Browse Items (14421 total)
Sort by:
-
Brinkman-Bard convection in a rotating-binary liquid saturated porous medium
The primary intent of the work is to investigate the linear and weakly non-linear stability analyses of natural convection in a rotating binary liquidsaturated porous medium. In the mathematical model, Newtonian binary liquid-saturated porous medium with uniform rotation subjected to stress-free isothermal boundaries and the validity of OseenBoussinesq approximation is considered in the study. Normal mode analysis is operated to acquire the DarcyRayleigh number expression in terms of the other parameters. The amount of heat and mass transfer rates are approximated at the lower boundary by performing weakly non-linear stability analysis using truncated Fourier series solution. The analysis of critical Rayleigh number, critical wave number, heat, and mass transfer is done for different values of parameters and discussed in detail with the help of plots and tables. Lewis number stabilizes the convective system, whereas increasing in the separation ratio coefficient destabilizes the convective system. Weakly nonlinear stability analysis reveals that the binary liquids with a smaller separation ratio coefficient transport the maximum heat and minimum mass compared to binary liquids with large separation ratio coefficient values. The amount of heat transport is enhanced by 14% with increase in the values of Ta whereas the same is diminished by 3.5 % and 5% respectively for the ? and Le. Thus, the effect of rotations pronounced on the onset of convection, heat and mass transports predominantly compared to the effect of binary mixtures parameters. The results of the classical RayleighBard convection and natural convection in a liquid-saturated porous medium with local thermal-equilibrium assumption can be obtained as a particular case of the study by setting the appropriate limits. 2025 Elsevier Ltd -
Stability Analyses of BrinkmanBard Convection in Hybrid-Nanoliquid Saturated-Porous Medium Using Local Thermal Non-equilibrium Model
This paper carries out linear and weakly non-linear stability analyses of natural convection in a Newtonian hybrid-nanoliquid saturated porous medium. The Boussinesq approximation is assumed to be valid in the study, and a two-phase energy model is used. The weighted residual Galerkin technique is employed to obtain the expression for the Rayleigh number and Lorenz model by using a truncated double Fourier series solution. The quadratic non-linear Lorenz model is solved numerically by using the RungeKuttaFehlberg method. Water is considered as a carrier liquid, and copper and alumina nanoparticles are considered with dilute concentration. Linear stability analysis reveals the onset of convection prepones in a hybrid nanoliquid-saturated porous medium. The amount of heat transport is maximum in a hybrid nanoliquid saturated porous medium and minimum in a liquid-saturated porous medium. Local thermal non-equilibrium situation ceases at higher rates of interphase heat transfer coefficient. The assumption of local thermal non-equilibrium is prominent in hybrid nanoliquid saturated porous medium. The results of the hybrid-nanoliquid channel, a hybrid nanoliquid saturated porous medium with the local thermal assumption, are presented as a limiting case of the study. 2024, The Author(s), under exclusive licence to Springer Nature India Private Limited. -
Linear and Global Stability Analyses on the Influences of Thermal Non-Equilibrium and Non-uniform Gravity Field on DarcyBrinkmanBard Convection
Global and linear stability analyses of DarcyBrinkmanBard convection in a liquid-saturated porous medium with a non-uniform gravity field using the local thermal non-equilibrium (LTNE) model are investigated. Linear and quadratic (parabolic) gravity field profiles are considered in the analysis. The OberbeckBoussinesq approximation is assumed to be a valid and the stationary mode of onset of convection is shown to be the preferred mode due to the validity of the principle of exchange of stabilities. Critical values of wavenumber and thermal Rayleigh number are obtained numerically using the higher-order Galerkin technique. The effect of an increase in the gravity fields strength is to delay the onset of convection, and to a growth in convective cell size. Further, linear convective profile is found to postpone convection compared to the quadratic one. Global stability ensures the existence of subcritical motions in the case of a non-uniform gravity field. In contrast, subcritical motions do not exist in constant gravity in LTE and LTNE situations. A non-uniform gravity field has a significant influence on the convective instability in a liquid-saturated high-porosity medium, lesser influence in the case of a low porosity medium and least in the case of a clear fluid layer. 2021, The Author(s), under exclusive licence to Springer Nature India Private Limited. -
