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41.
本文采用基于密度泛函理论的第一性原理计算,系统研究了完全Heusler合金Cr2ZrSb/Sc2FeSn(100)异质结中六种界面CrCr-ScFe-T、ZrSb-ScSn-T、CrCr-ScSn-B、ZrSb-ScFe-B、CrCr-ScFe-V和 ZrSb-ScSn-V的电磁特性及电子性质。结果表明,界面原子间的相互作用造成了界面间原子层的不均匀,导致界面层的力学失配率加大。与块体中的高自旋极化率相比,异质结的自旋极化率遭到不同程度的破坏。但是,ZrSb-ScFe-B界面保留了较高的自旋极化率值,通过Julliere模型预测该异质结在低温下隧道磁电阻值约为429.29%,在自旋电子学器件中具有潜在的应用前景。 相似文献
42.
Xu HX Cheng SF Yang XJ Chen B Chen Y Zhang LP Wu LZ Fang W Tung CH Weiss RG 《The Journal of organic chemistry》2012,77(4):1685-1692
Irradiations of alkyl 2-naphthoates are known to result in four isomeric "cubane-like" photodimers: anti(HH)-2, syn(HH)-2, anti(HT)-2, and syn(HT)-2 where the anti(HH)-2, anti(HT)-2, and syn(HT)-2 consist of pairs of diastereomers. Here, chiral auxiliary and chiral microreactor strategies have been combined to achieve high diastereoselectivity in photodimerizations of an enantiomeric pair of 2-naphthoates with (R)- and (S)-1-methoxycarbonylethyl esters as chiral auxiliaries (1R and 1S). Thus, irradiations of their γ-cyclodextrin (γ-CD) complexes have been conducted. Fluorescence, IR, and NMR spectra of both enantiomers of 1 demonstrate that their γ-CD complexes are mainly 2:2 with the molecules of 1 in head-to-head orientations. Irradiation of the complexes in the solid state mainly resulted in anti(HH)-2. The absolute configuration of each diastereomer of anti(HH)-2 has been established for the first time here. The diastereomeric excesses (de's) of anti(HH)-2 from 1R and 1S were 94% and 86%, respectively. These de's are much higher than those found from irradiations in solution (55% for 1R and 1S), where the opposite diastereomeric form is in excess! Calculations of the energies of various conformations of the head-to-head 2:2 inclusion complexes were performed using the PM3 approach. The predicted major diastereomers based on the calculation are consistent with those found experimentally. 相似文献
43.
光化学反应是最基本也是最重要的物理化学过程之一,在诸多领域有着广泛的应用。由于计算方法的限制以及光化学反应过程的错综复杂性,光化学反应机理的从头算研究是极具挑战性的国际前沿课题之一。本文综述了近20年来羰基化合物光化学反应机理从头算研究的一些进展,总结了羰基化合物电子激发态的特性和光化学反应过程的规律性,为深入研究光化学反应提供一些有用的信息。 相似文献
44.
45.
Yang Yang Dong Wang Yongjin Wu Xiaorui Tian Haili Qin Liang Hu Ting Zhang Weihai Ni Jian Jin 《Macromolecular rapid communications》2016,37(7):590-596
Herein, the use of a 2D soft template system composed of hundred‐nanometer‐thick water/ethanol mixed layers sandwiched by lamellar bilayer membranes of a self‐assembled amphiphilic molecule to produce ultrathin polyprrole (PPy) with a uniform thickness as thin as 3.8 nm and with large dimensions (>2 μm2) is presented. The obtained PPy nanosheets exhibit regioregularity with ordered chain alignment where the polymer chains in the nanosheets produced are well aligned with a clear interchain spacing as confirmed by small‐angle X‐ray scattering measurement. The molecular‐level‐thick PPy nanosheets exhibit extremely high conductivity up to 1330 S m−1, thanks to the ordered alignment of polymer chains in the nanosheets, and a high transparency in both the visible region (transmittance >99%) and near‐infrared region (transmittance >93%).
