211 research outputs found
Probing the sheath electric field with a crystal lattice by using thermophoresis in dusty plasma
A two-dimensional dust crystal levitated in the sheath of a modified Gaseous
Electronics Conference (GEC) reference cell is manipulated by heating or
cooling the lower electrode. The dust charge is obtained by measuring global
characteristics of the levitated crystal obtained from top-view pictures. From
the force balance, the electric field in the sheath is reconstructed. From the
Bohm criterion, we conclude that the dust crystal is levitated mainly above and
just below the classical Bohm point
Nitrous Oxide Emissions
End of project reportNitrous oxide (N2O) is one of the three most important greenhouse gases (GHG). Nitrous oxide emissions currently account for approximately one third of GHG emissions from agriculture in Ireland. Emissions of N2O arise naturally from soil sources and from the application of nitrogen (N) in the form of N fertilizers and N in dung and urine deposition by grazing animals at pasture.
Nitrous oxide emission measurements were conducted at three different scales. Firstly, a large-scale field experiment was undertaken to compare emission rates from a pasture receiving three different rates of N fertilizer application and to identify the effects of controlling variables over a two-year period. Variation in emission rates was large both within and between years.
Two contrasting climatic years were identified. The cooler and wetter conditions in year 1 gave rise to considerably lower emission levels than the warmer and drier year 2. However, in both years, peak emissions were associated with fertilizer N applications coincident with rainfall events in the summer months.
A small-plot study was conducted to identify the individual and combined effects of fertilizer, dung and urine applications to grassland. Treatment effects were however, difficult to obtain due to the overriding effects of environmental variables.
Thirdly, through the use of a small-scale mini-lysimeter study, the diurnal nature of N2O emission rates was identified for two distinct periods during the year. The occurrence of a diurnal pattern has important implications for the identification of a measurement period during the day which is representative of the true daily flux.
The research presented aims to identify the nature and magnitude of N2O emissions and the factors which affect emission rates from a grassland in Ireland. Further work is required to integrate the effects of different soil types and contrasting climatic regimes across soil types on N2O emissions.Environmental Protection Agenc
Novel evaluation of the two-pion contribution to the nucleon isovector form factors
We calculate the two-pion continuum contribution to the nucleon isovector
spectral functions drawing upon the new high statistics measurements of the
pion form factor by the CMD-2, KLOE, and SND collaborations. The general
structure of the spectral functions remains unchanged, but the magnitude
increases by about 10%. Using the updated spectral functions, we calculate the
contribution of the two-pion continuum to the nucleon isovector form factors
and radii. We compare the isovector radii with simple rho-pole models and
illustrate their strong underestimation in such approaches. Moreover, we give a
convenient parametrization of the result for use in future form factor
analyses.Comment: 9 pages, 2 eps figures, revtex4, CMD-2 and SND data included,
conclusions unchanged, version to appear in Phys. Lett.
