骨架状聚氨酯海绵模板导向制备多级孔碳材料

多级孔结构碳材料具有结构多样、比表面积高、孔体积大和化学稳定性好等性质,不同尺度的孔道能协同发挥各自的传质优势,在吸附和分离、化学化工、靶向给药和能源储存等方面有独特表现并得到了广泛应用.近年来,国内外将聚氨酯海绵与其他尺度的模板剂相结合制备了许多不同结构的多级孔状碳质材料并应用到不同的领域.本文从多级孔碳材料的制备、结构和应用等角度综述了相关研究工作,并指出合成石墨化、各级孔道合理分配、孔壁薄和机械强度好的多级孔结构的碳材料仍面临诸多问题.     

Mathematics and engineering in real life through mathematical competitions

We bring out an experience of organizing mathematical competitions that can be used as a medium to motivate the student and teacher minds in new directions of thinking. This can contribute to fostering research, innovation and provide a hands-on experience of mathematical concepts with the real world. Mathematical competitions can be used to build curiosity and give an understanding of mathematical applications in real life. Participation in the competition has been classified under four broad categories. Student can showcase their findings in various forms of expression like model, poster, soft presentation, animation, live performance, art and poetry. The basic focus of the competition is on using open source computation tools and modern technology, to emphasize the relationship of mathematical concepts with engineering applications in real life.     

完全图$K_{2m}$书本表示的唯一性

In the present paper we discuss some properties of book presentation of spatial graphs, and prove that the book presentation of minimum sheets of a complete graph K2m with even vertices is unique up to sheet translation and ambient isotopy. We also show this is true for K7.     

马尔可夫骨架过程的极限分布

本文运用基本更新定理和Smith关键更新定理等理论和方法,对马尔可夫骨架过程的极限分布进行深入研究,得到主要结果如下:去掉了原有结果中要求的绝对连续的条件,给出了马尔可夫骨架过程极限分布存在的充分条件;得到了马尔可夫骨架过程极限分布的具体公式,并证明了该极限分布为概率分布.     

马氏骨架过程理论在再生分支过程中的应用

本文旨在将经典的分支过程进行推广到再生分支过程,进而采用马氏骨架过程理论,特别是Doob骨架过程理论研究再生分支过程,得到它的瞬时分布和极限分布。     

Markov Skeleton Processes and Applications to Queueing Systems

In this paper, we apply the backward equations of Markov skeleton processes to qucueing systems. The transient distribution of the waiting time of a GI/G/1 queueing system, the transient distribution of the length of a GI/G/N queueing system and the transient distribution of the length of queueing networks are obtained.     

On Finite Presentability of Direct Products of Semigroups

A finite semigroup S is said to preserve finite generation (resp., presentability) in direct products, provided that, for every infinite semigroup T, the direct product S × T is finitely generated (resp., finitely presented) if and only if T is finitely generated (resp., finitely presented). The main result of this paper is a constructive necessary and sufficient condition for S to preserve both finite generation and presentability in direct products. The condition is that certain graphs, (s), one for each s S, are all connected. The main result is illustrated in three examples, one of which exhibits a 4-element semigroup that preserves finite generation but not finite presentability in direct products.1991 Mathematics Subject Classification: 20M05, 05C25The first author is financially supported by the Sub-Programa Ciência e Tecnologia do 2° Quadro Comunitário de Apoio (grant number BD/ 15623/98). The author also acknowledges the support of the Centro de Álgebra da Universidade de Lisboa and of the Projecto Praxis 2/2.1/MAT/73/94. The second author acknowledges partial financial support from the Nuffield Foundation.     

应力分量变化范围的描述方程及其图形

过应力空间一点的不同斜面上的正应力、剪应力以及全应力会随着斜面的变化而变化。全应力的变化范围常用应力椭球方程和应力椭球面来描述。首次给出了过一点不同斜面上正应力、剪应力变化的描述方程及其三维图形。该方程和应力椭球方程共同构成了所有应力分量的描述方程。针对剪应力、全应力作用方向与斜面的法向并不一致的问题,给出了一种能够直接描述不同斜面上正应力、剪应力和全应力变化的三维图形,该图形能够非常直观地表示正应力、剪应力以及全应力数值的变化。     

New structural motif of 18 valence electron molecules with a planar tetracoordinate heavier group 14 center: Unique stabilization effect of a π‐type skeleton

Proposing new valence electron counting rules and new structural motifs are both very important in chemistry. In this work, we unexpectedly found that by introducing a π‐type skeleton YCCY (Y = Al/Ga/In/Tl), a total of sixteen novel planar tetracoordinate heavier group 14 species, that is, ptM (M = Si/Ge/Sn/Pb) in neutral, can be designed as global minima. The underlying bonding situation contrasts sharply both with the well‐known 18ve‐ptC and the limited 18ve‐ptM, for which there is little multiple bonding character within the skeleton. The fact that each YCCY (Y = Al/Ga/In/Tl) can stabilize all heavier group 14 atoms in a planar tetracoordinate fashion strongly demonstrates the universality of such a π‐type skeleton. The present work firmly demonstrates that introducing the π‐type ligand skeleton can effectively enrich the planar tetracoordinate chemistry with the heavier group atoms.     

碳硼烷结构规则的量子化学计算

本文对一系列封闭型C_nB_5-n(n=0～5)和C_nB_6-n(n=0～6)碳硼烷骨架及巢型C₄B_5-n(n=0～5)碳硼烷骨架进行了EHMO量子化学计算,根据计算结果讨论了碳硼烷的结构规则.