Indian Institute of Technology Guwahati
  • Guwahati, State of Assam, India
Recent publications
This study employed the friction stir welding technique to find the optimal tool traverse speed for successfully joining the 304 stainless steel with 6061-T6 aluminum alloy. For this purpose, five different traverse speeds at a constant rotational speed of 875 rpm were considered. The welded joints were characterized based on the mechanical properties, micro/macrographs, and quantification of steel fragments and intermetallic compounds (IMCs) inside the stir zone (SZ). The composition and phase of the IMCs at the interface, SZ, and intercalated structure were confirmed through X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, field emission scanning electron microscope, and atomic force microscope. It is observed that the traverse speed of 90 mm/min produced the highest tensile strength with an IMC layer thickness of 1.47 ± 0.23 μm. At this traverse speed, the area fraction of IMCs and steel fragments is around 0.023 % and 6.05 % of the SZ area, respectively. Furthermore, the defects increased by reducing the traverse speed from 90 to 30 mm/min because of a higher fraction of IMCs (i.e., Al3Fe) and steel fragments inside the SZ. The traverse speed higher than 90 mm/min generated the cracks at the interface because of insufficient stirring at low heat input. The hardness improved by decreasing the traverse speed because of grain refinement in SZ and thermomechanically affected zone. The intercalated structure acted as the hardest zone because of the formation of IMCs, namely Al3Fe + AlFe at 30-70 mm/min, and Al3Fe + AlFe + AlFe3 at 90 and 120 mm/min.
Methanol was produced in a two-stage integrated process using Methylosinus trichosporium NCIMB 11131. The first stage involved sequestration of methane to produce methanotrophic biomass, which was utilized as biocatalyst in the second stage to convert CO2 into methanol. A combinatorial process engineering approach of design of micro-sparger, engagement of draft tube, addition of mass transfer vector and elevation of reactor operating pressure was employed to enhance production of biomass and methanol. Maximum biomass titer of 7.68 g L-1 and productivity of 1.46 g L-1 d-1 were achieved in an airlift reactor equipped with a micro-sparger of 5 µm pore size, in the presence of draft tube and 10% v/v silicone oil, as mass transfer vector. Maximum methane fixation rate was estimated to be 0.80 g L-1 d-1. Maximum methanol titer of 1.98 g L-1 was achieved under an elevated operating pressure of 4 bar in a high-pressure stirred tank reactor.
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.
Among the various sodium cathodes, the potential of Na-rich layered oxides is yet to be fully utilized. Unlike their Li counterparts, they are least explored and are at least a generation behind in development. Addressing the same, herein, Na-rich NaxMn2-xO1.5F0.5 (x = 1.05–1.3) type cathodes were synthesized successfully and analyzed as potential electrodes for Na-ion battery applications. Oxygen loss in Na-based transition metal oxides is a common issue, and it is effectively addressed by fluorine substitution. In contrast to exploring a particular stoichiometry as in other Na-deficient layered cathodes, herein, Na-content was gradually increased from 1.05 to 1.3. The cathodes were synthesized using a conventional solid-state approach and quenched to achieve high crystallinity. Compounds with different sodium stoichiometry were electrochemically tested in a half-cell configuration. Among these compounds, the Na1.2Mn0.8O1.5F0.5 electrode exhibited very high capacities of 178 and 122 mAhg⁻¹ at current densities of 10 and 1000 mA g⁻¹, respectively. The Na-rich Na1.2Mn0.8O1.5F0.5 cathode was systematically analyzed to understand the mechanism underlying its superior performance using various structural and electrochemical analyses. Furthermore, to demonstrate its practicality, the Na-rich Na1.2Mn0.8O1.5F0.5 cathode was coupled with a hard carbon and Na-In alloy anode in a full-cell assembly.
The flow of bubbles in a continuous liquid phase in a bifurcating microchannel is a commonly occurring phenomenon in micro-structured devices and physiological flows. Depending on the fluid properties, flow rates, and bifurcation geometry, different bubble dynamics can be observed at the bifurcation. In this work, the flow of bubbles in a continuous liquid stream is investigated experimentally in a Y-shaped bifurcating channel. Experiments are performed for three Newtonian liquids of different viscosities. For short bubbles and at low values of capillary numbers, bubbles remain unsplit and move to one of the daughter tube. On a Ca-Re plane, long bubbles (lb > dm) are observed to split for Re < 20, whereas bubble splitting does not occur for higher value of Reynolds numbers. When the bubble splitting occurs, the mother bubble squeezes against the carina of the bifurcation, and a neck forms. The thinning of the neck with time is investigated for the three liquids.
