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941.
942.
First-order Fréedericksz transition at the threshold point for weak anchoring nematic liquid crystal cell under external electric and magnetic fields 总被引:1,自引:0,他引:1 下载免费PDF全文
Based on the modified formula of Rapini-Papoular, the equilibrium equation and boundary condition of the director have been obtained and the behaviour of the Fréedericksz transition at the threshold point has been studied for weak-anchoring nematic liquid crystal cells under external electric and magnetic fields with the methods of analytical derivation and numerical calculation. The results show that, except for the usual second-order transition, the first-order Fréedericksz transition can also be induced by a suitable surface anchoring technique for the liquid crystal cell given in the paper. The conditions for the existence of the first-order Fréedericksz transition are obtained. They are related to the material elastic coefficient k_{11}, k_{33} the thickness of the liquid crystal cell, the external electric field and the strength of surface anchoring, etc. 相似文献
943.
944.
More and more attention has been focused on effectively generating
chaos via simple physical devices. The problem of creating chaotic
attractors is considered for a class of nonlinear systems with
backlash function in this paper. By utilizing the Silnikov
heteroclinic and homoclinic theorems, some sufficient conditions are
established to guarantee that the nonlinear system has
horseshoe-type chaos. Examples and simulations are given to verify
the effectiveness of the theoretical results. 相似文献
945.
Hong Gao Dong Wang Shaowei Guan Wei Jiang Zhenhua Jiang Weinan Gao Daming Zhang 《Macromolecular rapid communications》2007,28(3):252-259
A novel fluorinated hyperbranched polyimide (HBPI) is synthesized by using a new triamine monomer, 1,3,5‐tris(2‐trifluoromethyl‐4‐aminophenoxy)benzene (TFAPOB) (A3), as a ‘core’ molecule, 4,4‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) as a B2 monomer, and 3,5‐ditrifuoromethylphenyl as an endcapping reagent. The polymer shows a glass transition temperature of 232 °C and a temperature of 10% weight loss at 535 °C. The HBPI presents a birefringence as low as 0.002 at 650 nm. Near‐IR results indicate that HBPI exhibits desirable properties for low loss optical waveguide applications.
946.
Study of the selective catalysis of metalloporphyrins for 2-methyl-butane oxidation with PhIO under mild conditions 总被引:1,自引:0,他引:1
Can-Cheng Guo Guan Huang Zhi-Peng Li Jian-Xin Song 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):43-49
Nine ironporphyrins and eight manganeseporphyrins were synthesized, and their selective catalysis for the oxidation of the secondary and tertiary carbon–hydrogen bonds of 2-methyl-butane with PhIO was studied. The proportion of the oxidation product of tertiary carbon–hydrogen bond to the one of secondary carbon–hydrogen bond was 3:1 when ironporphyrins were used as catalysts, and 2.3:1 when manganeseporphyrins were used as catalysts. The research showed that the substituting groups on the porphyrin rings influenced the catalytic selectivity of metalloporphyrins for the oxidation of the secondary and tertiary carbon–hydrogen bonds as well as the reaction yields. The electron-attracting groups on benzene rings of ironporphyrins increased the catalytic selectivity of ironporphyrins for the tertiary carbon–hydrogen bond oxidation and the reaction speeds, and the electron-releasing groups increased the catalytic selectivity for secondary carbon–hydrogen bond oxidation and reduced the reaction speeds. Both electron-attracting and -releasing groups on benzene rings of manganeseporphyrins enhanced the catalytic selectivity of manganeseporphyrins for the secondary carbon–hydrogen bond oxidation. 相似文献
947.
我们用低压MOCVD在蓝宝石衬底生长了InGaN/GaN外延层.用X射线衍射(XRD),光致发光谱(PL),光吸收谱等测量手段,研究了InGaN的辐射发光机制.In组分利用Vegard定理和XRD测量得到.我们发现随着In组分的增加,在光吸收谱上发现吸收边的红移和较宽的Urbach带尾;PL谱中低能端的发射渐渐成为主导,并且在PL激发谱中InGaN峰也变宽.我们认为压电效应改变了InGaN的能带结构,从而影响了光学吸收特性.而在InN量子点中的辐射复合则是InGaN层发光的起源. 相似文献
948.
949.
950.
Bo Chen Fangyue Chen Junbiao Guan Genaro J. Mart ''{ i}nez 《Journal of Applied Analysis & Computation》2016,6(4):1164-1179
By introducing a sequence-block transformation and vector-block transformation, we explore the dynamical properties of hybrid cellular automation (HCA) and hybrid cellular automation with memory (HCAM) in the framework of symbolic dynamics. As the local evolution rules of HCA and HCAM are not-uniform, the new uniform cellular automata (CAs) with multiple states are constructed by specifical the block transformations. Furthermore, because the new CA rules are topologically conjugate with the originals, the complex dynamics of the HCA and HCAM rules can be investigated via the new CA rules. 相似文献