arXiv subjects

Y. Qiu

Publications and source records attributed to Y. Qiu.

At least 19 recordsLinked to original sources

arXiv2026

Early results from the SVOM Observatory Science program

We present the organisation and early results from the Observatory Science program of the Space-based multi-band astronomical Variable Objects Monitor (SVOM), based on data collected between July 2024 and December 2025. Although primarily designed for gamma-ray burst studies, SVOM's wide-field, multi-wavelength instruments enable a broad range of high-energy astrophysical investigations. We summarize the execution and performance of the General Program and Target-of-Opportunity observations, and we describe the frameworks used for serendipitous source detection and monitoring with the ECLAIRs coded-mask instrument. Over this period, SVOM carried out more than a thousand pointed observations and detected several hundred non-GRB high-energy sources, mainly X-ray binaries, as well as blazars, stellar flares, magnetars, and unidentified events. We highlight some key results, including the monitoring of the microquasar Cygnus X-1, the detection of burst oscillations from the Low-Mass X-ray Binary 4U 0614+091, the spectral-state monitoring of Aql X-1, the first SVOM detection of an X-ray blazar flare from 1ES 1959+650, and observations of a stellar flare from HD 22468. These results demonstrate SVOM's strong capabilities for time-domain astrophysics beyond its core GRB program.

astro-ph.HE↗

arXiv2026

Inversion of CHASE H$\alpha$ Spectral Line during Solar Flares Based on RADYN Dataset via Deep Learning

Solar flares represent one of the most intense forms of solar activity. Understanding the evolution of physical parameters in the solar atmosphere during flares is key to studying flare mechanisms and improving prediction capabilities. However, directly measuring quantities such as electron number density, temperature, and plasma velocity remains difficult. Here, we introduce a novel fully connected neural network, trained on synthetic data from the Radiative Hydrodynamics Code (RADYN) simulations, to perform rapid inversion of physical parameters from H$\alpha$ spectral profiles. The spectral data were processed to align with the observational resolution of the CHASE satellite, enabling seamless application of the model to real-world observations. Results demonstrate a high degree of consistency with RADYN simulations, achieving low errors under diverse flare conditions. Furthermore, we applied the developed model to analyze CHASE observations of a class X7.1 solar flare on October 1, 2024. The results reveal reasonable spatial and temporal evolution of key parameters throughout different flare phases. This work demonstrates the potential of deep learning techniques for fast and reliable spectral inversion, providing new tools for solar flare diagnostics based on H$\alpha$ data.

astro-ph.SR↗

arXiv2025

An nl-model with a full radiative transfer treatment for level populations of hydrogen atoms in a spherically symmetric H II region

Context. The radiation field consisting of hydrogen recombination lines and continuum emission might significantly affect the hydrogen-level populations in ultra- and hypercompact (U/HC) H II regions. The escape probability approximation was used to estimate the effect of the radiation field in previous models for calculating hydrogen-level populations. The reliability of this approximation has not been systematically studied, however. Aims. We investigate the appropriate ranges of previous models with the escape probability approximation and without the effects of the radiation field. We create a new model for simulating the integrated characteristics and the spatially resolved diagnostics of the hydrogen recombination lines throughout H II regions. Methods. We developed a new nl model with a full radiative transfer treatment of the radiation field causd by hydrogen recombination lines and continuum emission to calculate the hydrogen-level populations and hydrogen recombination lines. We then compared the level populations and the corresponding hydrogen recombination line intensities simulated by the new model and previous models. Results. We studied the applicability and the valid parameter ranges of previous models. Radiation fields exhibit negligible effects on the level populations in classical and UC H II regions. With the modified escape probability, the model with the escape probability approximation is suitable for most HC H II regions. The improved new model performs better in the HC H II region with an extremely high emission measure. To address the high computational costs inherent in numerical models, we trained a precise machine-learning model to enable a rapid estimation of hydrogen-level populations and the associated hydrogen recombination lines.

astro-ph.GA↗

arXiv2025

GRB 241105A: A test case for GRB classification and rapid r-process nucleosynthesis channels

