激光选区熔化Ti6Al4V合金的工艺参数优化

孔洞、未熔粉、裂纹是在激光选区熔化制备试样过程中常见的缺陷,迄今为止,大量研究均集中在减少缺陷上,关于工艺参数对缺陷影响的研究较少。本文系统研究了工艺参数对激光选区熔化Ti6Al4V合金相对密度、表面粗糙度、力学性能的影响。结果表明,低激光功率、高扫描速度和高层厚将会引起不充分的粉末熔化以及球化效应。最佳工艺参数为激光功率200 W,扫描速度500 mm/s,层厚10 μm,扫描间距105 μm。在该参数下,试样的抗拉强度1077 MPa,屈服强度907 MPa。     

A kinetic study of the thermally induced isomerization reactions of 9c,12c linoleic acid triacylglycerol using gas chromatography

In this study, the kinetics of the thermally induced isomerization of 9c,12c linoleic acid was studied in order to better understand the geometric and positional isomerization of triacylglycerol and the various factors controlling isomeric ratios. Trilinolein was placed in glass ampoules and sealed in the absence or presence of air (O₂) and then subjected to thermal treatment at 180, 200, 220, 230 or 240 °C for regular time intervals. The glass ampoules were removed and the contents were analyzed using gas chromatography. The results indicate that the consumption of trilinolein is a second-order reaction. The formation reactions of cis,trans, trans,cis and trans,trans isomers are zero-order and dependent on both temperature and time. The presence of O₂ does not change the order of the reaction. In addition, the rate constants and activation energies involved in the isomerization reaction of linoleic acid with or without O₂ are presented.     

沼气发酵猪粪管理系统对温室气体排放的影响

基于生命周期清单分析以及清洁发展机制,引入"碳足迹"概念,对我国散养猪以及规模化养猪场引入沼气发酵系统后猪粪管理系统温室气体排放及减排进行了估算。农户散养猪粪处理系统中,12 m3沼气池厌氧发酵过程碳足迹为223.40 kg CO2e/a,沼气代替原煤燃烧减少444.33 kg CO2e/a温室气体,沼气发酵净减少220.93 kg CO2e/a温室气体,我国散养生猪产生的猪粪以此沼气池发酵可减少温室气体20 984.62 Gg CO2e/a;分析运行规模约1 000 m3大型沼气工程的碳足迹,保守估计为2 835.32 t CO2e/a,运行沼气工程替代煤炭以及减少猪粪排放的温室气体共约2 914.23 t CO2e/a,故沼气工程年减少温室气体78.91 t CO2e,该项目共可减排1 578.20 t CO2e。在猪粪管理系统中采用沼气发酵系统可以更好地促进温室气体减排的进行。     

输电线路新型复合式基础试验研究

针对表层由薄粘土层覆盖的风化岩体输电线路地基,传统的原状土掏挖基础或岩石嵌固式基础均不能有效地发挥其功效,单独采用任何一种基础将不符合安全经济环保的要求,特将上述2种基础型式相结合,提出新型环保型复合式基础型式.选择典型场地进行原型试验,试验基础施工安全,坑壁稳定,根据试验结果,新型复合式基础充分发挥原状土和岩石地基的高承载、低变形的优势,并推导出新型复合式基础的抗拔承载力、抗倾覆承载力的计算公式,为新型复合式基础在输电线路杆塔基础中的应用提供技术资料.     

聚乙烯丙纶防水卷材用于种植屋面工程的特性

结合种植屋面的构造特点,对聚乙烯丙纶防水卷材用于种植屋面工程的特性进行了介绍,分别阐述了耐穿刺性、环保性能、施工特性三方面内容,指出GFZ聚乙烯丙纶防水卷材与现有其他有机类相比具有明显的综合优势。     

An improved gas chromatography-based approach for characterisation of fatty acids in fresh basil seed oil

An improved gas chromatography-based analytical method for the simultaneous separation of seventy-two fatty acids was developed. Twenty-six types of trans fatty acids and conjugated linoleic acids were separated and identified with this method, especially trans C18 isomers. This method was confirmed to be high throughput and have high sensitivity and a low detection limit. It was successfully applied to separate and identify fatty acids in fresh basil seed oil. The linolenic acid content (51.67 g/100 g) was highest in basil seed oil, followed by linoleic acid (20.16 g/100 g) and oleic acid (12.70 g/100 g). These unsaturated fatty acids in fresh basil seed oil were transformed into trans fatty acids, conjugated linoleic acids and saturated fatty acids after heating to a certain temperature for an adequate duration, and the formation mechanisms were characterised.     

