Department of Physics
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Item Alignment Of Liquid Crystalson Lb Films Of Stearic Acid(CIB Tech, 2012) Gupta, Raj Kumar; Manjuladevi, V.We formed the Langmuir monolayer of stearic acid at the air-water (A-W) interface. The Langmuir-Blodgett (LB) films were deposited on solid substrates at different surface pressures. The liquid crystal cells were prepared over such LB films. We found that these cells exhibit a tendency to align in planar orientation for the liquid crystal. We found that the liquid crystal alignment improves in cells prepared with substrates deposited at higher surface pressure like 25mN/m. We present the results on the liquid crystal alignment as a function of number of layers of LB films deposited on the substrates at various surface pressures. We propose that LB films of stearic acid can be used as an aligning agent for liquid crystals.Item Sensing Through Surface Plasmon Resonance Technique(Springer, 2017-03) Gupta, Raj KumarThe optical phenomenon, surface plasmon resonance (SPR) has become extremely popular owing to its high sensitivity, label-free and non-destructive measurement towards any molecular specific interaction. This is one of the widely used phenomena for biological, chemical and gas sensing devices. There are different ways that the SPR phenomenon can be employed for such sensing applications. In this chapter, we will review some of the important SPR techniques and their applications in sensing.Item Stabilization of Langmuir monolayer of hydrophobic thiocholesterol molecules(Elsevier, 2008-05) Gupta, Raj KumarThe self-assembled monolayer of the thiocholesterol (TCh) exhibits interesting properties that can be used for various technological applications. TCh is predominantly a hydrophobic molecule, and it does not spread at the air–water interface to form a stable Langmuir monolayer. We have stabilized the TCh molecules in the cholesterol (Ch) monolayer. We find the mixed monolayer to be stable upto 0.75 mole fraction of TCh in Ch. The mixed monolayer shows an initial and a final collapse. On compressing the monolayer beyond the initial collapse, the TCh molecules squeeze out irreversibly from the mixed monolayer phase. The calculation of excess area per molecule for the TCh and Ch mixed monolayer system indicates an attractive interaction between the component molecules. Interestingly, the elasticity of the Ch monolayer reduces to less than half, and the monolayer becomes more fluidic due to the presence of even very minute quantity (5%) of TCh.Item Smart Water Quality Monitoring System for Distribution Networks(SSRN, 2019-06) Gupta, Raj Kumar; Gupta, Karunesh KumarDrinking water quality monitoring is essential these days as the available water is polluted and can cause several diseases like cholera, diarrhea, dysentery, etc. This paper presents a low-cost wireless water quality monitoring system based on Arduino and Zigbee Module. Water quality parameters for monitoring is decided by the Central Pollution and Control Board, New Delhi, India. The water quality sensors are interfaced with the Arduino board through signal conditioning circuit. Acquired data is sent to the server over the wireless network through the Zigbee module. At the server, Raspberry Pi is used for data receiving and results have been shown on the graphical display.Item Monolayer of amphiphilic functionalized gold nanoparticles at an air-water interface(APS, 2008-09) Gupta, Raj KumarLangmuir films at the air-water interface exhibit a variety of surface phases which arise primarily due to the molecular interaction governed by intermolecular separation. We have studied the thermodynamical aspects of Langmuir monolayers of amphiphilic functionalized gold nanoparticles (AGNs) at the air-water (A−W) interface. Interestingly, the AGN monolayer exhibits phases like gas, a low-ordered liquid (L1), a high-ordered liquid (L2), and a collapsed state. We find that the first-order phase transition between L1 and L2 vanishes above a critical temperature of 28.4°C. Surprisingly, for a range of higher temperatures (⩾29.4°C and ⩽36.3°C), the L1 phase undergoes a transition to a bilayer of the L2 phase before entering into the collapsed state.Item Spatiotemporal patterns in a Langmuir monolayer due to driven molecular precession(APS, 2008-10) Gupta, Raj KumarLangmuir monolayers of chiral liquid crystals on the surface of water exhibit orientational waves with complex spatiotemporal patterns. These patterns arise from a collective precession of the mesogenic molecules, driven by the evaporation of water through the monolayer. We investigate the behavior of these orientational waves around topological defects in the molecular orientation. Through Brewster angle microscopy, we find that the waves form a reversing spiral pattern, which rotates about the central vortex. With increasing relative humidity, the rotation slows and then stops. We model the system theoretically, and show that predicted patterns are in good agreement with the experiments.Item Highly repeatable multilevel resistive switching characteristics of an Au/TiO 2 /Ti memory device(IOP, 2013) Gupta, Raj Kumar; Hazra, ArnabDevelopment of a highly repeatable multilevel resistive switching Au/TiO2/Ti memory device is reported in this paper. Undoped rutile TiO2 thin film, having a thickness of 480 nm, was grown on high-purity Ti (99.5%) by in situ thermal oxidation technique at 600 °C. Au metal contact was used as a top electrode. The developed Au/TiO2/Ti memory device was electrically characterized for resistive random access memory applications and found to have extremely repeatable, reproducible and stable bipolar resistive switching characteristics. With very low 'SET' and 'RESET' voltage requirement, the device offered highly symmetric multilevel high- to low-resistance state transitions. The two pairs of 'SET' and 'RESET' voltages were ±0.26 V and ±0.64 V. As there is no requirement of electroforming voltages, low electric field operation of the device is ensured, which eventually leads to the avoidance of high field hazards. The effect of operating temperature on the performance of Au/TiO2/Ti memory devices was also investigated in the temperature range of 27–80 °C, and the device offered negligible shift in the characteristics, ensuring high-temperature stability. The multilevel switching phenomenon was explained by appropriate defect models.Item Highly repeatable multilevel resistive switching characteristics of an Au/TiO2/Ti memory device(IOP, 2013) Gupta, Raj KumarDevelopment of a highly repeatable multilevel resistive switching Au/TiO2/Ti memory device is reported in this paper. Undoped rutile TiO2 thin film, having a thickness of 480 nm, was grown on high-purity Ti (99.5%) by in situ thermal oxidation technique at 600 °C. Au metal contact was used as a top electrode. The developed Au/TiO2/Ti memory device was electrically characterized for resistive random access memory applications and found to have extremely repeatable, reproducible and stable bipolar resistive switching characteristics. With very low 'SET' and 'RESET' voltage requirement, the device offered highly symmetric multilevel high- to low-resistance state transitions. The two pairs of 'SET' and 'RESET' voltages were ±0.26 V and ±0.64 V. As there is no requirement of electroforming voltages, low electric field operation of the device is ensured, which eventually leads to the avoidance of high field hazards. The effect of operating temperature on the performance of Au/TiO2/Ti memory devices was also investigated in the temperature range of 27–80 °C, and the device offered negligible shift in the characteristics, ensuring high-temperature stability. The multilevel switching phenomenon was explained by appropriate defect models.Item Raspberry Pi-based smart sensing platform for drinking-water quality monitoring system: a Python framework approach(Copernicus Publication, 2019) Gupta, Raj Kumar; Gupta, Karunesh KumarThis paper proposes the development of a Raspberry Pi-based hardware platform for drinking-water quality monitoring. The selection of water quality parameters was made based on guidelines of the Central Pollution and Control Board (CPCB), New Delhi, India. A graphical user interface (GUI) was developed for providing an interactive human machine interface to the end user for ease of operation. The Python programming language was used for GUI development, data acquisition, and data analysis. Fuzzy computing techniques were employed for decision-making to categorize the water quality in different classes like “bad”, “poor”, “satisfactory”, “good”, and “excellent”. The system has been tested for various water samples from eight different locations, and the water quality was observed as being good, satisfactory, and poor for the measured water samples. Finally, the obtained results were compared with the benchmark for authentication.Item High strain rate dynamic compressive behaviour of Al6061-T6 alloys(Elsevier, 2017-05) Gupta, Raj KumarThis paper investigated the compression behaviour of Al 6061-T6 alloys at various high strain rates through split Hopkinson pressure bar (SHPB) experiments. The compressive strength (σc) of Al 6061-T6 alloy was measured in the present work as a function of high strain rate . The measurements were done in the strain rate regime of 3 × 103 to 6.5 × 103 s− 1. The results showed that the corresponding (σc) increased exponentially with increase in (). But, the increase in strain with increasing was primarily linear. The work hardening coefficient decreased with the increase of strain. However, the decrease of work hardening coefficient with increasing strain rate did not follow a similar trend. With the increase of the strain rate sensitivity increased. As expected, the thermal activation volume decreased with increase in . Using the Zerilli-Armstrong equation attempt was made to evaluate the related material constants to predict the stress-strain curves. The predicted stress-strain behaviours matched reasonably well with those measured experimentally in the current SHPB experiments. The implication of these results in engineering design and simulation in the context of resisting high strain rate impact was also discussed.