arXiv subjects

Xiaoli Yan

Publications and source records attributed to Xiaoli Yan.

At least 37 records · Page 2Linked to original sources

arXiv2025

The Observations of Magnetic Reconnection During the Interaction Process of Two Active Region Filaments

We investigate the interaction between two filaments (F1 and F2) and their subsequent magnetic reconnection in active region (AR) NOAA 13296 and AR NOAA 13293 on May 9, 2023, utilizing high spatial and temporal resolution and multi-wavelength observational data from the Solar Dynamics Observatory, the New Vacuum Solar Telescope, and the Chinese Hα Solar Explorer. The movement of F1 from the southeast toward the northwest, driven by the motion of the positive magnetic polarity (P1), leads to a collision and reconnection with F2. This reconnection exchanges their footpoints, resulting in the formation of two new filaments (F3 and F4) consistent with "slingshot" type filament interaction. During the interaction, the current sheet moving due to the motion of F1 and the reconnection outflows moving along F3 and F4 were both observed. The current sheet is rarely observed in the slingshot type filament interaction, measuring approximately 2.17 Mm in length and 0.84 Mm in width. After the interaction, the F1 disappears whereas a portion of F2 remains, indicating that the interaction involves partial slingshot reconnection, due to the unequal magnetic flux between the filaments. The residual part of F2 will undergo another magnetic reconnection in the same interaction region with the magnetic loops connecting polarities N1 and P1. The material generated by the reconnection is continuously injected into F4, leading to its final morphology. The findings enhance our understanding of slingshot-type filament interactions, indicating that partial slingshot reconnections between filaments may be more common than full slingshot events.

astro-ph.SR↗

arXiv2025

Recurrent Jetlets Associated with the Disappearance of a Satellite Spot

Recurrent small-scale eruptions are fascinating phenomena in the solar atmosphere. However, their underlying physical mechanisms remain unclear. On 2021 May 23, five recurrent jetlets (J1-J5) were observed continuously ejecting from a satellite spot located at the north edge of AR 12824. Using high-resolution, multi-wavelength data from NVST, SDO, and IRIS, we investigate the physical characteristics of these jetlets and their relationship with the satellite spot. The widths of these jetlets range from 1300 to 2900 km, their lifetimes range span 3 to 10 minutes, and their projection speeds vary from 152.8 to 406.0 km s$^{-1}$. During the eruptions, the satellite spot moved northwest at a low speed of 376 $\pm$ 12 m s$^{-1}$. Its area gradually decreased due to magnetic cancellation with surrounding positive magnetic field, resulting in an average cancellation rate of 1.3$\times$10$^{18}$ Mx hr$^{-1}$. Dark lanes that separated from the satellite spot and small pores were observed to move toward nearby these features or dark lanes with opposite polarities, eventually disappearing during the magnetic cancellation process. J4 was driven by an eruption of a micro-filament. Spectral observations revealed a redshift on the right side of J4 and a blueshift on the left side of its base, suggesting a counterclockwise rotation. The horizontal magnetic field of the satellite spot consistently exhibited a vortex structure throughout its evolution until it vanished. The nonlinear force-free field extrapolation confirms that the satellite spot serves as one footpoint of a mini-flux rope. These observations reveal that these jetlets might result from three-dimensional null-point magnetic reconnection, initiated by the continuous eruption of a mini-flux-rope or multiple mini-flux-ropes, driven by sustained magnetic cancellation.

astro-ph.SR↗

arXiv2025

Tracking an eruptive intermediate prominence originating from the farside of the Sun