A study on entropy generation and heat transfer in a magnetohydrodynamic flow of a couple-stress fluid through a thermal nonequilibrium vertical porous channel
The effect of local thermal nonequilibrium (LTNE) on the entropy generation and heat transfer characteristics in the magnetohydrodynamic flow of a couple-stress fluid through a high-porosity vertical channel is studied numerically using the higher-order Galerkin technique. The Boussinesq approximation is assumed to be valid and the porous medium is considered to be isotropic and homogeneous. Two energy equations are considered one each for solid and fluid phases. The term involving the heat transfer coefficient in both equations renders them mutually coupled. Thermal radiation and an internal heat source are considered only in the fluid phase. The influence of inverse Darcy number, Hartmann number, couple-stress fluid parameter, Grashof number, thermal radiation parameter, and interphase heat transfer coefficient on velocity and temperature profiles is depicted graphically and discussed. The entropy generation, friction factor, and Nusselt number are determined, and outcomes are presented via plots. The effect of LTNE on the temperature profile is found to cease when the value of the interphase heat transfer coefficient is high, and in this case, we get the temperature profiles of fluid and solid phases are uniform. The physical significance of LTNE is discussed in detail for different parameters' values. It is found that heat transport and friction drag are maximum in the case of LTNE and minimum in the case of local thermal equilibrium. We observe that LTNE opposes the irreversibility of the system. The corresponding results of a fluid-saturated densely packed porous medium can be obtained as a limiting case of the current study. 2021 Wiley Periodicals LLC -
Analytical study of BrinkmanBard convection in a bidisperse porous medium: Linear and weakly nonlinear study
Linear and weakly nonlinear stability analyses of BrinkmanBard convection of a Newtonian fluid saturating a bidisperse porous medium (BDPM) are made. Local-thermal-non-equilibrium (LTNE) is assumed between the fluid and the porous spheres (micro-pores) that make up the macro porous medium. Two coupled linear momentum equations are considered one each for the macro- and micro-pores. Results of mono-disperse porous medium (MDPM) with solid spheres are recovered as a limiting case of the present study. Further, in the case of both types of porous media considered the results of DarcyBard and BrinkmanBard convection are extracted under suitable limiting procedures. To keep the work analytical, we reduce the intractable hexa-modal Lorenz model with four quadratic nonlinearities into the tractable mono-modal StuartLandau equation (SLE) with cubic and quintic nonlinearities. Subcritical instability is discounted in the study thereby suggesting that cubic SLE and cubicquintic SLE both expound similar results qualitatively. The concept of a BDPM is shown to be meaningful only when the pores are not large, and when they are very small, then the MDPM assumption applies. Similar observation can be made when the ratio of permeabilities is large. The presence of micro-pores does not alter the size of the convective cell significantly at the onset. The present study reiterates the findings of several earlier works. 2023 Elsevier Ltd -
A study on regular and chaotic convection in an anisotropic porous cavity
The primary intent of the work is to investigate the linear and weakly nonlinear stability analyses of the BrinkmanBard convection (BBC) problem in a horizontal thermally-anisotropic porous enclosure with temperature-dependent uniform heat source/sink analytically by using a weighted residual Galerkin scheme. The linear stability analysis of the study reveals that the conductive system is stabilized by increasing anisotropy, Darcy number, and internal heat source strength. Three modal Lorenz model is derived by performing weakly nonlinear stability analysis using truncated Fourier series solutions. Equilibrium points of the Lorenz model and stability analysis is studied. The conductive equilibrium point (zero equilibrium point) is asymptotically stable and the eigenvalues are negative, whereas the convective equilibrium points (non-zero equilibrium points) are asymptotically stable up to a threshold Rayleigh number. Later, Hf bifurcation or chaotic motions sets in. The effect of an increase in the values of internal heat source and thermal anisotropic term delays the onset of the chaotic convection, whereas the Darcy number exhibits the opposite fashion. Further, the amount of heat transport is estimated at the lower boundary of an enclosure, and it is seen that the amount of heat transfer is maximum in the case of heat source, Darcy medium, and heterogeneous medium compared within the Brinkman medium in the presence of heat sink. 2025 The Physical Society of the Republic of China (Taiwan) -
