Fabrication and investigation of ferroelectric memristors with various synaptic plasticities

In the post-Moore era, neuromorphic computing has been mainly focused on breaking the von Neumann bottlenecks. Memristors have been proposed as a key part of neuromorphic computing architectures, and can be used to emulate the synaptic plasticities of the human brain. Ferroelectric memristors represent a breakthrough for memristive devices on account of their reliable nonvolatile storage, low write/read latency and tunable conductive states. However, among the reported ferroelectric memristors, the mechanisms of resistive switching are still under debate. In addition, there needs to be more research on emulation of the brain synapses using ferroelectric memristors. Herein, Cu/PbZr_0.52Ti_0.48O₃ (PZT)/Pt ferroelectric memristors have been fabricated. The devices are able to realize the transformation from threshold switching behavior to resistive switching behavior. The synaptic plasticities, including excitatory post-synaptic current, paired-pulse facilitation, paired-pulse depression and spike time-dependent plasticity, have been mimicked by the PZT devices. Furthermore, the mechanisms of PZT devices have been investigated by first-principles calculations based on the interface barrier and conductive filament models. This work may contribute to the application of ferroelectric memristors in neuromorphic computing systems.     

散射效应强化纳米颗粒悬浮液太阳能吸收性能

本文基于有限元法-蒙特卡洛法研究了散射效应对纳米流体太阳能吸收性能的影响。结果表明,在一定范围内增强纳米流体的散射能力可以提高纳米流体的太阳吸收效率。此外,将具有强散射能力的TiO₂纳米颗粒分散到Au纳米流体中,通过调控TiO₂纳米颗粒的体积分数(f_v-TiO₂),在考虑纳米流体稳定性的同时,可以提高混合纳米流体的太阳能吸收效率。当f_v-TiO₂=0.05%时,混合纳米流体的太阳吸收效率提高了16.6%(f_v-Au=0.0005%,厚度d=5.0 cm)。对于强散射的纳米流体,增大d,可以进一步提高混合纳米流体的太阳能吸收效率。当d=5.0 cm时,混合纳米流体的太阳吸收效率为78.7%,比d=1.0 cm时高35.7%(f_v-Au=0.0005%,f_v-TiO₂=0.05%)。     

融合欧拉弹性能及边缘检测项的图像分割模型

欧拉弹性能量作为正则项已经被成功应用于图像处理模型中.Egil Bae等人在L²欧拉弹性模型的基础上提出的ECV-L1模型具有偏向于分割凸轮廓的性质,但分割结果易受参数及弹性项的影响,使得分割结果不易紧贴目标物体边缘.在ECV-L1模型基础上引入边缘检测项提出新模型,并应用增广拉格朗日算法和交替方向乘子法对新模型进行数值求解.数值实验表明,新模型具有使分割结果保持为凸的性质,同时新模型的分割结果更易靠近目标物体边缘.     

Gate tunable Rashba spin-orbit coupling at CaZrO3/SrTiO3 heterointerface

High mobility quasi two-dimensional electron gas (2DEG) found at the CaZrO₃/SrTiO₃ nonpolar heterointerface is attractive and provides a platform for the development of functional devices and nanoelectronics. Here we report that the carrier density and mobility at low temperature can be tuned by gate voltage at the CaZrO₃/SrTiO₃ interface. Furthermore, the magnitude of Rashba spin-orbit interaction can be modulated and increases with the gate voltage. Remarkably, the diffusion constant and the spin-orbit relaxation time can be strongly tuned by gate voltage. The diffusion constant increases by a factor of ～ 19.98 and the relaxation time is reduced by a factor of over three orders of magnitude while the gate voltage is swept from -50 V to 100 V. These findings not only lay a foundation for further understanding the underlying mechanism of Rashba spin-orbit coupling, but also have great significance in developing various oxide functional devices.     

基于二值化计算鬼成像的图像隐藏方法

图像隐藏技术在当今大数据时代扮演着重要角色,尤其在版权保护和保密通信等领域中有着巨大的应用价值.提出了一种基于计算鬼成像的图像隐藏方法,目标图像经过计算鬼成像系统加密,随机散斑作为系统密钥,将密文进行二值化后的结果采用最低有效位算法嵌入到宿主图像中,利用相应的水印提取规则和二阶相关算法恢复目标图像.仿真结果表明,该方法...     

(3+1)-dimensional localized self-accelerating Airy elegant Ince-Gaussian wave packets and their radiation forces in free space

We construct analytically linear self-accelerating Airy elegant Ince–Gaussian wave packet solutions from(3+1)-dimensional potential-free Schr odinger equation. These wave packets have elliptical geometry and show different characteristics when the parameters(p, m) and ellipticity ε are adjusted. We investigate these characteristics both analytically and numerically and give the 3-dimensional intensity and phase distribution of these wave packets. Lastly, we analyze the radiation forces on a Rayleigh dielectric particle. In addition, we also find an interesting phenomenon that if the energy distribution between every part of wave packets is uneven at the input plane, the energy will be transferred between every part in the process of transmission.     

