FCloSM,FGenSM: two efficient algorithms for mining frequent closed and generator sequences using the local pruning strategy

Mining frequent sequences in sequential databases are highly valuable for many real-life applications. However, in several cases, especially when databases are huge and when low minimum support thresholds are used, the cardinality of the result set can be enormous. Consequently, algorithms for discovering frequent sequences exhibit poor performance, showing an important increase in execution time, memory consumption and storage space usage. To address this issue, researchers have studied the tasks of mining frequent closed and generator sequences, as they provide several benefits when compared to the set of frequent sequences. One of the most important benefits is that the cardinalities of frequent closed and generator sequences are generally much less than the cardinality of frequent sequences. Hence, humans find it more convenient to analyze the information provided by closed and generator sequences. Moreover, it was shown that frequent closed sequences have the advantage of being lossless, and they thus preserve information about the frequency of all frequent subsequences, while generator sequences can provide higher accuracy for sequence classification tasks since they are the smallest patterns that characterize groups of sequences. Besides, frequent closed sequences can be combined with generators to produce non-redundant sequential rules and recover the complete set of frequent sequences and their frequencies. This paper proposes two novel algorithms named FCloSM and FGenSM to mine frequent closed and generator sequences efficiently. These algorithms are based on new pruning conditions called extended early elimination (3E) and early pruning techniques named EPCLO and EPGEN, designed to identify non-closed and non-generator patterns early. Based on these techniques, two local pruning strategies called LPCLO and LPGEN are proposed to eliminate non-closed and non-generator patterns more efficiently at two successive levels of the prefix search tree without performing subsequence relation checking. These theoretical results, which are the basis of FCloSM and FGenSM, are mathematically proved and are shown to be more general than those presented in previous work. Extensive experiments show that FCloSM and FGenSM are one to two orders of magnitude faster than the state-of-the-art algorithms for discovering frequent closed sequences (CloSpan, BIDE, ClaSP and CM-ClaSP) and for mining frequent generators (FEAT, FSGP and VGEN), and that FCloSM and FGenSM consume much less memory.     

Thermal stability of TiY membrane

Three mol % yttria-doped titania membranes were prepared by the sol-gel method. Their pore and phase structures were determined by N₂ sorption and X-ray diffraction. It was shown that these membranes had superior properties over the undoped membranes in having higher thermal stability. In practice, yttria doping can be developed for high temperature applications.     

Reliability Prediction Techniques for Complex Systems

As electronic systems continue to evolve into more and more complex structures, the search for better and more efficient reliability prediction techniques naturally takes on added momentum. Needed are not only systematic methods of mathematical model building that will simplify the procedures involved but also noncomplex ways of obtaining solutions to many practical problems. This paper illustrates the applicability of transition diagram in describing the state space of a complex system, repairable or nonrepairable, and shows the methodology of writing the set of first-order linear differential equations representing the system performance by inspection of the transition diagram. A discussion of some applicable properties of linear signal-flow graphs is included. Methods of solving problems by inspection techniques are clearly explained and specific examples are given to illustrate the concepts. The mean time Tm for a system to pass for the first time from its initial state to a failed state is usually a statistic of prime interest. Certain properties of Laplace transform are used to illustrate how Tm of a general complex system, repairable or nonrepairable, can be obtained by solving a set of simultaneous algebraic equations. Flow graph techniques of solution by inspection are shown to be a valuable tool in obtaining analytical solutions for Tm of many practical systems.     

线性电光效应引起晶体介电张量变化的简单表示

晶体的光折变效应已被广泛应用于全息存贮、四波混频及相位共轭光学中,这些研究不仅对单轴晶体,而且已涉及到双轴晶体,它们的基本原理均基于晶体中全息光栅的衍射原理,而光衍射效率的大小又与晶体线性电光效应引起的光频介电常数的变化有关。文献[2]曾考虑到晶体中电场的方向,给出了部分点群晶体介电张量的变化形式,本文导出线性电光效应作用下所有晶体介电张量变化的普遍表达式,给出主要光折变晶体所属点群的介电张量的变化矩阵。     

Application of ICME to Engineer Fatigue-Resistant Ni-Base Superalloys Microstructures

Critical rotating components used in the hot section of gas turbine engines are subject to cyclic loading conditions during operation, and the life of these structures is governed by their ability to resist fatigue. Since it is well known that microstructural parameters, such as grain size, can significantly influence the fatigue behavior of the material, the conventional processes involved with the manufacture of these structures are carefully controlled in an effort to engineer the resulting microstructure. For a commercial Ni-base superalloy, RR1000, the development of process models and deformation mechanism maps has enabled not only control of the resultant grain size but also the ability to tailor and manipulate the resulting grain boundary character distribution. The increased level of microstructural control was coupled with a physics-based fatigue model to form an integrated computational materials engineering framework that was used to guide the design of damage-tolerant microstructures. Simulations from a 3D crystal plasticity finite element model were used to identify microstructural features associated with strain localization during cyclic loading and to guide the design of polycrystalline microstructures optimized for fatigue resistance. Conventionally processed and grain boundary engineered forgings of a commercial Ni-based superalloy, RR1000, were produced to validate the design methodology. For nominally equivalent grain sizes, high-resolution strain maps generated via digital image correlation confirmed that the high density of twin boundaries in the grain boundary engineered material were desirable microstructural features as they contribute to limiting the overall length of persistent slip bands that often serve as precursors for the nucleation of fatigue cracks.     

A novel effect of sandblasting on titanium surface: static charge generation

Recent advances in biomaterials’ research suggest that electrical charges on a dental implant surface significantly improve its osseointegration to living bone, as a result of selective osteoblast activation and fibroblast inhibition. This study aims at investigating the possibility of using sandblasting to modify the electrical charges on the surface of titanium materials. Our experiments used Al₂O₃ grits to blast on CP2 titanium plates, for durations between 3 and 30?s. After sandblasting, Ti surfaces were measured for their electrostatic voltage. The results indicate a novel finding, i.e. negative static charges are generated on the titanium surface, which may stimulate osteoblast activity to promote osseointegration around dental implant surface. This finding may at least partially explain the good osseointegration results of sandblasted titanium dental implants, in addition to other known reasons, such as topological changes on the implant’s surface. However, the static charges accumulated on the titanium surface during sandblasting decayed to a lower level with time. It remains a challenging task to seek ways to retain these charges after quantification of desired level of negative charges needed to promote osteoblast activity for osseointegration around dental implants.     

含铬合成鞣剂的结构和性能的关系(Ⅰ)

铬-合成单宁铬合合成鞣剂目前在制革界颇受欢迎。国际上有多种牌号的这类鞣剂,其制法、形态、结构和性能都有所不同。有的是机械混合物;有的是铬和合成单宁铬合的;有的络合后完全变成了黄绿色,铬离子本身的兰绿色完全消失;有的溶解于水后呈清亮、透明的溶液;有的则不完全溶于水,水溶液呈浑浊状态。其复鞣后的兰革的手感和染色性能也有很大差别。国内研究这类鞣剂做了大量工作.为了更好地认识这类鞣剂,我们选用A、B、C三种铬-砜桥合成单宁鞣剂,它们分别是国内外认为好的、差的和曾经研究过的产品,用凝胶渗透法(GC)、阳离子交换色谱法(CIEC)和红外光谱法