A unique QPO often occurs at 6 Hz in Z type Neutron star sources radiating close to the Eddington limit. From radio observations, it is known that a jet is present during the 6 Hz QPO and sometimes ultra relativistic flow is also associated. In general these sources the QPO varies from ~20-50 Hz during which the inner region of accretion disk is truncated and a Compton cloud/corona is present inside the truncation radius. As the truncated front approaches close to the last stable orbit (50 Hz), suddenly a unique 6 Hz QPO appears. I will discuss a model which probably explains the sudden emergence of the 6 Hz QPO along with 50 Hz QPO. In this model, I study the disk oscillation during which the inner region of the disk dominated by radiation pressure assuming that the oscillation is driven by the gravitational force. I will also use this model explain the sudden occurrence of type-B/A QPOs in black hole X-ray binaries which are similar to the 6 Hz QPO in neutron star source.
Most globular clusters in the Milky Way show signs of multiple stellar subpopulations. These may be due to distinct star formation events, as suggested by differing chemical abundance patterns. Photometric coordinates designed to be sensitive to light-element abundances -the so-called chromosome-map plane- were recently introduced to distinguish subpopulations without resorting to spectroscopy. However, drawing boundaries between subpopulations on the chromosome-map plane is somewhat subjective, as it ultimately depends on the judgment of a human expert. I will discuss unsupervised machine learning strategies to make this process automatic so that it can become reproducible and be generalised to a large set of GC observations. In particular I will show that the AGglomerative NESting (AGNES) algorithm with Ward's linkage produces results similar to expert expectations on NGC 2808.
양자광학에서 가장 기초적이고 중요한 실험중의 하나는 Hanbury-Brown—Twiss (HBT) 실험이다. Robert Hanbury-Brown은 2차 세계대전 중 레이더의 개발에 깊이 관여했었고 2차대전 후에는 Richard Twiss와 함께 전파망원경 분야에 전념하였다. Hanbury-Brown과 Twiss는 Intensity interferometer를 최초로 제안하였는데, 그 가능성을 보여주는 (HBT 실험이라고 불리는) photon bunching 실험을 1956년 발표하였다. HBT 실험은 그 자체로는 빛의 양자적 특성을 보여주지는 않지만, 현대 양자광학에서는 빛의 양자성을 구별하는데 필수적인 테스트로 사용된다. 이번 발표에서는 Hanbury-Brown과 Twiss의 전파망원경 연구가 실험실 양자광학의 태생으로 이어진 과정을 소개하고 현대 양자광학에서 중요한 몇 가지 개념과 실험들을 소개한다. 최근 실험실 양자광학은 장거리 양자통신의 중요성과 연결되면서 장거리 양자광학 실험으로 확장되고 있다. 지난 몇 년간 보고된 장거리 양자통신 실험 또한 간단히 소개한다.
온라인 게임, 특히 '대규모 다중 사용자 온라인 역할 수행 게임 (Massively Multi-Online Role Playing Game, MMORPG)'에서 사람들은 채집이나 수렵 등의 생산, 퀘스트 수행 및 레벨업을 통한 성장, 거래를 통한 경제 활동, 파티/혈맹/친구 관계와 같은 협업과 전투를 통한 경쟁 등의 다양한 사회 활동을 수행한다. 이렇게 사람들이 가상 세계에서 벌이는 다양한 활동 및 사회 관계 정보는 로그와 DB 형태로 기록된다. 따라서 게임 데이터는 기존의 사회 과학에서는 접하기 거의 불가능한 수준의 폭넓고 세밀한 정보를 갖고 있는, 세상에서 가장 흥미로운 데이터 중 하나이다. 한편, 최근 기계 학습 분야의 큰 발전으로 인해 다양한 분야에서 이를 실전에 적용하려는 시도가 이뤄지고 있다. 그러나 괄목할 만한 연구 성과에 비해 아직까지 실전에서의 성공 사례는 많지 않다. 여러 가지 원인이 있겠으나 기계 학습 모델링 측면에서 보자면 학습 데이터 확보의 어려움, 높은 특성 공학 비용, 데이터가 가진 통계적 특성의 변화에 의한 빠른 모델 노후화 등의 문제를 꼽을 수 있다. 온라인 게임 분야 역시 이 세 가지 문제가 기계 학습 모델을 실전에 적용하는데 큰 걸림돌이 되고 있다. 엔씨소프트는 2009년부터 하둡을 이용한 빅데이터 인프라를 구축하였으며, 2019년 현재 일일 발생량 11테라바이트, 축적 용량 6페타바이트에 달하는 대규모 데이터를 이용해 기본적인 현황 분석부터 고객 세그먼테이션, 이상 탐지, 어뷰징 탐지, 이탈 예측 등 다양한 분석에 활용하고 있다. 본 강연에서는 엔씨소프트에서 진행하는 분석 사례와 함께 기계 학습 모델을 실제 서비스에 적용하기 위해 극복해야 할 도전 과제에 대해 소개한다.
