235,879 research outputs found
Comment on "Potential Energy Landscape for Hot Electrons in Periodically Nanostructured Graphene"
In a recent letter [Phys. Rev. Lett. 105 (2010) 036804] the unoccupied
electronic states of single layers of graphene on ruthenium are investigated.
Here we comment on the interpretation, which deviates in four points from [J.
Phys.: Condens. Matter 22 (2010) 302001] and outline the corresponding
consequences
Analysis of Exotic Hybrid eta pion, eta-prime pion Decays
Investigations of the mass and decays of the exotic hybrid are reviewed,
including calculation of the pion1 to eta pion, eta-prime pion decay widths
within the QCD sum rules technique. In this calculation, the recently-proposed
eta, eta-prime quark mixing scheme is employed. The results indicate that the
decay width Gamma(pion1 to eta pion) around 250 MeV is large compared with the
decay width Gamma(pion1 to eta-prime pion) around 20 MeV. Inspired by these
results, some phenomenological approaches are suggested to gain an
understanding of the underlying mechanism of eta pion and eta-prime pion hybrid
decays.Comment: 4 pages, talk presented at the 10th International Symposium on
Meson-Nucleon Physics and the Structure of the Nucleon(MENU2004), Beijing,
China, August 29 to September 4, 200
A zero dimensional model of lithium-sulfur batteries during charge and discharge
Lithium-sulfur cells present an attractive alternative to Li-ion batteries due to their large energy density, safety, and possible low cost. Their successful commercialisation is dependent on improving their performance, but also on acquiring sufficient understanding of the underlying mechanisms to allow for the development of predictive models for operational cells. To address the latter, we present a zero dimensional model that predicts many observed features in the behaviour of a lithium-sulfur cell during charge and discharge. The model accounts for two electrochemical reactions via the Nernst formulation, power limitations through Butler-Volmer kinetics, and precipitation/dissolution of one species, including nucleation. It is shown that the precipitation/dissolution causes the flat shape of the low voltage plateau, typical of the lithium-sulfur cell discharge. During charge, it is predicted that the dissolution can act as a bottleneck, as for large enough currents smaller amounts dissolve. This results in reduced charge capacity and an earlier onset of the high plateau reaction, such that the two plateaus merge. By including these effects, the model improves on the existing zero dimensional models, while requiring considerably fewer input parameters and computational resources. The model also predicts that, due to precipitation, the customary way of experimentally measuring the open circuit voltage from a low rate discharge might not be suitable for lithium-sulfur. This model can provide the basis for mechanistic studies, identification of dominant effects in a real cell, predictions of operational behaviour under realistic loads, and control algorithms for applications
NLTE study of scandium in the Sun
We investigate the formation of neutral and singly ionized scandium lines in
the solar photospheres. The research is aimed derive solar (Sc) values for scandium lines, which will later be used in
differential abundance analyses of metal-poor stars. Extensive statistical
equilibrium calculations were carried out for a model atom, which comprises 92
terms for \ion{Sc}{i} and 79 for \ion{Sc}{ii}. Photoionization cross-sections
are assumed to be hydrogenic. Synthetic line profiles calculated from the level
populations according to the NLTE departure coefficients were compared with the
observed solar spectral atlas. Hyperfine structure (HFS) broadening is taken
into account. The statistical equilibrium of scandium is dominated by a strong
underpopulation of \ion{Sc}{i} caused by missing strong lines. It is nearly
unaffected by the variation in interaction parameters and only marginally
sensitive to the choice of the solar atmospheric model. Abundance
determinations using the ODF model lead to a solar Sc abundance of between
and 3.13, depending on the choice of values.
The long known difference between photospheric and meteoritic scandium
abundances is confirmed for the experimental -values.Comment: 10 pages, 6 figures, A&A accepte
Switching ferromagnetic spins by an ultrafast laser pulse: Emergence of giant optical spin-orbit torque
Faster magnetic recording technology is indispensable to massive data storage
and big data sciences. {All-optical spin switching offers a possible solution},
but at present it is limited to a handful of expensive and complex rare-earth
ferrimagnets. The spin switching in more abundant ferromagnets may
significantly expand the scope of all-optical spin switching. Here by studying
40,000 ferromagnetic spins, we show that it is the optical spin-orbit torque
that determines the course of spin switching in both ferromagnets and
ferrimagnets. Spin switching occurs only if the effective spin angular momentum
of each constituent in an alloy exceeds a critical value. Because of the strong
exchange coupling, the spin switches much faster in ferromagnets than
weakly-coupled ferrimagnets. This establishes a paradigm for all-optical spin
switching. The resultant magnetic field (65 T) is so big that it will
significantly reduce high current in spintronics, thus representing the
beginning of photospintronics.Comment: 12 page2, 6 figures. Accepted to Europhysics Letters (2016). Extended
version with the supplementary information. Contribution from Indiana State
University,Europhysics Letters (2016
Novel dynamical effects and glassy response in strongly correlated electronic system
We find an unconventional nucleation of low temperature paramagnetic metal
(PMM) phase with monoclinic structure from the matrix of high-temperature
antiferromagnetic insulator (AFI) phase with tetragonal structure in strongly
correlated electronic system . Such unconventional
nucleation leads to a decease in resistivity by several orders with relaxation
at a fixed temperature without external perturbation. The novel dynamical
process could arise from the competition of strain fields, Coulomb
interactions, magnetic correlations and disorders. Such competition may
frustrate the nucleation, giving rise to a slow, nonexponential relaxation and
"physical aging" behavior.Comment: 5 pages, 4 figure
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