Missing Link between Helical Nano‐ and Microfilaments in B4 Phase Bent‐Core Liquid Crystals,and Deciphering which Chiral Center Controls the Filament Handedness

The range of possible morphologies for bent‐core B4 phase liquid crystals has recently expanded from helical nanofilaments (HNFs) and modulated HNFs to dual modulated HNFs, helical microfilaments, and heliconical‐layered nanocylinders. These new morphologies are observed when one or both aliphatic side chains contain a chiral center. Here, the following questions are addressed: which of these two chiral centers controls the handedness (helicity) and which morphology of the nanofilaments is formed by bent‐core liquid crystals with tris‐biphenyl diester core flanked by two chiral 2‐octyloxy side chains? The combined results reveal that the longer arm of these nonsymmetric bent‐core liquid crystals controls the handedness of the resulting dual modulated HNFs. These derivatives with opposite configuration of the two chiral side chains now feature twice as large dimensions compared to the homochiral derivatives with identical configuration. These results are supported by density functional theory calculations and stochastic dynamic atomistic simulations, which reveal that the relative difference between the para‐ and meta‐sides of the described series of compounds drives the variation in morphology. Finally, X‐ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) data also uncover the new morphology for B4 phases featuring p2/m symmetry within the filaments and less pronounced crystalline character.     

Ternary System with Controlled Structure: A New Strategy toward Efficient Organic Photovoltaics

Recently, a new type of active layer with a ternary system has been developed to further enhance the performance of binary system organic photovoltaics (OPV). In the ternary OPV, almost all active layers are formed by simple ternary blend in solution, which eventually leads to the disordered bulk heterojunction (BHJ) structure after a spin‐coating process. There are two main restrictions in this disordered BHJ structure to obtain higher performance OPV. One is the isolated second donor or acceptor domains. The other is the invalid metal–semiconductor contact. Herein, the concept and design of donor/acceptor/acceptor ternary OPV with more controlled structure (C‐ternary) is reported. The C‐ternary OPV is fabricated by a sequential solution process, in which the second acceptor and donor/acceptor binary blend are sequentially spin‐coated. After the device optimization, the power conversion efficiencies (PCEs) of all OPV with C‐ternary are enhanced by 14–21% relative to those with the simple ternary blend; the best PCEs are 10.7 and 11.0% for fullerene‐based and fullerene‐free solar cells, respectively. Moreover, the averaged PCE value of 10.4% for fullerene‐free solar cell measured in this study is in great agreement with the certified one of 10.32% obtained from Newport Corporation.     

Rational Tuning of Molecular Interaction and Energy Level Alignment Enables High‐Performance Organic Photovoltaics

The performance of organic photovoltaics (OPVs) has rapidly improved over the past years. Recent work in material design has primarily focused on developing near‐infrared nonfullerene acceptors with broadening absorption that pair with commercialized donor polymers; in the meanwhile, the influence of the morphology of the blend film and the energy level alignment on the efficiency of charge separation needs to be synthetically considered. Herein, the selection rule of the donor/acceptor blend is demonstrated by rationally considering the molecular interaction and energy level alignment, and highly efficient OPV devices using both‐fluorinated or both‐nonfluorinated donor/acceptor blends are realized. With the enlarged absorption, ideal morphology, and efficient charge transfer, the devices based on the PBDB‐T‐F/Y1‐4F blend and PBDB‐T‐F/Y6 exhibit champion power conversion efficiencies as high as 14.8% and 15.9%, respectively.     

复合保温墙体的耐火问题

随着节能建筑的大力推广,越来越多的保温材料被应用在复合墙体上,由此而产生的防火问题,必须引起各有关主管部门和建设单位的高度关注。为此,本刊特约建筑行业著名专家冯葆纯教授等人撰文,以期引起有关部门对复合保温墙体耐火问题的重视。     

高性能混凝土的早期极限拉应变

混凝土的早期抗拉性能是评价和预测混凝土结构早期开裂不可或缺的重要参数,但并未受到国内研究同行的重视。高性能混凝土较普通混凝土更易于发生早期开裂,故对其抗拉性能加以研究意义重大。本文通过自行设计的实验装置对高性能混凝土早龄期极限拉应变进行了试验研究。结果发现,高性能混凝土硬化期间极限拉应变极高,并随龄期迅速递减,达到最小值后又缓慢回升并渐趋稳定。基于试验结果和CEB-FIP MC 90对高性能混凝土的早期极限拉应变进行了初步评价。     

