Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

104 Biennial Report 2005-074.1 Experimental Condensed Matter Physics4.1.1 Experimental Studies of Electrical, Magnetic, Thermal and StructuralProperties4.1.1.1 Waveform distortion: Causes and consequencesThe nature of waveform deformation caused by factors like dispersion in the propagating media,bandwidth of the transmission and detecting systems have been investigated numerically using apropagating wave model. It has been observed that the distortion is caused by (i) the suppression ofthe frequency components lying outside the bandwidth of the transmission and detecting systems,(ii) the suppression of the frequency components (inside the bandwidth) that do not match the resonancefrequencies of the propagating medium due to its finite size, and (iii) the dispersion presentin the medium. The study reveals that even though the waveform gets distorted, it is possible todetermine the propagation parameters and dispersion relation from the Fourier components of thedistorted waves detected at different positions in the medium, by the method of computationalanalysis. This explores the possibility of developing Fourier transform spectroscopic technique forultrasonic characterization of materials. Further work is in progress to build up the experimentalfacility. Anarsi Ram, Sankari Chakrabarti and Anis Karmahapatro are providing technical assistancefor this work.Barnana Pal, Santwana RaychaudhuriECMP, PP4.1.1.2 Relaxation dynamics in small clusters: A modified Monte Carlo approachRelaxation dynamics in two-dimensional atomic clusters consisting of mono-atomic particles interactingthrough Lennard-Jones (L-J) potential has been investigated using Monte Carlo simulation.A modification of the conventional Metropolis algorithm is proposed to introduce realistic thermalmotion of the particles moving in the interacting L-J potential field. The proposed algorithm leadsto a quick equilibration from the nonequilibrium cluster configuration in a certain temperatureregime, where the relaxation time (τ), measured in terms of Monte Carlo Steps (MCS) per particle,vary inversely with the square root of system temperature (T) and pressure (P); τ ∼(P √ T) −1 .From this a realistic correlation between MCS and time has been predicted.Barnana PalECMP4.1.1.3 Structural transition in strongly correlated two-dimensional liquidA realistic model to study the properties of an aqueous electrolyte surface consisting of interactingparticles, ions and dipoles, has been developed. The complex liquid surface consisting of a largenumber of interacting particles, the ions and the dipoles, is modeled using Monte Carlo techniqueconsidering grand canonical sampling. The possible interactions existing in the system are chargecharge,charge-dipole, charge-quadrupole and dipole-dipole. The concentration dependence of thediffusion co-efficient suggests a first order phase transition (structural transition), while its temperaturedependence indicates the existence of a second order phase transition. A critical analysisof the effect of decreasing temperature of the system with added cations to limit the motion of the