天文現象及活動

物理系學生會議：磁場方向在絲狀雲中恆星形成率的影響

Talk:- The Effect of Magnetic Field Orientation on Star Formation Rate in Filament Clouds

With the rapid growth of computational power, numerical simulation has become more and more important in astrophysical researches in the last few decades. In this presentation, we will briefly introduce the simulation we are adopting in our group, as well as one of the currently undergoing simulation projects, aiming to reveal the effect of magnetic field orientation and other effects on star formation rate in filament clouds. The importance of magnetic field orientation in star formation has been gradually realised in the recent decades. However, the effect of different orientations on star formation rate in particular types of filaments is still yet to be understood, which will be the central topic of the project.　
　
時間：2017.05.20(六) 15:45 ~ 16:00
地點：香港中文大學 科學館LT4
講者：GUO Zitan
語言：英語

#131

此活動由香港中文大學物理系主辦。

物理系學生會議：具有限化學勢的大質量中微子於宇宙擴張史及大尺度結構的影響

Talk:- Influence of Massive Neutrinos with a Finite Chemical Potential on the Cosmic Expansion History and Large Scale Structure

Due to their high abundance, massive cosmic neutrinos would have a significant influence on cosmology, especially in terms of large scale structure. Ever since the discovery of neutrino oscillation, which confirmed that neutrinos have finite masses, many efforts have been made to constrain neutrino masses from cosmology. However, none of them has considered the possibility of a finite chemical potential, if the neutrinos are not majorana fermions. The work would be the first one to analyse the combined effect of masses and chemical potentials of neutrinos on matter power spectrum of large scale structure, through two physical processes, their influence on the cosmic expansion history, and the neutrino free-streaming. The result would serve as a correction to the constraints of neutrino masses from large scale structure.　
　
時間：2017.05.20(六) 16:15
地點：香港中文大學 科學館LT4
講者：
　　●Zhichao Zeng
　　●Shek Yeung
　　●Ming Chung Chu
語言：英語

#131

此活動由香港中文大學物理系主辦。

物理系學生會議：教科書編成《NSS Physics Insight – A Short Introduction to Special Relativity》

Talk:- NSS Physics Insight – A Short Introduction to Special Relativity

We have developed a textbook (NSS Physics Insight – A short introduction to Special Relativity) teaching Secondary Senior Form students Special Relativity. There are 6 major chapters about Special Relativity included, together with 4 supplementary chapters providing required mathematics skills, like limits and differentiation, integration, vectors and matrices, for students to tackle Special Relativity problems. Time dilation, length contraction, Lorentz transformation and the application of Spacetime diagrams are included in the textbook. We adopted the example-based approach in the textbook, that is, we provided examples for students to follow and some follow-up challenges for them to apply what they have learnt. To arouse interest of the readers, we also made use of comics and dialogues to exemplify the physics concepts and theories. Problem sets are available at the end of each chapter, in which students can test their understanding. It is notable that most of the problems in the textbook were originally designed, with extra features like problems are implemented based on novels, increasing difficulty of problems of similar situations. A full solution manual is also available for students to check their answers and steps. Supplementary notes and explanation are also provided in the manual.　
　
時間：2017.05.20(六) 16:00 ~ 16:15
地點：香港中文大學 科學館LT4
講者：Li Ka Yue Alvin 及 Pang Yiu Yung
語言：英語

#131

此活動由香港中文大學物理系主辦。

Plenary talks:- Twinkle twinkle dirty stars, how I wonder how you die

In the standard theory of stellar evolution, stars die and become white dwarfs, neutron stars, or black holes, depending on their masses. Many stars go through spectacular explosion and become supernovae before their final deaths. However, this standard theory ignores possible admixture of dark matter – invisible matter that interact only gravitationally and maybe weakly – and their effects on the stellar structure, even though dark matter is known to be the dominant form of matter in the universe. the speaker will briefly introduce work done in CUHK investigating dark matter admixed stars, particularly how they die!　
　
時間：2017.05.20(六) 09:30 ~ 10:00
地點：香港中文大學 科學館LT4
講者：朱明中 教授
語言：英語

