Cones and foci: A mechanical framework for protocol verification

We define a cones and foci proof method, which rephrases the question whether two system specifications are branching bisimilar in terms of proof obligations on relations between data objects. Compared to the original cones and foci method from Groote and Springintveld, our method is more generally applicable, because it does not require a preprocessing step to eliminate τ-loops. We prove soundness of our approach and present a set of rules to prove the reachability of focus points. Our method has been formalized and proved correct using PVS. Thus we have established a framework for mechanical protocol verification. We apply this framework to the Concurrent Alternating Bit Protocol.

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Technologies towards patterned optical foils applied to transflective LCDs

Abstract— For better front‐of‐screen performance for transflective LCDs, a technology with extra free optimization parameters for the optical stack is needed. Thin wet coatable retarders which enable adjustment of the optical activity on the (sub)pixel level have been developed. Isotropic domains have been created in nematic retardation films by thermal patterning or photopatterning. Employing such a patterned retarder in a transflective LCD leads to an LCD that is lighter and thinner with good reflectivity, high transmission, and low chromaticity at all gray levels and wide viewing angles. The patterned thin‐film technology has been proven to be versatile and applicable in various LCD designs.     

How to keep from falling forward: elementary swing leg action for passive dynamic walkers

Stability control for walking bipeds has been considered a complex task. Even two-dimensional fore-aft stability in dynamic walking appears to be difficult to achieve. In this paper we prove the contrary, starting from the basic belief that in nature stability control must be the sum of a number of very simple rules. We study the global stability of the simplest walking model by determining the basin of attraction of the Poincare/spl acute/ map of this model. This shows that the walker, although stable, can only handle very small disturbances. It mostly falls, either forward or backward. We show that it is impossible for any form of swing leg control to solve backward falling. For the problem of forward falling, we devise a simple but very effective rule for swing leg action: "You will never fall forward if you put your swing leg fast enough in front of your stance leg. In order to prevent falling backward the next step, the swing leg shouldn't be too far in front." The effectiveness of this rule is demonstrated with our prototype "Mike.".     

A system to test the ground surface conditions of construction sites--for safe and efficient work without physical strain

Ground surface conditions on construction sites have an important influence on the health and safety of workers and their productivity. The development of an expert-based "working conditions evaluation" system is described, intended to assist site managers in recognising unsatisfactory ground conditions and remedying these. The system was evaluated in the period 2002-2003. The evaluation shows that companies recognize poor soil/ground conditions as problematic, but are not aware of the specific physical workload hazards. The developed methods allow assessment of the ground surface quality and selection of appropriate measures for improvement. However, barriers exist at present to wide implementation of the system across the industry. Most significant of these is that responsibility for a site's condition is not clearly located within contracting arrangements, nor is it a topic of serious negotiation.     

Behavioural change phases of different stakeholders involved in the implementation process of ergonomics measures in bricklaying

The objective of this qualitative study was to assess whether a hypothesised sequential order of behavioural change phases would be fulfilled in different groups of stakeholders involved at the start of a process to implement ergonomic [corrected] measures in bricklaying teams. The measures include trestles, bricklaying scaffolds, mast climbing work platforms [corrected] and cranes. The behavioural change phases were: (1) being aware of measures, (2) understanding measures, (3) wanting measures, (4) intention to buy or hire measures, (5) ability to use measures, (6) using measures (experience), and (7) continuing to use measures. Structured interviews were conducted to examine the change phases in two groups of stakeholders (employers/work planners (n=11) [corrected] and foremen/bricklayers (n=9) [corrected] from nine companies) thought to be relevant in the decision to adopt and use the ergonomic [corrected] measures. The results show that the fulfilled behavioural change phases differ between individual stakeholders, groups of stakeholders, companies and also between ergonomic measures. The hypothesised order of fulfilled consecutive behavioural change phases for individual stakeholders has not been confirmed by this study. The relationship between [corrected] fulfilled and unfulfilled change phases by each stakeholder (group) and actual use of each ergonomic measure requires further study, so as to improve the selection of suitable implementation strategies [corrected]     

Correlations between Horn fractions, satisfiability and solver performance for fixed density random 3-CNF instances

An enhanced concept of sub-optimal reverse Horn fraction of a CNF-formula was introduced in [18]. It was shown that this fraction is very useful in effectively (almost) separating 3-colorable random graphs with fixed node-edge density from the non-3-colorable ones. A correlation between this enhanced sub-optimal reverse Horn fraction and satisfiability of random 3-SAT instances with a fixed density was observed. In this paper, we present experimental evidence that this correlation scales to larger-sized instances and that it extends to solver performances as well, both of complete and incomplete solvers. Furthermore, we give a motivation for various phases in the algorithm aHS, establishing the enhanced sub-optimal reverse Horn fraction, and we present clear evidence for the fact that the observed correlations are stronger than correlations between satisfiability and sub-optimal MAXSAT-fractions established similarly to the enhanced sub-optimal reverse Horn fraction. The latter observation is noteworthy because the correlation between satisfiability and the optimal MAXSAT-fraction is obviously 100%. AMS subject classification 90C05, 03B99, 68Q01, 68W01     

Verification of a sliding window protocol in μCRL and PVS

We prove the correctness of a sliding window protocol with an arbitrary finite window size n and sequence numbers modulo 2n. The correctness consists of showing that the sliding window protocol is branching bisimilar to a queue of capacity 2n. The proof is given entirely on the basis of an axiomatic theory, and has been checked in the theorem prover PVS. Received November 2004 Revised June 2005 Accepted July 2005 by J. V. Tucker     

Effects of antagonistic co-contraction on differences between electromyography based and optimization based estimates of spinal forces

Estimates of spinal forces are quite sensitive to model assumptions, especially regarding antagonistic co-contraction. Optimization based models predict co-contraction to be absent, while electromyography (EMG) based models take co-contraction into account, but usually assume equal activation of deep and superficial parts of a muscle. The aim of the present study was to compare EMG based and optimization based estimates of spinal forces in a wide range of work tasks. Data obtained from ten subjects performing a total of 28 tasks were analysed with an EMG driven model and three optimization models, which were specifically designed to test the effects of the above assumptions. Estimates of peak spinal forces obtained using the different modelling approaches were similar for total muscle force and its compression component (on average EMG based predictions were 5% higher) and were closely related (R > 0.92), while differences in predictions of the peak shear component of muscle force were more substantial (with up to 39% lower estimates in optimization based models, R > 0.79). The results show that neither neglecting antagonistic co-contraction, nor assuming equal activation of deep and superficial muscles, has a major effect on estimates of spinal forces. The disparity between shear force predictions was due to an overestimation of activity of the lateral part of the internal oblique muscle by the optimization models, which is explained by the cost function preferentially recruiting larger muscles. This suggests that a penalty for active muscle mass should be included in the cost function used for predicting trunk muscle recruitment.