A modified Flory theory along with the Auerbach and Altenberg relations has been employed for the computation of ultrasonic velocity of three quaternary liquid mixtures and a comparative study of all the three relations has then been carried out.

Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC) have been presented by including the effects of free-carrier doping and three-body interactions in the rigid shell model. The short-range overlap repulsion is operative up to the second neighbour ions. An excellent agreement has been obtained between theory and experiment for their phonon dispersion curves and Debye temperature variations. It is concluded that the contributions of free-carrier doping and three-body interactions are essential for the description of the lattice dynamics of these carbides.

A new type of discrete VLF emissions recorded at the low-latitude ground station Varanasi (geomag. lat. 14°55′ N, geomag. long. 154°E;L = 1.07) during the strong magnetic activity on 29–30 April 1990 have been reported. A generation mechanism for various temporal and spectral features of discrete VLF emissions recorded at Varanasi is presented on the basis of cyclotron resonance interaction between whistler mode wave and energetic electrons ejected by substorm electric fields. An attempt is also made to determine parallel energy and wave growth relevant to the generation process of discrete VLF emissions. Finally, our results are discussed with other published works

In the present work, results of upconversion emission in various powder samples have been discussed. The powder upconversion phosphors such as La₂O₃:Er³⁺/Yb³⁺, LaF₃:Er³⁺/Yb³⁺, CeO₂ :Er³⁺/Yb³⁺, CeF₃:Er³⁺/Yb³⁺ were prepared and their upconversion emission, using 976 nm wavelength excitation, was investigated in depth. These phosphors have shown good upconversion emission in the visible region except for the CeF₃:Er³⁺/Yb³⁺ phosphor. Two intense bands around 525 and 550 nm due to the ²H_11/2$\to$⁴I_15/2 and ⁴S_3/2 $\to$ ⁴I_15/2 transitions, respectively, are found to be in a thermally coupled state in these samples. The intensity ratio of these two bands permitted us to estimate the temperature of the environment. The pump power studies of the emission bands of these samples are also made to understand the dynamics of the upconversion emission.

AMichelson interferometer-based technique has been used to measure the deformation of dielectric-coated mirror, caused by an incident repetitive pulsed laser beam with high average power. Minimum measurable deformation of 17 nm is reported.