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991.
Guizhong Xie Jianming ZhangYunqiao Dong Cheng HuangGuangyao Li 《International Journal of Solids and Structures》2014
This paper presents an improved exponential transformation for nearly singular boundary element integrals in elasticity problems. The new transformation is less sensitive to the position of the projection point compared with the original transformation. In our work, the conventional distance function is modified into a new form in the polar coordinate system. Based on the refined distance function, an improved exponential transformation is proposed in the polar coordinate system. Moreover, to perform integrations on irregular elements, an adaptive integration scheme considering both the element shape and the projection point associated with the improved transformation is proposed. Furthermore, when the projection point is located outside the integration element, another nearest point is introduced to subdivide the integration elements into triangular or quadrilateral patches of fine shapes. Numerical examples are presented to verify the proposed method. Results demonstrate the accuracy and efficiency of our method. 相似文献
992.
993.
Cross‐Coupling of Organolithium with Ethers or Aryl Ammonium Salts by C−O or C−N Bond Cleavage 下载免费PDF全文
Ze‐Kun Yang Dong‐Yu Wang Hiroki Minami Hiroyuki Ogawa Takashi Ozaki Dr. Tatsuo Saito Dr. Kazunori Miyamoto Dr. Chao Wang Prof. Dr. Masanobu Uchiyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15693-15699
Various aryl‐, alkenyl‐, and/or alkyllithium species reacted smoothly with aryl and/or benzyl ethers with cleavage of the inert C?O bond to afford cross‐coupled products, catalyzed by commercially available [Ni(cod)2] (cod=1,5‐cyclooctadiene) catalysts with N‐heterocyclic carbene (NHC) ligands. Furthermore, the coupling reaction between the aryllithium compounds and aryl ammonium salts proceeded under mild conditions with C?N bond cleavage in the presence of a [Pd(PPh3)2Cl2] catalyst. These methods enable selective sequential functionalizations of arenes having both C?N and C?O bonds in one pot. 相似文献
994.
Quantum dots (QDs) have shown great potential to provide spatial, temporal, and structural information for biological systems. However, blinking, photobleaching, and spectral blueshift are adverse effects on their practical applications in biomedical research. An investigation of the effects of six reducing agents including cysteine (Cys), 1,4‐dithiothreitol (DTT), ethyl gallate (EG), L ‐glutathione (GSH), mercaptoacetic acid (MAA), and thiourea (TU) on the photostability of single QDs was studied. Our experiments demonstrate that both DTT and EG effectively inhibit blinking, photobleaching, and spectral blueshift. GSH molecules block blinking and photobleaching of QDs. The other reagents, Cys, MAA, and TU, only have the ability to counteract blinking. Possible explanations are given on the basis of research evidence. The results suggest possibilities for significant improvements in QDs for biological applications by adjusting the environmental conditions. 相似文献
995.
996.
Suppression of the Charge Density Wave State in Two-Dimensional 1T-TiSe2 by Atmospheric Oxidation 下载免费PDF全文
Lifei Sun Chuanhui Chen Dr. Qinghua Zhang Christian Sohrt Tianqi Zhao Dr. Guanchen Xu Jinghui Wang Prof. Dong Wang Prof. Kai Rossnagel Prof. Lin Gu Prof. Chenggang Tao Prof. Liying Jiao 《Angewandte Chemie (International ed. in English)》2017,56(31):8981-8985
Two-dimensional (2D) metallic transition-metal dichalcogenides (TMDCs), such as 1T-TiSe2, have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1T-TiSe2 undergoes rapid oxidation under ambient conditions, significantly affecting its CDW phase-transition behavior. We comprehensively investigate the oxidation process of 2D TiSe2 by tracking the evolution of the chemical composition and atomic structure with various microscopic and spectroscopic techniques and reveal its unique selenium-assisting oxidation mechanism. Our findings facilitate a better understanding of the chemistry of ultrathin TMDCs crystals, introduce an effective method to passivate their surfaces with capping layers, and thus open a way to further explore the functionality of these materials toward devices. 相似文献
997.
Lian-Hua Fu Yan-Yan Dong Ming-Guo Ma Wen Yue Shao-Long Sun Run-Cang Sun 《Ultrasonics sonochemistry》2013,20(5):1188-1193
Vaterite is an important biomedical material due to its features such as high specific surface area, high solubility, high dispersion, and small specific gravity. The purposes of this article were to explore the growth mechanism of vaterite on the cellulose matrix via sonochmistry process. In the work reported herein, the influences of experimental parameters on the polymorph of calcium carbonate were investigated in detail. The calcium carbonate crystals on the cellulose matrix were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Experimental results revealed that all the reactants, solvent, and synthesis method played an important role in the polymorph of calcium carbonate. The pure phase of vaterite polymorph was obtained using Na2CO3 as reactant in ethylene glycol on the cellulose matrix via sonochmistry process. Based on the experimental results, one can conclude that the synthesis of vaterite polymorph is a system process. 相似文献
998.
Weihan Li Zongquan Wu Anqiu Zhang Marke E. Leland Jae-Young Park Frank W. Harris 《Journal of Macromolecular Science: Physics》2013,52(3):315-333
A high-performance aromatic polyimide fiber has been spun from a high molecular weight polyimide synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-dimethyl-4,4′-diaminobiphenyl (DMB). The fiber exhibits not only excellent tensile properties and high temperature resistance but also a high compressive strength of 655 MPa. Morphological observations of BPDA-DMB fibers indicate that the fiber shows a skin-core structure and microfibrillar textures. A banded texture can also be found with a spacing of about 2μm, which may be introduced by the liquid crystalline behavior that appears during processing. Compressed BPDADMB fibers form kink and microkink bands over different size scales. The detailed formation mechanism of these banded textures is discussed. The structure parameter changes during compression-including crystal unit cell parameters, apparent crystallinity, crystal and overall orientation, and apparent crystallite sizes-are monitored. It is found that after restretching, the crystal and overall orientation is almost fully recovered while the apparent crystallinity is not recoverable. The structural changes during compression are critically associated with the loss of macroscopic mechanical property in the fibers. 相似文献
999.
1000.