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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.
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.
BM FO-PVDF elect rospun fiber based t unable met amat erial st ruct ures for elect romagnet ic int erference shielding in microwave frequency region
(2016-01-07T11:17:17Z) Revathi, Venkatachalam; Dinesh Kumar, Sakthivel; Subramanian, Venkatachalam; Chellamuthu, Muthamizhchelvan
Met amat erial st ruct ures are art ificial st ruct ures t hat are useful in controlling t he flow of elect romagnet ic radiat ion. In t his paper, composit e fibers of sub-micron t hickness of barium subst it ut ed magnesium ferrit e (Ba0.2Mg0.8 Fe2O4 ) – polyvinylidene fluoride obt ained by elect rospinning is used as a subst rat e t o design elect romagnet ic int erference shielding st ruct ures. While elect rospinning improves t he ferroelect ric propert ies of t he polyvinylidene fluoride, t he presence of barium magnesium ferrit e modifies t he magnet ic property of t he composit e fiber. T he dielect ric and magnet ic propert ies at microwave frequency measured using microwave cavity pert urbat ion t echnique are used t o design t he reflect ion as well as absorpt ion based t unable met amat erial st ruct ures for elect romagnet ic int erference shielding in microwave frequency region. For one of t he st ruct ures, t he simulat ion indicat es t hat single negat ive met amat erial st ruct ure becomes a double negat ive met amat erial under t he ext ernal magnet ic field.
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.
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.
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.
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.
Facile combustion synthesized orthorhombic GdAlO3:Eu3+ nanophosphors: Structural and photoluminescence properties for WLEDs
(2015-08-13T05:07:28Z) Jisha, P K; Ramachandra, Naik; Prashantha, S.C.; Nagabhushanad, H.; S.C. Sharmae, B.; Premkumarg, H.B; Nagaswarupac, H.P.; Anantharajuc, K.S.; Prasadf, Daruka
Nanoparticles of Eu3+ doped (1–11 mol%) GdAlO3 were prepared using low temperature (350 °C) solution combustion technique with gadalonium nitrate as oxidizer and oxalyl di-hydrazide (ODH) as a fuel. The synthesized samples were calcined at 1000 °C for 3 h and used for Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and UV–visible absorption (UV–vis) characterization techniques. A pure orthorhombic was obtained in calcined samples. The average crystallite sizes were estimated using Scherrer's formula, W–H and size–strain plots and found to be in the range 25–50 nm and the same was confirmed by Transmission electron microscopy (TEM) studies. The phosphors exhibit bright red emission upon 395 nm excitation. The characteristic emission peaks recorded at ~591, 612, 654 and 694 nm (5D0→7Fj=1,2,3,4) were attributed to the 4f–4f intra-shell transitions of Eu3+ ions. The CIE chromaticity co-ordinates were calculated from emission spectra, the values (x, y) were very close to NTSC standard value of red emission. Further, the average CCT value was found to be ~2369 K, as a result the prepared nanophosphor was highly useful for red component of white light emitting devices and also for solid state display applications.
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.
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.
gsΛ Continuous Function in Topological Space
(2013-07-12T11:58:32Z) Missier, Pious, S.; Vijilius, Helena Raj
Judd Ofelt ANALYSIS OF Eu3+ DOPED Mg2S104 NANOPHOSPHORS
(2016-03-01T07:16:53Z) Ramachandra, Naik; Prashantha, S C; Nagabhushana, H; Sharma, S C; Nagaswarupa, HP
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.
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.
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 note on mathematical programming problems
(2016-01-07T11:11:56Z) Rashi, Khubnani; Tarunika, Sharma
A review has been done on the growth and improvement of solution of non linear programming problems under various factors. The mathematical work of Kuhn-Tucker, Fritz John, Mangasarian, Wolfe, Vond, Kanniappan has been traced and compared.
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.
Penetrative Marangoni Convection in Fluid Layer with Soret Effect
(2016-01-07T11:08:13Z) Gangadharaiah, Y. H
The effects of internal heat source and Soret effect under zero gravity in a fluid layer is studied. The bottom boundary of the fluid layer is assumed to be either conducting or insulating to temperature and solute concentration perturbations while the top boundary is free and insulating. The linear stability analysis is followed and an exact solution is obtained for the corresponding eigen value problem by assuming that stationary convection is exhibited at the neutral state. The Soret parameter and the presence of volumetric internal heat source in a fluid layer play a decisive role on the stability characteristics of the system. It is observed that both stabilizing and destabilizing factors can be enhanced due to the simultaneous presence of a volumetric source and Soret effect so that a more precise control (suppress or augment) of Marangoni instability in a binary fluid mixture of fluid layer is possible.
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.

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