In this paper, we carry out multiwavelength and multiview observations of the eruption of an intermediate prominence originating from the farside of the Sun on 2023 March 12. The southeast footpoint of the prominence is located in active region (AR) 13252. The eruption generates a B7.8 class flare and a partial halo coronal mass ejection (CME). The prominence takes off at 02:00 UT and accelerates for nearly three hours. Rotation of the southeast leg of the prominence in the counterclockwise direction is revealed by spectroscopic and imaging observations. The apex of the prominence changes from a smooth loop to a cusp structure during the rising motion and the northwest leg displays a drift motion after 04:30 UT, implying a writhing motion. Hence, the prominence eruption is most likely triggered by ideal kink instability. For the first time, we apply the Graduated Cylindrical Shell (GCS) modeling in three-dimensional reconstruction and tracking of the prominence for nearly two hours. Both the source region (110$\degr$E, 43$\degr$N) and northwest footpoint (162$\degr$E, 44$\degr$N) are located. The edge-on and face-on angular widths of the prominence are $\sim$6$\degr$ and $\sim$86$\degr$, respectively. The axis has a tilt angle of $\sim$70$\degr$ with the meridian. The heliocentric distance of the prominence leading edge increases from $\sim$1.26\,$R_{\sun}$ to $\sim$2.27\,$R_{\sun}$. The true speed of the CME increases from $\sim$610 to $\sim$849 km s$^{-1}$.

astro-ph.SR↗

arXiv2025

MOFA: Discovering Materials for Carbon Capture with a GenAI- and Simulation-Based Workflow

We present MOFA, an open-source generative AI (GenAI) plus simulation workflow for high-throughput generation of metal-organic frameworks (MOFs) on large-scale high-performance computing (HPC) systems. MOFA addresses key challenges in integrating GPU-accelerated computing for GPU-intensive GenAI tasks, including distributed training and inference, alongside CPU- and GPU-optimized tasks for screening and filtering AI-generated MOFs using molecular dynamics, density functional theory, and Monte Carlo simulations. These heterogeneous tasks are unified within an online learning framework that optimizes the utilization of available CPU and GPU resources across HPC systems. Performance metrics from a 450-node (14,400 AMD Zen 3 CPUs + 1800 NVIDIA A100 GPUs) supercomputer run demonstrate that MOFA achieves high-throughput generation of novel MOF structures, with CO$_2$ adsorption capacities ranking among the top 10 in the hypothetical MOF (hMOF) dataset. Furthermore, the production of high-quality MOFs exhibits a linear relationship with the number of nodes utilized. The modular architecture of MOFA will facilitate its integration into other scientific applications that dynamically combine GenAI with large-scale simulations.

cs.DC↗

arXiv2024

Variation in the intensity ratio at each wavelength point of the Si iv 1394/1403 Å lines. Spectral diagnostics of a bifurcated eruption

Aims. This study aims to investigate the deviation of the intensity ratio of the \ion{Si}{IV} 1394 Å and 1403 Å emission lines from the expected value of 2 in the optically thin regime, as observed in many recent studies. Methods. We analyzed the integrated intensity ratio ($R$) and the wavelength-dependent ratio ($r(Δλ)$) in a small bifurcated eruption event observed by the Interface Region Imaging Spectrograph (IRIS). Results. Despite the relatively complex line profiles, most of the intensity ratio $R$ of \ion{Si}{IV} lines remained greater than 2 in the loops. The ratio $r(Δλ)$ varied in the line core and wings, changing distinctly from 2.0 to 3.3 along the wavelength. At certain positions, the \ion{Si}{IV} 1394 Å and 1403 Å lines exhibited different Doppler velocities. Conclusions. When diagnosing the spectra of small active region events, not only the impact of opacity but also the influence of resonance scattering should be considered. We propose that the ratio $r(Δλ)$ can serve as an indicator of the resonance scattering and opacity effect of the \ion{Si}{IV} line.

astro-ph.SR↗

arXiv2024

The nature of elongated granulations and stretched dark lanes in a newly emerging flux region

