三项记忆梯度法及其投影算法的收敛性分析

对于无约束优化问题,提出了一类新的三项记忆梯度算法．这类算法是在参数满足某些假设的条件下,确定它的取值范围,从而保证三项记忆梯度方向是使目标函数充分下降的方向．在非单调步长搜索下讨论了算法的全局收敛性．为了得到具有更好收敛性质的算法,结合Solodov and Svaiter(2000)中的部分技巧,提出了一种新的记忆梯度投影算法,并证明了该算法在函数伪凸的情况下具有整体收敛性．     

静态随机访问存储器型现场可编程门阵列辐照效应测试系统研制

在调研静态随机访问存储器型现场可编程门阵列(FPGA)器件空间辐照效应失效机理的基础上,详细论述FPGA辐照效应测试系统内部存储器测试、功能测试及功耗测试的实现原理,给出了系统的软硬件实现方法。所建立的系统可以测试FPGA器件的配置存储器翻转截面、块存储器翻转截面、功能失效截面、闭锁截面等多个参数,其长线传输距离达到50 m以上,最大可测门数达到了100万门,为FPGA辐照效应研究提供了测试平台。     

Composition, structure and magnetic properties of sputter deposited Ni-Mn-Ga ferromagnetic shape memory thin films

Polycrystalline Ni-Mn-Ga thin films were deposited by the d.c. magnetron sputtering on well-cleaned substrates of Si(1 0 0) and glass at a constant sputtering power of 36 W. We report the influence of sputtering pressure on the composition, structure and magnetic properties of the sputtered thin films. These films display ferromagnetic behaviour only after annealing at an elevated temperature and a maximum saturation magnetization of 335 emu/cc was obtained for the films investigated. Evolution of martensitic microstructure was observed in the annealed thin films with the increase of sputtering pressure. The thermo-magnetic curves exhibited only magnetic transition in the temperature range of 339-374 K. The thin film deposited at high sputtering pressure of 0.025 mbar was found to be ordered L2₁ austenitic phase.     

基于免疫记忆克隆算法的指数化投资组合优化构建策略

本文基于克隆选择学说及基于克隆选择学说及生物免疫响应过程的相关机理,提出用于指数化投资的免疫记忆克隆算法,并将其应用于指数化投资组合优化构建模型的求解,旨在探索指数化投资的优化构建策略。文章首先提出多目标的指数化投资组合构建模型。其次,分别设计了适用于指数化投资组合构建策略的抗原、抗体、亲和度函数、克隆选择算子、免疫记忆算子和相应的进化算法。该算法有效避免了传统遗传算法所存在的计算后期解的多样性差、易早熟以及收敛速度慢等缺点。同时,提出了限制投资组合中股票数量的启发式算法。最后,使用包括上证180指数在内的6组世界主要股票市场指数及其成份股的历史数据对模型及算法进行测算,结果表明算法具有良好的求解能力和收敛速度,所建模型的合理性和有效性亦被论证,模型和算法均具有很强的实践价值;     

Ni54Fe19Ga27单晶的形状记忆和超弹性

本文研究了单晶Ni₅₄Fe₁₉Ga₂₇不同方向的形状记忆效应、超弹性和磁性. 研究发现,单晶样品具有良好的双向形状记忆效应.不同晶体学方向的相变应变随着热循环次数的变化而改变. 在外应力作用下,通过应力诱发马氏体相变,样品在[001],[110],[111]方向分别产生了3.3%, 2% 和3%的可回复应变平台.磁性测量结果表明马氏体的磁晶各向异性能约为4.8× 10⁵ erg/cm³,远远小于变体孪生所需机械应力能,因此磁场的作用是使磁矩发生转动而不是使孪晶界移动, 成功揭示了不能在NiFeGa中获得大磁感生应变的物理根源.     

Dynamic control of retrieval contrast in a Λ-type atomic system

We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in Λ configuration. The memory procedure consists of write-in, storage, and retrieval phases. By applying a weak microwave field in the storage stage, additional phase-dependent terms are included, and the contrast of the output signal pulses can be dynamically controlled (enhanced or suppressed) through manipulating the relative phase φ between optical and microwave fields. Our numerical analysis shows that the contrast is enhanced to the most extent when φ=1.5π. In addition, the contrast is in proportion to the Rabi frequency of the microwave field with a certain relative phase.     

工作记忆、中央执行功能与流体智力的关系分析

探讨工作记忆、中央执行功能子成分与流体智力的关系.以秦巴山区18～40岁健康成人为研究对象,通过对中央执行功能子成分、工作记忆广度以及流体智力的测量,分析了各变量之间的关系,并进一步探讨了中央执行功能各子成分的可分离性.得到 （1）工作记忆中的中央执行功能具有可分离性;（2）工作记忆广度与瑞文测验成绩之间的显著相关是刷新功能的作用;（3）相对于抑制功能和转换功能,刷新功能对流体智力具有更强的预测效应和解释力.     

Thermodynamic and shape memory properties of TPI/HDPE hybrid shape memory polymer

The traditional processing technology of shape memory polymer composites is complex and the cost of high performance filler is high. Therefore, low-cost high density polyethylene (HDPE) was introduced into trans-1,4-polyisoprene (TPI) matrix as reinforcing phase, and a novel shape memory polymer was prepared by mechanical melt blending, which fully exerted the excellent properties of plastic and rubber. Because of the difference in molecular chain distribution between different blend ratios of TPI/HDPE hybrid SMPCs specimens, the change of the blend ratio of the two components affects the thermodynamic and shape memory properties of the SMPCs. A series experimental results show that the TPI/HDPE hybrid SMPCs with the blend ratio of 80/20 has excellent thermodynamic and shape memory properties. And we believe that the relevant conclusions of this study can provide valuable design reference for the development of high-performance TPI SMPCs.     

Flash memory effects based on styrene/maleimiade copolymers with pendant azobenzene chromophores

Two styrene/maleimiade copolymers with pendant azobenzene chromophores, poly(styrene-1-(4-phenylazo-phenyl)-pyrrole-2,5-dione) (PS-DP) and poly((4-vinyl-benzyl)-9H-carbazole-1-(4-phenylazo-phenyl)-pyrrole-2,5-dione) (PVCz-DP), were synthesized. The polymeric memory devices based on each of the two polymer films (ITO/Polymer/Al) show similar rewritable flash memory behaviors but different transition voltages. By introduction of carbazole groups in the polymer side chains, the voltage difference from OFF to ON state of ITO/PVCz-DP/Al is reduced obviously in comparison with that of ITO/PS-DP/Al, which is beneficial to the protection of devices. Both ITO/PS-DP/Al and ITO/PVCz-DP/Al show high stability under a constant stress or continuous read pulses voltage of 1.0 V. The memory mechanism is governed by space-charge limited conduction (SCLC) on the basis of the I–V curves of these fabricated memory devices. With excellent flash memory characteristics and simple processability, the memory devices fabricated with these two styrene/maleimiade copolymers have potential applications for the future electronic memory devices.