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Effect of non-uniform basic temperature gradients on Marangoni convection with a boundary slab of finite conductivity
(2011-07-12T08:55:02Z) Shivakumara, I. S; Suma, S. P; Gangadharaiah, Y. H
The linear stability analysis of Marangoni convection in a fluid layer with a boundary slab of finite conductivity is considered. The effects of various non uniform temperature gradients are investigated. The lower boundary is a considered to be a thin slab of finite conductivity instead of a regular rigid surface. At the contact surface between the thin slab and the fluid layer the thermal boundary conditions are used and the upper surface is considered to be free and insulating to temperature perturbation and also surface tension effects are allowed. The resulting eigen value problem is solved exactly. The critical values of the Marangoni numbers for the onset of Marangoni convection are calculated for different temperature profile and the latter is found to be critically dependent on the depth ratio and conductivity ratio. The effects of the thermal conductivity and the thickness of the solid plate on the onset of convective instability with different temperature profile are studied in detail.
Marangoni convection in a fluid layer overlying a layer of an anisotropic porous layer with deformable free surface
(2011-11-08T11:08:34Z) Suma, S. P; Gangadharaiah, Y. H; Indira, R
The linear stability analysis of Marangoni convection in a composite system comprised of an incompressible fluid-saturated anisotropic porous layer underlying a layer of same fluid is considered. The upper fluid surface, free to atmosphere is considered to be deformable and subjected to temperature-dependent surface tension. The fluid flow in the porous layer is governed by the Darcy equation and Beavers-Joseph condition is employed at the interface between the two layers. The resulting eigen value problem is solved exactly. It is found that the Crispation number, Bond number, depth of the relative layers, mechanical and thermal anisotropy parameters have a profound effect on the stability of the system. Decreasing the Crispation number and mechanical anisotropy parameter and increasing the Bond number and thermal anisotropy parameter leads to stabilization of the system. Also, the effect of the ratio of the fluid to porous layer thickness along with the other various physical parameters on the control of convection is analyzed in detail.
Effect of throughflow and variable gravity field on thermal convection in a porous layer
(2011-11-08T11:12:42Z) Suma, S. P; Gangadharaiah, Y. H; Indira, R
The problem deals with the criterion for the onset of Rayleigh-Benard convection with a throughflow and variable gravity field in a porous layer. Both boundaries are considered to be insulating to temperature perturbations. Flow in the porous layer is governed by Darcy-Forchheimer equation. The resulting eigen value is solved using regular perturbation technique with wave number ‘ a ’ as a perturbation parameter. The Prandtl number arising due to throughflow and variable gravity parameter plays a crucial role in determining the stability. It is found that to stabilize or destabilise the system depends on types of boundary conditions, direction of throughflow and variable gravity field are discussed in details.
Exact analysis of Effect of Non-uniform Temperature Gradient on Marangoni Convection with Free Slip Condition
(2012-01-25T07:20:46Z) Suma, S.P.; Gangadharaiah, Y.H.
The effect of non-uniform basic temperature gradient on the onset of Marangoni convection in a horizontal layer with a free-slip bottom heated from below and cooled from above is considered. A linear stability analysis is performed to undertake a detail investigation. The eigenvalues are obtained for lower rigid isothermal and upper free adiabatic boundaries. The resulting eigenvalue problem is solved exactly and single-term Galerkin expansion procedure. The influence of various parameters on the onset of convection has been analyzed. Three non-uniform basic temperature profiles are considered and the results obtained from both the methods are compared and are found to be in good agreement. Some general conclusions about their destabilizing effects are presented.
g*Λ Closed Sets in Topological Space
(2012-01-25T07:44:02Z) Missier, S. Pious; Raj, Vijilius Helena
The generalized closed sets in point set topology have been found considerable interest among general topologists. In this paper, we introduce and study topological properties of g*Λ closed and open sets and its relationships with other generalized closed sets are investigated.
Effect of Internal Heat Generation on the Onset of Marangoni Convection in a Fluid Layer Overlying a Layer of an Anisotropic Porous Medium
(2012-01-25T07:56:38Z) Shivakumara, I. S.; Suma, S. P.; Indira, R.; Gangadharaiah, Y. H.
