| |  | Lian, S. | Commutative Encryption and Watermarking in Video Compression read moreAbstract: A scheme is proposed to implement commutative video encryption and watermarking during advanced video coding process. In H.264/AVC compression, the intra-prediction mode, motion vector difference and discrete cosine transform (DCT) coefficients' signs are encrypted, while DCT coefficients' amplitudes are watermarked adaptively. To avoid that the watermarking operation affects the decryption operation, a traditional watermarking algorithm is modified. The encryption and watermarking operations are commutative. Thus, the watermark can be extracted from the encrypted videos, and the encrypted videos can be re-watermarked. This scheme embeds the watermark without exposing video content's confidentiality, and provides a solution for signal processing in encrypted domain. Additionally, it increases the operation efficiency, since the encrypted video can be watermarked without decryption. These properties make the scheme a good choice for secure media transmission or distribution.  This article is not yet tagged | 2007 |
| | | Liu, Z. | Development of High-Voltage Vacuum Circuit Breakers in China read moreAbstract: This paper introduces a research work on the development of high-voltage (HV) vacuum circuit breakers (VCBs) in China from its start point 1989 to 2006. In this period, a 126-kV two breaks VCB prototype and a 126-kV single break VCB prototype were developed. A latest 252-kV single break interrupter prototype is introduced. Five HV VCBs technologies are discussed, which include HV vacuum insulation, high current interrupting technology with long contact gaps, increasing nominal current, operating mechanism characteristics, and contact bouncing damping. In vacuum insulation, adding a metal ring at electrode back can decrease breakdown possibilities in the gap between the electrode back and main shield. Surface melting layer of contact material could have influence on voltage withstanding capability of a vacuum gap. For interrupting high current with long contact gaps, strong axial magnetic field (AMF) is needed for a better vacuum arc control. Therefore, a single coil AMF electrode is introduced. Heat radiators are effective to increase nominal current of VCBs. Thermal analysis can help to give appropriate design parameters. There is an optimum opening characteristic that is helpful to improve the interrupting performance of VCBs. Permanent magnet operating mechanism and spring-type operating mechanism are suitable for HV VCBs. Contact bouncing in HV VCBs can be damped by installing contact spring and bellows on stationary end of VCBs. This article is not yet tagged | 2007 |
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