双分布聚乙二醇接枝纳米二氧化硅的高效可控制备

在混合溶剂中通过"grafting to"的方法将2种分子量不同的聚乙二醇单甲醚(MPEG M_w=750,4000)接枝到氨基修饰的St?ber法二氧化硅(SiO_2-NH_2)表面,制备双分布纳米接枝复合物.采用二步法,先将带环氧端基的低分子量聚乙二醇单甲醚(MPEG-EO)与SiO_2-NH_2在甲苯溶剂中充分反应后,与高分子量的MPEG-EO在甲苯和正癸烷的混合溶剂中使用相同的反应条件和后处理方法,能便捷制备出具有双分布接枝的纳米复合物.在接枝反应体系中,分子链的链段尺寸和接枝密度之间存在着密切关系.一定的范围内,接枝密度随链段尺寸减小而增大.通过改变混合溶剂比例来调控接枝链段的尺寸,可以很好控制聚合物的接枝密度.在双分布接枝的纳米复合物中,低分子量的接枝密度为0.85 chains/nm~2,高分子量的接枝密度能达到0.40 chains/nm~2,体现出了简单、高效、可控的特点,与聚环氧乙烷(PEO)共混后分散良好,对于制备出均匀分散的纳米复合材料起到了一定的指导作用.     

聚羟基丁酸酯/碳纳米管复合纳米纤维膜的制备及其对重金属离子吸附分离性能的研究

以聚羟基丁酸酯和碳纳米管为原料,采用三氯甲烷/二甲基甲酰胺混合溶液为溶剂,利用静电纺丝技术制备了聚羟基丁酸酯/碳纳米管复合纳米纤维膜.研究了碳纳米管的含量对纳米纤维膜形貌和力学性能的影响,探讨了复合纳米纤维膜对重金属Cu(II)、Cd(II)和Pb(II)的吸附特性.实验结果表明:加入1 wt%碳纳米管能够将纳米纤维的平均直径从(728±146)nm降低至(468±89)nm,纳米纤维膜的比表面积从27.24 m~2/g提高至43.45 m~2/g;碳纳米管的复合能够有效增强聚羟基丁酸酯纳米纤维,当碳纳米管含量1 wt%为最佳,拉伸强度可达5.85 MPa,较纯聚羟基丁酸酯纳米纤维提升了115%.复合纳米纤维膜对重金属离子具有良好的吸附特性,其对Cu(II)、Cd(II)和Pb(II)的最佳吸附pH值为5,此时最大吸附容量分别为91.04、171.05和197.03mg/g,平衡吸附时间分别约为50、60和60 min,吸附率分别为1.79、2.83和3.28 mg/g/min;热力学和动力学分析表明,复合纳米纤维膜对重金属Cu(II)、Cd(II)和Pb(II)的吸附行为更符合Freundlich模型,吸附过程更符合Pseudo-second order模型;循环使用实验表明,重复使用5次后,其吸附容量可保持在初始值的87%以上,具有较好的使用寿命.     

The graph structure of a deterministic automaton chosen at random

An n‐state deterministic finite automaton over a k‐letter alphabet can be seen as a digraph with n vertices which all have k labeled out‐arcs. Grusho (Publ Math Inst Hungarian Acad Sci 5 (1960), 17–61). proved that whp in a random k‐out digraph there is a strongly connected component of linear size, i.e., a giant, and derived a central limit theorem. We show that whp the part outside the giant contains at most a few short cycles and mostly consists of tree‐like structures, and present a new proof of Grusho's theorem. Among other things, we pinpoint the phase transition for strong connectivity. © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 51, 428–458, 2017     

Hom-Gel'fand–Dorfman Super-bialgebras and Hom-Lie Conformal Superalgebras

The aim of this paper is to introduce and study Hom-Gel'fand–Dorfman super-bialgebras and Hom-Lie conformal superalgebras. In this paper, we provide different ways for constructing HomGel'fand–Dorfman super-bialgebras. Also, we obtain some infinite-dimensional Hom-Lie superalgebras from affinization of Hom-Gel'fand–Dorfman super-bialgebras. Finally, we give a general construction of Hom-Lie conformal superalgebras from Hom-Lie superalgebras and establish the equivalence between quadratic Hom-Lie conformal superalgebras and Hom-Gel'fand–Dorfman super-bialgebras.     

Nanostructured heterogeneous catalysts for electrochemical reduction of CO2

Electrochemical reduction of CO₂ provides a sustainable solution to address the intermittent renewable electricity storage while recycling CO₂ to produce fuels and chemicals. Highly efficient catalytic materials and reaction systems are required to drive this process economically. This Review highlights the new trends in advancing the electrochemical reduction of CO₂ by developing and designing nanostructured heterogeneous catalysts. The activity, selectivity and reaction mechanism are significantly affected by the nano effects in nanostructured heterogeneous catalysts. In the future, energy efficiency and current density in electrochemical reduction of CO₂ need to be further improved to meet the requirements for practical applications.     

用固体润滑剂改善汽车刮水胶条使用性能的研究

作者将含有MoS_2和石墨的不同配方的固体润滑涂料刷涂在几种国产汽车刮水胶条上,并分别于干摩擦和水润滑的两种刮刷状态下,就固体润滑剂改善刮水胶条的擦拭性能进行了试验研究,指出这是使刮水胶条降低擦拭阻力、提高刮刷效果的可行途径,同时强调配制涂料时应当选用颗粒细小而均匀的固体润滑剂粉末。     

大挠度弯曲直梁混合变量最小势能原理的应用

应用大挠度弯曲直梁混合变量最小势能原理,求解均载两端固定大挠度柱面弯曲板条的轴向挠度分布和轴向弯矩分布．实例计算表明:该方法简单实用、精度高,是一种计算大挠度柱面弯曲板条变形的有效方法．     

城区爆破作业对环境的影响

本文用一个城区爆破作业的实例说明,只要采取可靠的技术措施,就可将爆破对环境的影响,如振动、噪声、飞石等,控制在允许的范围内,从而可以在人口稠密的城区顺利地进行较大规模的爆破施工,加快工程进度。