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1.
Aromatic polyimides (PIs) are high-performance polymers with rigid heterocyclic imide rings and aromatic benzene rings in their macromolecular backbones. Owing to excellent mechanical properties and thermal stability, as well as readily adjustable molecular structures, PIs have been widely adopted for many applications related to electronics, aerospace, automobile, and other industries. In recent years, PI fibers prepared by electrospinning of polyamic acid (PAA) precursor nanofibers followed by imidization (commonly known as electrospun PI nanofibers) have attracted growing interests. Herein, the preparation, evaluation, and application of electrospun PI nanofibers are reviewed. PI polymers and the electrospinning technique are introduced first followed by the preparation of electrospun nanofibers of homo-PI, co-PI, blend-PI, and PI composite. Subsequently, the mechanical and thermal properties of electrospun PI nanofibers are presented; in particular, the mechanical properties of individual electrospun PI nanofibers are highlighted. Thereafter, various applications of electrospun PI nanofibers are outlined, including reinforcement of composites, Li-ion battery separators, fuel cell proton exchange membranes, sensors, microelectronics, high-temperature filtration media, super-hydrophobic PI nanofibers, and PI-based carbon nanofibers. In the final section of conclusions and perspectives, future research endeavors and high-value applications of electrospun PI nanofibers are discussed. 相似文献
2.
TS-1 has been treated with different concentrations of tetrapropyl ammonium hydroxide (TPAOH), characterized by a series of techniques, and studied in cyclohexanone ammoximation. The results show that the MFI structure of TS-1 is not destroyed, while mesopores are formed in TS-1 crystals and the pore diameters increase with the TPAOH concentrations; the amount of the framework Ti species decreases slightly at low concentrations of TPAOH, but decreases appreciably at the concentrations of TPAOH above 0.0125 mol/L; the activity and the selectivity of TS-1 are not affected by the treatment, but the catalyst stability is markedly increased after the TPAOH treatment. The increase of the stability is attributed to the mesopore formation. But when the pore diameters are larger than 6.51 nm, the catalyst stability begins decreasing due to the appreciable damage of the framework titanium by TPAOH. 相似文献
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The paper presents a formal and practical approach to dependable algorithm development. First, starting from a formal specification based on the Eindhoven quantifier notation, a problem is regularly reduced to subproblems with less complexity by using a concise set of calculation rules, the result of which establishes a recurrence based algorithm. Second, a loop invariant is derived from the problem specification and recurrence, which certifies the transformation from the recurrence based algorithm to one or more iterative programs. We demonstrate that our approach covers a number of classical algorithm design tactics, develops algorithmic programs together with their proof of correctness, and thus contributes fundamentally to the dependability of computer software. 相似文献
4.
传统文本聚类方法只适合处理静态样本,且时间复杂度较高。针对该问题,提出一种基于簇相合性的文本增量聚类算法。采用基于词项语义相似度的文本表示模型,利用词项之间的语义信息,通过计算新增文本与已有簇之间的相合性实现对文本的增量聚类。增量处理完部分文本后,对其中错分可能性较大的文本重新指派类别,以进一步提高聚类性能。该算法可在对象数据不断增长或更新的情况下,避免大量重复计算,提高聚类性能。在20 Newsgroups数据集上进行实验,结果表明,与k-means算法和SHC算法相比,该算法可减少聚类时间,提高聚类性能。 相似文献
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