學術演講


<專題討論>2019/6/13(四)14:10綜合大樓2樓48218教室演講 : 羅文斌 (中央研究院天文所)

張貼者:2019年6月10日 下午10:57Dabby Lu

講題: Event Horizon Telescope Imaging of the Black Hole Shadow in M87
摘要: The first results from the Event Horizon Telescope revealed the first images of the shadow of a supermassive black hole, observed in the centre of galaxy M87. In this talk, I briefly describe the observations, data processing, imaging, and interpretation of the results. The image of the shadow confines 6.5 billion solar masses, consistent with the stellar dynamical mass, within the photon orbit of the black hole. This provides the strongest evidence to date for the existence of supermassive black holes.

<專題討論>2019/5/16(四)14:10綜合大樓2樓48218教室演講 : 林昆模 助理教授 (中正大學機械工程學系)

張貼者:2019年5月12日 下午8:30Dabby Lu

講題: Characterization of a Single Microdischarge in Atmosperic-Pressure Air Dielectric Barrier Discharges
摘要: Atmospheric-pressure air dielectric barrier discharges (APADBDs) can be considered as one of the important plasma sources due to the developments in applications such as ozone generation, plasma-assisted combustion, active flow control, and pollution control. APADBDs are generated typically in either the coaxial or planar reactors featured as filamentary discharges with many current events observed during each voltage period as generally sustained by an AC power under few kHz frequency. These filaments, named microdischarges (MDs) in the literature, seem to occur randomly in both space and time. A single MD is the basic element producing reactive species (O, N, O3, etc.) and transferring charges across the gap between electrodes. Therefore, it is critical to understand the fundamental properties of a single MD for characterizing the APADBDs. An experimental platform was designed to investigate the statistical behavior of MDs generated in a planar APADBD reactor using a kHz sinusoidal power source. The features of a single MD are measured and compiled statistically. Moreover, numerical simulations provide another alternative to characterize a single MD generated in APADBDs. A semi-empirical 1.5D plasma fluid model is proposed to reveal the underneath chemical mechanisms taking place within the discharge column of a single MD. 

<專題討論>2019/5/2(四)14:10綜合大樓2樓48218教室演講 : 蘇彥勳 副教授 (成大材料科學及工程學系)

張貼者:2019年4月28日 下午9:06Dabby Lu

講題: Surface plasmon resonance of layer-by-layer gold nanoparticles inducing photoelectric current in solar cell and Generating Hydrogen by Water Splitting Photochemistry

摘要: Layer-by-layer gold nanoparticles are used to generate photocurrent in an environmentally-friendly plasmon-sensitized solar cell towing to surface plasmon resonance. The efficiency of the photoelectric conversion of gold nanoparticle layers is increased as the intensity of surface plasmon resonance increases. The way of using light to carry the energy in electronic scattering regime runs the system for the enhancement of solar water splitting efficiency. It was significantly tuned in environmentally sustainable applications for power generation and development of alternative energy.

<專題討論>2019/4/23(二)13:10綜合大樓2樓48218教室演講 : Prof. Alexander Trofimovich Karpachev (Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Moscow, Russia)

張貼者:2019年4月17日 下午7:08Dabby Lu

講題: Investigation of the equatorial ionization anomaly structure
摘要: The second lecture is devoted to the study and modeling of the structure of the equatorial ionosphere. The behavior of the equatorial ionosphere is completely determined by the extremely variable equatorial ionization anomaly (EIA). The characteristics of the EIA depend strongly on local time, longitude, altitude, geomagnetic and solar activity. The longitudinal and altitudinal variations can be investigated only by satellite data. Therefore, it is possible to explore entirety the EIA only by using the COSMIC data (Taiwan) for low solar activity and the Intercosmos-19 satellite (IZMIRAN) for high solar activity. This lecture is based on the results of the analysis of the EIA characteristics from the topside sounding onboard the Intercosmos-19. For the first time, a comprehensive pattern of variations in the EIA structure with local time, altitude, and longitude for all seasons was constructed and studied in detail. The EIA starts at 08 LT with the formation of a winter crest. The formation of EIA is associated with the action of solar ionization and the so-called fountain effect: electromagnetic drift directed upward takes the ionosphere plasma from the heights of the F2-layer maximum to great heights where it spreads along the magnetic field lines under the action of ambipolar diffusion, forming the crests of the anomaly. The summer crest appears only by 10 LT, it is located 3-4° farther from the equator than the winter one. During the equinox, the EIA at the development phase is also asymmetric: the southern crest appears first, but at noon the crests become symmetrical. During the day, EIA reaches its maximum development at 14 LT. The foF2 value over the equator and the degree of EIA development (EAI) at 12–14 LT vary with longitude according to changes in the velocity of the vertical plasma drift W. In the longitudinal variations of W, foF2 and EAI, the 4-th harmonic prevails at this time. In the evening 1.5–2.0 h after sunset (18-19 LT) burst in the vertical plasma drift velocity, the degree of EIA development rises to a maximum. The degree of EIA development after a maximum of 20-22 LT falls, but at midnight the anomaly is still rather well developed. After midnight, the foF2 maxima in the region of the crests of the anomaly, on the contrary, are farther from the equator, but this is apparently due to the action of the neutral wind. At 02 LT, in contrast to the morning hours, only the northern crest of the anomaly is clearly expressed. Thus, with high solar activity in any season, a well-pronounced EIA is observed from 12 to 24 LT. It reaches its maximum development by 20-22 LT. This is very different from the time of low solar activity, when EIA reaches the maximum at ~17 LT and completely decays by 20 LT.

