學術演講


<專題討論>2018/5/10(四)14:10綜合大樓2樓48218教室演講 : 龔慧貞 副教授(成功大學地科系)

張貼者:2018年5月6日 下午8:20Dabby Lu

講題:地球內部構造與地球磁場 Earth’s interior structure and geodynamo
摘要:眾所皆知地球因本身磁場所形成的磁層,保護地球生物免於太陽的高能帶電粒子襲擊。從地質資料顯示地球磁場每隔一段時間都會反轉的,也觀察到南北磁極已不同的速度「漫遊」。 近170年來觀測結果顯示,地球磁場強度已減弱~15%。在這報告中,將以地球內部構造來談地球磁場機制,即「地球發電機理論」。

<專題討論>2018/5/3(四)14:10綜合大樓2樓48218教室演講 : 江偉宏 副教授(臺灣科技大學化學工程學系)

張貼者:2018年4月29日 下午7:13Dabby Lu

講題:Nanostructure Engineering using Microplasmas: Synthesis and Applications
摘要:Microplasmas are a special class of electrical discharges formed in geometries where at least one dimension is less than 1 mm. As a result of their unique scaling, microplasmas operate stably at atmospheric pressure and contain large concentrations of energetic electrons (1-10 eV). These properties are attractive for a range of nanomaterials synthesis and nanostructure engineering such as metal nanostructures and carbon-based materials [1-3]. 
In this presentation, I will discuss these topics in detail, highlighting the advantages of microplasma-based systems for the synthesis of well-defined nanomaterials. These experiments will aid in the rational design and fabrication of nanomaterials and may also have significant impact in emerging applications. Recently, we found that the energetic species including radicals, ions and electrons generated in the microplasmas were capable of initiating electrochemical-assisted reactions for the nucleation and growth of graphene quantum dots [4]. Moreover we develop a simple synthesis of metal nanoparticles/graphene composites using a unique atmospheric-pressure microplasma-assisted electrochemical method. Systematic micro Raman study indicates that the as-produced AgNP/graphene composites show exceptional SERS performance [5].

Reference: 
[1] W-H. Chiang and R. M. Sankaran, Adv. Mater. 20, 4857 (2008) 
[2] W-H. Chiang and R. M. Sankaran, Nature Mater. 8, 882 (2009)
[3] W-H. Chiang et al., J. Mater. Chem. A 4, 7624 (2016)
[4] W-H. Chiang et al., MRS Fall Meeting (2016)
[5] W-H. Chiang et al., MRS Fall Meeting (2016).

<專題討論>2018/4/26(四)14:10綜合大樓2樓48218教室演講 : 林俊良 博士(國家太空中心主任)

張貼者:2018年4月23日 上午2:32Dabby Lu

講題:我國太空計畫發展-過去及未來
摘要:本簡報將簡介我國太空長程發展計畫第一期(1991-2004)和第二期(2004-2018)的源起及成果。另介紹即將開展的第三期長程計畫(2019-2028),其目標和執行內容。希望藉這個簡報讓大家知悉十年後台灣太空科技發展對國家、產業和人才培育的影響。

<專題討論>2018/3/29(四)14:10綜合大樓2樓48218教室演講 : 方惠寬 博士(成功大學電漿所)

張貼者:2018年3月25日 下午8:09Dabby Lu

講題: In-situ plasma measurements in the Earth’s ionosphere
摘要:Measurements of plasma are fundamental for space physics, especially for space weather. Recently, giant progress of the CubeSat technologies greatly lowers the barrier to insert a satellite into a lower earth orbit for space exploration. Satellite constellation missions consisting of tens of CubeSats is planned and launched. These missions provide multi-point measurements and make it possible to separate spatial and temporal effects regarding couplings between ionosphere, atmosphere and even lithosphere. And the altitude of these missions are rarely explored by conventional satellites because of large air drag and short mission lifetime. In addition to Cubesat missions, simultaneous multi-instrument measurements onboard sounding rockets aiming for the plasma characteristic investigations in the ionosphere D layers, which is the least-explored region in the ionosphere, is planned. In this presentation, the plasma diagnostic techniques onboard CubeSats and sounding rockets will be introduced. The design concepts and preliminary results of the solar EUV probe onboard the Phoenix CubeSat in QB50 mission and the “Mesosphere and Ionosphere Plasma Exploration complex (MIPEX)” instrument onboard the NCKU sounding rocket, which is planned to be launched in 2020, will be shown. These experiments can provide unique high-quality data of the plasma environment to explore the ion distribution and the electrodynamic processes in the Ionosphere.

