Faculty Publications
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Publications by NITK Faculty
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Item CHARACTERIZING TEMPO CHANGE IN MUSICAL PERFORMANCES(International Computer Music Association, 2011) Dannenberg, R.B.; Mohan, S.Tempo change is an essential feature of live music, yet it is difficult to measure or describe because tempo change can exist at many different scales, from inter-beat-time jitter to long-term drift over several minutes. We introduce a piece-wise linear tempo model as a representation for tempo analysis. We focus on music where tempo is nominally steady, e.g. jazz and rock. Tapped beat data was collected for music recordings, and tempo was approximated as piece-wise linear functions. We compare the steadiness of tempo in recordings by accomplished, professional artists and in those by amateur artists, and show that professionals are steadier. This work offers new insights into the nature of tempo change based on actual measurements. In principle, improved models of tempo change can be used to improve beat tracking reliability and accuracy. In addition to technical applications, observations of music practice are interesting from a musicological perspective, and our techniques might be applied to a wide range of studies in performance practice. Finally, we present an optimal function approximation algorithm that that has broader applications to representation and analysis in many computer music applications. © 2011 ICMC. All Rights Reserved.Item Deriving temporal trends in user preferences through short message strings(Institute of Electrical and Electronics Engineers Inc., 2016) Deb, S.; Mohan, S.; Venkatraman, P.; Bindu, P.V.; Santhi Thilagam, P.S.Short message strings are widely prevalent in the age of social networking. Taking Facebook as an example, a user may have many other users in his contact list. However, at any given time frame, the user interacts with only a small subset of these users. In this paper, we propose a recommender system that determines which users have common interests based on the content of the short message strings of different users. The system calculates the similarity between two users based on the contents of short message strings by the users over a certain time period. A similarity measure based on short message strings must be temporal study as the contents of the short messages vary rapidly over time. Experimental study is conducted in the Facebook domain using status updates of users. © 2016 IEEE.Item Photonic crystal ring resonator: A promising device for a multitude applications(SPIE spie@spie.org, 2017) Yadunath, T.R.; Kumar, R.R.; Tupakula, T.; Kandoth, A.; John, K.; Ramakrishnan, R.K.; Das, P.P.; Badrinarayana, T.; Mohan, S.; Hegde, G.M.; Srinivas, T.In this paper a 2D Photonic Crystal array in SOI platform having hexagonal periodicity with a ring defect incorporated along with two bus waveguides is conceptualized and realized for various applications of optical communication, sensing etc. The ring structure filters out a resonant wavelength from the spectrum carried to it through the line defect where the resonated peak is determined by the effective ring radius. The hexagonal architecture enables more coupling length than an ideal ring structure which helps in better intensity accumulation. The resonant peak exhibited at 1554nm in simulation, which is observed in the optical characterization at 1543nm. This is attributed to the fabrication tolerance. © 2017 SPIE.Item Novel fabrication technique for NiTi and TiN micro-structures by femtosecond lasers(IOP Publishing Ltd custserv@iop.org, 2020) M.a, M.A.; Lakshmi Ganapathi, K.L.; Udayashankar, N.K.; Mohan, S.NiTi shape memory alloy (SMA) thin films were deposited onto silicon substrate using pulsed DC magnetron sputtering technique. To obtain crystalline NiTi thin films has to be synthesized at higher temperatures (475 - 525) C. This high temperature requirement restricts the ease in conventional lithographic procedures. The recent advancements in the laser micromachining lend their applications into the fabrication of miniaturized systems. The femtosecond lasers (FSL) allow non-thermal processing of materials by ablation. This work focuses on the deposition and fabrication of NiTi (≈1.5 μm. thick) and titanium nitride (TiN ≈0.3 μm. thick) thin films based miniaturized systems by femtosecond laser bulk micromachining. The NiTi and TiN microstructures were release by bottom silicon etch using reactive ion etching chlorine chemistry (RIE-Cl). © Published under licence by IOP Publishing Ltd.Item Physical model studies on the stability of emerged seaside perforated semicircular breakwaters(National Institute of Science Communication and Policy Research, 2018) Hegde, A.V.; Mohan, S.; Pinho, J.L.S.; Sharhabeel, P.S.Present study discusses experiments conducted in a two dimensional monochromatic wave flume to determine the critical (minimum) weight required to resist the sliding of an emerged seaside perforated semicircular breakwater model. It is observed from a detailed review that there is hardly any literature, stressing the critical weight determination for the sliding stability of this breakwater type. Hence, the present research was taken up to study the variations in the critical weight required for sliding stability with different wave and structural specific parameters. The variations were recorded graphically using non-dimensional parameters obtained from a dimensional analysis using Buckingham’s ? theorem. © 2018, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.Item Pulsed DC magnetron sputtered titanium nitride thin films for localized heating applications