arXiv subjects

Cheng Cheng

Publications and source records attributed to Cheng Cheng.

At least 55 records · Page 3Linked to original sources

arXiv2026

Conjugate phase retrieval in shift-invariant spaces generated by a Gaussian

Conjugate phase retrieval considers the recovery of a function, up to a unimodular constant and conjugation, from its phaseless measurements. In this paper, we explore the conjugate phase retrieval in a shift-invariant space generated by a Gaussian funciton. First, we show that the modulus function in the Gaussian shift-invariant space can be determined from the phaseless Hermite samples taken on a discrete sampling set. We then show that a function in the shift-invariant space generated by a Gaussian can be uniquely determined, up to a unimodular constant and conjugation, from its phaseless Hermite samples on a discrete set. For the functions with finite coefficient sequences, we provide an explicit reconstruction procedure.

math.FA↗

arXiv2026

Detect Repair Verify for Securing LLM Generated Code: A Multi-Language Empirical Study

Large language models are increasingly used to produce runnable software. In practice, security is often addressed through a Detect--Repair--Verify (DRV) loop that detects issues, applies fixes, and verifies the result. This work studies such a workflow for project-level artifacts and addresses four gaps: L1, the lack of project-level benchmarks with executable function and security tests; L2, limited evidence on pipeline-level effectiveness beyond studying detection or repair alone; L3, unclear reliability of detection reports as repair guidance; and L4, uncertain repair trustworthiness and side effects under verification. A new benchmark dataset\footnote{https://github.com/Hahappyppy2024/EmpricalVDR} is introduced, consisting of runnable web-application projects paired with functional tests and targeted security tests, and supporting three prompt granularities at the project, requirement, and function level. The evaluation compares generation-only, single-pass DRV, and bounded iterative DRV variants under comparable budget constraints. Outcomes are measured by secure and correct yield using test-grounded verification, and intermediate artifacts are analyzed to assess report actionability and post-repair failure modes such as regressions, semantic drift, and newly introduced security issues.

cs.SE↗

arXiv2026

Non-linear Dynamics and Primordial Black Hole Formation During Kination

We investigate the effects of large scalar inhomogeneities during the kination epoch, a period in which the universe's dynamics are dominated by the kinetic energy of a scalar field, by fully evolving the Einstein equations using numerical relativity. By tracking the non-linear growth of scalar perturbations with both sub-horizon and super-horizon initial wavelengths, we are able to compare their evolution to perturbative results. Our key findings show that in the deep sub-horizon limit, the perturbative behaviour remains valid, whereas in the super-horizon regime, non-linear dynamics exhibit a much richer phenomenology. Finally, we discuss the possibility of primordial black hole formation from the collapse of such perturbations and assess whether this process could serve as a viable mechanism to reheat the universe in the post-inflationary era.

astro-ph.CO↗

arXiv2026

Twisted multilayer moiré water waves topologically robust to disorder

Moiré patterns, stacking and twisting multilayer periodic lattices into superlattices, have become cornerstones of many physical systems from condensed matter to wave phenomena, but have never been properly studied in water waves. Here, we demonstrate twisted multilayer moiré water surface waves carrying robust skyrmionic topologies. Using a custom water tank of circular multi-channel phased array, we precisely generate water-wave skyrmion lattices and superimpose them into moiré superlattices with higher-order topological textures, e.g., skyrmion bags and clusters, programmed via the twist angle. We also quantitatively compare the topological robustness of bilayer and trilayer configurations under spatiotemporal perturbations. The trilayer moiré superlattices exhibit more enhanced stability, stronger field localization and energy concentration than the bilayer. Our work establishes water waves as a macroscopic, tunable, and visually accessible platform for moiré physics, towards robust particle manipulation and classical analogues of topological quantum phenomena.

physics.optics↗

arXiv2026

From Prediction to Perfection: Introducing Refinement to Autoregressive Image Generation

