TEDE Communidade:
http://www.bdtd.uerj.br/handle/1/3677
2024-03-29T08:37:22ZAvaliação comparativa de métodos de reconstrução inversa
http://www.bdtd.uerj.br/handle/1/20937
Título: Avaliação comparativa de métodos de reconstrução inversa
Autor: Fontes, Allan de Oliveira
Primeiro orientador: Lovisolo, Lisandro
Abstract: This dissertation compares tomographic reconstruction algorithms. Sixteen reconstruction algorithms from five classes, with different models and operating principles, were studied and compared using descriptive, quantitative, and qualitative criteria. Firstly, in the descriptive comparison, the algorithms were grouped according to their common elements. That is, the classes and their fundamental characteristics are presented. The data set used for the quantitative evaluation is generated from three (3) complete base images, which have different qualitative characteristics to consider application groups that are not correlated with each other: health, architecture, and industry. We obtain a group of 60 projection sets (sinograms) from the 03 base images through a simulated acquisition process with progressive corruption. Corruption occurs by directly adding Gaussian noise to a single part of the acquisition process at a time, either in the full image of the target object or in the full image of the sinogram. The first approach accommodates applications where the error is associated with propagation phenomena and the interaction of the probe beams with the target object. In contrast, the second approach accommodates applications where the error is associated with the measurement process. For each algorithm iteration, a reconstruction image corresponding to a sinogram of the set is obtained. When applicable to the algorithm, 50 iterations are used. The quantitative analysis uses different image quality measures to compare the reconstructions. An Aggregate Quality Index is proposed in order to condense the information obtained. We assess the computational cost of the reconstruction based on the processing time of one iteration (the first). Finally, the qualitative comparison evaluates sections of the reconstructions of the images obtained in the sequence of iterations of the algorithm. The discernment of structures (changes in values, speed or inclination, and oscillations when they occur) is evaluated by inspection and statistical indices: Mean, Standard Deviation, and Otsu threshold. The evaluation indicates that algorithms based on likelihood function maximization are more effective (quality) and stable (the quality trend as iterations progress and error is added shows to be monotonous), with a reasonable efficiency compromise (computational cost). The results also suggest criteria for choosing the appropriate reconstruction methods for different application scenarios and suggestions for improving some algorithms.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Dissertação2023-05-29T00:00:00ZTransporte coletivo por enjaulamento em robótica de enxame
http://www.bdtd.uerj.br/handle/1/20751
Título: Transporte coletivo por enjaulamento em robótica de enxame
Autor: Cardoso, Karen da Silva
Primeiro orientador: Nedjah, Nadia
Abstract: Collective transport in swarm robotics is based on the transportation of objects by swarms of robots characterized by having significantly smaller dimensions compared to the object to be transported. The set of robots of the swarm generally have the same architecture. Individually, the robots are able to perform simple functions, such as sensing, locomotion, and basic communication. However, cooperatively, they can perform complex task. Collective transport has diverse applications that encompass the transportation of both large-scale objects and nanoscale objects. Consequently, numerous studies have been driven by this topic, highlighting three transport strategies: pushing, grasping, and caging. In this work, the caging strategy is adopted. It can be defined as the complete enclosure of the object. Allowing it a certain degree of freedom but preventing it from escaping the formation of robots around it. The main advantage of this strategy is the coordinated and cohesive progression of the transport since the forces applied to the object by the swarm complement each other and prevent significant deviations in its trajectory towards the planned destination. This work proposes a method to approach collective transport by caging, which operates in four stages: the search for the object by the swarm, the recruitment of swarm of robots, the initial positioning of the robots around the object, enclose it, and the transportation stage. The implementation of the proposed strategy is carried out in the CoppeliaSim platform, wherein the swarm is composed of Khepera IIItype robots. This robot is chosen due to the arrangement of its sensors along its perimeter, which allows for a wide view of the environment. The arena, which is the scenario where the simulations are conducted is discretized into different configurations. This space discretization has a significant impact on the performance of the search and transport stages. The performance evaluation of the search and recruitment stages are based on the execution time, while for the transport stage, in addition to the execution time, the normalized error of the object’s trajectory is evaluated for different arena discretization configurations and path lengths. The evaluation of the transportation stage also involves analyzing the impact of the number of robots and the dimensions of the object to be transported. The proposed method proves to be effective, as the caging is maintained throughout the entire path, thus ensuring the uniform transport of the object.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Dissertação2023-10-20T00:00:00ZRepresentação de sinais de atividade eletrodérmica usando decomposições atômicas com aceleração via redes neurais artificiais
http://www.bdtd.uerj.br/handle/1/20419
Título: Representação de sinais de atividade eletrodérmica usando decomposições atômicas com aceleração via redes neurais artificiais
Autor: Lima, Paulo Victor Martins Rosa Huguenin de
Primeiro orientador: Tcheou, Michel Pompeu
Abstract: The profusion of devices incorporating sensors capable of monitoring and capturing biomedical signals in real-time, including electrodermal activity (EDA), demands techniques capable of efficiently representing the EDA signal and, at the same time, allowing analysis to provide useful information for interpretation. Greedy adaptive decomposition algorithms, such as Matching Pursuit (MP), have been used to obtain coherent approximations of signals, i.e., those related to the phenomena represented in the signals. The MP obtains a weighted sum of a few waveforms (atoms) selected from a redundant dictionary iteratively to represent the signal. The set of candidate atoms is the dictionary from which the ones to use in the approximation are selected. When it contains multiple prototype waveforms, from which the atoms are defined by parameters, we can say that the dictionary is composed of subdictionaries. In this dissertation, we investigate the use of a composite dictionary for the representation of EDA signals via MP, motivated by the fact that such a dictionary can provide more sparse decompositions of EDA signals. Appropriate parameterizations for different subdictionaries containing atoms similar to the phenomena represented in EDA signals are investigated. On the other hand, a composite dictionary entails greater computational complexity to obtain the representation. We propose a subdictionary selection method that acts in the loop of the MP algorithm using an artificial neural network (ANN) to reduce the computational cost of the algorithm without impairing the quality of the representation obtained. ANN models capable of predicting with good accuracy the subdictionary to be used in the MP decomposition loop are investigated. The results indicate that this approach allows dividing the computational complexity by the number of subdictionaries without strongly compromising the quality (measured as a function of the approximation error) as a function of the number of atoms (MP iterations) of the representation thus obtained.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Dissertação2023-05-31T00:00:00ZControle por modo deslizante para sistemas com atrasos de comunicação estocásticos
http://www.bdtd.uerj.br/handle/1/20222
Título: Controle por modo deslizante para sistemas com atrasos de comunicação estocásticos
Autor: Alves, Rômulo Thaygor Hatakeyama
Primeiro orientador: Cunha, José Paulo Vilela Soares da
Abstract: This work proposes the use of a state observer in order to compensate stochastic time-delays in a sliding mode control system. The proposed strategy is able to compensate the delays and provide the controller the state estimates in continuous time. Signals from sensors located in the plant are periodically sampled and sent over a network to the state observer. The networked induced delays are considered as known and they vary stochastically. Furthermore, in the stability analysis, the concept of almost sure stability is used, which provides a very satisfactory and less conservative result. Thus, combining known techniques with new methodologies, a good result is obtained in compensating delas with stochastic characteristics. Illustrative examples are presented throughout this study, simulating normal operating conditions and conditions that aim to stress and reinforce the importance of delay compensation in the case of sliding mode controllers.
Instituição: Universidade do Estado do Rio de Janeiro
Tipo do documento: Dissertação2022-12-13T00:00:00Z