逐渐睁开的中国天眼 | 本周物理学讲座

申报人：姜鹏，中国科学院国度天文台 研究员、 FAST总工程师 [原文来自：www.ii77.com]

时间：9月6日（周五）14:00

单元单子：中科院物理研究所

所在：M236会议室

在贵州与世阻隔的群山深处，有一片叫“大窝凼”的自然凹地，2016年9月25日，“500米口径球面射电千里镜”（FAST）在此落成启用。这口深山里的“超等大锅”，是今朝世界上最大和最活络的单口径射电千里镜。它的扶植、调试和运行履历了如何的故事，凝聚了几多中国人的聪明和勤劳，又杀青了哪些主要的科学功效？本次讲座将为您具体介绍“中国天眼” 的故事。

申报人：Steffen Wirth，Max Planck Institute for Chemical Physics of Solids

时间：9月3日（周二）10:00

单元单子：中科院物理研究所

所在：M楼236会议室

Electronic correlations give rise to a plethora of interesting phenomena and phases. For example, hybridization between 4f and conduction electrons in heavy fermion metals may result in the generation of low-energy scales that can induce quantum criticality and unconventional superconductivity. One of the most important techniques that helped shaping our understanding of nonlocal correlations, both magnetic and superconducting, has been scanning tunneling spectroscopy (STS) with its unique ability to give local, microscopic information that directly relates to the one-particle Green's function. We combine STS with bulk measurements to obtain complementary information on different length scales. We compare hybridization effects as observed by STS, focusing on the model heavy fermion metal YbRh2Si2 and the intermediate-valence Kondo insulator SmB6. Investigation of high-quality single crystals of YbRh2Si2 allows to study the evolution the single-ion Kondo effect and lattice Kondo coherence upon lowering temperature. We also show how Kondo coherence connects with quantum criticality. Low-temperature in-situ cleaving of SmB6 single crystals mostly resulted in reconstructed surfaces, while non-reconstructed patches were found less frequently. The different surface terminations give rise to marked differences in the STS results; in our analysis, however, we concentrate on STS of non-reconstructed areas. These spectra confirm the hybridization picture typically considered for this material. At the surface, the Kondo effect is suppressed to lower temperatures as compared to the bulk material. We show the development of the surface states at low temperatures and how it is locally suppressed around magnetic impurities. The latter is consistent with a topological nature of these surface states.

申报人：Wenwei Liu，University of Surrey

时间：9月3日（周二）10:00

单元单子：中科院理论物理所

所在：ITP South Building 6420

This work presents a hybrid numerical framework for modelling solid-liquid flow with particle adhesion based on a coupled single-relaxation-time lattice Boltzmann method (LBM) and a discrete element method (DEM) for adhesive particles. The LBM is implemented with an improved immersed moving boundary (IMB) method for solving complex fluid-particle interactions using a fast linear approximation of partially intersected volume between a particle and a lattice cell. It is shown that the linear approximation of the solid fraction is very efficient with good accuracy. In order to model particle adhesion, the Johnson-Kendall-Roberts (JKR) adhesive contact mechanics is adopted with a novel implicit solution to obtain the particle-particle normal force in the DEM. The developed hybrid IMB-LBM-DEM numerical framework is verified with several benchmark tests. The results confirm that the hybrid numerical approach is capable of deriving more detailed flow field between dense particles with relatively low grid resolution, as well as effectively capturing the adhesive mechanics between microspheres.

申报人：马承德，South China Normal University & University of Cape Town

时间：9月3日（周二）14:30

单元单子：中科院理论物理所

所在：ITP South Building 6420

In the simple case of bosonic closed string theory with one of the twenty-five spatial directions being a circle of radius $R$, one has to take the field-theory limit $R\gg\sqrt{\alpha^{\prime}}$ to study the low-energy physics. The corresponding massless spectrum, which does not have the winding number and internal momenta excitation, is obtained when the left-moving and right-moving oscillator numbers equal to one, i.e.  $N_L=N_R=1$. This condition characterizes the strong constraint solutions in Double Field Theory. When, in the context of this letter,  one considers instead $N_L\neq N_R$, then the strong constraint solution is not enough to take into account the massless states with nontrivial internal momentum and winding number. This stringy effect in the low-energy limit should be expected from a perturbation in the parameter $\sqrt{\alpha^{\prime}}/R$. We use a linear gauge transformation to construct the quadratic action with a new mass term for the state $(N_L, N_R)=(2, 0), (0, 2)$, and the action is T-dual invariant. By obtaining a gauge transformation for a non-linear extension, a constraint acting on fields can be uniquely defined in triple-products. Finally, we show that the stringy effects only appear in the higher dimensional compact dimensions.

申报人：王育华，兰州大学

时间：9月3日（周二）15:30

单元单子：北京航空航天大学

所在：凝聚态物理研究中心113二楼会议室

申报人：Congyao Zhang，MPA, Garching Germany

时间：9月4日（周三）12:00

单元单子：北京大学

所在：KIAA 1st Meeting Room

Galaxy clusters are the largest virialized structures in our Universe, which contains massive dark matter halos and very hot intracluster medium (ICM). Generally speaking, galaxy clusters evolve in a self-similar way. But there are two main processes that could break the self-similarity of galaxy clusters, i.e. active galactic nucleus (AGN) feedback and cluster mergers. In this talk, I will discuss the effects of these two processes on the formation of galaxy clusters. In the cluster center, X-ray bubbles are inflated by the powerful jets and buoyantly rise outwards. Internal waves excited by these buoyant bubbles may play a very important role in heating the ICM. On the other hand, cluster mergers could re-distribute the matter in galaxy clusters on the Mpc scale. Shock fronts and contact discontinuities are naturally formed during this supersonic process. Our study shows that the merger shock could detach from the gas halo which drives it and travels to the large cluster radius. A "habitable zone" populated by the runaway merger shocks may exist in cluster outskirts, where the shock strength can be maintained or even amplified. 

7基于电子自旋的靠得住而环保的物联网终端

申报人：刘小晰

时间：9月4日（周三）14:00

单元单子：北京航空航天大学

所在：沙河校区国实C座626

申报人：刘玉鑫，北京大学

时间：9月5日（周四）13:30

单元单子：中国科学院大学

所在：雁栖湖校区 教1-208

申报人：Katsuya Hashino，Peking University

时间：9月5日（周四）15:00

单元单子：中科院理论物理所

所在：ITP South Building 6620

The baryon asymmetry of the universe is one of the phenomena beyond the standard model and can be explained by the electroweak baryogenesis. This scenario require the strongly first-order electroweak phase transition in order to realize the asymmetry. The model with extended Higgs sector can easily satisfy the condition. Also, if the phase transition occurs discontinuously, the gravitational wave can be produced by the phase transition and the spectrum of it depend on the form of the potential. Therefore, we may use not only collider experiments but also the gravitational observation experiments to test the new model. In this talk, we discuss wether we can complementarily test the extended Higgs model by the synergy between measurements of gravitational waves and Higgs couplings.

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