Size separation of graphene oxide using preparative free‐flow electrophoresis

Graphene oxide nanosheets often bear a wide size distribution. However, it is critical to have nanosheets with narrow size distribution for their unique size‐dependent physiochemical properties, and nanosheets with a narrow size distribution are the cornerstones for application. Therefore, efficient separation methods of graphene nanosheets have been given considerable attention in many scientific areas recently. Free‐flow electrophoresis is extensively used in the separation and purification of biological molecules with continuous flow separation. The charged graphene oxide nanosheets to some extent are very close in size to biological molecules and share similarity in motion behavior in an electric field. Thus, in the present work, we present a new and simple means to separate graphene oxide nanosheets into more mono‐dispersed size groups by using the free‐flow electrophoresis technique. By optimizing the separation conditions, we were able to obtain graphene oxide sheets with narrow size distribution. The separated samples were characterized by atomic force microscopy, and the size measurements were made by using the software “Image Pro Plus.” In addition, a brief discussion is also given into the theoretic background of the separation of graphene oxide according to the size by the technique of preparative free‐flow electrophoresis.     

理论设计ZnTiS3化合物光电性能的第一性原理计算

根据实验上合成LiNbO₃(LN)构型的ZnTiO₃铁电化合物,基于第一性原理的方法设计研究了化合物LN-ZnTiS₃(LN构型)的特性。计算结果表明LN-ZnTiS₃化合物满足力学稳定条件。根据化学势平衡相图分析,LN-ZnTiS₃在常压下不会形成稳定结构,但施加外部压力可以形成稳定结构。电子态密度和带隙的计算结果表明,LN-ZnTiS₃的价带顶(VBM)主要由S-p轨道组成,导带底(CBM)则由Ti-d轨道组成,硫原子的替代可以促进体系费米能级以上的电子状态大幅度下降到较低的能级,从而减小LN-ZnTiS₃的带隙。LN-ZnTiS₃的带隙计算值为1.04 eV,可以促进可见光的吸收,可以看出LN-ZnTiS₃是一种潜在的高效率光伏材料。     

Aggregation‐Induced Emission Active Probe for Light‐Up Detection of Anionic Surfactants and Wash‐Free Bacterial Imaging

Anionic surfactants are widely used in daily life and industries, but their residues can cause serious damage to the environment. The current detection methods for anionic surfactants suffer from various limitations and a new detection strategy is highly desirable. Based on 2‐(2‐hydroxyphenyl)benzothiazole fluorogen with aggregation‐induced emission characteristics, we have developed a fluorescent probe HBT‐C₁₈ for selective and sensitive detection of anionic surfactants. By in situ formation of catanionic aggregates or micelles with anionic surfactants, the emission intensity of the HBT‐C₁₈ probe can increase with increasing keto/enol emission ratio through restriction of intramolecular motion and excited‐state intramolecular proton‐transfer mechanisms. The probe can also be used for wash‐free imaging of bacteria enveloped by a negatively charged outer membrane. The results of this study provide a new strategy for sensitive detection of anionic surfactants and wash‐free bacterial imaging.     

一种新的股市风险度量指标及其应用

本文充分利用了多元统计分析的技术 ,提出了用收益的方差协方差矩阵引出的特征根作为股市风险的一种量度指标 ,在此基础上 ,推导出了第一特征向量的分块结构公式 ,并给出了具有实际意义的解释。本文的思想及技术路线 ,为以后对股市风险定量研究及开发金融工程产品打开了新的研究视野     

Global Solution for Massive Maxwell-Klein-Gordon Equations

We derive the asymptotic properties of the mMKG system (Maxwell coupled with a massive Klein-Gordon scalar field) in the exterior of the domain of influence of a compact set. This complements the previous well-known results, restricted to compactly supported initial conditions, based on the so-called hyperboloidal method. That method takes advantage of the commutation properties of the Maxwell and Klein-Gordon equations with the generators of the Poincaré group to resolve the difficulties caused by the fact that they have, separately, different asymptotic properties. Though the hyperboloidal method is very robust and applies well to other related systems, it has the well-known drawback of requiring compactly supported data. In this paper we remove this limitation based on a further extension of the vector field method adapted to the exterior region. Our method applies, in particular, to nontrivial charges. The full problem can then be treated by patching together the new estimates in the exterior with the hyperboloidal ones in the interior. This purely physical space approach introduced here maintains the robust properties of the old method and can thus be applied to other situations such as the coupled Einstein Klein-Gordon equation. © 2019 Wiley Periodicals, Inc.     

Rational design and first-principles studies of phenothiazine-based dyes for dye-sensitised solar cells

We investigate a series of phenothiazine (PT)-based organic dyes by adopting different donors and different donor substitution positions as photosensitisers for application in dye-sensitised solar cells (DSSCs). First-principles calculations reveal systematic improvements of key parameters including light-harvesting efficiency, redox potential, electron injection and non-linear optical properties with donor substitutions. The non-planar structure also suppresses dye aggregation and reduces the rate of internal charge recombination. In particular, photosensitisers with combination of donor functional groups show outstanding performance on these key parameters. This study demonstrates that PT-based dyes with the studied donor groups could serve as excellent candidates of photosensitisers for future DSSC applications.     

Descriptions of equivalence of O-connectivity

We first study some properties of the subspace, and investigate into the relationship of separation between a fuzzy topological space (fts) and its subspace. Then we obtain the equivalence conditions for O-connectivity. The results on O-connectivity and separation are very similar to those in general topology. Finally we discuss the relationship of connectivity between an O-connected set A in the fts (X, ω ($\text{T}$)) induced by the crisp topological space (X, $\text{T}$) and the crisp set A₀ (=supp A) in (X, $\text{T}$).     

Vibrational recognition of hydrogen-bonded water networks on a metal surface

The adsorption of water on Pt(111) surface has been studied with ab initio molecular dynamics simulation. Both the energetics and vibrational dynamics indicate the existence of a well-ordered molecular bilayer on this surface. This conclusion is in contrast to the recent result of water on Ru(0001) surface, but agrees with available experiments. In addition, our calculation identifies two different hydrogen bonds in the bilayer. Both can be directly recognized from the vibrational spectra of the OH stretch modes.     

Two-dimensional hydration shells of alkali metal ions at a hydrophobic surface

We study the hydration shell formation of alkali metal ions at a graphite surface. Two-dimensional shell structures are found in the initial stage of hydration, in contrast to the three-dimensional structures in bulk water and clusters. Comparison of vibrational spectra with experiments identifies the shell structures and the thermally induced transition from the first to the second shell. We also found intriguing competition between hydration and ion-surface interaction, leading to different solvation dynamics between K and Na. Implications of these results in ionic processes at interfaces are elaborated.     

激光外差探测超声位移的原理、方法和实验

本文介绍了激光外差探测超声位移的原理，用布喇格声光衍射盒作为激光移频，锁相环作调相信号解调等方法组成的外差干涉探测装置和实验结果，并分析了空间准直性对激光外差干涉信噪比的影响以及减小探测极限和抑制噪声的途径。