中性点不接地的企业供电系统事故分析

通过对两个中性点不接地的企业供电系统事故实例的分析,找出了事故发生的原因,指出避免类似事故的技术要点,并给出了具体的解决方法和技术措施.     

太原秋季大气PM2.5中糖类物质的组成及来源解析

糖类物质是一类重要的生物标志物,可用于大气颗粒物的来源识别.采用高效阴离子交换色谱-脉冲安培检测法(HPAEC-PAD)于2018年秋季对山西太原PM_(2.5)中的糖类物质进行定量分析.结果表明,此次检测共检出8种糖类物质,包括4种糖醇(肌醇、赤藓糖醇、阿拉伯糖醇、甘露糖醇)、3种脱水糖(左旋葡聚糖、甘露聚糖、半乳聚糖)和1种单糖(葡萄糖).3种脱水糖总浓度明显大于其他糖类,且与PM_(2.5)之间呈显著相关性(r=0.74、0.59、0.99),表明生物质燃烧对太原地区PM_(2.5)有明显贡献.应用正定矩阵因子分解模型(PMF5.0)进行源解析发现,太原秋季(9月)PM_(2.5)中的糖类物质主要来源于生物质燃烧、花粉和植物碎屑、真菌孢子和土壤灰尘4类.同时应用特征分子比值并结合太原地区农业生产情况识别出太原市的生物质燃烧源主要为硬木和作物残渣的混合贡献.     

Direct utilization of kitchen waste for bioethanol production by separate hydrolysis and fermentation (SHF) using locally isolated yeast

Kitchen wastes containing high amounts of carbohydrates have potential as low-cost substrates for fermentable sugar production. In this study, enzymatic saccharification of kitchen waste was carried out. Response surface methodology (RSM) was applied to optimize the enzymatic saccharification conditions of kitchen waste. This paper presents analysis of RSM in a predictive model of the combined effects of independent variables (pH, temperature, glucoamylase activity, kitchen waste loading, and hydrolysis time) as the most significant parameters for fermentable sugar production and degree of saccharification. A 100 mL of kitchen waste was hydrolyzed in 250 mL of shake flasks. Quadratic RSM predicted maximum fermentable sugar production of 62.79 g/L and degree of saccharification (59.90%) at the following optimal conditions: pH 5, temperature 60°C, glucoamylase activity of 85 U/mL, and utilized 60 g/L of kitchen waste as a substrate at 10 h hydrolysis time. The verification experiments successfully produced 62.71 ± 0.7 g/L of fermentable sugar with 54.93 ± 0.4% degree of saccharification within 10 h of incubation, indicating that the developed model was successfully used to predict fermentable sugar production at more than 90% accuracy. The sugars produced after hydrolysis of kitchen waste were mainly attributed to monosaccharide: glucose (80%) and fructose (20%). The fermentable sugars obtained were subsequently used as carbon source for bioethanol production by locally isolated yeasts: Saccharomyces cerevisiae, Candida parasilosis, and Lanchancea fermentati. The yeasts were successfully consumed as sugars hydrolysate, and produced the highest ethanol yield ranging from 0.45 to 0.5 g/g and productivity between 0.44 g L^–1 h^–1 and 0.47 g L^–1 h^–1 after 24-h incubation, which was equivalent to 82.06–98.19% of conversion based on theoretical yield.     

Organic acid profile and phenolic and sugar content in Salix purpurea × viminalis L. cultivated with different spent mushroom substrate and copper additions

The aim of the study was to determine the response of Salix purpurea?×?viminalis L. growing on Pleurotus ostreatus spent mushroom substrate (SMS) with different copper (Cu) addition. The content of Cu in roots, leaves and shoots was reduced by SMS addition. A decrease of biomass was observed with simultaneous Cu concentration increase. SMS induced leaf and root elongation of Cu-treated plants. Variation in the profile of low molecular weight organic acids with the domination of oxalic and acetic acids was observed. The total phenolic content significantly increased for plants cultivated with SMS, while the biosynthesis of salicylic acid was considerably weakened. The content of sugars was generally reduced by SMS. Alteration in the level of the stress-related molecules suggests mitigation of the harmful effect of Cu on Salix hybrid metabolism by SMS addition. This pointed to the possibility of using SMS in contaminated soil to reduce the toxic effect of metals on plants used in phytoextraction.     

