Enantioselective Addition of Iodine Azide to α,β-Unsaturated Carboxylic Acid Derivatives

The addition of iodine azide to chiral conjugated N-enoyl-sultam or α,β-unsaturated N-acyloxazolidinones generated two asymmetric centers at C(α) and C(β) with high π-face differentiation and regioselectivity. The diastereomerically pure product was easily obtained by crystallization with purity up to 94% de. The structure of 2a was determined by X-ray diffraction analysis which also indicated that B and 4 are reactive conformations.     

The RS-.HSR Hydrogen Bond: acidities of alpha,omega-dithiols and electron affinities of their monoradicals

Gas-phase acidities (deltaGo(acid)) have been measured for 1,2-ethanedithiol, 1,3-propanedithiol, and 1,4-butanedithiol, using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Adiabatic electron affinities (EAs) of the thiolate monoradicals of these compounds were assigned from electron photodetachment spectra of their corresponding thiolate monoanions, acquired using a cw-ICR. The dithiols exhibit enhanced acidities (up to 8.7 kcal/mol in deltaGo(acid)) and greater EAs (up to 6.7 kcal/mol) than analogous monothiol species. These differences are attributed to an intramolecular RS-.HSR hydrogen bond in the thiolate anion. Considerations of the RO-.HOR hydrogen bond in monoanions of alpha,omega-diols and in the [CH(3)O-.HOCH(3)] complex anion suggest that the RS-.HSR hydrogen bond provides up to 9 kcal/mol extra stabilization.     

Theoretical study of the effect of frit quality on chromatography using computational fluid dynamics

Summary Frits at both ends of a chromatographic column, especially for a preparative column, have significant influence on the flow distribution within the column and thus the column efficiency. However, frits have received little attention from chromatographers in the past. Here a theoretical study was conducted with the aid of CFD software FLUENT to investigate the effect of frits on the performance of homogeneous and heterogeneous chromatographic columns. A dimensionless number,FQ, was applied to characterize frit quality. This study visualized how frit quality affects the flow distribution and the concentration band, the shape of eluted pulse at the colum exit and column efficiency. Simulation results show that the development length of the flow distribution is related toFQ but has nothing to do with the packing heterogeneity. The curvature of the concentration band in a column depends onFQ and packing quality. This study shows column efficiency can be improved significantly by increasingFQ and/or frit permeability.     

Isoochotensine,a New Spirobenzyusoquinoline Alkaloid from: Corydalis Ochotensis Turcz

Separation of the phenolic fraction of Corydalis ochotensis afforded a new spirobenzylisoquinoline alkaloid, isoochotensine ( 1 ) and three known alkaloids, ochotensine ( 3 ), cheilanthifoline ( 7 ), and lienkonine ( 9 ) as their acetyl derivatives together with a known nonphenolic alkaloid, ochotensimine ( 5 ). Their structures were elucidated by the spectral data.     

Comparative Study on the Structure of Water in Reverse Micelles Stabilized with Sodium Bis(2-ethylhexyl) Sulfosuccinate or Sodium Bis(2-ethylhexyl) Phosphate in n-Heptane

The microstructure of water solubilized in H(2)O/surfactant/n-heptane ternary systems has been investigated by employing (1)H-NMR and FT-IR spectroscopic techniques. Two reverse micellar systems were prepared and studied, i.e., sodium bis(2-ethylhexyl) sulfosuccinate in n-heptane (H(2)O/AOT/n-heptane) and sodium bis(2-ethylhexyl) phosphate in n-heptane (H(2)O/NaDEHP/n-heptane). (1)H-NMR data showed that the chemical shift of water protons for the AOT and NaDEHP reverse micelles varied downfield and upfield, respectively, with an increase of the water content. The opposite shift directions with increasing water content are interpreted as due to a composition change of the solubilized water associated with head-groups and sodium counterions in reverse micellar systems. On the basis of deconvolution results of FT-IR spectra, a four-component model is proposed to interpret the FT-IR and (1)H-NMR results. Copyright 2000 Academic Press.     

基于轻量化深度学习网络的数字仪表识别

数字式仪表常用于变电站、工厂等生产环境,是一种直观的设备监测仪器。然而当前数字式仪表的读取方式还依赖于人工巡检,手动记录等,这些传统的巡检方式来监测设备的运行状态大大降低了巡检效率。为了实现传统行业的数字化转型,本文提出基于轻量化深度学习的数字仪表识别方法,通过改进的YOLOv5的目标检测框架,针对数字仪表目标区域在整张图片大小不一致的情况,提出对于感兴趣区域（ROI）的迭代目标检测方法,首次检测将感兴趣区域进行检测并切割统一到相同的尺度,随后迭代检测网络针对感兴趣区域内的字符进行检测并分类,以达到精确读数的目的。为提升多尺度检测性能,本文采用Res2Net模块主干网络中的的残差模块。采用GIoU取代通用的IoU作为位置损失函数加速模型训练效果的收敛。实验表明,改进后的框架实现了99.62%的准确率和99.55%的召回率,相比基线网络分别提升了12.72%和5.85%。通过将框架在边缘计算平台上的终端部署,在实际生产中取代了人工巡检,实现了商业化运行。     

“新文科”建设背景下经济学人才培养的路径研究

“新文科”建设是新时代对人文社会科学教育提出的新要求。如何在“新文科”理念下培养经济学人才,是中国经济学建设的一个重要课题。首先,从时代性、战略性、创新性、交融性和发展性5个特征维度阐释“新文科”建设的内涵;其次,探讨“新文科”建设背景下经济学人才培养存在的主要问题;最后,提出经济学人才培养需要持续优化经济学专业培养目标和培养方案;加强经济学的课程思政教育,推动济学与其他学科的交叉融合,推动经济学人才培养模式创新以及培养学生解决问题的能力等路径。研究结果可为培养适应新时代发展的经济学人才提供理论参考。     

When does gradient Ricci soliton have one end?

Annals of Global Analysis and Geometry - In this paper, we study a problem of finding compact hypersurfaces of prescribed mean curvature with free boundary in a ball. We transform the problem to an...     

用于焊缝跟踪的调制式红外光学传感器

叙述了一种以脉冲调制的红外光束为信号光源的焊缝跟踪传感器。通过对接 收信号的滤波及“自适应消噪”处理,可以有效地克服电弧光的干扰;利用光源的脉冲 驱动特性,加大了瞬时信号功率,改善了光学传感器对工件表面的适应性。传感器结构简 单、体积小、灵敏度高、能同时实现对焊缝在水平及高度两个方向的自动跟踪在埋弧 及明弧自动焊中均能准确地跟踪。     

钼对低合金钢硝酸盐体系应力腐蚀的影响

以高风温热风炉用钢的沿晶应力腐蚀开裂问题为背景,研究了Ｍｏ对低合金钢在硝酸盐溶液中的应力腐蚀行为。结果表明,低合金钢中加入合金元素将使钢中贝氏体和／或珠光体含量增大,从而提高了材料的稳定性和抗ＳＣＣ耐蚀性。提出了低合金钢／硝酸盐溶液体系的“温度－钼含量－ＳＣＣ图”。