Active asteroids are objects that orbit in the main asteroid belt but show transient, comet-like dust emission. Newly discovered active asteroid P/2018 P3 (PANSTARRS) has a semimajor axis 3.006 AU, eccentricity 0.415, inclination 8.9 deg, placing it within the dynamical boundary region between asteroids and comets. This object has been recurrently active near two successive perihelia (at 1.75 AU), indicative of the sublimation of volatile ices. We obtained Hubble Space Telescope observations of P/2018 P3 from 2018 September to 2018 December, in order to study the morphology of the ejected dust at superb spatial resolutions. Numerical modeling of P/2018 P3's dust emission showed that the properties of the ejected dust are remarkably consistent with those found in other sublimating active asteroids (e.g., the continuous emission of >10 μm particles at 0.2-3 m/s speeds). Unlike low-eccentricity active asteroids which are assumed to be native to the main belt, our dynamical analysis suggests that P/2018 P3 appears unstable on timescales >10 Myr and is likely to be a recently implanted interloper. We also find that several synthetic Jupiter-family comets studied by Brasser & Morbidelli (2013) briefly take on P/2018 P3-like orbital elements during their evolution. As such, we speculate that P/2018 P3 is a captured Jupiter-family comet that has been residing in the main belt for >10 Myr, finally becoming indistinguishable from weakly sublimating active asteroids in terms of the dust properties.
In my talk, I will give a brief introduction to thermal and thermophysical models that are widely used for interpretation of the thermal infrared radiation of asteroids. These include the NEATM model developed by Harris (1998) and the thermophysical model of Lagerros (1996, 1997, 1998). I will discuss the effects of thermal inertia and surface roughness on the emitted radiation and show how these properties can be derived by the means of a thermophysical model. I will apply the thermophysical model to hundreds of asteroids with known shape model and available thermal infrared data from the WISE satellite. Finally, I will also discuss the thermophysical properties of near-Earth asteroid (3200) Phaethon, the target of the proposed DESTINY+ mission of JAXA.
This pioneering work ties the origin of probabilities we use (both in scientific analysis and everyday life) to quantum fluctuations. One important conclusion is that in many cases people have been using probabilities incorrectly when applied to multiverse theories.
Optical quantum information processing can be classified into two categories depending on the way of encoding quantum information on light: one harnesses the particle nature (photon)−called discrete-variable approach−, and the other exploits the wave nature (electric field)−called continuous-variable approach. Basic nonclassical lights for the two are single photon and squeezed vacuum, respectively. Recently, a new field of study is emerging, called hybrid quantum information processing that combines the two conventional approaches to complement each other. In this talk, I will present generation of non-Gaussian quantum states of multimode light based on the hybrid quantum information processing. Squeezed vacuum, which is employed in the continuous-variable approach, is a Gaussian state, which can be used to build a large-scale quantum system in a deterministic way. However, non-Gaussian features are required in some quantum protocols, especially to reach a quantum computation advantage. Single-photon subtraction used in the discrete-variable approach can provide the non-Gaussian characteristics. We have implemented a single-photon subtractor compatible with multimode Gaussian states and generated non-Gaussian multimode quantum states. The resulting non-Gaussian multimode quantum states will have broad applications for universal quantum computing, entanglement distillation, and a nonlocality test.
