Henry J. Gardner

A Wii remote, a game engine, five sensor bars and a virtual reality theatre

The Nintendo Wii Remote is having a huge impact on the computer games industry. This paper describes a project which is integrating this controller into a game environment in a multi-wall virtual reality theatre. Aspects considered include interaction taxonomies of the Wii controller, the extension of driver software to have the Wii controller deal with multiple Sensor Bars at once, and the porting of the game engine into the virtual reality theatre.

The bootstrap current in stellarators

A method of calculating the bootstrap current in asymmetric devices, such as the stellarator, is developed. The features that determine the bootstrap current are the variation of the magnetic‐field strength within a magnetic surface and the rotational transform. The shape of the magnetic surfaces is shown to be irrelevant. If the fraction of trapped particles is small, the device dependence of the bootstrap current is determined by a single constant which can be calculated by integrations of the field strength along the field lines. The relative dependence of the bootstrap current on the density and the temperature gradients is the same in any device with a small fraction of trapped particles as in a large aspect ratio tokamak.

Analyzing Ordinal Scales in Studies of Virtual Environments: Likert or Lump It!

Likert scaled data, which are frequently collected in studies of interaction in virtual environments, demand specialized statistical tools for analysis. The routine use of statistical methods appropriate for continuous data in this context can lead to significant inferential flaws. Likert scaled data are ordinal rather than interval scaled and need to be analyzed using rank based statistical procedures that are widely available. Likert scores are lumpy in the sense that they cluster around a small number of fixed values. This lumpiness is made worse by the tendency for subjects to cluster towards either the middle or the extremes of the scale. We suggest an ad hoc method to deal with such data which can involve a further lumping of the results followed by the application of nonparametric statistics. Averaging Likert scores over several different survey questions, which is sometimes done in studies of interaction in virtual environments, results in a different sort of lumpiness. The lumped variables which are obtained in this manner can be quite murky and should be used with great caution, if at all, particularly if the number of questions over which such averaging is carried out is small.

Head Tracking in First-Person Games: Interaction Using a Web-Camera

Recent advances in face-tracking technology have made it possible to recognize head movements using a commodity web-camera. This development has created exciting possibilities for enhancing player enjoyment during computer game play. In order to ascertain the real-world potential for head gestural input to First Person Shooter games, we have developed seven diverse interaction techniques and integrated these with a modern games engine. Evaluation of the techniques was carried out with four focus groups made up of expert games developers and experienced end-users. One of the techniques was further refined and subjected to a follow-up comparison test with promising results. A set of guidelines for the future development of head interaction techniques for computer games has been derived from the studies. All of the techniques have been built upon freely available software and open-sourced to encourage further research in this area.

Toroidally localized and nonlocalized ballooning instabilities in a stellarator

It is shown that the coexistence of toroidally nonlocalized ideal-hydromagnetic ballooning instabilities, with a quasidiscrete spectrum, and toroidally localized ballooning instabilities with a broad continuous spectrum, as predicted by Dewar and Glasser [Phys. Fluids 26, 3038 (1983)] can be realized in a Mercier-unstable equilibrium case modeling the Large Helical Device (LHD) [A. Iiyoshi et al., Fusion Technol. 17, 148 (1990)] with a broad pressure profile. The quasidiscrete, interchange branch corresponds to extended modes that can be understood on the basis of a ripple-averaged ballooning equation, whereas the broad-continuum, ballooning branch corresponds to modes localized along a flux tube. The physical origin of the two branches is discussed.

Calculation of Mercier stability limits of toroidal heliacs

The Mercier stability behaviour of toroidal heliacs can be dominated by pressure induced current parallel to the field lines which are resonant with values of the rotational transform per field period included in, or close to, the configuration. This issue is discussed with reference to a parameter survey for the H-1 heliac. It is shown that the calculated magnitude of the critical (β) against Mercier instability may vary, depending on whether the parallel currents are calculated directly from the curl of the magnetic field obtained from a 3D equilibrium code or, alternatively, from an algebraic expression derived from the appropriate magnetic differential equation

The transition and adoption to modern programming concepts for scientific computing in Fortran

This paper describes our experiences in the early exploration of modern concepts introduced in Fortran90 for large-scale scientific programming. We review our early work in expressing object-oriented concepts based on the new Fortran90 constructs - foreign to most programmers at the time - our experimental work in applying them to various applications, the impact on the WG5/J3 standards committees to consider formalizing object-oriented constructs for later versions of Fortran, and work in exploring how other modern programming techniques such as Design Patterns can and have impacted our software development. Applications will be drawn from plasma particle simulation and finite element adaptive mesh refinement for solid earth crustal deformation modeling.

Evolution of magnetic islands in a Heliac

Simulations of three‐dimensional equilibria in the H‐1 Heliac [Fusion Technol. 17, 123 (1990)] with the hint code [Phys. Fluids B 4, 1539 (1992)] show that the size of a dangerous magnetic island should increase with plasma pressure, but that a destruction of the equilibrium at low β is avoided because the rotational transform evolves to exclude the rational surface concerned. At higher pressures there is evidence of near‐resonant flux surface deformations, which may lead to an equilibrium limit. A reconnected equilibrium at still higher pressures exhibits a double island structure, which is similar to homoclinic phase portraits that have been observed after separatrix reconnection in Hamiltonian systems.

The Wiimote with multiple sensor bars: creating an affordable, virtual reality controller

A low-cost virtual-reality controller has been constructed from the Nintendo Wii Remote using multiple sensor bars. An agent-based algorithm has been used to allow the controller to move from one sensor bar to another, enabling it to be used in a surround, multiple-screen environment. User testing has verified that the system is suitable for use with a demanding, fast-paced, first-person-shooter game. The tuned version of the system was found to have a low error rate and to be favourably received by test participants. Our work has been open-sourced to encourage further research in this area.

Object-oriented design patterns in Fortran 90/95: mazev1, mazev2 and mazev3

This paper discusses the concept, application, and usefulness of software design patterns for scientific programming in Fortran 90/95. An example from the discipline of object-oriented design patterns, that of a game based on navigation through a maze, is used to describe how some important patterns can be implemented in Fortran 90/95 and how the progressive introduction of design patterns can usefully restructure Fortran software as it evolves. This example is complemented by a discussion of how design patterns have been used in a real-life simulation of Particle-in-Cell plasma physics. The following patterns are mentioned in this paper: Factory, Strategy, Template, Abstract Factory and Facade.