In this study, we explore the elongated granulations and stretched dark lanes within the emerging anti-Hale active region NOAA 12720. Utilizing high-resolution observations from the New Vacuum Solar Telescope, we discern a prevalence of elongated granules and stretched dark lanes associated with the emergence of new magnetic flux positioned between two primary opposing magnetic polarities. These elongated granulations and stretched dark lanes exhibit an alignment of strong transverse fields and a significant inclination angle. The endpoints of these features separate from each other, with their midpoints predominantly characterized by blue-shifted signals in the photosphere. This suggests a close association between elongated granules and stretched dark lanes with the newly emerging flux. Additionally, we find that the stretched dark lanes display a more pronounced correlation with strong blue shifts and photospheric transverse magnetic fields compared to the elongated granulations. The transverse magnetic field within these stretched dark lanes reaches magnitudes of approximately 300 to 400 G, and the inclination angle demonstrates an "arch-like" pattern along the trajectory of the stretched dark lane. Based on these observed characteristics, we infer the presence of an emerging flux tube with an "arch-like" shape situated along the stretched dark lane. Consequently, we conclude that the stretched dark lanes likely represent manifestations of the emerging flux tube, while the elongated granulations may correspond to the gaps between the emerging flux tubes.

astro-ph.SR↗

arXiv2024

Origin of the Chromospheric Umbral Waves in Sunspots

Oscillations are ubiquitous in sunspots and the associated higher atmospheres. However, it is still unclear whether these oscillations are driven by the external acoustic waves (p-modes) or generated by the internal magnetoconvection. To obtain clues about the driving source of umbral waves in sunspots, we analyzed the spiral wave patterns (SWPs) in two sunspots registered by IRIS MgII 2796 Å slit-jaw images. By tracking the motion of the SWPs, we find for the first time that two one-armed SWPs coexist in the umbra, and they can rotate either in the same or opposite directions. Furthermore, by analyzing the spatial distribution of the oscillation centers of the one-armed SWPs within the umbra (the oscillation center is defined as the location where the SWP first appears), we find that the chromospheric umbral waves repeatedly originate from the regions with high oscillation power and most of the umbral waves occur in the dark nuclei and strong magnetic field regions of the umbra. Our study results indicate that the chromospheric umbral waves are likely excited by the p-mode oscillations.

astro-ph.SR↗

arXiv2024

Imaging and spectroscopic observations of a confined solar filament eruption with two-stage evolution

Solar filament eruptions are often characterized by stepwise evolution due to the involvement of multiple mechanisms, such as magnetohydrodynamic instabilities and magnetic reconnection. In this article, we investigated a confined filament eruption with a distinct two-stage evolution by using the imaging and spectroscopic observations from the Interface Region Imaging Spectrograph (IRIS) and the Solar Dynamics Observatory (SDO). The eruption originated from a kinked filament thread that separated from an active region filament. In the first stage, the filament thread rose slowly and was obstructed due to flux pile-up in its front. This obstruction brought the filament thread into reconnection with a nearby loop-like structure, which enlarged the flux rope and changed its connectivity through the foot-point migration. The newly formed flux rope became more kink unstable and drove the rapid eruption in the second stage. It ascended into the upper atmosphere and initiated the reconnection with the overlying field. Finally, the flux rope was totally disintegrated, producing several solar jets along the overlying field. These observations demonstrate that the external reconnection between the flux rope and overlying field can destroy the flux rope, thus playing a crucial role in confining the solar eruptions.

astro-ph.SR↗

arXiv2024

A generative artificial intelligence framework based on a molecular diffusion model for the design of metal-organic frameworks for carbon capture

Metal-organic frameworks (MOFs) exhibit great promise for CO2 capture. However, finding the best performing materials poses computational and experimental grand challenges in view of the vast chemical space of potential building blocks. Here, we introduce GHP-MOFassemble, a generative artificial intelligence (AI), high performance framework for the rational and accelerated design of MOFs with high CO2 adsorption capacity and synthesizable linkers. GHP-MOFassemble generates novel linkers, assembled with one of three pre-selected metal nodes (Cu paddlewheel, Zn paddlewheel, Zn tetramer) into MOFs in a primitive cubic topology. GHP-MOFassemble screens and validates AI-generated MOFs for uniqueness, synthesizability, structural validity, uses molecular dynamics simulations to study their stability and chemical consistency, and crystal graph neural networks and Grand Canonical Monte Carlo simulations to quantify their CO2 adsorption capacities. We present the top six AI-generated MOFs with CO2 capacities greater than 2 $m mol/g$, i.e., higher than 96.9% of structures in the hypothetical MOF dataset.

