Faculty Publications
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Item New shape resonances in one dimension(Institute of Physics, 2015) Ahmed, Z.; Pavaskar, S.; Prakash, L.Hitherto, a finitely thick barrier next to a well or a rigid wall has been considered the potential of simplest shape giving rise to resonances (metastable states) in one dimension: x ?(-?, ?). In such a potential, there are three real turning points at an energy below the barrier. Resonances are Gamow's (time-wise) decaying states with discrete complex energies.(?n = En - i?n/2) These are also spatially catastrophic states that manifest as peaks/wiggles in Wigner's reflection time delay at E = ? ? En Here we explore potentials with simpler shapes giving rise to resonances - two-piece rising potentials having just one-turning point. We demonstrate our point by using rising exponential profile in various ways. © 2015 IOP Publishing Ltd.Item Infinitely Many Trees with Maximum Number of Holes Zero, One, and Two(Hindawi Limited, 2018) Kola, S.R.; Gudla, B.; Niranjan, P.K.An L(2,1)-coloring of a simple connected graph G is an assignment f of nonnegative integers to the vertices of G such that fu-fv2 if d(u,v)=1 and fu-fv1 if d(u,v)=2 for all u,v∈V(G), where d(u,v) denotes the distance between u and v in G. The span of f is the maximum color assigned by f. The span of a graph G, denoted by (G), is the minimum of span over all L(2,1)-colorings on G. An L(2,1)-coloring of G with span (G) is called a span coloring of G. An L(2,1)-coloring f is said to be irreducible if there exists no L(2,1)-coloring g such that g(u)f(u) for all u∈V(G) and g(v)Item Comparative computational appraisal of supercritical CO2-based natural circulation loop: effect of heat-exchanger and isothermal wall(Springer Science and Business Media B.V., 2020) Thimmaiah, S.; Wahidi, T.; Yadav, A.; Mahalingam, A.Natural circulation loop (NCL) is a geometrically simple heat transfer device in which fluid flow occurs due to density gradient of loop fluid, induced by the temperature difference between the source and the sink. NCL has an inherent problem of instability caused by the combined effect of buoyancy, friction and inertia forces at varying operating conditions, and hence it requires an elegant solution of instability. The primary objective of the present work is to do a comparative study on the dynamic performance between two different configurations of NCL based on supercritical CO2, i.e. (i) NCL with isothermal heater and a cold heat-exchanger (ISO-CHX), and (ii) NCL with hot and cold heat-exchangers (HHX-CHX). To explore these NCLs, two-dimensional transient computational fluid dynamics studies have been carried out on the stability of supercritical CO2-based natural circulation loop. Results are obtained for different operating pressures and temperatures in the form of mass flow rate and velocity variation with respect to time. Results show the higher instabilities in both side heat-exchanger loop than an isothermal heater with heat-exchanger loop. At a lower rate of heat input at source in the HHX-CHX loop, the mass flow is bidirectional, whereas it is unidirectional in the ISO-CHX loop at all level of heat input. It is also observed that as pressure increases, flow instability also increases. Obtained results are validated with the published experimental and numerical data and found in good agreement. © 2020, Akadémiai Kiadó, Budapest, Hungary.Item Simple carbazole derivatives with mono/dimethoxyphenylacrylonitrile substituents as hole-transporting materials: Performance studies in hybrid perovskite solar cells(John Wiley and Sons Inc, 2021) Keremane, K.S.; Vasudeva Adhikari, A.V.Herein, we report the development of two new low-cost 9-(2-ethylhexyl)-9H-carbazoles carrying the mono/dimethoxyphenyl substituted cyanovinylene units symmetrically at 3- and 6-positions of the carbazole core (CZ1-2), as potential hole-transporting materials (HTMs) for perovskite solar cell (PSC) application. The current work highlights their structural, photophysical, electrochemical, theoretical, and photoelectrochemical studies, including evaluation of their structure-property relationships. Evidently, the optical studies showcased their excellent fluorescence ability due to their push-pull natured structure; their ?abs and ?emi values were found to be in the order of 410–430 nm and 530–560 nm, respectively, with a bandgap in the range of 2.5–2.6 eV. Further, their theoretical studies, performed by using the DFT simulations clearly revealed in-depth information on their molecular geometries, FMO, and electronic properties. Finally, new PSCs were fabricated successfully by