Faculty Publications
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Publications by NITK Faculty
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Item Waves in Gulf of Mannar and Palk Bay around Dhanushkodi, Tamil Nadu, India(2013) Gowthaman, R.; Sanil Kumar, V.; Dwarakish, G.S.; Mohan, S.S.; Singh, J.; Ashok Kumar, K.Surface wave characteristics around Dhanushkodi are studied based on the measured data in the Gulf of Mannar and in the Palk Bay. Wave spectra are mainly double-peaked in the Gulf of Mannar and singlepeaked in the Palk Bay. High waves (maximum wave height up to 5.4 m) are observed in the Gulf of Mannar compared to the Palk Bay (maximum wave height is 3.6 m). Wave heights are more in the Gulf of Mannar during the southwest monsoon period and the waves are from south-southwest. In the Palk Bay, high waves are found during the northeast monsoon period. Swells dominate the Gulf of Mannar, except during the southwest monsoon period, whereas wind seas exist in the Palk Bay as distant swells cannot reach the bay due to the protection by Indian peninsula and northern extremity of Sri Lanka. Influence of cyclone Laila is observed during the study period in both the Gulf of Mannar and the Palk Bay.Item Enhanced production of napthoquinone metabolite (shikonin) from cell suspension culture of Arnebia sp. and its up-scaling through bioreactor(Springer Verlag, 2014) Gupta, K.; Garg, S.; Singh, J.; Kumar, M.Cell culture in shake flask and air-lift bioreactor was carried out to exploit the potential of Arnebia sp. for napthoquinone metabolite production. Cell suspension cultures of Arnebia were established from friable callus in liquid MS medium supplemented with 6-benzylaminopurine (BAP) (10 ?M) and indole-3-butyric acid (IBA) (5 ?M). Growth kinetic studies were done by using settled cell volume and fresh/dry cell weight method. Suspension cultures were maintained by sub-culturing at 10 days interval. A two-stage culture system is employed using growth medium (GM) and modified M9 medium (production medium) for cell biomass and naphthoquinone pigment production, respectively. Results showed that cultivation of cells under dark conditions at room temperature (25 ± 2 °C) enhanced the cell biomass from 100 to 625 g l-1. The pigment production was also found to be increased in dark conditions at room temperature. Alkaline pH found to have positive effect on pigment yield. In case of M9 medium constituents, absence of Na2SO4 does not affect the pigment yield. The current approaches have the cumulative effect to meet an increased level of (25.5 ?g/ml) metabolite production in air-lift bioreactor. © 2013 The Author(s).Item Nearshore waves and longshore sediment transport along Rameshwaram island off the east coast of India(Society of Naval Architects of Korea jnaoe@jnaoe.org, 2015) Gowthaman, R.; Sanil Kumar, V.; Dwarakish, G.S.; Shanas, P.R.; Jena, B.K.; Singh, J.Wave-induced Longshore Sediment Transport (LST) play an important role in the dynamics of the Dhanushkodi sandspit located southeast of Rameshwaram. The LST along the Dhanushkodi coast is studied based on data collected simultaneously in Gulf of Mannar (GoM) and Palk Bay (PB) using directional waverider buoys. The numerical model REF/DIF1 was used to calculate the nearshore waves and the LST rate was estimated using three different formulae. The model validation was done based on the measured nearshore waves using InterOcean S4DW. Numerical model LITPACK was also used for simulating non-cohesive sediment transport and the LITLINE module was used to study the shoreline evolution over 5 years. Low net annual LST along PB (~ 0.01×106 m3) compared to the GoM region (0.3×106 m3) were due to the weak waves. Accretion in the region led to growth of the Dhanushkodi sandspit by 65 m during the period 2010-2015. © SNAK, 2015.Item Modified Selective Harmonics Mitigation PWM for a Switched Diode Multilevel Inverter(IOP Publishing Ltd, 2021) Sahaya Ponrekha, A.; Jagabar Sathik, J.; Lakshmanan, P.; Singh, J.; Mani, L.; Mandal, A.; Madhavan, J.A modified selective harmonic mitigation (SHM) technique for multilevel inverters considering the RMS output voltage magnitude is presented. The harmonic contents in the output voltage of these inverters must satisfy the specified grid code requirement standards. In conventional SHM techniques, the firing angles of the multilevel inverters have been derived by taking into account grid code harmonic reduction standards. When the multi-level inverters are driven with these firing pulses generated, it results in reduction of the magnitude of the inverter output voltage. In order to overcome this issue of output voltage reduction, the modified SHM optimization problem includes another constraint on the RMS output voltage limits, which results in different set of firing angles. This facilitates the use of firing angles, which takes into account the grid code standards of harmonic mitigation without compromising the value of the RMS output voltage of the inverters. The proposal has been simulated and validated in MATLAB Simulink and the experimental results are obtained for a single-phase seven level inverter with Silicon made semiconductor switches. By using the proposed method, output voltage THD (upto 40th harmonics were considered) of 5.9% was obtained, which is well below the harmonic standards specified by EN 50160. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.Item Mango Leaves (Mangifera indica)-Derived Highly Florescent Green Graphene Quantum Dot Nanoprobes for Enhanced On-Off Dual Detection of Cholesterol and Fe2+ Ions Based on Molecular Logic Operation(American Chemical Society, 2024) Ratnesh, R.K.; Singh, M.K.; Kumar, V.; Singh, S.; Chandra, R.; Singh, M.; Singh, J.In the present study, we have engineered a molecular logic gate system employing both Fe2+ ions and cholesterol as bioanalytes for innovative detection strategies. We utilized a green-synthesis method employing the mango leaves extract to create fluorescent graphene quantum dots termed “mGQDs”. Through techniques like HR-TEM, i.e., high-resolution transmission electron microscopy, Raman spectroscopy, and XPS, i.e., X-ray photoelectron spectroscopy, the successful formation of mGQDs was confirmed. The photoluminescence (PL) characteristics of mGQDs were investigated for potential applications in metal ion detection, specifically Fe2+ traces in water, by using fluorescence techniques. Under 425 nm excitation, mGQDs exhibited emission bands at 495 and 677 nm in their PL spectrum. Fe2+-induced notable quenching of mGQDs’ PL intensity decreased by 97% with 2.5 μM Fe2+ ions; however, adding 20 mM cholesterol resulted in a 92% recovery. Detection limits were established through a linear Stern-Volmer (S-V) plot at room temperature, yielding values of 4.07 μM for Fe2+ ions and 1.8 mM for cholesterol. Moreover, mGQDs demonstrated biocompatibility, aqueous solubility, and nontoxicity, facilitating the creation of a rapid nonenzymatic cholesterol detection method. Selectivity and detection studies underscored mGQDs’ reliability in cholesterol level monitoring. Additionally, a molecular logic gate system employing Fe2+ metal ions and cholesterol as a bioanalyte was established for detection purposes. Overall, this research introduces an ecofriendly approach to craft mGQDs and highlights their effectiveness in detecting metal ions and cholesterol, suggesting their potential as versatile nanomaterials for diverse analytical and biomedical applications. © 2024 American Chemical Society.