Nucleon Form Factors in Dispersion Theory
Dispersion relations provide a powerful tool to analyse the electromagnetic
form factors of the nucleon both in the space-like and time-like regions with
constraints from other experiments, unitarity, and perturbative QCD. We give a
brief introduction into dispersion theory for nucleon form factors and present
first results from our ongoing form factor analysis. We also calculate the
two-pion continuum contribution to the isovector spectral functions drawing
upon the new high statistics measurements of the pion form factor by the CMD-2,
KLOE, and SND collaborations.Comment: 9 pages, 9 figures, invited talk at the Symposium "20 Years of
Physics at the Mainz Microtron MAMI", October 20-22, 2005, Mainz, German
The interactive effects of fertiliser nitrogen with dung and urine on nitrous oxide emissions in grassland
The authors wish to thank the Environmental Protection Agency for funding support under the Environmental Research Technological Development and Innovation programme and the Irish Department of Agriculture, Food and the Marine for
funding support (Grant numbers RSF 13S430 and 11S138).peer-reviewedNitrous oxide (N2O) is an important and potent greenhouse gas (GHG). Although application of nitrogen (N) fertiliser is a feature of many grazing systems, limited data is available on N2O emissions in grassland as a result of the interaction between urine, dung and fertiliser N. A small plot study was conducted to identify the individual and interactive effects of calcium ammonium nitrate (CAN) fertiliser, dung and urine. Application of CAN with dung and urine significantly increased the mass of N2O-N emission. Importantly, the sum of N2O-N emitted from dung and CAN applied individually approximated the emission from dung and CAN fertiliser applied together, that is, an additive effect. However, in the case of urine and CAN applied together, the emission was more than double the sum of the emission from urine and CAN fertiliser applied individually, that is, a multiplicative effect. Nitrous oxide emissions from dung, urine and fertiliser N are typically derived individually and these individual emission estimates are aggregated to produce estimates of N2O emission. The presented findings have important implications for how individual emission factors are aggregated; they suggest that the multiplicative effect of the addition of CAN fertiliser to urine patches needs to be taken into account to refine the estimation of N2O emissions from grazing grasslands.The authors wish to thank the Environmental Protection Agency for funding support under the Environmental Research Technological Development and Innovation programme and the Irish Department of Agriculture, Food and the Marine for funding support (Grant numbers RSF 13S430 and 11S138)
Experimental and computational characterization of a modified GEC cell for dusty plasma experiments
A self-consistent fluid model developed for simulations of micro- gravity
dusty plasma experiments has for the first time been used to model asymmetric
dusty plasma experiments in a modified GEC reference cell with gravity. The
numerical results are directly compared with experimental data and the
experimentally determined dependence of global discharge parameters on the
applied driving potential and neutral gas pressure is found to be well matched
by the model. The local profiles important for dust particle transport are
studied and compared with experimentally determined profiles. The radial forces
in the midplane are presented for the different discharge settings. The
differences between the results obtained in the modified GEC cell and the
results first reported for the original GEC reference cell are pointed out
Structures and functions of mitochondrial ABC transporters
A small number of physiologically important ATP-binding cassette (ABC) transporters are found in mitochondria. Most are half transporters of the B group forming homodimers and their topology suggests they function as exporters. The results of mutant studies point towards involvement in iron cofactor biosynthesis. In particular, ABC subfamily B member 7 (ABCB7) and its homologues in yeast and plants are required for iron-sulfur (Fe-S) cluster biosynthesis outside of the mitochondria, whereas ABCB10 is involved in haem biosynthesis. They also play a role in preventing oxidative stress. Mutations in ABCB6 and ABCB7 have been linked to human disease. Recent crystal structures of yeast Atm1 and human ABCB10 have been key to identifying substrate-binding sites and transport mechanisms. Combined with in vitro and in vivo studies, progress is being made to find the physiological substrates of the different mitochondrial ABC transporters
Real and Virtual Compton Scattering: the nucleon polarisabilities
We give an overview of low-energy Compton scattering (gamma^(*) p --> gamma
p) with a real or virtual incoming photon. These processes allow the
investigation of one of the fundamental properties of the nucleon, i.e. how its
internal structure deforms under an applied static electromagnetic field. Our
knowledge of nucleon polarisabilities and their generalization to non-zero
four-momentum transfer will be reviewed, including the presently ongoing
experiments and future perspectives.Comment: 20 pages, 12 figures. Minireview/Proceedings of "Many-Body Structure
of Strongly Interacting Systems", Mainz, Germany, Feb. 23-25 2011 . V2: typos
corrected. version to appear in EPJ Special Topic
Testing the handbag contribution to exclusive virtual Compton scattering
We discuss the handbag approximation to exclusive deep virtual Compton
scattering. After defining the kinematical region where this approximation can
be valid, we propose tests for its relevance in planned electroproduction
experiments, e + p -> e + p + gamma. We focus on scaling laws in the cross
section, and the distribution in the angle between the lepton and hadron
planes, which contains valuable information on the angular momentum structure
of the Compton process. We advocate to measure weighted cross sections, which
make use of the data in the full range of this angle and do not require very
high event statistics.Comment: 14 pages, LaTeX, 3 figures included using epsf.st
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