http://nopr.niscair.res.in/handle/123456789/480 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/539 Title: Three site hole hopping in high Tʗ superconductors <br/> <br/>Authors: Tiwari, M; Singh, R A <br/> <br/>Abstract: Dynamics of holes containing three site hole hopping and parallel hopping has been studied. A new type of hole-hole correlation is discussed. The effect of three site term and parallel hopping term on hole-hole correlation has been investigated. <br/> <br/>Page(s): 139-144 Tue, 29 Jan 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/538 Title: Design a tunable cavity resonator for complex permittivity measurement of low-loss material at L band <br/> <br/>Authors: Calla, O P N; Mishra, Sanjeev Kumar; Bohra, Dinesh; Khandelwal, Nitin; Kalla, Paritosh; Sharma, Charu; Gathania, Neha; Bohra, Naveen; Shukla, Saurabh <br/> <br/>Abstract: The value of loss tangent (tanδ) of the low loss material is of the order of 10⁻⁴. There are different methods used to measure loss tangent as well as complex permittivity. Out of different methods, Cavity Resonator method is the best method for the measurement of complex permittivity of low loss materials i.e. teflon, duroid, polystyrene and stycast. In this present paper, a cylindrical cavity resonator is designed and fabricated in the frequency range 2.2-2.3 GHz and the complex permittivity of low loss material teflon using cavity resonator method has been measured. <br/> <br/>Page(s): 134-138 Tue, 29 Jan 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/537 Title: Multiple relaxation investigations in polyetherimide: Thermally stimulated depolarization current technique <br/> <br/>Authors: Singh, Randhir; Kaushik, B K; Quamara, J K <br/> <br/>Abstract: Thermally stimulated depolarization current (TSDC) technique has been used for investigating various dielectric relaxation processes in polyetherimide. The TSD currents in the temperature range 20º-250ºC (in certain cases up to 300ºC) were obtained as functions of polarizing field (Ep; 20-350 kV/cm), polarizing temperature (Tp; 60 º-180ºC), poling time (tp; 0.5-2 h), sample thickness (d; 25-120 µm), heating rate (h; 2º-6ºC/min), and storage time (ts; 0-552 h). The current maxima in the TSDC spectra reveal the presence of two major relaxation processes termed as β- (around 130ºC) and ⍺- (around 190ºC), associated with dipolar relaxation and space-charge relaxation processes, respectively. However, in certain cases, we observe merging of β- and ⍺-relaxation processes to become the ⍺β-relaxation process (140º-180ºC). The observed dependence of the peak temperature Tm on polarizing temperature and poling time indicates a continuous distribution of relaxations. The high Ep/Tp samples also show a relaxation (ρ) around 260ºC associated with charge injection phenomenon. The low temperature region of TSDC spectra (30º-70ºC) shows the presence of a weak relaxation (β′), considered as a satellite of the main dipolar relaxation process. The activation energies for various relaxation processes have been calculated using Bucci plot method. <br/> <br/>Page(s): 127-133 Tue, 29 Jan 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/536 Title: Effect of L-arginine, L-histidine and glycine on the growth of KDP single crystals and their characterization <br/> <br/>Authors: Kumar, B Suresh; Babu, K Rajendra <br/> <br/>Abstract: Optically good quality single crystals of pure and amino acid doped KDP have been grown by slow evaporation method at constant temperature (40°C). The effect of amino acid dopants on the growth and characterization of KDP crystals has been studied. The grown crystals are characterized by density, melting point determination and X-ray powder diffraction. The presence of functional groups of crystals are qualitatively analysed from FTIR spectra. Thermal properties like decomposition temperatures and weight loss have been reported from the TGA and DTA analysis. The transparency of the grown crystals has been confirmed using UV-Vis spectra. It has been found that SHG efficiency of KDP, containing amino acids is higher than pure KDP crystals. Dielectric behaviour of pure and doped samples has been studied at a temperature range 30 - 180ºC and a constant frequency 1 kHz. <br/> <br/>Page(s): 123-126 Tue, 29 Jan 2008 22:58:59 GMT