The role of π electrons in the formation of benzene-containing lithium-bonded complexes

The intermolecular interactions in C₆H₆???LiX (X=OH, NH₂, F, Cl, Br, NC, CN) complexes are investigated by using second‐order Møller–Plesset perturbation theory (MP2) calculations and quantum theory of “atoms in molecules” (QTAIM) studies, and the role of π electrons is studied in the formation of these benzene‐containing lithium‐bonded complexes. The molecular electrostatic potentials of benzene and LiX determine the geometries of the lithium‐bonded complexes. The electron densities at the lithium bond critical points in the πC₆H₆???LiX complexes are obviously stronger than those in the σC₆H₆???LiX complexes, which indicates that the intermolecular interactions in the C₆H₆???LiX complexes are mainly attributable to π‐type interaction. The topological and energy properties at the lithium bond critical points in both the C₆H₆???LiX and πC₆H₆???LiX complexes are linear with the interaction energies, thereby showing the crucial role of the π electrons in the formation of these complexes. Electron localization function (ELF) analysis indicates that the formation of the lithium bonds leads to the reduction of the ELF π‐electron density and volume, and the reduction of the π‐electron volume is linear with the interaction energies with the correction coefficient 0.9949.     

High-performance silicon nanowire array photoelectrochemical solar cells through surface passivation and modification

Nanowire solar cells: Pt nanoparticle (PtNP) decorated C/Si core/shell nanowire photoelectrochemical solar cells show high conversion efficiency of 10.86 % and excellent stability in aggressive electrolytes under 1-sun AM 1.5 G illumination. Superior device performance is achieved by improved surface passivation of the nanowires by carbon coating and enhanced interfacial charge transfer by PtNPs.     

Atomistic mechanism of charge separation upon photoexcitation at the dye-semiconductor interface for photovoltaic applications

Charge separation in excited states upon visible light absorption is a central process in photovoltaic solar cell applications. Employing state-of-the-art first principles calculations based on time-dependent density functional theory (TDDFT), we simulate electron-hole dynamics in real time and illustrate the microscopic mechanism of charge separation at the interface between organic dye molecules and oxide semiconductor surfaces in dye-sensitized solar cells. We found that electron-hole separation proceeds non-adiabatically on an ultrafast timescale <100 fs at an anthocyanin/TiO(2) interface, and it is strongly mediated by the vibrations of interface Ti-O bonds, which anchor the dye onto the TiO(2) surface. The obtained absorption spectrum and electron injection timescale agree with experimental measurements.     

在半金属表面上应力诱导的红荧烯晶态薄膜

报道了在Bi（001）衬底上从第一层开始形成的红荧烯晶体薄膜.随着覆盖度的增加,红荧烯薄膜的结构会发生从自组装到混合相的转变.在混合相中存在着红荧烯的晶体畴和分子自组装形成的畴壁.特别是,我们在这种晶体畴中发现了Kurdjunov-Sachs（KS）转动外延和巨大的压缩应力.随着覆盖度的增加,红荧烯薄膜会按照逐层生长的模式进行,直至第四个分子单层.我们认为,转动外延过程中所产生的巨大压缩应力是导致晶态红荧烯薄膜的形成原因.     

Aerodynamics of indirect thrust measurement by the impulse method

The aerodynamic aspects of indirect thrust measurement by the impulse method have been studied both experimentally and numerically. The underlying basic aerodynamic principle is outlined, the phenomena in subsonic, supersonic and arc-heated jets are explored, and factors affecting the accuracy of the method are studied and discussed. Results show that the impulse method is reliable for indirect thrust measurement if certain basic requirements are met, and a simple guideline for its proper application is given.     

The dynamics of a high-dimensional delayed pest management model with impulsive pesticide input and?harvesting prey at different fixed moments

In this paper, a delayed pest control model with stage-structure for pests by introducing a constant periodic pesticide input and harvesting prey (Crops) at two different fixed moments is proposed and analyzed. We assume only the pests are affected by pesticide. We prove that the conditions for global asymptotically attractive ??predator-extinction?? periodic solution and permanence of the population of the model depend on time delay, pulse pesticide input, and pulse harvesting prey. By numerical analysis, we also show that constant maturation time delay, pulse pesticide input, and pulse harvesting prey can bring obvious effects on the dynamics of system, which also corroborates our theoretical results. We believe that the results will provide reliable tactic basis for the practical pest management. One of the features of present paper is to investigate the high-dimensional delayed system with impulsive effects at different fixed impulsive moments.     

钨合金三点弯曲破坏的细观数值模拟

运用有限元方法模拟了钨合金材料的三点弯曲实验;采用单胞单元计算模型,分析了断口形貌与材料力学性能之间的关系;建立了宏观断裂形式与微观结构参数之间的关联.结果表明:裂纹主要产生在 W-W 界面、W-M 界面,且在基体中向前发展,钨合金材料的破坏可归结为延性材料的破坏;裂纹的尖端始终处于应力集中的状态,随着裂纹的扩展,拉应力集中不断释放,并且转移到新的裂纹尖端;裂纹尖端的单元为拉伸破坏,拉应力是导致裂纹扩展的主要因素.     

气体钻水平井井径扩大环空流动特征的数值模拟

由于气体钻水平井中岩屑受力状态与直井有很大不同,特另0是遇到井径扩大,更是携岩的关键点。因此,在分析了气体钻水平并岩屑运移特点以及建立环空连续性方程和动能方程的基础上,以实际并为例考虑了不同井径扩大率,数值模拟了其扩径段气固两相的流动状态,包括气固速度、岩屑浓度、压力分布等。研究结果表明：气体在经历扩径段时环空压力有个降落又回升的过程,随着井眼扩径系数的增大,压力下降又回升,所经历的长度会逐渐增长;扩径系数大于一定值时,扩径变径处存在一定区域的零流动区;扩径系数越大,低速区和回流区就越大越长,扩径下部区域越容易堆积岩屑,填充井眼。     

倾斜微孔端面气体密封的动压特性研究

为提高多孔端面气体密封的动压特性, 提出 １种双列倾斜椭圆微孔端面密封结构． 基于气体润滑理论模 型, 采用数值方法分析了操作参数和微孔几何参数对密封泄漏率和开启力的影响规律, 探讨了倾斜微孔的上、 下游 泵送作用对气体密封动压特性的作用机理． 结果表明： 与单列倾斜微孔端面气体密封相比, 双列倾斜微孔端面气体 密封可使动压开启力显著增加, 低压侧微孔环带可将下游流体沿微孔倾斜方向向上游泵送, 使得泄漏率显著降低, 气体密封动压效应明显增强; 密封动压性能受反向开孔比、 微孔倾角、 面积比和孔深等几何参数的影响, 本文给出了 这些参数的优化取值范围．