The comparison of the EA structure for the high solar activity according to Intercosmos-19 and for low solar activity according to COSMIC will be discussed.

<專題討論>2019/4/16(二)13:10綜合大樓2樓48218教室演講 : 苗君易 特聘教授 (成功大學航太系)

張貼者:2019年4月11日 上午2:48Dabby Lu

講題: On the blunt body drag
摘要: Aerodynamic flow around a blunt body is featured with flow separation taking place on its contoured surface where the adverse pressure gradient is in effect.  For such a flow, the aerodynamic drag is dominated by the form drag which is basically determined by the extent of the flow separation region.  In the sub-critical range, which can be described in terms of Reynolds number based on the characteristic length of the blunt body and the incoming freestream velocity, the drag coefficient of the blunt body stays almost constant.  This signifies that the phenomenon of flow separation, or the extent of the flow separation region noted, is not sensitive to the Reynolds number.  Nevertheless, as the Reynolds number is further increased and falls in the critical regime, a drastic reduction in drag coefficient is discerned.  This pronounced transition in drag is known as the drag crisis.  Physically, this phenomenon is involved with the development of laminar separation bubbles on the contoured surface, followed by turbulent reattachment, then turbulent separation further downstream.  As a result, the extent of the flow separation region is much reduced. Meanwhile, flow in the critical regime is characterized as highly unsteady, even non-stationary, which is intimately linked with the development of the laminar separation bubbles.

<專題討論>2019/4/11(四)14:10綜合大樓2樓48218教室演講 : 趙怡欽 講座教授 (成大航太系/成大航太中心)

張貼者:2019年4月1日 下午8:02Dabby Lu

講題: Challenges of Space Technology Research: Taiwan's Option for the Next Decade
摘要: In this talk, the first and second stages of the national space programs of the National Space Organization (NSPO) are first reviewed and the current difficulties and ambiguities of policy of the third stage national space program are then discussed. The current situation of space technology research in Taiwan, especially space technology research that supports the development of the national space program is reviewed. The challenges of Taiwan’s space technology researches to support the third stage national space program are evaluated and discussed. The feasible space technology developments for the next decade in Taiwan are also proposed, exclusively, the developments of boosted hybrid rockets as launch vehicles for future Taiwan sounding rocket programs and national space programs, and the development of power mobilized cubeSats for scientific and engineering payloads for orbital and suborbital experiments and exploration are discussed. 

<專題討論>2019/3/28(四)14:10綜合大樓2樓48218教室演講 : 張存續 教授 (清華大學物理系)

張貼者:2019年3月21日 下午8:26Dabby Lu

講題: The Impossible is Possible: Using TM Modes for the Electron Cyclotron Maser
摘要: First, I will provide a brief overview about what we are doing at National Tsing Hua University (NTHU). Our research main themes include: (a) Frequency-tunable, high-power terahertz gyrotrons; (b) Microwave/material interaction and characterization, (c) Microwave physics and applications. Then, I will focus on the physics of the TM-mode gyrotrons. TM (transverse magnetic) modes have long been considered as the unsuitable modes for the electron cyclotron maser (ECM). This study, however, reveals that certain TM modes might be suitable for gyrotrons-ECM based devices. The findings are encouraging and imply that TM modes might be advantageous to the gyrotron backward-wave oscillators. 

