Hydrogen bonding in blends of polyesters with dipeptide‐containing polyphosphazenes

New biomedically erodible polymer composites were investigated. Polyphosphazenes containing the dipeptide side groups alanyl–glycine ethyl ester, valinyl–glycine ethyl ester, and phenylalanyl–glycine ethyl ester were blended with poly(lactide‐co‐glycolide) (PLGA) with lactic to glycolic acid ratios of 50 : 50 [PLGA (50 : 50)] and 85 : 15 [PLGA (85 : 15)] with solution‐phase techniques. Each dipeptide ethyl ester side group contains two N? H protons that are capable of hydrogen bonding with the carbonyl functions of PLGA. Polyphosphazenes that contain only the dipeptide ethyl ester groups are insoluble in organic solvents and are thus unsuitable for solution‐phase composite formation. To ensure solubility during and after synthesis, cosubstituted polymers with both dipeptide ethyl ester and glycine or alanine ethyl ester side groups were used. Solution casting or electrospinning was used to fabricate polymer blend matrices with different ratios of polyphosphazene to polyester, and their miscibilities were estimated with differential scanning calorimetry and scanning electron microscopy techniques. Polyphosphazenes with alanyl–glycine ethyl ester side groups plus the second cosubstituent were completely miscible with PLGA (50 : 50) and PLGA (85 : 15) when processed via solution‐casting techniques. This suggests that the hydrogen‐bonding protons in alanyl–glycine ethyl ester have access to the oxygen atoms of the carbonyl units in PLGA. However, when the same pair of polymers was electrospun from solution, the polymers proved to be immiscible. Solution‐cast miscible polymer blends were obtained from PLGA (50 : 50) plus the polyphosphazene that was cosubstituted with valinyl–glycine ethyl ester and glycine ethyl ester side groups. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microstructural studies of PMMA impregnated mortars

Studies on cement concrete microstructures are carried out to explain experimentally observed phenomenon and for modeling of concrete at the macroscopic level. In this article, the preparation of polymer impregnated mortar (PIC) is carried out by partially or fully replacing the pores in the cement mortars (OPC) by PMMA. The effect of this polymer impregnation on density and morphology of the cement matrix is studied. The microstructural changes in the mortar, on exposure of these specimens to hydrochloric acid and sea water for 7 and 28 days, are also investigated in this article. The above studies indicated that the polymer addition decreased the voids in the mortar thereby preventing leaching of water soluble salts present in the OPC. It was observed that the polymer also prevented the external chemical media from permeating into the cement matrix and undergoing interactions with it. It is concluded that the durability and chemical resistance properties of the PIC are better compared with OPC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solid waste removes toxic liquid waste: adsorption of chromium(VI) by iron complexed protein waste

The leather processing industry generates huge amounts of wastes, both in solid and liquid form. Fleshing from animal hides/skins is one such waste that is high in protein content. In this study, raw fleshing has been complexed with iron and is used for removal of chromium(VI). The effect of pH and the initial concentration of chromium(VI) on the removal of Cr(IV) by iron treated fleshing is presented. Iron treatment is shown to greatly improve adsorption of the fleshing for hexavalent chromium. The ultimate adsorption capacity of iron treated fleshing is 51 mg of chromium(VI) per gram of fleshing. That of untreated fleshing is 9 mg/g such that iron treatment increases the adsorption capacity of fleshing by 10-fold. The measured adsorption kinetics is well described by a pseudo-second-order kinetic model. The uptake of chromium(VI) by fleshing is best described by the Langmuir adsorption isotherm model. X-ray photoelectron spectroscopic (XPS) studies show that the iron is incorporated into the protein matrix. Shifts in XPS spectra suggest that dichromate binding occurs with iron at active adsorption sites and that iron treated fleshing removes chromium(VI) without reducing it to chromium(III).     

