Foam stability and polymer phase morphology of flexible polyurethane foams synthesized from castor oil

Foam stability and segmented polymeric phase morphology of polyurethane foams synthesized partially and completely from castor oil are investigated. Preliminary analysis of the impact of alterations in the polymeric phase on macroscopic stress dissipation in foams is also carried out. The stability and morphology show unique trends depending on the concentration of castor oil used in foam synthesis. While low and intermediate concentrations of castor oil does not significantly affect the foaming process; at high concentrations, the volumetrically expanding liquid matrix remains in a nonequilibrium state during the entire foaming period, resulting in significant foam decay from top. This increases the final foam cell density and decreases the plateau border thickness at bottom. In the polymeric phase of castor oil based foams, the fraction of monodentate urea increases at the cost of non‐hydrogen bonded urea. These monodentate urea domains undergo flocculation in foams synthesized completely from castor oil, thus prominently modifying the segmented morphology. The glass transition temperature of soft segments of partially substituted foams shows moderate increase, with indications of phase mixing between the polyether and castor oil generated urethane domains. Foams synthesized entirely from castor oil have significant sol fraction due to unreacted oligomers. The microscopic alterations in polymeric phase reduce the elastic recovery of partially substituted castor oil foams compared to its viscous dissipation under an applied stress. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40668.     

Flow field during eccentric discharge from quasi‐two‐dimensional silos–extension of the kinematic model with validation

A comprehensive investigation of granular discharge through the eccentric opening of rectangular silos has been presented. Slip flow of the grains over the vertical wall closer to the orifice was observed experimentally. This has not been emphasized by the earlier researchers. Considering slip flow at the wall, the kinematic model of granular discharge has been extended to simulate the hydrodynamics during drainage through any eccentric opening. The simulation is applicable over the entire range of eccentricity possible and for both the uniform and the triangular velocity profile through the orifice. Results from the experiments using sand grains (300–500 μm) and glass beads (400–600 μm) have been used for validating the model. The excellent agreement not only justifies the application of the kinematic model for eccentric discharge, it also extends the model for irregular and much smaller grain size. Finally, some limitations of the kinematic model have been examined critically. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1439–1453, 2016     

Uranium speciation and its site occupancy in alkaline‐earth borophosphates

Alkaline‐earth (calcium, strontium, and barium) borophosphates doped with uranium (U) are prepared through conventional solid‐state reaction route. The form of stabilized uranium in these solid matrices was characterized and investigated using X‐ray diffraction (XRD), photo luminescence (PL) and extended X‐ray absorption fine structure (EXAFS). XRD measurements confirmed the single phase formation of uranium‐doped alkaline‐earth borophosphate samples. The PL characteristics of uranium in calcium and barium borophosphate are studied for the first time. Photoluminescence studies indicated presence of uranium as Uranyl in SrBPO₅ and CaBPO₅ matrices whereas in case of BaBPO₅ the indication was for uranate species. The life time data corroborated the presence of a different uranium species in SrBPO₅, CaBPO₅, and BaBPO₅. The site occupancy of uranium was further probed using EXAFS which confirmed that in case of BaBPO₅, uranium enters the host as uranate whereas in case of SrBPO₅ and CaBPO₅, uranium enters as Uranyl.     

A robust layer adapted difference method for singularly perturbed two-parameter parabolic problems

A finite difference method for a time-dependent singularly perturbed convection–diffusion–reaction problem involving two small parameters in one space dimension is considered. We use the classical implicit Euler method for time discretization and upwind scheme on the Shishkin–Bakhvalov mesh for spatial discretization. The method is analysed for convergence and is shown to be uniform with respect to both the perturbation parameters. The use of the Shishkin–Bakhvalov mesh gives first-order convergence unlike the Shishkin mesh where convergence is deteriorated due to the presence of a logarithmic factor. Numerical results are presented to validate the theoretical estimates obtained.     

A dependency annotation scheme for Bangla treebank

Dependency grammar is considered appropriate for many Indian languages. In this paper, we present a study of the dependency relations in Bangla language. We have categorized these relations in three different levels, namely intrachunk relations, interchunk relations and interclause relations. Each of these levels is further categorized and an annotation scheme has been developed. Both syntactic and semantic features have been taken into consideration for describing the relations. In our scheme, there are 63 such syntactico–semantic relations. We have verified the scheme by tagging a corpus of 4167 Bangla sentences to create a treebank (KGPBenTreebank).     

Analysis of parameters affecting the performance of gas turbines and combined cycle plants with vapor absorption inlet air cooling

The integration of an aqua‐ammonia inlet air‐cooling scheme to a cooled gas turbine‐based combined cycle has been analyzed. The heat energy of the exhaust gas prior to the exit of the heat recovery steam generator has been chosen to power the inlet air‐cooling system. Dual pressure reheat heat recovery steam generator is chosen as the combined cycle configuration. Air film cooling has been adopted as the cooling technique for gas turbine blades. A parametric study of the effect of compressor–pressure ratio, compressor inlet temperature, turbine inlet temperature, ambient relative humidity, and ambient temperature on performance parameters of plants has been carried out. It has been observed that vapor absorption inlet air cooling improves the efficiency of gas turbine by upto 7.48% and specific work by more than 18%, respectively. However, on the adoption of this scheme for combined cycles, the plant efficiency has been observed to be adversely affected, although the addition of absorption inlet air cooling results in an increase in plant output by more than 7%. The optimum value of compressor inlet temperature for maximum specific work output has been observed to be 25 °C for the chosen set of conditions. Further reduction of compressor inlet temperature below this optimum value has been observed to adversely affect plant efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

Anisotropic modelling and numerical simulation of brittle damage in concrete

A framework for damage mechanics of brittle solids is presented and exploited in the design and numerical implementation of an anisotropic model for the tensile failure of concrete. The key feature exploited in the analysis is the hypothesis of maximum dissipation, which specifies a unique damage rule for the elastic moduli of the solid once a failure surface is specified. A complete algorithmic treatment of the resulting model is given which renders a useful tool for large-scale inelastic finite element calculations. A rather simple three-surface failure model for concrete, containing essentially no adjustable parameters, is shown to produce results in remarkably good agreement with sample experimental data.