A robust nonlinear observer for real-time attitude estimation using low-cost MEMS inertial sensors.

This paper deals with the attitude estimation of a rigid body equipped with angular velocity sensors and reference vector sensors. A quaternion-based nonlinear observer is proposed in order to fuse all information sources and to obtain an accurate estimation of the attitude. It is shown that the observer error dynamics can be separated into two passive subsystems connected in "feedback".

[Flow characteristics in 3 kinds of heart valve prosthesis].

Transvalvular turbulence caused by the blood flow in implanted cardiac valvular prosthesis is the cause of thrombosis at the post-valvular region. The literature in this connection indicates that thromboembolic complications are more common with the tilting disc mechanical valves. In order to study the turbulence caused by porcine biological prosthetic valves, by a caged-ball Biomed mechanical valve and by a tilting disc Björk-Shiley valve, a device was developed which permits to visualize and to photograph flow characteristics in the three types of valves with the purpose of determining the degree of turbulence generated in each case.