【物理人·讲座】一周物理讲座(3.27-4.2)

 

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一周物理讲座(3.27-4.2)
北京大学
报告题目:

Ultra-high energy cosmic rays from low-luminosity GRBs

报告人:

Peter Meszaros

时间:3月29日 (星期四) 16:00-17:00

地点:KIAA-PKU Auditorium

报告摘要:

Cosmic rays in the energy range of 1E17 to 3E20 eV havebeen measured by the Auger and TA arrays, whose compositionappear to include a significant fraction of heavy elements.An explanation for the energy input rate, the spectrum andthe composition is a matter of current debate. Here, aftera review of the cosmic ray observations, I discuss a modelfor the production of this radiation in low-luminosity GRBs,followed by their propagation through intergalactic spacebefore reaching Earth.
报告题目:

A Tale of Two Bursts

报告人:

Dr Zhang Binbin

时间:3月30日 (星期五) 12:00-13:00

地点: KIAA, 1st meeting room

报告摘要:

In the talk I will review our recent work on the most remarkable Gamma-Ray Bursts (GRBs) in the past two years: GRB 160625B and GRB 170817A. GRB 160625B was an extraordinarily bright burst with three isolated episodes separated by long quiescent intervals. By conducting detailed time-resolved spectral analysis in each episode, we found that the spectral properties of the first two sub-bursts are distinctly different, allowing us to for the first time observe a clear transition from thermal to non-thermal radiation between well-separated emission episodes within one single GRB. Such a transition is a strong indication of the change of jet composition from a fireball to a Poynting-flux-dominated jet. GRB 170817A was the first confirmed short GRB associated with gravitational event GW170817. By performing detailed analysis on the prompt emission data, we show that the fluence and spectral peak energy of this sGRB fall into the lower portion of the distributions of known sGRBs. Its peak isotropic luminosity is abnormally low. The estimated event rate density above this luminosity is at least ~190 Gpc^-3yr^-1, which is close to but still below the double neutron star merger event rate density. The physical implications of the data including the jet structure will also be discussed.
报告题目:

Plastic Deformation in a Quantum Solid:Dislocation Avalanches and Creep in Helium

报告人:

Zhigang Cheng

时间:3月28日 (星期三) 16:00

地点:物理楼 西563

报告摘要:

Conventional solids defonn   elastically for small stresses - reversibly with a linear, rate-independent   relationship between stress and strain. Beyond tlie yield point, plastic   defomiaiion begins - irreversible, nonlinear and time dependeni. Plasticity   involves tlie motion and multiplication of dislocations and in Uiis talk I   will report our recent observations of such “metalhirgical” phenomena in a   solid whose defect behavior is dominated by quantum effects - hep 4He.   whose zero-point motion is magnificently larger than conventional solids.   Below 0.4 K; there is a strain threshold for elastic defonnation   above which sudden stress drops and acoustic emissions (AE) appear - the   signatures of dislocation avalanches. Tlie dimensions of these slip events   range from mm to (im. Tlie smallest slips are consisieiit viili ballistic   motions of dislocations. At Mglier temperatures ihe avalanches are replaced   by continuous creep involving dislocations and we observe steady flow at   stresses as low as 400 Pa.
报告题目:

类脑计算及其核心器件

报告人:

施路平 教授

时间:3月29日 (星期四) 15:00-16:30

地点:物理楼 西202

报告摘要:

类脑计算系统是借鉴人脑信息处理方式,打破“冯•诺依曼”架构束缚,适于实时处理非结构化信息、具有学习能力的超低功耗新型计算系统。当前欧盟、美国等均斥巨资长期支持此研究,但是这项研究目前均处于起步阶段,尚未形成公认技术方案。此报告将从为什么(why)?做什么(what)?和怎样做(how)?三方面来分析类脑计算及其核心器件研究,分析发展类脑计算的挑战和前景。
清华大学
报告题目:

GW170817/GRB170817A from a binary neutron star merger

报告人: Prof. Zigao Dai

(Nanjing Univ.)

地点:蒙民伟科技南楼 S727

时间:3月29日(星期四)14:00

报告摘要:

2017年8月17日,LIGO/Virgo引力波天文台发现了双中子星并合产生的引力波事件GW170817。在该事件之后的1.7秒,Fermi卫星探测到了来自这个源的持续时标约为2秒的伽玛射线暴GRB170817A。随后,大量的地面和空间望远镜观测到了GW170817在X射线、紫外、光学、近红外、射电波段的电磁对应体。这些观测发现不仅开创了引力波天文学的新纪元,而且证明至少一部分短伽玛射线暴起源于双中子星的并合。在本报告中,南京大学戴子高教授将全面介绍双中子星并合产生的GW170817/GRB170817A以及相应的千新星和长达100多天的多波段余辉的观测和理论,讨论在宇宙学和基本物理检验方面的可能应用,并分析亟待解决的关键科学问题。
报告题目:

Neutron Stars, viewed through Photons, Gravitational Waves and Neutrinos

报告人:Prof. Peter Meszaros

(Pennsylvania State Univ.)

时间:3月30日(星期五) 19:00

地点:清华大学大礼堂

报告摘要:

Neutron stars are one of the earliest and best studied high energy sources.They were first discovered as pulsars, a story which is one of the highlights of 20th century astrophysics, and they are linked to a number of other phenomena, including supernovae, short GRBs and Kilonovae. They  are among the most promising sources for producing multiple non-electromagnetic signals, including gravitational waves, cosmic rays and  very high energy neutrinos. Recently, a sub-class of short gamma-ray bursts arising from neutron star megers was, for the first time, observed both via gravitational waves, as well as electromagnetically, establishing multi-messenger astrophysics as a new approach to understand cosmic high energy objects. I will discuss some of the latest observational and theoretical developments in  the Neutron Star, GRB, Kilonova  and multi-messenger  fields.


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