Indian Institute of Technology Kanpur

Recent publications
This paper proposes an accurate three-dimensional framework for elastic and viscoelastic free vibration investigation of in-plane functionally graded (IPFG) orthotropic rectangular plates integrated with piezoelectric sensory layers. The developed {analytical} framework is capable of considering layer-wise unidirectional linear functional gradation in both stiffness and density of the orthotropic composite layers. 3D piezoelasticity-based governing equations of motion are formulated in mixed form by employing Hamilton's principle, and further solved analytically for Levy-type support conditions using the power-series-based extended Kantorovich method (EKM) jointly with Fourier series. The displacements, stresses, and electrical variables (electric field and electric potential) are solved as the primary variables that ensure the point-wise interlayer continuity and electro-mechanical support conditions. The viscoelastic property of the orthotropic interlayer is defined by employing Biot model, which is similar to the standard linear viscoelastic model. The correctness and efficacy of the present mathematical model are established by comparing the present numerical results with published literature and 3D finite element results, obtained by utilizing user material subroutine in the commercial FE software ABAQUS. An extensive numerical study is performed for various configurations and thickness ratios to investigate the influences of in-plane gradation, viscoelasticity and their coupled effects on the free-vibration response of hybrid laminated plates. It is found that in-plane gradation of stiffness and density remarkably alters the flexural frequencies and corresponding mode shapes of the hybrid intelligent rectangular plates. The flexural frequencies and stresses in the plate can be modified by selecting suitable grading indexes. Another interesting observation is that the in-plane gradation shows a considerably less effect on the electrical response of piezoelectric layers, which can play a vital role in the design of sensors and actuators for dynamic applications. Further, the numerical study demonstrates a potential time-dependent structural behaviour based on the present viscoelastic modelling. The consideration of viscoelasticity could be crucial for analysing the mechanical behaviour of a wide range of polymer composites more realistically and for prospective temporal programming in smart structural systems by exploiting the viscoelastic effect. Although the present analytical solution has been proposed for the free-vibration investigation of smart in-plane functionally graded (IPFG) viscoelastic plates, it can also be utilized directly to analyze the symmetric and asymmetric laminated piezoelectric smart plates with constant properties.
Laminar free convection in yield-pseudoplastic fluids (the Herschel-Bulkley model) for concentric and eccentric cylindrical annuli has been studied numerically. The combined effects of shear-thinning viscosity and yield stress on the heat transfer characteristics have been examined for the following ranges of parameters: Rayleigh number, Ra (10³ to 10⁶), Oldroyd number, Od (0 to Odmax), power-law index, n (0.2–1), Prandtl number, Pr (10–100), eccentricity, ε (0–1.18) and angular position of the inner cylinder, ϕ (0° to 180°). The results are interpreted in terms of the yield surfaces, fraction of yielded fluid, streamlines, isotherms, local Nusselt number and average Nusselt number. Overall, the eccentric positioning of the heated cylinder along the vertical centreline fosters convective transport with reference to that for the case of the concentric annulus. It is possible to achieve augmentation of up to 30% in heat transfer for the case of ε = 1.18, ϕ = 0° with respect to the concentric case at Ra = 10⁵, Pr = 10. This is ascribed to the greater fraction of the annular area occupied by the yielded fluid-like regions. Conversely, horizontal shifting of the inner cylinder to an off-centre position has an adverse effect on heat transfer. Limited transient simulations have also been run to identify the conditions for the loss of steady flow behaviour. A predictive correlation has been developed for the average Nusselt number for its estimation in new applications.
Ferrocene since its inception in the year 1951, has been extensively exploited as a crucial redox probe to unravel electrochemical charge-transfer dynamics in a variety of platforms ranging from solution-based systems and molecular thin-films to solid-state molecular electronics and spintronic devices. Having completed almost 71 years of its existence, ferrocene has now become one of the most widely studied organometallic compounds. Several experimental and theoretical frameworks are made to understand ferrocene's electronic and electrochemical properties. Ferrocene is an 18-electron metallocene that shows interesting metal–ligand coordination and has led to the preparation of a great number of important molecules. Ferrocene and its numerous derivatives have brought a breakthrough in metallocene chemistry. Ferrocene represents a chemically and thermally stable system that undergoes reversible electrochemical oxidation and reduction processes. Ferrocene-based self-assembled monolayers (SAMs) are considered as model system for performing on-surface redox reactions and have been applied to create nanoelectronic devices for molecular switching, rectification, and low-voltage operational memory devices. The present review discusses the recent progress made toward a ferrocene-containing molecular system that have been utilized in redox reactions, surface attachment, spin-dependent electrochemical processes to understand spin polarization, photo-electrochemistry, and molecular electronic devices. This review provides an excellent platform for understanding the electrochemical properties and the rational design of ferrocene-based molecular systems for optoelectronic applications.
