BITS Faculty Publications

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    Investigating degradation & mitigation strategies for proton conducting membrane in proton exchange membrane fuel cell: An approach to develop an active & stable membrane
    (Elsevier, 2024-06) Pandey, Jay
    Low-temperature proton exchange membrane fuel cells (PEMFCs) share many significant challenges in the performance, life-span, and industrial use of these membranes because of their degradation. This review synthesizes the current state of knowledge of the dominant degradation mechanisms acting on PEMs, namely mechanical stress, thermal degradation, and chemical attacks by reactive oxygen species (ROS). It is concluded that although mechanical degradation brought about by varying pressure and hydration cycles, membrane reinforcement with materials such as expanded polytetrafluoroethylene (ePTFE) and diverse composite membranes has somewhat mitigated the structural strength and toughness. Thermal and chemical degradation remains as principal challenges which are most often hastened by elevated temperatures and formation of reactive free radicals such as hydroxyl and hydrogen peroxide. Hence, to counteract chemical degradation, the addition of radical scavengers like cerium oxide (CeO2) and manganese-based additives can scavenge the destructive species even before this cause significant damage. Other new materials for PEM such as perfluorosulfonic acid (PFSA) composites have demonstrated enhanced resistance in chemical environments and a longer life. This includes research on innovative approaches such as introducing ionomers with improved thermal stability and evaluating hybrid organic-inorganic membranes in fighting the degradation mechanism of thermal degradations. This review brings out the need to understand the degradation mechanisms and advance mitigation strategies to ensure elongation of PEMFCs' life, thus paving a way for their reliability and feasibility as clean energy.
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    Dynamics and stability analysis of enzymatic cooperative chemical reactions in biological systems with time-delayed effects
    (Elsevier, 2024-09) Sharma, Bhupendra Kumar
    The mathematical modeling and dynamic analysis of time-delayed enzymatic chemical reactions in biological systems are presented in this research. The objective is to examine the function of time lags in these reactions and to get a complete knowledge of the behavior of biological systems in a reaction to modifications in the quantity present of reactants and products. The model, which is based on delay differential equations, includes a time delay term to account for the lag between changes in the concentration of reactants, reaction rate constants and product responses. The findings give insight into how enzymatic processes behave dynamically and how stability is impacted by time lags, oscillation and general efficiency of the system. These results have significant importance for our comprehension of how biological processes are regulated and for the creation of biological control structures
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    The impact of radio-chemotherapy on tumour cells interaction with optimal control and sensitivity analysis
    (Elsevier, 2024-03) Dubey, Balram; Dubey, Uma S.
    Oncologists and applied mathematicians are interested in understanding the dynamics of cancer-immune interactions, mainly due to the unpredictable nature of tumour cell proliferation. In this regard, mathematical modelling offers a promising approach to comprehend this potentially harmful aspect of cancer biology. This paper presents a novel dynamical model that incorporates the interactions between tumour cells, healthy tissue cells, and immune-stimulated cells when subjected to simultaneous chemotherapy and radiotherapy for treatment. We analysed the equilibria and investigated their local stability behaviour. We also study transcritical, saddle–node, and Hopf bifurcations analytically and numerically. We derive the stability and direction conditions for periodic solutions. We identify conditions that lead to chaotic dynamics and rigorously demonstrate the existence of chaos. Furthermore, we formulated an optimal control problem that describes the dynamics of tumour-immune interactions, considering treatments such as radiotherapy and chemotherapy as control parameters. Our goal is to utilize optimal control theory to reduce the cost of radiotherapy and chemotherapy, minimize the harmful effects of medications on the body, and mitigate the burden of cancer cells by maintaining a sufficient population of healthy cells. Cost-effectiveness analysis is employed to identify the most economical strategy for reducing the disease burden. Additionally, we conduct a Latin hypercube sampling-based uncertainty analysis to observe the impact of parameter uncertainties on tumour growth, followed by a sensitivity analysis. Numerical simulations are presented to elucidate how dynamic behaviour of model is influenced by changes in system parameters. The numerical results validate the analytical findings and illustrate that a multi-therapeutic treatment plan can effectively reduce tumour burden within a given time frame of therapeutic intervention.
