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Cu matrix composites reinforced by ex-situ added CrB2 ceramic particles were prepared by powder metallurgy and hot extrusion, and then the effect of CrB2 content on microstructure and mechanical properties was studied. Results show that the strength of Cu matrix composites depends mainly on the dispersion degree of CrB2 particles, which is closely corresponded to the content of CrB2 particles. When the content is below 3vol.%, CrB2 particles disperses uniformly in the Cu matrix, and the strength of Cu matrix composites increases continuously with the content of CrB2. However, when the content is above 3vol.%, the strength of Cu matrix composites decreases significantly with the increase of CrB2 content, which is ascribed to the serious agglomeration phenomenon. Although both the electrical conductivity and plasticity decrease with the increase of CrB2 content, they remain quite a high level. The excellent combination properties are obtained when the content of CrB2 is 3vol.%, viz. The tensile strength is 304 MPa, the elongation is 22% and the electrical conductivity is 90 %IACS, better than most of the reported Cu matrix composites especially electrical conductivity prepared by in-situ method. Furthermore, dislocation strengthening caused by thermal mismatch and Orowan strengthen of CrB2 is demonstrated as the main strengthening mechanism of Cu/CrB2 composites, based on the theoretical and experimental investigations.

A code is said to possess the combination property if $k$ source packets are mapped into $n \geq k$ packets and any $k$ out of these $n$ packets are able to recover the information of the original $k$ packets. While the class of maximum-distance-separable codes are well known to have this property, its decoding complexity is generally high. For this reason, a new class of codes which can be decoded by the zigzag-decoding algorithm is considered. It has a lower decoding complexity at the expense of extra storage overhead in each parity packet. In this work, a new construction of a zigzag decodable code is proposed. The novelty of this new construction lies in the careful selection of the amount of bit-shift of each source packet in obtaining each parity packet. Besides, an efficient on-the-air repair scheme based on physical-layer network coding is designed. [ABSTRACT FROM AUTHOR]