arXiv subjects

Zhixiang Yin

Publications and source records attributed to Zhixiang Yin.

5 recordsLinked to original sources

arXiv2026

Photon rings and shadows of black holes with non-minimal couplings between curvature and electromagnetic field

We investigate black holes with non-minimal couplings between the electromagnetic field and spacetime curvature, focusing on their event horizons, shadows, and photon rings. Such couplings can naturally arise from both classical effective field theories of gravity and quantum effects in curved spacetime. Starting from a general action with three independent coupling terms, we derive static and spherically symmetric black hole solutions using a series expansion method. We find that all couplings enlarge the event horizon and photon sphere, while their observational consequences differ. The coupling $F^μ_{\ ν}F_{μρ}R^{νρ}$ slightly increases the shadow size and the separation between the zeroth- and first-order photon rings, leaving higher-order spacings nearly unchanged. The coupling $F_{μν}F_{σρ}R^{μνσρ}$ significantly enlarges the shadow and the zeroth-first ring separation, but rapidly suppresses the spacing between higher-order rings. In contrast, the $F^2R$ coupling reduces the shadow size and causes the zeroth- and first-order rings to nearly coincide, leading to an enhanced brightness, while increasing the separation of higher-order rings and leaving them easier to resolve observationally. We further generate black hole images via backward ray tracing and confirm these features within the observationally resolvable regime. These findings can make observational constraints on the non-minimal couplings or might provide new evidence for the modifications to gravity caused by classical or quantum effects.

gr-qc↗

arXiv2023

Exploring Interacting Dark Energy with Chaos Quantum-Behaved Particle Swarm Optimization

Models with an interaction between dark energy and dark matter have already been studied for about twenty years. However, in this paper, we provide for the first time a general analytical solution for models with an energy transfer given by $\mathcal{E} = 3H(ξ_1 ρ_c + ξ_2 ρ_d)$. We also use a new set of age-redshift data for 114 old astrophysical objects (OAO) and constrain some special cases of this general energy transfer. We use a method inspired on artificial intelligence, known as Chaos Quantum-behaved Particle Swarm Optimization (CQPSO), to explore the parameter space and search the best fit values. We test this method under a simulated scenario and also compare with previous MCMC results and find good agreement with the expected results.

astro-ph.CO↗

arXiv2023

A bias using the ages of the oldest astrophysical objects to address the Hubble tension

Recently different cosmological measurements have shown a tension in the value of the Hubble constant, $H_0$. Assuming the $Λ$CDM model, the Planck satellite mission has inferred the Hubble constant from the cosmic microwave background (CMB) anisotropies to be $H_0 = 67.4 \pm 0.5 \, \rm{km \, s^{-1} \, Mpc^{-1}}$. On the other hand, low redshift measurements such as those using Cepheid variables and supernovae Type Ia (SNIa) have obtained a significantly larger value. For instance, Riess et al. reported $H_0 = 73.04 \pm 1.04 \, \rm{km \, s^{-1} \, Mpc^{-1}}$, which is $5σ$ apart of the prediction from Planck observations. This tension is a major problem in cosmology nowadays, and it is not clear yet if it comes from systematic effects or new physics. The use of new methods to infer the Hubble constant is therefore essential to shed light on this matter. In this paper, we discuss using the ages of the oldest astrophysical objects (OAO) to probe the Hubble tension. We show that, although this data can provide additional information, the method can also artificially introduce a tension. Reanalyzing the ages of 114 OAO, we obtain that the constraint in the Hubble constant goes from slightly disfavoring local measurements to favoring them.

astro-ph.CO↗

arXiv2020

Cloud detection in Landsat-8 imagery in Google Earth Engine based on a deep neural network

Google Earth Engine (GEE) provides a convenient platform for applications based on optical satellite imagery of large areas. With such data sets, the detection of cloud is often a necessary prerequisite step. Recently, deep learning-based cloud detection methods have shown their potential for cloud detection but they can only be applied locally, leading to inefficient data downloading time and storage problems. This letter proposes a method to directly perform cloud detection in Landsat-8 imagery in GEE based on deep learning (DeepGEE-CD). A deep neural network (DNN) was first trained locally, and then the trained DNN was deployed in the JavaScript client of GEE. An experiment was undertaken to validate the proposed method with a set of Landsat-8 images and the results show that DeepGEE-CD outperformed the widely used function of mask (Fmask) algorithm. The proposed DeepGEE-CD approach can accurately detect cloud in Landsat-8 imagery without downloading it, making it a promising method for routine cloud detection of Landsat-8 imagery in GEE.

eess.IV↗

arXiv2019

Spatially Continuous and High-resolution Land Surface Temperature: A Review of Reconstruction and Spatiotemporal Fusion Techniques

Remotely sensed, spatially continuous and high spatiotemporal resolution (hereafter referred to as high resolution) land surface temperature (LST) is a key parameter for studying the thermal environment and has important applications in many fields. However, difficult atmospheric conditions, sensor malfunctioning and scanning gaps between orbits frequently introduce spatial discontinuities into satellite-retri1eved LST products. For a single sensor, there is also a trade-off between temporal and spatial resolution and, therefore, it is impossible to obtain high temporal and spatial resolution simultaneously. In recent years the reconstruction and spatiotemporal fusion of LST products have become active research topics that aim at overcoming this limitation. They are two of most investigated approaches in thermal remote sensing and attract increasing attention, which has resulted in a number of different algorithms. However, to the best of our knowledge, currently no review exists that expatiates and summarizes the available LST reconstruction and spatiotemporal fusion methods and algorithms. This paper introduces the principles and theories behind LST reconstruction and spatiotemporal fusion and provides an overview of the published research and algorithms. We summarized three kinds of reconstruction methods for missing pixels (spatial, temporal and spatiotemporal methods), two kinds of reconstruction methods for cloudy pixels (Satellite Passive Microwave (PMW)-based and Surface Energy Balance (SEB)-based methods) and three kinds of spatiotemporal fusion methods (weighted function-based, unmixing-based and hybrid methods). The review concludes by summarizing validation methods and by identifying some promising future research directions for generating spatially continuous and high resolution LST products.

physics.ao-ph↗