58 research outputs found
Classification of the electronic correlation strength in the Fe-pnictides: The case of the parent compound BaFe2As2
Electronic correlations in the Fe-pnictide BaFe2As2 are explored within
LDA+DMFT, the combination of density functional theory with dynamical
mean-field theory. While the correlated band structure is substantially
renormalized there is only little transfer of spectral weight. The computed
k-integrated and k-resolved spectral functions are in good agreement with
photoemission spectroscopy (PES) and angular resolved PES experiments. Making
use of a general classification scheme for the strength of electronic
correlations we conclude that BaFe2As2 is a moderately correlated system.Comment: 4 pages, 3 figure
Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a [Formula Presented] source
The neutrino capture rate measured by the Russian-American Gallium Experiment is well below that predicted by solar models. To check the response of this experiment to low-energy neutrinos, a 517 kCi source of [Formula Presented]Cr was produced by irradiating 512.7 g of 92.4%-enriched [Formula Presented]Cr in a high-flux fast neutron reactor. This source, which mainly emits monoenergetic 747-keV neutrinos, was placed at the center of a 13.1 ton target of liquid gallium and the cross section for the production of [Formula Presented]Ge by the inverse beta decay [Formula Presented] was measured to be [Formula Presented] The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 ±0.12 [Formula Presented] (theor) and to the cross section of Haxton is 0.87±0.11 (expt)±0.09 (theor). This good agreement between prediction and observation implies that the overall experimental efficiency is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement. © 1999 The American Physical Society
The russian-american gallium experiment (sage) cr neutrino source measurement
The solar neutrino capture rate measured by SAGE is well below that predicted by solar models. To check the overall experimental efficiency, we exposed 13 tonnes of Ga metal to a reactor-produced 517 kCi source of 51Cr. The ratio of the measured production rate to that predicted from the source activity is 0.95+/-0.11+0.05/-0.08. This agreement verifies that the experimental efficiency is measured correctly, establishes that there are no unknown systematic errors at the 10% level, and provides considerable evidence for the reliability of the solar neutrino measurement. © 1996 The American Physical Society
Preliminary results from the Russian-American Gallium Experiment Cr-neutrino source measurement
The Russian-American Gallium Experiment has been collecting solar neutrino data since early 1990. The flux measurement of solar neutrinos is well below that expected from solar models. We discuss the initial results of a measurement of experimental efficiencies by exposing the gallium target to neutrinos from an artificial source. The capture rate of neutrinos from this source is very close to that which is expected. The result can be expressed as a ratio of the measured capture rate to the anticipated rate from the source activity. This ratio is 0.93 + 0.15, - 0.17 where the systematic and statistical errors have been combined. To first order the experimental efficiencies are in agreement with those determined during solar neutrino measurements and in previous auxiliary measurements. One must conclude that the discrepancy between the measured solar neutrino flux and that predicted by the solar models can not arise from an experimental artifact
The Russian-American gallium experiment (SAGE) Cr neutrino source measurement
No description supplie
Genes Suggest Ancestral Colour Polymorphisms Are Shared across Morphologically Cryptic Species in Arctic Bumblebees
email Suzanne orcd idCopyright: © 2015 Williams et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a 51Cr source
The neutrino capture rate measured by the Russian-American Gallium Experiment
is well below that predicted by solar models. To check the response of this
experiment to low-energy neutrinos, a 517 kCi source of 51Cr was produced by
irradiating 512.7 g of 92.4%-enriched 50Cr in a high-flux fast neutron reactor.
This source, which mainly emits monoenergetic 747-keV neutrinos, was placed at
the center of a 13.1 tonne target of liquid gallium and the cross section for
the production of 71Ge by the inverse beta decay reaction was measured to be
(5.55 +/- 0.60 (stat.) +/- 0.32 (syst.)) x 10^(-45) cm^2. The ratio of this
cross section to the theoretical cross section of Bahcall for this reaction is
0.95 +/- 0.12 (exp.) +/- 0.03 (theor.) and to the cross section of Haxton is
0.87 +/- 0.11 (exp.) +/- 0.09 (theor.).
This good agreement between prediction and observation implies that the
overall experimental efficiency for the solar neutrino measurements is
correctly determined and provides considerable evidence for the reliability of
the solar neutrino measurement.Comment: 20 pages including figures in two column forma
Coulomb repulsion and correlation strength in LaFeAsO from Density Functional and Dynamical Mean-Field Theories
LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field
Theory) computation scheme has been used to calculate spectral properties of
LaFeAsO -- the parent compound for new high-T iron oxypnictides. Coulomb
repulsion and Hund's exchange parameters for iron 3d electrons were
calculated using \textit {first principles} constrained density functional
theory scheme in Wannier functions formalism. Resulting values strongly depend
on the number of states taken into account in calculations: when full set of
O-, As-, and Fe-3d orbitals with corresponding bands are included,
computation results in 4 eV and J=0.8 eV. In contrast to that when the
basis set is restricted to Fe-3d orbitals and bands only, computation gives
much smaller parameter values =0.8 eV, =0.5 eV. However, DMFT
calculations with both parameter sets and corresponding to them choice of basis
functions result in weakly correlated electronic structure that is in agreement
with experimental X-ray and photoemission spectra.Comment: 13 pages, 9 figure
Point contact Andreev reflection spectroscopy of NdFeAsO_0.85
The newly discovered oxypnictide family of superconductors show very high
critical temperatures of up to 55K. Whilst there is growing evidence that
suggests a nodal order parameter, point contact Andreev reflection spectroscopy
can provide crucial information such as the gap value and possibly the number
of energy gaps involved. For the oxygen deficient NdFeAsO0.85 with a Tc of
45.5K, we show that there is clearly a gap value at 4.2K that is of the order
of 7meV, consistent with previous studies on oxypnictides with lower Tc.
Additionally, taking the spectra as a function of gold tip contact pressure
reveals important changes in the spectra which may be indicative of more
complex physics underlying this structure.Comment: 11 pages, 3 figures. New references included, extra discussion. This
version is accepted in Superconductor Science and Technolog
Nitrates and nitrites in production vegetative
In spring the years period all vegetable production contains a plenty of nitrates. Therefore there is a necessity to establish a way of its hit and reduction of concentration to a plant. In work the main reasons and features of accumulation of nitrates and nitrites in crop are shown production. Maximum permissible concentration and their toxic influence on an organism of the person are given. In work as the basic ways of reduction of the maintenance of nitrates and nitrites in production
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