Soft-wall induced structure and dynamics of partially confined supercritical fluids

The interplay between the structure and dynamics of partially confined Lennard Jones (LJ) fluids, deep into the supercritical phase, is studied over a wide range of densities in the context of the Frenkel line (FL), which separates rigid liquidlike and non-rigid gaslike regimes in the phase diagram of the supercritical fluids. Extensive molecular dynamics simulations carried out at the two ends of the FL (P = 5000 bars, T = 300 K, and T = 1500 K) reveal intriguing features in supercritical fluids as a function of stiffness of the partially confining atomistic walls. The liquidlike regime of a LJ fluid (P = 5000 bars, T = 300 K), mimicking argon, partially confined between walls separated by 10 {\AA} along the z-axis, and otherwise unconstrained, reveals amorphous and liquidlike structural signatures in the radial distribution function parallel to the walls and enhanced self-diffusion as the wall stiffness is decreased. In sharp contrast, in the gas-like regime (P = 5000 bars, T = 1500 K), soft walls lead to increasing structural order hindering self-diffusion. Furthermore, the correlations between the structure and self-diffusion are found to be well captured by excess entropy. The rich behavior shown by supercritical fluids under partial confinement, even with simple interatomic potentials, is found to be fairly independent of hydrophilicity and hydrophobicity. The study identifies persisting sub-diffusive features over intermediate time scales, emerging from the strong interplay between density and confinement, to dictate the evolution and stabilization of structures. It is anticipated that these results may help gain a better understanding of the behavior of partially confined complex fluids found in nature

Doping and Field-Induced Insulator-Metal Transitions in Half-Doped Manganites

We argue that many properties of the half-doped manganites may be understood in terms of a new two-(eg electron)-fluid description, which is energetically favorable at intermediate Jahn-Teller (JT) coupling. This emerges from a competition between canting of the core spins of Mn promoting mobile carriers and polaronic trapping of carriers by JT defects, in the presence of CE, orbital and charge order. We show that this explains several features of the doping and magnetic field induced insulator-metal transitions, as the particle-hole asymmetry and the smallness of the transition fields.Comment: 4 pages, 4 figure

High contrast optical modulation by surface acoustic waves

Numerical Calculations are employed to study the modulation of light by surface acoustic waves (SAWs) in photonic band gap (PBG) structures. The on/off contrast ratio in PBG switch based on optical cavity is determined as a function of the SAW induced dielectric modulation. We show that these structures exhibit high contrast ratios even for moderate acousto-optic couplingComment: 7 manuscript pages and 5 figures; submitted to Applied Physics Letters on April 24, 200

The Exotic Barium Bismuthates

We review the remarkable properties, including superconductivity, charge-density-wave ordering, and metal-insulator transitions, of lead- and potassium-doped barium bismuthate. We discuss some of the early theoretical studies of these systems. Our recent theoretical work, on the negative-U\/, extended-Hubbard model for these systems, is also described. Both the large- and intermediate-U\/ regimes of this model are examined, using mean-field and random-phase approximations, particularly with a view to fitting various experimental properties of these bismuthates. On the basis of our studies, we point out possibilities for exotic physics in these systems. We also emphasize the different consequences of electronic and phonon-mediated mechanisms for the negative U.\/ We show that, for an electronic mechanism, the \secin \,\,phases of these bismuthates must be unique, with their transport properties {\it dominated by charge $\pm 2e$ Cooperon bound states}. This can explain the observed difference between the optical and transport gaps. We propose other experimental tests for this novel mechanism of charge transport and comment on the effects of disorder.Comment: UUencoded LaTex file, 122 pages, figures available on request To appear in Int. J. Mod. Phys. B as a review articl

Status of seaweed industry in India

Forty percent of the population in India is estimated to be vegetarian. Seaweeds with its high nutritive value constitute a potential resource of valuable supplementary food. India has a coastline of 5698 km. Rocky and coral formations are found in Tamil Nadu, Grujarat states, and in the vicinities of Bombay, Karawar, Batnagiri, Goa, Vizhinjam, Varkala, Vishakapatnam, and in few other places like Chilka and Pulicat lakes, Andaman and Nicobar Islands. The coastal areas of Tamil Nadu and Grujarat states are the important seaweed growing regions of the country

Internal avalanches in models of granular media

We study the phenomenon of internal avalanching within the context of recently introduced lattice models of granular media. The avalanche is produced by pulling out a grain at the base of the packing and studying how many grains have to rearrange before the packing is once more stable. We find that the avalanches are long-ranged, decaying as a power-law. We study the distriution of avalanches as a function of the density of the packing and find that the avalanche distribution is a very sensitive structural probe of the system.Comment: 12 pages including 9 eps figures, LaTeX. To appear in Fractal

Status of seaweed culture in India

In India, Gulf of Mannar, Gulf of Kuteh, Palk Bay, Lakshadweep and Bay islands are the important areas having considerable natural resources along the 6 100 km long coast line of the country. About 680 species of seaweeds belonging to the groups Chlorophyta, Phaeophyta, Rhodophyta and Cyanophyta occur naturally in varying degrees of abundance in shallow bays, lagoons and coastal areas which offer suitable substrata for their growth and propagation. Apart from their utility as a source of food, food derivatives, vitamins, proteins, etc., seaweeds provide the raw material for many agar and algin-based industries. The exploitation of carrageenophytes such as species of Hypnea, Acanthophora, Laurencia, etc. has yet to make a beginning in the country as these are available in sizeable quantities. In view of the constant demand for the seaweeds, research programmes on seaweed resources and their culture were taken up by the Central Marine Fisheries Research Institute, and Central Salt and Marine Chemicals Research Institute at Mandapam at their Regional and Field Centre, respectively, and various other research organizations belonging to the State Fisheries Departments/Universities. As regards sea-weed farming, experiments were mainly carried out on species of Ulva, Gelidiella acerosa, Gracilaria edulis, Gracilaria corticata, Gelidiopsis variabilis, Gelidium pusillum, Hypnea musiformis, Acanthophora spicifera, Hormophysa triquetra, Cystoseira sp. and species of Sargassum

Robust continuous-time smoothers without two-sided stochastic integrals

Copyright © 2002 IEEEWe consider the problem of fixed-interval smoothing of a continuous-time partially observed nonlinear stochastic dynamical system. Existing results for such smoothers require the use of two-sided stochastic calculus. The main contribution of the paper is to present a robust formulation of the smoothing equations. Under this robust formulation, the smoothing equations are nonstochastic parabolic partial differential equations (with random coefficients) and, hence, the technical machinery associated with two sided stochastic calculus is not required. Furthermore, the robust smoothed state estimates are locally Lipschitz in the observations, which is useful for numerical simulation. As examples, finite dimensional robust versions of the Benes and hidden Markov model smoothers and smoothers for piecewise linear dynamics are derived; these finite-dimensional smoothers do not involve stochastic integrals.Vikram Krishnamurthy and Robert Elliot

Seaweed culture and its prospects in India

For centuries, seaweeds of various kinds have been put to several uses in the countries of south and south-east Asia (Chapman and Chapman, 1980). The utilisation of these seaweeds has come up step by step starting with using them as food, later as raw material for industrial, medicinal, pharmaceutical and cosmetic purposes. The extended coastline of India of about 7500 kIn long with wide shelf area of 0.451 million sq. kIn. provide the most suitable environment for seaweed growth. The extensive shallow bays, coral reefs and lagoons, characterised by slow to moderately strong currents coupled with sandy and coralline bottoms make the Indian coastal belts, the ideal habitat for many economic seaweeds