Cu2+‐Induced Structural Isomers: Effect of Foreign Metal Ions on the Structure and Properties of Silver Nanoclusters

Metal ions have an important impact on the precise control of the synthesis and atomic structural arrangement of noble metal nanoclusters. In this work, the effect of metal ions on the isomer generation of metal nanoclusters is revealed for the first time. Compared with the previous Ag₂₃ nanoclusters with two face‐centered cubic (fcc) unit cells twisting 27°, the Ag₂₃ isomer had a higher symmetry structure with two fcc unit cells almost overlapping. In addition, the UV/Vis absorption spectrum of the isomer showed a slight redshift of approximately 14 nm. The redshift might be because of the modulation of electronic structure, which is derived from fine‐tuned crystal structure. Based on the experimental results, we provide mechanisms to explain the Cu²⁺ effect on the structural isomer. This work reports a significant finding to tune precisely the crystal structure and understand the mechanism of shape‐controlled synthesis of metal nanoclusters.     

Structural Transformation Pathways of Alkaline Earth Family Coordination Polymers Containing 3,3′,5,5′‐Biphenyl Tetracarboxylic Acid

The understanding of crystal stepwise transformation is very important to enclose the “black box” in the preparation of crystal materials. In this work, different structural intermediates were isolated prior to the formation of the final alkali earth coordination polymers (CPs) during the preparation of three pairs of alkali earth CPs through solvothermal method and convenient oil‐bath reactions. Single crystal X‐ray diffraction analysis demonstrated the structural transformation from a 0 D to 1 D inorganic connectivity for the Ca‐CPs and Sr‐CPs, but a 1 D to 0 D inorganic connectivity for Ba‐CPs, involving the breakage/formation of chemical bonds in the reaction solutions. Further analyses indicated that these two different structural transformation pathways are determined by the deprotonation of organic acid, competitive balance between the inorganic and organic connectivity, and the twist of the linker. FT‐IR spectra, thermogravimetric and luminescence behaviors agree with their structural characteristics.     

CdII‐Organic Frameworks Fabricated with a N‐Rich Ligand and Flexible Dicarboxylates: Structural Diversity and Multi‐Responsive Luminescent Sensing for Toxic Anions and Ethylenediamine

Three metal‐organic frameworks {[Cd( L )(glu)]?3 H₂O}_∞ ( 1 ), {[Cd₂( L )₂(adi)₂]?5 H₂O}_∞ ( 2 ) and {[Cd( L )(sub)]?3 H₂O?DMA }_∞ ( 3 ) ( L =pyridine‐3,5‐bis(5‐azabenzimidazole), H₂glu=glutaric acid, H₂adi=adipic acid and H₂sub=suberic acid) were obtained under solvothermal conditions. Complex 1 shows a 2D (4,4) network constructing of Cd₂‐glu and Cd‐ L chains. Complex 2 presents a 2‐fold interpenetrating 3D framework with pcu topology. Complex 3 is a 3D framework with cds topology. Three complexes with versatile structures were obtained by changing aliphatic dicarboxylate ligands with different lengths based on a N‐rich ligand. Moreover, the fluorescence measurements indicate that complex 1 is a good multifunctional chemosensor for the detection of Cr₂O₇^2? and MnO₄^? anions by fluorescence quenching effect, and ethylenediamine by fluorescence enhancement effect, with detection limits of 1.196 ppm, 0.551 ppm and 64.572 ppm, respectively. Both complexes 2 and 3 can selectively sense Cr₂O₇^2? anion with detection limits of 1.126 ppm for 2 and 0.831 ppm for 3 by a fluorescence quenching effect.     

Structural Diversity in Luminescent MOFs Containing a Bent Electron‐rich Dicarboxylate Linker and a Flexible Capping Ligand: Selective Detection of 4‐Nitroaniline in Water

A combination of a bent bis(naphthalene) and hydroxy‐based dicarboxylate linker and a flexible bis(tridentate)polypyridyl ligand has been employed to self‐assemble with two different d¹⁰ metal centers, Zn^II and Cd^II, to form structurally diversified luminescent metal–organic frameworks, [Zn₂(tpbn)(mbhna)₂(H₂O)₂]?4 H₂O?1.5DMF ( 1 ) and {[Cd₂(tpbn)(mbhna)₂]?2DMF}_n ( 2 ), respectively (where, tpbn=N,N′,N′′,N′′′‐tetrakis(pyridine‐2‐ylmethyl)butane‐1,4‐diamine and H₂mbhna=4,4′‐methylene‐bis[3‐hydroxy‐2‐naphthalene carboxylic acid]). Both 1 and 2 are characterized and analyzed by various analytical techniques including single‐crystal X‐ray diffractometry. Their excellent emissive nature is studied in different solvents and further utilized to selectively detect aromatic amines, particularly 4‐nitroaniline in water with detection limits at sub‐ppm level. The difference in sensing activity of 1 and 2 toward 4‐NA is corroborated well with their structures. The mechanism of action has been established through Stern–Volmer plot, spectral overlap, time‐resolved lifetime studies and HOMO–LUMO energy calculations. In addition, 1 and 2 are found to be recyclable and display good stability after sensing experiments.     