A Study on the Stability of DarcyBrinkmanBard Convection in a Binary Fluid-Saturated Porous Medium: RigidRigid Boundaries
The linear stability analysis of DarcyBrinkmanBard convection (DBBC) in a binary fluid-saturated porous layer is studied numerically using n term Galerkin approach for rigidrigid, isothermal boundaries. The occupied binary fluid and porous medium are assumed to be in thermal non-equilibrium. Thus, two energy equations are used for each phase. The critical values of the DarcyRayleigh and wave numbers for theonset of convectionare obtained by considering ten terms in the Galerkin solution. The effect of the five parameters of the model, namely the Darcy number, Da, the modified ratio of thermal conductivity ?, theLewis number Le, theseparation ratio coefficient, ?, and the inter-phase heat transfer coefficient, H, on the stability of the system is discussed in detail and presented with the aid of plots and tables. The onset of convection in a binary fluid-saturated porous medium is delayed for realistic boundary conditions compared with ideal boundary conditions (stress-free, isothermal boundary conditions). Increasing the values of theDarcy number, inter-phase heat transfer coefficient, and the separation ratio coefficient stabilizes DBBC. In contrast, the thermal conductivity ratioand Lewis number aredestabilize the system. Furthermore, convective cell size remains unaltered with increasing ?. Convection is delayed in thepure fluid medium compared to thebinary fluid medium. Local thermal non-equilibrium ceases for small and large inter-phase heat transfer coefficient values. The Author(s), under exclusive licence to Springer Nature B.V. 2025. -
Brinkman-Bard convection in a rotating-binary liquid saturated porous medium
The primary intent of the work is to investigate the linear and weakly non-linear stability analyses of natural convection in a rotating binary liquidsaturated porous medium. In the mathematical model, Newtonian binary liquid-saturated porous medium with uniform rotation subjected to stress-free isothermal boundaries and the validity of OseenBoussinesq approximation is considered in the study. Normal mode analysis is operated to acquire the DarcyRayleigh number expression in terms of the other parameters. The amount of heat and mass transfer rates are approximated at the lower boundary by performing weakly non-linear stability analysis using truncated Fourier series solution. The analysis of critical Rayleigh number, critical wave number, heat, and mass transfer is done for different values of parameters and discussed in detail with the help of plots and tables. Lewis number stabilizes the convective system, whereas increasing in the separation ratio coefficient destabilizes the convective system. Weakly nonlinear stability analysis reveals that the binary liquids with a smaller separation ratio coefficient transport the maximum heat and minimum mass compared to binary liquids with large separation ratio coefficient values. The amount of heat transport is enhanced by 14% with increase in the values of Ta whereas the same is diminished by 3.5 % and 5% respectively for the ? and Le. Thus, the effect of rotations pronounced on the onset of convection, heat and mass transports predominantly compared to the effect of binary mixtures parameters. The results of the classical RayleighBard convection and natural convection in a liquid-saturated porous medium with local thermal-equilibrium assumption can be obtained as a particular case of the study by setting the appropriate limits. 2025 Elsevier Ltd -
FEDGE: FEDerated learning at the EDGE on space platforms using deep neural network architectures
We introduce FEDGE: FEDerated Learning at the EDGE, a framework designed for efficient AI deployment in resource-constrained satellite constellations. FEDGE integrates federated learning with edge computing to address communication overhead and latency challenges in distributed space environments. The framework features a novel edge-enhanced ground station protocol that dynamically schedules model aggregation based on satellite-provided metadata, combined with local stochastic gradient descent training at satellite edge devices and gradient compression via quantization. Experimental validation on MNIST and EuroSAT datasets demonstrates the practical viability of the approach. On MNIST, FEDGE achieved 94.33% training accuracy with 0.21 loss and 90.05% test accuracy with 0.24 loss. On EuroSAT, the framework reached 93.47% training accuracy with 0.18 loss and 91.51% test accuracy with 0.21 loss. Gradient quantization reduces data exchange by up to 14 with approximately 4% impact on test loss. These results validate FEDGE as a communication-efficient solution for decentralized AI deployment in satellite systems, enabling autonomous spacecraft intelligence and addressing the unique constraints of space-based computing platforms. The Author(s) 2025. -
