智能材料及其空间应用技术探索 | 本周物理学讲座

1智能材料及其空间应用技术探索

报告人：王鹏飞，中国空间技术研究院钱学森空间技术实验室

时间：3月5日（周二）14:00

单位：中科院物理研究所

地点：D楼210

智能材料可利用外部电、光、热、磁等刺激方式控制其产生显著的变形响应实现仿生驱动，此外，部分柔性智能材料亦可将机械能转变为电能实现柔性传感，即具有驱动-传感一体化特性。这类智能材料可用于设计和制造多种驱动结构或换能器件，可在服役过程中，根据系统需要，接收数字指令，经量化调控，实现快速、精确、可控的驱动与传感，具有智能化、轻量化、多功能等多种优势，在航天航空领域具有重要应用前景，例如：基于智能驱动材料的空间大型展开结构、空间仿生抓捕手、高收纳比三维折叠机器人、宽频减振器等.

2Observational Signatures from Modulated Preheating

报告人：黄志琦，中山大学物理与天文学院

时间：3月5日（周二）10:00

单位：中科院理论物理所

地点：Room 6420, ITP NEW BUILDING

After early-universe inflation, the inflaton decays into other fields via a reheating process. If the decay begins with a preheating stage, where the fluctuations of coupled fields are exponentially excited by parametric resonance, the energy transfer can be much more efficient and possibly producing observable signatures to reveal exciting new physics beyond the standard model. In 2009 my collaborators and I proposed that, if the equation of the state of the multi-field system is modulated by the background field values, large-scale metric fluctuations can indeed be generated from the modulated preheating process. Continuing on this topic, I will discuss my recent work on the impact of modulated preheating on the formation of high-redshift mini-haloes, which is a key ingredient for the direct-collapse scenario of supermassive black holes.

3航天群智能技术研究

报告人：周庆瑞，中国空间技术研究院钱学森空间技术实验室

时间：3月5日（周二）14:00

单位：中科院物理研究所

地点：D楼210

群智能技术作为人工智能技术的一个重要分支，在无人系统领域有广泛的应用前景并开展了大量研究。随着电子和信息技术发展，卫星存储、计算和通信能力得到大幅提升；研制和发射成本逐步下降，卫星在轨数量迅速增加。在此背景下，航天器已具备涌现群体智能的技术基础。本报告探讨了群体智能技术在航天领域的潜在应用，提出基于人工智能技术尤其是群体智能技术的航天系统新应用模式，并分析了其中的挑战性技术和理论问题。

4The HKU Laboratory for Space Research: Reaching for the Moon, Mars and the Stars

报告人：Quentin Parker，University of Hong Kong

时间：3月6日（周三）12:00

单位：北京大学

地点：1st Meeting Room, KIAA

In this seminar I will concentrate on describing The Laboratory for Space Research (LSR). The LSR  is a multi-disciplinary research entity mainly based in the HKU Faculty of science but also with members from the Faculty of Engineering. We focus on space-based earth remote sensing; atmospheric science, near Earth environment, planetary and associated geological sciences, high-energy astrophysics from satellite-based telescopes and late stage stellar evolution, where our group is ranked 8th  globally (SciVal). We are currently adding important, additional research capacity to these LSR activities as we emerges as a real interdisciplinary force at HKU. We have strong international and mainland collaborations established off the back of strong research outputs, with co- leveraged funding with key international partners including jointly funded postdoctoral fellows with Peking/KAVLI, Nanjing and Zhejiang universities in the mainland.We have now established a sister laboratory at HKU-ZIRI that will concentrate on space-based satellite missions in partnership with the Zhejiang University microsatellite research group. Stronger involvement with computing science, big-data (via the FoS big-data research cluster) and the Faculty of Engineering is promised. This is germane given our planned satellite ground station and mission plans for the LSR both at HKU and in HKU-ZIRI.Our strategic directions are clear. Success will depend on grasping opportunities in HK, Mainland China and elsewhere and having sufficient research capacity to make the most of these opportunities when they arise. So we are aggressively growing capacity. We are actively seeking (and finding) key, high-level partners to facilitate LSR capacity building, including via MoU’s, shared funding and new agreements with elite Mainland universities including Nanjing, Peking and Zhejiang and with our partner companies such as BISME. The greatest discoveries will likely be at the boundaries of disciplines and carried out by our highly capable LSR faculty, PDFs, RAPs and RPG students. This is a model that will be replicated at HKU-ZIRI LSR.