Autoregressive (AR) image generators offer a language-model-friendly approach to image generation by predicting discrete image tokens in a causal sequence. However, unlike diffusion models, AR models lack a mechanism to refine previous predictions, limiting their generation quality. In this paper, we introduce TensorAR, a new AR paradigm that reformulates image generation from next-token prediction to next-tensor prediction. By generating overlapping windows of image patches (tensors) in a sliding fashion, TensorAR enables iterative refinement of previously generated content. To prevent information leakage during training, we propose a discrete tensor noising scheme, which perturbs input tokens via codebook-indexed noise. TensorAR is implemented as a plug-and-play module compatible with existing AR models. Extensive experiments on LlamaGEN, Open-MAGVIT2, and RAR demonstrate that TensorAR significantly improves the generation performance of autoregressive models.

cs.CV↗

arXiv2026

Conjugate Relation Modeling for Few-Shot Knowledge Graph Completion

Few-shot Knowledge Graph Completion (FKGC) infers missing triples from limited support samples, tackling long-tail distribution challenges. Existing methods, however, struggle to capture complex relational patterns and mitigate data sparsity. To address these challenges, we propose a novel FKGC framework for conjugate relation modeling (CR-FKGC). Specifically, it employs a neighborhood aggregation encoder to integrate higher-order neighbor information, a conjugate relation learner combining an implicit conditional diffusion relation module with a stable relation module to capture stable semantics and uncertainty offsets, and a manifold conjugate decoder for efficient evaluation and inference of missing triples in manifold space. Experiments on three benchmarks demonstrate that our method achieves superior performance over state-of-the-art methods.

cs.CL↗

arXiv2026

Discovery of a gas-enshrouded broad-line AGN at z $\sim$ 7

The Lyman-alpha (Ly$α$) absorption profile in star-forming galaxies serves as a powerful tracer of the extended, dense neutral hydrogen in their surroundings during the Epoch of Reionization (EoR). We report a unique galaxy, A2744-z7DLA, at $z\approx 6.87$ gravitationally lensed by the foreground galaxy cluster Abell 2744, which exhibits both moderate Ly$α$ emission and damped Ly$α$ absorption, suggesting the presence of a dense neutral hydrogen environment. Our analysis suggests that the UV continuum turnover near Ly$α$ is more likely shaped by a damped Ly$α$ system rather than nebular continuum from two photon process. We analyze the physical properties of A2744-z7DLA with spectroscopic and photometric data from the JWST and the HST. The galaxy shows a compact morphology ($r_e \sim 0.3\ {\rm kpc}$) and a broadened H$α$ emission line, suggesting possible AGN activity. The broad component of H$α$ has a FWHM of $2721 \pm 200\ {\rm km\ s^{-1}}$, corresponding to a black hole mass of $M_{\rm BH}=2.90^{+2.35}_{-1.28}\times 10^7 M_\odot$ and a black hole-to-stellar mass ratio of $\log (M_{\rm BH}/M_{\rm stellar}) = -1.58^{+0.45}_{-0.34}$. The Balmer decrement ($\rm Hα/Hβ$) yields a dust attenuation of $\rm A_V \approx 1.15 \pm 0.23$, indicating that this system is less dust-rich than some "little red dots". Furthermore, we perform SED fitting using both stellar and AGN models. The results show that the UV and optical wavelengths are dominated by star-forming regions, while the AGN component contributes primarily at longer wavelengths. This work provides new insights into the interplay between star formation, neutral gas, and potential AGN activity in galaxies during the EoR.

astro-ph.GA↗

arXiv2026

PEARLS: 21 Transients Found in the Three-Epoch NIRCam Observations in the Continuous Viewing Zone of the James Webb Space Telescope