机械产品基于变更影响和升级复杂度的升级潜力评估

基于信息熵理论和产品结构关联性研究, 提出了一个机械产品升级潜力评估模型, 从升级变更影响程度(前端)和升级复杂度(后端)两方面进行综合分析, 得出机械产品的升级潜力量化值, 并用实例验证了所提出模型的有效性.     

悬停状态下无铰式旋翼动力学参数试验研究

旋翼结构参数及动力学参数对旋翼动力学特性有着重要影响。随着旋翼结构型式的不断更新,在旋翼设计中需要考虑的动力学参数也相应增加,从而使旋翼的动力学问题更加复杂化。本文通过在２米旋翼试验台上进行的试验,用测量桨叶频响函数和稳态响应的方法研究了悬停状态预锥角、预掠角和总距角等旋翼结构参数对桨叶固有特性及气动弹性稳定性的影响规律,并同计算结果进行了比较,得到了一些对旋翼设计有实用意义的结论     

高层建筑结构施工力学分析

通常高层结构设计是以建造好结构在使用荷载下的计算模型为依据。然而这是同结构在实际施工过程产生的力学状态有差异的。为此本文将采用超级有限元－有限元耦合法对高层结构进行施工模拟分析,按照施工顺序及施工时的实际情况进行力学分析,从而对保证结构建造全过程的可靠性和安全性,指导选用合理的施工方案,具有一定的理论意义和现实意义。     

特征值问题的边界形状灵敏度

研究连续系统振动特征值问题的边界形状灵敏度满足什么方程和边界条件,如何离散化作近似计算结果表明：如果采用相同的有限单元剖分模式,边界形状灵敏度方程和特征值问题方程具有相同的系数矩阵,但前者是非齐次方程,后者是齐次方程;前者需要施加非齐次边界条件,后者施加齐次边界条件。     

基于扰动状态概念的结构性粘土本构模型研究

考虑结构性粘土的本构模型研究中存在的问题．引入了Desai C S的扰动状态概念,并对关键参数——扰动函数进行了扩展,增加了土体体积应变的影响,建立了结构性粘土的弹塑性扰动状态本构模型．最后通过三轴不排水剪切试验对模型进行了检验,结果表明该模型反映了上体的变形特征,说明在类似条件下能较好的满足工程实际的要求．     

Structural and Biological Properties of Water Soluble Polysaccharides from Lotus Leaves: Effects of Drying Techniques

In the present study, the influence of five drying techniques on the structural and biological properties of polysaccharides from lotus leaves (LLPs) was investigated. Results revealed that the yields, contents of basic chemical components, molecular weights, and molar ratios of compositional monosaccharides of LLPs varied by different drying technologies. Low molecular weight distributions were observed in polysaccharides obtained from lotus leaves by hot air drying (LLP-H), microwave drying (LLP-M), and radio frequency drying (LLP-RF), respectively. The high contents of bound polyphenolics were measured in LLP-H and LLP-M, as well as polysaccharides obtained from lotus leaves by vacuum drying (LLP-V). Furthermore, both Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectra of LLPs were similar, indicating that drying technologies did not change their basic chemical structures. Besides, all LLPs exhibited obvious biological properties, including in vitro antioxidant capacities, antiglycation activities, and inhibitory effects on α-glucosidase. Indeed, LLP-H exhibited higher 2,2-azidobisphenol (3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging ability (IC₅₀ values, LLP-H, 0.176 ± 0.004 mg/mL; vitamin C, 0.043 ± 0.002 mg/mL) and 2,2-diphenyl-1-(2,4,6-trinitrate phenyl) hydrazine radical scavenging ability (IC₅₀ values, LLP-H, 0.241 ± 0.007 mg/mL; butylated hydroxytoluene, 0.366 ± 0.010 mg/mL) than others, and LLP-M exerted stronger antiglycation (IC₅₀ values, LLP-M, 1.023 ± 0.053 mg/mL; aminoguanidine, 1.744 ± 0.080 mg/mL) and inhibitory effects on α-glucosidase (IC₅₀ values, LLP-M, 1.90 ± 0.02 μg/mL; acarbose, 724.98 ± 16.93 μg/mL) than others. These findings indicate that both hot air drying and microwave drying can be potential drying techniques for the pre-processing of lotus leaves for industrial applications.