Hydrodynamics with heated microelectrodes

Voltammetry with continuously heated microelectrodes yields well-defined sigmoidal current-voltage curves. Unlike hydrodynamic electrodes, the surface temperature of a heated electrode can be adjusted arbitrarily within a certain range. Inside a thermal layer, a virtually stagnant diffusion layer of constant thickness _diff exists. _diff is independent of temperature within a certain range. On the basis of this theory, equations are derived which play a similar role to, for instance, the Levich equation for the rotating disk electrode. Reasonable agreement of the derived relationship with the results from voltammetric experiments is obtained.     

Influence of crystal structure on the Co diffusion behavior in the Zn1−xCoxO system

The solid state interaction of the Zn_1−xCo_xO nominal system is investigated by means of diffusion couples and analysis of co-precipitated samples. The formation of a homogeneous Co:ZnO solid solution is found to be determined by the crystal structure from which Co^II ions diffuse into the wurtzite lattice. No diffusion is observed whenever the CoO rock-salt structure is formed from the Co^II precursor. On the contrary, the diffusion from the Co₃O₄ spinel phase is feasible but has a limited temperature range defined by the reduction at a high temperature of Co^III-Co^II, since this process again leads to the formation of the rock-salt structure. However, when using a highly reactive and homogeneous co-precipitated starting powder, neither the spinel phase nor the rock-salt structure is formed, and a Co^II:ZnO solid solution is obtained, which remains stable up to high temperatures.     

Quality control of medicinal herbs Fructus gardeniae, Common Andrographis Herb and their preparations for their active constituents by high-performance liquid chromatography-photodiode array detection-electrospray mass spectrometry

Dehydroandrographolide, andrographolide and geniposide are the main active constituents of many herbal medicines, e.g., Fructus gardeniae, Common Andrographis Herb. They are used as the markers to control the quality of such herbal medicines and their herbal preparations. In this paper, a simple and sensitive high-performance liquid chromatographic (HPLC) method coupled with photodiode array detection (DAD) and electrospray mass spectrometry (ESI/MS) were developed to determine the three compounds simultaneously in extracts of medicinal herbs and herbal preparations produced by different companies. The extracts were separated on a C₁₈ reversed phase HPLC column, with a gradient solvent system, the time for the separation of the three target analytes was 10 min. The abundance ions were recorded using selected ion monitoring (SIM) mode with m/z 297.3, 297.3 and 411.1 for dehydroandrographolide, andrographolide and geniposide, respectively. The limit of detection for dehydroandrographolide, andrographolide and geniposide were 20, 30 and 150 ng mL⁻¹, respectively. The proposed method was successfully applied to the determination of the contents of the compounds in related to medicinal herbs and preparations.     

不同气氛环境中钢/铜摩擦副的高速干滑动摩擦磨损特性研究

采用MMS-1G型高温高速摩擦磨损试验机研究了在氧气和二氧化碳2种气氛环境中CrNiMo钢/H96黄铜摩擦副的高速干滑动摩擦磨损特性,采用扫描电子显微镜和X射线光电子能谱仪对CrNiMo钢销试样的磨损表面形貌及其元素的化学状态进行分析,结合摩擦表面宏观温度的测量,分析了不同气氛环境中pv值对摩擦副摩擦磨损特性的影响.结果表明,在不同气氛环境中,摩擦副表现出完全不同的摩擦磨损特性,在二氧化碳气氛环境中,摩擦副的摩擦系数与CrNiMo钢的磨损率均高于氧气气氛环境中,这是由于2种气氛环境中的摩擦表面温度及其磨损机制的差异所致.二氧化碳气氛环境中的摩擦表面温度高于氧气气氛环境中的摩擦表面温度,其主要磨损机制为磨粒磨损、金属流变和粘着磨损;而氧气气氛环境中主要表现为氧化磨损和粘着磨损.     

一类特殊非齐次树上马氏链的若干强大数定律

首先给出了一类特殊非齐次树上可数状态马氏链的局部收敛定理,作为推论,得到了此类树上可数状态马氏链关于状态与状态序偶出现频率的若干极限性质,最后得到了这类特殊非齐次树上有限状态马氏链关于状态与状态序偶出现频率的强大数定律.     

傅里叶变换红外光谱分析三种彝药材

傅里叶变换红外光谱研究三种彝药材的指纹图谱,并初步分析了它们的有效药物成分和图谱的关系.在金丝杜仲的块根中,淀粉纤维素含量高,而在真金草和回心草中,纤维素和蛋白质的含量更高些.实验发现,金丝杜仲的止血功能和溶血功能可能与所含鞣质类物质和四环三萜类成分有关.真金草的抗梅毒作用可能源于其中的生物碱的生理活性,其活血作用也与四环三萜类物质成分有关,所含多糖和苷则对治疗肝炎有效.回心草的安神作用可能与所含的三萜皂元成分有关,三萜皂元具有安定作用.利用傅里叶变换红外光谱法可以方便、快速和准确地分析中药材的某些有效成分,文章对三种药材的部分药物疗效在分子水平上给出了一定的科学依据.     

Tetrazole thiolate/disulfide organic redox couples carrying long alkyl groups in dye-sensitized solar cells with Pt-free electrodes

Colorless tetrazole thiolate/sulfide redox couples carrying long alkyl groups, such as n-butyl, n-hexyl, and n-octyl groups, were synthesized as electrolytes in iodine/iodide-free dye-sensitized solar cells (DSSCs). Among N719/TiO₂-based DSSCs employing these highly soluble redox couples for 3-methoxypropionitrile (3-MPN) and ionic liquid with PEDOT counter electrode, the DSSC with n-hexyl redox analogue gave an optimized η value of 4.32%. An observed respectable quantum efficiency for 400–500 nm light is in sharp contrast to the decreased performance for iodine/iodide systems that originates from the substantial light absorption of iodine. On the other hand, the redox possessing n-octyl group significantly lowered the cell performance, which could be a result of the much increased resistance of electrolyte diffusion in the DSSC.     

Effect of wine processing and acute blood stasis on the serum pharmacochemistry of rhubarb: A possible explanation for processing mechanism

As a specific item mentioned in traditional Chinese medicine theory, processing can fulfill different requirements of therapies. Crude and wine‐processed rhubarbs are used as drastic and mild laxatives, respectively. In this study, a practical method based on ultra‐fast liquid chromatography coupled with diode‐array detection and ion trap time‐of‐flight mass spectrometry was developed to screen and analyze multiple absorbed bioactive components and metabolites in the serum of both normal and acute blood stasis rats after oral administration of crude or wine‐processed rhubarbs. A total of 16 compounds, mainly including phase II metabolites, were tentatively identified. Possible explanations for the processing‐induced changes in pharmacological effects of traditional Chinese medicines were first explored at serum pharmacochemistry level.     

Eremophilenolides from Cacalia Roborowskii

ThegenusCacaliabelongstothetribesenecioneae,facelyCompositae,andcomprisesmorethan60speciesoccurringinChina,'ofwhichca.26specieslacelongbeenusedasChinesetradihonalfolkherb.2SeveralspeciesofthegenusCacahawereinvestigatedduetotheirantioxidantantiradical,andantiltistamineactivities.3Thepresenceofpyrrolizidinealkaloidsandsesquitefpenesinmanyspeciesoftribesenencioneaceiswelldocumented.'"InacontinuahonoftileStudyontilesmictureswiUIbioactivitiesfromtileCacahagenus,wereportheretheisolahonandsmictta…