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41.
基于Agent技术,通过引入可信平台模块(TPM)并扩展系统信任链,提出一种新的层次化可信系统架构,在不可信的服务器与不可信的用户之间建立信任关系,实现了两者之间安全可靠的互操作.在TPM的支持下,从保密性和完整性两个维度以及能力和属性两个方面对数据访问操作的主客体进行量化评级,确定访问规则,实现了保密性与完整性相统一的安全访问策略,降低了用户与服务器被攻击的风险,保障了系统的可信运行,与现有的访问控制策略相比具有更高的安全性. 相似文献
42.
郭振华 《中国无机分析化学》2022,12(2):46-51
本文研究提出了一种混合四酸(硝酸-氢氟酸-高氯酸-硫酸)分解体系,解决了传统四酸(盐酸-硝酸-氢氟酸-高氯酸)或三酸(硝酸-氢氟酸-高氯酸)溶矿耗酸量大、部分元素溶解不完全等缺点。建立了四酸敞口分解-电感耦合等离子质谱法同时测定磷矿样品中钨、钼、铊、镉、铋、铀、钍、铬等8种微量元素的方法,结果和经典碱溶法比对,准确度满意。讨论了分解方法对易挥发元素、难溶元素的影响,选取了合适的分析同位素及采用干扰校正方程以消除质谱干扰,利用103Rh和186Re为内标元素,有效校正了分析信号的动态漂移,方法的检出限为0.010~0.35μg /g、精密度均小于6%、加标回收率在93.4%~108%间。在不增加分析成本的情况下,一份溶液还可以同时用于ICP-OES及ICP-MS法测定其它主量及微量元素,方法简单、快捷、实用,适合推广应用。 相似文献
43.
SHANG Anqi ZHAO Lele LI Zhenhua CHENG Zhuang JIN Haixu FENG Zijun CHEN Zhijun ZHANG Haiquan LU Ping 《高等学校化学研究》2022,38(6):1461-1466
Near-infrared(NIR) fluorescent materials with high photoluminescent quantum yields(PLQYs) have wide application prospects. Therefore, we design and synthesize a D-A type NIR organic molecule, TPATHCNE, in which triphenylamine and thiophene are utilized as the donors and fumaronitrile is applied as the acceptor. We systematically investigate its molecular structure and photophysical property. TPATHCNE shows high Tgof 110℃ and Td of 385℃ and displays an aggregation-induced emission(AIE) property. A narrow optical bandgap of 1.65 eV is obtained. The non-doped film of TPATHCNE exhibits a high PLQY of 40.3% with an emission peak at 732 nm, which is among the best values of NIR emitters. When TPATHCNE is applied in organic light-emitting diode(OLED), the electroluminescent peak is located at 716 nm with a maximum external quantum efficiency of 0.83%. With the potential in cell imaging, the polystyrene maleic anhydride(PMSA) modified TPATHCNE nanoparticles(NPs) emit strong fluorescence when labeling HeLa cancer cells, suggesting that TPATHCNE can be used as a fluorescent carrier for specific staining or drug delivery for cellular imaging. TPATHCNE NPs fabricated by bovine serum protein(BSA) are cultivated with mononuclear yeast cells, and the intense intracellular red fluorescence indicates that it can be adopted as a specific stain for imaging. 相似文献
44.
Silver(I)‐Catalyzed Hydroazidation of Ethynyl Carbinols: Synthesis of 2‐Azidoallyl Alcohols 下载免费PDF全文
Zhenhua Liu Jianquan Liu Lin Zhang Dr. Peiqiu Liao Prof. Jinna Song Prof. Xihe Bi 《Angewandte Chemie (International ed. in English)》2014,53(21):5305-5309
The hydroazidation of alkynes is the most straightforward pathway to synthetically useful vinyl azides. However, a general hydroazidation of alkynes remains elusive. Herein, a chemo‐ and regioselective transformation of ethynyl carbinols into vinyl azides is described. This reaction produces a wide variety of 2‐azidoallyl alcohols with high efficiency and in good to excellent yields. These compounds constitute a new class of densely functionalized synthetic intermediates. Their synthetic potential has been demonstrated by further transformations into NH aziridines. The mechanistic aspects of the reaction will attract the attention of chemists working on alkyne chemistry and silver catalysis. The findings that are described in this paper represent significant advances in the regioselective hydroelementation of alkynes and open a new reaction manifold for exploitation. 相似文献
45.
46.