Herein, we report synthesis of bare and Sulfur (S) doped SnO2 nanoparticles (NPs) using simple and low cost hydrothermal method. S with different concentration (0, 2, 4 and 6) were doped in SnO2 and named as bare SnO2, 2%S:SnO2, 4%S:SnO2 and 6%S:SnO2, respectively. The synthesized NPs were characterized for structural, functional, optical, morphological, electrochemical and magnetic properties. XRD confirms the tetragonal structure of bare SnO2 2%S:SnO2, 4%S:SnO2 and 6%S:SnO2 NPs. The crystallite size and microstrain was calculated using the Scherrer equation, W-H plot, SSP plot, and H-W plot and are in well agreement with each other. The FTIR confirmed formation of S-O and Sn-O bonding. The direct energy band gap values of bare SnO2, 2%S:SnO2, 4%S:SnO2 and 6%S:SnO2 are 3.8 eV, 3.6 eV, 3.1 eV and 2.2 eV, respectively. The electrochemical performance (ECP) of bare SnO2 and 2%S:SnO2 NPs were studied by making their electrodes through CV, GCDs, and EIS measurements. The bare SnO2 and 2%S:SnO2 electrodes show the specific capacitance of 125 F/g and 225 F/g at a current density of 3 A/g proves S doping enhances the capacitive performance of SnO2 NPs. The VSM shows paramagnetic behavior changes into ferromagnetic behavior with S doping.
The low-cost and highly flexible piezoelectric nanogenerators (PENGs) have potential applications in mechanical energy harvesting and low power electronics. The low piezo response of PVDF limits its use in commercial sensory applications. In this work, a Polyvinylidene fluoride (PVDF) is reinforced with fixed quantity of Barium titanate (BTO) and varying concentrations of reduced graphene oxide (rGO) to enhance piezoelectric behaviour of PVDF films. Effect of higher rGO reinforcement (over 0.45 wt%) on PVDF-BTO composite energy harvesting performance was studied for the first time using solvent casting approach followed by electrode poling process. Structural properties along with average crystalline size and lattice strain of PVDF-BTO-rGO nanocomposites were calculated using XRD technique with Williamson-Hall approach. Increment in electroactive β phase from 54 to 73% has been observed by loading rGO in PVDF-BTO nanocomposites. For the first time, optimal rGO content in PVDF-BTO nanocomposites to achieve maximum mechanical properties is studied. Young’s modulus, tensile strength, breaking strain, storage modulus, viscosity, and hardness of PVDF-BTO-rGO films showed remarkable increment compared to PVDF-BTO nanocomposites respectively. The PENG devices were subjected to continuous finger tapping, film twisting and thumb pressing using human hand to record piezoelectric output for poled and unpoled samples. The PENG devices displayed significant enhancement in piezoelectric output voltage from 0.98 V for pure PVDF to 4.1 V for PVDF-BTO-rGO when rGO content is 1.25 wt% for finger tapping condition.
The European Green Deal, which emphasizes zero-waste economies, and waste recycling in construction and building materials, has arisen due to significant worldwide needs for solid waste recovery and usage. This ambitious study focuses on recycling mixed construction and demolition (C&D) waste into burnt bricks and investigating the influence of firing temperature. While pursuing its objectives, this is dependent on raw material characterization and burnt-brick product quality assessment. The recycling of mixed C&D waste is explored by mixing the waste into two soil types (alluvial and laterite) in ratios ranging from 5% to 45% at three firing temperatures (700 °C, 850 °C and 900 °C). The utilization of mixed C&D waste in amounts of 10% at 700 °C and 25% at 850 °C and 900 °C fulfilled the Indian standard. Although a fire at 700 °C results in less optimal waste utilization, it is beneficial and recommended for reducing the carbon footprint and energy use. Additional mineralogical and microstructural analyzes are performed on the optimal fired samples. The study’s findings are promising for sustainable resource usage, reducing carbon footprint, and reducing waste disposal volume. This research is a big step toward the Sustainable Development Goals of the United Nations and a circular economy.
In recent years, sustainable composites have gained increased attention due to various reasons, such as the depletion of non‐renewable resources, environmental sustainability, and the introduction of plastic pollution. The present work aims to develop biocomposites (with a maximum biological content of 61.78%) based on Bambusa tulda fiber and cashew‐nut shell oil‐based bio‐epoxy resin. Different concentrations of NaOH (2%, 4%, 6%, 8%, and 10%) are used to determine the most suitable NaOH concentration for bamboo fiber treatment. The effect of different treatment concentrations on bamboo fiber has been analyzed by performing single‐fiber tensile testing, fiber pull‐out testing, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric analysis, and atomic force microscopy. The investigation revealed that the 6% NaOH‐treated fiber showed better thermo‐mechanical and interfacial properties. Various fiber weight fractions (10%, 20%, 30%, and 40%) are used for composite fabrication, and 30% fiber‐loaded composites show the best mechanical properties. The effect of chemical treatments on the mechanical properties of biocomposites was investigated using composites with a 30% fiber weight fraction and different NaOH treatments. It has been reported that 30% fiber weight fraction 6% NaOH treated composites show better tensile strength (132.916 MPa), tensile modulus (6.983 GPa), flexural strength (154.8 MPa), modulus (8.243 GPa), and impact strength (44.06 kJ/m2) with less moist absorption. The developed composites have shown excellent potential for advanced engineering applications when compared with previously reported composites.
