• Volume 41, Issue 1

      July 1993,   pages  1-73

    • Symmetry breaking in quantum chaotic systems

      Akhilesh Pandey Ramakrishna Ramaswamy Pragya Shukla

      More Details Abstract Fulltext PDF

      We show, using semiclassical methods, that as a symmetry is broken, the transition between universality classes for the spectral correlations of quantum chaotic systems is governed by the same parametrization as in the theory of random matrices. The theory is quantitatively verified for the kicked rotor quantum map. We also provide an explicit substantiation of the random matrix hypothesis, namely that in the symmetry-adapted basis the symmetry-violating operator is random.

    • Underwater optical generation of sound: Oblique incidence

      M S Sodha V Rai M P Verma S Konar K P Maheshwari

      More Details Abstract Fulltext PDF

      This paper addresses itself to the problem of thermoacoustic generation by an obliquely incident laser beam in a body of water. Far-field directivity pattern of thermoacoustic source (TS) has been studied analytically and numerically. Our study suggests the possibility of getting highly directional sound beams in a simple configuration.

    • Dielectric studies of some binary liquid mixtures using microwave cavity techniques

      V Subramanian B S Bellubbi J Sobhanadri

      More Details Abstract Fulltext PDF

      The excess parameter studies in the microwave frequency region (X-band) on complex dielectric permittivity for the binary mixtures are reported. The methods employed are fixed cavity perturbation technique and adjustable plunger cavity technique. Also Gopalakrishna method is used to calculate the relaxation time of the polar solute in a non-polar solvent. The samples under study are acetonitrile, chlorobenzene, dimethyl formamide, carbon tetrachloride and benzene.

    • Effect of strain on vibrational modes in strained layer superlattices

      Sujata Rath Sankar P Sanyal

      More Details Abstract Fulltext PDF

      We have investigated the lattice vibrational properties of a two-component strained layer semiconductor superlattice (GaAs)n1 (GaSb)n2 using a one-dimensional linear chain model and transfer matrix method [1]. Effect of strain, arising due to the lattice mismatch (∼ 7%) has been considered explicitly in the equation of motion. We show for the first time that the optical vibrational frequency increases (in the case of (GaAs)4 (GaSb)n) or decreases (in the case of (GaAs)n(GaSb)4) with increase of layer thicknessn, in either type of superlattices. Raman scattering measurements on some other similar systems support our findings.

    • Second order elastic anomalies in barium titanate from cubic to tetragonal phase transition

      B Subramanyam K S Viswanathan

      More Details Abstract Fulltext PDF

      The anomalies of the second order elastic constants have been derived for barium titanate for the phase transition from cubic to tetragonal. The equilibrium values of the components of the order parameter and the strain variables have been obtained from the stability conditions. The fluctuations in the order parameter have been derived from the Landau-Khalatnikov equations. Expression for the shift in the zero point energy in the tetragonal phase is obtained and is shown to be proportional to (TTc)2. The anomalies for all the second order elastic constants have been derived and relations among them reported. It is shown that the second order elastic anomalies suffer a discontinuity at the transition temperature.

    • The effect of second neighbour repulsion on fcc binary alloy phase diagrams: A Monte Carlo study

      Rita Khanna T R Welberry

      More Details Abstract Fulltext PDF

      We report the results of the Monte Carlo simulation of the phase diagram of fcc binary alloys using a 3-D Ising model with nearest and next-nearest neighbour repulsive interactions. Calculations are carried out for a ratio of second- to first-neighbour interaction energies of 0.4. The resulting phase diagram contains three superstructures A2B2, A2B and A5B, each separated by a disordered fcc phase. There was no evidence for the formation of an A3B phase. These results are in qualitative agreement with CVM results.

    • Field-cooled measurements of harmonic generation in magnetization of high-Tc superconductors

      S B Roy Shailendra Kumar A K Pradhan P Chaddah Ram Prasad N C Soni Kalyan Adhikary

      More Details Abstract Fulltext PDF

      We present measurements of harmonic generation in the magnetization of sintered pellets of YBa2Cu3O7 and Bi1.7Pb0.3Sr2Ca2Cu3O10 as a function of DC field. The DC field is applied in the field-cooled mode. Measurements are made at 77 K for various values of the AC field amplitude. A comparison is made with calculations done within the critical state model.

    • Critical current density of a sample of melt grown Y1.2Ba1.8Cu2.4Ox

      V Ganesan R Srinivasan R Gopalan T Rajasekaran

      More Details Abstract Fulltext PDF

      Melt grown samples of Y1.2Ba1.8Cu2.4Ox have been prepared and studied for their current carrying capacity. The composition was chosen to include Y2BaCuO5 (211) particles in the YBa2Cu3Ox (123) phase. The critical current density (Jc) of these samples was studied as a function of magnetic field using magnetization technique. The micrographic investigation shows well aligned grains in this material. The magnetic hysteresis measurements were done using a MPMS SQUID magnetometer up to the fields of 5.5 T. TheJc was estimated from the remanent magnetization using Bean model. Isothermal magnetization hysteresis loops at low fields reveal the presence of only one kind of hysteresis loops (corresponding to intragrain magnetizations). This is a valid proof that the weak links are greatly eliminated in these samples prepared by MG process. TheJc behaviour as a function of magnetic field has two components, a rapidly decaying exponential function of field and the other component that predominates at higher fields. This could be explained if we assume that the sample contains two phases of superconductors, one having a lowHc2 becoming normal at fairly medium fields of the order of a few kilogauss will act as pinning centres for the other phase having higherHc2 and hence higherJc at high fields.

    • Electronic structure of a superconducting Bi2212 crystal by angle resolved ultra violet photoemission

      N L Saini J Kanski P Srivastava L Ilver K B Garg S Durcok

      More Details Abstract Fulltext PDF

      The electronic structure of a high quality superconducting Bi2Sr2CaCu2O8+δ (Bi2212) single crystal is studied by angle resolved ultra violet photoemission (ARUPS) using He I (21.2 eV). Our results appear to show two bands crossing the Fermi level in ΓX direction of the Brillouin zone as reported by Takahashiet al. The bands at higher binding energy do not show any appreciable dispersion. The nature of the states near the Fermi level is discussed and the observed band structure is compared with the band structure calculations.

  • Pramana – Journal of Physics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.