Search

Your search keyword '"Liu, Wen-Fang"' showing total 134 results
Start Over Author "Liu, Wen-Fang"
134 results on '"Liu, Wen-Fang"'

1. Parameter constraints from shadows of Kerr-Newman-dS black holes with cloud strings and quintessence

Author

Cao, Wen-Fu, Liu, Wen-Fang, and Wu, Xin

Subjects
General Relativity and Quantum Cosmology
Abstract

The motion of photons around the Kerr-Newman-dS black hole surrounded by quintessence and a cloud of strings is investigated. The existence of the Carter constant leads to that of unstable circular photon orbits on a two-dimensional plane not limited to the equatorial plane and unstable spherical photon orbits in the three-dimensional space. These circular or spherical photon orbits can determine two impact parameters, which are used to calculate black hole shadows. For the case of a spherically symmetric nonrotating black hole, the black hole shadow is circular and its size is independent of an observation angle and a plane on which a circular photon orbit exists. The shadow sizes are significantly influenced by the parameters involving the cloud of strings, quintessence parameter, magnitude of quintessential state parameter, and cosmological constant. When the black hole is spinning and axially symmetric, the black hole shadow is dependent on the observation angle. The effects of the parameters excluding the spin parameter on the sizes of black hole shadows in the rotating case are similar to those in the nonrotating case. Based on the Event Horizon Telescope observations of M87*, the constraint of the curvature radius is used to constrain these parameters. For slowly rotating black holes, the allowed regions of the parameters including the cosmological constant are given., Comment: 30 pages, 10 figures

Published
2023
Full Text
View/download PDF

2. Study of chaos in rotating galaxies using extended force-gradient symplectic methods

Author

Zhang, Li-Na, Liu, Wen-Fang, and Wu, Xin

Subjects
Physics - Computational Physics, Astrophysics - Astrophysics of Galaxies, Nonlinear Sciences - Chaotic Dynamics
Abstract

We take into account the dynamics of three types of models of rotating galaxies in polar coordinates in a rotating frame. Due to non-axisymmetric potential perturbations, the angular momentum varies with time, and the kinetic energy depends on the momenta and spatial coordinate. The existing explicit force-gradient symplectic integrators are not applicable to such Hamiltonian problems, but the recently extended force-gradient symplectic methods proposed in a previous work are. Numerical comparisons show that the extended force-gradient fourth-order symplectic method with symmetry is superior to the standard fourth-order symplectic method but inferior to the optimized extended force-gradient fourth-order symplectic method in accuracy. The optimized extended algorithm with symmetry is used to explore the dynamical features of regular and chaotic orbits in these rotating galaxy models. The gravity effects and the degree of chaos increase with an increase of the number of the radial terms in the series expansions of the potential. There are similar dynamical structures of regular and chaotical orbits in the three types of models for the same number of the radial terms in the series expansions, energy and initial conditions., Comment: 15 pages, 11 figures

Published
2023
Full Text
View/download PDF

18. Detection of Prochloraz and 2,4,6-Trichlorophenol Pesticide Residues in Pepper by GC-NCI MS/MS.

Author

LI Ping, XU Bei-bei, ZHENG Qin-Yue, WANG Lu-lu, and LIU Wen-Fang

Abstract

The simultaneous determination method for prochloraz and its metabolite 2,4,6 -trichlorophenol in pepper was established by gas chromatography-negative chemical ionization mass spectrometry. The results showed that, high response for the detection of the targets in the chemical ionization mode was achieved, the purification effects of purification adsorbents PSA, C18 and GCB were compared, and C18 was finally selected as the pretreatment purification adsorbent. The limits of detection (LOD) was 0.05 mg/kg for prochloraz and 2,4,6-trichlorophenol. The recovery rate of prochloraz in pepper ranged from 85.0% to 92.3% and the relative standard deviation (RSD) was 0.3% to 2.3%. While the recovery rate and RSD of 2,4,6-trichlorophenol were 82.3%~96.4% and 0.8%~1.7%, respectively. The developed method was simple, fast and efficient, and could be used for simultaneous detection of prochloraz and 2,4,6-trichlorophenol pesticide residues. [ABSTRACT FROM AUTHOR]

Published
2022

21. Consumption externalities, production externalities, and long-run macroeconomic efficiency

Author

Liu, Wen-Fang and Turnovsky, Stephen J.

Subjects
Macroeconomics -- Research, Developing countries -- Economic aspects, Production (Economics) -- Analysis, Consumption (Economics) -- Analysis, Business, Economics, Government
Abstract

The impact of consumption and production externalities on the welfare of a growing economy is discussed.

Published
2005

32. Preparation of opal photonic crystal infrared stealth materials

Author

Liu Wen-Fang, Zhang Lianchao, Wang Shu-Shan, Qiu Lili, Yu Ying-Jie, Meng Zihui, Lu Wei, and Xue Min

Subjects
010309 optics, Materials science, Infrared, business.industry, 0103 physical sciences, General Physics and Astronomy, Optoelectronics, 02 engineering and technology, 021001 nanoscience & nanotechnology, 0210 nano-technology, business, 01 natural sciences, Photonic crystal
Abstract

With the development of infrared detection technology, the survival of military target is now under serious threat. Therefore, new infrared stealth technologies and materials are now in an urgent demand. The photonic crystal (PhC) possesses regularly repeating structure which results in band-gap and diffraction satisfying Bragg's law of diffraction. The PhC presents unique optical properties and functionality. The PhC with band-gap located in visible band is used widely as biosensor, chemical sensor, optical filter, reflector, modulator, metasurface and solar cell. The PhC with band-gap located in infrared band can be used to control the propagations of the electromagnetic waves of infrared band, and could be used as a promising material in the infrared stealth technology. Photonic structure used to tune the infrared radiation usually has a one-dimensional layer-by-layer stack or three-dimensional wood pile structure. However, the poor flexibility, low strength, small area coverage, complicated fabrication process and high cost can prevent this new infrared stealth technology from being applied and developed. In this report, a simple and cost-effective method of preparing the opal PhC materials is proposed, and this infrared stealth material forbids electromagnetic waves of infrared band to propagate on account of band-gap.In this paper, opal PhCs materials with high quality are assembled from SiO2 colloidal microspheres with micrometer size by using optimized vertical deposition method. We calculate the relation between the diameter of SiO2 colloidal microsphere and the frequency of opal PhCs band-gap in theory and verified in experiment, which operates in the working band of infrared detector. The results show that the diameters of SiO2 colloidal microspheres should be 1.33-2.22 m and 3.56-5.33 m. A series of monodispersed micrometer SiO2 colloidal microspheres is prepared by the modified Stber method, and bigger microspheres are prepared by using the seeded polymerization method. Then, we choose the diameters of 1.5 m and 4.3 m SiO2 microspheres to prepare the opal PhCs materials. The PhCs materials assembled by 1.5 m SiO2 microspheres are prepared in alcohol under 60 ℃ or in acetone under 40 ℃; while the PhCs material assembled by 4.3 m SiO2 microspheres is prepared in alcohol/dibromomethane =3:1 under 60 ℃. Finally, the opal PhC materials with band-gap located in 2.8-3.5 m and 8.0-10.0 m are successfully prepared, and the widths of band-gap are 0.7 m and 1.9 m, respectively. These opal PhCs materials could change the infrared radiation characteristics of the target in infrared waveband, and meet the requirements of wide band-gap for infrared stealth materials.

Published
2017

Catalog

Books, media, physical & digital resources
See catalog results