Characterization of Lifshitz transitions in topological nodal line semimetals

We introduce a two-band model of three-dimensional nodal line semimetals, the Fermi surface of which at half-filling may form various one-dimensional configurations of different topology. We study the symmetries and "drumhead" surface states of the model, and find that the transitions between different configurations, namely, the Lifshitz transitions, can be identified solely by the number of gap-closing points on some high-symmetry planes in the Brillouin zone. A global phase diagram of this model is also obtained accordingly. We then investigate the effect of some extra terms analogous to a two-dimensional Rashba-type spin-orbit coupling. The introduced extra terms open a gap for the nodal line semimetals and can be useful in engineering different topological insulating phases. We demonstrate that the behavior of surface Dirac cones in the resulting insulating system has a clear correspondence with the different configurations of the original nodal lines in the absence of the gap terms.Comment: 7 pages, 6 figure

A Knowledge Management performance evaluation model based on fuzzy set theory

As the knowledge-based economy time comes, the core of business process is transforming financial intensive into technology intensive and knowledge intensive gradually. However, the value of knowledge itself can’t be measured easily. We must evaluate and investigate the performance of knowledge management through activities of knowledge management process. During the performance evaluation process, many uncertain factors must be considered. It is also involved ambiguity occurred by human subjective judgment. Therefore, a performance evaluation model of knowledge management is proposed in this paper by combining Fuzzy Delphi with Fuzzy AHP. Finally, a numerical example is given to demonstrate the procedure for the proposed method at the end of this paper