低浓缩铀靶辐照后溶液中铀的化学种态及主要裂变元素的影响

利用化学种态分析软件CHEMSPEC计算了低浓缩铀靶辐照后溶液中铀(U)的化学种态分布及其主要裂变元素对U化学种态的影响。结果表明,在单组分体系中,pH值和铀酰浓度都会显著影响U的化学种态分布。随着铀酰浓度的增大,溶液中将会生成多核配合物;在较高的NO₃^-浓度下,U在溶液中主要以UO₂²⁺和UO₂NO³⁺的形式存在。CO₂对不同浓度铀的种态分布影响结果表明,当铀酰浓度较低时,铀的化学种态多以碳酸铀酰的形式存在;当铀酰浓度较高时,铀的化学种态多以氢氧铀酰或柱铀矿沉淀的形式存在。计算发现,当裂片元素Tc、I、Mo的浓度小于0.01mol·L^-1并分别以TcO₄^-、I^-、MoO₄^2-的种态存在时,这些裂片元素不改变铀的各化学种态的分布。     

Recent Development of Anion Exchange Membrane Fuel Cells and Performance Optimization Strategies: A Review

Anion exchange membrane fuel cells (AEMFCs) are the most promising low-temperature fuel cells and have received extensive attention. Compared to PEMFCs, the cost per unit of power can be significantly reduced for AEMFCs because, in theory, they allow the usage of non-precious metal catalysts and low-cost cell components. Owing to the development of advanced materials and performance improvement strategies, AEMFCs have achieved new records in both initial performance and durability. However, the high performance currently achieved is contingent on certain conditions, e. g., high Pt loading, large gas flowrates, and operation in pure O₂, which are far from practical applications. Therefore, the transition to commercially relevant performance and durability is the next goal of AEMFCs. This paper reviews the performance data of H₂-fueled AEMFCs since 2010 and summarizes possible performance optimization schemes, which can provide useful insights for developing next-generation AEMFCs.     

Microstructures of (Fe0.88Co0.12)82La7Si11 prepared by arc-melting/melt spinning and subsequent annealing

In this study, we carried out a systematic investigation of the microstructures of (Fe_0.88Co_0.12)₈₂La₇Si₁₁ prepared by arc melting/melt spinning and subsequent annealing. The arc-melted sample contains 36 wt. % of the desired La(Fe,Co,Si)₁₃ phase (denoted by 1:13 in the following). Annealing of the arc-melted ingot at 1273 K for 200 h leads to a single 1:13 phase. Melt spinning enhances formation of the 1:13 phase. As the wheel speed reaches or is greater than 15 m/s, over 50 wt. % of 1:13 is directly formed in the melt-spun ribbons. A subsequent annealing of these melt-spun samples at 1273 K for 20 min results in a nearly single phase 1:13 structure. The samples prepared under different conditions were systematically studied by transmission electron microscopy in order to elucidate possible origins of the enhanced formation of the 1:13 phase when using the new technique. The presence of a high density of La-Fe-Co-Si clusters in the undercooled liquid is believed to contribute to the formation of the 1:13 phase in melt-spun ribbons. The enhanced atomic diffusivity as a result of structural refinement in melt-spun samples accounts for the subsequent fast transformation of the 1:13 phase during the annealing process. PACS 71.20.Eh; 81.07.Bc; 68.37.Lp     

Intramolecular transacylation: fragmentation of protonated molecules via ion‐neutral complexes in mass spectrometry

An intramolecular transacylation reaction was observed in the mass spectrometry of molecules containing both benzoyl and carboxymethyl groups on an aromatic heterocyclic core. The reaction is triggered by a dissociative protonation on the heterocyclic ring at the atom (carbon or nitrogen) that bonds to the benzoyl group, leading to an intermediate ion‐neutral complex. The incipient benzoyl cation in the complex migrates to attack the carboxyl group of the neutral partner at the carbonyl or hydroxyl oxygen under thermodynamic or kinetic control, respectively. Elimination of benzoic acid followed by loss of carbon monoxide takes place as a result of the transacylation. Copyright © 2009 John Wiley & Sons, Ltd.     

Ligand electronic effects in the palladium catalyzed asymmetric allylic alkylation reaction with planar chiral diphosphine-oxazoline ferrocenyl ligands

A series of planar chiral diphosphine-oxazoline ferrocenyl ligands with different electronic properties were successfully used in the asymmetric allylic substitutent reaction. The enantioselectivity of this reaction was affected by the electronic nature of the ligands. When the electronic effect was coincident with the steric effect of ligand, a higher ee value was observed.     

择优取向生长的Gd2O3高K栅介质薄膜

使用射频磁控溅射法在n型Si(001)基片上生长了Gd2O3薄膜。X射线衍射扫描研究和高分辨透射电子显微镜观察表明,薄膜由立方相和单斜相混合构成,且表现出立方(111)晶面和单斜(401)晶面的择优取向生长。XPS分析表明薄膜的元素组成接近化学计量比。电性能测试发现,薄膜拥有合适的介电常数,较小的漏电流密度和较大的击穿场强,厚度为15 nm的薄膜介电常数为23,漏电流密度为3.6×10-5A.cm-2(偏压为 1 V时),击穿场强为3.5 MV.cm-1。     

The studies of systems of variational inclusions problems and variational disclusions problems with applications

In this paper, we study existence theorems of solutions for systems of variational inclusions problems and systems of variational disclusions problems. From these existence results, we establish existence theorems of solutions for systems of generalized vector quasiequilibrium problems and systems of quasioptimization problems.     

Negative-pressure cavitation extraction for the determination of flavonoids in pigeon pea leaves by liquid chromatography-tandem mass spectrometry

A new method, namely negative-pressure cavitation extraction (NPCE), followed by liquid chromatography–tandem mass spectrometry (LC–MS/MS) is presented for the extraction and quantification of flavonoids in pigeon pea leaves. This method combines the high efficiency of NPCE and the sensitivity and accuracy of MS/MS. The influential parameters of the NPCE procedure including liquid/solid ratio, extraction time, nitrogen flow and number of extraction cycles were optimized. Under optimized conditions, the efficiency of NPCE for extracting five flavonoids was compared to microwave-assisted extraction (MAE), ultrasonic extraction (USE) and heating reflux extraction (HRE). Additionally, structural disruption to pigeon pea leaves samples with different extraction methods was investigated by scanning electron microscopy. The relative recovery with NPCE was equivalent to or higher than that with USE and obviously higher than those with MAE and HRE which are usually conducted in higher temperatures. Furthermore, because NPCE was performed with nitrogen at room temperature, the degradation and oxidation of analytes were avoided. In addition, the NPCE method was validated in terms of repeatability and reproducibility, relative standard deviation for relative recovery was lower than 5.84 and 8.83%, respectively. The method was also successfully applied for the quantification of five flavonoids in pigeon pea leaves. All these results suggest that the developed NPCE-LC–MS/MS method represents an excellent alternative for the extraction and quantification of flavonoids in other plant materials.