arXiv subjects

Yue Xiang

Publications and source records attributed to Yue Xiang.

16 recordsLinked to original sources

arXiv2026

Strain-controlled sign reversal of the anomalous Hall effect in Ru/[Co/Ni]$_N$ multilayers

The anomalous Hall effect (AHE) is a hallmark transport phenomenon in ferromagnets arising from relativistic spin-orbit interaction. Here, we report an unexpected sign reversal of the AHE in Ru/[Co/Ni]$_N$ multilayers controlled by the stacking sequence of the Ru layer. When Ru is placed beneath, rather than atop, the Co/Ni multilayers, the anomalous Hall signal switches from positive to negative. By systematically varying the multilayer repeat number N and combining transport measurements with first-principles calculations, we show that this reversal originates from in-plane tensile strain imposed by the Ru underlayer, which reshapes the electronic structure and redistributes Berry curvature near the Fermi level. Our findings establish interfacial strain as an effective knob for tuning Berry-curvature-driven transport and suggest a pathway toward strain-controlled topological transport phenomena in magnetic multilayers.

cond-mat.mtrl-sci↗

arXiv2026

Starspot activity and surface differential rotation on UX Arietis

We present new Doppler images of the K0 subgiant primary component of the RS CVn-type binary UX Arietis (UX Ari), derived from time-series spectra obtained in November--December of 2017 and 2024. Observations demonstrate that some spectral lines of the K0 IV component exhibit rapid changes on timescales of 1-2 hours, which seem not to be resulting from spot activity, meanwhile other spectral lines show no such fast variations. Through an investigation, we find that the Ca I 6439 $\unicode{x212B}$ profile shows variation that follows the rotational modulation of spots. Using this line as a reference, we derive the least-squares deconvolution (LSD) profile from the selected lines of each spectrum so as to generate a more reliable Doppler image, which is consistent with the shape of the corresponding Ca I 6439 $\unicode{x212B}$ line. The Doppler images are separately reconstructed from the Ca I 6439 $\unicode{x212B}$ and the LSD profiles for each dataset, and the surface maps are in good agreement with each other. All of the surface maps show dominant starspot structure at mid-to-high latitudes with appendages extending to the equator, while their locations differ by about 0.5 in the rotational phase between 2017 and 2024. In 2017 November-December, the main starspot group appears to be spatially associated with a large flare event just half a month later. Through the cross-correlation method, we have derived a weak anti-solar differential rotation for the primary component of UX Ari, while its equator belt is well tidally locked.

astro-ph.SR↗

arXiv2025

Magnetic activity of ultracool dwarfs in the LAMOST DR11

Ultracool dwarfs consist of lowest-mass stars and brown dwarfs. Their interior is fully convective, different from that of the partly-convective Sun-like stars. Magnetic field generation process beneath the surface of ultracool dwarfs is still poorly understood and controversial. To increase samples of active ultracool dwarfs significantly, we have identified 962 ultracool dwarfs in the latest LAMOST data release, DR11. We also simulate the Chinese Space Station Survey Telescope (CSST) low-resolution slitless spectra by degrading the LAMOST spectra. A semi-supervised machine learning approach with an autoencoder model is built to identify ultracool dwarfs with the simulated CSST spectra, which demonstrates the capability of the CSST all-sky slitless spectroscopic survey on the detection of ultracool dwarfs. Magnetic activity of the ultracool dwarfs is investigated by using the H$\alpha$ line emission as a proxy. The rotational periods of 82 ultracool dwarfs are derived based on the Kepler/K2 light curves. We also derive the activity-rotation relation of the ultracool dwarfs, which is saturated around a Rossby number of 0.12.

astro-ph.SR↗

arXiv2024

Further study of starspot activity and measurement of differential rotation for SZ Piscium

