Video-over-IP applications have recently attracted a large number of users on the Internet. Traditional client-server based video streaming solutions incur expensive bandwidth provision cost on the server. Peer-to-Peer (P2P) networking is a new paradigm to build distributed network applications. Recently, several P2P streaming systems have been deployed to provide live and on-demand video streaming services on the Internet at low server cost. In this paper, we provide a survey on the existing P2P solutions for live and on-demand video streaming. Representative P2P streaming systems, including tree, multi-tree and mesh based systems are introduced. We describe the challenges and solutions of providing live and on-demand video streaming in P2P environment. Open research issues on P2P video streaming are also discussed.

Outdoor insulators are widely accepted in power industry to maintain electrical insulation ranging from distribution to transmission lines. Such increasing development leads to a lack of appropriate diagnostic tools for assessing the performance of insulator in service, particularly in contaminated conditions. In order to monitor operating performance of contaminated outdoor insulators, a recurrent plot technique is proposed to analyze the leakage current passing through the insulator surface. Contamination tests were conducted in a laboratory by employing heavy salt fog with the deposition of non-soluble contamination. The leakage current was decomposed into different frequency components by using a wavelet transform technique. The temporal sequence of the extracted component was extended to mdimensional phase space by using a phase-space reconstructed method. The recurrent plot is obtained to show that the topological structure of the high-frequency components is prominent to identify non-linear properties of discharge activities. Based on the analysis of the high-frequency components, the quantitative indicators of recurrent plot are obtained to reflect the underlying mechanism of flashover process. The results obtained indicate that the recurrent plot technique gives visual recurrent patterns of discharge activities for monitoring outdoor insulator performance. The dynamic behaviors on the insulator surface are graphically illustrated on the rectangular block structures with higher density of points. The structure changes indicate the switches of discharge states during the flashover process.Index Terms -outdoor insulator, heavy salt fog, leakage current, frequency component, recurrent plot, monitoring, dynamic performance, flashover process.

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Urban sustainable development strategies are of great importance to rapidly urbanized countries such as China. One of the most challenging problems is how to coordinate urban spatial development with social efficiency and environmental protection, e.g., highly efficient low-carbon urban traffic. Despite broad research efforts with respect to the influence of urban form on travel patterns, questions persist as to the impact of compact urban form on travel distance and modes. In this study, we adopted urban form metrics to capture key dimensions of urban form with the aid of image processing and spatial analysis based on satellite images and statistical data from the cases of 35 cities. Combined with urban travel survey data, we empirically examined the relationships between urban form and travel patterns of local urban residents. The results showed that urban form and travel patterns have regionalized characteristics, e.g., the eastern cities are characterized by disperse urban development patterns and longer commuting times on average compared with western and central cities. We found that relatively smaller built-up areas, higher degrees of urban spatial agglomeration and more paved road area per person would decrease the commuting time of urban residents. We also found that the public transport choices of urban residents are positively associated with built-up areas and commuting times, which suggests the need for provision and promotion of facilities for a high-quality public transport system. The findings provide helpful suggestions for the planning of sustainable urban form and development of transportation.

Due to the wide application of composite insulators in the power industry, the insulator performance is challenged by various environments. To determine the flashover performance of rime-iced composite insulator, laboratory investigation was carried out in an artificial climate chamber to simulate different rime-ice morphology on the insulator surface. The configuration and characteristics of the rime-ice were demonstrated to establish the relationship between the rime-ice parameters and the flashover performance. In accordance with the discharge phenomena, the transition of leakage current (LC) until the flashover was analyzed by using a recurrent plot approach. After extracting the high frequency components by using a wavelet transform technique, the LC just before the flashover was extended to m dimensional phase space based on a phase space reconstructed method. The recurrent plot was obtained to reveal the non-linear characteristics of LC for identifying the dynamic behaviors on the insulator surface. It is shown that the propagation and properties of the discharges can be graphically projected on the topological structure of recurrent plot as a function of the rime-ice parameters. The process and underlying mechanism of flashover performance of rime-iced composite insulator can be visually reflected by the recurrent plot and the quantitative indicators of LC.Index Terms -composite insulator, rime-iced condition, flashover, leakage current, recurrent plot, dynamic behavior.

Space charges tend to accumulate on the surface and at the interface of ethylene–propylene–diene terpolymer (EPDM), serving as high voltage direct current (HVDC) cable accessory insulation, which likely induces electrical field distortion and dielectric breakdown. Direct fluorination is an effective method to modify the surface characteristics of the EPDM without altering the bulk properties too much. In this paper, the surface morphology, hydrophobic properties, relative permittivity, and DC conductivity of the EPDM before and after fluorination treatment were tested. Furthermore, the surface and interface charge behaviors in the HVDC cable accessory were investigated by the pulsed electroacoustic (PEA) method, and explained from the point of view of trap distribution. The results show that fluorination helps the EPDM polymer obtain lower surface energy and relative permittivity, which is beneficial to the interface match in composite insulation systems. The lowest degree of space charge accumulation occurs in EPDM with 30 min of fluorination. After analyzing the results of the 3D potentials and the density of states (DOS) behaviors in EPDM before and after fluorination, it can be found that fluorination treatment introduces shallower electron traps, and the special electrostatic potential after fluorination can significantly suppress the space charge accumulation at the interface in the HVDC cable accessory.