Seven new polyoxygenated steroids (1–7) were isolated together with seven known analogues (8–14) from the South China Sea soft coral, Sarcophyton sp. The structures of the new compounds were identified on the basis of extensive spectroscopic analysis and comparison with reported data. All the steroids are characterized with 3β,5α,6β-hydroxy moiety, displaying carbon skeletons of cholestane, ergostane, gorgostane and 23,24-dimethyl cholestane. In the in vitro bioassay, metabolites exhibited different levels of antimicrobial activity against bacterial species Escherichia coli and Bacillus megaterium, and fungal species Microbotryum violaceum and Septoria tritici. No inhibition was detected towards microalga Chlorella fusca. Preliminary structure-activity analysis suggests that the 11α-acetoxy group may increase both antibacterial and antifungal activities. The terminal-double bond and the cyclopropane moiety at the side chain may also contribute to the bioactivity.

A filter-based pseudo-negative-stiffness (FPNS) control is proposed for seismic control of base-isolated structures. The control algorithm is designed to produce a negative stiffness friction damping force with a gradual change at velocity switches, so that it is potential to prevent structures from experiencing significant jerks especially under earthquakes rich of high-frequency components. The control algorithm requires information only on device's displacement. The effect of the control parameters on structural performance is studied and the optimal combination of control parameters is obtained with the consideration of control efficiency and the economy of control force. The superior performance of an active control system employing the FPNS control algorithm over that employing the conventional PNS control algorithm is verified. A semi-active control design, MC-FPNS, is developed to produce the control force of the FPNS control algorithm by MR dampers. The effectiveness and robustness of the MC-FPNS control system are investigated through numerical analysis of the base-isolated benchmark problem under earthquakes scaled to different intensity levels. The proposed MC-FPNS control system is shown to be effective to not only prevent the isolator from failure but also improve the isolation functionality for a variety of earthquakes with different frequency contents and intensity levels. Moreover, the MC-FPNS control system is capable of suppressing transference of high-frequency components of ground motions to the superstructure. Figure 8. Evaluation criteria for the sample semi-active, DPNS and MC-FPNS control systems under earthquake ground motions at full intensity level. The left line is for the case of FP-X and FN-Y; the right line is for the case of FN-X and FP-Y.Figure 9. Evaluation criteria for the sample semi-active, DPNS and MC-FPNS control systems under earthquake ground motions at 0.25 times of the full intensity level. The left line is for the case of FP-X and FN-Y; the right line is for the case of FN-X and FP-Y.

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