employing CZ1-2 as HTMs to evaluate their photovoltaic performances. Their results indicated that the device with CZ1 displayed enhanced PCE of 2.55% (JSC= 7.85 mA/cm2, VOC= 0.79 V and FF = 40%) than the cell with CZ2 (PCE = 1.71%, JSC= 8.15 mA/cm2, VOC = 0.4 V, FF = 49%) and the obtained data are well comparable with reference, Sipro-OMeTAD (PCE = 4.76%, JSC= 12.27 mA/cm2, VOC = 0.84 V, FF = 45%). Conclusively, the study furnishes a deeper understanding of the intricacies involved in the structural modification of in low-cost HTM in achieving an enhanced performance of the devices. © 2021 The Authors. Electrochemical Science Advances published by Wiley-VCH GmbH.Item Influence of Copper Oxide Nanoparticles on AC Conductivity of Polyvinyl Alcohol-Polyaniline Polymer Blends(Springer, 2022) Kanavi, P.S.; Meti, S.; Fattepur, R.H.; Patil, V.B.Copper oxide (CuO) nanoparticles were synthesized using a simple co-precipitation method. CuO doped (0.2%, 0.4%, 0.6% and 1%) polyaniline (PANI)—polyvinyl alcohol (PVA) nanocomposites were prepared by solution casting techniques. The crystalline monoclinic phase of CuO was identified by XRD analysis. The peak widths in XRD spectra of PANI-PVA-CuO (PPC) become intense and sharp with the increase in loading of CuO, which implies the crystalline character of PPC that results in higher ionic diffusivity and conductivity. The CuO nanocrystal morphology, surface topography and thickness of the PPC films were recorded by scanning electron microscopy (FESEM). The chemical natures of the bonds were studied by the FTIR technique. The absorption spectra of CuO nanocrystals and PPC films were recorded using UV–visible spectroscopy. TGA and DSC techniques were used to examine the thermal stability of the PPC films. The prepared samples were kept to study electrical properties in the frequency range of 10 to 105 Hz in the temperature range of 30°C to 150°C. It was shown that as the applied frequency and temperature increased, the corresponding electrical conductivity increased abruptly. © 2022, The Minerals, Metals & Materials Society.Item A Simple Method to Design a Decoupler for a Proton Exchange Membrane Fuel Cell(John Wiley and Sons Inc, 2022) Goyal, I.; Reddy, S.; Sankar Rao, C.S.A decoupling control system is designed by a simple tuning-free method for the multi-input multi-output model of a proton exchange membrane fuel cell. The decoupler minimizes the interactions among the loops and is designed by estimating the relative normalized gain array and dynamic relative gain array for the closed-loop model. The proportional integral controller settings are estimated using the partial model matching method. The performances of the proposed method are studied based on closed-loop performances of control variables and time integral errors that are compared with the synthesis method. The proposed controller performs better in terms of integral of time-weighted absolute error. © 2022 Wiley-VCH GmbH.Item A Precise Switching Frequency Formulation of Hysteresis-Controlled Grid-Connected Inverters Considering Nonlinear Ripple Current(Institute of Electrical and Electronics Engineers Inc., 2022) Damodaran, R.; Venkatesa Perumal, B.V.Hysteresis current control (HCC) is one of the most simple and rapid modulation techniques for multilevel grid-connected inverters (MGCIs). It controls the output current by limiting its ripple within fixed hysteresis limits. This results in a varying switching frequency, which is not known implicitly. The knowledge of switching frequency is essential for filter design, device selection, and loss calculations of the MGCI. The existing frequency estimations for HCC assume linear ripple current considering high-frequency operation. This assumption is invalid for the range of low frequencies. This leads to inaccurate estimation of switching frequency, which can have a considerable effect on system design. In this article, a more precise and generalized expression to estimate the switching frequency of the MGCI is obtained. The improvement in accuracy is demonstrated with an example of second-order filter design. The effect of change in hysteresis limits and input voltage on the switching frequency is analyzed to determine the operating point for accurate system design. Simulation and experimental results are found to be in good agreement with the theoretical claims. © 1982-2012 IEEE.Item A capacitor based single source MLI with natural balancing and less component for EV/HEV application(John Wiley and Sons Ltd, 2022) Aditya, K.; Yellasiri, Y.; Shiva Naik, B.; Nageswar Rao, B.; Panda, A.K.Due to their remarkable performance, capacitor-based inverters have