arXiv subjects

Hanlin Yang

Publications and source records attributed to Hanlin Yang.

6 recordsLinked to original sources

arXiv2025

Atmospheric Heating Events Associated with Fine-scale Flux Emergence in Ephemeral Regions

Coronal heating has puzzled solar physicists for decades. The question of why the Sun's upper atmosphere is significantly hotter than its lower atmosphere remains a key mystery. It is commonly believed that the source of coronal heating comes from the Sun's magnetic field, and more complex magnetic dynamics is more efficient in heating. In an earlier work we studied the secondary (or finer-scale) flux emergence identified in five ephemeral regions (ERs), selected during the last solar minimum (Yang et al. 2024). Here we further explore the atmospheric response to the secondary flux emergences (SFEs) that were identified in the first paper. We further reveal that approximately 80 percent of the 172 identified SFEs are associated with atmospheric heating events. The heating is most likely associated with magnetic reconnection involved in the SFE. Overall, a solar quiet region is heated by several hundred thousand degrees, during flux emergence of an ER.

astro-ph.SR↗

arXiv2024

Diverse Policies Recovering via Pointwise Mutual Information Weighted Imitation Learning

Recovering a spectrum of diverse policies from a set of expert trajectories is an important research topic in imitation learning. After determining a latent style for a trajectory, previous diverse policies recovering methods usually employ a vanilla behavioral cloning learning objective conditioned on the latent style, treating each state-action pair in the trajectory with equal importance. Based on an observation that in many scenarios, behavioral styles are often highly relevant with only a subset of state-action pairs, this paper presents a new principled method in diverse polices recovery. In particular, after inferring or assigning a latent style for a trajectory, we enhance the vanilla behavioral cloning by incorporating a weighting mechanism based on pointwise mutual information. This additional weighting reflects the significance of each state-action pair's contribution to learning the style, thus allowing our method to focus on state-action pairs most representative of that style. We provide theoretical justifications for our new objective, and extensive empirical evaluations confirm the effectiveness of our method in recovering diverse policies from expert data.

cs.LG↗

arXiv2024

Complexity of emerging magnetic flux during lifetime of solar ephemeral regions

As a relatively active region, ephemeral region (ER) exhibits highly complex pattern of magnetic flux emergence. We aim to study detailed secondary flux emergences (SFEs) which we define as bipoles that they appear close to ERs and finally coalesce with ERs after a period. We study the SFEs during the whole process from emergence to decay of 5 ERs observed by the Helioseismic and Magnetic Imager (HMI) aboard Solar Dynamics Observatory (SDO) . The maximum unsigned magnetic flux for each ER is around $10^{20}$ Mx. Each ER has tens of SFEs with an average emerging magnetic flux of approximately 5$\times10^{18}$ Mx. The frequency of normalized magnetic flux for all the SFEs follows a power law distribution with an index of -2.08 . The majority of SFEs occur between the positive and negative polarities of ER , and their growth time is concentrated within one hour. The magnetic axis of SFE is found to exhibit a random distribution in the 5 ERs. We suggest that the relationship between SFEs and ERs can be understood by regarding the photospheric magnetic field observations as cross-sections of an emerging magnetic structure. Tracking the ERs' evolution, we propose that these SFEs in ERs may be sequent emergences from the bundle of flux tube of ERs, and that SFEs are partially emerged $\Omega$-loops.

astro-ph.SR↗

arXiv2015

Lipschitz-quadratic Regularization for Quadratic Semimartingale BSDEs

We refine the solvability of quadratic semimartingale BSDEs by employing a Lipschitz-quadratic regularization procedure. In the first step, we prove an existence and uniqueness result for a class of Lipschitz-quadratic BSDEs. A corresponding stability theorem and a Lipschitz-quadratic regularization are developed to solve quadratic BSDEs. The advantage of our approach is that much weaker conditions ensure the existence and uniqueness results.

math.PR↗

arXiv2015

On Quadratic BSDEs with Final Condition in L2

This thesis consists of three parts. In the first part, we study $\mathbb{L}^p$ solutions of a large class of BSDEs. Existence, comparison theorem, uniqueness and a stability result are proved. In the second part, we establish the solvability of quadratic semimartingale BSDEs. In contrast to current literature, we use Lipschitz-quadratic regularization and obtain the existence and uniqueness results with minimal assumptions. The third part is a brief summary of quadratic semimartingales and the monotone stability result. This provides an alternative proof of monotone stability result for quadratic semimartingales BSDEs.

math.PR↗

arXiv2015

Lp Solutions of Quadratic BSDEs

We study a general class of quadratic BSDEs with terminal value in Lp for p > 1. First of all, we give an Lp-type estimate and existence result. Under the additional assumption of monotonicity and convexity, we derive the comparison theorem, uniqueness and stability result via {\theta}-technique (Briand and Hu [7]). The assumptions employed throughout this paper are rather weak and extend the quadratic BSDE literature. Finally, a probabilistic representation for the viscosity solution to the associated quadratic PDEs is given.

math.PR↗