cond-mat.mtrl-sci↗

arXiv2024

Simultaneous observations of a breakout current sheet and a flare current sheet in a coronal jet event

Previous studies have revealed that solar coronal jets triggered by the eruption of mini-filaments (MFs) conform to the famous magnetic-breakout mechanism. In such scenario, a breakout current sheet (BCS) and a flare current sheet (FCS) should be observed during the jets. With high spatial and temporal resolution data from the SDO, the NVST, the RHESSI, the Wind, and the GOES, we present observational evidence of a BCS and a FCS formation during coronal jets driven by a MF eruption occurring in the active region NOAA 11726 on 2013 April 21. Magnetic field extrapolation show that the MF was enclosed by a fan-spine magnetic structure. The MF was activated by flux cancellation under it, and then slowly rose. A BCS formed when the magnetic fields wrapping the MF squeezed to antidirectional external open fields. Simultaneously, one thin bright jet and two bidirectional jet-like structures were observed. As the MF erupted as a blowout jet, a FCS was formed when the two distended legs inside the MF field came together. One end of the FCS connected the post-flare loops. The peak temperature of BCS was calculated to be 2.5 MK. The length, width and peak temperature of FCS was calculated to be 4.35-4.93 Mm, 1.31-1.45 Mm, and 2.5 MK, respectively. The magnetic reconnection rate associated with the FCS was estimated to be from 0.266 to 0.333. This event also related to a type III radio burst, indicating its influence on interplanetary space. These observations support the scenario of the breakout model as the trigger mechanism of coronal jets, and flux cancellation was the driver of this event.

astro-ph.SR↗

arXiv2023

Onset mechanism of an inverted U-shaped solar filament eruption revealed by NVST, SDO, and STEREO-A observations

Utilizing observations from the New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory (SDO), and Solar Terrestrial Relations Observatory-Ahead (STEREO-A), we investigate the event from two distinct observational perspectives: on the solar disk using NVST and SDO, and on the solar limb using STEREO-A. We employ both a non-linear force-free field model and a potential field model to reconstruct the coronal magnetic field, aiming to understand its magnetic properties. Two precursor jet-like activities were observed before the eruption, displaying an untwisted rotation. The second activity released an estimated twist of over two turns. During these two jet-like activities, Y-shaped brightenings, newly emerging magnetic flux accompanied by magnetic cancellation, and the formation of newly moving fibrils were identified. Combining these observational features, it can be inferred that these two precursor jet-like activities released the magnetic field constraining the filament and were triggered by newly emerging magnetic flux. Before the filament eruption, it was observed that some moving flows had been ejected from the site as the onset of two jet-like activities, indicating the same physical process as two jet-like activities. Extrapolations revealed that the filament laid under the height of the decay index of 1.0 and had strong magnetic field (540 Gauss) and a high twisted number (2.4 turns) before the eruption. An apparent rotational motion was observed during the filament eruption. We deduce that the solar filament, exhibiting an inverted U-shape, is a significantly twisted flux rope. The eruption of the filament was initiated by the release of constraining magnetic fields through continuous magnetic reconnection. This reconnection process was triggered by the emergence of newly magnetic flux.

astro-ph.SR↗

arXiv2023

An Interactive Polymer Building Toolkit for Molecular Dynamics Simulations: PolyMAPS

PolyMAPS is an open-source library that helps researchers to initialize LAMMPS molecular dynamics simulations. It introduces an integrated workflow by combining preparation, launching, visualization, and analysis into a single Jupyter notebook. PolyMAPS enables users to build small or polymeric molecules in a user-friendly interactive 3D plotting system that supports reading and writing systems in LAMMPS data file format. Hence, PolyMAPS demonstrates the potential of reducing the learning difficulties of new users of the LAMMPS software.