We present 21 transients from our three-epoch, four-band NIRCam observations covering 14.16 arcmin^2 in the Spitzer IRAC Dark Field (IDF), taken by the JWST Prime Extragalactic Areas for Reionization and Lensing Science program with a time cadence of ~6 months. A separate Hubble Space Telescope program provided Advanced Camera for Surveys optical imaging contemporaneous with the second and third epochs of the NIRCam observations. The NIRSpec spectroscopy on three transients confirmed a Type Ia supernova at z=1.63 and the host galaxies of the other two at z=2.64 and 1.90, respectively. Combining these with the photometric redshifts (z_ph) of the host galaxies in the rest of the sample, we find that the transients are in either a "mid-z" group at z>1.6 with M_V < -16.0 mag or a "low-z" group at z < 0.4 with M_H > -14.0 mag. The mid-z transients are consistent with supernovae. In contrast, the low-z transients' luminosities fall in the range of the so-called "gap transients" between supernovae and novae. However, this latter conclusion is only tentative due to possible catastrophic failures in z_ph that could bias them to low-z. Conversely, if they are indeed at z < 0.4, it would be worth studying similar transients in the future. Our work further demonstrates the power of NIRCam in transient science and also shows that it would be more fruitful to carry out a long-term monitoring program with more passbands, a higher cadence and prompt follw-up spectroscopy. Being in the continuous viewing zone of the JWST, the IDF is an ideal field for this purpose.

astro-ph.GA↗

arXiv2025

Replacing Gas with Low-cost, Abundant Long-duration Pumped Hydro in Electricity Systems

Fossil gas is sometimes presented as an enabler of variable solar and wind generation beyond 2050, despite being a primary source of greenhouse gas emissions from methane leakage and combustion. We find that balancing solar and wind generation with pumped hydro energy storage eliminates the need for fossil gas without incurring a cost penalty. However, many existing long-term electricity system plans are biased to rely on fossil gas due to using temporal aggregation methods that either heavily constrain storage cycling behaviour or lose track of the state-of-charge, failing to consider the potential of low-cost long-duration off-river pumped hydro, and ignoring the broad suite of near-optimal energy transition pathways. We show that a temporal aggregation method based on 'segmentation' (fitted chronology) closely resembles the full-series optimisation, captures long-duration storage behaviour (48- and 160-hour durations), and finds a near-optimal 100% renewable electricity solution. We develop a new electricity system model to rapidly evaluate millions of other near-optimal solutions, stressing the importance of modelling pumped hydro sites with a low energy volume cost (<US$50 per kilowatt-hour), long economic lifetime (~75 years), and low real discount rate akin to other natural monopolies (<=3%). Almost every region of the world has access to sufficient 50 - 5000 gigawatt-hour off-river pumped hydro options that enable them to entirely decarbonise their future electricity systems.

cs.CE↗

arXiv2025

HI-detected Dwarf Galaxies in the FASHI Survey: Insights from Single- and Double-Peaked Emission-Line Samples

We present a sample of low HI mass dwarf galaxies ($M_{\rm HI} < 10^8 M_\odot$) detected by The FAST All Sky HI Survey (FASHI) project. Due to the faint and irregular morphology of these galaxies, the default photometry is often inaccurate. Therefore, we utilized The Dark Energy Camera Legacy Survey (DECaLS) data to perform careful photometric measurements, and find that the low HI mass galaxies have similar stellar mass densities to dwarf elliptical (dE) galaxies. Compared to other dwarf galaxy populations, the HI-selected dwarfs exhibit higher stellar mass densities than ultradiffuse galaxies, and similar densities to HI-selected low-surface-brightness galaxies, albeit with lower stellar masses, suggesting a possible evolutionary connection among these populations. By classifying the galaxies according to their HI spectral-line profiles, we show that the double-peaked sources conform closely to the Tully-Fisher relation, whereas the single-peaked sources follow the Faber-Jackson relation but with large scatter. This indicates that the single-peaked systems are likely dispersion dominated and that the relationship between stellar mass and halo mass in such systems may remain consistent across both low- and high-mass regimes. These findings suggest that HI-selected dwarf galaxies with single-peaked HI profiles may share a similar dynamical state with massive ellipticals, offering new insights into their structural evolution and the diversity of formation pathways for low-mass galaxies.

