• Volume 41, Issue 3

      September 1993,   pages  1-289

    • Influence of various gases on single bubble sonoluminescence

      Vijay H Arakeri

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      Influence of various gases on the intensity of single bubble sonoluminescence has been studied. The gases used were air, oxygen, nitrogen, argon and helium. Among these oxygen gave the brightest intensity with nitrogen giving the least.

    • Anomalies in second order elastic constants and gyrotropic constants of triglycine sulphate near phase transition

      B Subramanyam K S Viswanathan

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      The anomalies in second order elastic constants and gyrotropic constants have been considered for the phase transition of triglycine sulphate. Expressions have been derived for the equilibrium values of order parameter and strain variables in both phases. Using Landau-Khalatnikov equation the fluctuation in order parameter is expressed in terms of fluctuations in strain variables. Substitution of these in free energy gives anomalies arising from Landau and coupling energies in second order elastic constants. The real part of the anomalies decreases steeply across the transition temperature and thereafter flatly tend to ferroelectric values. The anomalies in the components of the gyrotropic tensor have been derived and their temperature variation discussed.

    • Surface acoustic wave distribution and acousto-optic interaction in proton exchanged LiNbO3 waveguides

      P Annachelvi A Selvarajan G V Anand

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      The efficiency of acoustooptic (AO) interaction in YZ-cut proton exchanged (PE) LiNbO3 waveguides is theoretically analysed by determining the overlap between the optical and acoustic field distributions. The present analysis takes into account the perturbed SAW field distribution due to the presence of the PE layer on the LiNbO3 substrate determined by the rigorous layered medium approach. The overlap is found to be significant upto very high acoustic frequencies of the order of 5 GHz, whereas in the earlier analysis by vonHelmolt and Schaffer [6] for diffused waveguides, it was shown that the overlap integral rolls down to nearly zero at this high frequency range.

    • Switching of partially switched KNbO3 single crystals containing cooperatively ordered impurity dipoles

      S G Ingle R N Kakde

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      Switching studies have been carried out in partially switched KNbO3 single crystals by observing switching transients and hysteresis loops. The crystals used contained ordered impurity dipoles that are active in nucleating domains around them. Partial initial switching was obtained by applying known compressive stress to the crystal by means of a spring. The partially switched nature was determined by recording the photograph of the crystal surface. The changed domain structure on the surface gave a clear idea of the extent of partial switching. As the compressive stress was gradually increased, the crystal showed increased initial mechanical switching through the mechanism of evaporation of domain walls associated with ordered impurity dipoles. The dipoles then switch systematically converting 90° domains with polar axes in the plane of plate into 60° domains with polar axes in the perpendicular pseudocubic {001} planes. The initial switching condition changes the switching characteristics as determined by hysteresis loops and switching transients. The results are interpreted in terms of domains in the crystal. If the dipole density is quite high, the effect of the dipoles becomes negligible, and the switching behaviour approximates that of a normal ferroelectric. The switching transients and the hysteresis loops in the crystals containing cooperatively ordered dipoles are basically different from the ones observed in normal ferroelectrics. The anomalous behaviour is detrimental to the use of material in device applications. Hence, it is shown that the switching transients and hysteresis loops provide a ready means of detecting the presence of these ordered impurity dipoles.

    • Investigations on thermoelectric power of lanthanum oxide doped ferroelectric sodium vanadate

      D V Pawar T S Magdum S P Rasal S H Chavan

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      The thermoelectric power of ferroelectric sodium vanadate doped with different concentrations of lanthanum oxide has been measured in the temperature range covering their transition temperatures. It has been observed that the thermoelectric power increases with temperature, attains maximum value and with further increase in the temperature decreases to zero, indicating Curie temperature of the respective samples; however, it changes the sign for higher temperature. The thermoelectric power of sodium vanadate increases to maximum with increase in doping concentration of lanthanum oxide from 0.025 to 0.1 mol%; however, it decreases for higher concentrations. Pure as well as lanthanum oxide doped sodium vanadate samples showp-type behaviour in the ferroelectric region andn-type behaviour in the paraelectric region.

    • Electronic structure of hydrogen and muonium in Al, Mg and Cu

      Pawan Singh S Prakash

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      The electronic structure of hydrogen and muonium in simple metals is investigated. The spherical solid model potential is used for the discrete lattice and the Blatt correction for lattice dilation. The proton and muon are kept at the octahedral sites in the fcc and hcp lattices and self-consistent non-linear screening calculations are carried out. The scattering phase shifts, electronic charge density, effective impurity potential, self-energy, charge transfer, residual resistivity and Knight shift are calculated. The spherical solid potential changes the scattering character of impurity. The phase shifts are found slowly converging. The scattering is more prominent in Al than in Mg and Cu. The virtual bound states of proton and muon are favoured in all the three metals. The calculated value of residual resistivity for CuH is in good agreement with the experimental value. The results for Knight shift forμ+ in Cu and Mg are in reasonable agreement with the experimental values while those forμ+ in Al are lower than the experimental value. The analytical expressions for effective impurity potential and electronic charge density are suggested.

    • Laser produced plasma: A pumping source for cadmium photo-ionization laser

      Rekha Tambay Raj K Thareja

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      We report laser oscillations in Cd II on 4d95s22D5/2 − 4d105p2P3/2 transition at 441.6 nm using laser produced tungsten plasma as a pumping source. Mach Zehnder interferometer is used to measure electron density. Design and working of the crossed heat pipe used in the studies is discussed.

    • A translational energy spectrometer to probe interatomic potentials: Dissociation dynamics of CO2+ ions

      M Krishnamurthy U T Raheja D Mathur

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      A new ion translational energy spectrometer has been developed to carry out low-energy, gas-phase ion-molecule collision experiments which aim to probe molecular potential energy surfaces. The collisional technique employed relates small changes in the kinetic energy of a projectile ion after it has undergone collision with a static neutral atom/molecule to changes in the overall potential energy of the collision system; information can be furnished about the interaction potential between the projectile and the target. First measurements are reported of a high resolution target excitation spectrum obtained in 1.8 keV collisions of H2+ ions with N2. New results pertaining to collision-induced dissociation of CO2+ ions are presented and discussed in terms of potential functions of low-lying electronic states of the molecular ion.

    • Further studies on Ag/BPSCCO tapes using low purity materials

      S R Shukla Y S Reddy N Kumar S K Sharma R G Sharma

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      Transmission electron microscopic (TEM) studies are reported on Ag-clad Bi1.7 Pb0.4Sr1.8Ca2Cu3.5Ox tapes prepared by using low purity (98–99%) commercial grade materials. The self-fieldJc values of these tapes viz. 6.14 × 103 A.cm−2 at 77 K and 1.4 × 105 A.cm−2 at 4.2 K, reported in an earlier publication, were significantly higher than the correspondingJc values in tapes prepared with high purity (99.99%) materials. The TEM pictures on the low purity core material of the tapes reveal the presence of stacking faults and the intergrowth of the 2212 and 2223 phases which could be acting as flux pinning sites and responsible for enhancedJc values. These defects can perhaps be traced back to the presence of 60 ppm iron in the low purity CuO as revealed by atomic absorption analysis reported earlier.

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