Gap-dependent quasiparticle dynamics and coherent acoustic phonons in parent iron pnictide CaFe2As2 across the spin density wave phase transition

We report ultrafast quasiparticle (QP) dynamics and coherent acoustic phonons in undoped CaFe_2As_2 iron pnictide single crystals exhibiting spin-density wave (SDW) and concurrent structural phase transition at temperature TSDW ~ 165 K using femtosecond time-resolved pump-probe spectroscopy. The contributions in transient differential reflectivity arising from exponentially decaying QP relaxation and oscillatory coherent acoustic phonon mode show large variations in the vicinity of T_SDW. From the temperature-dependence of the QP recombination dynamics in the SDW phase, we evaluate a BCS-like temperature dependent charge gap with its zero-temperature value of ~(1.6+/-0.2)k_BT_SDW, whereas, much above T_SDW, an electron-phonon coupling constant of ~0.13 has been estimated from the linear temperature-dependence of the QP relaxation time. The long-wavelength coherent acoustic phonons with typical time-period of ~100 ps have been analyzed in the light of propagating strain pulse model providing important results for the optical constants, sounds velocity and the elastic modulus of the crystal in the whole temperature range of 3 K to 300 K.Comment: Revised version (to appear as Full Paper in Journal of Physical Society of Japan (2013)); http://jpsj.ipap.jp/link?JPSJ/82/044715

Effect of Particle Functionalization on Structural and Dielectric Properties of Flexible TPU/BaTiO3/MWCNTs Composite Films

Flexible, low-cost thermoplastic polyurethane (TPU) composite films with functionalized BaTiO3 (BT) and multiwall carbon nanotubes (MWCNTs) are prepared by solution casting and tested as dielectric materials. Different volume content loadings of BT filler (between 10 and 80 vol%) and 0.12 vol% of MWCNTs are applied. The effects of particle functionalization and BT content on the structural, mechanical, and energy storage properties are studied by Fourier infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), as well as puncture and dielectric measurements. It is found that the particle functionalization and BT content significantly affect the hydrogen bonding within the polymer matrix, and have a huge impact on the mechanical and dielectric properties. The optimal concentration (30 vol% of functionalized BT and 0.12 vol% of functionalized MWCNTs) giving the highest dielectric constant of 30.28 and dielectric breakdown strength of 42 kV mm−1 is determined

Protective role of vitamins E and C in carbon tetrachloride induced acute liver damage

The CCL4 hepatotoxic impact is achieved when it is activated to from highly reactive radicals, which have various effects; initiation of lipid peroxidation being probably the most important one. The toxic outcome may be prevented through use of antioxidants; vitamin E presenting the first line of defence. Keeping the concentration of reduced vitamin E,requires a network of other antioxidants that can reduce the radical from of vitamin E to its native from. Vitamin C is an antioxidant that is able to reduce vitamin E directly