46.
Regulatory Mechanism of the Enantioselective Intramolecular Enone [2+2] Photocycloaddition Reaction Mediated by a Chiral Lewis Acid Catalyst Containing Heavy Atoms 下载免费PDF全文
Dr. Hongjuan Wang Dr. Xiaoyan Cao Prof. Xuebo Chen Prof. Weihai Fang Prof. Michael Dolg 《Angewandte Chemie (International ed. in English)》2015,54(48):14295-14298
The asymmetric catalysis of the intramolecular enone [2+2] photocycloaddition has been subject of extensive experimental studies, however theoretical insight to its regulatory mechanism is still sparse. Accurate quantum chemical calculations at the CASPT2//CASSCF level of theory associated with energy‐consistent relativistic pseudopotentials provide a basis for the first regulation theory that the enantioselective reaction is predominantly controlled by the presence of relativistic effects, that is, spin–orbit coupling resulting from heavy atoms in the chiral Lewis acid catalyst. 相似文献
47.
Weihai Fang Shanjia Xu 《International Journal of Infrared and Millimeter Waves》2006,27(12):1667-1681
The frequency selective characteristics of a new dielectric periodic structure composed of left-handed materials (LHM) are
carefully studied by a method which combines the multimode network theory with the rigorous mode matching method. The variations
of the frequency selective characteristics with structure parameters and dielectric loss are presented and comparisons for
the frequency selective properties between RHM and LHM gratings are also shown with some explanations. Guidelines for accurate
design of the LHM dielectric frequency selective surface are given.
Supported by the National Natural Science Foundation of China (No. 60171037) (No. 60371010) and (No. 63531020) 相似文献
48.
Diazo compounds such as phenyldiazomethane (C6H5C(H)N2) exhibit intriguing phenomena including the ultrafast formation of singlet carbene and the excited‐state rearrangement reaction (RIES). In this work, we have used multi‐reference configuration interaction with single and double excitations (MRCI‐SD) and complete active space self‐consistent field (CASSCF) methods to study the photodissociation dynamics of C6H5C(H)N2. The equilibrium structures, transition states in the lowest three electronic states (S1, T1, and S0), and S1/S0 and T1/S0 minimum‐energy crossing points both in the Franck–Condon region and on the pathway of the CN bond dissociation have been optimized. On the basis of the calculated S1, T1, and S0 potential energy surfaces, we have uncovered the most efficient pathways to the lowest singlet and triplet phenylcarbenes (C6H5CH) in irradiated C6H5C(H)N2. 相似文献
49.
Herein, various polysaccharide-based nanoparticles were synthesized from dextran, hydroxypropyl cellulose, and hydroxyethyl
cellulose, respectively, by a self-assembly assisted approach. This approach enables us to prepare stable polysaccharide-based
nanoparticles with carboxy functional groups directly from monomers without using any surfactant and organic solvent. The
existence of abundant carboxyls in these polysaccharide-based nanoparticles provides them obvious pH sensitivity as verified
by 1H nuclear magnetic resonance as well as the potential in loading cationic drug. 相似文献
50.
Weihai Li Shanjia Xu Xuequan Chen 《International Journal of Infrared and Millimeter Waves》2005,26(7):967-979
The NRD/microstrip line hybrid integration structure shows good behavior for millimeter wave applications. This paper applies the integral equations method to analyze the transmission characteristics of the NRD/microstrip line hybrid integrated baluns coupling through slot and operating in LSE or LSM modes. To apply this method, a new Greens’ function of microstrip line is presented and the slot coupling problems between NRD guide and microstrip line and the practical LSE and LSM-mode baluns are analyzed respectively. The availability of the present approach is validated by rather good agreement between the theoretical results and the experiment data given in the literature.* Supported by the National Natural Science Foundation of China
(No. 60371010) (No. 60471037) 相似文献