952 research outputs found
Sorption of dissolved organic C and P to agricultural top- and subsoil
In order to study the mobility of dissolved organic carbon (DOC) and dissolved organic P (DOP) in soil, the pH-dependent sorption of dissolved organic matter to an agricultural top- and subsoil was investigated. In general, sorption isotherms had convex shapes and DOC and DOP sorption increased with time of reaction. There was a very pronounced effect of pH resulting in much higher sorption of DOC at pH 5 than at pH 7; actually extensive desorption was observed at pH 7 especially for the topsoil. Similar sorption patterns were observed for DOP, but they were not as pronounced as for DOC
What it takes to measure a fundamental difference between dark matter and baryons: the halo velocity anisotropy
Numerous ongoing experiments aim at detecting WIMP dark matter particles from
the galactic halo directly through WIMP-nucleon interactions. Once such a
detection is established a confirmation of the galactic origin of the signal is
needed. This requires a direction-sensitive detector. We show that such a
detector can measure the velocity anisotropy beta of the galactic halo.
Cosmological N-body simulations predict the dark matter anisotropy to be
nonzero, beta~0.2. Baryonic matter has beta=0 and therefore a detection of a
nonzero beta would be strong proof of the fundamental difference between dark
and baryonic matter. We estimate the sensitivity for various detector
configurations using Monte Carlo methods and we show that the strongest signal
is found in the relatively few high recoil energy events. Measuring beta to the
precision of ~0.03 will require detecting more than 10^4 WIMP events with
nuclear recoil energies greater than 100 keV for a WIMP mass of 100 GeV and a
32S target. This number corresponds to ~10^6 events at all energies. We discuss
variations with respect to input parameters and we show that our method is
robust to the presence of backgrounds and discuss the possible improved
sensitivity for an energy-sensitive detector.Comment: 15 pages, 8 figures, accepted by JCAP. Matches accepted versio
Laser-Annealing and Solid-Phase Epitaxy of Selenium Thin-Film Solar Cells
Selenium has resurged as a promising photovoltaic material in solar cell
research due to its wide direct bandgap of 1.95 eV, making it a suitable
candidate for a top cell in tandem photovoltaic devices. However, the
optoelectronic quality of selenium thin-films has been identified as a key
bottleneck for realizing high-efficiency selenium solar cells. In this study,
we present a novel approach for crystallizing selenium thin-films using
laser-annealing as an alternative to the conventionally used thermal annealing
strategy. By laser-annealing through a semitransparent substrate, a buried
layer of high-quality selenium crystallites is formed and used as a growth
template for solid-phase epitaxy. The resulting selenium thin-films feature
larger and more preferentially oriented grains with a negligible surface
roughness in comparison to thermally annealed selenium thin-films. We fabricate
photovoltaic devices using this strategy, and demonstrate a record ideality
factor of n=1.37, a record fill factor of FF=63.7%, and a power conversion
efficiency of PCE=5.0%. The presented laser-annealing strategy is universally
applicable and is a promising approach for crystallizing a wide range of
photovoltaic materials where high temperatures are needed while maintaining a
low substrate temperature
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