in MEMS devices(Elsevier B.V., 2018) M.a, M.A.; Lakshmi Ganapathi, L.G.; G N V R, V.; Udayashankar, N.K.; Mohan, S.Titanium nitride (TiN) thin films are deposited on Si/SiO2 substratesby using Pulsed DC magnetron sputtering and are characterized for their structural, mechanical and electrical properties for their application as localized heating elements in microsystem devices. The influence of substrate temperature on the properties of TiN films has been investigated. The correlation between the structural orientation with mechanical and electrical properties has been established. The films deposited at a substrate temperature of 300 °C have shown better structural, mechanical and electrical properties. This film has been chosen for the fabrication of microheater and its characterization. A maximum temperature of 250 °C is achieved by applying a power of 2.8 W to the microheater. © 2018 Elsevier B.V.Item RF Sputtered CeO2 Thin Films-Based Oxygen Sensors(Institute of Electrical and Electronics Engineers Inc., 2019) Ramshanker, N.; Lakshmi Ganapathi, K.L.; Bhat, M.S.; Mohan, S.In this paper, we report the scalable, high sensitivity, fast response, and low operating temperature Cerium oxide (CeO2) thin film-based oxygen sensors by optimizing CeO2 film thickness. CeO2 thin films of thickness ranging from 90 to 340 nm have been deposited at 400°C using radio frequency (RF) magnetron sputtering on Al2O3 substrates. Ellipsometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) have been used to characterize the CeO2 films for their thickness, structural, compositional/chemical, and surface morphology properties. Gas sensors have been fabricated using CeO2 film as a sensing material and tested in an oxygen gas environment. CeO2 film with an optimum thickness of 260 nm has shown high sensitivity (12.6) and fast response time (?10 s) along with fast recovery time (15 s) at a low operating temperature of 400°C. To the best of our knowledge, these are the best values reported till date for undoped CeO2 thin film-based oxygen sensors. Furthermore, from the sensor's response, it was observed that there was no drifting from the baseline. This superior performance of CeO2 thin film-based oxygen sensor may be attributed to the combination of three factors, i.e., 1) high surface energy and reactivity due to the presence of (200) oriented CeO2 plane; 2) low resistance due to better crystallinity; and 3) perfect stoichiometry with required roughness. © 2001-2012 IEEE.Item Development of CeO2-HfO2Mixed Oxide Thin Films for High Performance Oxygen Sensors(Institute of Electrical and Electronics Engineers Inc., 2021) Ramshanker, N.; Lakshmi Ganapathi, K.L.; Varun, N.; Bhat, M.S.; Mohan, S.In this work, the authors report the fabrication and characterization of CeO2 -HfO2 mixed oxide thin film based oxygen gas sensors. The atomic concentrations of the individual elements Ce and Hf in the mixed oxide (CeO2 -HfO2) thin films were controlled and tuned using a novel method in RF sputtering to achieve better oxygen sensing characteristics. The characteristics of the sensing film were evaluated using various characterization techniques such as TEM-EDS, FESEM-EDS, XPS and XRD. The XPS and EDS data revealed that the Hf concentration increases with an increase in size as well as number of the HfO2 pellets that are placed on a 3-inch CeO2 target during sputtering. From the XRD and XPS analysis, it was found that the mixed oxide film with 10-11% Hf atomic concentration has the best sensing characteristics. The superior sensing characteristics of the CeO2 -HfO2 film can be attributed to the existence of a highly reactive plane (200) with the highest surface energy and a strongly reduced surface with oxygen vacancy formation due to the presence of Ce3+ ions and HfOx, x < 2 on the surface of the mixed oxide film. The sensor film detected the presence of oxygen gas even at low temperatures (< 400°C); however, the response time and recovery time were slightly higher. The sensor film of thickness 220 nm with Hf concentration between 10-11% showed excellent sensitivity (15), fast response and recovery times of 8 s and 10 s respectively at an operating temperature of 400°C, which are the best values reported till date for CeO2 based oxygen sensors. © 2001-2012 IEEE.Item Development of titanium nitride thin film microheaters using laser micromachining(Elsevier Ltd, 2022) M.a, M.A.; Lakshmi Ganapathi, K.L.; Ambresh, M.; Nukala, P.; Udayashankar, N.K.; Mohan, S.In this paper, we report the fabrication and characterization of titanium nitride (TiN) thin-film-based microheaters. TiN thin films have been optimized on Si and SiO2 substrates for their optimum electrical resistivities by controlling the process parameters, including argon:nitrogen (Ar:N2) ratio in reactive pulsed DC magnetron sputter (PDCMS) deposition technique. An optical emission spectroscope (OES) was used for monitoring the plasma characteristics at various nitrogen flow rates. The microstructural and surface properties of the TiN films have been investigated and correlated with the electrical properties. It has been observed that the amount of nitrogen flux in the TiN plasma plays an essential role in the microstructural, surface, and electrical properties of the TiN thin films. Micro-heaters have been fabricated with TiN thin films with low electrical resistivity using laser engraving techniques instead of conventional lithographic and micromachining techniques. The TiN microheater has shown excellent performance. A temperature of 406 °C has been achieved by applying an input power of 8 W. This work paves the path for developing scalable and economic TiN microheaters using laser micromachining techniques. © 2021