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201.
L. Lam H. C. Morris R. F. Shao S. L. Yang Z. C. Liang S. Zheng 《Liquid crystals》2013,40(6):1813-1826
The theoretical and experimental developments in the interfacial dynamics and the formation of viscous fingering patterns in Hele-Shaw cells of liquid crystal-air systems are summarized and discussed. These include radial and linear cells with or without grooves engraved on the cell plates. Instabilities of fingers, the role of intrinsic and extrinsic anisotropies, etc., are emphasized. In a linear cell, when the injected air is kept at constant pressure, a whole sequence of successive instabilities of fingers (hump, tip-splitting, sidewrinkling, sidebranching and DLA-like structure) is observed in a single run of the experiment. In our theory, the equations of motion of nematic flows in Hele-Shaw cells are derived from the Ericksen-Leslie equations. In the linear approximation, the equations resemble those of isotropic liquids with the presence of effective viscosities and anisotropic surface tension. Experimental observations are interpreted with the introduction of an effective control parameter which may be time dependent. Special features of viscous fingers in liquid crystals in contrast to those in isotropic liquids, such as asymmetric dendritics, displacement of the finger from the central axis of the linear cell, and reentrant sequence of patterns, are pointed out. Plausible explanations of these phenomena are given. In this newly developed field, a large number of interesting problems remain to be solved. 相似文献
202.
Kongkai Zhu Junyan Lu Zhongjie Liang Xiangqian Kong Fei Ye Lu Jin Heji Geng Yong Chen Mingyue Zheng Hualiang Jiang Jun-Qian Li Cheng Luo 《Journal of computer-aided molecular design》2013,27(3):247-256
New Delhi metallo-β-lactamase-1 (NDM-1) has emerged as a major global threat to human health for its rapid rate of dissemination and ability to make pathogenic microbes resistant to almost all known β-lactam antibiotics. In addition, effective NDM-1 inhibitors have not been identified to date. In spite of the plethora of structural and kinetic data available, the accurate molecular characteristics of and details on the enzymatic reaction of NDM-1 hydrolyzing β-lactam antibiotics remain incompletely understood. In this study, a combined computational approach including molecular docking, molecular dynamics simulations and quantum mechanics/molecular mechanics calculations was performed to characterize the catalytic mechanism of meropenem catalyzed by NDM-1. The quantum mechanics/molecular mechanics results indicate that the ionized D124 is beneficial to the cleavage of the C–N bond within the β-lactam ring. Meanwhile, it is energetically favorable to form an intermediate if no water molecule coordinates to Zn2. Moreover, according to the molecular dynamics results, the conserved residue K211 plays a pivotal role in substrate binding and catalysis, which is quite consistent with previous mutagenesis data. Our study provides detailed insights into the catalytic mechanism of NDM-1 hydrolyzing meropenem β-lactam antibiotics and offers clues for the discovery of new antibiotics against NDM-1 positive strains in clinical studies. 相似文献
203.
Fangyuan Zheng Prof. Fang Zeng Changmin Yu Xianfeng Hou Prof. Shuizhu Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):936-942
Owing to the considerable significance of fluoride anions for health and environmental issues, it is of great importance to develop methods that can rapidly, sensitively and selectively detect the fluoride anion in aqueous media and biological samples. Herein, we demonstrate a robust fluorescent turn‐on sensor for detecting the fluoride ion in a totally aqueous solution. In this study, a biocompatible hydrophilic polymer poly(ethylene glycol) (PEG) is incorporated into the sensing system to ensure water solubility and to enhance biocompatibility. tert‐Butyldiphenylsilyl (TBDPS) groups were then covalently introduced onto the fluorescein moiety, which effectively quenched the fluorescence of the sensor. Upon addition of fluoride ion, the selective fluoride‐mediated cleavage of the Si? O bond leads to the recovery of the fluorescein moiety, resulting in a dramatic increase in fluorescence intensity under visible light excitation. The sensor is responsive and highly selective for the fluoride anion over other common anions; it also exhibits a very low detection limit of 19 ppb. In addition, this sensor is operative in some real samples such as running water, urine, and serum and can accurately detect fluoride ions in these samples. The cytotoxicity of the sensor was determined to be Grade I toxicity according to United States Pharmacopoeia and ISO 10993‐5, suggesting the very low cytotoxicity of the sensor. Moreover, it was found that the senor could be readily internalized by both HeLa and L929 cells and the sensor could be utilized to track fluoride level changes inside the cells. 相似文献
204.