Cinema and the non-violence versus violence discourse: a review of the film RRR
[No abstract available] -
Making the body public: Implications of the new standards of body-image
[No abstract available] -
A Cryptocurrency Price Prediction Study Using Deep Learning and Machine Learning
A cryptocurrency is a network-based computerized exchange that makes imitation and double-spending pretty much impossible. Many cryptocurrencies are built on distributed networks based on blockchain technology, which is a distributed ledger enforced by a network of computers. Thanks to blockchain technology, transactions are secure, transparent, traceable, and immutable. As a result of these traits, cryptocurrency has increased in popularity, especially in the financial industry. This research looks at a few of the most popular and successful deep learning algorithms for predicting bitcoin prices. LSTM and Random Forest outperform our generalized regression neural architecture benchmarking system in terms of prediction. Bitcoin and Ethereum are the only cryptocurrencies supported. The approach can be used to calculate the value of a number of different cryptocurrencies. 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. -
Nickel oxide modified with sodium alginate and dopamine nanoparticles for enhanced antimicrobial, antioxidant, and anticancer activity against HepG2 cells
Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality worldwide, while multidrug-resistant bacterial infections pose escalating health threats. To address these challenges, nickel oxide nanoparticles (NiO Nanoparticles) and sodium alginatedopamineNiO-SA-Dop nanoparticles (NiO-SA-Dop Nanoparticles) were synthesized and extensively characterized for multifunctional biomedical applications. X-ray diffraction revealed crystallite sizes of 40.6nm (NiO) and 29.76nm (NiO-SA-Dop). Transmission electron microscope analysis confirmed spherical morphology with reduced particle size upon modification, supporting improved surface properties. UVvisible spectroscopy showed band gap energies of 4.15eV (NiO) and 4.44eV (NiO-SA-Dop). Photoluminescence spectra indicated enhanced green emission in NiO-SA-Dop, suggesting a higher concentration of oxygen vacancies Linked to increased reactive oxygen species Generation. In functional assays, NiO-SA-Dop demonstrated superior free radical scavenging efficiency in the 2,2-diphenyl-1-picrylhydrazyl assay compared to NiO. Strong antibacterial activity was observed against Gram-negative pathogens including Pseudomonas aeruginosa, Klebsiella pneumoniae, Vibrio cholerae, Escherichia coli, and Shigella dysenteriae. Cytotoxicity assays against HepG2 cells yielded IC?? values of 11.9g/mL for NiO and 10.3g/mL for NiO-SA-Dop, underscoring the enhanced anticancer efficacy of the modified nanoparticles. Overall, NiO-SA-Dop Nanoparticles exhibit promising antibacterial, antioxidant, and anticancer activities, making them strong candidates for advanced therapeutic development. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025. -
Rayleigh-Bard Convection of Water-Copper and Water-Alumina Nanofluids Based on Minimal- and Higher-Mode Lorenz Models
Linear and nonlinear stability analyses of Rayleigh-Bard convection in water-copper and water-alumina nanofluids are studied in the paper by considering a minimal as well as an extended truncated Fourier representation. These representations respectively result in a third-order classical Lorenz model and a five-dimensional extended Lorenz model. The marginal stability plots reveal that the influence of added dilute concentration of nanoparticles in water is to destabilize the system. The rate of destabilization depends on the nanoparticles' thermophysical properties and their volume fraction. Influence of adding an additional mode in the horizontal direction is to modify the cell size. This can be observed through the marginal curves as well as the stream line plots. Further, from the Nusselt number plots it is evident that the presence of dilute concentration of nanoparticles in water is to enhance heat transport in the system significantly. The dynamical behavior of the minimal and the extended Lorenz models is investigated using the bifurcation diagram. From the study an important finding that emerges is that the Fourier truncated solution is predicted to have different effects in lower-order and higher-order models. The extended penta-modal Lorenz system predicts advanced onset of chaos compared to that predicted by the classical third-order Lorenz model. The individual influence of both nanoparticles in water is to advance the onset of convection as well as to advance the onset of chaos. 2023 World Scientific Publishing Company. -