Changes in the chemical composition of water-extractable organic matter during composting: distribution between stable and labile organic matter pools

Aerobic decomposition and stabilization of organic matter during the composting of waste materials is primarily due to the biochemical transformation of water-soluble compounds in the liquid phase by the microbial biomass. For this reason water-soluble organic matter represents the most active fraction of compost, both biologically and chemically, and thus should directly reflect the biochemical alteration of organic matter. This work aims to elucidate the microbial-mediated processes responsible for the distribution of soluble organic matter between stable and labile pools with composting time. Accordingly, chemical analysis as well as UV absorption, and ¹H and ¹³C-NMR spectroscopy of samples collected during the industrial composting of urban waste revealed microbial induced transformation of water-extractable organic matter over time. The chemical composition changed from labile, hydrophilic, plant-derived organic compounds in the beginning to predominately stable, hydrophobic moieties comprising lignin-derived phenols and microbially-derived carbohydrates at later stages of composting.     

基于材料分类的无人机部件中性盐雾加速实验研究

使用纯度≥95.5%的工业氯化钠配置5%的中性溶液作为腐蚀加速溶液,根据无人机部件的材料分类,选取金属和非金属典型部件进行中性盐雾实验.实验结果表明:非金属材料和部分表面经过特殊处理的金属材料构件具有较强的耐盐雾侵蚀能力,而部分金属表面经过实验后受到了较严重的侵蚀.针对这一实验结果,分析了盐雾对无人机典型部件的侵蚀机理,总结出中性盐雾环境下各部件的腐蚀规律,给出了提高无人机系统部件抗盐雾侵蚀能力的措施.     

水质评价模式识别的BP神经网络方法

水质受多个因素的影响，而且这些作用多是非线性的。其水质评价的实质是实现一个非线性映射。由于具有任意个隐层节点的前馈神经网络可以以任意精度逼近一个连续函数，因此，目前得到普遍应用的是采用BP算法的多层前馈神经网络。文中运用人工神经网络的反向传播（BP）算法进行了实例评价，与其它方法相比，评价精度较高，方法简单易行。     

论我国能源法的立法目的——兼评2020年《能源法（征求意见稿）》第一条

我国2020年《能源法（征求意见稿）》的立法目的在结构层次、推演逻辑等方面均有不足,无法统摄整个能源立法实践,极大影响了能源法的立法质量。不同的立法目的产生不同的法律实效,我国能源法的立法目的不仅取决于能源法的位阶,而且必须以实现“双碳”目标为价值指引。能源法需要遵循从“理念”到“价值”再到“目的”的推导逻辑,从形式诉求和实质要义出发,设置逻辑严密、层次清晰的立法目的条款。     

不同B_(4)C含量对冷喷涂Al/B_(4)C复合涂层防腐与耐磨性能的影响

目的分析不同B_(4)C含量对冷喷涂Al/B_(4)C复合涂层防腐和耐磨性能的影响,探索利用冷喷涂低温特点制备Al/B_(4)C复合涂层的可行性。方法利用冷喷涂方法制备4种B_(4)C含量的Al/B_(4)C复合涂层,并利用各种方法表征涂层的结合特征、耐磨性能和防腐性能。结果冷喷涂过程不会改变铝和碳化硼的物相,碳化硼颗粒主要以嵌入方式结合在涂层中,会产生结合缺陷。在本研究中,B_(4)C的质量分数最高可达到34.53%左右,涂层的结合强度随粉末中碳化硼含量的增加先增加、后降低,最高可达26.67 MPa。微区电化学试验分析涂层内部微电位差值,发现Al/B_(4)C界面存在电位差,腐蚀反应会优先在Al/B_(4)C界面发生,从而破坏金属Al成膜,使涂层的耐蚀性能与略低于铝块材。结论冷喷涂技术可以制备微观结构和结合性能良好的高B_(4)C含量Al/B_(4)C复合涂层,涂层中B_(4)C的质量分数最高达34.53%,预期具有良好的热中子吸收性能。同时,B_(4)C颗粒的加入,使得涂层的耐磨性能大大的提升,但是耐蚀性能相比于铝材料略有降低,是未来需要改善的方向。     

单桩负摩阻力计算方法比较分析

桩基工程中桩侧负摩阻力所产生的作用于桩体上的下拽力,可能引起桩体破坏、桩基不均匀沉降等诸多工程灾害。为此,工程师们建立了许多单桩负摩阻力计算公式,但是由于这些公式各自的适用性和局限性,计算结果差别较大。首先介绍了目前国内外用于计算单桩负摩阻力及确定中性点位置的几种常用方法:极限分析法、荷载传递法、弹性或弹塑性理论法、剪切位移法和数值分析法;再结合具体工程实例,对以上几种方法进行比较,指出各自的适用条件、优缺点等,为工程设计提供参考。