http://nopr.niscair.res.in/handle/123456789/3783 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/4717 Title: Study of amplitude spectrum of VLF sferics and vertical electric field at Kolkata <br/> <br/>Authors: De, S S; De, B K; Adhikari, S K; Sarkar, B K; Guha, A <br/> <br/>Abstract: From the measurements of atmospheric electric field and VLF sferics at Kolkata (22^o34´ N, 88^o30´ E), some correlation studies have been made. It is observed that the diurnal variation of vertical electric field averaged for 20 fair weather days maintains good connectivity with diurnal variation of VLF sferics activity. The variations are in contrast with the accepted unitary diurnal changes of vertical electric field and thunderstorm occurrence frequency curve with a maximum around 1900 hrs UT and a minimum around 0400 hrs UT. Some results in this context are presented in this paper. <br/> <br/>Page(s): 187-192 Mon, 29 May 2006 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3845 Title: Diurnal and seasonal variation of columnar ozone at Rajkot <br/> <br/>Authors: Ganguly, Nandita D; Ranjan, R R; Joshi, H P; Iyer, K N <br/> <br/>Abstract: Ozone data obtained from Earth-Probe Total Ozone Mapping Spectrometer (TOMS) has been used to calibrate a Microtops-II Sun photometer. Results of observed diurnal and seasonal variation of ozone at Rajkot, obtained using Microtops-II Sun photometer is reported. Since the ozone concentrations measured by Dobson spectrometers in India and TOMS are found to correlate well, it is possible to calibrate Microtops-II Sun photometer with the help of TOMS to get accurate ozone values over Indian low latitudes. This will in turn reduce the inconvenience of carrying the Microtops Sun photometer to a Dobson center for calibration. The diurnal variation of ozone measured by Microtops-II Sun photometer indicates a higher vertical column density of ozone during morning compared to evening hours. This may be due to an increase in daytime temperature and the corresponding increase in ozone by photolysis. An examination of the monthly mean ozone values obtained from Microtops-II Sun photometer indicates a marked seasonal variation with a maximum ozone concentration around June and a minimum around December. <br/> <br/>Page(s): 181-186 Mon, 29 May 2006 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3844 Title: Frequency agile microstrip antenna using symmetrically loaded tunnel diodes <br/> <br/>Authors: Gautam, Anil K; Vishvakarma, B R <br/> <br/>Abstract: A frequency agile microstrip antenna using symmetrically loaded tunnel diodes is proposed, in which the operating frequency of the rectangular microstrip antenna is electronically controlled by the bias voltage of the tunnel diode. Theoretical investigations, based on a modal cavity modal are carried out for the GaAs tunnel diode. The tuning range was found to be 55.92 MHz (6.67 %), which is much better than earlier reported result. <br/> <br/>Page(s): 212-216 Mon, 29 May 2006 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3843 Title: Theoretical and experimental investigations of circular sector microstrip antenna <br/> <br/>Authors: Tiwari, Vijay Kumar; Kimothi, Aradhana; Bhatnagar, D; Saini, J S; Saxena, V K; Kumar, P <br/> <br/>Abstract: An analysis of a general circular sector microstrip antenna (CSMA) with sector angle, ⍺, is presented in this paper. The theoretical analysis is carried out by applying cavity model-based modal expansion technique. The computed results are validated with measured results for CSMA geometry with ⍺ = 60º. The computed results show a fairly good agreement with measured results. A reasonably small deviation of 1.06% in the resonant frequency is recorded, while a fairly good agreement between measured and computed return loss and radiation patterns is recorded. This validates the proposed technique of treating CSMA geometry. <br/> <br/>Page(s): 206-211 Mon, 29 May 2006 22:58:59 GMT