We present a series of 9 Doppler images of the magnetically active K component of the RS CVn-type binary SZ Psc, based on the high-resolution spectroscopic data collected from 2014 to 2018. We apply least-squares deconvolution to all spectra to extract the average profiles with high signal-to-noise ratios (SNRs) for Doppler imaging. The surface maps of the K subgiant show starspots widely distributed along latitude and longitude. A prominent, non-axisymmetric polar spot around phase 0 is revealed by all images with sufficient phase coverage, which may be a stable feature on the K component. The starspots evolve in a time scale of one month. We have determined the surface shear rate of the K component from the starspot maps reconstructed 10 days apart in 2017 Nov--Dec, through the cross-correlation method. The surface differential rotation parameters are $Ω_{eq} = 1.591 \pm 0.002$ rad d$^{-1}$ and $ΔΩ= 0.035 \pm 0.003$ rad d$^{-1}$. The absorption lines contributed from the tertiary component are detected in all LSD profiles of SZ Psc, and we measure the radial velocity of the binary system and the tertiary component to derive an elliptical orbit with a period of $1530 \pm 3$ days and a mass of $0.75 \pm 0.06$ M$\odot$ for the tertiary component.

astro-ph.SR↗

arXiv2024

A method of photometric data extraction for asteroids from time-domain surveys

The lightcurves of asteroids are essential for determining their physical characteristics, including shape, spin, size, and surface composition. However, most asteroids are missing some of these basic physical parameters due to lack of photometric data. Although a few telescopes or surveys are specially designed for photometric lightcurve observations of asteroids, many ground-based and space-based sky surveys for hunting new exoplanets, transient events, etc., should capture numerous small Solar System objects. This will benefit the physical studies of these objects. In order to extract data of these moving objects from time-domain photometric surveys, we have developed a new method using the model tree algorithm in the field of machine learning. A dedicated module is built to automatically identify moving objects in dataset, and extract their photometric and astrometric data. As the first application of this novel method, we have analyzed data in five fields of the Yunnan-Hong Kong wide field photometric (YNHK) survey, from which 538 lightcurves of 211 asteroids are successfully extracted. Meanwhile, we also tested the method based on the data from NASA's Transiting Exoplanet Survey Satellite, and the result proves the reliability of our method. With derived lightcurves of 13 asteroids from the YNHK survey, we have determined their synodic spin periods, among which the periods of 4 asteroids are estimated for the first time. In future, we are going to apply this method to search for small objects in the outer part of the Solar System from the Chinese Space Station Telescope survey.

astro-ph.EP↗

arXiv2024

Stellar cycle and evolution of polar spots in an M+WD binary

Stellar activity cycles reveal continuous relaxation and induction of magnetic fields. The activity cycle is typically traced through the observation of cyclic variations in total brightness or Ca H&K emission flux of stars, as well as cyclic variations of orbital periods of binary systems. In this work, we report the identification of a semi-detached binary system (TIC 16320250) consisting of a white dwarf (0.67 $M_{\odot}$) and an active M dwarf (0.56 $M_{\odot}$). The long-term multi-band optical light curves spanning twenty years revealed three repeated patterns, suggestive of a possible activity cycle of about ten years of the M dwarf. Light curve fitting indicates the repeated variation is caused by the evolution, particularly the motion, of polar spots. The significant Ca H&K, H$α$, ultra-violet, and X-ray emissions imply that the M dwarf is one of the most magnetically active stars. We propose that in the era of large time-domain photometric sky surveys (e.g., ASAS-SN, ZTF, LSST, Sitian), long-term light curve modeling can be a valuable tool for tracing and revealing stellar activity cycle, especially for stars in binary systems.

astro-ph.SR↗

arXiv2023

First Chromospheric Activity and Doppler Imaging Study of PW And Using a New Doppler Imaging Code: SpotDIPy

