Supplementary data are available at Bioinformatics online.

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A design method to lay emphasis on differential geometric approach for decentralized nonlinear optimal excitation control of multimachine systems is suggested in this paper. The control law achieved is implemented via purely local measurements. Moreover, it is independent of the parameters of power networks. Simulations are performed on a six-machine system. It has been demonstrated that the nonlinear optimal excitation control could adapt to the conditions under large disturbances. Besides, this paper has verified that the optimal control in the sense of LQR principle for the linearized system is equivalent to an optimal control in the sense of a quasi-quadratic performance index for the primitive nonlinear control system.

System splitting, also called controlled system islanding, can effectively prevent blackouts. Following the OBDD-based three-phase method given in [3] for proper splitting strategies, which satisfy necessary steady-state constraints, this paper studies the feasibility of the proper splitting strategies by means of power system transient simulations on the IEEE 118-bus system. Simulation results show that a considerable proportion of proper splitting strategies can successfully split the power system into stable islands. Furthermore, considering a general knowledge that a controlled power system can easily maintain its stability after a small disturbance, this paper presents "threshold value constraint" to restrict the degrees of the disturbances caused by proper splitting strategies. An approach is proposed to select threshold values for the constraint. Further simulation results show that by checking the constraint for proper splitting strategies, feasible splitting strategies can be found, which can successfully split the system into islands satisfying transient stability constraints.

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Although three-dimensional fibroin scaffolds have been prepared with freeze drying method, the porosity and pore sizes still can not satisfy the requirement of tissue engineering. In this article, fibroin porous scaffold with high porosity and > 100 microm diameter interconnected pores was firstly prepared with freeze drying method through adjusting fibroin concentration. The morphology of different scaffolds lyophilized from different fibroin concentration was observed by SEM. A novel freeze drying improved method, freeze drying/foaming technique, was also devised to prepare fibroin scaffolds at different fibroin concentrations. Using the said method, the porosity and pore size of fibroin scaffolds prepared from 12% concentration were 85.8 +/- 4% and 109 +/- 20 microm respectively with yield strength up to 450 +/- 6 KPa while the porosity and pore size of fibroin scaffolds prepared from 8% concentration were 96.9 +/- 3.6% and 120 +/- 30 microm respectively with yield strength up to 30 +/- 1 KPa. The freeze drying/foaming technique produced scaffolds with a useful combination of high yield strength, interconnected pores, and pore sizes greater than 100 microm in diameter. Through adjusting fibroin concentration and thawing time, the porosity, pore sizes and mechanical properties could be controlled to satisfy the different requirements of tissue engineering. The results suggested that fibroin scaffolds prepared with the above methods could be formed for utility in biomaterial application.

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