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Lei Liu

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Journal article (2023) - Ben Hudson, Leonid I. Gurvits, Maciek Wielgus, Zsolt Paragi, Lei Liu, Weimin Zheng
Recent advances in technology coupled with the progress of observational radio astronomy methods resulted in achieving a major milestone of astrophysics - a direct image of the shadow of a supermassive black hole, taken by the Earth-based Event Horizon Telescope (EHT). The EHT was able to achieve a resolution of ∼20μas, enabling it to resolve the shadows of the black holes in the centres of two celestial objects: the supergiant elliptical galaxy M87 and the Milky Way Galaxy. The EHT results mark the start of a new round of development of next generation Very Long Baseline Interferometers (VLBI) which will be able to operate at millimetre and sub-millimetre wavelengths. The inclusion of baselines exceeding the diameter of the Earth and observation at as short a wavelength as possible is imperative for further development of high resolution astronomical observations. This can be achieved by a spaceborne VLBI system. We consider the preliminary mission design of such a system, specifically focused on the detection and analysis of photon rings, an intrinsic feature of supermassive black holes. Optimised Earth, Sun–Earth L2 and Earth–Moon L2 orbit configurations for the space interferometer system are presented, all of which provide an order of magnitude improvement in resolution compared to the EHT. Such a space-borne interferometer would be able to conduct a comprehensive survey of supermassive black holes in active galactic nuclei and enable uniquely robust and accurate tests of strong gravity, through detection of the photon ring features. ...
Journal article (2023) - Wenli Bai, Hao Yu, Longlong Liu, Esfandiar Pakdel, Bin Tang, Hongli Su, Christopher Hurren, Lei Liu, Jinfeng Wang, Xungai Wang
Malodor is regarded as a very significant nuisance, 2nd only to noise pollution, in the developed world. It directly impacts people's health and wellbeing. The prevention of odor build-up is a key property for both interior textiles and active sportswear. Traditional approaches for odor elimination rely on textile surface treatment. However, the role of intrinsic morphology and chemical composition of fibers in odor elimination has not been taken into account. In this study, the adsorption characteristics and mechanisms of three common types of fibers (wool, cotton and nylon) for two typical odors of acetic acid and ammonia were systematically investigated through kinetic modelling, the inverse gas chromatography (IGC) technique, and density functional theory (DFT) calculations. Both acetic acid and ammonia adsorption onto fibers followed a pseudo-second-order kinetic model. Among all the tested fibers, wool showed the highest adsorption ability towards both acetic acid and ammonia. The adsorption behaviors of cotton and nylon were explored based on quantitative measurement of surface Lewis acid-base properties using the IGC technique. These findings were further corroborated by DFT calculations via the interactions between fibers and the adsorbed odor. This study provides a new insight into odor adsorption onto commonly used fibers and their interactions, which is a key step in developing fibrous materials for odor control, including body odor and indoor air pollutants. ...
Abstract (2022) - Ben Hudson, Leonid I. Gurvits, Zsolt Paragi, Maciek Wielgus, Lei Liu, Weimin Zheng
Recent advances in technology coupled with the progress of observational radio astronomy methods resulted in achieving a major milestone of astrophysics - a direct image of the shadow of a supermassive black hole, taken by the Earth-based Event Horizon Telescope (EHT). The EHT was able to achieve a resolution of approximately 20 microarcseconds, enabling it to resolve the shadow of the black hole in two celestial objects, M87* and SgrA*. This pioneering result paves the way for a multitude of astrophysical research of galactic and extragalactic objects with unprecedented sharpness. The EHT results also mark the start of a new round of development of next generation Very Long Baseline Interferometers (VLBI) which will be able to operate at millimetre and sub-millimetre wavelengths. The inclusion of baselines exceeding the diameter of the Earth and observation at as short a wavelength as possible is imperative for further development of ultra-sharp astronomical observations. This can be achieved by a spaceborne VLBI system. TeraHertz Exploration and Zooming-in for Astrophysics (THEZA) is a concept of such a system, prepared in response to ESA's call for its next science program Voyage 2050. THEZA's goal is to improve upon the angular resolution of the next generation of the Earth-based EHT by an order of magnitude. We consider the preliminary mission design of the THEZA spaceborne interferometer, specifically focused on the detection and analysis of the pattern of photon rings, forming in a black hole observable image as a consequence of extreme gravitational deflection of light. This phenomenon is highly informative for deciphering the properties of space-time in strong gravitational fields and determining key characteristics of black holes. Earth, Sun-Earth L2 and Earth-Moon L2 orbit configurations for the space interferometer system are presented, optimised for the study of photon rings around supermassive black holes. It is shown that a THEZA mission operating in each of these configurations can detect the first order photon ring interferometric signature, enabling the mass and spin of black holes to be more accurately measured than with ground-based systems. Performing multi-epoch monitoring of the ring and associated emission would also enable tests of general relativity. Such a space-borne interferometer system will open up a new area of astrophysical observation, until now unreachable with Earth-based systems observing at the shortest possible wavelengths and past space interferometers operating at longer wavelengths. ...
Journal article (2016) - Lei Liu, Martin de Jong, Ying Huang
To tackle serious environmental problems and overcome the negative impact of an almost exclusively Gross Domestic Product (GDP) oriented performance management, a number of local governments in China have started to establish and promote Environmental Protection Performance Evaluation (EPPE) systems for their cadres since the early 2000s. How these systems work in practice within their wider administrative context has not been examined so far. This paper makes a first attempt to assess the efficacy of this EPPE system by looking at its indicator system, the policy process around it, its political implications, and its actual environmental consequences. It does so for the case of Shenzhen, one of China's most forward-looking cities in terms of socio-economic development and political reform. We find that the system can be flexibly used and does push environmental interests higher up the agenda of the local government, but is negatively affected by high levels of uncertainty in its actual use and the strict hierarchy of its application. The main impact of EPPE is on the impression municipal leaders have of the evaluated cadres and on their reputation among their peers, both indirect factors for their political career and thus incentives for the local environmental management. Empirical data show that Shenzhen's environmental quality has not changed significantly in the past five years, although an overall improvement should have been visible if the EPPE systems worked as intended. From this perspective, the efficacy of the EPPE system remains low. At the end a number of policy recommendations are given to enhance the system's effectiveness and fairness. ...