Particle simulation of vibrated gas-fluidized beds of cohesive fine powders

We use three-dimensional particle dynamics simulations, coupled with volume-averaged gas phase hydrodynamics, to study vertically vibrated gas-fluidized beds of fine, cohesive powders. The volume-averaged interstitial gas flow is restricted to be one-dimensional (1D). This simplified model captures the spontaneous development of 1D traveling waves, which corresponds to bubble formation in real fluidized beds. We use this model to probe the manner in which vibration and gas flow combine to influence the dynamics of cohesive particles. We find that as the gas flow rate increases, cyclic pressure pulsation produced by vibration becomes more and more significant than direct impact, and in a fully fluidized bed this pulsation is virtually the only relevant mechanism. We demonstrate that vibration assists fluidization by creating large tensile stresses during transient periods, which helps break up the cohesive assembly into agglomerates.Comment: to appear in I&EC Research, a special issue (Oct. 2006) in honor of Prof. William B. Russe

Valence instability of cerium under pressure in the Kondo-like perovskite La0.1_{0.1}Ce0.4_{0.4}Sr0.5_{0.5}MnO3_3

Effect of hydrostatic pressure and magnetic field on electrical resistance of the Kondo-like perovskite manganese oxide, La$_{0.1}$Ce$_{0.4}$Sr$_{0.5}$MnO$_3$ with a ferrimagnetic ground state, have been investigated up to 2.1 GPa and 9 T. In this compound, the Mn-moments undergo double exchange mediated ferromagnetic ordering at $T_{\rm C}$ $\sim$ 280 K and there is a resistance maximum, $T_{\rm max}$ at about 130 K which is correlated with an antiferromagnetic ordering of {\it cerium} with respect to the Mn-sublattice moments. Under pressure, the $T_{\rm max}$ shifts to lower temperature at a rate of d$T_{max}$/d$P$ = -162 K/GPa and disappears at a critical pressure $P_{\rm c}$ $\sim$ 0.9 GPa. Further, the coefficient, $m$ of $-logT$ term due to Kondo scattering decreases linearly with increase of pressure showing an inflection point in the vicinity of $P_{\rm c}$. These results suggest that {\it cerium} undergoes a transition from Ce$^{3+}$ state to Ce$^{4+}$/Ce$^{3+}$ mixed valence state under pressure. In contrast to pressure effect, the applied magnetic field shifts $T_{\rm max}$ to higher temperature presumably due to enhanced ferromagnetic Mn moments.Comment: to be published in Phys. Rev. B (rapid commun

Coarse Bifurcation Studies of Bubble Flow Microscopic Simulations

The parametric behavior of regular periodic arrays of rising bubbles is investigated with the aid of 2-dimensional BGK Lattice-Boltzmann (LB) simulators. The Recursive Projection Method is implemented and coupled to the LB simulators, accelerating their convergence towards what we term coarse steady states. Efficient stability/bifurcation analysis is performed by computing the leading eigenvalues/eigenvectors of the coarse time stepper. Our approach constitutes the basis for system-level analysis of processes modeled through microscopic simulations.Comment: 4 pages, 3 figure

Organic Production of Tuberous Vegetables: Agronomic, Nutritional and Economic Benefits

Global awareness of health and environmental issues has stimulated interest in alternative Agricultural systems like organic farming. Elephant foot yam (Amorphophallus paeoniifolius) and yams (Dioscorea spp.) are ethnic starchy vegetables with high energy, nutritive and medicinal values. Field experiments were conducted at the Central Tuber Crops Research Institute, Thiruvananthapuram, India, during 2004-2011 to assess the agronomic, nutritional and economic advantages of organic farming over conventional system in these crops. Organic farming resulted in 10-20% higher yield over conventional practice in these crops. A net profit of Rs 2,15,776 ha-1, which was 28% higher over chemical based farming was obtained under organic management in elephant foot yam. Elite and local varieties responded equally well to organic and conventional farming in elephant foot yam. White yam, greater yam and lesser yam responded similarly to both the systems, with slightly higher yield under organic practice. Soil physico-chemical properties and microbial count were also improved under organic management. Organic farming scored significantly higher soil quality index (1.93) than conventional practice (1.46). The soil quality index was driven by water holding capacity, pH and available Zn followed by soil organic matter. Tuber quality was improved with higher dry matter, starch, crude protein and lower oxalate contents. Cost effective technologies were field validated

Spin-phonon coupling in multiferroic RCrO3_3 (R-Y, Lu, Gd, Eu, Sm): A Raman study

Raman study on a select few orthochromites, RCrO$_3$ (R = Y, Lu, Gd, Eu and Sm) shows that the phonon behavior at TN in compounds with magnetic R-ion (Gd and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu). While anomalies in most of the observed phonon frequencies in all these compounds may result from the distortion of CrO$_6$ octahedra due to size effect and magnetostriction arising from Cr-ordering, the anomalous behavior of their linewidths observed at TN for the compounds with only magnetic R-ion suggests spin-phonon coupling. The presence of spin-phonon coupling and the anomalies in the low frequency modes related to R-ion motion in orthochromites (R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments play important role in inducing switchable electric polarization.Comment: 6 pages (two column format), 7 figures; The updated version of the manuscript can be found at Euro. Phys. Lett. 101, 17008 (2013

On Farm Validation of Organic Farming Technology in Elephant foot yam (Amorphophallus paeoniifolius (Dennst.) Nicolson)

Currently alternative agricultural systems, like organic farming, that are less chemical intensive, less exploitative and that can conserve the environment are gaining popularity. Tuber crops, especially aroids, like elephant foot yam, respond well to organic manures and offer scope for organic production. However, lack of package of practices recommendations hinders the promotion of this viable alternative farming practice. Hence, the organic farming technology for elephant foot yam developed at CTCRI was validated through on farm trials under State Horticulture Mission funded programme. Demonstration trials were conducted during 2008-2009 in 10 farmers’ sites to cover an area of 5 ha in Kollam and Pathanamthitta districts of Kerala to compare the yield, quality, economics and soil fertility under the organic management practices with the existing farmers’ practice and conventional practice (present package of practices recommendations) in elephant foot yam. Organic farming resulted in higher corm yield (34.60 t ha-1) and additional income (Rs. 43,651 ha-1) over conventional farming. Organically produced corms had significantly higher dry matter and Mg contents and significantly lower oxalate content. The chemical properties of the soil, especially K, were also seen favoured under organic farming. The organic farming technology standardized for elephant foot yam includes the application of farmyard manure (FYM) @ 36 t ha-1, green manuring with cowpea to generate 20-25 t ha-1 of green matter in 45-60 days, neem cake @ 1 t ha-1 and ash @ 3 t ha-1.FYM and neem cake are to be applied in pits at the time of planting. Ash may be applied at the time of incorporation of green manure at 45-60 days after planting

Coarse-grained computations of demixing in dense gas-fluidized beds

We use an "equation-free", coarse-grained computational approach to accelerate molecular dynamics-based computations of demixing (segregation) of dissimilar particles subject to an upward gas flow (gas-fluidized beds). We explore the coarse-grained dynamics of these phenomena in gently fluidized beds of solid mixtures of different densities, typically a slow process for which reasonable continuum models are currently unavailable