77 research outputs found
Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe2As2
Raman selection rules for electronic and magnetic excitations in BaFe2As2
were theoretically investigated and applied them to the separate detection of
the nodal and anti-nodal gap excitations at the spin density wave (SDW)
transition and the separate detection of the nearest and the next nearest
neighbor exchange interaction energies. The SDW gap has Dirac nodes, because
many orbitals participate in the electronic states near the Fermi energy. Using
a two-orbital band model the electronic excitations near the Dirac node and the
anti-node are found to have different symmetries. Applying the symmetry
difference to Raman scattering the nodal and anti-nodal electronic excitations
are separately obtained. The low-energy spectra from the anti-nodal region have
critical fluctuation just above TSDW and change into the gap structure by the
first order transition at TSDW, while those from the nodal region gradually
change into the SDW state. The selection rule for two-magnon scattering from
the stripe spin structure was obtained. Applying it to the two-magnon Raman
spectra it is found that the magnetic exchange interaction energies are not
presented by the short-range superexchange model, but the second derivative of
the total energy of the stripe spin structure with respect to the moment
directions. The selection rule and the peak energy are expressed by the
two-magnon scattering process in an insulator, but the large spectral weight
above twice the maximum spin wave energy is difficult to explain by the decayed
spin wave. It may be explained by the electronic scattering of itinerant
carriers with the magnetic self-energy in the localized spin picture or the
particle-hole excitation model in the itinerant spin picture. The magnetic
scattering spectra are compared to the insulating and metallic cuprate
superconductors whose spins are believed to be localized.Comment: 38 pages, 11 figure
Hippocampal-Dependent Spatial Memory in the Water Maze is Preserved in an Experimental Model of Temporal Lobe Epilepsy in Rats
Cognitive impairment is a major concern in temporal lobe epilepsy (TLE). While different experimental models have been used to characterize TLE-related cognitive deficits, little is known on whether a particular deficit is more associated with the underlying brain injuries than with the epileptic condition per se. Here, we look at the relationship between the pattern of brain damage and spatial memory deficits in two chronic models of TLE (lithium-pilocarpine, LIP and kainic acid, KA) from two different rat strains (Wistar and Sprague-Dawley) using the Morris water maze and the elevated plus maze in combination with MRI imaging and post-morten neuronal immunostaining. We found fundamental differences between LIP- and KA-treated epileptic rats regarding spatial memory deficits and anxiety. LIP-treated animals from both strains showed significant impairment in the acquisition and retention of spatial memory, and were unable to learn a cued version of the task. In contrast, KA-treated rats were differently affected. Sprague-Dawley KA-treated rats learned less efficiently than Wistar KA-treated animals, which performed similar to control rats in the acquisition and in a probe trial testing for spatial memory. Different anxiety levels and the extension of brain lesions affecting the hippocampus and the amydgala concur with spatial memory deficits observed in epileptic rats. Hence, our results suggest that hippocampal-dependent spatial memory is not necessarily affected in TLE and that comorbidity between spatial deficits and anxiety is more related with the underlying brain lesions than with the epileptic condition per se
New constitutive equations derived from a kinetic model for melts and concentrated solutions of linear polymers
ANALYSE DE SENSIBILITE GLOBALE PAR UNE METHODE NON INTRUSIVE DE COLLOCATION STOCHASTIQUE
International audienc
Time-dependent current source identification for numerical simulations of Maxwell's equations
International audienceThis paper discusses an inverse source problem for time-dependent linear Maxwell's equations. We propose a numerical procedure to compute a current density source that gives a specified electromagnetic field. The efficiency of our method is shown by numerical tests, first in 1D and then we move on to a 3D example with antennas. In that case, we show potential applications for fault detection
IDENTIFICATION OF TEMPORAL SOURCES FOR SOFTWARE DEFECT CORRECTION IN TRANSMISSION LINES
International audienc
An efficient SFE method using Lagrange polynomials: Application to nonlinear mechanical problems with uncertain parameters
International audienc
Time-dependent sources identification for transmission lines problems
This paper is devoted to introduce an extension to the Linear Combination of Configuration Fields (LCCF). This new numerical method was designed to compute the time profile of an electromagnetic source radiating a specified electromagnetic field in all or part of the computational domain, for a specified duration. Here, we extend this idea within the framework of a transmission lines network. The principle of the method is first validated numerically. Then we prospect the same ideas in a real-data experiment which shows that the method is ready for real-life investigations
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