不对称电网电压下基于正负序分量检测风电换流器控制策略

提出了不对称电网的概念,阐述了电网电压不平衡产生的原因和典型的故障类型,给出了滤波器法和1/4周期延时法2种正负序分量检测方法。在正负序分量检测的基础上,讨论了针对不对称电网的改进的双闭环控制方案,通过建立正负序d、q坐标轴下的电流、电压和功率的方程,使得改进以后的双闭环系统可以使PWM换流器工作在不对称电网中,并保持输入电流正弦以及输出直流电压恒定。使用Matlab/Simulink工具进行了仿真验证,结果表明:基于正负序分量检测的双闭环控制策略能够在对称和不对称电网下都有良好的表现,因此可以实现故障电网下的不间断运行。     

骨骼肌膜DNA结合蛋白

应用差速及蔗糖密度梯度离心法提取了骨骼肌非核的肌膜蛋白,发现在肌膜上有一种ＤＮＡ结合蛋白质,其分子量为２９ｋＤａ,能与环状质粒ＤＮＡ和双链线状ＤＮＡ发生特异性结合,它可能在肌肉介导的基因转移中起作用     

中波发射台站防雷技术选型实践

本文以江西832中波台的防雷工程技术选型为例,结合防雷工程实施前置选型工作对保护可靠性和使用期成本节能要求为评估要素,最终选定采用感应消雷保护措施进行升级改造,通过一个雷雨季节的应用,可以看出一个技术可靠的中波发射台防雷工程改造可带来安全和节效的综合效益,特此总结性文章,以供雷击严重的中波发射台适用防雷技术选型参考.     

融合知识图谱与注意力机制的短文本分类模型

针对短文本缺乏上下文信息导致的语义模糊问题,构建一种融合知识图谱和注意力机制的神经网络模型。借助现有知识库获取短文本相关的概念集,以获得短文本相关先验知识,弥补短文本缺乏上下文信息的不足。将字符向量、词向量以及短文本的概念集作为模型的输入,运用编码器-解码器模型对短文本与概念集进行编码,利用注意力机制计算每个概念权重值,减小无关噪声概念对短文本分类的影响,在此基础上通过双向门控循环单元编码短文本输入序列,获取短文本分类特征,从而更准确地进行短文本分类。实验结果表明,该模型在AGNews、Ohsumed和TagMyNews短文本数据集上的准确率分别达到73.95%、40.69%和63.10%,具有较好的分类能力。     

氧化锆零件激光选区烧结/冷等静压复合成形技术

氧化锆陶瓷材料以其优异的性能在工业生产中具有极大的应用前景,但由于脆性大、硬度高等原因,复杂形状氧化锆零件往往难以成形和加工。为了获得复杂形状氧化锆陶瓷零件,通过溶剂沉淀法将粘接剂尼龙12覆膜至纳米氧化锆粉末的表面,然后对覆膜后的粉体进行激光选区烧结(Selective laser sintering, SLS)成形,并通过传统的冷等静压(Cold isostatic pressing, CIP)技术对SLS零件进行致密化处理,同时满足氧化锆初坯成形时形状复杂度和密度的要求。通过试验得出在激光能量密度为0.415 J/mm2时,获得的SLS陶瓷件密度较大,对不同激光能量密度制备的SLS陶瓷件进行保压压力为200 MPa的冷等静压致密化处理,根据热脱脂机理以及粘接剂的TG曲线,分别制定了SLS/CIP试样的热脱脂工艺,最后对脱脂试样进行高温烧结,在后续处理的各环节,氧化锆零件的密度仍受SLS成形的影响,但该影响逐渐减弱,SLS/CIP/FS成形件最大相对密度和维氏硬度分别达到了97%和1180 HV1,已接近“模压-烧结”的致密氧化锆陶瓷的性能,在试样断口的扫描电子显微镜(SEM)分析基础上,对氧化锆复合成形的微观演变进行了研究。虽然最终烧结件密度和硬度仍有待提高,但是提出了一种极具潜力的氧化锆零件近净成形工艺方法,为制造高性能复杂形状的陶瓷零件奠定了基础。