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Broadcast ionospheric delay correction algorithm using reduced order adjusted spherical harmonics function for single frequency GNSS receivers

Abhigna M. S. R., Sridhar M., Harsha P. Babu Sree, Krishna K. Siva, Ratnam D. Venkata

Acta Geophysica

2021

Vol. 69, no. 1

335--351

Single-frequency Global Navigation Satellite System (GNSS) users require an efcient ionospheric delay correction model for improving their positional accuracy. GPS satellite range signals undergo time delay through the inhomogeneous and dynamic state of the ionosphere. The ionospheric delay is inverse proportional to the signal frequency square due to the dispersive nature of the ionospheric medium. There is a need for aid regional ionospheric broadcast correction model that is necessary for low-latitude ionospheric conditions. In this paper, a reduced order adjusted spherical harmonics function (ROASHF) ionospheric broadcast correction model with order and degree 2 is proposed for the Indian region. A dense GPS receiver network of 14 GPS receivers over the Indian region is analyzed to derive nine ROASHF broadcast coefcients. The performance of the proposed ionospheric broadcast correction model is compared with Klobuchar, NeQuickG, BDS-2, CODEKlob, and CODEGIM TEC models during March and September equinox and June and December solstice days in 2015 and 2016. The mean root mean square error (RMSE) of ROASHF, Klobuchar, NeQuickG, BDS-2, CODEKlob, and CODEGIM TEC models is 7.13 TECU, 9.52 TECU, 15.52 TECU, 11.44 TECU, 13.47 TECU, and 11.97 TECU, respectively. The results demonstrated that the proposed ROASHF ionospheric broadcast model could better predict the ionospheric delays for single-frequency GNSS users. The proposed ionospheric broadcast model is suitable for the Indian regional navigation system known as Navigation with Indian Constellation (NavIC).

Synthesis, Characterization and Crystal Structure Studies of 1-(4-Chloro-benzenesulfonyl)-piperidin-4-yl-diphenyl-methanol

Benakaprasad S., Naveen S., Anandakumar C., Sunilkumar Y., Sridhar M., Shashidhara Prasad J., Rangappa K.

Polish Journal of Chemistry

2007

Vol. 81, nr 5-6

1191-1199

1-(4-Chloro-benzenesulfonyl)-piperidin-4-yl-diphenyl-methanol was synthesized by the condensation of [piperidin-4-yl]-diphenyl-methanol with p-chlorobenzene sulfonylchloride in methylene dichloride as solvent and triethylamine as the base. The compound obtained was characterized by spectroscopic techniques and confirmed by X-ray crystallographic studies. The crystallographic data analysis reveals that the title compound crystallizes in the monoclinic space group P21/c with cell parameters a = 10.214(9capital A, ring, b = 11.371(5)cvapital A, ring, c = 20.939(16)capital A, ring, beta = 115.399(2), V = 2197(3) capital A, ring3 for Z = 4. The structure has been solved by direct methods and refined toR1 = 0.0560 for 3658 observed reflections with I > 2sigma(I). The piperidine ring is in a chair conformation. The geometry around the S atom is distorted from regular tetrahedron.