Biocompatible hyperbranched polyurethane/multi-walled carbon nanotube composites as shape memory materials

Multi-walled carbon nanotube (MWCNT)-based composites have been prepared by in situ technique using Mesua ferrea L. seed oil-based hyperbranched polyurethane (HBPU) as the matrix. The scanning electron microscope, transmission electron microscope and Fourier transform infrared spectroscopy analyses revealed good dispersion as well as interaction of MWCNT with the matrix. Remarkable recovery of shape to the extent of 98% was obtained after composite formation. More than 300% improvement in tensile strength was observed as compared to the pristine HBPU. Significant enhancement of thermal stability up to 275 °C was found even at low MWCNT loading (1 wt.%). Bacterial degradation of the composite films was tested using two strains of Pseudomonas aeruginosa, MTCC 7814 and MTCC 7815. The composites exhibited enhanced biodegradability as compared to the pristine polymer. The cytocompatibility test based on hemolysis of red blood cells showed that the material lacks cytotoxicity. The investigation indicates that the material has high potential as shape memory biomaterial.     

Hydroformylation of 1-octene using rhodium–phosphite catalyst in a thermomorphic solvent system

The use of a liquid–liquid biphasic thermomorphic or temperature-dependent multicomponent solvent (TMS) system, in which the catalyst accumulates in one of the liquid phases and the product goes preferably to the other liquid phase, can be an enabling strategy of commercial hydroformylation processes with high selectivity, efficiency and ease of product separation and catalyst recovery. This paper describes the synthesis of n-nonanal, a commercially important fine chemical, by the hydroformylation reaction of 1-octene using a homogeneous catalyst consisting of HRh(PPh₃)₃(CO) and P(OPh)₃ in a TMS-system consisting of propylene carbonate (PC), dodecane and 1,4-dioxane. At a reaction temperature of 363 K, syngas pressure of 1.5 MPa and 0.68 mM concentration of the catalyst, HRh(CO)(PPh₃)₃, the conversion of 1-octene and the yield of total aldehyde were 97% and 95%, respectively. With a reaction time of 2 h and a selectivity of 89.3%, this catalytic system can be considered as highly reactive and selective compared to conventional ones. The resulting total turnover number was 600, while the turnover frequency was 400 h^?1. The effects of increasing the concentration of 1-octene, catalyst loading, partial pressure of CO and H₂ and temperature on the rate of reaction have been studied at 353, 363 and 373 K. The rate was found to be first order with respect to concentrations of the catalyst and 1-octene, and the partial pressure of H₂. The dependence of the reaction rate on the partial pressure of CO showed typical substrate inhibited kinetics. The kinetic behavior differs significantly from the kinetics of conventional systems employing HRh(CO)(PPh₃)₃ in organic solvents. Most notable are the lack of olefin inhibition and the absence of a critical catalyst concentration. A mechanistic rate equation has been proposed and the kinetic parameters evaluated with an average error of 5.5%. The activation energy was found to be 69.8 kJ/mol.     

Multi-User Relaying of High-Rate Space–Time Code in Cooperative Networks

In this paper, we propose high-rate space–time coding for cooperative wireless networks to reduce the overall delay incurred in relaying signals to multiple receivers. The relay structure is optimized in order to achieve maximum SNR at the receiver nodes. The proposed scheme provides a significant reduction in the delay required for the relaying and transmission of the signals to the multiple receivers with a minute loss in performance. We have also shown by simulation that this loss in the performance could be recovered by selecting more number of relays. We propose two relaying strategies for high-rate space–time codes, which are very useful in providing high data-rate in wireless cooperative networks.     

Predicting Transient Storage Model Parameters of Rivers by Genetic Algorithm

The presence of transient storage zone modifies the riverine pollutant transport. In the present work, new empirical expressions for three key parameters of transient storage model (TSM), an important method for predicting concentration variation of pollutants in rivers, have been derived employing genetic algorithm on published hydraulic data on river reaches and TSM parameters. The proposed expressions use few hydraulic and geometric characteristics of rivers that are usually available. Based on various performance indices, it can be concluded that the proposed expressions predict TSM parameters more reliably in comparison to the other empirical expressions for predicting TSM parameters.     

Fe-Nd-B magnets via the hot extrusion of amorphous powders

A rapid solidification melt spinning technique has been developed to produce amorphous powders of Fe-Nd-B alloys modified with hafnium diboride. The amorphous powders are consolidated by the hot extrusion technique into bulk magnets of various cross sections. Consolidated magnets show ultrafine grain structure stabilized by ultrafine submicron hafnium diboride particles. The extruded magnets develop strong texture-induced magnetic anisotropy which leads to attractive energy product values of up to 16MGOe. Significant improvement in coercivity is also achieved due to ultrafine grain structure of the extruded magnets.     

An upper bound solution for closed die sinter forging of hexagonal shapes

The paper reports on an investigation into the various aspects of closed die cold forging of hexagonal powder preforms, which have been compacted and sintered from atomized powder. It is found that for certain dimensional ratios of the preform, the die pressure is minimum. An attempt has been made determine the die pressures developed during the closed die forging of the hexagonal powder preform by using an upper bound approach. The results so obtained are discussed critically to illustrate the interaction of various process parameters involved and are presented graphically     

Analytical formulation of small signal stability analysis of power systems with nonlinear loads

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