Mass formulae and strange quark matter

We have derived the popularly used parametrization formulae for quark masses at low densities and modified them at high densities within the mass-density-dependent model. The results are applied to investigate the lowest density for the possible existence of strange quark matter at zero temperature.Comment: 9 pages, LATeX with ELSART style, one table, no figures. Improvement on the derivation of qark mass formula

Blaschke's problem for timelike surfaces in pseudo-Riemannian space forms

We show that isothermic surfaces and S-Willmore surfaces are also the solutions to the corresponding Blaschke's problem for both spacelike and timelike surfaces in pseudo-Riemannian space forms. For timelike surfaces both Willmore and isothermic, we obtain a description by minimal surfaces similar to the classical results of Thomsen.Comment: 10 page

Macroscopic Quantum Tunneling Effect of Z2 Topological Order

In this paper, macroscopic quantum tunneling (MQT) effect of Z2 topological order in the Wen-Plaquette model is studied. This kind of MQT is characterized by quantum tunneling processes of different virtual quasi-particles moving around a torus. By a high-order degenerate perturbation approach, the effective pseudo-spin models of the degenerate ground states are obtained. From these models, we get the energy splitting of the ground states, of which the results are consistent with those from exact diagonalization methodComment: 25 pages, 14 figures, 4 table

Enhanced web log based recommendation by personalized retrieval

University of Technology, Sydney. Faculty of Engineering and Information Technology.With the rapid development of the Internet and WWW, it is more and more important for people to access quality web information. Thus the problem of enabling users to quickly and accurately find information has become an urgent issue. As one of the basic ways to solve this problem, personalized information services have been focusing on fulfilling the personalized information requirements of different users based on their actual demands, preference characteristics, behaviour patterns, etc. This thesis focuses on enhancing web log based recommendation by personalized retrieval, and its main works and innovations include: • For personalized retrieval, the thesis proposes two models to improve user experience and optimize search performance. The first is a query suggestion model based on query semantics and click-through data. This model calculates the subject relevance between queries, and then combines the semantic information and the relevance of the query-click matrix model as this can effectively eliminate the ambiguity and input errors of reminder queries. The second is a collaborative filtering retrieval model based on local and global features. By the integration of the local and global characteristics of the accessed information, this model overcomes the limitations of a single feature, and increases the degree of application of the retrieval model. • For recommendation by personalized retrieval, we propose two recommendation models based on the web log. The first is based on the user’s atomic retrieval transaction sequence and the browse characteristics. This model decomposes search transactions, and calculates the user’s degree of interest on the search term, which allows users to query information more clearly. Further, it incorporates the user feedback on the search results evaluation value, which overcomes the shortcomings of the model based on content filtering. The second model is based on user interests association findings, which can be used to: find the relationship between resources accessed by users, extract the associations of user interests, and address the problem of user interests isolation

Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain

Electronic structures of wurtzite GaAs nanowires in the [0001] direction were studied using first-principles calculations. It was found that the band gap of GaAs nanowires experience a direct-to-indirect transition when the diameter of the nanowires is smaller than ~28 {\AA}. For those thin GaAs nanowires with an indirect band gap, it was found that the gap can be tuned to be direct if a moderate external uniaxial strain is applied. Both tensile and compressive strain can trigger the indirect-to-direct gap transition. The critical strains for the gap-transition are determined by the energy crossover of two states in conduction bands.Comment: 4 pages, 4 figure