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941.
利用菲涅耳双镜测金属线膨胀系数 总被引:2,自引:0,他引:2
分析了菲涅耳双镜在干涉实验中 ,由金属受热膨胀引起的光源位置变化对干涉条纹的影响 ,导出金属受热时绝对伸长量与干涉条纹位置变化之间的关系 ,并通过它对黄铜棒的线膨胀系数进行测量。 相似文献
942.
Dr. Zhiqiang Ma Dr. Ruining Li Zhen Zhang Cheng Tao Dr. Bin Cheng Dr. Yun Li Dr. Huifei Wang Prof. Dr. Hongbin Zhai 《Angewandte Chemie (International ed. in English)》2016,55(38):11638-11641
Described herein is the first asymmetric total synthesis of (+)‐harringtonolide, a natural diterpenoid with an unusual tropone imbedded in a cagelike framework. The key transformations include an intramolecular Diels–Alder reaction and a rhodium‐complex‐catalyzed intramolecular [3+2] cycloaddition to install the tetracyclic core as well as a highly efficient tropone formation. 相似文献
943.
Application of porous metal enrichment probe sampling to single cell analysis using matrix‐assisted laser desorption ionization time of flight mass spectrometry (MALDI‐TOF‐MS) 下载免费PDF全文
Qiang Fu Jun Tang Meng Cui Junpeng Xing Zhiqiang Liu Shuying Liu 《Journal of mass spectrometry : JMS》2016,51(1):62-68
There is an increasing need for analyzing metabolism in a single cell, which is important to understand the nature of cellular heterogeneity, disease, growth and specialization, etc. However, single cell analysis is often challenging for the traces of samples. In the present study, porous metal enrichment probe sampling combined with matrix‐assisted laser desorption ionization time of flight mass spectrometry ( MALDI‐TOF‐MS) has been applied for in situ analysis of live onion epidemic cell. Porous probe, treated by corroding copper wire with HCl, was directly inserted into a single cell to get cell solution. A self‐made linear actuator was enough to control the penetration of probe into the target cell accurately. Then samples on the tip of probe were eluted and detected by a commercial MALDI‐TOF‐MS directly. The formation of porous microstructure on the probe surface increased the adsorptive capacity of cell solution. The sensitivity of porous probe sampling was 6 times higher than uncorroded probes generally. This method provides a sensitive and convenient way for the sampling and detection of single cell solution. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
944.
Xin Shang Zhiqiang Guo Wei Gan Ru Zhou Cheng Ma Ke Hu Haihong Niu Jinzhang Xu 《Ionics》2016,22(3):435-443
For the first time, we report a one-step fabrication of an environment-friendly approach to synthesize flower-like α-Fe2O3 hierarchical nanoparticles (NPs)/reduced graphene oxide (RGO) hybrids by combining the graphene oxide (GO) with the growth of α-Fe2O3 NPs. The GO sheet which possesses the functional group, such as hydroxyl (–OH) and carbonyl groups (–OOH), can be easily incorporated with the petal of the flower-like α-Fe2O3 in ethanol and water solution through a solvothermal process, during which GO is reduced to RGO without the addition of any strong reducing agent or requiring any post-high-temperature annealing process. The as-prepared samples are loose and porous with flower-like structure, and the RGO hybrids were wrapped up uniformly on the sheet of α-Fe2O3 NPs. To demonstrate the potential applications, we have fabricated dye-sensitized solar cells (DSSCs) from the as-synthesized hierarchical flower-like α-Fe2O3/RGO and investigated it for the photoanode of DSSCs. Results show that the hierarchical α-Fe2O3/RGO solar cell exhibits improved performances in comparison with the free α-Fe2O3 NPs. The enhancement of photovoltaic properties is attributed to the unique porous nature and good conductivity which allow more efficient diffusion of I? ions and facilitate the transfer of electron in the network. 相似文献
945.
采用程序升温氮化法制备了Mo2N/SiO2,在此基础上负载Ni盐,制备了Ni-Mo2N/SiO2复合纳米催化剂,并考察了催化剂对四氢萘加氢的催化活性.结果表明,与Ni2Mo3N/SiO2及Ni/SiO2催化剂相比,Ni-Mo2N/SiO2复合催化剂具有较高的催化活性.采用"分离床"方法研究了Ni和Mo2N对四氢萘加氢活性的影响.通过X射线粉末衍射、透射电镜、氢吸附、元素分析和比表面积测定等技术对Ni-Mo2N/SiO2催化剂进行了表征.结果表明,与Ni/SiO2催化剂相比,Ni-Mo2N/SiO2复合催化剂中Ni的分散度并未提高;催化活性的提高归因于Ni与Mo2N在四氢萘加氢中的协同作用.氮化物的引入增加了芳烃吸附活性位的数目.提出了四氢萘在Ni-Mo2N/SiO2催化剂上的可能加氢机理. 相似文献
946.
