Automated Guided Vehicle (AGV) Container-Job deployment is essentially a vehicle-dispatching problem. In this problem, the impact of vehicle dispatching polices on the ship makespan for discharging and/or loading operations is analyzed. In particular, given a storage location for each container to be discharged from the ship and given the current location of each container to be loaded onto the ship, the problem is to propose an efficient deployment scheme to dispatch vehicles to containers so as to minimize the makespan of the ship so as to increase the throughput. The makespan of the ship refers to the time a ship spends at the port for loading and unloading operations. In this paper, we will compare the performance of current deployment scheme used with the new proposed deployment scheme, both with deadlock prediction & avoidance algorithm done in previous study [1]. The prediction & avoidance algorithm predicts and avoids cyclic deadlock. The current deployment scheme, namely pmds makes use of a greedy heuristics which dispatches the available vehicle that will reach the quay with the minimum amount of time the vehicle has to spend waiting for the crane to discharge/load the container from/onto the ship. The new deployment scheme, namely mcf aims to formulate the problem as a minimum cost flow problem, which will then be solved by network simplex code. The two simulation models are implemented using discrete-event simulation software, AutoMod, and the performances of both deployment schemes are analyzed. The simulation results show that the new deployment scheme will result in a higher throughput and lower ship makespan than the current deployment scheme. / Singapore-MIT Alliance (SMA)

In this thesis, we consider how to reduce the communication cost of the key exchange procedures as many as possible, while the secure group communication can still be achieved. Due to the energy consumption is usually proportional to the distance, we use the shortest paths algorithm to find the shortest communication paths between any pair of the secure group members. We first propose a straightforward heuristic named Minimum-Energy First-Selected ( MEFS ). MEFS tries to select the pair of group members which has less communication cost than all other pairs have at every time. Though MEFS performs better than random selecting, it still has some weakness in solving the energy-aware key management problem. So we use the concept of the minimum cost flow problem, and by appropriate transformation, then we get the optimal solution of the energy-aware key management problem under some constraints. At last, the simulation results proves that the minimum cost flow approach actually works better than MEFS does.

[pt] Este trabalho busca desenvolver o método Simplex para Redes na solução de problemas de Fluxo de Custo Mínimo. Este método consiste em uma adaptação do método Simplex primal em que são exploradas as características específicas da rede subjacente ao problema ao se buscar a solução ótima em um número finito de árvores geradoras. A árvore geradora ótima será obtida iterativamente através de sucessivas melhorias na estrutura de cada árvore formada. A maior eficiência do Simplex para Redes se dá tanto no menor número de iterações necessárias para se atingir o ótimo, quanto na maior velocidade destas iterações, trata-se, portanto, de um método bastante poderoso na resolução de problemas de Fluxo de Custo Mínimo. Serão, também, abordados aspectos práticos da implementação do algoritmo além da aplicação deste algoritmo implementado em VBA (Visual Basic for Applications) em um problema prático a título de exemplificação. / [en] The current work intends to develop a Network Simplex Method for solving Minimum Cost Flow problems. Such method consists of a primal Simplex Method adaptation in which specific characteristics of the network underlying the problem are investigated by searching for the optimal solution within a finite number of spanning trees. The optimal spanning tree is iteratively obtained through successive structure improvements in each formed tree. The higher efficiency of Network Simplex lies both in fewer iterations necessary to achieve the optimum and in the higher speed of these iterations. Therefore, it is a powerful method for solving Minimum Cost Flow Problems. Practical aspects of implementing the algorithm will be discussed, as well as the algorithm´s implementation in VBA (Visual Basic for Applications) through a practical instance.

The evolution of Mobile Internet has led to the growth of bandwidth demanding applications like video streaming and social networking. The required data rates projected for such applications cannot be sustained by current cellular networks. New network architectures like Long Term Evolution (LTE) and LTE Advanced have been carefully engineered and introduced to fulfill such large data rates. The recent introduction of femtocells enabled high data rates and better coverage indoors, without the need for site establishment or upgrading the network infrastructure. Femtocells, however, will potentially suffer from major interference problems due to their expected dense and ad hoc deployment. The main contribution in this thesis is the introduction of a new and a very promising direction in deriving capable and efficient interference mitigation schemes, and comparing this direction to current techniques in the literature. Several works have studied the effect of interference on networks employing femtocells. In this thesis, we also survey such works and provide an overview of the elements considered in mitigating interference. We introduce a new scheme known for its optimality, and use it for frequency assignment in downlink femtocell networks. The algorithm is based on optimization search rather than greedy or heuristic methods. Experimental simulations will be shown to evaluate the proposed scheme against other schemes from the literature. / Thesis (Master, Computing) -- Queen's University, 2012-03-31 02:14:28.549

Made available in DSpace on 2016-08-17T14:52:43Z (GMT). No. of bitstreams: 1 Milson Monteiro.pdf: 1924077 bytes, checksum: 78f931b493f756dec0edee7a465e1099 (MD5) Previous issue date: 2002-06-07 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This works concern software development (graphical user interface) that makes possible to analyze the interconnection in a LAN (Local Area Network) using CORBA (Common Object Request Broker Architecture) on distributed and heterogeneous environment among several outlying machines. This works presents paradigms of graphs theory: shortest paths problems (Dijkstra-Ford-Moore-Belman), maximum flow problems (Edmonds-Karp) and minimum cost flow problems (Busacker-Gowen) to formalize the interface development. We discoursed on the graphs theory and networks flows that are essentials to guarantee theoretical insight. / O objeto de estudo deste trabalho é o desenvolvimento de um software (interface gráfica do usuário) que possibilita analisar a interconexão de uma LAN (Local Area Network) usando CORBA (Common Object Request Broker Architecture) em ambientes distribuídos e heterogêneos entre diversas máquinas periféricas. Este trabalho apresenta os paradigmas da teoria de grafos: menor caminho (Dijkstra, Ford-Moore-Belman), fluxo máximo (Edmonds-Karp) e fluxo de custo mínimo (Busacker-Gowen) para formalizar o desenvolvimento da interface. Discorremos sobre a teoria de grafos e fluxos em redes que são relevantes para garantir o embasamento teórico.