Revised insights into templating radical polymerization within nanoreactors

The field of polymer chemistry is currently experiencing major research efforts into development of novel techniques for synthesis of polymers with well‐controlled microstructure. Recently, a new method has been reported [McHale et al., Nat. Chem. 2012, 4, 491–497] whereby high molecular weight and low dispersity polymer can be obtained by a radical polymerization process via the use of solely physico‐chemical interactions. This work was based on the combination of H‐bonding templated polymerization confined within nanoreactors of self‐assembled block copolymers. Herein, this system is thoroughly investigated to fully elucidate the underlying mechanism. Modification of physico‐chemical parameters, kinetic parameters as well as observations of size exclusion chromatography (SEC) results and colloidal behavior in various solvents provide revised insights into the mechanism. Through detailed NMR and SEC investigations, it is demonstrated that the SEC secondary peak originally believed to be the high molecular weight “daughter” polymer actually corresponds to nanoparticles containing the daughter polymer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1590–1600     

Study of three-dimensional deformation of a pallet using phase-shiff shadow moiré and finite-element analysis

We present the results of a comparative study on the static deformation of a pallet, made from oil-palm fiberreinforced composite material, using the phase-shift shadow moiré method and finite-element analysis (FEA). The pallet was designed and analyzed using a commerical software package. The effect of various joint types on the deformation profile was studied to obtain a simplified model to represent the actual design. A one-fifth scale model of the pallet was fabricated and the deformation due to static loading was measured using the phase-shift shadow moiré method. The comparison between the measurement and FEA results on the deformed profile showed a maximum difference of 13.7% at the center of the some of the deck boards, but a smaller difference at other deck boards. The FEA results also produced a larger deformation gradient compared to the measurements.     

NUMERICAL SIMULATIONS OF HYDRODYNAMIC BEHAVIORS IN CONICAL SPOUTED BEDS

The axial and radial distributions of static pressures and vertical particle velocities of conical spouted beds have been simulated and compared with experimental data. Simulation results show that, among all factors investigated, the Actual Pressure Gradient (the APG term) in conical spouted beds, introduced as the default gravity term plus an empirical axial solid phase source term, has the most significant influence on static pressure profiles, followed by the restitution coefficient and frictional viscosity, while other factors almost have no effect. Apart from the solid bulk viscosity, almost all other factors affect the radial distribution of the axial particle velocity, although the influence of the APG term is less significant. For complex systems such as conical spouted beds where a fluidized spout region and a defluidized annulus region co-exist, the new term introduced in this work can improve the CFD simulation. Furthermore, for other systems with the Actual Pressure Gradient different from either fluidized beds or packed beds, the new approach can also be applied.     

The axisymmetric boundary layer beneath a Rankine-like vortex

 An experimental investigation of the three-dimensional boundary layer induced by a Rankine-like vortex with its axis normal to a stationary disk is described. The velocity field through the boundary layer was measured for Reynolds number Re (based on the tangential velocity and radius at the disk edge) ranging from 10 000 to 25 000 at various radial distances by means of a 4-beam, 2-component Laser Doppler Anemometer. Our results show that the nature of the boundary layer is affected by two factors: an inflexional instability caused by the crossflow velocity profile and a stability factor caused by the favorable pressure gradient. At lower Reynolds number, the radial pressure gradient has a very strong stabilizing effect on the boundary layer and acts to revert it to its laminar state upstream of the effusing core. At higher Re the inflexional instability caused by the crossflow velocity dominates while the stabilizing influence of the favorable pressure gradient recedes. As such, laminar reversion likely occurs closer to the effusion core. Thus, the point of laminar reversion moves closer to the effusion core as the Reynolds number is increased. Received 23 May 1996 / Accepted 29 July 1996     

Timoshenko curved beam bending solutions in terms of Euler-Bernoulli solutions

Summary  This paper presents the exact relationships between the deflections and stress resultants of Timoshenko curved beams and that of the corresponding Euler-Bernoulli curved beams. The curved beams considered are of rectangular cross sections and constant radius of curvature. They may have any combinations of classical boundary conditions, and are subjected to any loading distribution that acts normal to the curved beam centreline. These relationships allow engineering designers to directly obtain the bending solutions of Timoshenko curved beams from the familiar Euler-Bernoulli solutions without having to perform the more complicated shear deformation analysis. Accepted for publication 26 July 1996     

Large amplitude non-linear oscillations of a general conservative system

This paper presents new, approximate analytical solutions to large-amplitude oscillations of a general, inclusive of odd and non-odd non-linearity, conservative single-degree-of-freedom system. Based on the original general non-linear oscillating system, two new systems with odd non-linearity are to be addressed. Building on the approximate analytical solutions of odd non-linear systems developed by the authors earlier, we construct the new approximate analytical solutions to the original general non-linear system by combinatory piecing of the approximate solutions corresponding to, respectively, the two new systems introduced. These approximate solutions are valid for small as well as large amplitudes of oscillation for which the perturbation method either provides inaccurate solutions or is inapplicable. Two examples with excellent approximate analytical solutions are presented to illustrate the great accuracy and simplicity of the new formulation.     

Experimental investigation on fracture of viscoelastic materials under biaxial-stress fields

Fracture behavior of viscoelastic materials under various biaxial-stress fields was studied experimentally in a specially developed apparatus. The biaxial stresses were applied at various time rates of stress to study the effects of rate of loading on fracture behavior. Examination of experimental data indicated that a simple relationship could be established between octahedral shear stress and octahedral shear strain at fracture corresponding to various biaxial stresses. Finally, a criterion of failure based on the total strain energy at fracture was suggested. The strain energy at fracture predicted from the linear viscoelastic theory agrees reasonably well with that determined experimentally.     

On swirl development in a square cross-sectioned, S-shaped duct

The flow in a uniform square cross-sectioned, S-shaped duct was investigated experimentally, at Reynolds number (Re) = 4.73 × 10⁴ and 1.47 × 10⁵, using three S-ducts of different curvature and turning angle. The hydraulic diameter (D) for each S-duct is 150 mm. Besides studying the square cross-sectioned S-duct flow at moderately higher Re than current literature, the S-ducts’ geometry used in this study also have larger curvatures and higher turning angles than those reported in the literature. With surface pressure measurement and smoke wire flow visualization, flow separation at the inside wall of the first bend was detected. Using surface oil flow visualization on the bottom wall of the S-duct and cross-wires measurement at the duct exit, it is shown here that the swirl developed in the first bend was partly attenuated in the second bend due to the formation of swirl of opposite direction. The swirl of an opposite sign results in the formation of a clear dividing or separation line on the bottom wall (and top wall) of the duct. Additional flow features include the formation of streamwise vortices on the outer-wall of the second bend. These streamwise vortices can either be a pair of counter-rotating vortices or a single vortex. The formation mechanism of these streamwise vortices is explained using the Squire and Winter [J Aeronaut Sci 18(4):271–277, 1951] formula and it is shown that the said mechanism is applicable to both Re in the present study.