为确定以不同硒含量的大豆为原料生产豆腐过程中硒分布特性,用石墨炉原子吸收分光光度法对该过程中各种产物的硒含量进行了分析研究。结果表明,以硒含量分别为0.692、2.561、2.801 mg/kg的大豆为原料生产得到的豆腐、黄浆水、豆渣的硒含量分别为:0.089、0.250、0.138 mg/kg,0.462、0.760、0.507 mg/kg和0.532、0.764、0.524 mg/kg。豆腐生产过程中,以低硒大豆为原料生产豆腐,硒总回收率为75.59%;采用富硒大豆为原料生产,硒的回收率分别达到87.37%、87.20%;生产过程中豆腐、黄浆水和豆渣中硒含量占总回收硒的比率分别为39.01%~49.97%、23.92%~29.89%、26.11%~30.92%。 相似文献
47.
Li Liu Fanghua Tian Xingyan Wang Zhenhua Yang Quanqi Chen Xianyou Wang 《Journal of Solid State Electrochemistry》2012,16(2):491-497
Spherical LiNi1/3Co1/3Mn1/3O2 powders have been synthesized from co-precipitated spherical metal hydroxide. The electrochemical performances of the LiNi1/3Co1/3Mn1/3O2 electrodes in 1 M LiNO3, 5 M LiNO3, and saturated LiNO3 aqueous electrolytes have been studied using cyclic voltammetry and ac impedance tests in this work. The results show that
LiNi1/3Co1/3Mn1/3O2 electrode in saturated LiNO3 electrolyte exhibits the best electrochemical performance. An aqueous rechargeable lithium battery containing LiNi1/3Co1/3Mn1/3O2 cathode, LiV2.9Ni0.050Mn0.050O8 anode, and saturated LiNO3 electrolyte is fabricated. The battery delivers an initial capacity of 98.2 mAh g−1 and keeps a capacity of 63.9 mAh g−1 after 50 cycles at a rate of 0.5 C (278 mA g−1 was assumed to be 1 C rate). 相似文献
48.
The plasma technology served as a tool in unconventional catalysis has been used in natural gas conversion, because the traditional catalytic methane oxidative coupling reaction must be performed at high temperature on account of the stability of methane molecule. The focus of this research is to develop a process of converting methane to C2 hydrocarbons with non-equilibrium plasma technology at room temperature and atmospheric pressure. It was found that methane conversion increased and the selectivity of C2 hydrocarbons decreased with the voltage. The optimum input voltage range was 40-80 V corresponding to high yield of C2 hydrocarbons. Methane conversion decreased and the selectivity of C2 hydrocarbons increased with the inlet flow rate of methane. The proper methane flow rate was 20-40 ml/min (corresponding residence time 10-20 s). The experimental results show that methane conversion was 47% and the selectivity of C2 hydrocarbons was 40% under the proper condition using atmospheric DBD cold plasma technology. It was found that the breakdown voltage of methane VB was determined by the type of electrode and the discharge gap width in this glow discharge reactor. The breakdown voltage of methane VB,min derived from the Paschen law equation was established. 相似文献
49.
A Highly cis‐Selective and Enantioselective Metal‐Free Hydrogenation of 2,3‐Disubstituted Quinoxalines 下载免费PDF全文
Zhenhua Zhang Prof. Dr. Haifeng Du 《Angewandte Chemie (International ed. in English)》2015,54(2):623-626
A wide range of 2,3‐disubstituted quinoxalines have been successfully hydrogenated with H2 using borane catalysts to produce the desired tetrahydroquinoxalines in 80–99 % yields with excellent cis selectivity. Significantly, the asymmetric reaction employing chiral borane catalysts generated by the in situ hydroboration of chiral dienes with HB(C6F5)2 under mild reaction conditions has also been achieved with up to 96 % ee, and represents the first catalytic asymmetric system to furnish optically active cis‐2,3‐disubstituted 1,2,3,4‐tetrahydroquinoxalines. 相似文献
50.
The first montmorillonite‐supported surface single‐structure titanium complex: synthesis,characterization and catalytic activity in alkene epoxidation 下载免费PDF全文
Wei Xu Bo Yu Huaming Sun Jindou Yang Ying Zhang Zhenhua Wang Xi Chen Guofang Zhang Ziwei Gao 《Surface and interface analysis : SIA》2015,47(3):308-314
A well‐defined single‐site titanium‐modified montmorillonite (MMT) with only one geometric construction ((?SiO)3–Ti–NMe2) was obtained in moderate conditions. Reaction of tetrakis(dimethylamido)titanium with hydroxylated MMT was conducted by surface organometallic chemistry technique, and the surface structure was characterized by in situ Fourier transform infrared spectroscopy, 13C cross polarization magic angle spinning nuclear magnetic resonance, X‐ray photoelectron spectroscopy, extended X‐ray absorption fine structure, and elemental analysis. The catalytic activity in alkene epoxidation was evaluated, and the results revealed that the steric hindrance of the substances is responsible for the catalytic activity of the MMT‐supported titanium complex but to the characteristic restricted layer‐like structure of the MMT. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献