The presence of
planetary-mass companions around 2MASS J05591914-1404488 (T4.5V) has been
analyzed using five NIRSPEC radial velocity measurements obtained over a period
of 4.37 yr. We have computed UVW space motions for a total of 21 L and T dwarfs
within 20 pc of the Sun. This population shows UVW velocities that nicely
overlap the typical kinematics of solar to M-type stars within the same spatial
volume. However, the mean Galactic (44.2 km/s) and tangential (36.5 km/s)
velocities of the L and T dwarfs appear to be smaller than those of G to M
stars. A significant fraction (~40%) of the L and T dwarfs lies near the Hyades
moving group (0.4-2 Gyr), which contrasts with the 10-12% found for
earlier-type stellar neighbors. Additionally, the distributions of all three
UVW components (sigma_{UVW} = 30.2, 16.5, 15.8 km/s) and the distributions of
the total Galactic (sigma_{v_tot} = 19.1 km/s) and tangential (sigma_{v_t} =
17.6 km/s) velocities derived for the L and T dwarf sample are narrower than
those measured for nearby G, K, and M-type stars, but similar to the
dispersions obtained for F stars. This suggests that, in the solar
neighborhood, the L- and T-type ultracool dwarfs in our sample (including brown
dwarfs) is kinematically younger than solar-type to early M stars with likely
ages in the interval 0.5-4 Gyr.Comment: Accepted for publication in Ap
The incidence and risk factors for new onset atrial fibrillation in the PROSPER study
Aims Atrial fibrillation/flutter (AF) is the most common arrhythmia in older people. It associates with reduced exercise capacity, increased risk of stroke, and mortality. We aimed to determine retrospectively whether pravastatin reduces the incidence of AF and whether any electrocardiographic measures or clinical conditions might be risk factors for its development. Methods and results The PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) was a randomized, double-blind controlled trial that recruited 5804 individuals aged 70-82 years with a history of, or risk factors for, vascular disease. A total of 2891 were allocated to pravastatin and 2913 to placebo; mean follow-up was 3.2 years. Electrocardiograms (ECGs), which were recorded at baseline, annually thereafter, and at run-out, were processed by computer and reviewed manually. In all, 264 of 2912 (9.1%) of the placebo group and 283 of 2888 (9.8%) of the pravastatin-treated group developed AF [hazard ratio 1.08 (0.92,1.28), P = 0.35)]. Multivariate analysis showed that PR and QTc intervals, age, left ventricular hypertrophy, and ST-T abnormalities were related to development of AF after adjustment for many variables including alcohol consumption, which itself was univariately predictive of developing AF. Previous myocardial infarction on the ECG was not a risk factor. A history of vascular disease was strongly linked with developing AF but not diabetes and hypertension. Conclusion Pravastatin does not reduce the incidence of AF in older people at risk of vascular disease, at least in the short-medium term. Risk factors for AF include older age, prolongation of PR or QTc intervals, left ventricular hypertrophy, and ST-T abnormalities on the EC
Black carbon aerosol mixing state, organic aerosols and aerosol optical properties over the United Kingdom
Black carbon (BC) aerosols absorb sunlight thereby leading to a positive radiative forcing and a warming of climate and can also impact human health through their impact on the respiratory system. The state of mixing of BC with other aerosol species, particularly the degree of internal/external mixing, has been highlighted as a major uncertainty in assessing its radiative forcing and hence its climate impact, but few in situ observations of mixing state exist. We present airborne single particle soot photometer (SP2) measurements of refractory BC (rBC) mass concentrations and mixing state coupled with aerosol composition and optical properties measured in urban plumes and regional pollution over the United Kingdom. All data were obtained using instrumentation flown on the UK's BAe-146-301 large Atmospheric Research Aircraft (ARA) operated by the Facility for Airborne Atmospheric Measurements (FAAM). We measured sub-micron aerosol composition using an aerosol mass spectrometer (AMS) and used positive matrix factorization to separate hydrocarbon-like (HOA) and oxygenated organic aerosols (OOA). We found a higher number fraction of thickly coated rBC particles in air masses with large OOA relative to HOA, higher ozone-to-nitrogen oxides (NO<sub>x</sub>) ratios and large concentrations of total sub-micron aerosol mass relative to rBC mass concentrations. The more ozone- and OOA-rich air masses were associated with transport from continental Europe, while plumes from UK cities had higher HOA and NO<sub>x</sub> and fewer thickly coated rBC particles. We did not observe any significant change in the rBC mass absorption efficiency calculated from rBC mass and light absorption coefficients measured by a particle soot absorption photometer despite observing significant changes in aerosol composition and rBC mixing state. The contributions of light scattering and absorption to total extinction (quantified by the single scattering albedo; SSA) did change for different air masses, with lower SSA observed in urban plumes compared to regional aerosol (0.85 versus 0.9–0.95). We attribute these differences to the presence of relatively rapidly formed secondary aerosol, primarily OOA and ammonium nitrate, which must be taken into account in radiative forcing calculations
