Summary. cDNA clones for an S-allele, designated $5, of the self-incompatibility locus (S-locus) of Lycopersicon peruvianum have been isolated by probing a pistil cDNA library with cDNAs for S-alleles of Petunia inflata and Solanum chacoense. The longest Ss-cDNA is 869 bp and contains an open reading frame of 217 amino acids. An alignment of the deduced amino acid sequence of Ss-protein with that of the 18 S-proteins from five other solanaceous species is presented. Sequence comparison further refines the primary structural features of the S-proteins previously revealed from comparison of subsets of these sequences. Based on this comparison and evidence presented elsewhere, it is proposed that accumulation of point mutations, and not intragenic recombination, is responsible for the generation of new allelic specificities.

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The semi-active control approach has been recognized to be effective for vibration suppression of flexible structures. The electrorheological (ER) fluid-based device is a good candidate for such applications. In this research, a new control law is developed to maximize the damping effect of ER dampers for structural vibration suppression under actuator constraints and viscous-frictional-combined damping. Both numerical simulations and experimental work have been carried out to evaluate and validate the theoretical predictions. LINTRODUCTIONSemi-active structural vibration control has been of popular interest in recent2years.This approach is riot sensitive to the spillover problem encountered in fully-active systems1 ' , and at the same time much more effective than a passive approach. That is, it has the advantages of both the passive and active systems. With the recent development of adaptive materials, on-line damping variations can be physically achievable. Among the various materials, the electrorheological (ER) fluid can undergo significant instantaneous reversible changes in damping characteristics when subjected to electrostatic potentials. This makes its application to real-time semi-active vibration control very attractive.ER fluids have been used to design lumped dampers36. It was found that the energy dissipation mechanism of these dampers is composed of both viscous damping and frictional damping. Recently, ER fluids have also been embedded into composite beams to suppress structural vibrations7'8'9. While their feasibility for vibration controls was shown, the characteristics of these adaptive actuators/structures have not been coupled with feedback laws and thoroughly studied under closed-loop actions.The major considerations in semi-active control of structures, other than the distributed nature of the problem, are the nonlinear characteristic of such systems due to state-dependent parameters (variable da:mping parameters depending on feedback) and the constraints imposed upon the actuators (positive clamping constants). In most semi-active system studies, the control actions are simply "clipped" when actuator constraints are violated10" . Under these conditions, the system performance is not always guaranteed to be optimal. To improve this, one can directly use the variational principle and derive optimal controls by incorporating Lagrange Multipliers in the design process1'. While theoretically sound, this approach is computational intensive, especially when large number of modes are involved. Recently, Kim and Wang'3 proposed a modified Sliding Mode scheme which switches the actuator actions between passive and semi-active depending on O-8194-1150-.7/93/$6.OO SPIE Vol. 1917 Smart Structures and lntelligent Systems (1993) / 157 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx