1,550 research outputs found
Ten eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and Cloud distance
This is the author accepted manuscript. The final version is available from OUP via the DOI in this record.We present the first results of an observational programme to measure the fundamental parameters of over 100 eclipsing binaries in the Small Magellanic Cloud (SMC). The spectroscopic data have been obtained by using the two degree field (2dF) multi-object spectrograph on the 3.9-m Anglo-Australian Telescope, and have been used in conjunction with photometry from the Optical Gravitational Lensing Experiment (OGLE) data base of SMC eclipsing binaries. In this first paper, we discuss 10 systems: three are detached early-B binaries, six are in a semi-detached configuration, and one is in a marginal contact state. We conclude that the semi-detached systems are undergoing the slow mass-transfer phase of case-A binary evolution, in which the mass donor has reached its Roche lobe while still on the main sequence. Each system provides a primary distance indicator. By constructing a new calibration between spectral type and temperature for O and early B stars, we find a mean distance modulus to the SMC of 18.89±0.04 (statistical) ±0.10 (systematic). This value represents one of the most precise determinations to date of the distance to the SMC
Coupled biogeochemical cycles : eutrophication and hypoxia in temperate estuaries and coastal marine ecosystems
Author Posting. © Ecological Society of America, 2011. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Frontiers in Ecology and the Environment 9 (2011): 18â26, doi:10.1890/100008.Nutrient fluxes to coastal areas have risen in recent decades, leading to widespread hypoxia and other ecological damage, particularly from nitrogen (N). Several factors make N more limiting in estuaries and coastal waters than in lakes: desorption (release) of phosphorus (P) bound to clay as salinity increases, lack of planktonic N fixation in most coastal ecosystems, and flux of relatively P-rich, N-poor waters from coastal oceans into estuaries. During eutrophication, biogeochemical feedbacks further increase the supply of N and P, but decrease availability of silica â conditions that can favor the formation and persistence of harmful algal blooms. Given sufficient N inputs, estuaries and coastal marine ecosystems can be driven to P limitation. This switch contributes to greater far-field N pollution; that is, the N moves further and contributes to eutrophication at greater distances. The physical oceanography (extent of stratification, residence time, and so forth) of coastal systems determines their sensitivity to hypoxia, and recent changes in physics have made some ecosystems more sensitive to hypoxia. Coastal hypoxia contributes to ocean acidification, which harms calcifying organisms such as mollusks and some crustaceans.Funding
was supplied in part by NOAA through the Coastal
Hypoxia Research Program, by the NSF through the
Biocomplexity Coupled Biogeochemical Cycles competition,
and by DR Atkinson through an endowment given
to Cornell University
Assessment of Surface Water Contamination from Coalbed Methane Fracturing-Derived Volatile Contaminants in Sullivan County, Indiana, USA
There is a growing concern over the contamination of surface water and the associated environmental and public health consequences from the recent proliferation in hydraulic fracturing in the USA. Petroleum hydrocarbon-derived contaminants of concern [benzene, toluene, ethylbenzene, and xylene (BTEX)] and various dissolved cations and anions were spatially determined in surface waters around 14 coalbed methane fracking wells in Sullivan County, IN, USA. At least one BTEX was detected in 69% of sampling sites (n=13) and 23% of sampling sites were found to be contaminated with all of the BTEX. Toluene was the most common BTEX compound detected across all sites, both upstream and downstream from coalbed methane fracking sites. The calcium (~60 ppm) and sulfates (~175 ppm) were the dominant cations and anions, respectively, in surface water around the fracking sites. This study represents the first report of BTEX contamination in surface water from coalbed methane hydraulic fracturing wells
Climate impacts of energy technologies depend on emissions timing
Energy technologies emit greenhouse gases with differing radiative efficiencies and atmospheric lifetimes. Standard practice for evaluating technologies, which uses the global warming potential (GWP) to compare the integrated radiative forcing of emitted gases over a fixed time horizon, does not acknowledge the importance of a changing background climate relative to climate change mitigation targets. Here we demonstrate that the GWP misvalues the impact of CH[subscript 4]-emitting technologies as mid-century approaches, and we propose a new class of metrics to evaluate technologies based on their time of use. The instantaneous climate impact (ICI) compares gases in an expected radiative forcing stabilization year, and the cumulative climate impact (CCI) compares their time-integrated radiative forcing up to a stabilization year. Using these dynamic metrics, we quantify the climate impacts of technologies and show that high-CH[subscript 4]-emitting energy sources become less advantageous over time. The impact of natural gas for transportation, with CH[subscript 4] leakage, exceeds that of gasoline within 1â2 decades for a commonly cited 3 W m[superscript â2] stabilization target. The impact of algae biodiesel overtakes that of corn ethanol within 2â3 decades, where algae co-products are used to produce biogas and corn co-products are used for animal feed. The proposed metrics capture the changing importance of CH[subscript 4] emissions as a climate threshold is approached, thereby addressing a major shortcoming of the GWP for technology evaluation.New England University Transportation Center (DOT Grant DTRT07-G-0001
Reconciling carbon-cycle concepts, terminology, and methods
Author Posting. © The Author(s), 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Ecosystems 9 (2006): 1041-1050, doi:10.1007/s10021-005-0105-7.Recent patterns and projections of climatic change have focused increased scientific and public attention on patterns of carbon (C) cycling and its controls, particularly the factors that determine whether an ecosystem is a net source or sink of atmospheric CO2. Net ecosystem production (NEP), a central concept in C-cycling research, has been used to represent two different concepts by C-cycling scientists. We propose that NEP be restricted to just one of its two original definitionsâthe imbalance between gross primary production (GPP) and ecosystem respiration (ER), and that a new termânet ecosystem carbon balance (NECB)âbe applied to the net rate of C accumulation in (or loss from; negative sign) ecosystems. NECB differs from NEP when C fluxes other than C fixation and respiration occur or when inorganic C enters or leaves in dissolved form. These fluxes include leaching loss or lateral transfer of C from the ecosystem; emission of volatile organic C, methane, and carbon monoxide; and soot and CO2 from fire. C fluxes in addition to NEP are particularly important determinants of NECB over long time scales. However, even over short time scales, they are important in ecosystems such as streams,
estuaries, wetlands, and cities. Recent technological advances have led to a diversity of approaches to measuring C fluxes at different temporal and spatial scales. These approaches frequently capture different components of NEP or NECB and can therefore be compared across scales only by carefully specifying the fluxes included in the measurements. By explicitly identifying the fluxes that comprise NECB and other components of the C cycle, such as net ecosystem exchange (NEE) and net biome production (NBP), we provide a less ambiguous framework for understanding and communicating recent changes in the global C cycle.
