Modern Physics Letters B

The bifurcation structure and periodic orbits of the Lorenz system with the Prandt1 number as the control parameter are investigated. It is shown that new bifurcation phenomena, both positive (forward) and inverse (backward) bifurcations, which do not appear together in the Rayleigh number space, can appear. The orbit characteristics in typical periodic windows are also studied.

The relaxational heat capacity of an infinite linear polymer chain is computed. The result is derived within a kinetic Ising-like model previously introduced to provide for a dynamical generalization of the Gibbs-di Marzio lattice model. The questions of universality of the dynamic responses of the chain and of the existence of more than one relaxation time if one considers different probes are discussed.

Fluctuation in the distance between flux lines in a superconductor is calculated in a fractal dimension and from that using Lindemann criterion of melting, a field versus temperature phase boundary is deduced for the dendritic phase of a superconductor. This phase boundary is predicted to be B⁻⁴∝(1−T_FM/T_c) where T_FM is the flux-lattice melting temperature. When both the fractal as well as the spectral dimensionalities are considered the phase boundary is predicted to be determined by B^8/5∝(1−T_FM/T_c).

Magnetoresistivity measurements as a function of temperature, ρ(B, T) in applied magnetic field B up to 0.7 T have been carried out on a sample of the 110 K phase of the (Bi, Pb)-(Sr, Ba)-Ca-Cu-O system. The dρ/dT versus T curves in an applied magnetic field reveal the intra- and intergranular transitions. The behavior of these transitions as function of the magnetic field is presented. Thermally activated flux motion has been studied. The activation energy is proportional to (1−T/T_c)ln B, and suggests a 2D-state in which the dissipation is dominated by the cutting mechanism in an entangled flux liquid.

Dielectric measurements of cobalt substituted W-type barium–zinc hexagonal ferrites are undertaken both as a function of frequency and temperature. The dielectric constant is found to decrease continuously with increasing frequency while it increases continuously with increasing temperature. The variation of dielectric constant with dopants concentration is explained on the basis of magnetic cation orientation. From the temperature variation of dielectric constant two transitions, one due to the spin reorientation in the temperature range 450–500 K and the other one due to a ferri to paramagnetic transition have been observed. Suitable explanations for the observed behavior are given.

The temperature dependence of the second-order crystalline electric field (CEF) parameters of rare earth intermetallic compound CeZn₂ was deduced from the least-squares nonlinear fit to the reciprocal paramagnetic susceptibility along principal crystalline axes. The results of the calculation are in good agreement with the experimental values.