Inference of time-varying regression models

We consider parameter estimation, hypothesis testing and variable selection for partially time-varying coefficient models. Our asymptotic theory has the useful feature that it can allow dependent, nonstationary error and covariate processes. With a two-stage method, the parametric component can be estimated with a $n^{1/2}$-convergence rate. A simulation-assisted hypothesis testing procedure is proposed for testing significance and parameter constancy. We further propose an information criterion that can consistently select the true set of significant predictors. Our method is applied to autoregressive models with time-varying coefficients. Simulation results and a real data application are provided.Comment: Published in at http://dx.doi.org/10.1214/12-AOS1010 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

A new framework of decentralized social networks

Due to the increasing popularity of online social networking services, more and more people have been outsourcing their personal data to these service providers. Data privacy has gradually become a big concern. Decentralized social network proposed in recent researches has been a promising alternative. But there lacks an efficient system of decentralized social network with complete social networking functions. In this thesis, we design a new framework of decentralized social network and implement the prototype. Our experiments shows that our design protects data privacy as well as achieve communication efficiency

Theoretical and physical modelling of the thermal performance of water wall systems

Water wall is an excellent passive solar strategy which can maintain thermal comfort in buildings while reducing energy consumption. Existing water wall studies are mainly based on simple heat balance models, in which convective heat transfer coefficients are assumed constant and radiation exchange is commonly neglected. Further, the application of the CFD approach to water wall research is very rare. These research gaps are addressed in this study through the development of a comprehensive transient heat balance model and unsteady CFD modelling. The thesis covers three major topics. Firstly, the turbulent natural convection with and without radiation transfer in two-dimensional and three-dimensional air-filled differentially heated cavities is numerically investigated using various RANS (Reynolds Averaged Navier-Stokes) turbulence models and the Discrete Ordinates radiation model. It is found that the shear-stress transport k-ω model has the best overall performance in terms of capturing the main features of the flow and predicting the time-averaged quantities. Secondly, a comprehensive conjugate conduction-convection-radiation model for transient analysis of a semi-transparent water wall system is developed. It is found that reducing the transmissivity of the Perspex or glass walls is the most effective, practical and economical way to improve the thermal performance of the semi-transparent water wall system. Finally, the thermal performance of an opaque water wall system is numerically investigated and compared against a conventional concrete wall system for the typical climate conditions in Sydney, Australia. The results indicate that less supplementary energy is required in winter than that in summer to maintain a comfortable interior temperature. Further, the water wall system performs significantly better than the concrete wall system of the same thickness in the winter climate of Sydney, whereas both systems have a similar performance in summer