“高分子材料合成创新实验”线上教学探索与实践

依托"QQ分享屏幕+视频直播"平台,通过"在线讲授理论环节""开发居家替代实验""游戏式"实验操作和"虚拟仿真实验"相结合的形式,开展了融"理论+实践""虚拟+现实"为一体的高分子材料合成创新实验在线教学,同时也是一次很好的劳动教育。这些探索和实践有望为疫情期间化学类实验课程的在线教学提供一定的借鉴和参考。     

有机化学在线课堂教学实践探索

2020年春季学期受到新冠肺炎疫情的影响,全国各地高校的教学工作无法正常开展。我校积极响应教育部提出的"停课不停教、停课不停学"要求,利用"雨课堂"和"腾讯会议"等教学软件对学生进行在线课堂教学。本文以有机化学教学为例,介绍了在线课堂教学的实施过程和教学效果。针对在线课堂教学的特殊性,改变教学模式,确保教学工作正常有序进行。     

Use of large-volume sample stacking in on-line solid-phase extraction-capillary electrophoresis for improved sensitivity

We present a new system for the sensitive analysis of cephalosporins by CE using both on-line SPE and large-volume sample stacking (LVSS). Sample volumes of 250 muL were loaded onto the SPE microcolumn which was then desorbed with 426 nL of ACN. The SPE elution plug was injected into the CE system via an in-line valve interface filling approximately 60% of the volume of the separation capillary. Subsequently, LVSS was performed by applying a voltage of -5 kV, which resulted in the simultaneous removal of the elution solvent and the preconcentration of the analytes in a narrow zone. This way the amount of analyte loaded into the capillary could be considerably increased without serious loss of CE separation efficiency. LODs for cefoperazone and ceftiofur were in the ng/L range which represents an improvement of a factor of 8450 and 11 450 when compared with direct CE injection. The cephalosporin test compounds presented a good linear response (corrected peak area) between 0.5 and 10 mug/L with correlation coefficients higher than 0.995. The final method is compared with previously reported LVSS-CE and SPE-CE systems for the analysis of cephalosporins.     

Simultaneous determination of anthracyclines and taxanes in human serum using online sample extraction coupled to high performance liquid chromatography with UV detection

An online SPE‐LC method that can determine both anthracyclines and taxanes simultaneously in human serum samples is reported. The entire method of extraction, separation and UV detection was achieved online by column switching between an SPE column (Biotrap 500 (20×4 mm)) and an analytical column (Zorbax XDB C18, 150×4.6 mm, 5 μm) with a 23 min total cycle time. The method is linear (r²>0.998) over the range of 0.5–25 μg/mL. The analytes of interest are retained on the SPE column with good recovery (84–117%), while proteins and other serum components elute to waste. This online clean‐up is much faster (150 s) and less manual than traditional off‐line extraction methods. Using 0.1 mL spiked serum samples, the LOQ was 0.5 μg/mL. Intra‐ and inter‐day precision were acceptable (≤15% RSD) at and above the LOQ. The method was applied to the analysis of serum samples from patients undergoing chemotherapy with these agents.     

The structural evolution of an online discussion network

A discussion network is an important kind of social network, and it has been researched by many scholars in recent years. In this paper, we mainly studied its structural evolution based on an empirical study of a famous online discussion that happened in China in 2008. We found that the scale growth of the network shows an S shape, the degree distribution represents the power law in the first halfway, and the network shows a degree of disassortativity characteristic. We also classified the most active participants into different groups by their opinions and studied the structural evolution of opposite groups. It was observed that the evolution of nodes in each group were very similar, but the evolution of densities were obviously different. Specifically, we found that the most active participants preferred to converse with those belonging to the opposite groups at the beginning and tended to converse with anybody regardless of group as the discussion network grew. In the paper, these evolution patterns are revealed, and future lines of research are also considered.     

Mass spectrometric real-time monitoring of enzymatic glycosidic hydrolysis, enzymatic inhibition and enzyme complexes

The mass spectrometric development of an enzymatic assay resulting in enzymatic activity, its reaction pathway and its dissociation constant are described for the first time within a single experiment. The method combines the performance of a mass spectrometry-compatible enzyme assay with the direct detection of specific enzyme complexes using hen egg white lysozyme as a model. The continuous liquid-flow technique applied, when hyphenated with electrospray ionization (ESI)-time-of-flight (ToF)-mass spectrometry (MS), permitted the simultaneous detection of several substances involved in product screening as well as the direct observation of dissociation constants. Dissociation constants for the product inhibitor N, N', N'-triacetylchitotriose were calculated using a Scatchard plot (12 x 10(-6) M) and the law of mass action (18-24 x 10(-6) M), and these are in good agreement with constants obtained in earlier mass spectrometric (6-18 x 10(-6) M) or spectroscopic (6-8 x 10(-6) M) studies. Finally, the enzymatic hydrolysis of glycosidic substrate was monitored by ESI-ToF-MS in the presence of various inhibitors, thus leading to decreased activities in terms of their enzyme affinities. The associated inhibitor-enzyme complexes could be detected for up to lower micromolar K( d ) values.     

clever or smart: Strategies for the online target date assignment problem

In this paper, we consider the Online Target Date Assignment Problem (OnlineTDAP) for general downstream problems, where the downstream cost are nonnegative, additive and satisfy the triangle inequality.We analyze algorithm smart, which was introduced by Angelelli et al. [3] and give its exact competitive ratio depending on the number of requests. Since the obtained competitive ratio is at most we answer the question posed in Angelelli et al. [4] if smart has a competitive ratio strictly less than 2.Moreover, we introduce a new algorithm called clever and show that this strategy has a competitive ratio of 3/2. We show that this is asymptotically optimal by proving that no online algorithm can perform better than 3/2−ε.     

An adjustment scheme for nonlinear pricing problem with two buyers

We examine a contracting problem with asymmetric information in a monopoly pricing setting. Traditionally, the problem is modeled as a one-period Bayesian game, where the incomplete information about the buyers’ preferences is handled with some subjective probability distribution. Here we suggest an iterative online method to solve the problem. We show that, when the buyers behave myopically, the seller can learn the optimal tariff by selling the product repeatedly. In a practical modification of the method, the seller offers linear tariffs and adjusts them until optimality is reached. The adjustment can be seen as gradient adjustment, and it can be done with limited information and so that it benefits both the seller and the buyers. Our method uses special features of the problem and it is easily implementable.     

A revised approach for risk-averse multi-armed bandits under CVaR criterion

We study multi-armed bandit problems that use conditional value-at-risk as an underlying risk measure. In particular, we propose a new upper confidence bound algorithm and compare it with the state-of-the-art alternatives with respect to various definitions of regret from the risk-averse online learning literature. For each comparison, we demonstrate that our algorithm achieves either a strictly better or a comparable regret bound. Finally, we complement our theoretical findings by a numerical experiment to showcase the competitiveness of the proposed algorithm.     

Aqueous sec analysis of cationic polymers as gene carriers

Cationic polymers have been receiving much attention as non-viral gene vectors.The aqueous mobile phase was optimized in combination with Shodex OHpak SB columns for size-exclusion chromatography(SEC)analysis of disulfide-containing poly(ethylene imine)(PEI)derivatives used in gene delivery.Addition of acetonitrile in mobile phase was shown to be able to suppress the hydrophobic interactions between polymer analytes and the stationary phase.The absolute molecular weights and distributions of the cationic polymers were determined directly from online SEC-MALS(multi-angle light scattering)/RI(refractive index detector).The results demonstrate that a good SEC separation of disulfide-containing PEI derivatives used in gene delivery with little band broadening was achieved.