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In the past decade, the number of distributed computing paradigms and systems has been grown up rapidly due to the reduced cost of computing resources and the popularization of the Internet. Among those computing paradigms and sys...
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In the past decade, the number of distributed computing paradigms and systems has been grown up rapidly due to the reduced cost of computing resources and the popularization of the Internet. Among those computing paradigms and systems, mobile-agent-based systems are becoming prevalent because they are more flexible and more reconfigurable at runtime. Applications running on a mobile-agent system may produce mobile-agent garbage, which wastes system resources and eventually becomes harmful to system performance and reliability. The major challenge of the problem is that, the mobility property and the decentralization nature make it hard to trace and to collect mobile-agent garbage automatically. In this paper, we use the actor garbage collection model to theoretically depict how mobile-agent garbage is collected. We propose an efficient distributed garbage collecting mechanism called actor-based weighted reference counting algorithm to collect garbage of mobile agents. The experimental results show that the proposed algorithm is efficient than a recent similar method.
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Wireless sensor and actor networks (WSANs) have recently emerged with the idea of combining wireless sensor networks (WSNs) and mobile ad hoc networks (MANETs). In addition to resource constrained sensors, resource rich and mobile...
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Wireless sensor and actor networks (WSANs) have recently emerged with the idea of combining wireless sensor networks (WSNs) and mobile ad hoc networks (MANETs). In addition to resource constrained sensors, resource rich and mobile actor nodes are employed in WSANs. These actors can collect data from the sensors and perform appropriate actions as a result of processing such data. To perform the actions at all parts of the region in a timely manner, the actors should be deployed in such a way that they might be able to communicate with each other and cover the whole monitored area. This requires that the actors should be placed carefully prior to network operation in order to maximize the coverage and maintain the inter-actor connectivity. In this paper, we propose a distributed actor deployment algorithm that strives to maximize the coverage of actors without violating the connectivity requirement. The approach applies repelling forces between neighboring actors and from the sensors that sit on the boundaries in order to spread them in the region. The spreading of the nodes is done using a tree of actors which can provide more freedom for the movement of the nodes but at the same time maintain the required connectivity among the nodes. We present two techniques for creation of such an actor tree which are based on local pruning of the actor links and spanning tree of the inter-actor network. The performance of our approach is validated both analytically and experimentally.
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This research aims to further explore the civil war that is taking place in Syria. This paper questions fundamentally, why did the civil war in Syria become a prolonged armed conflict? Or are there other factors that strengthen th...
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This research aims to further explore the civil war that is taking place in Syria. This paper questions fundamentally, why did the civil war in Syria become a prolonged armed conflict? Or are there other factors that strengthen the strength of their resistance? This research offers a novelty of research on the situation of this conflict, is that the prolonged civil war in Syria is not only caused by internal conditions, but also the involvement of external actors. As with the approach of David E. Cunningham (2010) that the involvement of external actors in civil war produces two possibilities, namely; become a negotiating facilitator and help one party win. This research reveals that the involvement of external actors interventions - regional, international and transnational – actually prolongs the conflict. This is because the involvement of external actors causes the addition of combatants in the conflict, so the preference in the conflict increases.
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Modern environments for modelling and designing concurrent computational systems increasingly support heterogeneous system models, which are characterised by different coordination mechanisms governing the interaction between conc...
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Modern environments for modelling and designing concurrent computational systems increasingly support heterogeneous system models, which are characterised by different coordination mechanisms governing the interaction between concurrent components in different parts or at different levels of the model. These interaction semantics, also called models of computation, pose a major challenge to the definition of the meaning of heterogeneous models, especially if such a definition is to be independent of any specific set of models of computation, ways of describing actors, or notations for describing models. This paper makes three main contributions. (1) It presents a framework for describing the semantics of actors and models of computation. Its central notion is the concept of a model of computation as a program transformation that composes actor descriptions into a description of a composite actor. This framework is entirely independent of any specific syntax for describing actors, or any particular modelling language. (2) It uses this framework to describe properties of actor compositions and models of computation, and to classify and analyse them. (3) Finally, it discusses the implications of this theory for the design of languages for describing actors and models of computation.
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Expressing parallelism and coordination is central for modern concurrent programming. Many mechanisms exist for expressing both parallelism and coordination. However, the design decisions for these two mechanisms are tightly inter...
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Expressing parallelism and coordination is central for modern concurrent programming. Many mechanisms exist for expressing both parallelism and coordination. However, the design decisions for these two mechanisms are tightly intertwined. We believe that the interdependence of these two mechanisms should be recognised and achieved through a single, powerful primitive. We are not the first to realise this: the prime example is actor model programming, where parallelism arises through fine-grained decomposition of a program’s state into actors that are able to execute independently in parallel. However, actor model programming has a serious pain point: updating multiple actors as a single atomic operation is a challenging task. We address this pain point by introducing a new concurrency paradigm: Behaviour-Oriented Concurrency (BoC). In BoC, we are revisiting the fundamental concept of a behaviour to provide a more transactional concurrency model. BoC enables asynchronously creating atomic and ordered units of work with exclusive access to a collection of independent resources. In this paper, we describe BoC informally in terms of examples, which demonstrate the advantages of exclusive access to several independent resources, as well as the need for ordering. We define it through a formal model. We demonstrate its practicality by implementing a C++ runtime. We argue its applicability through the Savina benchmark suite: benchmarks in this suite can be more compactly represented using BoC in place of Actors, and we observe comparable, if not better, performance.
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To date, the field of transition research lacks a suitable vocabulary to analyse the (changing) interactions and relations of actors as part of a sustainability transition. This article addresses this knowledge gap by exploring th...
