Showing papers by "Anand Yethiraj published in 2014"
TL;DR: A simple and robust method to produce large 2-dimensional and quasi-3-dimensional arrays of tunable liquid microlenses using a time varying external electric field as the only control parameter, which is useful in designing adaptive optics.
Abstract: We demonstrate a simple and robust method to produce large 2-dimensional and quasi-3-dimensional arrays of tunable liquid microlenses using a time varying external electric field as the only control parameter. With increasing frequency, the shape of the individual lensing elements (~40 μm in diameter) evolves from an oblate (lentil shaped) to a prolate (egg shaped) spheroid, thereby making the focal length a tunable quantity. Moreover, such microlenses can be spatially localized in desired configurations by patterning the electrode. This system has the advantage that it provides a large dynamic range of shape deformation (with a response time of ~30 ms for the whole range of deformation), which is useful in designing adaptive optics.
9 citations
TL;DR: In this paper, the authors observed electro-hydrodynamically driven turbulent flows at low Reynolds numbers in a two-fluid emulsion consisting of micron-scale droplets, and characterized the dynamics associated with these structures by both video imaging and a simultaneous, in situ, measurement of the time variation of the bulk Reynolds stress with a rheometer.
Abstract: We observe electro-hydrodynamically driven turbulent flows at low Reynolds numbers in a two-fluid emulsion consisting of micron-scale droplets. In the presence of electric fields, the droplets produce interacting hydrodynamic flows which result in a dynamical organization at a spatial scale much larger than the size of the individual droplets. We characterize the dynamics associated with these structures by both video imaging and a simultaneous, in situ, measurement of the time variation of the bulk Reynolds stress with a rheometer. The results display scale invariance in the energy spectra in both space and time.
9 citations
TL;DR: Orientational order parameters determined from 1H NMR spectroscopy of solutes in liquid crystals that form both nematic and smectic A phases are used to determine the solute smECTic A order parameters and the smecting–nematic coupling term.
Abstract: Orientational order parameters determined from (1)H NMR spectroscopy of solutes in liquid crystals that form both nematic and smectic A phases are used to determine the solute smectic A order parameters and the smectic-nematic coupling term. For the analysis, it is necessary to know the nematic part of the potential in the smectic A phase: various ways of extrapolating parameters from the nematic phase to the smectic phase are explored.
2 citations
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TL;DR: The zero field equation of state (EOS) is hard sphere without any re-scaling of particle size, and the hydrodynamic corrections to the long-time self-diffusion coefficient are quantitatively consistent with the expected value for hard spheres.
Abstract: In this work, we use structure and dynamics in sedimentation equilibrium, in the presence of gravity, to examine, $via$ confocal microscopy, a Brownian colloidal system in the presence of an external electric field. The zero field equation of state (EOS) is hard sphere without any re-scaling of particle size, and the hydrodynamic corrections to the long-time self-diffusion coefficient are quantitatively consistent with the expected value for hard spheres. Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number $Pe_g$, and dipolar strength $\Lambda$ are of order unity. In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength $\Lambda \sim 1$. The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes.