http://nopr.niscair.res.in/handle/123456789/8607 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/8733 Title: Low-noise, high resolution microwave synthesis for atomic frequency standards <br/> <br/>Authors: Gupta, A Sen; Howe, D A <br/> <br/>Abstract: The performance of newer generations of ultra high stability atomic frequency standards based on laser cooled atoms and ions appears to be limited by the local oscillator and the microwave synthesis chain. To improve this performance, the design considerations of microwave synthesizers for Cs hyperfine clock transition at 9.192 GHz that emphasize high resolution, low phase modulation (PM) and amplitude modulation (AM) noise, low spurs near the carrier, and very high phase stability with respect to environmental effects have been studied. Typical performance achieved are: internal fractional frequency stability of 1.5 × 10^-15 at 10 s and 1 × 10^-18 at 1 day; fractional frequency step of 2 × 10^-17 and temperature coefficient less than 0.1-0.5 ps/K. Our design is quite general and enables generation of microwave outputs corresponding to several different atomic transitions. The phase locking of the synthesizer to a high stability external frequency reference based on a cavity stabilized oscillator has been studied. <br/> <br/>Page(s): 221-227 Sat, 26 Feb 2005 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/8732 Title: Theory and performance of an electrically controlled microwave phase shifter <br/> <br/>Authors: Sarkar, S; Banerjee, T; Mondal, D; Sarkar, B C <br/> <br/>Abstract: A microwave phase shifter (MPS) using a dc bias-controlled injection synchronized Gunn oscillator (ISGO) has been proposed. A continuous phase variation of a microwave frequency signal over a range of -<img src='/image/spc_char/pi.gif' border=0>/2 to <img src='/image/spc_char/pi.gif' border=0>/2 can be made by varying the dc bias of the oscillator. Analytically predicted results, verified with the experimental ones obtained in a novel phase-shift measuring set-up, have been described. <br/> <br/>Page(s): 215-220 Sat, 26 Feb 2005 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/8731 Title: Study of hyperfine fields in Co₂ScSn Heusler alloy <br/> <br/>Authors: Lakshmi, N; Pandey, Anil; Venugopalan, K <br/> <br/>Abstract: <smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="City"><smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place"> Heusler alloy Co₂ScSn has been prepared and studied. X-ray diffraction studies showed the structure to be L₂₁ type. Using Sn-119, Mössbauer studies were carried out to investigate the magnetic hyperfine fields present at the Sn site in this alloy.Applicability of the Blandin and Campbell model for this alloy is tested by calculating the hyperfine fields at Sn site. The results of these calculations are compared with the experimental results. </smarttagtype></smarttagtype> <br/> <br/>Page(s): 203-206 Sat, 26 Feb 2005 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/8730 Title: Catalyzed crystallization and some physical properties of Li₂O-MgO-B₂O₃:TiO₂ glasses <br/> <br/>Authors: Rao, R Balaji; Raju, G Naga; Veeraiah, N <br/> <br/>Abstract: Li₂O-MgO-B₂O₃:TiO₂ glasses were crystallized at three different temperatures. The samples were characterized by scanning electron microscopy and differential scanning calorimetry. Various physical properties viz., optical (optical absorption, IR spectra and thermoluminescence), magnetic (magnetic susceptibility and ESR spectra) have been studied as a function of temperature of crystallization. The investigation is further extended to the dielectric properties viz., dielectric constant, loss and a.c. conductivity over a moderately wide range of frequency and temperature. The analysis of these results indicated a considerable increase in the electrical insulating strength of the samples due to crystallization. <br/> <br/>Page(s): 192-202 Sat, 26 Feb 2005 22:58:59 GMT