Untitled

Mallik, Ranjan K.; Gogoi, Anup Kumar; Mahanta, Anil; Raghuram, R.

doi:10.1023/a:1025349931506

Cited by 3 publications

(1 citation statement)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We calculated the EWs and line depths of DM UMa for the Na i D 1 , D 2 , and H α lines. The line depth is used as a diagnostic criterion for the level of chromospheric activity (Mallik 1997;Eaton 1995;Mallik 1998;etc). All the Ca ii IRT lines show filled-in absorption with self-reversal core emission, with some of them being above the continuum.…”

Section: Analyses Of the Chromospheric Activitymentioning

confidence: 99%

Chromospheric activity on late-type star DM UMa using high-resolution spectroscopic observations

Zhang

Han

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

We present new 14 high-resolution echelle spectra to discuss the level of chromospheric activity of DM UMa in He i D 3 , Na i D 1 , D 2 , H α , and Ca ii infrared triplet lines (IRT). It is the first time to discover the emissions above the continuum in the He i D 3 lines on Feb. 9 and 10, 2015. The emission on Feb. 9 is the strongest one ever detected for DM UMa. We analyzed these chromospheric active indicators by employing the spectral subtraction technique. The subtracted spectra reveal weak emissions in the Na i D 1 , D 2 lines, strong emission in the H α line, and clear excess emissions in the Ca ii IRT lines. Our values for the EW 8542 /EW 8498 ratio are on the low side, in the range of 1.0 -1.7. There are also clear phase variations of the level of chromospheric activity in equivalent width (EW) light curves in these chromospheric active lines (especially the H α line). These phenomena might be explained by flare events or rotational modulations of the level of chromospheric activity.

show abstract

Section: Analyses Of the Chromospheric Activitymentioning

confidence: 99%

Chromospheric activity on late-type star DM UMa using high-resolution spectroscopic observations

Zhang

Han

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

show abstract

Diversity combining in FSO systems in presence of non-Gaussian noise

Kamboj

Mallik

Agrawal

et al. 2012

2012 International Conference on Signal Processing and Communications (SPCOM)

Self Cite

View full text Add to dashboard Cite

Free-space optics (FSO) communication has received much attention in recent years as a cost-effective, license-free, and wide-bandwidth access technique for high data rate applications. The performance of FSO communication, however, severely suffers from turbulence caused by atmospheric conditions. Multiple photodetectors can be placed at the receiver to mitigate the turbulence and exploit the advantages of spatial diversity combining. In this paper, we analyze the bit error rate (BER) performance of an FSO communication system employing binary phase-shift keying with additive non-Gaussian noise over negative exponential distributed atmospheric turbulence and spatial diversity at the receiver. The Laplace distribution is used to model the nonGaussian impulsive noise. We consider the case when perfect channel state information is available at the receiver for implementation of coherent detection. Analytical expressions for the BER of a single channel receiver as well as that of a diversity combining receiver using selection combining, dual-diversity equal-gain combining, and maximal-ratio combining are derived. The derived analytical expressions are verified by simulation results. Keywords -Bit error rate (BER), equal-gain combining (EGC), free-space optics (FSO), maximalratio combining (MRC), negative exponential fading, non-Gaussian noise, selection combining (SC). I. IntroductionFree-space optics (FSO) communication, also known as wireless optical communication, is a license-free, highcapacity, and cost-effective communication technique, which has received considerable attention recently for a variety of applications including the cellular communication backhaul, optical fibre communications back-up links, exhibition halls and disaster recovery, among other emerging applications [1]-[2]. However, a major concern in the performance of FSO systems is the dependence of its channel on atmospheric conditions. Atmospheric turbulence occurs due to variation in refractive index due to inhomogeneities in temperature, pressure, and humidity. This results in received signal fading or scintillation, which causes severe performance degradation.

show abstract

Symbol Error Rate of MPSK Over EGK Channels Perturbed by a Dominant Additive Laplacian Noise

Soury¹,

Alouini²

2015

IEEE Trans. Commun.

View full text Add to dashboard Cite

Untitled

Cited by 3 publications

References 17 publications

Chromospheric activity on late-type star DM UMa using high-resolution spectroscopic observations

Chromospheric activity on late-type star DM UMa using high-resolution spectroscopic observations

Diversity combining in FSO systems in presence of non-Gaussian noise

Symbol Error Rate of MPSK Over EGK Channels Perturbed by a Dominant Additive Laplacian Noise

Contact Info

Product

Resources

About