共振瑞利散射法测定盐渍食品中的亚铁氰化钾

1引言研究发现,在弱酸性介质中,当Fe(Ⅲ)与亚铁氰化钾反应生成普鲁士蓝时,在引起吸收光谱变化的同时,将导致共振瑞利散射(RRS)的显著增强,其最大散射波长在316nm,它不仅是灵敏度高,检出限达4.36μg/L,远远高于分光光度法(检出限为1mg/L),而且有色盐渍食品本身的颜色不产生共振瑞利散射,因此不干扰测定。从而解决了盐渍食品本身颜色对分光光度法测定亚铁氰化钾的困扰。据此提出了一种灵敏度高、选择性好、而且简便快速的RRS法。2实验部分2.1仪器与试剂F-2500型荧光分光光度计(日本岛津公司),狭缝宽度10nm;UV-8500型紫外-可见分光光度计(…     

超塑性变形晶界效应研究综述

自1934年超塑性现象被发现, 一直以其特殊的塑性变形机制而备受关注.本文以对超塑性变形晶界研究为主线, 从力学角度总结了近年来研究成果. 包括: 基于晶界拓扑构造、统计规律以及能量耗散的力学模型; 论述了由孔洞损伤导致的超塑性沿晶破坏、晶界结构演化与宏观率敏感性之间的关系; 列举了考虑晶界效应的典型超塑性数值模型; 总结并讨论了晶界滑移定量表征的重要实验手段, 指出超塑性研究中需进一步拓展的领域: 多尺度耦合的超塑性力学、材料制备及组合工艺中利用超塑性.      

气相色谱-质谱测定环境样品的质量控制与质量保证

以环境样品分析为例,指出了气相色谱-质谱技术分析测定过程的质量控制的主要因素及措施,并从内标物、替代品、进样系统、色谱柱、质谱运行状态、保留时间、标准曲线、仪器软件系统等方面对如何提高分析过程的准确度进行了讨论。     

基于支撑向量机算法的抗干扰混合波束成形系统

针对复杂电磁环境下毫米波阵列的空间辐射干扰抑制问题,设计了一种低成本的自适应波束成形系统。首先建立了复杂电磁环境下通信系统模型,建立目标函数。然后利用机器学习中支持向量机算法将原非凸约束问题转化为二阶锥优化问题,获得理想编码矢量。最后利用梯度追踪算法对理想波束矢量进行稀疏重构,完成抗干扰波束的低复杂度实现。仿真结果表明,提出的波束成形系统能够对干扰作出有效抑制,能提升通信质量。     

Heat and mass transfer characteristics of three-dimensional bell-shaped polysilicon chemical vapor deposition reactor

Journal of Thermal Analysis and Calorimetry - Polysilicon, the crucial material of photovoltaic field, is commonly produced in a Siemens chemical vapor deposition (CVD) reactor with a complex...     

Nonlinear vibrations of an axially moving plate in aero-thermal environment

Nonlinear Dynamics - In this paper, the nonlinear primary resonances of an axially moving plate in aero-thermal environment concerning on manufacturing background of the hot rolling are studied....     

Microwave‐assisted Ionothermal Synthesis and Characterization of Zeolitic Imidazolate Framework‐8

The zeolitic imidazolate framework‐8 (ZIF‐8) was successfully synthesized using ionic liquids as structure‐directing agent under microwave irradiation. Ionic liquids are green solvents with low vapour pressure and good thermal stability. They are appropriate templates for microporous materials and ideal microwave absorbers. The microwave‐assisted ionothermal synthesis applied in this paper was expected to be a promising method for the preparation of microporous materials. Results showed that the as‐synthesized samples (300–500 nm in diameter) could be synthesized in a short time (60 min) and possessed regular morphology, stable structure and high thermal stability (up to 720°C in argon atmosphere). Nitrogen adsorption‐desorption test illustrated that samples produced by microwave heating had a higher surface area. Carbon dioxide adsorption test indicated that the samples synthesized by microwave heating had better carbon dioxide adsorption ability than those by conventional heating.     

Initial DNA Interactions of the Binuclear Threading Intercalator Λ,Λ‐[μ‐bidppz(bipy)4Ru2]4+: An NMR Study with [d(CGCGAATTCGCG)]2

Binuclear polypyridine ruthenium compounds have been shown to slowly intercalate into DNA, following a fast initial binding on the DNA surface. For these compounds, intercalation requires threading of a bulky substituent, containing one Ru^II, through the DNA base‐pair stack, and the accompanying DNA duplex distortions are much more severe than with intercalation of mononuclear compounds. Structural understanding of the process of intercalation may greatly gain from a characterisation of the initial interactions between binuclear Ru^II compounds and DNA. We report a structural NMR study on the binuclear Ru^II intercalator Λ,Λ‐B (Λ,Λ‐[μ‐bidppz(bipy)₄Ru₂]⁴⁺; bidppz=11,11′‐bis(dipyrido[3,2‐a:2′,3′‐c]phenazinyl, bipy = 2,2′‐bipyridine) mixed with the palindromic DNA [d(CGCGAATTCGCG)]₂. Threading of Λ,Λ‐B depends on the presence and length of AT stretches in the DNA. Therefore, the latter was selected to promote initial binding, but due to the short stretch of AT base pairs, final intercalation is prevented. Structural calculations provide a model for the interaction: Λ,Λ‐B is trapped in a well‐defined surface‐bound state consisting of an eccentric minor‐groove binding. Most of the interaction enthalpy originates from electrostatic and van der Waals contacts, whereas intermolecular hydrogen bonds may help to define a unique position of Λ,Λ‐B. Molecular dynamics simulations show that this minor‐groove binding mode is stable on a nanosecond scale. To the best of our knowledge, this is the first structural study by NMR spectroscopy on a binuclear Ru compound bound to DNA. In the calculated structure, one of the positively charged Ru²⁺ moieties is near the central AATT region; this is favourable in view of potential intercalation as observed by optical methods for DNA with longer AT stretches. Circular dichroism (CD) spectroscopy suggests that a similar binding geometry is formed in mixtures of Λ,Λ‐B with natural calf thymus DNA. The present minor‐groove binding mode is proposed to represent the initial surface interactions of binuclear Ru^II compounds prior to intercalation into AT‐rich DNA.     