The marine yeast strain Kodamea ohmeri BG3 isolated from the gut of a marine fish (Hexagrammes otakii) was found to secrete a large amount of phytase into the medium. The crude phytase produced by this marine yeast showed the
highest activity at pH 5.0 and 65 °C. The optimal medium for phytase production contained oat 10.0 g/l, ammonium sulfate 15.0 g/l,
glucose 30 g/l, and NaCl 20.0 g/l, while the optimal cultivation conditions for phytase production were pH 5.0, a temperature
of 28 °C, and a shaking speed of 170 rpm. Under the optimal conditions, over 557.9 mU/ml of phytase activity was produced
within 72 h of fermentation at the shake flask level. This is a very high level of phytase activity produced by yeasts. We
think that the medium and process for phytase production by the marine yeast strain were very simple, and such marine yeast
from the gut of natural marine fish may have a potential application in the maricultural industry and marine environmental
protection. The results demonstrate that phytate was actively degraded by the crude phytase within a short period. 相似文献
947.
The asymmetric alpha-arylation of ketones with aryl triflates is described, and the use of this electrophile with nickel and palladium catalysts containing a segphos derivative increases substantially the scope of highly enantioselective arylations of ketone enolates. The combination of aryl triflates as reactant, difluorphos as ligand, palladium catalysts for reactions of electron-neutral or electron-rich aryl triflates, and nickel catalysts for reactions of electron-poor aryl triflates led to a series of alpha-arylations of tetralone, indanone, cyclopentanone, and cyclohexanone derivatives. Enantioselectivities ranged from 70% to 98% with 10 examples over 90%. Systematic studies on these alpha-arylations have revealed a number of factors that affect enantioselectivity. Ligands containing biaryl backbones with smaller dihedral angles generate catalysts that react with higher enantioselectivity than related ligands with larger dihedral angles. In addition, faster rates for reactions of aryl triflates versus those for reactions of aryl bromides allow the alpha-arylations of aryl triflates to be conducted at lower temperatures, and this lower temperature improves enantioselectivity. Finally, studies that compare the enantioselectivities of catalytic reactions to those of stoichiometric reactions of isolated [(segphos)Pd(Ar)(Br)], [(segphos)Pd(Ar)(I)], and [(segphos)Ni(C6H4-4-CN)Br] suggest that catalyst decomposition affects enantioselectivity. 相似文献
948.
Cr(Ⅲ)-取代磷钨杂多配合物对4-甲基吡啶的电催化氧化作用 总被引:2,自引:0,他引:2
利用Cr(Ⅲ)-取代磷钨杂多配合物PW11O39CrⅢ(H2O)4-的内球电子转移特性,通过与反应活性中心CrⅢ(H2O)第六配位水分子的交换反应,将4-甲基吡啶分子络合修饰到该活性中心上进行阳极催化氧化.可见吸收光谱证实4-甲基吡啶和CrⅢ(H2O)中心进行配体交换反应生成PW11O39CrⅢ(NC6H7)4-;而循环伏安和恒电位电解实验结果表明,修饰在Cr(Ⅲ)活性中心上的4-甲基吡啶分子每一步都经历2电子氧化,依次生成吡啶-4-甲醇,吡啶-4-甲醛和吡啶-4-甲酸.由此提出了一个关于这类反应的分子内电催化模板机制,为过渡金属取代杂多配合物作为间接氧化电催化剂的应用开辟了一条新途径. 相似文献
949.
Zhu S Zhang D Li Z Furukawa H Chen Z 《Langmuir : the ACS journal of surfaces and colloids》2008,24(12):6292-6299
A novel method for duplicating the hierarchical structures of biological substances at nanometer resolution in manganese oxides has been developed. This innovation uses natural biomorphic specimens, such as butterfly wing, cotton, and wood as templates. The biotemplates were first treated with either HCl/NaOH or HCl/H2O2/NaOH and then mixed with an aqueous solution of KMnO4. The treated biological materials were then ultrasonically irradiated, and finally, the biological templates were removed by calcination in air at temperatures between 500 and 800 degrees C. The structures of the resulting manganese oxides were characterized by a combination of XRD, FE-SEM, TEM and EDS. It was found that the fine hierarchical structures of the biological templates down to the nanometer scale were faithfully duplicated, and the duplication was positive. A mechanism for the positive replication is proposed and discussed in terms of the effects of the sonochemical reaction as well as the surface modification prior to the sonochemical reaction. The same sonochemical method can be extended to the duplication of intricate hierarchical structures of other biological forms in a large range of metal oxides. 相似文献
950.
Shi W Zhang Y Liu C Wang Z Zhang X 《Langmuir : the ACS journal of surfaces and colloids》2008,24(4):1318-1323
In this article, we have investigated the interaction between two poly(benzyl ether) dendrons directly by single-molecule force spectroscopy. For this purpose, one dendron was immobilized on an AFM tip through a poly(ethylene glycol) (PEG) spacer, and the other dendron was anchored on a gold substrate as a self-assembled monolayer. Two dendrons approached and then interacted with each other when the AFM tip and the substrate moved close together. The rupture force between dendrons was measured while the AFM tip and the substrate separated. PEG as a flexible spacer can function as a length window for recognizing the force signals and avoiding the disturbance of the interaction between the AFM tip and the substrate. The interaction between two first-generation dendrons is measured to be about 224 pN at a force loading rate of 40 nN/s. The interaction between second- and first-generation dendrons rises to 315 pN at the same loading rate. Such interactions depend on the force loading rate in the range of several to hundreds of nanonewtons per second, indicating that the rupture between dendrons is a dynamic process. The study of the interaction between surface-bound dendrons of different generations provides a model system for understanding the surface adhesion of molecules with multiple branches. In addition, this multiple-branch molecule may be used to mimic the sticky feet of geckos as a man-made adhesive. 相似文献