Self‐assembled honeycomb polyurethane nanofibers

Electrospinning uses a high voltage electric field to produce fine fibers. A new phenomenon of self‐assembly in the electrospinning of polyurethane nanofibers is observed. This report is the first known self‐assembling phenomenon in polyurethane electrospun nanofibers. Electrospun polyurethane nanofibers self‐assemble into unique honeycomb patterns on the collector surface. This novel observation opens up new and interesting opportunities for electrospun fibers in the areas of drug delivery devices, protective clothing, filters, and tissue scaffolds. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3121–3124, 2006     

Optimum cone angles in aeroelastic flutter

The determination of flutter frequencies and flutter boundary pressures of conical shells is carried out using finite element analysis. Static condensation procedure with Q.R. algorithm is used for the extraction of eigen values of the system. An empirical relation for determining the values of flutter boundary pressures of clamped-clamped conical shells is proposed. It is seen that there is an optimum semivertex angle at which a given conical shell of prescribed length and initial radius offers maximum resistance for flutter.     

Optimum shape design of rotating disks

This paper deals with optimum shape design of the rotating disks by nonlinear programming method. The shape of the cross section is defined by 5th degree polynomial which is completely determined by the boundary conditions and four design variables. The stress analysis of the disk is carried out by finite element method using isoparametric elements. The optimization technique used is with improved movelimit method of sequential linear programming. Progress of optimization is investigated with three different objective functions. After preliminary studies a weighted objective function is selected for detailed investigation. Optimum shapes are obtained for different speeds and for different fit pressures from hub. The results are presented in non-dimensionalised form.     

Asymptotic estimates for the error of Gauss-Jacobi quadrature formulas

Asymptotic estimates for the error of the Gauss-Jacobi quadrature formula are given for analytic functions. Our estimates for entire and meromorphic functions include those of Chawla and Jain [2]; for functions having branch-point and logarithmic singularities on the real axis we obtain improved estimates which, for the Gauss-Legendre case also, are better than those of Chawla and Jain. Numerical examples are given to illustrate the estimates obtained.     

Hydrogen generation rate enhancement by in situ Fe(0) and nitroarene substrates in Fe3O4@Pd catalyzed ammonia borane hydrolysis and nitroarene reduction tandem reaction

We report the catalytic enhancement of hydrogen generation by 1) in situ Fe (0) formed and 2) nitroarenes substrates during Fe₃O₄@Pd core-shell nanoparticles catalyzed tandem reaction. The active hydrogen species are generated in Pd shell, which either combine to form H₂ gas or take part in relatively faster nitroarene reduction reaction. The rate of hydrogen generation from ammonia borane is dependent on the nitroarene substrate and is higher when 4-nitrophenol is used. This is due to the difference in ammonia borane adsorption on the surface of the catalyst. During recyclability, the H₂ generation rate of 2 wt% Pd loaded samples is higher than other compositions. Such an enhancement has been attributed to the formation of Fe (0) via γ-FeOOH mediated by Pd species, presumably through Pd(OH)₂. The electronic connection between Fe and Pd interface is thus shown to play an important role in the catalytic enhancement of the tandem reaction.