由电池供应电量的无线通信网络中,数据需要通过作为路由的中间节点进行传输,所以这些中间节点的能量消耗对整个网络的生存有很大的影响。本文从延长网络生存时间的目的出发,提出了一种能量优化的编码感知路由协议COER(Coding-aware base...由电池供应电量的无线通信网络中,数据需要通过作为路由的中间节点进行传输,所以这些中间节点的能量消耗对整个网络的生存有很大的影响。本文从延长网络生存时间的目的出发,提出了一种能量优化的编码感知路由协议COER(Coding-aware based Optimal Energy Routing),利用能量门限值以及相对剩余能量来均衡网络节点能量的消耗,同时用网络编码来减少能量的消耗,并将两者统一来实现网络能量的优化。仿真结果表明:COER能够减少传输能耗,均衡网络能量消耗,延长网络生存时间。展开更多
目的探讨压缩感知结合层面编码金属伪影校正(compressed sensing-slice-encoding metal artifact correction,CS-SEMAC)技术用于脊柱金属植入物术后MRI的应用价值。材料与方法比较招募的35例脊柱金属植入物术后患者3.0 T MRI矢状位CS-SE...目的探讨压缩感知结合层面编码金属伪影校正(compressed sensing-slice-encoding metal artifact correction,CS-SEMAC)技术用于脊柱金属植入物术后MRI的应用价值。材料与方法比较招募的35例脊柱金属植入物术后患者3.0 T MRI矢状位CS-SEMAC序列、高带宽(high bandwidth,HBW)序列和水脂分离(Dixon)三种序列在金属植入物伪影面积、椎体信噪比(signal-to-noise ratio,SNR)、图像质量、图像清晰度、脂肪抑制效果以及植入物周围解剖结构的可见性方面的差异。结果CS-SEMAC在T1、T2矢状位图像上金属伪影面积分别为(15.45±6.84)、(22.23±9.76)cm^(2),显著低于其他两种序列,差异具有统计学意义(P<0.001);三种序列在T2抑脂矢状面图像上的SNR两两比较显示:HBW序列椎体SNR显著高于其他两种序列,Dixon序列椎体SNR显著低于其他两种序列,CS-SEMAC序列椎体SNR低于HBW序列,高于Dixon序列,差异均有统计学意义(P<0.001);在图像清晰度上,T2WI-tirm-CS-SEMAC序列评分低于其他两种序列,差异具有统计学意义(P<0.001);T2WI-tirm-CS-SEMAC序列在图像质量和脂肪抑制效果方面评分显著优于其他两种序列,差异具有统计学意义(P<0.001);并且CS-SEMAC序列相较于其他两种序列更能清晰显示植入物周围椎体、椎弓根、椎间孔及神经根,差异具有统计学意义(P<0.001)。结论CS-SEMAC序列相比于HBW、Dixon序列能够有效减少植入物周围的金属伪影,并且能显著提高T2抑脂序列的图像质量和脂肪抑制效果,虽然在T2抑脂上金属植入物邻近椎体SNR相比HBW序列有所下降,图像比HBW和Dixon图像略模糊,但是椎体周围关键解剖结构的可见度明显提升,对脊柱术后解剖结构的显示有一定优势。展开更多
Recent researches show that inter-session network coding could decrease the number of packets transmission and achieve higher throughput in wireless network compared with traditional forwarding mechanism. In most exis...Recent researches show that inter-session network coding could decrease the number of packets transmission and achieve higher throughput in wireless network compared with traditional forwarding mechanism. In most existing relay mechanisms based on inter-session network such as COPE, relay node demands to collect the messages from its neighbor nodes to get notice of which packets already overheard by them so as to determine whether there exists coding opportunity between or among forwarding packets. However, transmission overhead of this message collection and computing cost of opportunity determination will degrade the performance of these mechanisms. It is observed that coding opportunity at relay node is much more related with the local topology, and the opportunity of encoding three or more packets together is far less than that of encoding two packets together in wireless network with general density. Based on this, a new coding-aware routing mechanism, named TCAR, is proposed. TCAR ignores the oppommity of encoding three or more than three packets together. Each relay node maintains an encoding mapping table being established according to the result of its local topology detection, which can be used to calculate the path cost during routing setup phase, and determine that which two packets can be encoded together during the packets forwarding phase. In TCAR, instead of periodic messages collection, each relay nodes just need once local topology detection, and the encoding determination is much simpler than that of the former mechanisms. Simulation results show that compared with typical inter-session network coding mechanisms COPE and COPE-based routing, TCAR achieves 12% and 7% throughput gains, and keeps the minimum end to end delay.展开更多