In this work, we present a phenomenological cryogenic model for gallium nitride (GaN) high electron mobility transistors (HEMTs) with validity all the way down to a temperature of 10 K, benchmarked with experimental characterization results. The device under test (DUT) for cryogenic characterization is a GaN HEMT with a channel length of 250 nm and a gate width of 40 μ m. The characterization results exhibit the negative threshold voltage shifts of − 3.437, − 3.087, and − 2.998 V at the temperatures of 300, 60, and 10 K, respectively. Additionally, kink effects at cryogenic temperatures in output characteristics are observed that behave non-monotonically with gate-to-source bias. The impact of detrapping is modeled to investigate the negative shift in VTH with increasing temperature. To model the kink, the effects of temperature, impact ionization, and field-dependent trapping/detrapping on VTH have been explored and implemented as a submodel in the industry standard Advanced SPICE Model (ASM)-HEMT framework. Here, we aim to overcome the limitations of the prior GaN device models in the quest for enabling GaN-based circuits for cryogenic applications, such as deep space reception, radio astronomy, and quantum computing.
In an ac microgrid, reactive power sharing accuracy is affected due to unequal values of interconnecting cable impedances. To resolve this issue, secondary controllers are used to compensate the effect of cable impedances. Various types of secondary controllers are suggested in the literature which includes linear proportional plus integral (PI) controllers to minimize the difference in reactive power sharing created by conventional E−Q droop law. The reference value of the PI controller is the average value of reactive powers supplied by the sources. When the PI controller is used to minimize the difference between the actual and reference value of reactive power, the difference between the algebraic sum of reactive powers supplied by the sources and the reactive powers demanded by the loads has a nonzero value. Therefore, the performance of these controllers becomes poor in the case of ac microgrid having sources of unequal ratings. To resolve this issue, a proportional reactive power-sharing (PRPS) controller-based distributed secondary controller is proposed in this paper. The PRPS controller modifies the droop gain of the E−Q droop control loop of each source in such a way that each source supplies reactive power equal to its proportional value of reactive power. The proportional value of reactive power supplied by each source is the power when the equivalent output impedance of all sources as seen by the loads are identical. The key advantage offered by the proposed controller is the accurate reactive power-sharing in the case of ac microgrid having sources of unequal ratings. The proposed controller ensures zero value of the difference between the algebraic sum of reactive powers supplied by the sources and the reactive powers demanded by the loads. This ensures accurate sharing of reactive power among the sources. The validation of the proposed controller is carried out for islanded mode of operation of ac microgrid. Further, the proposed controller requires of low bandwidth communication for its implementation. The effect of the proposed controller on the stability of the system is demonstrated using reduced order small-signal model. The effect of communication delay on the performance of the system is analyzed with the help of roots locus plots. To validate the efficacy of the proposed controller, detailed simulation studies are carried out in Matlab/Simulink.
This paper studies the impact of multi-domain dynamics on the memory window (MW) of a Ferroelectric FET (FeFET). The memory window primarily depends on the density of domains in the ferroelectric region.We show that a maximum MW is possible if one domain wall is present in the ferroelectric layer. Furthermore, enhancing the ferroelectric layer thickness decreases the gradient energy leading to an expansion in the domain period. This increased domain period reduces the domain density and improves the MW. On the other hand, domain density increases with the increase in dielectric layer thickness, which reduces the MW. Additionally, the nature of the domain wall also alters the MW remarkably, causing a reduction in the MW when the domain wall gradually switches from hard to soft. The optimum range of the device’s physical parameters is obtained by minimizing the net ferroelectric thermodynamic energy corresponding to the maximum MW and serves as a device design guideline.
This paper investigates the potential demand for improved bus service quality in India using the stated preference method. This paper evaluates the effect of passengers’ socio-economic characteristics on their willingness-to-pay (WTP) for improved bus services by focusing on tradeoffs concerning the improvements to passengers’ in-vehicle travel time and comfort level. The paper further compares more preferred improvements among the bus passengers between in-vehicle travel time and comfort level. The paper uses the ordered logit model to analyze decisive factors affecting the opinion of passengers’ WTP for various improvement scenarios. Travel time, fare per trip, family monthly income, motor vehicle ownership, and age are found to be statistically significant to estimate the mean WTP. The results show that users consider the service quality of the public transportation system to be poor and are willing to pay for improved service qualities. As an exciting result, the collected data suggest that passengers are not willing to pay the same level towards improvements in travel time.
