Confinement Effects in Zeolite‐Confined Noble Metals

Confinement of noble nanometals in a zeolite matrix is a promising way to special types of catalysts that show significant advantages in size control, site adjustment, and nano‐architecture design. The beauty of zeolite‐confined noble metals lies in their unique confinement effects on a molecular scale, and thus enables spatially confined catalysis akin to enzyme catalysis. In this Minireview, the confined synthesis strategies of zeolite‐confined noble metals will be briefly discussed, showing the processes, advantages, features, and mechanisms. The confined catalysis carried on zeolite‐confined noble metals will be summarized, and great emphasis will be paid to the confinement effects involving size, encapsulation, recognition, and synergy. Great progress of atomic sites in the size effect, supercage stabilization in the encapsulation effect, site adsorption in the recognition effect, and cascade reaction in the synergy effect are highlighted. This Minireview is concluded with challenges and opportunities in terms of the synthesis of zeolite‐confined noble metals and their applications to design multifunctional catalysts with high catalytic activity, selectivity, and stability.     

Oxygen Evolution Reaction over the Au/YSZ Interface at High Temperature

The oxygen evolution reaction (OER) is a sluggish electrocatalytic reaction in solid oxide electrolysis cells (SOECs) at high temperatures (600–850 °C). Perovskite oxide has been widely investigated for catalyzing the OER; however, the formation of cation‐enriched secondary phases at the oxide/oxide interface blocks the active sites and decreases OER performance. Herein, we show that the Au/yttria‐stabilized zirconia (YSZ) interface possesses much higher OER activity than the lanthanum strontium manganite/YSZ anode. Electrochemical characterization and density functional theory calculations suggest that the Au/YSZ interface provides a favorable path for OER by triggering interfacial oxygen spillover from the YSZ to the Au surface. In situ X‐ray photoelectron spectroscopy results confirm the existence of spillover oxygen on the Au surface. This study demonstrates that the Au/YSZ interface possesses excellent catalytic activity for OER at high temperatures in SOECs.     

Intermolecular C−H Amidation of (Hetero)arenes to Produce Amides through Rhodium‐Catalyzed Carbonylation of Nitrene Intermediates

Amide bond formation is one of the most important reactions in organic chemistry because of the widespread presence of amides in pharmaceuticals and biologically active compounds. Existing methods for amides synthesis are reaching their inherent limits. Described herein is a novel rhodium‐catalyzed three‐component reaction to synthesize amides from organic azides, carbon monoxide, and (hetero)arenes via nitrene‐intermediates and direct C?H functionalization. Notably, the reaction proceeds in an intermolecular fashion with N₂ as the only by‐product, and either directing groups nor additives are required. The computational and mechanistic studies show that the amides are formed via a key Rh‐nitrene intermediate.     

固相萃取/超高效液相色谱-串联质谱法测定贝类中3种短裸甲藻毒素

建立了同时测定贝类中3种短裸甲藻毒素的超高效液相色谱-串联质谱法。样品采用丙酮提取、C18固相萃取柱净化;以5 mmol/L乙酸铵(含0. 1%甲酸)-乙腈为流动相,ACQUITYTMUPLC BEH C18色谱柱进行分离,在多反应监测模式下进行测定,外标法定量。结果表明,3种目标物在1. 0～100μg/L质量浓度范围内线性良好,相关系数(r~2)不小于0. 996,方法定量下限为3. 0μg/kg,回收率为80. 0%～87. 5%,相对标准偏差为1. 3%～5. 4%。该方法前处理简单,灵敏度高,稳定性好,适用于贝类中3种短裸甲藻毒素的同时测定。     

点缺陷石墨烯的电导

Graphene is one of the most promising materials in nanotechnology and has attracted worldwide attention and research interest owing to its high electrical conductivity, good thermal stability, and excellent mechanical strength. Perfect graphene samples exhibit outstanding electrical and mechanical properties. However, point defects are commonly observed during fabrication which deteriorate the performance of graphene based-devices. The transport properties of graphene with point defects essentially depend on the imperfection of the hexagonal carbon atom network and the scattering of carriers by localized states. Furthermore, an in-depth understanding of the effect of specific point defects on the electronic and transport properties of graphene is crucial for specific applications. In this work, we employed density functional theory calculations and the non-equilibrium Green's function method to systematically elucidate the effects of various point defects on the electrical transport properties of graphene, including Stone-Waals and inverse Stone-Waals defects; and single and double vacancies. The electrical conductance highly depends on the type and concentration of point defects in graphene. Low concentrations of Stone-Waals, inverse Stone-Waals, and single-vacancy defects do not noticeably degrade electron transport. In comparison, DV585 induces a moderate reduction of 25%–34%, and DV55577 and DV5555-6-7777 induce significant suppression of 51%–62% in graphene. As the defect concentration increases, the electrical conductance reduces by a factor of 2–3 compared to the case of graphene monolayers with a low concentration of point defects. These distinct electrical transport behaviors are attributed to the variation of the graphene band structure; the point defects induce localized states near the Fermi level and result in energy splitting at the Dirac point due to the breaking of the intrinsic symmetry of the graphene honeycomb lattice. Double vacancies with larger defect concentrations exhibit more flat bands near the Fermi energy and more localized states in the defective region, resulting in the presence of resonant peaks close to the Fermi energy in the local density of states. This may cause resonant scattering of the carriers and a corresponding reduction of the conductance of graphene. Moreover, the partial charge densities for double vacancies and point defects with larger concentrations exhibit enhanced localization in the defective region that hinder the charge carriers. The electrical conductance shows an exponential decay as the defect concentration and energy splitting increase. These theoretical results provide important insights into the electrical transport properties of realistic graphene monolayers and will assist in the fabrication of high-performance graphene-based devices.     

