A universal route with fine kinetic control to a family of penta-twinned gold nanocrystals

Some of the major difficulties hindering the synthesis of different types of colloidal nanocrystals are their complex synthetic methods and the lack of a universal growth mechanism in one system. Herein, we propose a general strategy of kinetically controlled seed-mediated growth to synthesize a family of penta-twinned gold nanocrystals. Specifically, different kinds of penta-twinned nanocrystals (truncated penta-twinned decahedra, truncated bipyramids, bipyramids, truncated bipyramids with tips, star-like penta-twinned nanocrystals, decahedra with concave edges, and decahedra) with tunable sizes and high purity were readily achieved in one system solely by tailoring the deposition kinetics of adatoms on different sites of decahedral seeds. The controllable deposition kinetics can be realized by changing the ratio of reductant/gold precursors (R), which dictates whether horizontal or vertical features along the 5-fold axis direction of Au decahedral seeds are produced. Additionally, the selective growth of a second metal (silver) on penta-twinned gold seeds can be reached through minor modification of R, which opens a new avenue for mechanistic investigation by visualizing the seed localization within the final particles. The present work demonstrates a general paradigm for the kinetic growth of penta-twinned crystals and would be extended to the synthesis of other families of nanocrystals.

We report the synthesis of linear ADPr oligomers of defined length up to a pentamer using an improved solid phase method. Binding study with human oncogenic helicase ALC1 shows that ADPr oligomers bind to ALC1 in a length-dependent manner.     

高效液相色谱-紫外光度法检测尿液和牛奶中多种头孢类抗生素

使用新型的亲水性较强的C16硅胶反相色谱柱,以水/磷酸缓冲液/乙腈为流动相,流速1mL/m in,在17m in内分离了头孢羟氨苄、头孢克洛、头孢氨苄、头孢拉定和头孢噻吩5种头孢类抗生素。分离后的化合物在紫外检测器上检测,检测波长270 nm,线性范围0.1~40 mg/L(r≥0.9993),5种化合物的检出限依次为9.7、6.9、5.6、6.4和4.9μg/L。该方法成功的应用于人尿液和牛奶中头孢类抗生素的检测,2 mg/L浓度水平的加标回收率在96.5%~105%之间。     

Local Stability of McKean–Vlasov Equations Arising from Heterogeneous Gibbs Systems Using Limit of Relative Entropies

A family of heterogeneous mean-field systems with jumps is analyzed. These systems are constructed as a Gibbs measure on block graphs. When the total number of particles goes to infinity, the law of large numbers is shown to hold in a multi-class context, resulting in the weak convergence of the empirical vector towards the solution of a McKean–Vlasov system of equations. We then investigate the local stability of the limiting McKean–Vlasov system through the construction of a local Lyapunov function. We first compute the limit of adequately scaled relative entropy functions associated with the explicit stationary distribution of the N-particles system. Using a Laplace principle for empirical vectors, we show that the limit takes an explicit form. Then we demonstrate that this limit satisfies a descent property, which, combined with some mild assumptions shows that it is indeed a local Lyapunov function.     

Nonlinear structural dynamics of a new sliding-mode triboelectric energy harvester with multistability

A new sliding-mode triboelectric energy harvester in the form of a cantilever beam with a tip mass that is acted upon by both magnetic and friction forces is modelled and simulated. A numerical scheme based on the trapezoidal rule with the second-order backward difference formula (TR-BDF2) method is introduced to solve the combined non-smooth mechanical and stiff electrical system. This is the first study of the structural dynamics of the sliding-mode triboelectric energy harvesting; additionally, a magnetic field that induces multistability is present. A comparison between the coupled and uncoupled electromechanical models suggests that the electrostatic force between the electrodes can be ignored, which makes the uncoupled model preferable in the dynamical analysis. The influence of the non-conservative force (the friction force) on the multistability of the system is investigated. It is found that the distribution of the multistability on the parametric plane changes even when a small amount of friction is involved, and the areas of bistability and tristability shrink while that of the monostability expands. A comparison among these three types of stability reveals the superiority of invoking bistability as it facilitates broadband energy harvesting. The excitation level plays an important role in inducing the snap-through motion (the interwell oscillation) by enabling the crossing of the energy barriers between wells. The increase in the friction shrinks the frequency band of interwell oscillations from high frequencies down to low frequencies on the discrete frequency sweep. An analysis of the basins of attraction finds that at low frequencies the bistable system can undergo only interwell oscillations, while the tristable system can merely experience intrawell oscillations. The basins can intermingle with each other in both bistable and tristable systems. Finally, an increase in the excitation level can break the basins into discrete pieces and/or points.

