72 research outputs found
Computational Fluid Dynamics and Numeric Analysis of Aortic Wall Shear Stress Alterations Induced by Fatty Streaks
No full textAtherosclerosis, a disease of the large arteries, is the primary cause of heart disease and stroke. It often begins with the formation of fatty streaks (FS). The FS consists of subendothelial accumulations of cholesterol-engorged macrophages, called ‘foam cells’. For this to happen, there needs to be a significant change in the permeability of the endothelial layer. Considering the established influence of mechanical stresses on endothelial properties, shear stress can increase the permeability of the endothelial layer. This study employs a hybrid approach, combining computational fluid dynamics (CFD) simulation with numerical analysis, on a simplified model of the aorta to Investigate Endothelial Shear Stress (ESS) changes in the FS. Our findings reveal that the presence of FS leads to quantitative changes in ESS. Further numerical analysis in MATLAB 9.14 suggests a pattern that metaphorically resembles a dam, potentially trapping ‘foam cells’. In an additional aspect of this study, our findings suggest that an increase in blood flow could potentially counteract the permeability increase, thus acting as a preventative measure against atherosclerosis progression. These results underscore the importance of early intervention strategies to mitigate atherosclerosis progression
A fault tolerant system using collaborative agents
No full text14th Turkish Symposium on Artificial Intelligence and Neural Networks -- JUN 16-17, 2005 -- Izmir, TURKEYReplication of data or processes is an effective way to provide enhanced performance, high availability and fault tolerance in distributed systems. For instance, in systems based on the client-server model, a server may serve many clients and because of heavy loads, the server cannot respond to the requests on time. In such a case, replicating data or servers may improve performance. Moreover, data and processes can be replicated to protect against failures. However, this is a very complex procedure. In this paper, I propose a method, to make systems fault tolerant based on replication, by way of exploiting the use of collaborative agents. This method is also used to improve fault tolerance in multi-agent systems.Izmir Inst Technol, EE & CE Depts, Turkish Sci & Res Council, Izmir Branch Chamber Elect & Elect Engineer
EXPLOITING THE USE OF COOPERATION IN SELF-ORGANIZING RELIABLE MULTIAGENT SYSTEMS
No full textIn this paper, a novel and cooperative approach is exploited introducing a self-organizing engine to achieve high reliability and availability in multiagent systems. The Adaptive Multiagent Systems theory is applied to design adaptive groups of agents in order to build reliable multiagent systems. According to this theory, adaptiveness is achieved via the cooperative behaviors of agents and their ability to change the communication links autonomously. In this approach, there is not a centralized control mechanism in the multiagent system and there is no need of global knowledge of the system to achieve reliability. This approach was implemented to demonstrate its performance gain in a set of experiments performed under different operating conditions. The experimental results illustrate the effectiveness of this approach
Implementing Fault-Tolerant Services in Goal-Oriented Multi-Agent Systems
No full textIn this paper, findings and analysis detail the implementation of fault tolerance services into a goal-oriented
multi-agent systems development platform. Fault tolerance services are used to provide replication-based fault
tolerance policies (i.e. static and adaptive) to multi-agent systems. This approach provided flexibility and
reusability to multi-agent systems because fault tolerance policies were implemented as reusable plan structures.
