Surface impedance of BaFe2-xNixAs2 in the radio frequency range

We report measurements of the temperature dependence of the surface impedance in superconducting BaFe1.93Ni0.07As2 crystals using the radiofrequency reflection technique in the 5<T<30K temperature range. An LC resonant circuit with a phase sensitive detection was used at 92MHz. A measurement assembly with point contacts was used at 30MHz. The recent discovery of iron based arsenide superconductors BaFe2-xNixAs2 has attracted much interest. For a Ni doping level of 7% the superconducting phase transition is found around 20K. The temperature dependence of the superconducting penetration depth was determined

Influence of measurement noise on the PSO based localization of an impact occurring on elastic plates

This paper presents the application of particle swarm optimization algorithm to reconstruct the characteristics of impacts occurring on homogeneous and isotropic elastic plates and which cannot be reduced to a concentrated force. Solution of this inverse problem was achieved through minimizing a fitness function defined in terms of the root mean square error between the measured and the calculated responses. This included information provided by numerous sensors. The impacting force was assumed to result from uniformly distributed pressure acting over a rectangular patch. Use was made of the reciprocity theorem to decouple the localization problem from the deconvolution part intended to reconstruct the pressure time signal. The particle swarm optimization based model was found to be highly efficient in finding the impact zone location. Focus was done on the robustness aspect of force impact localization when an additive white noise is assumed to perturb response measurements

Homogenization of the susceptibility kernel for bianisotropic media

LGEP 2010 ID = 64

Competition between the antiferomagnetic phase and the superconducting state in undoped BaFe2-xNixAs2 ( RF measurements).

 Strong anomalies are observed along antiferromagnetic phase  before reaching the superconducting state. The succession of variations in these two phases, confirms their competition.Drude type conductivity yields  reactance X and resistance R differ  from each other.The increase of the real conductivity  in the superconducting state is attributed to a rapid decrease of the quasiparticle scattering time. This result give evidence of  the coexistence and competition of the superconductivity and antiferromagnetism in the underdoped iron superconductors