考虑土-结构相互作用的核电站动力分析方法

考虑不同土．结构相互作用(SSI)，对核电站安全壳结构进行动力响应分析的程序很多，它们采用的分析方法各不相同，如地下结构基础分析法程序CLASSI、等效线性有限元程序FLUSH、非线性有限元分析程序DYNA3D。使用这3种程序简单分析了安全壳结构的动力响应，给出了动力响应分析结果。讨论了以上3种程序在进行SS1分析时的可靠性，比较了它们在峰值加速度和响应谱作用下的响应。     

全级配混凝土冻融循环后单轴动态抗压性能试验研究

为研究冻融及动力作用对全级配混凝土单轴抗压性能的影响,对全级配混凝土进行不同冻融循环次数(0、25、50、75、100次)的冻融循环试验及不同应变速率(10-5/s、10-4/s、10-3/s、10-2/s)的单轴动态抗压试验。实测了全级配混凝土经历不同冻融循环次数后的质量损失、损伤形态,以及不同应变速率下全级配混凝土的单轴动态极限抗压强度、应力-应变关系曲线。研究结果表明:全级配混凝土质量损失率与冻融循环次数呈二次曲线关系;在相同应变速率下,全级配混凝土单轴动态极限抗压强度随冻融循环次数的增加而降低;在相同冻融循环次数下,全级配混凝土单轴动态极限抗压强度随应变速率的增大而提高。对试验结果分析的基础上,建立了综合考虑冻融循环次数与应变速率影响的全级配混凝土的统一破坏准则,可为水工建筑物的设计、维修等提供试验及理论依据。     

融合混合注意力和改进YoloX的铁路落石检测方法

铁路周边危岩落石侵入铁路限界内会严重危害旅客生命财产与铁路行车安全。针对传统检测方法对复杂动态环境识别误检高、小目标识别准确率较低等问题,提出一种基于视频的铁路落石侵限检测深度学习方法。首先,融合混合注意力模块,增强网络对与背景相似落石检测能力。其次,改进YoloX部分网络结构为双向特征金字塔网络,加强了不同层级特征的相互交流,提升小目标识别能力。同时采集大量不同场景模拟落石数据,构建模拟落石数据集,并在训练中使用Mosaic数据增强方法,增强方法的泛化能力。实验结果表明,本文方法随着改进模块的添加,识别精度不断提高。对比多种主流目标检测方法,取得了最高识别准确度,不同大小目标识别稳定,证明了本文算法在实际铁路场景的应用价值。     

非周期长码直扩信号同步及伪码序列盲估计

非合作直接序列扩频系统中伪随机码的估计与同步是正确获取信息的关键。现有的研究成果多集中在短码或周期长码直扩信号的解扩,该文针对无伪码先验知识条件下NPLC-DSSS信号的失步时间估计问题,提出一种基于相关矩阵元素分布建模的方法,该方法以信息码宽分段的信号构建自相关矩阵,并以该矩阵的Frobenius 范数与失步时间之间的对应关系,实现NPLC-DSSS信号失步时间的精确估计。在此基础上,通过引入判决辅助思想构建了循环迭代结构实现了NPLC-DSSS信号伪码序列的盲估计。最后,推导了该伪码序列盲估计问题的Cramer-Rao理论界。数值分析结果表明,文中所述算法在相同的信噪比和数据量条件下具有更好的估计精度,且对伪码的估计性能接近理论界。     

Design Strategies of 3D Carbon-Based Electrodes for Charge/Ion Transport in Lithium Ion Battery and Sodium Ion Battery

