Generalised Nonblocking

This paper studies the nonblocking check used in supervisory control of discrete event systems and its limitations. Different examples with different liveness requirements are discussed. It is shown that the standard nonblocking check can be used to specify most requirements of interest, but that it lacks expressive power in a few cases. A generalised nonblocking check is proposed to overcome the weakness, and its relationship to standard nonblocking is explored. Results suggest that generalised nonblocking, while having the same useful properties with respect to synthesis and compositional verification, can provide for more concise problem representations in some cases

Compositional nonblocking verificationusing generalised nonblocking abstractions

This paper proposes a method for compositional verification of the standard and generalized nonblocking properties of large discrete event systems. The method is efficient as it avoids the explicit construction of the complete state space by considering and simplifying individual subsystems before they are composed further. Simplification is done using a set of abstraction rules preserving generalized nonblocking equivalence, which are shown to be correct and computationally feasible. Experimental results demonstrate the suitability of the method to verify several large-scale discrete event systems models both for standard and generalized nonblocking

Hierarchical interface-based supervisory control using the conflict preorder

Hierarchical Interface-Based Supervisory Control decomposes a large discrete event system into subsystems linked to each other by interfaces, facilitating the design of complex systems and the re-use of components. By ensuring that each subsystem satisfies its interface consistency conditions locally, it can be ensured that the complete system is controllable and nonblocking. The interface consistency conditions proposed in this paper are based on the conflict preorder, providing increased flexibility over previous approaches. The framework requires only a small number of interface consistency conditions, and allows for the design of multi-level hierarchies that are provably controllable and nonblocking

Seven abstraction rules preserving generalised nonblocking

This working paper proposes a compositional approach to verify the generalised nonblocking property of discrete-event systems. Generalised nonblocking is introduced in [15] to overcome weaknesses of the standard nonblocking check in discrete-event systems and increase the scope of liveness properties that can be handled. This paper addresses the question of how generalised nonblocking can be verified efficiently. The explicit construction of the complete state space is avoided by first composing and simplifying individual components in ways that preserve generalised nonblocking. The paper extends and generalises previous results about compositional verification of standard nonblocking and lists a new set of computationally feasible abstraction rules for standard and generalised nonblocking

Incremental verification of co-observability in discrete-event systems

Existing strategies for verifying co-observability, one of the properties that must be satisfied for synthesizing solutions to decentralized supervisory control problems, require the construction of the complete system model. When the system is composed of many subsystems, these monolithic approaches may be impractical due to the state-space explosion problem. To address this issue, we introduce an incremental verification of co-observability approach. Selected subgroups of the system are evaluated individually, until verification of co-observability is complete. The new method is potentially much more efficient than the monolithic approaches, in particular for systems composed of many subsystems, allowing for some intractable state-space explosion problems to be manageable. Properties of this new strategy are presented, along with a corresponding algorithm and an example

Hierarchical modelling of manufacturing systems using discrete event systems and the conflict preorder

This paper introduces Hierarchical Interface-Based Supervisory Control using the Conflict Preorder and applies it to the design of two manufacturing systems models of practical scale. Hierarchical Interface-Based Supervisory Control decomposes a large system into subsystems linked to each other by interfaces, facilitating the design of complex systems and the re-use of components. By ensuring that each subsystem satisfies its interface consistency conditions locally, it can be ensured that the complete system is controllable and nonblocking. The interface consistency conditions proposed in this paper are based on the conflict preorder, providing increased flexibility over previous approaches. The framework requires only a small number of interface consistency conditions, and allows for the design of multi-level hierarchies that are provably controllable and nonblocking

Farmers' perceived values in conventional and organic farming: A comparison between French, Irish and Swedish farmers using the Means-end chain approach

Values act as driving forces for individuals to behave in a certain way or to choose certain actions. They may explain current differences of converted organic land among EU countries. In this paper, we identified and compared the types of values, economic and other, that motivate farmers to choose certified organic or con-ventional production systems in France, Ireland and Sweden. To identify these values, we analysed and compared attribute-consequence-value representations of the choice of production systems among farmers, using a Means-end chain approach. Seventy-eight in-depth laddering interviews were conducted to explore how farmers characterised their choice, the consequences they perceived from these characteristics and the values they associated with these consequences. The uncovered values were classified along Rokeach's typology to distin-guish between instrumental and terminal values. Results indicate that both farmers with a conventional farm and farmers with a certified organic farm are driven by complex sets of financial, business, or productivity values and by non-financial, non-business, or non-productivity values. Findings are useful to policy makers and farm ad -visors, who can use these results to develop more efficient communication schemes to promote organic farming. The findings can also be communicated to consumers and the public in order to encourage consumption