Measuring coverage of dark spots on cool stars is important in understanding how stellar magnetic activity scales with the rotation rate and convection zone depth. In this respect, it is crucial to infer surface magnetic patterns on G and K stars, to reveal solar-like stellar dynamos in action. Molecular bands serve as invaluable indicators of cool spots on the surfaces of stars, as they play a crucial role in enabling accurate assessments of the extent of spot coverage across the stellar surface. Therefore, more reliable surface images can be obtained considering the inversion of atomic lines with molecular bands. In this context, we simultaneously carry out Doppler imaging (DI) using atomic lines as well as Titanium Oxide (TiO) band profiles of PW And (K2 V) and also investigate chromospheric activity indicators for the first time in the literature, using the high-resolution spectra. The surface spot distribution obtained from the inversion process represents both atomic line and TiO-band profiles quite accurately. The chromospheric emission is also correlated with photospheric spot coverage, except during a possible flare event during the observations. We detect frequent flare activity, using TESS photometry. We also introduce a new open-source, Python-based DI code SpotDIPy that allows performing surface reconstructions of single stars using the maximum entropy method. We test the code by comparing surface reconstruction simulations with the extensively used DoTS code. We show that the surface brightness distribution maps reconstructed via both codes using the same simulated data are consistent with each other.

astro-ph.SR↗

arXiv2023

LLM-based Frameworks for Power Engineering from Routine to Novel Tasks

The digitalization of energy sectors has expanded the coding responsibilities for power engineers and researchers. This research article explores the potential of leveraging Large Language Models (LLMs) to alleviate this burden. Here, we propose LLM-based frameworks for different programming tasks in power systems. For well-defined and routine tasks like the classic unit commitment (UC) problem, we deploy an end-to-end framework to systematically assesses four leading LLMs-ChatGPT 3.5, ChatGPT 4.0, Claude and Google Bard in terms of success rate, consistency, and robustness. For complex tasks with limited prior knowledge, we propose a human-in-the-loop framework to enable engineers and LLMs to collaboratively solve the problem through interactive-learning of method recommendation, problem de-composition, subtask programming and synthesis. Through a comparative study between two frameworks, we find that human-in-the-loop features like web access, problem decomposition with field knowledge and human-assisted code synthesis are essential as LLMs currently still fall short in acquiring cutting-edge and domain-specific knowledge to complete a holistic problem-solving project.

cs.HC↗

arXiv2023

Cerberus: A Deep Learning Hybrid Model for Lithium-Ion Battery Aging Estimation and Prediction Based on Relaxation Voltage Curves

The degradation process of lithium-ion batteries is intricately linked to their entire lifecycle as power sources and energy storage devices, encompassing aspects such as performance delivery and cycling utilization. Consequently, the accurate and expedient estimation or prediction of the aging state of lithium-ion batteries has garnered extensive attention. Nonetheless, prevailing research predominantly concentrates on either aging estimation or prediction, neglecting the dynamic fusion of both facets. This paper proposes a hybrid model for capacity aging estimation and prediction based on deep learning, wherein salient features highly pertinent to aging are extracted from charge and discharge relaxation processes. By amalgamating historical capacity decay data, the model dynamically furnishes estimations of the present capacity and forecasts of future capacity for lithium-ion batteries. Our approach is validated against a novel dataset involving charge and discharge cycles at varying rates. Specifically, under a charging condition of 0.25C, a mean absolute percentage error (MAPE) of 0.29% is achieved. This outcome underscores the model's adeptness in harnessing relaxation processes commonly encountered in the real world and synergizing with historical capacity records within battery management systems (BMS), thereby affording estimations and prognostications of capacity decline with heightened precision.

cs.LG↗

arXiv2023

Efficient Informed Proposals for Discrete Distributions via Newton's Series Approximation

