Growth and properties of Li,Ta modified (K,Na)NbO3 lead‐free piezoelectric single crystals

Li, Ta modified (K,Na)NbO₃ single crystals with the size of 18 mm × 18 mm × 10 mm were successfully grown by top‐seeded solution growth method, with orthorhombic–tetra‐gonal phase transition temperature ～79 °C and Curie temperature ～276 °C. The electromechanical coupling factors k₃₃ and k_t were found to be ～88% and ～65%, respectively. The piezoelectric coefficient d₃₃ for the [001]_c poled crystals reached 255 pC/N. In addition, the electromechanical coupling factor exhibited high stability over the temperature range of –50 °C to 70 °C, making these lead free crystals good candidates for electromechanical applications. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhanced Compression of Fundamental Solitons in Dispersion Decreasing Fibers with Negative Third-order Dispersion Ⅱ. Effects of Fiber Characteristics and Initial Soliton Width

Previous work have shown that the combined effects of negative third-order dispersion (TOD) and Raman self-scattering (RSS) can significantly enhance soliton compression in dispersion decreasing fibers (DDFs). In this paper, the effects of the negative TOD coefficient and the effective amplification of DDF′s on the performance of soliton compression are investigated. It is shown that for a given initial soliton width and a given effective amplification, there exists an optimum value of the negative TOD coefficient of the DDF at which the enhancement in soliton compression is maximum. It is also shown that the compression enhancement saturates when the effective amplification exceeds a certain value, which has been explained as a compromise between the higher-order effects induced increase of the ratio of input to output group-velocity dispersion coefficients of the DDF and the TOD induced non-adiabatic compression characteristics. The dependence of the compression enhancement on the initial soliton width have also be studied and the scheme is found works well for solitons with initial widths less than 3 ps.     

A second-order dynamic subgrid-scale stress model

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎＬＥＳ,ｔｈｅｌａｒｇｅｓｃａｌｅｓｉｎｔｈｅｆｌｏｗａｒｅｃｏｍｐｕｔｅｄｅｘｐｌｉｃｉｔｌｙａｎｄｔｈｅｓｕｂｇｒｉｄ＿ｓｃａｌｅｓ(ＳＧＳ),ｗｈｉｃｈａｒｅｆｉｌｔｅｒｅｄｏｕｔｂｙａｎａｖｅｒａｇｅｐｒｏｃｅｓｓｏｐｅｒａｔｉｏｎｏｎｔｈｅＮａｖｉｅｒ＿Ｓｔｏｋｅｓｅｑｕａｔｉｏｎｓ,ａｒｅｍｏｄｅｌｅｄ.ＳｉｎｃｅＬＥＳｒｅｑｕｉｒｅｓｌｅｓｓｃｏｍｐｕｔｅｒｔｉｍｅｔｈａｎｔｈｅｄｉｒｅｃｔｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎｓａｎｄｕｓｅｓｓｉｍｐｌｅｒａ…     

Experimental investigation of light storage of diffraction-free and quasi-diffraction-free beams in hot atomic gas cell

In this article we report on the experimental investigation of light storage for several types of diffractionfree beams (Bessel and Airy beams) and quasi-diffraction-free beams by utilizing electromagnetically induced transparency (EIT) technique in a hot atomic gas cell. The experimental results show that the diffraction-free and quasi-diffraction-free beams have better storage performances when compared with ordinary images possessing similar spatial profiles. Meanwhile, the Bessel beams and the quasidiffraction-free images are able to maintain their spatial profiles with a long storage time while the sidelobes of the Airy beam are gradually depleted with the increment of the storage time. We quantitatively analyze the storage results and give physical explanations behind these phenomena. Furthermore, the self-healing of the retrieved diffraction-free beams is verified, signifying that their characteristics preserve well after storage.     

Brain-like synaptic memristor based on lithium-doped silicate for neuromorphic computing

Artificial synapse is one of the potential electronics for constructing neural network hardware. In this work, Pt/LiSiO_x/TiN analog artificial synapse memristor is designed and investigated. With the increase of compliance current (C. C.) under 0.6 mA, 1 mA, and 3 mA, the current in the high resistance state (HRS) presents an increasing variation, which indicates lithium ions participates in the operation process for Pt/LiSiO_x/TiN memristor. Moreover, depending on the movement of lithium ions in the functional layer, the memristor illustrates excellent conduction modulation property, so the long-term potentiation (LTP) or depression (LTD) and paired-pulse facilitation (PPF) synaptic functions are successfully achieved. The neural network simulation for pattern recognition is proposed with the recognition accuracy of 91.4%. These findings suggest the potential application of the LiSiO_x memristor in the neuromorphic computing.     

