Modular Synthesis of Nona‐Decasaccharide Motif from Psidium guajava Polysaccharides: Orthogonal One‐Pot Glycosylation Strategy

The synthesis of long, branched, and complex carbohydrate sequences remains a challenging task in chemical synthesis. Reported here is an efficient and modular one‐pot synthesis of a nona‐decasaccharide and shorter sequences from Psidium guajava polysaccharides, which have the potent α‐glucosidase inhibitory activity. The synthetic strategy features: 1) several one‐pot glycosylation reactions on the basis of N‐phenyltrifluoroacetimidate (PTFAI) and Yu glycosylation to streamline the chemical synthesis of oligosaccharides, 2) the successful and efficient assembly sequences (first O3′, second O5′, final O2′) toward the challenging 2,3,5‐branched Araf motif, 3) the stereoselective 1,2‐cis‐glucosylation by reagent control, and 4) the convergent [6+6+7] one‐pot coupling reaction for the final assembly of the target nona‐decasaccharide. This orthogonal one‐pot glycosylation strategy can streamline the chemical synthesis of long, branched, and complicated carbohydrate chains.     

Synergistic Dual‐Additive Electrolyte Enables Practical Lithium‐Metal Batteries

A rechargeable Li metal anode coupled with a high‐voltage cathode is a promising approach to high‐energy‐density batteries exceeding 300 Wh kg^?1. Reported here is an advanced dual‐additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate‐based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F‐ and B‐containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg^?1 at cell‐level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.     

融合图卷积神经网络和注意力机制的PM2.5小时浓度多步预测

PM_2.5小时浓度多为单步预测。为实现PM_2.5小时浓度的多步预测,基于“编码器-解码器”的序列-序列预测（Seq2Seq）模型,集合图卷积神经网络提取非欧式空间数据特征的能力以及注意力机制自适应关注特征的能力,提出了融合图卷积神经网络和注意力机制的PM_2.5小时浓度多步预测（GCN_Attention_Seq2Seq）模型。并与Seq2Seq模型和使用了图卷积神经网络、未使用注意力机制的GCN_Seq2Seq模型进行了对照,以2015—2016年北京市22个空气质量监测站点的空气质量数据为样本进行实例验证,结果表明,Seq2Seq模型和图卷积神经网络（GCN）可对PM_2.5小时浓度数据的时空依赖进行有效建模,注意力机制有助于减缓多步预测中的预测精度衰减,提升PM_2.5小时浓度多步预测的精度。GCN_Attention_Seq2Seq模型可有效应用于多种长度的PM_2.5浓度预测窗口。     

白光LED用近紫外光激发的蓝绿色荧光粉Sr5(PO4)3F∶Eu2+的光谱性能及助熔剂的影响

本文采用还原氛下的高温固相法合成了荧光粉Sr5(PO4)3F∶ Eu2+并对其性能进行了表征,同时研究了助熔剂硼酸对该荧光粉的影响.结果 表明:在1200℃还原氛下制得的荧光粉Sr5(PO4)3F∶ Eu2+,激发峰位于418 nm,发射峰位于524 nm,是能与近紫外光LED相匹配的蓝绿色荧光粉.Eu2的最佳掺杂浓度为15mo1;,对应的色坐标为(0.2871,0.4036).添加助熔剂H3BO3可以使荧光粉Sr5(PO4)3F∶Eu2+的合成温度由1200℃降低到1100℃,最佳掺杂浓度为5wt;,同时可以增加荧光粉的发光强度.     

大视场反射式施密特光学系统设计与检测

大视场、低成本、高性能天文望远镜是当前研究和开发的热点。基于像差平衡原理,在正入射施密特矫正板基础上推导出斜入射反射式施密特矫正板方程,针对焦距1 700 mm,成像视场角4°,波段为0.4 μm～0.9 μm,F数为4.25的光学系统,求解出施密特矫正板方程,并作为初始结构参数代入Zemax软件进一步优化。设计结果表明,在全视场范围内,该系统在奈奎斯特频率100 lp/mm处的调制传递函数MTF大于0.35,畸变小于2.5%,成像质量达到了衍射极限。优化设计后施密特矫正板与最近球面最大偏差为0.005 mm,采用特制的补偿器结合干涉仪可完成面形高精度检测。该施密特系统的设计为大视场、宽波段天文望远镜的开发提供了参考。     

Modified Gerchberg–Saxton (G-S) Algorithm and Its Application

The Gerchberg–Saxton (G-S) algorithm is a phase retrieval algorithm that is widely used in beam shaping and optical information processing. However, the G-S algorithm has difficulty obtaining the exact solution after iterating, and an approximate solution is often obtained. In this paper, we propose a series of modified G-S algorithms based on the Fresnel transform domain, including the single-phase retrieval (SPR) algorithm, the double-phase retrieval (DPR) algorithm, and the multiple-phase retrieval (MPR) algorithm. The analysis results show that the convergence of the SPR algorithm is better than that of the G-S algorithm, but the exact solution is not obtained. The DPR and MPR algorithms have good convergence and can obtain exact solutions; that is, the information is recovered losslessly. We discuss the security advantages and verification reliability of the proposed algorithms in image encryption. A multiple-image encryption scheme is proposed, in which n plaintexts can be recovered from n ciphertexts, which greatly improves the efficiency of the system. Finally, the proposed algorithms are compared with the current phase retrieval algorithms, and future applications are discussed. We hope that our research can provide new ideas for the application of the G-S algorithm.     