Gamma-ray bursts (GRBs) offer a powerful window to probe the progenitor systems responsible for the formation of heavy elements through the rapid neutron capture (r-) process, thanks to their exceptional luminosity, which allows them to be observed across vast cosmic distances. GRB 241105A, observed at a redshift of z = 2.681, features a short initial spike (1.5 s) and a prolonged weak emission lasting about 64 s, positioning it as a candidate for a compact binary merger and potentially marking it as the most distant merger-driven GRB observed to date. However, the emerging ambiguity in GRB classification necessitates further investigation into the burst's true nature. Prompt emission analyses, such as hardness ratio, spectral lag, and minimum variability timescales, yield mixed classifications, while machine learning-based clustering places GRB 241105A near both long-duration mergers and collapsar GRBs. We conducted observations using the James Webb Space Telescope (JWST) to search for a potential supernova counterpart. Although no conclusive evidence was found for a supernova, the host galaxy's properties derived from the JWST observations suggest active star formation with low metallicity, and a sub-kpc offset of the afterglow from the host, which appears broadly consistent with a collapsar origin. Nevertheless, a compact binary merger origin cannot be ruled out, as the burst may plausibly arise from a fast progenitor channel. This would have important implications for heavy element enrichment in the early Universe.

astro-ph.HE↗

arXiv2025

Large-amplitude Oscillations of a Quiescent Filament Excited by an Extreme-ultravioletWave

In this paper, we carry out multiwavelength observations of simultaneous longitudinal and transverse oscillations of a quiescent filament excited by an extreme-ultraviolet (EUV) wave on 2023 February 17. A hot channel eruption generates an X2.3 class flare and a fast coronal mass ejection (CME) in active region (AR) NOAA 13229 close to the eastern limb. The CME drives an EUV wave, which propagates westward at a speed of ~459 km s-1. After arriving at the filament ~340.3 Mm away from the flare site, the filament is disturbed and starts large-amplitude oscillations, which are mainly observed in 171 {\AA}.The longitudinal oscillations last for nearly two cycles. The average initial amplitude, velocity, period, and damping time are ~4.7 Mm, ~26.5 km s-1, ~1099.1 s, and ~2760.3 s, respectively. According to the pendulum model, the curvature radius and minimum horizontal magnetic field strength of the dips are estimated to be 6.7-9.9 Mm and 4.6-5.6 G. The transverse oscillations last for 2-3 cycles. The average initial amplitude, velocity, period, and damping time are ~1.8 Mm, ~11.2 km s-1, ~994.4 s, and ~3576.2 s, respectively. The radial magnetic field strength of the dips are estimated to be 6.6-7.4 G.

astro-ph.SR↗

arXiv2024

Two successive EUV waves and a transverse oscillation of a quiescent prominence

In this paper, we carry out multiwavelength observations of two successive extreme-ultraviolet (EUV) waves originating from active region (AR) NOAA 13575 and a transverse oscillation of a columnar quiescent prominence on 2024 February 9. A hot channel eruption generates an X3.4 class flare and the associated full-halo coronal mass ejection (CME), which drives the first EUV wave front (WF1) at a speed of $\sim$835 km s$^{-1}$. WF1 propagates in the southeast direction and interacts with the prominence, causing an eastward displacement of the prominence immediately. Then, a second EUV wave front (WF2) is driven by a coronal jet at a speed of $\sim$831 km s$^{-1}$. WF2 follows WF1 and decelerates from $\sim$788 km s$^{-1}$ to $\sim$603 km s$^{-1}$ before arriving at and touching the prominence. After reaching the maximum displacement, the prominence turns back and swings for 1$-$3 cycles. The transverse oscillation of horizontal polarization is most evident in 304 {\AA}. The initial displacement amplitude, velocity in the plane of the sky, period, and damping time fall in the ranges of 12$-$34 Mm, 65$-$143 km s$^{-1}$, 18$-$27 minutes, and 33$-$108 minutes, respectively. There are strong correlations among the initial amplitude, velocity, period, and height of the prominence. Surprisingly, the oscillation is also detected in 1600 {\AA}, which is totally in phase with that in 304 {\AA}.

