Faculty Publications

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Author: search.filters.author.Thomas, J.

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    Weekly prediction of tides using neural networks
    (Elsevier Ltd, 2015) Salim, A.M.; Dwarakish, G.S.; Liju, K.V.; Thomas, J.; Devi, G.; Rajeesh, R.
    Knowledge of tide level is essential for explorations, safe navigation of ships in harbour, disposal of sediments and its movements, environmental observations and in many more coastal engineering applications. Artificial Neural Network (ANN) is being widely applied in coastal engineering field for solving various problems. Its ability to learn highly complex interrelationships based on the provided data sets, along with less amount of data requirement, makes it a powerful modelling tool. The present work is related to predicting the hourly tide levels at Mangalore, Karnataka, using a week's hourly tidal levels as input. The data has been obtained from NMPT, Mangalore and is made use of in predicting tide level using Feed Forward Back Propagation (FFBP) and Non-linear Auto Regressive with eXogenous input (NARX) network. FFBP network yielded correlation coefficient value of 0.564 and NARX network yielded very high correlation coefficient of the order 0.915 for predictions of yearlong hourly tide levels. The study proves that ANN technique can be successfully utilized for the prediction of tides at Mangalore. © 2015 Published by Elsevier Ltd.
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    Area and power optimised ASIC implementation of adaptive beamformer for hearing AIDS
    (Institute of Electrical and Electronics Engineers Inc., 2017) Samtani, K.; Thomas, J.; Deepu, S.P.; Sumam David, S.
    Beamforming is a technique used in hearing AIDS to improve the intelligibility of target sound by reducing the interference from other directions. An efficient ASIC implementation of a two omnidirectional microphone array based adaptive beamforming algorithm is presented in this paper with various optimisations proposed at different stages of the hardware design. The beamform patterns and improvements in SNR values obtained from experiments conducted in a conference room environment were analysed to verify the working of the design. The architecture was implemented with 0.18 μm standard cell libraries. Cell area and power reports were analysed for different optimisations. The final area and power obtained are 0.054 mm2 and 60.54 μW respectively. © 2017 IEEE.
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    FPGA implementation of adaptive beamforming in hearing aids
    (Institute of Electrical and Electronics Engineers Inc., 2017) Samtani, K.; Thomas, J.; Varma, G.A.; Sumam David, S.; Deepu, S.P.
    Beamforming is a spatial filtering technique used in hearing aids to improve target sound reception by reducing interference from other directions. In this paper we propose improvements in an existing architecture present for two omnidirectional microphone array based adaptive beamforming for hearing aid applications and implement the same on Xilinx Artix 7 FPGA using VHDL coding and Xilinx Vivador 2015.2. The nulls are introduced in particular directions by combination of two fixed polar patterns. This combination can be adaptively controlled to steer the null in the direction of noise. The beamform patterns and improvements in SNR values obtained from experiments in a conference room environment are analyzed. © 2017 IEEE.
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    Enhanced bremsstrahlung X-ray emission from Ag nanoparticles irradiated by ultrashort laser pulses
    (Elsevier B.V., 2019) Sankar, P.; Thomas, J.; Shashikala, H.D.; Philip, R.
    In this work, an Ag nanoparticle colloidal suspension flowing in the form of a thin jet (250 ?m) is irradiated by 150 femtosecond, 800 nm laser pulses to form a plasma which emits bremsstrahlung X-rays of up to 100 keV energy. The flowing jet ensures long-term durability of the plasma source during continuous laser irradiation. The laser pulse is p-polarized and the angle of incidence is normal to the jet surface, to optimize resonance absorption of laser radiation by the plasma electron density gradient. A 30-fold enhancement is observed in the X-ray yield in the nanoparticle suspension, compared to the precursor salt solution. This is because of the local field enhancement (LFE) associated with the localized surface plasmon resonance (LSPR) in Ag nanoparticles. Multiphoton ionization will be greatly enhanced in the presence of LFE, resulting in the generation of a relatively larger number of free electrons, which become “hot” electrons of high kinetic energy by resonance absorption. Bremsstrahlung in the X-ray regime occurs due to the deceleration of these hot electrons. Under identical excitation conditions the corresponding X-ray enhancement measured in Au nanoparticles is relatively lower at 18-fold. This decrease is due to the higher ionization potential of Au (9.22 eV) as compared to Ag (7.58 eV). On the other hand, absorption spectra and SEM images measured after continuous irradiation reveal that Au nanoparticles are more photostable compared to Ag nanoparticles. These studies show that Ag nanoparticles are better suited for X-ray generation compared to Au nanoparticles under the experimental conditions employed. Applications include dynamics studies, microscopy, and lithography. © 2019