physics.chem-ph↗

arXiv2023

Magnetic Reconnection as the Key Mechanism in Sunspot Rotation Leading to Solar Eruption

The rotation of sunspots around their umbral center has long been considered as an important process in leading to solar eruptions, but the underlying mechanism remains unclear. A prevailing physical picture on how sunspot rotation leads to eruption is that, by twisting the coronal magnetic field lines from their footpoints, the rotation can build up a magnetic flux rope and drive it into some kinds of ideal magnetohydrodynamics (MHD) instabilities which initiate eruptions. Here with a data-inspired MHD simulation we studied the rotation of a large sunspot in solar active region NOAA 12158 leading to a major eruption, and found that it is distinct from prevailing theories based on ideal instabilities of twisted flux rope. The simulation suggests that, through successive rotation of the sunspot, the coronal magnetic field is sheared with a central current sheet created progressively within the sheared arcade before the eruption, but without forming a flux rope. Then the eruption is instantly triggered once fast reconnection sets in at the current sheet, while a highly twisted flux rope is created during the eruption. Furthermore, the simulation reveals an intermediate evolution stage between the quasi-static energy-storage phase and the impulsive eruption-acceleration phase. This stage may correspond to the slow-rise phase in observation and it enhances building up of the current sheet.

astro-ph.SR↗

arXiv2023

Data-driven MHD simulation of a sunspot rotating active region leading to solar eruption

Solar eruptions are the leading driver of space weather, and it is vital for space weather forecast to understand in what conditions the solar eruptions can be produced and how they are initiated. The rotation of sunspots around their umbral center has long been considered as an important condition in causing solar eruptions. To unveil the underlying mechanisms, here we carried out a data-driven magnetohydrodynamics simulation for the event of a large sunspot with rotation for days in solar active region NOAA 12158 leading to a major eruption. The photospheric velocity as recovered from the time sequence of vector magnetograms are inputted directly at the bottom boundary of the numerical model as the driving flow. Our simulation successfully follows the long-term quasi-static evolution of the active region until the fast eruption, with magnetic field structure consistent with the observed coronal emission and onset time of simulated eruption matches rather well with the observations. Analysis of the process suggests that through the successive rotation of the sunspot the coronal magnetic field is sheared with a vertical current sheet created progressively, and once fast reconnection sets in at the current sheet, the eruption is instantly triggered, with a highly twisted flux rope originating from the eruption. This data-driven simulation stresses magnetic reconnection as the key mechanism in sunspot rotation leading to eruption.

astro-ph.SR↗

arXiv2022

Solar Ring Mission: Building a Panorama of the Sun and Inner-heliosphere

Solar Ring (SOR) is a proposed space science mission to monitor and study the Sun and inner heliosphere from a full 360° perspective in the ecliptic plane. It will deploy three 120°-separated spacecraft on the 1-AU orbit. The first spacecraft, S1, locates 30° upstream of the Earth, the second, S2, 90° downstream, and the third, S3, completes the configuration. This design with necessary science instruments, e.g., the Doppler-velocity and vector magnetic field imager, wide-angle coronagraph, and in-situ instruments, will allow us to establish many unprecedented capabilities: (1) provide simultaneous Doppler-velocity observations of the whole solar surface to understand the deep interior, (2) provide vector magnetograms of the whole photosphere - the inner boundary of the solar atmosphere and heliosphere, (3) provide the information of the whole lifetime evolution of solar featured structures, and (4) provide the whole view of solar transients and space weather in the inner heliosphere. With these capabilities, Solar Ring mission aims to address outstanding questions about the origin of solar cycle, the origin of solar eruptions and the origin of extreme space weather events. The successful accomplishment of the mission will construct a panorama of the Sun and inner-heliosphere, and therefore advance our understanding of the star and the space environment that holds our life.

astro-ph.SR↗

arXiv2022

Robust Newsvendor Problem in Global Market: Stable Operation Strategy for a Two-Market Stochastic System