Heat and mass transfer analysis of chemically reactive tangent hyperbolic fluid in a microchannel

This study addresses the fully developed magnetohydrodynamic flow of non-Newtonian fluid in a microchannel using tangent hyperbolic fluid model. The physical situation has been modeled by accessing boundary layer theory along with the physical aspects of thermophoresis and Brownian motion. The heat and mass transport phenomena are depicted through graphical interpretations. The modeled equations are nondimensionalized using dimensionless variables. The obtained corresponding equations are solved by employing Runge–Kutta–Fehlberg scheme accompanied with shooting technique. The fluctuations in distinct entities of physical connotations, like, the Nusselt number, friction factor and Sherwood number are explored in this examination. A notable reduction in the concentration field of the tangent hyperbolic fluid has been obtained for a larger chemical reaction parameter. The result shows that non-Newtonian fluids exhibit higher Nusselt number than Newtonian fluids. Furthermore, a significant enhancement in Nusselt number has been attained through a rise in the power-law index and thermophoresis aspect.     

Chemically reactive and radiative flow of ferro-aluminum (AA7075) hybrid nanofluid past a stretching cylinder

The present investigation throws light on the heat transfer behavior of hybridized (ferro-aluminum alloy [AA7075]) nanofluid. In addition to that, influences of thermal radiation, magnetic effect, and chemical reaction are also considered for the exploration. Here, the flow is deliberated due to a porous stretching cylinder. The equations that portray the fluid flow are transfused to simple ordinary differential equations by applying similarity elements. Then, the procured equations have been solved by adopting the Runge–Kutta–Fehlberg 4th–5th order tool. The extracted solution are exported to plot graphs for velocity, thermal, and solutal profiles with the concerned parameters, and using these plots, the discussion has been produced for the behavior of all flow fields. The behavior of the thermal profile shows substantial enhancement with an increase in the solid volume fraction of hybrid nanofluid. The velocity and concentration panel de-escalates for larger values of Reynolds number. A significant discussion on the skin friction drag, Nusselt number, and Sherwood number has been produced.     

Adaptive sampling scheme for monitoring oscillations using Prony analysis

Monitoring generator oscillations using Prony analysis is an application that is being increasingly implemented using phasor measurement units (PMUs) data. Most of the existing literature for power system oscillations using Prony method report implementing fixed sampling window that is obtained following a systematic iterative approach taking into account potential disturbances. The fixed sampling technique, although simple to implement, does not optimise the data acquisition time. Moreover, sampling using inadequate intervals can potentially lead to errors during Prony analysis. In this study mathematical formulations are derived to show the effect of small and large sampling intervals. Further, a technique using condition number is proposed as a quality index for signalling the errors arising because of the choice of sampling interval. To facilitate an efficient monitoring rate, while still maintaining sufficient accuracy, an adaptive sampling scheme is proposed. This study demonstrates that the proposed scheme can potentially exhibit faster monitoring rate with acceptable accuracy during practical implementation.     

Thermal behaviour of strontium tartrate single crystals grown in gel

Thermal behaviour of strontium tartrate crystals grown with the aid of sodium metasilicate gel is investigated using thermogravimetry (TG) and differential thermal analysis (DTA). Effect of magnetic field and dopant (Pb)²⁺ on the crystal stability is also studied using thermal analysis. This study reveals that water molecules are locked up in the lattice with different strengths in the grown crystals.     

A case study of the structural responses of a tall building in Singapore subjected to close‐in detonations

The response of tall buildings has been a major concern in metropolitan cities, especially with the recent surge in extreme activities targeted at structures with viable commercial values. This paper discusses a study carried out on the structural behaviour of a 2D frame, modelled to represent a tall building with ABAQUS. The model frame was subjected to a charge of the equivalent weight of 1 ton of TNT but placed at two varying cases of 5 and 10‐m standoff distances. Plane‐strain elements that incorporate the feature of material nonlinearity were utilized to model the structural components of the building and the simulated blast overpressures were obtained from the CONWEP software. The effects of large deformations of beams and columns corresponding to the short time loading duration depicted by the explosions were analysed from a local perspective. The extent of the damage is based on a local index defined as the ratio of curvatures. These local indices are consequently used to determine the possibility of disproportionate collapse of the frame from a global perspective. Finally, the provision of more ductile structural detailing is recommended to enhance the structural integrity of the building, increasing its resilience against blast attacks. Copyright © 2009 John Wiley & Sons, Ltd.