Integrability and chaotic behaviour in a two-coupled Duffing oscillators are studied. The coupling is nonlinear. Painlevé test is performed to identify integrable cases of damped- and force-free system. Exact analytical solutions are given for the integrable cases. Effect of external periodic forces for (i) single well with infinite height potential, (ii) potential with a hump at the centre and (iii) single well with finite height hump potential are numerically investigated. Occurrence of multiple attractors and period doubling cascades of coexisting attractors is presented.

We study the dissipative, classical dynamics of a charged particle in the presence of a magnetic field. Two stochastic models are employed, and a comparative analysis is made, one based on diffusion processes and the other on jump processes. In the literature on collision-broadening of spectral lines, these processes go under the epithet of weak-collision model and Boltzmann-Lorentz model, respectively. We apply our model calculation to investigate the effect of magnetic field on the collision-broadened spectral lines, when the emitter carries an electrical charge. The spectral lines show narrowing as the magnetic field is increased, the narrowing being sharper in the Boltzmann-Lorentz model than in the weak collision model.

We study the quantum Brownian motion of a charged particle in the presence of a magnetic field. From the explicit solution of a quantum Langevin equation we calculate quantities such as the velocity correlation function and the mean-squared displacement. Our calculated expressions contain as special cases the motion of aclassical particle in a magnetic field and that of afree (but quantum) particle, in a dissipative environment.

The radiative decays of heavy mesons are considered in heavy quark symmetry formalism. Introducing the interpolating fields for the heavy mesons we obtain the transition matrix element and the corresponding decay widths in the heavy quark symmetry limits. The Isgur-Wise function present in the expression is determined by ISGW quark model. The results obtained agree reasonably well with other estimations.

The nucleon electromagnetic form factorsG_E^P(q²),G_M^P(q²) and the axial-vector form factor G_A(q²) are studied in a relativistic model of independent quarks confined by an equally mixed scalar-vector square root potentialV_q(r)=1/2(1+γ⁰)(ar^1/2+ν₀) taking into account the appropriate centre-of-mass corrections. The respective root-mean-square radii associated withG_E^P(q²) and G_A(q²) come out as [〈r²〉_E^P]^1/2=0.86 fm and 〈r_A²〉^1/2=0.88 fm. Restoration of chiral symmetry in this model is discussed to derive the pion-nucleon form factorG_πNN(q²) and consequently the pion-nucleon coupling constant is obtained asg_πNN(q²)=12.81 as compared tog_πNN(q²)_exp⋍13.

A hyperspherical partial wave method of Das to calculate cross sections for ionization of hydrogen atoms by electrons has been applied for low energies. Here effect of coupling among different partial waves is neglected.

Intense Raman scattering by acetophenone molecules adsorbed on colloidal silver particles is reported. Greater enhancement is observed for the ring breathing and ring stretching vibrations. The orientation determination analysis shows that the adsorption of acetophenone molecule is neither through its co-ordinating site nor through itsπ-orbital system and there is no strong chemical interaction. However significant intensity enhancement for several vibrations suggests that the contribution is from classical electromagnetic field on the rough surface.