Pt-M (M = Co,Ni, Fe)/g-C3N4复合材料构建及其高效光解水制氢性能

Platinum (Pt) is recognized as an excellent cocatalyst which not only suppresses the charge carrier recombination of the photocatalyst but also reduces the overpotential for photocatalytic H₂ generation. Albeit of its good performance, the high cost and low abundance restricted the utilization of Pt in large-scale photocatalytic H₂ generation. Pt based transition metal alloys are demonstrated to reveal enhanced activities towards various catalytic reactions, suggesting the possibility to substitute Pt as the cocatalyst. In the present work, Pt was partially substituted with Co, Ni, and Fe and Pt-M (M = Co, Ni, and Fe)/g-C₃N₄ composites were constructed through co-reduction of H₂PtCl₆ and transition metal salts by the reductant of ethylene glycol. The crystal structure and valence states were measured by X-ray diffractometer (XRD) and X-ray photoelectron spectrometer (XPS), respectively. The higher degree of XRD peaks and larger binding energies for Pt 4f_5/2 and Pt 4f_7/2 after incorporating Co²⁺ ions indicated that Co was successfully introduced into the lattice of Pt and Pt-Co bimetallic alloys was attained through the solvothermal treatment. The morphology was subsequently observed by transmission electron microscope (TEM), which showed a good dispersion of Pt-Co nanoparticles on the surface of g-C₃N₄. Meanwhile, the shrinkage of lattice fringe after introducing cobalt salt further confirmed the presence of Pt-Co bimetallic alloys. The UV-Vis absorption spectra of g-C₃N₄ and Pt, Pt-Co deposited g-C₃N₄ were subsequently performed. It was found that the absorption edges were all consistent for all three samples as anticipated, implying that the band gap energy was maintained after hybridizing with Pt or Pt-Co alloys. Furthermore, the photocatalytic H₂ generation was carried out over the as-prepared composites with triethanolamine (TEOA) as sacrificial reagent. Under visible-light illumination, the1% (w) Pt_2.5M/g-C₃N₄ (M = Co, Fe, Ni) composites all exhibited higher or comparable activity towards photocatalytic H₂ generation when compared to 1% (w) Pt loaded counterpart. In addition, the atomic ratios of Pt/Co and the loading amount of Pt-Co cocatalyst were modified to optimize the photocatalytic performance, among which, 1% (w) Pt_2.5Co/g-C₃N₄ composite revealed the highest activity with a 1.6-time enhancement. Electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra indicated that the enhancement might be attributed to improved charge transfer from g-C₃N₄ to Pt_2.5Co cocatalyst and inhibited charge carrier recombination in the presence of Pt_2.5Co cocatalyst. Therefore, the present study demonstrates the great potential to partially replace Pt with low-cost and abundant transition metals and to fabricate Pt based bimetallic alloys as promising cocatalysts for highly efficient photocatalytic H₂ generation.     

Disulfide‐centered star‐shaped polypeptide‐PEO block copolymers for reduction‐triggered drug release

Disulfide‐centered star‐shaped poly(ε‐benzyloxycarbonyl‐l ‐lysine)‐b‐poly(ethylene oxide) block copolymers (i.e., A₂B₄ type Cy‐PZlys‐b‐PEO) were synthesized by the combination of ring‐opening polymerization and thiol‐yne chemistry. Their molecular structures and physical properties were characterized in detail by FTIR, ¹H NMR, gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscope. Despite mainly exhibiting an α‐helix conformation, the inner PZlys blocks within copolymers greatly prohibited the crystallinity of the outer PEO blocks and presented a liquid crystal phase transition behavior in solid state. These block copolymers Cy‐PZlys‐b‐PEO self‐assembled into nearly spherical micelles in aqueous solution, which had a hydrophobic disulfide‐centered PZlys core surrounded by a hydrophilic PEO corona. As monitored by means of DLS and TEM, these micelles were progressively reduced to smaller micelles in 10 mM 1,4‐dithiothreitol at 37 °C and finally became ones with a half size, demonstrating a reduction‐sensitivity. Despite a good drug‐loading property, the DOX‐loaded micelles of Cy‐PZlys‐b‐PEO exhibited a reduction‐triggered drug release profile with an improved burst‐release behavior compared with the linear counterpart. Importantly, this work provides a versatile strategy for the synthesis of the disulfide‐centered star‐shaped polypeptide block copolymers potential for intracellular glutathione‐triggered drug delivery systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2000–2010