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    The impact of social media advertisements and treatments on the dynamics of infectious diseases with optimal control strategies
    (Elsevier, 2024-05) Dubey, Uma S.; Dubey, Balram
    The dissemination of public health information through television and social media posts is essential for informing the public about the transmission of contagious diseases, which is crucial in preventing the spread of various infectious diseases. In this paper, we propose a non-linear mathematical model to assess the effect of advertisements through social media in creating awareness and limiting treatment on spreading infectious diseases. These initiatives may alter population behaviour and divide the susceptible population into subgroups. In addition, to comprehend these dynamics better, we use half-saturation constant rates for media coverage and treatment. The model’s well-posedness and feasibility are evaluated. The possible biological equilibrium points are calculated. Local and global stability are carried out. The objective of our study is to produce the model’s bifurcation. Transcritical, Saddle–node, Hopf bifurcation of codimension 1 and Cusp, Generalized-Hopf (Bautin), and Bogdanov–Takens (BT) bifurcation of codimension 2 are studied for this purpose. Due to the limited medical resources and supply efficiency, the model exhibits backward bifurcation, resulting in bistability. Moreover, the occurrence condition for stability and direction of Hopf bifurcation is discussed. This model study demonstrates that the system is significantly influenced by the pace with which awareness programmes are implemented and that raising this value above a threshold may result in continuous oscillation. Sensitivity analysis employs the normalized forward sensitivity index of the basic reproduction number to provide a comprehensive understanding of the effect of various parameters on accelerating and limiting disease spread. Further, the minimum possible cost is determined by formulating an optimal control system based on sensitivity analysis and applying Pontryagin’s maximum principle. Methods of cost-effectiveness, such as ACER and ICER, are used to determine the most cost-effective control intervention strategy among all the strategies. Numerical simulations have been done to support all theoretical findings.
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    SrTiO3-TiO2 heterostructured nanotubes array for selective acetone sensing
    (IEEE, 2023) Hazra, Arnab
    Efficient detection of acetone is essential for medical applications. In this context, we are reporting acetone selective SrTiO 3 -TiO 2 sensor. Initially, TiO 2 nanotube array was synthesized by the electrochemical anodization and then treated with Sr(OH)2 solution through the hydrothermal reaction. The morphology and crystallinity of the SrTiO 3 -TiO 2 nanotubes were investigated. The Au/SrTiO 3 -TiO 2 /Ti sensor exhibited its natural selectivity towards acetone and showed a high response (99.5%/50 ppm) at 150°C under 80% relative humidity. The sensor exhibited a remarkable 51.2% response even for 0.5 ppm acetone. The stability and hydrophobicity of SrTiO 3 result in consistency during repeated cycle study of the sensor.
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    Highly Reproducible and Reliable Methanol Sensor Based on Hydrothermally Grown TiO2 Nanoparticles
    (IEEE, 2023-10) Hazra, Arnab
    In the present paper, TiO2 nanoparticles were synthesized through low cost hydrothermal method at 150°C. Structural, morphological and optical properties of the grown materials were characterized through X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Raman Spectroscopy, and Photoluminescence spectroscopy, respectively. X-ray diffraction confirms the anatase phase with average crystalline size of 6.8 nm. Non-uniform particles having numerous pores with large number of active sites offered superior capability to detect methanol even at lower concentrations. Band gap of the material were found to be 3.4 eV. TiO2 nanoparticles in planner structure were investigated towards methanol (1-100 ppm) at the temperature ranging from (25-150°C). Sensor was found to be maximum responsive with response magnitude of 85% at 100°C and 47% at room temperature towards 100 ppm of methanol. At 1 ppm of methanol, sensor response was found to be 20%. Sensor response towards methanol was correlated with the surface state of nanoparticles with HOMO-LUMO energy.
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    SrTiO3 passivated MXene (Ti3C2Tx) for efficient VOC detection in hazardous humid ambient
    (Elsevier, 2024-02) Hazra, Arnab
    Humidity interference is a crucial consideration in gas sensing technology for real-time applications. MXenes are new-age two-dimensional (2D) materials with unique properties making them promising candidates for gas sensors. However, the MXene surface with the hydrophilic functional groups (e.g., =O, –OH) is susceptible to water vapor. The passivation by a hydrophobic layer on MXene could be the best option to overcome humidity intrusion. We are introducing super hydrophobic SrTiO3 passivation on the MXene layer for humidity-tolerant volatile organic compound (VOC) sensing. Herein, 2D MXene (Ti3C2Tx) was physically oxidized at 350 °C for 24 h to create a TiO2 layer and subsequent coating of moisture-blocking SrTiO3 (STO) overlayer was achieved by hydrothermal route. Sensors were tested in different VOCs and showed the optimum results towards the acetone. The TiO2 formation in MXene enhanced the acetone sensing response (217%/50 ppm) compared to the pure Ti3C2TX MXene sensor (175%/50 ppm) in air at 150 °C. However, the MX and TiO2/MX sensors were lacking in the acetone sensing performance in a humid atmosphere (80% RH). STO/MX-12 h sensor showed outstanding moisture-resistant sensing behavior in humid atmospheres (0–80% RH). Apart from this, the STO/MX-12 h sensor showed a high response of 68% for 100 ppb of acetone with adequate repeatability, and excellent stability in 80%RH and 150 °C operating temperature. The hydrophilicity change in MXene after SrTiO3 passivation was optimized by contact angle study.