<專題討論>2018/3/27(二)13:10綜合大樓2樓48218教室演講 : 周紹暐 博士(台灣積體電路製造股份有限公司)

張貼者:2018年3月20日 下午11:10Dabby Lu

講題:Laser and Plasma wakefield acceleration
摘要:Energetic particle beams are important tool in many application, from basic science to healthcare, also a crucial element to produce high quality X-ray radiation. Conventional accelerators are relative large, from  10 m to   several km, due to  material-breakdown-limited  acceleration gradient and energy loss via synchrotron  radiation.    Size and cost of maintenance of conventional accelerator  limit  the extent of application for daily life. Wakefield accelerator driven by either high energy or high energy particle is a promising way to build a table-top accelerator. For example, GeV-scale electron bunch driven by laser pulses has been demonstrated by  using  cm long gas targets . As a contrast, it needs almost 100 m of conventional accelerator to reach this energy. In this talk, I will first introduce fundamental physic  of wakefield accelerator and related experiment. In the end of discussion, a physical phenomenon called "collective deceleration"  associated to the  unique properties of laser-driven electron bunches will be studied by experiment and PIC simulation. 

<專題討論>2018/3/22(四)14:10綜合大樓2樓48218教室演講 : 李昆翰 博士(中央研究院地球科學研究所)

張貼者:2018年3月18日 下午9:37Dabby Lu

講題:Generation of hydrogen, helium and oxygen EMIC waves by fast magnetosonic shocks in the magnetosphere and in the solar wind
摘要:Electromagnetic ion cyclotron (EMIC) waves are often observed in the magnetosphere and in the solar wind. Here we propose a new generation mechanism for hydrogen, helium and oxygen EMIC waves associated with fast magnetosonic shocks in the magnetosphere and in the solar wind. In the magnetosphere, these shocks can be associated with either dynamic pressure enhancement or shocks in the solar wind and can lead to the formation of a “bunch” distribution of O+ ions in the perpendicular velocity phase space. The O+ bunch distribution can excite strong He+ EMIC waves and weak O+ and H+ waves. The dominant He+ EMIC waves are strong in quasi-perpendicular propagation and show harmonics in frequency spectrum of Fourier analysis. Further analysis by using Hilbert-Huang transform shows that these signals are similar to Duffing oscillations and exhibit frequency modulation in the instantaneous frequency spectrum. The proposed mechanism can explain the generation and some observed properties of He+ and O+ EMIC waves in the magnetosphere.
Strong fast magnetosonic shocks are often observed in the solar wind. In the shock downstream, the hydrogen and helium ions are strongly heated to achieve high ion beta and high temperature anisotropy. These conditions can lead to efficient generation of EMIC waves and mirror mode waves in the downstream, which are often identified in satellite observations in the solar wind. We find that the EMIC waves are generated both in the parallel and quasi-perpendicular directions. The parallel EMIC waves have been widely studied theoretically and observationally, while the excitation of quasi-perpendicular EMIC waves is usually overlooked. We also find coalescence of mirror waves as they drift with the plasma to further downstream.

<專題討論>2018/3/20(二)13:10綜合大樓2樓48218教室演講 : 丘政倫 博士(清華大學天文研究所)

張貼者:2018年3月14日 下午7:03Dabby Lu

講題:Exploring the extreme Universe with a new generation of telescopes
摘要:Experimental high energy astrophysics probes the most energetic and exotic objects and locations in our Universe by using a variety of X-ray, gamma-ray, and cosmic-ray instruments. These high-energy sources span many orders of magnitude in size and energetics, from cosmic gamma-ray bursts and supermassive black holes to supernovae and compact objects in our Galaxy. The underlying physical processes in these sources are often similar and usually inaccessible in a laboratory. But at the same time, many of the observations have important implications for fundamental physics. Therefore, a key to these studies is to develop and utilize novel instruments with excellent sensitivity and resolution. A current generation, NuSTAR, and a next generation telescope, COSI, which are and will be revolutionizing the observation of high-energy astrophysics phenomena, will be introduced here.   
(1) The Compton Spectrometer and Imager (COSI) is a balloon-borne soft gamma-ray (0.2-5 MeV) telescope designed to study astrophysical sources of nuclear-line emission and gamma-ray polarization. COSI employs a compact Compton telescope design, imaging gamma-rays through their scattering history in novel 3D-tracking Germanium detectors. As a balloon payload, this telescope performs sensitive observations of positron annihilation, nucleosynthesis, compact objects, GRBs, and AGN. (2) The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing high energy X-ray satellite in orbit (launched in June 2012), providing more than two orders of magnitude improvement in sensitivity compared to previous high energy missions. NuSTAR's primary science goals include conducting a survey of black holes, mapping young supernovae explosions, studying cosmic accelerators, and identifying high energy sources in our Galaxy.     
In this talk, I will present our current achievements with both instruments and future research plans based on these efforts.

