[en] The design considerations for high temperature superconducting microwave filters are presented. The filter designed is at C- band with 0.6% bandwidth. The error analysis, insertion loss calculation, power handling capability, input/output connections and package design are discussed. Theoretical calculations gave insertion loss of 0.8 dB at 6 GHz for a conductivity ratio of 50 between high T_c thin film and gold film. (author)

[en] Apparent molar volumes (V_φ) and viscosity B-coefficients of sodium molybdate and sodium tungstate in aqueous binary mixtures of acetonitrile have been determined from solution density and viscosity measurements at 298.15, 308.15 and 318.15 K and at various electrolytic concentrations. The experimental density and viscosity data were evaluated by Masson equation and Jones-Dole equation, respectively and the derived parameters were interpreted in terms of ion-solvent and ion-ion interactions. The activation parameters of viscous flow were also determined and discussed by the application of transition state theory

[en] Short surface cracks were generated by Vickers indentation on the polished surface of alumina and different zirconia toughened alumina (ZTA) specimens, and their morphology was studied by serial sectioning. These cracks were grown in three-point bend tests under stepwise loading, and variation of toughness with crack extension was plotted to graphically separate the contributions from residual stress intensity and applied stress intensity factors. The plateau toughness determined from the intercept height of the crack extension plots exhibited an upward trend with zirconia content up to 15 vol% ZrO₂ addition in the composition, which was proportional to the fraction of transformable tetragonal grains contributing to transformation toughening. copyright 1996 Materials Research Society

[en] The non-linear heating of electrons in the ionospheric plasma due to high-power radio wave propagation has been investigated through an integro-differential equation derived from Boltzmann velocity-moment equations. Various processes appropriate to the situation under study are taken into account. The numerical solution of the derived equation is presented graphically. 18 refs.; 1 figure

[en] The fatigue behaviour of fine grained Al₂O₃ and ZrO₂ toughened Al₂O₃ (ZTA) compositions with 15 vol% ZrO₂ (3 mol% Y₂O₃ stabilized: 3Y-TZP) have been investigated by using three different techniques. Primarily 4-point bending load was employed to generate tension-tension fatigue data under both static and cyclic conditions. The results clearly showed that the materials were susceptible to both the static and cyclic fatigue and the time to failure under cyclic loading was considerably shorter than the equivalent static loads. The repeated indentations at the same spot with varying loads showed a typical fatigue behaviour. In addition, both the materials were subjected to the repeated impact cycles at varying subcritical loads simulating impact fatigue. In all the cases typical fatigue curves were obtained having a progressive endurance at subcritical loads having an endurance limit. The fatigue behaviour of Al₂O₃ was much improved by the addition of 15 vol% 3Y -TZP, having micro-plasticity contributing towards the cyclic fatigue phenomena of these materials. (author)

[en] Short communication. 2 tabs

[en] Photoacoustic spectroscopic technique has been used to study the heat capacity (C_p) anomaly around 91 K in superconducting YBa₂Cu₃O_7-δ oxide. The thermal conductivity data required for the estimation of C_p values were taken from other experimental results. The photoacoustic signal amplitude is analysed with Rosencwaig and Gersho's(RG) theory. From the value of the ratio of excess heat capacity ΔC_p and superconducting transition temperature T_c the value of the electronic specific heat coefficient γ=19.98 mJ/mol.K² using the relation ΔC_p/T_c=1.43 γ according to the BCS weak-coupling limit has been estimated. This value of γ agrees quite well with those obtained from direct heat capacity measurements which vary from 15 to 37 mJ/mol.K² as reported by different research groups. (author). 17 refs., 4 figs

[en] Coupled wave equations are obtained in the study of radio wave propagation through the compressible and anisotropic plasma appropriate for the lower region of the ionosphere. A formal solution has been presented for the transverse components of the electric field within such a medium. (author). 9 refs

[en] One of the serious material problems with high T_c superconductors is their granularity which greatly affects their microwave transmission (as well as absorption) properties. High quality near-epitaxial thin films of these oxide superconductors have been found to be advantageous for microwave devices due to their low conduction loss. Pulsed laser ablation deposition (PLAD) technique has been extensively used for the growth of high quality films of oxide superconductors. Work carried out at TIFR during the last several years has convincingly shown that significant improvement in microstructure, and consequently, in microwave transmission properties of YBa₂Cu₃O_7-Δ(YBCO) thin films can be realised by incorporating a small quantity (about 5%) of Ag in the YBCO target used for PLAD. Microwave surface resistance of YBCO films has been measured using microstrip resonator configuration at various temperatures in the range 15-88K and in the frequency range 1.5 to 12 GHz. Due to the much improved microstructure, Ag-YBCO films have not only shown a low surface resistance but also a good power handling capability. Au-YBCO films too have shown improved properties with the added advantage of much improved environmental stability. This paper reviews significant advances in the growth and microwave measurements of Ag-YBCO and Au-YBCO thin films and show why they would be of great advantage for microwave passive devices operating at 77K. (author)

[en] Using photoacoustic technique we have studied the thermal variation of thermal diffusivity and heat capacity of a typical Bi-based superconductor viz. Bi_2-xPb_xSr₂Ca₂Cu₃O_y by Rosenewaig and Gersho's (R-G) theory. At the superconducting transition temperature around 108 K, the thermal diffusivity and specific heat showed anomaly. The value of the electronic specific heat co-efficient (γ), estimated using the relation ΔC_p/T_c = 1.43 γ (according to the BCS weak-coupling limit) has come out to be 16.19 mJ/mol.K². This value of γ agrees quite well with those obtained from direct heat capacity measurements, which vary from 11 to 35 mJ/mol.K². (author)