半开式离心叶轮变工况间隙流动特征

针对叶顶间隙对半开式离心压缩机叶轮内部流场和气动性能的影响,采用数值方法研究了不同工况下叶轮流道及间隙处的流场规律,对比分析了小流量、设计和大流量三个运行下况下叶顶马赫数分布、叶顶载荷与间隙泄漏量、间隙泄漏涡特征的变化,以及叶顶间隙随进口流量变化对叶轮气动性能的影响,得出间隙涡流在通道中下游与主流相互掺混是引起半开式叶轮能量损失的主要原因。     

发动机余热利用蒸气动力循环的工质筛选

本文针对汽油发动机余热温度的特点,采用有机Rankine循环(Organic Rankine Cycle,ORC)回收发动机的排气和冷却水废热。利用计算机程序对循环中各主要状态点的热力参数和热力性能进行了理论计算,确定了最佳参数值,进行了有机工质的筛选。最终选定环戊烷和R113作为发动机余热回收利用蒸气动力循环的工质。     

工质热物性对脉动热管运行性能的影响

工质热物性显著影响脉动热管的流动与传热特性。本文通过理论计算及实验研究,定性分析了工质热物性对临界直径、毛细滞后阻力、启动运行及传热极限等方面的影响。研究表明,为保证脉动热管的运行性能,在设计阶段应综合考虑工质、管材及管径大小等因素。首先,根据使用场合的热流密度及运行温度高低合理选取工质种类;然后,选用合适的管壁材料,尽可能减少液塞与管壁之间前、后接触角不同引起的毛细滞后阻力;最后,确定管内直径范围。本文工作旨在为脉动热管的设计和选用提供一些依据和参考。     

基于单重工作休假的离散时间排队稳态分析

详细地分析了一个单重工作休假的离散时间Geom/G/1排队系统.首先,构造二维嵌入马尔可夫链,得到其M/G/1型转移概率矩阵.其次,利用矩阵分析的方法,导出了稳态队长的概率分布,进一步得到稳态队长的随机分解结果和平均队长公式.最后,给出稳态等待时间的随机分解结构及其平均等待时间公式.     

Negative‐working photoresist based on a first‐generation dendrimer consisting of 4,4‐diphenylpentyloxy units

A first‐generation dendrimer ( 2 ), containing phenol groups in the exterior for solubilization in aqueous alkaline solutions, was evaluated as a new negative‐working, alkaline‐developable photoresist material. A negative‐working photoresist based on 2 , 4,4′‐methylenebis[2,6‐bis(hydroxymethyl)phenol] as a crosslinker, and diphenyliodonium 9,10‐dimethoxyanthracene‐2‐sulfonate as a photoacid generator was demonstrated. This resist gave a clear negative pattern through postbaking at 90 °C after exposure to UV light, which was followed by development with a 2.38% aqueous tetramethyl ammonium hydroxide solution at room temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1210–1215, 2005     

Novel positive‐working and aqueous‐base‐developable photosensitive poly(imide benzoxazole) precursor

A novel positive‐working and aqueous‐base‐developable photosensitive poly(imide benzoxazole) precursor based on a poly(amic acid hydroxyamide) bearing phenolic hydroxyl groups and carboxylic acid groups, a diazonaphthoquinone (DNQ) photosensitive compound, and a solvent was developed. Poly(amic acid hydroxyamide) was prepared through the polymerization of 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane, trimellitic anhydride chloride, and 4,4′‐oxydibenzoyl chloride. Subsequently, the thermal cyclization of the poly(amic acid hydroxyamide) precursor at 350 °C produced the corresponding poly(imide benzoxazole). The inherent viscosity of the precursor polymer was 0.17 dL/g. The cyclized poly(imide benzoxazole) showed a high glass‐transition temperature of 372 °C and 5% weight loss temperatures of 535 °C in nitrogen and 509 °C in air. The structures of the precursor polymer and the fully cyclized polymer were characterized with Fourier transform infrared and ¹H NMR. The photosensitive polyimide precursor containing 25 wt % DNQ photoactive compound showed a sensitivity of 256 mJ/cm² and a contrast of 1.14 in a 3‐μm film with a 0.6 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 5 μm was obtained from this composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5990–5998, 2004     

MRPC噪声和暗电流对温度和工作高压的依赖

不同混合气体不同高压,6个气隙的阻性板室工作在不同的环境温度下,测试其噪声和漏电流.噪声和漏电流随温度升高指数上升.     

Working point of the EFG process

A theoretical investigation of the EFG process working point based on the meniscus height control is carried out. The link between the two control parameters, which are the pulling rate and the upper die temperature, is found from the thermal equilibrium at the crystallization interface. Using the pressure equilibrium in the film and considering the meniscus shape, the change in meniscus height depending on the crystal radius is analyzed. Limited to small crystal radii, an algebraic formulation of the temperature gradient at the interface is established. Some die design parameters are taken into account and their impacts on the process working point are discussed.     

Electrochemistry/mass spectrometry as a tool in metabolism studies—A review

The combination of electrochemistry (EC) and mass spectrometry (MS) has become a more and more frequently used approach in metabolism studies in the last decade. This review provides insight into the importance of metabolism studies during the drug development process and gives a short overview about the conventionally used methods since electrochemistry is often intended to substitute or minimize animal-based studies. The optimization of the electrochemical conditions is of great importance for a successful comparison with in vitro approaches. The type of metabolism reactions, which can be simulated by EC, has been extended with new cell types and working electrodes. Although the mechanism differs from the enzyme-catalyzed turnover, electrochemistry can be used to simulate a significant number of the respective reactions.     

An accurate and reliable analysis of trimethylamine using thermal desorption and gas chromatography–time of flight mass spectrometry

Trimethylamine (TMA) is well-known for manifesting the odor of rotting fish and urine. The analysis of TMA in environmental samples generally suffers from low reproducibility and poor sensitivity. In this study, a technique for the quantitative analysis of gas phase TMA was developed using thermal desorption (TD)-gas chromatography (GC)-time of flight mass spectrometry (TOF-MS). This new approach yielded good linearity (R² = 0.9930), precision (RSE = 1.59%), and high sensitivity with the method detection limit (MDL) of 51 pg, i.e., detection of 0.021 ppb of TMA at 1 L sample (limit of detection (LOD): 5.32 pg (0.002 ppb). This method was tested against gas samples collected from two representative sources of TMA: (1) rotten thornback fish and (2) cat urine-soaked clay. The concentration of TMA in these samples, when analyzed after treatment at varying dilution ratios, averaged 293 ± 29.7 ppm (RSE = 3.82%) and 74.1 ± 5.78 ppb (RSE = 3.19%), respectively. The feasibility of this approach, when tested with TD–GC–Quadruple (Q) MS, showed a good compatibility with moderately reduced sensitivity. The results of this study demonstrated that one can achieve highly reliable and reproducible analysis of TMA from environmental samples when using thermal desorption (for pretreatment) and detection (by the TOF or Q-MS system).