LaAlO3/SrTiO3异质界面磁场调控的反常金属态

自LaAlO₃/SrTiO₃异质界面发现高迁移率的二维电子气以来,其二维超导电性、界面磁性和自旋轨道耦合等诸多物理性质已经被广泛研究.对于二维超导体,零温下超导-反常金属相变的起源仍然是一个悬而未决的问题.传统理论认为在超导-绝缘量子相变中只存在2种基态,即库珀对的超导基态和绝缘基态.然而在研究超导颗粒膜中超导电性的演化与厚度和温度的关系时发现,存在一个中间金属态破坏了超导体和绝缘体之间的直接过渡.这种中间金属态的标志性特征是,在超导转变温度之下存在饱和的剩余电阻,与之对应的基态称作反常金属态.本文主要对在LaAlO₃/SrTiO₃(001)异质界面磁场诱导的超导-反常金属量子相变进行了系统的研究.在没有外加磁场的情况下,电阻-温度(R-T)曲线和电流-电压(I-V)特性曲线表明样品在超导转变温度之下处于超导态.外加磁场会导致样品在低温下出现饱和电阻、正的巨磁阻和低电流范围内的线性I-V曲线.另外,霍尔电阻在一定的磁场之下会出现零电阻平台,而此时纵向电阻不为零,表现出明显的玻色金属态的特征.研究结果...     

蒲公英黄酮抗氧化活性的构效关系分析

蒲公英作为传统的中药材,具有抗氧化、抗肿瘤、抗菌、抗炎等多种药用价值。黄酮是蒲公英发挥抗氧化作用的重要活性成分。蒲公英黄酮抗氧化性能的实验研究备受关注,然而从分子水平对蒲公英黄酮结构与抗氧化活性之间的内在关系缺乏系统的研究。本文借助于密度泛函理论,针对蒲公英中5种重要的黄酮化合物(槲皮素、芦丁、木犀草素、芹菜素、香叶木素),通过优化结构参数、捕获DPPH自由基的热力学能量分析,NBO电荷分布、半醌自由基的自旋密度分析等方面深入探讨了蒲公英黄酮化合物抗氧化活性的构效关系及内在规律。结果表明：5种蒲公英黄酮化合物抗氧化活性为芦丁>槲皮素>木犀草素>>香叶木素>芹菜素,酚羟基的位置是影响蒲公英黄酮抗氧化活性差异的主要因素。蒲公英黄酮不同位点抗氧化活性的高低与其酚羟基上H原子的电荷分布、黄酮自由基的稳定性成正比关系,自由基单电子的离域程度和分子内氢键的稳定化作用共同决定了B环4’-OH是蒲公英黄酮的关键活性位点。     

光子晶格中新颖的空间带隙孤子——饶毓泰基础光学二等奖介绍

光子晶格作为一种光学周期性离散体系,具有通常均匀介质所无法比拟的独特性质,它为空间离散孤子、表面波以及衍射操控等一系列线性和非线性离散动力学行为的实验观测提供了便利条件,同时在全光路由、全光开关和光子计算机等方面具有重要的应用前景.文章简要回顾了南开大学的研究小组近期在二维光子晶格中有关空间带隙孤子的一系列研究工作,包括二维基本带隙孤子、类偶极带隙孤子、带隙孤子串以及涡旋带隙孤子等.在有的实验过程中,文章作者清晰地观测到探测光束的频谱整形,波常数从具有反常衍射的导带底部演化到光子禁带中,并且通过干涉图反映的相位关系验证了带隙孤子形成.实验的结果可以为其他离散系统中带隙孤子态的观测提供有益参考和启示.     

Sign reversal of anisotropic magnetoresistance and anomalous thickness-dependent resistivity in Sr2CrWO6/SrTiO3 films

High-quality Sr₂CrWO₆ (SCWO) films have been grown on SrTiO₃ (STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observed. The Hall measurements show that the thicker the film, the lower the carrier density. An extrinsic mechanism of charge doping due to the dominance of oxygen vacancies at SCWO/STO interfaces is proposed. The distribution and gradient of carrier concentration in SCWO films are considered to be related to this phenomenon. Resistivity behavior observed in these films is found to follow the variable range hopping model. It is revealed that with increase of the film thickness, the extent of disorder in the lattice increases, which gives a clear evidence of disorder-induced localization charge carriers in these films. Magnetoresistance measurements show that there is a negative magnetoresistance in SCWO films, which is considered to be caused by the magnetic scattering of magnetic elements Cr³⁺ and W⁵⁺. In addition, a sign reversal of anisotropic magnetoresistance (AMR) in SCWO film is observed for the first time, when the temperature varies across a characteristic value, T_M. Magnetization—temperature measurements demonstrate that this AMR sign reversal is caused by the direction transition of easy axis of magnetization from the in-plane ferromagnetic order at T > T_M to the out-of-plane at T < T_M.