Gradients have been exploited in proposal distributions to accelerate the convergence of Markov chain Monte Carlo algorithms on discrete distributions. However, these methods require a natural differentiable extension of the target discrete distribution, which often does not exist or does not provide effective gradient guidance. In this paper, we develop a gradient-like proposal for any discrete distribution without this strong requirement. Built upon a locally-balanced proposal, our method efficiently approximates the discrete likelihood ratio via Newton's series expansion to enable a large and efficient exploration in discrete spaces. We show that our method can also be viewed as a multilinear extension, thus inheriting its desired properties. We prove that our method has a guaranteed convergence rate with or without the Metropolis-Hastings step. Furthermore, our method outperforms a number of popular alternatives in several different experiments, including the facility location problem, extractive text summarization, and image retrieval.

cs.LG↗

arXiv2023

Magnetic topologies of two weak-line T Tauri stars TAP 4 and TAP 40

We present a Zeeman-Doppler imaging study of two weak-line T Tauri stars TAP 4 and TAP 40, based on the high-resolution spectropolarimetric observations with ESPaDOnS at the Canada-France-Hawaii Telescope in November 2013, in the framework of the MaTYSSE large programme. We apply two Zeeman-Doppler imaging codes to the Stokes I and V profiles to reconstruct their brightness and large-scale magnetic field images. The results given by the two imaging codes are in good agreement with each other. TAP 4 shows a large polar cool spot and several intermediate-latitude warm spots on its surface, whereas TAP 40 exhibits very weak variations in its Stokes I profiles suggesting a mostly unspotted photosphere. We detect Zeeman signatures in the Stokes V profiles of both stars. The reconstructed magnetic maps reveal dominantly toroidal fields, which enclose about 60 per cent of the total magnetic energy for both of TAP 4 and TAP 40. Both stars show prominent circular ring features of the azimuthal magnetic field. We derive a solar-like surface differential rotation on TAP 4 from the tomographic modelling. The brightness image of TAP 4 is used to predict the radial velocity jitters induced by its activity. After filtering out the activity jitter, the RMS of its RVs is reduced from 1.7 km s$^{-1}$ to 0.2 km s$^{-1}$, but we do not detect any periodic signals in the filtered RVs of TAP 4, implying that it is unlikely to host a close-in exoplanet more massive than $\sim$3.5 M$_{\rm Jup}$ at 0.1 au.

astro-ph.SR↗

arXiv2022

Investigation of stellar magnetic activity using variational autoencoder based on low-resolution spectroscopic survey

We apply the variational autoencoder (VAE) to the LAMOST-K2 low-resolution spectra to detect the magnetic activity of the stars in the K2 field. After the training on the spectra of the selected inactive stars, the VAE model can efficiently generate the synthetic reference templates needed by the spectral subtraction procedure, without knowing any stellar parameters. Then we detect the peculiar spectral features, such as chromospheric emissions, strong nebular emissions and lithium absorptions, in our sample. We measure the emissions of the chromospheric activity indicators, H$α$ and Ca II infrared triplet (IRT) lines, to quantify the stellar magnetic activity. The excess emissions of H$α$ and Ca II IRT lines of the active stars are correlated well to the rotational periods and the amplitudes of light curves derived from the K2 photometry. We degrade the LAMOST spectra to simulate the slitless spectra of the China Space Station Telescope (CSST) and apply the VAE to the simulated data. For cool active stars, we reveal a good agreement between the equivalent widths (EWs) of H$α$ line derived from the spectra with two resolutions. The result indicates the ability of identifying the magnetically active stars in the future CSST survey, which will deliver an unprecedented large database of low-resolution spectra as well as simultaneous multi-band photometry of stars.