Synthesis of Atom‐Precise Chiral Ag14 Clusters Protected by Penicillamine Ligands

A pair of atom‐precise chiral silver(I) nanocluster enantiomers ( Ag₁₄‐d and Ag₁₄‐l ) protected by d ‐ and l ‐penicillamine ligands is reported. Crystallographic structures reveal that the nanoclusters consist of a S^2? template and a chiral Ag₁₄ core stabilized by 12 penicillamine ligands. The penicillamine ligands show two binding fashions: (i) only thiolate coordination, and (ii) thiolate and carboxylate co‐coordination. Meanwhile, the two enantiomers show strong circular dichroism with opposite signals (mirror image relationship) owing to the chiral metallic core induced by chiral ligands, suggesting that the nanoclusters have well‐defined stereostructures as common chiral molecules do. The proton conductivity is also explored due to the existence of both amino groups and carboxylate groups from the penicillamine ligands, which is beneficial to construct H‐bond network for proton transfer.     

CONSTRUCTION OF MECHANISM MODES OF GEOMETRICALLY UNSTABLE SYSTEMS IN LARGE DEFORMATION

针对仅有一个自由度的几何可变体系,基于大变形机构模态的特性,提出常变、瞬变的判断方法,进而对常变体系提出大变形机构模态的二元体构建算法。该算法将问题简化为类似于一元二次方程的求解,无须求解非线性超越方程组,可给出完备的模态解答和完整的解答路径及其分叉点。本法具有原理直观、公式简洁、解答完备的优点,可作为结构力学几何构造分析教学的补充内容。     

Word frequencies: A comparison of Pareto type distributions

Mehri and Jamaati (2017) [18] used Zipf's law to model word frequencies in Holy Bible translations for one hundred live languages. We compare the fit of Zipf's law to a number of Pareto type distributions. The latter distributions are shown to provide the best fit, as judged by a number of comparative plots and error measures. The fit of Zipf's law appears generally poor.     

热-电应力下Cu/Ni/SnAg_(1.8)/Cu倒装铜柱凸点界面行为及失效机理

微互连铜柱凸点因其密度高、导电性好、噪声小被广泛应用于存储芯片、高性能计算芯片等封装领域,研究铜柱凸点界面行为对明确其失效机理和组织演变规律、提升倒装封装可靠性具有重要意义.采用热电应力实验、在线电学监测、红外热像测试和微观组织分析等方法,研究Cu/Ni/SnAg_1.8/Cu微互连倒装铜凸点在温度100—150℃、电流密度2×10~4—3×10~4 A/cm~2热电应力下的互连界面行为、寿命分布、失效机理及其影响因素.铜柱凸点在热电应力下的界面行为可分为Cu_6Sn_5生长和Sn焊料消耗、Cu_6Sn_5转化成Cu_3Sn、空洞形成及裂纹扩展3个阶段,Cu_6Sn_5转化为Cu_3Sn的速率与电流密度正相关.热电应力下,铜凸点互连存在Cu焊盘消耗、焊料完全合金化成Cu_3Sn、阴极镍镀层侵蚀和层状空洞4种失效模式.基板侧Cu焊盘和铜柱侧Ni镀层的溶解消耗具有极性效应,当Cu焊盘位于阴极时,电迁移方向与热迁移方向相同,加速Cu焊盘的溶解以及Cu_3Sn生长,当Ni层为阴极时,电迁移促进Ni层的消耗,在150℃,2.5×10~4 A/cm~2下经历2.5h后,Ni阻挡层出现溃口,导致Ni层一侧的铜柱基材迅速转化成(Cu_x,Ni_y)_6Sn_5和Cu_3Sn合金.铜柱凸点互连寿命较好地服从2参数威布尔分布,形状参数为7.78,为典型的累积耗损失效特征.研究结果表明:相比单一高温应力,热电综合应力显著加速并改变了铜柱互连界面金属间化合物的生长行为和失效机制.     

The Impact of Apple Variety and the Production Methods on the Antibacterial Activity of Vinegar Samples

Apple vinegar is a natural product widely used in food and traditional medicine as it contains many bioactive compounds. The apple variety and production methods are two factors that play a major role in determining the quality of vinegar. Therefore, this study aims to determine the quality of apple vinegar samples from different varieties (Red Delicious, Gala, Golden Delicious, and Starking Delicious) prepared by three methods using small apple pieces, apple juice, and crushed apple, through determining the physicochemical properties and antibacterial activity of these samples. The antibacterial activity was studied against five pathogenic bacteria: Staphylococcus aureus, Klebsiella pneumonia, Escherichia coli (ATB: 57), Escherichia coli (ATB: 97), and Pseudomonas aeruginosa, using two methods, disk diffusion and microdilution, for determining the minimum inhibitory concentrations and the minimum bactericidal concentrations. The results of this study showed that the lowest pH value was 3.6 for Stark Delicious, obtained by liquid fermentation, and the highest acetic acid values were 4.7 and 4% for the vinegar of Red Delicious and Golden Delicious, prepared by solid fermentation, respectively. The results of the antibacterial activity showed considerable activity of apple vinegar on the tested strains. Generally, the Staphylococcus aureus strain appears less sensitive and Pseudomonas aeruginosa seems to be very sensitive against all samples, while the other strains have distinct sensitivities depending on the variety studied and the method used. A higher antibacterial activity was found in vinegar obtained by the apple pieces method and the Red Delicious variety, with a low MIC and MBC recorded, at 1.95 and 3.90 µL/mL, respectively. This study has shown that the choice of both apple variety and production method is therefore an essential step in determining and aiming for the desired quality of apple vinegar.