2019/3/19(二)14:10綜合大樓1樓48111B教室演講 : Prof. Masayoshi Nagata(Graduate School of Engineering, University of Hyogo, Japan)

張貼者:2019年3月18日 上午12:12Dabby Lu

講題: Coaxial Helicity Injection and Compact Torus Injection Experiments by Magnetized Coaxial Plasma Gun
摘要: The magnetized coaxial plasma gun (MCPG) can produce successfully the compact torus (CT) of a spheromak configuration and spherical torus (ST) plasmas. Thus, the MCPG is well utilized in many fusion plasmas and basic plasma physics experiments. 
Coaxial Helicity Injection (CHI) and Compact Torus Injection (CTI) are attractive fusion applications of the MCPG technology. The CHI is one of non-inductive current drive (plasma start-up and sustainment) methods in spheromak and spherical torus (ST) plasmas. The CHI current drive has been successfully demonstrated in SSPX (LLNL), HIST (U. Hyogo), HIT-II (U. Washington), NSTX (PPPL) and SPECTOR (General Fusion) devices. In the HIST experiments, we have investigated MHD relaxation, dynamo and magnetic reconnection which are related to mechanism of current drive and formation of closed flux surfaces. One of recent topics of CHI on STs is the study of the fast reconnection based on plasmoid instabilities. Intensive internal magnetic field measurements on HIST have recently verified the flux closure due to plasmoid-driven reconnection. 
The CT injection is used for the central fueling, density profile control, plasma rotation, disruption mitigation, ELM-like pulsed heat flux irradiation and so on. The advanced fueling technology should be developed for the fusion reactor. So far, the deep fueling by CT injection has been successfully demonstrated in JFT-2M (JAERI and U. Hyogo), QUEST (Kyusyu U. and U. Hyogo), TdeV (CFFTP, Canada) and STOR-M (U. Saskatchewan, Canada) tokamak devices. We have been conducting pioneering research in this area. The CT is a high density plasma (>1022 m-3) and is magnetically confined by internally self-generated magnetic fields. Thus the CT can be accelerated by the MCPG to a high velocity (> 300 km/s). The penetration mechanism of an injected CT plasmoid into the core plasma is associated with the magnetic reconnection physics.
In this seminar, we will introduce firstly the fundamental of CT/ST magnetic configurations and how to use the MCPG, and then talk about the recent topics of CHI and CTI experiments.

<專題討論>2019/3/21(四)14:10綜合大樓2樓48218教室演講 : 張滋芳 特任助理教授 (日本名古屋大學宇宙地球環境研究所)

張貼者:2019年3月14日 下午10:45Dabby Lu   [ Ann-Chen Jang 已於 2019年3月17日 下午5:52 更新 ]

講題: Development of space weather research-A new approach to the substorm onset issue
摘要: Magnetospheric storms and substorms are the main manifestations of what are nowadays known as the “space weather” which has a practical impact on modern technology systems and our activities on Earth. Various spacecraft have been investigating the space environment around the Earth to explore the effects of substorms and storms-the THEMIS (Time History of Events and Macroscale Interactions during Substorms) and the ERG (Exploration of energization and Radiation in Geospace) missions for example. In particular, substorms are disturbances in the Earth's magnetosphere that causes energy to be released from the "tail" of the magnetosphere to the high-latitude ionosphere. The enhancement in electron fluxes during substorms can be a few orders greater than the pre-onset conditions. Since a fierce debate on substorm onset triggering has persisted for a long time, it highlights a pressing need for a better understanding of substorms in developing the space weather research. Two categories of substorm onset initiation models have been proposed-the Near-Earth Neutral Line model and the Current Disruption model. After the launch of the THEMIS quintet, some notable results even reported a new scenario – plasma intrusion to the inner plasma sheet. Thus starting a further exploration of substorms is inevitable. We will put forth a proposal to settle one of the center issues in dispute, the definition of substorm onset, by investigating the auroral streamers.

2019/3/15(五)14:00綜合大樓1樓48111B教室演講 : 畢可為 博士(捷克查理大學數學與物理學院)

張貼者:2019年3月11日 下午7:04Dabby Lu

講題:Long-lasting radial IMF events and their influence of dayside magnetosphere
摘要:Long-lasting radial interplanetary magnetic field (IMF) events are one of the special solar wind conditions. These events are usually accompanied with low density, weak magnetic field strength, low temperature, and low fluctuations of each solar wind parameters; however, the unique IMF orientation can cause numerous interesting features in the dayside magnetosphere. When the radial magnetic field transits through the bow shock, the magnetic field will be enhanced in all components. After that, Bx will divert to the Y and Z components and form an asymmetric Bz polarization in the Northern and Southern Hemispheres near the magnetopause. This asymmetry will lead the dayside reconnections occur at different locations and create a complex structure of magnetopause and its boundary sublayers. These sublayers of (1) the inner part of the low-latitude boundary layer (LLBL) on closed magnetic field lines; (2) the outer LLBL on open field lines; (3) the inner part of the magnetosheath boundary layer (MSBL) formed by dayside reconnection in the Southern Hemisphere; and (4) the outer MSBL resulting from lobe reconnection in the Northern Hemisphere are identified by observation.

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