arXiv subjects

Ke Shi

Publications and source records attributed to Ke Shi.

At least 37 records · Page 2Linked to original sources

arXiv2025

Narrowband Imaging of a z=3.24 Protocluster: Insights from [O III] Emitting Galaxies

We present a narrowband imaging on a spectroscopically confirmed protocluster ``D4UD01'' at z=3.24 using CFHT/WIRCam. We identify a sample of 24 [O III] emission line galaxies in the field, which forms a large overdensity in the protocluster region. The protocluster is expected to evolve into a Virgo-like cluster by z=0. Utilizing multiwavelength data, we derive the physical properties of these [O III] emitters and find they are medium mass normal star-forming galaxies ($\sim10^{10}$M$_\odot$) roughly following the star-forming main sequence. The [O III] emitters trace an overdensity spatially offset from that of photometric-redshift and quiescent galaxies, suggesting these distinct galaxy populations may inhabit dark matter halos that formed at different epochs. A comparative analysis of [O III] emitter properties shows similar characteristics in both protocluster and field environments. This protocluster likely represents an evolved structure that has progressed beyond its peak star-formation phase, although our limited sample size may prevent detection of subtle environmental effects.

astro-ph.GA↗

arXiv2024

TS-Align: A Teacher-Student Collaborative Framework for Scalable Iterative Finetuning of Large Language Models

Mainstream approaches to aligning large language models (LLMs) heavily rely on human preference data, particularly when models require periodic updates. The standard process for iterative alignment of LLMs involves collecting new human feedback for each update. However, the data collection process is costly and challenging to scale. To address this issue, we introduce the "TS-Align" framework, which fine-tunes a policy model using pairwise feedback data automatically mined from its outputs. This automatic mining process is efficiently accomplished through the collaboration between a large-scale teacher model and a small-scale student model. The policy fine-tuning process can be iteratively repeated using on-policy generations within our proposed teacher-student collaborative framework. Through extensive experiments, we demonstrate that our final aligned policy outperforms the base policy model with an average win rate of 69.7% across seven conversational or instruction-following datasets. Furthermore, we show that the ranking capability of the teacher is effectively distilled into the student through our pipeline, resulting in a small-scale yet effective reward model for policy model alignment.

cs.CL↗

arXiv2024

Almost optimum $\ell$-covering of $\mathbb{Z}_n$

A subset $B$ of the ring $\mathbb{Z}_n$ is referred to as a $\ell$-covering set if $\{ ab \pmod n | 0\leq a \leq \ell, b\in B\} = \mathbb{Z}_n$. We show that there exists a $\ell$-covering set of $\mathbb{Z}_n$ of size $O(\frac{n}{\ell}\log n)$ for all $n$ and $\ell$, and how to construct such a set. We also provide examples where any $\ell$-covering set must have a size of $Ω(\frac{n}{\ell}\frac{\log n}{\log \log n})$. The proof employs a refined bound for the relative totient function obtained through sieve theory and the existence of a large divisor with a linear divisor sum. The result can be used to simplify a modular subset sum algorithm.

cs.DM↗

arXiv2024

Possible Meissner effect near room temperature in copper-substituted lead apatite

With copper-substituted lead apatite below room temperature, we observe diamagnetic dc magnetization under magnetic field of 25 Oe with remarkable bifurcation between zero-field-cooling and field-cooling measurements, and under 200 Oe it changes to be paramagnetism. A glassy memory effect is found during cooling. Typical hysteresis loops for superconductors are detected below 250 K, along with an asymmetry between forward and backward sweep of magnetic field. Our experiment suggests at room temperature the Meissner effect is possibly present in this material.

