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Item 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, CThe 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.Item 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, HThe 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.Item Penetrative Marangoni Convection in Superposed Fluid and Porous Layers with Deformable Free Surface(2014-04-04T07:44:58Z) Gangadharaiah, Y. HThe 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.Item 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, BMtA 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.Item 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.PThe 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.Item 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.PThe 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.Item gs closed and open functions in Topological space(2013-07-12T12:17:50Z) Missier, Pious, S.; Vijilius, Helena RajIn 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.Item gsΛ Continuous Function in Topological Space(2013-07-12T11:58:32Z) Missier, Pious, S.; Vijilius, Helena Raj