Preparation and evaluation of solid-phase microextraction fiber based on molecularly imprinted polymers for trace analysis of tetracyclines in complicated samples

Molecularly imprinted polymer (MIP) is widely used in many fields because of its characteristics of high selectivity, chemical stability and easy preparation. To enhance the selectivity and applicability of solid-phase microextraction (SPME), a novel MIP-coated SPME fiber was firstly prepared by multiple co-polymerization method with tetracycline as template. It could be coupled directly to high-performance liquid chromatography (HPLC) and used for trace analysis of tetracyclines (TCs) in complicated samples. The characteristics and application of the fibers were investigated. The electron microscope provided a crosslinked and porous surface, and the average thickness of the MIP coating was 19.5 microm. Compared with the non-imprinted polymer (NIP) coated fibers, the special selectivity to tetracycline and structure-similar oxytetracycline, doxycycline, chlortetracycline were discovered with the MIP-coated fibers. The adsorption and desorption of TCs with the MIP-coated fiber could be achieved quickly. A method for the fluorimetric determination of four TCs by the MIP-coated SPME coupled with HPLC was developed. The optimized extraction conditions such as extraction solvent, desorption solvent, and stirring speed were studied. Linear ranges for the four TCs were 5.00-200 microg/L and detection limits were within the range of 1.0-2.3 microg/L. The method was applied to simultaneous multi-residue analysis of four TCs in the spiked chicken feed, chicken muscle, and milk samples with the satisfactory recoveries.     

Highly sensitive hydrogen peroxide sensor based on a glassy carbon electrode modified with platinum nanoparticles on carbon nanofiber heterostructures

We are presenting a sensor for hydrogen peroxide (H₂O₂) that is based on the use of a heterostructure composed of Pt nanoparticles (NPs) and carbon nanofibers (CNFs). High-density Pt NPs were homogeneously loaded onto a three-dimensional nanostructured CNF matrix and then deposited in a glassy carbon electrode (GCE). The resulting sensor synergizes the advantages of the conducting CNFs and the nanoparticle catalyst. The porous structure of the CNFs also favor the high-density immobilization of the NPs and the diffusion of water-soluble molecules, and thus assists the rapid catalytic oxidation of H₂O₂. If operated at a working voltage of −0.2 V (vs. Ag/AgCl), the modified GCE exhibits a linear response to H₂O₂ in the 5 μM to 15 mM concentration range (total analytical range: 5 μM to 100 mM), with a detection limit of 1.7 μM (at a signal-to-noise ratio of 3). The modified GCE is not interfered by species such as uric acid and glucose. Its good stability, high selectivity and good reproducibility make this electrode a valuable tool for inexpensive amperometric sensing of H₂O₂.

The Pt NPs/CNF heterostructure-based H₂O₂ sensor synergizes the advantages of both the conducting carbon nanofibers and the nanoparticle catalyst. The 3D structure of the nanofibers favor high density immobilization of the nanoparticles and penetration by water-soluble molecules, which assists the catalyic oxidation of H₂O₂. The sensor shows outstanding performance in terms of detection range, detection limit, response time, stability and selectivity.

     

高耸建筑物定向爆破倾倒时的后座及其对策

高耸建筑物定向爆破倾倒时,对周围保留建筑物、设施等的安全性产生影响的危害效应之一是后座问题。研究和探讨后座现象以及提出预防措施,对高耸建筑物在有限坍塌范围的复杂环境中,爆破拆除时安全性预测及合理选择爆破参数、确保良好的爆破效果将有很大帮助。本文通过对不同类型的高耸建筑物。文中分为两类:一类是筒式支撑的烟囱、水塔等;另一类是钢筋混凝土框架结构或砖混楼房、框架支撑的水塔等)在定向爆破倾倒过程中个同阶段的力学分析,较全面地讨论了后座产生的原因、现象及可能出现的后座范围。     

Pd单原子/团簇高效催化铃木偶联反应

铃木偶联反应是合成聚烯烃、苯乙烯和联苯衍生物等功能性有机化合物的有力工具,广泛应用于精细化工、制药和生化工业领域.钯(Pd)基催化剂是目前性能最好的铃木偶联反应催化剂,但钯的低丰度和高成本限制了其大规模应用.因此,提高Pd原子的利用效率,降低Pd用量至关重要.减小金属纳米粒子的尺寸,使其成为小团簇甚至孤立的金属原子是实...     

