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S R Hudson

Publications and source records attributed to S R Hudson.

3 recordsLinked to original sources

Eliminating islands in high-pressure free-boundary stellarator magnetohydrodynamic equilibrium solutions.

Magnetic islands in free-boundary stellarator equilibria are suppressed using a procedure that iterates the plasma equilibrium equations and, at each iteration, adjusts the coil geometry to cancel resonant fields produced by the plasma. The coils are constrained to satisfy certain measures of engineering acceptability and the plasma is constrained to ensure kink stability. As the iterations continue, the coil geometry and the plasma simultaneously converge to an equilibrium in which the island content is negligible. The method is applied with success to a candidate plasma and coil design for the National Compact Stellarator Experiment [Phys. Plasmas 8, 2083 (2001)]].

Journal Article↗

Loss of second-ballooning stability in three-dimensional equilibria.

The effect of three-dimensional geometry on the stability boundaries of ideal ballooning modes is investigated. In particular, the relationship between the symmetry properties of the local shear and the magnetic curvature is addressed for quasisymmetric configurations. The presence of symmetry breaking terms in the local shear can produce localized ballooning instabilities in regions of small average magnetic shear which lower first-ballooning stability thresholds and can potentially eliminate the second stability regime.

Journal Article↗

Working memory in chess.

Three experiments investigated the role of working memory in various aspects of thinking in chess. Experiment 1 examined the immediate memory for briefly presented chess positions from master games in players from a wide range of abilities, following the imposition of various secondary tasks designed to block separate components of working memory. Suppression of the articulatory loop (by preventing subvocal rehearsal) had no effect on measures of recall, whereas blocking the visuospatial sketchpad (by manipulation of a keypad) and blocking the central executive (by random letter generation) had equivalent disruptive effects, in comparison with a control condition. Experiment 2 investigated the effects of similar secondary tasks on the solution (i.e., move selection) of tactical chess positions, and a similar pattern was found, except that blocking the central executive was much more disruptive than in Experiment 1. Experiment 3 compared performance on two types of primary task, one concerned with solving chess positions as in Experiment 2, and the other a sentence-rearrangement task. The secondary tasks in each case were both designed to block the central executive, but one was verbal (vocal generation of random numbers), while the other was spatial in nature (random generation of keypresses). Performance of the spatial secondary task was affected to a greater extent by the chess primary task than by the verbal primary task, whereas there were no differential effects on these secondary tasks by the verbal primary task. In none of the three experiments were there any differential effects between weak and strong players. These results are interpreted in the context of the working-memory model and previous theories of the nature of cognition in chess.

Adult↗