15 research outputs found
Amplitude scintillations on earth-space propagation paths at 2 and 30 GHz
Amplitude scintillation measurements were made simultaneously at 2.075 and 30 GHz on earth-space propagation paths over elevation angles in the range 0.4 to 44 deg. The experiment was performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over Africa to a new synchronous position over the United States. The received signal, variance, level, covariance, spectra and fade distributions are discussed as functions of the path elevation angle. These results are also compared wherever possible with similar measurements made earlier at 20 and 30 GHz
Power law relationships for rain attenuation and reflectivity
The equivalent reflectivity, specific attenuation and volumetric backscatter cross section of rain are calculated and tabulated at a number of frequencies from 1 to 500 GHz using classical Mie theory. The first two parameters are shown to be closely approximated as functions of rain rate by the power law aR to the b power. The a's and b's are also tabulated and plotted for convenient reference
Effects of atmospheric turbulence on microwave and millimeter wave satellite communications systems
A model of the microwave and millimeter wave link in the presence of atmospheric turbulence is presented with emphasis on satellite communications systems. The analysis is based on standard methods of statistical theory. The results are directly usable by the design engineer
Amplitude scintillation at 2 and 30 GHz on earth space paths
Extensive amplitude scintillation measurements were made simultaneously at 2.075 and 30 GHz on earth-space propagation paths. These measurements were performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over India to a new synchronous position over the United States. The variance, path loss, covariance, and spectra are discussed as functions of the path elevation angle. These results are also compared with earlier simultaneous scintillation measurements at 20 and 30 GHz during the movement of ATS-6 to its position over India
Chickpea
The narrow genetic base of cultivated chickpea warrants systematic collection,
documentation and evaluation of chickpea germplasm and particularly wild
Cicer species for effective and efficient use in chickpea breeding programmes.
Limiting factors to crop production, possible solutions and ways to overcome
them, importance of wild relatives and barriers to alien gene introgression and
strategies to overcome them and traits for base broadening have been discussed.
It has been clearly demonstrated that resistance to major biotic and abiotic
stresses can be successfully introgressed from the primary gene pool
comprising progenitor species. However, many desirable traits including high
degree of resistance to multiple stresses that are present in the species
belonging to secondary and tertiary gene pools can also be introgressed by
using special techniques to overcome pre- and post-fertilization barriers.
Besides resistance to various biotic and abiotic stresses, the yield QTLs have
also been introgressed from wild Cicer species to cultivated varieties. Status
and importance of molecular markers, genome mapping and genomic tools
for chickpea improvement are elaborated. Because of major genes for various
biotic and abiotic stresses, the transfer of agronomically important traits into
elite cultivars has been made easy and practical through marker-assisted
selection and marker-assisted backcross. The usefulness of molecular markers
such as SSR and SNP for the construction of high-density genetic maps of
chickpea and for the identification of genes/QTLs for stress resistance, quality
and yield contributing traits has also been discussed