制备工艺对钯粉粒径的影响

探讨了利用液相还原法,以水合肼为还原剂,制备大颗粒钯粉,应用单变量对比试验的方法讨论了Pd2+浓度、温度、pH值对钯颗粒形核和生长过程的影响,这些因素的影响决定了钯颗粒粒度大小和服役性能。经分析和讨论,得出参数Pd2+浓度为0.1 mol·L-1,pH值为12,温度为50℃是最佳工艺参数的结论,并在此参数下制备出较大粒径的钯粉,且利用SEM,XRD,马尔文激光粒度仪、氮吸附等对其进行表面微观形貌、成分、粒度分布和比表面积等性能进行了分析,较有力地说明这种钯粉具有纯度高、比表面积大等优点,能够满足现排代服役条件的要求,对实际工业生产具有一定的指导意义。     

Electric field analysis of spinneret design for multihole electrospinning system

Electric field plays a key role in producing required nanofibers in electrospinning. This study aims to improve the electric field distribution of the multijet spinning system by designing the spinneret configuration. A novel 19-hole multistep electrospinning configuration is presented. The simulation results show that the electric field strength at the central position is intensified due to the protuberant step on the spinneret, and therefore more uniform electric field is obtained compared with the 19-hole flat spinneret. We demonstrate that the multistep spinneret configuration produces finer fibers and more continuous fiber mats compared with the flat spinneret configuration because of the improved electric field distribution. Jet repulsion in the multijet electrospinning process is studied. It is found that the electric field line distribution, which is determined by the spinneret configuration, plays a dominant role in influencing jet repulsion. Applied voltage is the main factor responsible for jet repulsion for a given spinneret configuration.     

亚硝基异戊酯催化的环境友好氧化脱肟反应

亚硝基异戊酯在分子氧存在下,可以有效的催化醛肟和酮肟为相应的醛和酮。结果表明催化体系的溶剂效应和苯环的取代基电子效应对反应影响很大。芳香酮肟可实现完全转化,醛肟和脂肪族肟也能获得良好的产率,所用催化体系反应条件温和,清洁高效。     

Two-step continuous synthesis of tetraethylthiuram disulfide in microstructured reactors

We present two-step continuous synthesis of tetraethyl thiuram disulfide using microstructured reactors, starting with the formation of N, N-diethyldithiocarbamic acid from carbon disulfide and diethylamine in the first mi- crostructured reactor, and the oxidation of N, N-diethyldithiocarbamic acid by hydrogen peroxide in the second one. We studied the effects of reaction temperature, LHSV and total flow rate on the yield of the product. In the first microstructured reactor assembled with an HPIMM micromixer and a stainless steel capillary as the delay loop, the yield of N, N-diethyldithiocarbamic acid reached 96.3% in the 40 wt% diethylamine ethanol solution under reaction conditions of the CS₂/(C₂H₅)₂NH molar ratio of 1.1: 1, total flow rate of 4 mL/min, LHSV of 42.4 h⁻¹, and reaction temperature of 25 °C. Consequently, the obtained N, N-diethyldithiocarbamic acid solution was reacted with H₂O₂ solution in another microstructured reactor assembled with SIMM-V2 and a PTFE capillary as the delay loop, the yield of the high purity tetraethylthiuram disulfide reached 89.3% under the optimized reaction conditions.     

如何做好屋面防水工程施工质量的控制

要想做好屋面防水工程施工，在进行屋面防水工程施工时应严格按照国家规定的要求进行，采用符合标准的防水材料进行。若在设计、建设和维护的任何一个环节中出现漏洞，那么屋面防水工程施工质量也会受到影响。     

《爱丽丝梦游仙境》制作技术与技巧探讨

《爱丽丝梦游仙境》采用了多种拍摄和制作技术,并且这些技术与技巧结合得非常好,给观众带来了一场非常完美的视听盛宴。本文主要介绍该片制作方案的确定、摄影器材的选择、为合成所作的准备、绿幕前拍摄和布光技巧、形象化预审视以及前后期如何完美结合实现2D转3D等制作技术与技巧等,并简要探讨现代电影制作中摄影师的职责和变化。     

工作过程为导向背景下的高职景观设计课程体系构建研究

改革开放以来,科教兴国观念深入人心,教育界也在逐渐博采众长丰富课程内容和教学模式。"工作过程导向"理论最初是由德国教育家提出的,于21世纪被我国学者引入,该理论虽被众多人认可,然而在实行中仍旧存在纰漏。景观设计是一门实践类的学科,将工作过程导向融入此门学科的课程中,构建新型课程体系,能够使整体教学产生质变。本文简要说明当前该专业课程现状,分析工作过程导向课程的价值,详细论述该课程体系的构建要点及过程。     

有关改性沥青混泥土面层施工技术的探讨

沥青路面具有良好的力学强度，在采用机械化施工时也非常方便。所以在现阶段的高等级公路中，沥青路面成为了主要的路面结构。但在实际施工中，改性沥青的施工技术要求非常高，所以对加强改性沥青混泥土施工技术的研究具有非常重要的意义。     

Carbody hunting investigation of a high speed passenger car

This paper describes the low frequency carbody hunting problem of a high speed passenger car emerged in the process of tests and service operations. It causes a significant deterioration of lateral comfort. First, the vehicle model is established as a multiple rigid body system. Using root locus analysis, the effect of system parameters on the carbody hunting stability has been studied. It shows that carbody hunting instability has something to do with suspension parameters and wheel/rail conditions. To find the causes of this carbody hunting problem, component tests have been carried out. Based on the theoretical hunting stability analysis and component tests, solutions are proposed and then validated in the field test.     

Spoilage of refrigerated (4 °C) Litopenaeus vannamei: cooperation between Shewanella species and contribution of cyclo‐(L‐Pro‐L‐Leu)‐dependent quorum sensing

The spoilage potential of Shewanella putrefaciens and S. baltica isolated from spoiled refrigerated Litopenaeus vannamei was evaluated by in vitro assays for trimethylamine oxide reduction, extracellular hydrolytic enzymes and biofilm formation, and in vivo inoculation into surface‐sterilised shrimp followed by microbial, biochemical and sensory analyses during storage for 5 days at 4 °C. S. baltica displayed higher spoilage potential than S. putrefaciens both in vitro and in vivo. Shrimp co‐inoculated with them had one‐day shorter shelf life than those mono‐inoculated, based on the results of bacterial density, volatile base nitrogen, trimethylamine, volatile organic compounds and sensory analysis, which strongly suggests cooperation of Shewanella species in shrimp spoilage. Exogenous cyclo‐(L‐Pro‐L‐Leu) boosted bacterial growth, extracellular protease and collagenase activities, and biofilm formation of S. putrefaciens and S. baltica at least before they entered the stationary phase, indicating that cyclo‐(L‐Pro‐L‐Leu)‐dependent quorum sensing, a recently suggested communication mechanism between them, contributes to the cooperation.