cond-mat.supr-con↗

arXiv2024

High magnetic field phase diagram and weak FM breaking in (Ni0.93Co0.07)3V2O8

We present magnetostriction and thermal expansion measurements on multiferroic (Ni0.93Co0.07)3V2O8. The high field phase diagrams up to 33 T along the a, b and c directions are built. For H//a, as the magnetic field increases, two intermediate phases appear between the incommensurate phase and the paramagnetic phase at about 7 K, and then a magnetically induced phase appears above the paramagnetic phase. For H//b,thermal expansion measurement indicates a mutation in the spin lattice coupling of the high field phases. The interlaced phase boundary suggests a mixed state in the optical high field phase. For H//c, an intermediate phase between the commensurate phase and the incommensurate phase is detected. A nonlinear boundary between the intermediate phase and the low temperature incommensurate phase, and a clear boundary between the commensurate phase and the paramagnetic phase are found. These results indicate that doping Co2+ breaks the weak ferromagnetic moment of the commensurate phase, which exists in the parent compound Ni3V2O8 and (Ni0.9Co0.1)3V2O8. This nonlinear influence reflects complicated spin modulation in Ni3V2O8 by doping Co2+.

cond-mat.str-el↗

arXiv2023

Nature vs. Nurture: Revisiting the environmental impact on star formation activities of galaxies

We present a systematic study of the environmental impact on star formation activities of galaxies using a mass-complete sample of $\sim$170k galaxies at $z<4$ from the latest COSMOS2020 catalog. At $z<1$, we find that the mean star-formation rate (SFR) of all galaxies decreases with increasing density of the environment. However when we consider only star-forming galaxies, the mean SFR becomes independent of the environment at $z<1$. At $z>2$ we observe a clear positive correlation between the SFR and density of the environment for all the galaxies. On the other hand, stellar mass of the galaxies increases significantly with the environments at all redshifts except for star-forming galaxies at $z<1$. The fraction of quiescent galaxies increases with increasing density of environment at $z<2$, and the ``morphology-density'' relation is confirmed to be present up to $z\sim1$. We also find that environmental quenching is negligible at $z>1$, whereas mass quenching is the dominant quenching mechanism for massive galaxies at all redshifts. Based on these results, we argue that stellar mass regulated physical processes might be the major driving force for star formation activities of galaxies. At low redshift ($z<1$) massive galaxies are quenched primarily due to their high mass, resulting in a normal ``SFR-density'' relation. At high redshift ($z>2$) most of the galaxies are star-forming ones tightly following the star-forming main sequence, and the difference in their stellar mass at different environments naturally leads to a reversal of ``SFR-density'' relation.

astro-ph.GA↗

arXiv2023

xDial-Eval: A Multilingual Open-Domain Dialogue Evaluation Benchmark

Recent advancements in reference-free learned metrics for open-domain dialogue evaluation have been driven by the progress in pre-trained language models and the availability of dialogue data with high-quality human annotations. However, current studies predominantly concentrate on English dialogues, and the generalization of these metrics to other languages has not been fully examined. This is largely due to the absence of a multilingual dialogue evaluation benchmark. To address the issue, we introduce xDial-Eval, built on top of open-source English dialogue evaluation datasets. xDial-Eval includes 12 turn-level and 6 dialogue-level English datasets, comprising 14930 annotated turns and 8691 annotated dialogues respectively. The English dialogue data are extended to nine other languages with commercial machine translation systems. On xDial-Eval, we conduct comprehensive analyses of previous BERT-based metrics and the recently-emerged large language models. Lastly, we establish strong self-supervised and multilingual baselines. In terms of average Pearson correlations over all datasets and languages, the best baseline outperforms OpenAI's ChatGPT by absolute improvements of 6.5% and 4.6% at the turn and dialogue levels respectively, albeit with much fewer parameters. The data and code are publicly available at https://github.com/e0397123/xDial-Eval.

cs.CL↗

arXiv2023

Overview of Robust and Multilingual Automatic Evaluation Metrics for Open-Domain Dialogue Systems at DSTC 11 Track 4

