Faculty Publications
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Item Scanning and resetting the phase of a pinned spiral wave using periodic far field pulses(Institute of Physics Publishing helen.craven@iop.org, 2016) Shajahan, T.K.; Berg, S.; Luther, S.; Krinski, V.; Bittihn, P.Spiral waves in cardiac tissue can pin to tissue heterogeneities and form stable pinned waves. These waves can be unpinned by electric stimuli applied close to the pinning center during the vulnerable window of the spiral. Using a phase transition curve (PTC), we quantify the response of a pinned wave in a cardiac monolayer to secondary excitations generated electric field pulses. The PTC can be used to construct a one-dimensional map that faithfully predicts the pinned wave's response to periodic field stimuli. Based on this 1D map, we predict that pacing at a frequency greater than the spiral frequency, over drive pacing, leads to phase locking of the spiral to the stimulus, which hinders unpinning. In contrast, under drive pacing can lead to scanning of the phase window of the spiral, which facilitates unpinning. The predicted mechanisms of phase scanning and phase locking are experimentally tested and confirmed in the same monolayers that were used to obtain the PTC. Our results have the potential to help choose optimal parameters for low energy antifibrillation pacing schemes. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.Item Evaluation of properties of nonfoaming Warm mix asphalt mixtures at lower working temperatures(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2017) Shiva Kumar, G.; Suresha, S.N.Warm mix asphalt (WMA) is a green technology which has the potential to replace hot mix asphalt (HMA) because it reduces greenhouse gas emissions and energy consumption by lowering the temperature at which asphalt mixtures are produced and placed. During the design process, evaluation of the mix design and mechanical properties of WMA mixtures is necessary. Therefore, the ability to quantify compactability would be very useful. This paper presents details on the evaluation of asphalt mix design, workability, and mechanical properties of asphalt mixtures modified with nonfoaming WMA additives at lower working (mixing and compaction) temperatures. Further, it seeks to provide a wider gap between mixing and compaction temperatures to ensure that WMA mixtures are suitable for longer haul distances. Asphalt mix design properties were evaluated by the Superpave method for various design gyrations (Ndes), and workability properties were evaluated in terms of Superpave gyratory compactor (SGC) densification indices using the Bahia and locking point methods. Mechanical properties such as resistance to moisture-induced damage were evaluated by the tensile strength ratio (TSR) approach, rutting resistance was evaluated by a laboratory wheel tracking test using a wheel rut tester (WRT), and flexural fatigue characteristics were evaluated by four point bending using a repeated load testing (RLT) machine. The effects of nominal maximumaggregate size (NMAS), working temperature, and type of mixture on the properties ofWMAmixtures were investigated. The experimental results were statistically analyzed to identify the major influencing factors and their significance. © 2017 American Society of Civil Engineers.Item Evaluation of workability and mechanical properties of nonfoaming warm mix asphalt mixtures(ASTM International, 2018) Shiva Kumar, G.; Suresha, S.N.Laboratory evaluation of mix design and mechanical properties of Warm Mix Asphalt (WMA) mixtures is necessary during the design process; consequently, the ability to quantify the compactability of WMA mixtures would be very helpful. This article presents the findings of an experimental study aimed at evaluation of the influence of mixing and compaction temperature on mix design and mechanical and workability properties of nonfoaming WMA mixtures. Asphalt mix design properties were evaluated by the Marshall method and the Superpave method. Mechanical properties such as rutting resistance were evaluated by a laboratory wheel tracking test using a Wheel Rut Tester (WRT), and the resistance to moisture-induced damage was evaluated by the Tensile Strength Ratio (TSR) approach. Workability properties were evaluated in terms of Superpave Gyratory Compactor (SGC) densification indexes using the Bahia and locking point methods. Test results indicate that WMA mixtures compacted using SGC at a lower compaction temperature of 110°C, which satisfied the Voids in Total Mixture (VTM) requirement. In order to ensure the Voids in Mineral aggregate (VMA) and Voids Filled with Asphalt (VFA) requirements of WMA mixtures, compaction temperature should be restricted to 120°C. Furthermore, WMA mixtures prepared at lower compaction temperatures exhibited higher resistance to rut deformation because of higher Traffic Densification Index (TDI) values. The energy needed to compact the WMA mixtures at lower compaction temperatures was lower due to lower Compaction Densification Index (CDI) values. WMA mixtures made with surface-saturated dry aggregates and compacted at 110°C marginally fulfilled the minimum TSR requirement because of significant reduction in the Indirect Tensile Strength (ITS) values of conditioned specimen. © © 2018 by ASTM InternationalItem Operation of the Microgrid with Improved Droop Control Strategy and an Effective Islanding Detection Technique for Automatic Mode Switching(Taylor and Francis Ltd., 2021) Kulkarni, S.V.; Gaonkar, D.N.; Guerrero, J.M.This paper presents the