Cardiovascular and Stride Frequency Differences During Land and Aquatic Treadmill Walking

This study examined heart rate (HR) and stride frequency (SF) values of 30 college-aged males and females during dry-land (DL) and aquatic walking (AW). Aquatic walking trials were completed in an underwater treadmill with the water depth at waist level; the water temperature (31℃ ± 0.1℃) and room temperature (26.6℃ ± 0.1℃) were maintained at thermoneutral levels throughout the study. During each walking condition, HR and SF were recorded at treadmill speeds of 1 mph, 2 mph, and 3 mph. Participants were instructed to walk with their hands at their sides swinging as they would when walking on dry-land unless they felt the need to use the handrails to steady themselves. Heart rate monitors were used to record cardiovascular changes, and strides were measured from consecutive left and right toe strikes. Results of the study indicated HR was significantly higher during DL than AW at 1 mph (p \u3c .001) and 3 mph (p \u3c .001) but was not significantly different (p = .64) at 2 mph. The SF of the participants was significantly lower (p \u3c .001) during AW than DL at all speeds. When comparing sex, females had significantly higher HR at 1 mph (p = .012), 2 mph (p = .007), and 3 mph (p \u3c .001) than males for DL conditions. No differences in HR were found during the AW conditions (F = 0.66, p = 0.44, ηp2 = 0.02). No differences in SF were observed between males and females in both DL (F = 2.96, p = 0.06, ηp2 = 0.09) and AW (F = 1.03, p = 0.32, ηp2 = 0.036) conditions. As a result, AW increased HR values similar to those of DL, but without the added stress to the lower extremities due to the buoyancy of the water. Thus, AW provided an exercise medium capable of meeting the ACSM intensity guidelines for PA and allowed adults to be physically active presumably with less stress on the lower body

European farmer perspectives and their adoption of ecological practices

Delivering an agricultural policy which meets ecosystem and climatic pressures and addresses weaknesses in our current food system presents complex challenges for food producers. Adoption of ecological practices will reduce the dependence on imports into the farm and is one way to meet some of these policy ambitions. Understanding why farmers do or don’t adopt these practices is key to enabling this transition. This study outlines a series of investigations into the key barriers, values and perceptions towards ecological practice adoption across European farming. We find that personal, technical and institutional forces influence the adoption of more sustainable practices but these forces have varying levels of influence. The tensions between environmental, compared to purely production orientated motivations, may be a key barrier to ecological practice adoption. We also find a strong influence of commodity supply chains which may either encourage or limit adoption of these approaches. Promoting efforts for co-ordinated approaches between the public and private sectors may mitigate some of the dissonance in messaging towards these practices and alleviate these tensions. We also identify a great deal of heterogeneity within the European farming community and argue for a more targeted approach that would encourage adoption of ecological approaches and promote the scaling up of these practices. <br/

European farmer perspectives and their adoption of ecological practices

Delivering an agricultural policy which meets ecosystem and climatic pressures and addresses weaknesses in our current food system presents complex challenges for food producers. Adoption of ecological practices will reduce the dependence on imports into the farm and is one way to meet some of these policy ambitions. Understanding why farmers do or don’t adopt these practices is key to enabling this transition. This study outlines a series of investigations into the key barriers, values and perceptions towards ecological practice adoption across European farming.We find that personal, technical and institutional forces influence the adoption of more sustainable practices but these forces have varying levels of influence. The tensions between environmental, compared to purely production orientated motivations, may be a key barrier to ecological practice adoption. We also find a strong influence of commodity supply chains which may either encourage or limit adoption of these approaches. Promoting efforts for co-ordinated approaches between the public and private sectors may mitigate some of the dissonance in messaging towards these practices and alleviate these tensions. We also identify a great deal of heterogeneity within the European farming community and argue for a more targeted approach that would encourage adoption of ecological approaches and promote the scaling up of these practices