“微信一站式化学史教学平台”开发与建设的可行性研究

文章分析了化学史学科特点及微信公众平台的特点,从微信与各类平台比较研究、微信公众平台技术在教学中的应用、微信公众平台在各类学校及研究单位使用情况调查、微信团队构成及分工、前期准备工作5个方面对开发和建设"微信一站式化学史教学平台"进行可行性分析。     

论我国环境污染损害鉴定评估推进的困境与发展建议

近年来,环境污染问题日益引起公众的高度关注。环境污染导致的人身、财产及环境资源损害问题日益显现,环境污染损害评估结论作为环境污染事件损害的量化结果,已经成为处理环境问题以及司法解决涉及环境案件的技术依据或定案根据。文章在阐述我国环境污染损害鉴定评估进展的基础上,分析了鉴定评估目前面临的问题:立法和方法研究滞后于现实需求、环境污染损害鉴定评估管理体系亟待完善、损害赔偿修复机制尚未建立,并对上述问题基础提出了相应的改进建议。     

丙烯压缩机透平结垢原因分析及在线清洗技术

神宁煤化工烯烃装置丙烯压缩机在运行过程中,由于水质原因造成透平结垢,出现了透平调速阀逐渐开大,效率下降,蒸汽耗量增加等现象。本文科学分析了透平结垢的原因及危害,提出以无负荷湿蒸汽冲洗法对透平进行冲洗的清洁技术,并在运行过程中成功实践,有效地确保压缩机组高效、安全、稳定运行。     

Reverse Microemulsion Synthesis and Characterization of Pd-Ag Bimetallic Alloy Catalysts Supported on Al2O3 for Acetylene Hydrogenation

Pd-Ag bimetallic alloy nanoparticles were synthesized by the reverse microemulsion method,and then deposited on Al2O3 to form the supported catalyst.The nanoparticles of Pd-Ag and Pd-Ag/Al2O3 samples were characterized by UV/Vis,HRTEM,EDX,XRD,and XPS.The test results indicated that Pd-Ag bimetallic alloy nanoparticles with a size of about 2 nm and a face-centered cubic(fcc) structure were formed in the measured area of microemulsion.The growth of nanoparticles was effectively limited within the droplet of micoremulsion.TEM image exhibited that the Pd-Ag alloy nanoparticles were well-dispersed on the Al2O3 support.The catalytic performance of various catalysts for selective hydrogenation of acetylene showed that a higher acetylene conversion and selectivity to ethylene upon acetylene hydrogenation was achieved on a nano-sized Pd-Ag bimetallic catalyst with a Pd/Ag alloy supported molar ratio of 1:1.5.     

Shock tube studies of methyl butanoate pyrolysis with relevance to biodiesel

Methyl butanoate pyrolysis and decomposition pathways were studied in detail by measuring concentration time-histories of CO, CO₂, CH₃, and C₂H₄ using shock tube/laser absorption methods. Experiments were conducted behind reflected shock waves at temperatures of 1200–1800 K and pressures near 1.5 atm using mixtures of 0.1%, 0.5%, and 1% methyl butanoate in Argon. A novel laser diagnostic was developed to measure CO in the ν₁ fundamental vibrational band near 4.56 μm using a new generation of quantum-cascade lasers. Wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) was used to measure CO₂ near 2752 nm. Methyl radical was measured using UV laser absorption near 216 nm, and ethylene was monitored using IR gas laser absorption near 10.53 μm. An accurate methyl butanoate model is critical in the development of mechanisms for larger methyl esters, and the measured time-histories provide kinetic targets and strong constraints for the refinement of the methyl butanoate reaction mechanism. Measured CO mole fractions reach plateau values that are the same as the initial fuel mole fraction at temperatures higher than 1500 K over the maximum measurement time of 2 ms or less. Two recent kinetic mechanisms are compared with the measured data and the possible reasons for this 1:1 ratio between MB and CO are discussed. Based on these discussions, it is expected that similar CO/fuel and CO₂/fuel ratios for biodiesel molecules, particularly saturated components of biodiesel, should occur.     

