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物理学院“博约学术沙龙”系列报告 (总第 126 期)

发布日期:2016年11月15日
时  间:   2016年11月10日(星期四)下午3:00
地  点:   中心教学楼610
报告一:硕士生报告    时间:15:10-15:40
题  目:电晕沿面放电及其在电推进上的应用
报告人:张岑               指导老师:欧阳吉庭
摘要:
沿面介质阻挡放电(SDBD)等离子体电推进作为一种新型的推进技术,在临近空间推进上有很好的应用前景。目前对于沿面介质阻挡放电的特性研究已有较长时间,但对其电推力特性的研究才刚刚起步。本文以实验的方法,研究在不同条件下,低气压下沿面介质阻挡放电及其电推力特性,并在同样条件下研究电晕沿面放电新型结构的放电特性及其电推力特性。由此可得到电晕沿面放电与一般结构沿面介质阻挡放电的对比,以此来研究设计沿面放电的最优结构。这对于探索新型电推进装置具有积极的意义。
实验中,我们用交流驱动装置,研究了不同电压、气压、高压电极宽度、低压电极宽度、电极间距对两种沿面介质阻挡放电击穿电压、放电功率、产生推力小及推力的效率(即比功率)的影响。也可得到不同工况下,两种沿面介质阻挡放电击穿电压、放电功率、产生推力小及推力的比功率的比较。经过对比结果可知,SDBD在60kpa,高压电极宽度w1=0.5cm,低压电极宽度w2=0.5cm,电极间距d=0cm时,此装置产生的推力效率是最大的。电晕沿面介质阻挡放电应属高压电极宽度较细的一种沿面介质阻挡放电,其最优化的工况为气压为60kpa,高压电极宽度w1=0.1mm,低压电极宽度w2=0.5cm,电极间距d=0.5mm时,此装置产生的推力效率是最大的。其中,电晕沿面介质阻挡放电属于高压电极很细的沿面介质阻挡放电,由于高压电极越细,电晕作用越强,装置消耗的电功率也越小,所以此种装置产生的电推力的效率比一般形式沿面介质阻挡放电的效率更高。
此篇文章,探究了不同工况对于装置产生的电推力效率的影响。最终得到结论,气压和高压电极宽度对放电功率影响较大。在气压为60kPa、高压电极越细时,装置产生的电推力较高。
关键词:沿面放电;电推进;放电特性;电推力

报告二:博士生报告    时间:15:40-16:10
题  目:  Possible soft-matter quasicrystals of 5- and 10- fold symmetries and hydrodynamics 
报告人:  成惠                  指导老师:   范天佑
摘要:
Soft-matter quasicrystal is a novel and cross discipline subject connecting two subfields of physics and chemistry---soft matter and quasicrystals, and presents important meaning.
Fan suggested a model for soft-matter quasicrystals based on elementary excitations---phonon, phason and fluid phonon, and derived the equations of motion of the soft-matter quasicrystals. On this basis Fan et al have carried out some work on specific heat and other thermodynamic functions, Stokes-Oseen flow, dislocations and other topics of soft-matter quasicrystals of 12- and 18-fold symmetry observed so far, in which the effects of fluid phonon and interaction between phonon and fluid phonon are explored. However, the decoupling between phonon and phason in soft-matter quasicrystals with 12- and 18-fold symmetries leads unfortunately to lack of response of phason field under the some boundary conditions studied in the work.

报告三:硕士生报告    时间:16:10-16:40
题 目:Optical Properties of an Individual Multi-branched CdS Comblike Micro/Nanostructure
报告人: 赵方银                        指导老师:刘瑞斌
摘要:
Using a simple in situ seeding chemical vapor deposition (CVD) process, comb-like (branched) monolithic CdS micro/nanostructures were grown based on VLS and VS mechanism. The SEM show branches are distributed at one side of the trunk part and TEM images demonstrate that the achieved structures are high quality, with the branches grown along [0001]. In addition, the spacing between branches and angle between branches and trunk can be tuned. Efficient optical coupling between the backbone and the teeth of the branched architecture is demonstrated by distributing light from an UV-laser-excited spot at one end of the backbone to all branch tips. Based on that, quantitative waveguide analysis using fiber probe (diameter is about 1 um) connected to PMT was done to investigate the optical loss from the excitation point at truck part to the branch part of the nanostructure, the calculated loss coefficient was calculated about 0.066 db/um. Furthermore, strong electron–phonon coupling at the junction part caused by the deformation potential has been demonstrated using temperature dependent Raman and and localized Raman mapping. Otherwise, temperature dependent photoluminescence and carrier dynamic behavior for the junction part of Sn-doped CdS comb-like structures are taken further study. The temperature dependent PL implies that the phonon assisted NBE (near bandgap emission) emission intensity becomes strong at low temperature and a blueshift of the emission peak can be clearly observed at junction part. The emission color will change from green to orange, finally become yellow with the temperature change from 300K to 78K, which make this nanostructure can be used as a micro zone thermometer.  Moreover, the lifetime of NBE and DLE (deep-level emission) will increase with temperature decrease due to thermally activated phonon decrease at lower temperatures.

报告四:硕士生报告    时间:16:40-17:10
题  目:含Ag纳米粒子染料掺杂向列相液晶的随机激光发射
报告人:杨明朝                       指导老师:邓罗根、衡成林
摘要:为探究Ag纳米粒子和向列相液晶对染料随机系统中随机激光形成的作用,本文对染料掺杂向列相液晶,含Ag纳米粒子的染料溶液和含Ag纳米粒子的染料掺杂向列相液晶三个随机系统中的随机激射现象进行了实验研究。在染料掺杂向列相液晶系统中我们没有观察到随机激光现象,发射谱的半高宽大于16 nm。在含Ag纳米粒子染料掺杂向列相液晶系统中我们观察到了随机激光现象,激光阈值和半高宽分别为5.12 uJ/pulse和 0.2nm,随机激光发射具有面积依赖性,样品上不同的激发位置都有随机激光发射,明显的激光发射主要集中在偏离泵浦光激发条纹方向约45°的角度范围内。在含Ag纳米粒子的染料溶液系统中我们也观察到了随机激光现象,激光阈值高达 45uJ/pulse。含Ag纳米粒子的染料掺杂向列相液晶随机系统中的相干随机激光现象的产生与向列相液晶指向矢波动引起的多重散射和Ag纳米粒子的周围局部电场的增强有关。
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