99 research outputs found
Impact of solid waste disposal on nutrient dynamics in a sandy catchment
Groundwaters impacted by mature landfill leachate are generally enriched in ammonium. In order to assess the dynamics of ammonium exchanges between leachates and the water system inside a sandy permeable catchment we measured ammonium, nitrate and chloride concentrations in the stream and in sediment pore waters of the streambed of a landfill impacted aquifer. Geophysical investigation methods complemented the biogeochemical survey. The studied zone is a 23 km² catchment located in a coastal lagoon area sensitive to eutrophication risk. Ammonium concentrations in the river were up to 800 µmol l−1 during low water period in summer. Three surveys of the river chemistry showed a regular increase in ammonium, nitrate and chloride concentrations along a 1 km section of the watercourse, downstream the landfill, implying that the leachate plume exfiltrates along this section. Sediment cores collected within this section showed all an increase in ammonium concentrations with depth in pore waters as a consequence of the landfill leachate dispersion, as attested by a simultaneous increase in chloride concentrations. Nitrate enrichment in the river water was due to nitrification of ammonium at the interface between groundwater and streamwater. The apparent nitrification rate obtained was within values reported for turbid estuaries, although the river contained very little suspended particulate matter. Actually, pore water chemistry suggests that nitrification occurred for the most part in subsurface permeable sediments, rather than in stream water. The overall topographic, hydrological, geochemical, and geoelectrical data set permit to estimate the extension of the chloride and ammonium plume. The estimation of the apparent ammonium plume velocity is 23 m year−1 whereas the chloride plume velocity should be 50 m year−1. The river is the outlet of the impacted groundwaters. Considering that the input of ammonium from the landfill is balanced by the present day output via the river, the residence time of ammonium in the aquifer is between 7 and 18 years
Experimental Limit on the Cosmic Diffuse Ultra-high Energy Neutrino Flux
We report results from 120 hours of livetime with the Goldstone Lunar
Ultra-high energy neutrino Experiment (GLUE). The experiment searches for <10
ns microwave pulses from the lunar regolith, appearing in coincidence at two
large radio telescopes separated by 22 km and linked by optical fiber. Such
pulses would arise from subsurface electromagnetic cascades induced by
interactions of >= 100 EeV neutrinos in the lunar regolith. No candidates are
yet seen, and the implied limits constrain several current models for
ultra-high energy neutrino fluxes.Comment: 4 pages, 4 figures, revtex4 style. New intro section, Fig. 2, Fig 4;
in final PRL revie
Six principles for assessing scientists for hiring, promotion, and tenure
The negative consequences of relying too heavily on metrics to assess research quality are well known, potentially fostering practices harmful to scientific research such as p-hacking, salami science, or selective reporting. The "flourish or perish" culture defined by these metrics in turn drives the system of career advancement in academia, a system that empirical evidence has shown to be problematic and which fails to adequately take societal and broader impact into account. To address this systemic problem, Florian Naudet, John P. A. Ioannidis, Frank Miedema, Ioana A. Cristea, Steven N. Goodman and David Moher present six principles for assessing scientists for hiring, promotion, and tenure
Six principles for assessing scientists for hiring, promotion, and tenure
The negative consequences of relying too heavily on metrics to assess research quality are well known, potentially fostering practices harmful to scientific research such as p-hacking, salami science, or selective reporting. The "flourish or perish" culture defined by these metrics in turn drives the system of career advancement in academia, a system that empirical evidence has shown to be problematic and which fails to adequately take societal and broader impact into account. To address this systemic problem, Florian Naudet, John P. A. Ioannidis, Frank Miedema, Ioana A. Cristea, Steven N. Goodman and David Moher present six principles for assessing scientists for hiring, promotion, and tenure
Observation of Ultra-high-energy Cosmic Rays with the ANITA Balloon-borne Radio Interferometer
We report the observation of sixteen cosmic ray events of mean energy of 1.5
x 10^{19} eV, via radio pulses originating from the interaction of the cosmic
ray air shower with the Antarctic geomagnetic field, a process known as
geosynchrotron emission. We present the first ultra-wideband, far-field