astro-ph.SR↗

arXiv2020

Doppler imaging and differential rotation of $σ^{2}$ Coronae Borealis using SONG

We present new Doppler images of both components of the double-lined binary $σ^{2}$ CrB, based on the high-resolution spectroscopic data collected during 11 nights in 2015 March--April. The observed spectra form two independent data sets with sufficient phase coverage. We apply the least-squares deconvolution to all observed spectra to obtain high signal-to-noise mean profiles, from which we derive the Doppler images of both components of $σ^{2}$ CrB simultaneously. The surfaces of both F9 and G0 components are dominated by pronounced polar spots. The F9 component exhibits a weak spot at latitude 30$^{\circ}$ and its mid-to-low latitudes are relatively featureless. The G0 star shows an extended spot structure at latitude 30$^{\circ}$, and its surface spot coverage is larger than that of the F9 star, which suggests a higher level of magnetic activity. With the cross-correlation method, we derive a solar-like surface differential rotation on the G0 star of $σ^{2}$ CrB for the first time, and the surface shear rate is $ΔΩ= 0.180 \pm 0.004$ rad d$^{-1}$ and $α= ΔΩ/ Ω_{eq} = 0.032 \pm 0.001$. We do not obtain a clear surface shear law for the F9 star due to the lack of mid-to-low latitude features, but detect a systematic longitude shift of high-latitude spots, which indicates a slower rotation with respect to the co-rotating frame.

astro-ph.SR↗

arXiv2020

The first Doppler imaging of the active binary prototype RS Canum Venaticorum

We present the first Doppler images of the prototypical active binary star RS CVn, derived from high-resolution spectra observed in 2004, 2016 and 2017, using three different telescopes and observing sites. We apply the least-squares deconvolution technique to all observed spectra to obtain high signal-to-noise line profiles, which are used to derive the surface images of the active K-type component. Our images show a complex spot pattern on the K star, distributed widely in longitude. All starspots revealed by our Doppler images are located below a latitude of about 70$^{\circ}$. In accordance with previous light-curve modeling studies, we find no indication of a polar spot on the K star. Using Doppler images derived from two consecutive rotational cycles, we estimate a surface differential rotation rate of $ΔΩ= -0.039 \pm 0.003 ~rad~d^{-1}$ and $α= ΔΩ/Ω_{eq} = -0.030 \pm 0.002$ for the K star. Given the limited phase coverage during those two rotations, the uncertainty of our differential rotation estimate is presumably higher.

astro-ph.SR↗

arXiv2015

The first Doppler images of the eclipsing binary SZ Piscium

We present the first Doppler images of the active eclipsing binary system SZ Psc, based on the high-resolution spectral data sets obtained in 2004 November and 2006 September--December. The least-squares deconvolution technique was applied to derive high signal-to-noise profiles from the observed spectra of SZ Psc. Absorption features contributed by a third component of the system were detected in the LSD profiles at all observed phases. We estimated the mass and period of the third component to be about $0.9 M_{\odot}$ and $1283 \pm 10$ d, respectively. After removing the contribution of the third body from the LSD profiles, we derived the surface maps of SZ Psc. The resulting Doppler images indicate significant starspot activities on the surface of the K subgiant component. The distributions of starspots are more complex than that revealed by previous photometric studies. The cooler K component exhibited pronounced high-latitude spots as well as numerous low- and intermediate-latitude spot groups during the entire observing seasons, but did not show any large, stable polar cap, different from many other active RS CVn-type binaries.

astro-ph.SR↗

arXiv2014

Doppler images of the eclipsing binary ER Vulpeculae

We present Doppler images of both components of the eclipsing binary system ER Vul, based on the spectra obtained in 2004 November, 2006 September and 2008 November. The least-squares deconvolution technique is used for enhancing the signal-to-noise ratios of the observed profiles. The new surface images reveal that both stars of ER Vul show strong starspot activities and the starspots appear at various latitudes. The surface maps of 2006 and 2008 both show the presence of large high-latitude starspots on each component of ER Vul. We find no obvious phase shift of the active regions during our observations. The longitude distributions of starspots are non-uniform on both stars. At low-to-mid latitudes, the active regions are almost exclusively found in the hemisphere facing the other star. However, we find no pronounced concentration of spots at the sub-stellar points.

astro-ph.SR↗