Atomic superfluids confined in a ring provide a remarkable paradigm for quantized circulation. Very recently, a technique based on cavity optomechanics has been proposed [Kumar et al., Phys. Rev. Lett. 127, 113601 (2021)] for sensing and manipulating the rotation of a bosonic ring condensate with minimal destruction, in situ and in real time. Here, we theoretically investigate other coherent interference effects that can be supported by the proposed configuration. Specifically, in the presence of a strong control beam, we analyze the influence of atomic rotation on the transmission spectrum of a weak probe laser through a cavity containing a ring condensate. We present a detailed study of the resulting narrow probe transmission profiles and group delay and show that they can be tuned by means of persistent currents. Our results explore a facet of rotating matter waves and are relevant to applications such as atomtronics, sensing, and information processing.
Intermolecular cross Rauhut‐Currier reactions have gained much importance in recent years. It has proved its importance through procedures involving various catalysts and resulting in complex structures with good regio‐ as well as stereo‐ selectivity. This review highlights the recent developments of these reactions, published in current years, involving both achiral and chiral catalysts to give products, having various utilities. In addition, the detailed mechanistic studies of the above‐mentioned reactions are also presented. This review summarizes the recent developments of intermolecular Rauhut‐Currier reactions. Both chiral and achiral variants have been discussed.
This article investigates the analytical and numerical solutions of a class of non-autonomous time-fractional integro-partial differential initial-boundary-value problems (IBVPs) with fractional derivative of Caputo-type. The existence and uniqueness of the analytical solution of the IBVP are established by using the Sumudu decomposition method and the maximum-minimum principle, respectively. To obtain the numerical solution, first, we semi-discretize the IBVP by discretizing the time-fractional derivative by using the L1-scheme and the integral term by using the trapezoidal rule on a graded mesh, and then we approximate the spatial derivatives by using the cubic spline method over a uniform mesh. The stability and convergence analysis of the numerical method are established. The performance of the proposed technique is validated through numerical experiments, and the results are compared with the method presented in Santra and Mohapatra (J. Comput. Appl Math. 400, 113746, 13, 2022).
The alkene-based o-[1-(p-MeO-phenyl)vinyl]benzoates (PMPVB) donors that can be remotely activated under catalytic Brønsted acidic conditions have been utilized to synthesize the C-linked indolyl glycosides in a regio- and stereoselective manner. The highly reactive glycosyl donors allow the usage of the poorly nucleophilic N-Boc and N-acetyl indole derivatives, leading to the indolyl glycosides in excellent yields and stereoselectivities. Also, conditions were developed for recycling the byproduct, which significantly improves the potential of these donors.
In this work, we analyze the scattering of water waves by a fully submerged bottom-mounted concentric cylindrical system consisting of three components: an impermeable inner cylinder surrounded by a porous cylindrical wall and a porous lid covering the annular region. Consideration of a porous lid in the annular region gives rise to two different dispersion relations in two sub-regions which in turn present an additional complexity in the system in the form of evanescent modes. Locus of the propagating mode for free surface gravity wave follows an analogous path in the complex plane as the porous-effect parameter moves in its own complex plane, except for low frequency at which the path of the mode distorts significantly. The mean drift wave forces on the system are calculated numerically by using pressure integration method, and the effect of different set of physical parameters on the wave forces is also examined. The key finding of this analysis is that the wave force on the impermeable cylinder gets minimized for lower values of porous-effect parameter whereas the drift force on the outer porous wall gets minimized corresponding to higher values of porous-effect parameter. This work is also verified with an existing work in the literature and then extended to the time-dependent analysis. The plane incident waves with the Gaussian profile and the focused wave group are both considered in the time domain simulation.
