In these versions, the required stiffness of {TAIL ~ the leaflets} is achieved by {HEAD ~ a mechanism} activated hydraulically, electrically or with other similar means 
In these versions , the required stiffness of { TAIL ~ the leaflets } is achieved by { HEAD ~ a mechanism } activated hydraulically , electrically or with other similar means
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH