Abstract. In this paper, we present a partial-order reduction method for timed systems based on a local-time semantics for networks of timed automata. The main idea is to remove the implicit clock synchronization between processes in a network by letting local clocks in each process advance independently of clocks in other processes, and by requiring that two processes resynchronize their local time scales whenever they communicate. A symbolic version of this new semantics is developed in terms of predicate transformers, which enjoys the desired property that two predicate transformers are independent if they correspond to disjoint transitions in different processes. Thus we can apply standard partial order reduction techniques to the problem of checking reachability for timed systems, which avoid exploration of unnecessary interleavings of independent transitions. The price is that we must introduce extra machinery to perform the resynchronization operations on local clocks. Finally, we present a variant of DBM representation of symbolic states in the local time semantics for efficient implementation of our method. MotivationDuring the past few years, a number of verification tools have been developed for timed systems in the framework of timed automata (e.g. Kronos and Uppaal) [HH95,DOTY95,BLL + 96]. One of the major problems in applying these tools to industrial-size systems is the huge memory-usage (e.g. [BGK + 96]) needed to explore the state-space of a network (or product) of timed automata, since the verification tools must keep information not only on the control structure of the automata but also on the clock values specified by clock constraints.Partial-order reduction (e.g., [God96,GW90,HP94,Pel93,Val90,Val93]) is a well developed technique, whose purpose is to reduce the usage of time and memory in state-space exploration by avoiding to explore unnecessary interleavings of independent transitions. It has been successfully applied to finite-state systems. However, for timed systems there has been less progress. Perhaps the major obstacle to the application of partial order reduction to timed systems is the assumption that all clocks advance at the same speed, meaning that all clocks are implicitly synchronized. If each process contains (at least) one local clock, this means that advancement of the local clock of a process is not independent of time advancements in other processes. Therefore, different interleavings

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Describing user activity plays an essential role in ambient intelligence. In this work, we review different methods for human activity recognition, classified as data-driven and knowledge-based techniques. We focus on context ontologies whose ultimate goal is the tracking of human behavior. After studying upper and domain ontologies, both useful for human activity representation and inference, we establish an evaluation criterion to assess the suitability of the different candidate ontologies for this purpose. As a result, any missing features, which are relevant for modeling daily human behaviors, are identified as future challenges.

A high pressure is put on mobile devices to support increasingly advanced applications requiring more processing capabilities. Among those, the emerging High Efficiency Video Coding (HEVC) provides a better video quality for the same bit rate than the previous H.264 standard. A limitation in the usability of a mobile video playing device is the lack of support for guaranteeing stand-by time and up time for battery driven devices. The Green Metadata initiative within the MPEG standard was launched to address the power saving issues of the decoder and defines the technology requirements. In this paper, we propose a HEVC decoder with tunable decoding quality levels for maximum power savings as suggested in the scope of the Green Metadata initiative. Our experiments reveal that the modified HEVC video decoder can save up to 28 % of power consumption in real-world platforms while keeping better quality than decoding with H.264.

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BackgroundLow levels of physical activity, musculoskeletal morbidity and weight gain are commonly reported problems in children with cancer. Intensive medical treatment and a decline in physical activity may also result in reduced motor performance. Therefore, simple and inexpensive ways to promote physical activity and exercise are becoming an increasingly important part of children’s cancer treatment.MethodsThe aim of this study is to evaluate the effect of active video games in promotion of physical activity in children with cancer. The research is conducted as a parallel randomized clinical trial with follow-up. Patients between 3 and 16 years old, diagnosed with cancer and treated with vincristine in two specialized medical centers are asked to participate. Based on statistical estimates, the target enrollment is 40 patients. The intervention includes playing elective active video games and, in addition, education and consultations for the family. The control group will receive a general recommendation for physical activity for 30 minutes per day. The main outcomes are the amount of physical activity and sedentary behavior. Other outcomes include motor performance, fatigue and metabolic risk factors. The outcomes are examined with questionnaires, diaries, physical examinations and blood tests at baseline and at 2, 6, 12 and 30 months after the baseline. Additionally, the children’s perceptions of the most enjoyable activation methods are explored through an interview at 2 months.DiscussionThis trial will help to answer the question of whether playing active video games is beneficial for children with cancer. It will also provide further reasoning for physical activity promotion and training of motor skills during treatment.Trial registrationClinicalTrials.gov identifier: NCT01748058 (October 15, 2012).