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371.
Jeng Liang Han 《Tetrahedron》2006,62(34):8169-8172
Diels-Alder reactions of tricarbonyl[(1-4-η)-2-methoxy-5-methylene-cyclohexa-1,3-diene]iron 1 with 1,2,4,5-tetrazine-3,6-disubstituted derivatives 2a,b,d and 2,3,4,5-tetrabromothiophene-1,1-dioxide 5 are reported. The (4+2) cycloaddition reactions took place exclusively with highly electron deficient dienes to form spiro[5.5]undecane system in good yield. The more electron rich nature of the 1,2,4,5-tetrazine-3,6-disubstituted derivatives 2b did not react. The reaction also took place stereospecifically exo to the Fe(CO)3 moiety. 相似文献
372.
The thermal degradation behaviour of epoxy/unsaturated polyester based polymer interpenetrating networks (IPNs), and unsaturated polyester containing various flame-retardants have been investigated by TGA and Py/GC/MS. The kinetic parameters of various polymers were analysed by conventional and modulated thermogravimetric analysis (MTGA) methods. The activation energies of degradation were calculated by the Coats-Redfern and MTGA methods, respectively. The results of both conventional and MTGA analyses reveal that the decomposition of IPNs consists of two non-interfering decomposition processes for epoxy polymer and cured unsaturated polyester, respectively. For the flame-retardant containing unsaturated polyesters, ammonium polyphosphate (APP) played an important role in the second-step of the pyrolysis reaction of APP-containing samples. It is important to note that the possibilities of reaction order for these pyrolysis processes are significantly distinguishable by Coats-Redfern method. Furthermore, the activation energies for various samples calculated by MTGA method are on average larger than those calculated from the Coats-Redfern method. The results also reveal that when either the flame-retardant or the epoxy was added to the unsaturated polyester, the heat resistance of the unsaturated polyester was enhanced. 相似文献
373.
Jeng‐Tzong Chen Wen‐Cheng Shen 《Numerical Methods for Partial Differential Equations》2009,25(1):63-86
In this article, a semi‐analytical method for solving the Laplace problems with circular boundaries using the null‐field integral equation is proposed. The main gain of using the degenerate kernels is to avoid calculating the principal values. To fully utilize the geometry of circular boundary, degenerate kernels for the fundamental solution and Fourier series for boundary densities are incorporated into the null‐field integral equation. An adaptive observer system is considered to fully employ the property of degenerate kernels in the polar coordinates. A linear algebraic system is obtained without boundary discretization. By matching the boundary condition, the unknown coefficients can be determined. The present method can be seen as one kind of semianalytical approaches since error only attributes to the truncated Fourier series. For the eccentric case, vector decomposition technique for the normal and tangential directions is carefully considered in implementing the hypersingular equation in mathematical essence although we transform it to summability to divergent series. The five advantages, well‐posed linear algebraic system, principal value free, elimination of boundary‐layer effect, exponential convergence, and mesh free, are achieved. Several examples involving infinite, half‐plane, and bounded domains with circular boundaries are given to demonstrate the validity of the proposed method. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009 相似文献
374.
This study is the first to demonstrate the selectivity quantum well intermixing process by using a femtosecond laser scanning-induced disordering technique. The advantages of the femtosecond laser are photochemical machining and the two-photon absorption mechanism. The femtosecond laser system can convert writing into the scan to create a nanostructure by adjusting the lens. The effect of power on the band gap shift during laser scanning was investigated. The band gap shift was small and unstable without the heating substrate. A wavelength shift higher than 77.3 nm for the InGaAsP MQW material was obtained at elevated temperatures. 相似文献
375.
An analytical solution to the three-dimensional scattering and diffraction of plane SV-waves by a saturated hemispherical alluvial valley in elastic half-space is obtained by using Fourier–Bessel series expansion technique. The hemispherical alluvial valley with saturated soil deposits is simulated with Biot’s dynamic theory for saturated porous media. The following conclusions based on numerical results can be drawn: (1) there are a significant differences in the seismic response simulation between the previous single-phase models and the present two-phase model; (2) the normalized displacements on the free surface of the alluvial valley depend mainly on the incident wave angles, the dimensionless frequency of the incident SV waves and the porosity of sediments; (3) with the increase of the incident angle, the displacement distributions become more complicated; and the displacements on the free surface of the alluvial valley increase as the porosity of sediments increases.The project was supported by the National Natural Science Foundation of China (50478062 and 10532070) and Open Fund at the Key Laboratory of Urban Security and Disaster Engineering (Beijing University of Technology), Chinese Ministry of Education. The English text was polished by Keren Wang. 相似文献
376.
Li-Der Jeng Fang-Biau Ueng Xi-Lin Wang 《International Journal of Communication Systems》2023,36(1):e5358
In the fourth-generation communication system (4G), orthogonal frequency division multiplexing (OFDM) is widely used. However, due to the cyclic prefix (CP) being added, the low spectrum efficiency and high out-of-band radiation (OOB) cause OFDM not to be suitable for the beyond fifth-generation (B5G) communication system. Therefore, to meet the rigorous demands in B5G for the Internet of Things (IoT) and massive machine-type communications (MMTC), generalized frequency division multiplexing (GFDM) technology has received significant attention. On the other hand, index modulation (IM) can provide flexible settings of different parameters to achieve the ideal system goals. Therefore, this paper considers the combination of spread spectrum (SS) and IM under the framework of GFDM, called SS-IM-GFDM. In this scheme, the information bits are jointly conveyed by the indices of spreading codes and the conventional M-ary modulated symbols, which increase the spectrum efficiency and improve the bit error rate performance. Furthermore, a low-complexity maximum likelihood (ML) detector is proposed to recover the transmitted signal effectively at the receiver. Finally, the space-time block code (STBC) is employed to construct the multi-input multi-output SS-GFDM-IM (MIMO SS-GFDM-IM) system to improve the system's reliability. The simulation results show that the proposed scheme is superior to the existing systems. 相似文献
377.
Heng Liu Yuang Fu Zeng Chen Jiayu Wang Jiehao Fu Yuhao Li Guilong Cai Chun-Jen Su U-Ser Jeng Haiming Zhu Gang Li Xinhui Lu 《Advanced functional materials》2023,33(36):2303307
All-small-molecule organic solar cells (ASM-OSCs), which consist of small-molecule donors and acceptors, have recently been studied extensively to eliminate the batch-to-batch variation from polymer-based donor or acceptor. On the other hand, the control of their active layer morphology is more challenging due to the similar chemical structure and miscibility of small-molecule donor and small-molecule accepter. Hence, this study develops a dual-additive-driven morphology optimization method for ASM-OSCs based on BTR-Cl:Y6. One solid additive – 1,4-diiodobenzene (DIB) and one liquid additive – diiodomethane (DIM) are selected, making use of their distinct interaction mechanisms with Y6 and BTR-Cl. It is found that DIB can form a eutectic phase with Y6, which can increase the intermolecular interactions and modulate the acceptor phase separation, while the simultaneous volatilization of DIM suppresses the over-aggregation of BTR-Cl during the film casting process. As a result of the synergistic morphology tuning, the optimized device delivers a power conversion efficiency (PCE) as high as 15.2%, among the highest PCE reported to date for binary ASM-OSCs without solvent annealing treatment. This work demonstrates the potential of morphology tuning via the incorporation of dual additives into ASM-OSCs, enabling them to achieve comparable efficiencies to those of conventional polymer/small-molecule based OSCs. 相似文献