A study of Darcy-Bard regular and chaotic convection using a new local thermal non-equilibrium formulation
The onset of Darcy-Bard regular and chaotic convection in a porous medium is studied by considering phase-lag effects that naturally arise in the thermal non-equilibrium heat transfer problem between the fluid and solid phases. A new type of heat equation is derived for both the phases. Using a double Fourier series and a novel decomposition, an extended Vadasz-Lorenz model with three phase-lag effects is derived. New parameters arise due to the phase-lag effects between local acceleration, convective acceleration, and thermal diffusion. The principle of exchange of stabilities is found to be valid and the subcritical instability is discounted. The new perspective supports the finding of an analytical expression for the critical Darcy-Rayleigh numbers representing, respectively, the onset of regular and chaotic convection. The understanding of the transition from the local thermal non-equilibrium situation to the local thermal equilibrium one is also best explained through the new perspective. In its present elegant form, the extended Vadasz-Lorenz system with three phase-lag effects is analyzed using the largest Lyapunov exponent and the bifurcation diagram. It is found that the lag effects not only give rise to a quantitative difference in the above two metrics concerning chaos, but also present a qualitative difference as well in the form of the very nature of chaos. 2021 Author(s). -
Influence of symmetric/asymmetric boundaries on axisymmetric convection in a cylindrical enclosure in the presence of a weak vertical throughflow
The linear and nonlinear stability of axisymmetric convection of a viscous fluid in a cylindrical enclosure heated from below is investigated for various radius to height ratios. A weak vertical throughflow is imposed in a gravity-aligned or a gravity-opposing manner. Symmetric and asymmetric boundaries of free-free, rigid-rigid and rigid-free types are considered for lower and upper boundaries with isothermal temperature boundary condition. The side-walls are assumed to be rigid and adiabatic. A convergent Maclaurin series representation is considered for the finding of axial trial eigenfunctions. In order to corroborate the results of the present study with those of a previous investigation, the critical Rayleigh number and the number of radial rolls manifesting for any given aspect ratio are determined in the case of no throughflow and an exact match is found. Further, the influence of boundaries and the effect of throughflow on chaotic and periodic regimes of motion are studied with the help of a time series solution and the largest Lyapunov exponent as indicators of chaos. The novelty of the present study is the use of a Maclaurin series representation for the eigenfunctions of the linear problem and using the same in determining the solution with the convective mode. 2023 Elsevier B.V. -
A Unified Approach to Two-Dimensional Brinkman-Bard Convection of Newtonian Liquids in Cylindrical and Rectangular Enclosures
A unified model for the analysis of two-dimensional BrinkmanBard/RayleighBard/ DarcyBard convection in cylindrical and rectangular enclosures ((Formula presented.)) saturated by a Newtonian liquid is presented by adopting the local thermal non-equilibrium ((Formula presented.)) model for the heat transfer between fluid and solid phases. The actual thermophysical properties of water and porous media are used. The range of permissible values for all the parameters is calculated and used in the analysis. The result of the local thermal equilibrium ((Formula presented.)) model is obtained as a particular case of the (Formula presented.) model through the use of asymptotic analyses. The critical value of the Rayleigh number at which the entropy generates in the system is reported in the study. The analytical expression for the number of Bard cells formed in the system at the onset of convection as a function of the aspect ratio, (Formula presented.), and parameters appearing in the problem is obtained. For a given value of (Formula presented.) it was found that in comparison with the case of (Formula presented.), more number of cells manifest in the case of (Formula presented.). Likewise, smaller cells form in the (Formula presented.) problem when compared with the corresponding problem of (Formula presented.). In the case of (Formula presented.), fewer cells form when compared to that in the case of (Formula presented.) and (Formula presented.). The above findings are true in both (Formula presented.) and (Formula presented.). In other words, the presence of a porous medium results in the production of less entropy in the system, or a more significant number of cells represents the case of less entropy production in the system. For small and finite (Formula presented.), the appearance of the first cell differs in the (Formula presented.) and (Formula presented.) problems. 2023 by the authors. -