Thus, whenever an agent was needed to be made fault-tolerant, plans for fault tolerance policies were simply
activated by sending a request message
Exploiting the Use of Cooperation in Self-Organizing Reliable Multiagent Systems
No full textIn this paper, a novel and cooperative approach is exploited introducing a self-organizing engine to achieve high reliability and availability in multiagent systems. The Adaptive Multiagent Systems theory is applied to design adaptive groups of agents in order to build reliable multiagent systems. According to this theory, adaptiveness is achieved via the cooperative behaviors of agents and their ability to change the communication links autonomously. In this approach, there is not a centralized control mechanism in the multiagent system and there is no need of global knowledge of the system to achieve reliability. This approach was implemented to demonstrate its performance gain in a set of experiments performed under different operating conditions. The experimental results illustrate the effectiveness of this approach
Parameter calibration with Modified Artificial Bee Colonies Algorithm
No full text26th IEEE Signal Processing and Communications Applications Conference (SIU) -- MAY 02-05, 2018 -- Izmir, TURKEYTan, Rabia Korkmaz/0000-0002-3777-2536Analytical solutions are not possible due to the complexity and large-scale data sets of complex systems. in order to facilitate the examination of these systems, agent based modeling and simulation techniques are often used. When studies done in recent years are examined, it is seen that meta-heuristic algorithms are often used for optimization with modeling and simulation. in this study, Artificial Bee Colonies algorithm is investigated for meta-heuristic algorithms for parameter calibration in complex systems with an optimization problem. The success of the parameter calibration process of complex systems has been tested with the Modified Artificial Bee Colonies Algorithm, which has been proven in this work.IEEE, Huawei, Aselsan, NETAS, IEEE Turkey Sect, IEEE Signal Proc Soc, IEEE Commun Soc, ViSRATEK, Adresgezgini, Rohde & Schwarz, Integrated Syst & Syst Design, Atilim Univ, Havelsan, Izmir Katip Celebi Uni
Experience with feedback control mechanisms in self-replicating multi-agent systems
No full text5th International Central and Eastern European Conference on Multi-Agent Systems -- SEP 25-27, 2007 -- Leipzig, GERMANYIn this paper, we present an approach for adaptive replication to support fault tolerance. This approach uses a feedback control theory methodology within an adaptive replication infrastructure to determine replication degrees of replica groups. We implemented this approach in a multiagent system to survive Byzantine failures. At the end of the paper, we also provide some experimental results to show the effectiveness of our approach
Replication Based on Role Concept for Multi-Agent Systems
No full text10th International Workshop on Engineering Societies in the Agents World -- NOV 18-20, 2009 -- Utrecht, NETHERLANDSReplication is widely used to improve fault tolerance in distributed and multi-agent systems. In this paper, we present a different point of view on replication in multi-agent systems. The approach we propose is based on role concept. We define a specific "fault tolerant role. which encapsulates all behaviors related to replication-based fault tolerance in this work. Our strategy is mainly focused on replicating instances of critical roles in the agent organization. However, while doing this, we simply transfer the critical role and the fault tolerant role to appropriate agents. Here, the fault tolerant role is responsible for coordination between replicated role instances (replicas). Moreover, our approach is flexible in terms of fault tolerance since it is possible to easily modify existing behaviors of the "fault tolerant" role, remove some of its behaviors, or include new behaviors to it due to its characteristic architecture.Almende, D CIS Lab, Benelux Assoc Artificial Intelligence, FIPA, Dutch Res Sch Informat & Knowledge Syst, Netherlands Org Sci Res, Utrecht Univ, Dept Informat & Comp Sc
Implementing a multi-agent organization that changes its fault tolerance policy at run-time
No full text6th International Workshop on Engineering Societies in the Agents World -- OCT 26-28, 2005 -- Kusadasi, TURKEYIn this paper, we present an approach that supports simultaneously applying different fault tolerance policies in multi-agent organizations. The main strategy of our approach is to implement fault tolerance policies as reusable agent plans using HTN (Hierarchical Task Network) formalism. In this way, different fault tolerance policies such as static and adaptive ones can be implemented as different plans. In a static fault tolerance policy, all parameters related to the fault tolerance are set by a programmer before run-time. However, an adaptive fault tolerance policy requires dynamically adapting resource allocation and replication mechanisms by monitoring the system. Monitoring of a system brings some cost to the system. If all agents in an organization apply the adaptive fault tolerance policy, the monitoring cost will become an important factor for the system performance. Hence by applying our approach, the adaptive policy can be applied only to the critical agents whose criticalities can be observed during the organization's lifetime and the static one can be applied to the remaining agents. This reduces the monitoring cost and increases the overall organization performance. A case study has been implemented to show the effectiveness of our approach
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