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    Effect of Calcination Time on the Catalytic Activity of Ni/γ-Al2O3 Cordierite Monolith for Dry Reforming of Biogas
    (Elsevier, 2021-02) Roy, Banasri; Srinivas, Appari
    Ni/γ-Al2O3 wash coated cordierite monolith catalysts are calcined in air at 800 °C for 4, 10, and 20 h in order to study the effect of calcination time on the activity of the catalysts for dry reforming of model biogas. Catalytic activity studies are performed at 800 °C with three different CH4/CO2 ratios of 1.0, 1.5, and 2.0. The catalyst calcined for the longest time (C-20) displays higher stability and activity in terms of CH4 and CO2 conversion compared to those calcined for 4 h (C-4) and 10 h (C-10). XRD data and TPR analysis detect the maximum amount of NiAl2O4/MgAl2O4 phases and strongest metal-support interaction, respectively, for the C-20 sample. FESEM reveals the particle size of the calcined and reduced C-20 sample to be smaller than that of the C-4 and C-10 samples. Whereas, H2 pulse-chemisorption characterization demonstrates the highest metal surface area, metal dispersion, and smallest Ni particle size for the C-20 catalyst. While, no carbon deposition on any catalyst occurs for the CH4/CO2 ratio of one, lowest amount of carbon nanotubes is formed on the C-20 sample for the CH4/CO2 ratio of 1.5 and 2.0, as observe by DTA-TGA. EDX reveals concentration variation of Mg and Si from the cordierite monolith wall along the thickness of the coating for all the samples. In addition, the maximum amount of these elements is observed for the calcined C-20 catalyst coating. These implies that the diffusion of Mg and Si from the cordierite monolith to the catalyst coating during calcination contribute significantly in controlling the physicochemical properties of the catalysts. As a result, the higher stability and activity of the C-20 could be attributed to the formation of higher amount of the Ni– Mg- alumina spinel complex in the catalyst coating during longer calcination time, which leads to the improved metal-support interaction and higher nickel dispersion over monolith.
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    Fractional differential equation with movable boundary conditions
    (Taru Publication, 2024-03) Mathur, Trilok; Agarwal, Shivi
    In this research paper, we discuss the complex-valued solutions for the nonlinear fractional boundary value problem (FBVP) of complex order (δ = τ + ιa; 1 < τ ≤ 2, a ∈ R+) with movable boundary conditions. The fractional operators are taken in the sense of Riemann-Liouville (R-L) with complex order. By using the concept of Green’s function, the existence and uniqueness of solutions are established in this article. Also, we prove that the FBVP of complex order with movable boundary conditions is Ulam-Hyers Stable. Using illustrative examples, the results for this nonlinear FBVP have been shown.
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    The study of the electronic structures and properties of pure and transition metal-doped silicon nanoclusters: a density functional theory approach
    (Taylor & Francis, 2009-03) Bandyopadhyay, Debashis
    This report presents the study of ab initio electronic structure and properties of pure and transition metal (TM = Ti, Zr and Hf)-doped silicon clusters, TM@Si(n), by using density functional theory with a polarised basis set (LanL2DZ) within the spin-polarised generalised gradient approximation for different values of n varying from 8 to 20. As the first step of the study, different optimised geometries of pure and doped clusters are calculated. These optimised clusters are then used to calculate different structural and physical parameters of the clusters, like binding energy, Highest Occupied Molecular Orbital – Lowest Unoccupied Molecular Orbital (HOMO–LUMO) gap, charge transfer, etc. In order to check the stability of the clusters, the second-order difference in the energy of the optimised structures is calculated. To study the optical behaviour of the clusters, infrared and Raman spectra are also calculated. Further calculations are also done on cation and anion clusters of both pure and doped nanoclusters to obtain their ionisation potential, electron affinity and chemical potential. An effort has been made to correlate the variation of different calculated parameters with the size of the clusters to explain the real existence and stabilities of different TM-doped clusters.