基于深度强化学习的近壁圆柱绕流控制

基于深度强化学习方法（deep reinforcement learning,DRL）,采用一对施加在圆柱表面的质量流量为零的射流,对Re=200,400,间隙比G/D=0.5,0.7,1.0,1.5,2.0的近壁圆柱进行主动流动控制研究。通过DRL方法获得不同参数下的射流控制策略与相应控制效果,并讨论了不同射流位置（90°,270°）、（90°,320°）、（90°,360°）对控制效果的影响。研究发现Reynolds数、间隙比和射流位置都对控制效果有重要的影响。射流位置为（90°,270°）时通过DRL控制可以有效降低阻力系数及其波动,控制后的圆柱尾迹被拉长且圆柱前后压差降低。射流位置为（90°,320°）和（90°,360°）的控制效果相似,都能使平均阻力系数有所降低,但控制位置的不对称性导致控制后的阻力系数波动较大。Reynolds数和间隙比的增大会增加控制射流的质量流量水平,在相同条件下,使用（90°,270°）的射流位置可以用相同的质量流量得到更好的控制效果。      

Longitudinal and transverse structure functions in decaying nearly homogeneous and isotropic turbulenceLongitudinal and transverse structure functions in decaying nearly homogeneous and isotropic turbulenceLongitudinal and transverse structure functions in decaying nearly homogeneous and isotropic turbulence

Streamwise evolution of longitudinal and transverse velocity structure functions in a decaying homogeneous and nearly isotropic turbulence is reported for Reynolds numbers Re;t up to 720. First, two theoretical relations between longitudinal and transverse structure functions are examined in the light of recently derived relations and the results show that the low-order transverse structure functions can be well approximated by longitudinal ones within the sub-inertial range. Reconstruction of fourth-order transverse structure functions with a recently proposed relation by Grauer et al. is comparatively less valid than the relation already proposed by Antonia et al. Secondly, extended self-similarity methods are used to measure the scaling exponents up to order eight and the streamwise evolution of scaling exponents is explored. The scaling exponents of longitudinal structure functions are, at first location, close to Zybin＇s model, and at the fourth location, close to She-Leveque model. No obvious wend is found for the streamwise evolution of longitudinal scaling exponents, whereas, on the contrary, transverse scaling exponents become slightly smaller with the development of a steamwise direction. Finally, the stremwise variation of the order-dependent isotropy ratio indicates the turbulence at the last location is closer to isotropic than the other three locations.     

Effects of acetone-soaking treatment on the performance of polymer solar cells based on P3HT/PCBM bulk heterojunction

The improvement of the acetone-soaking treatment to the performance of polymer solar cells based on the P3HT/PCBM bulk heterojunction is reported. Undergoing acetone-soaking, the PCBM does not distribute uniformly in the vertical direction, a PCBM enrichment layer forms on the top of the active layer, which is beneficial to the collec- tion of the carriers and blocking the inverting diffusion carriers. X-ray photoelectron spectroscopy （XPS） analysis reveals that the PCBM weight ratio on the top of the active layer increases by 20% after the acetone-soaking treatment. Due to the nonuniform distribution of PCBM, the short-circuit current density, the open-circuit voltage, and the fill factor are enhanced significantly. Finally, the power conversion efficiency of the acetone-soaking device increases by 31% compared with the control device.     

64Cu放射性药物化学

64Cu半衰期为12.7 h,其衰变过程既发射β+粒子(β+,0.655 MeV,17.8%),又发射β-粒子(β-,0.573 MeV,38.4%)。近20年来,随着铜配位化学的发展,新型配体不断出现(如DOTA、TETA、NOTA、CB-TE2A、C3B-DO2A等)。Cu(Ⅱ)的络合物在生物体内/外的稳定性不断提高,64Cu已经成功标记在氨基酸、多肽、蛋白、核酸等分子以及纳米颗粒上。64Cu可制成正电子显像药物用作诊断,同时也有发展为放射性治疗药物的潜力。新型铜配体和标记方法以及新的药物靶标的研究已经成为64Cu放射性药物研究的热点,至今已研制出了多种64Cu标记的放射性药物,如64Cu-ATSM是有效的肿瘤乏氧显像剂,64Cu-PTSM是优良的血流示踪剂等。本文旨在介绍64Cu(Ⅱ)几种主要类型的含氮配体以及64Cu标记的放射性药物在显像和治疗方面的最新研究进展,并展望其发展趋势。     