文摘由电池供应电量的无线通信网络中,数据需要通过作为路由的中间节点进行传输,所以这些中间节点的能量消耗对整个网络的生存有很大的影响。本文从延长网络生存时间的目的出发,提出了一种能量优化的编码感知路由协议COER(Coding-aware based Optimal Energy Routing),利用能量门限值以及相对剩余能量来均衡网络节点能量的消耗,同时用网络编码来减少能量的消耗,并将两者统一来实现网络能量的优化。仿真结果表明:COER能够减少传输能耗,均衡网络能量消耗,延长网络生存时间。
文摘目的探讨压缩感知结合层面编码金属伪影校正(compressed sensing-slice-encoding metal artifact correction,CS-SEMAC)技术用于脊柱金属植入物术后MRI的应用价值。材料与方法比较招募的35例脊柱金属植入物术后患者3.0 T MRI矢状位CS-SEMAC序列、高带宽(high bandwidth,HBW)序列和水脂分离(Dixon)三种序列在金属植入物伪影面积、椎体信噪比(signal-to-noise ratio,SNR)、图像质量、图像清晰度、脂肪抑制效果以及植入物周围解剖结构的可见性方面的差异。结果CS-SEMAC在T1、T2矢状位图像上金属伪影面积分别为(15.45±6.84)、(22.23±9.76)cm^(2),显著低于其他两种序列,差异具有统计学意义(P<0.001);三种序列在T2抑脂矢状面图像上的SNR两两比较显示:HBW序列椎体SNR显著高于其他两种序列,Dixon序列椎体SNR显著低于其他两种序列,CS-SEMAC序列椎体SNR低于HBW序列,高于Dixon序列,差异均有统计学意义(P<0.001);在图像清晰度上,T2WI-tirm-CS-SEMAC序列评分低于其他两种序列,差异具有统计学意义(P<0.001);T2WI-tirm-CS-SEMAC序列在图像质量和脂肪抑制效果方面评分显著优于其他两种序列,差异具有统计学意义(P<0.001);并且CS-SEMAC序列相较于其他两种序列更能清晰显示植入物周围椎体、椎弓根、椎间孔及神经根,差异具有统计学意义(P<0.001)。结论CS-SEMAC序列相比于HBW、Dixon序列能够有效减少植入物周围的金属伪影,并且能显著提高T2抑脂序列的图像质量和脂肪抑制效果,虽然在T2抑脂上金属植入物邻近椎体SNR相比HBW序列有所下降,图像比HBW和Dixon图像略模糊,但是椎体周围关键解剖结构的可见度明显提升,对脊柱术后解剖结构的显示有一定优势。
基金Projects(61173169,61106036)supported by the National Natural Science Foundation of ChinaProject(NCET-10-0798)Program for New Century Excellent Talents in University,China
文摘Recent researches show that inter-session network coding could decrease the number of packets transmission and achieve higher throughput in wireless network compared with traditional forwarding mechanism. In most existing relay mechanisms based on inter-session network such as COPE, relay node demands to collect the messages from its neighbor nodes to get notice of which packets already overheard by them so as to determine whether there exists coding opportunity between or among forwarding packets. However, transmission overhead of this message collection and computing cost of opportunity determination will degrade the performance of these mechanisms. It is observed that coding opportunity at relay node is much more related with the local topology, and the opportunity of encoding three or more packets together is far less than that of encoding two packets together in wireless network with general density. Based on this, a new coding-aware routing mechanism, named TCAR, is proposed. TCAR ignores the oppommity of encoding three or more than three packets together. Each relay node maintains an encoding mapping table being established according to the result of its local topology detection, which can be used to calculate the path cost during routing setup phase, and determine that which two packets can be encoded together during the packets forwarding phase. In TCAR, instead of periodic messages collection, each relay nodes just need once local topology detection, and the encoding determination is much simpler than that of the former mechanisms. Simulation results show that compared with typical inter-session network coding mechanisms COPE and COPE-based routing, TCAR achieves 12% and 7% throughput gains, and keeps the minimum end to end delay.
