关于超曲面的切面公式及其应用

本文给出任意ｎ维超曲面上任意一点的超切面方程的简洁的统一求法,将曲面方程微分即得切面方程．此法侧重对微分本质的理解,不需死记任何公式,计算简便．本文还讨论了此方法的理论意义,分别列举了到各种类型曲面的应用．     

Characteristic Volatile Fingerprints and Odor Activity Values in Different Citrus-Tea by HS-GC-IMS and HS-SPME-GC-MS

Citrus tea is an emerging tea drink produced from tea and the pericarp of citrus, which consumers have increasingly favored due to its potential health effects and unique flavor. This study aimed to simultaneously combine the characteristic volatile fingerprints with the odor activity values (OAVs) of different citrus teas for the first time by headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Results showed that the establishment of a citrus tea flavor fingerprint based on HS-GC-IMS data can provide an effective means for the rapid identification and traceability of different citrus varieties. Moreover, 68 volatile compounds (OAV > 1) were identified by HS-SPME-GC-MS, which reflected the contribution of aroma compounds to the characteristic flavor of samples. Amongst them, the contribution of linalool with sweet flower fragrance was the highest. Odorants such as decanal, β-lonone, β-ionone, β-myrcene and D-limonene also contributed significantly to all samples. According to principal component analysis, the samples from different citrus teas were significantly separated. Visualization analysis based on Pearson correlation coefficients suggested that the correlation between key compounds was clarified. A comprehensive evaluation of the aroma of citrus tea will guide citrus tea flavor quality control and mass production.     

Sensitive determination of organic acid preservatives in juices and soft drinks treated by monolith-based stir cake sorptive extraction and liquid chromatography analysis

A simple, efficient, and sensitive method for simultaneous determination of sorbic acid (SA), benzoic acid (BA), and cinnamic acid (CA) in juices and soft drinks was developed by stir cake sorptive extraction (SCSE) coupling to high-performance liquid chromatography with diode array detection. The SCSE based on polymeric ionic liquid-based monolith (PILM) as extractive medium was used to concentrate these three organic acid preservatives. Because hydrophobic and ion-exchange interactions co-contributed to the extraction, the PILM-SCSE exhibited a high extractive capability towards analytes. To obtain optimum extraction performance, several SCSE parameters were investigated and discussed, including desorption solvent, pH value, ionic strength in the sample matrix, and the extraction and desorption time. Under the optimized extraction conditions, limits of detection of 0.16, 1.08, and 0.18 μg/L (S/N?=?3) and quantification limits of 0.52, 3.42, and 0.61 (S/N?=?10) were obtained for SA, BA, and CA, respectively. The method also showed good linearity and reproducibility, as well as advantages such as simplicity, low cost, and high feasibility. Finally, the proposed method was successfully applied to the determination of SA, BA, and CA in real juices and soft drinks, and the recoveries ranged from 63.0 to 107 %.     

Theoretical investigation of excited-state proton transfer (ESPT) for 2,5-bis(2-benzothiazolyl)hydroquinone: single or double?

ABSTRACT

In this work, the single and double proton transfer dynamic process in the first excited state of 2,5-bis(2-benzothiazolyl)hydroquinone (BBTHQ) were theoretically investigated based on the time-dependent density functional theory (TD-DFT) method. The calculations of primary bond lengths, bond angles, IR vibrational spectra and NCI analysis reveal that two intramolecular hydrogen bonds of BBTHQ are strengthened in the first excited state, which provides a driving force for excited state proton transfer. The frontier molecular orbitals (FMOs) indicate the nature of intramolecular charge transfer. In addition, the potential energy surfaces (PESs) of the ground state and first excite state were also constructed to further elucidate the mechanism of intramolecular proton transfer of BBTHQ.     

离子色谱／氢化物发生／原子吸收法测定天然水中的砷形态

砷酸盐(As(Ⅴ))、亚砷酸盐(As(Ⅲ))、甲基胂酸盐(MMAA)和二甲基胂酸盐(DMAA),是天然水中砷的主要存在形态。本文用离子色谱分离这些砷形态,继以KBH_4还原、原子吸收法检测。分离用国产YSA-Ⅱ型阴离子交换色谱柱来完成。按上述砷形态的顺序,检出限以砷计是0.8μl、0.2μl、0.4μl和0.4μg/L。湖水样及市售矿泉水样的加标回收率为93.2％～107.5％。给出上述水样中砷形态的分析结果。     

First order absolute moment of Meyer-König and Zeller operators and their approximation for some absolutely continuous functions

A sharp estimate is given for the first order absolute moment of Meyer-König and Zeller operators M _n . This estimate is then used to prove convergence of approximation of a class of absolutely continuous functions by the operators M _n . The condition considered here is weaker than the condition considered in a previous paper and the rate of convergence we obtain is asymptotically the best possible.     

误差扩散法设计用于惯性约束聚变驱动器的色分离光栅-光束采样光栅集成元件

针对多次曝光法制作集成衍射光学元件时存在的加工制作复杂,会引入较大的对位误差等问题,基于计算全息中的误差扩散编码原理及部分相干光成像理论,提出采用误差扩散编码方法来设计用于制作浮雕结构集成元件的编码掩模的新方法。给出了利用误差扩散法设计的色分离光栅-光束采样光栅(CSG-BSG)集成元件编码掩模,模拟计算了经部分相干成像系统后的空间像光强分布,并与理想的集成元件面形进行了比较。结果表明,校正后均方差为7.5%,体积偏差为10.2%。     

Organic pH Buffer for Dendrite-Free and Shuttle-Free Zn-I2 Batteries

Aqueous Zn-Iodine (I₂) batteries are attractive for large-scale energy storage. However, drawbacks include, Zn dendrites, hydrogen evolution reaction (HER), corrosion and, cathode “shuttle” of polyiodines. Here we report a class of N-containing heterocyclic compounds as organic pH buffers to obviate these. We evidence that addition of pyridine /imidazole regulates electrolyte pH, and inhibits HER and anode corrosion. In addition, pyridine and imidazole preferentially absorb on Zn metal, regulating non-dendritic Zn plating /stripping, and achieving a high Coulombic efficiency of 99.6 % and long-term cycling stability of 3200 h at 2 mA cm⁻², 2 mAh cm⁻². It is also confirmed that pyridine inhibits polyiodines shuttling and boosts conversion kinetics for I⁻/I₂. As a result, the Zn-I₂ full battery exhibits long cycle stability of >25 000 cycles and high specific capacity of 105.5 mAh g⁻¹ at 10 A g⁻¹. We conclude organic pH buffer engineering is practical for dendrite-free and shuttle-free Zn-I₂ batteries.     

Correlation of grain boundary extra free volume with vacancy and solute segregation at grain boundaries: a case study for Al

Grain boundary extra free volume (GB EFV) can be considered as fundamental microstructural parameter for polycrystalline or nano-crystalline materials. Here, we present a systematic first principles study on a group of representative symmetric tilt grain boundaries of Al with various EFVs subjected to vacancy formation and Mg segregation. All grain boundaries were constructed using the coincident site lattice (CSL) and the structural unit (SU) models. It was found that the SU model is superior to the CSL in describing FCC-Al GBs, the same as we previously revealed for BCC-Fe. The predicted relation between GB misorientation angle and EFV, and the predicted EFV criteria for a stable GB, both agree with available experimental observations. Vacancy formation and Mg segregation show stronger preference to those GBs with high EFV values, due to the resultant high levels of atomic disorder. These findings not only provide a new, atomistic perspective on the significance of EFV, but also suggest a viable means of predicting GB properties based on direct experimental characterisation of GB EFVs.