islanding detection and automatic mode switching for inverter-based distributed generation sources (DGs) in the microgrid with an improved droop controlled scheme. The modification in the conventional droop among the DGs is contrived to share the load proportionate to their power capacity. And to reduce the circulating currents and to improve reactive power-sharing the virtual impedance is implemented for the microgrid in the stand-alone mode operation. Also, the modified Park synchronous reference frame based phase-locked loop (PSRF-PLL) is implemented for the operation of the microgrid in the grid-connected mode. The islanding detection and automatic mode switching depend on the PSRF-PLL, which uses the input obtained from the stationary reference frame. The proposed PLL implemented in this work is simple in construction and keeps the phase locking error to near zero, thus leading to proper locking with reduced complexity. The control scheme's performance in the microgrid is validated using the real time hardware in the loop platform. The performance of PSRF-PLL based islanding detection scheme is analyzed considering the various grid disturbances, and the comparative study with the other PLL based scheme is also presented in this paper to show the improved performance of the proposed PSRF-PLL scheme. © 2021 Taylor & Francis Group, LLC.Item HIL implementation of an islanding detection and an automatic mode switching for droop-based microgrid(Inderscience Publishers, 2022) Kulkarni, S.V.; Gaonkar, D.N.This paper presents the control schemes and performance study of parallel connected inverter based distributed generation sources (DGs) in microgrid for grid-connected and stand-alone modes of operation. This standalone mode of operation of inverter based DG system is mainly based on droop control scheme with the virtual complex impedance in the outer voltage loop. The microgrid load power is proportionally shared by the DGs according to their power ratings which features a good reliability and efficiency. Both the modes are switched automatically based on the Phase Locked Loop (PLL) phase error sin(γ – θ). This phase error is used to detect the islanding during disturbances in the system and also helps in seamless transfer between the modes. The PLL phase error response, islanding detection and mode switching are presented for various fault conditions. The hardware-in-the-loop (HIL) based platform is used to evaluate the performance of the microgrid in both the modes with islanding detection and automatic mode switching operation. © © 2022 Inderscience Enterprises Ltd.Item Analysis of Fault’s Effect on the Highwall Stability of Medapalli Open Pit Coal Mine(Springer Science and Business Media Deutschland GmbH, 2023) Kumar Reddy, S.K.Mining operations can have a significant impact on the stability of the surrounding area. One example is the Medapalli open pit coal mine in southern India. The mine is a large excavation working at a depth of 165 m that can reach up to 200 m. The western side highwall has locked-up coal reserves in the mine, but concerns about the geologically disturbed regions have resulted in complications and significant challenges. Surface tension cracks around the excavation became visible in 2018, prompting intensive monitoring, protective measures, and numerous geotechnical analyses. The area, however, has a rich tectonic history, with faults interacting with soil movements. Proper geotechnical investigations were used in this work to analyse the stability of the highwall due to faults' effects on the area's reaction due to mining operations. The findings in the study highlighted the significance of flaws in the ground movement due to improper design of the highwall fault interaction area. The presence of the fault increases the likelihood of tensile cracks and subsidence at the highwall's surface level, significantly worsening the mining activities in the area. The analysis reveals that complex geological features, such as the presence of faults roughly parallel to the highwall slope profile, can exacerbate the mining operations in the surrounding environment. The recommended slope design with protective measures towards the west side disturbed highwall area helps safely excavate the western side highwall locked-up coal reserves in the Medapalli open pit mine. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Low Power, High Speed, Inductor-less Cascaded Charge Pump Phase Locked Loop(Birkhauser, 2025) Kirankumar, H.L.; Rekha, S.; Laxminidhi, T.A wide frequency range, inductor-less, charge pump phase locked loop (CP-PLL) is presented in this paper. It has a multi-phase, two stage cascaded architecture. This design uses a dead-zone free, zero blind-zone phase frequency detector (PFD) and a low mismatch charge pump (CP) circuit to generate low jitter clocks. A 3-stage single ended ring oscillator of 625 MHz VCO is designed for the first stage. An 8-phase feed-forward coupled VCO with programmable multi band ranging from 1.25 to 5 GHz is designed for the second stage of this cascaded system. Overall, this proposed cascaded PLL achieves jitter FOM and jitter-N FOM of -227.1 and ? 250.1 dB, respectively for 5 GHz output frequency with 1.44 ps rms jitter while consuming 9.24 mW of power from 1.2 V supply. This proposed clock generator circuit, designed in UMC 65 nm CMOS technology, occupies an area of 0.079 mm2. This study contributes to the development of energy-efficient, high speed clock generation solutions derived from a low reference clock. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.