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Yanjun Qian

Yanjun Qian contributes to research discovery and scholarly infrastructure.

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Published work

3 published item(s)

preprint2026arXiv

Probabilistic Classification and Uncertainty Quantification of Sahara Desert Climate Using Feedforward Neural Networks

Climate classification plays a vital role in agricultural planning, hydrological studies, and climate science. One of the most widely used systems for classifying global climate zones is the Köppen-Trewartha (KT) classification. However, the KT classification is fundamentally deterministic, offering discrete labels to spatial locations without accounting for uncertainties in classification. In this paper, we provide a framework for probabilistic modeling of climatic zones. We implement a feedforward artificial neural network (ANN) for classification, allowing for efficient, uncertainty-aware categorization of climatic regions, thereby offering a more nuanced understanding of transitional climate zones compared to traditional deterministic methods. We apply this method to the Sahara Desert region over the 30-year period of 1960 - 1989, using data at more than 400,000 space-time locations from the first 11 years to train our model. We assess the model's short- and long-term classification capabilities to evaluate its stability and accuracy over time. We also compare the probabilistic classification from our model with the traditional KT classification. In addition, we use fluctuation analysis methods to highlight the temporal evolution of climatic zones across the Sahara region and identify areas undergoing significant flux of probabilities of their climate classes, providing insights into broader trends in desertification.

preprint2022arXiv

Constraining the $γ$-ray Emission Region for Fermi-Detected FSRQs by the Seed Photon Approach

The location of $γ$-ray emitting region in blazars has been an open issue for several decades and is still being debated. We use the Paliya et al. sample of 619 $γ$-ray-loud flat-spectrum radio quasars with the available spectral energy distributions, and employ a seed photon factor approach, to locate the $γ$-rays production region. This method efficiently set up a relation between the peak frequencies and luminosities for the synchrotron emission and inverse Compton scattering, together with a combination of the energy density and characteristic energy for the external seed photon field, namely, $\sqrt{U_0}/ε_0$, an indicative factor of seed photons (SF) in units of Gauss. By means of comparing it with canonical values of broad-line region and molecular dusty torus, we principally ascertain that the GeV emission is originated far beyond the BLR and close to the DT -- farther out at pc scales from the central black hole, which supports a {\it far-site} scenario for $γ$-ray blazars. We probe the idea that inverse Compton scattering of infrared seed photons is happening in the Thomson regime. This approach and our findings are based on the validity of the External Compton model, which is applicable to understand the GeV emission mechanism in FSRQs. However, the completeness of this framework has been challenged by reports of neutrino emission from blazars. Thus we also shed new light on the neutrino production region by using our derived results since blazars are promising neutrino emitters.

preprint2020arXiv

Effective Super-Resolution Method for Paired Electron Microscopic Images

This paper is concerned with investigating super-resolution algorithms and solutions for handling electron microscopic images. We note two main aspects differentiating the problem discussed here from those considered in the literature. The first difference is that in the electron imaging setting. We have a pair of physical high-resolution and low-resolution images, rather than a physical image with its downsampled counterpart. The high-resolution image covers about 25% of the view field of the low-resolution image, and the objective is to enhance the area of the low-resolution image where there is no high-resolution counterpart. The second difference is that the physics behind electron imaging is different from that of optical (visible light) photos. The implication is that super-resolution models trained by optical photos are not effective when applied to electron images. Focusing on the unique properties, we devise a global and local registration method to match the high- and low-resolution image patches and explore training strategies for applying deep learning super-resolution methods to the paired electron images. We also present a simple, non-local-mean approach as an alternative. This alternative performs as a close runner-up to the deep learning approaches, but it takes less time to train and entertains a simpler model structure.