The analytic radial acceleration relation for galaxy clusters

Recently, a tight correlation between the dynamical radial acceleration and the baryonic radial acceleration in galaxies - the radial acceleration relation - has been discovered. This has been claimed as an indirect support of the modified gravity theories. However, whether the radial acceleration relation could also be found in galaxy clusters is controversial. In this article, we derive and present an analytic radial acceleration relation for the central region of galaxy clusters. We examine the data of some large galaxy clusters and we find that the resulting radial acceleration relation has a very large scatter. Moreover, although the radial acceleration relation for galaxy clusters shows some agreement with the one discovered in galaxies for a certain range of baryonic radial acceleration, their functional forms are somewhat different from each other. This suggests that the radial acceleration relation may not be a universal relation in general.Comment: Accepted in Phys. Rev.

A severe challenge to the MOND phenomenology in our Galaxy

Modified Newtonian Dynamics (MOND) is one of the most popular alternative theories of dark matter to explain the missing mass problem in galaxies. Although it remains controversial regarding MOND as a fundamental theory, MOND phenomenology has been shown to widely apply in different galaxies, which gives challenges to the standard $\Lambda$ cold dark matter model. In this article, we derive analytically the galactic rotation curve gradient in the MOND framework and present a rigorous analysis to examine the MOND phenomenology in our Galaxy. By assuming a benchmark baryonic disk density profile and two popular families of MOND interpolating functions, we show for the first time that the recent discovery of the declining Galactic rotation curve in the outer region ($R \approx 17-23$ kpc) can almost rule out the MOND phenomenology at more than $5\sigma$. This strongly supports some of the previous studies claiming that MOND is neither a fundamental theory nor a universal description of galactic properties.Comment: Accepted in Ap

Communicating science in the COVID-19 news in the UK during Omicron waves: exploring representations of nature of science with epistemic network analysis

News media plays a vital role in communicating scientific evidence to the public during the COVID-19 pandemic. Such communication is important for convincing the public to follow social distancing guidelines and to respond to health campaigns such as vaccination programmes. However, newspapers were criticised that they focus on the socio-political perspective of science, without explaining the nature of scientific works behind the government’s decisions. This paper examines the connections of the nature of science categories in the COVID-19 era by four local newspapers in the United Kingdom between November 2021 to February 2022. Nature of science refers to different aspects of how science works such as aims, values, methods and social institutions of science. Considering the news media may mediate public information and perception of scientific stories, it is relevant to ask how the various British newspapers covered aspects of science during the pandemic. In the period explored, Omicron variant was initially a variant of concern, and an increasing number of scientific evidence showed that the less severity of this variant might move the country from pandemic to endemic. We explored how news articles communicate public health information by addressing how science works during the period when Omicron variants surge. A novel discourse analysis approach, epistemic network analysis is used to characterise the frequency of connections of categories of the nature of science. The connection between political factors and the professional activities of scientists, as well as that with scientific practices are more apparent in left-populated and centralist outlets than in right-populated news outlets. Among four news outlets across the political spectrum, a left-populated newspaper, the Guardian, is not consistent in representing relations of different aspects of the nature of scientific works across different stages of the public health crisis. Inconsistency of addressing aspects of scientific works and a downplay of the cognitive-epistemic nature of scientific works likely lead to failure in trust and consumption of scientific knowledge by the public in the healthcare crisis

The changing missions and effectiveness Of the Hong Kong International Film Festival over the years

published_or_final_versionMedia, Culture and Creative CitiesMasterMaster of Social Sciences in Media, Culture and Creative Citie

The Profitability of the Momentum Strategies and Their Transaction Costs in the Hong Kong Stock Market

This paper examines the profitability of the momentum trading strategies in Hong Kong over the period 1993 to 2008. We demonstrate that the returns from buying winners outperforms that of short-selling the losers. In particular, short selling losers would suffer a persistent loss across our observed strategies. Besides, we find that the associated transaction costs for short selling the losers is more than double as high as the costs of buying the winners. After deducting the transaction costs, we observe that the profitability of the momentum strategies vanishes for shorter terms but remains for the longer horizons based on the actual turnover approach. All in all, our findings deliver a message that short selling losers is expensive to trade and undermines the total momentum profitability in the Hong Kong Stock Market

Spot Focusing Coma Correction by Linearly Polarized Dual-Transmitarray Antenna in the Terahertz Region

Focus scanning is critically important in many terahertz (THz) imaging and sensing applications. A traditional single focusing transmitarray can achieve a good focus when the source is on-axis but moving the source off-axis produces a significant aberration. This paper presents a novel approach to reducing coma in off-axis scanning in the THz region. Here, a dual transmitarray solution is proposed, in which a transmitarray with an optimized phase profile is placed behind a regular phase profile transmitarray. A linearly polarized, dual-transmitarray antenna was fabricated for validation, and the focusing performances were experimentally characterized. The measured results are in good agreement with the theoretical ones. The generated spot of the dual-transmitarray antenna remains focused on an angle up to 50deg, with a -3 dB spot size of less than 4 mm at 290 GHz. The measured near-field sidelobes are all below -10 dB within the whole scanning range.Comment: 9 pages, 14 figure