http://nopr.niscair.res.in/handle/123456789/479 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/521 Title: Gaussian minimum shift keying systems with additive white Gaussian noise <br/> <br/>Authors: Saraf, A K; Tiwari, M <br/> <br/>Abstract: In this paper, the basic properties of an I-Q Gaussian minimum shift keying (GMSK) with additive white Gaussian noise have been investigated. The probability of error for non-fading and fading channels of communication has been analyzed and discussed. The hardware realization is simple and straight forward like minimum shift keying (MSK) system. Some analytical results have been achieved and compared with machine computed GMSK results of others. The modular circuits are available for VLSI design. Thus, the system developed is suitable for VLSI design of GMSK. <br/> <br/>Page(s): 65-70 Sat, 29 Dec 2007 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/520 Title: Magnetic behaviour of nano-sized and coarse powders of Cd-Ni ferrites synthesized by wet-chemical route <br/> <br/>Authors: Rangolia, M K; Chhantbar, M C; Tanna, A R; Modi, K B; Baldha, G J; Joshi, H H <br/> <br/>Abstract: Nano particles having particle size in the range (80 -100Å) for compositions (x = 0.2, 0.4, 0.6, 0.8) of CdxNi₁₋xFe₂O₄ spinel ferrite system are prepared by chemical co-precipitation route. The structural and magnetic properties have been studied by X-ray diffraction, magnetization, susceptibility and ⁵⁷Fe Mössbauer spectroscopy measurements, before and after high temperature annealing. The magnetic behaviour is explained by invoking the concept of superparamagnetism assuming core-shell structure of the nano-particles. <br/> <br/>Page(s): 60-64 Sat, 29 Dec 2007 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/515 Title: Dielectric relaxation studies of alkyl acrylates with phenol derivatives in carbon tetrachloride using microwave absorption techniques <br/> <br/>Authors: Khan, F Liakath Ali; Sivagurunathan, P; Asghar, J <br/> <br/>Abstract: The dielectric relaxation of alkyl acrylates (methyl acrylate, ethyl acrylate and butyl acrylate) with phenol derivatives (p-cresol, p-chlorophenol, 2,4-dichlorophenol and p-bromophenol) has been measured at microwave frequency 9.37 GHz in dilute solution of carbon tetrachloride at 308K. Different dielectric parameters like dielectric constant Ɛ‛ and dielectric loss Ɛ‛‛ at microwave frequency, static dielectric constant Ɛ₀ and dielectric constant Ɛ∞ at optical frequency have been determined. The relaxation time and activation energy have been determined using the measured dielectric data. The results show a linear dependence of relaxation time on alkyl chain length of acrylic esters and acidity of phenol derivatives. Comparative study of free energy of activation for the dielectric relaxation and viscous flow suggests that the process of viscous flow involves greater interference by neighbours than does dielectric relaxation, as the latter takes place by rotation only whereas the viscous flow involves both rotational and translational motion. The validity of the single frequency equation of Higasi et al. Bull Chem Soc Japan, 44(1971)988. For multiple relaxation time τ₁ is found to be function of the hydrogen bonding strength of phenolic hydrogen whereas the group rotation relaxation time τ₂ is a function of the steric interaction of proton donor. The relaxation time is maximum at 50:50 mol% ratio. <br/> <br/>Page(s): 54-59 Sat, 29 Dec 2007 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/514 Title: Synthesis and characterization of nanosized cobalt-manganese spinel oxide <br/> <br/>Authors: Tharayil, Nisha J; Raveendran, R; Vaidyan, Alexander Varghese <br/> <br/>Abstract: Nanoparticles of cobalt-manganese oxide were prepared by chemical co-precipitation method by decomposition of their respective metal chlorides, sodium carbonate and ethylene diamene tetra acetic acid (EDTA). The heat treatment of the ground precursor powders at their respective decomposition temperature and beyond, results in the evolution of heat from the combustion of the residual carbonaceous material. This facilitates the reaction among the constituent metal ions and the formation of the desired oxide phase at low temperature. The average crystallization size was determined from X-ray diffraction line broadening and the diffractogram was compared with JCPDS data to identify the crystallographic phase of the particle. The shift in d--value due to the nano nature was also analyzed.The internal elastic micro strain was calculated and it was seen that as the particle size increases strain decreases. The effect of sintering on the particle size was also analyzed. The nano nature of the mixed oxide was also analyzed from the TEM and AFM studies. The FTIR studies have been used to confirm the formation of metal oxide. The characteristic stretching and bending frequencies of the sample were also analyzed. The absorption spectra of the material in the UV-Vis –NIR range were recorded. Strong absorption bands are observed to occur at 550 nm and a weak band around 730nm. From the analysis of absorption spectra, the cobalt-manganese oxide (sintered at 500º, 700º and 900º C) have been found to have direct band gaps ranging from 2.07 to 1.59 eV. <br/> <br/>Page(s): 47-53 Sat, 29 Dec 2007 22:58:59 GMT