磨削粗糙表面法向接触刚度研究

为更加准确地描述机械磨削表面的接触刚度,本文在现有统计分析理论的基础上,提出了一种新的粗糙表面接触模型。模型针对接触表面微凸体形貌,将原有的球体假设采用cos函数曲线回转体代替,在假设形貌的基础上重新解算了微凸体弹塑性变形的临界压入深度,推导出了接触区域真实接触压力与接触刚度关系表达式。通过数值仿真方法得到了不同塑性指数下平均距离、接触刚度与接触压力之间的变化关系。对比结果显示,随着塑性指数的增大,本文模型的平均距离与球形模型的平均距离之间的差值逐渐增大。在接触刚度方面,本文模型相比球形模型更加贴近实验结果,并且随着塑性指数的增加,球形模型与本文模型之间的差值越来越大。本文模型结果与实验数据的相对偏差能够控制在5%以内,从而验证了本文模型的正确性,为更加准确地描述磨削表面零件的接触行为提供理论基础。     

Fatigue damage evolution in silicon films for micromechanical applications

In this paper we examine the conditions for surface topography evolution and crack growth/fracture during the cyclic actuation of polysilicon microelectromechanical systems (MEMS) structures. The surface topography evolution that occurs during cyclic fatigue is shown to be stressassisted and may be predicted by linear perturbation analyses. The conditions for crack growth (due to pre-existing or nucleated cracks) are also examined within the framework of linear elastic fracture mechanics. Within this framework, we consider pre-existing cracks in the topical SiO₂ layer that forms on the Si substrate in the absence of passivation. The thickening of the SiO₂ that is normally observed during cyclic actuation of Si MEMS structures is shown to increase the possibility of stable crack growth by stress corrosion cracking prior to the onset of unstable crack growth in the SiO₂ and Si layers. Finally, the implications of the results are discussed for the prediction of fatigue damage in silicon MEMS structures.     

Application of chromatography technology in the separation of active alkaloids from Hypecoum leptocarpum and their inhibitory effect on fatty acid synthase

A method that involved the combination of pH‐zone‐refining counter‐current chromatography and semipreparative reversed‐phase liquid chromatography has been established for the preparative separation of alkaloids from Hypecoum leptocarpum. From 1.2 g of crude sample, 31 mg N‐feruloyltyramine, 27 mg oxohydrastinine, 47 mg hydroprotopine, 25 mg leptopidine, and 18 mg hypecocarpine have been obtained. The structure of the new compound, hypecocarpine, is confirmed based on the analysis of spectroscopic data, including NMR, UV, and IR spectroscopy and positive electrospray ionization mass spectrometry. The known chemical structures were characterized on the basis of ¹H and ¹³C NMR spectroscopy. The purities of the five alkaloids are all over 92.7% as determined by high‐performance liquid chromatography. The alkaloids’ cytotoxicity in breast cancer cells is assessed by using a Cell Counting Kit assay and their inhibitory effect on fatty acid synthase expression is assessed by a Western blot assay. These results suggest that leptopidine could suppress growth and induce cytotoxicity in breast cancer cells and that the cytotoxicity of leptopidine may be related to its inhibitory effect on fatty acid synthase expression.     

Syntheses,crystal structures,electrochemical and photocatalytic properties of two mixed-ligand cobalt(II) coordination polymers based on flexible bis(2-methylbenzimidazole) dicarboxylic acid ligands

Two Co(II) coordination polymers (CPs), namely [Co(L)(tp)] _n (1) and [Co(L)_0.5(tbip)·H₂O] _n (2), (L = 1,6-bis(2-methylbenzimidazolyl) hexane, H₂tp = terephthalic acid, H₂tbip = 5-tert-butyl isophthalic acid), were hydrothermally synthesized and characterized by physicochemical and spectroscopic methods. CP 1 possesses a 2D (4,4) corrugated layer structure, which further extends into a 3D supramolecular framework by π–π stacking interactions, while CP 2 has a 1D ladder-like chain structure and combines into a 2D layer via O–H?O hydrogen-bonding interactions. The thermal stabilities, luminescence and electrochemical properties of both CPs, as well as photocatalytic activities for the decomposition of methylene blue, were presented. The photocatalytic mechanism was investigated by introducing t-butyl alcohol, EDTA-2Na and benzoquinone as ?OH, (hole)⁺ and ·O^2? scavengers, respectively.     