The term “microplastics (MPs)” refers to small solid particles with a size less than 5 mm made of non-biodegradable polymers like PE, PP, and PET. In India, plastics constitute to be a significant waste produced from every household, accounting for around 60% of the overall municipal solid waste generated. It finds an easy way of drifting into the river bodies and deteriorating the water quality. The presence of MPs in varying concentrations has been reported in Indian rivers. MPs pose a potential threat to the biosphere because of their better stability and greater potential to get fragmented. This creates a high chance of entering the food web and carrying harmful chemicals on their surfaces through adsorption. Different kinds of MPs exist in our environment that can be classified based on the origin of production and morphology differing in shape, colour, and size. These characteristics can be essentially utilized to find an efficient technique for assessing MPs from different environmental matrices. This review paper discusses various analytical techniques for assessing MPs from surface water bodies with their advantages and limitations. No single efficient assessment method for detecting MPs in water bodies could be relied entirely upon to date. Also, without further delay, it is required to visualize the current harm caused by these prevailing MPs around us and find ways to lower their production and impact. This aspect has been briefly highlighted. So, it needs to be researched intensively for efficient MPs identification, removal, and remediation.
The interfacial chemistry at the aqueous‐non‐aqueous interface can be use to trigger chemical transformation of perovskite nanocrystals. In this review, evolution of several dimensional halide (X) perovskites from non‐perovskite zero dimensional Cs4PbX6 phase has been revealed through water‐assisted approach, which further may use to transform other non‐perovskite phase (e.g., CsPb2X5), as well as doping in halide perovskites.
Formation of electrogenic microbial biofilm on the electrode is critical for harvesting electrical power from wastewater in microbial biofuel cells (MFCs). Although the knowledge of bacterial community structures in the biofilm is vital for the rational design of MFC electrodes, an in-depth study on the subject is still awaiting. Herein, we attempt to address this issue by creating electrogenic biofilm on modified graphite anodes assembled in an air–cathode MFC. The modification was performed with reduced graphene oxide (rGO), polyaniline (PANI), and carbon nanotube (CNTs) separately. To accelerate the growth of the biofilm, soybean-potato composite (plant) powder was blended with these conductive materials during the fabrication of the anodes. The MFC fabricated with PANI-based anode delivered the current density of 324.2 mA cm−2, followed by CNTs (248.75 mA cm−2), rGO (193 mA cm−2), and blank (without coating) (151 mA cm−2) graphite electrodes. Likewise, the PANI-based anode supported a robust biofilm growth containing maximum bacterial cell densities with diverse shapes and sizes of the cells and broad metabolic functionality. The alpha diversity of the biofilm developed over the anode coated with PANI was the loftiest operational taxonomic unit (2058 OUT) and Shannon index (7.56), as disclosed from the high-throughput 16S rRNA sequence analysis. Further, within these taxonomic units, exoelectrogenic phyla comprising Proteobacteria, Firmicutes, and Bacteroidetes were maximum with their corresponding level (%) 45.5, 36.2, and 9.8. The relative abundance of Gammaproteobacteria, Clostridia, and Bacilli at the class level, while Pseudomonas, Clostridium, Enterococcus, and Bifidobacterium at the genus level were comparatively higher in the PANI-based anode.
Incremental sheet formation (ISF) is extensively used versatile technique for newer manufacturing processes, such as creating skull prostheses, aerospace equipment, automobile, and so on. The current work describes the techniques, history, and classification of ISF-based on the results of few aspects such as force forming, stress triaxiality, force forming, bending stress, and so on. In addition, the influence of different parameters and their effect on building force, formability, spring-back, failure, surface roughness, rupture, and so on, have been analysed. It has been noticed that an investigation of the two degrees of freedom (DF) robot-manipulators with the ISF and its influences on surface coarseness and formability are greatly suggested.
This paper addresses a preliminary study on the emission control of pollutants from an industrial furnace. The stack sampling technique was implemented in this study, and the quantity of pollutants released from the furnace smoke was monitored. The transverse points required to collect the data were selected based on the upstream and downstream disturbances. At first, the investigation was made with the furnace oil. A 15.28% and 5.1% of CO2 and O2 were observed in the flue gas from of regular furnace oil. Hence, by considering the emission level observed, the analysis was repeated with the low sulphur-low stack and the coal tar fuel. The emission of SO2 and N2 was reduced with coal-tar fuel compared with the regular furnace fuel. Thus, the proposed operational adjustment attenuates the pollutant emission, which also helps to reduce the unfavorable impact on the environment. In the future, the authors intend to include a design change in the furnace burner, which would help to increase fuel efficiency and reduce pollution.
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9,603 members
Kaushik Bhattacharjee
  • Faculty of Biological Chemistry
Bhubaneswar Mandal
  • Department of Chemistry
Bimlesh Kumar
  • Department of Civil Engineering
Subbiah Senthilmurugan
  • Department of Chemical Engineering
North Guwahati, 781039, Guwahati, State of Assam, India
Head of institution
Prof. T. G. Sitharam