The ATLAS SCT grounding and shielding concept and implementation
This paper presents a complete description of Virgo, the French-Italian gravitational wave detector. The detector, built at Cascina, near Pisa (Italy), is a very large Michelson interferometer, with 3 km-long arms. In this paper, following a presentation of the physics requirements, leading to the specifications for the construction of the detector, a detailed description of all its different elements is given. These include civil engineering infrastructures, a huge ultra-high vacuum (UHV) chamber (about 6000 cubic metres), all of the optical components, including high quality mirrors and their seismic isolating suspensions, all of the electronics required to control the interferometer and for signal detection. The expected performances of these different elements are given, leading to an overall sensitivity curve as a function of the incoming gravitational wave frequency. This description represents the detector as built and used in the first data-taking runs. Improvements in different parts have been and continue to be performed, leading to better sensitivities. These will be detailed in a forthcoming paper
Ground-based aerosol characterization during the South American Biomass Burning Analysis (SAMBBA) field experiment
This paper investigates the physical and chemical
characteristics of aerosols at ground level at a site
heavily impacted by biomass burning. The site is located
near Porto Velho, Rondônia, in the southwestern part of the
Brazilian Amazon rainforest, and was selected for the deployment
of a large suite of instruments, among them an
Aerosol Chemical Speciation Monitor. Our measurements
were made during the South American Biomass Burning
Analysis (SAMBBA) field experiment, which consisted of
a combination of aircraft and ground-based measurements
over Brazil, aimed to investigate the impacts of biomass
burning emissions on climate, air quality, and numerical
weather prediction over South America. The campaign took
place during the dry season and the transition to the wet season
in September/October 2012.
During most of the campaign, the site was impacted by
regional biomass burning pollution (average CO mixing ratio
of 0.6 ppm), occasionally superimposed by intense (up
to 2 ppm of CO), freshly emitted biomass burning plumes.
Aerosol number concentrations ranged from ∼ 1000 cm−3
to
peaks of up to 35 000 cm−3
(during biomass burning (BB)
events, corresponding to an average submicron mass mean
concentrations of 13.7 µg m−3
and peak concentrations close
to 100 µg m−3
. Organic aerosol strongly dominated the submicron
non-refractory composition, with an average concentration
of 11.4 µg m−3
. The inorganic species, NH4, SO4,
NO3, and Cl, were observed, on average, at concentrations
of 0.44, 0.34, 0.19, and 0.01 µg m−3
, respectively. Equivalent
black carbon (BCe) ranged from 0.2 to 5.5 µg m−3
,
with an average concentration of 1.3 µg m−3
. During BB
peaks, organics accounted for over 90 % of total mass (submicron
non-refractory plus BCe), among the highest values
described in the literature.
We examined the ageing of biomass burning organic
aerosol (BBOA) using the changes in the H : C and O : C
ratios, and found that throughout most of the aerosol processing
(O : C ∼= 0.25 to O : C ∼= 0.6), no remarkable change
is observed in the H : C ratio (∼ 1.35). Such a result contrasts
strongly with previous observations of chemical ageing
of both urban and Amazonian biogenic aerosols. At higher
levels of processing (O : C > 0.6), the H : C ratio changes
with a H : C/O : C slope of −0.5, possibly due to the development
of a combination of BB (H : C/O : C slope =
0) and biogenic (H : C/O : C slope = −1) organic aerosol
(OA). An analysis of the 1OA/1CO mass ratios yields
very little enhancement in the OA loading with atmospheric
processing, consistent with previous observations. These
results indicate that negligible secondary organic aerosol
(SOA) formation occurs throughout the observed BB plume
Published by Copernicus Publications on behalf of the European Geosciences Union.
12070 J. Brito et al.: Ground-based aerosol characterization during SAMBBA
processing, or that SOA formation is almost entirely balanced
by OA volatilization.
Positive matrix factorization (PMF) of the organic aerosol
spectra resulted in three factors: fresh BBOA, aged BBOA,
and low-volatility oxygenated organic aerosol (LV-OOA).
Analysis of the diurnal patterns and correlation with external
markers indicates that during the first part of the campaign,
OA concentrations are impacted by local fire plumes
with some chemical processing occurring in the near-surface
layer. During the second part of the campaign, long-range
transport of BB plumes above the surface layer, as well as
potential SOAs formed aloft, dominates OA concentrations
at our ground-based sampling site.