1H NMR研究溶质浓度对三碳多元醇水溶液氢键作用以及玻璃化的影响

为考察溶质浓度对三碳多元醇水溶液氢键作用以及不同物质玻璃态形成能力的影响,采用¹H NMR外标法研究不同浓度的1-丙醇（NPA）,2-丙醇（IPA）,1,2-丙二醇（PG）,1,3-丙二醇（PD）和丙三醇（glycerol）的水溶液在室温常压下质子化学位移.结果表明:具有CH₃CH（OH）一基团的PG烷基质子的化学位移变化趋势与其他几种醇相比有较大差异.醇羟基质子与水分子的氧形成较强O-H…O氢键.相同摩尔分数下,羟基数的增加导致水质子和羟基质子的化学位移降低,而且羟基位置不同也会导致水质子和羟基质子化学位移差异.这几种三碳多元醇碱性强弱的顺序和降低冰的均相成核温度能力的顺序一致,即glycerol>PG>PD>IPA>NPA,¹H NMR技术表明glycerol和PG更适合用作低温保护剂.     

Effects of preparation conditions of Au/FeO_x /Al_2O_3 catalysts prepared by a modified two-step method on the stability for CO oxidation

Composite oxide FeO x /Al 2 O 3 -supported gold catalysts were prepared by a modified two-step method. The effects of preparation conditions on the initial catalytic activity and long-time stability were studied for CO oxidation. XRD, XPS and in situ FTIR were employed to investigate the state of FeO x and the species on the catalyst surface. The results showed that Au/FeO x /Al 2 O 3 catalysts prepared by this method exhibited high activity and high stability in a wide pH value range. Calcination pretreatm...     

Magnetic solid-phase extraction using magnetic hypercrosslinked polymer for rapid determination of illegal drugs in urine

A novel magnetic material Fe₃O₄/SiO₂/P(MAA‐co‐VBC‐co‐DVB) was prepared via the hypercrosslinking of its precursor which was produced via precipitation polymerization of methacrylic acid (MAA), vinylbenzyl chloride (VBC), and divinylbenzene (DVB) in the presence of Fe₃O₄/SiO₂ submicrospheres with the surface containing abundant reactive double bonds. The resultant sorbent was characterized by scan electron microscopy, N₂ adsorption, and Fourier transform infrared spectroscopy. It was found that this material had remarkable features such as large surface area (500 m²/g) and pore volume (0.32 cm³/g), as well as desirable chemical composition (including hydrophobic and ion‐exchange moieties). Taking advantages of the Fe₃O₄/SiO₂/P(MAA‐co‐VBC‐co‐DVB), a magnetic SPE (MSPE) coupled with capillary electrophoresis (CE) method was developed for the determination of illegal drugs in urine samples. The extraction time could be clearly shortened up to 3 min. The recoveries of these drug compounds were in the range of 84.0–123% with relative standard deviations ranging between 1.7 and 10.5%; the limit of detection was in the range of 4.0–6.0 μg/L. The proposed method is simple, effective, and low‐cost, and provides an accurate and sensitive detection platform for abused drug analysis.     

One-pot synthesis of Cu1.94S-CdS and Cu1.94S-Zn(x)Cd(1-x)S nanodisk heterostructures

Nanodisk heterostructures consisting of monoclinic Cu(1.94)S and wurtzite CdS have been colloidally synthesized for the first time. Initially, hexagonal-shaped nanodisks of Cu(1.94)S were produced upon thermolysis of a copper complex in a solvent mixture of HDA and TOA at 250 °C. Rapid addition of Cd precursor to the reaction mixture resulted in the partial conversion of Cu(1.94)S into CdS, yielding Cu(1.94)S-CdS nanoheterostructures. The original morphology of the Cu(1.94)S nanodisks was conserved during the transformation. When Zn precursor was added together with the Cd precursor, Cu(1.94)S-Zn(x)Cd(1-x)S nanodisks were generated. These two-component nanostructures are potentially useful in the fabrication of heterojunction solar cells.     

One-, two- and three-photon spectroscopy of π-conjugated dendrimers: cooperative enhancement and coherent domains

We use wavelength tunable femtosecond pulses to measure intrinsic (simultaneous) two-photon absorption (2PA) and three-photon absorption (3PA) molecular cross section in two series of π-conjugated dendrimers built of identical 4,4′-bis(diphenylamino) stilbene (BDPAS) and 4,4′-bis(diphenylamino) distyrylbenzene (BDPADSB) repeat units. Record large 2PA cross sections, σ₂=10⁻⁴⁶ cm⁴ s are obtained for the largest second-generation BDPAS-based dendrimer, as well as zeroth-generation 4-arm BDPADSB-based dendrimer. In both series, maximum 2PA cross section increases nonlinearly with the number of π-electrons, whereas for higher generations this dependence turns to linear one. 3PA cross section also increases nonlinearly with the size of the system in the series of BDPAS-based molecules, amounting a record large value, σ₃=10⁻⁷⁹ cm⁶ s², for the largest, second-generation dendrimer. We interpret these results in terms of direct inter-branch conjugation, which facilitates cooperative enhancement of the nonlinear-optical response. We propose a simple model which allows us to determine the effective size of coherent domains (extent of conjugation), which, in turn, determines the optimum dendrimer size for most efficient nonlinear response.