recently gained attention. Hence, a new capacitor-based multilevel inverter is presented in this paper for electric and hybrid electric vehicle (EV and HEV) applications. EV systems are quite well for their use of two-level inverters; however, the generated load voltage comprises substantial undesirable harmonic content. It is regarded as one of the most efficient methods since replacing a two-level inverter with a multilevel inverter improves the power quality despite significantly reducing total harmonic distortion. Therefore, the recommended filter dimension will also be minimized. A flurry of reliability concerns has arisen due to the increased number of devices, circuit complexity, and stress on the circuit devices. A nine-level voltage waveform is created with only ten IGBTs, a DC-Source, and two capacitors. In the proposed nine-level inverter, the capacitor voltage is balanced utilizing a simple control approach to regulate the flying capacitor (FC) voltages actively. Here described a simple logic gate-based pulse-width modulation technique that ensures capacitor power balancing. The proposed inverter operation and capability are validated by experimental results derived from a laboratory prototype. Finally, by contrasting the new and standard inverter topologies, the virtues of the suggested architecture by the number of devices and price of the equipment are highlighted, and it is a simpler structure that requires less space and footprint area. © 2022 John Wiley & Sons Ltd.Item Efficient Lubricity Improvers Derived from Methyl Oleate for Ultra Low Sulphur Diesel (ULSD)(Pleiades Publishing, 2022) Sruthi, H.; Udayakumar, D.U.; Hegde, P.; Manjunatha, M.G.; Nandakumar, V.Abstract: A new series of lubricity improvers for ultra-low sulphur diesel (ULSD) was synthesized starting from methyl oleate through simple chemical reactions. In the first step methyl oleate was epoxidized using formic acid and hydrogen peroxide mixture. Then the epoxide was subjected to esterification using different long chain (C4–C18 alkyl groups) organic acids to get the final diesters. The lubricating property of the newly synthesized diesters was studied by dosing them to ULSD at 300 ppm (wt/vol) concentration. Amongst them, diester LAMOSA derived from stearic acid showed the best lubrication enhancing property at 300 ppm dosage level. The SEM and EDS spectra of the HFRR (high frequency reciprocating rig) specimen also confirms the formation of metal-oxygen interaction supporting the friction reducing properties of LAMOSA. The study reveals that the newly synthesized methyl oleate derived diesters are promising materials as lubricity additives for ULSD. [Figure not available: see fulltext.] © 2022, Pleiades Publishing, Ltd.Item Transformation of refinery cracked naphtha stream into efficient lubricity improvers for ULSD(Springer, 2022) Sruthi, H.; Udayakumar, D.U.; Hegde, P.; Manjunatha, M.G.; Karthick, R.; Nandakumar, V.A new route for the conversion of refinery light cracked naphtha (LCN) stream into lubricity improvers for ultra-low sulphur diesel (ULSD) was developed through a simple chemical process involving olefin epoxidation and esterification reactions. Two different methods viz., H2O2/glacial acetic acid and m-chloroperbenzoic acid (m-CPBA), were found to be suitable for the epoxidation of LCN. The LCN epoxide was subjected to an esterification reaction via epoxide ring opening using different long chain (C4 - C18 alkyl groups) organic acids to get the hydroxy ester derivatives of LCN. The lubricating property of the newly synthesized hydroxy esters was studied by dosing them with ULSD at 300 and 150 ppm (wt/vol) concentrations. Amongst them, LCN hydroxy ester derived from stearic acid showed the best lubrication-enhancing property at both dosage levels. The scanning electron microscope (SEM) image and energy dispersive spectra (EDS) of the high-frequency reciprocating rig (HFRR) specimen support the lubricating action of the LCN esters through the formation of a protective layer between the metallic surfaces. The synergy of simple chemical processes and efficient lubricity action makes these LCN esters as promising materials for low-cost and scalable additives for ULSD. Graphical abstract: The olefin-rich light cracked naphtha obtained from the fluidized catalytic cracker unit of the oil refinery was converted into hydroxy esters through an epoxidation reaction followed by the esterification with different carboxylic acids. The hydroxy esters at low dosage levels (150/300 ppm) enhance the lubricating property of ultra-low sulfur diesel. [Figure not available: see fulltext.]. © 2022, Indian Academy of Sciences.