Electromechanical properties of Pb(In(1∕2)Nb(1∕2))O(3)-Pb(Mg(1∕3)Nb(2∕3))O(3)-PbTiO(3) single crystals

The Pb(In(1∕2)Nb(1∕2))O(3)-Pb(Mg(1∕3)Nb(2∕3))O(3)-PbTiO(3) (PIN-PMN-PT) crystals were studied as function of phase and orientation. The properties, including the Curie temperature T(C), ferroelectric-ferroelectric phase transition temperature T(R∕O-T), coercive field, and piezoelectric∕dielectric responses, were systematically investigated with respect to the composition of PIN-PMN-PT crystals. The Curie temperature T(C) was found to increase from 160 to 220 °C with ferroelectric-ferroelectric phase transition temperature T(R-T) and T(O-T) being in the range of 120-105 °C and105-50 °C, respectively. The piezoelectric activity of PIN-PMN-PT crystals was analyzed by Rayleigh approach. The ultrahigh piezoelectric response for domain engineered [001] (1600-2200 pC∕N) and [011] (830-1550 pC∕N) crystals was believed to be mainly from the intrinsic contribution, whereas the enhanced level of piezoelectric and dielectric losses at the compositions around morphotropic phase boundaries (MPBs) was attributed to the phase boundaries motion.     

Sandwich Photothermal Membrane with Confined Hierarchical Carbon Cells Enabling High‐Efficiency Solar Steam Generation

Solar‐driven vaporization is a sustainable solution to water and energy scarcity. However, most of the present evaporators are still suffering from inefficient utilization of converted thermal energy. Herein, a universal sandwich membrane strategy is demonstrated by confining the hierarchical porous carbon cells in two energy barriers to obtain a high‐efficiency evaporator with a rapid water evaporation rate of 1.87 kg m^?2 h^?1 under 1 sun illumination, which is among the highest performance for carbon‐based and wood‐based evaporators. The significantly enhanced evaporation rate is mainly attributed to the inherently optimized porous evaporation mode derived from the hierarchical hollow structures of pollen carbon cells, and the synergistically regulated water transporting and thermal management performance of the sandwich membrane. Moreover, the constructed sandwich membrane also exhibits excellent self‐regenerating performance in simulated seawater and high salinity water. The developed device can maintain an average evaporation rate of 4.3 L m^?2 day^?1 in a 25 day consecutive outdoor test.     

Band Structure Engineering of Interfacial Semiconductors Based on Atomically Thin Lead Iodide Crystals

To explore new constituents in two‐dimensional (2D) materials and to combine their best in van der Waals heterostructures is in great demand as being a unique platform to discover new physical phenomena and to design novel functionalities in interface‐based devices. Herein, PbI₂ crystals as thin as a few layers are synthesized, particularly through a facile low‐temperature solution approach with crystals of large size, regular shape, different thicknesses, and high yields. As a prototypical demonstration of band engineering of PbI₂‐based interfacial semiconductors, PbI₂ crystals are assembled with several transition metal dichalcogenide monolayers. The photoluminescence of MoS₂ is enhanced in MoS₂/PbI₂ stacks, while a dramatic photoluminescence quenching of WS₂ and WSe₂ is revealed in WS₂/PbI₂ and WSe₂/PbI₂ stacks. This is attributed to the effective heterojunction formation between PbI₂ and these monolayers; type I band alignment in MoS₂/PbI₂ stacks, where fast‐transferred charge carriers accumulate in MoS₂ with high emission efficiency, results in photoluminescence enhancement, and type II in WS₂/PbI₂ and WSe₂/PbI₂ stacks, with separated electrons and holes suitable for light harvesting, results in photoluminescence quenching. The results demonstrate that MoS₂, WS₂, and WSe₂ monolayers with similar electronic structures show completely distinct light–matter interactions when interfacing with PbI₂, providing unprecedented capabilities to engineer the device performance of 2D heterostructures.     

带有Levy Flight机制的引力搜索算法

引力搜索算法（gravitational search algorithm,GSA）是模拟万有引力定律进行搜索的一种新颖的优化算法,已有研究表明GSA算法相比一些传统的优化算法拥有较好的收敛性能,但其缺乏有效的全局寻优机制,易于被局部极值吸引,从而陷入早熟收敛。因此提出了一种基于Levy Flight和权值惯性递减的引力搜索算法QmuGSA,以加强算法的全局寻优能力。该算法通过Levy Flight独特的不均匀随机游走的机制扩大粒子的搜索范围,增加种群多样性,从而更容易跳出局部最优点。通过4个标准测试函数对所提算法进行了仿真测试,结果表明所提算法能够有效克服基本引力搜索算法易早熟、收敛精度低等缺陷,具有较好的寻优精度和全局收敛性能,能够解决一些复杂函数的优化问题。     

基于工业以太网的动态通信平滑过滤器研究

针对工业控制系统的特点,在不改变以太网协议的条件下,采用一种新的动态通信平滑过滤器来控制网络负荷以满足控制系统的实时通信要求.研究表明该动态通信平滑过滤器不仅可以为非实时数据提供合理的网络吞吐率,并且可以显著地控制实时数据传输的超时比率,其性能明显优于静态通信平滑过滤器.     

海量存储系统的发展与展望

从存储网络技术、系统架构、数据保护、绿色存储等方面综合分析了海量存储系统的发展趋势,并对新一代海量存储-并行海量存储系统的相关理论和关键技术做了分析。并行海量存储系统应具有自动负载均衡、高可用、支持重复数据删除、自动分层存储、绿色节能等先进特性。     

基于MPLS的IP组播在Linux环境下的设计与实现

基于MPLS的IP组播是目前网络研究的热点问题之一,MPLS和IP组播技术的结合可以获得MPLS的高速率、QoS、流量工程、VPN和IP组播的带宽节省两方面的益处,MPLS和组播是两种互补的技术.在Linux环境下已经可以支持MPLS的单播技术,本文研究了在Linux单播环境下MPLS组播的一种扩展技术,介绍了其实现原理,关键技术,并给出了C语言的API.     

基于超节点网络的多源并行数据分发研究

在P2P系统中,同一个数据往往拥有多个副本,这些副本分布在网络的不同节点上,为并行分发提供了可能.然而在传统的数据分发中,只有单一的源节点参与分发,这种模式不但浪费了系统中存在的多个副本资源,而且容易使单一的源节点成为系统的瓶颈.为了更有效地利用系统中存在的多个副本资源,提高分发的效率和系统的性能,提出了一个基于超节点网络的多源并行数据分发算法PPMSD,通过一个基于超节点网络的结构化拓扑来组织系统中的数据和索引,使得数据的查询和定位效率控制在O(log N)以内;根据分发速率动态地为每个数据源分配相应比例的分发数据量,并行地向目标节点传输数据以最小化分发时间;最后,实现了原型系统PPThor以验证算法的有效性.测试结果表明分发的效率得到了极大的提高.     

DAS模式下基于密文分组索引的完整性验证

目前关于DAS模式下的全概率完整性验证方法主要是建立在明文数据上,并没有建立在密文数据上的完整性验证方法。提出一种建立在密文数据上的适用于动态数据库的完整性验证方法。分组索引是在DAS模式下的一种高效的密文索引,在密文数据分组索引的基础上,提出利用无碰撞增量式哈希生成完整性验证信息的方法。这是一种验证速度快(可并行计算)、维护代价小(对于增删改操作可增量式维护)的全概率验证方法,适用于动态数据库中完整性的验证。