Potable water scarcity is a dire problem faced worldwide due to contaminated ground water. Microbial contaminants, heavy metals chromium (Cr) and metalloid such as arsenic (As) are some of the major pollutants of ground water and pose serious health hazards. The present work is focused to design a multifunctional three compartment integrated water filtration system for community use and its validation at both lab and pilot scale. The top compartment is mainly for removal of flocculating contamination with improvement of taste and odor of drinking water. The second compartment consists of functionalized sand layers for removal of metal and microbial contaminants and the third compartment comprises of nanoparticle embedded ceramic candles to further eliminate any remaining contaminants. The developed integrated water filter containing various types of materials were characterized through flow rate, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) before and after filtration. Moreover, the analysis of various physiological parameters such as pH, turbidity, total dissolved solids and hardness pre and post filtration elucidated stable and improved results. Micro-computed tomography (micro-CT) analysis of baked ceramic candle showed substantial increased porosity of ~83.11 ± 2.17 % in comparison to unbaked candle (26.09 ± 1.33 %). The inductively coupled plasma mass spectrometry (ICP-MS) analysis demonstrated significant reduction of As and Cr levels before and after filtration, which was further confirmed by EDS mapping. Microbial testing showed hierarchal decrease in microbial load after each stage at lab scale. This low-cost, multistage, gravity-based filtration system proved effective in removal of heavy metal and microbial contaminants in water and provides the potable filtrate for daily use. Thus, the integrated system with simple design without requiring major infrastructure and promising results may lead to its potential real-time application for supplying potable water to large populations, particularly in rural populations who cannot afford sophisticated water purification system.
Cuprous oxide (Cu $_{\text{2}}$ O) is a promising semiconductor for photovoltaic applications owing to its direct bandgap, facile fabrication possibilities, and cost effectiveness. However, the efficiency of single photovoltaic cells employing Cu $_{\text{2}}$ O is limited to 3%–4% necessitating investigations into material quality and reliable interface conductivity with contact metals. In this article, we systematically investigate the charge transport efficiency between electrodeposited (ED) Cu $_{\text{2}}$ O thin films and commonly used metallic stack contact materials, such as Ti/Au, Cr/Au, and Pt. We further explore a large-area CVD-grown graphene monolayer as a transparent contact for Cu $_{\text{2}}$ O thin films. Using transfer length measurements (TLMs), we observe thermal emission characteristics with no noticeable Fermi-pinning effects using the metal combinations employed on ED Cu $_{\text{2}}$ O. We achieve the lowest reported contact resistivity on Cu $_{\text{2}}$ O thin films ( $\boldsymbol{\rho}_{\textit{C}}=\text{2.15} \times \text{10}^{-\text{5}}~\Omega \text{cm}^{\text{2}}$ ) using a Ti–Au metal combination with the resistivity scaling exponentially with the barrier height on other metal stacks. In contrast, the true contact resistivity between a single monolayer of undoped graphene and a Cu $_{\text{2}}$ O thin film was measured to be an order of magnitude higher ( $\text{5.526}\times \text{10}^{-\text{4}}~\Omega \text{cm}^{\text{2}}$ ). Despite the higher resistance, this result indicates that further investigations into stacking multiple layers with careful doping control can make large area graphene attractive for photovoltaic applications using functional oxides.
Femtosecond laser-induced optical breakdown in liquids results in filamentation, which involves the formation and collapse of bubbles. In the present work, we elucidate spatio-temporal evolution, interaction, and dynamics of the filamentation-induced bubbles in a liquid pool as a function of a broad spectrum of laser pulse energies (∼1 to 800 µJ), liquid media (water, ethanol, and glycerol), and the number of laser pulses. Filament attributes such as length and diameter have been demarcated and accurately measured by employing multiple laser pulses and were observed to have a logarithmic dependence on laser energy, irrespective of the medium. The size distribution of persisting microbubbles is controlled by varying the pulse energy and the number of pulses. Our experimental results reveal that introducing consecutive pulses leads to strong interaction and coalescence of the pulsating bubbles via Bjerknes force due to laser-induced acoustic field generation. The successive pulses also influence the population density and size distribution of the micro-bubbles. We also explore the size, shape, and agglomeration of bubbles near the focal region by controlling the laser energy for different liquids. The insights from this work on filamentation-induced bubble dynamics can be of importance in diverse applications such as surface cleaning, fluid mixing and emulsification, and biomedical engineering.
We report a comparative study of a single plasma and a colliding laser produced plasma, investigated using a Faraday cup. An enhancement in ion emission and stagnation is observed in colliding plasma plume compared to single plasma plume. We observed that fast ion generation in laser ablated plasma can be achieved at large laser intensity on to the target. As laser intensity increases ionic yield increases for both colliding and single plume and at a fixed laser intensity ionic yield decreases with increase in ambient pressure. The double peak structure is observed in the ion signal at large fluence where the peaks correspond to fast and slow species. A Faraday cup composed of nine collectors is used to measure the spatial/angular distribution of ion of expanding plasma plume. Ionic yield is found to be larger in the colliding plasma plume than the single plasma plume at all spatial/angular positions.
