奥氏体不锈钢深冷低温冲击试验方法研究

以液氦作为冷源,结合G-M低温制冷机,实现-196~-269℃深冷温度环境,探索深冷低温冲击试验方法。结果表明,试样从低温环境中取出后置于大气环境中,温度出现快速回升。对于不同试验低温,可采用不同方法进行试验。试验温度T=4.2K时,可采用制冷机预冷+液氦持续喷淋的方法进行降温。试验温度10≤T77K时,可采用玻璃容器填充气凝胶粉体对试样进行绝热保温处理;或根据试验温度以及回温测试结果,以一定的过冷温度补偿值保证试验温度。过冷温度补偿方法可满足常规冲击试验的要求,但需要相对较大的过冷温度补偿值;玻璃容器填充粉体包裹试样,可减缓试样温度回升,但对材料冲击吸收能量有一定影响,可用多试样冲击试验并进行修正以反映材料冲击韧性水平。     

Reinvestigation of the Structure of Protonated Lysine Dimer

To better understand inconsistencies between the predicted infrared (IR) spectra of previously suggested isomers of Lys₂H⁺ reported by Wu et al. (J. Am. Soc. Mass Spectrom. 22:1651–1659, 18) and the experimental IR photon dissociation (IRPD) spectrum obtained by Oh et al. (J. Am. Chem. Soc. 127:4076–4083, 4), the structure of Lys₂H⁺ was reinvestigated using IRPD spectroscopy in the extended region 2700–3700 cm^?1 and theoretical calculations. The new experimental IRPD spectrum is in good agreement with Oh’s spectrum in the corresponding wavelength range. Based on calculations at the MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) and MP2/6-31?+?G(d,p)//MP2/6-31?+?G(d,p) levels, a new salt-bridged isomer, ZW1, was found to be the most stable isomer; it is more energetically favored than the previously suggested charge-solvated isomer LL-CS01 by 10 or 26 kJ mol^?1. Although the calculated IR spectrum of ZW1 is in good agreement with the experimental one in the range 2700–3700 cm^?1, it is in poor agreement with the previous IRPD spectrum in the range 1000–1900 cm^?1. This investigation shows that the intermolecular interactions inside the dimer are more complex than previously supposed. It is possible that both salt-bridged and charge-solvated isomers of Lys₂H⁺ are stable in the gas phase, and the isomers generated during ionization are sensitive to the experimental conditions.

Resonance Rayleigh scattering method for direct determination of polyacrylamide in water samples using basic phenothiazine dyes

Binding polyacrylamide (PAM) with some basic phenothiazine dyes such as methylene blue (MB), toluidine blue (TB) or Azure B (AB) etc. can result in a significant enhancement of resonance Rayleigh scattering (RRS). The maximum RRS wavelengths (λ_max) appear at 348, 340 and 342 nm for MB, TB, and AB systems, respectively. Accordingly, a new RRS method for the direct determination of PAM at nanogram levels has been established. The optimum conditions of these reactions, the influencing factors have been investigated. The RRS intensity is directly proportional to the concentration of PAM in the range of 0.040–5.0 μg/mL for three systems. The methods exhibit high sensitivities, and the detection limits are 15.9 ng/mL for MB system, 44.0 ng/mL for TB system, and 59.8 ng/mL for AB system. The selectivity of the method is investigated by using MB system owing to the highest sensitivity. Concentrations of PAM in tap water, synthetic water and practical waste water samples are determined satisfactorily. The reaction mechanism and RRS enhancement reasons are discussed.     

Optical properties of flower‐like CdS prepared by a hydrothermal method with SDBS as surfactant

In this article, flower‐like CdS structures have been prepared by a hydrothermal method with SDBS as surfactant. The influences of different experimental conditions on the morphologies, UV‐Vis and fluorescence properties of CdS have been investigated. The performances of CdS have been analyzed by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet‐visible (UV–Vis) and room‐temperature photoluminescence (PL). The XRD result indicates that the flower‐like CdS structures are of hexagonal phase. The FESEM results indicate that the main role of SDBS is to make the CdS crystals assemble together to form the flower‐like structures. The UV–Vis results show CdS has a strong absorption in the ultraviolet region and visible‐light region. The PL results show CdS has two emission peaks, respectively at 461 nm and 553 nm. The growth mechanism for the formation of flower‐like CdS structures is also described.     

Preparation of styrene–divinyl benzene copolymer-supported platinum complexes and their catalytic properties in hydrosilylation

A new type of catalyst for the hydrosilylation of unsaturated monomers with dichloromethylsilane (DCMS) was prepared, which consisted of thiolmethylene-substituted styrene–divinyl benzene copolymer and platinum. When using DCMS as a hydrosilylation agent, these catalysts showed a high activity in the hydrosilylation of vinyl and acetylene monomers as styrene, alkyl vinyl silanes, acetylene, phenyl acetylene, butyl acrylate. The activities of catalysts were not significantly reduced even after 20 reuse cycles.     

Unraveling the reactivity of a cationic iminoborane: avenues to unusual boron cations

A cationic terminal iminoborane [Mes*N B ← IPr₂Me₂][AlBr₄] (3⁺[AlBr₄]⁻) (Mes* = 2,4,6-tri-tert-butylphenyl and IPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) has been synthesized and characterized. The employment of an aryl group and N-heterocyclic carbene (NHC) ligand enables 3⁺[AlBr₄]⁻ to exhibit both B-centered Lewis acidity and BN multiple bond reactivities, thus allowing for the construction of tri-coordinate boron cations 5⁺–12⁺. More importantly, initial reactions involving coordination, addition, and [2 + 3] cycloadditions have been observed for the cationic iminoborane, demonstrating the potential to build numerous organoboron species via several synthetic routes.

An NHC-stabilized aryliminoboryl cation exhibits both boron-centered Lewis acidity and multiple bond reactivity and could be utilized as an effective synthon for unusual cationic boron species.     

Techniques and Algorithms for Hepatic Vessel Skeletonization in Medical Images: A Survey

Hepatic vessel skeletonization serves as an important means of hepatic vascular analysis and vessel segmentation. This paper presents a survey of techniques and algorithms for hepatic vessel skeletonization in medical images. We summarized the latest developments and classical approaches in this field. These methods are classified into five categories according to their methodological characteristics. The overview and brief assessment of each category are provided in the corresponding chapters, respectively. We provide a comprehensive summary among the cited publications, image modalities and datasets from various aspects, which hope to reveal the pros and cons of every method, summarize its achievements and discuss the challenges and future trends.