On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

Effects of Practicing Tandem Gait with and without Vibrotactile Biofeedback in Subjects with Unilateral Vestibular Loss

Subjects with unilateral vestibular loss exhibit motor control impairments as shown by body and limb deviation during gait. Biofeedback devices have been shown to improve stance postural control, especially when sensory information is limited by environmental conditions or pathologies such as unilateral vestibular loss. However, the extent to which biofeedback could improve motor performance or learning while practicing a dynamic task such as narrow gait is still unknown. In this cross-over design study, 9 unilateral vestibular loss subjects practiced narrow gait with and without wearing a trunk-tilt, biofeedback device in 2 practice sessions. The biofeedback device informed the subjects of their medial-lateral angular tilt and tilt velocity during gait via vibration of the trunk. From motion analysis and tilt data, the performance of the subjects practicing tandem gait were compared over time with and without biofeedback. By practicing tandem gait, subjects reduced their trunk-tilt, center of mass displacement, medial-lateral feet distance, and frequency of stepping error. In both groups, use of tactile biofeedback consistently increased postural stability during tandem gait, beyond the effects of practice alone. However, one single session of practice with biofeedback did not result in conclusive short-term after-effects consistent with short-term retention of motor performance without this additional biofeedback. Results from this study support the hypothesis that tactile biofeedback acts similar to natural sensory feedback to improve dynamic motor performance but does not facilitate a recalibration of motor performance to improve function after short-term use

Wearable inertial sensors detect anticipatory postural adjustments prior to step initiation in early Parkinson\u2019s Disease

Anticipatory postural adjustments (APA) prior to step have been detected using forceplates and EMG activity. APAs are impaired in advanced Parkinson\u2019s disease (PD) and could be an important parameter to monitor motor preparation. However, only one study has evaluated APAs in subjects with early PD. We recently demonstrated the ability to detect APAs in healthy subjects using accelerometric sensors. We hypothesized that inertial devices could provide sensitive measures of gait initiation deficits in early PD

Multi-microprocessor control of processes with pure time delay

In 1967 a novel scheme was proposed for controlling processes with large pure time delay (Fellgett et al, 1967) and some of the constituent parts of the scheme were investigated (Swann, 1970; Atkinson et al, 1973). At that time the available computational facilities were inadequate for the scheme to be implemented practically, but with the advent of modern microcomputers the scheme becomes feasible. This paper describes recent work (Mitchell, 1987) in implementing the scheme in a new multi-microprocessor configuration and shows the improved performance it provides compared with conventional three-term controllers