http://nopr.niscair.res.in/handle/123456789/9014 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/9606 Title: Simultaneous effect of collimator size and absorber thickness on the gamma ray build-up factor <br/> <br/>Authors: Singh, Charanjeet; Sidhu, Gurdeep S; Kumar, Ashok; Singh, Parjit S; Mudahar, Gurmel S <br/> <br/>Abstract: The build-up factor values have been measured for 662 keV gamma rays in the extended media of bakelite and perspex under different collimation conditions. A correlation effect has been obtained in the measurements due to collimator size and absorber thickness to prevent the multiple scatter photons reaching the detector. <br/> <br/>Page(s): 475-478 Mon, 28 Jun 2004 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/9605 Title: Dielectric relaxation studies of (Ge₂₀Se₈₀)_0.90Sn_0.10 glassy alloy <br/> <br/>Authors: Chandel, Pradeep S; Thakur, Anup; Sharma, Vineet; Goyal, N; Tripathi, S K <br/> <br/>Abstract: The frequency and temperature dependence of ac conductivity measurements have been made on (Ge₂₀Se₈₀)_0.90Sn_0.10 glassy alloy in the frequency range 2-50 kHz and in the temperature range 273-373K. Dielectric constant (<img src='/image/spc_char/italics_e.gif' border=0>') has been calculated using this data. The results indicate that dielectric dispersion occurs in this temperature and frequency range. The dielectric loss (<img src='/image/spc_char/italics_e.gif' border=0>'') and loss angle (tan<img src='/image/spc_char/delta1.gif' border=0>) have been calculated using Gever’s relation. The temperature dependence of dielectric loss (<img src='/image/spc_char/italics_e.gif' border=0>'') shows relaxation peaks as a function of temperature. These relaxation peaks shift towards the higher temperature as the frequency is increased. A detailed analysis of the data shows that the results can be explained in terms of dipolar relaxation with a distribution of relaxation times, which is quite expected in case of chalcogenide glasses. <br/> <br/>Page(s): 539-543 Mon, 28 Jun 2004 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/9604 Title: Effect of grain size on the mobility and transfer characteristics of polysilicon thin-film transistors <br/> <br/>Authors: Gupta, Navneet; Tyagi, B P <br/> <br/>Abstract: The effect of the grain size on the effective carrier mobility (<img src='/image/spc_char/micro.gif' border=0>_eff) and transfer characteristics of a polycrystalline silicon thin-film transistor (poly-Si TFT) have been theoretically investigated by developing an analytical model. The dependence of <img src='/image/spc_char/micro.gif' border=0>_eff is studied as a function of doping concentrations and gate voltage for different values of grain size. It is observed that at low as well as at high doping concentrations, the effective carrier mobility (<img src='/image/spc_char/micro.gif' border=0>_eff) increases with increase in grain size, whereas the observed dip at the intermediate doping concentration is getting confirmed. The effect of the grain size on transfer characteristics of poly-Si TFT in its linear region is also presented. It is found that at low gate voltages, <img src='/image/spc_char/micro.gif' border=0>_effand <i>I</i>_Dincrease rapidly with the increase in <i>V</i>_G for all values of grain sizes due to the grain boundary barrier lowering effect. At high gate voltage the grain boundary barrier lowering effect becomes insignificant and causes the saturation of <img src='/image/spc_char/micro.gif' border=0>_effand <i>I</i>_D. The model was found to account correctly for the experimentally observed mobility variation and yield a reasonably good agreement. <br/> <br/>Page(s): 528-532 Mon, 28 Jun 2004 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/9603 Title: Crystallographic analysis of 1H, 4H-tetrahydro-8-methyl-quinolizino-(9,9a,1gh)coumarin <br/> <br/>Authors: Rajnikant; Dinesh; Kamni; Sharma, Bandhan <br/> <br/>Abstract: The crystal structure of 1H,4H-tetrahydro-8-methyl-quinolizino-(9,9a,1gh)coumarin (C₁₆H₁₇NO₂) has been determined by X-ray crystallographic techniques. The compound crystallizes in monoclinic space group P2₁/n with unit cell parameters: <i>a</i> = 8.657(5) Å, <i>b</i> = 10.251(5) Å, <i>c</i> = 14.508(5) Å, <img src='/image/spc_char/beta.gif' border=0> = 96.61(1)°, <i>Z</i> = 4, <i>V</i> = 1278.91(11) ų. The structure has been solved by direct methods and refined upto reliability index of 4.8%. The fused benzene and pyrone rings are planar. Both the piperidine rings exist in distorted <i>sofa</i> conformation. The crystal structure is stabilized by C-H...O hydrogen bonds. <br/> <br/>Page(s): 524-527 Mon, 28 Jun 2004 22:58:59 GMT