基于辛对偶体系的层合板自由边缘效应的分析解

在原变量——位移和其对偶变量——应力组成的辛几何空间,建立了Pipes-Pagano模型的复合材料层合板问题的辛对偶求解体系．与传统的单类变量不同,辛对偶变量有利于同时描述层间位移连续性条件和应力平衡条件．进入辛对偶体系以后,就可以应用辛对偶体系的统一解析求解方法,如分离变量和辛本征展开的方法对层合板问题进行解析分析和求解．对层合板自由边缘效应的分析求解,验证了辛对偶体系的方法对层合板问题的分析求解是十分有效的．     

Stability and optoelectronic property of lead-free halide double perovskite Cs2B'BiI6 (B' = Li,Na and K)

Although lead-based perovskite solar cells have achieved more than 25% power conversion efficiency, the toxicity of lead and instability are still urgent problems faced in industrial application. Lead-free halide double perovskite (DP) materials are promising candidates to resolve these issues. Based on the density functional theory, we explore the geometric stability, thermodynamic stability, mechanical stability, electronic structures, and optical properties of the Cs₂B'BiI₆ (B' =m Li, Na and K) DP materials. By analyzing the tolerance factor and octahedral factor, we find the geometric stabilities of Cs₂NaBiI₆ and Cs₂KBiI₆ DPs are better than Cs₂LiBiI₆. By calculating the total energy, formation energy and decomposition energy, we propose that the most favorable structure of Cs₂B'BiI₆ is the orthorhombic phase, and Cs₂LiBiI₆ is less stable relative to the other two counterparts from an energetic viewpoint. Mechanical stability evaluations reveal that the orthorhombic Cs₂LiBiI₆ material is less stable relative to the isostructural Cs₂NaBiI₆ and Cs₂KBiI₆ DPs. The mechanical property calculations indicate that the Cs₂B'BiI₆ DPs possess good ductility, which can be used as flexible materials. Electronic structures and optical property calculations show that the orthorhombic Cs₂B'BiI₆ DPs have suitable band gap values, weaker exciton binding energies, and excellent optical absorption performance in the visible-light range. Based on the above comprehensive assessments, we can conclude that the orthorhombic Cs₂NaBiI₆ and Cs₂KBiI₆ DPs with good stability are promising candidates for solar cell applications.     

具有多重权值的时滞复杂网络固定时间同步问题研究

文章研究了基于非周期间歇性控制的具有多重权值和耦合时滞的复杂网络固定时间同步问题.通过构建具有多重权值的复杂网络模型,并基于固定时间稳定性引理和矩阵理论,给出了实现复杂网络固定时间同步的充分条件.此外,文章设计了固定时间非周期切换控制器,获得了实现复杂网络同步的时间上界的估计值.结论证明了实现网络同步的时间与网络的初始状态无关,最后数值模拟说明了理论结果的正确性和有效性.     

Dependence of Electromagnetically Induced Transparency on Laser Linewidth

The influence of the linewidth of coupling laser on the electromagnetically induced transparency (EIT) spectral width is theoretically investigated. The model to describe the EIT spectral width is based on the standard semi-classical theory. The result shows that the effect of the linewidth of coupling laser is equivalent to an additional relaxation between two ground states in the A-type configuration. A broadening linewidth of coupling laser implies the increasing relaxation between the two ground states, which will make the wider EIT spectral linewidth.     

Observation of Electromagnetically Induced Transparency in a Zeeman—Sublevel System in Rubidium Atomic Vapour

We observed electromagnetically induced transparency (EIT) in a Zeeman-sublevel system using rubidium atomic vapour at the temperature of 75~C, in which the width of the EIT signal is only 0.6 MHz. Two different methods were performed to observe the EIT signal in our experiment.     

Tunable microwave signal generation based on an Opto-DMD processor and a photonic crystal fiber

Frequency-tunable microwave signal generation is proposed and experimentally demonstrated with a dual-wavelength single-longitudinal-mode （SLM） erbium-doped fiber ring laser based on a digital Opto-DMD processor and four-wave mixing （FWM） in a high-nonlinear photonic crystal fiber （PCF）. The high-nonlinear PCF is employed for the generation of the FWM to obtain stable and uniform dual-wavelength oscillation. Two different short passive sub-ring cavities in the main ring cavity serve as mode filters to make SLM lasing. The two lasing wavelengths are electronically selected by loading different gratings on the Opto-DMD processor controlled with a computer. The wavelength spacing can be smartly adjusted from 0.165 nm to 1.08 nm within a tuning accuracy of 0.055 nm. Two microwave signals at 17.23 GHz and 27.47 GHz are achieved. The stability of the microwave signal is discussed. The system has the ability to generate a 137.36-GHz photonic millimeter signal at room temperature.     

Dependence of electromagnetically induced transparency on temperature

We performed an experimental study on the dependence of the linewidth of electromagetically induced transparency (EIT) on the temperature of medium in a Λ-type configuration using caesium vapour. We found that the transparent window is narrowed in the EIT whose two ground levels are composed of two hyperfine levels, and broadened in the case when the two ground levels are degenerated Zeeman sublevels, as the temperature of vapour cell is increased. The explanation for the phenomena is given qualitatively.     

基于FDFD方法周期结构的薄膜太阳能电池特性

利用非均匀媒质界面等效参量提取方案结合频域有限差分方法对周期结构薄膜太阳能电池的光学特性进行了数值分析及机理探究.结合等离子体共振条件,研究了两种设计结构的反射、传输、吸收特性及场分布特性,结果表明在低频点,介质和银分界面的场强明显增强,吸收明显增大.探讨了增强因子与结构、入射波长及入射角度间的关系,并分析了其内在的物理机理.结果表明,增强因子在低频时较大且随入射角度增大而增大,最大可达5.7.     

Plasmonic Corrugated Horn Structure for Optical Transmission Enhancement

We propose and theoretically analyze a plasmonic corrugated horn structure for enhanced optical transmission. It makes use of the enhancement of unidirectional propagating surface plasmon polaritons at oblique incidence. Geometric parameters such as the groove depth and width are optimized. Analysis shows that it presents a better performance than the bull＇s eye structure for a small number of grooves.     

WDM网络中基于多核心的组播路由算法

提出了一种WDM网络中组播的分布式路由算法。该算法是一种基于核心树的算法,其关键是找到一个核心节点集,使得以该核心节点集为树根、包含组中所有节点的树满足延迟时限的要求,同时使树的成本尽量小。算法首先根据目的节点确定组中的核心节点集,并生成核心节点内部的稳定树;然后以核心节点集为树根构造包含所有目的节点的组播核心树。由于采用了分布式的方法建立核心树,并且采用的是多个核心,所以在一定程度上减少了建立组播树所需要的时间,并且有效地解决了系统在核心处的瓶颈问题。