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    Entropy generation and heat transfer in nonlinear Buoyancy–driven Darcy–Forchheimer hybrid nanofluids with activation energy
    (De Gruyter, 2025-04) Sharma, Bhupendra Kumar; Yadav, Sangita
    This study investigates the influence of a magnetic field, activation energy, and heat source on the heat and mass transfer within a cross fluid embedded with mono-, di-, and tri-nanoparticles, considering thermal radiation and Darcy–Forchheimer effects. Utilizing the Cattaneo–Christov theory, non-Fourier heat transfer is modeled for a vertical moving surface. A mathematical model is developed and subsequently converted into a dimensionless form through an appropriate similarity transformation, resulting in a system of first-order ordinary differential equations. The numerical approach to solve the system is BVP4C solver in MATLAB, a tool specifically designed for boundary value problems. Graphical representations have been analyzed for velocity profiles, temperature profiles, and concentration distributions for different values of physical parameters. It is observed that the velocity profiles exhibit an upward trend with an increase in the parameters associated with nonlinear thermal convection and nonlinear concentration convection. Additionally, the analysis of surface shear stress, heat transfer coefficients, and mass transfer coefficients revealed that an increase in the porosity parameter and Forchheimer number results in decreased shear stress. Entropy generation is also investigated to quantify irreversibilities in the system. The analysis showed that increasing the Brinkman number, diffusion parameter, and temperature and concentration difference parameters leads to higher entropy generation, indicating greater irreversibility in the system. A comparative analysis demonstrates that tri-nanoparticles substantially improve flow velocity, thermal conductivity, and solute diffusion compared to di- and mono-nanoparticles, with tri-nanofluids exhibiting the most optimal overall performance.
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    Impact of arrhenius activation energy on mhd nanofluid flow past a stretching sheet with exponential heat source: a modified buongiorno’s model approach
    (World Scientific, 2023) Sharma, Bhupendra Kumar
    Nanofluids have a wide range of applications in biological research. They are employed in targeted medication administration, hyperthermia (for cancer treatment) and differential diagnostics like magnetic resonance image (MRI). In light of these medical applications, the impact of an external magnetic field and an exponential heat source on the dynamics of TiO2–H2O over a nonlinearly stretched surface has been investigated. A realistic modified Buongiorno model has been used which includes the effects of reaction rate, Biot number and activation energy. The boundary value problem governing the model is solved on MATLAB R2022a using the solver, BVP5C. Further, the consequences of different parameters on rate of heat transfer coefficient (Nusselt number), rate of mass transfer coefficient (Sherwood number), drag coefficient, velocity, temperature and volume fraction profile are observed graphically. It is noted that volume fraction and uniform heat source intensity have a positive effect on the Nusselt number and negative effect on Sherwood number. The effects of thermal radiation and magnetic field on volume fraction profile are, respectively, positive and negative. The current physics of flow across a vertical stretching surface is expected to serve as the foundation for various medical science, engineering and technology applications.
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    Nanoribbons of discotic liquid crystal molecules
    (Elsevier, 2021) Gupta, Raj Kumar; Manjuladevi, V.
    Discotic liquid crystal molecules are interesting not only due to their mesophases as a function of temperature but also due to their potential to self-assemble into nanostructures. In this article, we facilitate the self-assembly of triphenylene based discotic liquid crystal (TP) molecules in solvent medium to obtain nanoribbons. The flat nanoribbons undergo a morphological transformation to twisted helical nanoribbons due to incorporation of silver nanoparticles. The electrical characterization by measuring current–voltage (I-V) curves from flat and twisted nanoribbons indicated semiconducting behavior. The charge transfer is governed by the classical hopping mechanism. The activation energy reduces due to incorporation of silver nanoparticles in the liquid crystal matrix. The lowest activation energy was found for a doped system of 0.1 wt%.
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    Significance of Activation Energy in Eyring-Powell Nanofluid Flow Exposed to Inclined Magnetic Field: Entropy Analysis
    (Springer, 2023-03) Bhattacharyya, Suvanjan
    In the present report, we explore the highlights of activation energy and first-order chemical reaction on the Eyring-Powell nanofluid flow in an upstanding channel with the imposed inclined magnetic field along with the heat generation/absorption. The equations regulating the flow are modelled using Buongiorno model by incorporating the brownian movement and thermophoresis effects of nanofluids. No slip and convective conditions are applied on velocity and temperature respectively at the boundaries of the channel. The governing equations are then changed to dimensionless form by defining suitable non dimensional physical variables. The system of coupled differential equations is solved using bvp4c MATLAB code. The velocity, temperature, nanoparticle concentration and entropy generation are analyzed through graphs and flow rate, heat and mass transfer rate are analyzed through tabular values for a scale of values of various physical variables. It can be reported that entropy generation can be minimized by incrementing the fluid parameter and the strength of imposed magnetic field.
