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Self-powered neutron detectors (SPNDs) have been utilized within in-core instrumentation to measure neutron flux for control and core flux mapping in nuclear reactors. To estimate neutron flux with SPNDs, a mathematical dynamic model correlating neutron flux and SPND material has been established. Estimation and signal compensation for neutron flux have primarily been developed using transfer-function-based methods or state-space-based methods. Particularly for the rhodium SPND, to compensate for its delayed response to incident neutron flux input, both groups of compensation methods have been widely applied. This Review details the signal compensation methods of neutron flux using transfer-function-based methods, such as those employing analog circuits, dynamic modeling of neutron flux, compensation of neutron flux, and direct inversion. In addition, signal compensation and estimation of neutron flux using state-space-based methods, such as the Kalman filter and H-infinity filter, are reviewed, along with basic calculations based on certain assumptions. Since there are differences in the characteristics of the two groups of methods for the same type of SPND, review comments are also included regarding the stability of compensation methods, based on results obtained from calculations using certain assumptions. [ABSTRACT FROM AUTHOR]

The advent of high-precision magnetic and robotic computer-controlled neurosurgery systems makes it necessary to determine the range of forces that will be encountered by the probes of such devices as they are guided through the brain tissues to intraparenchymal targets. We have measured the penetration forces on 2.5-mm spheres and the drag forces on 3.0-mm ventricular shunt catheters advanced 2.0-3.5 cm deep into in vivo human brain tissues (in patients about to have those tissues resected during epilepsy surgery) at rates of [approximately equal to]0.33 mm [s.sup.-1]. Penetration forces of (8 [+ or -] 2) grams were found for the spherical probe once it passed 0.5 cm below the cortical surface, and frictional drags of 12.8 [+ or -] 0.3) grams [cm.sup.-1] were exerted on the catheters. The variable nature of these forces is discussed and the results are compared with earlier studies on experimental animal tissues and brain phantom gelatins. The implications of these results for magnetic and robotic surgery systems are considered. Index Terms - Bulk brain tissue, friction, magnetic stereotaxis, penetration force, robotic stereotaxis.

Magnetic bearings are often designed using magnetic circuit theory. When these bearings are built, however, effects not included in the usual circuit theory formulation have a significant influence on bearing performance. Two significant sources of error in the circuit theory approach are the neglect of leakage and fringing effects and the neglect of eddy current effects. This work formulates an augmented circuit model in which eddy current and flux leakage and fringing effects are included. Electrical impedance predictions from the model are found to be in good agreement with experimental data from a typical magnetic bearing.

Piezoelectric actuators must be preloaded to prevent damage due to tensile loading. Spring-preloaded actuators sacrifice some of the total stroke of the actuator. The authors propose a preload device using permanent magnets. By employing magnetic preload, the static performance of the actuator is improved, while increasing the total stroke. The proposed preload device decouples the lateral motion of the actuator from the actuating direction, thus eliminating the need for a complex flexure hinge mechanism. Index Terms--Nanoscale actuators, permanent magnets, piezoelectric devices.

Self-bearing motors (SBM) use a single magnetic structure for rotational motoring as well as for noncontact levitation. They are sometimes referred to as bearingless motors or combined motor-bearings. In this paper, we propose a new type of self-bearing motors based on toroidally-wound brushless DC machines. This type of SBM can be made to be passively stable in the axial direction and for out-of-plane rotations. To achieve self-bearing operation, we derive a force-current model and show that the levitation force is decoupled from the rotational torque. To overcome the singularity problem in the force-current model, we propose a phase selection algorithm in which the phase that may cause singularity is counted out when inverting the force-current model. Through finite element analyses and experiments, we validate the force-current model and the phase selection algorithm. [ABSTRACT FROM AUTHOR]

For the development of cardiovascular devices and the study of the dynamics of blood flow through the cardiovascular system, hardware fluidic models are commonly used to minimize animal experiments and clinical trials. These systems, called ‘mock circulatory systems,’ are also critical for the development of ventricular assist devices. The passive and active elements in these systems are frequently ‘hard-plumbed’ and are difficult to modify in experimental studies. Therefore, we propose a concept of novel fluidic operational amplifier comprised of a high-gain feedback-controlled gear pump. With pressure being the analog of voltage, design with the fluidic op-amp is analogous to electrical op-amp circuit design. Initial computer and hardware simulation results demonstrate that the device may be programmed for use in mock circulatory systems to emulate the function of the energy sources (the ventricles) or passive networks (hemodynamic loads). [ABSTRACT FROM AUTHOR]