Linear stability analysis has been performed to investigate the effect of internal heat generation on the criterion for the onset of Marangoni convection in a two-layer system comprising an incompressible fluid-saturated anisotropic porous layer over which lies a layer of the same fluid. The upper non-deformable free surface and the lower rigid surface are assumed to be insulated to temperature perturbations. The fluid flow in the porous layer is governed by the modified Darcy equation and the Beavers–Joseph empirical slip condition is employed at the interface between the two layers. The resulting eigenvalue problem is solved exactly. Besides, analytical expression for the critical Marangoni number is also obtained by using regular perturbation technique with wave number as a perturbation parameter. The effect of internal heating in the porous layer alone exhibits more stabilizing effect on the system compared to its presence in both fluid and porous layers and the system is least stable if the internal heating is in fluid layer alone. It is found that an increase in the value ofmechanical anisotropy parameter is to hasten the onset of Marangoni convection while an opposite trend is noticed with increasing thermal anisotropy parameter. Besides, the possibilities of controlling (suppress or augment) Marangoni convection is discussed in detail.
Throughflow Effects on Penetrative Convection in Superposed Fluid and Porous Layers
(2012-07-03T08:17:14Z) Suma, S. P.; Gangadharaiah, Y. H.; Indira, R.; Shivakumara, I. S.
The effect of vertical throughflow on the onset of penetrative convection simulated via internal heating in a two-layer system in which a layer of fluid overlies and saturates a layer of porous medium is studied. Flow in the porous medium is governed by Forchheimer-extended Darcy equation, and Beavers–Joseph slip condition is applied at the interface between the fluid and the porous layers. The boundaries are considered to be rigid, however permeable, and insulated to temperature perturbations. The eigenvalue problem is solved using a regular perturbation technique with wave number as a perturbation parameter. The ratio of fluid layer thickness to porous layer thickness, ζ , the direction of throughflow, and the presence of volumetric internal heat source in fluid and/or porous layer play a decisive role on the stability characteristics of the system. In addition, the influence of Prandtl number arising due to throughflow is also emphasized on the stability of the system. It is observed that both stabilizing and destabilizing factors can be enhanced because of the simultaneous presence of a volumetric heat source and vertical throughflow so that a more precise control (suppress or augment) of thermal convective instability in a layer of fluid or porous medium is possible.
Variable Gravity Field and Throughflow Effects on Penetrative Convection in a Porous Layer
(2013-05-15T11:29:07Z) Gangadharaiah, Y. H; Suma, S.P; Ananda, K
Variable Viscosity Effects on Penetrative Convection in a Fluid Layer
(2013-05-15T11:31:23Z) Gangadharaiah, Y. H; Suma, S.P
Bernard-Marangoni Penetrative Convection In A Fluid Layer With Variable Viscosity
(2013-05-15T11:33:56Z) Gangadharaiah, Y. H
In the present study, onset of stationary Benard-Marangoni convective instability in a fluid layer, with internal heating and thermally dependent viscosity has been investigated by means of linear stability analysis. The upper surface of a fluid layer is assumed to be deformably free and dependence of viscosity is assumed to be exponential. The resulting eigen value problem is solved using a regular perturbation technique with wave number a as a perturbation parameter. The viscosity parameter, surface deformation and the presence of internal heat source play a decisive role on the stability characteristics of the system. It is observed that both stabilizing and destabilizing factors can be enhanced because of the simultaneous presence of a volumetric heat source and variable viscosity so that a more precise control (suppress or augment) of Benard-Marangoni convective instability in a fluid layer is possible.
gsΛ Continuous Function in Topological Space
(2013-07-12T11:58:32Z) Missier, Pious, S.; Vijilius, Helena Raj
gs closed and open functions in Topological space
(2013-07-12T12:17:50Z) Missier, Pious, S.; Vijilius, Helena Raj
In this paper we introduce the different notions of a new class of closed and open maps called generalised semi Lambda(gs ) closed and generalised semi Lambda(gs ) open maps in topological spaces, which turns out to be weaker forms of closed and open maps. We also introduce a map called M.gs closed and M.gs open maps.
Effect of Internal Heat Generation on the Onset of Darcy–Benard Convection in Porous Media
(2013-07-12T12:20:30Z) Gangadharaiah, Y H; Suma, S.P
The onset of Darcy–Benard penetrative convection in a liquid saturated porous layer of high permeability of practical importance is investigated by employing the Brinkman–Forchheimer–Lapwood extended Darcy flow model with fluid viscosity different from effective viscosity. The lower boundary is taken to be rigid and isothermal and the upper surface is free and subject to the general thermal condition. The critical eigen values are obtained numerically, in general, using Galerkin method. The stability of the system is found to be dependent on the dimensionless internal heat source strength Ns, permeability parameter and the ratio of effective viscosity to fluid viscosity. It is observed that the increase in the value of permeability parameter is to delay while increase in the value of internal heat source strength is to hasten the onset of convection in a fluid saturated porous layer.
