316,875 research outputs found

    Fatigue crack propagation in microcapsule toughened epoxy

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    The addition of liquid-filled urea-formaldehyde (UF) microcapsules to an epoxy matrix leads to significant reduction in fatigue crack growth rate and corresponding increase in fatigue life. Mode-I fatigue crack propagation is measured using a tapered doublecantilever beam (TDCB) specimen for a range of microcapsule concentrations and sizes: 0, 5, 10, and 20% by weight and 50, 180, and 460 micron diameter. Cyclic crack growth in both the neat epoxy and epoxy filled with microcapsules obeys the Paris power law. Above a transition value of the applied stress intensity factor, which corresponds to loading conditions where the size of the plastic zone approaches the size of the embedded microcapsules, the Paris law exponent decreases with increasing content of microcapsules, ranging from 9.7 for neat epoxy to approximately 4.5 for concentrations above 10 wt% microcapsules. Improved resistance to fatigue crack propagation, indicated by both the decreased crack growth rates and increased cyclic stress intensity for the onset of unstable fatigue-crack growth, is attributed to toughening mechanisms induced by the embedded microcapsules as well as crack shielding due to the release of fluid as the capsules are ruptured. In addition to increasing the inherent fatigue life of epoxy, embedded microcapsules filled with an appropriate healing agent provide a potential mechanism for self-healing of fatigue damage.published or submitted for publicationis peer reviewe

    Changing Identity: The Emergence of Social Groups

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    The original Homo Economicus has progressed from an atomistic and self-interested individual to a socially embedded agent in modern economics. In particular, social interaction models suggest that the individual’s own utility of undertaking an action may be influenced by the number of peers taking this same action. Hence, people gain by conforming to, or differentiating their behaviour from that of others. A number of papers have also suggested why people want to conform. In particular, Akerlof and Kranton (2000, 2002, 2005) suggest that people belong to certain groups and wish to adopt the corresponding social identity by behaving according to the behavioural prescriptions of these groups. In this paper, we present a social interaction model that is based on a different account of identity. The concept of identity used here is on a more personal level and suggests that people have desired self-images of themselves that they wish to attain at some time in the future. Hence, individuals aim to transform their current individual characteristics into those of their self-image. They try to achieve this by joining social groups and adopting the typical characteristics of these groups. However, groups will be modified over time by the people joining them. This may induce individuals to revise their previous choices and eventually to move on and to choose different groups. The model thus presents an endogeneous interaction structure and offers an account of endogenous group formation as well as an endogenous evolution of personal identity. We further study in what sense and under what conditions the dynamics at the individual and at the social level will reach an “equilibrium” and what the nature of such an equilibrium is.Economic agent, social interaction, conformity, personal identity, self-image, change

    The Rational Agent or the Relational Agent: Moving from Freedom to Justice in Migration Systems Ethics

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    Most accounts of immigration ethics implicitly rely upon neoclassical migration theory, which understands migration as the result of poverty and unemployment in sending countries. This paper argues that neoclassical migration theory assumes an account of the human person as solely an autonomous rational agent which then leads to ethics of migration which overemphasize freedom and self-determination. This tendency to assume that migration works as neoclassical migration theory describes is shared by political philosophers, such as Joseph Carens, Michael Walzer, and David Miller. This paper argues that all three philosophers incorrectly frame migration as a contest between the freedom of the migrant and the communal self-determination of the political community. Migration systems theory is presented as a theory that draws upon a relationally embedded understanding of autonomy in order to begin to develop a migration systems ethics. This paper concludes by arguing that the central ethical category for an ethics of migration is not freedom or self-determination, but justice-in-relation

    Engineering self-organizing urban superorganisms

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    Progresses in ubiquitous, embedded, and social networking and computing make possible for people in urban areas to dynamically interact with each other and with ICT devices around. This can result in a system with a very large number of agents working together in an orchestrated and self-organizing way to achieve specific urban-level goals, i.e., as if they were a “superorganism”. In this paper, we sketch the future vision of urban superorganisms and overview some emerging application areas heading towards the vision. Following, we identify the key challenges in engineering self-organizing multi-agent systems that can work as a superorganism, i.e., seamlessly involving ICT agents and human agents so to achieve some required urban level goals. Finally, we introduce the reference architecture for an infrastructure to support our future vision of self-organizing urban superorganisms

    ProDial – an annotated proactive dialogue act corpus for conversational assistants using crowdsourcing

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    Proactive behaviour is an integral interaction concept of both human-human as well as human-computer cooperation. However, modelling proactive systems and appropriate interaction strategies are still an open quest. In this work, a parameterised and annotated dialogue corpus has been created. The corpus is based on human interactions with an autonomous agent embedded in a serious game setting. For modelling proactive dialogue behaviour, the agent was capable of selecting from four different proactive actions (None, Notification, Suggestion, Intervention) in order to serve as the user’s personal advisor in a sequential planning task. Data was collected online using crowdsourcing (308 participants) resulting in a total of 3696 system-user exchanges. Data was annotated with objective features as well as subjectively self-reported features for capturing the interplay between proactive behaviour and situational as well as user-dependent characteristics. The corpus is intended for building a user model for developing trustworthy proactive interaction strategies

    Robotic ubiquitous cognitive ecology for smart homes

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    Robotic ecologies are networks of heterogeneous robotic devices pervasively embedded in everyday environments, where they cooperate to perform complex tasks. While their potential makes them increasingly popular, one fundamental problem is how to make them both autonomous and adaptive, so as to reduce the amount of preparation, pre-programming and human supervision that they require in real world applications. The project RUBICON develops learning solutions which yield cheaper, adaptive and efficient coordination of robotic ecologies. The approach we pursue builds upon a unique combination of methods from cognitive robotics, machine learning, planning and agent- based control, and wireless sensor networks. This paper illustrates the innovations advanced by RUBICON in each of these fronts before describing how the resulting techniques have been integrated and applied to a smart home scenario. The resulting system is able to provide useful services and pro-actively assist the users in their activities. RUBICON learns through an incremental and progressive approach driven by the feed- back received from its own activities and from the user, while also self-organizing the manner in which it uses available sensors, actuators and other functional components in the process. This paper summarises some of the lessons learned by adopting such an approach and outlines promising directions for future work

    Damage detection and healing performance monitoring using embedded piezoelectric transducers in large-scale concrete structures

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    Concrete keeps being the leading structural material due to its low production cost and its great structural design flexibility. However, concrete is prone to various ambient and operational loads which are responsible for crack initiation and extension, leading to decrease of its anticipated operational service life. The current study is focusing on the use of ultrasonic wave propagation techniques based on low-cost and aggregate-size embedded piezoelectric transducers for the online monitoring of the damage state and the healing performance in concrete structures with an autonomous healing system in the form of encapsulated polyurethane-based healing agent embedded in the matrix of concrete. The crack formation triggers the autonomous healing mechanism which promises material recovery and extension of the operational service life. The proposed technique is applied on large-scale, steel reinforced, concrete beams (150mm × 250 mm × 3000 mm), subjected to four-point bending. After the capsules are broken and the healing agent is released, which results in filling of the crack void, and polymerized, the concrete beams are reloaded. The results demonstrate the ability of the monitoring system to detect the initiation and propagation of the cracking as well as to assess the performance of the self-healing system
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