This manuscript describes the first ground-based deployment
of the aerosol mass spectrometry at a site heavily impacted
by biomass burning in the Amazon region, allowing
a deeper understanding of aerosol life cycle in this important
ecosystem.This work was supported by the Foundation
for Research Support of the State of São Paulo (FAPESP,
projects 2012/14437-9 and 2013/05014-0), CNPq project 475735-
2012-9, INCT Amazonia, and Natural Environment Research
Council (NERC) project NE/J010073/1. We thank A. Ribeiro,
A. L. Loureiro, F. Morais, F. Jorge, and S. Morais for technical and
logistics support. We thank the National Institute of Meteorology
for providing valuable meteorological data. We gratefully acknowledge
S. Hacon, J. Silva, and W. Bastos for support in the successful
operation of the sampling site
Corotation: its influence on the chemical abundance pattern of the Galaxy
A simple theory for the chemical enrichment of the Galaxy which takes into
account the effects of spiral arms on heavy elements output was developed. In
the framework of the model with the corotation close to the position of the Sun
in the Galaxy the observed abundance features are explained.Comment: LaTeX, 6 pages, 5 jpg figures, uses aastex.sty, submitted to ApJ Let
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Airborne measurements of trace gases and aerosols over the London metropolitan region
The Emissions around the M25 motorway (EM25) campaign took place over the megacity of London in the United Kingdom in June 2009 with the aim of characterising trace gas and aerosol composition and properties entering and emitted from the urban region. It featured two mobile platforms, the UK BAe-146 Facility for Airborne Atmospheric Measurements (FAAM) research aircraft and a ground-based mobile lidar van, both travelling in circuits around London, roughly following the path of the M25 motorway circling the city. We present an overview of findings from the project, which took place during typical UK summertime pollution conditions. Emission ratios of volatile organic compounds (VOCs) to acetylene and carbon monoxide emitted from the London region were consistent with measurements in and downwind of other large urban areas and indicated traffic and associated fuel evaporation were major sources. Sub-micron aerosol composition was dominated by secondary species including sulphate (24% of sub-micron mass in the London plume and 29% in the non-plume regional aerosol), nitrate (24% plume; 20% regional) and organic aerosol (29% plume; 31% regional). The primary sub-micron aerosol emissions from London were minor compared to the larger regional background, with only limited increases in aerosol mass in the urban plume compared to the background (~12% mass increase on average). Black carbon mass was the major exception and more than doubled in the urban plume, leading to a decrease in the single scattering albedo from 0.91 in the regional aerosol to 0.86 in the London plume, on average. Our observations indicated that regional aerosol plays a major role on aerosol concentrations around London, at least during typical summertime conditions, meaning future efforts to reduce PM levels in London must account for regional as well as local aerosol sources
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Evaluation of biomass burning aerosols in the HadGEM3 climate model with observations from the SAMBBA field campaign
We present observations of biomass burning aerosol from the South American Biomass Burning Analysis (SAMBBA) and other measurement campaigns, and use these to evaluate the representation of biomass burning aerosol properties and processes in a state-of-the-art climate model. The evaluation includes detailed comparisons with aircraft and ground data, along with remote sensing observations from MODIS and AERONET. We demonstrate several improvements to aerosol properties following the implementation of the Global Model for Aerosol Processes (GLOMAP-mode) modal aerosol scheme in the HadGEM3 climate model. This predicts the particle size distribution, composition, and optical properties, giving increased accuracy in the representation of aerosol properties and physical–chemical processes over the Coupled Large-scale Aerosol Scheme for Simulations in Climate Models (CLASSIC) bulk aerosol scheme previously used in HadGEM2. Although both models give similar regional distributions of carbonaceous aerosol mass and aerosol optical depth (AOD), GLOMAP-mode is better able to capture the observed size distribution, single scattering albedo, and Ångström exponent across different tropical biomass burning source regions. Both aerosol schemes overestimate the uptake of water compared to recent observations, CLASSIC more so than GLOMAP-mode, leading to a likely overestimation of aerosol scattering, AOD, and single scattering albedo at high relative humidity. Observed aerosol vertical distributions were well captured when biomass burning aerosol emissions were injected uniformly from the surface to 3 km. Finally, good agreement between observed and modelled AOD was gained only after scaling up GFED3 emissions by a factor of 1.6 for CLASSIC and 2.0 for GLOMAP-mode. We attribute this difference in scaling factor mainly to different assumptions for the water uptake and growth of aerosol mass during ageing via oxidation and condensation of organics. We also note that similar agreement with observed AOD could have been achieved with lower scaling factors if the ratio of organic carbon to primary organic matter was increased in the models toward the upper range of observed values. Improved knowledge from measurements is required to reduce uncertainties in emission ratios for black carbon and organic carbon, and the ratio of organic carbon to primary organic matter for primary emissions from biomass burning
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