astro-ph.SR↗

arXiv2024

Current progress in corrosion of multi principal element alloys

Whilst multi-principal element alloys (MPEAs) remain a promising class of materials owing to several attractive mechanical properties, their corrosion performance is also unique. In this concise review, we present an emerging overview of some of the general features related to MPEA corrosion, following a decade of work in the field. This includes highlighting some of the key aspects related to the electrochemical phenomena in MPEA corrosion, and the relevant future works required for a holistic mechanistic understanding. In addition, a comprehensive database of the reported corrosion performance of MPEAs is presented, based on works reported to date. The database is assembled to also allow users to undertake machine learning or their own data analysis, with a parsed representation of alloy composition, test electrolyte, and corrosion related parameters.

cond-mat.mtrl-sci↗

arXiv2024

Developing an Automated Detection, Tracking and Analysis Method for Solar Filaments Observed by CHASE via Machine Learning

Studies on the dynamics of solar filaments have significant implications for understanding their formation, evolution, and eruption, which are of great importance for space weather warning and forecasting. The H$\alpha$ Imaging Spectrograph (HIS) onboard the recently launched Chinese H$\alpha$ Solar Explorer (CHASE) can provide full-disk solar H$\alpha$ spectroscopic observations, which bring us an opportunity to systematically explore and analyze the plasma dynamics of filaments. The dramatically increased observation data require automate processing and analysis which are impossible if dealt with manually. In this paper, we utilize the U-Net model to identify filaments and implement the Channel and Spatial Reliability Tracking (CSRT) algorithm for automated filament tracking. In addition, we use the cloud model to invert the line-of-sight velocity of filaments and employ the graph theory algorithm to extract the filament spine, which can advance our understanding of the dynamics of filaments. The favorable test performance confirms the validity of our method, which will be implemented in the following statistical analyses of filament features and dynamics of CHASE/HIS observations.

astro-ph.SR↗

arXiv2024

Can Channels be Fully Inferred Between Two Antenna Panels?

This letter considers a two-panel massive multiple-input multiple-output (MIMO) communication system, where the base station (BS) is equipped with two antenna panels that may use different frequency bands for communication. By exploiting the geometric relationships between antenna panels, efficient channel inference methods across antenna panels are proposed to reduce the overhead of real-time channel estimation. Four scenarios are considered, namely far-field free-space, near-field free-space, multi-path sharing far-field scatterers, and multi-path sharing near-field scatterers. For both far-field and near-field free-space scenarios, we show that the channel of one panel can be fully inferred from that of the other panel, as long as the multi-path components (MPCs) composing the channel can be resolved. On the other hand, for the multi-path scenarios sharing far-field or near-field scatterers, only the angles or range of angles of the MPCs can be inferred, respectively. Simulation results based on commercial 3D ray-tracing software are presented to validate our developed channel inference techniques.

cs.IT↗

arXiv2023

FENDL: A library for fusion research and applications

The Fusion Evaluated Nuclear Data Library (FENDL) is a comprehensive and validated collection of nuclear cross section data coordinated by the International Atomic Energy Agency (IAEA) Nuclear Data Section (NDS). FENDL assembles the best nuclear data for fusion applications selected from available nuclear data libraries and has been under development for decades. FENDL contains sub-libraries for incident neutron, proton, and deuteron cross sections including general purpose and activation files used for particle transport and nuclide inventory calculations. We describe the history, selection of evaluations for the various sub-libraries (neutron, proton, deuteron) with the focus on transport and reactor dosimetry applications, the processing of the nuclear data for application codes, and the development of the TENDL-2017 library which is the currently recommended activation library for FENDL. We briefly describe the IAEA IRDFF library as the recommended library for dosimetry fusion applications. We also present work on validation of the neutron sub-library using a variety of fusion relevant computational and experimental benchmarks. A variety of cross section libraries are used for the validation work including FENDL-2.1, FENDL-3.1d, FENDL-3.2, ENDF/B-VIII.0, and JEFF-3.2 with the emphasis on the FENDL libraries. The results of the experimental validation showed that the performance of FENDL-3.2b is at least as good and in most cases better than FENDL-2.1. Future work will consider improved evaluations developed by the International Nuclear Data Evaluation Network (INDEN). Additional work will be needed to investigate differences in gas production in structural materials. Covariance matrices need to be updated to support the development of fusion technology. Additional validation work for high-energy neutrons, protons and deuterons, and the activation library will be needed.

