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Li L.,Qinghai Nationalities College | Sun W.-N.,Tsinghua University | Chen C.-X.,Tsinghua University | Li J.-D.,Tsinghua University
Gaofenzi Cailiao Kexue Yu Gongcheng/Polymeric Materials Science and Engineering | Year: 2010

Polyethersulphone (PES), phenodiazine polyether-sulfone-ketone (PPESK) are developed engineering thermoplastic and membrane materials with high glass transition temperature. Gel phase inversion method was used to produce a series of PES/DMAc, PPESK/NMP ultrafiltration membrane with flat membrane casting equipment through changing the content of nonsolvent additives (formamide). In this process, PES and PPESK were taken as solute, dimethylacetamide (DMAc) and N-methyl pyrrolidone (NMP) were taken as solvent. The effect of formamide on the viscosity of casting solution and the structure and performance of membrane was investigated and the action rules of formamide in PES/DMAc and PPESK/NMP membrane-forming system were studied. Source

Hu S.,Qinghai Nationalities College
International Journal of Computer Mathematics | Year: 2010

A H-shape is a tree with exactly two of its vertices having maximal degree 3. In this paper, we show that 2 ≤ λ1 (H) < √5, where λ1 (H) is the spectral radius of H. © 2010 Taylor & Francis. Source

Li Y.,Qinghai Nationalities College | Zhang S.,Northwestern Polytechnical University
Computers and Mathematics with Applications | Year: 2010

The rupture degree of an incomplete connected graph G is defined by r(G)=maxω(G-X)-|X|-τ(G-X):X⊂V(G),ω(G-X)>1, where ω(G-X) is the number of components of G-X and τ(G-X) is the order of a largest component of G-X. In Li and Li [5] and Li et al. (2005) [4], it was shown that the rupture degree can be well used to measure the vulnerability of networks. In this paper, the maximum and minimum networks with prescribed order and the rupture degree are obtained. Finally, we determine the maximum rupture degree graphs with given order and size. © 2010 Elsevier Ltd. All rights reserved. Source

Li Y.,Qinghai Nationalities College | Wei Z.,Xian University of Architecture and Technology | Yue X.,Northwestern Polytechnical University | Liu E.,Qinghai Nationalities College
International Journal of Foundations of Computer Science | Year: 2014

Communication networks must be constructed to be as stable as possible, not only with the respect to the initial disruption, but also with respect to the possible reconstruction. Many graph theoretical parameters have been used to describe the stability of communication networks. Tenacity is a reasonable one, which shows not only the difficulty to break down the network but also the damage that has been caused. Total graphs are the largest graphs formed by the adjacent relations of elements of a graph. Thus, total graphs are highly recommended for the design of interconnection networks. In this paper, we determine the tenacity of the total graph of a path, cycle and complete bipartite graph, and thus give a lower bound of the tenacity for the total graph of a graph. © World Scientific Publishing Company. Source

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