HII regions are an excellent tracer of high-mass star-forming regions and current star formation in galaxies. In particular, young O/B stars produce powerful outflows and intense UV radiation that appreciably change the chemistry and physical conditions in the surrounding HII regions. First, I will present large surveys studies of the (sub)millimeter hydrogen radio recombination lines (RRLs) and molecular lines toward 967 compact dust clumps (409 clumps for molecular lines) identified in the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). The atomic/molecular lines surveys, taken from the IRAM 30m, Mopra 22m, and APEX 12m telescopes, show the HII regions are obviously associated with the dense clumps and some of them show evidence of high-velocity ionized gas. By determining column densities and abundances of the selected eight molecular transitions (HCO, HOC+, C2H, c-C3H2, CN, H13CN, HC15N, HN13C), HCO and C2H known as photodissociation tracers show excellent correlations with the presence of the young HII regions and their abundances decrease with an increase of H2 column densities. In the second part, I will show recent 1.3 mm ALMA data analyses of three ATLASGAL HII regions. The ALMA data with high angular resolutions (0.7-0.8’’) has resolved detailed molecular gas structures surrounding the HII regions with cometary morphology and hidden hot cores in the regions.
Immediate vicinity of a supermassive black hole (SMBH) is an important place to test general relativity in strong gravity regime. Also, this is a place where mass accretion and jet formation actively occurs at the centers of active galaxies. Theoretical studies predict presence of bright ring-like emission encircling an accreting SMBH with a diameter of about 5 Schwarzschild radii, and a flux depression at the center (i.e., BH shadow). Direct imaging of the BH shadow is accordingly of great importance in modern astrophysics. However, the angular sizes of the horizon-scale structures are desperately small (e.g., ~40-50 microarcseconds (uas) diameter for the nearest best candidates). This poses serious challenges to observe them directly. Event Horizon Telescope (EHT) is a global network of sensitive radio telescopes operating at 230 GHz (1.3 mm), providing ultra-high angular resolution of 20 uas by cutting-edge very long baseline interferometry techniques. With this resolution, EHT aims to directly image the nearest SMBHs; M87 and the galactic center Sgr A* (~40-50 uas diameters). In Spring 2017, the EHT collaboration conducted a global campaign of EHT and multiwavelength observations of M87 and Sgr A*, with addition of the phased ALMA to the 1.3mm VLBI array. On April 10th, the first images of the BH shadow in M87 were published by the EHT collaboration. On behalf of the collaboration, we present main results from the EHT 2017 observations and their astrophysical implications. In addition, we will also focus on particular topics including (i) how the EHT data processing and imaging have been validated, (ii) what are contributions to the EHT project from Korean side, and (iii) other multiwavelength observations during the EHT campaigns.
In this talk, I will report our recent implementation of squeezed vacuum states at 1064 nm. With a bow-tie, optical parametric oscillator cavity, and our home-made balanced homodyne detectors, noise reduction upto 10dB below the vacuum is measured. With the operation of a 300 m filter cavity prototype installed at theNational Astronomical Observatory of Japan, application of such a vacuum squeezed state to the gravitational wave detector, in order to achieve a broadband reduction, will be discussed.
The importance of a Mars surface network mission has long been emphasized since it can provide unique measurements from globally distributed landers. To date, however, no surface network has been deployed to Mars despite the expected scientific promises. One of the challenges in the mission is to establish an optimized thermal design that survives in the extreme thermal environments and low insolation especially observed at high latitudes in winter. In this talk, I will present the conceptual thermal design of the miniaturized Mars network mission, neoPASCAL, and discuss the feasibility of the design and the scientific capabilities.
