Optimization of weakly coupled subsystems by a two-level method

A two-level method to find the optimal control of a linear system is presented. We consider that the system is composed of coupled subsystems. And we solve two decoupled first-level problems and one coordinating second-level problem iteratively. When the system can be decoupled into weakly coupled subsystems, the solution fast converges to the optimal.     

Sodium Transport in the Na2O-H2O-SiO2 Glass System

The variation with water content of dc conductivity and Na diffusion coefficient for the Na₂O · 4siO₂ and Na₂O · 2SiO₂ glass systems was found to be similar to that of the Na₂O.3SiO₂ series reported earlier. The conductivity was estimated for the ternary system Na₂O-H₂O-SiO₂ by combining the present results with the previous data on the Na₂O · 3SiO₂ system. When the conductivity of those glasses with a constant [Na₂O] + [H₂O] content was plotted against water content, a pronounced mixed "alkali" effect was demonstrated. The Haven ratio, calculated by comparison of the dc conductivity to the Na diffusion coefficient at 100°C for each of the three glass systems, was found to increase toward unity with increasing water content. This suggests that the addition of water reduces the number of sodium charge carriers. The subsequent increase in conductivity beyond the minimum with the introduction of larger amounts of water is, probably, due to an increase in the mobility of the Na⁺ ions.     

Effect of Water Content on Transport in Na2O·3SiO2 Glass

Na₂O·₃SiO₂ glasses of high water content were prepared under high-pressure, hydrothermal conditions. The sodium diffusion coefficient, DNa , in these glasses measured at 100°C depended strongly on H₂O content. With increasing H₂O content, DNa . at 100°C decreased initially to a minimum at 3∼4 wt% H,O and then increased. This behavior of DNa . Was similar to that of dc conductivity.     

Dependence of Electrical Conductivity of ZnO on Degree of Sintering

The electrical resistivity of ZnO doped with Al₂O₃ was measured in air and under reduced pressure (∼0.5 mm Hg) in the range from 30° to 680°C as a function of the degree of sintering. The data obtained were explained in terms of the effects of the microstructure of the sintered body and the chemisorbed oxygen. There are two mechanisms of electrical conduction involved, only one of which is affected by the microstructure.     

采用Ni—Cr合金热喷涂延长连铸结晶器寿命

三岛光产所开发的Ni-Cr合金热喷涂结晶器,是通过对连铸结晶器表面喷涂Ni-Cr合金涂层,使其寿命达到原来镀Ni结晶器的3-6倍,本文介绍Ni-Cr合金热喷涂结晶器的特性、使用效果和使用上的注意点。     

Optimization of linear systems with integral control for time-weighted quadratic performance indices

The necessary conditions to be satisfied by the feedback control constructed by available variables, minimizing time-weighted quadratic performance indices for linear systems incorporating integral action, are developed using the parameter optimization technique. To remove the dependence of the solution on a reference input and an external disturbance, a performance index based on the statistical expectation and a minimax solution are considered. An algorithm based on a gradient technique is given to solve the necessary conditions of the minimax solution. Numerical examples are given to illustrate the effect of a time-weighted performance index on the transient response of the output, and they show that the integral-square-time-square error performance index is acceptable for a reference input.     

Study of the fatigue lifetimes and crack propagation behaviour of a high speed steel as a function of the R value

High speed steels, such as the alloy H‐13, when used as forging dies are subjected to both wear and cyclic loading, and both of these factors can affect the useful life of such dies. It follows that it is of some importance to determine the fatigue characteristics of such steels. However, fatigue studies of such alloys are limited, especially with respect to fatigue crack propagation (FCP) behaviour as a function of mean stress, and therefore more detailed studies are necessary. In the present study, the fatigue lifetimes and the crack propagation behaviour of a high speed steel were experimentally investigated in laboratory air under different stress ratios, R. A modified linear‐elastic fracture mechanics (LEFM) approach was applied to analyze the experimentally‐obtained FCP behaviour. The predicted S–N curves and crack growth behaviour for a wide range of R ratios agree well with the experimental data, and the modified LEFM approach is therefore considered to be useful for evaluation of the fatigue behaviour of this class of high strength steels.     

Dielectric Characteristics of Na2O · 3SiO2 Glasses with High Water Contents

Dielectric characteristics of Na₂O·3SiO₂ glasses with water contents up to ∼12 wt% were found to be drastically affected by incorporated water. The high-frequency dielectric constant increased with water content, while both the static dielectric constant and the low-frequency dielectric relaxation strength showed a pronounced minimum at a water content of ∼3 wt%.     

Dielectric Loss of Microstructurally Anisotropic Borosilicate Glass

Dhdelectric characteristics were determined for a microstructurally anisotropic borosilicate glass prepared by uniaxiallhd stretching phase-separated glass rods. The specimen showed a dielectric loss peak caused by the inhomogeneous microstructure; its magnitude varied with the orientation of the specimen with respect to the electric field direction. The results are in agreement with Sillars' theory.     

Effect of Water Content on the Electrical Conductivity of Na2O≅3SiO2 Glass

Na₂O–3SiO₂ glasses with up to ≅12 wt% water were prepared under high-pressure, hydrothermal conditions and their electrical conductivities were measured. The conductivity (σ) was found to depend on H₂O content in a manner similar to the "mixed-alkali" effect. At constant temperature, σ decreased initially with increasing H₂O content to a minimum at 3≅4 wt% H₂O and increased with further increase in water content. Infrared spectroanalysis of these glasses was made to determine the type of water present in the glass and the results were interpreted in the context of the measured activation energy and preexponential factor of dc conductivity. The sodium ion diffusion coefficient for a glass containing 0.76 wt% H₂O was less than that of water-free glass and in agreement with the electrical conductivity results.