Search

Your search keyword '"Kumar, Pramoda"' showing total 20 results
Start Over Author "Kumar, Pramoda"
20 results on '"Kumar, Pramoda"'

1. Lubricated gravity currents of power-law fluids

Author

Kumar, Pramoda, Zuri, Shahar, Kogan, David, Gottlieb, Moshe, and Sayag, Roiy

Subjects
Physics - Fluid Dynamics, Condensed Matter - Soft Condensed Matter, Physics - Geophysics
Abstract

The motion of glaciers over their bedrock or drops of fluid along a solid surface can vary dramatically when these substrates are lubricated. We investigate the coupled flow of a gravity current (GC) of strain-rate softening fluid that is lubricated by a denser, lower-viscosity Newtonian fluid. We present a set of experiments in which such GCs are discharged axisymmetrically and at constant flux over a flat surface. Using imaging techniques we follow the front evolution of each fluid and their thickness field. We find that the two fronts of our lubricated GCs evolve faster than non-lubricated GCs, though with similar time exponents. In addition, the thickness of the non-Newtonian fluid is nearly uniform while that of the lubricating fluid is nonmonotonic with localised spikes. Nevertheless, lubricated GCs remain axisymmetric as long as the flux of the lubricating fluid is sufficiently smaller than the non-Newtonian fluid flux.

Published
2020
Full Text
View/download PDF

2. Interfacial and morphological features of a twist-bend nematic drop

Author

Krishnamurthy, Kanakapura S., Kumar, Pramoda, Palakurthy, Nani B., Yelamaggad, Channabasaveshwar V., and Virga, Epifanio G.

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

In this experimental and theoretical study, we examine the equilibrium shapes of quasitwo-dimensional twist-bend nematic (Ntb) drops formed within a planarly aligned nematic layer of the liquid crystal CB7CB. Initially, at the setting point of the Ntb phase, the drops assume a nonequilibrium cusped elliptical geometry with the major axis orthogonal to the director of the surrounding nematic fluid; this growth is governed principally by anisotropic heat diffusion. The drops attain equilibrium through thermally driven dynamical evolutions close to their melting temperature. They are associated with a characteristic twin-striped morphology that transforms into the familiar focal conic texture as the temperature is lowered. At equilibrium, large millimetric drops are tactoidlike, elongated along the director of the surrounding nematic fluid. This geometry is explained by a mathematical model that features two dimensionless parameters, of which one is the structural cone angle of the Ntb phase and the other, the relative strength of mismatch elastic energy at the drop's interface. Both parameters are extracted from the observations by measuring the aspect ratio of the equilibrium shapes and the inner corner angle of the cusps.

Published
2016

3. Converse flexoelectric effect in bent-core nematic liquid crystals

Author

Kumar, Pramoda, Marinov, Y. G., Hinov, H. P., Hiremath, Uma S., Yelamaggad, C. V., Krishnamurthy, K. S., and Petrov, A. G.

Subjects
Dielectrics -- Evaluation, Liquid crystals -- Structure, Liquid crystals -- Chemical properties, Liquid crystals -- Electric properties, Polarization (Electricity) -- Analysis, Chemicals, plastics and rubber industries
Published
2009

4. Electroconvection in a homeotropic bent-rod nematic liquid crystal beyond the dielectric inversion frequency

Author

Kumar, Pramoda, Hiremath, Uma S., Yelamaggad, C.V., Rossberg, Axel C., and Krishnamurthy, K.S.

Subjects
Liquid crystals -- Structure, Liquid crystals -- Chemical properties, Dielectric devices -- Structure, Dielectric devices -- Chemical properties, Chemicals, plastics and rubber industries
Abstract

The structural transitions in an initially homeotropic bent-rod nematic liquid crystal excited by ac fields of frequency f well above the dielectric inversion point [f.sub.i] are characterized. The studies have shown many new features associated with the secondary instabilities that develop at umbilical sites of the bend Freedericksz (BF) state.

Published
2008

5. Drifting periodic structures in a degenerate-planar bent-rod nematic liquid crystal beyond the dielectric inversion frequency

Author

Kumar, Pramoda, Hiremath, Uma S., Yelamaggad, C.V., Rossberg, Axel G., and Krishnamurthy, K.S.

