arXiv subjects

Yanjun Chen

Publications and source records attributed to Yanjun Chen.

41 records · Page 3Linked to original sources

arXiv2021

Rendering Discrete Participating Media with Geometrical Optics Approximation

We consider the scattering of light in participating media composed of sparsely and randomly distributed discrete particles. The particle size is expected to range from the scale of the wavelength to the scale several orders of magnitude greater than the wavelength, and the appearance shows distinct graininess as opposed to the smooth appearance of continuous media. One fundamental issue in physically-based synthesizing this appearance is to determine necessary optical properties in every local region. Since these optical properties vary spatially, we resort to geometrical optics approximation (GOA), a highly efficient alternative to rigorous Lorenz-Mie theory, to quantitatively represent the scattering of a single particle. This enables us to quickly compute bulk optical properties according to any particle size distribution. Then, we propose a practical Monte Carlo rendering solution to solve the transfer of energy in discrete participating media. Results show that for the first time our proposed framework can simulate a wide range of discrete participating media with different levels of graininess and converges to continuous media as the particle concentration increases.

cs.GR↗

arXiv2020

Dynamical instabilities for model with point-coupling interactions: Vlasov formalism method

We explore the effects of the density dependence of symmetry energy on the dynamical instabilities and crust-core phase transition in the cold and warm neutron stars in the RMF theory with point-coupling interactions using the Vlasov approach. The role of the temperature and neutrino trapping has also been considered. The distillation effect, crust-core transition density and pressure, the cluster size and growth rates have been discussed. The present work shows that the slope of symmetry energy, temperature, and neutrino trapping have obvious effects.

nucl-th↗

arXiv2013

The period ratio for standing kink and sausage modes in solar structures with siphon flow. I. magnetized slabs

In the applications of solar magneto-seismology(SMS), employing the ratio of the period of the fundamental mode to twice the one of its first overtone, $P_1/2P_2$, plays an important role. We examine how field-aligned flows affect the dispersion properties, and hence the period ratios, of standing modes supported by magnetic slabs in the solar atmosphere. We numerically solve the dispersion relations and devise a graphic means to construct standing modes. For coronal slabs, we find that the flow effects are significant, for the fast kink and sausage modes alike. For the kink ones, they may reduce $P_1/2P_2$ by up to 23% compared with the static case, and the minimum allowed $P_1/2P_2$ can fall below the lower limit analytically derived for static slabs. For the sausage modes, while introducing the flow reduces $P_1/2P_2$ by typically $\lesssim 5$ % relative to the static case, it significantly increases the threshold aspect ratio only above which standing sausage modes can be supported, meaning that their detectability is restricted to even wider slabs. In the case of photospheric slabs, the flow effect is not as strong. However, standing modes are distinct from the coronal case in that standing kink modes show a $P_1/2P_2$ that deviates from unity even for a zero-width slab, while standing sausage modes no longer suffer from a threshold aspect ratio. We conclude that transverse structuring in plasma density and flow speed should be considered in seismological applications of multiple periodicities to solar atmospheric structures.

astro-ph.SR↗

arXiv2008

Reading molecular messages from the intersections of high-order harmonic spectra at different orientations

We investigate the orientation dependence of high-order harmonic generation (HHG) from H$_2^+$ with different internuclear distances irradiated by intense laser fields both numerically and analytically. The calculated molecular HHG spectra are found to be sensitive to molecular axis orientation relative to incident laser field polarization and internuclear separation. In particular, the spectra calculated for different orientation angles demonstrate a kind of intersection, which is identified as arising due to intramolecular two-center interference in the HHG. The striking "intersection" phenomenon can be used to probe the molecular instantaneous structure.

physics.atom-ph↗

arXiv2006

Charge-Resonance Effect on Harmonic Generation by Symmetric Diatomic Molecular Ions in Intense Laser Fields

In present paper we develop an analytic theory for the harmonic generation of symmetric diatomic molecular ions beyond two-level model, emphasizing the influence of charge-resonance (CR) states those are strongly coupled to electromagnetic fields for large internuclear distance. With taking into account the continuum states that is ignored in the two-level model and become important for intense laser case, our model is capable to produce spectrum for the whole range of harmonic orders consisting of a molecular plateau due to the CR transition and an atomic-like plateau for a long-wavelength excitation, and in good agreement with numerical results from directly solution of the Schrödinger equation. Our theory also identifies the crucial role of the CR states in the fine structure of harmonic spectrum and shows that the harmonic generation in molecular system can be effectively controlled by adjusting the internuclear distance.

physics.atom-ph↗