Effect of homogeneous chemical reaction on the dispersion of a solute in a threedimensional flow of a Newtonian liquid through a porous medium
All-Time dispersion of a reactive solute in a Newtonian fluid flow through a Darcy-Brinkman-Forchheimer Porous medium is carried out using the approach of Gill - Sankarasubramanian (1970) and Doshi etal. (1978). The velocity profile of the non - linear porous medium flow equation is solved using the Maclaurin series of two variables. The three - dimensional model brings into the focus the convective and dispersion coefficients. The chemical reaction is assumed to be homogeneous. The chemical reaction is shown to increase the value of the convective coefficient while it decreases with increase in the value of the reaction rate parameter. The effect of the presence of the porous medium is to decrease the flow and hence the convective coefficient. Similar effect of the porous parameter is seen on the dispersion coefficient. The reaction rate parameter and the porous parameter have opposite effect on the mean concentration distribution. 2023 Taylor & Francis Group, LLC. -
A New Series Solution Applicable to a Class of Boundary Layer Equations with Exponential Decay in Solution
A new series solution for the coupled nonlinear boundary value problem (BVP) of the FalknerSkan-type, resulting from the use of the boundary layer approximation to a mixed convective flow is obtained. The solution domain is transformed from the semi-infinite interval of physical interest to the unit interval by using the transformation z= 1 - e-?. The coupled nonlinear BVP is converted into an equivalent initial value problem (IVP) by supplying appropriate initial conditions. Series solution of the equivalent IVP is obtained in powers of 1 - e-? with assistance from the NewtonRaphson method. Convergence of the series is assured by the very design of the series as confirmed by the DombSykes plots and the plots of partial sums. The results of the series solution compare well with the numerical results obtained by the shooting method based on the RungeKuttaFehlberg45 and NewtonRaphson methods. The novelty of the methodology lies in the construction of a new series solution for a class of problems with exponential decay in their solution. Such a work has not been reported before. 2020, Springer Nature India Private Limited. -
BrinkmanBard Convection with Rough Boundaries and Third-Type Thermal Boundary Conditions
The BrinkmanBard convection problem is chosen for investigation, along with very general boundary conditions. Using the Maclaurin series, in this paper, we show that it is possible to perform a relatively exact linear stability analysis, as well as a weakly nonlinear stability analysis, as normally performed in the case of a classical free isothermal/free isothermal boundary combination. Starting from a classical linear stability analysis, we ultimately study the chaos in such systems, all conducted with great accuracy. The principle of exchange of stabilities is proven, and the critical Rayleigh number, (Formula presented.), and the wave number, (Formula presented.), are obtained in closed form. An asymptotic analysis is performed, to obtain (Formula presented.) for the case of adiabatic boundaries, for which (Formula presented.). A seemingly minimal representation yields a generalized Lorenz model for the general boundary condition used. The symmetry in the three Lorenz equations, their dissipative nature, energy-conserving nature, and bounded solution are observed for the considered general boundary condition. Thus, one may infer that, to obtain the results of various related problems, they can be handled in an integrated manner, and results can be obtained with great accuracy. The effect of increasing the values of the Biot numbers and/or slip Darcy numbers is to increase, not only the value of the critical Rayleigh number, but also the critical wave number. Extreme values of zero and infinity, when assigned to the Biot number, yield the results of an adiabatic and an isothermal boundary, respectively. Likewise, these extreme values assigned to the slip Darcy number yield the effects of free and rigid boundary conditions, respectively. Intermediate values of the Biot and slip Darcy numbers bridge the gap between the extreme cases. The effects of the Biot and slip Darcy numbers on the HopfRayleigh number are, however, opposite to each other. In view of the known analogy between Bard convection and TaylorCouette flow in the linear regime, it is imperative that the results of the latter problem, viz., BrinkmanTaylorCouette flow, become as well known. 2023 by the authors.