The advent and fast development of neural networks have revolutionized the research on dialogue systems and subsequently have triggered various challenges regarding their automatic evaluation. Automatic evaluation of open-domain dialogue systems as an open challenge has been the center of the attention of many researchers. Despite the consistent efforts to improve automatic metrics' correlations with human evaluation, there have been very few attempts to assess their robustness over multiple domains and dimensions. Also, their focus is mainly on the English language. All of these challenges prompt the development of automatic evaluation metrics that are reliable in various domains, dimensions, and languages. This track in the 11th Dialogue System Technology Challenge (DSTC11) is part of the ongoing effort to promote robust and multilingual automatic evaluation metrics. This article describes the datasets and baselines provided to participants and discusses the submission and result details of the two proposed subtasks.

cs.CL↗

arXiv2023

Huge magnetostriction in superconducting single-crystalline BaFe$_{1.908}$Ni$_{0.092}$As$_{2}$

The performance of iron-based superconductors in high magnetic fields plays an important role for their practical application. In this work, we measured the magnetostriction and magnetization of BaFe$_{1.908}$Ni$_{0.092}$As$_{2}$ single crystals using pulsed magnetic fields up to 60 T and static magnetic fields up to 33 T, respectively. A huge longitudinal magnetostriction (of the order of 10$ ^{-4} $) was observed in the direction of the twin boundaries. The magnetization measurements evidence a high critical-current density due to strong bulk pinning. By using magnetization data with an exponential flux-pinning model, we can reproduce the magnetostriction curves qualitatively. This result shows that the magnetostriction of BaFe$_{1.908}$Ni$_{0.092}$As$_{2}$ can be well explained by a flux-pinning-induced mechanism.

cond-mat.supr-con↗

arXiv2023

Calculation of Special Spin Behavior of Dy3+ in DyFe1-xCrxO3 System by Molecular Field Model

In this study, the sol-gel method synthesized the magnetic measurement and analysis of single-phase polycrystalline perovskite DyFe1-xCrxO3 (DFCO). The experimental data were fitted and calculated by a four-sublattice molecular field model. Unlike previous studies, we found that in DyFe1-xCrxO3, the spin of the A-site rare earth ion Dy3+ also changed simultaneously with the spin reorientation of the Fe3+/Cr3+ ions. The effective spin is defined as the projection of the A site's total spin on the B site's spin plane, and the curve of temperature changes is obtained after fitting. With this theory, a very accurate thermomagnetic curve is obtained by fitting. This is convincing and, at the same time, provides a reference for the development of spintronic devices in the future.

cond-mat.mtrl-sci↗

arXiv2023

A Non-gradient DG method for second-order Elliptic Equations in the Non-divergence Form

$L^1$ based optimization is widely used in image denoising, machine learning and related applications. One of the main features of such approach is that it naturally provide a sparse structure in the numerical solutions. In this paper, we study an $L^1$ based mixed DG method for second-order elliptic equations in the non-divergence form. The elliptic PDE in nondivergence form arises in the linearization of fully nonlinear PDEs. Due to the nature of the equations, classical finite element methods based on variational forms can not be employed directly. In this work, we propose a new optimization scheme coupling the classical DG framework with recently developed $L^1$ optimization technique. Convergence analysis in both energy norm and $L^{\infty}$ norm are obtained under weak regularity assumption. Such $L^1$ models are nondifferentiable and therefore invalidate traditional gradient methods. Therefore all existing gradient based solvers are no longer feasible under this setting. To overcome this difficulty, we characterize solutions of $L^1$ optimization as fixed-points of proximity equations and utilize matrix splitting technique to obtain a class of fixed-point proximity algorithms with convergence analysis. Various numerical examples are displayed to illustrate the numerical solution has sparse structure with careful choice of the bases of the finite dimensional spaces. Numerical examples in both smooth and nonsmooth settings are provided to validate the theoretical results.

math.NA↗

arXiv2022

Unraveling Thermally Induced Spin reorientation of Strongly Disordered NdFe0.5Cr0.5O3 System

