水的溶剂效应对植物防晒剂UV-B吸收的影响（英文）

抵御UV-B(280～320 nm)对地球生命至关重要.研究UV-B防晒分子周边的环境对UV-B吸收的影响有助于了解防晒剂的光吸收机制.水作为溶剂在细胞中无处不在,但是其对防晒剂吸收UV-B的影响还未被充分研究.本文基于第一性原理,重点研究了芥子酸酯及其相关植物防晒分子的UV-B吸收中水的溶剂作用.芥子酸酯阴离子对UV-B的吸收作用来自与其周边水溶剂环境的相互作用,因此其也是在实际环境中起到防晒功能的防晒物种.在第一性原理模拟中,隐式水溶剂模型可以提供溶剂化的介电环境,显式水溶剂模型可以与芥子酸酯阴离子形成氢键,这些因素都可以显著改变与芥子酸酯阴离子吸收UV-B相关的跃迁轨道性质.同时,发现了植物防晒剂的分子偶极矩可以作为衡量其UV-B吸收能力对周围极性环境敏感程度的指标.本工作为开发新型水溶性UV-B防晒剂提供了起点.     

3维电磁粒子模拟程序设计

 在3维Yee网格模型以及蛙跳模型的基础上,分析了3维电磁场离散算法及其稳定条件,讨论了3维空间网格上电磁场作用于粒子的平均场权重法和粒子作用于电磁场的Charge-conserving法,同时也讨论了3维空间网格上理想导体边界条件、自由吸收边界条件、爆炸式发射模型的模拟实现方法。以向内发射同轴二极管为例从其电流电压关系及电子束运动特性方面验证了模拟的正确性。     

Terahertz radiation from interaction between an electron beam and a planar surface plasmon structure

The possibility of an electron beam exciting surface plasmons in conducting metal is discussed in this paper. A planar perfect-structure with subwavelength holes is proposed. The phenomenon that mimicking surface plasmon waves can be excited and amplified by an electron beam is proved theoretically and numerically. The mechanism of transmission through a subwavelength hole array is exploited to enhance the interaction between the electron beam and the mimicking surface plasmons.     

Surface plasmon polaritons frequency-blue shift in low confinement factor excitation region

Surface plasmon polaritons' (SPPs') frequency blue shift is observed in finite-difference time-domain (FDTD) simulation of parallel electron excitation Au bulk structure. Comparing with cold dispersion of SPPs, an obvious frequency blue shift is obtained in low confinement region excitation simulation results. Then, according to SPPs' transverse attenuation characteristics, the excited frequency mode instead of cold dispersion corresponding frequency mode matches it. Thence, this excited mode is confirmed to be SPPs' mode. As is well known the lower the frequency, the smaller the confinement factor is and the lower the excitation efficiency, the wider the bandwidth of excited SPPs is. And considering the attenuation in whole structure, the excited surface field contains attenuation signal. In a low confinement factor region, the higher the SPPs' frequency, the higher the excitation efficiency is, while broadband frequency information obtained in attenuation signal provides high frequency information in stimulation signal. Thence, in the beam-wave interaction, as the signal oscillation time increases, the frequency of the oscillation field gradually increases. Thus, compared with cold dispersion, the frequency of excited SPP is blueshifted This hypothesis is verified by monitoring the time domain signal of excited field in low and high confinement factor regions and comparing them. Then, this frequency-blue shift is confirmed to have commonality of SPPs, which is independent of SPPs' material and structure. Finally, this frequency-blue shift is confirmed in an attenuated total reflection (ATR) experiment. Owing to frequency dependence of most of SPPs' devices, such as coherent enhancement radiation and enhancement transmission devices, the frequency-blue shift presented here is of great influence in the SPPs applications.     

粒子模拟软件吸收边界的研究

 实现了时域有限差分法的Gedney完全匹配层吸收边界条件,并进行了数值验证和参数优化。从结果可以看出其有较低的反射,性能优良;对吸收媒质厚度和电导率分布阶数的参数优化结果与Gedney经验值基本一致。将此吸收边界模块加入到国产粒子模拟软件CHIPIC中,同美国商业粒子模拟软件MAGIC相比有更好的吸收效果。通过对2维极坐标下磁控管的模拟,证明了此吸收边界具有实际应用价值。     

强流相对论电子束双腔纵向自调制研究

当强流相对论电子束在类双腔速调管系统中传输时，会发生自调制现象. 利用这一现象可以 在无微波注入的情况下得到较好的微波输出，这是一种由强流相对论效应引起的自激振荡. 利用这一原理有可能研制出一类新型的微波器件. 对强流相对论电子束在这种物理机制作用 下发生起振的条件及传输机理进行了理论分析，并进行了数值模拟. 优化结果显示，利用4k A, 500kV的强流相对论电子束，可得到099GHz，800MW的微波输出，效率约40％. 关键词： 强流相对论电子束 自调制 反馈机制 数值模拟