nucl-th↗

arXiv2023

The evolution of galaxies and clusters at high spatial resolution with AXIS

Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks and producing a dynamic interstellar medium. On large scales bordering the cosmic web, feedback drives enriched gas out of galaxies and groups, seeding the intergalactic medium with heavy elements. In this way, feedback shapes galaxy evolution by shutting down star formation and ultimately curtailing the growth of structure after the peak at redshift 2-3. To understand the complex interplay between gravity and feedback, we must resolve both the key physics within galaxies and map the impact of these processes over large scales, out into the cosmic web. The Advanced X-ray Imaging Satellite (AXIS) is a proposed X-ray probe mission for the 2030s with arcsecond spatial resolution, large effective area, and low background. AXIS will untangle the interactions of winds, radiation, jets, and supernovae with the surrounding ISM across the wide range of mass scales and large volumes driving galaxy evolution and trace the establishment of feedback back to the main event at cosmic noon.

astro-ph.IM↗

arXiv2022

Monte-Carlo simulations for wall-bounded fluid flows via random vortex method

In this paper a Monte-Carlo method for simulating the motion of fluid flow moving along a solid wall is proposed. The random vortex method in the present paper is established by using the reflection technology and perturbation technique. The Monte-Carlo method based on this random vortex dynamic may be implemented, and several Monte-Carlo simulations are then carried out for the flows near the solid wall.

physics.flu-dyn↗

arXiv2022

cardiGAN: A Generative Adversarial Network Model for Design and Discovery of Multi Principal Element Alloys

Multi-principal element alloys (MPEAs), inclusive of high entropy alloys (HEAs), continue to attract significant research attention owing to their potentially desirable properties. Although MPEAs remain under extensive research, traditional (i.e. empirical) alloy production and testing is both costly and time-consuming, partly due to the inefficiency of the early discovery process which involves experiments on a large number of alloy compositions. It is intuitive to apply machine learning in the discovery of this novel class of materials, of which only a small number of potential alloys has been probed to date. In this work, a proof-of-concept is proposed, combining generative adversarial networks (GANs) with discriminative neural networks (NNs), to accelerate the exploration of novel MPEAs. By applying the GAN model herein, it was possible to directly generate novel compositions for MPEAs, and to predict their phases. To verify the predictability of the model, alloys designed by the model are presented and a candidate produced; as validation. This suggests that the model herein offers an approach that can significantly enhance the capacity and efficiency of development of novel MPEAs.

cond-mat.mtrl-sci↗

arXiv2022

Spin dynamics in the skyrmion-host lacunar spinel GaV4S8

In the lacunar spinel GaV4S8, the interplay of spin, charge, and orbital degrees of freedom produces a rich phase diagram that includes an unusual Neel-type skyrmion phase composed of molecular spins. To provide insight into the interactions underlying this complex phase diagram, we study the spin excitations in GaV4S8 through inelastic neutron scattering measurements on polycrystalline and single-crystal samples. Using linear spin-wave theory, we describe the spin-wave excitations using a model where V4 clusters decorate an FCC lattice. The effective cluster model includes a ferromagnetic interaction and a weaker antisymmetric Dzyaloshinskii-Moriya (DM) interaction between the neighboring molecular spins. Our work clarifies the spin interactions in GaV4S8 and supports the picture of interacting molecular clusters.

