微秒脉冲下极性效应对碳酸丙烯酯击穿场强的影响

通过对比碳酸丙烯酯在针板电极间距分别为0.5、1.0和2.0 mm下的击穿电压大小的实验,研究碳酸丙烯酯的极性效应.实验设备包含一个充电时间在5～20毫秒的电容储能型脉冲型脉冲功率源和一个内置针板电极的击穿试件. 每一组的击穿电压通过示波器显示记录. 三组不同间距下的击穿实验数据表明碳酸丙烯酯的正电极击穿场强高于负电极击穿场强,并且击穿场强随着电极间距的增大而增 大. 对碳酸丙烯酯针板电极的击穿进行了仿真模拟实验. 基于实验结果对碳酸丙烯酯的极性效应给出了相应的解释.     

Fluorescence spectroscopy of a naturally occurring carbazole alkaloid: murrayanine

The fluorescence properties of a naturally occurring carbazole alkaloid, murrayanine, have been studied in various polar solvents and micellar systems. It was found that fluorescence peak position and intensity are extremely sensitive to the nature of the solvent medium. Murrayanine fluorescence has been further utilized to determine the critical micellization concentration of Pluronic F68, an amphiphilic copolymer with potential applications in drug-delivery. Time-resolved fluorescence and fluorescence anisotropy decay of murrayanine measured in several n-alcohols display a monotonic retardation with increasing chain-lengths of the alcohols.     

基于分子表面静电势参数分析溶剂的极性性质

用理论教育处导出的分子表面静电势参数II和σ^2tot对一系列溶剂的五种极性 批E^N T、π^*、Py、SPP和S‘进行了相关分析,与Catalan的理论热力分析结果进行了比较。结果显示：S‘是一个适用性委有好的溶剂极性参数,而质子性溶剂的E ^NT值、芳香化合物和多卤代化合物的π ^*值和SPP值则存在着一定的非极性因素。     

Improved surface morphology of flow-modulated MOVPE grown AIN on sapphire using thin medium-temperature AIN buffer layer

High-temperature (HT) AIN films were grown on (0 0 0 1) sapphire by low-pressure flow-modulated (FM) metal organic vapor phase epitaxy (MOVPE) with and without inserting a thin medium-temperature (MT) AIN layer. To suppress parasitic reactions between the sources of trimethylaluminum (TMA) and ammonia (NH₃), TMA and NH₃ was introduced to the reactor of MOVPE by alternating supply way. Surface morphology and crystalline quality were characterized by a scanning electronic microscopy (SEM), atomic force microscopy (AFM) and X-ray rocking curve (XRC) measurements of (0 0 0 2) and (10-12) diffractions. The AFM and SEM measurements indicated that the thin MT-AIN layer had a strong influence on the surface morphology of the HT-AIN films. The surface morphology became quite smooth by inserting the thin MT-AIN layer and surface RMS roughness values were 0.84 nm and 13.4 nm for the HT-AIN films with and without inserting the thin MT-AIN buffer layer, respectively. By etching the samples in aqueous KOH solution, it was found that the polarity of AIN films was different, the HT-AIN film with the thin MT-AIN layer could not be etched, indicating that the film had an Al-polar surface; however, the film without the MT-AIN layer was etched, which was explained that that film had a N- or mixed-polar surface. The mechanism for the origin of the different polarity of HT-AIN with and without the thin MT-AIN layer was proposed and discussed in detail.     

Control of polarity and defects in the growth of AlN films on Si (111) surfaces by inserting an Al interlayer

We discuss the role of the Al interlayer in the suppression of pinhole formations and also look at the polarity transition of the AlN layers from N-polarity to Al-polarity when this Al interlayer is present. The AlN layers were grown by molecular beam epitaxy on an AlN nucleation layer. A thin Al interlayer was deposited on the initial nucleated AlN layer after the nitridation of the Al-soaked Si (111) substrates. The AlN layer with an Al interlayer showed a relatively smooth surface with a reduced density of pinholes compared with the AlN layer grown without an Al interlayer. In addition, the AlN layer with an Al interlayer showed some stacking faults in the interface between the Si substrate and the A1N layer. We also identify the polarity change of the AlN layer after the insertion of a thin Al interlayer from N-polarity to Al-polarity by chemical etching. A simple model is constructed to explain the polarity change and the pinhole suppression due to the Al interlayer.     

