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关键词： Alpine grassland   Denitrifier   Grazing   Microbial functional genes   Nitrifier   Quantitative PCR  

摘要： Grazing can degrade grassland soil and increase nitrous oxide (N2O) emissions, but the underlying mechanism is poorly understood. We investigated the relationship of soil N2O emission with nitrifying enzyme activity (NEA), denitrifying enzyme activity (DEA), and the abundances of N2O-producing and N2O-reducing functional genes, in response to three grazing intensities (none, light, intensive) over two growing seasons on an alpine grassland on Kunlun Mountain in semi-arid North China. Compared to the non-grazed control, light and intensive grazing treatments increased the 2-yr total N2O emissions by 27.5% and 68.1%, respectively. Daily N2O flux rate correlated positively with soil water-filled pore space (WFPS), temperature, and dissolved organic carbon (DOC) but not with the abundances of nitrifiers (AOB, AOA, Nitrobacter-like nxrA), nitrate reducers (narG) and denitrifiers (nirS, nirK, and nosZ). These results suggest that soil environmental factors rather than nitrifier, N2O-producer and N2O-reducer abundances were more important in determining the grazing enhancement of N2O emissions from the alpine grassland in semi-arid areas. The abundance of AOB and Nitrobacter-like nxrA but not AOA correlated positively with NEA, indicating they are good indicators for the potential nitrification in this arid alpine grassland. Reducing grazing intensity from intensive to light resulted in more above-ground biomass and N uptake in both years and less N2O emissions in 2018. These results highlight the importance of establishing a proper grazing intensity to reduce N2O emissions from the degraded grassland while maintaining productivity for livestock.

关键词： 物理化学   实验教学   虚拟仿真实验   二组分金属相图   步冷曲线  

摘要： 二组分金属相图实验是一个非常适合以虚拟仿真形式开展的物理化学实验。学生通过在虚拟实验室的学习和操作完成实验,不仅可以解决该实验实际开设时的安全问题,还可以突破时间和空间的局限性,获得接近实际实验的体验。如果能在虚拟实验中为学生提供更多的选择性和试错空间,那么他们就可以在有限的学习时间中获得更多的实践知识和经验,有利于培养学生独立思考和分析问题、解决问题能力,并提高科学素养。

关键词： 物理化学   3-氨基-4-亚硝基呋咱   ANSF   自催化   热分解   模型动力学  

摘要： 为了解3-氨基-4-亚硝基呋咱(ANSF)的热稳定性,用差示扫描量热仪(DSC)研究了ANSF在不同升温速率及等温条件下的热分解特性,分别采用无模型法和模型拟合法计算了该物质分解反应动力学参数。动态测试结果表明,ANSF分解反应具有起始温度低、比放热量大的特点,其平均比放热量可达2945J/g;等温测试结果表明,其在液态和固态条件下都具有自催化分解特性,通过无模型法计算得到该反应活化能随转化率的变化明显,表明反应过程复杂,不能用单步反应动力学进行描述。根据简化的Benito-Perez模型计算得到引发反应阶段活化能为114.75kJ/mol,自催化阶段活化能为109.02kJ/mol。ANSF热稳定性差,液态和固态分解均具有自催化特性,反应活化能低。

关键词： 钴酸锂正极材料   综合性实验   课程思政   教学实验  

摘要： 本文介绍了一个综合性物理化学实验,钴酸锂正极材料的制备、电池的封装及其相关电化学性能如充放电图、循环性能图、倍率性能图、循环伏安图等测试,将综合性思维能力和科学探究能力的培养与实验课堂教学活动紧密地结合起来,从而较好地实现提高学生综合素质和化学学科素养的目的,经过多轮实验和实践,效果良好。

关键词： 物理化学   Al/PTFE反应材料   细观模型   物态方程   图像处理  

摘要： 为了研究铝/聚四氟乙烯(Al/PTFE)反应材料的细观冲击响应,采用理论与数值模拟的方法对Al/PTFE反应材料的冲击压缩行为进行了研究。基于三项式物态方程和混合物叠加原理,计算了Al/PTFE反应材料的冲击Hugoniot曲线及Al与PTFE材料的冲击压力—冲击温升关系;采用纳米CT获得了材料的三维细观图像,并采用数字图像处理和网格映射方法,建立了基于材料真实细观结构的三维有限元模型,计算获得的冲击Hugoniot关系与理论结果吻合较好。数值模拟研究结果表明,Al/PTFE反应材料在细观冲击压缩过程中,材料细观尺度上的波阵面呈不平整状态;铝颗粒主要受到沿冲击方向上的压缩作用,形状并未发生明显改变,W颗粒的加入使邻近的Al颗粒剧烈变形;冲击压缩后PTFE基体的温度明显高于Al颗粒的温度。当撞击速度为1500m/s时,PTFE基体的温度达3000K以上,而铝颗粒仅为400K左右。