Zheng Wang Shuai Luo Dr. Shoude Zhang Wu‐Lin Yang Yang‐Zi Liu Prof. Dr. Honglin Li Prof. Dr. Xiaoyan Luo Prof. Dr. Wei‐Ping Deng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(21):6739-6745
The first catalytic enantioselective 1,3‐dipolar cycloaddition of azomethine ylides to α‐aminoacrylate catalyzed by a AgOAc/ferrocenyl oxazolinylphosphine (FOXAP) system was developed, which exhibits excellent exo‐ and enantioselectivity (92–99 % ee). This process provides efficient access to useful 4‐aminopyrrolidine‐2,4‐dicarboxylic acid (APDC)‐like compounds containing a unique quaternary α‐amino acid unit. 相似文献
205.
206.
A novel one-pot two-step protocol has been developed to synthesize various spiro[benzofuran-2,2′-naphthalen]-1′-one derivatives from the three-component reaction of tetralones, 2-hydroxyphenyl functionalized α,β-unsaturated ketones, and iodine. One C–C bond and one C–O bond have formed during this process. The notable features of this protocol are simple and mild reaction conditions, applicable to a wide range of readily available starting materials, good yields (up to 91%), and excellent stereoselectivities (up to 97:3). 相似文献
207.
Transition-metal-catalyzed isoquinoline synthesis that profits from the strategy of chelation-assisted C−H activation has flourished over the past decade. By virtue of the directed C−H bond cleavage of imines, amines, amidines, oximes, hydroximoyl halides, hydrazones, or azines, diverse isoquinoline derivatives have been accessed from alkynes, conjugated dienes, or diazo compounds under the catalysis of rhodium, ruthenium, palladium, nickel, or manganese. This digest summarizes the annulation reactions via chelation-assisted C−H activation leading to isoquinolines, isoquinolinium salts, or isoquinoline N-oxides. 相似文献
208.
Yiqi Zhang Zhenkun Wu Milivoj R. Beli Huaibin Zheng Zhiguo Wang Min Xiao Yanpeng Zhang 《Laser \u0026amp; Photonics Reviews》2015,9(3):331-338
The feasibility of realizing a photonic Floquet topological insulator (PFTI) in an atomic ensemble is demonstrated. The interference of three coupling fields will split energy levels periodically, to form a periodic refractive index structure with honeycomb profile that can be adjusted by different frequency detunings and intensities of the coupling fields. This in turn will affect the appearance of Dirac cones in momentum space. When the honeycomb lattice sites are helically ordered along the propagation direction, gaps open at Dirac points, and one obtains a PFTI in an atomic vapor. An obliquely incident beam will be able to move along the zigzag edge of the lattice without scattering energy into the PFTI, due to the confinement of edge states. The appearance of Dirac cones and the formation of a photonic Floquet topological insulator can be shut down by the third‐order nonlinear susceptibility and opened up by the fifth‐order one.
209.
Ding Congming Yuan Meini Cao Xiaochen Zheng Lirong Wang Kai 《Journal of Solid State Electrochemistry》2022,26(11):2445-2455
Journal of Solid State Electrochemistry - In order to meet the growing energy demand, it is of great significance to develop high-performance electrochemical energy storage materials. In this... 相似文献
210.
HengYan Wang WenQiang Zheng NengKun Yu KeRen Li DaWei Lu Tao Xin Carson Li ZhengFeng Ji David Kribs Bei Zeng XinHua Peng JiangFeng Du 《中国科学:物理学 力学 天文学(英文版)》2016,59(10):100313
We investigate quantum state tomography(QST) for pure states and quantum process tomography(QPT) for unitary channels via adaptive measurements. For a quantum system with a d-dimensional Hilbert space, we first propose an adaptive protocol where only 2d. 1 measurement outcomes are used to accomplish the QST for all pure states. This idea is then extended to study QPT for unitary channels, where an adaptive unitary process tomography(AUPT) protocol of d2+d.1measurement outcomes is constructed for any unitary channel. We experimentally implement the AUPT protocol in a 2-qubit nuclear magnetic resonance system. We examine the performance of the AUPT protocol when applied to Hadamard gate, T gate(/8 phase gate), and controlled-NOT gate,respectively, as these gates form the universal gate set for quantum information processing purpose. As a comparison, standard QPT is also implemented for each gate. Our experimental results show that the AUPT protocol that reconstructing unitary channels via adaptive measurements significantly reduce the number of experiments required by standard QPT without considerable loss of fidelity. 相似文献