measurements of the radio spectral density of geosynchrotron emission in the
range from 300-1000 MHz. The emission is 100% linearly polarized in the plane
perpendicular to the projected geomagnetic field. Fourteen of our observed
events are seen to have a phase-inversion due to reflection of the radio beam
off the ice surface, and two additional events are seen directly from above the
horizon.Comment: 5 pages, 5 figures, new figure adde
Probing the Rho Spectral Function in Hot and Dense Nuclear Matter by Dileptons
We present a dynamical study of and production in
proton-nucleus and nucleus-nucleus collisions at CERN-SPS energies on the basis
of the covariant transport approach HSD employing a momentum-dependent
-meson spectral function that includes the pion modifications in the
nuclear medium as well as the polarization of the -meson due to resonant
scattering. We find that the experimental data from the CERES and
HELIOS-3 Collaborations can be described equally well as within the dropping
-mass scenario. Whereas corresponding dilepton -spectra are found to
be very similar, the inclusive dilepton yield in the invariant mass range GeV should allow to disentangle the two scenarios
experimentally.Comment: 13 pages RevTeX slightly revised, 6 eps-figure
Inclusive Dielectron Cross Sections in p+p and p+d Interactions at Beam Energies from 1.04 to 4.88 GeV
Measurements of dielectron production in p+p and p+d collisions with beam
kinetic energies from 1.04 to 4.88 GeV are presented. The differential cross
section is presented as a function of invariant pair mass, transverse momentum,
and rapidity. The shapes of the mass spectra and their evolution with beam
energy provide information about the relative importance of the various
dielectron production mechanisms in this energy regime. The p+d to p+p ratio of
the dielectron yield is also presented as a function of invariant pair mass,
transverse momentum, and rapidity. The shapes of the transverse momentum and
rapidity spectra from the p+d and p+p systems are found to be similar to one
another for each of the beam energies studied. The beam energy dependence of
the integrated cross sections is also presented.Comment: 15 pages and 16 figure
Diffractive Photoproduction of Jets with a Direct Pomeron Coupling at HERA
We investigate in detail the effect of a direct pomeron coupling to quarks on
the production of jets in scattering with almost real photons. Jet
production via a direct pomeron coupling is compared with the resolved--pomeron
mechanism. We consider both direct and resolved photoproduction. Rapidity and
transverse momentum distributions are calculated and compared with preliminary
H1 and ZEUS data.Comment: 21 pages, Latex file, 7 figures (uuencoded) enclosed, Preprint DESY
94-140, KEK-TH-407 and KEK Preprint 94-7
Behavior and Impact of Zirconium in the Soil–Plant System: Plant Uptake and Phytotoxicity
Because of the large number of sites they pollute, toxic metals that contaminate terrestrial ecosystems are increasingly of environmental and sanitary concern (Uzu et al. 2010, 2011; Shahid et al. 2011a, b, 2012a). Among such metals is zirconium (Zr), which has the atomic number 40 and is a transition metal that resembles titanium in physical and chemical properties (Zaccone et al. 2008). Zr is widely used in many chemical industry processes and in nuclear reactors (Sandoval et al. 2011; Kamal et al. 2011), owing to its useful properties like hardness, corrosion-resistance and permeable to neutrons (Mushtaq 2012). Hence, the recent increased use of Zr by industry, and the occurrence of the Chernobyl and Fukashima catastrophe have enhanced environmental levels in soil and waters (Yirchenko and Agapkina 1993; Mosulishvili et al. 1994 ; Kruglov et al. 1996)
Intermediate-mass dilepton spectra and the role of secondary hadronic processes in heavy-ion collisions
We carry out a study of intermediate-mass (between 1 and 2.5 GeV) dilepton
spectra from hadronic interactions in heavy-ion collisions. The processes
considered are , , , , , and . The elementary cross sections for those are obtained
from chiral Lagrangians involving pseudoscalar, vector, and axial-vector
mesons. The respective electromagnetic form factors are determined by fitting
to experimental data for the reverse processes of . Based on
this input we calculate cross sections and thermal dilepton emission rates and
compare our results with those from other approaches. Finally we use these
elementary cross sections with a relativistic transport model and calculate
dilepton spectra in S+W collisions at SPS energies. The comparison of our
results with experimental data from the HELIOS-3 collaboration indicates the
importance of the secondary hadronic contributions to the intermediate-mass
dilepton spectra.Comment: 25 pages, including 20 postscript figure
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