cond-mat.str-el↗

arXiv2021

Shapes, Softness and Non-Yrast Collectivity in 186W

Non-yrast, excited states in neutron-rich $^{186}$W were populated via inelastic-scattering reactions using beams of $^{136}$Xe nuclei accelerated to 725 and 800 MeV. Levels populated in the reactions were investigated via particle-$ γ$ coincidence techniques using the Gammasphere array of High-Purity Germanium detectors and the compact heavy-ion counter, CHICO2. The $ K^π = 2 ^{+} $ ($γ$), $ K^π = 0^{+}$ and $ K^π = 2^{-} $ (octupole) rotational side bands were extended to spins $ 14\hbar $, $ 12\hbar $, and $ 13\hbar $, respectively. A staggering pattern observed in the energies of levels in the $ K^π = 2^{+} $ band was found to be consistent with a potential that gets softer to vibration in the $ γ$ degree of freedom with increasing spin. The odd-even staggering of states in the $ K^π = 2^{-}$ band was found to exhibit a phase opposite to that seen in the $ γ$ band; an effect most probably associated with Coriolis coupling to other, unobserved octupole vibrational bands in $^{186}$W.

nucl-ex↗

arXiv2021

Non-magnetic ion site disorder effects on the quantum magnetism of a spin-1/2 equilateral triangular lattice antiferromagnet

With the motivation to study how non-magnetic ion site disorder affects the quantum magnetism of Ba3CoSb2O9, a spin-1/2 equilateral triangular lattice antiferromagnet, we performed DC and AC susceptibility, specific heat, elastic and inelastic neutron scattering measurements on single crystalline samples of Ba2.87Sr0.13CoSb2O9 with Sr doping on non-magnetic Ba2+ ion sites. The results show that Ba2.87Sr0.13CoSb2O9 exhibits (i) a two-step magnetic transition at 2.7 K and 3.3 K, respectively; (ii) a possible canted 120-degree spin structure at zero field with reduced ordered moment as 1.24{\mu}B/Co; (iii) a series of spin state transitions for both H // ab-plane and H // c-axis. For H // ab-plane, the magnetization plateau feature related to the up-up-down phase is significantly suppressed; (iv) an inelastic neutron scattering spectrum with only one gapped mode at zero field, which splits to one gapless and one gapped mode at 9 T. All these features are distinctly different from those observed for the parent compound Ba3CoSb2O9, which demonstrates that the non-magnetic ion site disorder (the Sr doping) plays a complex role on the magnetic properties beyond the conventionally expected randomization of the exchange interactions. We propose the additional effects including the enhancement of quantum spin fluctuations and introduction of a possible spatial anisotropy through the local structural distortions.

cond-mat.str-el↗

arXiv2021

Pristine quantum criticality in a Kondo semimetal

The observation of quantum criticality in diverse classes of strongly correlated electron systems has been instrumental in establishing ordering principles, discovering new phases, and identifying the relevant degrees of freedom and interactions. At focus so far have been insulators and metals. Semimetals, which are of great current interest as candidate phases with nontrivial topology, are much less explored in experiments. Here we study the Kondo semimetal CeRu$_4$Sn$_6$ by magnetic susceptibility, specific heat, and inelastic neutron scattering experiments. The power-law divergence of the magnetic Grünesien ratio reveals that, surprisingly, this compound is quantum critical without tuning. The dynamical energy over temperature scaling in the neutron response, seen throughout the Brillouin zone, as well as the temperature dependence of the static uniform susceptibility indicate that temperature is the only energy scale in the criticality. Such behavior, which has been associated with Kondo destruction quantum criticality in metallic systems, may well be generic in the semimetal setting.

cond-mat.str-el↗

arXiv2021

Inelastic neutron scattering determination of the spin Hamiltonian for BaCdVO(PO$_4$)$_2$

Single crystal inelastic neutron scattering is used to study spin wave excitations in the fully polarized state of the frustrated quantum ferro-antiferromagnet BaCdVO(PO$_4$)$_2$. The data analysis is based on a Heisenberg spin Hamiltonian that includes as many distinct nearest-neighbor and next-nearest neighbor interactions as allowed by crystal symmetry. All 8 such exchange constants are obtained in a simultaneous fit to over 150 scans across the dispersion manifold. This establishes a definitive quantitative model of this material. It turns out to be substantially different from the one assumed in numerous previous studies based on powder experiments.

cond-mat.str-el↗