Traditional temporal association rules mining algorithms cannot dynamically update the temporal association rules within the valid time interval with increasing data. In this paper, a new algorithm called incremental fuzzy temporal association rule mining using fuzzy grid table (IFTARMFGT) is proposed by combining the advantages of boolean matrix with incremental mining. First, multivariate time series data are transformed into discrete fuzzy values that contain the time intervals and fuzzy membership. Second, in order to improve the mining efficiency, the concept of boolean matrices was introduced into the fuzzy membership to generate a fuzzy grid table to mine the frequent itemsets. Finally, in view of the Fast UPdate (FUP) algorithm, fuzzy temporal association rules are incrementally mined and updated without repeatedly scanning the original database by considering the lifespan of each item and inheriting the information from previous mining results. The experiments show that our algorithm provides better efficiency and interpretability in mining temporal association rules than other algorithms.
The structures and dehydrogenation properties of pure and Ti/Ni-doped Mg(AlH4)2 were investigated using the first-principles calculations. The dopants mainly affect the geometric and electronic structures of their vicinal AlH4 units. Ti and Ni dopants improve the dehydrogenation of Mg(AlH4)2 in different mechanisms. In the Ti-doped case, Ti prefers to occupy the 13-hedral interstice (TiiA) and substitute for the Al atom (TiAl), to form a high-coordination structure TiHn (n = 6, 7). The Ti 3d electrons hybridize markedly with the H 1s electrons in TiAl and with the Al 3p electrons in TiiA, which weakens the Al–H bond of adjacent AlH4 units and facilitates the hydrogen dissociation. A TiAl3H13 intermediate in TiiA is inferred as the precursor of Mg(AlH4)2 dehydrogenation. In contrast, Ni tends to occupy the octahedral interstice to form the NiH4 tetrahedron. The tight bind of the Ni with its surrounding H atoms inhibits their dissociation though the nearby Al–H bond also becomes weak. Therefore, Ti is the better dopant candidate than Ni for improving the dehydrogenation properties of Mg(AlH4)2 because of its abundant activated hydrogen atoms and low hydrogen removal energy. 相似文献