Dynamic relaxation process of a 3D super crystal structure in a Cu:KTN crystal

In this Letter,we report the existence and relaxation properties of a critical phenomenon on called a 3D super crystal that emerges at T=TC?3.5℃,that is,in the proximity of the Curie temperature of a Cu:KTN sample.The dynamics processes of a 3D super crystal manifest in its formation containing polarized nanometric regions and/or polarized clusters.However,with strong coupling and interaction of microcomponents,the characteristic relaxation time measured by dynamic light scattering demonstrates a fully new relaxation mechanism with a much longer relaxation time.As the relaxation mechanism of a relaxator is so-far undetermined,this research provides a novel perspective.These results can help structure a fundamental theory of ferroelectric relaxation.     

纳米Ru-Mn/ZrO2催化剂上苯选择加氢制环己烯

采用共沉淀法制备了一系列不同Mn含量的纳米Ru-Mn催化剂,考察了纳米ZrO₂作分散剂时它们催化苯选择加氢制环己烯的反应性能,并采用X射线衍射、透射电镜、N₂物理吸附、X射线荧光、原子吸收光谱和俄歇电子能谱等手段对催化剂进行了表征.结果表明,Ru-Mn催化剂上Mn以Mn₃O₄存在于Ru的表面上.在加氢过程中,Mn₃O₄可以与浆液中ZnSO₄发生化学反应生成一种难溶性的(Zn(OH)₂)₃(ZnSO₄)(H₂O)₃盐.该盐易化学吸附在Ru催化剂表面上,从而在提高Ru催化剂上环己烯选择性起关键作用.当催化剂中Mn含量为5.4%时,环己烯收率为61.3%,同时具有良好的稳定性和重复使用性能.     

钾改性氧化铝基羰基硫水解催化剂及其失活机理

天然气、油田伴生气、高炉煤气等化工生产过程中伴生COS气体,不仅会腐蚀管道和毒害催化剂,还会严重污染环境并危害人类健康。COS催化水解反应可在温和条件下高效的将COS脱除,是最具应用前景的COS脱除技术之一。碱金属元素因其具有独特的电子供体性质、表面碱性和静电吸附等特性,常被用作助催化剂以提高Al₂O₃的COS催化水解性能。近年来,以钾为助剂改性的Al₂O₃催化剂(K₂CO₃/Al₂O₃)在COS催化水解反应中得到广泛的应用,但由于负载在Al₂O₃上的K物种的组成复杂,目前研究者对K₂CO₃/Al₂O₃催化剂上COS水解机理的理解仍存在一定的困惑和争议。本论文通过湿法浸渍法合成出一系列钾盐和钠盐改性的Al₂O₃催化剂,并利用各类先进的表征技术对这些催化剂进行分析。活性测试表明,以K₂CO₃、K₂C₂O₄、NaHCO₃、Na₂CO₃和NaC₂O₄改性Al₂O₃催化剂均有助于COS的水解。其中K₂CO₃/Al₂O₃拥有最佳的COS水解性能,连续运行20 h后其COS转化率仍高于~93%,远远优于未改性的Al₂O₃ (~58%)。我们利用原位红外光谱和X射线光电子能谱探明了反应过程中催化剂的化学结构特征,阐明了H₂O分子在K₂CO₃/Al₂O₃上的水解作用机制。原位红外表明COS在K₂CO₃/Al₂O₃上的水解过程中形成了硫代碳酸氢盐中间产物。X射线光电子能谱表征证明催化剂的失活主要是因为催化剂表面积累了硫酸盐和单质硫。此外,我们还研究了水蒸气含量对COS水解性能的影响,研究发现,由于H₂O和COS分子在催化剂表面存在竞争吸附,过量的H₂O会引起催化活性的下降。上述研究表明,K₂CO₃/Al₂O₃催化剂上COS水解性能的提高主要是形成了HO-Al-O-K界面活性位。更为重要的是,所制备的催化剂都是在模拟工业工况条件下进行的,这为后续的工业应用提供了宝贵理论指导。本工作为理解助剂钾在Al₂O₃催化剂上COS水解活性的增强提供了新的见解,这为未来设计稳定高效的COS水解催化剂打开了新的发展方向。     

Enantiomeric Discrimination by Surface‐Enhanced Raman Scattering–Chiral Anisotropy of Chiral Nanostructured Gold Films

A surface‐enhanced Raman scattering‐chiral anisotropy (SERS‐ChA) effect is reported that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films (CNAFs) equipped in the normal Raman scattering Spectrometer. The CNAFs provided remarkably higher enhancement factors of Raman scattering (EFs) for particular enantiomers, and the SERS intensity was proportional to the enantiomeric excesses (ee) values. Except for molecules with mesomeric species, all of the tested enantiomers exhibited high SERS‐ChA asymmetry factors (g), ranging between 1.34 and 1.99 regardless of polarities, sizes, chromophores, concentrations and ee. The effect might be attributed to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and chiral plasmonic modes of CNAFs.