Local thermal non-equilibrium effects on thermal convection in a rotating anisotropic porous layer

Effects of local thermal non-equilibrium (LTNE) on thermal convection in a rotating fluid-saturated anisotropic porous layer are investigated. The analysis has been carried out by constructing a simplified model consisting of six coupled nonlinear ordinary differential equations. The study reveals the equivalence of linear and nonlinear stability boundaries indicating the linearized instability theory captures completely the physics of the onset of convection. Results show that the presence of rotation is to introduce oscillatory convection once the Taylor number exceeds a threshold value. The preferred mode of instability is found to be influenced significantly by the mechanical anisotropy parameter as well and it is demonstrated that it has both stabilizing and destabilizing effects on the steady onset in the presence of rotation. Besides, asymptotic analyses for small and large values of the interphase heat transfer coefficient are presented. Heat transport is calculated in terms of Nusselt number. Also, the coupled nonlinear ordinary differential equations are solved numerically using Runge-Kutta method and the transient behavior of Nusselt number is demonstrated for various values of physical parameters. © 2015 Elsevier Inc

Effect of Thermal Non-Equilibrium on Convective Instability in a Ferromagnetic Fluid-Saturated Porous Medium

The effect of local thermal non-equilibrium (LTNE) on the onset of thermomagnetic convection in a ferromagnetic fluid-saturated horizontal porous layer in the presence of a uniform vertical magnetic field is investigated. A modified Forchheimer-extended Darcy equation is employed to describe the flow in the porous medium, and a two-field model is used for temperature representing the solid and fluid phases separately. It is found that both the critical Darcy–Rayleigh number and the corresponding wave number are modified by the LTNE effects. Asymptotic solutions for both small and large values of scaled interphase heat transfer coefficient Ht are presented and compared with those computed numerically. An excellent agreement is obtained between the asymptotic and the numerical results. Besides, the influence of magnetic parameters on the instability of the system is also discussed. The available results in the literature are recovered as particular cases from the present study

Linear and weakly nonlinear magnetoconvection in a porous medium with a thermal nonequilibrium model

Two-dimensional magnetoconvection in a layer of Brinkman porous medium with local thermal nonequilibrium (LTNE) model is investigated by performing both linear and weakly nonlinear stability analyses. Condition for the occurrence of stationary and oscillatory convection is obtained in the case of linear stability analysis. It is observed that the presence of magnetic field is to introduce oscillatory convection once the Chandrasekhar number exceeds a threshold value if the ratio of the magnetic diffusivity to the thermal diffusivity is sufficiently small. Besides, asymptotic solutions for both small and large values of the inter-phase heat transfer coefficient are presented for the steady case. A weakly nonlinear stability analysis is performed by constructing a system of nonlinear autonomous ordinary differential equations. It is observed that subcritical steady convection is possible for certain choices of physical parameters. Heat transport is calculated in terms of Nusselt number. Increasing the value of Chandrasekhar number, inter-phase heat transfer coefficient and the inverse Darcy number is to decrease the heat transport, while increasing the ratio of the magnetic diffusivity to the thermal diffusivity and the porosity modified conductivity ratio shows an opposite kind of behavior on the heat transfer

Ferromagnetic Convection in a Heterogeneous Darcy Porous Medium Using a Local Thermal Non-equilibrium (LTNE) Model

The combined effects of vertical heterogeneity of permeability and local thermal non-equilibrium (LTNE) on the onset of ferromagnetic convection in a ferrofluid saturated Darcy porous medium in the presence of a uniform vertical magnetic field are investigated. A two-field model for temperature representing the solid and fluid phases separately is used. The eigenvalue problem is solved numerically using the Galerkin method for different forms of permeability heterogeneity function Γ(z) and their effect on the stability characteristics of the system has been analyzed in detail. It is observed that the general quadratic variation of Γ(z) with depth has more destabilizing effect on the system when compared to the homogeneous porous medium case. Besides, the influence of LTNE and magnetic parameters on the criterion for the onset of ferromagnetic convection is also assessed

A thermal non-equilibrium model with Cattaneo effect for convection in a Brinkman porous layer

This paper aims to investigate the onset of thermal convection in a layer of fluid-saturated Brinkman porous medium taking into account fluid inertia and local thermal non-equilibrium (LTNE) between the solid and fluid phases with Cattaneo effect in the solid. A two-field model is used for the energy equations each representing the solid and fluid phases separately. The usual Fourier heat-transfer law is retained in the fluid phase while the solid phase is allowed to transfer heat via a Cattaneo heat flux theory. It is observed that the Cattaneo effect has a profound influence on the nature of convective instability. In contrast to the standard Brinkman convection with LTNE model, instability is found to occur through oscillatory convection depending on the value of solid thermal relaxation time parameter which in turn depends on other parametric values. The instability characteristics of the system are analyzed in detail for a wide range of parametric values including those for copper oxide and aluminium oxide solid skeletons.postprin