Sophisticated spin instruments require high-precision spin control. In this study, we accurately study the intrinsic magnetic properties of the strongly disordered system NdFe0.5Cr0.5O3 through molecular field models combined with ASD theory. The three constituent sub-magnetic phases of the system are separated, and their magnetization contributions are calculated separately. Fitting the angle of the A/B magnetic moment at a given temperature, the reorientation temperature point and temperature dependence of different magnetic phases are obtained. This research will provide a very good theoretical support for studying complex disordered systems and applying high-precision spin control and lay a foundation for the design of new functional materials.

physics.app-ph↗

arXiv2021

DMRST: A Joint Framework for Document-Level Multilingual RST Discourse Segmentation and Parsing

Text discourse parsing weighs importantly in understanding information flow and argumentative structure in natural language, making it beneficial for downstream tasks. While previous work significantly improves the performance of RST discourse parsing, they are not readily applicable to practical use cases: (1) EDU segmentation is not integrated into most existing tree parsing frameworks, thus it is not straightforward to apply such models on newly-coming data. (2) Most parsers cannot be used in multilingual scenarios, because they are developed only in English. (3) Parsers trained from single-domain treebanks do not generalize well on out-of-domain inputs. In this work, we propose a document-level multilingual RST discourse parsing framework, which conducts EDU segmentation and discourse tree parsing jointly. Moreover, we propose a cross-translation augmentation strategy to enable the framework to support multilingual parsing and improve its domain generality. Experimental results show that our model achieves state-of-the-art performance on document-level multilingual RST parsing in all sub-tasks.

cs.CL↗

arXiv2021

Coreference-Aware Dialogue Summarization

Summarizing conversations via neural approaches has been gaining research traction lately, yet it is still challenging to obtain practical solutions. Examples of such challenges include unstructured information exchange in dialogues, informal interactions between speakers, and dynamic role changes of speakers as the dialogue evolves. Many of such challenges result in complex coreference links. Therefore, in this work, we investigate different approaches to explicitly incorporate coreference information in neural abstractive dialogue summarization models to tackle the aforementioned challenges. Experimental results show that the proposed approaches achieve state-of-the-art performance, implying it is useful to utilize coreference information in dialogue summarization. Evaluation results on factual correctness suggest such coreference-aware models are better at tracing the information flow among interlocutors and associating accurate status/actions with the corresponding interlocutors and person mentions.

cs.CL↗

arXiv2021

Lyman Alpha line properties at $z \simeq 3.78$ and their environmental dependence: a case study around a massive proto-cluster

Ly$α$-emitting galaxies (LAEs) are easily detectable in the high-redshift Universe and are potentially efficient tracers of large scale structure at early epochs, as long as their observed properties do not strongly depend on environment. We investigate the luminosity and equivalent width functions of LAEs in the overdense field of a protocluster at redshift $z \simeq 3.78$. Using a large sample of LAEs (many spectroscopically confirmed), we find that the Ly$α$ luminosity distribution is well-represented by a Schechter (1976) function with $\log(L^{\ast}/{\rm erg s^{-1}}) = 43.26^{+0.20}_{-0.22}$ and $\log(ϕ^{\ast}/{\rm Mpc^{-3}})=-3.40^{+0.03}_{-0.04}$ with $α=-1.5$. Fitting the equivalent width distribution as an exponential, we find a scale factor of $ω=79^{+15}_{-15}$ Angstroms. We also measured the Ly$α$ luminosity and equivalent width functions using the subset of LAEs lying within the densest cores of the protocluster, finding similar values for $L^*$ and $ω$. Hence, despite having a mean overdensity more than 2$\times$ that of the general field, the shape of the Ly$α$ luminosity function and equivalent width distributions in the protocluster region are comparable to those measured in the field LAE population by other studies at similar redshift. While the observed Ly$α$ luminosities and equivalent widths show correlations with the UV continuum luminosity in this LAE sample, we find that these are likely due to selection biases and are consistent with no intrinsic correlations within the sample. This protocluster sample supports the strong evolutionary trend observed in the Ly$α$ escape fraction and suggest that lower redshift LAEs can be on average significantly more dusty that their counterparts at higher redshift.

