333 research outputs found
Isotope tracing of submarine groundwater discharge offshore Ubatuba, Brazil : results of the IAEA–UNESCO SGD project
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Environmental Radioactivity 99 (2008): 1596-1610, doi:10.1016/j.jenvrad.2008.06.010.Results of groundwater and seawater analyses for radioactive (3H, 222Rn, 223Ra, 224Ra, 226Ra, 228Ra) and stable (2H, 18O)
isotopes are presented together with in situ spatial mapping and time-series 222Rn measurements in seawater, direct seepage
measurements using manual and automated seepage meters, pore water investigations using different tracers and piezometric
techniques, and geoelectric surveys probing the coast. This study represents first time that such a new complex arsenal of radioactive
and non-radioactive tracer techniques and geophysical methods have been used for simultaneous submarine groundwater discharge
(SGD) investigations. Large fluctuations of SGD fluxes were observed at sites situated only a few meters apart (from 0 cm d-1 to 360
cm d-1; the unit represents cm3/cm2/day), as well as during a few hours (from 0 cm d-1 to 110 cm d-1), strongly depending on the tidal
fluctuations. The average SGD flux estimated from continuous 222Rn measurements is 17±10 cm d-1. Integrated coastal SGD flux
estimated for the Ubatuba coast using radium isotopes is about 7x103 m3 d-1 per km of the coast. The isotopic composition (δ2H and
δ18O) of submarine waters was characterised by significant variability and heavy isotope enrichment, indicating that the contribution
of groundwater in submarine waters varied from a small percentage to 20%. However, this contribution with increasing offshore
distance became negligible. Automated seepage meters and time-series measurements of 222Rn activity concentration showed a
negative correlation between the SGD rates and tidal stage. This is likely caused by sea level changes as tidal effects induce variations of hydraulic gradients. The geoelectric probing and piezometric measurements contributed to better understanding of the spatial distribution of different water masses present along the coast. The radium isotope data showed scattered distributions with offshore distance, which imply that seawater in a complex coast with many small bays and islands was influenced by local currents and
groundwater/seawater mixing. This has also been confirmed by a relatively short residence time of 1-2 weeks for water within 25 km
offshore, as obtained by short-lived radium isotopes. The irregular distribution of SGD seen at Ubatuba is a characteristic of fractured
rock aquifers, fed by coastal groundwater and recirculated seawater with small admixtures of groundwater, which is of potential
environmental concern and has implications on the management of freshwater resources in the region.This research was
supported by IAEA and UNESCO (IOC and IHP) in the framework of the joint SGD project.
Science support for some U.S. investigators was provided by grants from the National Science
Foundation (OCE03-50514 to WCB and OCE02-33657 to WSM)
Unravelling the transport mechanism of pore-filled membranes for hydrogen separation
The permeation characteristics of palladium pore filled (PF) membranes have been investigated with gas permeation and structural characterization of the membranes. PF membranes have been prepared by filling with Pd the nanoporous γ-Al2O3/YSZ (or pure YSZ) layer supported onto porous α-Al2O3 and ZrO2. The number of nanoporous layers and the applied vacuum level during the electroless plating process have been studied. Gas permeation properties of the PF membranes have been determined in a temperature range of 300-550 °C. The measured hydrogen permeances have been found to be lower than previously reported for similar membranes. It has been found that the hydrogen fluxes do not depend on the thickness of the nanoporous layers (γ-Al2O3/YSZ or pure YSZ) or on the vacuum pump employed for filling with Pd. The physicochemical characterization performed showed that the palladium deposited does not form a percolated network across the mesoporous layer(s), leading to low hydrogen permeances and thus low H2/N2 perm-selectivities.The presented work is funded within FERRET project as part of European Union’s Seventh
Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology
Initiative under grant agreement n° 621181.
The Talos TEM was funded as part of HEFCE funding in the UK
Research Partnership Investment Funding (UKRPIF) Manchester RPIF Round 2
Isotopic, geophysical and biogeochemical investigation of submarine groundwater discharge : IAEA-UNESCO intercomparison exercise at Mauritius Island
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Environmental Radioactivity 104 (2012): 24-45, doi:10.1016/j.jenvrad.2011.09.009.Submarine groundwater discharge (SGD) into a shallow lagoon on the west coast of Mauritius Island (Flic-en-Flac) was
investigated using radioactive (3H, 222Rn, 223Ra, 224Ra, 226Ra, 228Ra) and stable (2H, 18O) isotopes and nutrients. SGD
intercomparison exercises were carried out to validate the various approaches used to measure SGD including radium and radon
measurements, seepage-rate measurements using manual and automated meters, sediment bulk conductivity and salinity surveys.