Bernard-Marangoni Convection in a Fluid Layer Overlying a Layer of an Anisotropic Porous Layer with Deformable Free Surface
(2013-08-06T06:52:23Z) Gangadharaiah, Y. H.; Suma, S.P
The linear stability of Bernard-Marangoni convection in a two-layer system consisting of a fluid layer overlying a porous layer with anisotropic permeability and thermal diffusivity is studied. The upper fluid surface, free to atmosphere is considered to be deformable. Flow in the porous medium is assumed to be governed by Darcy’s law; the Beavers-Joseph condition is applied at the interface between the two layers. The boundaries are considered to be rigid, however permeable, and insulated to temperature perturbations. The eigen value problem is solved using a regular perturbation technique with wave number a as perturbation parameter. It is found that the Crispation number, Bond number, depth of the relative layers, mechanical and thermal anisotropy parameters have a profound effect on the stability of the system. Decreasing the Crispation number and mechanical anisotropy parameter and increasing the Bond number and thermal anisotropy parameter leads to stabilization of the system. Also, the effect of the ratio of the fluid to porous layer thickness along with the other various physical parameters on the control of convection is analysed in detail.
Low temperature synthesis and photoluminescence properties of redemitting Mg2SiO4:Eu3+nanophosphor for near UV light emittingdiodes
(2014-03-13T10:17:32Z) Ramachandra, Naika; Prashantha, SC; Nagabhushana, H; Sharma, SC; Nagabhushana, BM
tA simple and low-cost solution combustion method was used to prepare Eu3+(1–11 mol%) doped Mg2SiO4nanophosphors at 350◦C using metal nitrates as precursors and ODH (Oxali di-hydrazide) as fuel. Thefinal products were well characterized by powder X-ray diffraction (PXRD), fourier transform infraredspectroscopy (FTIR), scanning electron microscopy (SEM) and UV–visible absorption (UV–Vis). The PXRDpatterns of the as-formed products show single orthorhombic phase. The crystallite size was estimatedusing Scherrer’s method and found to be in the range 20–25 nm. The effect of Eu3+cations on the lumi-nescence properties of Mg2SiO4:Eu3+nanoparticles were understood from the luminescence studies.The phosphors exhibit bright red emission upon 393 nm excitation. The characteristic emission peaksrecorded at ∼577, 590, 612, 650 and 703 nm (5D0→7FJ=0,1,2,3,4) were attributed to the 4f–4f intra shelltransitions of Eu3+ions. The intensity of red emission was found to be related with the concentration ofintrinsic defects, especially oxygen-vacancies, which could assist the energy transfer from the Mg2SiO4host to the Eu3+ions. The Commission International De I-Eclairage (CIE) chromaticity co-ordinates werecalculated from emission spectra, the values (x,y) were very close to National Television System Commit-tee (NTSC) standard value of red emission. Therefore, the present phosphor was highly useful for displayapplications.
Penetrative Marangoni Convection in Superposed Fluid and Porous Layers with Deformable Free Surface
(2014-04-04T07:44:58Z) Gangadharaiah, Y. H
The linear stability analysis of Marangoni convection in a composite system comprised of an incompressible fluid-saturated porous layer underlying a layer of same fluid is considered. The upper fluid surface, free to atmosphere is considered to be deformable and subjected to temperature-dependent surface tension. The fluid flow in the porous layer is governed by the Forchheimer-extended Darcy equation and Beavers-Joseph condition is employed at the interface between the two layers. The resulting eigen value problem is solved exactly. The ratio of fluid layer thickness to porous layer thickness, ζ, the Crispation number, Bond number and the presence of volumetric internal heat source in fluid and/or porous layer play a decisive role on the stability characteristics of the system. In addition, the effects of boundary conditions and along with the other various physical parameters on the control of convection is analyzed in detail.
Penetrative convection via internal heating in superposed fluid and anisotropic porous layers with throughflow
(2014-04-04T07:49:39Z) Gangadharaiah, Y. H; Suma, S.P; Nagarathnamma, H
The onset of thermal convection due to heating from below in a system consisting of a fluid layer overlying a porous layer with anisotropic permeability and thermal diffusivity is studied. The onset of penetrative convection simulated via internal heating in the presence of a vertical throughflow. Flow in the porous medium is governed by Forchheimer-extended Darcy equation and the Beavers–Joseph slip condition is applied at the interface between the fluid and the porous layers. The boundaries are considered to be rigid, however permeable, and insulated to temperature perturbations. The eigen value problem is solved using a regular perturbation technique with wave number as a perturbation parameter. It is found that the depth of the relative layers, the direction of throughflow, the presence of volumetric internal heat source in fluid and/or porous layer and mechanical and thermal anisotropy parameters have a profound effect on the stability of the system. Decreasing the mechanical anisotropy parameter and increasing the thermal anisotropy parameter leads to stabilization of the system. Besides, the possibility of control of thermal convection by suitable choice of physical parameters is discussed in detail.