astro-ph.GA↗

arXiv2025

CFCEval: Evaluating Security Aspects in Code Generated by Large Language Models

Code-focused Large Language Models (LLMs), such as CodeX and Star-Coder, have demonstrated remarkable capabilities in enhancing developer productivity through context-aware code generation. However, evaluating the quality and security of LLM-generated code remains a significant challenge. Existing evaluation protocols for Code LLMs lack both methodological rigor and comprehensive scope. A key limitation is dataset bias, which arises from unintentional overlap between training and testing data. Furthermore, while CodeBLEU, a BLEU-based metric, is widely used to assess code similarity, it suffers from critical shortcomings, including imprecise tokenization, structural limitations, and low reference diversity. To address these challenges, we introduce CFCEval, a novel framework for evaluating the quality and security of code generated by LLMs. CFCEval mitigates dataset bias by creating a new benchmark, MLVBench, and incorporates ELRM, a new metric designed to assess the relevance between reference code and generated code. CFCEval evaluates generated code across four dimensions: programming quality, vulnerability-fixing capability, post-transformation fixing capability, and relevance. Our experiments show that CFCEval not only captures both quality and security aspects of generated code more effectively but also that its ELRM aligns more closely with human judgments than CodeBLEU, thus paving the way for future advancements in Code LLMs evaluation.

cs.SE↗

arXiv2025

Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. IV. Broad Emission Line Evolution Sequence Among Hα, Mg II, and Hβ

From a parent catalog of 561 changing-look active galactic nuclei (CL-AGNs) identified by Guo et al. (2025), we investigate the evolutionary sequence of broad emission lines using a redshift-selected subset (0.35 < z < 0.45) of 54 CL-AGNs whose Dark Energy Spectroscopic Instrument (DESI) spectra simultaneously cover the Hα, H\b{eta}, and Mg II emission lines. To provide a baseline for comparison, we construct a control sample of 19,897 normal Type 1 AGNs within the same redshift range from the DESI Year 1 data. Through stacked spectral analysis and line-continuum luminosity correlations, we identify a clear evolutionary sequence in all AGN where broad H\b{eta} fades first, followed by Mg II, and then Hα, as the AGN luminosity declines - consistent with expectations from reverberation mapping. This trend reflects a radially stratified broad line region (BLR), where each line's responsivity depends on its ionization potential and radial distance from the central engine. In addition, we find that more massive supermassive black holes (SMBHs) require lower Eddington ratios to fully suppress broad emission lines, suggesting that the critical accretion threshold for the CL phenomenon is mass-dependent. Our results present the first statistical confirmation of a stratified broad line fading sequence in AGNs, reinforcing the central role of accretion state in shaping BLR structure and visibility.

astro-ph.GA↗

arXiv2025

Little red dots as embryos of active galactic nuclei

As an unprecedented large population in the early universe, the JWST-discovered little red dots (LRDs) have garnered much attention for formation of massive black holes and galaxies, but their nature remains a mystery. The LRDs appearing as ``Chimeras" like both active galactic nuclei (AGNs) and galaxies have stimulated renewed interest in the roadmap of central massive black hole (cMBH) formation in AGNs. In this paper, we suggest that the LRDs contain $M_{\bullet}\lesssim 10^6\,M_{\odot}$ cMBHs as demonstrated by the Sołtan argument and there is a large population of stellar-mass black holes (sMBHs with total mass of $\mathscr{M}_{m_{\bullet}}$) embedded inside cMBH accretion disks (cMBH-disk) as motivated by anomalous reverberations of broad H$β$ line in local AGNs. This embryo structure of LRDs ($M_{\bullet}<\mathscr{M}_{m_{\bullet}}$) is formed as a consequence of gravitational collapse of primordial clouds. In this Chimera, accretion onto sMBHs powers the rest-frame optical continuum of the LRDs but the UV continuum is jointly contributed by slim parts of the cMBH-disks and nuclear starbursts in the core of collapsing clouds governing the appearance of the observed V-shaped spectral energy distributions (SEDs). Outflowing clumped-envelopes are unavoidably formed by radiation pressure leading to absorption features of the Balmer lines. The present model works very well for LRDs' SEDs and avoids the issues of overly massive cMBHs. Evolution of LRDs is briefly discussed including gravitational waves.

astro-ph.GA↗

arXiv2025

Targeting cluster galaxies for the 4MOST CHANCES Low-z sub-survey with photometric redshifts

