Field emission vacuum power switch using vertically aligned carbon nanotubes

The best field emission properties from carbon nanotube cathodes were obtained when their heights, diameters and spacings were optimized. Field emission currents as high as 10 mA were obtained from 1 cm × 1 cm vertically aligned CNT cathode with optimized parameters grown using dc plasma CVD in situ. It was found that in order to obtain large emission current of >10 mA, space charge effects within the electron beam must be taken into account.

Internal models in the cerebellum.

This review will focus on the possibility that the cerebellum contains an internal model or models of the motor apparatus. Inverse internal models can provide the neural command necessary to achieve some desired trajectory. First, we review the necessity of such a model and the evidence, based on the ocular following response, that inverse models are found within the cerebellar circuitry. Forward internal models predict the consequences of actions and can be used to overcome time delays associated with feedback control. Secondly, we review the evidence that the cerebellum generates predictions using such a forward model. Finally, we review a computational model that includes multiple paired forward and inverse models and show how such an arrangement can be advantageous for motor learning and control.

Dynamic properties of superconducting magnetic bearings

The potential use of YBa2j as an active component in a magnetic bearing is being investigated. Although the load bearing capacity is high and increases with the square of the magnetic field trapped, the stiffness is low. Both the stiffness and the lévitation height are a function of the loading history of the bearing. At Cambridge we have been investigating the effects of dynamic loading such as single large excursions from steady state loads and cyclically applied loads such as vibrations. Since a superconducting bearing has little inherent damping cyclic loads applied at or near its natural frequency can have catastrophic effects. The information being gathered at Cambridge will be used to enable these effects to be mitigated in the bearing design process. © 1997 IEEE.