Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Citation - WoS: 12Citation - Scopus: 17Abstraction-Based Verification of Codiagnosability for Discrete Event Systems(Pergamon-elsevier Science Ltd, 2010) Schmidt, K.In this paper, we investigate the verification of codiagnosability for discrete event systems (DES). That is, it is desired to ascertain if the occurrence of system faults can be detected based on the information of multiple local sites that partially observe the overall DES. As an improvement of existing codiagnosability tests that resort to the original DES with a potentially computationally infeasible state space, we propose a method that employs an abstracted system model on a smaller state space for the codiagnosability verification. Furthermore, we show that this abstraction can be computed without explicitly evaluating the state space of the original model in the practical case where the DES is composed of multiple subsystems. (c) 2010 Elsevier Ltd. All rights reserved.Article Citation - WoS: 15Citation - Scopus: 15A Density Functional Study of Small Li-B and Li-B Clusters(Pergamon-elsevier Science Ltd, 2009) Yildirim, E. K.; Guvenc, Z. B.In this work we present the results of a detailed theoretical research for the small LinBm clusters and their hydrogen storage properties by means of density functional theory. All calculations were performed by using Gaussian03 program. For the optimization of the clusters 6-311++G(d,p) basis set was employed. We have chosen global minimum of B-6 cluster as the starting point and replaced the boron atoms one at a time, in a stepwise manner, with Li atoms. For these new structures we have searched for the stable configurations, and calculated their energies, HOMO-LUMO energy gaps, Raman and infrared data, average boron, and lithium charge distribution, and vibrational frequencies. Our results show that as the number of Li atoms increases, stability of the clusters decreases and they become more reactive. In addition to that, there are significant charge transfers from boron atoms to lithium atoms on average. The hydrogen storage capabilities of the most stable isomers of LinBm and B-6 clusters have also been investigated by the same methods, and the results are compared. The Li3B3 has the highest hydrogen storage capacity among the clusters investigated in this study. Furthermore, formation of hydrogen molecules is observed in the vicinity of the clusters, some of which are attached to the Li atoms. In addition, as the number of hydrogen atoms increases, the boron atoms are separated from the other boron atoms, and they form satellite BHx (x = 3,4) clusters around the center. These are attached to the system by a bridging bond of a hydrogen or a Li atom. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.