SGD measurements using benthic chambers placed on the floor of the Flic-en-Flac Lagoon showed discharge rates up to 500
cm/day. Large variability in SGD was observed over distances of a few meters, which were attributed to different
geomorphological features. Deployments of automated seepage meters captured the spatial and temporal variability of SGD with
a mean seepage rate of 10 cm/day. The stable isotopic composition of submarine waters was characterized by significant
variability and heavy isotope enrichment and was used to predict the contribution of fresh terrestrially derived groundwater to
SGD (range from a few % to almost 100 %). The integrated SGD flux, estimated from seepage meters placed parallel to the
shoreline, was 35 m3/m day, which was in a reasonable agreement with results obtained from hydrologic water balance
calculation (26 m3/m day). SGD calculated from the radon inventory method using in situ radon measurements were between 5
and 56 m3/m per day. Low concentrations of radium isotopes observed in the lagoon water reflected the low abundance of U and
Th in the basalt that makes up the island. High SGD rates contribute to high nutrients loading to the lagoon, potentially leading to
eutrophication. Each of the applied methods yielded unique information about the character and magnitude of SGD. The results
of the intercomparison studies have resulted a better understanding of groundwater-seawater interactions in coastal regions. Such
information is an important pre-requisite for the protection management of coastal freshwater resources.The
financial support provided by the IOC and IHP of UNESCO for travel arrangements, and by the IAEA’s Marine
Environment Laboratories for logistics is highly acknowledged. MAC and MEG were supported in part by the US
National Science Foundation (OCE-0425061 and OCE-0751525). PPP acknowledges a support provided by the EU
Research & Development Operational Program funded by the ERDF (project No. 26240220004), and the Slovak
Scientific Agency VEGA (grant No. 1/108/08). The International Atomic Energy Agency is grateful to the
Government of the Principality of Monaco for support provided to its Marine Environment Laboratories
Measurement of the dijet invariant mass cross section in proton anti-proton collisions at sqrt{s} = 1.96 TeV
The inclusive dijet production double differential cross section as a
function of the dijet invariant mass and of the largest absolute rapidity of
the two jets with the largest transverse momentum in an event is measured in
proton anti-proton collisions at sqrt{s} = 1.96 TeV using 0.7 fb^{-1}
integrated luminosity collected with the D0 detector at the Fermilab Tevatron
Collider. The measurement is performed in six rapidity regions up to a maximum
rapidity of 2.4. Next-to-leading order perturbative QCD predictions are found
to be in agreement with the data.Comment: Published in Phys. Lett. B, 693, (2010), 531-538, 8 pages, 2 figures,
6 table
Search for W' bosons decaying to an electron and a neutrino with the D0 detector
This Letter describes the search for a new heavy charged gauge boson W'
decaying into an electron and a neutrino. The data were collected with the D0
detector at the Fermilab Tevatron proton-antiproton Collider at a
center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity
of about 1 inverse femtobarn. Lacking any significant excess in the data in
comparison with known processes, an upper limit is set on the production cross
section times branching fraction, and a W' boson with mass below 1.00 TeV can
be excluded at the 95% C.L., assuming standard-model-like couplings to
fermions. This result significantly improves upon previous limits, and is the
most stringent to date.Comment: submitted to Phys. Rev. Let
Search for a scalar or vector particle decaying into Zgamma in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for a narrow scalar or vector resonance decaying into
Zgamma with a subsequent Z decay into a pair of electrons or muons. The data
for this search were collected with the D0 detector at the Fermilab Tevatron
ppbar collider at a center of mass energy sqrt(s) = 1.96 TeV. Using 1.1 (1.0)
fb-1 of data, we observe 49 (50) candidate events in the electron (muon)
channel, in good agreement with the standard model prediction. From the
combination of both channels, we derive 95% C.L. upper limits on the cross
section times branching fraction (sigma x B) into Zgamma. These limits range
from 0.19 (0.20) pb for a scalar (vector) resonance mass of 600 GeV/c^2 to 2.5
(3.1) pb for a mass of 140 GeV/c^2.Comment: Published by Phys. Lett.
Measurement of the ratios of the Z/G* + >= n jet production cross sections to the total inclusive Z/G* cross section in ppbar collisions at sqrt(s) = 1.96 TeV
We present a study of events with Z bosons and jets produced at the Fermilab
Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV.
The data sample consists of nearly 14,000 Z/G* -> e+e- candidates corresponding
to the integrated luminosity of 0.4 fb-1 collected using the D0 detector.
Ratios of the Z/G* + >= n jet cross sections to the total inclusive Z/G* cross
section have been measured for n = 1 to 4 jet events. Our measurements are
found to be in good agreement with a next-to-leading order QCD calculation and
with a tree-level QCD prediction with parton shower simulation and
hadronization.Comment: 7 pages, 2 figures, slightly modified, submitted to Phys. Lett.
Search for scalar bottom quarks and third-generation leptoquarks in ppbar collisions at sqrt(s) = 1.96 TeV
We report the results of a search for pair production of scalar bottom quarks
(sbottom) and scalar third-generation leptoquarks in 5.2 fb-1 of ppbar
collisions at the D0 experiment of the Fermilab Tevatron Collider. Scalar
bottom quarks are assumed to decay to a neutralino and a quark, and we set
95% C.L. lower limits on their production in the (m_sbottom, m_neutralino) mass
plane such as m_sbottom>247 GeV for m_neutralino=0 and m_neutralino>110 GeV for
160<m_sbottom<200 GeV. The leptoquarks are assumed to decay to a tau neutrino
and a quark, and we set a 95% C.L. lower limit of 247 GeV on the mass of a
charge-1/3 third-generation scalar leptoquark.Comment: Published by Phys. Lett.
Search for the associated production of a b quark and a neutral supersymmetric Higgs boson which decays to tau pairs
We report results from a search for production of a neutral Higgs boson in
association with a quark. We search for Higgs decays to pairs with
one subsequently decaying to a muon and the other to hadrons. The data
correspond to 2.7fb of \ppbar collisions recorded by the D0 detector
at TeV. The data are found to be consistent with background
predictions. The result allows us to exclude a significant region of parameter
space of the minimal supersymmetric model.Comment: Submitted to Phys. Rev. Letter
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