各位数院研究生同学：

　　研究生学术午餐会是在学院领导的大力支持下，由研究生会负责组织的系列学术交流活动。午餐会每次邀请一位同学作为主讲人，面向全院各专业背景的研究生介绍自己科研方向的基本问题、概念和方法，并汇报近期的研究成果和进展，是研究生展示自我、促进交流的学术平台。

　　研究生会已经举办了三十九期活动，我们将于2019年11月1日周五举办第四十期学术午餐会活动，欢迎感兴趣的老师和同学积极报名参加。

　　报告人简介：韩雨岑，北京大学数学科学学院2015级博士研究生，师从张磊教授，研究方向为材料软物质。

　　Abstract: Liquid crystals are classical examples of partially ordered materials that combine the fluidity of liquids with a degree of long-range orientational order. There is substantial interest in defect pattern formation in liquid crystals. Defects are discontinuities in the alignment direction of liquid crystals mainly because of the topological constraint when certain boundary conditions are presented. To study the effects of geometry on the structure, locations and dimensionality of defects, we investigate the nematic equilibria on regular two-dimensional polygons with Dirichlet tangent boundary conditions, in a reduced two-dimensional framework, discussing their relevance in the full three-dimensional framework too. We work at a fixed temperature and study the reduced stable equilibria in terms of the edge length of the regular polygon.

　　We analytically compute a novel"ring solution"in the area of domain to zero limit, with a unique point defect at the center of the polygon except square. The ring solution is unique. For sufficiently large area of domain, we deduce the existence of the number of classes of stable equilibria and numerically compute bifurcation diagrams for reduced equilibria on a pentagon and hexagon, as a function of the area of domain, thus illustrating the effects of geometry on the structure, locations and dimensionality of defects in this framework.

　　报名方式：请有意参加的同学于2019年10月30日(周三)中午12点前填写报名问卷，复制问卷链接https://www.wjx.top/jq/48094579.aspx至浏览器或点击阅读原文进入问卷报名。

　　特别注意：如果您报名却没有参与活动，需要您自己承担已经购买的午餐费用。由于客观条件限制，本次午餐会的名额为40人，先报先得。

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