1,250 research outputs found
Connected Network of Minima as a Model Glass: Long Time Dynamics
A simple model to investigate the long time dynamics of glass-formers is
presented and applied to study a Lennard-Jones system in supercooled and glassy
phases. According to our model, the point representing the system in the
configurational phase space performs harmonic vibrations around (and activated
jumps between) minima pertaining to a connected network. Exploiting the model,
in agreement with the experimental results, we find evidence for: i) stretched
relaxational dynamics; ii) a strong T-dependence of the stretching parameter;
iii) breakdown of the Stokes-Einstein law.Comment: 4 pages (Latex), 4 eps figure
Upper ocean manifestations of a reducing meridional overturning circulation
Most climate models predict a slowing down of the Atlantic Meridional Overturning Circulation during the 21st century. Using a 100year climate change integration of a high resolution coupled climate model, we show that a 5.3Sv reduction in the deep southward transport in the subtropical North Atlantic is balanced solely by a weakening of the northward surface western boundary current, and not by an increase in the southward transport integrated across the interior ocean away from the western boundary. This is consistent with Sverdrup balance holding to a good approximation outside of the western boundary region on decadal time scales, and may help to spatially constrain past and future change in the overturning circulation. The subtropical gyre weakens by 3.4Sv over the same period due to a weakened wind stress curl. These changes combine to give a net 8.7Sv reduction in upper western boundary transport. © 2012. American Geophysical Union. All Rights Reserved
Impact of changes in barometric pressure on landfill methane emission
Citation: Xu, Liukang, Xiaomao Lin, Jim Amen, Karla Welding, and Dayle McDermitt. âImpact of Changes in Barometric Pressure on Landfill Methane Emission.â Global Biogeochemical Cycles 28, no. 7 (2014): 679â95. https://doi.org/10.1002/2013GB004571.Landfill methane emissions were measured continuously using the eddy covariance method from June to December 2010. The study site was located at the Bluff Road Landfill in Lincoln, Nebraska, USA. Our results show that landfill methane emissions strongly depended on changes in barometric pressure; rising barometric pressure suppressed the emission, while falling barometric pressure enhanced the emission, a phenomenon called barometric pumping. There was up to a 35-fold variation in day-to-day methane emissions due to changes in barometric pressure. Wavelet coherence analysis revealed a strong spectral coherency between variations of barometric pressure and methane emission at periodicities ranging from 1 day to 8 days. Power spectrum and ogive analysis showed that at least 10 days of continuous measurements was needed in order to capture 90% of the total variance in the methane emission time series at our landfill site. From our results, it is clear that point-in-time measurements taken at monthly or longer time intervals using techniques such as the trace plume method, the mass balance method, or the closed-chamber method will be subject to large variations in measured emission rates because of the barometric pumping phenomenon. Estimates of long-term integrated methane emissions from landfills based on such measurements could yield uncertainties, ranging from 28.8% underestimation to 32.3% overestimation. Our results demonstrate a need for continuous measurements to quantify annual total landfill emissions. This conclusion may apply to the study of methane emissions from wetlands, peatlands, lakes, and other environmental contexts where emissions are from porous media or ebullition. Other implications from the present study for hazard gas monitoring programs are also discussed
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Contrasting fast precipitation responses to tropospheric and stratospheric ozone forcing
The precipitation response to radiative forcing (RF) can be decomposed into a fast precipitation response (FPR), which depends on the atmospheric component of RF, and a slow response, which depends on surface temperature change. We present the first detailed climate model study of the FPR due to tropospheric and stratospheric ozone changes. The FPR depends strongly on the altitude of ozone change. Increases below about 3 km cause a positive FPR; increases above cause a negative FPR. The FPR due to stratospheric ozone change is, per unit RF, about 3 times larger than that due to tropospheric ozone. As historical ozone trends in the troposphere and stratosphere are opposite in sign, so too are the FPRs. Simple climate model calculations of the time-dependent total (fast and slow) precipitation change, indicate that ozone's contribution to precipitation change in 2011, compared to 1765, could exceed 50% of that due to CO2 change
The Lore of Low Methane Livestock:Co-Producing Technology and Animals for Reduced Climate Change Impact
Methane emissions from sheep and cattle production have gained increasing profile in the context of climate change. Policy and scientific research communities have suggested a number of technological approaches to mitigate these emissions. This paper uses the concept of co-production as an analytical framework to understand farmersâ evaluation of a 'good animalâ. It examines how technology and sheep and beef cattle are co-produced in the context of concerns about the climate change impact of methane. Drawing on 42 semi-structured interviews, this paper demonstrates that methane emissions are viewed as a natural and integral part of sheep and beef cattle by farmers, rather than as a pollutant. Sheep and beef cattle farmers in the UK are found to be an extremely heterogeneous group that need to be understood in their specific social, environmental and consumer contexts. Some are more amenable to appropriating methane reducing measures than others, but largely because animals are already co-constructed from the natural and the technical for reasons of increased production efficiency
High School Exit Examinations: When Do Learning Effects Generalize?