The global markets provide enterprises with selling opportunities and challenges in stabilizing operational strategies. From the perspective of production management, it is important to improve the profitability of an enterprise by exploiting the different timing of the selling season in different markets to develop an operational strategy that is optimized and configured on a global scale. This paper examines the above issue with an insightful model of selling the product to two markets (a primary and a secondary market) with multiple risks of changes in the market environment and nonoverlapping selling seasons. We refer to this problem as the "global robust newsvendor" problem. We provide closed-form solutions of the optimal operation strategy for demand-independent and demand-related scenarios for the above two market stochastic systems. The closed-form solutions fully reflect the influence of the relationship between supply and demand on strategy selection. We find that the demand correlation and the lack of demand information will not substantially affect the operation strategy, and the enterprise's industrial chain and supply chain remain stable. However, the reduction of inter-market tariffs or logistics costs will cause changes, and the existence of the secondary market will lead to more capacity planning in the primary market. In addition, our model explicitly considers the impact of exchange rate uncertainty on operating strategies.

cs.LG↗

arXiv2022

A formation mechanism for the large plumes in the prominence

To understand the formation mechanism of large plumes in solar prominences, we investigate the formation process of two such phenomena. We studied the dynamic and thermal properties of two large plumes using observations from New Vacuum Solar Telescope, the Solar Dynamic Observatory, and the Solar Terrestrial Relations Observatory-Ahead. We find that two large plumes observed with high-resolution data are quite different from previously studied small-scale plumes. They are born at the top of a prominence bubble with a large projected area of 10-20 Mm^2 . Before the occurrence of each large plume, the bubble expands and takes on a quasi-semicircular appearance. Meanwhile, the emission intensity of extreme-ultra-violet (EUV) bands increases in the bubble. A small-scale filament is found to erupt in the bubble during the second large plume. At the point at which the height of the bubble is comparable with half the width of the bubble, the bubble becomes unstable and generates the plumes. During the formation of plumes, two side edges of the top of the bubble, which are dominated by opposite Doppler signals, approach each other. The large plume then emerges and keeps rising up with a constant speed of about 13-15 km/s. These two large plumes have temperatures of 1.3 x 10^6 Kelvin and densities of 2.0 x 10^9 cm^-3, two orders hotter and one order less dense than the typical prominence. We also find that the bubble is a hot, low-density volume instead of a void region beneath the cold and dense prominence. Therefore, we conclude that these two large plumes are the result of the breakup of the prominence bubble triggered by an enhancement of thermal pressure; they separate from the bubble, most likely by magnetic reconnection.

astro-ph.SR↗

arXiv2021

Naked emergence of an anti-Hale active region I. Overall evolution and magnetic properties

{In order to understand the emergence of the active region, we investigate the emerging process and magnetic properties of a naked anti-Hale active region during the period between August 24 to 25, 2018.} {Using the data from Helioseismic and Magnetic Imager on board the Soar Dynamic Observatory and the New Vacuum Solar Telescope, we calculated different evolving parameters (such as pole separation, tilt angle) and magnetic parameters (such as vertical electric current, force-free parameter, relative magnetic helicity) during the emergence of the active region. With these calculated parameters and some reasonable assumptions, we use two different methods to estimate the twist of the active region.} {The magnetic flux and pole separation continue increasing while the tilt angle exhibits a decreasing pattern during the emergence of the active region. The increase of the pole separation is mainly contributed as a result of the enhancement in the longitude direction. A power-law relationship between pole separation and total flux is found during the emergence of the active region. On the other hand, it is found that both the positive and negative electric currents increased equivalently and the average flux-weighted force-free parameter $\tilde α$ remains almost consistently positive, on the order of $\sim$ 10$^{-8}$ m$^{-1}$. The relative magnetic helicity is mainly contributed by the shear term, while the relative magnetic helicity injection flux of the shear term changes its sign at the latter stage of the emergence. The twist number of the whole active region remains on the order of 10$^{-1}$ turns during the emergence of the active region.} {We find that the magnetic flux tube with low twist also could emerge into the solar atmosphere.}

astro-ph.SR↗