Showing papers by "Indian Institute of Technology, Jodhpur published in 2006"

Polymer in a double well: dynamics of translocation of short chains over a barrier

Abstract: We consider the dynamics of a short chain polymer crossing over a free energy barrier in space. Adopting the continuum version of the Rouse model, we find exact expressions for the activation energy and the rate of crossing. For this model, the analysis of barrier crossing is analogous to semiclassical treatment of quantum tunnelling. Finding the saddle point for the process requires solving a Newton-like equation of motion for a fictitious particle. The analysis shows that short chains would cross the barrier as a globule. The activation free energy for this would increase linearly with the number of units N in the polymer. The saddle point for longer chains is an extended conformation, in which the chain is stretched out. The stretching out lowers the energy and hence the activation free energy is no longer linear in N. The rates in both the cases are calculated using a multidimensional approach and analytical expressions are derived, using a new formula for evaluating the infinite products. However, due to the harmonic approximation made in the derivation, the rates are found to diverge at the point where the saddle point changes over from the globule to the stretched out conformation. The reason for this is identified to be the bifurcation of the saddle to give two new saddles, and a correction formula is derived for the rate in the vicinity of this point. Numerical results using the formulae are presented. As a function of N, it is possible for the rate to have a minimum. This is due to confinement effects in the initial state.

Stochastic Finite Element Failure Analysis of Laminated Plates under Uniaxial Compressive Loading

Abstract: A first-ply failure and buckling failure of laminated composite plates with and without centrally located cutout having random material properties are presented under uniaxial compressive loading. In both cases, an accurate pre-buckled stress analysis is needed. A layerwise plate model is used to solve both pre-buckling and buckling problems. The stochastic failure analysis is carried out using mean centered first order perturbation technique based stochastic finite element method. Micromechanics based approach is used to see the effect of variation in microlevel constituents, like fiber phase, matrix phase and volume fraction of each phase, on the effective macrolevel properties like the elastic moduli. Consequently the effect of uncertainty in these material properties on the first-ply failure load and buckling strength of the laminated plates is studied. The mean buckling strength of composite plates is validated with results available in literature. The validation of stochastic analysis is done with analytical result based on Kirchhoff-Love plate theory in conjunction with first-order perturbation technique. Parametric studies are also done to see the effect of lay-ups and boundary conditions on the mean and variance of buckling strength of plates.

Working group report: Flavor physics and model building

Abstract: This is the report of flavor physics and model building working group at WHEPP-9. While activites in flavor physics have been mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently.