Adhesion and Debonding of Soft Elastic Films on Rough and Patterned Surfaces

With the help of simulations based on energy minimization, we have studied the effect of roughness of a rigid contactor with sinusoidal and step patterns on the adhesion-debonding cycle of a soft thin elastic film. The surface instability engendered by attractive forces between the contactor and the film produces a regularly spaced array of columns in the bonding phase. The inter-column spacing is governed largely by periodicity of the contactor pattern. Decreased periodicity of the pattern favors intermittent collapse of columns rather than a continuous peeling of contact zones. An increase in the amplitude of roughness decreases the maximum force required for debonding and increases the snap-off distance. The net effect results in a reduced work for debonding. Introduction of noise and increased step-size in simulations decreases the pull-off force and the snap-off distance, as in the case of a smooth contactor. Finally the study reveals that a patterned contactor can be used as a potential template in the patterning of soft interfaces.     

Application of the phase extension method in virus crystallography

The procedure for phase extension (PX) involves gradually extending the initial phases from low resolution (e.g. ～8?Å) to the high-resolution limit of a diffraction data set. Structural redundancy present in the viral capsids that display icosahedral symmetry results in a high degree of non-crystallographic symmetry (NCS), which in turn translates into higher phasing power and is critical for improving and extending phases to higher resolution. Greater completeness of the diffraction data and determination of a molecular replacement solution, which entails accurately identifying the virus particle orientation(s) and position(s), are important for the smooth progression of the PX procedure. In addition, proper definition of a molecular mask (envelope) around the NCS-asymmetric unit has been found to be important for the success of density modification procedures, such as density averaging and solvent flattening. Regardless of the degree of NCS, the PX method appears to work well in all space groups, provided an accurate molecular mask is used along with reasonable initial phases. However, in the cases with space group P1, in addition to requiring a molecular mask, starting the PX at a higher resolution (e.g. 6?Å) overcame the previously reported problems due to Babinet phases and phase flipping errors.     

Influence of shear in the crystallization of polyethylene in the presence of SWCNTs

It is well accepted that due to epitaxy matching, carbon nanotubes are good nucleating agent for linear polyethylene. We demonstrate that not only in the quiescent conditions but also at the relatively low shear rates the presence of single-walled carbon nanotube (SWCNT) accelerates the crystallization kinetics of polyethylene (PE). The influence of SWCNTs on the crystallization kinetics in the quiescent condition is followed with the help of rheological and differential scanning calorimetry studies. The influence of flow on the stretch of the polymer chain is probed using time-resolved small-angle X-ray scattering (SAXS) and is verified with the Deborah number. SAXS data indicates that the strong shearing conditions (shear rate > 50/s for 1 s) are requisite to form shish-kebab structure in the neat polymer. However, for the low shear (shear rate < 50/s for 1 s), the shish-kebab structure that arises due to chain orientation is enhanced in the presence of SWCNTs. The development of oriented structures in SWCNT/PE composites and their absence in the neat polymer under low shear rate indicates that the presence of SWCNTs plays a significant role in the chain orientation. Overall, the results manifest the influence of SWCNTs on chain relaxation of the polymer.     

Enhancement of resistance to galvanic corrosion of ZE41 Mg alloy by equal channel angular pressing

The galvanic corrosion behavior of as-received and ECAPed ZE41 Mg alloy coupled with Al7075 alloy is investigated using zero resistance ammeter in three different corrosive environments, 0, 0.1, and 1 M NaCl, to mimic the conditions experienced in engineering applications. The mechanism of galvanic corrosion for the ZE41 Mg–Al7075 aluminum alloy is explained. It is observed that a robust surface film containing a composite layer of oxide/hydroxide of magnesium and aluminum is established in deionized water (0 M). However, only a single layer of magnesium oxide/hydroxide is detected in chloride-containing environments. Equal channel angular pressing (ECAP) improved the resistance to galvanic corrosion by 58% and 54% when compared with the as-cast counterparts in 0 and 1 M NaCl solution, respectively. In contrast, galvanic corrosion resistance decreased by 26% in 0.1 M NaCl after ECAP while the as-received samples evinced pits unfavorable to be used in engineering applications. ECAP is a promising method to combat galvanic corrosion encountered by ZE41 magnesium alloy used in automobiles and components of military vehicles.     

Sol-gel auto-combustion synthesis of Ba–Sr hexaferrite ceramic powders

We report the mechanism involved in sol-gel auto-combustion synthesis of Ba–Sr-hexaferrite (Ba_1-xSr_xFe₁₂O₁₉; x = 0, 0.25, 0.5, 0.75 and 1, BSFO) ceramic powders through the analysis of the phases evolved during annealing of the as-synthesized powders, along with their structure and morphological studies. The XRD patterns of the as-synthesized samples indicate the formation of barium/strontium monoferrite ((Ba/Sr)Fe₂O₄) and maghemite (γ-Fe₂O₃) phases along with a minute amount of hematite (α-Fe₂O₃) phase. Annealing of these samples facilitates formation of BSFO phase through the solid state reaction between BaFe₂O₄ and γ-Fe₂O₃ phase. Interestingly, after annealing the samples with x = 0, 0.5 and 1, at 1000 °C for 2 h, we observed that phase pure Ba–Sr hexaferrite structure forms, but for samples with x = 0.25 and 0.75, high amount of hematite (α-Fe₂O₃) phase is observed, especially for x = 0.75. The reason associated with this could be the large difference between the ionic radii of Ba²⁺ and Sr²⁺ ions occupying the oxygen site. Furthermore, our study on annealing dependent phase evolution confirms that, this difference in ionic radii forbids the formation of a single phase Ba–Sr hexaferrite. The growth of clear hexagonal-shaped plate-like particles with varied particle sizes was observed for all the samples. The particle size variation may be due to the influence of the ionic radii difference on the sinterability of the samples. Our study provides a better understanding of synthesis mechanism of Ba–Sr hexaferrite samples.     

Comprehending household cooking energy choice in rural India

Energy is essential to attain the quality of life and economic prosperity in a society. In the rural areas of India, cooking dominates the aggregate consumption of energy. This energy demand is mostly met by biomass fuels, which have many associated inherent disadvantages. Hence, it is important to understand the decision making process in rural households regarding the choice of cooking fuels. For this purpose, household information using the 61st round of National Sample Survey is analyzed for the rural parts of India. The logistic regression model is used to explain the determinants of clean fuel use for cooking purposes. The study shows that number of educated females between 10 and 50 years of age, average household education index, regular salary, and monthly per capita consumption expenditure have a positive and significant impact on probability of using clean cooking fuels, whereas possessing a Below Poverty Line ration card, belonging to reserved caste categories, family size and size of farm land have a significant negative linkage.     

Microfiltration of thin stillage: Process simulation and economic analyses

In plant scale operations, multistage membrane systems have been adopted for cost minimization. We considered design optimization and operation of a continuous microfiltration (MF) system for the corn dry grind process. The objectives were to develop a model to simulate a multistage MF system, optimize area requirements and stages required for a multistage system and perform economic analysis of a multistage MF system for a 40 million gal/yr ethanol plant. Total area requirement decreased with number of stages but there was tradeoff between higher capital costs involved at higher number of stages. To achieve thin stillage total solids concentration from 7 to 35%, a 5 stage membrane system was found to be optimum with area requirement of 655 m² for minimum cost. Increase in the input stream flow rate from 1.54 × 10⁶ to 2.89 × 10⁶ L/day significantly increased the total capital cost of the system by 47%. Compared to a single stage system, an optimal system had a 50% reduction in operating costs. Optimal system also showed potential to process more than twice the amount of thin stillage compared to a 4 effect evaporator system for given conditions.     

Numerical simulation of mixed convection in a porous medium filled with water/Al2 O3 nanofluid

The present work encloses the application of a Brinkman–extended Darcy model in a problem concerning mixed convection ina lid–driven porous cavity using nanofluids. The transport equations are solved numerically by the finite volume method on a co–located grid arrangement using the Quadratic Upstream Interpolation for Convective Kinematics (QUICK) scheme. The effects of governing parameters, namely, Grashof number (Gr), Darcy number (Da), and solid volume fraction $(\chi )$ , on the streamlines and the isotherms are studied. The present results are validated by favorable comparisons with previously published results and are in good agreement with them. The present numerical results show that the addition of nanoparticles to a base fluid has produced an augmentation of the heat transfer coefficient and it is found to increase significantly with an increase of the particle volume concentration. It is observed from the results that at the higher value of the Grashof number (Gr = 10⁴ ), the average Nusselt number increases with an increase in the Darcy number for a constant solid volume fraction. The detailed results are reported by means of streamlines, isotherms, and Nusselt numbers. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21029     

Magnetohydrodynamic Slip Flow and Heat Transfer in a Porous Medium over a Stretching Cylinder: Homotopy Analysis Method

This study considers magnetohydrodynamic flow and heat transfer outside a hollow stretching cylinder immersed in a fluid saturated porous medium of sparse distribution of particles with high permeability. Partial slip boundary conditions for the velocity and temperature fields are assumed at the stretching surface of the cylinder. Using similarity transformations, the nonlinear partial differential equations governing the flow and heat transfer are converted into nonlinear ordinary differential equations which are then solved by the homotopy analysis method. The effects of the pertinent parameters on the velocity and temperature profiles are investigated and discussed graphically.