This paper reviews international and domestic evidence on the effects of three types of high school exit exam systems: voluntary curriculum-based external exit exams, universal curriculum-based external exit exam systems and minimum competency tests that must be passed to receive a regular high school diploma. The nations and provinces that use Universal CBEEES (and typically teacher grades as well) to signal student achievement have significantly higher achievement levels and smaller differentials by family background than otherwise comparable jurisdictions that base high stakes decisions on voluntary college admissions tests and/or teacher grades. The introduction of Universal CBEEES in New York and North Carolina during the 1990s was associated with large increases in math achievement on NAEP tests. Research on MCTs and high school accountability tests is less conclusive because these systems are new and have only been implemented in one country. Cross-section studies using a comprehensive set of controls for family background have not found that students in MCT states score higher on audit tests like the NAEP that carry no stakes for the test taker. The analysis reported in table 1 tells us that the five states that introduced MCTs during the 1990s had significantly larger improvements on NAEP tests than states that made no change in their student accountability regime. The gains, however, are smaller than for the states introducing Universal CBEEES. New York and North Carolina. The most positive finding about MCTs is that students in MCT states earn significantly more during the first eight years after graduation than comparable students in other states suggesting that MCTs improve employer perceptions of the quality of the recent graduates of local high schools
Validation of Aura Microwave Limb Sounder O-3 and CO observations in the upper troposphere and lower stratosphere
International audienceGlobal satellite observations of ozone and carbon monoxide from the Microwave Limb Sounder (MLS) on the EOS Aura spacecraft are discussed with emphasis on those observations in the 215â100 hPa region (the upper troposphere and lower stratosphere). The precision, resolution and accuracy of the data produced by the MLS âversion 2.2â processing algorithms are discussed and quantified. O3 accuracy is estimated at ~40 ppbv +5% (~20 ppbv +20% at 215 hPa) while the CO accuracy is estimated at ~30 ppbv +30% for pressures of 147 hPa and less. Comparisons with expectations and other observations show good agreements for the O3 product, generally consistent with the systematic errors quoted above. In the case of CO, a persistent factor of ~2 high bias is seen at 215 hPa. However, the morphology is shown to be realistic, consistent with raw MLS radiance data, and useful for scientific study. The MLS CO data at higher altitudes are shown to be consistent with other observations
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Synthesis and Assessment Product
This Climate Change Science Program Synthesis and Assessment Product addresses current capabilities to integrate observations of the climate system into a consistent description of past and current conditions through the method of reanalysis. In addition, the Product assesses present capabilities to attribute causes for climate variations and trends over North America during the reanalysis period, which extends from the mid-twentieth century to the present.
This Product reviews Past Climate Variability and Change in the Arctic and at High Latitudes. Paleoclimate records play a key role in our understanding of Earth's past and present climate system and in our confidence in predicting future climate changes. Paleoclimate data help to elucidate past and present active mechanisms of climate change by placing the short instrumental record into a longer term context and by permitting models to be tested beyond the limited time that instrumental measurements have been available. Recent observations in the Arctic have identified large ongoing changes and important climate feedback mechanisms that multiply the effects of global-scale climate changes. As discussed in this report, paleoclimate data show that land and sea ice have grown with cooling temperatures and have shrunk with warming ones, amplifying temperature changes while causing and responding to ecosystem shifts and sea-level changes
Ideological cultures and media discourses on scientific knowledge: re-reading news on climate change
Focusing on the representation of climate change in the British âquality press,â this article argues that the discursive (re)construction of scientific claims in the media is strongly entangled with ideological standpoints. Understood here as a set of ideas and values that legitimate a program of action vis-Ă -vis a given social and political order, ideology works as a powerful selection device in deciding what is scientific news, i.e. what the relevant âfactsâ are, and who are the authorized âagents of definitionâ of science matters. The representation of scientific knowledge has important implications for evaluating political programs and assessing the responsibility of both governments and the public in addressing climate change
Elevated Atmospheric Carbon Dioxide Concentrations Amplify Alternaria alternata Sporulation and Total Antigen Production
Background
Although the effect of elevated carbon dioxide (CO2) concentration on pollen production has been established in some plant species, impacts on fungal sporulation and antigen production have not been elucidated.
Objective
Our purpose was to examine the effects of rising atmospheric CO2 concentrations on the quantity and quality of fungal spores produced on timothy (Phleum pratense) leaves.
Methods
Timothy plants were grown at four CO2 concentrations (300, 400, 500, and 600 ÎŒmol/mol). Leaves were used as growth substrate for Alternaria alternata and Cladosporium phlei. The spore abundance produced by both fungi, as well as the size (microscopy) and antigenic protein content (ELISA) of A. alternata, were quantified.
Results
Leaf carbon-to-nitrogen ratio was greater at 500 and 600 ÎŒmol/mol, and leaf biomass was greater at 600 ÎŒmol/mol than at the lower CO2 concentrations. Leaf carbon-to-nitrogen ratio was positively correlated with A. alternata spore production per gram of leaf but negatively correlated with antigenic protein content per spore. At 500 and 600 ÎŒmol/mol CO2 concentrations, A. alternata produced nearly three times the number of spores and more than twice the total antigenic protein per plant than at lower concentrations. C. phlei spore production was positively correlated with leaf carbon-to-nitrogen ratio, but overall spore production was much lower than in A. alternata, and total per-plant production did not vary among CO2 concentrations.
Conclusions
Elevated CO2 concentrations often increase plant leaf biomass and carbon-to-nitrogen ratio. Here we demonstrate for the first time that these leaf changes are associated with increased spore production by A. alternata, a ubiquitous allergenic fungus. This response may contribute to the increasing prevalence of allergies and asthma
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