The evolution of galaxies is shaped by both internal processes and their external environments. Galaxy clusters and their surroundings provide ideal laboratories to study these effects, particularly mechanisms such as quenching and morphological transformation. The Chilean Cluster galaxy Evolution Survey (CHANCES) Low-z sub-survey is part of the CHileAN Cluster galaxy Evolution Survey, a 4MOST community survey designed to uncover the relationship between the formation and evolution of galaxies and hierarchical structure formation as it happens, through deep and wide multi-object spectroscopy. We present the target selection strategy followed to select galaxy cluster candidate members for the CHANCES low-z sub-survey, in and around 50 clusters and two superclusters at z<0.07, out to (5XR200) and down to mr= 20.4. Combining public photometric redshift estimates from the DESI Legacy Imaging Survey and T80S/S-PLUS iDR5, with custom photometric redshifts, we identify likely galaxy cluster candidate members whose photometric redshifts are consistent with being at the known redshift of the cluster and measure the average deviations of their photometric redshifts with respect to the spectroscopic redshift measurements σNMAD. We have successfully compiled our CHANCES-low-redshift catalogues, split into three different sub-surveys: low-z bright (mr<18.5), low-z faint (18.5<=mr<20.4) and low-z faint supplementary, by selecting>= 500,000 galaxy cluster candidate members and including confirmed spectroscopic galaxy cluster members, from which we expect to obtain 4MOST low-resolution (R~6500) spectra for ~320,000 galaxies. The CHANCES Low-z target catalogues form a statistically robust sample for spectroscopic follow-up, allowing studies of galaxy evolution and environmental effects in nearby cluster and supercluster environments.

astro-ph.GA↗

arXiv2025

Disturbed cold gas in galaxy and structure formation

Cold and cool gas (T $\leq 10^4$ K) in the circumgalactic medium (CGM) and its interaction with galaxies remain poorly understood. Simulations predict that cold gas flows into galaxies through cosmic filaments, determining the disk formation and galaxy evolution. The cold gas accretion modes in the CGM and their dependence on dark matter halo mass and redshift remain puzzling. Resolving the kiloparsec-scale kinematics and dynamics of cold gas interacting with the disk, dust, and metals in different environments is particularly lacking at z > 2. Here we report two disturbed cold gas structures traced by ultra-strong MgII absorbers (rest-frame equivalent width Wr > 2 Å) exhibiting high kinematic velocities (> 500 km/s) and their environments at z ~ 4.9 and z ~ 2.6. Observations were conducted with VLT/MUSE, JWST/NIRCam, and ALMA to detect Lya and nebular emission lines, as well as dust continuum emission in the vicinity of these two absorbing gas structures. We identify two Lya emitters associated with a strong MgII absorber pair separated by ~1000 km/s at z~ 4.87. The pair exhibits relative differences in metallicity, dust content, and ionization states, suggesting internal metal and dust exchange within the ultra-large cold gas structure. For the strong MgII absorber at z = 2.5652, we detect a dusty star-forming galaxy at a projected distance of $D = 38$ kpc. This galaxy exhibits prominent HeI, [SIII], and Paschen$γ$ lines, along with significant dust continuum. It has a star formation rate of ~ 121 +/- 33 $M_{\odot}$/yr and likely harbors a rotating disk. These findings tentatively suggest that cold gas at high redshifts plays a critical role in driving disk formation and actively participates in the transfer of metals and dust within the overdense regions of the CGM.

