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排序方式: 共有138条查询结果,搜索用时 531 毫秒
31.
In this paper, we study the existence of positive solutions of a two-point boundary value problem for a system of fourth-order nonlinear singular semipositone differential equations by the fixed point index theorem. Some new existence results are established, and an example is given to demonstrate the application of our main results. 相似文献
32.
Fengling Li 《Topology and its Applications》2010,157(7):1188-2243
Let Mi be a compact orientable 3-manifold, and Ai a non-separating incompressible annulus on ∂Mi, i=1,2. Let h:A1→A2 be a homeomorphism, and M=M1h∪M2 the annulus sum of M1 and M2 along A1 and A2. In the present paper, we show that if Mi has a Heegaard splitting ViSi∪Wi with distance d(Si)?2g(Mi)+3 for i=1,2, then g(M)=g(M1)+g(M2). Moreover, if g(Fi)?2, i=1,2, then the minimal Heegaard splitting of M is unique. 相似文献
33.
红外辐射材料的制备与光谱研究 总被引:5,自引:0,他引:5
本文开展了红外辐射材料ZrO2、Al2O3及其复合氧化物ZrO2-Al2O3的纳米材料制备方法研究,对其开展了FTIR,NIR FT-Raman、XRD和红外发射光谱研究,研究表明复合氧化物具有较好的红外发射性能。在构效关系的研究基础上,探讨其实际应用价值。 相似文献
34.
Swati De Tero Kesti Manisankar Maiti Fengling Zhang Olle Ingans Arkady Yartsev Torbjrn Pascher Villy Sundstrm 《Chemical physics》2008,350(1-3):14
Exciton dynamics in alternating copolymer/fullerene solar cell blends have been investigated using femtosecond transient absorption spectroscopy. The acceptor concentrations have been varied over a wide range. Experimental data, kinetic modeling and simulations, all indicate that the efficiency of exciton conversion to charges is 100% even at acceptor concentrations as low as 20 wt%. The reported dependence of solar cell efficiency on fullerene concentration may thus arise from other factors. However, there exists an acceptor concentration threshold (5 wt%) below which a substantial fraction of the excitations remain unquenched. The results, we believe are very relevant to optimization of performance efficiency by clever manipulation of morphology. We have also observed exciton–exciton energy transfer in these blends at low acceptor concentrations. 相似文献
35.
36.
A hybrid time stepping scheme combining explicit Runge–Kutta with implicit LU‐SGS for Navier–Stokes equations
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Fengling Lu 《国际流体数值方法杂志》2016,82(4):218-227
A hybrid time stepping scheme is developed and implemented by a combination of explicit Runge–Kutta with implicit LU‐SGS scheme at the level of system matrix. In this method, the explicit scheme is applied to those grid cells of blocks that have large local time steps; meanwhile, the implicit scheme is applied to other grid cells of blocks that have smaller allowable local time steps in the same flow field. As a result, the discretized governing equations can be expressed as a compound of explicit and implicit matrix operator. The proposed method has been used to compute the steady transonic turbulent flow over the RAE 2822 airfoil. The numerical results are found to be in excellent agreement with the experimental data. In the validation case, the present scheme saved at least 50% of the memory resources compared with the fully implicit LU‐SGS. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
37.
A series of novel γ,γ‐difluorinated Goniothalamin analogues 4a – 4i and 6a – 6i were synthesized. The key steps included the construction of C‐5 stereocenter adjacent to gem‐difluoromethylene group by way of lipase AK catalyzed kinetic resolution, the introduction of aryl group via Stille coupling, and lactonization by 1,5‐oxidative cyclization. These γ,γ‐difluorinated Goniothalamin analogues 4a – 4i and their enantiomers 6a – 6i , together with several corresponding γ‐monofluorinated Goniothalamin analogues were biologically evaluated against four different cancer cell lines. Compound 7h showed a nearly equivalent potency as the parent (R)‐Goniothalamin in the micromolar range. The different fluorine effects between fluoromethylene and gem‐difluoromethylene on antitumor activity were discussed through the analysis of bioassay data. 相似文献
38.
A new daunorubicin has been synthesized and structurally characterized. The interaction of native calf thymus DNA (ctDNA) with 3′-azido-daunorubicin thiosemicarbazone (ADNRT) was investigated under simulated physiological conditions by multi-spectroscopic techniques, viscometric measurements and molecular modeling study. It concluded that ADNRT could intercalate into the base pairs of ctDNA, and the fluorescence quenching by ctDNA was static quenching type. Thermodynamic parameters calculated suggested that the binding of ADNRT to ctDNA was mainly driven by hydrophobic interactions. The relative viscosity of ctDNA increased with the addition of ADNRT, which confirmed the intercalation mode. Furthermore, molecular modeling studies corroborate the above experimental results. 相似文献
39.
Wang E Ma Z Zhang Z Vandewal K Henriksson P Inganäs O Zhang F Andersson MR 《Journal of the American Chemical Society》2011,133(36):14244-14247
A new, low-band-gap alternating copolymer consisting of terthiophene and isoindigo has been designed and synthesized. Solar cells based on this polymer and PC(71)BM show a power conversion efficiency of 6.3%, which is a record for polymer solar cells based on a polymer with an optical band gap below 1.5 eV. This work demonstrates the great potential of isoindigo moieties as electron-deficient units for building donor-acceptor-type polymers for high-performance polymer solar cells. 相似文献
40.
Liming Hu Shengmei Lu Fengling Yang Juhong Feng Zhaojie Liu Hansheng Xu 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2785-2790
A series of 2-phosphonoalkyl 1,2-benzisoselenazol-3(2H)-ones were designed and synthesized via reaction 2-chloroselenobenzoyl chloride with 1-hydrazinobenzyl phosphonate. The structures of all new compounds were confirmed by spectroscopic methods and microanalyses. 相似文献