5 Amplitudes Meet Cosmology

报告人：Siyi Zhou，香港科技大学

时间：3月6日（周三）14:00

单位：中国科学院理论物理所

地点：Room 322, ITP MAIN BUILDING

In the flat space time, there are many things we can say about scattering amplitudes. It is tempting to think about is there similar relations also in cosmology. The talk consists of three parts. The first part is about translating the recursion relation in the flat spacetime to recursion relations among inflationary correlation functions or wave function of the universe. The second part is about the four-point KLT relations in inflation. The third part is about my ongoing work about positivity bounds in inflation. I will also talk about my thoughts in general about applying scattering amplitudes technique in cosmology。

6Stationary phase approximation to path integral based on time-dependent mean field

报告人：倪放，University of Tsukuba

时间：3月6日（周三）15:00

单位：中科院理论物理所

地点：Room 6420, ITP NEW BUILDING

We aim to describe the low-lying excited states in nuclei based on the time-dependent mean field theory. Quantum fluctuation is large in low-lying excitation energy region, such as shape coexistence. Some theoretical frameworks, such as generator coordinate method (GCM) and Bohr collective model, are often applied to describe the large amplitude collective motions. Here, we introduce a method which is called stationary phase approximation (SPA) to the path integral. Using SPA, we can obtain microscopic wave functions with good quantum number without any artificial assumption. In this presentation, I will explain the theoretical framework of SPA, and discuss a new method about the application of SPA in non-integrable systems. Also I will show some results about the advantage of SPA to describe the pairing collective motions.

7A Review on Loop Quantum Gravity

报告人：马永革，北京师范大学物理系

时间：3月6日（周三）15:30

单位：中科院理论物理所

地点：Room 6620, ITP NEW BUILDING

How to unify general relativity with quantum mechanics is still a central challenge in theoretical physics. As a nonperturbative and background independent theory of quantum gravity, loop quantum gravity has caused increasing attention in recent years. In this talk, the basic structure of canonical loop quantum gravity and some of its recent advances will be reviewed.

82D Materials Photonics and Optoelectronic Device Applications

报告人：Qiaoliang Bao，Monash University

时间：3月7日（周四）09:30

单位：中科院物理研究所

地点：M楼236会议室

Our research interests are mainly focused on the light-matter interactions in 2D materials in the forms of nonlinear light absorption, light modulation (amplitude, phase and polarisation), photo-electrical conversion, wave-guiding and polaritonic behaviours. This talk will give an overview of photonic and optoelectronic device applications based on these optical phenomena in 2D materials. Firstly, to overcome the limit light absorption in graphene and obtain large nonlinear optical modulation depth, we developed a serial of new saturable absorbers based on graphene heterostructures and other 2D materials, including graphene/Bi2Te3, black phosphorus and self-doped plasmonic 2D Cu3-xP nanosheets as well as 2D halide perovskite. Depending on their nonlinear optical properties, either high energy Q-switched laser or ultrafast mode-locked pulse generation were demonstrated. Secondly, in order to fabricate improved graphene photodetectors working in different spectral ranges, we integrated graphene with other 2D materials with variant electronic structures, for example, graphene/perovskite for visible light detection, graphene/MoTe2 and graphene/Cu3-xP for near infrared light detection, and graphene-Bi2Te3 for broadband infrared light detection. We show how photo-gating effect plays a significant role to amplify the photocurrent in the photodetectors as well solar cell device. By fine tuning or aligning the electronic structure, we are able to engineer the depletion width in 2D material heterostructures, such as graphene/WS2, MoS2/WS2 and WSe2/WS2heterojunction, monolayer-bilayer WSe2 heterojunction and 2D perovskite p-n junction, so as to achieve higher photo-responsivity and large photo-active area. Lastly, the THz light modulation associated with plasmonic excitation in graphene/Bi2Te3, topological insulator Bi2Te3, graphene nanoribbon and 3D graphene was investigated using either spectroscopic or real space imaging techniques. We show how the plasmonic coupling happens in two Dirac materials, how high-order plasmonic modes are observed in 3D graphene structure, how multiple plasmonic polariton modes at sub-wavelength are achieved in graphene nanoribbon and how edge chirality controls the polaritonic shift. In particular, we update our recent progress on the observation of anisotropic and ultra-low-loss polariton propagation along the surface of natural vdW material α-MoO3. We visualized and verified phonon polaritons with elliptic and hyperbolic in-plane dispersion, which have been theoretically predicted but never experimentally observed in natural materials before. We measured polariton amplitude lifetimes of 8 picoseconds, which is more than ten times larger than that of graphene plasmon polaritons at room temperature. In-plane anisotropic and ultra-low-loss polaritons in 2D materials could enable directional and strong light–matter interactions, nanoscale directional energy transfer and integrated flat optics in applications ranging from bio-sensing to quantum nanophotonics. In summary, the advances of 2D materials research may pave the way for the next generation photonic and optoelectronic device applications.

9The kinematics of globular clusters and planetary nebula in the core of the Fornax Cluster: intracluster light and the search of stellar streams

报告人：Nicola R. Napolitano，Sun Yat-sen University

时间：3月7日（周四）16:00

单位：北京大学

地点：KIAA-PKU Auditoriu

I will present recent results of the kinematics of planetary nebulae (PNe) and globular clusters (GCs) out to about 200 kpc from the center of the Fornax cluster. We have collected more than 2000 new radial velocities using VIMOS and FORS2 spectrographs at the VLT which, combined with previous literature, make a unique data sample covering a volume of a galaxy cluster up to about 1/4 of its viral radius.I discuss the signature of an intracluster stellar population both on the velocity field of PNe and GCs and show some preliminary results on the identification of stellar streams in the phase space of the two combined populations. 

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