<專題討論>2018/3/15(四)14:10綜合大樓2樓48218教室演講 : 藍永強 教授(成功大學光電系)

張貼者:2018年3月11日 下午6:10Dabby Lu

講題:Generation of light beams by electron beam excited surface plasmons
摘要:When the electron beam moves along or normally onto the plasmonic nanostructures (PNs), it can excite the surface plasmons (SPs) on PNs along with the transition radiation (TR). In the former case, the SPs have specific frequencies determined by the intersection of dispersion curves of electron beam and SPs. In the latter case, conversely, the SPs have a wide frequency band [1]. Furthermore, SPs can be transferred into light emission (SP emission) by the surface structures of PNs. In this work, we will consider three types of light beam generation by electron beam excited SPs. First, we will investigate SP-manipulated and localized SP (LSP)-manipulated Smith-Purcell radiation (SPR) on metallic periodic gratings and disk arrays, respectively [2]. The SPR can be enhanced by exciting SPs and LSPs if their frequencies are within the emission bands of SPRs. Second, the generation of convergent beam by electron-excited SPs is examined. Here the mechanism of SPR on metallic chirped gratings is proposed to generate the convergent light beam. Finally, the SP-manipulated TR and SP emission from the electron beam normally incident PNs with designed slit structures are studied [3]. This work offers potential applications in the fields of optical imaging, holography, cryptography and tunable visible light source, etc.

[1] S. Gong, M. Hu, R. Zhong, X. Chen, P. Zhang, T. Zhao and S. Liu, “Electron beam excitation of surface plasmon polaritons,” Opt. Express 22, 19252-19261 (2014).

[2] Y. C. Lai, T. C. Kuang, B. H. Cheng, Y. C. Lan and D. P. Tsai, “Generation of convergent light beams by using surface plasmon locked Smith-Purcell radiation,” Scientific Reports 7, 11096 (2017).

[3] T. Coenen, B. J. M. Brenny, E. J. Vesseur and A. Polman, “Cathodoluminescence microscopy: Optical imaging and spectroscopy with deep-subwavelength resolution,” MRS Bulletin 40(4), 359-365 (2015).

<專題討論>2018/3/13(二)13:10綜合大樓2樓48218教室演講 : 蔡勖升 博士(清華大學核子工程與科學研究所)

張貼者:2018年3月7日 下午6:14Dabby Lu

講題:Facile Synthesis of Single-Elemental Two-Dimensional Materials via Plasma and/or Implantation Assisted Process
摘要:Synthesis and growth of two-dimensional (2D) materials have been extensively investigated in order to achieve high quality, scalability, and reduce the complexity of process in recent years. Mechanical exfoliation is a quite unpractical method owing to the scale limitation while chemical vapor deposition (CVD) on metal substrates must be combined with the manual transfer step, which seriously damages the materials for device applications. Ultrahigh vacuum (UHV) growth cannot accomplish the high production and reduce the cost of process. The conditions of some particular syntheses are quite difficult to be performed, thus they do not have potential for commercialization. This study announces that a facile synthesis method, so called plasma and/or implantation assisted process, has been successfully utilized to synthesize several single-elemental 2D materials. The process divided into plasma and/or implantation and thermal treatment almost solves all of the issues mentioned above. In addition to demonstrate the feasibility of plasma and/or implantation assisted process for synthesis of the single-elemental 2D materials, superior properties of these 2D materials were measured for seeking real applications.

<專題討論>2018/3/8(四)14:10綜合大樓2樓48218教室演講 : Prof. O. A. Troshichev(Arctic and Antarctic Research Institute, St/Petersburg, Russia)

張貼者:2018年3月4日 下午6:57Dabby Lu   [ 已更新 2018年3月4日 下午7:07 ]

講題:The polar cap magnetic activity (PC) index as an indicator of the solar wind energy incoming into the magnetosphere.
摘要:The polar cap (PC) magnetic activity index was approved by the International Association of Geomagnetism and Aeronomy (IAGA) in 2013 as a new international index assigned to monitor the energy that enters into the magnetosphere under the solar wind-magnetosphere coupling. The following experimental data form the basis for this statement: (1) the PC index strongly follows the time evolution of interplanetary electric field (EKL) reduced to the magnetopause, (2) delay time ΔT in response of PC index to EKL variations is controlled by the EKL field growth rate (dEKL/dt), (3) magnetic storms and substorms are always preceded and accompanied by a growth in РС index, (4) substorms and magnetic storms start to develop as soon as the PC index exceeds the threshold level of 1.5 mV/m, (5) the substorm sudden onsets are commonly associated with a sharp increase in the PC (and EKL) growth rate, (6) the solar wind drivers (ICMEs or SIRs) determine the type of magnetic storm, such as “classic” storm, related to ICME impact, with well-defined PC maximum and clearly expressed one maximum of depression, “pulsed” storm, related to SIR impact, with periodically repeating oscillations in PC and geomagnetic field depression, and “combined storms”, which are regarded as effect of simultaneous ICME and SIR action, (7) maximal depression of magnetic field responds to maximal PC value with a delay of ~1 hour, the storm intensity (Dstmin) being linearly depending on PCmax value. In ~10% of the substorm events the correlation between EKL and PC was practically absent, in spite of the PC index rise before the substorm onset, which means that solar wind, measured in the Lagrange point, passes by the magnetosphere in these cases. Therefore the РС index can be used also to verify whether or not the solar wind measured in Lagrange point L1 is in contact with the magnetosphere.

All these statistically justified relationships testify that the PC index is an indicator of the solar wind energy incoming into the magnetosphere. In this context, the PC index can be successfully used as a new reliable ground-based technique for exploration of short-term changes in space weather and magnetosphere state.

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