Effect of Rotation on Ferromagnetic Porous Convection with a Thermal Non-Equilibrium Model

The effect of rotation on the onset of thermal convection in a horizontal layer of ferrofluid saturated Brinkman porous medium is investigated in the presence of a uniform vertical magnetic field using a local thermal non-equilibrium (LTNE) model. A two-field model for temperature representing the solid and fluid phases separately is used for energy equation. The condition for the occurrence of stationary and oscillatory convection is obtained analytically. The stability of the system has been analyzed when the magnetic and buoyancy forces are acting together as well as in isolation and the similarities as well as differences between the two are highlighted. In contrast to the non-rotating case, it is shown that decrease in the Darcy number Da and an increase in the ratio of effective viscosity to fluid viscosity Λ is to hasten the onset of stationary convection at high rotation rates and a coupling between these two parameters is identified in destabilizing the system. Asymptotic solutions for both small and large values of scaled interphase heat transfer coefficient H t are presented and compared with those computed numerically. Besides, the influence of magnetic parameters and also parameters representing LTNE on the stability of the system is discussed and the veracity of LTNE model over the LTE model is also analyzed

Ferromagnetic convection in a rotating ferrofluid saturated porous layer

The effect of Coriolis force on the onset of ferromagnetic convection in a rotating horizontal ferrofluid satd. porous layer in the presence of a uniform vertical magnetic field is studied. The boundaries are considered to be either stress free or rigid. The modified Brinkman-​Forchheimer-​extended Darcy equation with fluid viscosity different from effective viscosity is used to characterize the fluid motion. The condition for the occurrence of direct and Hopf bifurcations is obtained anal. in the case of free boundaries, while for rigid boundaries the eigenvalue problem has been solved numerically using the Galerkin method. Contrary to their stabilizing effect in the absence of rotation, increasing the ratio of viscosities, Λ, and decreasing the Darcy no. Da show a partial destabilizing effect on the onset of stationary ferromagnetic convection in the presence of rotation, and some important observations are made on the stability characteristics of the system. Moreover, the similarities and differences between free-​free and rigid-​rigid boundaries in the presence of buoyancy and magnetic forces together or in isolation are emphasized in triggering the onset of ferromagnetic convection in a rotating ferrofluid satd. porous layer. For smaller Taylor no. domain, the stress-​free boundaries are found to be always more unstable than in the case of rigid boundaries. However, this trend is reversed at higher Taylor no. domain because the stability of the stress-​free case is increased more quickly than the rigid case

A Golgi-localized Hexose Transporter Is Involved in Heterotrimeric G Protein-mediated Early Development in Arabidopsis

Signal transduction involving heterotrimeric G proteins is universal among fungi, animals, and plants. In plants and fungi, the best understood function for the G protein complex is its modulation of cell proliferation and one of several important signals that are known to modulate the rate at which these cells proliferate is d-glucose. Arabidopsis thaliana seedlings lacking the β subunit (AGB1) of the G protein complex have altered cell division in the hypocotyl and are d-glucose hypersensitive. With the aim to discover new elements in G protein signaling, we screened for gain-of-function suppressors of altered cell proliferation during early development in the agb1-2 mutant background. One agb1-2-dependent suppressor, designated sgb1-1D for suppressor of G protein beta1 (agb1-2), restored to wild type the altered cell division in the hypocotyl and sugar hypersensitivity of the agb1-2 mutant. Consistent with AGB1 localization, SGB1 is found at the highest steady-state level in tissues with active cell division, and this level increases in hypocotyls when grown on d-glucose and sucrose. SGB1 is shown here to be a Golgi-localized hexose transporter and acts genetically with AGB1 in early seedling development

Touch induces ATP release in Arabidopsis roots that is modulated by the heterotrimeric G-protein complex

Amongst the many stimuli orienting the growth of plant roots, of critical importance are the touch signals generated as roots explore the mechanically complex soil environment. However, the molecular mechanisms behind these sensory events remain poorly defined. We report an impaired obstacle-avoiding response of roots in Arabidopsis lacking a heterotrimeric G protein. Obstacle avoidance may utilize a touch-induced release of ATP to the extracellular space. While sequential touch stimulation revealed a strong refractory period for ATP release in response to mechanostimulation in wild-type plants, the refractory period in mutants was attenuated, resulting in extracellular ATP accumulation. We propose that ATP acts as an extracellular signal released by mechanostimulation and that the G-protein complex is needed for fine-tuning this response