Key words: Net ecosystem production, net ecosystem carbon balance, gross primary production, ecosystem respiration, autotrophic respiration, heterotrophic respiration, net ecosystem exchange, net biome production, net primary production
Fracking in the UK press: threat dynamics in an unfolding debate
Shale gas is a novel source of fossil fuel which is extracted by induced hydraulic fracturing, or âfrackingâ. This article examines the socio-political dimension of fracking as manifested in the UK press at three key temporal points in the debate on the practice. Three newspaper corpora were analysed qualitatively using Thematic Analysis and Social Representations Theory. Three overarching themes are discussed: âAprilâMay 2011: From Optimism to Scepticismâ; âNovember 2011: (De-)Constructing and Re-Constructing Risk and Dangerâ; âApril 2012: Consolidating Social Representations of Frackingâ. In this article, we examine the emergence of and inter-relations between competing social representations, discuss the dynamics of threat positioning and show how threat can be re-construed in order to serve particular socio-political ends in the debate on fracking
A review of physical supply and EROI of fossil fuels in China
This paper reviews Chinaâs future fossil fuel supply from the perspectives of physical output and net energy output. Comprehensive analyses of physical output of fossil fuels suggest that Chinaâs total oil production will likely reach its peak, at about 230Â Mt/year (or 9.6Â EJ/year), in 2018; its total gas production will peak at around 350Â Bcm/year (or 13.6Â EJ/year) in 2040, while coal production will peak at about 4400Â Mt/year (or 91.9Â EJ/year) around 2020 or so. In terms of the forecast production of these fuels, there are significant differences among current studies. These differences can be mainly explained by different ultimately recoverable resources assumptions, the nature of the models used, and differences in the historical production data. Due to the future constraints on fossil fuels production, a large gap is projected to grow between domestic supply and demand, which will need to be met by increasing imports. Net energy analyses show that both coal and oil and gas production show a steady declining trend of EROI (energy return on investment) due to the depletion of shallow-buried coal resources and conventional oil and gas resources, which is generally consistent with the approaching peaks of physical production of fossil fuels. The peaks of fossil fuels production, coupled with the decline in EROI ratios, are likely to challenge the sustainable development of Chinese society unless new abundant energy resources with high EROI values can be found
Tidal and groundwater fluxes to a shallow, microtidal estuary : constraining inputs through field observations and hydrodynamic modeling
This paper is not subject to U.S. copyright. The definitive version was published in Estuaries and Coasts 35 (2012): 1285-1298, doi:10.1007/s12237-012-9515-x.Increased nutrient loading to estuaries has led to
eutrophication, degraded water quality, and ecological transformations.
Quantifying nutrient loads in systems with significant
groundwater input can be difficult due to the
challenge of measuring groundwater fluxes. We quantified
tidal and freshwater fluxes over an 8-week period at the
entrance of West Falmouth Harbor, Massachusetts, a eutrophic,
groundwater-fed estuary. Fluxes were estimated from
velocity and salinity measurements and a total exchange
flow (TEF) methodology. Intermittent cross-sectional measurements
of velocity and salinity were used to convert point
measurements to cross-sectionally averaged values over the
entire deployment (index relationships). The estimated
mean freshwater flux (0.19 m3/s) for the 8-week period
was mainly due to groundwater input (0.21 m3/s) with
contributions from precipitation to the estuary surface
(0.026 m3/s) and removal by evaporation (0.048 m3/s).
Springâneap variations in freshwater export that appeared
in shorter-term averages were mostly artifacts of the index
relationships. Hydrodynamic modeling with steady groundwater
input demonstrated that while the TEF methodology resolves the freshwater flux signal, calibration of the indexâ
salinity relationships during spring tide conditions only was
responsible for most of the springâneap signal. The mean
freshwater flux over the entire period estimated from the
combination of the index-velocity, indexâsalinity, and TEF
calculations were consistent with the model, suggesting that
this methodology is a reliable way of estimating freshwater
fluxes in the estuary over timescales greater than the springâ
neap cycle. Combining this type of field campaign with
hydrodynamic modeling provides guidance for estimating
both magnitude of groundwater input and estuarine storage
of freshwater and sets the stage for robust estimation of the
nutrient load in groundwater.Funding was provided by the USGS Coastal and
Marine Geology Program and by National Science Foundation Award
#0420575 from the Biocomplexity/Coupled Biogeochemical Cycles
Program
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