A study of random Weyl trees

We study binary search trees constructed from Weyl sequences {nθ}, n≥1, where θ is an irrational and {·} denotes “mod 1.” We explore various properties of the structure of these trees, and relate them to the continued fraction expansion of θ. If H_n is the height of the tree with n nodes when θ is chosen at random and uniformly on [0, 1], then we show that in probability, H_n∼(12/π²)log n log log n. © 1998 John Wiley & Sons, Inc. Random Struct. Alg., 12, 271–295, 1998     

脂肪酸光脱羧酶及其在有机合成中应用的研究进展

生物基脂肪酸是极具应用潜力的可再生资源。以绿色、低碳的方式对生物基脂肪酸进行转化合成高价值的化学品和燃料可满足现代社会可持续发展的迫切需要,也符合绿色生物制造的需求。生物催化因反应条件温和、选择性高等特点受到众多学者的广泛关注,其中,近年来新发现的由可见光驱动的脂肪酸光脱羧酶（fatty acid photodecarboxyase, CvFAP）可催化不同链长的脂肪酸进行脱羧反应用来合成燃料和化学品,反应过程具有极高原子经济性,在绿色催化工艺及能源领域具有广阔的应用前景。本综述旨在对脂肪酸光脱羧酶（CvFAP）的最新研究进展进行总结分析,并对脂肪酸光脱羧酶的发展趋势进行展望,以期为脂肪酸光脱羧酶（CvFAP）在绿色合成领域的进一步开发利用提供参考。     

贵金属基纳米催化剂在乙醇电催化氧化中的应用

乙醇电催化氧化反应是直接乙醇燃料电池的核心步骤之一,制备高效稳定的电催化材料已经成为提升其电催化反应效率和选择性的关键。贵金属基纳米催化剂以其独特的物理和化学特性,在乙醇电催化氧化中表现出优异的电催化性能,在燃料电池领域具有重要的应用前景。近来贵金属基乙醇氧化催化剂受到广泛关注并取得系列重要研究进展。本文主要介绍催化剂元素组成调变形成多元素协同作用、形貌调控暴露高指数晶面和载体选择提升分散性等三个方面对贵金属基纳米催化剂性能的影响,为后续研究设计高效稳定的直接乙醇燃料电池催化剂提供参考。     

Biodegradable hybrid polymer films based on poly(vinyl alcohol) and collagen hydrolyzate

Hybrid blends of poly(vinyl alcohol) (PVA) and collagen hydrolyzate (CH), an added value waste from leather indutry, have been converted by blown molding extrusion, to environmentally degradable films. Blown extruded films comprising 5-15% of CH, were tested as sel fertilizing mulching films and analyzed for their propensity to enviromental degradation. PVA/CH films rapidly disintegrate when buried in soil, and resulted promising for application such as transplanting films, with additional fertilizing action of CH.     

The influence of partial emulsification on coalescence suppression and interfacial tension reduction in PP/PET blends

This study examines how the relative role of coalescence suppression and interfacial tension reduction influence the particle size at various levels of in situ compatibilization. The polymers studied are polyethylene terephthalate (PET) as matrix and a polypropylene (PP) as dispersed phase compatibilized by a triblock copolymer of poly(styrene–hydrogenated butadiene–styrene) (SEBS) grafted with maleic anhydride. The interfacial tension was studied by the breaking‐thread method, and it was used along with the morphology to characterize the emulsification efficacy of the copolymers. By modifying the concentration of MA grafted on the SEBS, different levels of emulsification of the blends were obtained. A comparison of 1/99 and 10/90 PP/PET blends compatibilized by SEBS‐g‐MA allows one to distinguish the relative role of interfacial tension and coalescence suppression in diminishing particle size. It is shown that varying degrees of residual coalescence remain, depending on the level of %MA in the copolymer. A detailed study of the 2%MA system below interfacial saturation was carried out to shed further light on the dependence of coalescence suppression on emulsification level and interfacial coverage. After separating out the contribution of interfacial tension on particle size reduction, it is shown that coalescence suppression for this system increases gradually with areal density of modifier at the interface right up to the region of interfacial saturation. Finally, the interfacial and morphological data were used to test the ability of the Lee and Park model to describe coalescence in polymer blends. Reasonable agreement was found between the parameter c₁, describing the coalescence in that model, and the trends related to residual coalescence from this study. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 939–951, 1999     

Crew‐cut aggregates from self‐assembly of blends of polystyrene‐b‐poly(acrylic acid) block copolymers and homopolystyrene in solution

The formation and morphological characteristics of crew‐cut aggregates from blends of polystyrene‐b‐poly(acrylic acid) diblock copolymer and polystyrene homopolymer in solution were studied by static light scattering, transmission electron microscopy and size exclusion chromatography. The crew‐cut aggregates, consisting of a polystyrene core and a poly(acrylic acid) corona, were prepared by direct dissolution of the polymer blends in a selective solvent mixture consisting of 93 wt % dimethylformamide and 7 wt % water. It is found that the aggregation behavior depends strongly on the relative volume fractions of the block copolymer and homopolymer in the blends. This is a result of the difference in solubility between the copolymer and the homopolymer in solution which, in turn, influences their miscibility and mutual solubility and consequently the morphology of the formed crew‐cut aggregates. Specifically, when the homopolymer fraction is low, it is mainly dissolved in the cores of the crew‐cut aggregates formed by the block copolymer. When the homopolymer fraction exceeds its solubility limit in the copolymer micelles, aggregates of another type are formed which contain a major fraction of the homopolymer. These aggregates are usually much larger than the primary micelles and have an internal structure due to the formation of reverse micelles from the dissolved block copolymer chains. The importance of thermodynamic vs. kinetic aspects during the formation of the crew‐cut aggregates is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1469–1484, 1999     

