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261.
建设有深度、有难度、有挑战度的"金课",是每个教师都面临的挑战.本文以"电磁场工程应用"课程的"电导和接地电阻"为例,介绍其高阶课堂的构建过程.在课程教学中,采取线上线下混合式教学模式.在线下课程中,采取"思考"+"讨论"的"问号课堂",激发学生思考和讨论.采取适当"吊胃口"的方式,达到让学生"既疑又懂"的效果,尽量做到"思中学"、"做中学",培养学生主动学习和主动实践能力. 相似文献
262.
Yue Sun Zeshuai Yao Guangyu Wang Lisha Wang Prof. Min Bai Prof. Dr. Hu Shi 《Chemphyschem》2023,24(6):e202200710
Zn2+ is a very important factor in promoting the formation of amyloid beta (Aβ) aggregates and amyloid plaques. The Zn2+-bound Aβ species generate amorphous or low molecular-weight oligomers. However, it is a lack of studies to approach the starting structural features (dimerization) in Aβ nucleation processes with and without Zn2+, which is the key point in understanding Zn2+-induced nucleation mechanisms. To better understand the effect of concentration, structural properties, and the driving force, 14 independent replica exchange molecular dynamics simulations were performed in Aβ28 dimerization with and without Zn2+ (zAβ28) cooperation. Our scanning results show that the aggregation propensity is easier in Aβ28-Aβ28 and Aβ28-zAβ28 systems than zAβ28-zAβ28 system. In binding property, the Aβ28-Aβ28 model (−61.5 kcal mol−1) is stronger than zAβ28-zAβ28 (−26.6 kcal mol−1) and Aβ28-zAβ28 (−7.24 kcal mol−1) models. Further analysis confirmed that H13 and H14 residues play specific roles in the three systems. The key point is the orientation of N atom of the imidazole ring in histidine residues. Furthermore, we discovered different driving forces for each system. Our current study contributes to the understanding of how the Aβ28 dimer interacts with Zn2+, which could lead to new insights into Zn2+-induced nucleation mechanisms. 相似文献
263.
Linyan Yang Yamin Zong Lisha Yang Rui Lv Liyuan Jing Jifei Ma 《Journal of Coordination Chemistry》2017,70(12):2161-2173
One-pot solvothermal treatment of Co(NO3)2·6H2O, H2L (5-(3-methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-4-yl) isophthalic acid), and 4,4′-bipyridine (4,4′-bipy) in H2O/DMF (V/V = 1?:?1) yielded a cobalt-organic chain, [Co(L)(O)(H2O)2]n·1.25nH2O (1). Compound 1 as raw materials was calcined to obtain Co3O4, which could be confirmed by PXRD and SEM. Via the modification, Co3O4@SiO2-NH2 and Co3O4@SiO2-NH2-FA samples could be obtained. Compared to Co3O4@SiO2-NH2, Co3O4@SiO2-NH2-FA seems to have better peroxidase-mimetic properties. UV–vis results showed that optimal conditions of peroxidase-mimetic experiments were at 50°C in sodium acetate-acetic acid buffer (pH 3.6, 0.2 M), when the concentration of tetramethylbenzidine (TMB) was 0.2 mM. A concentration-dependent manner was shown between the concentration of glucose and absorbance in the measurement experiments for glucose. 相似文献
264.
报道了室温超声辐射下, 水相中通过乙酰乙酸甲酯、盐酸羟胺和芳香醛的三组分一锅反应, 合成了一系列3-甲基-4-芳亚甲基-异噁唑-5(4H)-酮衍生物. 在超声波辐射下, 参与反应的醛无论芳环上连有吸电子基或供电子基, 该一锅反应在室温下都能较好地进行; 对于α,β-不饱和醛、杂环芳醛以及二元芳醛与乙酰乙酸甲酯、盐酸羟胺的一锅反应也能在室温下顺利进行, 获得中等以上的收率. 产物的结构通过元素分析, IR, 1H NMR及单晶解析表征. 该方法具有操作简单和环境友好等优点. 相似文献
265.
钐钆富集物中钐、钆的同时测定 总被引:4,自引:0,他引:4
本文初步探讨了稀土的DBC偶氮刖络合物与CyDTA取代反应机理。对于不同显色剂和取代剂进行了选择,建立了测量钐、钆的最佳反应体系,用速差动力分析法进行了钐钆富集物中钐、钆的同时测定。速差动力分析结果与ICP发射光谱法结果相符。本法测定钐、钆相对含量在1:2-4:1范围,误差约为10%。 相似文献
266.