#131

此活動由香港中文大學物理系主辦。

Invited talks:- Multi-scale Magnetic Field Orientation and its Observation

The role of magnetic fields is an important problem in star formation. We investigate the orientations of magnetic fields at different spatial scales by comparing the optical data with the single dish and interferometer data. We found that the magnetic field orientations are well correlated from 300 pc to 0.1-1 pc, and show a bimodal distribution when deep into ~0.01pc. In order to verify this result and further investigate the field morphology problem, our group is constructing a polarimeter, APol which will allow us to do experiment and get our own data.　
　
時間：2017.05.20(六) 11:15 ~ 11:40
地點：香港中文大學 科學館LT4
講者：Yapeng Zhang
語言：英語

#131

此活動由香港中文大學物理系主辦。

相關流星群：天蠍-人馬座流星雨群組(SAG)

出現日期：
4月15日至7月15日
極大日期(香港時間)：
5月20日(星期六)9時09分
月閃高峰期：
遲0.2小時

天頂每時出現率ZHR：5顆
速度：每秒30公里(低速)
亮度指標：2.5(中等)

輻射點(曆元2000)：
赤經16.5時/247°赤緯-22°

有關今次天象更詳細資料請按左下角「外部連結」

http://forum.hkas.org.hk/thread-9675-1-1.html

物理系學生會議：銀河尺度內量子效應 – 模糊暗物質宇宙模擬及大尺度結構

Talk:- Quantum Effect in Galactic Scale: Fuzzy Dark Matter Cosmological Simulation and Large Scale Structure

The Ultra-Light Axion (ULA) is a dark matter candidate with mass o(10^-22) eV and de Broglie wavelength of order kpc. Such an axion, also called the Fuzzy Dark Matter (FDM), thermalizes via the gravitational force and forms a Bose-Einstein condensate. Recent studies suggested that the quantum pressure from the FDM can significantly affect the structure formation in small scales, thus alleviating the so-called “small-scale crisis”. We develop a new technique to discretize the quantum pressure and illustrate the interactions among FDM particles in the N-body simulation. With our highly efficient algorithm, the largest scale cosmological simulation of FDM model has been performed. The non-trivial effect of quantum pressure on Large Scale Structure (LSS) has been revealed. The constraints from recent Lyman-alpha Forest observations are discussed.　
　
時間：2017.05.20(六) 13:30 ~ 13:45
地點：香港中文大學 科學館LT4
講者：Jiajun Zhang
語言：英語

#131

此活動由香港中文大學物理系主辦。

宇宙中危機四伏，強烈的太陽風暴、不可抵禦的近地天體撞擊事件及來源不明的伽馬射線暴都有可能於一瞬間令地球上全人類滅亡。講者將會在是次講座中向觀眾解說各項危害背後的成因及科學原理。

時間：2017.05.20(六) 15:00 ~ 16:30
地點：香港太空館演講廳
講者：
●丘澄峰 (星匯點委員)
●梁家榮 (星匯點委員)

免費講座，歡迎公眾參加，座位先到先得

此活動由香港太空館主辦。

物理系學生會議：貝氏變分法到參數估算重力波天文學

Talk:- Variational Bayesian to Parameter Estimation in Gravitational Wave Astronomy

The traditional way of conducting parameter estimation in gravitational-wave data analysis is done by obtaining the posterior and evidence through Markov-Chain Monte Carlo methods. These computational methods are time consuming as they rely on wandering randomly in parameter spaces of high dimensions. Instead of randomly sampling, variational Bayesian makes use of an approximated probability distributions, which resembles the true distribution. Minimizing the differences between the true and approximated distributions can then be a more directional way of conducting parameter estimation. In this presentation, we will discuss the possibility of implementing variational Bayesian to parameter estimation in gravitational-wave data analysis.　
　
時間：2017.05.20(六) 14:00 ~ 14:15
地點：香港中文大學 科學館LT4
講者：Adrian, K.W. Chung
語言：英語

#131

此活動由香港中文大學物理系主辦。

13時31分，海王星合月，海王星在月球北0.47度