Atmospheric oxidation chemistry of 1–methoxy 2–propyl acetate initiated by OH radicals: kinetics and mechanisms

Kinetics and mechanism of the gas-phase reaction of CH₃C(O)OCH(CH₃)CH₂OCH₃ (MPA) with OH radicals in the presence of O₂ and NO have been investigated theoretically by performing a high and reliable level of theory, viz., CCSD(T)/6-311?+?G(d,p)//BH&HLYP/6-311++G(d,p)?+?0.9335×ZPE. The calculations predict that the H-abstraction from the ?CH₂?O? position of MPA is the most facile channel, which leads to the formation of the corresponding alkoxy radicals CH₃C(O)OCH(CH₃)C(O ?)HOCH₃ under atmospheric conditions. This activated radicals CH₃C(O)OCH(CH₃)C(O ?)HOCH₃ will undergo further rearrangement, fragmentation and oxidative reactions and predominantly leads to the formation of various products (methyl formate HC(O)OCH₃ and acetic anhydride CH₃C(O)OC(O)CH₃). In the presence of water, acetic anhydride can convert into acetic acid CH₃C(O)OH via the hydrolysis reaction. The calculated total rate constants over the temperature range 263–372?K are used to derive a negative activation energy (E_a= ?5.88 kJ/mol) and an pre-exponential factor (A?=?1.78×10^?12 cm³ molecule^?1 s^?1). The obtained Arrhenius parameters presented here are in strong agreement with the experimental values. Moreover, the temperature dependence of the total rate constant over a temperature range of 263?1000?K can be described by k?=?5.60 × 10^?14×(T/298?K)^3.4×exp(1725.7?K/T) cm³ molecule^?1 s^?1.     

Change of evaporation rate of single monocomponent droplet with temperature using time-resolved phase rainbow refractometry

Droplet evaporation characterization, although of great significance, is still challenging. The recently developed phase rainbow refractometry (PRR) is proposed as an approach to measuring the droplet temperature, size as well as evaporation rate simultaneously, and is applied to a single flowing n-heptane droplet produced by a droplet-on-demand generator. The changes of droplet temperature and evaporation rate after a transient spark heating are reflected in the time-resolved PRR image. Results show that droplet evaporation rate increases with temperature, from ?1.28$\times {10}^{?8}$ m²/s at atmospheric 293 K to a range of (?1.5, ?8)$\times {10}^{?8}$ m²/s when heated to (294, 315) K, agreeing well with the Maxwell and Stefan–Fuchs model predictions. Uncertainty analysis suggests that the main source is the indeterminate gradient inside droplet, resulting in an underestimation of droplet temperature and evaporation rate. With the demonstration on simultaneous measurements of droplet refractive index as well as droplet transient and local evaporation rate in this work, PRR is a promising tool to investigate single droplet evaporation in real engine conditions.     

甲烷浓度对碳化硅基底金刚石薄膜摩擦性能影响

利用热丝化学气相沉积法(HFCVD)在碳化硅基底上制备金刚石薄膜,采用场发射扫描电子显微镜、拉曼光谱仪、原子力显微镜研究了在不同甲烷浓度条件下制备的金刚石薄膜表面形貌及物相组成,在干摩擦条件下通过往复式摩擦磨损实验测试并计算了已制备金刚石薄膜的摩擦系数和磨损率,结合物相分析及摩擦磨损实验结果分析了甲烷浓度的改变对金刚石薄膜摩擦磨损性能的影响。结果表明,由于甲烷气体含量的升高,金刚石薄膜结晶质量下降,薄膜由微米晶向纳米晶转变。摩擦磨损实验结果显示:3%甲烷浓度条件下制备的金刚石薄膜耐磨性较好,磨损率为2.2×10^-7 mm³/mN;5%甲烷浓度条件下制备的金刚石薄膜摩擦系数最低(0.032),磨损率为5.7×10^-7 mm³/mN,制备的金刚石薄膜的耐磨损性能相比于碳化硅基底(磨损率为9.89×10^-5 mm³/mN)提升了两个数量级,显著提高了碳化硅基底的耐磨性。     