astro-ph.GA↗

arXiv2025

Ionized gas components in low surface brightness galaxy AGC 111629

We present integral field spectroscopy of ionized gas components in AGC 111629, an edge-on low surface brightness galaxy (LSBG) with a stellar mass of 5.7$\times$10$^{8}$ M$_{\odot}$. AGC 111629 displays an irregular H$α$ morphology and an arch-like structure in the extraplanar region, which is absent in continuous stellar image. The irregular H$α$ morphology may be related to a past merger event with its satellite galaxy AGC 748815. A peanut-shaped structure at the center in the integrated [OIII]$λ$5007 map, with a position angle that differs from that of the main stellar disk. This structure exhibits a higher [OIII]$λ$5007/H$β$ flux ratio, a larger equivalent width (EW) of [OIII]$λ$5007, and a lower H$α$/H$β$ flux radio ($<$ 2.86). Some spaxels associated with the peanut-shaped structure fall within the composite region of the BPT diagram based on [NII]$λ$6583. These features may be associated with the central AGN. Additionally, a sub-peak in the southern disk is clearly visible in the [OIII]$λ$5007 map. An extended region ($\sim$ 2 kpc) with an extremely low value of H$α$/H$β$ flux ratio is observed near this sub-peak. We interpret the sub-peak as a superbubble likely driven by supernova explosions in the southern disk. We derive the gas-phase metallicity, 12+log(O/H), using the [NII]$λ$6583/H$α$ diagnostic and find that AGC 111629 exhibits low central metallicity. This may result from feedback associated with AGN activity and supernova explosions.

astro-ph.GA↗

arXiv2025

Formation of A Nuclear Star Cluster Through A Merger Event In The Low Surface Brightness Galaxy AGC 223218

We present the properties of the nuclear star cluster (NSC) in the low surface brightness galaxy AGC 223218. The disk of the galaxy can be modeled using two S$\acute{\rm e}$rsic components with distinct central positions: one representing the inner bright disk and the other corresponding to the extended outer disk. We estimate the stellar masses of the NSC and the host galaxy using two methods: spectral energy distribution (SED) fitting and mass-to-light versus color relations (MLCRs). The stellar mass ratio of the NSC to AGC 223218 is 0.094 based on the SED method and 0.072 using MLCRs. The NSC presents a younger stellar population and a lower [Fe/H] value than the host, as determined from SDSS and LAMOST spectra analysis using pPXF fitting. AGC 223218 is located at the boundary between the Seyfert and star-forming regions in the [SII]-BPT diagram, whereas in the [NII]-BPT diagram, it falls in the track of star-forming SDSS galaxies. This suggests the presence of strong shocks in AGC 223218. We propose that the NSC in AGC 223218 may have formed as a result of a merger event. Furthermore, the observed X-ray luminosity of AGC 223218 with eROSITA is two orders of magnitude higher than the expected X-ray luminosity from X-ray binaries, suggesting the presence of an intermediate-mass black hole (IMBH) in the NSC. To account for the observed X-ray luminosity, we estimate the IMBH accretion rate to be approximately 0.001.

astro-ph.GA↗

arXiv2025

An Exploratory Study on Fine-Tuning Large Language Models for Secure Code Generation

AI-powered coding assistants such as GitHub's Copilot and OpenAI's ChatGPT have achieved notable success in automating code generation. However, these tools rely on pre-trained Large Language Models (LLMs) that are typically trained on human-written code sourced from open-source project hosting sites like GitHub, which often contains inherent security vulnerabilities. These vulnerabilities may then be mirrored in the code generated by these LLMs, a critical risk revealed and highlighted by recent empirical studies. In this work, we present an exploratory study on whether fine-tuning pre-trained LLMs on datasets of vulnerability-fixing commits can promote secure code generation. We explored full fine-tuning and two parameter-efficient fine-tuning techniques (LoRA and IA3) on four pre-trained LLMs for code generation. We crawled a fine-tuning dataset (14,622 C/C++ files) for secure code generation by collecting code fixes of confirmed vulnerabilities from open-source repositories. Our evaluation dataset comprises 52 vulnerability scenarios designed to cover the top most dangerous C/C++ CWEs. Our exploration reveals that fine-tuning LLMs using PEFT techniques can enhance secure code generation. We observe maximum improvements in security of 6.4% in C language and 5.0% in C++ language. In addition, we compared between the fine-tuning approaches and the prompt-based approaches. The LoRA-tuned models outperform the prompt-based approaches in secure code generation. We found that fine-tuning with function-level and block-level datasets achieves the best secure code generation performance, compared to the alternatives (file-level and line-level).

cs.SE↗