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41.
Abstract Different methods for the determination of the local field anisotropy in liquid crystals are analysed and the problems resulting from their application are outlined. One such method, namely that based on the comparison of the polarization of resonance Raman scattering and absorption bands is studied in more detail. The method is applied to determine the structural anisotropy for the 4-n-pentyl-(4′-cyanophenyl) derivatives of benzene, cyclohexane and bicyclooctane. To account for the difference between the optical properties of the probe and of the solvent at the wavelength of the scattered light the local field factor is treated theoretically within the framework of an anisotropic continuous dielectric medium. 相似文献
42.
Özlem Yeşiltaş 《Central European Journal of Physics》2013,11(12):1674-1679
In this paper, we have provided a matrix Hamiltonian model for honeycomb lattices and subsequently obtained the dispersion relation. Furthermore, we have constructed the C operator for the given non-Hermitian Hamiltonian model. The quadratic surfaces are sketched and the quantum Brachistochrone problem is discussed for the given honeycomb lattice model. 相似文献
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45.
Le Wang Yong Ye Zhiyu Ju Shangbin Zhong Yufen Zhao 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1958-1963
A modified method for preparing large-scale quantities of pure hexachlorocyclophosphazene (N3P3Cl6) and octachlorocyclotetraphosphazene (N4P4Cl8), phosphorus pentachloride with ammonium chloride, in the presence of zinc chloride, has been developed. The time of the reaction and the quantities of the catalyst are also studied. It is found that the optimum reaction time is 1.5 h and by-products are remarkably reduced by addition of 10% zinc chloride. As indicated by the 31 P NMR spectra, the synthesis and separation of cyclophosphazenes can be accomplished in moderate yield of tetramer (39%) and good yield of trimer (83%). 相似文献
46.
The anti-friction and wear-resistant performances of bonded MoS2 solid lubricating films filled with nano-LaF3 filler were investigated under in drying wear conditions, the corrosion-resistant performances of bonded lubricating films was evaluated according to ASTM-B117, and the characteristics of the bonded lubricating films were examined by TEM and elemental x-ray map. The wear-resistant performance of the bonded lubricating films filled with nano-LaF3 filler increases with increasing content of nano-LaF3 filler within a content range between 0 and 5 wt%, whereas the bonded lubricating films filled with 0.5–1 wt% micro-LaF3 filler exhibit the better wear-resistant performances. The incorporation of both nano-LaF3 and micro-LaF3 filler leads the increase of the coefficient of friction of the bonded lubricating films. The LaF3 filler can improve the corrosion-resistant performance of the bonded MoS2 solid lubricating films, whereas the incorporation of nano-LaF3 filler is more effective to improve the corrosion-resistant performance of the bonded lubricating films than micro-LaF3 filler. The improvement in the wear-resistant and corrosion-resistant performances of the bonded lubricating films by the incorporation of the nano-LaF3 filler is attributed to the strengthened interfacial bonding among the nano-LaF3 and the MoS2 lubricant and the polymeric matrix. However, a too high mass fraction of the nano-LaF3 filler in the bonded lubricating films will increase surface and interface defects, and lead the worsening of corrosion-resistant performance of the bonded lubricating films. 相似文献
47.
Yashao Chen Jinhong Yi Qiang Gao Xiaoling Zhou Yanling Luo Peng Liu 《Plasma Chemistry and Plasma Processing》2013,33(6):1153-1165
To improve the biocompatibility of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film, a technique based on Ar plasma pretreatment and UV-induced grafting polymerization was used to immobilize carboxymethyl chitosan (CMCS) on the FEP film surfaces. Initially Ar plasma was used to treat FEP film. Then, plasma treated FEP film was modified via UV-induced grafting polymerization with hydrophilic acrylic acid (AAc) monomer. The following immobilization of CMCS on the FEP-pAAc surface was carried out via an amidation reaction. The change of chemical composition and surface morphology of FEP film were characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM) and atomic force microscopy (AFM). Results of water contact angles measurement showed that the hydrophilicity of the surface has improved significantly after surface modification. Furthermore, methyl thiazolyl tetrazolium (MTT) assay and cell morphology analysis confirmed that mouse fibroblasts (L929 cells) attachment and proliferation were improved remarkably on the modified FEP surface. These results suggest that CMCS were successfully employed to surface engineering FEP film, and enhanced its cell biocompatibility. The approach presented here may be exploited for surface modification of biomaterials. 相似文献
48.
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
49.
Wenbo Wu Dr. Guohua Xu Prof. Conggang Li Prof. Gui Yu Prof. Yunqi Liu Prof. Cheng Ye Prof. Jingui Qin Prof. Zhen Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(21):6874-6888
Through the combination of the divergent and convergent approaches, coupled with the utilization of the powerful Sharpless “click‐chemistry” reaction, two series of sulfonyl‐based high‐generation NLO dendrimers were conveniently prepared with high purity and in satisfactory yields. Thanks to the perfect three‐dimensional (3D) spatial isolation from the highly branched structure and the isolation effect of the exterior benzene moieties and the interior triazole rings, these dendrimers exhibited large second harmonic generation coefficient (d33) values up to 181 pm V?1, which, to the best of our knowledge, is the highest value so far for polymers containing sulfonyl‐based chromophore moieties. Meanwhile, compared with the nitro‐chromophore‐based analogues, their optical transparency and NLO stability were improved in a large degree, due to the lower dipole moment (μ) and the special main‐chain structure of sulfonyl‐based chromophore in these dendrimers. 相似文献
50.
Preparation and characterization of ZrCO/C composite aerogels 总被引:1,自引:0,他引:1
Li Ye Wenfeng Qiu Hao Li Aijun Zhao Tao Cai Tong Zhao 《Journal of Sol-Gel Science and Technology》2013,65(2):150-159
Zr-containing organic aerogels were synthesized by ligand substitution reaction of polyzirconoxone and 2, 4-dihydroxybenzoic acid, followed by polymerization with formaldehyde, and then supercritical drying using CO2. After carbonization and carbothermal reduction under an argon atmosphere, ZrCO/C composite aerogels with controllable zirconium content (47.8–78.6 wt%) were obtained. The carbothermal reduction was substantially completed at 1,500 °C, and the obtained ZrCO/C composite aerogels exhibit low oxygen contents (9.4–6.7 wt%) and high surface areas (589–147 m2/g). Pore morphologies of the ZrCO/C composite aerogels were investigated in detail by nitrogen sorption measurements, scanning electron microscopy and its associated energy-dispersive X-ray microanalysis measurements. The results show that the aerogels are composed of carbon framework and Zr-conglomerations, and the surface area of aerogel is severely affected by its zirconium content. The presence of reductive ZrC crystals can greatly enhance the oxidation resistance ability of amorphous carbon framework and prevent collapse. 相似文献