Comparison of Exact and perturbative Results for Two Metrics

We compare the exact and perturbative results in two metrics and show that the spurious effects due to the perturbation method do not survive for physically relevant quantities such as the vacuum expectation value of the stress-energy tensor.Comment: 12 page

Vacuum fluctuations for spherical gravitational impulsive waves

We propose a method for calculating vacuum fluctuations on the background of a spherical impulsive gravitational wave which results in a finite expression for the vacuum expectation value of the stress-energy tensor. The method is based on first including a cosmological constant as an auxiliary constant. We show that the result for the vacuum expectation value of the stress-energy tensor in second-order perturbation theory is finite if both the cosmological constant and the infrared parameter tend to zero at the same rate.Comment: Class. Quantum Grav. 13(1996) 2683-269

Temperature Dependence of Susceptibility in the Ferrielectric Phase of Ammonium Sulphate

We have developed a mean field model for the paraelectric-ferrielectric phase transition in ammonium sulphate. In our model we assume that the quadrupolar. interactions are the dominant mechanism for this type of transition. The fit of our calculated susceptibility to the experimental data shows that the free energy, with a quadrupolar coupling term, can also adequately explain the observed behaviour of ammonium sulphat

T-X phase diagram of Na2S2O7-NaHSO 4

In this study we obtain a T-X phase diagram of Na2S2O7-NaHSO4 using the mean field theory. We fit our calculated phase line equation to the experimental T-X phase diagram. By choosing appropriately the coefficients in the free energy expansions, our calculated phase diagram agrees well with the experimentally observed phase diagram of Na2S2O7-NaHSO4

T-P Phase Diagram of Nitrogen at High Pressures

By employing a mean field model, calculation of the T-P phase diagram of molecular nitrogen is performed at high pressures up to 200 GPa. Experimental data from the literature are used to fit a quadratic function in T and P, describing the phase line equations which have been derived using the mean field model studied here for N-2, and the fitted parameters are determined. Our model study gives that the observed T-P phase diagram can be described satisfactorily for the first-order transitions between the phases at low as well as high pressures in nitrogen. Some thermodynamic quantities can also be predicted as functions of temperature and pressure from the mean field model studied here and they can be compared with the experimental data

Temperature dependence of the IR mode frequency calculated from the volume data for DMNaFE

We analyze the infrared (IR) frequencies of the internal mode of asymmetric close to phase transition in DMNaFe. By means of the mode Gruneisen parameter , the IR frequencies are calculated from the observed volume data given in the literature. Calculated frequencies are fitted to the observed data for both below and above as the varies with the temperature in the low and high temperature phases in this compound. Our results show that the critical behavior of the observed IR frequencies can be explained from the volume data to describe a first order structural phase transition in DMNaFe