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    Impact of Arrhenius activation energy on MHD nanofluid flow past a stretching sheet with exponential heat source: A modified Buongiorno’s model approach
    (World Scientific, 2023) Sharma, Bhupendra Kumar
    Nanofluids have a wide range of applications in biological research. They are employed in targeted medication administration, hyperthermia (for cancer treatment) and differential diagnostics like magnetic resonance image (MRI). In light of these medical applications, the impact of an external magnetic field and an exponential heat source on the dynamics of TiO2–H2O over a nonlinearly stretched surface has been investigated. A realistic modified Buongiorno model has been used which includes the effects of reaction rate, Biot number and activation energy. The boundary value problem governing the model is solved on MATLAB R2022a using the solver, BVP5C. Further, the consequences of different parameters on rate of heat transfer coefficient (Nusselt number), rate of mass transfer coefficient (Sherwood number), drag coefficient, velocity, temperature and volume fraction profile are observed graphically. It is noted that volume fraction and uniform heat source intensity have a positive effect on the Nusselt number and negative effect on Sherwood number. The effects of thermal radiation and magnetic field on volume fraction profile are, respectively, positive and negative. The current physics of flow across a vertical stretching surface is expected to serve as the foundation for various medical science, engineering and technology applications.
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    Exponential space and thermal-dependent heat source effects on electro-magneto-hydrodynamic Jeffrey fluid flow over a vertical stretching surface
    (World Scientific, 2022) Sharma, Bhupendra Kumar
    This paper deals with the study of an incompressible electro-magneto-hydrodynamic (EMHD) Jeffrey fluid flow over a vertical nonlinear stretching surface of variable thickness. Heat and mass transfer effects are analyzed by considering different source terms like viscous dissipation, Ohmic heating, thermophoresis, Brownian motion, thermal heat source, exponential heat source and activation energy. Governing equations for the flow system are converted into dimensionless forms using appropriate similarity transformations. The solution for the resulting governing equations is obtained by using the shooting technique with RK-4 method. The effects of various physical parameters such as magnetic field parameter (M), Grashof number (Gr), solutal Grashof number (Gc), Brownian diffusion parameter (Nb), thermophoresis diffusion parameter (Nt), thermal heat source parameter (Qt), exponential heat source parameter (Qe), Prandtl number (Pr) and Lewis number (Le) are presented with the help of graphs. It is observed that the heat transfer effects increase by increasing thermal and exponential heat sources, and mass transfer effects enhance by increasing the activation energy. Entropy generation for this flow system is also analyzed. Entropy decreases with an increase in the electric field parameter. In contrast, the Bejan number initially increases with an increase in the electric field parameter. After some particular value of electric field parameter, it changes its behavior in the boundary layer and decreases with an increase in the electric field parameter. Entropy and Bejan number increase with an increment in the concentration difference parameter. The accuracy of the results is validated by those of published literature and found in reasonable justification. The present results may be helpful in many engineering and industrial applications like manufacturing lubrication, natural gas networks, cooling nuclear reactors and spray processes.
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    On the mobility, turn-on characteristics and activation energy of polycrystalline silicon thin-film transistors
    (Elsevier, 2006-05) Gupta, Navneet
    In the present paper we propose a turn-on current model of polycrystalline silicon thin-film transistors (poly-Si TFTs). It is found that at low as well as at high doping concentrations, effective carrier mobility (μeff) increases with increase in temperature whereas a dip is observed at intermediate doping concentration. At very high and very low doping concentration the effect of temperature on the mobility is found to be almost negligible. Calculations reveal that effective carrier mobility and drain current increases as the gate bias increases and are larger for a lower trap state density. The calculated value of activation energy decreases as the gate bias increases and is larger for a larger poly-Si inversion layer thickness. A fair agreement is observed between the present predictions and the experimental results.
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    Shifting the Reactivity of Bis-propargyl Ethers from Garratt–Braverman Cyclization Mode to 1,5-H Shift Pathway To Yield 3,4-Disubstituted Furans: A Combined Experimental and Computational Study
    (ACS, 2015-12-16) Addy, Partha Sarathi
    Aryl or vinyl substituted bis-propargyl ethers upon base treatment generally form phthalans via the Garratt–Braverman (GB) cyclization pathway. In a major departure from this usual route, several aryl/vinyl bis-propargyl ethers with one of the acetylenic arms ending up with 2-tetrahydropyranyloxy methyl or ethoxy methyl have been shown to follow the alternative intramolecular 1,5-H shift pathway upon base treatment. The reaction has led to the formation of synthetically as well as biologically important 3,4-disubstituted furan derivatives in good yields. The initially formed E isomer in solution (CDCl3) slowly isomerizes to the Z isomer, indicating greater stability of the latter. The factors affecting the interplay between the 1,5-H shift and GB rearrangement have also been evaluated, and the results are supported by DFT-based computational study.
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    Modeling Polymer Crystallization Kinetics in the Meltblowing Process
    (ACS, 2020-12-06) Ghosal, Arkaprovo
    A novel model of the crystallization process in meltblowing process is proposed and implemented in numerical simulations. The spinline crystallization is studied using numerical solutions of the system of coupled quasi-one-dimensional equations describing the dynamics of multiple polymer jets moving in the surrounding high-speed air. Cooling, crystallization, and solidification accompany three-dimensional motion of polymer jets resulting in their vigorous stretching by the air flux including the aerodynamically driven bending/flapping. The numerical solutions predict distribution of the degree of crystallinity in polymer jets in flight, as well as in the laydown formed on the collecting screen, with the three-dimensional structure of the laydown being fully reconstructed. The effect of the collector screen temperature, die-to-collector distance (DCD), and the activation energy of the viscous flow in the polymer melt on the laydown features is studied in detail.