     

Influence on Emulsification in Binary Flooding of Oil Displacement Effect

As one of the important mechanisms of EOR for SP binary flooding, emulsification attracts much attention of researchers. But there have not yet unified methods or clear understandings of evaluation of the emulsion function on flooding system and emulsification's impact on enhanced oil recovery. A comprehensive evaluation method of emulsifying properties is established in this paper for the first time. It characterizes the emulsifying properties of different flooding system by using the emulsifying integrated index, and examines the corresponding core flooding results of different emulsifying properties. Results of Berea core test show that the flooding system runs better with a higher emulsifying composite index in cores whose permeability is 300 ～ 400 mD. When emulsifying integrated index increases from 23.9% to 80.2%, the corresponding oil displacement efficiency reaches 12%. When emulsifying integrated index is under the medium level of 50% or less, the SP flooding system efficiency increases rapidly with the index changes, then increases slowly. The influencing rule of emulsification of SP binary flooding is obtained in this paper, which is important to optimize the formulation of SP binary flooding system, provide an important basis and technical support for the design of field experiments and SP flooding promotion.     

化学催化葡萄糖异构化果糖

基于糖平台的生物炼制可以制备各种碳基化学品、材料和燃料。相较于葡萄糖和纤维素,果糖更容易高选择性地催化转化制备5-羟甲基糠醛等重要的生物质基平台分子,因此葡萄糖异构化果糖已经成为生物炼制过程中的重要反应步骤之一。本文详细介绍了葡萄糖经化学催化异构化果糖的反应机理,并基于异构化催化剂全面总结了近年来化学催化葡萄糖异构化果糖的研究进展。此外,本文在分析各种葡萄糖异构化催化剂及其催化作用的基础上,进一步对化学催化葡萄糖异构化果糖的未来研究方向进行了展望。     

Characterization of Remaining Oil After Polymer Flooding by Laser Scanning Confocal Fluorescence Microscopy

In the mid- to late period of oil field development, it is important to consider the microscopic distribution of remaining oil of the reservoir in time, for it is the foundation of enhanced oil recovery. Focusing on the present insufficient research status of microscopic distribution of remaining oil after polymer flooding, this article first put forward and developed a set of fluorescence microscope technology of frozen core analysis of remaining oil, and used this technology combined with laser confocal microscopic detection technology to study microscopic distribution rules of remaining oil before and after polymer flooding. Through comparison and analysis on the difference of microscopic distribution form of remaining oil, the experimental results show that polymer flooding has different effects on different types of remaining oil. Using this technology, analysis of many different distribution forms of remaining oil involving the same mode of occurrence in different layers, different parts of the same layer, and different types of the same layer can be more clearly distinguished. Using polymer flooding pertinently according to the different distribution form of remaining oil will make the use of polymer more efficiently and the recovery higher.     

Light‐Induced Ion Rectification in Zigzag Nanochannels

Ion transport through nanoporous systems has attracted broad interest due to its crucial role in physiological processes in living organisms and artificial bionic devices. In this work, a nanochannel system with a zigzag inner surface was fabricated by using a two‐step anodizing technique. The rectification performance of the zigzag channels was observed by I–V measurement in KCl solution. Unlike channels with asymmetric geometry, the mechanism was analyzed based on the “point effect” of charge distribution and “shape effect” of the zigzag channel. The current rectification ratio decreases from nearly 3.0 to 1.0 when the KCl concentration increased from 0.1 mm to 100 mm . The fabrication of different nanopore systems and exploration of novel mechanisms will help to develop biomimetic membranes for practical applications.     

Residues of four triazole fungicides in tobacco leaves under field condition and during curing

Residues of four triazole fungicides (triadimefon, myclobutanil, tebuconazole and difenoconazole) in tobacco leaves under field condition and during curing were investigated. Following extraction with acetonitrile, the samples were cleaned up by a Florisil solid phase extraction column, and then determined by gas chromatography–mass spectrometry in selected ion monitoring mode. The average recoveries of the four triazole fungicides were found in the range of 82.7–97.3% with relative standard deviations of 1.1–4.6% in green and cured tobacco leaves. The residues of triadimefon, myclobutanil, tebuconazole and difenoconazole in Shandong, Sichuan, Yunnan, Liaoning and Jiangxi were found in the range of 0.02–0.32 mg/kg, 0.41–4.93 mg/kg, 0.37–9.84 mg/kg and 0.25–4.85 mg/kg in cured tobacco leaves when measured 14 days after the last application. The residue levels of the four triazole fungicides in most cured tobacco samples were lower than that in green tobacco samples, indicating that high temperature degradation surpassed dehydration concentration during the curing process.