On a problem of Neumann

A conjecture widely attributed to Neumann is that all finite non-desarguesian projective planes contain a Fano subplane. In this note, we show that any finite projective plane of even order which admits an orthogonal polarity contains many Fano subplanes. The number of planes of order less than $n$ previously known to contain a Fano subplane was $O(logn)$, whereas the number of planes of order less than $n$ that our theorem applies to is not bounded above by any polynomial in $n$.     

牛血清白蛋白与十二烷基硫酸钠作用的机理

利用电动势法得到了牛血清白蛋白(BSA)与十二烷基硫酸钠(SDS)相互作用的结合等温线. 通过四阶导数紫外光谱法和荧光光谱法研究了相互作用过程中芳香族氨基酸残基微环境极性的变化. 通过研究发现, 随着SDS浓度的逐渐增大, SDS在BSA上的平均结合数(v)逐渐增大, 色氨酸(Trp)残基所处微环境的极性在减弱后保持基本不变, 酪氨酸残基所处微环境的极性在明显增强后稍有减弱, 苯丙氨酸残基所处微环境的极性略有增强. 结果表明, 当v由0增大到14时, SDS主要结合在BSA的Trp-213附近并逐渐形成聚集体, 从而诱导BSA由结构域ⅡA 开始逐渐展开. 此后, SDS呈正协同作用的特点与BSA 结合, v急剧增大. 当v约为302 时, SDS在BSA上的结合基本达到饱和, BSA的构象趋于稳定.     

Versatile lipid profiling by liquid chromatography–high resolution mass spectrometry using all ion fragmentation and polarity switching. Preliminary application for serum samples phenotyping related to canine mammary cancer

Lipids represent an extended class of substances characterized by such high variety and complexity that makes their unified analyses by liquid chromatography coupled to either high resolution or tandem mass spectrometry (LC–HRMS or LC–MS/MS) a real challenge. In the present study, a new versatile methodology associating ultra high performance liquid chromatography coupled to high resolution tandem mass spectrometry (UHPLC–HRMS/MS) have been developed for a comprehensive analysis of lipids. The use of polarity switching and “all ion fragmentation” (AIF) have been two action levels particularly exploited to finally permit the detection and identification of a multi-class and multi-analyte extended range of lipids in a single run. For identification purposes, both higher energy collision dissociation (HCD) and in-source CID (collision induced dissociation) fragmentation were evaluated in order to obtain information about the precursor and product ions in the same spectra. This approach provides both class-specific and lipid-specific fragments, enhancing lipid identification. Finally, the developed method was applied for differential phenotyping of serum samples collected from pet dogs developing spontaneous malignant mammary tumors and health controls. A biological signature associated with the presence of cancer was then successfully revealed from this lipidome analysis, which required to be further investigated and confirmed at larger scale.     

介质极性敏感膜的制备和性能研究

以交联壳聚糖膜为载体,芘为介质极性探针,制备并表征了一种介质极性敏感膜,研究了该膜对醇-水混合溶剂极性的响应行为.基于极性测定,对十二烷基硫酸钠(SDS)和十二烷基磺酸钠(SLS)水溶液中胶束的形成进行了检测.结果表明,该膜具有较好的可逆性和重现性,且制膜方法简单、快速.     

New stationary phase polarity parameters considering the electric intermolecular interactions in gas chromatographic column

Summary The possibility of evaluation of the parameters representing the dispersive solute-solvent interactions is presented. B_N and B_s values can be used to describe the liquid phase polarity and to predict the retention indices of alcohols when the model polyxyethylene glycol dialkyl ethers and their sulphur analogs are used as stationary phases. The possibility of the first ionization potentials estimation is also presented.