Mathematical models of grinding manufacture and tooth contact analysis of spherical gears

The spherical gear is a gear-driven mechanism with two degrees of freedom (DOF), which can transfer spatial motion and power. Grinding machining of the spherical gear is performed with a plate grinding wheel by using generating method, and based on mathematical model of the plate grinding wheel, the mathematical model of the spherical gear is set up. And then, the meshing model of a spherical gear pair is developed and the tooth contact analysis (TCA) of the spherical gear pairs is performed. After that, th...     

Discrimination for ablative control mechanism in solid-propellant rocket nozzle

The ablation in solid-propellant rocket nozzle is a coupling process resulted by chemistry, heat and mass transfer. Based on the heat and mass transfer theory, the aero-thermo-dynamic, and thermo-chemical kinetics, the thermal-chemical ablation model is established. Simulations are completed on the heat flow field and chemical ablation in the nozzle with different concentrations, frequency factors and activation energy of H2. The calculation results show that the concentration and the activation energy of H...     

Examining the use of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles to enhance the NH<Subscript>3</Subscript> sensitivity of polypyrrole films

Summary Polypyrrole (PPy) composite films with different contents of Fe₃O₄ were prepared by in-situ polymerization of pyrrole in aqueous solutions. The dependence of dc current changes on the response of the samples exposure to NH₃ vapor has been investigated. The results shows the composite films are more stable than the pristine ones after being exposed to NH₃ vapor. Meanwhile, the response time was reduced with increasing the Fe₃O₄ content in the films. The results might be originated from the structural changes in the PPy films caused by the addition of Fe₃O₄.     

Lyso platelet activating factor (LysoPAF) and its enantiomer. Total synthesis and carbon-13 NMR spectroscopy

Described is a reaction sequence for the total synthesis of lyso platelet activating factor (lysoPAF; 1-O-alkyl-sn-glycero-3-phosphocholine) and its enantiomer. The procedure is versatile and yields optically pure isomers of defined chain length. The synthesis is equally suited for the preparation of lysoPAF analogues and its enantiomers with unsaturation in the long aliphatic chain. First,rac-1(3)-O-alkylglycerol is prepared by alkylation ofrac-isopropylideneglycerol with alkyl methanesulfonate followed by acid-catalyzed removal of the ketal group. The primary hydroxy group of alkylglycerol is then protected by tritylation, the secondary hydroxy group is acylated, and the protective trityl group is removed under mild acidic conditions with boric acid on silicic acid, essentially without acyl migration. Condensation of the diradylglycerol with bromoethyl dichlorophosphate in diethyl ether, hydrolysis of the resulting chloride, and nucleophilic displacement of the bromine with trimethylamine givesrac-1-O-alkyl-2-acylglycero-3-phosphocholine in good overall yield. The racemic alkylacylglycerophosphocholine is finally treated with snake venom phospholipase A₂ (Ophiophagus hannah) which affords 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) of natural configuration in optically pure form. The “unnatural” 3-O-alkyl-2-O-acyl-sn-glycerol-1-phosphocholine enantiomer, which is not susceptible to phospholipase A₂ cleavage, gives 3-O-alkyl-sn-glycero-1-phosphocholine upon deacylation with methanolic sodium hydroxide. Homogeneity and structure of the intermediates and final products were ascertained by carbon-13 nuclear magnetic resonance spectroscopy on monomeric solutions.     

Thermal gas effusion from diamond-like carbon films

Good-quality diamond-like carbon films (6 at.% H₂, 2400 kgf/mm² microhardness, 2.7 eV bandgap, higly insulating) have been obtained by the DC glow discharge decomposition of acetylene. Mass spectroscopic thermal effusion measurements were carried out on the films deposited under different deposition conditions. Analyses of hydrogen in conjunction with hydrocarbon effusing species yield information on the microstructure and nature of C---H bonding configurations. It is shown to be a useful analytical tool to study hydrogenated amorphous carbon films of different microstructures varying from polymer-like to diamond-like.     

Estimating performance enhancement with alternate control strategies for multiloop control systems

A filter based methodology, studied earlier for SISO systems, is extended to MIMO systems. The presented approach facilitates the calculation of best achievable performance for proportional-integral (PI) controller and the optimal multiloop (ML) PI settings for stochastic disturbance rejection in ML control systems. The filter based approach is further extended to answer some of the key questions for ML control systems such as: (a) performance enhancement possible with the alternate pairing scheme, (b) benefits that will accrue through the employment of decouplers and (c) the performance achievable with the use of multivariable controller (as opposed to an ML controller). Further, the trade-off curve between output variance and control effort is generated for the various control configurations within PI controller domain.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Study of the influence of reaction conditions on the degree of substitution,intrinsic viscosity,and yield of oxidized cellulose acetate by factorial experimental design

A half‐fraction, two‐level, four‐factor factorial experimental design was used to study the effects of the acetic anhydride concentration, reaction temperature, reaction time, and sulfuric acid concentration on the degree of substitution, intrinsic viscosity, and yield of oxidized cellulose acetate (OCA). Oxidized cellulose containing 20% (w/w) carboxylic acid was used as the starting material. The data were fitted by multiple regression analysis with SAS software. The correlation coefficients obtained from plots of the predicted and observed values for the degree of substitution, intrinsic viscosity, and yield were 0.985, 0.993, and 0.991, respectively. Residual normal plots of the regression models showed a linear relationship. Lenth and main‐factor‐effect plots revealed an increase in the degree of substitution of OCA with an increasing concentration of acetic anhydride. The latter had no effect on the intrinsic viscosity and yield of OCA. An increase in the reaction temperature led to an increase in the degree of substitution and a decrease in the intrinsic viscosity and yield of OCA. The influence of the reaction time on the degree of substitution and intrinsic viscosity followed a trend similar to that observed with the reaction temperature, but the yield of OCA was unaffected. Increasing the concentration of sulfuric acid reduced the degree of substitution, intrinsic viscosity, and yield of OCA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 696–705, 2005     

A class of discontinuous dynamical systems IV. A laboratory air-water system

An air-water experimental system consisting of two inlets and one outlet is constructed and characterised. It reaches the state of sliding mode, or equivalently, two phase slug flow. The linear hydraulic model proposed in the literature is adequate to describe it. Experimental data are used to tune this model. The resistance to the flow of air through the outlet valve during the two phase flow is much larger than that when air alone flows out. At the operating range, the resistance to water flow is not affected by the presence of air.     

Thermo gravimetric analysis and morphological behavior of castor oil based polyurethane–polyester nonwoven fabric composites

Castor oil (CO) based polyurethane (PU)– polyester nonwoven fabric composites were fabricated by impregnating the polyester nonwoven fabric in a reactive composition containing CO and diisocyanate. Composites were fabricated with two different isocyanates such as toluene‐2, 4‐diisocyanate (TDI) and hexamethylene diisocyanate (HMDI). Thermogravimetric analysis (TGA) studies of the composites were performed to establish the thermal stability and their mode of thermal degradation. It was found that degradation of neat PU takes place in two steps and that of polyester nonwoven fabric reinforced PU composites takes place in three steps. From the TGA thermograms, a little improvement in thermal stability incase of polyester nonwoven fabric reinforced PU composites were noticed compared to unreinforced PUs. Degradation kinetic parameters were obtained for the composites using Broido, Coats and Redfern, and Horowitz and Metzger methods. Tensile fractured composite specimens were used to analyze the morphology of the composites by scanning electron microscopic technique. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007