Structural, Dielectric, and Magnetic Studies on Electrospun Magnesium Ferrite-Polyvinylidene Fluoride Core–Shell Composite Fibers
(2014-07-08T06:32:38Z) Revathi, V; Dinesh Kumar, S; Chithra Lekha, P; Subramanian, V; Natarajan, T. S; Muthamizhchelvan, C
The sub-micron (of the order of 150 nm) thick core–shell composite fibers of magnesium ferrite-polyvinylidene fluoride are prepared by electrospinning. The loading of magnesium ferrite is varied from 1 to 10 wt%. The study results by X-ray diffraction, scanning electron microscope, and infra-red spectroscopy indicate the formation of core–shell structure and an enhancement in the amount of b-phase compared to a-phase in the polyvinylidene fluoride. The particle size of the magnesium ferrite in the fiber is evaluated to be 30 nm. The low frequency dielectric studies indicate that the addition of the magnesium ferrite increases the polarization resulting in the increase in the dielectric constant but decreases the dielectric loss. The magnetization measurements indicate an increased value of coercivity compared to bulk due to the nano-size of the magnesium ferrite. The microwave absorption at the ferromagnetic resonance increases with the increase in the concentration of magnesium ferrite. The resonance field is found to vary with the loading of MFO.
Mg2SiO4:Tb3+ nanophosphor: Auto ignition route and near UV excited photoluminescence properties for WLEDs
(2014-09-12T07:56:06Z) Ramachandra, Naik; Prashantha, S C; Nagabhushana, H; Nagaswarupa, H P
For the first time nanoparticles of Tb3+ doped (1–11 mol%) Mg2SiO4 have been prepared using low temperature (350 C) solution combustion technique with magnesium nitrate as precursor and oxalyl di-hydrazide (ODH) as fuel. The Powder X-ray diffraction (PXRD) patterns of the sample revealed orthorhombic structure with a-phase. The average crystallite size using Scherer’s formula, W–H plot and Size– strain plot is found to be 28 nm and the same is confirmed by Transmission electron microscopy (TEM) studies. Scanning electron microscopy (SEM) pictures show a porous structure and the crystallites were agglomerated. The effect of Tb3+ cations on luminescence characteristics of Mg2SiO4 is studied and the results are discussed in detail. The phosphors exhibit bright green emission upon near ultra violet (NUV) 377 nm excitation. The characteristic photoluminescence emission peaks at 417, 436, 458 nm in blue region due to 5D3?7FJ (J = 5, 4, 3) of Tb3+ ions and the emission peaks at 486, 541, 584 and 621 nm in green region corresponds to 5D4?7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions owing to f–f transitions of Tb3+ cations in the given host lattice and are due to dipole–quadropole interactions. The CIE chromaticity co-ordinates are calculated from emission spectra and falls in green region. Therefore the present phosphor is highly useful for mercury free solid state lighting (SSL) and also for display applications.
A single phase, red emissive Mg2SiO4:Sm3+ nanophosphor prepared via rapid propellant combustion route
(2015-05-05T07:14:12Z) Ramachandra, Naik; Prashantha, S C; Nagabhushana, H
Mg2SiO4:Sm3+ (1–11 mol%) nanoparticles were prepared by a rapid low temperature solution combustion route. The powder X-ray diffraction (PXRD) patterns exhibit orthorhombic structure with a-phase. The average crystallite size estimated using Scherer’s method, W–H plot and strain–size plots were found to be in the range 25–50 nm and the same was confirmed by Transmission Electron Microscopy (TEM). Scanning electron microscopy (SEM) pictures show porous structure and crystallites were agglomerated. The effect of Sm3+ cations on luminescence of Mg2SiO4 was well studied. Interestingly the samples could be effectively excited with 315 nm and emitted light in the red region, which was suitable for the demands of high efficiency WLEDs. The emission spectra consists of four main peaks which can be assigned to the intra 4-f orbital transitions of Sm3+ ions 4G5/2?6H5/2 (576 nm), 4G5/2?6H7/2(611 nm), 4G5/2?6H9/2 (656 nm) and 4G5/2?6H11/2 (713 nm). The optimal luminescence intensity was obtained for 5 mol% Sm3+ ions. The CIE (Commission International de I’Eclairage) chromaticity co-ordinateswere calculated from emission spectra, the values (0.588, 0.386) were close to the NTSC (NationalTelevision Standard Committee) standard value of red emission. Coordinated color temperature (CCT)was found to be 1756 K. Therefore optimized Mg2SiO4:Sm3+ (5 mol%) phosphor was quite useful for solid state lighting.

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