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991.
992.
为了获得较高的空间分辩率,设计了一种新型小束斑驻波电子直线加速器,该加速器取消了加速腔中的鼻锥结构,而在耦合腔中设置鼻锥结构。用狭缝法代替小孔法测得X射线源的焦斑尺寸为1.4mm。讨论了射线源焦点对成像质量的影响,分析了在高能条件下小孔法不适合用于焦点测量的物理原因,用4种测量方法测量了该高能X射线源的参数,测得该系统的成像极限分辩率为2.5 lp/mm,最后对实验结果进行了分析。 相似文献
993.
Titanium-doped ordered mesoporous alumina with specific structural properties has been prepared by the evaporation induced self-assembly sol-gel method. The results show that the doped titanium helps to stabilize the ordered mesoporous alumina material without influencing the ordered mesoporosity. The textural properties of the obtained sample are related to the amount of doped titanium. When the molar ratio of aluminum to titanium(n(Al)/n(Ti)) is controlled as 10.2, the titanium-doped ordered mesoporous alumina exhibits high surface area(up to 218 m2 g-1), large pore volume(0.42 cm3 g-1) and narrow pore diameter(6.1 nm) after treating at 900 ℃, showing high thermal stability. Moreover, the obtained sample calcined at 900 ℃ still maintains ordered mesoporous structure and exhibits high thermal stability. 相似文献
994.
Guangping Wan Hongjun Xia Jun Wang Jiawei Liu Botao Song Ying Yang Quan Bai 《中国化学快报》2018,29(1):213-216
The monodisperse superficially porous core-shell silica microspheres (CSSMs) with controllable shell thickness and pore size were synthesized by an improved polymerization-induced colloid aggregation (PICA) approach for fast separation of small solutes and proteins. 相似文献
995.
Experimental and numerical investigation of aramid fibre reinforced laminates subjected to low velocity impact 总被引:1,自引:0,他引:1
The low velocity impact performance of domestic aramid fibre reinforced laminates is investigated experimentally and numerically. Laminates with different thicknesses are impacted by drop-weight test machine under different impact energies. The time histories of impact force are recorded and ultrasonic C-scan technology is used to inspect the internal damage of the laminates. Numerical simulation is conducted using finite element method (FEM), taking into account both intralaminar and interlaminar damage. The intralaminar damage model is based on the continuum damage mechanics (CDM) approach, which consists of the strain-based Hashin failure criteria and the exponential damage evolution law, and considers the nonlinear shear behaviour of the material. The interlaminar damage is simulated by interface elements with cohesive zone model. The numerical results show good agreements with the experiments, thus verifying the validity of the presented numerical model. 相似文献
996.
A novel class of low-viscosity benzoxazines has been synthesized from melamine and formaldehyde with phenol or bisphenol A. The striking feature of the class of benzoxazines is the subtle combination of their inherently low viscosity at room temperature, good film-forming characteristics and high chemical and thermal stability mainly due to the introduction of melamine into the network of the polymers. The structure of the benzoxazines has been confirmed by proton nuclear magnetic resonance spectroscopy and fourier transform infrared spectroscopy. Thermal properties of polybenzoxazine have been studied by differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis. Transparent polybenzoxazine films were easily obtained under solvent-free conditions, exhibiting significantly improved toughness compared to the conventional polybenzoxazines. Our research may open a new path for overcoming the present drawbacks of polybenzoxazines such as high brittleness, the difficulties in preparing films and poor processibility via tailoring the structures and properties of amine in the benzoxazines. 相似文献
997.
Chromatographia - A novel method for the rapid simultaneous determination of multiple fungicide residues in tobacco was established using ultra-performance liquid chromatography–tandem mass... 相似文献
998.
Shichang Liu Weiqi Chen Kai Fang Xiangning Jiang Ying Gai 《Rapid communications in mass spectrometry : RCM》2012,26(17):2075-2082
999.
Zucheng Wu Ying Sing Fung 《International journal of environmental analytical chemistry》2013,93(7):431-442
The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water. 相似文献
1000.
The steric effect of an aryloxido group on the synthesis and molecular structures of ytterbium aryloxides supported by β‐diketiminato ligand L (L = [N(2,6‐Me2C6H3)C(Me)]2CH?) is reported. Reactions of β‐diketiminatoytterbium dichloride, LYbCl2(THF)2, with NaOAr1 in THF (Ar1 = [2,6‐tBu2‐4‐MeC6H2], THF = tetrahydrofuran) at 60°C gave the corresponding ytterbium complexes LYb(OAr1)Cl(THF) ( 1 ) and LYb(OAr1)2 (1), depending on the molar ratio of dichloride to sodium aryloxide, respectively, while the same reactions with NaOAr2 and NaOAr3 (Ar2 = [2,6‐iPr2C6H3], Ar3 = [2,6‐Me2C6H3]) in 1:1 or 1:2 molar ratio in THF afforded only bisaryloxide complexes LYb(OAr2)2(THF) (1) and LYb(OAr3)2(THF) ( 4 ) in good yields, respectively. Complexes 1 , 2 , 3 , 4 were fully characterized, including X‐ray crystal structure analyses. All the complexes are efficient pre‐catalysts for the catalytic addition of amines to carbodiimides giving guanidines. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献