An Nb-14Si-22Ti-4Cr-2AI-2Hf-0.15Y（at.%） alloy was prepared by directional solidification （DS） with liquid metal cooling, and the withdrawal rates selected were 1.2, 6, and 18 mm-min1, respectively. The Influence o...An Nb-14Si-22Ti-4Cr-2AI-2Hf-0.15Y（at.%） alloy was prepared by directional solidification （DS） with liquid metal cooling, and the withdrawal rates selected were 1.2, 6, and 18 mm-min1, respectively. The Influence of withdrawal rate and heat treatment on the microstructural evolution, fracture toughness and tensile strength at room temperature were investigated. Results show that the directionally solidified microstructure is composed of primary （Nb, X）ss dendrites and （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells aligning with the growth direction. The formation of bulk Nb3Si is suppressed. With an increase in withdrawal rate, the dendrite arm spacing of （Nb, X）ss decreases, and the （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells become finer and distribute homogeneously. Directional solidification can significantly improve the room temperature fracture toughness, especially the alloy with a withdrawal rate of 6 mm.min-1; its average value reaches 14.1 MPa.m^0.5, about 34% higher than that of the alloy without directional solidification. The withdrawal rate has obvious effect on tensile strength, and the tensile strength is improved from 200 MPa to 429 MPa as the withdrawal rate increases from 1.2 mm.min-1 to 1.8 mm-min-1. After heat treatment, the primary （Nb, X）ss branches become coarser; both the room temperature fracture toughness and tensile strength of the alloys solidified at 1.2 and 6 mm.min 1 are somewhat lower than the corresponding values of the alloy without heat treatment, while they are higher than the corresponding values of the alloy without heat treatment when solidified at 18 mm-min4.展开更多
针对医疗数据共享场景下区块链系统跨分片通信复杂度高的问题,设计了一种基于交叉节点的跨分片数据共享架构,采用了将BLS(Boneh-Lynn-Shacham)门限签名嵌入到HotStuff共识算法的跨分片共识方案,降低由信标链或全局共识带来的跨分片通信...针对医疗数据共享场景下区块链系统跨分片通信复杂度高的问题,设计了一种基于交叉节点的跨分片数据共享架构,采用了将BLS(Boneh-Lynn-Shacham)门限签名嵌入到HotStuff共识算法的跨分片共识方案,降低由信标链或全局共识带来的跨分片通信开销,使用审计仲裁机制保证交叉节点在跨分片电子病历(electronic medical record, EMR)数据共享时的安全性。实验结果表明,相比于全局共识的跨分片数据共享方案,所提方案在50个节点的联盟链分片情况下吞吐量提升16.9%,在高负载的交易场景中跨分片交易时延降低35.7%,能够在满足安全性的同时提升跨分片数据共享效率。展开更多
针对现有保序加密(order-preserving encryption,OPE)方案中客户端与服务端多轮交互导致的较大通信开销问题,提出一种基于本地临时缓存表和自平衡二叉搜索树的保序加密方案。在数据插入阶段通过客户端临时缓存表对插入数据预处理确定初...针对现有保序加密(order-preserving encryption,OPE)方案中客户端与服务端多轮交互导致的较大通信开销问题,提出一种基于本地临时缓存表和自平衡二叉搜索树的保序加密方案。在数据插入阶段通过客户端临时缓存表对插入数据预处理确定初始交互节点,避免从根节点开始交互,降低算法的通信开销;并使用平衡因子为k的AVL(Adelson-Velsky and Landis)树作为编码树,避免频繁的编码更新带来的较大计算开销。此外,采用格式保留加密算法FF1-SM4对数据进行加密,不仅能够提高存储效率,而且无需对数据库表结构进行大幅修改,也无需对应用程序进行修改以适应密文的变化。实验结果表明,当插入5000条数据时,该方案相较gmOPE加密效率提升约13.91%,单次插入的平均交互次数下降约69.81%。展开更多
基金financially supported by the National Natural Science Foundation of China(No.51101005)
文摘An Nb-14Si-22Ti-4Cr-2AI-2Hf-0.15Y（at.%） alloy was prepared by directional solidification （DS） with liquid metal cooling, and the withdrawal rates selected were 1.2, 6, and 18 mm-min1, respectively. The Influence of withdrawal rate and heat treatment on the microstructural evolution, fracture toughness and tensile strength at room temperature were investigated. Results show that the directionally solidified microstructure is composed of primary （Nb, X）ss dendrites and （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells aligning with the growth direction. The formation of bulk Nb3Si is suppressed. With an increase in withdrawal rate, the dendrite arm spacing of （Nb, X）ss decreases, and the （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells become finer and distribute homogeneously. Directional solidification can significantly improve the room temperature fracture toughness, especially the alloy with a withdrawal rate of 6 mm.min-1; its average value reaches 14.1 MPa.m^0.5, about 34% higher than that of the alloy without directional solidification. The withdrawal rate has obvious effect on tensile strength, and the tensile strength is improved from 200 MPa to 429 MPa as the withdrawal rate increases from 1.2 mm.min-1 to 1.8 mm-min-1. After heat treatment, the primary （Nb, X）ss branches become coarser; both the room temperature fracture toughness and tensile strength of the alloys solidified at 1.2 and 6 mm.min 1 are somewhat lower than the corresponding values of the alloy without heat treatment, while they are higher than the corresponding values of the alloy without heat treatment when solidified at 18 mm-min4.
文摘针对医疗数据共享场景下区块链系统跨分片通信复杂度高的问题,设计了一种基于交叉节点的跨分片数据共享架构,采用了将BLS(Boneh-Lynn-Shacham)门限签名嵌入到HotStuff共识算法的跨分片共识方案,降低由信标链或全局共识带来的跨分片通信开销,使用审计仲裁机制保证交叉节点在跨分片电子病历(electronic medical record, EMR)数据共享时的安全性。实验结果表明,相比于全局共识的跨分片数据共享方案,所提方案在50个节点的联盟链分片情况下吞吐量提升16.9%,在高负载的交易场景中跨分片交易时延降低35.7%,能够在满足安全性的同时提升跨分片数据共享效率。
文摘针对现有保序加密(order-preserving encryption,OPE)方案中客户端与服务端多轮交互导致的较大通信开销问题,提出一种基于本地临时缓存表和自平衡二叉搜索树的保序加密方案。在数据插入阶段通过客户端临时缓存表对插入数据预处理确定初始交互节点,避免从根节点开始交互,降低算法的通信开销;并使用平衡因子为k的AVL(Adelson-Velsky and Landis)树作为编码树,避免频繁的编码更新带来的较大计算开销。此外,采用格式保留加密算法FF1-SM4对数据进行加密,不仅能够提高存储效率,而且无需对数据库表结构进行大幅修改,也无需对应用程序进行修改以适应密文的变化。实验结果表明,当插入5000条数据时,该方案相较gmOPE加密效率提升约13.91%,单次插入的平均交互次数下降约69.81%。
