Synthesis and characterization of new soluble multisite phase transfer catalysts and their catalysis in free radical polymerization of methyl methacrylate aided by ultrasound—A kinetic study

Four different soluble phase transfer catalysts (PTCs) containing single, di, tri, and tetra active sites have been prepared and proved by FT-IR, ¹H NMR, ¹³C NMR, mass, elemental analysis, and conductivity measurement. The presence of the number of active sites in each catalyst was also been confirmed by determining their rate of polymerization of methyl methacrylate (MMA) using potassium peroxydisulfate (PDS) as a water soluble initiator in biphase medium. The comparative study reveals that the R_p of MMA determined in the presence of PTC combined with ultrasound has shown twofold enhancement in the activity than PTC alone. The observed order of activity was found to be of single-site < di-site < tri-site < tetra-site. Further, the thorough kinetic study of free radical polymerization of MMA has been investigated using superior tetra site viz., HBTAMPDTC and by varying the experimental parameters such as [MMA], [K₂S₂O₈], [MPTC], and the temperature. Based on the observed kinetic results and activation parameters, a suitable mechanism was proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of Traverse Speed on Microstructure and Microhardness of Cu/B4C Surface Composite Produced by Friction Stir Processing

Friction stir processing (FSP) has evolved as a potential candidate to fabricate surface composites. This paper investigates the influence of traverse speed on microstructure and microhardness of Cu/B₄C surface composite fabricated using FSP. The traverse speed was varied from 20 to 60 in steps of 20 mm/min. The tool rotational speed, axial force and groove width were kept constant. Optical microscopy and scanning electron microscopy were employed to study the microstructure of the fabricated surface composites. The results indicated that the traverse speed significantly influenced the area of the surface composite and distribution of B₄C particles. The area of the surface composite was found to bear an inversely proportional relationship to traverse speed. Lower traverse speed exhibited homogenous distribution of B₄C particles while higher traverse speed caused poor distribution of B₄C particles in the surface composite.     

Evaluation of antioxidant potential in selected green leafy vegetables

Green leafy vegetables represent a class of underexploited plants that are stipulated to be rich sources of natural antioxidants. A fundamental study of free radical-scavenging activity in four plant species, namely Trigonella foenum-graecum, Centella asiatica, Sauropus androgynus and Pisonia alba, was carried out by measuring the ability of methanol extracts of these plants to scavenge radicals generated by in vitro systems and by their ability to inhibit lipid peroxidation. The levels of non-enzymatic antioxidants were also determined by standard spectrophotometric methods. Correlation and regression analysis established a positive correlation between some of these antioxidants and the in vitro free radical-scavenging activity of the plant extracts. The conclusions drawn from the study indicate that in vivo studies, isolation and analysis of individual bioactive components will reveal the crucial role that these plants may play in several therapeutic formulations.     

On the specific heat of Al-Si and Al-Ge alloys—A simulation study

The large variation in specific heats with concentration between temperatures 50 K and 200 K for Al-Si and Al-Ge alloys are analysed in detail by lattice dynamical and Monte Carlo approaches. The large deviation from linearity at low temperatures does not seem to be due to the Debye’s low temperature contribution. It is shown that an anharmonic vibration in the above solid solutions, particularly at 200 K, is the cause for the small variation in the specific heat.     

Plain fatigue and fretting fatigue behaviour of plasma nitrided Ti-6Al-4V

Fatigue tests with and without fretting against unnitrided fretting pads were conducted on unnitrided and plasma nitrided Ti-6Al-4V samples. Plasma nitrided samples exhibited higher surface hardness, higher surface compressive residual stress, lower surface roughness and reduced friction force compared with the unnitrided specimens. Plasma nitriding enhanced the lives of Ti-6Al-4V specimens under both plain fatigue and fretting fatigue loadings. This was explained in terms of the differences in surface hardness, surface residual stress, surface roughness and friction force between the unnitrided and nitrided samples.     

Target vector optimization of composite box beam using real-coded genetic algorithm: a decomposition approach

This paper aims to obtain the optimal composite box-beam design for a helicopter rotor blade. The cross-sectional dimensions and the ply angles of the box beam are considered as design variables. The objective is to optimize the box beam to attain a target vector of stiffness values and maximum elastic coupling. The target vector is the optimal stiffness values of helicopter rotor blade obtained from a previous aeroelastic optimization study. The elastic couplings introduced by the box beam have beneficial effects on the aeroelastic stability of helicopter. The optimization problem is addressed by decomposing the optimization into two levels, a global level and a local level. The box-beam cross-sectional dimensions are optimized at the global level. The local-level optimization is a subproblem which finds optimal ply angles for each cross-sectional dimension considered in the global level. Real-coded genetic algorithm (RCGA) is used as the optimization tool in both the levels of optimization. Hybrid operators are developed for the RCGA, thereby enhancing the efficiency of the algorithm. Min–max method is used to scalarize the multiobjective functions used in this study. Optimal geometry and ply angles are obtained for composite box-beam designs with ply angle discretization of 1010, 1515, and 45^o45^o.     

A transaction mapping algorithm for frequent itemsets mining

In this paper, we present a novel algorithm for mining complete frequent itemsets. This algorithm is referred to as the TM (transaction mapping) algorithm from hereon. In this algorithm, transaction ids of each itemset are mapped and compressed to continuous transaction intervals in a different space and the counting of itemsets is performed by intersecting these interval lists in a depth-first order along the lexicographic tree. When the compression coefficient becomes smaller than the average number of comparisons for intervals intersection at a certain level, the algorithm switches to transaction id intersection. We have evaluated the algorithm against two popular frequent itemset mining algorithms, FP-growth and dEclat, using a variety of data sets with short and long frequent patterns. Experimental data show that the TM algorithm outperforms these two algorithms.     

Development of Ni-Al2O3In-Situ Nanocomposite by Reactive Milling and Spark Plasma Sintering

In the present study, Ni-30 vol pct Al₂O₃ in-situ nanocomposite was developed by reactive milling of NiO-Al-Ni powder mixture followed by spark plasma sintering (SPS). During milling, fcc to hcp transformation was observed in Ni(Al) phase and it transformed back to fcc phase around 773 K (500 °C). The hardness and yield strength of Ni-30 vol pct Al₂O₃ nanocomposite are approximately two times higher than that of pure Ni of similar grain size. The improved mechanical properties of nanocomposite are attributed to the presence of alumina particles of nanometer size.     

Analysis of Stress Control on 33-kV Non-ceramic Insulators Using Finite-element Method

In this article, analysis of electric field stress and electric potential distributions of a 33-kV composite insulator and factors that affect the electric field are discussed. Accordingly, the article is classified into two parts. In the first part, the designs of three different configurations of non-ceramic (composite) insulator based on their geometry modification in end fittings and water shed are discussed. The electrical performances are analyzed using electric field and electrical potential distribution. In the second part, a reduction of the electric field near the end fittings is done to control the electric field stress intended for long-term performance. For that, the grading material is placed between the core and housing materials by fitting the arcing horn near the end fittings. A 33-kV composite insulator is modeled in two dimensions by the finite-element method to investigate the electric field and electric potential distribution under normal and polluted conditions. The results reveal that an optimum installation of an arcing horn at the high-voltage end in the composite insulator with silicone rubber overlapping the edges of metal end fittings made a significant reduction in electric field stress on 33-kV non-ceramic insulators.