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941.
Gui‐Zhong Yang Xiao‐Lei Chen Lu‐Min Wang Jian‐Gao Shi Chun‐Zhong Li Tianxi Liu 《先进技术聚合物》2009,20(2):104-110
A series of fluorene‐based rod–coil liquid crystal polymers with different lengths of the coil segments on backbones were designed and synthesized by a palladium‐catalyzed Suzuki coupling‐reaction. The thermal stability, the UV–Vis absorption and fluorescence spectra in chloroform solution and thin film, the electrochemical properties, thermal behavior, and morphology of these rod–coil polymers were investigated. The thermal stability of these polymers steadily decreased on increasing the length of the coil segments on the backbone; their optical and electrochemical properties did not exhibit noticeable dependence on the weight fraction of the coil segments. However, the shoulder emission and the full width at the half‐maximum (FWHM) in PL spectra of the films increased, whereas the oxidation onset potentials and the corresponding HOMO energy levels decreased with the increase in the weight fraction of the coil segments, which was assigned to microphase separation and formation of folded chain conformation as the weight fraction of the coil segments increased. These polymers displayed a characteristic liquid crystalline texture. The variation of the weight fraction of the coil segments obviously affected the thermal behavior and morphology of these rod–coil polymers. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
942.
With the newly developed octonion analytic function theory, we confirm the octonionic analogue of the Calderón's conjecture. As application, we obtain the Plemelj formula in octonionic space. 相似文献
943.
Ji‐Fang Fu Li‐Yi Shi Shuai Yuan Qing‐Dong Zhong Deng‐Song Zhang Yi Chen Jun Wu 《先进技术聚合物》2008,19(11):1597-1607
New hyperbranched poly(trimellitic anhydride‐triethylene glycol) ester epoxy (HTTE) is synthesized and used to toughen diglycidyl ether of bisphenol A (DGEBA) 4,4′‐diaminodiphenylmethane (DDM) resin system. The effects of content and generation number of HTTE on the performance of the cured systems are studied in detail. The impact strength is improved 2–7 times for HTTE/DGEBA blends compared with that of the unmodified system. Scanning electron microscopy (SEM) of fracture surface shows cavitations at center and fibrous yielding phenomenon at edge which indicated that the particle cavitations, shear yield deformation, and in situ toughness mechanism are the main toughening mechanisms. The dynamic mechanical thermal analyzer (DMA) analyses suggest that phase separation occurred as interpenetrating polymer networks (IPNs) for the HTTE/DGEBA amine systems. The IPN maintains transparency and shows higher modulus than the neat epoxy. The glass transition temperature (Tg) decreases to some extent compared with the neat epoxy. The Tg increases with increase in the generation number from first to third of HTTE and the concentrations of hard segment. The HTTE leads to a small decrease in thermal stability with the increasing content from TGA analysis. The thermal stability increases with increase in the generation number from first to third. Moreover, HTTE promotes char formation in the HTTE/DGEBA blends. The increase in thermal properties from first to third generation number is attributed to the increase in the molar mass and intramolecular hydrogen bridges, the increasing interaction of the HTTE/DGEBA IPNs, and the increasing crosslinking density due to the availability of a greater number of end hydroxyl and end epoxide functions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
944.
945.
Thecoordinationchemistryofbinuclearmetalcomplexeshasbeenasubjectofextensiveinvestigationrelatingtothesynthesisofmodelcompoundsforthemetal-bindingsitesofmetal1oproteinsthatrequirethepresenceoftWometalcentersl.Duringthe1astdecade,anumberofsyntheticstructuraImodeIsfortheseproteinswiththeuseofseveraltypesofligandshavebeenreportedinIiterature2-4.ForIigandswithanappropriatedispositionofdonoratoms,ithasbeenpossibletoshowthepresenceofhydroxo,imidazolato,azido,andthiocyanatobridgesbetweenmetalions5.T… 相似文献
946.
The enlargement of the emitting aperture is usually one of the important methods of increasing vertical- cavity surface-emitting laser (VCSEL) optical output power. However, in a VCSEL with a larger aperture, the inhomogeneity in the injected current often causes inhomogeneous or even no emission. To solve this problem and to increase VCSEL output power, as well as to improve its thermal characteristics, we develop a new type of injected VCSEL with a larger aperture and a reticular electrode, where the conventional circular injection electrode of the P side is turned into a reticular one, and the heat sink is on the N side. The tests of the new VCSEL show an improvement in homogeneity in not only the injected current but also the emission intensity. The optical output power is also considerably increased, and the device optoelectronic performance is improved. 相似文献
947.
Mei Zhong JIN Li YANG Long Ming WU You Chen LIU Zhong Li LIU* National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2001,(4)
Reduction of C=N double bonds has been recognized as an important reaction both in organic chemistry and bio-chemistry1. Hantzsch 1,4-dihydropyridine (HEH, one of NADH model compounds) has been reported as a reductive reagent for imines2. However, application of dihydropyridines as practical reducing reagents in organic synthesis is limited because of their instability3. Like NADH models, 2-phenyl-N, N-dimethylbenzimidazoline (PDMBI) is an efficient electron and hydrogen donor (Eox = 0… 相似文献
948.
The inversion of strong scatterer embedded in the half-space is an important problem in engineering and a very difficult nonlinear
problem in mathematics, for which the Born iterative method is of no effect. In this paper the moment method is used in the
discretization procedure. A numerical approach is presented by employing the regularization technique and DBI (distorted Born
iterative) method. The simulation results show that the approach presented is efficient.
Project supported by the Research Fund for the Doctoral Program of Higher Education (RFDP: 98048705). 相似文献
949.
Phytochemical investigation of the whole plant of Leontopodium nanum afforded a new coumarin named leontonanin ( 1 ), together with six known compounds, umbelliferone ( 2 ), 3,4′, 7‐trihydroxyflavone ( 3 ), oleanolic acid ( 4 ), β‐sitosterol ( 5 ), daucosterol ( 6 ) and stearic acid ( 7 ). The structure of compound ( 1 ) was elucidated by spectroscopic methods including 2D‐NMR techniques. 相似文献
950.
Given a positive function F on S^n which satisfies a convexity condition, we introduce the r-th anisotropic mean curvature Mr for hypersurfaces in R^n+1 which is a generalization of the usual r-th mean curvature Hr. We get integral formulas of Minkowski type for compact hypersurfaces in R^n+1. We give some new characterizations of the Wulff shape by the use of our integral formulas of Minkowski type, in case F=1 which reduces to some well-known results. 相似文献