331 research outputs found
The resolution function of single-crystal diffractometers at a synchrotron-radiation source: the influence of absorption and extinction on the FWHM
The half-widths of Bragg intensity profiles measured with a triple-crystal diffractometer at a synchrotron-radiation source. I. Derivation of a simple expression for the full width at half-maximum
X-ray measurement of the root-mean-square displacement of atoms in zinc single crystals. A case of high anisotropic extinction
A study of the antisymmetric and symmetric parts of the anharmonic vibration in zinc using synchrotron radiation
Isotopic constraints on lightning as a source of fixed nitrogen in Earth's early biosphere
Bioavailable nitrogen is thought to be a requirement for the origin and
sustenance of life. Before the onset of biological nitrogen fixation, abiotic
pathways to fix atmospheric N2 must have been prominent to provide bioavailable
nitrogen to Earth's earliest ecosystems. Lightning has been shown to produce
fixed nitrogen as nitrite and nitrate in both modern atmospheres dominated by
N2 and O2 and atmospheres dominated by N2 and CO2 analogous to the Archaean
Earth. However, a better understanding of the isotopic fingerprints of
lightning-generated fixed nitrogen is needed to assess the role of this process
on the early Earth. Here, we present results from spark discharge experiments
in N2-CO2 and N2-O2 gas mixtures. Our experiments suggest that lightning-driven
nitrogen fixation may have been similarly efficient in the Archaean atmosphere,
compared to modern times. Measurements of the isotopic ratio {\delta}15N of the
discharge-produced nitrite and nitrate in solution show very low values of -6
to -15 permil after equilibration with the gas phase with a calculated
endmember composition of -17 permil. These results are much lower than most
{\delta}15N values documented from the sedimentary rock record, which supports
the development of biological nitrogen fixation earlier than 3.2 Ga. However,
some Paleoarchean records (3.7 Ga) may be consistent with lightning-derived
nitrogen input, highlighting the potential role of this process for the
earliest ecosystems.Comment: Accepted manuscript. Version of record published in Nature
Geoscience. 29 pages (main text, methods, supplementary material), 5 figures
+ 4 supplementary figure
Generation of x-ray radiation in a storage ring by a superconductive cold-bore invacuum undulator
The first beam measurements with a cold-bore superconducting in-vacuum undulator in a storage ring are reported. Undulators are x-ray generators in light sources. The physical limitations of these devices limit the intensity and the brilliance of the x-ray beam. At present the undulators are made from permanent magnets. It was shown in earlier papers that at low electron beam intensities superconductive wires in the vacuum beam pipe can overcome the limitations inherent to permanent magnet undulators. It was argued that the use of these novel devices in light sources with high beam currents may be limited by the extreme anomalous skin effect regime in Cu at 4.2 K, which has so far undergone very little investigation, and the power deposited by the infrared part of the synchrotron radiation. The purpose of this paper is to present measurements of these effects at the synchrotron light source ANKA with stored currents up to 200 mA
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