astro-ph.GA↗

arXiv2021

The Role of Dust, UV Luminosity and Large-scale Environment on the Escape of Lya Photons: A Case Study of a Protocluster field at z = 3.1

We present a detailed characterization of the Lya properties for 93 Lya emitters (LAEs) at z~3.1 selected from the D1 field of the Canada-France-Hawaii-Telescope Legacy Survey, including 24 members of a massive protocluster. The median-stacked Lya image shows an extended Lya halo (LAH) surrounding the galaxy with the exponential scale length 4.9+/-0.7kpc, which accounts for roughly half of the total line flux. Accounting for the LAH contribution, the total Lya escape fraction, f_esc, is 40+/-26%. Combining the dataset with existing measurements, we find a dependence of f_esc on the galaxy's UV slope (beta) and UV luminosity (L_UV). The simultaneous use of both parameters allows prediction of f_esc within 0.18dex, a substantial improvement over 0.23dex when only beta is used. The correlation between f_esc and E(B-V) suggests that Lya photons undergo interstellar dust attenuation in a similar manner to continuum photons. Yet, Lya transmission is typically higher than that expected for continuum photons at similar wavelength by a factor, which depends on UV luminosity, up to 2 in the samples we studied. These results hint at complex geometries and physical conditions of the interstellar medium, which affect the Lya transmission or production. Alternatively, the dust law may change with luminosity leading to over-or under-estimation of f_esc. Finally, we report that protocluster member LAEs tend to be bluer and more UV-luminous than their field cousins, resulting in systematically higher f_esc values. We speculate that it may be due to the widespread formation of young low-mass galaxies in dense gas-rich environments.

astro-ph.GA↗

arXiv2021

Multilingual Speech Evaluation: Case Studies on English, Malay and Tamil

Speech evaluation is an essential component in computer-assisted language learning (CALL). While speech evaluation on English has been popular, automatic speech scoring on low resource languages remains challenging. Work in this area has focused on monolingual specific designs and handcrafted features stemming from resource-rich languages like English. Such approaches are often difficult to generalize to other languages, especially if we also want to consider suprasegmental qualities such as rhythm. In this work, we examine three different languages that possess distinct rhythm patterns: English (stress-timed), Malay (syllable-timed), and Tamil (mora-timed). We exploit robust feature representations inspired by music processing and vector representation learning. Empirical validations show consistent gains for all three languages when predicting pronunciation, rhythm and intonation performance.

cs.CL↗

arXiv2021

Accelerated galaxy growth and environmental quenching in a protocluster at z=3.24

We present a multiwavelength study of galaxies around D4UD01, a spectroscopically confirmed protocluster at z = 3.24 to investigate environmental trends. 450 galaxies are selected based on Ks band detection with photometric redshifts (photo-z) at 3.0 < z < 3.4, among which ~ 12% are classified as quiescent galaxies. The quiescent galaxies are among the most massive and reddest ones in the entire sample. We identify a large photo-z galaxy overdensity in the field, which lies close to the previously spectroscopically confirmed sources of the protocluster. We find that the quiescent galaxies are largely concentrated in the overdense protocluster region with a higher quiescent fraction, showing a sign of environmental quenching. Galaxies in the protocluster are forming faster than the field counterparts as seen in the stellar mass function, suggesting early and accelerated mass assembly in the overdense regions. Although weak evidence of suppressed star-formation is found in the protocluster, the statistics are not significant enough to draw a definite conclusion. Our work shed light on how the formation of massive galaxies is affected in the dense region of a protocluster when the Universe was only 2 Gyr old.

astro-ph.GA↗