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This work demonstrates the significance of the synthesis routes, namely microwave and hydrothermal methods, of green-emitting carbon dots prepared from the same precursors in the selective detection of Hg2+ ions. Aside from providing the advantage of a shorter time scale for the synthesis of C-dots (5 min) compared to the hydrothermal route (8 h) at a synthesis temperature of 180°C, the C-dots prepared via the microwave synthesis route exhibit higher absolute quantum yield (1.8 times) while retaining similar pH and concentration-dependent emission properties. Due to the difference in surface nitrogen content, the microwave synthesized C-dot fluorescence emission exhibit a linear behavior from 8 nM to 64 nM of Hg2+ ions and provides a limit of detection of 3.09 nM whereas hydrothermally synthesized particles exhibit linear variation from 0.5 µM to 4 µM with a detection limit of 0.22 µM. [ABSTRACT FROM AUTHOR]

Fractional domain optimum combining (OC) using fractional Fourier transform has been considered in this article. It has already been established that in an interference-dominated environment, OC is the best among all the diversity techniques used for single-input multiple-output systems. This technique is based on the principle of maximising the signal-to-interference plus noise ratio at the output of the combiner. In this article, a new combiner, which calculates the weights in fractional domain, has been proposed to further enhance the performance of OC in terms of bit error rate (BER). Fractional domain combining gives better signal-to-noise ratio (SNR) at the output of the combiner as compared to time- or frequency-domain combiner due to complete removal of noise. For two receive antennas, the proposed combiner gives an SNR improvement of 7.2 and 2.4 dB as compared to time- and frequency-domain combiners, at a BER of 10−2. It has been concluded that the proposed technique clearly outperforms the existing technique. [ABSTRACT FROM PUBLISHER]

This article proposes various combinations of optical amplifiers for a dense wavelength division multiplexed system and investigates the impact of reduced channel spacing at high bit rates in terms of quality factor, bit error rate, eye closure, and output power. It is reported that the hybrid optical amplifier (Raman–erbium-doped fiber amplifier [EDFA]) provides better results with a maximum covered single span distance (220 km) at channel spacing of 6.25 GHz. The maximum acceptable bit rate for the 12.5-GHz channel spacing dense wavelength division multiplexed system is also investigated, and the recommendation is provided that for the Raman–EDFA, Raman–EDFA–Raman, EDFA–Raman–EDFA, and EDFA–semiconductor optical amplifier–EDFA, the operating bit rate should not be greater than 20, 16, 19, and 20 Gbps, respectively. [ABSTRACT FROM AUTHOR]