Glass transition and miscibility in blends of two semicrystalline polymers: Poly(aryl ether ketone) and poly(ether ether ketone)

Binary melt‐blended mixtures of two aryl ether ketone polymers (i.e., a new poly(aryl ether ketone) (code name PK99) and poly(ether ether ketone) (PEEK), have been studied. Polymer miscibility in glassy amorphous (or melt) domains has been demonstrated for the binary blend comprising of two aryl‐ether‐ketone‐type semicrystalline polymers. Composition‐dependent, single T_g was observed within full composition range in the PK99/PEEK blends, and the narrow T_g breadth also suggests that the scale of mixing was fine and uniform. To better resolve any possible overlapping T_g's, physical aging was imposed on a comparison set of blend samples for the purpose of improving detectability of overlapped multiple transitions if existing. The result still showed one single T_g. The relative sharp T_g and lack of cloud point transition suggest that the scale of molecular intermixing is good. Phase homogeneity was further confirmed using optical and scanning electron microscopy. The X‐ray diffractograms suggest that isomorphism does not exist in the PK99/PEEK blends and that the crystal forms of the respective polymers remain distinct and unchanged by the miscibility in the amorphous region. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1485–1494, 1999     

吸热型碳氢燃料的结焦研究Ⅰ含硫抑制剂

在连续进样微反测焦系统上考察了二硫化碳、噻酚等含硫化合物添加前后碳氢燃料S-1裂解结焦速率的变化。结果显示,两种含硫抑制剂均可明显降低燃料裂解时的结焦速率,二硫化碳的抑制效果较好,可以使初始结焦速率降低90％。同时,气相色谱的分析结果显示,含硫抑制剂对燃料裂解产物的分布情况有一定影响,促进了烯烃选择性的提高,有利于改善燃料的吸热能力。利用扫描电镜以及元素分析手段对焦形态结构和元素组成的研究结果显示,含硫抑制剂还有利于改善焦的形态结构以及氢碳元素组成,对清焦工作有一定帮助。     

An Intricate Review on Nutritional and Analytical Profiling of Coconut,Flaxseed, Olive,and Sunflower Oil Blends

Vegetable oils (VOs), being our major dietary fat source, play a vital role in nourishment. Different VOs have highly contrasting fatty acid (FA) profiles and hence possess varying levels of health protectiveness. Consumption of a single VO cannot meet the recommended allowances of various FA either from saturated FA (SFA), monounsaturated FA (MUFA), polyunsaturated FA (PUFA), Ω-3 PUFAs, and medium-chain triglycerides (MCTs). Coconut oil (CO), flaxseed oil (FO), olive oil (OO), and sunflower oil (SFO) are among the top listed contrast VOs that are highly appreciated based on their rich contents of SFAs, Ω-3 PUFAs, MUFAs, and Ω-6 PUFA, respectively. Besides being protective against various disease biomarkers, these contrasting VOs are still inappropriate when consumed alone in 100% of daily fat recommendations. This review compiles the available data on blending of such contrasting VOs into single tailored blended oil (BO) with suitable FA composition to meet the recommended levels of SFA, MUFA, PUFA, MCTs, and Ω-3 to Ω-6 PUFA ratios which could ultimately serve as a cost-effective dietary intervention towards the health protectiveness and improvement of the whole population in general. The blending of any two or more VOs from CO, FO, OO, and SFO in the form of binary, ternary, or another type of blending was found to be very conclusive towards balancing FA composition; enhancing physiochemical and stability properties; and promising the therapeutic protectiveness of the resultant BOs.     

Recent Progress in ZIF-Derived Carbons for Enhanced Oxygen Reduction Reaction Electrocatalysis

The oxygen reduction reaction (ORR) represents a cornerstone for many clean energy conversion technologies such as fuel cells and metal-air batteries. Nevertheless, the commercialization of these technologies is largely impeded by the slow kinetics of ORR, for which active, durable and cost-effective ORR catalysts are needed. In recent years, zeolitic imidazolate framework (ZIF) derived carbon materials emerge as a new class of non-precious metal catalysts (NPMCs) toward ORR, largely benefiting from their high surface area, abundant porosity, tunable chemical/electronic structure, and superior ORR activity which is comparable or even surpasses those state-of-the-art Pt-based ORR catalysts. This review offers a comprehensive overview of the recent advances in ZIF-derived carbons for ORR. The synthesis strategies and the key factors affecting the ORR performance of ZIF-derived carbon materials are discussed. Future research directions and perspectives on exploring ZIF derived carbons as efficient ORR catalysts are highlighted, with a focus on the principles of rationally engineering the coordination structures of active sites.