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971.
Gilles Gasser 《Journal of organometallic chemistry》2008,693(15):2478-2482
The deprotection of the tert-butyl group of a ferrocenyl uracil Peptide Nucleic Acid (PNA) monomer, Fmoc-aeg(R)-OtBu (1) was achieved using a two step synthesis involving hydrolysis in basic conditions to give first the zwitterion of +NH3-aeg(R)-O− (7). Compound 7 was reacted in situ with N-(9-fluorenylmethoxycarbonyloxy)succinimide to obtain the expected compound Fmoc-aeg(R)-OH (2) (Abbreviations: Aeg = (2-aminoethyl)-glycine; Fmoc = 9-fluorenylmethoxycarbonyl; OtBu = tert-butyl; R = 5-(N-ferroce-nylmethylbenzamido)uracyl). 相似文献
972.
973.
考虑双重介质建立了井眼围岩力学模型,考虑井眼围岩岩体为孔隙、裂缝双重介质,将围岩区域分为破坏区、损伤区和弹性区,建立双重介质渗流作用下的井壁围岩不同区域的损伤力学计算模型和井眼损伤区域的计算方法,计算结果表明理论计算模型与有限元模拟结果吻合较好. 相似文献
974.
We study two novel decoupled energy‐law preserving and mass‐conservative numerical schemes for solving the Cahn‐Hilliard‐Darcy system which models two‐phase flow in porous medium or in a Hele–Shaw cell. In the first scheme, the velocity in the Cahn–Hilliard equation is treated explicitly so that the Darcy equation is completely decoupled from the Cahn–Hilliard equation. In the second scheme, an intermediate velocity is used in the Cahn–Hilliard equation which allows for the decoupling. We show that the first scheme preserves a discrete energy law with a time‐step constraint, while the second scheme satisfies an energy law without any constraint and is unconditionally stable. Ample numerical experiments are performed to gauge the efficiency and robustness of our scheme. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 936–954, 2016 相似文献
975.
Influence of Metal Oxides on Platinum Activity towards Methanol Oxidation in H2SO4 solution
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Dr. R. M. Abdel Hameed Dr. R. S. Amin Prof. K. M. El‐Khatib Dr. Amani E. Fetohi 《Chemphyschem》2016,17(7):1054-1061
Pt–CeO2/C, Pt–TiO2/C, and Pt–ZrO2/C electrocatalysts were prepared by using a modified microwave‐assisted polyol process. Physical characterization was performed by using XRD, TEM, and EDX analyses. The incorporation of different metal oxides increased the dispersion degree of Pt nanoparticles and reduced their diameter to 2.50 and 2.33 nm when TiO2 and ZrO2 were introduced to Pt/C, respectively. The electrocatalytic activity of various electrocatalysts was examined towards methanol oxidation in H2SO4 solution by using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Among the studied composites, Pt–ZrO2/C was selected to be a candidate electrocatalyst for better electrochemical performance in direct methanol fuel cells. 相似文献
976.
977.
本文用激光闪光光解技术研究了光诱导生物醌杜醌激发三重态(3DQ*)和色氨酸(Trp)与酪氨酸(Tyr)在乙腈-水(MeCN-H2O)及乙二醇-水(EG-H2O)均相溶液中的光化学反应,分析了反应的机理,并基于Stern-Volmer方法测量了反应速率常数. 光解DQ体系可以生成3DQ*,3DQ*与Trp、Tyr发生的氢原子转移反应占主导地位. 对于DQ/Trp/MeCN-H2O和DQ/Trp/EG-H2O溶液,3DQ*与Trp反应生成杜醌中性自由基DQH·、以碳为中心的色氨酸中性自由基Trp·/NH和以氮为中心的色氨酸中性自由基Trp/N·. 对于DQ/Tyr/MeCN-H2O和DQ/Tyr/EG-H2O溶液,3DQ*与Tyr反应生成DQH·和酪氨酸中性自由基Tyr/O·. 3DQ*与Trp、Tyr的氢原子转移反应速率常数都在109 L·mol-1·s-1量级,反应近似受扩散控制. MeCN/H2O均相溶液中3DQ*与Trp、Tyr的反应速率常数要明显高于EG/H2O均相溶液中的反应速率常数,这与Stokes-Einstein方程定性一致. 相似文献
978.
ZHANG Tian-yao ZHANG Zhao-hui ZHAO Xiao-yan WEI Qing-yang CAO Can YU Yang LI Ying LI Xing-yue 《光谱学与光谱分析》2021,41(6):1688-1694
极化率作为材料的重要微观属性,与其呈现出的多种宏观属性等紧密相关,在新型药物及功能材料的设计中扮演着关键角色。对于微观结构存在复杂分子间作用的物质体系,获取其太赫兹波段的动态极化率具有重要意义。极化率的实验测定建立在其本征介电常数的准确测定之上,太赫兹时域光谱系统凭借其相干探测属性,可直接提供太赫兹波在穿透样品后的相位变化信息,用于精确测定样品的介电常数。当样品由待测物纯物质组成时,实验测得的介电常数可直接用于计算极化率。但对于大多数的有机晶体,其自身对太赫兹波的特征吸收以及与颗粒尺寸与波长相当造成的散射,使其纯样品的太赫兹时域光谱表征受到系统信噪比的限制,通常需要将待测物均匀分布于对太赫兹波透明且可塑性极强的聚合物载体中。聚合物载体的使用导致实验直接测定的混合物介电常数中也包含了聚合物的介电影响,无法直接用于计算待测物质的极化率。针对这一问题,将嵌于聚合物载体中的有机晶体整体等效为聚合物、空气气隙和待测样品三组份混合介质模型,结合各组份体积占比以Landau, Lifshitz and Looyenga有效介质模型从实验测得的混合物介电常数中移除聚合物和空气气隙的影响,获取待测物的太赫兹本征介电常数,从而进一步结合Clausius-Mossotti关系式计算其太赫兹极化率。选取水杨酸晶体为研究对象,利用所提出的理论方案,从聚乙烯和聚四氟乙烯两种聚合物载体三种浓度混合物的原始介电常数中,提取出了具有高度一致性的本征介电常数和太赫兹极化率,验证了方法的有效性,并利用实验结果首次报道了水杨酸晶体的太赫兹极化率,在聚乙烯和聚四氟乙烯载体中的测定值分别为(17.2±0.2)和(17.6±1.0)Å3。 相似文献
979.
Husnu Deniz Basdemir 《等离子体物理论文集》2021,61(2):e202000103
An integral theory that is associated with the scattered fields is considered for the solution of H-polarized line source diffraction by a conductive half-plane, which is surrounded by an anisotropic plasma. As the anisotropy does not affect an E-polarized incident wave, only one polarization case is considered. The cold plasma medium is characterized by the dielectric tensor. The constant external magnetic field producing the anisotropy in a cold plasma is applied parallel to the edge of the half-plane. The total, scattered, and diffracted waves are derived in terms of the Fresnel functions. Therefore, finite magnitude values at the transition boundaries are obtained. The wave behaviours are investigated numerically for different quantities of the medium. 相似文献
980.
Ghazaleh Ghani-Moghadam Somayeh Rezaei Mohammad J. Jafari Amir H. Farahbod 《等离子体物理论文集》2021,61(9):e202100042
Plasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X-ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X-ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double-pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne-like germanium soft X-ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X-ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X-ray laser intensity with 294 cm−1 gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium. 相似文献