Design guidelines and characteristics for a kind of four-layer large flattened mode fibers

A theoretical method to analyze a kind of four-layer large flattened mode (LFM) fibers is presented. The properties of the fiber, including the fundamental and higher-order modal fields, effective area and bending loss are discussed by comparison. At the same time, the reasons for the different characteristics are considered. The obtained results indicate that the effective area of the four-layer LFM fiber is about 1.3 times larger than that of the conventional standard step-index fiber and the fiber can suppress the higher-order modes via bending effectively. The four-layer LFM fiber has less efficient bend-induced filtering ability than the conventional step-index fiber; however, it has more efficient filtering ability than the three-layer LFM fiber.     

A Chinese Postman Problem based on DNA computing

DNA computing is a novel method for solving a class of intractable computational problems, in which the computing can grow exponentially with the problem size. Up to now, many accomplishments have been achieved to improve its performance and increase its reliability. A Chinese Postman Problem has been solved by means of molecular biology techniques in the paper. A small graph was encoded in molecules of DNA, and the "operations" of the computation were performed with standard protocols and enzymes. This work represents further evidence for the ability of DNA computing to solve NP-complete search problems.     

Stepwise synthesis of siloxane chains

Siloxane chains of designated lengths can be synthesized with high yields by reacting tris(tert-butoxy)silanol alternately with dichlorosilane and silanediol.     

Studies directed toward asymmetric synthesis of cardioactive steroids via anionic polycyclization

[reaction: see text] The use of anionic polycyclization (AP) in constructing the steroidal backbone of cardenolides was investigated. The reaction of 2-carbomethoxy-2-cyclohexenone I with the enolate of Nazarov reagent II gave, after decarboxylation and aldol condensation, steroid III with control of stereochemistry.     

Smoothing the side lobes of a focused pattern by spectral dispersion in the broadband laser

Starting from the Huygens–Fresnel diffraction integral, the propagation equations of a broadband laser passing through a dispersive lens and a dispersive wedge are derived. Smoothing effect on the side lobes of the focused pattern is achieved as the broadband laser passes through the lens because of the spectral dispersion of the lens. By inserting a dispersive wedge behind the lens, better smoothing effect is realized because a relative position shift between focused patterns of different frequency components is generated due to the spectral dispersion of the wedge. Smoothing effect on the side lobe is obtained even with small bandwidth of the broadband laser as the wedge is used.     

Negative refraction in a honeycomb-lattice photonic crystal

In this paper we theoretically investigate a photonic crystal with dielectric rods in a honeycomb lattice. Two left-handed frequency regions are found in the second and third photonic band by using the plane wave expansion method to analyze the photonic band structure and equifrequency contours. Subwavelength imaging by the photonic crystal flat lens are systematically studied by numerical simulations using the multiple scattering method. Different from the photonic crystals with noncircular dielectric rods in air, this structure is almost isotropic at the optimal frequency for superlensing. As a comparison, flat slab focusing is also demonstrated at other frequencies in the two left-handed regions.     

聚环氧乙烷聚合物电解质基高电压固态锂金属电池的研究进展

采用液态碳酸酯电解质的锂离子电池在遭遇极端工况时, 极易发生泄露、燃烧、甚至爆炸等重大安全事故. 相对比, 聚环氧乙烷(PEO)固态聚合物电解质可以显著提升锂电池的安全性, 并且其优异的可塑性使其可以被制成特定形状进而满足特殊领域的差异化需求; 更为重要的是: PEO固态聚合物电解质与锂金属负极兼容性好. 然而, PEO固态聚合物电解质电化学氧化窗口低, 难以匹配高电压正极材料(≥4 V), 极大限制了其在高电压、高能量密度固态聚合物锂金属电池中的进一步应用. 近期经过国内外科研工作者在PEO固态聚合物电解质结构设计、PEO端羟基改性、含硼锂盐引入、功能型粘结剂设计开发以及正极界面层构筑等方面所做出的不懈努力, PEO固态聚合物电解质基高电压固态锂金属电池取得了系列化重大科研进展. 基于此, 本综述主要从以下八个方面: (1)高电压正极片表面修饰超薄聚合物层、(2)高电压正极颗粒包覆、(3)对碳黑颗粒进行包覆、(4)使用富含羧基的粘结剂、(5)不对称固态聚合物电解质结构设计、(6)正极界面原位形成耐高电压界面层、(7)醚氧官能团(-OCH₃)封端PEO, 提升其本征耐高电压性能、(8)含硼锂盐做添加剂, 详细综述了采用PEO固态聚合物电解质构建的高电压固态锂金属电池所取得的最新研究进展以及相应的高电压固态锂金属电池界面稳定作用机制. 最后还对未来PEO固态聚合物电解质在高电压固态锂金属电池方面所存在的巨大挑战和发展趋势进行了详细展望和总结阐述.     

Interfacial structure and tribological behaviours of epoxy resin coating reinforced with graphene and graphene oxide

Graphene (G) and graphene oxide (GO) were added into epoxy resin (EP) respectively via chemical modification and physical ultrasound technology to improve the tribological behaviour of EP coating. The topographies of G and GO were detected by scanning probe microscopy. The chemical structures of the fillers before and after modification were identified by Fourier transform infrared spectrometer. The across‐section topographies of the coatings were detected by scanning electron microscopy. The tribological behaviour of the coatings was evaluated by UMT‐3 tribology tester, surface profiler and scanning electron microscopy. The results revealed that the coefficient of friction of the coatings decreased, and the wear resistance of the coatings improved with the addition of the G and GO. GO could improve the tribological performance of EP further compared to G. When containing 0.5 wt% G and 0.75 wt% GO, the coatings had the lowest coefficient of friction and best wear resistance. When the contents of G reached 0.75 wt%, and GO reached 1 wt%, the tribological performance of the composite coatings decreased as a result of the agglomeration of the fillers. Finally, the anti‐friction and anti‐wear mechanisms of G‐EP and GO‐EP composite coatings were discussed in detail based on the results obtained in the preceding texts. Copyright © 2016 John Wiley & Sons, Ltd.