Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 6 Articles
This investigation presents a heuristic method for consumable resource allocation problem in multi-class dynamic\r\nProject Evaluation and Review Technique (PERT) networks, where new projects from different classes (types) arrive\r\nto system according to independent Poisson processes with different arrival rates. Each activity of any project is\r\noperated at a devoted service station located in a node of the network with exponential distribution according to\r\nits class. Indeed, each project arrives to the first service station and continues its routing according to precedence\r\nnetwork of its class. Such system can be represented as a queuing network, while the discipline of queues is first\r\ncome, first served. On the basis of presented method, a multi-class system is decomposed into several single-class\r\ndynamic PERT networks, whereas each class is considered separately as a minisystem. In modeling of single-class\r\ndynamic PERT network, we use Markov process and a multi-objective model investigated by Azaron and\r\nTavakkoli-Moghaddam in 2007. Then, after obtaining the resources allocated to service stations in every minisystem,\r\nthe final resources allocated to activities are calculated by the proposed method....
One of the well-known combinatorial optimization problems is travelling salesman problem (TSP). This problem is in the fields of\r\nlogistics, transportation, and distribution. TSP is among the NP-hard problems, andmany differentmetaheuristics are used to solve\r\nthis problem in an acceptable time especially when the number of cities is high. In this paper, a new meta-heuristic is proposed to\r\nsolve TSP which is based on new insight into network routing problems....
The performance of plastic gears in wide variety of power and motion transmission applications is rather limited due to weak\r\nmechanical properties and divergent mechanism of failures. Amethodical simulation is carried out to analyze the gear performance\r\nwith various gating system types, gate locations, and processing parameters via grey-based Taguchi optimization method.With the\r\nobtained optimum results in simulation stage, the flow patterns of polymer melt inside the mould during filling, packing, and\r\ncooling processes are studied and the plastic gear failures mechanism related to processing parameters are predicted. The output\r\nresults in the future can be used as guidance in selecting the appropriatematerials, improving part and mould design, and predicting\r\nthe performance of the plastic gear before the real process of the part manufacturing takes place....
Real-time group communication is an indispensable part of many interactive multimedia applications over the\r\ninternet. In scenarios that involve large group sizes, sporadic sources, high user churns, and random network\r\nfailures, gossip-based protocols can potentially provide advantages over structure-based group communication\r\nalgorithms in ease of deployment, scalability, and resiliency against churns and failures. In this paper, we propose\r\na novel protocol called Redundancy Reduced Gossip for real-time N-to-N group communication. We show that\r\nour proposed protocol can achieve a considerably lower traffic load than conventional push-based gossip\r\nprotocols and conventional push-pull gossip protocols for the same probability of successful delivery, with higher\r\nperformance gains in networks with smaller delays. We derive a mathematical model for estimating the frame nondelivery\r\nprobability and the traffic load from overhead, and demonstrate the general correctness of the model by\r\nsimulation. We implement a functioning prototype conferencing system using the proposed protocol, completed\r\nwith functions including NTP synchronization, dynamic group size estimation, redundancy suppression, and other\r\nfeatures needed for proper operation. We perform experiments over the campus network and PlanetLab, and\r\nthe prototype system demonstrates the ability of our protocol to maintain robust performance in real-world\r\nnetwork environments....
This paper presents a neural scheme for controlling an actuator of pneumatic control valve system. Bondgraph method has been\r\nused to model the actuator of control valve, in order to compare the response characteristics of valve. The proposed controller is\r\nsuch that the system is always operating in a closed loop, which should lead to better performance characteristics. For comparison,\r\nminimum- and full-order observer controllers are also utilized to control the actuator of pneumatic control valve. Simulation results\r\ngive superior performance of the proposed neural control scheme....
Clustering parts and machines into part families and machine cells is a major decision in the design of cellular\r\nmanufacturing systems which is defined as cell formation. This paper presents a non-linear mixed integer\r\nprogramming model to design cellular manufacturing systems which assumes that the arrival rate of parts into cells\r\nand machine service rate are stochastic parameters and described by exponential distribution. Uncertain situations\r\nmay create a queue behind each machine; therefore, we will consider the average waiting time of parts behind\r\neach machine in order to have an efficient system. The objective function will minimize summation of idleness cost\r\nof machines, sub-contracting cost for exceptional parts, non-utilizing machine cost, and holding cost of parts in the\r\ncells. Finally, the linearized model will be solved by the Cplex solver of GAMS, and sensitivity analysis will be\r\nperformed to illustrate the effectiveness of the parameters....
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