Kenneth Holmlund

Using a virtual reality system to study balance and walking in a virtual outdoor environment: a pilot study.

Using a virtual reality system to study balance and walking in a virtual outdoor environment : a pilot study.

Langevin simulations of two-dimensional vortex fluctuations: Anomalous dynamics and IV exponent.

The dynamics of two-dimensional (2D) vortex fluctuations is investigated through simulations of the 2D Coulomb gas model in which vortices are represented by soft disks with logarithmic interactions. The simulations strongly support a recent suggestion that 2D vortex fluctuations obey an intrinsic anomalous dynamics manifested in a long-range 1/{ital t} tail in the vortex correlations. A nonlinear {ital IV} exponent {ital a}, which is different from the commonly used Ambegaokar-Halperin-Nelson-Siggia exponent {ital a}{sub AHNS} and is given by {ital a}=2{ital a}{sub AHNS}{minus}3, is confirmed by the simulations. The results are discussed in the context of earlier simulations, experiments, and a phenomenological description. {copyright} {ital 1996 The American Physical Society.}

Altered walking pattern in a virtual environment

Falls and fractures among elderly persons constitute a major health problem. Many falls occur while walking and falls that occur during turning often result in a fracture. Methods aimed at understanding the complex mechanisms involved in walking should therefore assess tested individuals during walks and turns. In order to identify persons at risk and take the correct preventive measures, it is important to find methods that quantify movements as the tested persons are processing multisensory input. In a clinical setting this is sometimes difficult to achieve in a controlled manner, since tests are difficult to set exactly the same from one time to another. Using a virtual environment (VE) and a tracker system, conditions such as light, sound, events, body movements, and room size can be controlled and measured. Tests in VE can therefore be identically reproduced over and over again to evaluate if a person can withstand changing outer demands at any given moment. In order to perform quantitative measures 8 persons (2174 years) were tested in immersive virtual reality. The VE was a corridor in which expected and unexpected events could be produced. Events studied were doors swinging open in front of the subjects during a walk and a virtual tilting of the environment. Trackers were used for collecting and analyzing the movement data. Our results show that the system was well tolerated among the subjects and that there was a clear tendency that the system could generate fall tendency among the subjects. There was also a difference among the subjects regarding walking strategies when subjected to the various events.

The development of a virtual reality system to study tendency of falling among older people

Injuries related to falls are a major threat to older persons health. A fall may not only result in an injury, but also in a decreased sense of autonomy in the persons daily life. In order to be able to prevent such falls there is a need to further understand the complex mechanisms involved in balance and walking. Here we present an immersive virtual reality system in which a person can move around, while being subjected to various events, which may influence balance and walking.

I–V characteristics for 2D superconductors from simulations of the 2D Coulomb gas: density dependence and exponents

Abstract The two-dimensional Coulomb gas with Langevin dynamics is simulated. The relation between the Coulomb gas charge current, I CG , an applied electric field, E , and the particle density, n p , is investigated. To leading order it is found that I CG ∝ E a n p 1− b below the Kosterlitz-Thouless transition. The new exponent b is determined together with the exponent a and the exponents are compared to current theories. Consequences for the non-linear I – V characteristics of two-dimensional superconductors are described.