微波消解-电感耦合等离子体质谱测定大气颗粒物中痕量稀土元素 总被引:10,自引:0,他引:10
研究了电感耦合等离子体质谱(ICP-MS)测定大气颗粒物中痕量稀土元素(REEs)的分析方法。在微波条件下,采用HNO3 + H2O2(3 + 1)混合介质能快速而有效地分解颗粒物样品。详细讨论了测定稀土元素的质谱干扰。通过分析不同粒径颗粒物中稀土元素的含量,初步探讨了大气颗粒物中稀土元素的分布规律。结果表明:颗粒物试样的粒径越小,稀土元素的含量越高。分析方法的检出限为0.7~2.8pg/mL,用于大气颗粒物国际标样(SRM 1648)中稀土元素分析,结果与推荐值有良好的一致性。 相似文献
267.
衍生化气相色谱-质谱法测定玩具和食品接触材料中双酚A 总被引:2,自引:0,他引:2
建立了玩具和与食品接触的材料中双酚A的衍生化气相色谱-质谱(GC-MS)检测方法。通过索氏萃取富集样品中的双酚A,与乙酸酐反应,终产物用GC-MS进行测定。优化了衍生化时间、衍生化试剂用量等衍生化条件。在最佳条件下,双酚A衍生物稳定且峰形良好,在0.05~50 mg/L范围内,相关系数(r2)在0.999以上。在0.05、1.00、10.00 mg/kg 3个添加水平下,双酚A的加标回收率为80%~93%,相对标准偏差(RSD)均小于3.7%;检出限(以信噪比(S/N)=3计)为10 μg/kg。该方法精密度好、回收率高,可用于玩具和食品接触材料中双酚A的定量检测。 相似文献
268.
The zeolitic imidazolate framework‐8 (ZIF‐8) was successfully synthesized using ionic liquids as structure‐directing agent under microwave irradiation. Ionic liquids are green solvents with low vapour pressure and good thermal stability. They are appropriate templates for microporous materials and ideal microwave absorbers. The microwave‐assisted ionothermal synthesis applied in this paper was expected to be a promising method for the preparation of microporous materials. Results showed that the as‐synthesized samples (300–500 nm in diameter) could be synthesized in a short time (60 min) and possessed regular morphology, stable structure and high thermal stability (up to 720°C in argon atmosphere). Nitrogen adsorption‐desorption test illustrated that samples produced by microwave heating had a higher surface area. Carbon dioxide adsorption test indicated that the samples synthesized by microwave heating had better carbon dioxide adsorption ability than those by conventional heating. 相似文献
269.
Disulfide‐centered star‐shaped polypeptide‐PEO block copolymers for reduction‐triggered drug release
Xiao Chang Lisha Liu Yanfei Guan Chang‐Ming Dong 《Journal of polymer science. Part A, Polymer chemistry》2014,52(14):2000-2010
Disulfide‐centered star‐shaped poly(ε‐benzyloxycarbonyl‐l ‐lysine)‐b‐poly(ethylene oxide) block copolymers (i.e., A2B4 type Cy‐PZlys‐b‐PEO) were synthesized by the combination of ring‐opening polymerization and thiol‐yne chemistry. Their molecular structures and physical properties were characterized in detail by FTIR, 1H NMR, gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscope. Despite mainly exhibiting an α‐helix conformation, the inner PZlys blocks within copolymers greatly prohibited the crystallinity of the outer PEO blocks and presented a liquid crystal phase transition behavior in solid state. These block copolymers Cy‐PZlys‐b‐PEO self‐assembled into nearly spherical micelles in aqueous solution, which had a hydrophobic disulfide‐centered PZlys core surrounded by a hydrophilic PEO corona. As monitored by means of DLS and TEM, these micelles were progressively reduced to smaller micelles in 10 mM 1,4‐dithiothreitol at 37 °C and finally became ones with a half size, demonstrating a reduction‐sensitivity. Despite a good drug‐loading property, the DOX‐loaded micelles of Cy‐PZlys‐b‐PEO exhibited a reduction‐triggered drug release profile with an improved burst‐release behavior compared with the linear counterpart. Importantly, this work provides a versatile strategy for the synthesis of the disulfide‐centered star‐shaped polypeptide block copolymers potential for intracellular glutathione‐triggered drug delivery systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2000–2010 相似文献
270.