Control of nonlinear systems with output tracking error constraints and its application to magnetic bearings

A constructive method is presented to design controllers that force the output of nonlinear systems in a strict feedback form to track a bounded and sufficiently smooth reference trajectory asymptotically. Under a suitable condition on the initial output tracking error, the proposed controllers guarantee the output tracking error within a symmetric or an asymmetric pre-specified limit range, and boundedness of all signals of the closed-loop system. A transformation is introduced to take care of the output tracking error constraint. Smooth and/or p-times differentiable step functions are proposed and incorporated in the output tracking error transformation to overcome difficulties due to the asymmetric limit range on the output tracking error. As a result, there are no switchings in the proposed controllers despite the asymmetric limit range. The proposed control design is then applied to design a tracking controller for active magnetic bearings as an illustrating application. © 2010 Taylor & Francis

Long-term effect of ventral root re-implantation on motoneuron survival following spinal root avulsion in adult rat

We have previously reported that re-implantation of ventral root can enhance motoneuron (MN) survival up to 6 weeks after root avulsion and surviving motoneurons can regenerate their axons into the re-implanted root. The aim of the present study is to investigate the long-term survival effect of root re-implantation. Axonal regeneration and myelination are also studied. Following root avulsion and re-implantation, animals in all groups were allowed to survival for 3, 6 or 12 months. Regenerating MNs were retrogradely labeled by fluorescent dye. In root re-implanted animals, about 60-70% of injured motoneurons survived up to 12 months after injury, while only 20% survival were found in the control animals. About 80% of the surviving motoneurons were found to regenerate their axons into the re-implanted ventral root. By 3 weeks after avulsion, myelin degeneration was widely spread throughout the lesioned ventral roots. In re-implantation groups, at 3 and 6 weeks after treatment, scattered Schwann cell myelinated axons within the demyelinated regions were observed. At 6 and 12 months after treatment, numerous thinly oligodendrocyte-myelinated axons were mixed with Schwann cell myelinated axons. Compared with the normal axons, newly formed myelinated axons were irregular in shape and orientation. Results of the present study show that re-implantation of avulsed ventral root can greatly enhance long-term motoneuron survival and these surviving motoneurons can regrow their axons into the original ventral root and get remyelinated. Supported by RGC grants, Hong Kon