Enhancement in High-Field J c Properties and the Flux Pinning Mechanism of MgB2 Thin Films on Crystalline SiC Buffer Layers

We have studied the influence of crystalline SiC buffer layers on the critical current density and on the flux pinning mechanism in MgB₂ thin films. Crystalline SiC buffer layers were deposited on the Al₂O₃ (0001) substrates by using a pulsed laser deposition method, and then MgB₂ thin films were grown on the SiC-buffered layer by using a hybrid physical-chemical vapor deposition technique. MgB₂ thin films with crystalline SiC-buffered layers showed a significant critical current density’s enhancement in the high magnetic field region. An uncommon plateau-like behavior was also observed when the normalized flux pinning force density was scaled with the reduced magnetic field. Based on the analyses of the scaling behavior of the flux pinning force, grain boundary pinning is likely to be a dominant pinning mechanism in the SiC-buffered MgB₂ thin films.     

大型医疗设备电气设计要点

本文详细介绍了磁共振设备（MRI）、加速器、X射线设备等医院建筑中常用的大型医疗设备的工作原理、临床应用、负荷特性和主要电气参数，并对相应设备的供电方案、配电系统、照明和接地等主要电气设计要点加以说明，可为电气设计人员提供参考。     

Sidelobe suppression in NC-OFDM systems using constellation adjustment

In this letter, a new method for sidelobe suppression in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) systems is proposed. Unlike the conventional approach, sidelobes are suppressed by iteratively adjusting the constellation points for the subcarriers that are close to the edges of the used bandwidth. The constellation points corresponding to the maximum sidelobe suppression are chosen for transmission. Simulation results show that the proposed algorithm yields good performance improvement in terms of sidelobe suppression, and does not have a significant impact on the peak-to-average power ratio (PAPR).     

Identification of the gene PaEMT1 for biosynthesis of mannosylerythritol lipids in the basidiomycetous yeast Pseudozyma antarctica

The yeast Pseudozyma antarctica produces a large amount of glycolipid biosurfactants known as mannosylerythritol lipids (MELs), which show not only excellent surface‐active properties but also versatile biochemical actions. To investigate the biosynthesis of MELs in the yeast, we recently reported expressed sequence tag (EST) analysis and estimated genes expressing under MEL production conditions. Among the genes, a contiguous sequence of 938 bp, PA_004, showed high sequence identity to the gene emt1, encoding an erythritol/mannose transferase of Ustilago maydis, which is essential for MEL biosynthesis. The predicted translation product of the extended PA_004 containing the two introns and a stop codon was aligned with Emt1 of U. maydis. The predicted amino acid sequence shared high identity (72%) with Emt1 of U. maydis, although the amino‐terminal was incomplete. To identify the gene as PaEMT1 encoding an erythritol/mannose transferase of P. antarctica, the gene‐disrupted strain was developed by the method for targeted gene disruption, using hygromycin B resistance as the selection marker. The obtained ΔPaEMT1 strain failed to produce MELs, while its growth was the same as that of the parental strain. The additional mannosylerythritol into culture allowed ΔPaEMT1 strain to form MELs regardless of the carbon source supplied, indicating a defect of the erythritol/mannose transferase activity. Furthermore, we found that MEL formation is associated with the morphology and low‐temperature tolerance of the yeast. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of trace Na additions on the hydriding kinetics of hypo-eutectic Mg–Ni alloys

Mg–Ni alloys are among the most promising candidates for solid-state hydrogen storage systems. This paper reveals the effect of Na doping in accelerating initial hydrogen uptake in Mg–Ni alloys using in-situ Synchrotron X-ray powder diffraction. A minimum concentration of approximately 0.2 wt.% Na must be achieved for the alloys to show reasonably fast hydriding kinetics. Surface analysis shows that a Na-modified Mg–Ni surface facilitates the chemisorption and dissociation of hydrogen molecules in the early stage of hydriding as evidenced by a rapid formation of the saturated hydrogen solid solution Mg₂NiH_0.3 from the original Mg₂Ni. The subsequent hydrogen absorption is based on a mechanism of nucleation and growth of MgH₂ where a high density of dislocations develops ahead of the growing hydride-metal interface.