Rheology of semi-dilute solutions of calf-thymus DNA

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 (τ₀/τ₁) ∼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.     

Energy Index technique for detection of Acoustic Emissions associated with incipient bearing failures

The application of Acoustic Emission (AE) technique to condition monitoring of gears and bearings is gaining significance as it can detect early symptoms of defects such as pitting, wear and flaking of surfaces. Such early detection of defects is of vital importance so as to avoid major failures with catastrophic consequences. This article presents results on the Energy Index (EI) technique, used in detecting masked AE signatures associated with the loss of mechanical integrity in bearings. Both simulated and real experimentally generated AE signatures were used to investigate the efficiency and applicability of the technique at signal-to-noise ratios as low as 0.25. In conclusion it is shown that the EI technique is effective in detecting AE burst buried in random noise thereby offering a complementary tool for the diagnostician.     

Dynamic response of twisted nematic liquid crystal cells to transiently pulsed fields

The transient optical response of a TN cell to single field pulses is experimentally investigated. The optical threshold for pulses is investigated as a function of pulse width and cell parameters d and θ. The subsequent relaxation of the cell below optical threshold is inferred by investigation of the sensitivity of the cell to a second delayed pulse. A method of calculating tilt angles from capacitance measurements of LC cells is also described.     

Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the ²⁸Si+⁶⁸Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.     

Comparison of thermomagnetic history effects in weakly pinned single crystals of R 3Rh4Sn13 (R=Yb, Ca)

A comparative study of the thermomagnetic memory effects of J _c in two weakly pinned low T _c superconductors, Ca₃Rh₄Sn₁₃ (CaRhSn) and Yb₃Rh₄Sn₁₃ (YbRhSn), is presented. In both the systems, the peak effect (PE) phenomenon appears as an order-disorder transformation through stepwise amorphization of the flux line lattice (FLL). However, in CaRhSn. we can witness another disorder-driven transition (Bragg glass (BG) to a vortex glass (VG) in a distinct manner as in a single crystal of high T _c YBa₂Cu₃O_7-δ for H‖c.