• AK Sood

      Articles written in Pramana – Journal of Physics

    • Photon transport in thin disordered slabs

      Venkatesh Gopal S Anantha Ramakrishna AK Sood N Kumar

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      We examine using Monte Carlo simulations, photon transport in optically ‘thin’ slabs whose thickness L is only a few times the transport mean free path l*, with particles of different scattering anisotropies. The confined geometry causes an auto-selection of only photons with looping paths to remain within the slab. The results of the Monte Carlo simulations are borne out by our analytical treatment that incorporates directional persistence by the use of the Ornstein-Uhlenbeck process, which interpolates between the short time ballistic and long time diffusive regimes.

    • Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

      Janhavi P Joshi Subhasis Sarangi AK Sood Dilip Pal SV Bhat

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      Non-resonant microwave absorption (NRMA) studies of superconducting MgB2 and a sample containing ∼10% by weight of MgO in MgB2 are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB2 sample. A linear temperature dependence of the lower critical field Hc1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB2 + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB2 sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below Tc while in the MgB2 + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.

    • Rheology of semi-dilute solutions of calf-thymus DNA

      Ranjini Bandyopadhyay AK Sood

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      We study the rheology of semi-dilute solutions of the sodium salt of calf-thymus DNA in the linear and nonlinear regimes. The frequency response data can be fitted very well to the hybrid model with two dominant relaxation times τ0 and τ1. The ratio (τ01) ∼5 is seen to be fairly constant on changing the temperature from 20 to 30°C. The shear rate dependence of viscosity can be fitted to the Carreau model.

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