面向空间平台的小型化量子纠缠源

随着量子信息科学的迅速发展,以光子为物理载体的量子纠缠源已成为量子非定域性检验、量子通信、量子计算以及量子精密测量等领域必不可少的资源和重要技术手段。利用非线性介质中的自发参量下转换过程,从早期的β相偏硼酸钡晶体到后来的基于准相位匹配的周期性极化晶体等,双光子极化纠缠源凭借其在亮度和品质方面的优势得到了快速发展,这为基于卫星平台的广域量子通信和量子物理的基础检验提供了可能。从基本原理出发,系统介绍了近年来面向空间平台应用的量子纠缠源的发展和最新成果,特别是以“墨子号”量子科学实验卫星为代表的星载量子纠缠源载荷;此外,对国际上近几年关于星载量子纠缠源的进展以及未来发展趋势也进行了较为全面的介绍和分析。     

热电型太赫兹探测器响应度校准技术

为保证太赫兹辐射强度测量的准确可靠,对热电型太赫兹探测器的响应度进行了校准。首先,基于替代法构建了太赫兹探测器响应度校准装置,该装置的合成标准不确定度为2.4%。然后,在1.63 THz频率点处,利用校准装置对12D-3S-VP型太赫兹探测器进行了校准,得到的响应度校准结果为197.6 mV/W,与厂家标称值一致。对自主研制的热电型太赫兹探测器进行了校准,得到的响应度和合成标准测量不确定度分别为362.2 mV/W和2.7%。最后,将校准结果的标准偏差值与合成标准不确定度进行了比较,发现标准偏差值在合理范围内,这进一步证明了校准方法、校准结果以及不确定度分析的合理性。     

基于压缩感知理论的大规模MIMO系统下行信道估计中的导频优化理论分析与算法设计

针对大规模多输入多输出(multiple input multiple output, MIMO)系统信道估计中的导频设计问题,在压缩感知理论框架下,提出了一种基于信道重构错误率最小化的自适应自相关矩阵缩减参数导频优化算法.首先以信道重构错误率最小化为目标,推导了正交匹配追踪(orthogonal matching pursuit, OMP)算法下信道重构错误率与导频矩阵列相关性之间的关系,并得出优化导频矩阵的两点准则,即导频矩阵列相关性期望和方差最小化;然后研究了优化导频矩阵的方法,并提出相应的自适应自相关矩阵缩减参数导频矩阵优化算法,即在每次迭代过程中,以待优化矩阵平均列相关程度是否减小作为判断条件,调整自相关矩阵缩减参数值,使参数不断趋近于理论最优.仿真结果表明,与采用Gaussian矩阵、Elad方法、低幂平均列相关方法得到的导频矩阵相比,本文所提方法具有更好的列相关性,且具有更低的信道重构错误率.     

Prediction model of K2CsSb photocathode reflectivity based on LSTM北大核心CSCD

针对目前K₂CsSb光阴极制备过程中无法预判光阴极生长状态的问题,提出一种基于长短期记忆（LSTM）循环神经网络的K₂CsSb光阴极反射率预测模型。一维原始反射率数据集经过清洗、筛选、序列化等预处理手段后重构为二维数据输入模型。为充分利用反射率数据在时序上高度相关的特性,采用双层LSTM网络提取特征,预测结果通过全连接层输出,以均方误差（MSE）作为模型预测效果的评判标准。实验结果表明,该模型的网络结构合理且在不同数据集下的表现良好,预测准确率可达99.21%。该模型可运用在K₂CsSb光阴极的制作过程中,通过反射率预测值反馈调节工艺参数以趋近目标走势,对提高光阴极性能具有促进作用。     

Synthesis and Investigation of Derivatives of 1,8-Naphthalimide with a Red Emission via an Aromatic Nucleophilic Substitution Reaction

1,8-Napthalimides (NIs) have been widely used as fluorescent molecules in biological, chemical, and medical fields because NIs shows high stability and various fluorescence properties under different conditions. However, NIs typically display a fluorescence emission wavelength in the range of 350 – 550 nm which can be notably interfered with by autofluorescence in living cells, significantly limiting their bio-applications. Moreover, low solubility in aqueous media is another major limitation for NIs. In this project, four derivatives of NIs (1–4) have been synthesized via an aromatic nucleophilic substitution reaction and their photophysical properties have been investigated in various media (water, MeOH, MeCN, DMSO, EtOAc, and THF). All of these derivatives (1–4) show a long emission wavelength around 600 nm and high solubility in polar solvents. Particularly molecules (1–4) show the longest emission (624–629 nm) in water and the fluorescence intensity is not significantly varied in the range of pH 4–11. These unique features, long emission wavelength, high solubility, and high stability in difference pH media, will allow these derivative (1–4) to be used as excellent labeling reagents in the biological system.