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Piloting a manual wheelchair is an important necessity for the everyday life and social activities of people with physical and sometimes cognitive disabilities. It requires complex capacities and may become tiring and stressful during indoor as well as outdoor activities. The enactment of laws relating to accessibility and discrimination, all around the world, has motivated researchers to verify building standards and to improve wheelchair ergonomics. Nowadays, the potential of Virtual Reality (VR) in training and daily living activities simulation is already well-known. The aim of this paper is to provide an updated review which explores various VR-based systems and studies related to wheelchair simulators. In particular, we consider wheelchair simulator characteristics according to a user centred view driven by perception and interaction, and wheelchair behavioral simulation. We continue with a description of wheelchair simulator application fields as well as a review of the various objectives for carrying out wheelchair simulation studies.

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EINLEITUNG: Das mentale Üben realer Bewegungsabläufe gewinnt als Instrument zur Verbesserung der Qualität von Bewegungsausführungen zunehmend an Bedeutung. Diese Methode des motorischen Lernens findet Anwendung sowohl im Bereich der sportlichen Ausbildung [1] als auch in der Rehabilitation motorischer Störungen, wie sie zum Beispiel nach einem zerebrovaskulärem Insult zu beobachten sind [2]. Die Entwicklung von Strategien des geistigen Übens motorischer Aktionen ohne sichtbare, real ausgeführte Bewegungen, hier im folgenden kurz als ideomotorisches Training oder mentales Üben bezeichnet, resultiert aus der Erkenntnis, daß motorisches Lernen kognitiv kontrolliert wird. Das mentale Training ist damit ein experimentelles und zunehmend auch klinisches Modell, an dem zentralnervale Aktivierungsprozesse der Handlungsregulation untersucht werden können. Ziel ist eine eindeutige Beschreibung mentaler Beanspruchungsphasen und ihre Differenzierung von anderen Versuchsabschnitten, z. B. von Phasen realer Bewegungsausführung oder von eingeschobenen Ruhephasen. Ein geeignetes physiologisches Korrelat zur qualitativen und quantitativen Charakterisierung zentralnervaler Aktivitätsänderungen während mentaler Beanspruchungsphasen ist die EEG-Grundaktivität. Die mehrkanalige, versuchsbegleitende Messung und numerische Auswertung des EEG ermöglicht sowohl topographische Aussagen über regionale Änderungen zentralnervaler Aktivierung als auch über ihre zeitliche Dynamik. Dafür wurde ein anpassungsfähiges EEG-Analyse-Programmpaket für IBM-kompatible PC/AT entwickelt, dessen aktueller Leistungsumfang und Erweiterungsmöglichkeiten vorgestellt werden.

Modern storage engines and key-value stores have come to rely on the log-structured merge-tree (LSM-tree) as their core data structure. LSM-tree operates by gradually merge-sorting data across levels of exponentially increasing capacities in storage. A crucial design dimension of LSM-tree is its compaction granularity. Some designs perform Full Merge , whereby entire levels get compacted at once. Others perform Partial Merge , whereby smaller groups of files with overlapping key ranges are compacted independently. This paper shows that both strategies exhibit serious flaws. With Full Merge, space-amplification is exorbitant. The reason is that while compacting the LSM-tree's largest level, there must be at least twice as much storage space as data to store both the original and new files until the compaction is finished. On the other hand, Partial Merge exhibits excessive write-amplification. The reason is twofold. (1) The files getting compacted typically do not have perfectly overlapping key ranges, and so some non-overlapping data is superfluously rewritten in each compaction. (2) Files with different lifetimes become interspersed within the SSD leading to high SSD garbage-collection overheads. As the data size grows, these problems grow in magnitude. We introduce Spooky, a novel compaction granulation method to address these problems. Spooky partitions data at the largest level into equally sized files, and it partitions data at smaller levels based on the file boundaries at the largest level. This allows merging one group of perfectly overlapping files at a time to limit space-amplification and compaction overheads. At the same time, Spooky writes larger though fewer files simultaneously so that files with different lifetimes do not become as interspersed within the SSD. This cheapens garbage-collection. We show empirically that Spooky achieves >2x lower space-amplification than Full Merge and >2x lower write-amplification than Partial Merge at the same time.