Corrosion and anodic performance of newly developed composite sacrificial anodes based on high phosphorus pig iron, Al, and Zn with the stoichiometry xP-yAl and xP-y(Al0.75Zn0.25) (x = 1.5, 3.5, and 8.0 wt% P and y = 2.5, 5.0, and 10.0 wt%) in 3.5% NaCl and artificial seawater are studied. The incorporation of Zn in the xP-y(Al0.75Zn0.25) anodes decreases the potential below the potential required for the protection of steel during cathodic protection (− 0.778 V vs saturated calomel electrode). However, the xP-yAl anodes without the presence of Zn are unable to reach protection potential due to passivity. The preferential dissolution of Zn leads to destabilization of the passive layer (ϒ-Al2O3), and this attributes to greater active potential and better anodic performance of the xP-y(Al0.75Zn0.25) anodes. Hence, the presence of Zn is necessary for the xP-y(Al0.75Zn0.25) composites to become effective sacrificial anodes. Graphical abstract
The Himalayas sustain the water sources for ∼2 billion people in South and East Asia. The Himalayan cryosphere is particularly sensitive to climate change as a result of long-range transport of anthropogenic emissions from the Indo-Gangetic Plain. Atmospheric warming as a result of light-absorbing aerosols, i.e., black carbon (BC) and brown carbon (BrC), is responsible for accelerated loss of glaciers in the region. The BrC lifetime in the atmosphere over the Himalayan cryosphere has never been studied before, and observational determination of the lifetime of BrC is imperative in improving model performance. In this work, we collected bulk water-soluble BrC (WS-BrC) data from multiple campaigns conducted over the past 15 years in South Asia and the Himalayas, with an aim to provide constraints for two distinct receptor regions: South Asia outflow and Himalayan atmosphere. We observed decay in WS-BrC absorptivity for both receptor regions as air masses undergo long-range transport from the source region. However, the decay rate of the WS-BrC imaginary refractive index (kWS-BrC-365) in the Himalayan atmosphere (0.09 ± 0.02 day–1) was ∼2 times slower than the South Asian outflow (0.17 ± 0.04 day–1), implying their longer atmospheric half-life in the Himalayan atmosphere than the South Asian outflow (∼8 and 4 days, respectively). The comparison in the evolution of kWS-BrC-365 and absorption Ångström exponent revealed the less pronounced role of photochemical bleaching in the decay of BrC in the Himalayan atmosphere than in the South Asian outflow. Slower decay is consistent with highly viscous organic aerosol as a result of a low temperature and relative humidity in the cryospheric atmosphere.
The hydrogen evolution process in the as-cast Mg-0.6Ca alloy was investigated using real-time optical imaging of the corroding surface. It was revealed that hydrogen evolved as large stable bubbles and continuous streams of tiny bubbles because of high localised current density. To the best of the author’s knowledge, this is the first attempt to characterise the hydrogen evolution behaviour of Mg-Ca binary alloy employing a mechanistic model based on real-time imaging.
4H,8H-bis[1,2,5]oxadiazolo[3,4-b:3',4'-e]pyrazine (bis-oxadiazolo-pyrazine) represents a versatile CHNO backbone for the design of energetic materials. In this paper, we report a comprehensive computational study using density functional theory to improve detonation properties of this CHNO backbone by introducing pyrazine rings, nitro groups, and N-oxide functionalities. The heat of formation, oxygen balance, density, and detonation properties of a series of furazan-pyrazine fused ring derivatives are computed. Their sensitivity and stability has been correlated with bandgap (ΔELUMO-HOMO), maximum heat of detonation (Q), and impact energy (h50). Introduction of –NO2 and N–oxide on the parent furazan-pyrazine fused ring derivatives is favorable for improving the heat of formation, oxygen balance and density. The heat of formation varies between 464.46 and 1043.57 kJ/mol, and the densities range from 1.75 to 2.01 g/cm³. The positive heat of formation and high densities achieved good detonation velocities (6.74 to 9.61 km/s) and pressures (19.96–43.65 GPa). Among the bis-oxadiazolo-pyrazine derivatives, P5, P6, Q5, Q6, R4, R5, and R6 are fascinating due to their high detonation performances, have calculated detonation velocities and pressures above 9.30 km/s and 40.0 GPa, respectively. Some furazan-pyrazine fused ring derivatives reveal good performance parameters with reasonable stability, confirming them as potential energetic compounds relative to RDX and HMX.
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