Effect of initial deposition behavior on properties of electroless Ni–P coating on ZK60 and ME20 magnesium alloys

The composition of magnesium alloys is greatly associated with initial deposition behavior of electroless Ni–P coatings. Thus, the initial deposition behavior of electroless Ni–P coatings on ZK60 and ME20 alloys was investigated. The results indicated that differences in the alloy compositions significantly influenced the initial deposition process and the adhesive strength, corrosion resistance, and crystal structure. The initial deposition of coatings on ZK60 and ME20 alloys preferentially occurred on the precipitates. The precipitates in ZK60 alloy had higher chemical activity after HF activation and controlled the initial deposition rate of the coating. The initial deposition rate of the coating on ME20 alloy mainly depended on the density of the MgF₂ film formed by HF activation rather than on the precipitates. Owing to differences in the initial deposition process, the coating on ZK60 alloy had higher adhesive strength and better corrosion resistance than that on ME20 alloy. The coatings on ZK60 and ME20 alloys mainly had crystalline structures, and the coating on ME20 alloy had also a slight microcrystalline structure.     

Offshore wave energy resource assessment in the East China Sea

The offshore wave energy resource in the East China Sea (ECS) off the coast of the southern East China is assessed using wave buoy data covering the period of 2011−2013. It is found that the averaged offshore wave power was approximately 13 kW m⁻¹ in the region of interest. Most of the offshore wave energy in the ECS is contributed by the sea states with significant wave heights between 1.5 m and 3.5 m and with wave energy periods between 6 s and 8 s. Seasonal variations are detected in the wave characteristics of significant wave height and wave power. The predominant wave directions are mainly from the II quadrant and the IV quadrant, respectively, in winter and summer, in accordance with the monsoon characteristics in the ECS. Wave heights, periods and power are generally higher in winter and autumn, and weaker in spring and summer; however, extreme values occur in some summer and autumn months due to the extreme conditions caused by typhoons passing over this region. These extreme sea states do not contribute much to the total annual energy, mainly because of their low occurrence, but may bring risks to the wave energy converters.     

智能配电网自愈控制技术体系框架研究

智能配电网是智能电网的重要组成部分，自愈作为智能配电网的“免疫系统”，是智能配电网最重要的特征。首先阐述智能配电网自愈控制主要解决的问题及其作用，然后分析智能配电网自愈控制体系的结构及其技术组成，包括基础层、支撑层和应用层。其中，电网及其设备为基础层，数据和通信为支撑层，监测、评估、预警/分析、决策、控制、恢复为应用层。通过研究应用智能配电网自愈控制技术将使电网的供电可靠性明显提高，停电时间显著减少。尤其是在极端天气情况下，配电网将充分发挥它的自我预防、自我恢复能力，优先保障人们的生活，最大限度地为人们提供电力。     

Effect of pulse frequency on hardness characteristics of Al-Cu alloy HPVP-GTAW joints

AA 2219-O Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding (HPVP-GTAW) process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardness characteristics which mainly depicted by microhardness and its gradient were investigated systematically. The results show that pulse frequency has a great effect on the hardness characteristics. The weld zone microhardness and its gradient with different pulse frequency present an evident fluctuant trend. The fluctuation of gradient is slight, illustrating that the microstructure is uniform with pulse frequency varied from 35 kHz to 60 kHz. The fusion zone microhardness and its gradient follow the similar trends but fluctuate greatly. Maximum value of gradient appears around the fusion boundary due to the coarse and non-uniform microstructure. The maximum gradient at 60 kHz is only 25.5% of that at 45 kHz. According to the study, the best hardness characteristics are achieved at 60 kHz frequency.