芴-噁二唑类聚合物的合成及光谱特性

通过缩聚反应,制得了高分子量的线型和超支化的芴-噁二唑类聚合物．它们均可溶于常用的有机溶剂。在固态薄膜时,它们的紫外-可见光吸收光谱在大约398nm和376nm处有两个强的吸收峰。它们的薄膜PL光谱在蓝光波长范围内有强发射峰,薄膜PL效率约为16％。电化学测试显示它们的的LUMO能级比芴的均聚物高,而与钙、镁这样典型的阴极材料的功函数较接近．这表明此类聚合物具有较好的电子注入和传输性能。     

多刚体系统分离策略及释放动力学研究

紧密连接的多刚体系统可在脱离运载航天器后在轨自主分离,无需多次利用航天器发射装置或在航天器中安装多个发射装置进行分离释放,从而有效提高运载航天器空间利用率, 简化分离释放操作和降低碰撞风险.本文针对多刚体系统的在轨分离释放问题, 研究在轨分离策略及释放过程动力学.首先, 考虑刚体相对运动及姿态变化,基于虚功原理及自然坐标方法建立单个刚体的动力学模型.考虑多刚体系统在轨分离释放阶段的轨道运动和连接约束变化,计入分离时刚体间的相互作用,利用拉格朗日乘子法获得含连接约束的非线性动力学模型. 考虑到实际工程应用,在多刚体系统分离释放阶段,通过安装在刚体间每个接触表面4个角上的弹射装置实现自主分离. 其次,为保证分离过程中刚体之间无碰撞发生, 规划了多刚体系统的分离时序,并基于不同弹射方向及分离顺序设计了两种分离释放方案. 最后,通过算例研究分析了在轨分离释放过程中刚体的非线性动力学行为,验证了分离释放方案的有效性.      

Electrochromic Two-dimensional Covalent Organic Framework with a Reversible Dark-to-transparent Switch

Electrochromic(EC)materials with a dark-to-transmissive switch have potential applications in optical communications,infrared wavelength detectors for spacecraft,and infrared camouflage coatings.Recently,Yu et al.proposed an innovative low-voltage dark-to-transparent switchable electrochrome based on a donor-acceptor two-dimensional covalent organic framework(COF)material.The compound can be facilely processed in a large-area thin film,which allows for the wide applications in smart displays,windows,and clothing.This work has been published online in Nature Communications on November 2nd,2020.     

Ice as Solid Electrolyte To Conduct Various Kinds of Ions

Water, considered as a universal solvent to dissolve salts, has been extensively studied as liquid electrolyte in electrochemical devices. The water/ice phase transition at around 0 °C presents a common phenomenon in nature, however, the chemical and electrochemical behaviors of ice have rarely been studied. Herein, we discovered that the ice phase provides efficient ionic transport channels and therefore can be applied as generalized solid‐state ionic conductor. Solid state ionic conducting ices (ICIs) of Li⁺, Na⁺, Mg²⁺, Al³⁺, K⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺, frozen from corresponding sulphate solutions, exhibit ionic conductivities ranging from ≈10^?7 S cm^?1 (Zn²⁺) to ≈10^?3 S cm^?1 (Li⁺) at temperatures spanning from ?20 °C to ?5 °C. The discovery of ICIs opens new insight to design and fabrication of solid‐state electrolytes that are simple, inexpensive, and versatile.     

Generalized Picard—Fuchs Operators From Whitham Hierarchy in $${\mathcal N} = 2$$N=2 Supersymmetric Gauge Theory with Massless Hypermultiplets

Theoretical and Mathematical Physics - Using the Whitham hierarchy, we obtain the Picard—Fuchs equations in$${\mathcal N} = 2$$supersymmetric Yang—Mills theory for a classical gauge...     

基于人工智能和互联网时代的化合物毒性预测综述

随着商品中所含各种化合物的不断使用,人们日益关注其对人类及生态环境的安全危害。在过去的几年里,通过计算方法预测化合物毒性已经显示出极大的潜力。在此,总结了常用的机器学习和深度学习算法在建立毒性预测模型上的优缺点,并系统回顾了近三年发表的可免费访问的毒性预测网络服务器。此外,还讨论了基于人工智能和互联网时代下毒性预测所面临的机遇和挑战。希望指导人们合理的选择算法和网络服务器进行建模及化合物毒性评估。