Catalysis of Gas Hydrates by Biosurfactants in Seawater‐Saturated Sand/Clay

Biosurfactants catalyzed natural gas hydrate formation in sand/clay packs saturated with seawater. Representative samples from the five possible biosurfactant classifications enhanced hydrate formation rate and decreased hydrate induction time. Biosurfactants increased rates 96% to 288% and decreased induction times 20% to 71% relative to the control. Micellar‐forming rhamnolipid reached a critical micellar concentration at 13 ppm at hydrate‐forming conditions; these micelles migrated readily through a seawater‐saturated sand pack to catalyze hydrate formation in another zone. The type of biosurfactant, in conjunction with specific porous media, help determine massive, dispersed, nodular, or stratified forms of hydrates. Results suggested that minimal microbial activity in ocean‐floor sands can greatly influence gas hydrate formation.     

Optimal mix of technologies in rural India: The cooking sector

In the paper, an attempt is made towards the development of a linear programming micromodel for determining an optimal mix of technologies for domestic cooking in the rural areas of India. A mathematical model involving common sources (including biomass, commercial and solar) and commercially available technologies is formulated along with the detailed technoeconomics of the different energy conversion routes. In order to make the developed model flexible, the cooking sector is divided into two subsectors, namely the low temperature thermal energy requirement and end uses requiring thermal energy at mediumhigh temperatures. The marginal costs of both, the different energy resources, and the possible energy conversion routes are discussed in the context of rural India. The paper forms a part of a larger exercise of formulating a micromodel for the design of a rural energy supply system involving the three major end uses of energy in rural areas of India, i.e. cooking, irrigation and lighting.     

Studies on the fungicidal properties of some organo-tin compounds

The results of an investigation into the fungicidal properties of some bi-functional organo-tin compounds containing mono- and dithiocarbamate ligands are reported. These experiments were conducted against a number of soil and plant pathogenic fungi. While all the compounds examined proved to be powerful fungicides, differences at the concentration levels tested were not sufficiently significant to relate degree of toxicity to ligand structure. Comparison between the fungicidal activity of the di-and triphenyl-tin compounds is in agreement with earlier observations that the latter are more toxic than the former.     

Energy Release Rate due to Friction at Bimaterial Interface in Dams

The interface between concrete dam and rock foundation is one of the most important regions governing the strength and stability of gravity dams. Many researchers have attempted to extend the fracture mechanics approach to study this rock concrete interface assuming stress free crack surfaces. In a real-life situation, because of the combined compression and shear loading, the crack faces come in contact resulting in a sizeable contact zone near the crack tip. Thus, frictional contact of the crack surfaces cannot be neglected. The frictional contact alters the stress singularity to become either weaker or stronger than the inverse square root singularity observed in homogeneous crack problems. Consequently, the strain-energy release rate as conventionally defined, either vanishes or becomes unbounded and thus cannot be used as a fracture parameter. In this work, an attempt is made to include the effect of friction associated with the sliding of crack surfaces and compute the energy dissipated during crack propagation. It is shown that the total energy release rate decreases with crack length when friction is accounted for between the rock-concrete interface in gravity dams.     

Disturbed State Model for Porous Saturated Materials

The widely used Terzaghi theory for deformation or consolidation in porous materials is based on the effective stress, a rather fictitious quantity, carried by the soil skeleton through the particle contact area, which is assumed to be negligible. This note presents a new generalized model based on the disturbed state concept, in which the average or weighted stress carried by the soil skeleton and fluid is defined on the basis of the change in contact area during deformation, that can be proportional to quantities such as the void ratio. A simple problem is solved in which the predictions from the proposed model and Terzaghi theory are compared. The proposed model has potential application as a general procedure for deformation in porous materials.     

Arsenic Removal from Groundwater by Iron Impregnated Sand

A granular media known as iron impregnated sand (IIS), developed in the laboratory by impregnating iron on a quartz sand surface by a simple and easy process has proved more effective than iron oxide coated sand (IOCS). Kinetic and isothermal studies showed that the uptake potential of IIS media was much more than IOCS media. The sequence of anions studied competing with respect to As(III) on IIS media was SO42?>HCO31?>Cl?. The presence of Ca2+ ions significantly improved the removal efficiency. During column studies the breakthrough loadings of IOCS (qb = 0.042 and 0.068) and IIS (qb = 0.097 and 0.217) for water and simulated water, respectively, show that qb for IOCS is lower than for IIS under similar experimental conditions. A filter effluent of 68 L of simulated water passed through 250 g IIS contained less than 0.05 mg As/L.     

A study of CaO (Fe2O3)1−x (Al2O3)x system

The members of the ferrite series CF_1?1A_x and with O ? × ? 0.8 have been studied by x-ray diffraction and Mössbauer spectroscopic techniques. The observed Mössbauer parameters are explained in the light of the following model, which is supported by the x-ray data. For non-zero x, the two phases CF and CA co-exist such that Al and Fe are distributed in these, respectively. With increase in x, the CF phase decreases and the CA phase increases.     

The electrical resistance of a graph captures its commute and cover times

View ann-vertex,m-edge undirected graph as an electrical network with unit resistors as edges. We extend known relations between random walks and electrical networks by showing that resistance in this network is intimately connected with thelengths of random walks on the graph. For example, thecommute time between two verticess andt (the expected length of a random walk froms tot and back) is precisely characterized by the effective resistanceR _st betweens andt: commute time=2mR _st . As a corollary, thecover time (the expected length of a random walk visiting all vertices) is characterized by the maximum resistanceR in the graph to within a factor of logn:mR<-cover time<-O(mRlogn). For many graphs, the bounds on cover time obtained in this manner are better than those obtained from previous techniques such as the eigenvalues of the adjacency matrix. In particular, we improve known bounds on cover times for high-degree graphs and expanders, and give new proofs of known results for multi-dimensional meshes. Moreover, resistance seems to provide an intuitively appealing and tractable approach to these problems.     

Erosion efficiency-a new parameter to characterize the dominant erosion micromechanism

A new parameter called erosion efficiency, capable of identifying the dominant micromechanism leading to solid particle erosion, has been introduced in this paper. The objective of this paper is to demonstrate the usefulness of this parameter by considering the large body of data in the literature pertaining to the solid particle erosion of metallic materials, ceramics, cermets and coatings under normal impact conditions.