먼저 인류의 문명 발전에서 과학기술이 어떤 역할을 했는지 간단히 기술한다. 다음으로 4차 산업혁명의 본질을 살펴보고, 빅데이터의 정의, 역량, 적용 사례 등을 들어 보고, 그 역할이 무엇인지 조감한다. 빅데이터의 기반 학문으로서의 데이터 과학(data science)에 대하여 그 발전과정, 프로세스 흐름도, 대학에서의 주요 커리큘럼 등을 살펴본다. 다음으로 통계적 정보 창출에서 중요한 데이터 마인드(data mind)에 대하여 설명하고, 간단한 사례를 들어본다. 그리고 빅데이터 분석 이전에 필요한 스몰 데이터의 분석 사례도 살펴보고, 어떻게 통계분석을 해야 하는지 설명한다. 마지막으로 비즈니스 플랫폼의 현황과 성격을 살펴보고, 데이터 산업의 현황과 ‘데이터 강국’으로 가는 길을 모색해 보기로 한다.
Multi-wavelength observations become very popular in astronomy. Even though there are some correlations among different sensor images, it is not easy to translate from one to the other one. In this talk, we apply a deep learning method for image-to-image translation, based on conditional generative adversarial networks (cGANs), to astronomical images. To examine the validity of the method for scientific data, we consider several different types of pairs: (1) Generation of stack images from single SDSS images, (2) Generation of SDO/EUV images from SDO/HMI magnetograms, (3) Generation of farside magnetograms from STEREO/EUVI images, (4) Generation of EUV & X-ray images from Carrington sunspot drawing, and (5) Generation of solar magnetograms from Ca II images. It is very impressive that AI-generated ones are quite consistent with actual ones. We will discuss several scientific application of such an image translation method scuh as the sunspot evolution from backside to frontside. In addition, we apply the convolution neural network to the forecast of solar flares and find that our method is better than the conventional method. Our study also shows that the forecast of solar proton flux profiles using Long and Short Term Memory method is better than the autoregressive method. We will discuss several applications of these methodologies for scientific research.
With unprecedented angular resolution of 0.02" of ALMA, we have resolved the disk and jet system in the young protostellar system HH 212 in Orion. The disk is resolved for the first time in the vertical direction, showing a dark lane sandwiched between two bright features, appearing as a hamburger. The disk is flared as expected for an accretion disk. A highly collimated jet is also detected ejecting from the disk, consisting of a train of fast-moving bullets. It is resolved, showing a rotation across the jet axis. Thus, our ALMA observations show that a hungry baby star is spitting a chain of spinning bullets when eating a space hamburger. I will also report the detection of prebiotic complex organic molecules in the disk atmosphere and discuss their possible formation on icy grains.
First of all, I shall give an overview on the research status about stellar magnetic activity and exoplanetary systems at Yunnan Observatories. Then, some more detailed results derived during recent years will be introduced. For stellar activity, I shall talk about the study on chromospheric and photospheric activities by using high-resolution spectroscopy, magnetic field by using Zeeman Doppler imaging method. For exoplanetary systems, I shall talk about the study on wide field transit survey project, TTV follow-up observations. Finally, the prospects in the near future will be given.
The ground-based photometric observations of asteroids still is the main source to understand their basic physical properties, even though some space mission and space-based instruments have been applied in physical studies of asteroids. With the help of developments on scattering theories and 3D shape models of asteroid, more and more asteroids are studies their basic physical parameters of asteroids from the photometric data. In this presentation, I will present photometric studies for some selected asteroids. In detail, they are: (1)To determine photometric phase functions of asteroids (107) Camilla and (106) Dione assuming an ellipsoid shape and a cellinoid shape respectively; and (2) To inverse convex shape of main-belt slow rotating asteroids (168) Sibylla and (346)Hermentaria and a near Earth asteroid (3200) Phaethon. Based on derived photometric phase functions, the geometric albedo, and even rough taxonomic classification of asteroids are inferred. With the virtual photometry Monta Carlo method, the uncertainties of spin parameters of selected asteroids were compared.