Subjects
Dielectrics -- Analysis, Liquid crystals -- Structure, Liquid crystals -- Electric properties, Chemicals, plastics and rubber industries
Abstract

The electric-field-generated effects in the nematic phase of a twin mesogen formed of bent-core and calamatic units, aligned homeotropically in the initial ground state, are examined beyond the dielectric inversion point. The sustained propagative instability is shown to be a novel aspect common to the patterned states.

Published
2008

7. Drifting undulations in an achiral smectic C liquid crystal driven by a static electric field

Author

Krishnamurthy, K.S. and Kumar, Pramoda

Subjects
Electric fields -- Research, Smectite -- Electric properties, Polarization (Electricity) -- Analysis, Chemicals, plastics and rubber industries
Abstract

A novel dc field-driven propagative instability associated with the thermally induced layer undulations of the smectic C phase in a phenyl benzoate is reported. The mechanism responsible for the drift has involved a coupling between transverse field gradients due to the conductivity anisotropy and the transverse component of the flexoelectric polarization.

Published
2007

19. Solubilization of ThermotropicLiquid Crystal Compoundsin Aqueous Surfactant Solutions.

Author

Peddireddy, Karthik, Kumar, Pramoda, Thutupalli, Shashi, Herminghaus, Stephan, and Bahr, Christian

Subjects
*SOLUBILIZATION, *LIQUID crystals, *AQUEOUS solutions, *IONIC surfactants, *MICELLES, *AMMONIUM bromide, *LOW temperatures
Abstract

We study the micellar solubilization of three thermotropicliquidcrystal compounds by immersing single drops in aqueous solutions ofthe ionic surfactant tetradecyltrimethylammonium bromide. For bothnematic and isotropic drops, we observe a linear decrease of the dropsize with time as well as convective flows and self-propelled motions.The solubilization is accompanied by the appearance of small aqueousdroplets within the nematic or isotropic drop. At low temperatures,nematic drops expell small nematic droplets into the aqueous environment.Smectic drops show the spontaneous formation of filament-like structureswhich resemble the myelin figures observed in lyotropic lamellar systems.In all cases, the liquid crystal drops become completely solubilized,provided the weight fraction of the liquid crystal in the system isnot larger than a few percent. The solubilization of the liquid crystaldrops is compared with earlier studies of the solubilization of alkanesin ionic surfactant solutions. [ABSTRACT FROM AUTHOR]

Published
2012
Full Text
View/download PDF

20. COSMIC MICROWAVE BACKGROUND POLARIZATION AND TEMPERATURE POWER SPECTRA ESTIMATION USING LINEAR COMBINATION OF WMAP 5 YEAR MAPS

Author

Kumar, Pramoda, Saha, Rajib, Delabrouille, Jacques, Prunet, Simon, Jain, Pankaj, and Souradeep, Tarun

Abstract

We estimate cosmic microwave background (CMB) polarization and temperature power spectra using Wilkinson Microwave Anisotropy Probe (WMAP) 5 year foreground contaminated maps. The power spectrum is estimated by using a model-independent method, which does not utilize directly the diffuse foreground templates nor the detector noise model. The method essentially consists of two steps: (1) removal of diffuse foregrounds contamination by making linear combination of individual maps in harmonic space and (2) cross-correlation of foreground cleaned maps to minimize detector noise bias. For the temperature power spectrum we also estimate and subtract residual unresolved point source contamination in the cross-power spectrum using the point source model provided by the WMAP science team. Our TT, TE, and EE power spectra are in good agreement with the published results of the WMAP science team. We perform detailed numerical simulations to test for bias in our procedure. We find that the bias is small in almost all cases. A negative bias at low l in TT power spectrum has been pointed out in an earlier publication. We find that the bias-corrected quadrupole power (l(l + 1)Cl /2p) is 532 mK2, approximately 2.5 times the estimate (213.4 mK2) made by the WMAP team.

Published
2010

Catalog

Books, media, physical & digital resources
See catalog results