Synthesis and epoxy curing of Mannich bases derived from bisphenol A and poly(oxyalkylene)diamine

A family of Mannich bases were prepared from the reaction of 2,2‐bis‐(4‐hydroxyphenyl)propane (bisphenol A or BPA), formaldehyde, and poly(oxyalkylene)diamines at 1 : 1 : 1 or 1 : 2 : 2 molar ratio. By varying the molar ratio of bisphenol A to amine and the chemical structures of poly(oxyalkylene)diamines, a series of products with multiple functionalities of primary/secondary amines, phenols, and poly(oxyalkylene) were prepared. The curing profiles of these products toward the diglycidyl ether of bisphenol A (DGEBA) were examined by a differential scanning calorimeter (DSC). The physical properties of these cured materials were correlated with the chemical structures of the Mannich bases. Compared with the poly(oxyalkylene)diamines, the built‐in phenol moiety in Mannich bases accelerated the curing rate. Both amine and phenol functionalities could be reactive sites toward diglycidyl ethers in a step‐wise fashion under catalytic (triphenylphosphine) and different temperature conditions. Furthermore, the cured polymers demonstrated improved properties including tensile and flexural strength in comparison with those cured by the corresponding poly(oxyalkylene)diamines. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 615–623, 2000     

Effect of quadratic radial variation of phase on single slit diffraction of Laguerre–Gauss vortex beams

Effect of quadratic radial phase variation in the plane of the aperture on Fraunhofer diffraction of Laguerre–Gauss vortex beams by a slit is studied experimentally. For slit positions near the incident beam waist, its effect is to shear the diffraction pattern relative to that at the waist. The magnitude and sense of shear depend on the topological charge and slit location relative to the incident beam waist. For slit positions far from the waist, the diffraction pattern evolves to be significantly different and is dominated by two strong peaks. A closed form analytical expression for the diffraction pattern is presented, which reproduces experimental results quite well for all slit positions.     

Using a fed-batch culture strategy to enhance rAAV production in the baculovirus/insect cell system

Recombinant adeno-associated virus (rAAV) is one of the most promising vectors for human gene therapy. However, the production systems that are currently available have a limited capacity and cannot provide sufficient quantities of rAAV for preclinical or clinical trials. Many novel methods for improving rAAV production have been developed, but few researchers have focused on the culture process. In this study, we use a fed-batch culture system to enhance rAAV yield in the baculovirus/insect cell system. When the insect cells were co-infected with MOI = 5 of Bac-GFP at a ratio of 1:9:9 (Bac-GFP: Bac-Rep: Bac-VP), the fed-batch culture achieved optimal rAAV yields. In batch culture, the optimal cell density for producing rAAV was found to be 1 × 10⁶ cells/ml, and the highest rAAV yield (1.22 × 10⁸ IVP/ml, 122 IVP/cell) occurred at day 5 post-infection. In the fed-batch culture, rAAV yield reached 2.13 × 10⁸ IVP/ml at day 4 post-infection, and the highest rAAV yield was 2.40 × 10⁸ IVP/ml (240 IVP/cell) at day 5 post-infection. The cost of the batch and fed-batch cultures is similar; however, the rAAV yield was 2.6-fold higher in the fed-batch culture system compared with that in the batch culture system. Therefore, here we demonstrated an economical and efficient strategy for rAAV production.     

Analysis of volume change effects in a fluidized bed catalytic reactor

A mathematical model based on the concept of an improved bubble assemblage model is developed for calculating the conversion of a reaction system involving a volume change in fluidized beds. The influence of volume change on the hydrodynamic behavior of gas in the bed, such as bubble size variation, superficial gas velocity change, and volume fraction occupied by each phase, is also investigated. It is found that increasing stoichiometric coefficient values results in larger bubble size, higher superficial gas velocities, higher crossflow rate between emulsion phase and bubble phase, and greater volume fraction of bubble phase, but smaller volume fraction occupied by the emulsion phase as well as lower conversions.     

Finite Element Limit Analysis of Passive Earth Resistance in Cohesionless Soils

This note examines the classic passive earth resistance of cohesionless soil by using two newly developed numerical procedures based on finite element formulations of the bound theorems of limit analysis and non-linear programming techniques. Solutions using upper and lower bounds are presented to complement the previous studies of this problem. The parameters studied are soil-wall interface friction, wall inclination, backfill surface configuration and the wall's weight.     

Flutter of Thermally Buckled Composite Sandwich Plates

A high precision high order triangular plate element is developed for the linear flutter analysis of thermally buckled composite sandwich plates. Due to uneven thermal expansion in the two local material directions, the buckling mode of the plate may be shifted from one pattern to another for certain fiber orientation or plate aspect ratio as the aerodynamic pressure is present. This buckle pattern change alters the frequencies and modes of the plate and that in turn changes the flutter coalescent modes. Numerical results show that temperature has a destabilizing effect on the flutter boundary but the aerodynamic pressure has a stabilizing effect on the buckling boundary.     

Surface and subsurface damages and magnetic recording pattern degradation induced by indentation and scratching

Magnetic recording pattern degradation due to head–disk impact and scratching are simulated by static indentation and scratch testing, respectively, on a pre-recorded thin film magnetic recording disk. Different magnitude of controlled stresses were used to induce stress and physical damage to the magnetic recording disk resulting in erasure and distortion of the magnetic recording pattern. Both nanoindentation and scratching resulted in the elastic–plastic deformation of the multilayer coating of the magnetic recording disk but in different relative magnitude and types of in-plane stresses (which are effective in causing magnetization changes). For residual indentation and scratch depths of the order of the magnetic disk coating thickness, magnetization changes in the recording pattern were observed even though the protective carbon overcoat was not damaged. Large magnetic pattern distortion and erasure results where cracks and pileups, and delamination and buckling damages were observed for deeper indentation marks and scratch grooves, respectively.     

FOUR-PHASE MODEL FOR FLUIDIZED-BED CATALYTIC REACTORS

A four-phase model for fluidized-bed catalytic reactors is developed. The bed is divided into four phases, i.e., bubble, cloud-wake, emulsion upflow, and emulsion downflow phases. In the model, gas back mixing in the emulsion phase and gas interchange as well as gas cross flow between phases are all considered. Model predictions are shown to compare well with various published experimental data on both axial concentration profiles and overall conversions. Parameters effects on the reaction performance were also illustrated. It was found that neglecting cross flow will result in 13% lower on the predicted conversion.     

Selective extraction of metal ions through liquid surfactant membranes

Selective separation of metal ion from a liquid solution with the help of different permeation rate of solutes through liquid membranes was performed. The salts used were ZnCl₂, CdCl₂, NiCl₂. D2EHPA and LIX64N were used as carrier to study the extraction rate of the solutes. The results show that at low pH value of external phase the order of degree of extraction by D2EHPA or LIX64N is Zn > Cd > Ni, while at high pH value with the presence of ammonia in the feed solution the order of degree of extraction is reversed to Ni > Cd > Zn. The results also indicate that when the mixed carrier is used an enhanced effect on the extraction was observed. Synergistic effect was also noted when comparing the cases with mixed carriers to those with pure carriers.