基于稀土掺杂光纤的强度调制型弯曲传感器

研究了一种基于稀土掺杂材料的新型周期性微拉锥玻璃光纤及其弯曲传感应用技术. 该光纤的纤芯和包层分别由两种硅酸铅玻璃材料组成,具有可塑性好和易于形成微拉锥的特点. 该传感器的核心敏感体由聚焦的CO₂激光束对稀土掺杂光纤进行周期性和等间距加热方式制备. 论文以该敏感体为核心,结合精密位置移动平台和光学测量平台,构建了基于强度调制的弯曲传感测量系统. 理论研究和实验结果表明,这种弯曲传感测量系统的传输光强灵敏度达到-28.2 μW/m,测量误差低于±1%,具备实际的工程应用价值. 关键词： 稀土掺杂光纤 微拉锥 弯曲传感 强度调制     

Noether symmetry and conserved quantities of the analytical dynamics of a Cosserat thin elastic rod

In this paper, we investigate the Noether symmetry and Noether conservation law of elastic rod dynamics with two independent variables： time t and arc coordinate s. Starting from the Lagrange equations of Cosserat rod dynamics, the criterion of Noether symmetry with Lagrange style for rod dynamics is given and the Noether conserved quantity is obtained. Not only are the conservations of generalized moment and generalized energy obtained, but also some other integrals.     

A comparison of the field emission characteristics of vertically aligned graphene sheets grown on different SiC substrates

The field emission （FE） properties of vertically aligned graphene sheets （VAGSs） grown on different SiC substrates are reported. The VAGSs grown on nonpolar SiC （10-10） substrate show an ordered alignment with the graphene basal plane-parallel to each other, and show better FE features, with a lower turn-on field and a larger field enhancement factor. The VAGSs grown on polar SiC （000-1 ） substrate reveal a random petaloid-shaped arrangement and stable current emission over 8 hours with a maximum emission current fluctuation of only 4%. The reasons behind the differing FE characteristics of the VAGSs on different SiC substrates are analyzed and discussed.     

关于叶果洛夫定理证明的一个注记

给出了一种函数列收敛的等价刻画,并利用此等价刻画来给出实变函数中叶果洛夫定理的另一种证明方法.     

等离子体风洞中释放二氧化碳降低电子密度

航天器从近地空间进入大气层过程中,由于激波加热,会在航天器外表面形成等离子体鞘套,导致航天器与地面之间的无线电通信中断,即“黑障”效应.为了缓解“黑障”效应,国内外学者进行了多方面的技术研究,其中化学物质释放被认为是一种有效的方法.以往,主要针对卤族元素和水开展理论和实飞研究.本文基于二氧化碳不易在高温流场中发生裂解的特性,利用电弧和高频风洞产生等离子体流场,主动释放二氧化碳降低等离子体电子密度.结果表明,在风洞等离子体中,释放不同流量的二氧化碳可使电子密度下降1—2个量级,为解决再入过程中黑障问题提供了一种可行方法.     

基于自适应阈值和动态更新因子的ViBe改进算法

针对传统ViBe算法不能及时反映场景变化,动态场景适应性差等问题,提出一种改进的ViBe算法。改进内容包括:采用随机选取背景样本和24邻域法获取初始背景,可以加速“鬼影”消融;结合大津法（OTSU）和均匀性度量法的平均自适应阈值计算方法,可以提高算法对树叶晃动、水波纹和光照变化等环境的适应性,最大限度保留有效像素;更新阶段引入自适应更新因子,可以有效减少被误判的概率,从而增强算法的鲁棒性;最后通过形态学处理和滤波使目标更加完整。采用标准数据集视频对改进算法进行了测试和对比分析,改进算法相对于KDE算法、GMM算法和传统ViBe算法各项指标均有大幅度提高,精确度分别提高30.44%、40.72%和20.95%,错分比分别降低了43.28%、40.59%和29.43%。