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To date, the field of transition research lacks a suitable vocabulary to analyse the (changing) interactions and relations of actors as part of a sustainability transition. This article addresses this knowledge gap by exploring the potential of the concept of 'roles' from social interaction research. The role concept is operationalized for transition research to allow the analysis of (changing) roles and relations between actor roles as indicative of changes in the social fabric and shared values, norms and beliefs. It also allows considering the use of roles as a transition governance intervention. This includes creating new roles, breaking down or altering existing ones and explicitly negotiating or purposefully assigning roles, as well as the flexible use of roles as resources.
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Forest conservation is a major challenge in Bangladesh. It is believed that mass media is a powerful channel in political communication of different political actors in communicating their perception on certain issues. Forest disc...
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Forest conservation is a major challenge in Bangladesh. It is believed that mass media is a powerful channel in political communication of different political actors in communicating their perception on certain issues. Forest discourses are not limited to the scientific and political sphere but also a popular topic for mass media in Bangladesh. In this study, media discourses from 1989 to 2009 from the "The Daily Ittefaq" of Bangladesh are analyzed. A quantitative-qualitative content analysis of newspaper articles on forest topics was the chosen methodology. The forest discourses in the Bangladeshi print media from 1989 to 2009 was built around the crisis argumentation i.e. the forest of Bangladesh is in a crisis. Deforestation and wildlife conservation dominated the Bangladesh forest media discourse where genuine events like illegal logging, forest destruction, wildlife poaching and wildlife human conflicts were most prominent issues discussed in the mass media of Bangladesh. journalists were the prominent speaker in the print media and primarily shaped the discussion around the problems of the Bangladeshi forest sector. This study finds that the presence of center political actors like politicians and administration do not have much media standing in forest discourse. Therefore they have limited influence or interest in the formulation of forest discourse in the Bangladeshi print media. On the contrary the peripheral actors enjoyed dominant standing in the Bangladeshi print media discourse and thus influence the forest discourses in the print media. (C) 2016 Elsevier B.V. All rights reserved.
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In large-scale and distributed actor systems, there are situations where processing messages
within one of the actors fails, often due to failures that had occurred earlier in the system. In such
cases, tracing down the origin o...
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In large-scale and distributed actor systems, there are situations where processing messages
within one of the actors fails, often due to failures that had occurred earlier in the system. In such
cases, tracing down the origin of the failure is difficult since existing monitoring tools only provide
ways to collect metrics and statistical information about system execution. In this paper, we
describe a new tool for tracing distributed actor systems, Akka Tracing Tool, a library that allows
users to generate a trace graph of messages.To address the distributed nature of the environment,
we proposed an efficient data collection mechanism based on the one-way replication technique
implemented in CouchDB, a popular document database. The tool was evaluated in a distributed
environment of up to 50 nodes set up in the Amazon Web Services (AWS) computing cloud on
a real application: car traffic simulation. The measured overhead when tracing all messages was
between 39% to 45% on average. The library also proved to be scalable with respect to the number
of nodes in the actor system and to be user-friendly. Owing to these properties,weexpect that
the tool can simplify finding errors and speed up the development process of actor systems.
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A mobile agent system consists of mobile agents, each of which can transport its state and code to any computing host in the system. The system is able to perform dynamic network reconfiguration and user customization to keep it f...
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A mobile agent system consists of mobile agents, each of which can transport its state and code to any computing host in the system. The system is able to perform dynamic network reconfiguration and user customization to keep it flexible and effective. A mobile agent system can be theoretically depicted by the mobile actor model, in which a mobile actor is an autonomous computing entity and communicates with other actors by using asynchronous messages. Automatic distributed actor garbage collection, one of the important issues of lifetime management of mobile actors, can help high-level programming and efficient resource management in such a mobile actor system. Therefore, it is beneficial to design an intelligent management strategy to automatically detect and collect mobile actor garbage. In this paper, we propose a mechanism for mobile actor garbage collection using a novel conservative snapshot-based algorithm. Compared with prior similar work, the proposed mechanism is more flexible because it does not assume FIFO communication and any network topology. Moreover, it can perform actor garbage collection in a partial set of computing nodes, and thus can reduce the synchronization overhead while taking a global snapshot on a particular distributed application. In addition, the proposed mechanism does not restrict mutation operations such as actor creation and actor migration while taking a global snapshot. We have conducted experiments to evaluate the overhead of the proposed mechanism, and the results showed that the proposed mechanism is practical.
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Though the importance of linkage was recognized in 1980s in Ethiopia, linkage mechanism of dairying of West Shewa zone was not adequately studied. This study was carried out to assess the extent of convergence of different actors ...
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Though the importance of linkage was recognized in 1980s in Ethiopia, linkage mechanism of dairying of West Shewa zone was not adequately studied. This study was carried out to assess the extent of convergence of different actors promoting dairy development employing cross sectional survey with 250 respondents. A simple random sampling technique was used to identify the respondents of the study. Mixed methods such as focus group discussion, key informant interview, survey and observation were used for data collection to capture the holistic information. The data were analyzed using descriptive statistics, convergence matrix and linkage matrix. The study brought out the prevailing weak linkage in the study area which was mainly attributed to budget constraints, absence of commitment from the actors, poor coordination, limited representations of actors, absence of external pressure from policy makers, and absence of independent unit for taking responsibility for effecting linkage activities. Though dairy actors' had possibilities of creating convergence in the activities of problem identification, research review meetings, on-farm trial, demonstration and others; there were no collaborative efforts among the actors. Thus, it necessitates the integrated action of multi-actors (research, extension, university, input suppliers, marketing agency, livestock agency, cooperatives etc.). For the purpose, the better strategy would be to establish independent unit that entirely takes care of roles and responsibilities of executing the activities of linkage.
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