基于横向莫尔条纹的自准直测角方法

本文提出了基于横向莫尔条纹的自准直测角方法,用遮光原理分析了莫尔条纹的位移放大作用.并基于该方法搭建了原理光路,得到的莫尔条纹信号稳定且能够满足测量需求.在此基础上对系统进行了定量标定,简化了数据处理步骤,实现了动态测量,系统分辨率达到10″,进一步明确将该方法应用到自准直仪中可以有效提高仪器分辨率.     

Monte Carlo simulation of electric conductivity for pure and doping fullerene (C60)

In this paper, we have used Monte Carlo (MC) method to simulate and study the temperature and doping effects on the electric conductivity of fullerene (C60). The results show that the band gap has reduced by the doping and the charge carrier transport is facilitated from valence band to conduction band by the temperature where is touched a 300 K. In this case, the conductivity reached a value of $4\times {10}^{-7}\text{S}{\text{cm}}^{-1}$. The electric conductivity of C60 can increase by the triphenylmethane dye crystal violet (CV) alkali metal to reach $4\times {10}^{-3}\text{S}{\text{cm}}^{-1}$ at 303 K. Our results of MC simulation have a good agreement with those extracted from literature [10], [33].     

油-气-水三相流超声传感器持气率测量*

为探索油-气-水三相流持气率测量难题,该文开展了脉冲透射式超声传感器持气率测量动态实验研究。首先,利用超声传感器与光纤传感器组合,测取了油-气-水三相流中段塞流、混状流、泡状流的响应信号;其次,提取了超声脉冲信号的最大值序列来反映不同流型时超声传感器响应特性,同时,借助双头光纤传感器与相关测速法,计算得到了流体中气泡弦长序列;最后,结合流型与泡径信息,利用超声传感器测量了不同流型下持气率,并分析了不同流型持气率预测的误差来源,为其他油-气-水三相流持气率测量传感器设计提供了借鉴。     

Optic Fiber Interferometer for Absolute Distance Measurement

1.IntroductionAbsolutedistancemeasurementisfarfromanewtopic.However,itisstillafieldstimulatinggreatinterestsnowadaysduetoitSimportantroleinmanufacturingandassembly['J.SincethegreatsuccessachievedbyMichelsonandBenoitwhentheyfirstdevelopedaninterferometertodeterminethestandardmeterintermsofthemonochromaticredcadmiumline,theopticinterferometerhasbeenprovedtobeoneofthemostpreciseandefficientwayindisplacementmeasurementbecauseofitshighdiscriminationandsimplestructure.However,thetraditionalinterfe…     

数字散斑相关方法及其在碳纤维复合材料压力容器变形测量中的应用

提出了一种新的基于图像灰度梯度迭代的数字散斑相关方法(DSCM,digital speckle correlation method)。通过使用DSCM测量碳纤维复合材料压力容器在水压下的局部区域的位移场和应变场,分析了复合材料压力容器的轴向和环向的变形特征,为碳纤维复合材料压力容器的优化设计提供了理论和实验依据。     

一种利用电光效应测量微小转角的新方法

利用线性电光效应发展出一种新的、高准确度的微小转角测量法.根据W.L. She等人提出的线性电光效应耦合波理论，求得出射光强与入射光强比值（即出射率）对入射光方向的依赖曲线，利用该曲线，通过测量出射率可以确定入射光的方向.并根据此原理，设计了一套简单的装置，该装置可以测量出物体微小转角的变化量，同时测量范围及准确度都可通过外加电场和入射光波长加以调节.对此微小转角测量法作了理论分析，在LiNbO3器件上，得到测量范围大于3′，准确度为3.5″的设计结果.