http://nopr.niscair.res.in/handle/123456789/10789 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/10844 Title: Field dependent specific heat of PbTiO₃ and KNbO₃ ferroelectric perovskites <br/> <br/>Authors: Singh, Talvinder; Kumar, Ashok; Naithani, U C <br/> <br/>Abstract: An expression has been obtained for the specific heat of anharmonic pure PbTiO₃ and KNbO₃ferroelectric perovskites using double-time Green’s function along with Silverman-Joseph modified Hamiltonian which includes anharmonicity up to the fourth order due to the interaction of the soft mode. The electric field and temperature dependence of the soft mode and the specific heat has been studied for both the crystals. The specific heat decreases with increasing external electric field and increases with increasing temperature. In the low field’s region, the effect of temperature ceases and the change in specific heat arises mainly due to higher order anharmonic terms. Anharmonicity is necessary in these crystals to observe these effects. <br/> <br/>Page(s): 59-63 http://nopr.niscair.res.in/handle/123456789/10843 Title: Effect of order parameters on the pairing properties of high-<i style="">T</i>_c superconductors <br/> <br/>Authors: Tiwari, M; Khatik, Deepa <br/> <br/>Abstract: Green’s function theory of high <i style="">T</i>_c superconductor has been developed for two hole motion surrounded by spins in presence of antiferromagnetism and ferromagnetism generated by distorted spins due to hole motion. Some analytical results have been achieved using low temperature series expansion method for a two dimensional lattice and a half spin system. The gap parameter and the transition temperature have been derived. The effect of interaction parameter on transition temperature has been studied and the existence of <i style="">S</i>-symmetry, <i style="">d</i>-symmetry and symmetry breaking is discussed. <br/> <br/>Page(s): 53-58 http://nopr.niscair.res.in/handle/123456789/10842 Title: Dielectric dispersion and relaxation mixtures of 1-butanol and phenol at lower microwave frequencies <br/> <br/>Authors: Vyas, A D; Rana, V A; Bhatnagar, S P; Vashisth, V M <br/> <br/>Abstract: Complex dielectric permittivity of 1-butanol, phenol and mixtures of 1-butanol+phenol at nine different concentrations of phenol in 1-butanol were measured in the frequency range 0.2-3.0 GHz using Vector Network Analyzer (VNA) at three different temperatures. Open ended co-axial probe technique suggested by Wei and Sridhar [<i style="">Rev Sci Instr,</i> 60(9) (1989) 3041]was used to obtain complex permittivity spectra of the liquid samples. The measured values of real part of complex permittivity (<img src='http://www.niscair.res.in/jinfo/epsilon-dash1.gif' border=0>) and imaginary part of complex permittivity (<img src='http://www.niscair.res.in/jinfo/epsilon-dash2.gif' border=0>) were fitted to Debye equation to determine dielectric relaxation parameters, viz., relaxation time, static dielectric permittivity and high frequency limit dielectric permittivity. Concentration dependent plots of relaxation time and excess inverse relaxation time were used to gain information about the molecular interaction among the molecular species of the liquid mixtures. Information regarding the orientation of electric dipoles in the liquid mixtures is obtained from the evaluated values of the Kirkwood Correlation factor ‘<i>g</i>’. <br/> <br/>Page(s): 47-52 http://nopr.niscair.res.in/handle/123456789/10841 Title: Dielectric relaxation studies of binary mixtures of tetrahydrofuran and N,N-dimethylacetamide in benzene solutions using microwave absorption data <br/> <br/>Authors: Kumar, Raman; Chaudhary, Raman Kumar; Rangra, V S <br/> <br/>Abstract: The dielectric relaxation times (t) and dipole moments (m) of the binary mixtures of different molar concentrations of tetrahydrofuran (THF) in the binary mixtures of tetrahydrofuran (THF) and N,N-dimethylacetamide (DMA) in benzene solutions have been studied. The physical parameters t and µ have been calculated by using standard standing wave microwave techniques and Gopala Krishna’ssingle frequency (9.90GHz) concentration variational method at different temperatures (25°, 30°, 35° and 40°C). The energy parameters (<img src='/image/spc_char/delta.gif' border=0><i style="">H</i>_s, <img src='/image/spc_char/delta.gif' border=0><i style="">F</i>_s, <img src='/image/spc_char/delta.gif' border=0><i style="">S</i>_s) for the dielectric relaxation process for THF+DMA binary mixture containing 50 mol% THF have been calculated at 25°, 30°, 35° and 40°C and compared with the corresponding viscosity parameters. From the observations, it is found that the dielectric relaxation process like the viscous flow process can be treated as the rate process. On the basis of above studies, solute-solvent type of the molecular association has been proposed. <br/> <br/>Page(s): 42-46