Virtual reality in neurologic rehabilitation of spatial disorientation

BACKGROUND: Topographical disorientation (TD) is a severe and persistent impairment of spatial orientation and navigation in familiar as well as new environments and a common consequence of brain damage. Virtual reality (VR) provides a new tool for the assessment and rehabilitation of TD. In VR training programs different degrees of active motor control over navigation may be implemented (i.e. more passive spatial navigation vs. more active). Increasing demands of active motor control may overload those visuo-spatial resources necessary for learning spatial orientation and navigation. In the present study we used a VR-based verbally-guided passive navigation training program to improve general spatial abilities in neurologic patients with spatial disorientation. METHODS: Eleven neurologic patients with focal brain lesions, which showed deficits in spatial orientation, as well as 11 neurologic healthy controls performed a route finding training in a virtual environment. Participants learned and recalled different routes for navigation in a virtual city over five training sessions. Before and after VR training, general spatial abilities were assessed with standardized neuropsychological tests. RESULTS: Route finding ability in the VR task increased over the five training sessions. Moreover, both groups improved different aspects of spatial abilities after VR training in comparison to the spatial performance before VR training. CONCLUSIONS: Verbally-guided passive navigation training in VR enhances general spatial cognition in neurologic patients with spatial disorientation as well as in healthy controls and can therefore be useful in the rehabilitation of spatial deficits associated with TD

Integration of Expert Systems and Neural Networks for the Control of Fermentation Processes

Expert systems and neural networks are new tools for the control of fermentation processes. With expert systems the fermentation plant and the process itself is modelled via a generalized, qualitative system description based on the experience of human experts. On the other hand neural networks and interpolating associative memories can learn the process behaviour directly by process observation. The paper at hand reports, how both control techniques can be combined for purposes like process supervision, modelling and optimization of biological plants

Sublimation of organic-rich comet analog materials and their relevance in fracture formation

Aims. The morphology of cometary nuclei is the result of an ongoing evolution and can provide valuable information to constrain the composition of comets. In our laboratory experiments we investigated the morphological evolution of comet analog materials, which consist of volatile, dust, and organic components. The laboratory results are aimed to help understand the evolution of cometary surfaces. Methods. We used spherical particles of fly ash and mixtures of ice, glycine, and sodium acetate as analog materials in different mass ratios to reproduce observed cometary morphologies. The cohesive and gravitational properties in the laboratory are scaled to cometary conditions to draw meaningful conclusions from the experimental results. The samples were placed in a vacuum sublimation chamber, cooled down to below 150 K, and were insolated with an external light source. To analyze the morphology of the samples, a camera was used to monitor the alterations of the surface. Results. Organic components in volatile-rich samples can have a distinct adhesive effect after the volatiles sublimate. During the sublimation process the sample volume decreases and fractures form on the sample surface. Due to the stability of the remaining volatile-depleted material, significant cliff collapses or ejected particles were not observed in the laboratory

Tensile strength of dust-ice mixtures and their relevance as cometary analog material

Aims. The tensile strength of granular matter is of great importance to our understanding of the evolution of comets and to our attempts to reproduce processes on cometary surfaces in laboratory experiments. In this work, we investigate the tensile strength of three different materials and their mixtures, which can be used as cometary analog materials in the laboratory. Methods. We used two types of siliceous dusts and granular water ice whose polydisperse particles were either angular or spherical. Our samples were cooled to below 150 K to better simulate the conditions of a cometary surface and to avoid thermal alteration of the material. We used the Brazilian disk test method to exert stress on the cooled samples and determine the tensile strength at the moment the samples broke. Results. We find that the tensile strength of two component mixtures is strongly dominated by the component with the higher tensile strength. The materials made of mostly angular dust particles have a lower filling fraction, but a higher tensile strength compared to materials made of spherical particles. Furthermore, the tensile strength of the cooled components is substantially lower than the tensile strength of the same components at room temperature. This implies that the surface energy of the investigated materials at low temperatures is significantly lower than previously assumed