Advanced 3D carbon-based electrodes have the potential to significantly enhance the energy-power density of lithium ion batteries and sodium ion batteries, due to their continuous conductive networks, proper porosity distribution, and integrated stable structure. However, it still remains a fundamental scientific challenge to accurately understand the charge/ion transport in 3D carbon-based electrodes. In this review, the operating mechanism of charge/ion transport in 3D carbon-based electrodes are comprehended by introducing a useful architectural analogy to provide a physical insight. In order to better understand the relationship between 3D carbon-based electrode structure and electrode process characteristics, the main design strategies of 3D carbonbased electrodes according to the specific characteristic of pore tortuosity is proposed. Through analysis of 3D carbon electrode architectural models, several key scientific issues and related characterization technologies that are beneficial to improving the charge/ion transport efficiency are also raised. The kinetics difference of ionic transport between Li⁺ and Na⁺ ions is also taken into account. Furthermore, the critical parameters of porous structure including porosity and tortuosity to investigate the parameter-structure-performance relationships of 3D carbon-based architecture electrodes are highlighted, which in turn would guide more rational battery design in tradeoff between the high capacity and fast transport.     

弹性介质中充液圆柱壳的轴对称振动分析

从理论上分析了各向同性弹性介质中有限长充液圆柱壳的自由振动特性。利用经典FLUGGE壳体运动方程,结合弹性动力学方程,得到了弹性介质中充液圆柱壳耦合系统的特征方程。利用数值方法得到了弹性介质中圆柱壳中空和充液时的实固有频率。计算结果表明弹性介质中圆柱壳的实固有频率比真空中圆柱壳的实固有频率高,而且存在截止轴向模态。弹性介质刚度不仅对充液圆柱壳的实固有频率影响显著,而且影响其截止轴向模态。     

High-precision symbol timing algorithm for specific emitter identification

The existing symbol timing algorithms have the problems that the method of delay estimation is improper and the calculation precision of the interpolation is insufficient for the pretreatment of specific emitter identification.A high-precision symbol timing algorithm was proposed to solve these problems.Aiming at the former problem,a two-step estimation method was adopted,rough estimation of delay was firstly obtained by the forward algorithm,and then the accurate value was acquired through local search with the demodulated symbols.For the latter problem,a window-based approach was used to design an interpolating filter which could optimize the anti-aliasing characteristics and improve the calculation accuracy.Simulation results show that the proposed algorithm can effectively solve the above problems and achieve better recognition results in the radiation source recognition compared with the conventional symbol timing algorithm.     

A High‐Performance Sodium‐Ion Hybrid Capacitor Constructed by Metal–Organic Framework–Derived Anode and Cathode Materials

Sodium‐ion hybrid capacitors (SIHCs) can potentially combine the virtues of high‐energy density of batteries and high‐power output as well as long cycle life of capacitors in one device. The key point of constructing a high‐performance SIHC is to couple appropriate anode and cathode materials, which can well match in capacity and kinetics behavior simultaneously. In this work, a novel SIHC, coupling a titanium dioxide/carbon nanocomposite (TiO₂/C) anode with a 3D nanoporous carbon cathode, which are both prepared from metal–organic frameworks (MOFs, MIL‐125 (Ti) and ZIF‐8, respectively), is designed and fabricated. The robust architecture and extrinsic pseudocapacitance of TiO₂/C nanocomposite contribute to the excellent cyclic stability and rate capability in half‐cell. Hierarchical 3D nanoporous carbon displays superior capacity and rate performance. Benefiting from the merits of structures and performances of anode and cathode materials, the as‐built SIHC achieves a high energy density of 142.7 W h kg^?1 and a high power output of 25 kW kg^?1 within 1–4 V, as well as an outstanding life span of 10 000 cycles with over 90% of the capacity retention. The results make it competitive in high energy and power–required electricity storage applications.     

基于小波变换和邻域特征的多聚焦图像融合算法

提出了一种基于小波变换和邻域特征的多聚焦图像融合算法。该算法首先采用小波变换对源图像进行多尺度分解,得到低频和高频子图像;然后对低频子图像采用基于邻域归一化梯度的方法得到低频融合系数,对高频子图像采用基于邻域方差的方法得到高频融合系数;最后进行小波重构得到融合图像。采用均方根误差、信息熵以及峰值信噪比等评价标准,将该算法与传统融合方法的融合效果进行了比较。实验结果表明,该算法所得融合图像的效果和质量均有明显提高。