关键词： 物理化学   做题   公式   单位换算   负号  

摘要： 做题是物理化学学习的重要环节,需注意技巧和细节,做题细节是提高做题准确率的重要手段。做到精确记忆基本概念和公式、原理,做题过程中分别计算某些物理量、注意单位换算、不遗漏负号、正确读取表中数据等细节,力求达到更好的学习效果。

关键词： Thin film composite membrane   Reverse osmosis   Membrane rinsing   Interfacial polymerization   Air-drying  

摘要： Transport behaviour of thin film composite (TFC) reverse osmosis (RO) membrane is highly dependent on the physicochemical property of the uppermost polyamide (PA) layer. In this work, we provide a comprehensive understanding of the impacts of post interfacial polymerization (IP) rinsing using either organic solvents (i.e., hexane, cyclohexane and isoparaffin-G) or aqueous solution on the structure and chemistry of PA layer and correlate the properties change to membrane performance. Evidently, the desalination performance of the aqueous-rinsed membrane is better than the organic solvents-rinsed membrane. Compared to the un-rinsed membrane, the aqueous-rinsed membrane also showed 28% higher pure water flux and 13% lower water contact angle (i.e., greater hydrophilicity) with least compromised NaCl rejection (97.70%). This is possibly caused by its reduced PA cross-linking degree and/or hydrolysis of acyl chloride monomers that alter the membrane surface chemistry. It is also found that the introduction of air-drying prior to the rinsing process could improve the membrane reproducibility as a result of extensive polymerization. The findings from this experimental work confirmed that aqueous solution is the best rinsing solution for TFC RO membrane fabrication, improving both physicochemical properties and water permeability of membrane.

关键词： Cassava starch   Ferulic acid   Mechanical activation   Antioxidant activity  

摘要： Although research on phytochemicals has been a hot topic due to positive effects on human health, modification of starch with phytochemicals has been limited. In the present work, cassava starch-ferulic acid (CS-FA) complexes were acquired using different times of mechanical activation via stirring ball milling, and their characterization and physicochemical properties were investigated. Scanning electron microscopy showed the broken structure of native cassava starch, but the smooth structure of CS-FA complexes. The X-ray diffraction indicated that the C-type crystalline structure of native cassava starch completely disappeared with the increase time of mechanical activation. The complexation was characterized by Fourier transform infrared (FT-IR) spectroscopy and Solid carbon nuclear magnetic resonance (C-13 NMR) studies. The TGA analysis showed that the thermal stability was decreased by mechanical activation, but it could be improved with the existence of ferulic acid. The solubility of CS-FA complexes increased with increasing of the time by mechanical activation. Therefore, mechanical activation is considered a suitable method for preparing CS-FA complexes. As a new material with considerable antioxidant activity, it would be a great potential for CS-FA complexes in functional food, biomedical materials, and cosmetic products. (C) 2020 Published by Elsevier B.V.

关键词： Surimi gel   Cross-linking degree   liquid nitrogen spray freezing  

摘要： Physicochemical properties of microbial transglutaminase (MTGase) cross-linked surimi gels subjected to liquid nitrogen (LN) spray freezing with different temperatures and cross-linking degrees were investigated. Gels with lower LN spray temperature (-90 degrees C) were found taking less time in cooling down themselves to maximum-icecrystal generating temperature. Microstructure images showed the pores of gels became smaller and the structure gradually became denser, as freezing temperature decreased and cross-linking degree increased. It also revealed T-22 relaxation time of gels decreased significantly with surimi gels cross-linking degree increasing, indicating the binding ability of gels to moisture was enhanced accordingly. Meanwhile, the proton density weighted image brightness declined along with the LN spray temperature decreasing, and the image brightness showed a decreasing trend from outside to inside, indicating that water migrated and permeated easier from the inside of the gel network to the outside undergone higher LN temperature and lower cross-linking degree. Besides, the L* and W values of LN groups decreased along with LN spray temperature and cross-linking degree increasing. Moreover, -90 degrees C LN group with 46.70% cross-linking degree presented the highest breaking force which ascribed to their synergistic efforts in maintaining a stable and dense structure of gels via controlling ice crystals and cross-linkages' generation. (C) 2020 Elsevier B.V. All rights reserved.

关键词： 教学重点   教改实践   薄弱环节   前瞻构想  

摘要： 物理化学实验是具有承上启下桥梁作用的重要基础实验课程。该课程一般要使用多种常规物理化学实验仪器,测量体系物理量的变化,综合分析得出实验结论。此类实验具有综合性强、知识点多及能力要求高的特点再加上分组化教学方式的影响,使得学生普遍反馈该课程难学,任课教师同样反馈该课程难教。为尽量克服以上不利影响,提高实验教学质量,课程教学小组对物理化学实验课程作出多处改革并付诸实践,同时指出该课程现存的不足之处,提出今后课程改革发展构想。